Gravitational Wave Observations
Blanets: Worlds around Black Holes
Note4Students
From UPSC perspective, the following things are important :
Prelims level: Blanets, Black Holes
Mains level: NA
Introduction
- In Christopher Nolan’s 2014 sci-fi masterpiece Interstellar, three planets (aside from Earth) captivate viewers with their extreme environments.
- Surprisingly, these worlds, technically termed Blanets, may not be purely fictional and could exist in reality.
What are Blanets?
- Formation Theory: In 2019, Japanese scientists proposed a theory suggesting that planets could form within massive dust and gas clouds surrounding supermassive black holes.
- Unique Characteristics: Blanets, unlike Earth, are not expected to resemble habitable worlds due to their formation near black holes.
- Surrounding Environment: Black holes are encircled by colossal discs of gas and dust, influenced by the black hole’s gravitational pull and heating effects.
- Galactic Presence: Nearly every galaxy is believed to harbor a supermassive black hole at its center, acting as a gravitational nucleus around which stars organize.
Formation Process
- Similar Mechanism: Planets near young stars form from the collision and aggregation of dust and gas particles in swirling disks. A comparable process could occur near supermassive black holes.
- Blanet Characteristics: Blanets are anticipated to be approximately 3,000 times larger than Earth and must orbit the black hole at a distance of about 100 trillion km to avoid gravitational disruption during their formation.
Implications and Speculations
- Extreme Environments: Blanets represent worlds of extremes, vastly different from habitable planets like Earth.
- Scientific Inquiry: The study of blanets offers insights into the dynamic interactions between black holes and their surrounding environments, pushing the boundaries of astrophysical understanding.
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Gravitational Wave Observations
Event Horizon Telescope (EHT) confirms Black Hole Shadow
Note4Students
From UPSC perspective, the following things are important :
Prelims level: Black Hole and related terminologies
Mains level: Evidences confirming gravitational waves, relativity theory and black holes
Introduction
- Scientists have revealed new insights into a colossal black hole located 53 million light-years away, initially captured by the Event Horizon Telescope (EHT) in 2017.
- This groundbreaking achievement provided the first visual confirmation of the existence of black holes, validating a key prediction of Einstein’s theory of general relativity.
Key Findings by EHT
- The new data, obtained with improved telescope coverage and resolution, reiterated the previous discovery of the black hole’s ‘shadow’.
- The findings confirmed the presence of an asymmetric ring structure consistent with strong gravitational lensing effects.
- Observations indicated a stable ring formation process over time, with subtle changes suggesting variations in the magnetic field structure.
About Event Horizon Telescope (EHT)
| Description | |
| About | A large telescope array consisting of a global network of radio telescopes.
Uses Very-long-baseline interferometry (VLBI). Resolution of 25 micro-arc-seconds |
| Collaboration | International collaboration involving over 300 members and 60 institutions across 20 countries and regions |
| Launch Year | Initiated in 2009 |
| First Image Published | April 10, 2019 (First image of a black hole, M87*) |
| Objective | Observation of objects the size of a supermassive black hole’s event horizon |
| Key Targets | Black holes including M87* and Sagittarius A* (Sgr A*) |
| Recent Developments | First image of black hole (March 2021), first image of Sgr A* (May 12, 2022) |
| Reconstructive Algorithms | Includes CLEAN algorithm and regularized maximum likelihood (RML) algorithm |
| Scientific Implications | Verification of general relativity, measurement of black hole mass and diameter, study of accretion processes |
Back2Basics: Black Holes and Related Concepts
| Definition | |
| Black hole | A region in space where gravity is so strong that nothing, not even light, can escape from it. |
| Event horizon | The boundary surrounding a black hole beyond which nothing can escape its gravitational pull. |
| Singularity | A point within a black hole where gravity becomes infinitely strong and spacetime curvature becomes infinite. |
| Gravitational collapse | The process by which massive stars collapse under their own gravity to form black holes. |
| Schwarzschild radius | The radius of the event horizon of a non-rotating black hole. |
| Hawking radiation | Radiation emitted by black holes due to quantum effects near the event horizon, predicted by physicist Stephen Hawking. |
| Accretion disk | A rotating disk of matter that forms around a black hole as it pulls in surrounding gas and dust. |
| Supermassive black hole | A black hole with a mass millions or billions of times greater than that of the Sun, found at the center of most galaxies. |
| Quasar | A luminous object powered by an active galactic nucleus, thought to be fueled by the accretion of material onto a supermassive black hole. |
| Neutron star | A highly compact star composed primarily of neutrons, formed from the collapsed core of a massive star. |
| White dwarf | A small, dense star composed of electron-degenerate matter, formed from the remnants of a low to medium mass star. |
| Gravitational waves | Ripples in spacetime caused by the acceleration of massive objects, such as black holes or neutron stars. |
| Black Hole Information Paradox | The theoretical problem concerning the loss of information about the initial state of matter swallowed by a black hole, which contradicts the principles of quantum mechanics. |
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Gravitational Wave Observations
Astronomers spot Unusual Object falling in Black Hole ‘Mass Gap’
Note4Students
From UPSC perspective, the following things are important :
Prelims level: Neutron Stars
Mains level: Read the attached story
Introduction
- In the field of astronomy, astronomers sometimes stumble upon celestial objects that leave them scratching their heads.
- In a recent study published in Science, a discovery was reported that is likely to get scientists talking and asking questions.
Neutron Stars: Exceptionally Dense
- Incredibly Dense Objects: Neutron stars are some of the densest things in the universe. They’re as compact as an atomic nucleus but as big as a city, pushing our understanding of super-dense matter to the limit.
- A Weighty Matter: The heavier a neutron star is, the more likely it is to eventually collapse and become something even denser, like a black hole.
Puzzling the Boundary
- A Cosmic Mystery: To understand what happens when neutron stars turn into black holes, objects that are in-between need to be found. These objects also need to be studied very carefully over a long time.
- A New Discovery: A cosmic system has been found in the NGC 1851 star cluster that doesn’t fit neatly into the categories of neutron stars or black holes.
NGC 1851E: The Revelation
- Seeing Something New: Inside NGC 1851, a pair of stars has been spotted that provides fresh insights into the extreme matter in the universe. This system has a millisecond pulsar, a fast-spinning neutron star that sends out beams of radio light, and a massive, dark companion that can’t be seen at any wavelength of light.
- The Pulsar’s Role: Millisecond pulsars are like cosmic clocks. They spin steadily, and any changes in their spin can tell important things about what’s around them.
Unveiling the Weight of Secrets
- Very Precise Measurements: The MeerKAT radio telescope in South Africa was used to closely watch the NGC 1851E system.
- What Was Found: Observations allowed figuring out exactly how the two objects move around each other and how heavy they are together. The system’s mass is almost four times that of the Sun, and the invisible companion is denser than a regular star but not as heavy as a black hole.
- A Strange Mass Gap: The companion’s mass falls in a range that’s puzzling to scientists, between the heaviest neutron stars and the lightest black holes. Understanding objects in this range is a big mystery in astrophysics.
A Stellar Dance: Cosmic Partnerships
- A Fascinating Idea: One intriguing possibility is that a pulsar is circling around what’s left after two neutron stars collided, something made possible because there are many stars packed closely together in NGC 1851.
- Starry Dance Floor: In this crowded group of stars, they twirl around each other, changing partners as they go. If two neutron stars get too close, they collide, creating a black hole. This black hole can then disturb the dance of other stars in the cluster.
- Still Many Questions: The work isn’t finished. Research is continuing to figure out exactly what the companion is. Is it the lightest black hole, the heaviest neutron star, or something completely different?
- Exploring New Frontiers: When at the border between neutron stars and black holes, there’s a chance of discovering completely new types of objects.
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Gravitational Wave Observations
Amal Kumar Raychaudhuri and the Raychaudhuri Equation
Note4Students
From UPSC perspective, the following things are important :
Prelims level: Raychaudhuri Equation
Mains level: NA
Central Idea
- Amal Kumar Raychaudhuri, an Indian physicist, overcame obstacles and restrictions to make a profound contribution to the field of general relativity.
A.K. Raychaudhuri: Early Life
- Born in Barisal, now in Bangladesh, in 1923.
- Educated in Kolkata.
- Developed a deep interest in general relativity during his time at the Indian Association of Cultivation of Science (IACS).
Challenges Faced
- While passionate about general relativity, Raychaudhuri was instructed by the director of IACS, Meghnad Saha, to work on topics of the director’s choosing or leave.
- Raychaudhuri, with limited career options, complied with Saha’s directive but continued to explore the mysteries of gravity in his spare time.
Theoretical Breakthrough: The Raychaudhuri Equation
- Raychaudhuri focused on the problem of singularities in general relativity, specifically points where gravity could become infinitely strong.
- Developed a unique approach that bypassed complex mathematical challenges.
- Introduced the Raychaudhuri equation, a simple and elegant formula that showed the inevitable convergence of matter in curved spacetime.
- The equation hinted strongly at the existence of singularities, a critical aspect of general relativity.
Influence on Renowned Physicists
- Raychaudhuri’s equation played a pivotal role in the work of Stephen Hawking and Roger Penrose.
- Hawking’s area theorem, demonstrating that the surface area of black holes never decreases, relied on the Raychaudhuri equation.
Recognition and Legacy
- Despite his groundbreaking work, Raychaudhuri received limited recognition in India.
- He faced obstacles in career advancement, including rejection by Calcutta University.
- Raychaudhuri eventually joined Presidency College, Kolkata, where he became a revered teacher, inspiring future generations of physicists.
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Gravitational Wave Observations
Insights into White Holes, Time, and the Universe
Note4Students
From UPSC perspective, the following things are important :
Prelims level: White Hole
Mains level: NA
Central Idea
- In a discussion with a theoretical physicist, we explore the intriguing concepts of white holes, the nature of time, and their profound implications for our comprehension of the cosmos.
- We delve into theories, from the transition of black holes to white holes to the fundamental granularity of space-time, providing a glimpse into the forefront of contemporary physics.
White Holes and Their Significance
- Reverse of Black Holes: White holes are essentially the opposite of black holes, with objects entering them behaving like a reversed movie.
- Simplicity in Behavior: White holes exhibit a straightforward behaviour: objects fall in, rebound, and ascend along the same path with reduced velocity.
- Quantum Mechanics Role: Quantum mechanics introduces the concept of a bounce within black holes, resulting in the formation of white holes.
- Altering Space-Time: White holes challenge conventional notions of space-time, suggesting that it undergoes quantum leaps and is not uniform or local.
Universe Emerging from a White Hole
- Analogous to a Bouncing Ball: The transition from a black hole to a white hole shares similarities with a ball bouncing back from the ground, albeit with reduced energy.
- Energy Dissipation: Energy dissipates as heat during this transition, a concept pioneered by Stephen Hawking known as Hawking radiation.
- Black Hole to Big Bang: The theory posits that a universe entering a black hole could bounce and generate an event akin to the Big Bang, potentially leading to the creation of our universe.
Understanding Time
- Relativity of Time: Time does not progress uniformly for all observers; it varies based on factors such as velocity.
- Einstein’s Insight: Albert Einstein introduced the idea that time is not a fixed entity like a clock but rather a flexible concept, akin to a stretchable rubber band.
- The Time Field: Einstein envisioned time as an integral component of a gravitational field, influenced by mass and gravity.
- Granular Space-Time: Combining quantum mechanics and gravity suggests that space-time is granular, consisting of discrete “time-steps,” challenging the notion of continuous space-time.
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Gravitational Wave Observations
LIGO-India: India’s Contribution to the Growth of Modern Astronomy
Note4Students
From UPSC perspective, the following things are important :
Prelims level: LIGO India and other such developments
Mains level: LIGO India and its Significance
Central Idea
The Union Cabinet approved the full budget for the LIGO-India mega-science project, which includes the construction, commissioning and joint scientific operation of a state-of-the-art, advanced Laser Interferometer Gravitational-Wave Observatory (LIGO) in India in collaboration with the NSF-funded LIGO Laboratory, USA, operated by Caltech and MIT.
About LIGO-India
- LIGO-India will be the fifth node of this international network of gravitational wave observatories, and possibly the last.
- The instrument is so sensitive that it can easily get influenced by events like earthquakes, landslides, or even the movement of trucks, and produce a false reading.
- That is why multiple observatories are needed to revalidate the signals.
- India’s involvement in LIGO is crucial to demonstrating its intent and capability to pull-off complex science projects independently
Facts for prelims: What is LIGO?
|
What is it? |
Laser Interferometer Gravitational-Wave Observatory (LIGO)
|
| Purpose | Detect and study gravitational waves |
| Cause | Ripples in spacetime caused by violent and energetic events in the universe |
| Location | Livingston, Louisiana and Hanford, Washington |
| Detector | Michelson interferometer |
| Function | Measure changes in length caused by passing gravitational waves
|
| Benefits | Improving our understanding of the universe and its origins |
| Discovery | Detected gravitational waves for the first time in 2015
|
| Significance | Confirmed a prediction made by Albert Einstein’s theory of general relativity
|
| Field | Gravitational wave astronomy |
| Discoveries | Many exciting discoveries about the nature of the universe
|
Significance of LIGO-India
- Advancement in gravitational-wave astronomy and astrophysics: LIGO-India will significantly enhance global capabilities in the field of gravitational-wave astronomy and astrophysics. The project will enable an entirely new window to our universe and open up opportunities to study the cosmos in ways that were previously impossible.
- Boosting research careers: LIGO-India will provide opportunities for Indian youth to pursue research careers in cutting-edge areas of science and technology, thereby supporting the growth of the Indian science industry and economy.
- Development of cutting-edge technologies: LIGO-India will lead to the development of cutting-edge technologies such as lasers, optics, vacuum, quantum metrology and control-system technologies, which have great national relevance. The project will bring together researchers in fundamental and applied sciences from national research laboratories, IITs and IISERs to universities in partnership with the industry, and attract talent from the large pool of Indian researchers spread worldwide.
- Galvanizing India’s industry: The project will galvanize India’s industry to enhance capability and capacity to engineer and manufacture complex components with precision to meet stringent scientific requirements, thereby enhancing the reputation of Indian industry.
- Contributing to India’s mega-science ventures: LIGO-India is part of India’s mega-science ventures, which aim to lead or partner in very high-science goals through large-scale collaborative efforts requiring highly skilled human resources, significant fiscal capital and infrastructural investment, and close academia-industry partnerships. LIGO-India is expected to extend the legacy of successful world-class facilities such as the Giant Metrewave Radio Telescope (GMRT) near Pune and Himalayan Chandra Telescope (HCT) in Ladakh.
Facts for prelims: Other Important science projects
|
Mega-science Project |
Description |
| Large Hadron Collider (LHC) | Particle accelerator located in Switzerland, aims to study subatomic particles |
| Indian-based Neutrino Observatory (INO) | A proposed underground neutrino laboratory to be located in Tamil Nadu, India |
| Facility for Antiproton & Ion Research (FAIR) | A particle accelerator located in Germany, used for research in nuclear and particle physics |
| Thirty Meter Telescope (TMT) | A proposed astronomical observatory, with a mirror diameter of 30 meters, to be located in Hawaii |
| Square Kilometre Array (SKA) | A radio telescope that will be the largest and most sensitive in the world, to be located in Australia and South Africa |
| Laser Interferometer Gravitational-Wave Observatory (LIGO) | A facility designed to detect gravitational waves, with observatories located in the USA and India |
Way ahead: Mega-Science Projects and India’s S&T Policy
- Mega-science projects like LIGO-India inculcate invaluable elements of work ethic in the scientific community.
- The key is the ability to create a focused but adequately large well-knit collaborative ecosystem that remains open to growing by bringing in wider participation.
- There is need for a culture within S&T communities to anticipate breakthroughs and appreciate new findings that may often deviate from the current comfort zone for policymakers to be receptive and for executing agencies to create robust mechanisms to assess, evaluate, and respond expeditiously to allow sufficient time to set up the enterprise.
Conclusion
The LIGO-India mega-science project is a significant milestone in India’s contribution to the growth of modern astronomy. The project will prompt Indian S&T in academia, national laboratories, and industries to leapfrog in a range of cutting-edge technologies. It reinforces the view that a healthy sprinkling of mega-science efforts in the overall S&T policy empowers and enriches the nation.
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Gravitational Wave Observations
LIGO-India: India’s Node in Global Universe Probe
Note4Students
From UPSC perspective, the following things are important :
Prelims level: LIGO
Mains level: Gravitational waves study
India has given the final approval to build its biggest scientific facility, Laser Interferometer Gravitational-Wave Observatory (LIGO), in the Hingoli district of Maharashtra. The facility will join the global project to detect and study gravitational waves.
Gravitation and General Theory of Relativity
|
What is LIGO?
|
What is it? |
Laser Interferometer Gravitational-Wave Observatory (LIGO) |
| Purpose | Detect and study gravitational waves |
| Cause | Ripples in spacetime caused by violent and energetic events in the universe |
| Location | Livingston, Louisiana and Hanford, Washington |
| Detector | Michelson interferometer |
| Function | Measure changes in length caused by passing gravitational waves |
| Benefits | Improving our understanding of the universe and its origins |
| Discovery | Detected gravitational waves for the first time in 2015 |
| Significance | Confirmed a prediction made by Albert Einstein’s theory of general relativity |
| Field | Gravitational wave astronomy |
| Discoveries | Many exciting discoveries about the nature of the universe |
About LIGO-India
- LIGO-India will be the fifth node of this international network of gravitational wave observatories, and possibly the last.
- The instrument is so sensitive that it can easily get influenced by events like earthquakes, landslides, or even the movement of trucks, and produce a false reading.
- That is why multiple observatories are needed to revalidate the signals.
- India’s involvement in LIGO is crucial to demonstrating its intent and capability to pull-off complex science projects independently.
Significance
- The detection and study of gravitational waves could help in understanding the universe’s structure, the origin of the universe, and the functioning of black holes.
- The LIGO project also has huge spin-off benefits for India’s science and technology sector.
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Gravitational Wave Observations
Black Hole, Resolving the Mistry
Note4Students
From UPSC perspective, the following things are important :
Prelims level: space developments
Mains level: space developments,black hole, merging of Stars, Energy, Gravitation
Context
- For the very first time, scientists noted that this observation of the Laser Interferometer Gravitational Wave (LIGO) observatories coincided with the measurements made by other telescopes that measured visual and electromagnetic signals.
What is Black hole?
- A black hole is a place in space where gravity pulls so much that even light can not get out. The gravity is so strong because matter has been squeezed into a tiny space. This can happen when a star is dying.
- Because no light can get out, people can’t see black holes. They are invisible. Space telescopes with special tools can help find black holes. The special tools can see how stars that are very close to black holes act differently than other stars.
What is the background?
- LIGO Observations: In 2017, astrophysicists observed an unusual feat among the stars. The Laser Interferometer Gravitational Wave(LIGO)observatories recorded a signal which indicated that two massive and dense stellar bodies had merged to form a third body, likely a black hole.
- Generation gravitational waves: In the process they gave off vibrations that quite literally shook the universe and its very fabric of space time.
- Neutron stars: Scientists, piecing together evidence from complementary measurements, surmised that the event they had observed was of two neutron stars merging and forming a black hole and, in the process, giving off light.
What are the observations through telescopes?
- The matter moving faster than light: An unusual jet of matter was observed that gave an illusion of travelling faster than light. These were all exciting phenomena observed for the very first time by telescopes and observatories.
- Confirmation by Hubble Space Telescope: Now, using data that had been recorded by the Global astro metric Interferometer for Astrophysics (GAIA) spacecraft and Hubble Space Telescope instruments, scientists have confirmed that the above picture is correct. They have made it more precise and descriptive.
- Seven times the speed of light: In a paper published in Nature, they describe measuring the “apparent speed” of the jet to be about seven times the speed of light.
- Lorenz factor: They have also measured more accurately a factor called the Lorenz factor which scales with the actual speed of the particles in the jet. Unlike earlier estimates which placed this factor at about 4, the present paper estimates this factor to be over 40. This is because they measure the speed of the relativistic jet to be close to 0.9997c, where “c” is the speed of light.
- Clarity about the source as neutron star in block hole generation: This resolves the earlier fuzziness about what the source was and puts the source clearly as massive neutron stars merging to give a black hole and throwing off relativistic jets of particles in the process.
Merging of Neutron stars
- Born out of Supernova explosion: Neutron stars are stellar corpses, left behind after a star has undergone a supernova explosion and reached the end of its lifetime. They are extremely dense, containing more mass than the sun in a sphere that is a few tens of kilometre wide.
- Produces fast moving material: This has been seen in many active galactic nuclei galaxy centres that harbour black holes and binary star systems within our galaxy, where one of the stars is a black hole. “Mostly, black holes are responsible for producing such fast moving material
Why present observations about black Hole are significant?
- Estimating changing position of sky: The present measurements and observations made with GAIA data are extremely challenging. They amount to measuring the position of an object in sky coordinates. These authors measured a change in sky position one millionth the span of the full moon. Normally, if one were making these measurements from earth-based telescopes, it would require data from radio telescopes spaced apart by intercontinental distances.
- VLBI technique: This technique is called Very Long Baseline Interferometry (VLBI) and was used in the earlier papers. “Here, the authors could beat VLBI in precision because they calibrated Hubble Space Telescope data with GAIA, which is a precision astrometry mission.
- It’s an estimate not a measurement: the researchers used both their Hubble Space Telescope and GAIA optical position measurement along with the earlier VLBI position measurement to get a better estimate of the speed of the source and angle (viewing angle) with which it is travelling with respect to us on earth. This estimate requires plugging in equations of the special theory of relativity. “So, it is an estimate as opposed to a measurement.
- Improvement in estimation: we have learnt that neutron star mergers can result in material moving with speeds as high as 0.9997c.Earlier results using Very Long Baseline Interferometry had pegged this value at about 0.938c. with the new results this lower limit has been improved. Even earlier, with VLBI, it was understood that it was a neutron star merger that produced such ultra-relativistic material. Before the VLBI results, there were several models that could replicate the observations.
- Explanation using ultra realistic material: The observations could be explained both by ultra-relativistic material and non relativistic material, with some differences in assumptions. That study indicated that the observed gamma ray bursts were produced along with the ultra-relativistic material.
Conclusion
- Current discovery strengthens the hypothesis that such neutron star mergers are responsible for a class of gamma ray bursts. Gamma ray bursts are flashes of extreme gamma ray photons that release a huge amount of energy nearly 1047 They come from different galaxies in the universe and are observed here quite frequently.
Mains Question
Q. What is the neutron star and how the merger of two stars produces a black hole? How LIGO and Hubble space telescope are useful in demystifying the black Hole phenomenon?
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Gravitational Wave Observations
Sagittarius A*: Black Hole at the Centre of our Galaxy imaged
Note4Students
From UPSC perspective, the following things are important :
Prelims level: Event Horizon Telescope (EHT), Black Hole, Saggitarious A*
Mains level: Read the attached story
Scientists from the Event Horizon Telescope (EHT) facility revealed the first image of the black hole at the centre of our galaxy i.e. the Milky Way.
The Milky Way is a spiral galaxy that contains at least 100 billion stars. Viewed from above or below it resembles a spinning pinwheel, with our sun situated on one of the spiral arms and Sagittarius A* located at the centre.
What is Sagittarius A*?
- Pronounced Sagittarius ‘A’ star, it refers to the believed location of the supermassive black hole in the centre of our galaxy.
- About 50 years ago, astronomers identified an area within the constellation of Sagittarius that was the strongest region of radio emission – thus making it the likely centre of the Milky Way.
- It possesses 4 million times the mass of our sun and is located about 26,000 light-years—the distance light travels in a year, 5.9 trillion miles (9.5 trillion km)—from Earth.
What is an event horizon?
- Black holes are extraordinarily dense objects with gravity so strong that not even light can escape, making viewing them extremely challenging.
- A black hole’s event horizon is the point of no return beyond which anything—stars, planets, gas, dust and all forms of electromagnetic radiation—gets dragged into oblivion.
- The closer someone came to a black hole, the greater the speed they would need to escape that massive gravity.
- The event horizon is the threshold around the black hole where the escape velocity surpasses the speed of light.
What are the recent observations?
- The image of Sagittarius A* (SgrA*) gave support to the idea that the compact object at the centre of our galaxy is indeed a black hole, strengthening Einstein’s general theory of relativity.
- The image was obtained using the EHT’s global network of observatories working collectively to observe radio sources associated with black holes.
- It showed a ring of light —super-heated disrupted matter and radiation circling at tremendous speed at the edge of the event horizon—around a region of darkness representing the actual black hole.
- This is called the black hole’s shadow or silhouette.
How did Einstein’s theory found its proof here?
- According to Einstein’s theory, nothing can travel faster through space than the speed of light.
- This means a black hole’s event horizon is essentially the point from which nothing can return.
- The name refers to the impossibility of witnessing any event taking place inside that border, the horizon beyond which one cannot see.
About EHT Facility
- EHT project is a large telescope array consisting of a global network of radio telescopes.
- It combines data from several very-long-baseline interferometry (VLBI) stations around Earth, which form a combined array.
- It provides an angular resolution sufficient to observe objects the size of a supermassive black hole’s event horizon.
- In 2019, the eHT facility made history by releasing the first-ever image of a black hole, M87* — the black hole at the centre of a galaxy Messier 87, which is a supergiant elliptic galaxy.
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Gravitational Wave Observations
Was it really a black hole that the EHT imaged in 2019?
Note4Students
From UPSC perspective, the following things are important :
Prelims level: Event Horizon Telescope (EHT), Black Hole
Mains level: Not Much
A new research says that M87* which was imaged by the Event Horizon Telescope (EHT) is not necessarily a black hole but could even be a naked singularity with a gravitomagnetic monopole.
About M-87*
- In 2019, astronomers of the Event Horizon Telescope (EHT) captured the first ever image of a supermassive black hole (M87*) which was located at the centre of a galaxy Messier 87.
- This black hole was calculated to be 6.5 billion times the Sun’s mass and is 55 million light years away from the Earth.
- The discovery set the world of astronomy on fire and also found a mention in the “popular information” section of the announcement of the Nobel Prize in physics for 2020.
- Andrea Ghez and Rheinhard Genzel were awarded half the share of the prize for their study of the black hole at the centre of the Milky Way galaxy, Sagittarius A*.
A black hole has two parts:
- Singularity at its core– a point that is infinitely dense, as all the remnant mass of the star is compressed into this point.
- Event horizon – an imaginary surface surrounding the singularity, and the gravity of the object is such that once anything enters this surface, it is trapped forever.
- Not even light can escape the pull of the singularity once it crosses the event horizon.
- That is why, we cannot see the singularity at the heart of a black hole but only see points outside the event horizon.
- Hence, all the physics happening within the black hole’s event horizon is indeed blocked from the view of the observer.
What is the recent explanation of M87*?
Ans. Naked Singularity
- When stars much more massive than the Sun reach the end of their lives, they collapse under their own gravity, and the product of this collapse is a black hole.
- In many scenarios of stellar collapse, the event horizon does not form, and the singularity is exposed to the outside, without any event horizon shielding it.
- This is called naked singularity.
Monopoles and gravity
- In the nineteenth century, James Clerk Maxwell unified electricity and magnetism as one combined phenomenon, showing that light is an electromagnetic wave.
- But there is an asymmetry between electricity and magnetism.
- While positive and negative electric charges can be found to exist independently, the poles of a magnet are always found in pairs, north and south bound together.
- There is an analogy between gravitational force and electromagnetism to say that mass is like electric charge and can exist independently, thus it can be called a “gravito-electric charge”.
But then, what is the gravito-magnetic charge?
- In 1963, Newman, Tamburino and Unti (NUT) proposed a theoretical concept called a “gravito-magnetic charge” also called a gravitomagnetic monopole.
- The new research has shown that M87* could be a black hole (with or without gravitomagnetic monopole) or a naked singularity (with or without gravitomagnetic monopole).
Try this PYQ:
Q. “Event Horizon” is related to:
(a) Telescope
(b) Black hole
(c) Solar glares
(d) None of the above
Post your answers here.
Back2Basics: Event Horizon Telescope (EHT)
- The EHT project is an international partnership formed in 2012.
- It is a network of 10 radio telescopes on four continents that collectively operate like a single instrument nearly the size of the Earth.
- Its main objective is to directly observe the immediate environment of a black hole.
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Gravitational Wave Observations
[pib] Merging of three Supermassive Black Holes
Note4Students
From UPSC perspective, the following things are important :
Prelims level: Supermassive Black Holes
Mains level: Gravitational waves observation
Indian researchers have discovered three supermassive black holes from three galaxies merging together to form a triple active galactic nucleus, a compact region at the centre of a newly discovered galaxy that has a much-higher-than-normal luminosity.
What are Supermassive black holes?
- A supermassive black hole is the largest type of black hole, with mass on the order of millions to billions of times the mass of the Sun.
- Black holes are a class of astronomical objects that have undergone gravitational collapse, leaving behind spheroidal regions of space from which nothing can escape, not even light.
- They are difficult to detect because they do not emit any light. But they can reveal their presence by interacting with their surroundings.
Active galactic nuclei (AGN) from such black holes
- When the dust and gas from the surroundings fall onto a supermassive black hole, some of the mass is swallowed by the black hole, but some of it is converted into energy.
- This is emitted back as electromagnetic radiation that makes the black hole appear very luminous.
- They are called active galactic nuclei (AGN) and release huge amounts of ionized particles and energy into the galaxy and its environment.
- Both of these ultimately contribute to the growth of the medium around the galaxy and ultimately the evolution of the galaxy itself.
How does merger of black holes occur?
- A major factor impacting galaxy evolution is galaxy interactions, which happen when galaxies move close by each other and exert tremendous gravitational forces on each other.
- During such galaxy interactions, the respective supermassive black holes can get near each other.
- The dual black holes start consuming gas from their surroundings and become dual AGN.
What happens when galaxies collide?
- If two galaxies collide, their black hole will also come closer by transferring the kinetic energy to the surrounding gas.
- The distance between the blackholes decreases with time until the separation is around a parsec (3.26 light-years).
- The two black holes are then unable to lose any further kinetic energy in order to get even closer and merge.
- This is known as the final parsec problem.
Here comes the third black hole
- Many AGN pairs have been detected in the past, but triple AGN are extremely rare, and only a handful has been detected before using X-ray observations.
- The presence of a third black hole can solve this problem.
- The dual merging blackholes can transfer their energy to the third blackhole and merge with each other.
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Gravitational Wave Observations
Black Hole swallows Neutron Star
Note4Students
From UPSC perspective, the following things are important :
Prelims level: Neutron star, Black Holes
Mains level: Gravitational waves observation
In an entirely strange phenomenon, astronomers have spotted two neutron stars being swallowed by different black holes.
What are Black Holes?
- A black hole is a region of spacetime where gravity is so strong that nothing—no particles or even electromagnetic radiation such as light—can escape from it.
- Neutron stars and black holes are among the most extreme objects in the universe. They are the fossil relics of massive dead stars.
- When a star that is more than eight times as massive as the Sun runs out of fuel, it undergoes a spectacular explosion called a supernova.
- What remains can be a neutron star or a black hole.
There is no upper limit to how massive a black hole can be, but all black holes have two things in common: a point of no return at their surface called an “event horizon”, from which not even light can escape and a point at their centre called a “singularity”, at which the laws of physics as we understand them break down.
What about Neutron stars?
- Neutron stars are typically between 1.5 and two times as massive as the Sun but are so dense that all their mass is packed into an object the size of a city.
- At this density, atoms can no longer sustain their structure and dissolve into a stream of free quarks and gluons: the building blocks of protons and neutrons.
What is the news observation?
- Gravitational waves are produced when celestial objects collide and the ensuing energy creates ripples in the fabric of space-time which carry all the way to detectors on Earth.
- The reverberations from the two celestial objects were picked up using a global network of gravitational wave detectors.
What makes this strange phenomenon?
- This is the first time scientists have seen gravitational waves from a neutron star and a black hole.
- Previous gravitational wave detections have spotted black holes colliding, and neutron stars merging but not one of each.
Why study this?
- Neutron star-black hole systems allow us to piece together the evolutionary history of stars.
- Gravitational-wave astronomers are like stellar fossil-hunters, using the relics of exploded stars to understand how massive stars form, live and die.
Answer this PYQ in the comment box:
Q.“Event Horizon” is related to (CSP 2018):
(a) Telescope
(b) Black hole
(c) Solar glares
(d) None of the above
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Gravitational Wave Observations
[pib] Narrow-Line Seyfert 1 (NLS1) Galaxy
Note4Students
From UPSC perspective, the following things are important :
Prelims level: NLS1 Galaxy
Mains level: Black holes and gravitation waves
Astronomers have discovered a new active galaxy identified as the farthest gamma-ray emitting galaxy that has so far been stumbled upon. This active galaxy called the Narrow-Line Seyfert 1 (NLS1) galaxy.
Try this PYQ:
Q.Recently, scientists observed the merger of giant ‘blackholes’ billions of light-years away from the Earth. What is the significance of this observation?
(a) ‘Higgs boson particles’ were detected.
(b) ‘Gravitational waves’ were detected.
(c) Possibility of inter-galactic space travel through ‘wormhole’ was confirmed.
(d) It enabled scientists to understand ‘singularity’.
NLS1 Galaxy
- Indian scientists have studied around 25,000 luminous Active galactic nuclei (AGN) from the Sloan Digital Sky Survey (SDSS).
- They identified it as a gamma-ray emitting NLS1 galaxy, which is a rare entity in space.
- It is about 31 billion light-years away, opens up avenues to explore more such gamma-ray emitting galaxies that wait to meet us.
What makes it intriguing?
- Ever since 1929, when Edwin Hubble discovered that the Universe is expanding, it has been known that most other galaxies are moving away from us.
- Light from these galaxies is shifted to longer (and this means redder) wavelengths – in other words, it is red-shifted.
- Scientists have been trying to trace such red-shifted galaxies to understand the early Universe.
- Powerful relativistic jets, or sources of particles in the Universe travelling nearly at speed to light, are usually produced by AGN powered by large black holes and hosted in a giant elliptical galaxy.
Why NLS1 is unique?
- NLS1s are a unique class of AGN that are powered by the black hole of low mass and hosted in a spiral galaxy.
- As of today, gamma-ray emission has been detected in about a dozen NLS1 galaxies, which are a separate class of AGN identified four decades ago.
- All of them are at redshifts lesser than one, and no method was present to date to find NLS1 at redshifts larger than one.
- This discovery opens up a new way to find gamma-ray emitting NLS1 galaxies in the early Universe.
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Gravitational Wave Observations
What are Quasars?
Note4Students
From UPSC perspective, the following things are important :
Prelims level: Quasars
Mains level: Black holes and gravitation waves
An international team of astronomers have discovered the most distant ‘radio-loud’ quasar with the help of the European Southern Observatory’s Very Large Telescope (ESO’s VLT).
Ever found this on YouTube? Take time to watch this amazing video. It will literally blow up your mind and curiosity!
TIMELAPSE OF THE FUTURE: A Journey to the End of Time (4K)
This video will make up your perceptions and conceptions of how a galaxy dies after the sun runs out of fuel and what a black hole actually is!
What are Quasars?
- A quasar known as a quasi-stellar object is an extremely luminous active galactic nucleus (AGN), in which a supermassive black hole with mass ranging from millions to billions of times the mass of the Sun is surrounded by a gaseous accretion disk.
- As gas in the disk falls towards the black hole, energy is released in the form of electromagnetic radiation, which can be observed across the electromagnetic spectrum.
- The power radiated by quasars is enormous; the most powerful quasars have luminosities thousands of times greater than a galaxy such as the Milky Way.
- Most active galaxies have a supermassive black hole at the centre which sucks in surrounding objects.
- Quasars are formed by the energy emitted by materials spiralling around a black hole right before being sucked into it.
What makes this event special?
- 90 per cent of quasars do not emit strong radio waves, making this newly-discovered one special.
- It took 13 billion years for the quasar’s light to reach earth.
- Named P172+18, the quasar emitted wavelengths had a redshift of 6.8.
- Only three other ‘radio-loud’ sources with a redshift greater than six have been discovered so far and the most distant one had a redshift of 6.18.
- The higher the redshift of the radio wavelength, the farther away is the source.
As an object moves away from us, the sound or light waves emitted by the object are stretched out, which makes them have a lower pitch and moves them towards the red end of the electromagnetic spectrum, where light has a longer wavelength. In the case of light waves, this is called redshift.
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Gravitational Wave Observations
Type-II Supernova and the role of neutrinos
Note4Students
From UPSC perspective, the following things are important :
Prelims level: Neutrino, Supernovae
Mains level: NA
This newscard is an excerpt from the original article published in The Hindu.
Another space-based abstract terminology has appeared in TH.
What is the news about?
- Many stars, towards the end of their lifetimes, form supernovas – massive explosions that send their outer layers shooting into the surrounding space.
- Most of the energy of the supernova is carried away by neutrinos – tiny particles with no charge and which interact weakly with matter.
- Researching the mechanisms of the so-called Type II supernovas, a team from IIT Guwahati has come up with new insights into the part played by neutrinos in this dramatic death of massive stars.
What are Neutrinos?
- Proton, neutron, and electron are tiny particles that makeup atoms.
- The neutrino is also a tiny elementary particle, but it is not part of the atom.
- Neutrino has a very tiny mass, no charge and spins half.
- It interacts very weakly with other matter particles.
- Neutrinos come from the sun (solar neutrinos) and other stars, cosmic rays that come from beyond the solar system, and from the Big Bang from which our Universe originated.
- They can also be produced in the lab.
Their types
- Neutrinos come in three ‘flavours’, another name for ‘types’, and each flavour is associated with a light elementary particle.
- For instance, the electron-neutrino is associated with the electron; the muon-neutrino with the muon and the tau-neutrino with the tau particle.
What is Supernova?
- All the stars burn nuclear fuel in their cores to produce energy.
- The heat generates internal pressure which pushes outwards and prevents the star from collapsing inward due to the action of gravity on its own mass.
- But when the star ages and runs out of fuel to burn, it starts to cool inside.
- This causes a lowering of its internal pressure and therefore the force of gravity wins; the star starts to collapse inwards.
- This builds up shock waves because it happens very suddenly, and the shock wave sends the outer material of the star flying. This is what is perceived as a supernova. This happens in very massive stars.
Try this PYQ:
Q. Which of the following is/are cited by the scientists as evidence/evidence for the continued expansion of the universe?
- Detection of microwaves in space
- Observation of redshirt phenomenon in space
- Movement of asteroids in space
- Occurrence of supernova explosions in space code
(a) 1 and 2 only
(b) 2 only
(c) 1, 3 and 4
(d) None of the above can be cited as evidence
The Type-II Supernova
- In stars that are more than eight times as massive as the Sun, the supernova is accompanied by a collapsing of the inner material of the dying star – this is also known as core-collapse supernova or Type II supernova.
Role of neutrinos
- The collapsing core may form a black hole or a neutron star, according to its mass.
- As they spew out of the raging supernova, the neutrinos can change from one flavour to another in a process known as neutrino oscillations.
- Due to the high density and energy of the supernova, it generates neutrino oscillations happening simultaneously over different energies (unlike normal neutrino oscillation), termed collective neutrino oscillation.
- The oscillation result may dramatically change when one allows the evolution with the angular asymmetry, the oscillations can happen at a nanosecond time scale, termed fast oscillation.
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Gravitational Wave Observations
‘Recoiling’ Black Holes
Note4Students
From UPSC perspective, the following things are important :
Prelims level: Black Holes, Recoils
Mains level: Black holes and gravitation waves
A supermassive black hole, which is estimated to weigh up to 100 billion times the mass of the Sun, is seemingly missing, leaving astronomers perplexed.
Try this PYQ:
Q.Recently, scientists observed the merger of giant ‘blackholes’ billions of light-years away from the Earth. What is the significance of this observation?
(a) ‘Higgs boson particles’ were detected.
(b) ‘Gravitational waves’ were detected.
(c) Possibility of inter-galactic space travel through ‘wormhole’ was confirmed.
(d) It enabled scientists to understand ‘singularity’.
The ‘missing’ black hole
- The black hole is supposed to be located in Abell 2261, an enormous galaxy cluster that is about 2.7 billion light-years away from our planet.
- So, when we look at a celestial object, we are looking at how it appeared that long ago in the past.
- At 2.7 billion light-years away, the Abell galaxy is at an overwhelmingly large distance away from us.
What could have happened?
- Every large galaxy in the universe has a supermassive black hole at its centre, whose mass is millions or billions of times that of the Sun, says NASA.
- The black hole at the centre of our galaxy– the Milky Way– is called Sagittarius A*, and is 26,000 light-years away from Earth.
- Scientists have been using data gathered in 1999 and 2004 to look for the centre of the Abell galaxy, but have so far been unable to find its black hole.
- A reason for this could be that Abell’s black hole has been ejected from the centre of the galaxy.
Recoil of Black Holes
- When two black holes merge, they release what is known as gravitational waves– invisible ripples travelling at the speed of light, which squeeze and stretch anything in their path.
- As per the theory of gravitational waves, during such a merger, when the amount of waves generated in one direction is stronger than another, the new big black hole can be sent away from the centre of the galaxy into the opposite direction.
- This is known as a “recoiling” black hole.
- So far, though, scientists are yet to find definitive evidence for recoiling black holes and are still to discover whether supermassive black holes can merge and release gravitational waves.
- As of now, only mergers of significantly smaller black holes have been verified.
Why it is significant?
- The researchers assert that this may have happened because of the merging of two smaller galaxies to form Abell– a process in which both of their black holes merged to form an even bigger black hole.
- If this hypothesis turns out to be true, it would mean a major breakthrough in astronomy.
Back2Basics:
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Gravitational Wave Observations
Galaxy NGC 6240
Note4Students
From UPSC perspective, the following things are important :
Prelims level: Merger of Black Holes
Mains level: Black holes and gravitation waves
NASA’s Chandra X-ray Observatory shared the images of Galaxy NGC 6240 that contains two supermassive Black Holes in the process of merging.
From astronomers to general space enthusiasts, black holes are a topic of interest for many. If you’re someone who spends a lot of their time researching facts about this region of space-time or watching videos on the same, then you must check out this news.
Galaxy NGC 6240
- The black holes, located in Galaxy NGC 6240 are 3,000 light-years apart and they will drift together to form a larger black hole millions of years from now.
- As per a blog post by the observatory, the merging process began some 30 million years ago
- The pairs of massive black holes in the process of merging are expected to be the most powerful sources of gravitational waves in the Universe.
- Seen as the bright ‘dots’ near the centre of this image, the black holes are just 3,000 light-years apart.
About Chandra X-ray Observatory
- It is a telescope specially designed to detect X-ray emissions from very hot regions of the universe such as exploded stars, clusters of galaxies, and matter around black holes.
- Orbiting at 139,000 km in space, the telescope was launched aboard the Space Shuttle Columbia during STS-93 by NASA in 1999.
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Gravitational Wave Observations
What is Einstein’s Eclipse?
Note4Students
From UPSC perspective, the following things are important :
Prelims level: Einstein’s Eclipse
Mains level: General Relativity
This newscard is an excerpt from the original article published in the DownToEarth.
Einstein’s Eclipse
- Albert Einstein’s prediction of the bending of light by the gravity of the Sun, one of the components of his general theory of relativity, can be tested during a solar eclipse.
- Following an unsuccessful attempt to validate this prediction during the Solar eclipse of June 8, 1918, two expeditions were made to measure positions of stars during this eclipse.
- The eclipse presented a rare chance to verify one of the essential consequences of general relativity, the bending of light by gravity.
- Einstein’s theory predicted that rays of light passing near a massive body in space would be visibly bent as they followed the curve in space-time created by the body’s mass.
- In the case of a ray of light originating from a distant star and passing near the edge of the Sun, Einstein calculated a deflection of about 1.75 arc seconds.
Try this PYQ:
Q.Consider the following phenomena:
- Light is affected by gravity.
- The Universe is constantly expanding.
- Matter warps its surrounding space-time.
Which of the above is/are the predictions of Albert Einstein’s General Theory of Relativity, often discussed in media?
(a) 1 and 2 only
(b) 3 only
(c) 1 and 3 only
(d) 1, 2 and 3
What was studied during the eclipse?
- Einstein published his theory and predictions in 1915, and in 1919 the British physicist Sir Arthur Eddington took advantage of a total solar eclipse to attempt to detect the shifting images of stars near the limb of the sun.
- The problem was that during totality the sky does not get perfectly dark, and only a handful of stars were visible near the sun from which to make the measurement.
- The darkness of an eclipse, though, would allow the astronomers to observe and photograph the field of stars around the Sun.
- By comparing the photographs with reference images taken at night, it would be possible to measure how much the presence of the Sun had bent the stars’ light.
- Conveniently, a cluster of bright stars known as the Hyades would appear near the Sun during the eclipse.
Significance
- After several months of analysis, researchers announced in November that their findings supported the theory of general relativity.
- Media coverage tended to dwell on the recondite nature of Einstein’s work, emphasizing that there were only a handful of people in the world who could understand it.
- It could be argued that 1919 was the year when Einstein’s name became a byword for superhuman intellectual ability—making possible the small industry of Einstein-themed merchandise that still exists today.
Back2Basics: General Relativity
- Einstein’s theory proposes that gravity is not an actual force, but is instead a geometric distortion of space-time not predicted by ordinary Newtonian physics.
- The more mass you have to produce the gravity in a body, the more distortion you get.
- This distortion changes the trajectories of objects moving through space, and even the paths of light rays, as they pass close-by the massive body.
- Even so, this effect is very feeble for an object as massive as our own sun, so it takes enormous care to even detect that it is occurring.
- General Relativity predicts how much of this bending of light you should see given the mass of the object.
- Called ‘gravitational lensing’ it has been detected on the cosmological scale as entire clusters of galaxies distort the light from more distant galaxies behind them as this image from the Hubble Space Telescope shows.
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Gravitational Wave Observations
New Shephard Rocket System
Note4Students
From UPSC perspective, the following things are important :
Prelims level: Karman Line, New Sphephard
Mains level: Micro-gravity experimentation
New Shephard, a rocket system meant to take tourists to space successfully completed its seventh test launch.
Note the features of the Karman Line. It is a new terminolgy in our recent space vocab.
What is New Shephard?
- New Shephard has been named after astronaut Alan Shephard, the first American to go to space, and offers flights to space over 100 km above the Earth and accommodation for payloads.
- Essentially, it is a rocket system that has been designed to take astronauts and research payloads past the Karman line – the internationally recognised boundary of space.
- The idea is to provide easier and more cost-effective access to space meant for purposes such as academic research, corporate technology development and entrepreneurial ventures among others.
- It is built by Amazon founder Jeff Bezos’s Space Company called Blue Origin.
- In 2018, Blue Origin was one of the ten companies selected by NASA to conduct studies and advance technologies to collect process and use space-based resources for missions to the Moon and Mars.
How does it work?
- The rocket system consists of two parts, the cabin or capsule and the rocket or the booster.
- The cabin can accommodate experiments from small mini payloads up to 100 kg.
- The cabin is designed for six people and sits atop a 60-feet tall rocket and separates from it before crossing the Karman line, after which both vehicles fall back to the Earth.
- The system is a fully reusable, vertical takeoff and vertical landing space vehicle that accelerates for about 2.5 minutes before the engine cuts off.
- After separating from the booster, the capsule free falls in space, while the booster performs an autonomously controlled vertical landing back to Earth.
- The capsule, on the other hand, lands back with the help of parachutes.
Back2Basics: Karman line
- The Karman line is an attempt to define a boundary between Earth’s atmosphere and outer space.
- The line is named after Theodore von Kármán (1881–1963), a Hungarian American engineer and physicist, who was active primarily in aeronautics and astronautics.
- He was the first person to calculate the altitude at which the atmosphere becomes too thin to support aeronautical flight and arrived at 83.6 km (51.9 miles) himself.
Locating the line
- The Fédération Aéronautique Internationale (FAI) defines Karman Line as the altitude of 100 kilometres (62 miles; 330,000 feet) above Earth’s mean sea level.
- However, other organizations do not use this definition. There is no international law defining the edge of space, and therefore the limit of national airspace.
- For instance, the US Air Force and NASA define the limit to be 50 miles (80 km) above sea level.
- The line is approximately at the turbopause, above which atmospheric gases are not well-mixed.
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Gravitational Wave Observations
What is Raychaudhuri Equation?
Note4Students
From UPSC perspective, the following things are important :
Prelims level: Raychaudhuri Equation
Mains level: Not Much
The Raychaudhuri Equation in General Relativity, derived by Raychaudhuri is in the spotlight after 2020 Physics Nobel was awarded to Penrose for throwing light on Black Holes.
Try this MCQ:
Q.The Raychaudhuri Equation is sometimes seen in news is related to:
Artificial Intelligence/Cloud Computing/Quantum Mechanics/Space Sciences
What is Raychaudhuri Equation?
- Raychaudhuri (1923–2005) was an Indian physicist, known for his research in general relativity and cosmology.
- In general relativity, the Raychaudhuri equation is a fundamental result describing the motion of nearby bits of matter.
- It was discovered independently by the Indian physicist Amal Kumar Raychaudhuri and the Soviet physicist Lev Landau.
- The equation offers a simple and general validation of our intuitive expectation that gravitation should be a universal attractive force between any two bits of mass-energy in general relativity, as it is in Newton’s theory of gravitation.
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Gravitational Wave Observations
Physics Nobel for discoveries about Black Holes
Note4Students
From UPSC perspective, the following things are important :
Prelims level: Black Holes
Mains level: Black holes and gravitation waves
Three scientists won this year’s Nobel Prize in Physics for advancing our understanding of black holes, the all-consuming monsters that lurk in the darkest parts of the universe.
Try this PYQ:
Q.Recently, scientists observed the merger of giant ‘blackholes’ billions of light-years away from the Earth. What is the significance of this observation?
(a) ‘Higgs boson particles’ were detected.
(b) ‘Gravitational waves’ were detected.
(c) Possibility of inter-galactic space travel through ‘wormhole’ was confirmed.
(d) It enabled the scientists to understand ‘singularity’.
Who are these laureates?
- Briton Roger Penrose received half of this year’s prize for the discovery that black hole formation is a robust prediction of the general theory of relativity.
- German Reinhard Genzel and American Andrea Ghez received the second half of the prize for the discovery of a supermassive compact object at the centre of our galaxy.
What are black holes?
- A black hole is formed when stars collapse and can be defined as a space in the universe with an escape velocity so strong that even light cannot escape it.
- Escape velocity is the speed at which an object must travel to override a planet or an object’s gravitational force.
- For instance, for a spacecraft to leave the surface of the Earth, it needs to be travelling at a speed of about 40,000 km per hour.
- Since light cannot get out, black holes are invisible and can only be tracked with the help of a space telescope or other special tools.
- And the reason light cannot escape is mainly that the gravity inside a black hole is very strong as a result of a lot of matter being squeezed into a small space.
Their contributions
- Penrose has been awarded the prize for the discovery that black hole formation is a robust prediction of the general theory of relativity.
- Genzel and Ghez have been awarded the prize for the discovery of a supermassive compact object at the centre of our galaxy.
- Penrose’s work has shown that black holes are a direct consequence of Albert Einstein’s general theory of relativity.
- Einstein himself did not believe that black holes exist and presented his theory in November 1915, providing a new way to look at and understand the gravity that shapes the universe “at the largest scale”.
- Penrose used Einstein’s general theory of relativity in order to prove that the process of formation of black holes is a stable one.
- Genzel and Ghez, on the other hand, have discovered that an invisible and an extremely heavy object governs the stars’ orbit at the centre of the Milky Way.
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Gravitational Wave Observations
Black Holes Merger
Note4Students
From UPSC perspective, the following things are important :
Prelims level: Black Holes
Mains level: Black holes merger
Billions of years ago, a collision between two black holes sent gravitational waves rippling through the universe. In 2019, signals from these waves were detected at the gravitational wave observatory LIGO (United States) and the detector Virgo (Italy).
Try this PYQ:
Q.Recently, scientists observed the merger of giant ‘blackholes’ billions of light-years away from the Earth. What is the significance of this observation?
(a) ‘Higgs boson particles’ were detected.
(b) ‘Gravitational waves’ were detected.
(c) Possibility of inter-galactic space travel through ‘wormhole’ was confirmed.
(d) It enabled the scientists to understand ‘singularity’.
Why in news?
- The cause of curiosity is the mass of one of the parent black holes, which defies traditional knowledge of how black holes are formed.
What exactly was detected?
- It was a signal from a gravitational wave, a relatively new field of discovery.
- Gravitational waves are invisible ripples that form when a star explodes in a supernova; when two big stars orbit each other; and when two black holes merge.
- Travelling at the speed of light, gravitational waves squeeze and stretch anything in their path.
Detecting gravitational waves
- Gravitational waves were proposed by Albert Einstein in his General Theory of Relativity over a century ago.
- It was only in 2015, however, that the first gravitational wave was actually detected — by LIGO. Since then, there have been a number of subsequent detections of gravitational waves.
- The signal detected at LIGO and Virgo, as described by the LIGO Collaboration, resembled “about four short wiggles” and lasted less than one-tenth of a second.
Where did it come from?
- Subsequent analysis suggested that GW190521 had most likely been generated by a merger of two black holes. The signal likely represented the instance that the two merged.
- It was calculated to have come from roughly 17 billion light-years away, and from a time when the universe was about half its age.
Some questions to verify
- The findings led to further questions.
- One of the two merging black holes falls in an “intermediate-mass” range — a misfit that cannot be explained by traditional knowledge of how black holes form.
Why is it unusual?
- All the black holes observed so far belong to either of two categories.
- One category ranges between a few solar masses (one solar mass is the mass of our Sun) and tens of solar masses. These are thought to form when massive stars die.
- The other category is of supermassive black holes. This range from hundreds of thousands, to billions of times that of our sun.
- According to traditional knowledge, stars that could give birth to black holes between 65 and 120 solar masses do not do so — stars in this range blow themselves apart when they die, without collapsing into a black hole.
Observing for the first time
- In the merger leading to the GW190521 signal, the larger black hole was of 85 solar masses —well within this unexpected range, known as the pair-instability mass gap.
- It is the first “intermediate-mass” black hole ever observed. (In fact, the smaller black hole to is borderline, at 66 solar masses.)
- The two merged to create a new black hole of about 142 solar masses. Energy equivalent to eight solar masses was released in the form of gravitational waves, leading to the strongest ever wave detected by scientists so far.
Possible reasons for its formation
- The researchers suggest that the 85-solar-mass black hole was not the product of a collapsing star, but was itself the result of a previous merger.
- Formed by a collision between two black holes, it is likely that the new black hole then merged with the 66-solar-mass black hole — leading to gravitational waves and the signal received by LIGO and Virgo.
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Gravitational Wave Observations
GW190412: The first merger of two black holes with unequal masses
Note4Students
From UPSC perspective, the following things are important :
Prelims level: General Relativity, Black Holes, Black Holes merger
For the first time since it started functioning, the gravitational wave observatories at LIGO scientific collaboration have detected a merger of two unequal-mass black holes.
This newscard contains few basic terms that one must know-
GW190412
- The event, dubbed GW190412, was detected nearly a year ago, and this is almost five years after the first-ever detection of gravitational-wave signals by these powerful detectors.
- Subsequent analysis of the signal coming from the violent merger showed that it involved two black holes of unequal masses coalescing.
- One of them was some 30 times the mass of the Sun and the other which had a mass nearly 8 times the solar mass.
- The actual merger took place at a distance of 2.5 billion light-years away.
Significant feature observed
- The detected signal’s waveform has special extra features in it when it corresponds to the merger of two unequal-sized black holes as compared with a merger of equal-sized black holes.
- These features make it possible to infer many more things about the characters such as- a more accurate determination of the distance from the event, the spin or angular momentum of the more massive black hole and the orientation of the whole event with respect to viewers on Earth.
- While the mass of the black hole bends the space-time close to it, the spin or angular momentum of this inscrutable object drags the nearby space-time, causing it to swirl around, along with it.
- Hence both these properties are important to estimate.
Confirmed General Relativity
- An Indian team consisting of researchers verified the consistency of the signal with the prediction of General Relativity.
- The existence of higher harmonics was itself a prediction of General Relativity.
Must refer for an easy and illustrated understanding of General Relativity-
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Eureka moment: Gravitational waves found
Recently, Gravitational waves, the cosmic ripples that distort space-time itself, have been directly detected for the first time. Let’s know about this unprecedented discovery!
What is so special about this eureka moment?
- For the first time, scientists have observed ripples in the fabric of space-time called gravitational waves, arriving at the earth from a cataclysmic event in the distant universe
- This confirms a major prediction of Albert Einstein’s 1915 general theory of relativity and opens an unprecedented new window onto the cosmos
- Physicists have concluded that the detected gravitational waves were produced during the final fraction of a second of the merger of two black holes to produce a single, more massive spinning black hole
- This collision of two black holes had been predicted but never observed
Let’s first know about Albert Einstein’s general theory of relativity?
- In 1905, Albert Einstein determined that the laws of physics are the same for all non-accelerating observers, and that the speed of light in a vacuum was independent of the motion of all observers. This was the theory of special relativity
- It introduced a new framework for all of physics and proposed new concepts of space and time
- Einstein then spent 10 years trying to include acceleration in the theory and published his theory of general relativity in 1915
- In it, he determined that massive objects cause a distortion in space-time, which is felt as gravity
[ Einstein’s mathematics showed that massive accelerating objects (such as neutron stars or black holes orbiting each other) would disrupt space-time in such a way that ‘waves’ of distorted space would radiate from the source ]
What are Gravitational waves?
- Gravitational waves are distortions or ‘ripples’ in the fabric of space-time caused by some of the most violent and energetic processes in the Universe
- These ripples would travel at the speed of light through the Universe, carrying with them information about their cataclysmic origins, as well as invaluable clues to the nature of gravity itself
What are the Sources of Gravitational Waves?
- Any object with mass that accelerates (which in science means changes position at a variable rate, and includes spinning and orbiting objects) produces gravitational waves, including humans and cars and airplanes etc.
- But the gravitational waves made by us here on Earth are much too small to detect
- The strongest gravitational waves are produced by catastrophic events such as colliding black holes, the collapse of stellar cores (supernovae), coalescing neutron stars or white dwarf stars, the slightly wobbly rotation of neutron stars that are not perfect spheres, and the remnants of gravitational radiation created by the birth of the Universe itself
Not one but four types of Gravitational Waves!
- In order to understand the types of gravitational waves, Laser Interferometer Gravitational Wave Observatory (LIGO) scientists have defined 4 categories of gravitational waves
- These categories are: Continuous Gravitational Waves, Compact Binary Inspiral Gravitational Waves, Stochastic Gravitational Waves, and Burst Gravitational Waves
But, Why Detect Them?
- This will open up a new window of study on the Universe, giving us a deeper understanding of these cataclysmic events, and usher in brand new cutting-edge studies in physics, astronomy, and astrophysics
- More importantly, since gravitational waves don’t interact with matter (unlike electromagnetic radiation), they travel through the Universe completely unimpeded giving us a crystal clear view of the gravitational wave
- This will provide astronomers and other scientists, first glimpses of previously unseen and unseeable wonders, and greatly adding to our understanding of the nature of space and time itself
So, How does LIGO come into the Picture?
- LIGO( Laser Interferometer Gravitational Wave Observatory) is the world’s largest gravitational wave observatory and a cutting edge physics experiment
- LIGO exploits the physical properties of light and of space itself to detect and understand the origins of gravitational waves
- LIGO has 2 widely separated identical detector sites working in unison as a single “observatory”: one in Hanford, southeastern Washington State and the other in rural Livingston, Louisiana
- LIGO has a very close collaboration with the VIRGO collaboration that analyzes data from VIRGO, a 3 km gravitational wave interferometer located near Pisa, Italy
- Data from LIGO and Virgo are combined and analyzed together by the LIGO and Virgo collaborations
- Thus significantly increasing the capability of combined data for detecting and using gravitational waves to learn about nature
Is there any Way ahead for India?
- Yes, because Union cabinet has approved a proposal to establish a state-of-the-art gravitational wave observatory in India in collaboration with LIGO in the US
- The project will bring unprecedented opportunities for scientists and engineers to dig deeper into the realm of gravitational wave and take global leadership in this new astronomical frontier
- This will also bring considerable opportunities in cutting-edge technology for the Indian industry which will be engaged in the construction of the 8-km long beam tube at ultra-high vacuum on a leveled terrain
- With its establishment, India will join the global network of gravitational wave detectors
- The establishment of an observatory in India assumes importance because the further the distance between the observatories, the greater will be the accuracy in locating gravity waves
- Maharashtra and Madhya Pradesh are among the states shortlisted for the experiment
Can we expect some answers from you guys?
#Q. Recently, Union cabinet has approved a proposal to establish a gravitational wave observatory, one of the mega science projects in India. Discuss, how will this project help India if it becomes a reality.
Published with inputs from Arun | Image: space.com
In my opinion, although the discovery of Gravitational Waves has been rewarded with the Nobel Prize in Physics in 2017, the discovery is still on a shaky footing- because it assumes the STC to be real. Actually, the real / imaginary issue is being discussed for 100 years, with no globally accepted conclusion. In fact, as a common teacher of physics (teacher of HSC physics) I have raised a conceptual difficulty in a European review journal in April 2017. Americans and Europeans are planning the new generation of detectors (See Physics Today, October 2018) but I have raised the same issue in two comments on that article, title: Future gravitational wave detectors aim to probe early universe. Our national leaders have to consider economy because Americans and Europeans also are considering economy.