Gravitational Wave Observations

Event Horizon Telescope (EHT) confirms Black Hole Shadow

event horizon

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


  • 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)

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

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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