Gravitational Wave Observations

Was it really a black hole that the EHT imaged in 2019?


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:

  1. Singularity at its core– a point that is infinitely dense, as all the remnant mass of the star is compressed into this point.
  2. 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.
Please leave a feedback on thisx

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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