Black Hole

Q What is the context  ?

A 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.

Q What are details about M-87* ?

A 

• 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*.

Q What is a black hole ?

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.

Q 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.

Q What are Monopoles and gravity ?

A 

• 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”.

Q But then, what is the gravito-magnetic charge?

A 

• 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).

Q What are details about Event Horizon Telescope (EHT) ?

A 

• 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.