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

What is the News?

A paper published in The European Physical Journal C has said that M87* (a compact object that was imaged by the Event Horizon Telescope) is not necessarily a black hole but could even be a “naked singularity with a gravitomagnetic monopole”.

About the research

In 2019, astronomers of the Event Horizon Telescope captured the first-ever image of a supermassive black hole (M87*) which was located at the centre of a galaxy Messier 87 (M87). 

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. 

This discovery also found a mention in the “popular information” section of the announcement of the Nobel Prize in physics for 2020.

However, recent research has said that M87 is not necessarily a black hole but could even be a “naked singularity with a gravitomagnetic monopole”.

What is a Black Hole?

The simplest definition of a black hole is an object that is so dense that not even light can escape its surface.

Formation of Black Hole: 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, most astronomers believe is a black hole. 

Parts of Black Hole: A black hole has two parts: 

• Singularity: At the core of a black hole is a singularity. It is a point that is infinitely dense, as all the remnant mass of the star is compressed into this point. 
• Event horizon: It is 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. 

What is Naked Singularity?

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 has been called as “naked singularity” or a “troublesome sibling” of a black hole.

What is a Gravitomagnetic Monopole?

In the 19th 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. 

Hence, the researcher based on this analogy between gravitational force and electromagnetism explains that in 1963, Newman, Tamburino and Unti (NUT) proposed a theoretical concept called a “gravito-magnetic charge” also called a gravitomagnetic monopole.

Source: This post is based on the article “Was it really a black hole that the EHT imaged in 2019?” published by The Hindu on 15th November 2021.