Messier 87

Messier 87

Subject: Science and Tech

Context: The European Physical Journal C brings in an alternative explanation for the compact object that was imaged by the Event Horizon Telescope. The authors say it (M87*) is not necessarily a black hole but could even be a “naked singularity with a gravitomagnetic monopole.

Content:

Black hole:

• This black hole is calculated to be 6.5 billion times the Sun’s mass and is 55 million light years away from the Earth. 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).
• 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.
• A black hole has two parts: At its core is a singularity a point that is infinitely dense, as all the remnant mass of the star is compressed into this point. Then there is the 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 It can only see points outside the event horizon.
• 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.

Naked singularity with a gravitomagnetic monopole

• In general relativity, a naked singularity is a hypothetical gravitational singularity without an event horizon.
• In a black hole, the singularity is completely enclosed by a boundary known as the event horizon, inside which the gravitational force of the singularity is so strong that light cannot escape. Hence, objects inside the event horizon including the singularity itself cannot be directly observed. A naked singularity, by contrast, would be observable from the outside.
• The theoretical existence of naked singularities is important because their existence would mean that it would be possible to observe the collapse of an object to infinite density.
• In generic black holes, this is not a problem, as an outside viewer cannot observe the space-time within the event horizon.
• Naked singularities have not been observed in nature
• M87* could be either a black hole or a naked singularity and each of these possibilities could be plain or coupled with what is called a gravitomagnetic monopole.
• In the nineteenth century, James Clerk Maxwell unified electricity and magnetism as one combined phenomenon, showing that light is an electromagnetic wave.
• In 1963, Newman, Tamburino and Unti (NUT) proposed a theoretical concept called a “gravito-magnetic charge” also called a gravitomagnetic monopole.
• A gravitomagnetic monopole 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.
• The Kerr and the Schwarzschild solutions of Einstein’s equations [namely black holes with spin and having an event horizon] are considered appropriate for describing astrophysical black holes, like the one imaged in M87.