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Scientists have for the first time imaged the black hole at the center of the Milky Way

Image of Sagittarius A*. Credits: Event Horizon Telescope.

What is a black hole ?

A black hole is a place in space where matter has been squeezed so tightly together that its gravitational attraction prevents anything from getting out, not even light, which as we know it, usually happens in the case of dying stars. While the star is alive, the nuclear fusion occurring inside its core manages to balance out its gravitational attraction - preventing it from collapsing. At the final stages of their lives, most stars such as the Sun will expand into Red Giants, lose mass, and calmly turn into White Dwarfs.

In the case of larger stars whose masses reach up to 10-20 times the mass of our Sun, as the core begins to collapse, shockwaves weave through the stellar core, eventually causing a massive explosion called a supernova. In the remnant of the supernova, no forces are left to counteract the force of gravity, causing the stellar core to collapse on itself into an infinitely small point, creating a black hole.

Artist rendition of a black hole. Credits: NASA

However, Sagittarius A* is no ordinary black hole. It is what we call a Supermassive black hole, something scientist believe can be found at the centre of each galaxy. In the 1980's, scientists came to the conclusion that a black hole as heavy as 4 million times the mass of our Sun was located at the centre of our galaxy. Although this black hole is unusually massive compared to stellar black holes that occurs when ordinary stars die, it is of ordinary size and mass when comparing to other supermassive black holes.

If Black holes don't emit light, how can we see them ?

As one can imagine, it is very difficult to see a black hole, as they do not emit any detectable type of light. Despite this, astronomers are able to detect them by measuring the visible light, radio wave and X-rays emitted by the material surrounding the black hole.

X-rays and radio waves are just electromagnetic radiation at other wavelengths than visible light. Although everything we see is in visible light, this is only a small part of the electromagnetic spectrum. In this article, we previously discussed how the James Webb Space Telescope will observe the universe in infrared light, and how much more it will see compared to ordinary visible light telescopes.