Black holes are regions of space where the gravitational pull is so strong that nothing - not even light - can escape. The gravity is so strong because matter has been squeezed into a tiny place. Most famously, black holes were predicted by Einstein's theory of general relativity, which shows that when a massive star dies, it leaves behind a small, dense remnant core. If the core's mass is more than about three times the mass of the sun, the force of the gravity overwhelms all other forces and produces a black hole.

Black holes are just that, they're "black" in that they do not emit light. For some black holes, primarily the supermassive ones, astronomers can see them because of Quasars (intensely bright sources of radio emissions) they produce. When matter falls onto black hole, it compressed and heats up in a souped-up version. The disk of material surrounding the black hole can glow brighter than its entire host galaxy, and is capable of launching jets of super-heated, nearly-light-speed particles out for tens of thousands of light-years. To date, astronomers have identified 50 black hole merger events.

Weighing 3 billion times that of the sun and sitting in a galaxy over 50 million light-years away, M87 (name given to an image of black hole in 2019 which astronomers took using Event Horizon telescope) looked like a distorted orange donut. It is good thing that the nearest black holes are thousands of light- years away from us.

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