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Recently, the first event image of asupermassive black hole was taken in the giant elliptical galaxy of M87. This is agargantuan black hole with the mass of 6.5 billion suns and an event horizon widerthan our entire solar system. While the photo confirmed many things such as theappearance of an accretion disk around the black hole, it also confirmed that a supermassive black hole does indeed exist in the center of M87. You mightthink this is an obvious statement but how did we know that there was asupermassive black hole in the center of m87 and in every galaxy for that matter? First off, let's make it clear that thescientific explanations for why there are supermassive black holes in thecenter of galaxies is not one hundred percent certain but I'll provide a fewof the most likely answers.
We have discovered several supermassive blackholes in the center of galaxies, our own one in the Milky Way is calledSagittarius A* and has a mass of 2.6 million times our Sun. However,supermassive black holes are not the same kind as stellar black holes. Stellarblack holes are ones that formed when a star with at least five times the mass ofthe Sun goes supernova. However, these black holes are extremelysmall around 30 kilometers wide. When compared to the largest supermassiveblack hole, TON 618 which has a diameter of 390 billion kilometerslarger than the entire solar system, stellar black holes are practicallyinsignificant. Another difference is that most supermassive black holes have anaccretion disk whereas stellar black holes do not. An accretion disk is gasand dust which is slowly consumed by the black hole it orbits.Strangely enough a black hole cannot consume the mass instantly because themass assumes a slowly decaying orbit. Therefore, it takes some time to fallinto the black hole and this is why the accretion disk forms. This is why stellarblack holes do not have accretion disks. There is not enough mass around them tocreate the disk, unlike the mass in the center of agalaxy. Hence, a supermassive black hole with an accretion disk is called aquasar.
The strange thing about supermassiveblack holes is that the size of the black hole is directly proportional tothe size of the galaxy. The bigger the galaxy, the bigger the supermassive blackhole at its heart. These black holes were thought to have formed in the early universe,when the density of space was much greater. Gravity created stars of immensesized, which in turn created black holes of equal magnitude. These first blackholes swallowed all the matter in the surrounding area, which in turn increasedtheir size further. Their violent feeding frenzy caused matter and radiation to beshot out in jets millions of light-years long and this is what is thought tohave formed the stars that make up our galaxy. These long jets of matter and radiationcondensed and slowly rotated around the supermassive black hole. Thereforesupermassive black holes must have come before galaxies and are key to theirevolution. We owe our very existence to these supermassive black holesand without them, our Sun and planet would never have formed. Because nowadayswe observe the galaxies to be of proportional size to their supermassiveblack hole, the best theory we have is that the black holes not just form butdrive the evolution of galaxies.
However we can divide supermassive black holesinto two separate categories based on how the black hole feeds. Black holesthat actively feed on the mass and energy around them are extremelydangerous and can produce violent bursts of radiation and energy. These are thefirst category and are said to be active galaxies such as NGC 4258.From this image of the galaxy, you can see there is an extra set of red arms ontop of the existing bluer arms. Scientists now know that these extra arms wereproduced by one such radiation burst and were able to work out that this is anactive galaxy. The other type of black hole is a dormant and non-feeding onesuch as Sagittarius A* in the Milky Way. This kind is much more safe and does notproduce the high levels of radiation as an active galaxy black hole. It is morefriendly to life and allowed us to thrive on Earth without constant wavesof lethal radiation that might occur in an active galaxy.
However, if Sagittarius A* was active we wouldn't be able to survive and probablywould never have existed. To create a galaxy, it is becoming clearer andclearer to scientists that a supermassive black hole is required.Without it, not a single galaxy would have formed. This is because black holesdrive the evolution of galaxies and shoot jets of material and energyrequired to create stars and the planets. Because Sagittarius A* is now an inactiveblack hole, life has thrived on this planet and without this simple fact, we mightnot have existed. Anyway, thank you for watching and I hope you enjoyed thevideo. Remember to leave a like and subscribe to the channel for moreastronomy and cosmology content. Until next time. Goodbye.
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