A Supermassive Black Hole is just like a black hole but more massive and more powerful hence the Supermassive description. These giant black holes can be millions or billions more massive than a normal black hole.
They are normally found at the centres of most large galaxies including our own, the milky way. The Supermassive Black Hole in our galaxy is known as Sagittarius A*, name comes from the fact it can be located in the constellation of the same name.
Small a.k.a dwarf galaxies might have a supermassive black hole at the centre or have a star cluster. According to Indian Express, most dwarf galaxies do have a supermassive black hole. One of the galaxies, VUCD3 is equivalent to 4.4 million Suns and takes up 13% of the total mass of the galaxy. To put that into context, Sagittarius A* has about the same mass but only takes up 0.01% of the total mass of our galaxy.
Discovering Supermassive Black Holes at the heart of a dwarf galaxy opens up a can of worms as they were once thought to only exist in large galaxies. It has a knock on effect of how the galaxy could have formed in the first place and the big bang. Futurism
The A2261-BCG - Abelle 2261 Brightest Cluster Galaxy located in the constellation of Hercules is the largest galaxy that scientists have not yet seen a supermassive black hole. Scientists do believe that there is a Supermassive Black Hole but have not yet seen it. There are a couple of reasons why and they both relate to the black hole interacting with another black hole thereby hiding itself. One theory says that the merging black holes have scattered the stars and therefore hiding itself. The other theory is that the black hole got ejected from its location.
Its not the only time a black hole is believed or known to have been ejected from the centre of the galaxy, in 3c 186, the supermassive black hole has been seen to be off-centre which further analysis showed that the reason for the move was because of gravitational influences of another black hole pulling on it.
Galaxy 4C +37.11 or 0402+379 that is located in the constellation of Perseus has two supermassive black holes that will one day merge and create a super-supermassive black hole. Sorry, for the explanation but couldn't think of a better one. When they do, the resulting explosion will create gravitational waves which may be felt here but we'll all be gone by then, in a few million years. Wiki
A normal black hole occurs when a star reaches the end of its life and collapses in on itself to become a black hole. There are a couple of possible ways in which a supermassive black hole could have been created.
At the beginning of the universe, some 13.8 billion years ago, the first stars were giant, massive, blue stars, many times bigger than the biggest stars today. It is believed that these stars could have collapsed and turned into the supermassive black holes that exist today. The most massive star that is known is R136a1 which is in the Large Magellanic Cloud, a nearby galaxy. The star would not be massive enough to create a supermassive black hole.
Before a star is born, there is a large amount of gas and dust that gradually clumps together and turns into a star. Before our star, the Sun existed, there would have been a large stellar cloud existing in this space where we are now for billions of years before nuclear reactions began and the star was born. Our Sun is only about five billion years old so its quite young compared to the age of the universe.
Some black holes were born not long after the creation of the universe. When I say not long, I mean hundreds of millions of years after the event. ULAS J1342+0928 in the constellation of Bootes was born a mere 690 million years after the Big Bang, not long enough to go through the stellar cycle of being a dust cloud then a star and then a black hole, it could have gone from cloud to supermassive, skipping the stellar phase.
We know that Black Holes have been known to collide and create gravitational waves which have been picked up on Earth by LIGO. The Black Holes merging will create a larger black hole. We known that in about five billion years time so there's no need to panic, the Milky Way and the Andromeda Galaxy will collide, the result of which will be that the supermassive black holes will merge and result in a rebirth of the galaxy.
Colliding with an asteroid is not good and they are many many times smaller, collision with a black hole and its bigger brother, the Supermassive Black Hole is a lot worse. It an asteroid got too close to a star, it would vapourise but a star getting too close to a Supermassive Black Hole, the star would end up the worse for it. The star would be ripped to shreads and even be consumed by the black hole.
If a multiple star system such as Regulus in the constellation of Leo which has four stars in its system, some of the stars could be consumed by the black hole but the others could be sent shooting out of the galaxy at Hypervelocity. Star SDSS J090745.0+024507 has the highest velocity rate of any star in the galaxy and it is believed to be caused by it being in a multi-star system where the other stars were consumed.
When a Supermassive Black Hole has eaten gas, star or planet, it can quite literally burp it out for want of a better expression. It has happened in the relatively close nearby galaxy of Messier 51 galaxy. N.A.S.A.
Everything is born, lives and dies, things in space are no different. The Universe was born 13.8 billion years ago, it lives and then when it dies, the stars will turn into black holes and even then they will eventually die. Supermassive Black Holes will eventually dissipate but how long is unclear, there's only calculated guesses. We're talking in the order of not billions or trillions but googols (1 followed by 100 zeroes) of years.
Prof. Stephen Hawkings, the brilliant British astrophyscist who was wheel chaired bound due to suffering Motor Neurone Disease put forward the theory of Hawking Radiation which said that Black Holes leaked radiation back out and thereby if the black hole wasn't fed, it would eventually disappear.
Our solar system is located about 28,000 light years away from Sagittarius A* so we have no worries about being pulled into or destroyed by the supermassive black hole. If was a large city, we would be located in the suburbs. Although we are located a long way away, we are still affected by the black hole, the Sun including us orbits the centre every 230 million years. Starchild
The centre of the galaxy is known as the Galactic Centre and you'll notice on some star pages the Galacto-Centric Distance which is the distance to the centre of the galaxy from where it is. For example, the star Vega is 24,126.30 Light Years or 7,397.00 Parsecs away from the Galactic Centre.
The opposite direction of the Centre of Galaxy is referred to by some as the Anticentre and the nearest major star to that point is Elnath, blue giant star in the constellation of Taurus. Going towards Elnath is not the quickest way out of the galaxy, the galaxy is believed to be like Andromeda Galaxy and therefore, the shortest way out of the galaxy is to go up, more specifically head towards a spot near Beta and Gamma Coma Berenices. Wiki
Sagittarius A* was first theorized by Donald Lynden-Bell and Martin Rees (later Sir Martin Rees, Astronomer Royal) in 1971. It was not until three years later that Sagittarius A* was discovered by Bruce Balick and Robert Brown at the National Radio Astronomy Observatory, headquartered in Virgina, United States. Wiki
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