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Asked by anon-219936 to Bella on 11 Jun 2019.
Question: How big is a supermassive blackhole?
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Bella Boulderstone answered on 11 Jun 2019:
Supermassive black holes can be really hard to weigh! They generally come in two ‘flavors’ ones called ‘stellar mass’ black holes which are generally 5-40ish as massive as our Sun and then there are the ‘supermassive’ black holes (my variety) which are a thousand to a million times the mass of our Sun these live at the centre of galaxies.
The closest supermassive black hole to us is the one at the centre of our own galaxy, The Milky Way. We got to measure how heavy it is from watching the closest-in stars go around it. What the orbits of these stars look like tells us about how heavy the thing is in the middle. We found that it was about four million times the mass of the Sun.
Comments
anon-219717 commented on :
How close can a human get to a supermassive black hole without being spaghettified?
Bella commented on :
Really good question! So spaghettification happens when the gravitational forces at your head and at your feet are super different. So what we’re looking for is a place where the change in the gravity is really steep. This might come as a bit of a surprise, but this doesn’t happen at supermassive black holes. They are so big, that they are felt for ages away and so the change (before falling in) can be quite gradual.
The stellar mass black holes, they’re the spaghettifiers (is that a word??), they’re the ones that’ll pull you into a piece of a spaghetti. This is because their gravitational forces aren’t felt until you’re quite close and then it’s super strong. So it means that you will feel that difference between the top of your head and the tips of your toes. (Here’s a news story about a star being spaghettified, I think the pictures are really quite nice: https://public.nrao.edu/news/black-hole-destroys-star/)
I’m not exactly sure how close you have to be to the black hole before you get spaghettified, it depends on how heavy each black hole is. I suspect it has something to do with what is called the ‘Hill Sphere’ of an object. A Hill Sphere, for example, is the area around a planet where all the moons of that particular planet live. It’s where the planet’s gravity is the most important (or black holes’ or star).
But nobody’s been spaghettified yet so it’s hard to find out!
anon-219235 commented on :
What draws objects into a black hole
anon-219235 commented on :
What would happen if 2black holes colided
Bella commented on :
It’s kind of weird to think about, but the thing that draws objects into a black hole is the same force that keeps you on the surface of the Earth, it’s just gravity. The black hole itself is the weird object because you can’t escape from it and it warps space and time around it, but the force is just gravity.
Bella commented on :
If two black holes collided, then the space and time gets warped and ripples as they circle each other and eventually collide. A whole bunch of energy is released after they collide, and the ripples can be detected on Earth by an instrument called LIGO, this was Laurence’s area of expertise.