Science Questions

Do black holes on the periphery move into the centre of a galaxy?

Tue, 24th Jul 2012

Listen Now    Download as mp3 from the show Finding Impossible Stars


Jerry asked:

If black hole is born at the edge of a galaxy, is it eventually pulled into the centre? If so, wouldn't it create a visible distortion as it falls to the massive black hole in the centre? Or does dark matter maintain a balanced galaxy?






Subscribe Free

Related Content


Make a comment

There seem to be Black holes existing in the outskirts of galaxies.

As for if they will wander inwards?
I guess it depends on the gravity/mass surrounding them, but they should at least do it at some time? It seems as if "our neighbouring galaxy Andromeda and the Milky Way will fall together and have a close collision. They will likely merge and be reborn as a single giant elliptical galaxy over the course of another billion years or so. How might this metamorphosis play out and what might you see if you looked up at night over the next 4 billion years! The space between stars is so vast compared to their size that during a galaxy collision no individual stars actually collide with one another. So our sun and its family of planets will be taking a passive but exciting ride through the pair of coalescing galaxies and take on a spectacular view of the unfolding disaster in relative safety."

As a byside, there's recently been found 'a group of 675 stars on the outskirts of our Milky Way galaxy, having been shot out by the black hole at the core of the galaxy.' and 'The recently discovered black hole would have accelerated the stars to more than three million kilometres per hour to throw them out of the galaxy.' And the speed of light is  (669, 600 000 miles per hour) .

Ouch, misread the speed here, ah well, got my imagination turning anyway :) yor_on, Sun, 29th Jul 2012

It may not be that a black hole would move to the middle of a galaxy, but rather a galaxy (without a black hole) would tend to engulf a black hole.

Think of our solar system.

Say you drop the sun, Earth, Mars, Venus, Mercury, the Moon, and etc into space.  Give them enough differential momentum that it doesn't collapse in on itself. 

Would you expect to find the sun orbiting our moon?
If you place all the planets on the same side of the sun...  does the sun migrate to the middle? 

What you would find is that the planets would start orbiting the sun, and distribute themselves around the sun.

There is apparently a 2 body problem, in that 2 bodies that aren't orbiting each other can't "capture" each other.  But, say you had a small galaxy that encountered a "rogue" black hole.  The galaxy would likely reform itself around the black hole.

The question then is what would happen if you have two black holes of similar size.  They may begin orbiting themselves as a binary system.  The stars within their orbit would be constantly stirred up, but I'm having troubles imagining the impact to the system to have binary black holes with a bunch of stars. CliffordK, Mon, 30th Jul 2012

Nice idea Clifford :)

If I assume that different mass will present a different attraction/gravity it then comes back to one thing, where is that mass 'concentrated'? Do we have super massive Black Holes in the centers of all Galaxies? yor_on, Tue, 31st Jul 2012

A black hole forming at the edge of the galaxy will not behave any differently from the star it came from.  unless the supernova explosion that created it was very asymmetrical it would continue in essentially the same orbit that it was before. Soul Surfer, Tue, 31st Jul 2012

Assuming there are, in fact, super-massive black holes in the center of most of the larger galaxies (not the dinky galaxies), it may be that the large galaxies tend to capture & surround the large black holes that they encounter.  Even if the combined mass of the stars is greater than the mass of the black hole, there would still be a tendency to move to surround the black hole.

As Soul Surfer mentioned, though, a black hole could be created from a neutron star.  And, could thus be just more dense, but no more massive than the parent star.  And, thus, in many senses, would behave gravitationally similarly to the parent star.

It is possible, however, that black holes would tend to behave differently with stellar collisions than stars, and might grow quicker.

How old are the black holes?

While stars are divide by age into population 3, 2, and 1 by metallicity, it is quite possible that the super-massive black holes are also extremely old, and have been slowly growing since the beginning of the universe. CliffordK, Wed, 1st Aug 2012

My own interpretation :) is that the Black Holes we can 'infer' are from around the Big Bang, but that's just a guess of mine. yor_on, Wed, 1st Aug 2012

See the whole discussion | Make a comment

Not working please enable javascript
Powered by UKfast
Genetics Society