Why don't black holes consume dark matter if dark matter responds to gravity?

[stunner5000pt]

Hello everyone

if black holes have a gravitational pull so strong that nothing can escape, then why is it that they do not continuously consume dark matter? Yes i know its called dark matter because it doesn't not interact with other matter but it does have an effect on the rotational curves of galaxies for example. In this case the dark matter is contained within the galaxy rather than some kind of an ether theory. Would that not imply that dark matter is affected by gravity? Wouldnt that also imply that dark matter would feed a blakc hole located at the center of a galaxy, for example?

 

[Nabeshin]

Would that not imply that dark matter is affected by gravity?

The whole point of dark matter is that it DOES interact gravitationally with all other matter. This is the reason why it affects the rotation curves of galaxies. It simply does not interact electromagnetically (i.e. with light), hence, why we call it dark.

 

[DaveC426913]

Hello everyone

if black holes have a gravitational pull so strong that nothing can escape...

Also, you may misunderstand what black holes do. They do not suck matter in like a giant vacuum cleaner. A black hole of mass X has no greater effect on matter at a distance than a star of mass X. i.e. if the sun were magically replaced by a black hole of the same mass, we would not notice here on Earth.

 

[ibysaiyan]

Hello everyone

if black holes have a gravitational pull so strong that nothing can escape, then why is it that they do not continuously consume dark matter? Yes i know its called dark matter because it doesn't not interact with other matter but it does have an effect on the rotational curves of galaxies for example. In this case the dark matter is contained within the galaxy rather than some kind of an ether theory. Would that not imply that dark matter is affected by gravity? Wouldnt that also imply that dark matter would feed a blakc hole located at the center of a galaxy, for example?

Just to add what the gentlemen before me mentioned,it's not like a black hole keeps on taking in matter,we all know that it depends on their size(the event horizon being the boundary).Some stay for quite a long period others evaporate very quickly. About a month ago I read an article in which the conclusion they had come up with was that there is no direct correlation between the center of galaxies(Supermassive black holes) and dark matter which was initially assumed to be.

I believe you have misunderstood the whole rotational velocities of the galaxies against the center phenomenon.One of the ways in which we assume hypothetically the presence of DM is by studying the observed and our expected values of the rotational velocities of the galaxy cluster (elliptical ones I assume).What we notice is that at close to the center of the galaxy there isn't much deviation between our observed and expected values but as we go further from the center we surprisingly note that the observed curve has a fairly constant velocity (implying dark matter).We would expect the velocity to decrease by r^-1/2.
So you see dark matter isn't concentrated at the center.Someone correct me if I am mistaken.

Regards,
ibysaiyan

 

[Polyrhythmic]

Just to add what the gentlemen before me mentioned,it's not like a black hole keeps on taking in matter,we all know that it depends on their size(the event horizon being the boundary).Some stay for quite a long period others evaporate very quickly.

Hawking radiation isn't really an issue on astronomical scales, since temperature and power of emission scale with inverse mass and mass squared, respectively. Even light astronomical black holes already exist in the range of solar masses, so the radiation is almost nonexistant (which makes it hard to detect).

 

[Nabeshin]

I believe you have misunderstood the whole rotational velocities of the galaxies against the center phenomenon.One of the ways in which we assume hypothetically the presence of DM is by studying the observed and our expected values of the rotational velocities of the galaxy cluster (elliptical ones I assume).What we notice is that at close to the center of the galaxy there isn't much deviation between our observed and expected values but as we go further from the center we surprisingly note that the observed curve has a fairly constant velocity (implying dark matter).We would expect the velocity to decrease by r^-1/2.
So you see dark matter isn't concentrated at the center.Someone correct me if I am mistaken.

That's right. We find that rather than being distributed strongly towards the center like luminous matter is, the dark matter forms a fairly diffuse halo around (and in) the galaxy, which can often be quite a bit larger than the visual extent of the galaxy.