Is there a blackhole in the centre of EVERY galaxy?

[CoolGrey6]

I've been reading some books on Galactic Structures and Galactic Evolutions, evidence from rotation curves of stars near the centre of our Milky Way and also M31 suggest that there is a blackhole in the centre. But is this true for all galaxies regardless of their Hubble Type? is there a galaxy that does not have a blackhole at its centre?? What type of evidences beside rotation curves suggest that there is a blackhole?? X-ray emissions from its accretio disk?

[theEVIL1]

if one looks at regular (spiral) galactic bodies, (as I said in print years ago and was told I was WRONG!) the gravitational displacement of Ha and HII is INSUFFICENT in only 13.9 X9 years to create the velocities required to form a spiral galaxy. So...I may still be "wong" but I agree with you. Of course they also said I was wrong about:
1. water on mars
2. Permafrost on Mars
3. Past life on mars

no. 3 will have to wait (but I am betting on me)

Laters:

Dr. Bill

[Jess]

It looks very much as if every galaxy with a central bulge has a black hole. But bulgeless galaxies such as M33 do not appear to have sufficient central stellar velocity dispersions to contain central supermassive black holes. Until enough nearby galaxies have been surveyed, however, that'll have to remain a tentative conjecture - the sample size isn't big enough at present to make any definite statements.

Jess

[Nereid]

Originally posted by CoolGrey6
I've been reading some books on Galactic Structures and Galactic Evolutions, evidence from rotation curves of stars near the centre of our Milky Way and also M31 suggest that there is a blackhole in the centre. But is this true for all galaxies regardless of their Hubble Type? is there a galaxy that does not have a blackhole at its centre?? What type of evidences beside rotation curves suggest that there is a blackhole?? X-ray emissions from its accretio disk? This Hubble Space Telescope press release contains a good summary:
http://hubblesite.org/newscenter/newsdesk/archive/releases/2000/22/

The difficulty with *proving* the existence of a black hole is that all other possible explanations for what are very difficult observations must be discounted first. X-rays from accretion disks may provide hints of a black hole. At the centre of the Milky Way, the motion of individual stars can be used to estimate the mass of the object around which they are moving.

Galaxies without an apparent nucleus, such as several types of irregulars, may not have a BH core.

[Phobos]

Welcome to Physics Forums, CoolGrey6!

Originally posted by CoolGrey6
But is this true for all galaxies regardless of their Hubble Type?


It's a relatively (excuse the pun) new finding that large galaxies like our own harbor supermassive black holes in their center. It seems to be true that all such galaxies are likely to have this (research is still underway though).

However, there are many kinds & sizes of galaxies. Elliptical or irregular galaxies, particularly small ones, probably do not have supermassive black holes at their center.

What type of evidences beside rotation curves suggest that there is a blackhole?? X-ray emissions from its accretio disk? [/B]

Rotation rates (of stuff nearby the black hole) and emissions from accretion disks are pretty much it for direct evidence. Math & the laws of physics provide indirect evidence. In other words, the equations predict black holes should exist and there are some observed phenomena (such as stuff being immensely accelerated what looks like emptiness) which are only explained (or are easiest to explain) by black holes.

[Nereid]

Here's a nice one-page summary about detection of black holes, including super-massive ones at the centres of galaxies, from the European Space Agency:
http://www.esa.int/export/esaCP/SEMPUMXLDMD_FeatureWeek_0.html

Quote: " How do astronomers detect black holes if they are unable to see them? Well, to be precise, astronomers do not detect black holes. But they do detect the phenomena that can only be explained by the existence nearby of objects that match the description of black holes!"