The M–sigma (or M–σ) relation is an empirical correlation between the stellar velocity dispersion σ of a galaxy bulge and the mass M of the supermassive black hole at its center.





Sort of. It depends on what you're asking exactly.

Massive Black-hole (MBH) mass and stellar velocity dispersion are two independent properties of a galaxy, which are observed to be related. Any galaxy (or bulge) that has stars (which is required for them to exist) can have a velocity dispersion. That being said, a MBH doesn't necessarily need to have a host-galaxy, and similarly a galaxy doesn't necessarily need to have a MBH*.

The observed $M-\sigma$ relation is usually interpreted to mean that somehow MBHs are able to effect their large-scale environments (i.e. their galaxy as a whole). The growing consensus is that the mechanism of this interaction is via 'Feedback', e.g. This paper by Fabian, or this pop-sci article. It is not interpreted to mean that the stars in the galaxy's bulge are physically orbiting the BH, and the dispersion is directly caused by that orbital velocity.

*Although, statistically it looks like basically all galaxies tend to have BHs.


Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.