[CraigS]

In the News (and continuing on our Black Hole theme we seem to have running at the moment): scientists are speculating about the symbiotic relationship between Super Massive Black hole growth and Galaxy formation.

Astronomy without a telescope - black hole evolution

While only observable by inference, the existence of supermassive black holes (SMBHs) at the centre of most – if not all – galaxies remains a compelling theory supported by a range of indirect observational methods. Within these data sources, there exists a strong correlation between the mass of the galactic bulge of a galaxy and the mass of its central SMBH – meaning that smaller galaxies have smaller SMBHs and bigger galaxies have bigger SMBHs.

For the record, a nice summary of the present status of the observational supporting 'evidence' for SMBHs is:

i) the mass of a galactic bulge is generally inferred from the velocity dispersion of its stars;
ii) the presence of supermassive black holes in the centre of such bulges is inferred from the very fast radial motion of inner stars (at least in closer galaxies where we can observe individual stars);

For galaxies too far away to observe individual stars:

iii) the velocity dispersion and the presence of a central supermassive black hole are both inferred, drawing on the what we have learnt from closer galaxies;
iv) direct observations of broad emission lines are interpreted as the product of very rapid orbital movement of gas around an SMBH (where the ‘broadening’ of these lines is a result of the Doppler effect).

Overall, despite the assumptions built on assumptions nature of this work, ongoing observations continue to support and hence strengthen the theoretical model.

Cheers