Quasar feeding and star formation
in the central parts of galaxies.
Galaxies are formed when gas, cooling in massive dark
matter halos, contracts gravitationally into stars. A small fraction of
the gas apparently reaches supermassive black holes that reside in the
centres of galaxies. The resulting energy release is enourmous and
affects evolution of the galaxies themselves. The details of these
processes are still poorly understood. However, exciting progress is
being made on all fronts. Numerical simulations allow us to stage
experiments that expand our analytical understanding of the complicated
physics. Observations of distant quasars and AGN (actively accreting
black holes) constrains the gross picture of quasar feeding.
Observations of our Galactic Centre, with its supermassive black hole,
revealed that accretion and star formation might be taking place
simultaneously in the inner parsecs of galaxies. The prospective PhD
student will use a range of tools -- numerical, analytical or data
interpretation, depending on the student's interests and abilities --
to advance our knowledge in the linked areas of supermassive black
holes, star formation and galaxy evolution.
Snapshot of a simulation by the 1st
year PhD student Alex Hobbs. The simulation shows the result of two
massive gaseous clouds colliding in the central parsec of our Galaxy.
The inner circular disc is gravitationally unstable and forms stars.
The outer eccentric filament also forms stars. These results are
relevant to the origin of two discs of young stars recently discovered
in the centre of our Galaxy.
More detailed description of the projects:
1. Quasar/AGN feeding and star formation
Quasars and AGN are supermassive black holes powered by
gravitational energy release by the gas that falls or "accretes" onto
these. At the moment, the only certain thing about this process is that
it happens in Nature but we do not understand how. There are several
challenges here. On small (sub-parsec) scales, gas probably forms a
disc since there is too much angular momentum. Theories predict that
these discs should be very massive and cool, and form stars much more
readily that transfer matter inside the supermassive black holes.
However, models need to be developed further to include additional
effects, such as outflows and radiation from massive stars.
On the larger scales, the challenge is to understand how the gas is
delivered into the central regions of galaxies: via larger scale
quasi-static discs or rather via chaotic deposition of individual
molecular clouds. Are mergers of galaxies important? And finally, how
does this work when supermassive black hole turns on its powerful
radiation and gas outflows?
To answer these questions, a numerically-minded student would use
existent numerical codes and the in-house super-computing facilities to
simulate the important processes ab initio. He/she would then analyse
the results in order to understand understand implications of these
simulations to the real AGN and galaxies. The sudent would also gain
hands on experience coding and modifying some of the best available
astrophysical codes. An analytically capable student could instead
build models to search the parameter space and compare to the results
of numerical simulations obtained by other people in the group.
Finally, the eventual goal is to relate this work to observations of
AGN and our Galactic Centre, in particular. The project
might include collaborative visits to MPA-Garching, Germany, for code
2. Star formation in extreme environment
The theoretical prediction of star formation within massive
accretion discs (see the project above) has been recently dramatically
confirmed with discovery of several tens of massive young stars near
Sgr A*, the supermassive black hole in the centre of our Galaxy.
Apparently, these stars "stole" about 10,000 solar masses of gas that
Sgr A* managed to lure into the inner parsec. An extremely interesting
and important point to address is what do these observations imply for
star formation as a process. Specifically, star formation has been
studied for half a century in our Galaxy and other galaxies, and one
normally observes it to take place in a relatively similar
environments, e.g., a certain ambient gas density, temperature,
external radiation background, etc. In contrast, the supermassive black
hole produces a very strong tidal field that shreds "normal gas clouds"
in pieces, and holds on to matter tightly. This changes the conditions
for star formation to very extreme, never observed before.
This project could involve students of a wide range of interests and
abilities. Simulations with the existing code and the results analysis
would be main tools for the numerically able. (Semi)analytical
modelling and probably light programming for those thinking in terms of
equations. Finally, literature reading and contrasting star formation
near Sgr A* with that elsewhere in the galaxy,
and interpretation of observational results, including the latest ones,
such as stellar orbits and stellar types, would
be the tool of for those wishing to be in between theory and