Research in Theoretical Astrophysics  
Ben Bromley
Physics & Astronomy
University of Utah
  planet formation  ◊  outer solar system  ◊  galactic dynamics  ◊  relativistic astrophysics  ◊  cosmology  ◊  home

Hypervelocity stars and the growth of supermassive black holes

Scott Kenyon, Margaret Geller, Warren Brown, and I worked on the origin of hypervelocity stars. These stars are very fast moving, up to 800 kilometers per second. Following an idea from J. Hills at Los Alamos, we studied how these fast moving stars likely start off as one of a pair or triplet of stars that strays close to the supermassive black hole in the center of the Galaxy. We show, among other things, how to learn about the distribution of matter in the our Galaxy, the Milky Way, from the way in which hypervelocity stars travel through it. Along the way we found that the captured binary partners could grow the central black hole. These links have more on this subject and related work.

Hypervelocity stars (HVS's), their captured partners (S stars) and disrupted stars in nearby galaxies can tell us how to grow a supermassive black hole.

Hypervelocity stars and their slower moving counterparts, runaway stars, can tell us about the structure of our Galaxy and the neighborhood of its supermassive black hole.

Planet formation

Scott Kenyon and I have a simulation code to study the formation of planets from small rocky or icy bodies around a young star. Planets form from these small "planetesimals" by a process of coagulation, in which smaller bodies glom onto each other to become bigger bodies like dust under someone's bed becomes dustbunnies. The biggest ones consume the smaller ones with the help of gravity, but this creates a lot of of dust, which we can observe around young stars (as in the image to the left, from a simulation). Eventually, even the big objects collide with each other, leaving relatively few planets. The biggest ones may gravitationally draw in gas to become planets like Jupiter. The ones closer to the host star may end up rocky like the Earth, while planets further away may be smaller and icy like the dwarf planet Pluto. Below is a partial list of our work describing this process.

Planet formation seems to be universal; our simulations show how planets form around a variety of stars.

Dusty rings around stars are the signposts of on-going planet formation:

The Outer Solar System

Our planet formation and dynamics codes have helped us to understand some processes that may have occured in distant regions of our Solar System. For example we studied the growth of icy objects in the Kuiper belt, out beyond Neptune's orbit. We predict the sizes of these objects, and give a possible explanation of the unusual orbit of some distant dwarf planets: they may have been captured by the Sun from another star's planetary system. (The image to the left shows planetary material being exchanged between two passing stars.) Here are more details:

Galactic dynamics

Betsy Barton, Margaret Geller, Scott Kenyon and I worked on galactic structure and dynamics, using simulations. While our more recent research focuses on probing the Milky Way's gravitational potential with hypervelocity stars, an entire galaxy can serve to "probe" another, in a large collision, like particles in an eccelerator.

We use a dynamics code to track the motion of hypervelocity stars from their original pass by the Galaxy's central supermassive black hole to the Galaxy's halo. This code is a simple version of one we use for full galactic dynamics (image above and left).

Relativistic astrophysics

Black holes are masses that warp space and time enough to inexorably trap everything with in a certain region, including light. One part of my research is to track light from a glowing (or illuminated) disk of gas flowing toward a black hole, and another component involves the production of gravity waves -- ripples in space time -- by black holes that are merging (e.g., image at left). Here is an overview of some of the things we have done.

Richard Price has championed the idea that as a pair of black holes spiral inward toward each other, they go through a long phase where the inspiral is slow. This facilitates calculating the physics of the black hole pair.

Excellent clues to the uncertain physics (or even existence) of a black hole come from looking at the emission of gas flowing near it:

Astrophysical cosmology

Much of our concrete knowledge of the evolution of the Universe comes from its structure at very large scales -- e.g., the way galaxies are clustered. Back in the day, I did a thesis and other stuff (below) on this type of large-scale structure. The field continues to blossom, and people in the Department do very interesting work in galaxy clustering, dark matter (which pervades the Universe, perhaps) and dark energy (which mediates how it expands). It is really important and exciting, and maybe one day I will try to help out again. Ya never know.

Here is a sample of miscellaneous papers on galaxies, clustering and large scale structure:

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Last updated: Fri Nov 5 21:30:01 MDT 2010