Chandra X-ray Observatory image of the center of Omega Centauri; each dot represents one X-ray photon
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My research focuses on globular clusters--big balls of about 100,000 to 1,000,000 stars each,
held together by gravity. The Milky Way is home to more than 150 of these star clusters.
They're more than 10 billion years old, having formed before the galaxy's disk took shape.
Here's
one
that you can see from the
SFSU Observatory
on a clear night.
I'm particularly interested in the dynamical evolution of globular clusters--how their
structure changes over time, and whether intermediate-mass black holes form at their centers. Understanding cluster dynamics has sometimes been called the
million-body problem.
Here's an
N-body simulation
of a globular cluster created by theorist Simon Portegies Zwart a few years ago.
My students and I have been using
Hubble Space Telescope and
Chandra X-ray Observatory
to peer into the dense centers of these clusters. That's where binary stars, which are
thought to play a critical role in cluster dynamics, tend to congregate. Clusters, in
turn, can alter the binary stars that inhabit them, through stellar interactions.
Globluar clusters are one of the few places in the Galaxy where stars actually collide.
Here is a listing of my
papers
from ADS. Here are the
refereed papers only.
Two of the clusters that my students and collaborators and I have studied have been chosen to be part of the
Hubble Heritage project:
- Omega Centauri
is the largest globular cluster in the Milky Way--it may actually be the remnant of dwarf galaxy accreted by the Milky Way.
- NGC 6397
is the nearest dense-core cluster; stars near its center are lightweeks apart--vs. lightyears in the solar neighborhood.