Tim Linden

The Galactic Center Gamma-Ray Excess

The Milky Way Galactic Center

High Mass X-Ray Binaries

The Galactic Center

Our sun is a rather ordinary star, sitting in a rather ordinary part of the Galaxy. The closest star to our sun, is Alpha Centauri, which lies about 4 light-years away. But just 25,000 light-years away, in the center of the Milky Way galaxy, the situation is much more complicated. The central light-year of our galaxy hosts millions of stars, in all stages of their life. Some of the stars are super-giants, on the cusp of exploding in supernovae. Others are locked in tight binaries, ripping material off of their companion stars. At the center of it all lies a supermassive black hole, with a mass 4 million times that of the sun, concentrated into a region only about 5 times as large as the Sun.

This composite image, produced by Dr. Andrea Ghez and collaborators shows the unique Galactic center environment. Stars in this region revolve around the central black hole so rapidly, that we can observe the full rotation of stars within only 10 years. High resolutions of this environment has allowed us to chart the full orbits of several dozen bright stars.

One way we can learn about the Galactic center is to look at all the stars there, recent work in the field of adaptive optics has provided us with incredible angular resolution, allowing us to resolve individual stars in close to the Galactic center. Perhaps the most interesting stars in the Galactic center are those in dense binary, or tertiary systems - these stars undergo intense interactions which produce systems like X-Ray Binaries, binary pulsars, and even black hole binaries. The number of binary interactions in the Galactic center is enhanced by the very high stellar density -- stars in the Sun's neighborhood are too widely spaced to make it likely that two will ever come into close contact. In the Galactic center, on the other hand, stars tend to run into each other all the time, with fantastic results.

Latest Results

TeV Halos

TeV electrons accelerated by pulsars may explain the diffuse TeV excess observed by Milagro.

Dark Kinetic Heating

Dark Matter collisions with neutron stars set a minimum neutron star temperature. This may be observable with next-generation instruments.

Star-Forming Galaxies

An analysis of 584 SFGs finds significant dispersion in their far-IR to gamma-ray correlation. SFGs significantly contribute to the IGRB.