Joint Astrophysics Colloquium

Joint Astrophysics Seminar

X-Ray Binaries in Distant Elliptical Galaxies and Galactic Millisecond Radio Pulsars

Lars Bildsten

Kavli Institute, UCSB

Chandra observations of distant elliptical galaxies have revealed large numbers of Low Mass X-ray Binaries (LMXBs) accreting near the Eddington limit. The majority of these LMXBs reside in globular clusters (GCs) and it has been suggested that many of the field LMXBs also originated in GCs. I will present our recent work (Bildsten and Deloye) which shows that ultracompact binaries with orbital periods of 8-10 minutes and He or C/O donors of 0.06-0.08 solar masses naturally provide the observed accretion rates and explain the observed luminosity function. The observed numbers of LMXBs per GC mass allows us to find the accumulated number of ultracompact binaries, which is in reasonable agreement with both the dynamical interaction calculations and the observations of millisecond radio pulsars.