NGC 6266:
X-Ray Binaries In Globular Clusters

Chandra's unique ability to precisely locate and resolve individual X-ray sources in 12 globular clusters in our Galaxy has given astronomers a crucial clue as to the origin of these sources. Two clusters, known as NGC 6266 (or M62) and NGC 7099 (or M30), are shown here.

A globular cluster is a spherical collection of hundreds of thousands and even millions of stars buzzing around each other in a gravitationally bound stellar beehive that is about a hundred light years in diameter. The stars in a globular cluster are often only about a tenth of a light year apart. For comparison, the nearest star to the Sun, Proxima Centauri, is 4.2 light years away.

Most of the point-like sources in these images are binary star systems containing a collapsed star, such as a neutron star or a white dwarf star, that is pulling matter off a normal companion star. While direct, head-on collisions between stars are rare even in these crowded circumstances, close encounters occur and can lead to the formation of binary star systems containing a collapsed star.

The images illustrate a general trend observed for globular clusters. Clusters such as M62 where the stars are packed very closely together and the rate of close encounters is high have more X-ray binaries than those such as M30 in which close encounters occur less often. This is strong evidence that the X-ray binaries in globular clusters are formed by close encounters.

Fast Facts for NGC 6266: Credit  NASA/CXC/MIT/D.Pooley et al. Scale  Image is approx. 1.9 arcmin on a side. Category  Normal Stars & Star Clusters, Neutron Stars/X-ray Binaries Coordinates (J2000)  RA17h 01m 12.60s | Dec -30° 06' 44.50" Constellation  Scorpius Observation Date  May 12, 2002 Observation Time  18 hours Obs. ID  2677 Also Known As  M62,  References  D. Pooley et al. 2003, Dynamical Formation of Close Binary Systems in Globular Clusters. Astrophys. Journal, 591, L131 C. Heinke et al. Analysis of the Quiescent Low-Mass X-ray Binary Population in Galactic Globular Clusters, 2003, Astrophysical Journal (in press) Color Code  Energy (Red 0.5-1.2 keV, Green 1.2-2.5 keV, Blue 2.5-6 keV) Instrument  ACIS Distance Estimate  About 20,000 light years from Earth Release Date  July 30, 2003

Fast Facts for NGC 7099: Credit  NASA/CXC/UIn/H.Cohn & P.Lugger et al. Scale  Image is approx. 1.9 arcmin on a side. Category  Normal Stars & Star Clusters, Neutron Stars/X-ray Binaries Coordinates (J2000)  RA 21h 40m 22.00s | Dec -23° 10' 45.00" Constellation  Capricornus Observation Date  November 19, 2001 Observation Time  13.9 hours Obs. ID  2679 Also Known As  M30,  References  D. Pooley et al. 2003, Dynamical Formation of Close Binary Systems in Globular Clusters. Astrophys. Journal, 591, L131 C. Heinke et al. Analysis of the Quiescent Low-Mass X-ray Binary Population in Galactic Globular Clusters, 2003, Astrophysical Journal (in press) Color Code  Energy (Red 0.5-1.2 keV, Green 1.2-2.5 keV, Blue 2.5-6 keV) Instrument  ACIS Distance Estimate  About 30,000 light years from Earth Release Date  July 30, 2003