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X-Ray Binaries In Globular Clusters: NGC 6266 & NGC 7099
Close Encounters Of The Stellar Kind
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.
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Fast Facts for
NGC 6266:
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Credit
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NASA/CXC/MIT/D.Pooley et al.
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Scale
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Image is approx. 1.9 arcmin on a side.
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Category
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Normal Stars & Star Clusters
Neutron Stars/X-ray Binaries
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Coordinates
(J2000)
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RA 17h 01m 12.60s | Dec -30º 06' 44.50"
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Constellation
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Scorpius
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Observation
Date
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May 12, 2002
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Observation
Time
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17.5 hours
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Obs.
ID
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2677
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Color
Code
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Energy (Red 0.5-1.2 keV, Green 1.2-2.5 keV, Blue 2.5-6 keV)
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Instrument
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ACIS
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Distance
Estimate
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About 20,000 light years from Earth
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Release Date
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July 30, 2003
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Reference
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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)
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Also Known As
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M62
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Fast Facts for
NGC 7099:
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Credit
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NASA/CXC/UIn/H.Cohn & P.Lugger et al.
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Scale
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Image is approx. 1.9 arcmin on a side.
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Category
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Normal Stars & Star Clusters
Neutron Stars/X-ray Binaries
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Coordinates
(J2000)
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RA 21h 40m 22.00s | Dec -23º 10' 45.00"
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Constellation
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Capricornus
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Observation
Date
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November 19, 2001
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Observation
Time
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13.9 hours
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Obs.
ID
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2679
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Color
Code
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Energy (Red 0.5-1.2 keV, Green 1.2-2.5 keV, Blue 2.5-6 keV)
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Instrument
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ACIS
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Distance
Estimate
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About 30,000 light years from Earth
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Release Date
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July 30, 2003
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Reference
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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)
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Also Known As
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M30
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