NGC 6357
Credit X-ray: NASA/CXC/PSU/L.Townsley et al;
Optical: UKIRT; Infrared: NASA/JPL-Caltech
Although there are no seasons in space, this cosmic vista invokes
thoughts of a frosty winter landscape. It is, in fact, a region called
NGC 6357 where radiation from hot, young stars is energizing the cooler
gas in the cloud that surrounds them.
This composite image contains X-ray data from NASA's Chandra X-ray Observatory
and the ROSAT telescope (purple), infrared data from NASA's Spitzer
Space Telescope (orange), and optical data from the SuperCosmos Sky
Survey (blue) made by the United Kingdom Infrared Telescope.
Located in our galaxy about 5,500 light years from Earth, NGC 6357 is actually a "cluster of clusters," containing at least three clusters of young stars, including many hot, massive, luminous stars. The X-rays from Chandra and ROSAT reveal hundreds of point sources, which are the young stars in NGC 6357, as well as diffuse X-ray emission from hot gas. There are bubbles, or cavities, that have been created by radiation and material blowing away from the surfaces of massive stars, plus supernova explosions.
Astronomers call NGC 6357 and other objects like it "HII" (pronounced
"H-two") regions. An HII region is created when the radiation from hot,
young stars strips away the electrons from neutral hydrogen atoms in
the surrounding gas to form clouds of ionized hydrogen, which is denoted
scientifically as "HII".
Researchers use Chandra to study NGC 6357 and similar objects because
young stars are bright in X-rays. Also, X-rays can penetrate the
shrouds of gas and dust surrounding these infant stars, allowing
astronomers to see details of star birth that would be otherwise missed.
A recent paper on Chandra observations of NGC 6357 by Leisa Townsley of Pennsylvania State University appeared in The Astrophysical Journal Supplement Series and is available online.
NASA's Marshall Space Flight Center in Huntsville, Alabama, manages
the Chandra program for NASA's Science Mission Directorate in
Washington. The Smithsonian Astrophysical Observatory in Cambridge,
Massachusetts, controls Chandra's science and flight operations.
Fast Facts for NGC 6357:
Scale: Image is about 44 arcmin across (70 light years)
Category: Normal Stars & Star Clusters
Coordinates (J2000): RA 17h 25m 34.2s | Dec -34° 23' 12"
Constellation: Scorpius
Observation Date: 7 pointings between July 2004 and July 2016
Observation Time: 72 hours 13 min. (3 days 13 min)
Obs. ID: 4477, 10987, 10988, 13267, 13622, 18453
Instrument: ACIS
References: Townsley, L. et al, 2014, ApJS, 213, 1; arXiv:1403.2576
Color Code: X-ray (Purple); Optical (Blue); Infrared (Orange)
Distance Estimate: About 5,500 light years
Source: NASA’s Chandra X-ray Observatory
