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NGC 6357: Cosmic 'Winter' Wonderland
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Name: NGC 6357, Sharpless 11, Lobster nebula, War and Peace nebula
Description: Normal Stars & Star Clusters
Position (J2000): RA 17h 25m 34.2s Dec -34° 23' 12"
Constellation: Scorpius
Distance Estimate: About 5,500 light years
Scale: Image is about 44 arcmin across (70 light years)
Observation Date: 7 pointings between July 2004 and July 2016
Observation Time: 72 hours 13 min. (3 days 13 min)
Color Code: X-ray (Purple); Optical (Blue); Infrared (Orange)
Image Credit: X-ray: NASA/CXC/PSU/L.Townsley et al; Optical: UKIRT; Infrared:      NASA/JPL-Caltech
Release Date: December 19, 2016

Related images:
  N1309   S1015   S0654   N1226   N1612
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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. The nebula is home to the Pismis-24 star cluster, which contains some of the most massive stars in the Milky Way. It is also known as the Lobster Nebula. This nebula was also given the name War and Peace nebula by the Midcourse Space Experiment scientists because of its appearance. They said that in infrared images the bright, western part resembles a dove, while the eastern part looks like a skull. It was discovered by John Herschel on June 8, 1837

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.