October 26, 2002
On the day you were born, the universe was already ancient beyond measure — and yet, in all those billions of years, it had never once...
Dark Matter, X-rays, and NGC 720
Birthday · October 26, 2002
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APOD published October 26, 2002. Full image credits are on the original APOD entry below. A publication-date match, not a photo taken on your date. Independent of NASA.
cal galaxy NGC 720 is enveloped in a cosmic cloud of x-ray emitting gas. Seen in this false color image from the Chandra X-ray Observatory, the extreme temperature of the gas - about 7 million degrees Celsius - makes it impossible to confine the cloud to the vicinity of NGC 720 based on the gravity of this galaxy's visible stars alone. In fact, the x-ray cloud is taken as solid evidence for the presence of dark matter surrounding NGC 720 -- unseen material which has gravitational influence that can keep the x-ray hot gas cloud from escaping. Chandra's remarkable vision clearly distinguishes the bright point-like x-ray sources from the diffuse cloud. Astronomers can then use the detailed shape of the cloud to infer the distribution of dark matter in NGC 720 and even test theories about the fundamental nature of dark matter. According to modern understanding, the mysterious dark matter, whatever it is, is by far the most common form of matter in the Universe. Galaxy NGC 720 lies about 80 million light-years distant toward the constellation Cetus.