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G1.9+0.3
Supernova remnant G1.9+0.3 in the constellation Sagittarius is the youngest known supernova remnant (SNR) in the Milky Way Galaxy. The remnant's young age was established by combining data from NASA's Chandra X-ray Observatory and the VLA radio observatory. It was a type Ia supernova〔http://chandra.harvard.edu/photo/2013/g19/〕 believed to have exploded about 25,000 years ago, and the signal began reaching us 140 years ago (as of 2008). The light from the supernova would have been visible to 19th century astronomers, had it not been obscured by the dense gas and dust of the Galactic Center.〔 Prior to this discovery, the youngest-known Milky Way supernova remnant was Cassiopeia A, at about 330 years. The remnant has a radius of over 1.3 light years.
==Discovery==
G1.9+0.3 was first identified as a SNR in 1984 from observations made with the VLA radio telescope. Because of its unusually small angular size, it was thought to be young—less than about one thousand years old. In 2007, X-ray observations made with the Chandra X-ray Observatory revealed that the object was about 15% larger than in the earlier VLA observations. Further observations made with the VLA in 2008 verified increase in size, implying it is no more than 150 years old.
The coordinates of G1.9+0.3 are right ascension 17 hours 48 minutes 45.4 seconds, declination –27 degrees 10 minutes 06 seconds, which places it in the constellation Sagittarius, near its border with Ophiuchus.
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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