The Youngest Known Supernova Remnant

Composite of Chandra X-ray and VLA Radio Images The most recent supernova in our Galaxy has been discovered by determining the age of the supernova remnant known as G1.9+0.3. To determine the age, astronomers tracked how quickly it is expanding, by comparing a radio image from 1985 (blue) to a Chandra image taken in 2007 (orange). The expansion rate was confirmed with another radio observation with the VLA in 2008. The difference in size between the composite images gives clear evidence for expansion, allowing the age of the remnant and the time since the original supernova explosion (about 140 years) to be estimated.

Introduction:

Supernova remnant G1.9+0.3 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, and is believed to have exploded about 25,000 years ago, and the signal began reaching us 140 years ago. 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:

Located about 25,000 light years from Earth, G1.9+0.3 was first identified as a SNR in 1985 as a radio source inside our galaxy by astronomers using the VLA. In 2007, images of it were made using the Chandra X-Ray observatory, and compared with the 1985 images. The differences in size allowed astronomers to calculate when the supernova exploded, sometime around 1868 C.E (relative to Earth-time). In 2008, observations by the VLA confirmed that G1.9+0.3 was expanding rapidly, and is calculated to be doing so at about 56 million km/h / 35 million mph, or about 5% the speed of light.The supernova was not observed visually by astronomers at the time of explosion, because it is located near the centre of the galaxy, and is obscured by dust clouds. It is only since the advent of radio astronomy and X-ray astronomy that astronomers have been able to penetrate the dust clouds.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.

Announcement:

The discovery was announced on May 14, 2008 at a NASA press conference. In the days leading up to the announcement, NASA would only hint that they were going "to announce the discovery of an object in our Galaxy astronomers have been hunting for more than 50 years."