Measurements of supernova rates in other galaxies have led scientists to conclude that at least three supernovae should erupt in the Milky Way galaxy per century. However, for the most part, the remnants of such supernovae are yet to have been found.
At least one supernova has been found, the ghostly remnant Cassiopeia A, which is likely to have occurred around the year 1680. The supernova occurred approximately 11,000 light years away within the Milky Way galaxy, in the Cassiopeia constellation.
A supernova remnant near the center of the Milky Way though has recently added to the list of remnants within our galaxy, and has taken the place of youngest known remnant in our galaxy. Known as G1.9+0.3, the remnant lies about 28,000 light years away, and was first identified as a ring-like supernova remnant in the early 80’s.
More recently though, observations by NASA's Chandra X-ray Observatory and the Very Large Array in New Mexico have shown that the diameter of the remnant – akin to a glowing gas shell – has expanded by 16% over the past 22 years.
From this, and assuming that the speed of expansion is roughly constant, that makes the remnant approximately 140 years old.
The supernova would not have been visibly to astronomers back then however, given that it occurred in dense gas and dust towards the galactic center. "The best telescopes at that time would not have been able to collect enough light to see it," says Stephen Reynolds of North Carolina State University in Raleigh, who led the Chandra study and revealed the results this week. "But the remnant shines in radio waves and X-rays, so X-ray and radio telescopes can see it."
The discovery of this remnant does help plug the relatively small amount of remnants found in our galaxy. But according to Reynolds, many of the “missing” remnants may simply never be found, whether it be because they leave no trace, or because the star creates a bubble of empty space around it before it goes kablooie.
Posted by Josh Hill.