A tricky aspect of modern astronomy is keeping all the wavelengths straight. Take the case of G1.9+0.3, a supernova remnant (SNR) near the center of the Milky Way. If you look at an X-ray image of this object made with the Chandra satellite in 2007, you’ll see clear signs of growth compared to what the Very Large Array saw in 1985. But the VLA was working at radio wavelengths, making the image comparison problematic. Scientists studying G1.9+0.3 therefore went back to the VLA to observe the object for a second time in order to verify their initial impression.
The later study confirmed that this supernova remnant — consisting of the materials ejected by the vast explosion — really is growing at what seems to be an unprecedented pace. Fifteen percent growth in 23 years is no small matter in astronomical terms, and the growth also makes it possible to work backwards in time to arrive at the time the supernova went off, now pegged at 150 years ago. That makes G1.9+0.3 the youngest of the 250 known supernova remnants in the Milky Way.
Image: The growth of supernova remnant G1.9+0.3 is clearly visible in this comparison shot. The colour scheme (dark blue -> light blue -> green -> yellow -> red) is increasing radio intensity. The width of each of the above images is about 3 arcmin, i.e. 1/20th of a degree. Credit: VLA/Dave Green.
Intriguingly, this SNR holds one other distinction: Its brightness at radio wavelengths has been increasing over the last few decades, a process unique among galactic supernova remnants. We’ll learn much from future observations. Says Dave Green (University of Cambridge):
“The discovery that G1.9+0.3 is so young is very exciting. It fits into a large gap in the known ages of supernova remnants, and since it is expanding so quickly, we will be able to follow its evolution over the coming years.”
Those observations will continue to be made at X-ray and radio wavelengths for now, the object being obscured by gas and dust so that it is not otherwise visible. Nor would the supernova that created it have been detectable to Victorian astronomers, buried behind dust lanes whose nature and location they did not yet suspect. The paper, accepted by Monthly Notices of the Royal Astronomical Society, is Green, Reynolds et al., “The radio expansion and brightening of the very young supernova remnant G1.9+0.3” (abstract).