More recent supernovas have been discovered in other galaxies, such as the 21-year-old blast called SN 1987A, which is 160,000 light-years away in the Large Magellanic Cloud.
But supernovas in our own Milky Way are easier to study and visible for far longer.
G1.9+0.3 has increased in size by 16 percent in the last 22 years, suggesting that the initial explosion occurred only 140 years ago—or less, if the rate of expansion has been slowing, researchers point out.
"Normally, we deal with older remnants and have to work very hard to see even tiny changes," Reynolds said.
"This supernova is getting brighter, which means it's still on its way up. Studying it will go a long way toward filling in gaps in our knowledge of these events and their effect on galaxies."
Eager for More
Richard Arendt, a scientist with the University of Maryland, Baltimore County, and the Goddard Space Flight Center, said G1.9+0.3 was suspected as being a young supernova but wasn't confirmed until now.
"The results are very interesting and important, but I wouldn't really call them a surprise," he said.
Arendt said most astronomers believe there must be around ten supernova remnants younger than Cassiopeia A.
"So SNR G1.9+0.3 now fills part of that gap," he said. "The real surprises may come in the discovery of and in the nature of the other very young SNRs that are almost certainly out there."
Supernova expert Craig Wheeler is a professor at the University of Texas at Austin and president of the American Astronomical Society. He suggested researchers should now focus on discovering the nature of G1.9+0.3.
"The issues that are top on my mind are how to determine whether this was a Type Ia—an exploding white dwarf—or a core collapse [supernova]," he said, adding that "some means of directly measuring the nearby magnetic field would be great."
If G1.9+0.3 resulted from the core collapse of a star, for example, the explosion could be sending out a powerful energy jet, he pointed out. Otherwise, its boundaries could be limited magnetically.
Reynold said that the best strategy will be to spy on G1.9+0.3 with "every possible astronomical instrument that can observe it."
His team submitted a proposal in March for longer observation time using Chandra.
"We've just never had the opportunity to study a remnant in this phase of its life," Reynolds said.
"Now that we know how fast it's changing, it will be useful to re-observe it again and again and watch its evolution—pretty rare for an astronomical event!"
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