‘Fireworks’ spotted in stellar explosion 15 million light-years away
Popular Science...
Fourth of July celebrations got an early start in a nearby galaxy. Astronomers using NASA’s Chandra X-ray Observatory to observe galaxy Messier 83 (M83) spotted the unexpected explosive aftermath of a supernova. Typically, the aftermath of a stellar explosion is a slowly fading cloud of piping hot gas. In this case, the supernova debris was dramatically bright—like a firework. The supernova is detailed in a study recently published in The Astrophysical Journal.
M83 is located about 15 million light-years away from Earth and is forming stars at a high rate. Using 14 years of Chandra data of the galaxy (2000 to 2014), the team caught some surprising variations in the X-ray brightness of sources of light previously identified as supernova remnants.
Initially, the team expected that the supernova remnants that were over 100 years old would have X-ray flares whose brightness stayed the same. But they were in for a surprise. Instead, roughly half of the 22 X-ray sources associated with supernova remnants showed changes in X-ray brightness over the 14 years.
“We knew that individual X-ray sources could vary dramatically,” Andrea Prestwich, a study co-author and astronomer from The Catholic University of America, said in a statement. “But finding that so many supernova remnants were behaving this way was a real surprise. Something unusual is going on in these objects. Pinpointing the cause remains a challenge, as M83’s distance limits the detail we can observe.”
One of the 22 changing supernova remnants has a fairly straightforward explanation—SN 1957D. This supernova debris was first observed nearly 70 years ago and is ramming into material surrounding the explosion site. This collision is producing X-ray flares that the team observed. However, it does not explain the flares seen in the rest of the sample.
The team believes a population of stars that survived their partner’s destruction in a supernova explosion could be causing the flares. In this scenario, each variable X-ray source started out as a pair of massive stars orbiting each other. When the bigger star collapsed and exploded as a supernova, a black hole or ultra-dense neutron star was left behind. As for the companion star? It survived.
“It may be that this galaxy contains a collection of supernova remnants where one massive star survives the supernova and becomes locked into an orbit with a black hole or neutron star,” added study co-author and Harvard University astrophysicist Michael McCollough. “The neutron star or black hole can then start pulling material from the massive star’s surface.”
They also found another possible explanation. Instead of pulling in material from a companion star, that black hole or neutron star could be taking back some of the material that was blasted outward by the original explosion.
“This could be an example of cosmic recycling, where debris from the explosion falls back onto the very object the supernova created,” said co-author and astronomer Roy Kilgard from Wesleyan University. “And it’s quite possible that both explanations are at play — different sources in our sample may have different origins.”
These results are also not unique to M83. A follow-up study of the nearby star-forming galaxy M51 by Kilgard and Zoe Hoiland of Vassar College and Kilgard found a similar population of variable X-ray sources associated with supernova remnants. These kinds of systems may be a feature of galaxies undergoing vigorous star formation.
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