Scientists have discovered a telltale sign that a star is on the verge of a supernova. The new discovery could help astronomers develop an “early warning system” before one of these cosmic explosions happens that would allow scientists to watch one in real time, a new study suggests.
“With this early warning system, we can prepare to observe them in real time to point the world’s best telescopes at the progenitor stars,” said study lead author Benjamin Davies. With this early warning, scientists can then “watch as they are literally torn apart before our eyes.”
The study, published Oct. 13 in the Monthly Notices of the Royal Astronomical Society, simulated data on what red supergiant stars would look like in the year before their supernova. Such stars increase in size and can self-destruct in a Type II-P supernova, or violent explosion that occurs in stars between eight and 40 to 50 solar masses. The simulations show that prior to this explosion, a cocoon of circumstellar dust forms around the star.
“Recent studies of supernovae have shown that the star that exploded was embedded in a thick cocoon of material that was believed to have been ejected from the star just before it died,” said Davies, an astrophysicist at Liverpool John Moores University in the UK. said Live Science in an email.
The paper found that stars between eight and 20 times the mass of the Sun and in the last red supergiant phase undergo dramatic changes in their final months.
“We have no idea why stars do this — it wasn’t expected, and images of stars taken about a year before they died show nothing unusual,” Davies said.
Such stars suddenly dim about 100 times in visible light in the last few months before their death. This dimming may be caused by a sudden accumulation of material around the star obscuring its light, although scientists aren’t sure how this happens.
“Our best bet is that the very late stages of core combustion trigger gravity/pressure waves that propagate to the surface of the collapsing star,” Davies said. scientists had previously theorized (opens in new tab) that this occurs in the most extreme supernovas. “But we won’t know until we can watch it happen,” added Davies.
The possibility of observing a supernova explosion in real time has eluded astronomers until now. The closest observation so far was SN 2013fs, a supernova explosion from a red supergiant star in the spiral galaxy NGC 7610, about 160 million light-years away Earth in the constellation Pegasus. It was was observed in October 2013, just three hours after its light reached Earth (opens in new tab).
“When you see the supernova this early, you see the outer edge of the ‘cocoon’ lit from within by the oncoming explosion,” Davies said. “By monitoring it continuously [the astronomers] were able to determine when the supernova overran the cocoon, and thus determine how far it had traveled from the star.”
Because the dense material almost completely obscures the star just before an explosion, astronomers hoping to capture a supernova in real time need telescopes that can warn them of a star that has faded about 100 times in the visible part of the spectrum, compared to the paper .
That will be possible with the forthcoming Vera Rubin Observatory (VRO), due to come online in 2023, whose 3.2 gigapixel camera-powered sky survey will look for tiny changes across the visible sky every three nights.
“The VRO will be able to see about half of the red supergiant stars within about 10 million light-years, allowing us to monitor them every few days or so,” Davies said. “If we see one suddenly dim dramatically, it could be an indication that the countdown to a supernova has begun.”
With this information, astronomers will be able to point other telescopes at the target to study the physical conditions of the star’s atmosphere as it is ejected and transformed into the cocoon around it.
The star closest to the red supergiant solar system is Betelgeuse in the constellation of Orion, whose loss was observed in February 2020 two-thirds of its normal luminosity after an enormous sputum from its surface. However, this dimming was not the result of an imminent supernova.
“A red supergiant on its ‘supernova countdown’ would be like Betelgeuse on steroids,” Davies said. “It would get much fainter, much faster, and possibly disappear entirely from view at visible wavelengths within a few weeks.”
Other red supergiant stars in the night sky are Antares in the constellation of Scorpio, about 555 light-years away, and Aldebaran in the constellation of Taurus, about 65 light-years away.
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