Don’t you hate it when you only care about your own affairs, and a star suddenly decides to go supernova? Well, good news: Scientists have figured out what these stars look like before they die.
According to new simulations, massive stars that are the progenitors of neutron stars have dwindled dramatically in the past few months before they explode. Therefore, if a massive star fades into complete obscurity without fanfare, there is likely to be a supernova on the horizon.
Red giant stars with a mass of about 8 to 20 times the mass of the Sun are among the most interesting. At the end of their lifespan, these monsters are dangerously running out of the fuel they need to support nuclear fusion at their core.
This fusion provides an external pressure against the internal pressure of gravity. Remove the fusion and things will get violent. The star turns into a kaboom, the entrails of stars explode into space, and the core of the star (for most stars) collapses.
For the giant red giants in question here, that core turns into a super-dense neutron star, something between 1.1 and 2.3 times the mass of the Sun, and stacked into a sphere just 20 kilometers (12 miles) wide.
However, before the big show starts, the star loses a lot of his mass. We don’t really understand the red giant’s mass loss very well on a theoretical level.
By looking at the light and dust from the death of the red giant giant after the fact, scientists made sure that the red giant planets spewed out a lot of gas and dust in the lead up to the supernova, but the timeline in which this happens is unclear.
Could it be over decades, as previous research suggests, or in less than a year, as some other modeling studies have predicted?
Led by astrophysicist Benjamin Davis of Liverpool John Moores University in the UK, a team of researchers used observational and simulation evidence to reconstruct how a dying red giant evolved.
They run simulations and find that the massive cloud of material around the star blocks optical light by a factor of 100 and near-infrared light by a factor of 10 before the star turns into a supernova.
“The dense matter almost completely obscures the star, making it 100 times fainter in the visible part of the spectrum,” Davies explains. “This means that the day before the star exploded, you probably wouldn’t be able to see that it was there.”
To measure how long it takes to lose mass, the researchers went looking for evidence of observation. They found several archival images of red giant stars that later transformed into a supernova, about a year after the image was taken. They say this is evidence that widespread, opaque mass loss occurs at least within a year.
This rules out the imminent demise of Betelgeuse (although we already knew that). The episode of mass loss that darkened Betelgeuse in 2019 appears to be part of a slower process; The latest estimates place the star 1.5 million years away from the supernova.
When that day comes, we’ll now know what to be alert for… if we’re still around.
“Until now, we haven’t been able to get detailed observations of supernovae until hours after they actually happen,” Davies says.
“With this early warning system, we can prepare to monitor them in real time, to point the world’s best telescopes at precursor stars, and watch them disperse before our very eyes.”
The search was published in Monthly Notices of the Royal Astronomical Society.
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