Supernovas may be way more violent than we thought.
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An artist's rendition of a red supergiant star transitioning
into a Type II supernova, emitting a violent eruption of radiation and gas on
its dying breath before collapsing and exploding. (Image credit: W. M. Keck
Observatory/Adam Makarenko) |
Astronomers have watched a giant star blow up in a fiery
supernova for the first time ever — and the spectacle was even more explosive
than the researchers anticipated.
Scientists began watching the doomed star — a red supergiant
named SN 2020tlf and located about 120 million light-years from Earth — more
than 100 days before its final, violent collapse, according to a study
published in the Astrophysical Journal. During that lead-up, the
researchers saw the star erupt with bright flashes of light as great globs of
gas exploded out of the star's surface.
These pre-supernova pyrotechnics came as a big surprise, as
previous observations of red supergiants about to blow their tops showed no
traces of violent emissions, the researchers said.
"This is a breakthrough in our understanding of what
massive stars do moments before they die," lead study author Wynn
Jacobson-Galán, a research fellow at the University of California, Berkeley
said in a statement. "For the first time, we watched a red supergiant star
explode!"
When big stars go boom
Red supergiants are the largest stars in the universe in
terms of volume, measuring hundreds or sometimes more than a thousand times the
radius of the sun. (Bulky though they may be, red supergiants are not the
brightest nor the most massive stars out there.)
Like our sun, these massive stars generate energy through
the nuclear fusion of elements in their cores. But because they are so big, red
supergiants can forge much heavier elements than the hydrogen and helium that
our sun burns. As supergiants burn ever more massive elements, their cores
become hotter and more pressurized. Ultimately, by the time they start fusing
iron and nickel, these stars run out of energy, their cores collapse and they
eject their gassy outer atmospheres into space in a violent type II supernova
explosion.
Scientists have observed red supergiants before they go
supernova, and they have studied the aftermath of these cosmic explosions —
however, they've never seen the whole process play out in real time until now.
The authors of the study began observing SN 2020tlf in
the summer of 2020, when the star flickered with bright flashes of radiation
that the team later interpreted as gas exploding off of the star's surface.
Using two telescopes in Hawaii — the University of Hawaii Institute for
Astronomy Pan-STARRS1 telescope and the W. M. Keck Observatory on Mauna Kea —
the researchers monitored the cranky star for 130 days. Finally, at the end of
that period, the star went boom.
The team saw evidence of a dense cloud of gas surrounding
the star at the time of its explosion — likely the same gas that the star
ejected during the prior months, the researchers said. This suggests that the
star started experiencing violent explosions well before its core collapsed in
the fall of 2020.
"We've never confirmed such violent activity in a dying
red supergiant star where we see it produce such a luminous emission, then
collapse and combust, until now," study co-author Raffaella Margutti, an
astrophysicist at UC Berkeley, said in the statement.
These observations suggest that red supergiants undergo
significant changes in their internal structures, resulting in chaotic
explosions of gas in their final months before collapsing, the team concluded.