January 26, 2023

Astronomers Watch a Star Die and Then Explode as a Supernova

A group of astronomers watched the drama unfold through the eyes of two observatories in Hawaii: Pan-STARRS on Haleakala, Maui, and the W. M. Keck Observatory on Maunakea, Hawaii Island. Their observations belonged to the Young Supernova Experiment (YSE) transient survey. They watched the supernova explosion, named SN 2020tlf, during the last 130 days leading up to its detonation.
” For the very first time, we watched a red supergiant star explode!” Wynn Jacobson-Galán, UC Berkeley
The title of the paper providing the discovery is “Final Moments. I. Precursor Emission, Envelope Inflation, and Enhanced Mass Loss Preceding the Luminous Type II Supernova 2020tlf.” The paper is published in The Astrophysical Journal and the lead author is Wynn Jacobson-Galán, an NSF Graduate Research Fellow at UC Berkeley.
” This is an advancement in our understanding of what massive stars do moments before they pass away,” said Jacobson-Galán, in a news release. “Direct detection of pre-supernova activity in a red supergiant star has never ever been observed prior to in a common Type II supernova. For the very first time, we saw a red supergiant star take off!”
” Its like viewing a ticking time-bomb.” Raffaella Margutti, UC Berkeley
The discovery goes back to the Summer of 2020. At that time, the progenitor star experienced a remarkable increase in luminosity. Pan-STARRS detected that lightening up, and when Fall happened the star took off as SN 2020tlf. The supernova is a Type II supernova, where an enormous star experiences a rapid collapse and then explodes.

Its another very first for astronomy.
For the very first time, a group of astronomers have imaged in real-time as a red supergiant star reached the end of its life. They viewed as the star convulsed in its death throes prior to finally taking off as a supernova.
And their observations oppose previous believing into how red supergiants behave before they blow up.

This video is an artists performance of the red supergiant star transitioning into a Type II supernova, discharging a violent eruption of radiation and gas on its dying breath prior to exploding and collapsing. Credit: W. M. Keck Observatory/Adam Makarenko
The team utilized the Keck Observatorys Low-Resolution Imaging Spectrometer (LRIS) to catch the supernovas very first spectrum. The LRIS data showed circumstellar product around the star when it blew up. That product is likely what Pan-STARRS saw the star ejecting in the summer prior to it exploded.
” Keck was important in supplying direct proof of a huge star transitioning into a supernova explosion,” stated senior author Raffaella Margutti, an associate professor of astronomy at UC Berkeley. “Its like watching a ticking time bomb. Weve never ever verified such violent activity in a dying red supergiant star where we see it produce such a luminous emission, then collapse and combust, until now.”
This figure from the study shows the supernova pre- and post-explosion. The leading panel reveals the total of all electro-magnetic radiation emitted by the event throughout all wavelengths, in green. The middle panel reveals black-body temperatures in red, and the bottom panel reveals the radii in blue. Image Credit: Jacobson-Galán et al, 2022.
After the surge, the group turned to other Keck instruments to continue their observations. Data from the DEep Imaging and Multi-Object Spectrograph (DEIMOS) and Near Infrared Echellette Spectrograph (NIRES) revealed that the progenitor star was 10 times more enormous than the Sun. The star remains in the NGC 5731 galaxy about 120 million light-years away.
The groups observations caused some brand-new insight into Type II supernovae and their progenitor stars. Prior to these observations, no one had actually seen a red supergiant display screen such a spike in luminosity and go through such powerful eruptions before exploding. They were far more placid in their last days as if they accepted their fates.
Red supergiant stars eject material prior to core collapse. However that material ejection occurs on a lot longer timescales than SN 2020tlf. This supernova released circumstellar material (CSM) for 130 days prior to collapse, which makes it a bit of a puzzle. The brilliant flash prior to the stars explosion is in some way related to the ejected CSM, however the team of scientists isnt certain how they all connected.
Artists impression of a Type II supernova surge which includes the damage of a huge supergiant star. Credit: ESO
The substantial irregularity in the star leading up to collapse is confusing. The powerful burst of light originating from the star prior to exploding suggests that something unidentified occurs in its internal structure. Whatever those modifications are, they result in a massive ejection of gas prior to the star collapsed and took off.
Present wave-driven designs do not match the progenitor stars ejection of gas. Theyre consistent with the progenitor stars radius in its last 130 days, however not consistent with the burst of luminosity.
“Given the progenitor mass range derived from nebular spectra, it is most likely that the boosted mass loss and precursor emission are the results of instabilities deeply rooted in the stellar interior, most likely associated with the last nuclear burning stages. Energy deposition from either gravitational waves produced in neon/oxygen burning phases or a silicon flash in the progenitors last?
If theres one supernova that acts like this, there need to be more. The groups findings imply that studies like the Young Supernova Experiment transient survey now have a method to find more of them in the future. If the survey discovers more stars ejecting product like this one, then they understand to keep an eye on it to see if it collapses and takes off.
” I am most thrilled by all of the new unknowns that have been unlocked by this discovery,” stated Jacobson-Galán. “Detecting more events like SN 2020tlf will dramatically affect how we specify the last months of outstanding advancement, unifying observers and theorists in the quest to solve the mystery of how enormous stars spend the last moments of their lives.”
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” Keck was crucial in providing direct proof of an enormous star transitioning into a supernova surge,” stated senior author Raffaella Margutti, an associate teacher of astronomy at UC Berkeley. The groups observations led to some new insight into Type II supernovae and their progenitor stars.

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“Direct detection of pre-supernova activity in a red supergiant star has actually never been observed before in an ordinary Type II supernova. For the first time, we enjoyed a red supergiant star take off!”
The supernova is a Type II supernova, where a huge star experiences a rapid collapse and then takes off.

Citation W. V. Jacobson-Galán et al 2022 ApJ 924 15. DOI: https://doi.org/10.3847/1538-4357/ac3f3a

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