Sat. Jan 22nd, 2022

the explosive end of the dying star

Like living things, stars eventually reach the end of their lives. And the most massive stars die by exploding like supernovae. Now, for the first time, astronomers have gotten pictures of the latter moments of a massive red supergiant star before its supernova launched. The astronomers captured the explosive end of the dying star during their research program, called the Young Supernova Experiment. They observed the star during its last 130 days. The giant star is (or rather) was) located in the galaxy NGC 5731, about 120 million light-years away. These astronomers called their observations “a breakthrough.”

Astronomer Wynn Jacobson-Galán of UC Berkeley, and lead author of the study of this star, said in a statement:

This is a breakthrough in our understanding of what massive stars do moments before they die. Direct detection of pre-supernova activity in a red supergiant star has never been observed before in a common type II supernova. For the first time we saw a red supergiant star explode!

Jacobson-Galán and his colleagues used two different observatories in Hawaii, the Pan-STARRS and the WM Keck Observatory, to acquire their observations. They published their peer-reviewed results on January 6, 2022 in The Astrophysical Journal.

They said it was only lucky timing to catch the star’s end.

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Explosive star of the dying star: A giant star surrounded by gas with other stars in the background.
This is an artist’s illustration of a red supergiant star, like SN 2020tlf, just before it explodes in a supernova. Astronomers have now witnessed the explosion of a dying star when it happened for the first time. Image via WM Keck Observatory / Adam Makarenko.

To witness the explosive end of a dying star

Remarkably, this is the first time that a spectrum – a rainbow array of starlight, divided into its component colors – has been obtained from a supernova since its inception. The Pan-STAARS telescope obtained the first data about this star in the summer of 2020. The following autumn, the star had disappeared boom. Fortunately, scientists were able to get a spectrum of the explosion, which is now called supernova 2020tlf, aka SN 2020tlf.

The results showed signs of dense circumferential material around the star. This is thought to be the same gaseous material that Pan-STARRS had depicted being violently ejected a few months earlier.

According to senior author Raffaella Margutti at UC Berkeley:

It’s like watching a ticking bomb. We have never confirmed such violent activity in a dying red supergiant star, where we see it produce such a luminous emission and then collapse and burn, until now.

Man in polka dot shirt with arms crossed and vines behind him.
Wynn Jacobson-Galán at the University of California Berkeley led the new study on the red supergiant and supernova SN 2020tlf. Image via Wynn Jacobson-Galán.

New insight into the last moments of red supergiants

The event provides valuable new insights into how supernovae arise, and also some surprises. Previously, scientists thought red supergiants tended to be fairly quiet just before they exploded. In the case of SN 2020tlf, however, the star was does not so quiet. Light, intense radiation was detected from the star in the last year up to the supernova.

This is evidence of significant changes in the internal structure of at least some similar stars. The massive ejection of gaseous material then occurs just before the explosion and collapses itself.

Telescopic dome with clouds below it and a clear twilight sky.
Pan-STARRS on Haleakala, Maui was one of the telescopes used to observe the explosion of SN 2020tlf. Image via Space Telescope Science Institute (STScI).

Follow the luminous radiation

As you have probably heard, the proverb “follow the water” is often used about the search for life elsewhere. Now, in the case of identifying red supergiants that are about to explode, the saying may be more like “follow the luminous radiation.” If the results of these observations can be extrapolated to other red supergiants, such radiation could be the signal of an impending supernova.

Overall, the results from SN 2020tlf will provide valuable clues about how giant stars behave in their last moments. Jacobson-Galán said:

I am most excited about all the new ‘unknowns’ that this discovery has unlocked. Discovering more events like SN 2020tlf will dramatically affect how we define the last months of star evolution, uniting observers and theorists in their quest to solve the mystery of how massive stars spend the last moments of their lives.

Bottom line: For the first time, the explosive end of a dying star has been captured since it happened. Two telescopes in Hawaii observed the star in its last 130 days before its supernova.

Source: Final Moments. I. Precursor emission, envelope inflation and increased mass loss prior to the luminous type II Supernova 2020tlf

Via WM Keck Observatory


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