Astronomers have found that red supergiants in the last months of their lives can actively lose mass and demonstrate increased luminosity due to processes in their depths. This was done during observations of the progenitor star of the supernova SN 2020tlf before and after the explosion.
The behavior of supergiant stars
One of the important directions in the physics of supernova explosions is the description of the behavior of massive (more than 8 solar masses) supergiant stars in the last years of their life, in particular, understanding the nature of dense circumstellar matter.
It may consist of the primary matter of the star or elements synthesized at different stages of its life and is enriched as the progenitor star loses mass due to winds and strong flares.
Scientists are interested in exactly how and at what rate a star can lose mass before the explosion and how shock waves interact with the circumstellar matter after the explosion. Early (a few hours or days after the outbreak) observations of supernovae, which is considered a difficult task, can help to understand this.
Supernova SN 2020tlf
A team of astronomers has published the results of an analysis of multiwavelength observations (from X-ray to radio) of the Type II-P/L supernova SN 2020tlf, which was detected by the ground-based ATLAS 16 system in September 2020 in the spiral galaxy NGC 5731, located 120 million light-years from the Sun.
The observations were made with a number of ground-based telescopes and the Swift space telescope and covered the period from 130 days before the explosion to 300 days after the explosion.
The result of the work was a model of the evolution of the supernova progenitor star at the end of its life. It was a red supergiant, with a radius of 1100 solar radii and a mass of 10–12 solar masses, which was losing mass at an increased rate (10 -2 solar masses per year) in the last months before the explosion.
This led to the formation of a dense inner shell of circumstellar matter (at distances less than 10 15 centimeters from the star) and a less dense outer shell (up to 8×10 15 centimeters from the star).
The total mass of circumstellar matter is estimated at 0.05–0.07 solar masses, it consisted of helium, hydrogen, carbon and nitrogen ions.
SN 2020tlf is the first instance of a Type II supernova whose progenitor star exhibited an increased level of radiation prior to the explosion that had not been observed before.
Conclusions
Scientists believe that this, as well as the increased level of mass loss, can be explained by instability in the interior of the star, most likely associated with the last stages of nuclear combustion, such as neon/oxygen, or silicon.
The researchers concluded that increased levels of activity may be common for progenitor stars of type II-P/L supernovae, and the phenomenon has simply not been detected in sky surveys due to sensitivity limitations.
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Sources:
• Jacobson-Galán, W. V., Dessart, L., Jones, D. O., & Margutti, R. (2022, January 6). Final Moments. I. Precursor Emission, Envelope Inflation, and Enhanced Mass Loss Preceding the Luminous Type II Supernova 2020tlf. The Astrophysical Journal.
• O’Neill, M. (2022, January 16). Explosion of supergiant star captured by astronomers. SciTechDaily.
• Specktor, B. (2022, January 10). Scientists watched a star explode in real time for the first time ever. LiveScience.
• W. M. Keck Observatory. (n.d.). Astronomers witness a dying star reach its explosive end.
• Young, M. (2022, January 10). The flames of orion and a supergiant star’s end. Sky & Telescope.
