From AAS NOVA: “Simulating a Plateauing Supernova”

AASNOVA

From AAS NOVA

9.21.22
Kerry Hensley

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The Hubble Space Telescope captured this image of a supernova shining in the outskirts of the galaxy NGC 2525. Supernova light curves have a variety of behaviors, which can tell us about the cause of the supernova as well as its surroundings. [NASA/ESA Hubble, A. Riess and the SH0ES team; Acknowledgment: Mahdi Zamani]

Supernovae show a wide variety of behaviors as they fade and these behaviors encode information about the exploding star and its surroundings. Can simulations help us understand why some supernovae maintain the same brightness for weeks or months?

Light Curve Characterization

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The Pencil Nebula, located at the center image, is thought to be evidence of a shock wave created by a supernova. [ESO/Digitized Sky Survey 2; Acknowledgment: Davide De Martin; CC BY 4.0]

When massive stars end their lives as supernovae, researchers dissect their light curves to reconstruct the details of their demise. Some supernovae, known as Type IIP, hit a plateau after they begin to fade, sustaining the same brightness for weeks or months before starting to dim again. Modeling suggests that these supernovae get their characteristic brightness plateaus when the expanding shock wave heats and ionizes nearby gas, but more work is needed to understand the origin of this gas.

In a recent publication, Alexandra Kozyreva (Max Planck Institute for Astrophysics, Germany) and collaborators modeled supernova SN 2021yja to understand if its light curve can be explained by this emerging picture of Type IIP supernova evolution.

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A comparison of the observed brightness of SN 2021yja (cyan circles) with modeled light curves for a model with (m15ni175; red) and without (m15 basic; black) circumstellar material. [Kozyreva et al. 2022]

Plateau Possibilities

Kozyreva and collaborators modeled SN 2021yja as a collapsing 15-solar-mass red supergiant — a star so large that it would engulf Mercury, Venus, Earth, and Mars if placed in our solar system. To test the impact of circumstellar gas on the exploding star’s light curve, the team compared models that incorporated a cloud of dense, hydrogen-rich material surrounding the star to those that didn’t. These simulations showed that circumstellar material is necessary to explain several features of SN 2021yja’s light curve, including its rapid rise and high peak brightness.

The best-fitting models incorporated 0.55 solar mass of surrounding material that extended from very close to the star’s surface out to 2,700 solar radii, and several facets of the model output indicated that this gas was distributed asymmetrically around the star. Given the density and proximity of the surrounding gas, the team found that the material was likely expelled in the span of just a few years. These results confirm that SN 2021yja fits the emerging picture of Type IIP supernovae, but they raise new questions about the source of the material in the star’s neighborhood.

Outflow Options

Kozyreva and coauthors outlined several possible sources for this material:

Stellar winds. Red supergiant stars produce vigorous stellar winds, but these winds typically expel material at a rate 100,000 times slower than necessary for stellar winds to explain the predicted amount of circumstellar material.

Binary interaction. If the star had a binary companion, the circumstellar material could have been generated by an enormous transfer of mass — large enough that it destabilizes the system and causes the stars to merge. However, this scenario likely causes less than one in 10,000 supernovae.

Convective behavior. The atmospheres of red supergiant stars undergo a slow churning motion called convection, which creates the conditions for gas in the star’s atmosphere to be lofted upwards and eventually lost. The gravitational tug of a binary companion could cause this mass loss to be asymmetrical.

The team suggested that convection in the star’s atmosphere is the most likely source of the gas surrounding SN 2021yja — and since convection is common in red supergiant stars, it may provide an explanation for the curious light curves of many Type IIP supernovae.

Citation

The Circumstellar Material around the Type IIP SN 2021yja, Alexandra Kozyreva et al 2022 ApJL 934 L31.

https://iopscience.iop.org/article/10.3847/2041-8213/ac835a

See the full article here .


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The mission of the American Astronomical Society is to enhance and share humanity’s scientific understanding of the Universe.

The Society, through its publications, disseminates and archives the results of astronomical research. The Society also communicates and explains our understanding of the universe to the public.
The Society facilitates and strengthens the interactions among members through professional meetings and other means. The Society supports member divisions representing specialized research and astronomical interests.
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The Society, through its members, trains, mentors and supports the next generation of astronomers. The Society supports and promotes increased participation of historically underrepresented groups in astronomy.
The Society assists its members to develop their skills in the fields of education and public outreach at all levels. The Society promotes broad interest in astronomy, which enhances science literacy and leads many to careers in science and engineering.

Adopted June 7, 2009

The society was founded in 1899 through the efforts of George Ellery Hale. The constitution of the group was written by Hale, George Comstock, Edward Morley, Simon Newcomb and Edward Charles Pickering. These men, plus four others, were the first Executive Council of the society; Newcomb was the first president. The initial membership was 114. The AAS name of the society was not finally decided until 1915, previously it was the “Astronomical and Astrophysical Society of America”. One proposed name that preceded this interim name was “American Astrophysical Society”.

The AAS today has over 7,000 members and six divisions – the Division for Planetary Sciences (1968); the Division on Dynamical Astronomy (1969); the High Energy Astrophysics Division (1969); the Solar Physics Division (1969); the Historical Astronomy Division (1980); and the Laboratory Astrophysics Division (2012). The membership includes physicists, mathematicians, geologists, engineers and others whose research interests lie within the broad spectrum of subjects now comprising contemporary astronomy.

In 2019 three AAS members were selected into the tenth anniversary class of TED Fellows.

The AAS established the AAS Fellows program in 2019 to “confer recognition upon AAS members for achievement and extraordinary service to the field of astronomy and the American Astronomical Society.” The inaugural class was designated by the AAS Board of Trustees and includes an initial group of 232 Legacy Fellows.