Double-topped supernovae offer clues to pre-supernova outbursts

New research helps to understand the evolution and final stages of massive stars, the role of binary interactions, and the mechanisms behind mass loss, which ultimately influence the properties of the resulting supernova and its remnant. This work also provides insight into the different progenitor masses and the scenarios that can lead to different types of mass loss, shedding light on the complex processes that determine the life cycles of massive stars.

The group of researchers provides constraints on the physical properties of these progenitors and suggests possible mechanisms for mass loss, increasing understanding of stellar evolution and the diversity of supernovae.

Dr. Shing-Chi Leung, assistant professor of physics at SUNY Polytechnic Institute, was one of the authors of the paper titled “Probing Presupernova Mass Loss in Double-peaked Type Ibc Supernovae from the Zwicky Transient Facility,” in a joint research project with the Zwicky Transient Facility (ZTF) team. The ZTF is a telescope built in Palomar, California, and maintained primarily by researchers at the California Institute of Technology (CalTech).

The article was published in the The astrophysical journaland the project was led by CalTech graduate student Kaustav K. Das.

Supernovae are the explosion of stars. Depending on the progenitor, their brightness can evolve to their full brightness within 20-100 days after the explosion, and then fade away again in the dark sky.

Traditionally, astronomers must compare the night sky to a reference image and look for unexplained bright spots that could be supernova candidates. Astronomers then make follow-up observations to record the detailed evolution of the supernova’s optical signals. The process can be slow because it is not automated, and the long response time can miss rapidly evolving objects.

The Zwicky Transient Factory is designed to solve this problem with an automated real-time data reduction pipeline, a dedicated photometric follow-up telescope, and a full archive of all detected astronomical sources. This allows for the continuous recording, classification, and analysis of transient events in the sky. Since the ZTF was launched in 2017, the telescope has detected about 9,000 supernovae.

With the large number of newly discovered supernovae, a new class of supernovae has emerged. These supernovae have no hydrogen or silicon in the ejecta (also known as Type Ib/c supernovae) and a prominent double peak in brightness, with the first peak occurring immediately, about 10 days after the explosion.

Normal supernovae usually show a single peak in their luminosity throughout the entire explosion. The double peak indicates that the star has an outburst phase prior to its final explosion. The outburst is like a “mini explosion” that ejects some matter to the outskirts of the star. After the outburst, the final explosion occurs and the high-speed matter interacts with this previously ejected matter and creates the double peak signals that were observed.

“In the past, we knew that such supernovae happened very occasionally, but we don’t know whether they were one-off events or whether there was a systematic picture behind these supernovae,” Dr. Leung explained. “With the statistics supported by ZTF, we can believe that there is a robust mechanism behind such outbursts. The question then becomes: do we have a consistent picture to explain these outbursts, while still being able to explain regular supernovae?”

In this project, Dr. Leung reviewed his previous models predicting pre-supernova outbursts. They found that the outburst parameter could be consistent with a less common class of supernovae, known as Pulsational Pair-Instability Supernovae. However, this class of supernovae is also known to be rare. So it is a matter of debate whether this can fully explain this unusual subclass along with the number of events.

“Although the conclusion is still open, it is still exciting to know that supernovae may be more mysterious than we once thought,” said Dr. Leung.

“And we expect that much more data will become available later this decade. The Rubin Observatory (formerly known as the Large Synoptic Survey Telescope) will be deployed in 2025, and the community expects to detect about 10 times more supernovae. Such a substantial amount of new data will certainly provide new insights into revealing the lesser-known side of supernova physics and these curious objects.”