Double-peak supernovae offer clues to pre-supernova explosions

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 affect the properties of the resulting supernova and its remnant. The work also sheds light on the different masses of progenitors and the scenarios that could lead to different types of mass loss, shedding light on the complex processes that govern the life cycles of massive stars.

The group of researchers proposes constraints on the physical properties of these progenitors and suggests possible mechanisms of mass loss, thus improving the understanding of stellar evolution and supernova diversity.

Dr. Shing-Chi Leung, Assistant Professor of Physics at SUNY Polytechnic Institute, is a co-author of the paper, “Probing Pre-Supernova Mass Loss in Double-Peak Type Ibc Supernovae from the Zwicky Transient Facility,” as part of a collaborative research project with the Zwicky Transient Facility (ZTF) team. The ZTF is a telescope built in Palomar, California, and primarily maintained by researchers at the California Institute of Technology (CalTech).

The article is published in the The Journal of Astrophysicsand the project was led by CalTech graduate student Kaustav K. Das.

Supernovae are explosions of stars. Depending on their progenitor, their brightness can reach its maximum within 20 to 100 days after the explosion, then disappear again into the dark sky.

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

The Zwicky Transient Factory is designed to address this challenge with an automated real-time data reduction pipeline, a dedicated photometric tracking telescope, and a comprehensive archive of all detected astronomical sources. This allows for the continuous capture, classification, and analysis of transient events in the sky. Since ZTF was launched in 2017, the telescope has detected approximately 9,000 supernovae.

With the large number of newly discovered supernovae, a new class of supernovae has emerged. These supernovae contain neither hydrogen nor silicon in the ejections (they are called type Ib/c supernovae) and exhibit a large double peak in luminosity, with the first peak occurring about 10 days after the explosion.

Normal supernovae typically exhibit a peak in brightness throughout the duration of the explosion. The double peak indicates that the star is having an explosion phase before its final explosion. The explosion is like a “mini-explosion” that sends material to the outskirts of the star. After the explosion, the final explosion occurs and the high-speed material interacts with this previously ejected material and creates the observed double-peak signals.

“We know that such supernovae occur very occasionally, but we don’t know whether they are isolated events or whether there is a systematic picture behind these supernovae,” Dr. Leung explained. “With the statistics confirmed by ZTF, we can think that there is a robust mechanism behind these explosions. The question then becomes: do we have a consistent picture to explain these explosions when we can still explain ordinary supernovae?”

In this project, Dr. Leung studied his previous models in which a pre-supernova explosion is predicted. They found that the explosion parameter could be consistent with a less common class of supernovae known as pulsating pair instability supernovae. However, this class of supernovae is also known to be rare. Thus, it is unclear whether this can be the complete explanation for this unusual subclass as well as the number of events.

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

“We expect more data to become available by the end of the decade. The Rubin Observatory (formerly known as the Large Synoptic Survey Telescope) will be deployed in 2025 and the scientific community expects to detect about 10 times more supernovae. Such a large amount of new data will certainly provide new perspectives to reveal the lesser-known side of supernova physics and these special objects.”