Understanding the origin of the most energetic stellar explosions in the Universe

The IEEC, through the Institute of Cosmos Sciences (ICCUB), has participated in this research led by prof. Xiaofeng Wang from Tsinghua University and published in Nature Astronomy.
 
The study suggests that during its final instability period the star emitted four shells of circumstellar material, which later interacted with the material ejected in the explosion creating a very intense and complex luminosity pattern.

At the end of their lives, massive stars usually undergo core-collapse and explode in a highly energetic burst called supernova. However, what happens to very massive stars with more than 100 times the mass of the Sun? How do they evolve and explode? How are they related to the brightest supernovae in the universe, called superluminous supernovae?

A team of scientists led by Prof. Xiaofeng Wang of Tsinghua University, in collaboration with national and international research teams, including the Institute of Space Studies of Catalonia (IEEC — Institut d’Estudis Espacials de Catalunya) through the Institute of Cosmos Sciences of the University of Barcelona (ICCUB), has monitored the nearby superluminous supernova SN2017egm for more than one year. The study reveals an extremely complex luminosity evolution (see image).

Caption: The image shows an artistic rendering of a supernova and its complex environment, where one can observe the four shells of circumstellar material. The yellow and pink lines represent the integrated luminosity light curve of the observed superluminous supernova and a non-superluminous supernova, respectively. 
Credits: Drawing by Jingchuan Yu at the Beijing Planetarium.

By fitting the total luminosity evolution of the object with various kinds of energy source models, the team found that such a “bumpy” light curve mainly originated from the interaction of material ejected during the supernova explosion with four shells of circumstellar material (CSM). The existence of these CSM shells reveals that the progenitor star of the supernova experienced frequent mass ejections right before the final collapse, with an average rate of 1-10 solar masses per year.

Such a frequent and massive mass ejection is inconsistent with ordinary stellar wind and binary interaction models, but they are likely driven by a mechanism called pulsational pair-instability (PPI).

Combining these models, the initial core of the star is estimated to be about 50 solar masses. During the final burst of the supernova, the ejected material interacted with the previous circumstellar shells creating one of the most luminous stellar explosions observed in our Universe and leaving behind a corpse consisting of a black hole of about 40 solar masses.
This has important implications for the formation of the tens of solar masses black holes, which have been recently detected by LIGO-Virgo gravitational wave observatories. This work shows that such heavy black holes can be produced through the mentioned mechanisms, and not only via the merger of lighter black holes.

In order to trigger the PPI mechanism, stars need to have a very heavy helium core, which usually evolves from a massive star with a low metal abundance, according to the single stellar evolution theory.

However, the progenitor star of SN2017egm is located in a metal-rich environment, which opens up many questions about its mysterious origin. “We got really excited about SN2017egm, because its host was a large spiral galaxy, in contrast to previous superluminous supernovae, which usually exploded in dwarf galaxies,” explains Nadia Blagorodnova, IEEC researcher at the ICCUB, who contributed to the study. “This challenged all our previous assumptions about how superluminous supernovae are formed,” she adds.

The research of this supernova is of great significance for testing current theory of stellar evolution and explosion, and for understanding the origin of superluminous supernovae and massive stellar-mass black holes.

Press release prepared in collaboration with the Communication Office of the Institute of Cosmos Sciences (ICCUB).

Main Image

Caption: Remnant of SN 1572 (Tycho's Supernova, Tycho's Nova), one of eight supernovae visible to the naked eye in historical records.

Links
– IEEC
– ICCUB
– Tsinghua University

More information

This research is presented in a paper entitled “A superluminous supernova lightened by collisions with pulsational pair-instability shells”, by Lin, W., Wang, X., Yan, L. et al., which appeared in the journal Nature Astronomy on 1 May 2023.

The Institute of Space Studies of Catalonia (IEEC  — Institut d’Estudis Espacials de Catalunya) promotes and coordinates space research and technology development in Catalonia for the benefit of society. IEEC fosters collaborations both locally and worldwide and is an efficient agent of knowledge, innovation and technology transfer. As a result of more than 25 years of high-quality research, done in collaboration with major international organisations, IEEC ranks among the best international research centres, focusing on areas such as: astrophysics, cosmology, planetary science, and Earth Observation. IEEC’s engineering division develops instrumentation for ground- and space-based projects, and has extensive experience in working with private or public organisations from the aerospace and other innovation sectors.

IEEC is a private non-profit foundation, governed by a Board of Trustees composed of Generalitat de Catalunya and four other institutions that each have a research unit, which together constitute the core of IEEC R&D activity: the Universitat de Barcelona (UB) with the research unit ICCUB — Institute of Cosmos Sciences; the Universitat Autònoma de Barcelona (UAB) with the research unit CERES — Center of Space Studies and Research; the Universitat Politècnica de Catalunya · BarcelonaTech (UPC) with the research unit CTE — Research Group in Space Sciences and Technologies; the Spanish Research Council (CSIC) with the research unit ICE — Institute of Space Sciences. The IEEC is a CERCA (Centres de Recerca de Catalunya) centre.

Contacts

IEEC Communication Office
Barcelona, Spain
E-mail: comunicacio@ieec.cat 

Lead Researcher at the IEEC
Barcelona, Spain
Nadia Blagorodnova
Institute of Space Studies of Catalonia (IEEC)
Institute of Cosmos Sciences (ICCUB)
E-mail: nblago@icc.ub.edu