Researchers from University of Turku Involved in Discovering Extremely Bright Supernova Explosions

​The study concentrates on a bright explosion which was discovered with a telescope on Hawaii as part of an all-sky survey that aims to discover transient objects, such as supernovae which are explosions of massive stars. The host galaxy of the discovered explosion is located more than 3 billion light years from the Earth. The event appeared to be extremely interesting based on its brightness and location in the central region of its host galaxy. The event has been monitored for several years.

– The total energy radiated by the event is 1,000 times that of normal supernova explosions. The host galaxy of the event is also an active, so-called Seyfert galaxy, with a roughly 10-million-solar-mass supermassive black hole in its nucleus. The spectroscopic properties of the event, and the slow and smooth evolution of the brightness, showed that it was not a normal outburst of a supermassive black hole in an active galaxy, says Kankare.

Based on the data analysis, the research group converged on two possible paths of origin for the event. If it is one of the brightest supernova explosions ever, it originates from an extremely massive star of at least several tens or even hundreds of solar masses. It can also be a disruption of a star by the gravitational tidal forces of the supermassive black hole in the galaxy nucleus. In both cases, the observations suggest that during the event, explosively expanding material collided with dense ambient gas.

– If this is a tidal disruption event, the observations tell us something new about the mechanism of these kinds of events, sums Kankare.

Tools for Probing the Properties of Galaxies

The team’s study also presents five other discovered objects with similar properties. According to Professor Seppo Mattila from the Department of Physics and Astronomy at the University of Turku, who is a member of the group, the new observations help researchers better understand universe.

– Future observations of new similar events will enable a better understanding of these extremely energetic events. Because of their significant brightness, these events can also be used in future as tools to probe the properties of distant galaxies, describes Mattila.

Observations were carried out mainly with the 2.56-metre NOT on La Palma, Canary Islands, which is one of the best observatory sites in the world. The NOT has an important role both for astronomy research in Finland and in the training of a new generation of researchers.  Its flexibility makes the NOT a very competitive telescope internationally and extremely well suited for observing supernovae and other transients.

From Finland, Doctor Tuomas Kangas and Doctoral Candidates Jussi Harmanen and Thomas Reynolds from the Tuorla Observatory of the Department of Physics and Astronomy at the University of Turku are also involved in the study.

An article based on the study called "A population of highly energetic transient events in the centres of active galaxies" has been published in the Nature Astronomy journal.
 
HK/SY