An unusually brilliant transient in the galaxy Messier 85

TL;DR

This paper reports the discovery of a bright optical transient in galaxy M85, likely caused by a stellar merger, providing insights into hyper-Eddington sources and binary star evolution.

Contribution

It presents the first detailed observation of a luminous transient in M85, suggesting stellar mergers as a possible origin, and highlights the importance of such events for understanding stellar evolution.

Findings

Transient brighter than novae but fainter than supernovae

Energy emitted over two months was nearly 10^47 erg

Likely caused by a stellar merger event

Abstract

Historically, variable and transient sources have both surprised astronomers and provided new views of the heavens. Here we report the discovery of an optical transient in the outskirts of the lenticular galaxy Messier 85 in the Virgo Cluster. With a peak absolute R magnitude of -12 this event is distinctly brighter than novae, but fainter than type Ia supernovae (expected from a population of old stars in lenticular galaxies). Archival images of the field do not show a luminous star at that position with an upper limit of ~-4.1, so it is unlikely to be a giant eruption from a luminous blue variable star. Over a two month period the transient emitted radiation energy of almost 10E47 erg and subsequently faded in the opical sky. It is similar to, but more luminous at peak by a factor of 6 than, an enigmatic transient in the galaxy M31. A possible origin of M85 OT2006-1 is a stellar merger. If so, searches for similar events in nearby galaxies will not only allow to study the physics of hyper-Eddington sources, but also probe an important phase in the evolution of stellar binary systems.