Red Nova: A New Violent Event
A cool but violent event has made its debut in stellar astronomy, the Red Novae.
Large area and continuous sky coverage has yielded the unexpected – actual observations of mergers of binaries into single stars. It has been found that these events are culminated by a bright and long-lasting peculiar Novae – a Red Novae. The colour is not the usual blue, high temperature event as expected for novae and supernovae, but rather has a peculiar red spectra (~1000K).
This is the final coalescence of a contact binary into fast rotating, blue straggler-like, single star. The recovery of archived observations of a contact binary with high fill-out at the site of the red nova V1309 Sco (Tylenda et al. 2011, Tylenda and Kamiński 2016) has underlined the need for study of the characterisation and continued monitoring of such binaries in transition.
Archival data has also revealed that these have happened in the past. Thus binaries have undergone a complete metamorphosis inside of the age of the universe – covering time intervals much shorter of that imagined by secular astronomers. We have shown that the rate of transition is more than 100 times faster than expected. This speed has led to the nickname “Mergebursts”.
These events range in luminosities or energies intermediate between classical novae (explosions within compact binary systems) and supernovae (which often involve the annihilation of the star or stars involved). The duration of the eruption also lays between that of novae and supernovae.
V1309 Sco, V838 Mon and M31-RV are examples. The typical lightcurve of red novae show an irregular rise of about 10 magnitudes (10,000 times increase in brightness) and an irregular decrease occurring over the course of ~100 days. These violent, relatively cool events mark the transition from binaries to single stars. It may turn out that these are the most common of the novae.