Astronomers Spot What Could Be The Most Luminous Nova Ever

Artist impression of a nova. NASA's Goddard Space Flight Center/S. Wiessinger

An international collaboration of astronomers has observed an old dwarf star turning into a nova, suddenly becoming much brighter than it usually is. The event, known as SMCN 2016-10a, is actually a record-breaker. Being 185 times brighter than the Sun, it’s one of the most luminous nova ever seen.

Although the term is used to describe several cosmic events, novae like this are not like supernovae where a star explodes. SMCN 2016-10a happened when a white dwarf was covered in material from a companion, where it eventually undergoes nuclear fusion making the object brighter for a short time.

As reported in the study, which is accepted for publication in the Monthly Notices of the Royal Astronomical Society, the nova is likely to have happened in the Small Magellanic Cloud, one of the satellite galaxies surrounding the Milky Way. It is about 200,000 light-years and is the brightest nova we have ever witnessed coming from the Small Magellanic Cloud.

“We are very excited to discover such extreme events which occur only rarely, especially in the SMC,”  lead author Elias Aydi, from the University of Cape Town said in a statement. "A combination of several factors such as the mass of the white dwarf, its temperature and chemical composition might be responsible for such a luminous eruption

While the brightness is impressive, the importance of the study rests on the level of details the team was able to obtain about this event. Novae are transient events, they happen quickly and with no warnings and they begin to fade immediately. Getting in early with a wide range of instruments is crucial. The researchers were able to use observatories across the southern hemisphere, like the South African Astronomical Observatory, as well as the X-ray space telescope, Swift.

“Swift's ability to respond rapidly, together with its daily-planned schedule, makes it ideal for the follow-up of transients, including novae. It was able to observe the nova throughout its eruption, starting to collect very useful X-ray and UV data within a day of the outburst first being reported,” co-author Dr Kim Page from the University of Leicester said in a statement.

The data collected by Swift was key to estimating the mass of the white dwarf. It also told the team, that the star is not long for this world. While the process of becoming a nova throws a lot of mater back into space, some of it remains, making the white dwarf heavier. If the white dwarf’s mass goes over a certain value it collapses in on itself, turning into a supernova. SMCN 2016-10a is very close to that limit.

There’s no timeline on when the white dwarf will succumb to gravity and even if it’s not in our lifetime, this object has given researchers many interesting details into the mysterious lives of novae.

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