In a nearby dwarf galaxy called the Small Magellanic Cloud, astronomers have discovered possibly the most luminous nova ever.
SMCN 2016-10a was discovered on October 14, 2016. Novae occur frequently in our Milky Way Galaxy, with a rate of around 35 each year, but SMCN 2016-10a is the first nova to have been detected in the Small Magellanic Cloud since 2012. Left: the nova system before eruption. Right: the nova system in outburst. Image credit: OGLE Survey.
A nova happens when an old star erupts dramatically back to life.
In a close binary star system consisting of a white dwarf and a Sun-like companion star, material is transferred from the companion to the white dwarf, gradually building up until it reaches a critical pressure. Then uncontrolled nuclear burning occurs, leading to a sudden and huge increase in brightness.
Novae are usually found in visible light, but often go on to emit higher energy X-rays as well. Together, these different datasets provide information on the white dwarf, such as its temperature and chemical composition.
Using NASA’s Swift observatory and ground-based telescopes in South Africa, Australia, and Chile, an international team of astronomers has revealed that a nova dubbed SMCN 2016-10a is the most luminous nova ever discovered in the Small Magellanic Cloud and one of the brightest ever seen in any galaxy.
“Swift’s ability to respond rapidly, together with its daily-planned schedule, makes it ideal for the follow-up of transients, including novae,” said team member Dr. Kim Page, from the University of Leicester.
“It was able to observe SMCN 2016-10a throughout its eruption, starting to collect very useful X-ray and UV data within a day of the outburst first being reported.”
“The X-ray data were essential in showing that the mass of the white dwarf is close to the theoretical maximum; continued accretion might cause it eventually to be totally destroyed in a supernova explosion.”
“The present observations provide the kind of coverage in time and spectral color that is needed to make progress for gaining understanding of a nova in a neighboring galaxy,” added team member Dr. Paul Kuin, from the Mullard Space Science Laboratory, University College London.
“Observing the nova in different wavelengths using world-class telescopes such as Swift and the Southern African Large Telescope help us reveal the condition of matter in nova ejecta as if it were nearby.”
“Although it is difficult to measure the distance to novae directly, its position in the Small Magellanic Cloud on the sky, and everything else we know about this nova point to it being in this dwarf galaxy,” said team member Professor Julian Osborne, who leads the Swift team at the University of Leicester.
“This makes the nova as intrinsically bright as the most luminous ever seen, and thus very interesting in trying to understand these explosions.”
Details of the research will be published in the Monthly Notices of the Royal Astronomical Society. The article is also publicly available at arXiv.org.
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E. Aydi et al. 2017. Multiwavelength observations of nova SMCN 2016-10a — one of the brightest novae ever observed. MNRAS, in press; arXiv: 1710.03716
