Scientists discover one of the most luminous ‘new stars’ ever

Scientists discover one of the most luminous 'new stars' ever

Left: the nova system before eruption. Right: the nova
system in outburst. Credit: OGLE survey

Astronomers have today announced that they have discovered
possibly the most luminous ‘new star’ ever – a nova
discovered in the direction of one of our closest neighboring
galaxies: The Small Magellanic Cloud.

Astronomers from the University of Leicester contributed to the
discovery by using the Swift satellite observatory to help
understand what was likely the most luminous white dwarf
eruption ever seen.

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. It
is called a nova because it appeared to be a new star to the
ancients.

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 telescopes from South Africa to Australia to South
America, as well as the orbiting Swift observatory, a team led
by the South African Astronomical Observatory has revealed that
the nova SMCN 2016-10a, which was discovered on 14th October
2016, is the most luminous nova ever discovered in the SMC, and
one of the brightest ever seen in any galaxy. The observations
that they made are the most comprehensive ever for a nova in
this galaxy.

The SMC, 200,000 light-years away, is one of our closest
companion ; it is a dwarf galaxy, very much
less massive than our own. Novae occur frequently in our
Galaxy, with a rate of around 35 each year, but SMCN 2016-10a
is the first nova to have been detected in the SMC since 2012.

Dr Kim Page, a member of the Swift team at the University of
Leicester, led the X-ray analysis, while Paul Kuin, from the
Mullard Space Science Laboratory, University College London,
organised the UV data.

Dr Page said: “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. 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.”

Dr Kuin added:”The present observations provide the kind of
coverage in time and spectral colour that is needed to make
progress for gaining understanding of a nova in a neighbouring
galaxy. 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.”

Professor Julian Osborne, who leads the Swift team at the
University of Leicester, and was also involved in this study,
said: “Although it is difficult to measure the distance to
novae directly, its position in the SMC on the sky, and
everything else we know about this nova point to it being in
this . This makes the nova as
intrinsically bright as the most luminous ever seen, and thus
very interesting in trying to understand these explosions.”

The paper, entitled “Multiwavelength observations of nova SMCN
2016-10a – Probably the brightest in the SMC and one of the brightest on
record” has been accepted for publication in Monthly Notices
of the Royal Astronomical Society
, and is available as a
preprint at https://arxiv.org/abs/1710.03716 .

Explore further:

Scientists recover nova first spotted 600 years ago by Korean
astrologers

Journal reference:
Monthly Notices of the Royal Astronomical Society

Provided by: University
of Leicester

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