Page 14 - BBC Sky at Night - September 2017 UK

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CUTTING

clear it was destined to be a superluminous
Our experts examine the EDGE event. Previous supernovae of this type have been
hottest new research found exclusively in small, dwarf galaxies, but
NGC 3191 is a massive spiral. Just by observing
it, we’ve learnt something; these rare events
An exciting death (only 40 or so have ever been seen) can happen
in massive galaxies, rich in elements other than
hydrogen and helium produced by eons of
Supernova SN 2017egm is a rare ‘superluminous’ vigorous star formation.
What’s more, the thing is still bright. In a recent
explosion – only 40 or so have ever been seen paper, a team led by Matt Nicholl of Harvard points
out that while currently hidden behind the Sun, the
The supernova is in slow fading of the supernova means it may remain
NGC 3193 in Leo and bright enough for observation for another two
should remain bright for years. Understanding that decay is essential if we
another two years
want to understand what causes these unusual and
powerful explosions; when we see light from a
supernova, we’re not seeing the explosion itself, but
rather light released from the radioactive decay of
elements produced in the initial maelstrom.
Watching the decay therefore helps us understand
what happened right at the beginning, when a star
“Watching the decay
SN 2017egm
helps us understand

what happened right
at the beginning,

when a star reaches

the end of its life”

in this galaxy reaches the end of its life and
collapses in on itself. Its core will have become
supernova is always exciting, but one either a neutron star or a black hole, and both
in a relatively nearby galaxy is even offer possibilities. Elsewhere in the Universe,
more so. Supernova SN 2017egm, which at the centres of galaxies with growing black
A lit up nearby spiral NGC 3191 in May, holes, the inflow of material onto an accretion
is a spectacular and potentially important find, disc surrounding the black hole produces energetic
and not just because of its proximity to us. jets. Something similar could happen here,
At a distance of just over 400 million lightyears, boosting the luminosity of the supernova. Or a
it’s not the closest supernova of the past few years, newly created magnetar – a neutron star with a
but it is the nearest example yet of a very special strong magnetic field – could be slowing down
kind – the still mysterious ‘superluminous by interacting with its surroundings, pumping
energy into its surroundings.
supernova’. As the name suggests, these explosions
STERNBERG ASTRONOMICAL INSTITUTE/MOSCOW UNIVERSITY visible for a long time after the initial explosion. CHRIS LINTOTT is an presented by its proximity to us. Even after only
are more powerful than their luminous
Further study of SN 2017egm will help distinguish
counterparts, shining brightly and remaining
these models from each other, a unique opportunity
SN 2017egm was spotted on 23 May 2017 by
a couple of months of observation, it’s already
a strong candidate for being the most exciting
the Gaia team; the Milky Way-mapping satellite
event to be observed this year.
had recorded the appearance of a star that wasn’t
there when it last looked in April. Swift work by
astrophysicist and
a team at the Xinglong Station Observatory in
CHRIS LINTOTT was reading… The superluminous
co-presenter of The Sky
the north of China just three days later seemed
supernova SN 2017egm in the nearby galaxy NGC
at Night on BBC TV.
to suggest it was a Type II event, representing the
3191: a metal-rich environment can support a typical
death of a massive star, but further follow-up
of the Zooniverse project.
Read it online at https://arxiv.org/abs/1706.08517
from telescopes in the Canaries and the US made
skyatnightmagazine.com 2017 He is also the director SLSN evolution by Matt Nicholl et al.