Discovery of supernova Gaia14aaa
Copyright: ESA/Gaia/DPAC/Z.
Kostrzewa-Rutkowska (Warsaw University Astronomical Observatory) &
G. Rixon (Institute of Astronomy, Cambridge)
Copyright: M. Fraser/S. Hodgkin/L. Wyrzykowski/H. Campbell/N. Blagorodnova/Z. Kostrzewa-Rutkowska/Liverpool Telescope/SDSS
This powerful event, now named Gaia14aaa, took place in a distant galaxy
some 500 million light-years away, and was revealed via a sudden rise
in the galaxy’s brightness between two Gaia observations separated by
one month.
Gaia, which began its scientific work on 25 July, repeatedly scans the
entire sky, so that each of the roughly one billion stars in the final
catalogue will be examined an average of 70 times over the next five
years.
“This kind of repeated survey comes in handy for studying the changeable
nature of the sky,” comments Simon Hodgkin from the Institute of
Astronomy in Cambridge, UK.
Many astronomical sources are variable: some exhibit a regular pattern,
with a periodically rising and declining brightness, while others may
undergo sudden and dramatic changes.
“As Gaia goes back to each patch of the sky over and over, we have a
chance to spot thousands of ‘guest stars’ on the celestial tapestry,”
notes Dr Hodgkin. “These transient sources can be signposts to some of
the most powerful phenomena in the Universe, like this supernova.”
Dr Hodgkin is part of Gaia’s Science Alert Team, which includes
astronomers from the Universities of Cambridge, UK, and Warsaw, Poland,
who are combing through the scans in search of unexpected changes.
It did not take long until they found the first ‘anomaly’ in the form of
a sudden spike in the light coming from a distant galaxy, detected on
30 August. The same galaxy appeared much dimmer when Gaia first looked
at it just a month before.
“We immediately thought it might be a supernova, but needed more clues
to back up our claim,” explains Łukasz Wyrzykowski from the Warsaw
University Astronomical Observatory, Poland.
Other powerful cosmic events may resemble a supernova in a distant
galaxy, such as outbursts caused by the mass-devouring supermassive
black hole at the galaxy centre.
However, in Gaia14aaa, the position of the bright spot of light was
slightly offset from the galaxy’s core, suggesting that it was unlikely
to be related to a central black hole.
So, the astronomers looked for more information in the light of this new
source. Besides recording the position and brightness of stars and
galaxies, Gaia also splits their light to create a spectrum. In fact,
Gaia uses two prisms spanning red and blue wavelength regions to produce
a low-resolution spectrum that allows astronomers to seek signatures of
the various chemical elements present in the source of that light.
Copyright: ESA/Gaia/DPAC/N. Blagorodnova,
M. Fraser, H. Campbell, A. Hall (Institute of Astronomy, Cambridge)
“In the spectrum of this source, we could already see the presence of
iron and other elements that are known to be found in supernovas,” says
Nadejda Blagorodnova, a PhD student at the Institute of Astronomy in
Cambridge.
In addition, the blue part of the spectrum appears significantly
brighter than the red part, as expected in a supernova. And not just any
supernova: the astronomers already suspected it might be a ‘Type Ia’
supernova – the explosion of a white dwarf locked in a binary system
with a companion star.
While other types of supernovas are the explosive demises of massive
stars, several times more massive than the Sun, Type Ia supernovas are
the end product of their less massive counterparts.
Low-mass stars, with masses similar to the Sun’s, end their lives
gently, puffing up their outer layers and leaving behind a compact white
dwarf. Their high density means that white dwarfs can exert an intense
gravitational pull on a nearby companion star, accreting mass from it
until the white dwarf reaches a critical mass that then sparks a violent
explosion.
To confirm the nature of this supernova, the astronomers complemented
the Gaia data with more observations from the ground, using the Isaac
Newton Telescope (INT) and the robotic Liverpool Telescope on La Palma,
in the Canary Islands, Spain.
A high-resolution spectrum, obtained on 3 September with the INT,
confirmed not only that the explosion corresponds to a Type Ia
supernova, but also provided an estimate of its distance. This proved
that the supernova happened in the galaxy where it was observed.
“This is the first supernova in what we expect to be a long series of
discoveries with Gaia,” says Timo Prusti, ESA’s Gaia Project Scientist.
Supernovas are rare events: only a couple of these explosions happen
every century in a typical galaxy. But they are not so rare over the
whole sky, if we take into account the hundreds of billions of galaxies
that populate the Universe.
Astronomers in the Science Alert Team are currently getting acquainted
with the data, testing and optimising their detection software. In a few
months, they expect Gaia to discover about three new supernovas every
day.
In addition to supernovas, Gaia will discover thousands of transient
sources of other kinds – stellar explosions on smaller scale than
supernovas, flares from young stars coming to life, outbursts caused by
black holes that disrupt and devour a nearby star, and possibly some
entirely new phenomena never seen before.
“The sky is ablaze with peculiar sources of light, and we are looking
forward to probing plenty of those with Gaia in the coming years,”
concludes Dr Prusti.
More information
For details about Gaia's Science Alerts see the Notes for Editors.
For further information, please contact:
Markus Bauer
ESA Science and Robotic Exploration Communication Officer
Tel: +31 71 565 6799
Mob: +31 61 594 3 954
Email: markus.bauer@esa.int
Timo Prusti
Gaia Project Scientist
Email: timo.prusti@esa.int
Simon Hodgkin
Institute of Astronomy
Cambridge, UK
Tel: +44 1223 766657
Email: sth@ast.cam.ac.uk
Lukasz Wyrzykowski
Warsaw University Astronomical Observatory
Warsaw, Poland
Tel: +48 608 648817
Email: lw@astrouw.edu.pl
Nadejda Blagorodnova
Institute of Astronomy
Cambridge, UK
Tel: +44 1223 337548
Email: nblago@ast.cam.ac.uk
For details about Gaia's Science Alerts see the Notes for Editors.
For further information, please contact:
Markus Bauer
ESA Science and Robotic Exploration Communication Officer
Tel: +31 71 565 6799
Mob: +31 61 594 3 954
Email: markus.bauer@esa.int
Timo Prusti
Gaia Project Scientist
Email: timo.prusti@esa.int
Simon Hodgkin
Institute of Astronomy
Cambridge, UK
Tel: +44 1223 766657
Email: sth@ast.cam.ac.uk
Lukasz Wyrzykowski
Warsaw University Astronomical Observatory
Warsaw, Poland
Tel: +48 608 648817
Email: lw@astrouw.edu.pl
Nadejda Blagorodnova
Institute of Astronomy
Cambridge, UK
Tel: +44 1223 337548
Email: nblago@ast.cam.ac.uk
Source: ESA
