Astronomers at the Open University have discovered the first quintuple star system containing two eclipsing binary stars. Details of the five star system, the first of its kind to be found, will be presented by Marcus Lohr of the Open University in a talk on Wednesday 8 July at the National Astronomy Meeting at Venue Cymru, Llandudno, Wales.
Scientists think that about a third of stars are found in pairs or
multiple systems. To find five stars connected to each other though is
very rare.
The unusual star system was originally detected in archived data from the SuperWASP
(Wide Angle Search for Planets) project, which uses relatively small
and low-cost cameras in the Canary Islands and South Africa to image
almost the whole sky every few minutes. Over many years, its
measurements of the brightness of individual stars have been assembled
into light curves - plots of brightness against time - for some 30
million sources in the Milky Way.
Regular small dips in a light curve can reveal the presence of planets orbiting other stars, when they cross or transit the face of their host star, and SuperWASP has been extremely successful in finding these ‘exoplanets’
since it began operating in 2003. Light curves can also be used to
discover eclipsing binary stars, where a pair of stars orbit around
their mutual centre of gravity in our line of sight.
From the Earth, each star will pass in front of its companion once in
every orbit and eclipse some or all of its light. This produces a
regular pattern of pairs of dips in the binary's light curve, whose
depths and shapes are characteristic of the physical properties of the
two stars.
The light curve of the new quintuple system, designated as 1SWASP
J093010.78+533859.5, initially revealed the presence of a contact
eclipsing binary - a system in which the two stars are orbiting so close
together that they share an outer atmosphere. Contact binaries are
quite common, but this particular system is notable because its orbital
period - the time the two stars take to complete one orbital cycle - is
so short, just under six hours.
Then it was spotted that the light curve contained some additional
unexpected eclipses, and the data were reanalysed to reveal a second
eclipsing binary at the same location on the sky. The new binary is
detached - its component stars are well-separated by a distance of about
3 million km, or about twice the size of the Sun - and it has a longer
orbital period of one and a third days.
The two sets of stars are separated by about 21 billion km, rather larger than the size of Pluto’s
orbit around the Sun. The four stars were subsequently observed
spectroscopically - its light was broken up into different wavelengths -
so that the signatures of the different stars could be studied in
detail. This unexpectedly revealed the presence of a fifth star, up to 2
billion km away from the detached binary, but not apparently producing
any additional eclipses.
By combining the data from the five stars' light curve and their
spectra, the Open University researchers have been able to confirm that
they are all gravitationally bound together in a single system, around
250 light years away from us in the constellation of Ursa Major.
The data also let the team determine properties of the stars like their
masses, sizes and temperatures. All the stars are rather smaller and
cooler than our Sun, but the collective system is bright enough (9th
magnitude) to be visible in small telescopes and amateur astronomers
could see the eclipses for themselves.
Dr Lohr comments: “This is a truly exotic star system. In principle
there’s no reason it couldn’t have planets in orbit around each of the
pairs of stars. Any inhabitants would have a sky that would put the
makers of Star Wars to shame – there could sometimes be no fewer than
five Suns of different brightnesses lighting up the landscape. Days
would have dramatically varying light levels as the different stars were
eclipsed. They would though miss out on night for a large part of their
‘year’, only experiencing darkness (and a night sky) when the stars
were on the same side of their world.”
One particularly interesting finding is that the two binaries seem to
be orbiting in the same plane. This suggests that they may have
originally formed from a single disk of gas and dust, which broke up as
gravity concentrated it into clumps. Studying this bizarre system will
help astronomers to better understand how stars and planets, including
our own, came into being.
Media contacts
Royal Astronomical Society
Mob: +44 (0)794 124 8035
rm@ras.org.uk
Ms Anita Heward
Royal Astronomical Society
Mob: +44 (0)7756 034 243
anitaheward@btinternet.com
Dr Sam Lindsay
Royal Astronomical Society
Mob: +44 (0)7957 566 861
sl@ras.org.uk
Science contacts
Dr Marcus Lohr
Open University
marcus.lohr@open.ac.uk
Further information
The new research appears in Lohr, M. E.; Norton, A. J.; Gillen, E.;
Busuttil, R.; Kolb, U. C.; Aigrain, S.; McQuillan, A.; Hodgkin, S. T.;
González, E., (2015), "The doubly eclipsing quintuple low-mass star system 1SWASP J093010.78+533859.5", Astronomy & Astrophysics, Volume 578, A103, Astronomy & Astrophysics, vol. 578, A103.
Notes for editors
The Royal Astronomical Society National Astronomy Meeting (NAM 2015) will take place in Venue Cymru, Llandudno, Wales, from 5-9 July. NAM 2015 will be held in conjunction with the annual meetings of the UK Solar Physics (UKSP) and Magnetosphere Ionosphere Solar-Terrestrial physics (MIST) groups. The conference is principally sponsored by the Royal Astronomical Society (RAS) and the Science and Technology Facilities Council (STFC). Follow the conference on Twitter
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