A team of astronomers led by Dr Marcus Lohr of the Open University, UK, has discovered the first five star system containing two eclipsing binary stars.

This star system, known as 1SWASP J093010.78+533859.5 (J093010 for short) or TYC 3807-759-1, is located 115 light-years from Earth in the constellation Ursa Major.

It was originally detected in 2006 in archived data from the SuperWASP project, which uses small cameras at the Observatorio del Roque de los Muchachos on the island of La Palma in the Canary Islands, and at the Sutherland Station of the South African Astronomical Observatory, to image almost the whole sky every few minutes.

Over years, its measurements of the brightness of individual stars have been assembled into light curves for 30 million sources in our Milky Way Galaxy.

The light curve of J093010 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 6 hours.

Then it was spotted that J093010’s light curve contained some additional unexpected eclipses, and the data were reanalyzed 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.

The four stars were subsequently observed spectroscopically so that the signatures of the different stars could be studied in detail. This 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, Dr Lohr and his co-authors have been able to confirm that they are all gravitationally bound together in a single system.

The astronomers also found that all the stars in J093010 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.

“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,” said Dr Lohr, first author on the study published in the journal Astronomy & Astrophysics (arXiv.org preprint).

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M. E. Lohr et al. 2015. The doubly eclipsing quintuple low-mass star system 1SWASP J093010.78+533859.5. A&A, vol. 578, A103; doi: 10.1051/0004-6361/201525973