An international team of astronomers has precisely located one of the most-observed variable-star systems in the sky – a double-star system called SS Cygni – at 372 light-years away.
Artist’s conception of the double-star system SS Cygni (David T Hardy)
This new measurement of the distance to SS Cygni has finally allowed scientists to solve a decade-old puzzle, confirming understanding of the way exotic objects like black holes interact with nearby stars.
The measurement was made possible by amateur astronomers from the American Association of Variable Star Observers who alerted the team to changes in the compact star system, triggering the team to start observations with two of the world’s most accurate radio telescopes.
The accepted theory on why SS Cygni emits periodic bursts of light involves an interaction between the pair.
“One of the stars, a normal star that is a lower-mass cousin to our Sun, loses bits of its outer envelope to its neighbor, a white dwarf, which is as massive as our Sun, but squeezed down to the size of Earth,” explained Dr Gregory Sivakoff from the University of Alberta, second author of the study published in the journal Science.
“Gravity continuously draws material from the normal star’s envelope, but it is only when the material rushes towards the white dwarf that we get an outburst of light. We see these outbursts happen about every 35 to 65 days.”
The periodic light flash theory of SS Cygni was developed in the early 80s. A key factor in the theory’s calculations is the distance between Earth and SS Cygni.
In 1999, researchers with NASA’s Hubble Telescope came up with a larger distance from Earth to the binary star SS Cygni. “That put the established theory into question.”
To settle the distance issue, the astronomers set out to re-measure the distance between Earth and the binary star.
During two years the team worked with a world-wide network of 180 amateur astronomers who used their optical telescopes to watch the night skies and report whenever SS Cygni began one of its outbursts.
The researchers then called on ground based networks of radio telescopes to make the distance calculation. By the end of 2012, they confirmed a smaller distance of about 370 light years from Earth to the binary star was correct.
“That was what we need to reconfirm the theory for periodic bursts of light from SS Cygni,” Dr Sivakoff explained. “We would not have been able to vindicate the theory if dedicated amateur astronomers using their own equipment hadn’t volunteered to help us.”
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Bibliographic information: J. C. A. Miller-Jones et al. 2013. An Accurate Geometric Distance to the Compact Binary SS Cygni Vindicates Accretion Disc Theory. Science, vol. 340, no. 6135, pp. 950-952; doi: 10.1126/science.1237145
