Science

SS Cygni binary star system mystery solved with help from amateur astronomers

By James Maynard , May 26, 2013 07:06 PM EDT

SS Cygni, a binary star system in the constellation of Cygnus the Swan, is much closer than astronomers believed, and the new measurement helps to unravel a mystery surrounding the pair. This new finding was developed partly with the assistance of a network of amateur astronomers using backyard telescopes.

Once thought to reside 520 light years from Earth, new measurements indicate that SS Cygni is only a little over 70 percent of that distance from us, at 372 light years away.

This stellar system is composed of two stars - a normal star slightly smaller than our own star, still burning hydrogen fuel, and a collapsed remnant of a dead star called a white dwarf. This white dwarf is only about the size of the Earth.

In a cycle that lasts between 35 and 65 days, the binary system erupts in a blaze of energy called a dwarf nova. This is caused in such systems when the gravity of the smaller, denser white dwarf pulls material off its much-larger companion. The material forms a disk as it spirals down toward the star, and when the flow of matter slows down, the system becomes unstable and flashes in a burst of light. The earlier distance was measured in 1999 using the Hubble Space Telescope, beginning a 14-year-long mystery.

"That was a problem. At that distance, SS Cygni would have been the brightest dwarf nova in the sky, and should have had enough mass moving through its disk to remain stable without any outbursts," astronomer James Miller-Jones of Curtin University in Australia, said.

Parallax was used to more accurately measure the distance to SS Cygni. You can see parallax in action by holding your finger at arm's length and closing one eye. Align your finger with a background object and close your open eye while you open the other. Do this quickly back-and-forth and your finger will appear to move. As you bring your finger closer to your face, the effect becomes more pronounced.

Using two of the world's largest networks of radio telescopes, Miler-Jones was able to record the apparent positions of the stars during observations taken six months apart. The distance the Earth moved in that time acted like the distance between your eyes, providing parallax. By measuring this apparent difference in location, Miller-Jones was able to calculate the distance to the stellar system.

These observations could only be made while the system was in the process of an outburst, so that there was enough radio signal being generated to be measured by the research team. In order to know exactly when to time his observations, Miller-Jones brought in a network of 180 amateur astronomers from the American Association of Variable Star Observers (AAVSO). These skygazers stayed at their telescopes night after night for two years to know exactly when a flash was due to occur.

"That was what we need to reconfirm the theory for periodic bursts of light from SS Cygni," Doctor Gregory Sivakoff of the University of Alberta, said. "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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