May 23, 2013
Mystery Of Nearby SS Cygni Star System Finally Resolved
John P. Millis, PhD for redOrbit.com — Your Universe Online
In 1990 the Hubble Space Telescope measured the distance to a nearby star system known as SS Cygni. Composed of a low-mass main sequence star and a compact object known as a white dwarf — a stellar remnant about the mass of our Sun, but compressed to the size of the Earth.
The distance measured by Hubble puzzled scientists, as the measured brightness of the system was considerably higher than expected. If correct, it would call into question the mechanisms by which a white dwarf interacts with a nearby companion.
“If SS Cygni was actually as far away as Hubble measured, then it was far too bright to be what we thought it was, and we would have had to rethink the physics of how systems like this worked,” noted James Miller-Jones from the Curtin University campus of the International Centre for Radio Astronomy Research (ICRAR).
Miller-Jones and other astronomers have used two of the most powerful radio telescope networks in the world — the VLBA and EVA — to measure the distance to SS Cygni, attempting to resolve the dilemma created by the Hubble result. The team used a method known as parallax, whereby the cluster is observed at various points during the Earth´s orbit around the Sun, and then the position of the cluster is measured against the fixed, distant background.
“If you hold your finger out at arm´s length and move your head from side to side, you should see your finger appear to wobble against the background. If you move your finger closer to your head, you´ll see it starts to wobble more. We did the exact same thing with SS Cygni — we measured how far it moved against some very distant galaxies as the Earth moved around the Sun,” noted Miller-Jones.
“The wobble we were detecting is the equivalent of trying to see someone stand up in New York from as far as away as Sydney.”
The team found that SS Cygni is about 372 light-years from Earth, considerably closer than previous measurements made using the Hubble Space Telescope.
“The pull of gas off a nearby star onto the white dwarf in SS Cygni is the same process that happens when neutron stars and black holes are orbiting with a nearby companion, so a lot of effort has gone in to understanding how this works,” explained Miller-Jones.
“Our new distance measurement has solved the puzzle of SS Cygni´s brightness, it fits our theories after all.”