Two stars have been found in the constellation Cepheus that are spinning so fast and so close together that their contact releases the energy equivalent of more than 1 billion hydrogen bombs.
"The physical contact the two stars are making produces energies millions of times greater than we'd expect from either star alone," said Dr. Herbert Friedman, chief scientist at the Naval Research Laboratory where the stars were identified. "There is so much energy in the rotation of the two stars that we don't think it will run down for tens of millions of years."
Spinning in opposite directions, like the twin blades of an egg beater, the stars are moving so fast they make a full circle of each other every six hours. One star is a little bigger than our sun, the other half the size of the sun.
The finding was made by the NRL's X-Ray telescope aboard the orbiting High Energy Astronomy Observatory and confirmed by a more powerful instrument on the Einstein Observatory that was put into orbit late last year. The constellation is some 15 light years away, in the northern sky.
The satellites found a surprisingly intense X-ray emission from the two stars, which are so close they touch and may even be joined. Touching or not; the stars are separated by such a small distance that they are surrounded by the same corona of million-degree gas.
The corona is bound to both stars by a cage of looping magnetic lines of force, much like our own sun connects to its corona. Scientists believe that these magnetic field lines become twisted like ropes, then expand like rubber bands until the tension snaps them at the point where the two stars touch each other.
As soon as they snap, says the NRL's Friedman, the magnetic lines of force begin to reconnect to magnetic disturbances on the faces of both stars. This creates a "hot spot" at the reconnection that releases a huge amount of energy in the form of a continuous flare.
"Our sun produces a great flare once a year at the peak of the 11-year solar cycle," Friedman said. "Here, you have it going on continuously."
NRL scientists suspect that the two stars were formed at the same time about five billion years ago, meaning that they are about as old as our sun. Friedman said it is not known how the stars came in contact or what their fate will be. He said he expects they will goon flaring -rays for tens of millions of years.
"It could be that the bigger of the two stars will eventually swallow up the smaller one," Friedman speculated. "Or the smaller one could collapse to a dwarf star and become a separate entity."
Since finding the "binary contact" stars, the NRL's Russell Carroll has discovered two similar pairs in the Cepheus consellation in the northern hemisphere. Freidman said that the NRL intends to look at every one of the dozens of binary stars in Cepheus to see how many produce X-ray flares explosive enough to equal the energy of 1 billion hydrogen bombs.