Making waves

From Minneapolis, at a meeting of the American Astronomical Society

DENSE DUO. Illustration of two white dwarfs spiraling into each other. D. Berry, Goddard/NASAbinary

Locked in a deadly embrace, two white dwarf stars may be the strongest source of gravitational waves now flooding our galaxy. The stars appear to be separated by just one-fifth the Earth-moon distance.

New X-ray observations of the duo, which resides roughly 1,600 light-years from Earth, indicate that the dwarfs take just under 5.5 minutes to orbit each other and are the most-compact binary-star system known. NASA’s Chandra X-ray Observatory also found that the pair’s orbital period is declining by 1.2 milliseconds each year.

According to Einstein’s theory of gravitation, the white dwarfs are spiraling toward each other because they’re losing energy in the form of gravitational waves—invisible ripples in space-time that cause objects with mass to bob up and down.

Tod Strohmayer of NASA’s Goddard Space Flight Center in Greenbelt, Md., and his colleagues calculate that the white dwarf twosome, dubbed RX J0806.3+1527, is pouring out 100 times as much energy in the form of gravitational waves as the sun emits as electromagnetic radiation. Strohmayer notes that the intense waves will be prime targets for the Laser Interferometer Space Antenna, a gravitational-wave detector scheduled for launch early next decade.

The Chandra observations tighten previous estimates of the orbital period of the dwarf system, Strohmayer says. Even so, the new study doesn’t rule out a less likely explanation for the measured period. The waxing and waning of X rays observed by Chandra could represent the spin period of just one of the dwarfs rather than the orbital period of the pair.

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