RX J0806.3 1527

RX J0806.3 1527, sometimes abbreviated as J0806, also known under the variable name HM Cancri (HM Cnc ) is a binary star system consisting of two white dwarfs, each with about half a solar mass ( or per 150,000 Earth masses ), which in each orbiting at a distance of only 80,000 kilometers ( up to 100,000 km ) in about 5.4 minutes, corresponding to an average rotational speed of 450 km / sec. J0806 is about 16,000 light years from Earth and is located in the constellation Cancer. In the visual and X-ray brightness variations occur on with a period of 321.5 seconds.

HM Cancri was discovered by the Max Planck Institute for Extraterrestrial Physics built ROSAT satellite as a source of X-rays in 1999. The observed X-ray radiation is presumably formed at the magnetic poles of the two white dwarfs.

J0806 has two astronomical records: it is the binary star system with the shortest known orbital period and to date still the closest. The discovery was an international research team led by Gijs Roelofs of the Harvard- Smithsonian Center for Astrophysics in Cambridge (USA). About their findings, the researchers reported in the journal The Astrophysical Journal Letters.

Gijs Nelemans of the Radboud University in Nijmegen (Netherlands) said that the two stars would have lost at an earlier stage mass and closer together. What exactly led to do so was not yet known. The stars come out every year closer to about 0.5 meters. It is believed that the system will result in an x-ray or gamma Flash ( GRB ).

The system is also the largest known source of suspected gravitational waves. Their effect would be consistent with the observed reduction of the period by 1.2 milliseconds per year. The project eLISA / NGO, for a planned 2034 and consisting of three satellite interferometric gravitational wave detector ESA, gravitational waves should be measured by HM Cancri.

The stars are so close together that matter flows from one star to another, and there falls on the equator. It is believed that there is also a smaller accretion around the star in addition to the mass transfer. Using the 10-meter Keck I telescope in Hawaii, it was confirmed that the measured 11 years ago, 5.4 - minute period, in fact, is the orbital period of a binary star. As the two stars orbit, the circular motion of the stars causes each periodic shift of the spectral lines from the shorter to the longer blue red wavelength range and back.

This Doppler effect the researchers used to measure the orbital motion of HM Cancri. HM Cancri is very faint: The apparent brightness is only 21, which is one millionth of the brightness of the weakest in the night sky visible to the naked eye objects. Therefore, according to the observation manager had in Hawaii, Arne Rau of the Max Planck Institute for Extraterrestrial Physics, hundreds of spectra are recorded in no time.

Rau believes that the star system in a few million years could become a supernova of type Ia. First, he also expects a future drifting apart, because "if the lighter star loses mass, it becomes greater. Wherein the center of mass moves outwardly, and the periods are longer. " Also, he said regarding the determination of expected incurred by HM Cancri gravitational waves by LISA: "It would be a shock, HM Cancri should not be seen [ by LISA ], also it would represent one of the main statements of Einstein's general theory of relativity in question. "

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