HM Cancri
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Double star RX J0806.3 + 1527 |
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Observation dates equinox : J2000.0 , epoch : J2000.0 |
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| AladinLite | ||
| Constellation | cancer | |
| Right ascension | 8 h 06 m 23.2 s | |
| declination | + 15 ° 27 ′ 30.2 ″ | |
| Apparent brightness | 21 likes | |
| Astrometry | ||
| distance | 1600 ly (490 pc ) |
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| orbit | ||
| period | 321.5 s | |
| Major semi-axis | 0.0005 AU | |
| Individual data | ||
| Names | A; B. | |
RX J0806.3 + 1527 , sometimes abbreviated as J0806 , also known under the variable designation HM Cancri ( HM Cnc ), is a binary star system made up of two white dwarfs , each with about half the solar mass , which are located at a distance of only about 80,000 kilometers ( around 1/5 of the mean distance moon-earth) in just under 5½ minutes, corresponding to an average orbital speed of 400 kilometers per second. J0806 is about 1,600 light years from Earth and is in the constellation Cancer. In the visual and X-ray ranges , brightness variations occur with a period of 321.5 seconds.
HM Cancri was discovered in 1999 as a source of X-rays using the ROSAT satellite, built at the Max Planck Institute for Extraterrestrial Physics . The observed X-ray radiation is probably generated at the magnetic poles of the two white dwarfs.
J0806 holds two astronomical records: It is the binary star system with the shortest known orbital period and also the narrowest. This discovery was made by an international team of researchers led by Gijs Roelofs from the Harvard-Smithsonian Center for Astrophysics in Cambridge (USA). The scientists reported on their findings in The Astrophysical Journal Letters .
Gijs Nelemans from Radboud University in Nijmegen (Netherlands) said the two stars must have lost mass and approached each other at an earlier stage. What exactly led to this is not yet known. The stars come closer to each other by half a meter every year. It is believed that the system will end up in an X-ray or gamma flash . The stars are so close together that matter flows from one star to the other and there falls on the equator. Therefore it is assumed that there is an accretion disk around the smaller star.
Using spectral measurements at the 10-meter Keck-I telescope in Hawaii, it was confirmed that the 5.36-minute period measured 11 years ago is the orbit time of a double star. Because while the two stars orbit each other, the circular movement of the stars causes a periodic shift of the spectral lines from the shorter blue to the longer red wavelength range and back. The researchers used this optical Doppler effect to measure the orbital velocity of HM Cancri. Since HM Cancri is very faint , according to Arne Rau from the Max Planck Institute for Extraterrestrial Physics , the head of observation in Hawaii, hundreds of spectra had to be recorded in a very short time. The apparent magnitude of HM Cancri is only 21 mag . This corresponds to a millionth of the brightness of the weakest objects in the starry sky that can be seen with the naked eye.
Arne Rau also takes the view that the star system could become a Type Ia supernova in a few million years . Initially, he also anticipates a future drifting apart, because “if the lighter star loses mass, it will get bigger. This shifts the center of mass outwards and the periods become longer ”.
The system should also be the strongest known source of suspected gravitational waves . With the project eLISA / NGO , an interferometric gravitational wave detector of the ESA planned for 2034 and consisting of three satellites, the gravitational waves of HM Cancri are to be measured. The emission of gravitational waves would also explain well the observed decrease in the period of 1.2 milliseconds per year. Arne Rau said of the expected gravitational waves caused by HM Cancri: "It would be a shock if HM Cancri were not seen [by LISA], and it would also call into question one of the main statements of Einstein's general theory of relativity ."
Web links
- When does J0806 merge? from the alpha-Centauri television series(approx. 15 minutes). First broadcast on Oct 25, 2006.
- NASA Sees Orbiting Stars Flooding Space with Gravitational Waves - NASA press release of May 30, 2005
- TE Strohmayer: Precision X-Ray Timing of RX J0806.3 + 1527 with Chandra: Evidence for Gravitational Radiation from an Ultracompact Binary. In: The Astrophysical Journal, Edition 627, 2005, pp. 920 ff.
Individual evidence
- ↑ a b GHA Roelofs, A. Rau, TR Marsh, D. Steeghs, PJ Groot, G. Nelemans: Spectroscopic Evidence for a 5.4-Minute Orbital Period in HM Cancri . In: The Astrophysical Journal Letters . tape 711 , no. 2 , 2010, p. L138 , doi : 10.1088 / 2041-8205 / 711/2 / L138 .
- ↑ a b c Chandra X-ray telescope, RX J0806.3 + 1527: Orbiting Stars Flooding Space with Gravitational Waves
- ↑ NASA Factsheet on Earth's moons (English) and elementary calculations from this data
- ↑ a b c Video BR alpha / alpha-centauri
- ↑ a b c d e f BIG-SCREEN Internet portal, Lippstadt: HM Cancri ( Memento of the original from March 13, 2010 in the Internet Archive ) Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice.
- ↑ "Per year the orbital time is currently 1.2 milliseconds faster and the distance is half a meter shorter, so that the stars will collide in a few hundred thousand years" jumk.de
- ↑ a b Wilder Ringelreihen der Sterne - Press release of the Max Planck Society of March 8, 2010.
- ↑ a b c Der Standard, Austria
