An international team of scientists led by the Max Planck Institute for Extraterrestrial Physics investigated
The system was discovered thanks to the bright,ultrasoft X-rays, which arise as a result of nuclear fusion of leaked gas near the surface of a white dwarf. It has been known since the 1990s, when it was first observed with the ROSAT telescope, most recently with XMM-Newton, and now with eROSITA.
Astronomers used an optical telescope toidentify the radiation source located in the Large Magellanic Cloud. The analysis showed that the emission spectrum contains mainly helium emission lines emanating from the accretion disk surrounding the white dwarf. This observation shows that the companion star, from which the material flows to the white dwarf, is devoid of a hydrogen envelope.
Stars without hydrogen shells, such asthe companion star found in [HP99] 159 are an important intermediate step in the life cycle of binary stars, which should occur in about 30% of such systems. There should be many such stars, but only a few have been observed so far.
Julia Bodensteiner, study co-author at the European Southern Observatory
The [HP99] 159 system may beprogenitor of a type Iax supernova, scientists add. Until now, there has not been a clear understanding of how these types of explosions are formed, which are less bright compared to supernovae of the la type. Our measurements show that continuous helium burning in white dwarfs is possible even at lower accretion rates than theoretically predicted. The measured luminosity of [HP99] 159 is about 10 times less than expected according to the canonical norm, while the measured X-ray temperature is exactly in the expected range of stable helium burning.
Observed X-ray brightnesssuggests that the burning of helium falling on the surface of a white dwarf is stabilized by its rapid rotation, which makes a final supernova explosion in the system likely.
Norbert Langer, professor at the Argelander Institute for Astronomy and study co-author
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On the cover: artistic illustration of the dual system. Image: Composition: F. Bodensteiner; Hintergrundbild: ESO