A massive white-dwarf merger product prior to collapseстатья
Статья опубликована в высокорейтинговом журнале
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Статья опубликована в журнале из списка Web of Science и/или Scopus
Дата последнего поиска статьи во внешних источниках: 10 июля 2019 г.
Аннотация:Gravitational wave emission can lead to the coalescence of close pairs of compact objects orbiting each other. For the case of neutron stars such mergers may yield masses above the Tolman-Oppenheimer-Volkoff limit, leading to the formation of black holes. For white dwarfs the merger product may exceed the Chandrasekhar limit, leading either to a thermonuclear explosion as Type Ia supernova, or to a collapse forming a neutron star. The latter case is expected to result in a hydrogen- and helium-free circumstellar nebula and a hot and luminous, rapidly rotating and highly magnetized central star with a lifetime of some 10,000 yr. Here we report the discovery of a hot star with an emission line dominated spectrum which is located at the centre of a circular mid-infrared nebula. The widths of the emission
lines imply that wind material leaves the star with a record outflow velocity of 16,000 km/s, implying rapid stellar rotation and a strong magnetic field aiding the wind acceleration. Since, surprisingly, also hydrogen and helium are likely absent in the star and nebula, we conclude that both unique objects formed recently from the merging of two massive white dwarfs. Our stellar atmosphere and wind models indicate a stellar surface temperature of about 200,000 K, and, using the Gaia distance of the star, a luminosity of about 10^4.6 Lsun. All the derived properties of star and nebula match models of the
post-merger evolution of super-Chandrasekhar mass white dwarfs, predicting a bright optical and high-energy transient upon collapse of the star in the near future. Our observations indicate that super-Chandrasekhar mass white dwarf mergers can indeed avoid a thermonuclear explosion as Type Ia supernova, and provide empirical evidence for magnetic field generation
in stellar mergers.