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Unmasking strange dwarfs with gravitational-wave observations

par Perot, Loïc ;Chamel, Nicolas ;Vallet, Pierre
Référence Physical Review D, 107, page (103004)
Publication Publié, 2023-05-03

Article révisé par les pairs

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Résumé :

The advent of space-based gravitational-wave detectors like the Laser Interferometer Space Antenna willallow us to observe signals, most of which are expected to be emitted by white-dwarf binaries. Amongthese systems another kind of compact objects could be hidden, postulated by Glendenning, Kettner, andWeber in 1995, containing a small core made of strange quark matter surrounded by layers of hadronicmatter reaching densities much higher than in white dwarfs. These so-called strange dwarfs cannot beeasily distinguished from white dwarfs through electromagnetic observations alone; their outermostenvelopes are expected to have the same composition and their radii are quite similar (except for lowmasses). However, future measurements of the tidal deformability through gravitational-wave observationscould provide a new way to reveal their existence. In this paper, we revisit the structure and the tidaldeformability of strange dwarfs in full general relativity taking into account the possible crystallization oftheir envelope. Unlike most previous studies, we do not describe the hadronic layers using the equation ofstate of Baym, Pethick, and Sutherland, which was originally designed for the outer crust of a neutron star.The conditions leading to such heavy elements in gravitational-core collapse supernova explosions are notexpected to be met during the stellar evolution leading to the formation of strange dwarfs. Instead, weconsider the same light elements as found in white dwarfs but we take into account electron captures bynuclei and possibly pycnonuclear fusions that may be triggered by compression. We find that the radius ofstrange dwarfs is systematically smaller than that of their white dwarf relatives. These deviations can belarge for very low-mass stars but mostly lie within the current observational uncertainties for typical whitedwarf masses. On the other hand, the observable tidal deformability coefficient Λ2 is strongly reduced incomparison to white dwarfs and the deviation will be potentially measurable by future space-basedgravitational-wave detectors.