Hyper-runaway and hypervelocity white dwarf candidates in Gaia Data Release 3: possible remnants from Ia/Iax supernova explosions or dynamical encounters

Andrei P. Igoshev, Hagai Perets, Na'ama Hallakou

Submitted on 20 September 2022


Type Ia and other peculiar supernovae (SNe) are thought to originate from the thermonuclear explosions of white dwarfs (WDs). Some of the proposed channels involve the ejection of a partly exploded WD (e.g. Iax SN remnant) or the companion of an exploding WD at extremely high velocities (>400 km s1). Characterisation of such hyper-runaway/hypervelocity (HVS) WDs might therefore shed light on the physics and origins of SNe. Here we analyse the Gaia DR3 data to search for HVS WDs candidates, and peculiar sub-main-sequence (sub-MS) objects. We retrieve previously identified HVS, and find tens of new HVS candidates. We identify two new unbound WD HVS, 14 new likely-unbound sub-MS objects, and a handful of WDs and sub-MS objects with velocities comparable to the Galactic escape velocity (based only on tangential velocities). We find tens of additional likely bound hyper-runaway WDs (v>400 km s1). The numbers and properties of the HVS WD and sub-MS candidates suggest that extreme velocity ejections (>1000 km s1) can accompany at most a small fraction of type Ia SNe, disfavouring a significant contribution of the D6-scenario to the origin of Ia SNe. The rate of HVS ejections following the hybrid WD reverse-detonation channel could be consistent with the identified HVSs. The numbers of lower-velocity HVS WDs could be consistent with type Iax SNe origin and/or contribution from dynamical encounters. We also searched for HVS WDs related to known SN remnants, but identified only one such candidate.


Comment: Submitted to the MNRAS

Subjects: Astrophysics - Solar and Stellar Astrophysics; Astrophysics - Astrophysics of Galaxies