Deep and fast Solar System flybys: the controversial case of WD 0810-353

Abstract

Context. Most flybys in the Galactic disk are distant, beyond 10 ⁴ AU, and have characteristic velocities of ~70 km s ⁻¹. However, deep and fast encounters also take place, albeit with lower probability, particularly if one of the objects involved is a stellar remnant ejected during a supernova. WD 0810-353 might be a high velocity white dwarf, and it was recently identified as heading straight for the Solar System; however, the Gaia DR3 data that support its future deep and fast flyby are regarded as suspicious.

Aims. Here, we reanalyze the Gaia DR3 data set associated with WD 0810-353 to confirm or reject the reality of its Solar System flyby and also to investigate its possible runaway status.

Methods. We studied the evolution of WD 0810-353 forward in time using N-body simulations. We computed the distribution of distances of closest approach and their associated times of perihelion passage. We used a statistical analysis of the kinematics of this object to assess its possible hypervelocity. We compared its mean BP/RP spectrum to those of other well-studied white dwarfs.

Results. We confirm that WD 0810-353 is headed for the Solar System, but the actual parameters of the encounter depend strongly on its radial velocity. The Gaia DR3 value of −373.74 ± 8.18 km s ⁻¹ is strongly disfavored by our analyses. Its mean BP/RP spectrum suggests a value over ten times higher based on the position of its putative H α line. However, spectral matching using other white dwarfs with non- Gaia data indicate a radial velocity in the interval (−60, −70) km s ⁻¹.

Conclusions. These results confirm the future flyby of WD 0810-353 near the Solar System, although the relative velocity could be high enough or the minimum approach distance large enough to preclude any significant perturbation on the Oort cloud.