An ancient double degenerate merger in the Milky Way halo

TL;DR

This paper investigates the white dwarf LP 93-21, revealing it as a product of an ancient stellar merger and associating its unique properties with a past dwarf galaxy accretion event onto the Milky Way.

Contribution

It provides evidence linking a specific white dwarf's properties to an ancient merger event, offering insights into stellar evolution and galaxy assembly history.

Findings

LP 93-21 is a massive, carbon-enriched white dwarf with halo kinematics.

It likely resulted from an ancient white dwarf merger.

Its orbit suggests a past dwarf galaxy accretion event.

Abstract

We present an analysis and re-appraisal of the massive, carbon-enriched (DQ) white dwarf (WD) LP 93-21. Its high mass (~1 M_sun) and membership to the class of warm DQ WDs, combined with its peculiar halo kinematics suggest that this object is the product of an ancient stellar merger event, most likely that of two WDs. Furthermore, the kinematics places this object on a highly retrograde orbit driven by the accretion of a dwarf galaxy onto the Milky Way that occurred at a red shift greater than 1.5. As the product of a stellar merger LP 93-21 is probably representative of the whole class of warm/hot DQ WDs.