Massive white dwarfs
The relationship between the main sequence mass of a star and its white dwarf remnant mass, known as the Initial-Final Mass Relation (IFMR), has become the subject of significant interest over the past few decades due to the insight it provides into the final stages of stellar evolution. Unstable mass loss, fluctuations in internal nuclear reactions and convective processes make these later stages challenging to model. Analysis of the IFMR reveals tension in the linearity of the relation, a property difficult to constrain due to the sparsity and significant scatter of current data.
One of the largest gaps in the IFMR remains at the high-mass end, where white dwarfs are both rare and faint. Ultramassive white dwarfs from a single progenitor set a lower limit on type Ia supernova production. These supernovae are used as standard candles to measure distances within the universe, and their production rate governs nucleosynthesis and the chemical evolution of galaxies. White dwarfs have been found with masses approaching the Chandrasekhar limit (1.38Msun), but formed by gaining mass from accretion or merger events rather than a single progenitor. Until recently, there were only two objects defining the upper limit of the IFMR. One is the current record holder GD 50, with a mass of 1.26 Msun and progenitor mass as high as 7.8. However, this object has some uncertainty in its parent cluster origin, while the other, a member of the Pleiades, is much less massive with a precursor mass ~6 Msun.
With my group at UBC, using Gaia Data Release 2, we search nearby open star clusters to look for young ultramassive white dwarfs.
Read more:
A Massive Magnetic Helium Atmosphere White Dwarf Binary in a Young Star Cluster
Massive White Dwarfs in Young Star Clusters (in preparation)