The absence of white dwarfs in the Hyades cluster concerns astronomers, and this case helps reconstruct the cluster’s history. The Hyades star cluster is located about 153 light years away from us. At such a short distance, it can be seen with the naked eye in the constellation Taurus. This close distance allows professional astronomers to observe many other objects more easily. The Hyades Cluster contains many stars of the same age – about 625 million years, with the same metallicity and similar orbits. But it lacks white dwarfs: there are only eight in the center of the cluster.

The Hyades cluster is quite common. His research is very helpful in understanding star clusters. But such a feature as the almost complete absence of white dwarfs confuses astronomers. A new study has found one person who escaped the cluster. It is a white dwarf with a mass close to the limit value for this type of star. The study is titled “A White Dwarf Likely to Escape from the Hyades Star Cluster.”

Clusters like the Hyades are weakly gravitationally bound, and over time they lose stars through interactions with gas clouds, other clusters, and between stars within the cluster. Study author David Miller of the Department of Physics and Astronomy at the University of British Columbia and co-authors studied the absence of white dwarfs in the Hyades to reconstruct the cluster’s history. If we can identify the stars that were expelled, especially the white dwarfs in this case, it may be possible to reconstruct the cluster’s history. The European Space Agency’s Gaia space telescope monitors more than a billion stars in the Milky Way.

The team found three white dwarfs whose orbits suggest they could escape the Hyades group. For two of them, the mass range makes their origin in a cluster unlikely, but for the third object it is possible. “We estimate there is a 97.8% chance that the candidate is a genuine Hyades native.” White dwarfs have a mass comparable to the Sun, but their size is comparable to that of Earth. They are made from degenerate matter and only emit residual heat energy. This is the final state of about 97% of the stars in the Milky Way. Their mass is governed by the Chandrasekhar limit and can reach a maximum of about 1.44 solar masses.

White dwarfs leaving the Hyades are called extremely massive white dwarfs. They have a mass of 1.10 solar masses or more. This is much lower than the Chandrasekhar limit, but much higher than the average mass of a white dwarf, which is about 0.6 solar masses. Such massive objects typically come from two parent stars in a binary system, where one star has “taken” matter from the other, thereby increasing its mass. However, the supermassive white dwarf Hyades has a mass 1.317 times that of the Sun and has an age corresponding to a parent star. It appears to be the most massive white dwarf from a single ancestor.

source: https://arxiv.org/abs/2310.03204