Astronomers from the Italian University of Bologna have found that some white dwarfs were capable of maintaining thermonuclear activity.
Previously, scientists believed that if you know the temperature of a white dwarf and its cooling rate, you can roughly determine its age. But the authors of the new work refuted this theory. To understand how exactly the temperature of white dwarfs changes and when thermonuclear reactions stop, the authors examined white dwarfs from large globular clusters M 3 and M 13.
The researchers used the Hubble Space Telescope to make new observations of white dwarfs M 3 and M 13 in the near-ultraviolet range and compare them.
As a result, it turned out that, unlike cooler dwarfs in M 3, some stars in M 13 retained their hydrogen envelopes, in which slow thermonuclear reactions can take place. Therefore, the temperature of the M 13 stars is much higher than previously thought.
As a result of computer simulations, it turned out that due to such processes, about 70% of white dwarfs in M 13 cool more slowly than expected. Based on the results of the work, the authors found out that the temperature of white dwarfs is not connected with age as directly as is commonly thought.
Now, this scheme will have to be adjusted, since white dwarfs may look younger than they seem, and this discrepancy can reach a billion years.