The apparent mystery of stars that are too small to exist is a satisfying solution to a puzzling problem.
White dwarfs that are thought to be too small to exist in the current lifetime of the Universe have been spotted having their mass slurped off by their companions, a mechanism that has been suspected for a long time but never proven in the wild.
The discovery of evolved cataclysmic variables helps us understand one of the stages on the evolutionary path of dead stars.
The first physical proof of a new population of transitional stars has been observed by the astronomer.
This is exciting because it's a missing evolutionary link in the models we've been looking for.
White dwarfs are stars less than eight times the mass of the Sun when they run out of fuel.
The core of the dying star is packed into a sphere around the size of Earth, up to about 1.4 times the mass of the Sun.
On rare occasions, they can be so low in mass that they shouldn't exist. The white dwarfs are only a third of the mass of the Sun. The current lifetime of the Universe is only around 13 billion years.
If the star is isolated, that's all that's needed. The presence of ELMs in the Universe is explained by the speed with which mass is slurped off the white dwarf. The process had never been observed, so the problem remained.
The process should take place after the cataclysmic variable stage. A white dwarf is in a system with another star so close together that it is absorbing material from its companion.
The white dwarf will erupt as hydrogen fusion occurs in its atmosphere. The name of the cataclysms is variations in brightness.
Sometimes a white dwarf star will explode in a Type Ia supernova, but there is another option. The other star can steal mass from the white dwarf if the balance tips.
El-Badry and his colleagues used data from the Gaia space observatory and the Zwicky Transient facility to pick out 50 stars that could be in the intermediate stage. They used the Telescope at Lick Observatory to get detailed observations of 21 of the binaries.
They hit gold.
100 percent of the candidates were pre-ELMs. They were more bloated and puffed up. They were shaped like eggs because of the pull of the other star.
There is an evolutionary link between two classes of stars, cataclysmic variables and ELM white dwarfs.
The white dwarf was around 0.15 times the mass of the Sun, while the companions were around 0.8 times the mass of the Sun.
All of the white dwarfs showed signs of mass loss to their companion stars, but for 13 of them, the process was still ongoing, while the remaining eight were no longer losing mass, but were puffy. The stars were hotter and brighter than usually seen in a white dwarf.
More work is needed to fully understand the population of evolved cataclysmic variables, including more detailed observations of the 21 binaries. The team hopes to take a closer look at the other 29 binaries from the initial 50 candidates.
The team's research was published in the monthly Notices of the Royal Astronomical Society.
