In billions of years’ time, after our sun has burned through all of its fuel and puffed up to be a red giant, it will eventually shrink and cool until all that remains is the dense core of the former star, called a white dwarf. This is what will eventually happen to most stars, so white dwarfs are common in the universe. But there is much we still have to learn about these core remnants, and recent research using the Hubble Space Telescope has measured the mass of a lone white dwarf for the first time.
Previously, the mass of white dwarfs was measured when they were a part of a binary. When two stars orbit each other, astronomers can figure out their masses. However, there are also many single white dwarfs out there and it was difficult to work out their mass.
In order to measure the mass of a white dwarf called LAWD 37, astronomers took advantage of a phenomenon called gravitational microlensing. This is where the white dwarf passed in front of a background star, and the background star’s light was temporarily bent by the white dwarf’s gravity. The amount of bending could be used to work out the white dwarf’s mass.
“These events are rare, and the effects are tiny,” said the lead author of the research, Peter McGill of the University of California, Santa Cruz. “For instance, the size of our measured offset is like measuring the length of a car on the Moon as seen from Earth.”
The researchers were able to determine that LAWD 37 is 56% the mass of our sun, which is comparable to theoretical predictions of white dwarf mass. Having such an accurate measurement of its mass can also help researchers understand more about the structure and composition of these objects.
“The precision of LAWD 37’s mass measurement allows us to test the mass-radius relationship for white dwarfs,” said McGill. “This means testing the theory of degenerate matter (a gas so super-compressed under gravity that it behaves more like solid matter) under the extreme conditions inside this dead star.”