Astronomers directly measure mass of isolated white dwarf for the first time using Hubble

Astronomers have for the first time directly measured the mass of a lone white dwarf using the NASA/ESA Hubble Space Telescope. Prior to this, white dwarf masses were determined by observing them in binary star systems.

White dwarfs are the remnants of Sun-like stars that have exhausted their nuclear fuel and shed their outer layers. In this case, researchers found that the white dwarf, known as LAWD 37, is 56 per cent the mass of our Sun. It lies only 15 light-years away in the constellation Musca.

Using an astronomical phenomenon called gravitational microlensing, the researchers were able to measure the mass of this companion-less white dwarf. According to NASA, the light from a background star was slightly deflected by the gravitational warping of space by the foreground dwarf star. As the latter passed in front of the background star, microlensing caused the star to appear temporarily offset from its actual position in the sky.

"Because this white dwarf is relatively close to us, we’ve got lots of data on it - we've got information about its spectrum of light, but the missing piece of the puzzle has been a measurement of its mass," said the lead author Peter McGill, formerly of the University of Cambridge (now based at the University of California, Santa Cruz).

With Hubble, astronomers measured the mass of a single, isolated white dwarf – which is the surviving core of a burned-out star.The white dwarf, called LAWD 37, is 56% the mass of our Sun: https://t.co/wIg48n2jPYMore ⬇️ pic.twitter.com/Y3roR5csiv

— Hubble (@NASAHubble) February 2, 2023

Based on the data from the European Space Agency's Gaia space observatory, which makes extraordinarily precise measurements of nearly 2 billion star positions, astronomers were able to predict that LAWD 37 would briefly pass in front of a background star in November 2019. They then used Hubble to precisely measure over several years how the background star's apparent position in the sky was temporarily deflected during the white dwarf's passage.