Hubble Telescope Directly Measures a White Dwarf Mass for the First Time

The lifeless core of a star that exploded a billion years ago is the white dwarf.

For the first time, astronomers have used the Hubble Space Telescope to directly estimate the mass of a single white dwarf. The dwarf, also known as LAWD 37, is the core remnant of a star that went supernova around a billion years ago.

A group of astronomers used Hubble to see how light from a background star temporarily curved around the dwarf as it passed in front of the former. The scientists were able to estimate the mass of the dwarf based on how much of the ambient light was bent by it. The Monthly Notices of the Royal Astronomical Society reported their findings.

A white dwarf mass for a star remnant in a binary system was previously measured by Kailash Sahu, a co-author of the current research. In a statement issued by the European Space Agency, Sahu stated that "our most recent observation gives a new benchmark since LAWD 37 is all by itself."

The surface of LAWD 37 is still a scorching 180,000 degrees Fahrenheit (100,000 degrees C) even if nuclear fusion is no longer taking place on the star. About 15 light-years from Earth, the star remnant is currently roughly 56% the mass of the Sun.

Gravitational microlensing, a scaled-down variation of gravitational lensing, is a technique used to measure the dwarf's mass. In gravitational lensing, a big object bends space such that light from behind it bends around the object, enabling us to view objects that would otherwise be obscured. We can see objects that would otherwise be too faint to notice thanks to the lensing effect, which also intensifies the light.

For instance, Earendel, a star that is around 13 billion years old, was discovered last year as a result of this natural magnifying glass phenomena.

The scientists had to wait for the dwarf to pass in front of the background star in order to measure LAWD 37, an occurrence that could be predicted owing to information from the ESA's Gaia mission. The scientists then painstakingly separated the background star's light from the blinding glare of the considerably closer LAWD 37.

According to main author of the research Peter McGill of UC Santa Cruz, "the extent of our measured offset is like measuring the length of a vehicle on the Moon as seen from Earth." Since the white dwarf's glare may produce streaks in unpredictable directions, it was necessary to carefully consider each of Hubble's observations and their limitations in order to model the event and determine LAWD 37's mass.

Astronomers will be able to use this knowledge to investigate the link between mass and radius for additional white dwarfs, learning more about how matter behaves under such strong gravitational fields.

Our Sun will eventually turn into a white dwarf, which will happen in around 5 billion years. The Sun will go through its own spectacular death process when it runs out of fuel for its nuclear fusion, possibly leaving a dazzling nebula in its wake.

The Webb Space Telescope, Hubble's successor, will be able to detect white dwarfs in the same way via gravitational microlensing, however it primarily studies light at redder wavelengths than Hubble. Webb has already, in fact. Another white dwarf, LAWD 66, was the subject of several Webb observations in 2022, and more are scheduled for 2024.