We have completed maintenance on DiscoverMagazine.com and action may be required on your account. Learn More

Weighing a White Dwarf

With some help from Einstein, astronomers calculate the mass of a star named Stein 2051 B.

By Sylvia Morrow
Feb 1, 2018 6:00 AMNov 12, 2019 6:49 AM
Astronomers used the Hubble Space Telescope to learn a white dwarf's (middle) mass by seeing how much it deflected another star's light. The star's real position the top left, while its observed position is the top right. | NASA, ESA, K.SAHU (STCI)


Sign up for our email newsletter for the latest science news

Three years ago, astronomers put a white dwarf on a scale and watched the needle move. Not literally, says Kailash Sahu, an astronomer at the Space Telescope Science Institute, but their pioneering method of weighing the star really is that straightforward. Their findings appeared in Science in June.

When the dwarf, named Stein 2051 B, passed in front of another star from Earth’s perspective, Sahu’s team followed the position of the background star. As general relativity predicts, light from the background star bent around the white dwarf, distorted by its gravitational field. Like the deflection of a scale’s needle, the deflection of the background star’s light let astronomers calculate the white dwarf’s mass (roughly 67.5 percent the mass of our sun). The movement was minute, but the results were stunning. “I almost fell off my chair,” says Sahu.

The white dwarf’s mass was exactly in line with predictions made in a theory developed by Subrahmanyan Chandrasekhar in 1930. Previous attempts to confirm the theory had relied on shaky assumptions, but Sahu’s group demonstrated Chandrasekhar’s accuracy while proving their own new method really works.

1 free article left
Want More? Get unlimited access for as low as $1.99/month

Already a subscriber?

Register or Log In

1 free articleSubscribe
Discover Magazine Logo
Want more?

Keep reading for as low as $1.99!


Already a subscriber?

Register or Log In

More From Discover
Recommendations From Our Store
Shop Now
Stay Curious
Our List

Sign up for our weekly science updates.

To The Magazine

Save up to 40% off the cover price when you subscribe to Discover magazine.

Copyright © 2024 Kalmbach Media Co.