2 min read

Measuring a White Dwarf Star

Brilliant closeup burst of white light radiating outward against deep space

For astronomers, it's always been a source of frustration that the nearest white dwarf star is buried in the glow of the brightest star in the nighttime sky. This burned-out stellar remnant is a faint companion to the brilliant blue-white Dog Star, Sirius, located in the winter constellation Canis Major. Now, an international team of astronomers, using NASA's

Hubble Space Telescope

to isolate the light from the white dwarf, called Sirius B, has been able to measure precisely the white dwarf's mass based on how its intense gravitational field alters the wavelengths of light emitted by the star.

Sirius B is smaller than the Earth, but much denser with a gravitational field 350,000 times greater than Earth's, meaning that a 150-pound person would weigh 50 million pounds standing on its surface. Light from the surface of the white dwarf has to climb out of this gravitational field and is stretched to longer, redder wavelengths of light in the process. This effect, predicted by Einstein's theory of General Relativity in 1916, is called gravitational redshift. Based on the Hubble measurements of the redshift, Sirius B has a mass that is 98 percent that of our own Sun. Sirius itself has a mass two times that of the Sun and a diameter of 1.5 million miles (2.4 million kilometers).

At 8.6 light-years away, Sirius is one of the nearest known stars to Earth. Stargazers have watched Sirius since antiquity. Its diminutive companion, however, was not discovered until 1862.

Image Credit: NASA, ESA, H. Bond (STScI) and M. Barstow (University of Leicester)

Share

Details

Last Updated
Apr 17, 2023
Editor
NASA Hubble Mission Team

Related Terms

Explore More

Illustration of the Cygnus X-3 system
4 min read

NASA, JAXA XRISM Mission Looks Deeply Into ‘Hidden’ Stellar System

Article13 hours ago
A spiral galaxy seen directly from the side, such that its disk looks like a narrow diagonal band across the image. A band of dark dust covers the disk in the center most of the way out to the ends, and the disk glows around that. In the center of the galaxy, a whitish circle of light bulges out above and below the disk. Each end of the disk curves slightly. The background is black and mostly empty.
2 min read

Hubble Captures an Edge-On Spiral with Curve Appeal

Article4 days ago
Artist's concept of early stages of the young star FU Orionis outburst. The star, a bright yellow sphere near the center, and its fluffy disk of gas and dust are slightly tilted, extending from the top left corner to the bottom right. The swirling disk is bright yellow close to the star and gradually transitions to dark orange moving toward the edges of the frame. The top left and right corners reveal a black, starless background.
5 min read

NASA’s Hubble Finds Sizzling Details About Young Star FU Orionis

Article4 days ago
Keep Exploring

Discover More Topics From NASA

James Webb Space Telescope

The image is divided horizontally by an undulating line between a cloudscape forming a nebula along the bottom portion and a comparatively clear upper portion. Speckled across both portions is a starfield, showing innumerable stars of many sizes. The smallest of these are small, distant, and faint points of light. The largest of these appear larger, closer, brighter, and more fully resolved with 8-point diffraction spikes. The upper portion of the image is blueish, and has wispy translucent cloud-like streaks rising from the nebula below. The orangish cloudy formation in the bottom half varies in density and ranges from translucent to opaque. The stars vary in color, the majority of which have a blue or orange hue. The cloud-like structure of the nebula contains ridges, peaks, and valleys – an appearance very similar to a mountain range. Three long diffraction spikes from the top right edge of the image suggest the presence of a large star just out of view.

Perseverance Rover

Parker Solar Probe

Juno