White Dwarf Yields Key to Planet's Mass

Three unlikely companions - two burned-out stars and a planet - orbit each other near the crowded core of an ancient globular cluster of more than 100,000 stars. Only one companion, however, is visible in the images. In the image at right, taken by NASA/ESA Hubble Space Telescope, the white arrow points to a burned-out white dwarf star. Radio astronomers discovered the white dwarf and the other burned-out star - a rapidly spinning neutron star, called a pulsar - a decade ago. The third companion's identity was a mystery. Was it a planet or a brown dwarf? The object was too small and too dim to image.

Hubble observations of the dim white dwarf helped astronomers to precisely measure the mass of the mystery object (2.5 times larger than the mass of Jupiter), confirming that it is a planet. In fact, it is the farthest and oldest known planet. Hubble's Wide Field and Planetary Camera 2 resolved individual stars near M4's densely packed core [right] and pinpointed the white dwarf.


NASA/ESA and H. Richer (University of British Columbia)

About the Image

NASA press release
NASA caption
Release date:10 July 2003, 20:00
Size:3000 x 2400 px

About the Object

Name:B 1620+26, Messier 4, NGC 6121
Type:• Milky Way : Planet : Special Cases : Pulsar planet
Distance:5500 light years

Image Formats

Large JPEG
1.4 MB
Screensize JPEG
361.5 KB

Colours & filters

336 nm Hubble Space Telescope
555 nm Hubble Space Telescope
814 nm Hubble Space Telescope

Notes: Left image from NOAO, right image capture by HST.

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