A sub-stellar Jonah: Brown dwarf survives being swallowed

August 2, 2006

Using ESO's Very Large Telescope, astronomers have discovered a rather unusual system, in which two planet-size stars, of different colours, orbit each other. One is a rather hot white dwarf, weighing a little bit less than half as much as the Sun. The other is a much cooler, 55 Jupiter-masses brown dwarf.

"Such a system must have had a very troubled history", said Pierre Maxted, lead author of the paper that reports the study in this week's issue of Nature. "Its existence proves that the brown dwarf came out almost unaltered from an episode in which it was swallowed by a red giant."

The two objects, separated by less than 2/3 of the radius of the Sun or only a few thousandths of the distance between the Earth and the Sun, rotate around each other in about 2 hours. The brown dwarf moves on its orbit at the amazing speed of 800 000 km/h!

The two stars were not so close in their past. Only when the solar-like star that has now become a white dwarf was a red giant, did the separation between the two objects diminish drastically. During this fleeting moment, the giant engulfed its companion. The latter, feeling a large drag similar to trying to swim in a bath full of oil, spiralled in towards the core of the giant. The envelope of the giant was finally ejected, leaving a binary system in which the companion is in a close orbit around a white dwarf.

"Had the companion been less than 20 Jupiter masses, it would have evaporated during this phase", said Maxted."

The brown dwarf shouldn't rejoice too quickly to have escaped this doom, however. Einstein's General Theory of Relativity predicts that the separation between the two stars will slowly decrease.

"Thus, in about 1.4 billion years, the orbital period will have decreased to slightly more than one hour", said Ralf Napiwotzki, from the University of Hertfordshire (UK) and co-author of the study. "At that stage, the two objects will be so close that the white dwarf will work as a giant "vacuum cleaner", drawing gas off its companion, in a cosmic cannibal act."

The low mass companion to the white dwarf (named WD0137-349) was found using spectra taken with EMMI at ESO's New Technology Telescope at La Silla. The astronomers then used the UVES spectrograph on ESO's Very Large Telescope to record 20 spectra and so measure the period and the mass ratio.

Source: European Southern Observatory

Explore further: The (possible) dwarf planet 2007 OR10

Related Stories

The (possible) dwarf planet 2007 OR10

September 3, 2015

Over the course of the past decade, more and more objects have been discovered within the trans-Neptunian region. With every new find, we have learned more about the history of our solar system and the mysteries it holds. ...

The gas giant Jupiter

August 26, 2015

Ever since the invention of the telescope four hundred years ago, astronomers have been fascinated by the gas giant known as Jupiter. Between it's constant, swirling clouds, its many, many moons, and its red spot, there are ...

The dwarf planet Haumea

August 14, 2015

The Trans-Neptunian region has become a veritable treasure trove of discoveries in recent years. Since 2003, the dwarf planets and "plutoids" of Eris, Sedna, Makemake, Quaoar, and Orcus were all observed beyond the orbit ...

Stealing Sedna

August 7, 2015

Turns out, our seemly placid star had a criminal youth of cosmic proportions.

Can planets be rejuvenated around dead stars?

June 26, 2015

For a planet, this would be like a day at the spa. After years of growing old, a massive planet could, in theory, brighten up with a radiant, youthful glow. Rejuvenated planets, as they are nicknamed, are only hypothetical. ...

Can life emerge on planets around cooling stars?

November 20, 2012

(Phys.org)—Astronomers find planets in strange places and wonder if they might support life. One such place would be in orbit around a white or brown dwarf. While neither is a star like the sun, both glow and so could be ...

Recommended for you

Astronomers detect the farthest galaxy yet with Keck telescope

September 4, 2015

A team of Caltech researchers that has spent years searching for the earliest objects in the universe now reports the detection of what may be the most distant galaxy ever found. In an article published August 28, 2015 in Astrophysical ...

"Hedgehog" robots hop, tumble in microgravity

September 4, 2015

Hopping, tumbling and flipping over are not typical maneuvers you would expect from a spacecraft exploring other worlds. Traditional Mars rovers, for example, roll around on wheels, and they can't operate upside-down. But ...

0 comments

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.