Searching for orbiting companion stars

January 26, 2016
Searching for orbiting companion stars
A Hubble image of the star Gliese 229 together with its brown dwarf companion, Gliese 229B. A new systematic radial velocity search for brown dwarf and stellar-mass companions to stars has discovered one new giant exoplanet and four new companion stars. Credit: NASA/Hubble

The search for exoplanets via the radial velocity technique has been underway for nearly 30 years. The method searches for wobbles in a star's motion caused by the presence of orbiting bodies. It has been very successful, detecting hundreds of exoplanets, but has been overtaken (at least in numbers of detections) by the transit method, which looks for dips in the star's light.

The velocity technique also naturally spots orbiting bodies that are larger than planets, which can be either stellar-mass companions or smaller companions that are not quite large enough to become stars, called brown-dwarfs. These larger companions have been largely ignored by surveys dedicated to finding exoplanets, but they are valuable discoveries for astronomers trying to study the smallest classes of stars which are very dim and otherwise difficult to detect. The indications so far are that there are fewer brown dwarf stars than expected in the mass range from about 13 to 80 Jupiter-masses, a phenomenon known as the "brown dwarf desert" that is unexplained. There is another important puzzle: About half of all are binary systems yet there are very few known exoplanets around them - only about five percent of all known . The dynamics of forming a planetary system around (or within) a multiple-star system are complex and important but poorly understood.

CfA astronomer John Johnson and six colleagues decided to study brown dwarf stars directly with a dedicated, five-year survey that emphasized large companions (stars or brown dwarfs) to mid-sized stars. The scientists selected forty-eight candidate stars for detailed observations from an initial sample of 167 likely candidates based on preliminary observations. They discovered one new giant exoplanet in this set and four stellar-mass companions, one of which may in fact be a brown dwarf. All the objects orbit their at distances less than a few astronomical units (one AU is the average distance of the Earth from the Sun). The new results include the orbital parameters of the objects, and the paper considers the possibility of imaging directly these multiple systems with a new generation of optical instruments. The work also marks one of the first efforts to address the nature of the "brown-dwarf desert" by searching for them systematically in order to improve the statistics.

Explore further: Two giant planets detected around an evolved intermediate-mass star

More information: "The Pan-Pacific Planet Search III: five Companions orbiting giant stars," R. A. Wittenmyer, R. P. Butler, L. Wang, C. Bergmann, G. S. Salter, C. G. Tinney and J. A. Johnson, MNRAS 445, 1398, 2016.

Related Stories

Brown dwarf companion stars

September 2, 2013

( —Astronomers trying to understand how the Sun and Earth formed, and why they have their characteristic properties, have made progress on a closely related problem: the nature of the lowest mass stars, so-called ...

A hot Jupiter around a sun-like star

November 18, 2015

There are almost 1800 confirmed exoplanets known today, and over 4000 exoplanet candidates. Astronomers have obtained estimates for the masses and radii (and hence the average densities) of over four hundred of these confirmed ...

Brown Dwarfs Don't Hang Out With Stars

January 5, 2009

( -- Brown dwarfs, objects that are less massive than stars but larger than planets, just got more elusive, based on a study of 233 nearby multiple-star systems by NASA's Hubble Space Telescope. Hubble found only ...

Monster planet is 'dancing with the stars'

December 16, 2015

A team made up almost entirely of current and former Carnegie scientists has discovered a highly unusual planetary system comprised of a Sun-like star, a dwarf star, and an enormous planet sandwiched in between.

Recommended for you

Hubble catches a transformation in the Virgo constellation

December 9, 2016

The constellation of Virgo (The Virgin) is especially rich in galaxies, due in part to the presence of a massive and gravitationally-bound collection of over 1300 galaxies called the Virgo Cluster. One particular member of ...

Scientists sweep stodgy stature from Saturn's C ring

December 9, 2016

As a cosmic dust magnet, Saturn's C ring gives away its youth. Once thought formed in an older, primordial era, the ring may be but a mere babe – less than 100 million years old, according to Cornell-led astronomers in ...

Khatyrka meteorite found to have third quasicrystal

December 9, 2016

(—A small team of researchers from the U.S. and Italy has found evidence of a naturally formed quasicrystal in a sample obtained from the Khatyrka meteorite. In their paper published in the journal Scientific Reports, ...


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.