Brown Dwarfs Do Form Like Stars

December 3, 2008
This artist's conception shows the brown dwarf ISO-Oph 102. Observations by the Submillimeter Array suggest that it is forming like a star, by accumulating material from the surrounding accretion disk (orange) shown here. The brown dwarf sheds angular momentum by ejecting material in two oppositely directed jets (red). Blue bow shocks indicate where those jets are interacting with the interstellar medium. Credit: ASIAA

(PhysOrg.com) -- Astronomers have uncovered strong evidence that brown dwarfs form like stars. Using the Smithsonian's Submillimeter Array (SMA), they detected molecules of carbon monoxide shooting outward from the object known as ISO-Oph 102. Such molecular outflows typically are seen coming from young stars or protostars. However, this object has an estimated mass of 60 Jupiters, meaning it is too small to be a star. Astronomers have classified it as a brown dwarf.

Brown dwarfs are on the dividing line between planets and stars, and generally have masses between 15 and 75 Jupiters. (The theoretical minimum mass for a star to sustain nuclear fusion is 75 times Jupiter.) As a result, brown dwarfs are sometimes called failed stars. However, it is not clear whether they form like stars, from the gravitational collapse of gas clouds, or if they form like planets, agglomerating rocky material until they grow massive enough to draw in nearby gas.

A star forms when a cloud of interstellar gas draws itself together through gravity, growing denser and hotter until fusion ignites. If the initial gas cloud is rotating, that rotation will speed up as it collapses inward, much like an ice skater drawing her arms in. In order to gather mass, the young protostar must somehow shed that angular momentum. It does so by spewing material in opposite directions as a bipolar outflow.

A brown dwarf is less massive than a star, so there is less gravity available to pull it together. As a result, astronomers debated whether a brown dwarf could form the same way as a star. Previous observations provided hints that they could. The serendipitous discovery of a bipolar molecular outflow at ISO-Oph 102 offers the first strong evidence in favor of brown dwarf formation through gravitational collapse.

"We thought that any such outflow would be too weak to detect with current facilities and would have to wait until a next-generation instrument like ALMA [the Atacama Large Millimeter Array]," said Ngoc Phan-Bao of the Academia Sinica Institute of Astronomy and Astrophysics (ASIAA), lead author on the paper announcing the find. "This was a big surprise. Finding the molecular outflow with the SMA shows the extraordinary capabilities of the array."

As might be expected, the outflow contains much less mass than the outflow from a typical star: about 1000 times less, in fact. The outflow rate is also smaller by a factor of 100. In all respects, the molecular outflow of ISO-Oph 102 is a scaled-down version of the outflow process seen in young stars.

"These findings suggest that brown dwarfs and stars aren't different because they formed in different ways," said Paul Ho, an astronomer at the Harvard-Smithsonian Center for Astrophysics and director of ASIAA. "They share the same formation mechanism. Whether an object ends up as a brown dwarf or star apparently depends only on the amount of available material."

The paper on ISO-Oph 102 will be published in the December 20 issue of the Astrophysical Journal Letters.

Provided by Harvard-Smithsonian Center for Astrophysics

Explore further: A brown dwarf joins the jet-set

Related Stories

A brown dwarf joins the jet-set

May 23, 2007

Jets of matter have been discovered around a very low mass 'failed star', mimicking a process seen in young stars. This suggests that these 'brown dwarfs' form in a similar manner to normal stars but also that outflows are ...

Searching for orphan stars amid starbirth fireworks

September 30, 2015

A new Gemini Observatory image reveals the remarkable "fireworks" that accompany the birth of stars. The image captures in unprecedented clarity the fascinating structures of a gas jet complex emanating from a stellar nursery ...

New stars shed light on the past

January 8, 2007

This new image taken with the Advanced Camera for Surveys onboard the NASA/ESA Hubble Space Telescope depicts bright blue newly formed stars that are blowing a cavity in the centre of a fascinating star-forming region known ...

Image: Hubble looks in on a nursery for unruly young stars

February 10, 2014

(Phys.org) —This striking new image, captured by the NASA/ESA Hubble Space Telescope, reveals a star in the process of forming within the Chameleon cloud. This young star is throwing off narrow streams of gas from its poles—creating ...

Recommended for you

Freeze-dried food and 1 bathroom: 6 simulate Mars in dome

January 20, 2017

Crammed into a dome with one bathroom, six scientists will spend eight months munching on mostly freeze-dried foods—with a rare treat of Spam—and have only their small sleeping quarters to retreat to for solace.

Image: Wavemaker moon Daphnis

January 20, 2017

The wavemaker moon, Daphnis, is featured in this view, taken as NASA's Cassini spacecraft made one of its ring-grazing passes over the outer edges of Saturn's rings on Jan. 16, 2017. This is the closest view of the small ...

Video: A colorful 'landing' on Pluto

January 20, 2017

What would it be like to actually land on Pluto? This movie was made from more than 100 images taken by NASA's New Horizons spacecraft over six weeks of approach and close flyby in the summer of 2015. The video offers a trip ...

The evolution of massive galaxy clusters

January 20, 2017

Galaxy clusters have long been recognized as important laboratories for the study of galaxy formation and evolution. The advent of the new generation of millimeter and submillimeter wave survey telescopes, like the South ...

1 comment

Adjust slider to filter visible comments by rank

Display comments: newest first

gopher65
3 / 5 (1) Dec 03, 2008
It's nice to finally have some concrete evidence of this! Most people have suspected that (most) brown dwarves form like stars, but you can never say for sure until you actually see it happening:).

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.