CfA Press Release
Release No.: 04-24|
For Release: Thursday, July 8, 2004
Note to editors: An image of the newly discovered binary brown dwarf
taken with the 6.5-meter Magellan telescope, is online at:
How To Fail At Being A Star
Hamburg, Germany--Today at the 13th Cambridge Workshop on "Cool Stars,
Stellar Systems, and the Sun," Dr. Kevin L. Luhman (Harvard-Smithsonian
Center for Astrophysics) announced the discovery of a unique pair of
brown dwarfs in orbit around each other. Brown dwarfs are a relatively
class of objects discovered in the mid-1990s that are too small to
hydrogen fusion and shine as stars, yet too big to be considered
"Are brown dwarfs miniature failed stars, or super-sized planets, or are
they altogether different from either stars or planets?" asks Luhman.
unique nature of this new brown dwarf pair has brought astronomers a
closer to the answer.
One possible explanation for the origin of brown dwarfs is that they are
born in the same way as stars. Stars form in huge interstellar clouds in
which gravity causes clumps of gas and dust to collapse into "seeds,"
then steadily pull in more and more material until they grow to become
stars. However, when this process is studied in detail by computer, many
simulations fail to produce brown dwarfs. Instead, all the seeds grow
full-fledged stars. This result led some astronomers to wonder if brown
dwarfs and stars are created in different ways.
"In one alternative that has been proposed recently," explains Luhman,
seeds in an interstellar cloud pull on each other through their gravity,
causing a slingshot effect and ejecting some of the seeds from the cloud
before they have a chance to grow into stars. These small bodies are what
see as brown dwarfs, according to that hypothesis."
Testing these ideas for the birth of brown dwarfs is hampered by the
that brown dwarfs are normally extremely faint and hard to detect in the
sky. For most of their lives, they are not hot enough to ignite hydrogen
fusion, so they do not shine brightly like stars, and instead are
dim like planets. However, for a short time immediately following their
birth, brown dwarfs are relatively bright due to the leftover heat from
their formation. As a result, brown dwarfs are easiest to find and study
an age of around 1 million years, which is newborn compared to the 4.5
billion year age of our
Taking advantage of this fact, Luhman searched for newborn brown dwarfs in
cluster of young stars located 540 light-years away in the southern
constellation of Chamaeleon. Luhman conducted his search using one of
two 6.5-meter-diameter Magellan telescopes at Las Campanas Observatory
Chile, which are among the largest telescopes in the world.
Of the two dozen new brown dwarfs found, most were isolated and floating
space by themselves. However, Luhman discovered one pair of brown dwarfs
orbiting each other at a remarkably wide separation. All previously
pairs of brown dwarfs are relatively close to each other, less than half
distance of Pluto from the Sun. But the brown dwarfs in this new pair
much farther apart, about six times the distance of Pluto from the Sun.
Because these brown dwarfs are so far apart, they are very weakly bound
each other by gravity, and the slightest tug would permanently separate
them. Therefore, Luhman concludes, "The mere existence of this extremely
fragile pair indicates that these brown dwarfs were never subjected to
kind of violent gravitational pulls that they would undergo if they had
formed as ejected seeds. Instead, it is likely that these baby brown
formed in the same way as stars, in a relatively gentle and undisturbed
Dr. Alan P. Boss (Carnegie Institution) agrees, stating, "Luhman's
strengthens the case for the formation mechanism of brown dwarfs being
similar to that of stars like the Sun, and hence for brown dwarfs being
worthy of being termed 'stars,' even if they are too low in mass to be
to undergo sustained nuclear fusion."
The discovery of this binary brown dwarf will be published in an
issue of The Astrophysical Journal. The discovery paper currently is
in PDF format at http://www.cfa.harvard.edu/~kluhman/paper.pdf
Headquartered in Cambridge, Mass., the Harvard-Smithsonian Center for
Astrophysics (CfA) is a joint collaboration between the Smithsonian
Astrophysical Observatory and the Harvard College Observatory. CfA
scientists, organized into six research divisions, study the origin,
evolution and ultimate fate of the universe.
The Magellan telescopes are operated by the Carnegie Institution of
Washington, the University of Arizona, Harvard University, the University
Michigan, and the Massachusetts Institute of Technology.
Las Campanas Observatory is operated by the Carnegie Observatories,
was founded in 1904 by George Ellery Hale. It is one of six departments
the private, nonprofit Carnegie Institution of Washington, a pioneering
force in basic scientific research since 1902.
For more information, contact:
David Aguilar, Director of Public Affairs
Harvard-Smithsonian Center for Astrophysics
Phone: 617-495-7462 Fax: 617-495-7468
Public Affairs Specialist
Harvard-Smithsonian Center for Astrophysics
Phone: 617-495-7463, Fax: 617-495-7016