Baby 'planemos' can be born as twins: U.Toronto astronomy breakthrough (Forwarded)

Department of Public Affairs
University of Toronto
Toronto, Canada

Contact:
Ray Jayawardhana, Department of Astronomy and Astrophysics
Phone: 416-946-7291

Valentin D. Ivanov, European Southern Observatory, Chile
Phone: +56 2 463 3000

Sonnet L'Abb News Services Officer
Phone: (416) 978-6974

August 3, 2006

Baby 'planemos' can be born as twins: U of T astronomy breakthrough

Discovery of planetary masses in orbit of one another thrills astronomy
community

By Sonnet L'Abb

team led by a U of T astronomy professor is challenging an existing
theoretical model and thrilling the astronomy community with its discovery
of a seven-Jupiter-mass companion next to a planemo, or planetary mass
object, only twice as heavy. Both objects have masses similar to those of
extra-solar giant planets, usually found in orbit around a star.
Unexpectedly, these bodies appear to circle each other.

"This is a truly remarkable pair of twins -- each weighing some hundred
times less than our sun," says Ray Jayawardhana, an associate professor of
astronomy and astrophysics at the University of Toronto. "Their mere
existence is a surprise, and their origin and fate a bit of a mystery."

Jayawardhana and Valentin D. Ivanov of the European Southern Observatory
(Chile) report the discovery in the August 3 issue of Science Express, the
rapid online publication service of the journal Science.

The researchers discovered the companion candidate in an optical image taken
with the European Southern Observatory's 3.5-meter New Technology Telescope
on La Silla, Chile, and investigated it further with optical spectra and
infrared images obtained with ESO's 8.2-meter Very Large Telescope on
Paranal, Chile. These followup observations confirmed that both objects are
young, at the same distance, and much too cool to be stars. By comparing the
companion to widely used theoretical models, Jayawardhana and Ivanov
estimate that it weighs about seven times as much as Jupiter, while the
primary planemo is an estimated 14 times Jupiter's mass. The newborn pair,
barely a million years old, are separated by about six times the distance
between the sun and Pluto, and are located in the Ophiuchus star-forming
region approximately 400 light years away.

"Roughly half of all sun-like stars, and about a sixth of brown dwarfs, come
in pairs," says Jayawardhana. Brown dwarfs are 'failed stars' that weigh
less than 75 Jupiter masses and are unable to sustain nuclear fusion. "Oph
162225-240515, or Oph1622 for short, is the first planemo to be resolved
into a double."

The existence of this wide pair poses a challenge to a popular theory which
suggests that brown dwarfs and planemos are embryos ejected from multiple
proto-star systems. Since the two objects in Oph1622 are so far apart, and
only weakly bound to each other by gravity, they would not have survived
such a chaotic birth.

Planets are thought to form out of disks of gas and dust that surround
stars, brown dwarfs and even some planemos. The researchers think that these
planemo twins formed together out of a contracting gas cloud that
fragmented, like a miniature stellar binary.

"We are resisting the temptation to call it a 'double planet' because this
pair probably didn't form the way that planets in our solar system did,"
says Ivanov. "Now we're curious to find out whether such pairs are common or
rare. The answer could shed light on how free-floating planetary-mass
objects form."