Artist's conception of a very young, still-forming brown dwarf, with a disk of material orbiting it, and jets of material ejected outward from the poles of the disk.
Credit: Bill Saxton, NRAO/AUI/NSF
Astronomers using the Karl G. Jansky Very Large Array (VLA) have discovered jets of material ejected by still-forming young brown dwarfs. The discovery is the first direct evidence that brown dwarfs, intermediate in mass between stars and planets, are produced by a scaled-down version of the same process that produces stars.
The
astronomers studied a sample of still-forming brown dwarfs in a
star-forming region some 450 light-years from Earth in the constellation
Taurus, and found that four of them have the type of jets emitted by
more-massive stars during their formation. The jets were detected by
radio observations with the VLA. The scientists also observed the brown
dwarfs with the Spitzer and Herschel space telescopes to confirm their
status as very young objects.
"This is the first time that such
jets have been found coming from brown dwarfs at such an early stage of
their formation, and shows that they form in a way similar to that of
stars," said Oscar Morata, of the Institute of Astronomy and
Astrophysics of the Academia Sinica in Taiwan. "These are the
lowest-mass objects that seem to form the same way as stars," he added.
Brown
dwarfs are less massive than stars, but more massive than giant planets
such as Jupiter. They have insufficient mass to produce the
temperatures and pressures at their cores necessary to trigger the
thermonuclear reactions that power "normal" stars. Theorists suggested
in the 1960s that such objects should exist, but the first unambiguous
discovery of one did not come until 1994.
A key question has been
whether brown dwarfs form like stars or like planets. Stars form when a
giant cloud of gas and dust in interstellar space collapses
gravitationally, accumulating mass. A disk of orbiting material forms
around the young star, and eventually planets form from the material in
that disk. In the early stages of star formation, jets of material are
propelled outward from the poles of the disk. No such jets mark planet
formation, however.
Previous evidence strongly suggested that
brown dwarfs shared the same formation mechanism as their larger
siblings, but detecting the telltale jets is an important confirmation.
Based on this discovery, "We conclude that the formation of brown dwarfs
is a scaled-down version of the process that forms larger stars,"
Morata said.
Morata led an international team of astronomers with
members from Asia, Europe, and Latin America. They reported their
findings in the Astrophysical Journal.
The National
Radio Astronomy Observatory is a facility of the National Science
Foundation, operated under cooperative agreement by Associated
Universities, Inc.
Contact:
Dave Finley, Public Information Officer
(575) 835-7302
dfinley@nrao.edu
