An artist’s impression of a brown dwarf similar to J1047+21. |
Penn
State astronomers using the world’s largest radio telescope, at
Arecibo, Puerto Rico, have discovered flaring radio emissions from an
ultra-cool star, not much warmer than the planet Jupiter, shattering the
previous record for the lowest stellar temperature at which radio waves
were detected.
The
team from Penn State’s Department of Astronomy and Astrophysics and the
Center for Exoplanets and Habitable Worlds, led by Alex Wolszczan, the
discoverer of the first planets ever found outside our solar system, has
been using the giant 305-m (1,000-foot) telescope to look for radio
signals from a class of objects known as brown dwarfs. These objects are
small, cold stars that bridge the gap between Jupiter-like giant
planets and normal, more-massive, hydrogen-fusing stars. The astronomers
hit the jackpot with a star named J1047+21, a brown dwarf 33.6 light
years away in the constellation Leo, in a result that could boost the
odds of discovering life elsewhere in the universe.
Matthew
Route, a graduate student at Penn State and the lead author of the
discovery paper, said, “This object is the coolest brown dwarf ever
detected emitting radio waves—it’s half the temperature of the previous
record holder, making it only about five times hotter than Jupiter.”
The
new radio-star is much smaller and colder than our Sun. With a surface
temperature not much higher than that of a giant planet, and a size
comparable to Jupiter’s, it is scarcely visible in optical light. Yet
the radio flares seen at Arecibo show it must have a strong magnetic
field, implying that the same could be true of other similar stars.
Wolszczan,
an Evan Pugh Professor of Astronomy and Astrophysics and the leader of
the project, said, “This is a really exciting result. We hope that in
the future we’ll be able to detect yet colder brown dwarfs, and possibly
even giant planets around other stars.”
The
possibility that young, hot planets around other stars could be
detected in the same manner—because they still maintain strong magnetic
fields—has implications for the chances of finding life elsewhere in our
Milky Way Galaxy, Wolszczan explained. “The Earth’s field protects life
on its surface from harmful particles of the solar wind. Knowing
whether planetary magnetic fields are common or not throughout the
Galaxy will aid our efforts to understand chances that life may exist
beyond the Solar System.”
The
discovery of radio signals from J1047+21 dramatically broadens the
window through which astronomers can study the atmospheres and interiors
of these tiny stars, using the radio detection of their magnetic fields
as a tool. At the temperature of this brown dwarf, its atmosphere must
be made of neutral gas, which would not give off radio signals like
those seen. The energy to drive the signals is likely to come from
magnetic fields deep inside the star, similar to the field that protects
the Earth from dangerous high-energy particles. By monitoring the radio
flares from J1047+21, astronomers will be able to tell how stable the
magnetic field is over time, and, from flare duration, they can infer
the size of the emitter itself. The results were published in the March
10 2012 edition of the Letters section of the Astrophysical Journal.
The
Arecibo Observatory is operated by SRI International under a
cooperative agreement with the National Science Foundation
(AST-1100968), and in alliance with Ana G. Méndez-Universidad
Metropolitana, and the Universities Space Research Association.
