NASA’s Wide-field Infrared Survey Explorer (WISE) is a space telescope which performed an all-sky astronomical survey in the infrared-wavelength. One of its mission objectives was to detect a class of cool and dim objects known as brown dwarfs. In fact, data from WISE has allowed the discovery of a bonanza of such objects. A brown dwarf is more massive than a planet but is short of being a “true” star since it is not massive enough to fuse hydrogen in its core to produce energy. Brown dwarfs do not produce much visible light. Instead, they are warm and glow in the infrared. Because brown dwarfs are extremely faint, some of them may lie as close as the nearest stars and still remain undiscovered.
A paper published in the Astrophysical
Journal Letters announced the discovery of a pair of brown dwarfs located at a
mere 6.5 light years from the Sun. This binary brown dwarf system is known as
WISE 1049-5319 and the discovery was made by Kevin Luhman, an associate
professor of astronomy and astrophysics at Pennsylvania State University. WISE
1049-5319 is the third closest star system to us, after the Alpha Centauri
triple-star system at about 4.3 light years away and Barnard’s Star at about 6
light years away.
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This diagram illustrates the locations
of the star systems that are closest to the Sun. Credit: Janella Williams, Penn
State University.
The closeness of WISE 1049-5319 was
revealed by its large proper motion. Since proper motion is the observed change
in position of an object over time, nearby stars have large proper motions
while stars further away have smaller proper motions. This is like looking out
from a car window and seeing nearby trees fly by while distant mountains appear
almost motionless. The large proper motion of WISE 1049-5319 was revealed in
older images taken between the years 1978 to 1999 from the Digitized Sky Survey
(DSS), the Two Micron All-Sky Survey (2MASS) and the Deep Near-Infrared Survey of
the Southern Sky (DENIS).
WISE 1049-5319 shows up as a single
object in the WISE data and in older images. Its binary nature was only
revealed from follow-up observations using the large Gemini telescope on the
night of 23 February 2013. The sharper image from Gemini shows WISE 1049-5319
as two brown dwarfs separated from each other by approximately 3 times the
Earth-Sun distance. It is estimated that the two brown dwarfs circle each other
every 25 years or so.
Image of WISE 1049-5319 from the WISE
satellite and the Gemini imagery (inset) that revealed it to be a binary
system. Credit: NASA/JPL/Gemini Observatory/AURA/NSF
The close proximity of WISE 1049-5319
makes it a unique target for the detection of planets around it. Furthermore,
the signature of a planet orbiting a brown dwarf is more easily detectable than
for a planet orbiting a star because a brown dwarf is much fainter and less
massive than a star. In the distant future, WISE 1049-5319 may turn out to be
one of the first few destinations for interstellar exploratory missions beyond
our solar system. The presence of planets around WISE 1049-5319 will make it an
even more interesting target. Recall that in late 2012, an Earth-sized planet
was discovered in a close-in orbit around one star in the Alpha Centauri triple-star system.
Reference:
K. L. Luhman (2013), “Discovery of a
Binary Brown Dwarf at 2 Parsecs from the Sun”, arXiv:1303.2401 [astro-ph.GA]