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Astronomers have discovered what appears to be a tiny star with a
giant, cloudy storm, using data from NASA's Spitzer and Kepler space
telescopes. The dark storm is akin to Jupiter's Great Red Spot: a
persistent, raging storm larger than Earth.
"The star is the size of Jupiter, and its storm is the size of
Jupiter's Great Red Spot," said John Gizis of the University of
Delaware, Newark. "We know this newfound storm has lasted at least two
years, and probably longer." Gizis is the lead author of a new study
appearing in The Astrophysical Journal.
While planets have been known to have cloudy storms, this is the best
evidence yet for a star that has one. The star, referred to as
W1906+40, belongs to a thermally cool class of objects called L-dwarfs.
Some L-dwarfs are considered stars because they fuse atoms and generate
light, as our sun does, while others, called brown dwarfs, are known as
"failed stars" for their lack of atomic fusion.
The L-dwarf in the study, W1906+40, is thought to be a star based on
estimates of its age (the older the L-dwarf, the more likely it is a
star). Its temperature is about 3,500 degrees Fahrenheit (2,200 Kelvin).
That may sound scorching hot, but as far as stars go, it is relatively
cool. Cool enough, in fact, for clouds to form in its atmosphere.
"The L-dwarf's clouds are made of tiny minerals," said Gizis.
In the new study, the astronomers were able to study changes in the
atmosphere of W1906+40 for two years. The L-dwarf had initially been
discovered by NASA's Wide-field Infrared Survey Explorer in 2011. Later,
Gizis and his team realized that this object happened to be located in
the same area of the sky where NASA's Kepler mission had been staring at
stars for years to hunt for planets.
Kepler identifies planets by looking for dips in starlight as planets
pass in front of their stars. In this case, astronomers knew observed
dips in starlight weren't coming from planets, but they thought they
might be looking at a star spot -- which, like our sun's "sunspots," are
a result of concentrated magnetic fields. Star spots would also cause
dips in starlight as they rotate around the star.
Follow-up observations with Spitzer, which detects infrared light,
revealed that the dark patch was not a magnetic star spot but a
colossal, cloudy storm with a diameter that could hold three Earths. The
storm rotates around the star about every 9 hours. Spitzer's infrared
measurements at two infrared wavelengths probed different layers of the
atmosphere and, together with the Kepler visible-light data, helped
reveal the presence of the storm.
While this storm looks different when viewed at various wavelengths,
astronomers say that if we could somehow travel there in a starship, it
would look like a dark mark near the polar top of the star.
The researchers plan to look for other stormy stars and brown dwarfs using Spitzer and Kepler in the future.
"We don't know if this kind of star storm is unique or common, and we don't why it persists for so long," said Gizis.
Other authors of the study are: Adam Burgasser--University of
California, San Diego; Kelle Cruz, Sara Camnasio and Munazza
Alam--Hunter College, New York City, New York; Stanimir
Metchev--University of Western Ontario, Canada; Edo Berger and Peter
Williams--Harvard-Smithsonian Center for Astrophysics, Cambridge,
Massachusetts; Kyle Dettman--University of Delaware, Newark; and Joseph
Filippazzo--College of Staten Island, New York.
NASA's Ames Research Center in Moffett Field, California, manages the
Kepler and K2 missions for NASA's Science Mission Directorate. JPL
managed Kepler mission development. Ball Aerospace & Technologies
Corp. operates the flight system with support from the Laboratory for
Atmospheric and Space Physics at the University of Colorado in Boulder.
JPL manages the Spitzer Space Telescope mission for NASA. Science
operations are conducted at the Spitzer Science Center at the California
Institute of Technology in Pasadena. Spacecraft operations are based at
Lockheed Martin Space Systems Company, Littleton, Colorado. Data are
archived at the Infrared Science Archive housed at the Infrared
Processing and Analysis Center at Caltech.