Astronomers fund copy of Jupiter’s Big Red Spot on dwarf star

March 30, 2016

Astronomers have discovered what appears to be a tiny star with a giant, cloudy storm looks like Jupiter’s Big Red Spot, using data from NASA’s Spitzer and Kepler space telescopes. However, this “exo-storm” hasn’t been spied on another gas giant, it’s been spotted in the uppermost layers of a cool, small star.

Dwarf Stars shows both of tar-like and planet-like characteristics

L-dwarfs are a special subset of tiny stellar objects that possess both star-like and planet-like characteristics. Known colloquially as “failed stars,” brown dwarfs are too massive to be classified as planets, but they are too small to be clearly defined as stars. They form a bridge between planets and stars and can weigh-in at many times the mass of Jupiter (although their physical size is approximately that of Jupiter). They are celestial mongrels in a way; they have qualities of both stars and planets, but can be clearly defined as neither.

For example, although some of the more massive brown dwarfs (such as M- and L-dwarfs) can experience some low-level fusion in their cores (a star-like quality), it’s not enough to raise the object’s temperature beyond a couple of thousand degrees. Therefore, their atmospheres can become stratified (layered) and possess very planet-like phenomena such as clouds and, in this case, powerful storms.

NASA’s Wide-field Infrared Survey Explorer discovered W1906+40 in 2011 and astronomers realized that the object was within the field of view of NASA’s exoplanet-hunting Kepler Space Telescope. Usually, Kepler will look out for “transits” of exoplanets that orbit in front of their host stars — the slight dimming caused by the planet blocking star light causes a dip in brightness. But sometimes “starspots” can also be detected by Kepler — basically huge dark patches of magnetic activity in the uppermost stellar layers.

So, using Kepler, although the light generated by W1906+40 is faint, astronomers detected a huge dark patch rotate with the L-dwarf’s spin. Could it just be another star sporting a vast, dark cluster of star spots, like our sun does during periods of high magnetic activity?

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.
Spitzer has observed other cloudy brown dwarfs before, finding evidence for short-lived storms lasting hours and perhaps days.

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.

Jupiter’s Big Red Dot fund on W1906+40

Viewing the brown dwarf in infrared light, Spitzer was able to determine that the large dark feature on W1906+40 isn’t driven by magnetism, so it isn’t a star spot, it’s actually an atmospheric phenomenon. It’s a big, dark storm near the north polar region.

“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, lead author of the study to be published in The Astrophysical Journal. “We know this newfound storm has lasted at least two years and probably longer.”

He added: “We don’t know if this kind of star storm is unique or common, and we don’t why it persists for so long.”

It goes to show that the moniker “failed star” may be a misnomer; perhaps brown dwarfs should in fact be known as “overachieving planets.”

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