Free Astronomy Magazine January-February 2016

SPACE CHRONICLES sachusetts. The team used ALMA to study the well-known red dwarf star TVLM 513-46546, which is located about 35 light-years from Earth in the constellation Boötes. The star is a mere 10 percent the mass of the Sun and is so small and cool that it's right on the dividing line between stars (which fuse hy- drogen) and brown dwarfs (which don’t). One of the things that make this small star remarkable is that it spins rapidly, completing a full ro- tation about every two hours. Our Sun takes about 25 days to rotate once about its equator. Previous da- ta from the Nation- al Radio Astrono- my Observatory’s Karl G. Jansky Very Large Array in So- corro, New Mex- ico, show that this star exhibits a mag- netic field that ri- vals the Sun’s most extreme magnetic regions and is sev- eral hundred times stronger than the Sun's average mag- netic field. This puz- zled as- tronomers b e c a u s e the physical processes that generate the Sun’s magnet- ic field shouldn’t operate in such a small star. "This star is a very different beast from our Sun, magnetical- ly speaking," states CfA as- tronomer and co-author Edo Berger. When the researchers exam- ined the star with ALMA they detected emission at a particularly high frequency (95 GHz or a wavelength of about 3 millimeters). Such a radio signal is pro- duced by a process known as synchrotron emission, in which electrons zip around powerful magnetic field lines: the more powerful the magnetic field, the higher the frequency. This is the first time that flare-like emission at such high frequencies has been detected from a red dwarf star. It is also the first time that such a star has been detected at millimeter wavelengths, opening up a new avenue of study with ALMA. Our Sun generates similar emission from solar flares but only intermittently. What's more, the emission from this star is 10,000 times brighter than what our own Sun produces, even though it has less than one-tenth of the Sun's mass. The fact that ALMA detected this emission in a brief 4-hour obser- vation suggests that the red dwarf is continuously active. This has important implications for the search for habitable planets out- side the Solar System. Red dwarfs are the most common type of star in our Galaxy, which makes them promising targets for planet searches. But because a red dwarf is so cool, a planet would have to orbit very close to the star to be warm enough for liquid water to exist at its sur- face. That proximity would put the planet right in the bull's-eye for ra- diation that could strip its atmo- sphere or destroy any complex mol- ecules on its surface, the astrono- mers speculate. Astronomers will study similar stars in the future to determine whether this one is an oddball or an example of an entire class of stormy stars. A nimation of artist impression of red dwarf star TVLM 513-46546. This star is a mere 10 percent the mass of the Sun and is so small and cool that it's right on the dividing line between stars and brown dwarfs. [NRAO/AUI/NSF; Dana Berry / SkyWorks] n