“We find a hot spot that covers half of the surface of the star like a giant lighthouse that rotates in and out of our field of view. We still do not know why only half of the star is lit up in hydrogen and if this situation remains unchanged over days, weeks, years, or centuries.”
~ Dr. Edo Berger, Princeton University
Using four of the world’s most powerful telescopes, astronomers have
found a bizarrely magnetic star with some very strange features. The
M-type dwarf has a massive “hot spot”, which covers half of its surface
area, and an unusually active magnetic field. The star lies about 35
light-years away in the constellation Boötes. If these strange
“anomalies” turn out to be common for M-type stars, astronomers will
have a radically altered view of the ultracool dwarfs.
“With such a unique set of observations you always expect to find the
unexpected,” said Berger, “but we were shocked at the level of
complexity that this object exhibits.”
The star’s radio emission is frequently interrupted with spectacular
fireworks displays of minute-long flares coming from the catastrophic
collisions and merging of the magnetic fields in star’s corona. The
team also observed soft x-ray emission and an x-ray flare, and for the
first time, charted optical hydrogen-alpha emission with a period of
two hours that matches the two-hour rotation period of the star.
Similar to other ultracool M-type dwarf stars, this magnetic star known
as TVLM513-46546 features surface temperatures below about 2400K (2127
Celsius) and a mass of less than 10% of our Sun. By contrast, the Sun
is a G-type star with an average surface temperature of 6000K (5727
Celsius). Scientists previously believed that stars likeTVLM513-46546
were relatively simple, quiet objects, with little to no magnetic field
activity.
“Theory has always said that as we look at cooler and cooler stars, the
coolest will be essentially dead,” said Berger. “It turns out that
stars like TVLM513-46546 have very complex magnetic activity around
them, activity more like our Sun than that of a star that is barely
functional.”
Berger believes the complicated magnetic field environment and possible
hot spot may indicate unusual activity beneath the star’s surface (in
its dynamo) or possibly even the existence of a hidden companion. The
research team will continue with observations of similar stars in order
to find out if this stellar oddity is indeed a rarity, or if it is
actually a typical prototype for other ultracool dwarfs.
The new discovery was made possible through simultaneous observations
made by four of the world’s most powerful telescopes, combining radio
data from the Very Large Array, optical spectra from the Gemini North
8-meter telescope, ultraviolet images from the orbiting Swift
observatory and x-ray data from NASA’s Chandra X-ray Observatory. This
is the first time that such a powerful set of telescopes has been
trained on one of the smallest known stars. The study is part of a
program attempting to reveal the origins of magnetic fields in
ultracool dwarfs, stars that astronomers previously thought were more
tranquil than their massive siblings.
Posted by Rebecca Sato
* These findings will be published in the February 10, 2008 issue of the Astrophysical Journal.
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Links:
http://xxx.lanl.gov/abs/0708.1511
http://gemini.edu/magneticpersonality