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The Question
(Submitted December 15, 2008)
I read the news online that a red dwarf named EV Lacertae 16 light years away
has released solar flares so bright in x-rays, so powerful, it would have been
visible to the naked-eye if it was on the night sky instead of the day sky.
They also said it was also so bright, it caused instruments on board Swift to
automatically shut down. How can a star so small, so much less energetic than
the Sun release that much energy? If the Sun relatively emitted the same amount
of energy as that red dwarf did, it would probably be deadly for life on the
day side on the Earth. Maybe the Sun has emitted a similar deadly amount of
energy sometime ago and caused extinctions. The red dwarf is 15 times younger
than the Sun.
The Answer
Thank you for your question! The key point here is the last sentence of
what you wrote - EV Lac is much younger than the Sun. Because of that,
it is still rotating rapidly, which creates a strong magnetic field in
the star's atmosphere (much stronger than our Sun's). Flares are
consequences of magnetic fields in stars. In particular, when magnetic
fields get "twisted" by stellar rotation, material in the star's outer
atmosphere can be ejected in a flare. Because EV Lac is rotating much
more quickly than the Sun, and consequently has a stronger magnetic
field, the flares it experiences are much stronger and brighter than the
Sun's, despite its relatively small mass. However, the Sun could have
experienced such powerful flares a few billion years ago, when it was
much younger. You can learn more about this topic here:
http://blogs.discovermagazine.com/badastronomy/2008/05/19/the-red-dwarf-that-roared
http://en.wikipedia.org/wiki/Flare_stars
Nick Sterling and Jason Link,
for "Ask an Astrophysicist"
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