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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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