(credit: M. Garlick/University of Warwick/ESO)

When observing AR Scorpii, researchers noticed that its brightness varied over a 3.5 hour period. So they labelled it a periodic variable and paid it no further attention. Now, however, a large international team of astronomers has gone back and taken a more careful look at the star. The astronomers found that AR Scorpii is much more variable than first thought, with 400 percent changes in brightness occurring within only 30 seconds. The reason for this? AR Scorpii is actually two stars, and one of them is launching relativistic electrons at the other.

The paper describing these results was published this week in Nature.

The researchers were drawn to AR Scorpii because of seven years of archival images that revealed a lot of additional variability layered on top of its well-described 3.5 hour period. Rather than peaking at a similar level each time, the output could vary by as much as a factor of four.