Object: Xi-1 Canis Majoris
Superpower: Surprise X-ray pulses
Sometimes monsters hide in plain sight, and it takes a hero with X-ray vision to find them.
A European space telescope has spotted a massive star that is pulsing with brilliant X-rays. Studying the bizarre beast might yield important insights into stellar evolution, for instance, why some stars have strong magnetic fields while others don鈥檛, and what controls their powerful winds of charged particles.
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The European Space Agency鈥檚 XMM-Newton satellite has been zooming overhead since 1999, revealing details about objects such as galaxies, stars and black holes based on the X-rays they emit. at the University of Potsdam in Germany and her colleagues were using the telescope to take a closer look at Xi-1 Canis Majoris, a large blue star near the .
Giant鈥檚 pulse
The team got more than they bargained for. Although the star is well-known for emitting X-rays, it was a surprise to find these emissions were pulsing. Until now, almost all stars known to throb with such radiation were rapidly spinning neutron stars, the leftover cores of massive stars that have exploded. Some of these stellar corpses give off jets of high-energy particles from their poles. As the stars spin, we only detect the jets when they are aimed at Earth, so we see them as periodic pulses of light.
But Xi-1 Canis Majoris is still very much alive. It is between 13 and 15 times as massive as our sun and is visible in the winter sky roughly to the southeast of the bright 鈥渄og star鈥� Sirius. Xi-1 Canis Majoris is known to vary in brightness over the course of a few hours, because heat fluctuations from the nuclear furnace at its core cause it to regularly expand and contract.
This shouldn鈥檛 affect the star鈥檚 X-ray emissions, however. The X-rays are produced by interactions in its stellar wind, so its slight size changes should not interfere with this flow of charged particles.
Magnetic mystery
Oddly, Oskinova and her team found that the X-ray pulses are in time with the star鈥檚 brightness changes. The reason is still a mystery, but the star鈥檚 strong magnetic field might be a clue 鈥� the astronomers were first interested in Xi-1 Canis Majoris because its magnetic field is thousands of times stronger than our sun鈥檚. It could be that the field is interacting with the star鈥檚 wind in a way that creates the pulses, but it is too early to know for sure.
at the Royal Military College of Canada says that astronomers had previously seen pulsing X-rays in only one other large object. Called Beta Crucis, this blue star is about 14 times as massive as the sun and marks the left point of the . However, it seems to have a much weaker magnetic field than Xi-1 Canis Majoris. A team that with the Chandra X-ray Observatory in 2008 wasn鈥檛 able to detect its magnetic field. The Beta Crucis team instead suggest this star鈥檚 X-ray pulses are being influenced by oddities in its stellar wind.
鈥淚n principle it isn鈥檛 hard to produce X-ray pulsations,鈥� says Wade. 鈥淭he trick is to figure out what the mechanism actually is, and we haven鈥檛 done that yet.鈥�
Journal reference: Nature Communications,
