Giant stellar eruption detected for the first time

A group of researchers has identified and characterized for the first time in a complete way a powerful eruption in the atmosphere of the active star HR 9024, marked by an intense X – ray flash followed by the emission of A giant plasma bubble, that is, hot gas containing charged particles. This is the first time that a coronal mass ejection, or CME, has been seen in another star than our Sun. The crown is the outer atmosphere of a star.

The work, published in an article of the last issue of the journal Nature Astronomy, used data collected by NASA's Chandra X-ray observatory. The results confirm that CMEs are produced in magnetically active stars and are relevant for stellar physics, and they also provide the opportunity to systematically study such dramatic events in stars other than the Sun.

"The technique we used is based on monitoring the speed of plasmas during a stellar eruption," said Costanza Argiroffi (University of Palermo Italy and Associate Researcher at the National Institute of Petrochemicals). astrophysics in Italy) who led the study. "This is because, by analogy with the solar environment, it is expected that, during a flare, the plasma confined in the coronal loop where the flare takes place is first moves up, then down to reach the lower layers of the stellar atmosphere., one also expects an additional movement, always directed upwards, because of the associated CME to the flare. "

The team analyzed a particularly favorable thrust on the active star HR 9024, about 450 light-years away from us. The High Energy Transmission Network (HETGS) spectrometer aboard Chandra is the only instrument for measuring coronal plasma movements at a speed of only a few tens of thousands of kilometers per hour.

The results of this observation clearly show that, at the torch, very hot materials (between 18 and 45 million degrees Fahrenheit) rise first and then fall at speeds between 225,000 and 900,000 miles at hour. This is in excellent agreement with the expected behavior of the material related to the stellar flare.

"This result, never achieved before, confirms that our understanding of the main phenomena that occur in flares is solid," said Argiroffi. "We were not convinced that our predictions could correspond to observations, because our understanding of eruptions rests almost entirely on the observation of the solar environment, where the most extreme eruptions are a hundredfold. a thousand times less intense in the X -radiation issued. "

"The most important point of our work, however, is another: we found, after the flare, that the coldest plasma – at a temperature of" only "seven million degrees Fahrenheit – was coming out of the air. Star, at a constant speed of about 185,000 miles per hour, "said Argiroffi. "And this data is exactly what we could have expected for the CME associated with the rocket."

Chandra's data yielded, in addition to the speed, the mass of the studied CME, equivalent to two billion pounds, about ten thousand times greater than the most massive CMEs launched into interplanetary space by the Sun. , consistent with the idea that CMEs of active stars are larger-scale versions of solar CMEs. The observed speed of the CME is, however, much lower than expected. This suggests that the magnetic field in active stars is probably less effective at accelerating CMEs than the solar magnetic field.