Astronomers Detect a Coronal Mass Ejection From Another Star For The First Time

Artist impression of HR 9024 flaring up, compared to the Sun (top left corner). NASA/GSFC/S. Wiessinger 

The most powerful magnetic phenomena produced by the Sun are coronal mass ejections. These are the dramatic releases of plasma from the Sun into a solar wind, and they are associated with solar flares and solar prominence eruptions. Researchers have now observed a coronal mass ejection from another star for the first time.

As reported in Nature Astronomy, an Italian-American team used NASA’s X-ray observatory, Chandra, to observe HR 9024, an active star 450 light-years from Earth. They saw X-rays flashes associated with the emission of giant bubbles of plasma. The coronal mass ejection was strong enough to throw into space 1.2 million billion tonnes of plasma, about 10,000 times more massive than the biggest ejection ever produced by the Sun.

The observations conducted by the team confirmed some predictions of stellar flares beyond the power that has (so far) been seen from the Sun. They saw the extremely hot plasma, at temperatures between 10 to 25 million degrees Celsius (18 to 45 million degrees Fahrenheit), rise and fall.

"This result, never achieved before, confirms that our understanding of the main phenomena that occur in flares is solid," lead author Dr Constanza Argiroffi, from the University of Palermo, said in a statement. "We were not so confident that our predictions could match in such a way with observations, because our understanding of flares is based almost completely on observations of the solar environment, where the most extreme flares are even a hundred thousand times less intense in the X-radiation emitted."

"The most important point of our work, however, is another: we found, after the flare, that the coldest plasma — at a temperature of 'only' 7 million degrees Fahrenheit — rose from the star, with a constant speed of about 185,000 miles per hour," added Argiroffi. "And these data are exactly what one would have expected for the CME associated with the flare."

Something that was unexpected in the study was the velocity of the flare. The plasma was thrown out with speed between 100 and 400 kilometers per second (225,000 to 900,000 miles per hour), quite a high speed in human terms, but theories suggested that it could be even faster. The discrepancy could indicate that HR 9024's magnetic field is not as efficient as expected.

HR9024 is a G-type giant, almost three times the mass of our Sun, and 843 times its volume. The team considers the object quite representative of the active star class.


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