Science

Record solar eruption on Proxima Centauri

Proxima of the Centaur got angry. On May 1, 2019, the closest star to Earth, 4.2 light years away, was rocked by a very strong solar flare. In the ultraviolet, it is even the most violent observed on this type of star, a red dwarf: its intensity has been multiplied by 14,000! The event, which lasted a total of seven seconds, was recorded by 5 telescopes simultaneously (including the indestructible Hubble), as part of a study conducted by the University of Boulder (Colorado, United States), and published in Astrophysical Journal Letters April 21, 2021. With a total of 9 instruments, and 40 hours of observation spread between April and June 2019, the team closely monitored the small star, one eighth of the mass of the Sun. Objective: to record its activity in a wide range of wavelengths. They were not disappointed… In addition to this record in UV, they also recorded a surge, by a factor of 1000 this time, in the field of radio waves. Overall, this eruption is 100 times stronger than the one the Sun sometimes gives us …

Bad news for alien life?

The planet Proxima Centauri b, which revolves around the star, had a front row seat to admire the spectacle. But were there spectators? Nothing is less certain now. The “Earth” -type planet lies in the star’s habitability zone, and it made an interesting candidate for harboring life. But imagine that our Sun, all of a sudden, increases its UV dose by a factor of 14,000 …

“If there is life on Proxima Centauri b, it must be different from anything we know on Earth, explains on the site of the University of Boulder Meredith MacGregor, co-signer of the study. A human being on this planet would have had a hard time. ” This record eruption is therefore above all bad news for the quest for life in the Universe, and for several reasons. Red dwarfs constitute the most widespread star population in the galaxy, and therefore also the largest number of suns for exoplanets. For example, the 7 planets of the Trappist system revolve around a red dwarf. However, these little suns are customary with great anger. Eruptions have already been observed on other stars of the same type. And during the 40 hours of observations, the astronomers participating in the study recorded several other peaks of activity. “The planets of Proxima Centauri [l’étoile en compte au moins deux] are not affected by this kind of event once a century, but once a day or even more ”, concludes Meredith MacGregor. If life was able to develop, it therefore had to put in place mechanisms to protect itself from these devastating bursts of energy.

The star’s magnetic field is believed to be involved in these eruptions

It remains for researchers to understand how these reddish stars, much darker than the Sun, and which very slowly deplete their hydrogen reserve, can be shaken by more frequent and intense eruptions. The study, conducted in a wide range of wavelengths, a first, should provide answers. The researchers suggest the role of the star’s magnetic field: its field lines near the surface, twisting and then breaking, could generate this type of explosive event. If the eruptions are perhaps bad news for extraterrestrial life, they are on the other hand a great opportunity to study physics on these particular stars.

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