Humungous flare from sun’s nearest neighbor breaks records

April 21, 2021

(Nanowerk News) Scientists have seen the largest flare ever recorded by the sun’s closest neighbor, the star Proxima Centauri.

The research, which appears in Letters of the Astrophysical Journal (“Extremely Short Length Flame Detection of Proxima Centauri Using a Millimeter by Far-UV) was led by Boulder University of Colorado and could help shape the hunt for life beyond the Earth’s solar system. Concept of a violent flare-up artist exploding from star Proxima Centauri Concept of a violent flare-up artist exploding from star Proxima Centauri. (Image: NRAO / S. Dagnello)

Meredith MacGregor, astrophysicist CU Boulder, explained that Proxima Centauri is a small but powerful star. It sits just four light years or more than 20 trillion miles from our own sun and supports at least two planets, one of which can look like Earth. It’s also “dwarf red,” the name of a class of stars that are unusually petite and dim.

Proxima Centauri has about one-eighth of the mass of our own sun. But don’t let that fool you.

In their new study, MacGregor and her colleagues observed Proxima Centauri for 40 hours using nine telescopes on the ground and in space. In the process, they got a surprise: Proxima Centauri threw a missile, or burst of radiation starting near the surface of a star, which rates as one of the most violent seen anywhere in the galaxy.

“The star went from normal to 14,000 times brighter when viewed in ultraviolet wavelengths over a few seconds,” said MacGregor, an assistant professor at the Center for Astronomy and Space Astronomy (CASA) and the Department of Astrophysical and Astronomical Sciences. Planning (APS)) at CU Boulder.

The team’s findings suggest a new physics that could change the way scientists think about stellar flares. Neither do they bode well for any squishy organism brave enough to live near the ever-shifting star.

“If life was on the planet closest to Proxima Centauri, it would have to look very different than anything on Earth,” MacGregor said. “A human being on this planet would have a bad time.”

Active stars

The star has long been a target for scientists hoping to find life beyond the Earth’s solar system. Proxima Centauri is nearby, for starters. It is also home to one planet, designated Proxima Centauri b, that lives in what researchers call a “habitable zone” – a region around a star that has the right temperature range for a liquid water harbor on the surface of a planet.

But there’s a twist, says MacGregor: Red dwarves, who rank as the coolest stars in the galaxy, are also unusually vibrant.

“Many of the exoplanets we’ve discovered so far are around these types of stars,” he said. “But the catch is that they are much more active than our sun. They flash much more often and intensely.”

To see how many Proxima Centauri flames, she and her colleagues drew on the approaching coup of astrophysics: They pointed to nine different instruments at the star for 40 hours over several months in 2019. Those eyes were includes the Hubble Space Telescope, the Atacama Large Millimeter Array (ALMA) and the NASA Exoplanet Transmission Survey (TESS) Satellite. Five of them recorded the massive flare by Proxima Centauri, capturing the incident as it produced a broad spectrum of radiation.

“This is the first time we’ve ever had this kind of multi-wavelength stellar flare coverage,” said MacGregor. “Usually you’re lucky if you can have two instruments.”

Crimson planet

The technique presented one of the most detailed anatomies of any star in the galaxy.

The incident in question was observed on May 1, 2019 and lasted for only 7 seconds. Although it did not produce much visible light, it did produce a huge surge in ultraviolet and radio radiation, or “millimeter” radiation.

“In the past, we didn’t know that stars could flame in the millimeter range, so this was the first time we went looking for millimeter flares,” said MacGregor.

Those millimeter signals, MacGregor added, could help researchers gather more information about how stars produce flares. Currently, scientists suspect that these bursts of energy occur when magnetic fields near the surface of a star spin and snap with explosive results.

Overall, the observed flare was about 100 times more powerful than any similar flare seen from Earth’s sun. Over time, such energy can obliterate the atmosphere of a planet and even expose life forms to deadly radiation.

That kind of flare may not be a rare occurrence on Proxima Centauri. In addition to the big boom in May 2019, the researchers recorded many other flares during the 40 hours they spent watching the star.

“Proxima Centauri planets are hit by something like this not once in a century, but at least once a day if not several times a day,” said MacGregor.

The findings suggest that there may be more surprises in store from Sun’s closest companion.

“There are probably even more strange types of flares that show different kinds of physics that we haven’t thought of before,” said MacGregor.