Scientists just saw the largest solar flare ever recorded from the closest star to our Sun, Proxima Centauri — so big that scientists think it may have spelled doom for any life present on nearby exoplanets in orbit, reshaping the search for life beyond Earth's solar system, according to a recent study published in the journal The Astrophysical Letters.
Solar flares from red dwarf stars can threaten alien life
Meredith MacGregor, a CU Boulder astrophysicist, said that while Proxima Centauri is small, it's also powerful. Positioned only four light-years — more than 20 trillion miles (32 trillion km) from our sun — Proxima Centauri serves as a solar host to at least two planets, one of which might resemble Earth. The star is also a "red dwarf:" the classification for stars that are atypically small and dim.
As one of these, Proxima Centauri is roughly one-eighth the mass of our sun — but, as they say, big surprises can come in small packages. MacGregor and her colleagues observed the star for 40 hours via nine space- and ground-based telescopes. And with their eyes trained on the star, they saw it eject a flare, which is a gigantic burst of deadly radiation spewing out from the surface of a star.
This was one of the most violent solar flares ever seen in the Milky Way.
"The star went from normal to 14,00 times brighter when seen in ultraviolet wavelengths over the span of a few seconds," said MacGregor, who's also an assistant professor at the Center for Astrophysics and Space Astronomy (CASA) and CU Boulder's department of astrophysical and planetary sciences (APS), in a CU Boulder blog post. The research team's discovery promises the discovery of a new physics that might fundamentally alter the way we think about stellar flares.
However, the colossal solar flare probably spelled doom for any alien life still alive on Proxima Centauri's potentially Earth-like planet. "If there was life on the planet nearest to Proxima Centauri, it would have to look very different than anything on Earth," explained MacGregor. "A human being on this planet would have a bad time."
The first ultraviolet and radio flare recorded in the Milky Way
At an incredibly close distance to our sun, Proxima Centauri has long been a candidate for the possible existence of extraterrestrial life beyond our solar system. One of its planets, called Proxima b, orbits within what astronomers call the "habitable zone" — a concentric region surrounding stars where the range of temperatures a planet would experience are apt for liquid surface water. But red dwarves have a dark side: while they're the most common type of star in the galaxy, they're also the least hospitable to planets that might otherwise support life.
"A lot of the exoplanets that we've found so far are around these types of stars," said MacGregor. "But the catch is that they're way more active than our sun. They flare much more frequently and intensely." To understand how often and much Proxima Centauri flares, MacGregor and her colleagues executed what treads close to to a coup in the field of astrophysics: They directed nine different instruments at Proxima Centauri for 40 through the course of many months in 2019 — including NASA's Transiting Exoplanet Survey Satellite (TESS), the Hubble Space Telescope, and the Atacama Large Millimeter Array (ALMA). Five of the telescopes employed in this venture recorded the gigantic flare emanating from the star, capturing the violent reaction's wide spectrum of deadly radiation.
"It's the first time we've ever had this kind of multi-wavelength coverage of a stellar flare," said MacGregor. "Usually, you're lucky if you can get two instruments."
This latest study provided one of the most in-depth anatomies of a solar flare from any Milky Way star. It lasted only seven seconds, and didn't create a lot of visible light, but the surge in ultraviolet and radio was both extremely scary and unprecedented. With this new data, researchers can better grasp how stars generate flares — expanding the current view, which holds that bursts of energy in flares happen when magnetic fields near the surface of a star twists and snaps in a violent explosion — one that could kill alien life on orbiting exoplanets.