Proxima b, the closest exoplanet to our solar system, has been a focus of scientific studies since it was first confirmed (in 2016). This terrestrial planet (also known as rocky) orbits Proxima Centauri, an M (red dwarf) -type star located 4.2 light years behind our solar system – and part of the Alpha Centauri system. In addition to its proximity and rocky composition, it is also located in the habitable zone (HZ) of its parent star.
Until a mission can be sent to this planet (e.g. Breakthrough Starshot), astrobiologists must posit the possibility that life could exist there. Unfortunately, an international campaign that monitored Proxima Centauri for months with nine space- and ground-based telescopes recently discovered an extreme flare from the star that would have made Proxima b uninhabitable.
The campaign was led by Meredith A. MacGregor, an assistant professor of astrophysics at the University of Colorado Boulder, and included members of the Carnegie Institution for Science, the Sydney Institute for Astronomy (SIfA), the CSIRO Astronomy and Space Science, and the Space Telescope Science Institute (STScI), the Harvard-Smithsonian Center for Astrophysics (CfA) and several universities.
This artist’s impression shows the planet Proxima b orbiting the red dwarf star Proxima Centauri, the closest star to the solar system. Photo credit: ESO / M. Kornmesser
M stars like Proxima Centauri are a class of low mass, low luminosity stars that are known to be variable and unstable compared to other classes. In particular, these stars have a tendency to flicker, which occurs when their magnetic fields shift, accelerating electrons to near the speed of light (NLS). These electrons interact with the star’s plasma, causing a burst that creates emissions across the electromagnetic spectrum (EM).
To determine how much Proxima Centauri flickered, the research team observed the star for 40 hours over several months in 2019. These included the Australian Square Mile Array Pathfinder (ASKAP), the Atacama Large Millimeter / Submillimeter Array (ALMA) and Hubble Space Telescope (HST), Transiting Exoplanet Survey Satellite (TESS) and the du Pont Telescope.
These telescopes recorded a massive flare on May 1, 2019 that recorded the event as it produced a wide spectrum of EM radiation and tracked its timing and energy in unprecedented detail. As MacGregor recently stated in a Carnegie Science press release:
“The star went from normal to 14,000 times brighter when viewed in ultraviolet wavelengths over a period of a few seconds. If there were life on the planet closest to Proxima Centauri, it would have to look very different from anything on earth. A person on this planet would have a bad time. “
Since red dwarfs tend to be faint compared to other types of stars, flares are unlikely to produce much visible light. Astronomers are usually happy to see such torches with just two instruments. This campaign marked the first time astronomers were able to cover a multi-wavelength star wave flare, allowing them to observe the tremendous fluctuations in ultraviolet and millimeter wave radiation.
Artist’s impression of the interior of a low-mass star, as seen in an X-ray of Chandra in the inset. Photo credit: NASA / CXC / M.Weiss
The team’s findings, published April 21 in The Astrophysical Journal Letters, form one of the most profound anatomies of a star’s torch in our galaxy. In the future, these signals could help researchers gather more information about how stars create flares, which could have immense implications for exoplanet and habitability studies. Unfortunately, it’s not a good sign for planets like Proxima b.
This research is the latest in a series of papers and studies since the discovery of Proxima b showing that the system is unsuitable for life. Proxima b is the closest exoplanet to Earth and is located in the star’s HZ. It is the most likely candidate for follow-up and astrobiological examinations. But according to this latest study, the torches it emits would likely have made the planet sterile long ago. As Weinberger explained:
“Proxima Centauri is as old as the sun and has been blowing up its planets with high-energy torches for billions of years. By examining these extreme flares with multiple observatories, we can understand what their planets endured and how they might have changed. Now we know that these very different observatories, operating at very different wavelengths, can see the same fast, energetic impulse. “
Beyond Proxima Centauri, the results could also have an impact on all planets orbiting in the HZs of the red dwarf stars. Type M dwarfs are the most common type of stars in our galaxy, making up about 70% of the stars in the entire universe. Of the more than 4,375 exoplanets confirmed to date, a statistically significant number of “Earth-like” planets orbiting M-type dwarfs was found.
An artist’s illustration of a hypothetical exoplanet orbiting a red dwarf. Photo credit: NASA / ESA / G. Speck (STScI)
This has led many astronomers to speculate that the best place to find potentially habitable rocky planets is in the system of red dwarf stars. For this to be true, most of these stars would have to be significantly less active than Proxima Centauri. On a more positive note, our closest star neighbor holds more surprises in store for astronomers, such as previously unknown types of torches that demonstrate exotic physics.
This research was carried out with support from NASA’s Goddard Space Center.
Further reading: Carnegie Science, The Astrophysical Journal Letters
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