Using ALMA, astronomers discovered that Proxima Centauri produces frequent, high-energy millimeter-wavelength flares that could significantly alter or strip the atmospheres of its habitable-zone planets.
Located just over four light-years away, Proxima Centauri is our closest stellar neighbor and a highly active M dwarf star. While its frequent flaring has long been observed in visible light, a recent study using the Atacama Large Millimeter/submillimeter Array (ALMA) reveals that Proxima Centauri also exhibits intense activity at radio and millimeter wavelengths. These observations provide new insights into the particle-driven nature of its flares and raise important questions about the star’s impact on the habitability of its surrounding planets.
Proxima Centauri is known to host at least one potentially habitable, Earth-sized planet within its habitable zone. Like solar flares on our Sun, Proxima’s flares emit energy across the electromagnetic spectrum and release bursts of high-energy particles known as stellar energetic particles.
The intensity and frequency of these flares could pose a serious threat to nearby planets. If powerful enough, they can erode planetary atmospheres, stripping away critical components like ozone and water, and potentially rendering these worlds uninhabitable.
Investigating Proxima’s Flare Activity with ALMA
A team of astronomers, led by Kiana Burton of the University of Colorado and Meredith MacGregor of Johns Hopkins University, utilized archival data and new ALMA observations to study the millimeter-wavelength flare activity of Proxima Centauri. Proxima Centauri’s small size and strong magnetic field indicate that its entire internal structure is likely convective—unlike the Sun, which has both convective and nonconvective layers. As a result, the star is much more active.
Its magnetic fields become twisted, develop tension, and eventually snap, sending streams of energy and particles outward in what astronomers observe as flares.
MacGregor summarized the study’s core question, “Our Sun’s activity doesn’t remove Earth’s atmosphere and instead cause beautiful auroras, because we have a thick atmosphere and a strong magnetic field to protect our planet. But Proxima Centauri’s flares are much more powerful, and we know it has rocky planets in the habitable zone. What are these flares doing to their atmospheres? Is there such a large flux of radiation and particles that the atmosphere is getting chemically modified, or perhaps completely eroded?”
Unprecedented Multi-Wavelength Study
This research represents the first multi-wavelength study using millimeter observations to uncover a new look at the physics of flares. Combining 50 hours of ALMA observations using both the full 12-meter array as well as the 7-meter Atacama Compact Array, a total of 463 flare events were reported at energies ranging from 1024 to 1027 erg. The flares themselves were short events, ranging from 3 to 16 seconds.
“When we see the flares with ALMA, what we’re seeing is the electromagnetic radiation–the light in various wavelengths. But looking deeper, this radio wavelength flaring is also giving us a way to trace the properties of those particles and get a handle on what is being released from the star,” says MacGregor. To do so, astronomers characterize the star’s so-called flare frequency distribution in order to map out the number of flares as a function of their energy.
Typically, the slope of this distribution tends to follow a power law function: smaller (less energetic) flares occur more frequently while larger, more energetic flares occur less frequently. Proxima Centauri experiences so many flares that the team detected many flares within each energy range. Furthermore, the team was able to quantify the asymmetry of the star’s highest energy flares, describing how the flares’ decay phase was much longer than the initial burst phase.
Radio- and millimeter-wavelength observations help to put constraints on the energies associated with these flares and their associated particles. MacGregor highlighted ALMA’s key role: “The millimeter flaring seems to be much more frequent–it’s a different power law than we see at the optical wavelengths. So if we only look in optical wavelengths, we’re missing critical information. ALMA is the only millimeter interferometer sensitive enough for these measurements.”
Reference: “The Proxima Centauri Campaign—First Constraints on Millimeter Flare Rates from ALMA” by Kiana Burton, Meredith A. MacGregor, Rachel A. Osten, Ward S. Howard, Alycia J. Weinberger, Evgenya Shkolnik, David J. Wilner, Jan Forbrich and Thomas Barclay, 17 March 2025, The Astrophysical Journal.
DOI: 10.3847/1538-4357/ada5f2
Never miss a breakthrough: Join the SciTechDaily newsletter.
Follow us on Google and Google News.