Neomi Lewis ‘21

Analysis of observations taken by the Atacama Large Millemeter/sub millimeter Array, a radio telescope, shows that last March, Proxima Centauri, the closest star to the Sun, experienced significant stellar flares. This alarming behavior casts further doubt into the habitability of the Solar System’s nearest exoplanetary neighbor, Proxima b, which orbits Proxima Centauri.

Stellar flares occur when electrons accelerate at very high speeds, as a result of shifts in the star’s magnetic field, and emit electromagnetic radiation across the entire spectrum. This radiation is typically intense and has very high-energy; solar flares (stellar flares from the Sun) can cause electromagnetic interference on the earth including disrupting telecommunication signals. The stellar flare Proxima Centauri emitted was 10 times brighter at peak luminosity than the Sun’s largest flares (when similar wavelengths were compared).

The event increased the brightness of the star by 1,000 times over 10 seconds. Prior to this, there was a smaller flare and the two flares lasted fewer than two minutes in total. ALMA observed the star for 10 hours between January and March last year so the flare’s duration was rather insignificant. In addition, stellar flares have not yet been studied well in the radio wavelengths detected, especially for stars of Proxima’s Centauri’s type M dwarfs, which are also the most common type in our galaxy.

MacGregor, one of the leading astronomers on the team, explained, “it’s likely that Proxima b was blasted by high energy radiation during this flare.” Considering the environment and possible habitability of the exoplanet, she believes that “over the billions of years since Proxima b formed, flares like this one could have evaporated any atmosphere or ocean and sterilized the surface, suggesting that habitability may involve more than just being the right distance from the host star to have liquid water.”

Earlier in November, another paper interpreted the average brightness provided by the ALMA data as being caused by disks of dust around the star, quite like our Solar System’s asteroid and Kuiper belts. The authors even went on to say that this dust pointed to the existence of more planetary bodies in the system. However, given that we now know that this high average brightness is largely attributable to the stellar flare, these claims are no longer valid. In addition, as Weinberger says, “nor is there any information yet that indicates the star has a rich planetary system like ours.”

The discovery of Proxima Centauri’s enormous flare continues to confirm the general unpredictability of stellar behavior and the precariousness of orbiting around flaming bodies of plasma.

References

1. M. MacGregor, et. al. Detection of a millimeter flare from proxima centauri. The Astrophysical Journal Letters 855, (2018).
2. Image retrieved from: https://www.flickr.com/photos/gsfc/15403844862