NASA's Hubble Space Telescope has been observing stars that pose a risk to their environment - and the planets that orbit them - through a large programme called HAZMAT, which stands for HAbitable Zones and M dwarf Activity across Time. Yes, it's a bit of a cheat acronym: it should be HZMDAT.
'M dwarf' is the astronomical term for a red dwarf star, the smallest, most abundant, and longest-lived type of star in our galaxy. The HAZMAT programme is an ultraviolet survey of red dwarfs at three different ages: young, intermediate, and old.
Stellar flares from red dwarfs are particularly bright in ultraviolet wavelengths, compared with Sun-like stars. Hubble's ultraviolet sensitivity makes the telescope very valuable for observing these flares. The flares are believed to be powered by intense magnetic fields that get tangled by the roiling motions of the stellar atmosphere.
The Hubble team has found that the flares from the youngest red dwarfs they surveyed, which were about 40 million years old, are 100 to 1,000 times more energetic than when the stars are older.
"The goal of the HAZMAT programme is to help understand the habitability of planets around low-mass stars," explained Arizona State University's Evgenya Shkolnik, the programme's chief investigator.
"These low-mass stars are critically important in understanding planetary atmospheres."
The first part of this Hubble programme has just been published, and examined the flare frequency of 12 young red dwarfs.
"Getting these data on the young stars has been especially important, because the difference in their flare activity is quite large as compared to older stars," said Arizona State University's Parke Loyd, the first author on the study.
The observing programme detected one of the most intense stellar flares ever observed in ultraviolet light. Dubbed the "Hazflare," this event was more energetic than the most powerful flare from our Sun ever recorded.
"With the Sun, we have a hundred years of good observations," Loyd explained. "And in that time, we've seen one, maybe two, flares that have an energy approaching that of the Hazflare.
"In a little less than a day's worth of Hubble observations of these young stars, we caught the Hazflare, which means that we're looking at superflares happening every day or even a few times a day."
According to Loyd, super-flares of such frequency and intensity bathe young planets in so much ultraviolet radiation that they forever doom chances of human habitability.
"Flares like we observed have the capacity to strip away the atmosphere from a planet. But that doesn't necessarily mean doom and gloom for life on the planet. It just might be a different life than we imagine.
"Or there might be other processes that could replenish the atmosphere of the planet. It's certainly a harsh environment, but I would hesitate to say that it is a sterile environment."
The next part of the HAZMAT study will be to study intermediate-aged red dwarfs, around 650 million years old. Finally, the oldest red dwarfs will be analysed and compared with the young and intermediate stars to understand the evolution of the ultraviolet radiation environment of low-mass planets around these low-mass stars.
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