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Violent gas explosions in boiling young red dwarf stars can make the conditions uninhabitable on the nascent planets. In the rendering of the artist, a young active red dwarf (right) is stripping the atmosphere of a planet in orbit (left). Scientists have discovered that the eruptions of the youngest red dwarves studied – about 40 million years ago – were 100 to 1,000 times more energetic than when the stars were older. They also detected one of the most intense stellar eruptions ever observed under ultraviolet light – more energetic than the most powerful eruption ever recorded by our Sun. Credit: NASA, ESA and D. Player (STScI)
The word "HAZMAT" describes substances that pose a risk to the environment or even to life itself. Imagine the term applied to whole planets, where violent flares of the star host can render uninhabitable worlds by changing their atmospheres.
NASA's Hubble Space Telescope observes these stars through an extensive program called HAZMAT – Living Areas and Dwarf M activity over time.
"M dwarf" is the astronomical term for a red dwarf star, the smallest, most abundant and most enduring star type in our galaxy. The HAZMAT program is an ultraviolet study of red dwarfs of three different ages: young, intermediate and old.
Stellar eruptions of red dwarfs are particularly bright in ultraviolet wavelengths, compared to stars similar to those of the Sun. The ultraviolet sensitivity of Hubble makes the telescope very useful for observing these flares. Eruptions are thought to be fed by intense magnetic fields that become entangled by the swirling motions of the stellar atmosphere. When entanglement becomes too intense, the fields break and reconnect, releasing huge amounts of energy.
The team discovered that the light eruptions of the youngest red dwarves they surveyed – about 40 million years – are 100 to 1000 times more energetic than when the stars are older. It is at this age that terrestrial planets form around their stars.
About three quarters of the stars in our galaxy are red dwarfs. Most planets "in the livable zone" of the galaxy – planets orbiting their stars at a temperature where temperatures are moderate enough to leave liquid water on their surface – are probably red dwarfs in orbit. In fact, the closest star to our Sun, a red dwarf named Proxima Centauri, has a planet the size of the Earth in its habitable zone.
However, young red dwarfs are active stars, producing ultraviolet rays producing such energy that they could influence atmospheric chemistry and possibly strip the atmospheres of these nascent planets.
"The goal of the HAZMAT program is to help understand the livability of planets around low-mass stars," said Evgenya Shkolnik, senior researcher of the program at the University of New York. State of Arizona State. "These low-mass stars are of paramount importance for the understanding of planetary atmospheres."
The results of the first part of this Hubble program are published in The Astrophysical Journal. This study examines the frequency of flares of 12 young red dwarfs. "Getting this data on young stars has been particularly important because the difference in activity between their flares is quite large compared to older stars," said Parke Loyd, of Arizona State University, the first author of this article.
The observation program detected one of the most intense stellar eruptions ever observed in ultraviolet light. Nicknamed "Hazflare", this event was more energetic than the most powerful light of our Sun ever recorded.
"With the Sun, we have a hundred years of good observations," said Loyd. "And meanwhile, we've seen one, if not two, flares that have energy close to that of the Hazflare.In a little less than a day of Hubble's observations of these young stars, we have captured the Hazflare, which means we're seeing super events happening every day or even several times a day. "
Could super-rockets of such frequency and intensity soak the young planets with so much ultraviolet rays that they would never lose their habitability again? According to Loyd, "flares, as we have seen, have the ability to strip the planet's atmosphere, but that does not necessarily mean that life on the planet is dark and dreary. It's certainly a harsh environment, but I would hesitate to say it's a sterile environment. "
The next part of the HAZMAT study will be studying middle aged red dwarfs aged 650 million years old. Then the oldest red dwarfs will be analyzed and compared to young and intermediate stars in order to understand the changing environment of the ultraviolet radiation of low-mass planets around these low-mass stars.
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Astronomers catch a red dwarf star in an explosion of superflare
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