Eternal youth of orange dwarfs was a threat to life on their planets

(ORDO NEWS) — Hubble telescope observations show that orange dwarfs are not as good for life development as is commonly thought. These stars remain highly active for too long, emitting streams of hard ultraviolet radiation capable of destroying planetary atmospheres.

Orange dwarfs are considered one of the most habitable stars. However, the new work of American astrophysicists casts doubt on their high status. Evgenia Shkolnik of Arizona State University and her colleagues found that orange dwarfs remain highly active for too long, showering their planets with ultraviolet light.

Hard radiation sharply reduces the possibility of not only the development of life, but at least the preservation of the atmosphere. Scientists write about this in an article presented in the arXiv online preprint library.

Earth is the only example of a habitable planet known to us. However, it is believed that life can be distributed much more widely in space, and our planet is not even the most convenient for it. And the Sun is probably not the most suitable star. Some astronomers believe that planets in orange dwarf systems may be more comfortable to support life.

These stars are intermediate between yellow dwarfs like the Sun and dull reds. They live longer and evolve more slowly than yellows, leaving more time for life to develop.

At the same time, yellow dwarfs radiate more strongly than red ones, and they do not throw out flashes so often that threaten to sterilize any nearby planet. It would seem that such stars are optimal for life. However, new work by American and Canadian astronomers calls into question this “buoyant” status of orange dwarfs.

Professor Shkolnik and her colleagues used data from the Hubble Space Telescope to study orange dwarfs from three groups of stars located in the Milky Way. The first group (Toucan – Hours association) is very young, the age of its stars is estimated at 40-45 million years.

The second (the Hyades cluster) is older, about 650 million years old. Finally, the third group consisted of individual distant stars about five billion years old. In total, scientists examined 39 orange dwarfs.

With age, the activity of stars should decrease, as has already been shown for both yellow and red dwarfs. Therefore, one would expect that “adult” orange dwarfs emit much less in the hard ultraviolet spectrum than stars from the “youth” association. However, the researchers found that the activity of those and others is almost the same.

The authors of the article attribute this to an unusual feature of orange dwarfs, which was revealed several years ago. The fact is that with age, sun-like yellow stars slow down the rotation – this leads to a decrease in their activity and brightness in the UV spectrum.

However, orange dwarfs practically do not stop, even when they reach maturity. This allows them to remain highly active, radiating as powerfully as during the time of “reckless youth”. But this also threatens the possible life on planets around such stars.

Hard ultraviolet is dangerous even for planetary atmospheres. A stream of such photons is capable of ionizing their particles, after which they are easily carried away into outer space, leaving the planet airless and not at all so suitable for life.

The only salvation can be a powerful magnetic field capable of deflecting particle streams from the parent star. Such a planet could develop life even in an “forever young” orange dwarf.


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