Flaring red dwarf stars

Photo: Take 27/Science Photo Library

Proxima Centauri b orbits in the habitable zone around Proxima Centauri, where the temperature may be suitable for liquid water to exist on its surface.

The nearest known star to us after the Sun is a red dwarf star called Proxima Centauri.

It is 4.25 light years away, which means its light takes 4.25 years to reach us. This star has about an eighth of the Sun's mass, is about a seventh of the Sun's diameter, and its energy output compared with our star is microscopic.

Its fuel consumption is so low that it should be able to keep shining happily for tens of billions of years. This suggests that Proxima Centauri, along with the countless other red dwarf stars scattered around the universe, could be ideal hosts for inhabited planets.

They can provide a stable environment over a long enough time for life to appear and evolve. It turns out that Proxima Centauri has a potentially inhabitable planet, but on the downside, this star, along with many other red dwarfs, produces large flares.

Stars are big spheres of hot, churning plasma, atoms so hot they have lost some of their electrons. This means plasma is a good conductor of electricity. Fluorescent lights contain a little bit of plasma.

Stars are also threaded by complex systems of strong magnetic fields. The continuous churning leads to the magnetic fields getting crowded, twisted and/or stretched.

These distortions lead to a colossal amount of energy being stored. In most cases this energy gets slowly dissipated again. However, sometimes the tangle of plasma and magnetic fields is too complicated or severe to just relax.

In this situation, the stresses build up until something snaps, and all the stored energy, which in the case of the Sun could add to millions of hydrogen bombs, is released in seconds.

The result is blasts of X-rays, even gamma rays in some cases, beams of high-energy particles, and often a large chunk of material is shot off into space at thousands of kilometres a second. These are called coronal mass ejections, or solar storms.

Flares don't threaten living things on the ground, but can pose a risk to those at high altitudes or in space. On other hand, flares can severely degrade or even destroy the complex power, transportation and communications infrastructure our lives depend on.

It does help that we live about 150 million kilometres away from the Sun. However, imagine living 20 times closer, to a star that produces even bigger flares.

For any star there is a Goldilocks Zone, the distance from the star where a planet would be at the right temperature for liquid water to exist on its surface.

For dimmer stars that zone lies close to the star, and is quite narrow. So the chance of a planet orbiting a dim, red dwarf star lying in the zone is smaller than it would be for a brighter star. However, red dwarf stars are the commonest stars in the universe, so there must be lots of them out there with planets lying in the zone.

Red dwarf stars produce much larger flares than do more massive stars like the Sun, which is why we can detect them from so far away.

The result for a planet in the Goldilocks Zone for Proxima Centauri or other red dwarf stars is that even a solar flare of the size produced by the Sun would hit the planet hundreds of times harder than we get hit.

Imagine a flare tens of times larger than what our Sun produces. The environmental impacts would be huge, let alone the disruption of any technological infrastructure.

It is likely that whether there is liquid water, the radiation and wild environmental instabilities would stop life getting going on any of these worlds.

However, not all red dwarf stars we observe are producing these huge flares. This could mean some of these stars could have inhabited worlds. That is unless this flaring behaviour is something all these stars go through at some points in their lives.

Of course, our arguments are based on life as we know it. There could be other forms of life.

• Mars is still high in the southwest after dark.
• Jupiter and Saturn lie low in the southeast before dawn.
• The Moon be New on the 11th.

This article is written by or on behalf of an outsourced columnist and does not necessarily reflect the views of Castanet.