This article was originally published on The conversation. The publication contributed the article to Space.com’s Expert Voices: Op-Ed & Insights.
If you look up at the southern sky, you can see the “pointer” stars pointing to the Southern Cross. One of these tips is Alpha Centauri, which is actually a pair of sunny stars that are too close together to be distinguished by each other.
There is also a third member of the Alpha Centauri system: Proxima Centauri (Proxima Cen for short), which circles the central two stars in a wide orbit. It is the closest neighbor of the Sun, at a distance of only 4.2 light-years.
It is possible that one of Proxima Cen’s planets is suitable for life. However, we recently spotted the sign of Proxima Cen’s violent space weather, implying that an orbiting planet could be blown up with dangerous particles and magnetic fields.
Our neighbor is not like the sun
Our sun is a relatively inconspicuous yellow dwarf star and is the only known life-bearing planet in the universe: our earth.
Proxima Cen is very different. It is a red dwarf star with a diameter of only 15% of the sun and a surface temperature of 3000 K (degrees Kelvin), much cooler than the sun’s 6000 K.
Because Proxima Cen is relatively cool, the “Golden Curl Zone” of orbits around it – where the temperature is right for liquid water – is about one-twentieth of the earth’s distance from the sun. We are interested in planets in a star’s Goldilocks zone, because liquid water is needed for life as we know it.
Read more: Greet the Earth’s nearest neighbor of the exoplanet: Proxima Centauri b
We know that Proxima Cen has at least two planets: Proxima Cen b, a rocky ‘super-Earth’ located in the center of Proxima Cen’s Goldilocks zone, and Proxima Cen c, a ‘sub-Neptune’ that further located.
Astronomers have suspected for years that planets like Proxima Cen b could be a dangerous home for life because they are so close to their host stars. Many red dwarf stars produce regular, powerful torches – intense bursts of radiation that move into space. If planets like Proxima Cen b do not have protective features such as a thick atmosphere or a strong magnetic field, they will be exposed to dangerous radiation levels.
But what does the weather look like around these stars?
The ‘space weather’ of red dwarfs is another important factor in determining how hospitable they are in life. While torches include intense bursts of light, weather conditions in space mean that the star’s magnetic field and charged particles can alternate directly with planets.
The most energetic space weather events are known as coronal mass ejections (or CMEs). These massive eruptions escape the atmosphere of a star and move millions of kilometers per hour through space.
If the weather conditions in space are extreme enough, the planet’s atmosphere can be blown away and the magnetic field can be pushed backwards, exposing the surface to deadly flare radiation.
CMEs have been detected around the sun since the 1970s, but it is much more difficult to detect space weather events around distant stars.
Turn on the radio for weather news
CMEs on the sun produce characteristic bursts of radio noise, such as ‘type II’ and ‘type IV’ bursts. By locating similar signatures on other stars, we can indirectly identify star CMEs.
In early 2019, we aimed our telescopes for 11 nights at Proxima Cen. We used CSIRO’s new radio telescope, the Australian Square Kilometer Array Pathfinder (ASKAP), as well as the Zadko telescope, the ANU 2.3m telescope and NASA’s Transiting Exoplanet Survey Satellite (TESS).
Our goal was to track down the signature of a CME.
On the night of May 2, 2019, we observed a massive optical torch with an estimated total energy output of 16 septillion joules. (This is about 17 million years of current electricity production in Australia.) On the sun, the big torches happen only once every decade or two. But at Proxima Cen, it happens every few weeks.
Using ASKAP, we observed a spectacular series of intense radio bursts.
With the amazing details that ASKAP reveals, we were able to see that we have discovered the best example of a sunny type IV radio from another star so far.
This explosion of radio waves implies that the space weather environment around Proxima Cen is quite violent.
‘One swallow does not make a summer’
In 1859, British astronomers Richard Carrington and Richard Hodgson made the first observations of a solar flare, followed by a massive storm called the “Carrington event”. We now know that the storm was caused by a great coronal mass ejection that struck the earth.
Carrington noted the coincidence between these extraordinary events, but was careful to draw any connection between them, and famously declared that ‘one swallow does not make a summer’. We now find ourselves in a similar situation to Carrington.
We observed a radio signature implying that a CME erupted from Proxima Cen. But to confirm the relationship between these star radio bars with CMEs, we need to use information from other wavelengths. Once we can do that, we should soon know exactly how dangerous it is to live next to a star like Proxima Centauri.
Read more: Is Alpha Centauri the right place to look for life elsewhere?
This article was published from The Conversation under a Creative Commons license. Read the original article.
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