When we think of next-door neighbours, the first word that may come to mind is "closeness".
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However, in space, our next-door neighbour star system is anything but close: in fact, it is a mind boggling four light years away.
Today, we will take a closer look at Alpha Centauri - this "nearby" star system that contains both mysteries and intrigue.
Alpha Centauri is not hard to spot in the southern night sky. In fact, to us Australians it is associated with one of the best-known constellations: the brighter of the two pointers of the Southern Cross. If you go outside and find the Southern Cross in the sky, you will see two bright stars "pointing" towards it; the brighter star that is further away from the cross is Alpha Centauri.
Our neighbour star, due to its relative closeness, is the third brightest star in the sky, only beaten by the stars Sirius and Canopus.
But Alpha Centauri is not as it seems; it hides a clever secret when you stargaze without a telescope. You see, Alpha Centauri is not a single star, but in fact three stars very close together.
The two brighter, sun-sized stars (named Rigel Kentaurus and Toliman) are in a binary pair, orbiting each other every 80 years. The third star, Proxima Centauri, is the odd one out, being a small faint red dwarf many times fainter than our sun.
With a decent telescope, you should be able to separate the single point of Alpha Centauri into two brighter points, but Proxima Centauri will still be too faint to see. Despite this, Proxima is the closest of the three components, getting the true title of the closest star to our sun.
Proxima Centauri itself hides a secret: the closest star to us has a planet orbiting around it! Named the inventive "Proxima Centauri b", this planet was found using the radial velocity method of planet detection. This is where the star is seen to wobble slightly due to the gravity of the planet tugging on the star as it orbits.
What is exciting, though, is that Proxima Centauri b is only slightly larger than the Earth and orbiting in the "habitable zone" of the star; the region where liquid water can exist.
Before you get too excited about the prospect of aliens on this world, there is a problem.
You see, Proxima Centauri b is tidally locked. This is where the same side of the planet always faces the star. Our moon is also tidally locked, which is where we get the term "dark side of the moon": we never see the other side!
This means that one half of Proxima Centauri b will always be daytime (very hot), while the other side will be an eternal night (very cold). Any life on the planet would have to live in perpetual twilight on the terminator line separating day and night. Another problem is that Proxima Centauri is prone to flaring, and so could wipe out any liveable atmosphere surrounding the planet.
Nevertheless, with our next-door stellar neighbour hosting a potentially habitable planet, it's no wonder there are plans to go and visit it!
- Jonah Hansen is a PhD student specialising in space interferometry at Mount Stromlo Observatory, at the Australian National University.
