Written by Shanna Freeman

This tiny star has captured our interest in a big way as it’s the closest one to Earth after our own Sun.

Red dwarfs are the most common type of star in our galaxy, but they’re impossible to observe from the Earth with the naked eye because they’re the dimmest stars. They’re also very small and relatively cool due to their low mass. The red dwarf Proxima Centauri is among the smallest and dimmest, but it has the special significance of being the closest star to us other than the Sun.

Proxima Centauri is approximately 4.24 light years (268,000 AU) away, located in the Centaurus constellation. The star is estimated to remain the closest star to ours for another 30,000 years or so, at which point the star Ross 248 in the Andromeda constellation will come closer (it’s currently about 10.3 light years away).

Proxima Centauri is located about 15,000 AU from the next-closest star, the binary system Alpha Centauri. This relative closeness is how Proxima came to be discovered. In 1915, Scottish-South African astronomer Robert Innes observed a star that had the same proper motion – the apparent change of a star’s position on the celestial sphere – as Alpha Centauri, which had been first observed in 1689. Depending on who you ask, Proxima is either a companion to Alpha Centauri or a third star in the system.

Since its discovery, Proxima has been closely observed. Because it’s a red dwarf, it will be around for much longer than our Sun – at least four trillion more years – thanks to its slow consumption of fuel. And unlike the Sun, Proxima will completely use up its hydrogen during the fusion process. Satellite X-ray telescopes have provided crucial information about its activities. The Einstein Observatory, an X-ray telescope that orbited the Earth from 1978 to 1982, took the first X-ray images of the star and recorded a solar flare – flashes of brightness and heat caused by magnetic activity. This confirmed astronomer Howard Shapley’s announcement in 1951 that Proxima Centauri was a flare star. The European Space Agency’s European X-ray Observatory Satellite (EXOSAT), German ROSAT, and the Japan Aerospace Exploration Agency’s Advanced Satellite for Cosmology and Astrophysics (ASCA) have all observed numerous solar flares on Proxima.

Land-based telescopes have also given us data about Proxima. Operated by the European Southern Observatory, the Very Large Telescope (VLT) helped to determine Proxima’s distance and size. The star has a mass about one-eighth that of the Sun’s, but it’s about 40 times denser. Proxima’s corona, or plasma ‘atmosphere’ extending into space beyond the surface, can actually be hotter than that of the Sun – 3.5 million Kelvin as opposed to 2 million Kelvin. On average, its overall temperature is about 3,000 Kelvin. Observations of Proxima’s chromosphere indicate that it has a rotation period of about 31 days.

Although the closeness of Proxima Centauri has made for plenty of observation, there are* still some burning questions. Are there any planets orbiting the star? And if so, are they habitable? The Hubble Space Telescope hinted at the possibility of a planet near Proxima Centauri during observations in 1998, but no further evidence has appeared upon subsequent imaging. Proxima was to have been a target of the Space Interferometry Mission (SIM), a NASA space telescope mission that ultimately got cancelled. The star’s closeness continues to make it a promising destination for both observation and actual interstellar travel, and eventually we’ll get a better look at our neighbouring star.

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