A new study suggests that Proxima Centauri, the closest star to our Sun, may have been captured from elsewhere in the galaxy by its two companion stars. And this may have implications for the possibility of life on Proxima b.
The research was carried out by Fabo Feng and Hugh Jones from the University of Hertfordshire in the UK. They propose that key differences between Proxima Centauri 4.25 light-years away and the two stars it orbits with, Alpha Centauri A and B, suggest it might be an imposter.
Available online, the paper has been submitted to the Monthly Notices of the Royal Astronomical Society for publication.
“My study suggests that there is a considerable probability (at least one quarter) that Proxima was not formed together with Alpha Centauri,” Feng told IFLScience.
To come to this conclusion, the researchers studied the orbits of the triple Alpha Centauri system (Proxima is sometimes called Alpha Centauri C) over the past and future 5 billion years. They found that 74 percent of possible orbits corresponded to Proxima being a true sister star, with a quarter hinting that it was captured from elsewhere.
Another piece of evidence for this theory is the difference in metallicity between the stars. Proxima is a red dwarf star, much dimmer than our Sun, whereas A and B are more like our Sun. This raises the possibility the three of them were not born from the same cloud of dust and gas.
If the capture scenario is true, Feng thinks it might have occurred about 3 to 4 billion years ago. The importance of this relates to Proxima b, a potentially habitable exoplanet that orbits Proxima Centauri and the closest exoplanet we know of to Earth.
“If the capture scenario is true, Proxima b would be more likely to be in the habitable zone for a long time and allow potential life to develop,” said Feng. The reason for this is that if the stars were born together, their proximity means Proxima b may have been pushed into or pulled out of the habitable zone at some point, lowering its window for life to emerge.
There is clearly still a long way to go with this theory. But whether it’s confirmed or not, it further highlights the complication of trying to find out if Proxima b is habitable. It might be the closest exoplanet to Earth, but the jury is far from a verdict on whether it could support life.