Astronomers have discovered a ring of planetary debris that appears to contain 65 moon-sized structures orbiting close to a white dwarf star. The curious part: each structure passes in front of the star on a regular basis, precisely every 23.1 minutes – a mystery, researchers say, they “cannot currently explain”.
In the study, published in Monthly Notices of the Royal Astronomical Society, an international team of researchers measured light from a white dwarf in the Milky Way known as WD1054–226. By monitoring dips in the light received from stars, astronomers can detect exoplanets and other structures as they transit between the star and telescopes during their orbits.
To their surprise, in this case they found pronounced dips in light corresponding to 65 evenly spaced clouds of planetary debris orbiting the star every 25 hours.
The moon-sized structures we have observed are irregular and dusty (e.g. comet-like) rather than solid, spherical bodies. Their absolute regularity, one passing in front of the star every 23 minutes, is a mystery we cannot currently explain.
Furthermore, the researchers concluded that the precise regularity of the transits suggests they are kept in such a precise arrangement by a nearby planet – and that planet would be in the “habitable zone” of the star, an orbit of the right distance to allow water, and therefore life, to exist:
An exciting possibility is that these bodies are kept in such an evenly-spaced orbital pattern because of the gravitational influence of a nearby planet. Without this influence, friction and collisions would cause the structures to disperse, losing the precise regularity that is observed. A precedent for this ‘shepherding’ is the way the gravitational pull of moons around Neptune and Saturn help to create stable ring structures orbiting these planets.
The unfortunate news, for those wondering if these curious structures might have been created by an advanced alien civilization, is that the habitable zone for a white dwarf is smaller and closer to the star – the white dwarf stage of a star’s life occurs when it runs out of its hydrogen fuel, shrinks and loses its heat.
What this means is that the structures orbit in an area that previously would have been enveloped by the star when it was in its previous red giant stage of stellar evolution. As such, they are likely to have only existed since recently (relatively speaking in space terms…perhaps a billion years).
However, alien life still has a chance in this system: astronomers think that during this white dwarf stage period of the star’s existence, the ‘Goldilocks zone’ that is conducive to the presence of water and life would be habitable for at least two billion years.
Link: Planetary bodies observed for first time in habitable zone of dead star