| Unusual light from star probably caused by comets, not aliens, say astronomers |
Unusual behaviour from a distant star is probably the result of a family of comet fragments on a highly elliptical orbit, not a giant structure built by an alien civilisation, astronomers say.
"What the star is doing is very strange," Associate Professor Massimo Marengo from Iowa State University said in a statement.
So strange, in fact, that astronomer Jason Wright from Penn State University published a paper in the Astrophysical Journal suggesting that an alien megastructure could be to blame.
"Aliens should always be the very last hypothesis you consider, but this looked like something you would expect an alien civilization to build," Professor Wright told The Atlantic.
The star KIC 8462852, about 1,500 light years away in the Milky Way galaxy, was discovered by NASA's Kepler Space Telescope in 2009 and has been observed ever since.
In October this year, citizen scientists examining Kepler data online reported that it was displaying regular and extreme dips in brightness.
Examining the light from distant stars is a good way to find exoplanets, explained astronomer Phil Plait on his blog Bad Astronomy.
However, Dr Plait, who worked on the Hubble Space Telescope while at NASA, said that although stars might show a regular dimming of 1 per cent when a planet the size of Jupiter passes in front of it, KIC 8462852 was dimming by as much as 22 per cent and on an irregular basis.
The astronomers who discovered this behaviour eliminated equipment error and starspots (sunspots, on other stars) as possible explanations.
Alien megastructures...?
A popular explanation in online commentary was a Dyson sphere, a hypothetical megastructure that surrounds a star and captures most or all of its energy output.
Dyson spheres were proposed by science fiction writer Olaf Stapledon in 1937, but named after theoretical physicist Freeman Dyson after he wrote a 1950 paper suggesting that the infrared output of stars could be examined as a way of finding alien civilisations.
It has been widely reported in recent years that Mr Dyson wishes the concept of a Dyson sphere was not named after him, and that he thinks a cloud of objects surrounding a star is more likely than a single structure.
The latest analysis of data from KIC 8462852, published in Astrophysical Journal Letters, examined data from NASA's Spitzer Space Telescope from January 2015, two years after the Kepler measurements that found the anomaly.
No infrared emissions were discovered from any debris around the star, allowing the researchers to reject numerous explanations that included collisions, which generate heat.
A cloud of comets the most likely cause
"The lack of strong infrared excess two years after the events responsible for the unusual light curve observed by Kepler further disfavours the scenarios involving a catastrophic collision in a KIC 8462852 asteroid belt, a giant impact disrupting a planet in the system, or a population of dust-enshrouded planetisimals (a cloud of rocks and debris)", the researchers wrote in the paper.
"The scenario invoking the fragmentation of a family of comets on a highly elliptical orbit is instead consistent with the lack of strong infrared excess found by our analysis."
However, the researchers are not able to entirely discount the idea of an alien megastructure.
"We can't really say it is, or is not," said lead researcher Associate Professor Massimo Marengo from Iowa State University.
"But what the star is doing is very strange. It's interesting when you have phenomena like that. Typically it means there's some new physical explanation or a new concept to be discovered."
Professor Marengo said that when pulsars, which emit strong radio pulses, where first seen, the first one discovered was named LGM-1 after "Little Green Men".
"We may not know yet what's going on around this star, but that's what makes it so interesting," he said.
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