Mystery of dimming star deepens

Observations to explain why a star in our Galaxy is periodically dimming in brightness have added to the mystery behind its puzzling behaviour.

DimmingStarMAIN

Artist’s impression of a star’s light being obscured by debris from a broken up comet. This is one of the theories put forward to explain the star’s unusual dimming. Credit: NASA/JPL-Caltech

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The mystery of an oddly behaving star in the Milky Way has deepened following further research into its puzzling activity.

KIC 8462852 was observed in 2015 by a team of astronomers using NASA’s Kepler space telescope, who spotted that the star was undergoing a series of sporadic yet brief dimming events.

No-one has yet been able to account for this behaviour, and now further observations have added to the mystery.

Josh Simon and Ben Montet from the Carnegie Institution for Science and Caltech, respectively, looked at the Kepler data and found that in addition to these periods of dimming, the star’s overall brightness faded during the first four years it was being observed.

These additional observations were carried out following a claim that the star’s brightness had decreased by 14 per cent between 1890 and 1989.

“We thought that these data could confirm or refute the star’s long-term fading, and hopefully clarify what was causing the extraordinary dimming events observed in KIC 8462852,” says Simon.

Kepler data showed that KIC 8462852 had indeed faded in brightness by about one per cent during the first three years, before dropping in brightness by about two per cent over six months and remaining at that level for the final six months.

Comparing these observations to those of over 500 other stars by Kepler, the pair found that only a small fraction displayed fading similar to that of KIC 8462852.

“The steady brightness change in KIC 8462852 is pretty astounding,” says Montet.

Our highly accurate measurements over four years demonstrate that the star really is getting fainter with time.

It is unprecedented for this type of star to slowly fade for years, and we don’t see anything else like it in the Kepler data.”

One way to explain the sudden drop in brightness over six months is a collision or breakup of a large body in the star system such as a planet or comet, but this wouldn’t explain the slower dimming that took place during the first three years.

“It’s a big challenge to come up with a good explanation for a star doing three different things that have never been seen before,” Montet says.

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“But these observations will provide an important clue to solving the mystery of KIC 8462852.”