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Astronomers may have solved the mystery behind an unusually brighter star.
University of Washington doctoral student Anastasios Tzanidakis and research assistant professor of astronomy James Davenport were searching for “strangely behaving stars” when they received an alert about a potential starmark from the Gaia spacecraft.
Launched by the European Space Agency in 2013, the space observatory is on a mission to create the most accurate 3D map of the Milky Way galaxy to date. The astronomers focused on Gaia17bpp, a star that had gradually increased in brightness over a 2.5-year period.
The results of their investigation and analysis of the star, shared Tuesday at 241st Meeting of the American Astronomical Society in Seattle, revealed that the star itself did not change. Instead, the star has a strange companion responsible for what scientists estimate is a “seven-year photobomb.”
“We believe this star is part of an exceptionally rare type of binary system, between a large, bloated parent star – Gaia17bpp – and a small companion star surrounded by a vast disc of dusty material,” Tzanidakis said in a statement .
“Based on our analysis, these two stars orbit each other for an exceptionally long period of time – as much as 1,000 years. So capturing this bright star eclipsed by its dusty companion is a once-in-a-lifetime opportunity.”
The Gaia spacecraft began observing the star in 2014. The researchers pulled together all of Gaia’s observations of the star and tracked other observations of Gaia17bpp taken by the Pan-STARRS1 telescope in Hawaii, the NASA WISE/NEOWISE mission, and the Zwicky Transient Facility in California dating back to 2010.
By comparing the images of Gaia17bpp, the researchers determined that the star’s brightness was dimmed by 4.5 magnitudes, or 67 times. It remained so for 7 years, from 2012 to 2019.
The astronomers just happened to observe the star at the end of an eclipse that lasted several years.
No other stars in the vicinity of Gaia17bpp have exhibited dimming of this magnitude. The team also searched a digital catalog of astrophotographic plates at Harvard University dating back to the 1950s.
“Over 66 years of observational history, we found no other signs of significant dimming in this star,” Tzanidakis said.
So what happened to Gaia17bpp? “Based on the data currently available, this star appears to have a slow companion that is surrounded by a large disc of material,” Tzanidakis said. “If that material existed in the solar system, it would extend from the sun to Earth’s orbit or beyond.”
Although Gaia17bpp is unique in having such a long eclipse, it is not the only binary star system to exhibit dimming behavior. Astronomers are also fascinated by Epsilon Aurigae, a star that experiences an eclipse every two out of every 27 years by a large companion – but the identity of the actual companion remains a mystery.
The giant star Betelgeuse also attracted the attention of astronomers when it dimmed dramatically in late 2019, prompting speculation that it was about to explode into a supernova. Instead the star had a dusty eruption.
For Gaia17bpp, the dust-forming stellar companion may be a small dead star called a white dwarf, but they’re not entirely sure what might be contributing to the disk of debris around it.
Regardless of the identity of its companion, Gaia17bpp and its mysterious cosmic partner are so far apart that another eclipse is hundreds of years away.
“This was an incredible discovery,” Tzanidakis said. “If we had been off for a few years, we would have missed it. It also indicates that these types of binaries may be much more common. If so, we must come up with theories about how this type of pairing even came about. It is definitely an oddity, but it may be much more common than anyone has appreciated.”
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