Scientists have combined modern spacecraft data with vintage observations to piece together a 125-year-long story of the antics of a nearby triple-star system dubbed HS Hydra — and predict its future.
When the first of those observations were made, in 1893, HS Hydra was just another star twinkling in the heavens. Now, it’s a strange, dynamic system — and one that may have a few more surprises in store.
Astronomers may soon unearth those surprises, thanks to NASA’s Transiting Exoplanet Survey Satellite (TESS). And scientists think this spacecraft, better known for discovering alien worlds, could unveil similar mysteries in bright but seemingly humdrum binary star systems, according to research presented at the 237th meeting of the American Astronomical Society, held virtually this week due to the coronavirus pandemic.
“It’s just been one of those topics that we knew was going to be really exciting, that TESS was going to be really powerful for,” James Davenport, an astronomer at the University of Washington, told Space.com of bright, binary star systems. But it isn’t the first time astronomers have turned to these objects, he said. “This was like your grandfather’s astrophysics or whatever; binary stars were really hot 60 or 70 years ago because that was the really dynamic thing they could study.”
TESS isn’t technically an astrophysics mission: The spacecraft was designed to spot exoplanets by looking for small, regular dips in the light of a bright star — the shadows of an alien world coming between its star and the spacecraft.
But a dip doesn’t necessarily mean a planet. Sometimes, for instance, it means that the star is actually two stars, which are circling each other edge-on to Earth. And when the stars overlap in the spacecraft’s view, the light dips: ta-da, a binary star system in an exoplanet mission’s data.
So Davenport read up on binary stars, tracking down an old article for amateur astronomers that profiled intriguing binary stars. “It was one of those great moments, like, … ‘I bet TESS observed a bunch of these,'” he said. “It was one of those late-night, ‘Gosh, what if I just dig into this for an hour’ — and then it was two in the morning and I was up too late.”
Of these binaries, HS Hydra was the system that particularly caught his attention. That’s because in 2012, astronomers took a new look at the system, which is about 342 light-years away from Earth, and realized it wasn’t just two stars circling each other every day and a half or so: There was a third, more distant and much smaller star tugging at the main pair. This companion was slowly pulling their dance out of humans’ edge-on view, the researchers realized.
Given the observations, the scientists predicted that the eclipses as seen from Earth would end around 2022. And Davenport was looking at 2019 TESS data that still showed small eclipses. “The prediction that they should end in 2022 wasn’t obviously wrong,” he said.
Using the new TESS data, Davenport and his student co-authors have predicted that HS Hydra’s eclipses will end not in 2022, but early this year, perhaps in February — just in time for the…