A binary star system shines 20 per cent more brightly whenever the smaller star gets close to its giant partner, because of the immense waves that break on the larger star.
Towering waves more three times the size of the sun are crashing on an enormous, distant star.
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| Artist’s depiction of binary star system MACHO 80.7443.1718, with huge waves rising on the larger star Melissa Weiss/Center for Astrophysics/Harvard & Smithsonian |
The star in question is paired with another in a highly elliptical orbit. As the stars swing close together, their gravities pull on each other to produce tidal waves, much like how the moon creates tides on Earth. This stretches the stars, causing them to bulge out at the equator, which makes them seem brighter for a while.
“The brightness varies in a way that is similar to a heartbeat,” says Avi Loeb at the Harvard-Smithsonian Center for Astrophysics in Cambridge, Massachusetts.
Now, Loeb and his colleague Morgan MacLeod, also at the Center for Astrophysics, have spotted the most extreme “heartbeat star” yet recorded.
The binary star system MACHO 80.7443.1718 sits in the Large Magellanic Cloud, about 160,000 light years away from us, and was detected in the 1990s. Its primary star has a mass 34.5 times that of the sun and a diameter 24 times larger.
Soon after its discovery, astronomers realised it was a heartbeat star. But more recent observations have revealed that its changes in brightness are much greater than usual pulses. For typical heartbeat stars, the difference in brightness over an orbit would be less than 1 per cent, says Loeb. “This particular star is varied by 20 per cent.”
Loeb and MacLeod ran computer simulations of how the two stars must be interacting and found that as they reach the closest part of their orbit of each other, the bigger star has tidal waves that rise to a height three times the size of our sun and crash back into the star’s surface – just like waves that break into the ocean on Earth.
“It’s amazing that we can understand what’s going on out in the universe through observing the nature around us,” says MacLeod. “My hope is that next time people look at a breaking wave on a beach, they think of this star.”
“This particular binary happened to be such that there is a companion coming from a large distance and getting really close,” says Loeb, which explains why the brightness changes so dramatically.
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