The light from stars isn’t steady, instead it tends to pulsate. This is usually uniform across the whole surface of the star, but now astronomers have discovered an object that only pulses on one side. That’s thanks to its teardrop shape, as a close binary companion pulls it out of whack.
Known as HD74423, the star in question is about 1.7 times the mass of the Sun and sits about 1,500 light-years from Earth. But it’s not alone out there – HD74423 is accompanied by a red dwarf, and the two stars orbit each other in less than two days.
This tight orbit creates a gravitational attraction between the two stars, which is pulling HD74423 into a teardrop shape. And that seems to be making the larger star pulsate in an unexpected pattern.
“Stars that pulsate have been known in astronomy for a long time,” says Zhao Guo, an author of the study. “The rhythmic pulsations of the stellar surface occur in young and in old stars, can have long or short periods, a wide range of strengths, and different causes. There is however one thing that, until now, all of these stars had in common: The oscillations were always visible on all sides of the star.”
But that’s not the case with HD74423 – it appears to pulse only on one side. Astronomers discovered this when they noticed that the spikes and troughs of the pulses lined up perfectly with the star’s rotation time.
"Stars in close binaries can have a teardrop-like shape, so we see different cross-sections of the star at different times," says Guo. “This is how we could be certain that the pulsations were only found on one side of the star, with the tiny fluctuations in brightness always appearing in our observations when the same hemisphere of the star was pointed towards the telescope.”
The researchers say that the observation of this phenomenon is the culmination of decades of hypothesis. As far back as the 1940s it was suggested that a close companion could affect a star’s pulse timings, while the idea that it could push the pulsations onto just one hemisphere has been around since the 1980s. This marks the first direct observation, and the team says that it’s most likely a common occurrence.
The research was published in the journal Nature Astronomy.
Sources: University of Sydney, Pennsylvania State University