The universe does not stop giving us surprises. For the first time, an international team of astronomers has discovered a star that pulses on only one side . Although it had certainly been predicted decades ago, we hadn’t seen any until now. The star is about 1,500 light years distant from Earth and is about 1.7 times the mass of our Sun.
“Theoretically we have known that stars like this should have existed since the 1980s, ” said astronomer Don Kurtz of the University of Central Lancashire (UK). “I’ve been looking for a star like this for almost 40 years and now we’ve finally found one.”
Christened HD74423, it is a type A main sequence star younger than our Sun.
A pulsating teardrop star
Its bizarre behavior was first observed by citizen scientists scrutinizing data from NASA’s TESS exoplanet hunting space telescope, looking for anomalies. Not quite sure what they found, they turned to professional astronomers.
Is it something unusual?
Not really . Many stars have large and small pulsations, caused by waves bouncing off the star. These waves are believed to be created by convection and the star’s magnetic field. What is peculiar in this case is that the star only pulses on one side.
“What first caught my attention was the fact that it was a chemically strange star,” explained Simon Murphy of the Sydney Institute of Astronomy at the University of Sydney and a co-author of the paper published in the journal Nature. “Stars like this are usually quite metal-rich, but this one is metal-poor, so it’s a rare type of hot star.”
Low metallicity is one of the defining characteristics of older stars but HD 74423 is different . It is a chemically peculiar type of object known as a Lambda Boötis star, and its low metallicity is believed to be the result of the star extracting metal-depleted gas from its closest environment.
What causes it?
These tidal pulsations observed in a single hemisphere are due to the presence of a stellar companion close to HD 74423: a red dwarf that orbits the star every 39 hours (1.6 days) and is so close to it that its gravity has changed. the shape of the star from a sphere to a teardrop, trapping the pulsations in only one half of the star.
” T he pulsation mode in HD 74423 is currently unique , but there must be a class of stars that have their pulsation axes aligned with their tidal axes, and this discovery is an impetus to look for more,” the authors wrote.
” We expect to find many more asymmetric stars hidden in the TESS data, ” added Saul Rappaport of the Massachusetts Institute of Technology. As always, better technology will help us uncover everything that until now remains hidden in plain sight.
Referencia: Tidally trapped pulsations in a close binary star system discovered by TESS, Nature Astronomy (2020). DOI: 10.1038/s41550-020-1035-1 , https://nature.com/articles/s41550-020-1035-1
