The universe has brought another surprise, and this time it's practically under our noses. Just 1,500 light years away, astronomers found a pulsating star, but only on one side.
Although such an object was predicted several decades ago, we first saw it.
“We know theoretically that such stars should have existed since the 1980s,” said astronomer Don Kurz of the University of Central Lancashire in the UK.
'I have been looking for such a star for almost 40 years, and now it has been found.'
The star is called HD74423, a type A main sequence star, about 1.7 times the mass of the Sun.
Its strange, pulsating behavior was first discovered by amateur astronomers studying data from NASA's exoplanet-hunting space telescope in search of anomalies.
Unsure of what they saw, they passed their results on to professional astronomers at the Copernicus Astronomical Center in Poland.
The pulsations inside the star are not unusual. Many stars – perhaps even all stars – oscillate in rhythmic patterns caused by waves bouncing inside the star. It is believed that these waves are created by convection and the magnetic field of the star; just as earthquakes can be used to probe the depths of the earth, waves can show what is happening inside stars.
Star HD74423. (Gabriel Pérez Díaz / IAC)
But in all other stars prior to HD74423, these oscillations were detected globally; that is, over the entire surface of the star. So why is HD74423 different?
Well, she has a friend. A really close friend. The pulsating star's double companion is a red dwarf, and both are in super-rigid orbit. In this proximity, the gravity of the red dwarf distorts HD74423, pulling it out in the shape of an egg or droplet.
And it's not just the HD74423. The red dwarf's companion also distorts the oscillation of the larger star. This is what is causing the strange behavior.
“When binary stars orbit each other, we see different parts of a pulsating star,” said astronomer David Jones of the Canary Islands Astrophysics Institute in Spain. “Sometimes we see the side that points to the companion star, and sometimes the opposite.”
But that's not the only thing that's weird about the HD74423. As researchers began to investigate the object more closely, astronomer Simon Murphy of the University of Sydney in Australia noticed some unusual chemical properties.
“The first thing that caught my attention was that it was a chemically strange star,” Murphy said. 'Stars like this are usually quite rich in metals, but there is almost no metal in it, making it a rare type of hot star.'
Low metallicity is one of the defining characteristics of really old stars, but HD74423 is different. It is a type of chemically distinctive object known as the Boitis lambda star, and its low metallicity is believed to be a result of the star emitting metal-depleted gas.
“When there is such a revolution in data quality, you often see new phenomena,” Murphy said. “We could find many more of these targeting pulsation stars, but they are still quite rare. It's just that when you observe hundreds of thousands of stars, you can find super rare objects from time to time. '
Now that astronomers know what a star looks like in data, they can apply that knowledge to search archives.
Meanwhile, astronomers continue to work on HD74423. They are still collecting observations and working on a mathematical description of the behavior of the binary system.
The study was published in the journal Nature Astronomy.
