First Pulsating White Dwarf Star Discovered in a Double Star System

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An ancient pulsating star in an eclipsing double-star system was recently discovered by researchers at the University of Sheffield. This discovery will enable the scientists to access crucial information relating to the history of how stars, such as the Sun, emerge and die ultimately.

For the first time, the discovery of the world’s first pulsating white dwarf star in an eclipsing binary by Sheffield physicists will allow the research team to comprehensively view the way the binary evolution had impacted the internal structure of a white dwarf.

A double star system, or an eclipsing binary, is composed of a pair of stars that orbit each other and intermittently pass in front of one another, as observed from the Earth.

When a star like the Sun dies, it leaves behind the burnt-out cores in the form of white dwarf stars. For the first time, this specific white dwarf could offer a significant understanding of the evolution, structure, and death of these stars.

It was believed that a majority of the white dwarfs are mainly made of oxygen and carbon; however, this specific white dwarf is mostly comprised of helium. The researchers believe that this outcome can be attributed to its binary companion that cut short its evolution before it had an opportunity to fuse the helium into oxygen and carbon.

The pulsations produced from this white dwarf star were identified with the help of an advanced high-speed camera called HiPERCAM. This camera was created by a research team headed by Professor Vik Dhillon from the Department of Physics and Astronomy at the University of Sheffield

The HiPERCAM is positioned on the 10.4-m Gran Telescopio Canarias (GTC), which happens to be the world’s largest optical telescope on La Palma. The camera can capture a single picture every millisecond concurrently in five different colors. This enabled the team to identify the slight but rapid pulsations produced by this specific white dwarf star.

The eclipsing binary system and the pulsations of the white small star allowed the researchers to study the structure of this star using two methods—that is, eclipse studies and asteroseismology. The latter method involves the measurement of the speed at which sound waves passing through the white dwarf star.

Determining what a white dwarf is made of is not straightforward because these objects have about half of the mass of the Sun, packed into something about the size of the Earth. This means that gravity is extremely strong on a white dwarf, around one million times larger than here on Earth, so on the surface of a white dwarf an average person would weigh about 60,000,000kg.

Dr Steven Parsons, Study Lead, Department of Physics and Astronomy, University of Sheffield

Dr Parsons continued, “The gravity causes all of the heavy elements in the white dwarf to sink to the centre, leaving only the lightest elements at the surface and so the true composition of it remains hidden underneath.”

This pulsating white dwarf we discovered is extremely important since we can use the binary motion and the eclipse to independently measure the mass and radius of this white dwarf, which helps us determine what it is made of. Even more interestingly, the two stars in this binary system have interacted with each other in the past, transferring material back and forth between them.

Dr Steven Parsons, Study Lead, Department of Physics and Astronomy, University of Sheffield

We can see how this binary evolution has affected the internal structure of the white dwarf, something that we’ve not been able to do before for these kinds of binary systems,” added Dr Parsons.

Going forward, the researchers will continue to view the white dwarf star to capture as many pulsations as possible using the Hubble Space Telescope and the HiPERCAM camera.

Source: https://www.sheffield.ac.uk/

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