A white dwarf star in a binary star system is siphoning material from its “companion” and orbits it at an extremely close distance.
Discovered in images captured by the ZTF camera at the Palomar Observatory in California, the binary star system named ZTF J1813 + 4251 is located approximately 3,000 light-years from Earth. It consists of a white dwarf star and the remnants of a red giant star orbiting each other every 51 minutes, Space reported on October 7.
Simulation of a white dwarf devouring a red giant star. (Image: Mark Garlick)
ZTF J1813 + 4251 is a prime example of a cataclysmic variable star, where the gravitational pull of the white dwarf is strong enough to “steal” gaseous material from the hydrogen envelope surrounding its companion star. This gas then forms a bridge between the two celestial bodies and is eventually pulled onto the surface of the white dwarf.
As the density of the accumulated material increases, it ignites in a thermonuclear explosion known as a nova. This event is not powerful enough to destroy the star and occurs periodically, causing the system to brighten unexpectedly before returning to a quiescent state, hence the name “cataclysmic variable star.”
Astronomer Kevin Burdge from the Massachusetts Institute of Technology utilized an algorithm to search for cataclysmic variable star systems through images of a billion stars captured by the ZTF instrument. The ZTF J1813 + 4251 system stands out as it is also a flashing binary system, meaning that as the two stars orbit each other, one star passes in front of the other, dimming its brightness, causing the system to flash periodically in accordance with the stars’ orbital period.
Burdge and his team employed the WM Keck Observatory in Hawaii and the Gran Telescopio Canarias in the Canary Islands to accurately measure the mass, radius, and orbital period of the star system.
“The 51-minute orbital period is the shortest ever observed for cataclysmic variable star systems,” the study emphasizes.
As the two stars of ZTF J1813 + 4251 move closer together, the white dwarf begins to consume its companion. This companion star is an aging sun-like star that has evolved into a red giant. Its outer hydrogen layers swell and become vulnerable to being siphoned off by the white dwarf. Over millions of years, a significant amount of hydrogen gas has been stripped from the red giant, exposing its helium-rich core.
The two stars are predicted to continue drawing closer over the next 70 million years, with their orbital period gradually decreasing until they orbit each other in just 18 minutes. After that point, when the accretion process halts due to the depletion of available gas, both stars will slowly drift apart.
