'Cosmic vampire': ESA's Einstein Probe discovers two stars eating each other
Produced by Tarun Mishra
Produced by Tarun Mishra
On 27 May 2024, astronomers using the Chinese-European Einstein Probe observed a powerful X-ray flash from a nova explosion in the Small Magellanic Cloud. This event was traced to a binary star system containing a white dwarf and a massive Be star.
The system presents an unusual puzzle: the white dwarf originates from a sun-like star, which should take billions of years to evolve, while its Be star companion, with 12 times the mass of the Sun, should have exploded as a supernova within 20 million years. Their coexistence challenges standard stellar evolution models.
Scientists propose that the system initially contained two stars of six and eight solar masses. The more massive star exhausted its fuel first, expanded into a giant, and transferred mass to its smaller companion. This transfer caused the less massive star to grow into the present 12-solar-mass Be star while the original massive star shrank into a 1.23-solar-mass white dwarf.
The white dwarf is now reclaiming material from its massive companion. As this matter accumulates on the white dwarf’s surface, the pressure and temperature increase, leading to periodic thermonuclear explosions—novae that emit X-ray bursts like the one detected by Einstein Probe.
Astronomers highlight that this system offers a rare look into the intermediate stages of stellar evolution. The findings provide new insights into how binary systems evolve through complex mass exchange, shaping their ultimate fates.
The ongoing mass transfer has altered the evolutionary paths of both stars. The 12-solar-mass Be star is now destined to end its life in a supernova, while the white dwarf may also undergo a Type Ia supernova if it continues accreting mass and reaches the Chandrasekhar limit of 1.44 solar masses.
The system’s future depends on which star undergoes a supernova first. If the Be star explodes first, the white dwarf may survive. If the white dwarf accretes too much mass before then, it will self-destruct in a supernova. Astronomers will continue monitoring this system to understand the final outcome. The study was published in The Astrophysical Journal Letters on 18 February 2025.