Probe catches rare evidence of massive star evolution

European Space Agency announced on Wednesday that the Einstein Probe satellite has captured a rare X-ray flash from an unusual celestial pair, shedding new light on the interactions and evolution of massive stars.

"The discovery opens a new way to explore how massive stars interact and evolve, confirming the unique power of the mission to uncover fleeting X-ray sources in the sky," said Yuan Weimin, EP's principal investigator.

The discovery, made by the Widefield X-ray Telescope of EP, a space science satellite led by the Chinese Academy of Sciences, with participation from the ESA, the Max Planck Institute for Extraterrestrial Physics and the French National Centre for Space Studies, marks a significant breakthrough in understanding fleeting X-ray sources in the universe.

The celestial duo consists of a massive Be star, 12 times the mass of sun, and a white dwarf, a dense stellar remnant with a mass similar to the sun. This rare pairing, found in the Small Magellanic Cloud, a neighboring galaxy, was observed from its initial flare-up to its fading phase — a first for scientists.

On May 27 last year, the WXT detected X-rays from a new source, labeled EP J0052. Follow-up observations were conducted using EP's Follow-up X-ray Telescope, as well as NASA's Swift and NICER telescopes and ESA's XMM-Newton.

"We were chasing fleeting sources, when we came across this new spot of X-ray light in the SMC. We realized that we were looking at something unusual, that only Einstein Probe could catch," says Alessio Marino, a postdoctoral researcher at the Institute of Space Sciences, Spain and lead author of the new study published on Wednesday.

The data revealed that the white dwarf's intense gravity pulls material from its massive companion, triggering a nuclear explosion that emits a bright flash across multiple wavelengths, including X-rays.

"This study gives us new insights into a rarely observed phase of stellar evolution, which is the result of a complex exchange of material that must have happened among the two stars," said Ashley Chrimes, research fellow and X-ray astronomer at ESA.

"It's fascinating to see how an interacting pair of massive stars can produce such an intriguing outcome," he said.

"Outbursts from a Be-white dwarf duo have been extraordinarily hard to catch, as they are best observed with low energy X-rays. The advent of Einstein Probe offers the unique chance to spot these fleeting sources and test our understanding of how massive stars evolve," said Erik Kuulkers, ESA Project Scientist for Einstein Probe.

"This discovery showcases the game-changing capabilities of this mission," he said.

The EP mission, a global collaboration involving 300 researchers, continues to provide valuable data for the international scientific community.

"We hope the EP satellite will continue to drive advancements in high-energy time-domain astronomy," said EP's principal investigator Yuan, who is also a researcher at the National Astronomical Observatories, CAS.

This groundbreaking discovery not only showcases the power of the Einstein Probe, but also opens new avenues for exploring the dynamic lives of massive stars and their remnants, he said.

yandongjie@chinadaily.com.cn