Indian-led study finds one of the fastest shrinking star systems yet

According to Dr Sharma, a post-doctoral fellow at IUCAA, the system is spiralling inward so quickly that it stands out even among the most extreme examples we know of. “These systems are an important new laboratory for studying a fleeting phase in the evolution of the most compact stellar binaries,” he said.

According to Prof Maitra, the measurements indicate that eRASSU J0608 may be among the most massive and rapidly evolving ultracompact white dwarf binaries currently known. Its rapid orbital evolution also makes it a promising verification source for future space-based gravitational-wave observatories such as LISA.

According to an official statement issued on Tuesday, the system, originally discovered with the SRG eROSITA all-sky survey, is known as eRASSU J060839.5–704014 (or “eRASSU J0608” for short). The two stars circle each other once every six minutes. Their orbit is decaying faster than almost any other known system of its kind.

White dwarfs are what remain after a Sun-like star exhausts its nuclear fuel and sheds its outer layers. What’s left is an extremely dense core roughly the size of Earth but packing the mass of a star. When two white dwarfs end up orbiting each other at very close range, they form what astronomers call an “ultracompact“ binary system.

The orbit is so tight that a complete orbit can take just minutes rather than years. These double white-dwarf systems with such extraordinarily short periods are among the most compact binaries known. They are thought to be passing through a brief, special stage of stellar evolution, one where gravitational waves strongly influence their orbital motion.

Some of these binaries are possible progenitors of certain types of supernova explosions. Studying how they lose orbital energy over time helps astronomers understand the physics of extremely compact binaries in general. eRASSU J0608 is one of the most extreme examples known. By combining new observations from the NICER and Einstein Probe missions with earlier data from the XMM-Newton observatory, the team precisely tracked the system’s orbit over a baseline of three and a half years. They found that it is shrinking exceptionally rapidly.