PUNE, Aug. 14 -- An international team led by astronomers from the Inter-University Centre for Astronomy and Astrophysics (IUCAA) Pune, has identified an extraordinarily compact pair of white dwarfs that orbit each other once every six minutes and are spiralling towards one another at a rate faster than almost any other known system of the kind. The discovery could provide an important target for future Space-based gravitational wave observatories. The system known as eRASSU J060839.5-704014 (eRASSU J0608) was originally discovered through the SRG eROSITA all-sky survey. The latest study, led by Rahul Sharma and professor Chandreyee Maitra, used observations from the Chinese-led Einstein Probe mission and NASA's NICER telescope along with earlier observations from the XMM-Newton observatory to track the binary's orbital evolution over three-and-a-half years. The study was recently published on August 10 in The Astrophysical Journal Letters. White dwarfs are dense, burnt-out cores left behind when Sun-like stars exhaust their nuclear fuel and shed their outer layers. Although roughly the size of Earth, a white dwarf can contain a substantial fraction of the mass of a star. In eRASSU J0608, two such stellar remnants are locked in an ultracompact binary system, completing an orbit in just 374 seconds or about six minutes. Such extremely short-period double white dwarf systems are among the most compact binaries known and are believed to represent a brief and important stage of stellar evolution. Astronomers believe the two white dwarfs are so close that material from one star may be flowing directly onto the surface of its companion instead of first forming a conventional accretion disc. This process, known as direct-impact accretion, heats the receiving star's surface to temperatures exceeding one million degrees Celsius producing a bright, pulsing X-ray signal that repeats every 374 seconds. The team found that the system's orbit is shrinking exceptionally rapidly. Its measured rate of orbital decay is greater than that observed in two other well-known ultracompact white dwarf binaries, HM Cnc and V407 Vul. The rapid loss of orbital energy and angular momentum is most likely being driven primarily by gravitational waves ripples in Spacetime produced by the motion of massive objects....