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 central development
The researchers plan to continue monitoring the system using X-ray telescopes and search for a visible light counterpart. Such observations could help determine its distance and masses more precisely and improve predictions of the gravitational wave signal that future missions may detect.
Rahul Sharma, lead author of the study and a post-doctoral fellow at IUCAA, said, “The system is spiralling inward exceptionally quickly even compared with other extreme binaries, making such systems important laboratories for studying a fleeting phase in the evolution of compact stellar binaries”.
How this developed
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. 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 measured rate of orbital decay also allowed the researchers to estimate the system’s combined chirp mass, a quantity that determines the strength of its gravitational wave signal.
The system known as eRASSU J060839.5-704014 (eRASSU J0608) was originally discovered through the SRG eROSITA all-sky survey. The study was recently published on August 10 in The Astrophysical Journal Letters. 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 estimated chirp mass is about 0.43 times the mass of the Sun, placing eRASSU J0608 among the higher mass systems known in this class.
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.
