Indian-led team discovers two dead stars spiralling inward at record speed
Record-Breaking Binary Stars Detected in Rapid Descent
Bharatmorningnews.com – An international research group, spearheaded by scientists at the Inter-University Centre for Astronomy and Astrophysics in Pune, has uncovered a remarkably tight pair of white dwarfs. These stellar remnants circle each other in just six minutes while drawing closer at a pace surpassing nearly all comparable systems. This finding positions the pair as a prime candidate for upcoming space-based gravitational wave detectors.
Tracing Orbital Evolution
Originally cataloged during the SRG eROSITA all-sky survey, the binary system carries the designation eRASSU J060839.5-704014, or simply eRASSU J0608. Rahul Sharma and professor Chandreyee Maitra directed the newest investigation, which combined data from NASA’s NICER instrument, the Chinese Einstein Probe mission, and historical XMM-Newton observations. By analyzing these records over a span of three and a half years, the team tracked how the binary’s orbit changed. Their findings appeared in The Astrophysical Journal Letters on August 10.
Understanding the Compact Pair
When Sun-like stars consume their nuclear fuel and eject outer layers, they leave behind dense, burned cores called white dwarfs. Despite being roughly Earth-sized, these remnants hold significant stellar mass. Within eRASSU J0608, two such objects form an ultracompact binary, completing each revolution in 374 seconds. Scientists consider such brief-period double white dwarf configurations to be among the tightest known binaries, representing a crucial yet short-lived phase in stellar development.
Researchers suggest the stars sit so near each other that material transfers directly from one to the other rather than settling into a standard accretion disc. Called direct-impact accretion, this mechanism raises the receiving star’s surface temperature beyond one million degrees Celsius. The result is a luminous, rhythmic X-ray emission that cycles every 374 seconds.
Rapid Orbital Decay and Gravitational Waves
The orbit of eRASSU J0608 is contracting at an unusually swift pace. Measurements show its orbital decay exceeds rates seen in two other famous ultracompact white dwarf pairs: HM Cnc and V407 Vul. This swift loss of orbital energy and angular momentum likely stems mainly from gravitational waves—ripples in spacetime generated by moving massive bodies. As gravitational radiation drains energy, the stars approach each other, causing their mutual orbit to accelerate.
By calculating the orbital decay rate, scientists determined the system’s combined chirp mass, which indicates gravitational wave signal strength. At approximately 0.43 solar masses, eRASSU J0608 ranks among the heavier members of its category.
A Future Verification Source
The swift and predictable progression of eRASSU J0608 makes it an excellent prospect for gravitational wave detection. The European Space Agency’s Laser Interferometer Space Antenna (LISA), slated for launch within the coming decade, aims to capture low-frequency gravitational waves from compact binaries like this one. Systems with forecastable signals hold special value as verification sources for space-based observatories.
“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,” said Rahul Sharma, the study’s lead author and a post-doctoral fellow at IUCAA.
“The observations indicate that eRASSU J0608 may be among the most massive and rapidly evolving ultracompact white dwarf binaries currently known. Its rapid orbital evolution, that makes it a promising verification source for future Space-based gravitational wave observatories such as LISA,” added Prof. Chandreyee Maitra.
The research team intends to keep watching the system with X-ray telescopes while searching for a visible light counterpart. These additional observations could refine distance and mass calculations and enhance predictions for gravitational wave signals that future missions might record.
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