Indian astronomers find dead stars spiralling in six-minute orbit

Discovery of a cosmic clockwork

An international team led by Indian astronomers has discovered a pair of dead stars locked in a remarkably tight orbital dance. The two compact objects, likely white dwarfs, complete a full revolution around each other every six minutes — one of the fastest known orbits for such a system.

The finding, published recently, reveals that the stars are spiralling inward at a rate that makes them a prime target for studying gravitational waves, ripples in spacetime first predicted by Albert Einstein over a century ago.

What are dead stars?

Dead stars are the collapsed remnants of once-active suns. When stars like our Sun exhaust their nuclear fuel, they shed their outer layers, leaving behind a dense core known as a white dwarf. A teaspoon of white dwarf material would weigh several tonnes on Earth.

In this system, two such remnants are caught in a gravitational embrace, orbiting so closely that their combined mass distorts the fabric of space around them. This distortion generates gravitational waves, which carry away orbital energy and cause the stars to draw nearer to each other over time.

Rapid inward spiral

The team measured the orbital period decay — the rate at which the stars are closing in on each other. The results show a dramatic shrinkage, with the orbital period decreasing by several milliseconds each year. This rapid inspiral is a direct consequence of gravitational wave emission, making the pair a natural laboratory for testing general relativity.

According to the researchers, the system will eventually merge, producing a powerful explosion or a larger compact object. However, that event is likely millions of years away, giving scientists ample time to study its evolution.

Significance for gravitational wave astronomy

Gravitational waves from such compact binaries are expected to be detectable by future space-based observatories like the Laser Interferometer Space Antenna (LISA), a project led by the European Space Agency with NASA involvement. The Indian team's work provides a precise model for what these observatories might see.

“This system is a one-of-a-kind laboratory,” said a co-author from the team. “It allows us to measure how gravity behaves in the most extreme conditions we can observe.”

The discovery also highlights the growing role of Indian institutions in cutting-edge astrophysics. The team used data from ground-based telescopes and archival surveys to identify and characterise the binary.

What lies ahead

Astronomers will now monitor the system closely, refining their estimates of its mass and orbital parameters. The next few years could see more such discoveries, as surveys like the Zwicky Transient Facility and the upcoming Vera C. Rubin Observatory scan the skies for similar compact binaries.

For now, the pair of dead stars serves as a reminder that even the most inert objects in the universe can hold dynamic secrets — and that the study of their death throes can illuminate the fundamental laws of physics.