2 Dead Stars Are Locked in a Timeless Embrace

They may have danced together for millions of years, but eventually, these stars will become one. Jakub Grygier/Shutterstock

These stars have only ever known each other.

When they first formed millions of years ago, they were a pair. They went through awkward adolescence together, their bodies turning orange and ballooning outward as red giants.

And together, they burned through all their precious life fuel, the process of nuclear fusion that powers every star.

They became white dwarfs — their outer layers fading, their cores hardening, and their radiant days essentially behind them.

But their relationship still somehow burns brightly. They remain locked in a timeless, even feverish, embrace.

At least that's the picture scientists paint of a newly discovered pair of dead stars orbiting each other so closely that they fully twirl around one another in just seven minutes.

A peculiar blinking pattern

The companions, dubbed ZTF J1539+5027 are described this week in the journal Nature.

The study's lead author, Kevin Burdge, noted the pair after sifting through data from the California Institute of Technology's Zwicky Transient Facility (ZTF). The Caltech physicist spotted a peculiar blinking pattern suggesting one star was frequently passing in front of another. After following up with a glimpse through the Kitt Peak telescope in the Arizona-Sonoran desert, he confirmed this peculiar binary star system.

"As the dimmer star passes in front of the brighter one, it blocks most of the light, resulting in the seven-minute blinking pattern we see in the ZTF data," Burdge explained in a release.

Their orbital period — 6.91 minutes, to be exact — is the shortest ever detected for an eclipsing binary. Indeed, both stars could fit comfortably in a space the size of Saturn.

That’s not to say these stars, which smolder some 8,000 light-years away, are twins. While one star is bigger, the other burns much hotter at around 50,000 degrees Celsius. That's 10 times the heat produced by our own sun.

"It's a really weird binary and that's part of the reason we found it," Burdge told Space.com.

But will they ever consummate their quirky relationship? Binary stars, like this pair, are constantly shortening their orbit, edging ever closer to becoming one. In fact, researchers estimate ZTF J1539+5027 draws in its orbit by about 10 inches every day. That gives them another 130,000 years before the dance becomes a death spiral. Once their orbit reaches a critical point — likely around five minutes — the denser, primary star won't so much kiss as consume its partner.

And then a couple of stars that spent their whole lives together will become one.

An illustration of a binary star system.
Two stars orbiting each other make up a binary star system. Catmando/Shutterstock

We'll know more about these celestial consorts by the gravitational waves — disturbances in the fabric of spacetime — they emit. But that will take some time as the Laser Interferometer Space Antenna, or LISA, doesn't launch until 2034.

But then it won’t take long for the new gravitational wave-sniffing equipment to tell us more about these incredibly intimate stars.

"Within a week of LISA turning on, it should pick up the gravitational waves from this system. LISA will find tens of thousands of binary systems in our galaxy like this one, but so far we only know of a few. And this binary-star system is one of the best characterized yet due to its eclipsing nature," study co-author Tom Prince noted in the statement.

Until then, we can only squint at these whirling white dwarfs through a telescope and perhaps take comfort in knowing that some star-crossed love affairs last forever.

Or at least until someone gets hungry.