This pair of white dwarf stars orbit each other at record-breaking speeds

Astronomers have observed two stars orbiting each other every seven minutes, making them the fastest eclipsing white dwarf binary system ever discovered. As they move around each other at such great speeds, the stars are expected to be a strong source of gravitational waves which could be observed using space-based gravitational wave detectors.

The binary system is called ZTF J1539+5027 (J1539 for short) and its two stars are nearing the end of their lives. They have shrunk down to become dense white dwarfs, rotating around each other in a dramatic ballet, orbiting each other so closely that the whole system could fit inside the planet Saturn.

The discovery is noteworthy because white dwarfs in pairs are expected to be strong emitters of gravitational waves, but few have been discovered so far. This means the J1539 system could be used to test out gravitational wave detectors like the upcoming LISA (Laser Interferometer Space Antenna), the space-based cousin to the LIGO detector.

white dwarf fast binary system image 7429 ztf j1539 5027 1
An artist’s impression of a pair of orbiting white dwarfs, ZTF J153932.16+502738.8. Caltech / IPAC

Part of the discovery was made with a remarkably old piece of equipment: the 2.1-meter telescope at Kitt Peak National Observatory, which has been in continuous operation since 1964. The findings began with the powerful Zwicky Transient Facility (ZTF), a survey using the 48-inch telescope at Palomar Observatory, which surveys the sky for interesting celestial objects every night. When the ZTF finds something of note, it is passed to other instruments like the 55-year-old telescope at Kitt Peak.

The telescope at Kitt Peak was recently upgraded with an instrument called the Kitt Peak 84-inch Electron Multiplying Demonstrator (KPED) which identifies short-period eclipsing binaries. NSF Program Officer Chris David said the observations were “further proof that cutting-edge science can be done on modest-sized telescopes like the 2.1-meter in the modern era.”

Astronomers were able to find the J1539 system by investigating a distinctive blinking pattern caused by the movements of the stars around each other. “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,” Caltech graduate student Kevin Burdge explained in a statement.

The findings are published in the journal Nature.

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