Astronomers have discovered a pair of stars with an orbit so short they seem to orbit each other in just 51 minutes.
The system appears to be part of a rare class of binaries known as the “Cataclysmic Variable”, in which a star similar to our sun orbits closely around a white dwarf – a hot, dense core of a scorched star.
A cataclysmic variable occurs when the two stars come together, over billions of years, causing the white dwarf to accrete or eat material away from its partner star.
This process can emit huge, variable flashes of light that centuries ago astronomers assumed were the result of an unknown cataclysm.
The “cataclysmic” system, which resides about 3,000 light-years from Earth in the constellation of Hercules, has the shortest orbit of its kind detected to date.
It was discovered by astronomers at MIT and named ZTF J1813+4251.
Astronomers have discovered a pair of stars with an orbit so short they seem to orbit each other in just 51 minutes. The system is known as a cataclysmic variable, which occurs when two stars come together, over billions of years, causing the white dwarf to accrete or eat material away from its partner star (as pictured above)
Unlike other such systems seen in the past, the experts detected this cataclysmic variable as the stars eclipsed multiple times, allowing the team to precisely measure the properties of each star.
They then ran simulations of what the system is likely to do today and how it is expected to evolve over the next few hundred million years.
This led the researchers to hypothesize that the stars are currently in transition and that the sun-like star is spinning around and “donating” much of its hydrogen atmosphere to the voracious white dwarf.
Over time, astronomers say the sun-like star will eventually shrink to a mostly dense, helium-rich core.
In another 70 million years, the stars will migrate even closer to each other, with an ultrashort orbit reaching just 18 minutes, before they begin to expand and move away.
Decades ago, researchers at MIT and elsewhere predicted that such cataclysmic variables would transition to ultrashort orbits — but this is the first time such a transition system has been directly observed.
“This is a rare case where we caught one of these systems transitioning from hydrogen accretion to helium,” said Kevin Burdge of MIT’s Department of Physics.
“People have predicted that these objects should transition to ultrashort orbits, and there has long been debate about their ability to become short enough to emit detectable gravitational waves. This discovery puts an end to that.
Burdge and his colleagues discovered the new system in a large catalog of stars, observed by the Zwicky Transient Facility (ZTF), a survey that uses a camera attached to a telescope at the Palomar Observatory in California to take high-resolution photos. wide swathes of the sky.
The survey took more than 1,000 images of each of the more than a billion stars in the sky, recording how each star’s brightness changes over days, months and years.
Burdge scoured the catalog for signals from systems with ultrashort orbits, whose dynamics can be so extreme that they should emit spectacular bursts of light and emit gravitational waves.
These appeared to flash repeatedly, with a period of less than an hour – a frequency that typically signals a system of at least two objects in close orbit, one passing each other and briefly blocking its light.
The discovery was made by the Zwicky Transient Facility (ZTF), which operates at Caltech’s Palomar Observatory, with help from the WM Keck Observatory in Hawaii (pictured)
Burdge used an algorithm to weed out over a billion stars, each of which was recorded in over 1,000 images, and ultimately centered on ZTF J1813+4251.
“This thing appeared, where I saw an eclipse happening every 51 minutes, and I said, okay, that’s definitely binary,” Burdge said.
He and his colleagues then focused on the system using the WM Keck Observatory in Hawaii and the Gran Telescopio Canarias in Spain.
They discovered that the first object was probably a white dwarf, 1/100th the size of the sun and about half its mass.
The second was a sun-like star near the end of its life, one-tenth the size and mass of the sun (about the size of Jupiter).
However, something didn’t quite fit.
“This star looked like the sun, but the sun can’t go into an orbit of less than eight hours – what’s going on here?” said Burge.
He realized that ZTF J1813+4251 was likely a cataclysmic variable – a finding that means it is the shortest-orbit cataclysmic variable detected to date.
“It’s a special system,” Burge added. “We’ve been doubly lucky to find a system that answers a big open question and is one of the most admirably known cataclysmic variables.”
The discovery was published in the journal Nature.
