Astronomers have discovered a pair of stars with the shortest orbit yet discovered

Astronomers have discovered a pair of stars with such a short orbit that they appear to orbit each other in just 51 minutes.

The system appears to be one of a rare class of binaries known as “catastrophic variable,” in which a star similar to our Sun tightly orbits a white dwarf — the hot, dense core of a burning star.

The cataclysmic variant occurs when, over billions of years, the two stars get close, causing the white dwarf to start accumulating, or eating material away from the partner star.

This process can produce massive, variable flashes of light that astronomers assumed, centuries ago, were the result of an unknown cataclysm.

The “catastrophic” system, located about 3,000 light-years from Earth in the constellation Hercules, has the shortest orbit of its kind so far discovered.

It was discovered by astronomers at the Massachusetts Institute of Technology and named ZTF J1813 + 4251.

Unlike other systems observed in the past, experts discovered this cataclysmic variable as the stars dimmed each other several times, allowing the team to accurately measure the properties of each star.

Then they ran simulations of what the system likely does today and how it should evolve over the next hundreds of millions of years.

This led researchers to theorize that stars are currently in transition, and that the sun-like star is rotating and donating much of its hydrogen envelope to the insatiable white dwarf.

Over time, astronomers say, the sun-like star will eventually be stripped down to a dense, helium-rich core.

In another 70 million years, the stars will then migrate closer to each other, with an extremely short orbit of only 18 minutes, before they start expanding and drifting away.

Decades ago, researchers at MIT and elsewhere predicted that such catastrophic variables should travel to ultrashort orbits — but this is the first time such a transition system has been directly observed.

“This is a rare case where we discovered one of these systems during the transition from hydrogen to accumulating helium,” said Kevin Burdge, of the MIT Department of Physics.

People expected these objects to travel to ultrashort orbits, and it was debated for a long time whether they could get short enough to emit detectable gravitational waves. This discovery relieves that.

Burdge and colleagues discovered the new system within an extensive catalog of stars, spotted by the Zwicky Transient Facility (ZTF), a survey that uses a camera attached to a telescope at Palomar Observatory in California to capture high-resolution images of large swaths of the sky.

The survey took more than 1,000 images of each star from more than a billion stars in the sky, recording each star’s variable brightness over days, months and years.

Burdge combed the catalog, looking for signs of systems with ultrashort orbits, whose dynamics can be so intense that they must release dramatic bursts of light and emit gravitational waves.

These appear to flash frequently, with a period of less than an hour – a frequency usually referring to a system of at least two objects orbiting each other, where one intersects the other and briefly blocks its light.

The discovery was made by the Zwicky Transit Facility (ZTF), which operates at Caltech’s Palomar Observatory, with help from the WM Keck Observatory in Hawaii (pictured)

Bridge used an algorithm to weed out more than a billion stars, each recorded in more than 1,000 images, that were eventually identified on ZTF J1813+4251.

“This thing showed up, where I saw an eclipse that happens every 51 minutes, and I said, OK, that’s definitely a binary,” said Bridge.

He and his colleagues focused on the system using the WM Keck Observatory in Hawaii and the Gran Telescopio Canarias in Spain.

They found that the first object was likely a white dwarf, 1/100th the size of the Sun and about half its mass.

The second was a sun-like star towards the end of its life, the size and mass of a tenth of the sun (about the size of Jupiter).

However, there is something that does not add anything.

“This star is like the sun, but the sun can’t fit into an orbit shorter than eight hours – what’s up here?” Bridge said.

He realized that ZTF J1813+4251 was most likely a catastrophic variable—a discovery that means it’s the shortest orbital catastrophic variable discovered to date.

“This is a special system,” Bridge added. We were doubly lucky to find a system that answers a big open question, one of the most beautifully behaved catastrophic variables known.

The discovery was published in the journal temper nature.