Meet AR Scorpii, a star system located about 380 light-years from Earth. It’s a binary star system made up of a white dwarf and a red dwarf orbiting each other every 3.6 hours. Astronomers estimate the white dwarf is about the size of Earth, but with 200,000 times more mass. Its red dwarf companion is about one-third the mass of the Sun.

What makes AR Scorpii unique is the entire system pulses (brightens and fades) nearly every two minutes.

Did You Know: AR Scorpii’s white dwarf used to be a star up to 8 times more massive than our Sun. Once it uses up all of its nuclear fuel at its core, it expands into a red giant. The dramatic expansion is followed by an equally dramatic contraction. The star’s outer layers rip off in huge clouds of dust and gas. All that’s left is a white dwarf. An Earth-sized star. What it lacks in size, it makes up for in density. According to the ESO, if you could dip a spoonful of white dwarf matter, it would weigh as much as an elephant on Earth.

“AR Scorpii was discovered over 40 years ago, but its true nature was not suspected until we started observing it in 2015,” said lead researcher Tom Marsh. “We realized we were seeing something extraordinary within minutes of starting the observations.”

How can an entire star system pulse with intense radiation ranging from ultraviolet to radio at consistent intervals? That white dwarf I mentioned above? It’s also highly magnetic and spins incredibly fast. Electrons are accelerated to nearly the speed of light. Couple that with the rapid spinning and the electrons release radiation in what the astronomers describe as a “lighthouse-like beam” across the face of the red dwarf star.

As this “lighthouse-like beam” hits the red dwarf, the entire star system dramatically brightness and then fades over the course of nearly two minutes.

The discovery of a pulsing binary star system is fascinating, but there’s also an air of mystery around it. Astronomers aren’t sure where the electrons responsible for the radiation are coming from. They know the white dwarf and its powerful magnetic fields can explain the fast moving electrons and the radiation emitted from them. But they’re not sure about the origins of the electrons themselves.

“We’ve known pulsing neutron stars for nearly fifty years, and some theories predicted white dwarfs could show similar behavior,” says co-author Boris Gänsicke. “It’s very exciting that we have discovered such a system, and it has been a fantastic example of amateur astronomers and academics working together.”

Finding and understanding AR Scorpii

ESO very large telescope

ESO’s Very Large Telescope

The binary star system was first spotted in the early 1970s. Back then, astronomers thought regular changes in brightness every 3.6 hours (which we now know is the orbital period for two stars) was caused by a lone variable star.

Fast forward 40 years and we now know much more about AR Scorpii. The team of astronomers from Germany, Belgium and the UK took advantage of several ground and space-based telescopes to observe the binary star system.

Check out the impressive hardware they used:

ESO’s Very Large Telescope in Chile.
The William Herschel and Isaac Newton Telescopes on La Palma (the Canaries).
The Australia Telescope Compact Array
NASA’s Hubble Space Telescope
NASA’s Swift satellite

You may not have heard of NASA’s Swift satellite. It observes the cosmos in gamma-ray. X-ray, ultraviolet and optical wavebands. Swift’s primary mission is to hunt down and determine the origin of gamma-ray bursts. It spots about 100 of them per year.


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