A few years ago, a radio telescope operating in the Western Australian desert observed something very strange. Just 4,000 light-years away from Earth, something was emitting a bright radio signal unlike anything we’d ever seen: it glowed like a pulsar, but with a very long period of time between the pulses and an ultra-long pulse. At that time it was impossible to distinguish the nature of the source.

So astronomers began looking for an answer and found another, coming from 15,000 light-years away. It was also difficult to identify him in the crowded area where he came from.

Now they’ve found a third one, about 5,000 light-years away. This period has the longest period, emitting bursts of 30 to 60 seconds every 2.9 hours, and astronomers have narrowed down these strange emissions to a single source that may finally tell us what’s producing them: a small red dwarf star in a binary orbit. or even a smaller white dwarf star.

“Long-period transits are very exciting, and we need an optical image for astronomers to understand what they are. But when you look at them, there are so many stars it seems like 2001: A Space Odyssey “Oh my God, it’s full of stars!” said astrophysicist Natasha Hurley-Walker of the International Radio Centre’s Curtin University node. he says. Astronomical Research in Australia (ICRAR).

“Our new discovery is located far from the galactic plane, so there are only a few stars nearby, and we are now confident that one star system in particular is producing the radio waves.”

These events, called long-period transits, attracted great attention in 2022 when astronomers reported the detection of a pulsating signal in archived data from the Murchison Widefield Array (MWA), a powerful telescope operating at low radio frequencies. This satellite, named GLEAM-X J162759.5−523504.3, was recorded to emit radio waves for 30-60 seconds every 18.18 minutes until March 2018, when it stopped.

A second signal recorded in 2023 was detected during follow-up MWA observations. In a different but still crowded part of the sky, something has been found emitting five-minute bursts of radio waves every 22 minutes. Examination of archived data revealed that this institution had been active since at least 1988. It was GPM J1839-10.

One type of star that emits pulsating signals is a type of neutron star called a pulsar, which is the collapsed core of a massive star that goes supernova. Pulsars emit beams of radio waves as they rotate, so when we observe them they appear like flares; But pulsar explosions never happen that slowly and occur on time scales ranging from seconds to milliseconds.

A third signal, called GLEAM-X J0704-37, is also very similar. In archived data, MWA was also found to emit a signal lasting 30 to 60 seconds every 2.9 hours. But it is located in a much less cramped region of space, on the outskirts of the Milky Way in the southern constellation of the Doll.

This meant the researchers were better able to pinpoint the exact source of the signals. They used the MeerKAT radio telescope in South Africa to zoom in on the area of ​​sky where the signal came from and found only one faint star matching that location. Analysis of the star’s spectrum revealed its identity: an M-type red dwarf.

Red dwarfs are now legion in the Milky Way. They constitute the most numerous category of stars in the galaxy. If a regular red dwarf could just spit out the long-period radio emission we see from GLEAM-X J0704-37, we’d probably see it doing much more. This suggests something unusual in GLEAM-X J0704-37; It’s a hard thing to see. The team believes it is most likely a white dwarf left over from the destroyed core of a dead sun. These super-dense objects have a mass of up to 1.4 Suns, squeezed into a sphere somewhere between the Earth and the Moon.

“M-dwarfs are low-mass stars that have only a fraction of the mass and luminosity of the Sun. They make up 70 percent of the stars in the Milky Way, but none of them are visible to the naked eye,” says Gurley-Walker. “Our data shows that it is in a binary system with another object that is likely to be a white dwarf, the stellar core of a dying star. “Together they provide radio emissions.”

According to the team’s calculations, the binary system could consist of a red dwarf with a mass of about 0.32 times the mass of the Sun and a white dwarf with a mass of 0.8 times the mass of the Sun. If they orbit close enough, the white dwarf can collect material from the red dwarf; This process can lead to continuous beams of radiation from the poles of the white dwarf. We can’t see the rays, but when they hit the red dwarf they can cause it to burn up temporarily, as seen in Scorpii’s dual AR system.

The next step will be further observations in both radio and ultraviolet light to try to find direct evidence of the white dwarf’s existence. If confirmed, this would make GLEAM-X J0704-37 a white dwarf pulsar, one of the rarest types of stars in the Milky Way. The team’s research was published on: Astrophysics Journal Letters.