A burst of bright energy has been appearing at the edge of the Milky Way for the past 10 years, occurring every three hours and lasting about one minute. Astronomers believe they have found the source of the signal, but the discovery brought a new mystery—one they now claim to have solved.
A team of researchers from the Curtin node of the International Center for Radio Astronomy Research (ICRAR) first detected the radio signal while analyzing archived data from the Murchison Widefield Array (MWA), a radio telescope located in Western Australia. The energy pulse is the longest radio wave ever detected, with most signals appearing on time scales between tens and thousands of seconds.
Long-period radio waves are new, and a few have just been discovered. Celestial objects with a changing magnetic field, such as the Sun or Jupiter, can generate radio waves. Those on shorter time scales are known as radio transients—sudden, short-lived bursts of energy emission typically produced by rotating neutron stars (the collapsed core of a dead star).
“Long-term transients are very interesting, and for astronomers to understand what they are, we need a visual image,” said Natasha Hurley-Walker, associate professor at ICAR, and lead author of the paper on the published discovery. The Astrophysical Journal Letters, said the statement. “However, if you look around them, there are a lot of stars that lie in the same way 2001: A Space Odyssey. ‘My God, it’s full of stars!’
Fortunately, the newly discovered radio, GLEAM-X J0704-37, was not hidden behind the stars. Instead it was discovered at the edge of the Milky Way about 5,000 light-years away in the constellation Puppis, the least dense region of the galaxy. “Our new discovery is far from the Galactic Plane, so there are few stars nearby,” added Hurley-Walker.
With a clear view of the signal, the team that made this discovery used the MeerKAT telescope in South Africa to pinpoint the location of the radio waves in one particular star. Using another telescope, the SOAR observatory in Chile, the researchers then measured the spectrum of the star, and found it to be an M dwarf star, also known as a small red star.
Although the team solved one mystery by finding the source of the signal, another mystery now remains. “The IM dwarf alone could not produce the amount of energy we see,” Hurley-Walker said. “M dwarfs are very small stars with only half the size 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.”
Instead, the data suggested that the M dwarf was associated with another type of star, the two working together to produce a transient radio frequency. The IM dwarf is probably in a binary system with a white dwarf—the remnants of a star that has exhausted its nuclear energy and shed its outer layers. “Together, they have the power to emit radio,” Hurley-Walker said.
Although the MWA data archive showed that the time relay radio was active for 10 years, it may have been emitting bursts of energy for a much longer period of time that had not been detected. The team behind this discovery wants to make observations of GLEAM-X J0704-37’s follow-up, and analyze the data to find some long-term transients. There may be many strange cosmic sources that are pulling energy around the universe.
