Astronomers have identified one of the most mysterious sources of radio signals in the Milky Way, a discovery that could shed light on a phenomenon that has puzzled researchers for years. It is about the so-called “long-period radio transients” (LPT), strong radio pulses that repeat at unusually long intervals, from minutes to hours.
So far, only a few such objects have been identified in the Milky Way, and their origin has remained a mystery. Explanations proposed over time have ranged from extremely slowly rotating neutron stars to binary systems consisting of a white dwarf and a companion star. However, none has been fully confirmed.
An international team led by researchers from the University of Sydney now claims to have found the most solid answer yet, according to material published by Wired.
An extremely compact star system
Using the Australian Square Kilometer Array Pathfinder (ASKAP) radio telescope, researchers studied an object cataloged as ASKAP J174508.9-505149, known for short as ASKAP J1745-5051.
“For the first time we have identified the origin of these signals,” said Kovi Rose, a PhD student at the University of Sydney’s School of Physics. “We were able to demonstrate that the source of one of these phenomena is a white dwarf that is actively pulling matter from its companion star.”
ASKAP J1745-5051 is a system of two extremely close stars: a white dwarf and a red dwarf. A white dwarf is the core left over from the death of a Sun-like star. Although it is comparable in size to Earth, its mass is close to that of the Sun. The companion star is a red dwarf with a mass about one-tenth that of the Sun. The two revolve around each other and complete their orbit in just over an hour.
Radio signals and X-rays come from different places
Observations have shown that radio pulses and X-ray emissions are produced by different mechanisms. The matter attracted by the white dwarf from the companion star is strongly heated and emits X-rays. However, the radio pulses appear in the region where the magnetic fields of the two stars interact. The fact that the radio and X-ray emission peaks do not coincide suggests that they are generated in different areas of the system.
The Chinese Academy of Sciences’ Einstein Probe satellite detected X-ray emissions that repeat every 1.32 hours. According to the researchers, the strong variations in these emissions suggest that the rate at which the white dwarf is accreting matter is not constant.
The first time we see the whole picture
ASKAP J1745-5051 is only the third LPT-type object also detected in X-rays, and the first for which the periodicity of the signals has been confirmed to originate from the orbital motion of a binary system, rather than some other mechanism.
The radio signal also has some quirks. The pulses are elliptically polarized and their intensity varies in a banded pattern (a phenomenon called “modulation lanes”) observed so far only in the Jupiter-Io system, never in a binary star system.
The “Rosetta Stone” for mysterious signals from space
Researchers believe that ASKAP J1745-5051 could become the key to deciphering other similar sources. Kovi Rose compares it to the Rosetta Stone, the artifact that opened the way to understanding Egyptian hieroglyphs.
“This object could help us understand these signals and determine whether other similar sources are related to neutron stars or white dwarf systems,” he explained.
Tara Murphy, head of the Department of Physics at the University of Sydney, points out that this is the first time researchers can see the whole mechanism: “Similar objects have been associated with binary systems, but this is the first case where we clearly see both stars and the process of accreting matter actually unfolding.”
Systems like ASKAP J1745-5051 can function as natural cosmic laboratories for studying matter subject to extreme magnetic fields and gravitational forces, conditions impossible to reproduce on Earth. The team plans to continue observations at multiple wavelengths: radio, optical and X-ray, to understand what triggers these signals.
