Northwestern University scientists have detected the first radio pulses that can be traced to a dead-star binary. This was after astronomers detected constant stream of radio pulses emitted from across the galaxy. The stars’ orbit is so tight that their magnetic fields interact, causing the pulses.
This discovery marks the first radio pulse traced to a binary source. The readings began to be detected a decade ago when astronomers detected a pulse of radio emission every two hours, which was coming from the direction of the Big Dipper. However, the significance of the data was only realised last year.
The information was drawn from Low Frequency Array (LOFAR), the largest radio telescope operating at the lowest frequencies that can be observed from Earth. Follow-up observations were made at the Multiple Mirror Telescope (MMT) Observatory in Arizona and the McDonald Observatory in Texas. Those observations revealed the source was not one flashing star — but two stars pulsing together.
These additional observations allowed the scientists to track variations in the system’s movement and gain optical spectra from the red dwarf. By taking light emitted from a star and splitting it into its component colours (or spectra), the researchers were able to gain information about the star itself.
After combining observations from multiple telescopes, the researchers identified the point of origin: a binary system with a dead star. This is in the form of a red dwarf and white dwarf orbiting each other so tightly that their magnetic fields interact. Each time they ‘bump’ together — which is every two hours — the interaction emits a long radio blast.
Each radio pulse, a type of fast radio burst, lasts anywhere from seconds to minutes in length. The pulses also repeat at regular intervals, like a cosmic clock that ticks once every two hours.
This shows the movement of stars within a binary system also can emit long-period radio bursts, adding to previous findings that highly magnetized neutron stars exhibit radio pulses.
These stars are located just 1,600 lightyears from Earth. Both orbit a common centre of gravity, making a full revolution every 125.5 minutes.
Initially the spectroscopic lines showed the presence of a red dwarf, one moving back and forth very rapidly with exactly the same two-hour period as the radio pulses. It was realised that the “back-and-forth” motion was due to a companion star’s gravity, pulling the red dwarf around.
By precisely calculating the variation in these motions, the scientists measured the mass of the much fainter companion. The calculated mass aligned with the typical mass of a white dwarf. While white dwarfs can range from low- to medium-mass, red dwarfs are much smaller and cooler.
In the future, astronomers plan to study the ultraviolet emission of the binary source, dubbed ILTJ1101, in more detail. The findings could help determine the temperature of the white dwarf and reveal more about the history of white and red dwarfs.
The research paper appears in the journal Nature Astronomy and it is titled: “A white dwarf binary showing sporadic radio pulses at the orbital period.”
