An unknown source has been sending radio signals to Earth since at least 1988, scientists say.
Researchers do not know what object is sending the radio waves to Earth. The nature of waves is such that they do not conform to any models that attempt to explain them.
For 35 years, the source sent out regular 20-minute bursts of energy that varied greatly in brightness, the researchers said.
The emissions look like bursts that come out of pulsars, or fast radio bursts that last from milliseconds to a few seconds. But the newly discovered source sends out radio signals that pulsate over a period of 21 minutes – something previously thought to be impossible according to expected explanations.
Pulsars are neutron stars that spin rapidly, throwing out radio emissions. As one traverses the Earth, the emissions can be picked up very briefly and brightly, as if you were in the path of light from a rotating beacon.
Scientists believe that this process can only work if the pulsar’s magnetic field is strong and it rotates fast enough – otherwise there wouldn’t be enough energy to see the pulsar from Earth. This led to the development of the “pulsar death line”, which suggests that the sources must be spinning rapidly and strongly enough to be detected.
However, the newly discovered object, named GPMJ1839-10, is far beyond that death line. If it is a pulsar, then it appears to be working in ways that scientists thought were impossible.
It may also be a highly magnetized white dwarf or magnetar, an additional type of neutron star with incredibly strong magnetic fields. But they are reluctant to send emissions of this kind, the researchers believe.
The signals have been detected on Earth since at least 1988, the scientists found, reviewing old records, but they had gone unnoticed by those collecting the data. After the source was discovered, the researchers checked the radio archives and found that the source had been repeating for at least 35 years.
Still, more discoveries could be made this way in the future, said Victoria M. Caspi, a professor of physics at McGill University who did not work on the study. “Only time will tell what else is hidden in these data and what observations on many astronomical time scales will reveal,” she wrote in an accompanying article.
This may include some explanation of how unusual the newly discovered source is. By examining whether there is a similar collection of other objects in the data, researchers may be able to understand the mechanisms behind the newly discovered emissions.
The findings are reported in a new paper, “Long-period radio transition active for three decades,” published in the journal Nature.