Thanks to a new calibration technique, astronomers have achieved the first clear radio maps of the universe at low frequencies without disturbance of the Earth’s ionosphere.
The team, led by Leiden University, have used the new method to study plasmas from ancient black hole explosions. Potentially, the technique could be useful for finding exoplanets orbiting small stars.
The researchers report on their technique in the journal Nature Astronomy.
The technique allowed astronomers to take clear radio images of the universe for the first time at frequencies between 16 and 30 MHz. This was thought to be impossible because the ionosphere, about 80 kilometers above Earth, interferes with observations at these frequencies.
The researchers used the LOFAR telescope in Drenthe, the Netherlands. This is currently one of the best low-frequency radio telescopes in the world. To test their technique, they studied a series of galaxy clusters that until now had only been studied in detail at higher frequencies.
Thanks to the new images, it appears that the radio emission from these clusters is not evenly distributed throughout the cluster, but rather there is a patchy pattern. “It’s like putting on glasses for the first time and not seeing blurry anymore,” said research leader Christian Groeneveld of Leiden University.
The motivation for the research was that in recent years many improvements had already been made in calibration at high frequencies, around 150 MHz.
“We hoped to be able to extend this technique also to lower frequencies, below 30 MHz,” says the creator of the idea, Reinout van Weeren, from Leiden University. “And we did it.”
At the moment, researchers are processing more data to map the entire northern sky at the lowest frequencies.
According to the researchers, the new calibration technique makes it possible to study phenomena that were previously hidden. It could be used to detect exoplanets orbiting small stars. And, Groeneveld concludes, “there is, of course, the possibility that we will eventually discover something unexpected.”
