Radio astronomers avoid disturbing Earth’s atmosphere with new calibration technology

An international team of researchers, led by Leiden astronomers, has created sharp radio maps of the universe at low frequencies for the first time. Thanks to a new calibration technique, they circumvented the disturbances of the Earth’s ionosphere. With the new method they studied plasmas from old black hole outbursts. The technique may be suitable for finding exoplanets that orbit small stars. The researchers publish their technique in Nature Astronomy.

For the first time, the technology allows astronomers to make sharp radio images of the universe at frequencies between 16 and 30 MHz. Until now, it was always thought that this was impossible because the ionosphere about 80 kilometers above the Earth interferes with observations at these frequencies.

The researchers used the LOFAR telescope in Drenthe. This is currently one of the best radio telescopes in the world for low frequencies. To test their technique, they studied a number of galaxy clusters that until now could only be viewed in detail at higher frequencies.

Glasses
The new images show that the radio emission from these clusters is not evenly distributed over the entire cluster, but that there is a spot pattern. “It’s as if you put on glasses for the first time and your vision is no longer blurry,” says study leader Christian Groeneveld (Leiden University).

The reason for the research into the new technology was that many improvements in calibration had already been made in recent years at the high frequencies, around 150 MHz. “We hoped that we could also extend this technology to lower frequencies, below 30 MHz,” says creator of the idea Reinout van Weeren (Leiden University). “And that worked out.”

The researchers are currently processing more data so that they can map the entire northern sky at low frequencies.

According to the researchers, the new calibration technique makes it possible to study phenomena that were previously hidden. It may be possible to discover exoplanets orbiting small stars. And, Groeneveld concludes, “There is of course also a chance that we discover something unexpected.”

Scientific article
Characterization of the decameter sky at sub-arcminute resolution. By: C. Groeneveld, RJ van Weeren, E. Osinga, WL Williams, JR Callingham, F. de Gasperin, A. Botteon, T. Shimwell, F. Sweijen, J. de Jong, LF Jansen, GK Miley, G. Brunetti, M. Brüggen & HJA Röttgering. In: Nature AstronomyMay 6, 2024. [origineel | preprint (pdf)]

The left shows an image of a piece of sky observed with the best calibration technique to date. The right shows the same piece of sky with the new technique. More details are visible and what used to be large, blurry spots now appear to be individual points. (c) LOFAR/Groeneveld et al. [hoge resolutie]