The LOw Frequency ARray(LOFAR) is a radio telescope array operating at low frequencies ranging from 10  to 240 MHz, being one of the few low-frequency arrays. Now, a team of astronomers has used this array to create the most crips map of the sky at ultra-low radio frequencies, revealing over 25,000 supermassive black holes in distant galaxies.

Supermassive black holes

The survey’s data is collected by a set of antennas distributed across many countries. LOFAR is primarily located in the Netherlands, where most of the antennas are located, while the others are located in Germany, Poland, France, UK, Ireland, Latvia, and Sweden. So far, LOFAR has only visualized a small part of the northern sky (much more data will be released in 2022)

But even this small part of the sky has a lot to show, especially as it’s providing data from a part of the sky we haven’t truly explored yet.

LOFAR’s main findings from this preliminary release include 25,247 radio sources — by “radio sources” we essentially mean galaxies with very bright nuclei. Astronomers call these sources AGN (Active Galactic Nuclei), and these AGNs are powered by supermassive black holes. This is what is shown in the image above: The bright dots are the AGN’s found by LOFAR, each AGN emits radio waves that travel space to reach the detectors. 

A helping hand for geophysics

Observations in this low-frequency range are a challenge. Low frequency means long wavelength, and the frequency range is not so different from those of the regular radio transmitters, which makes it much more difficult to filter out the unwanted radiowaves and keep the useful ones. But there’s also an advantage to this type of data.

Ultra-low frequencies instruments can help researchers understand the properties of the ionosphere, the ionized part of Earth’s upper atmosphere. The ionosphere consists of a shell of electrons and alters its shape daily due to the sun’s influence. It makes things hard for astronomers looking for radio sources, because the ionosphere ‘moves’ the sources, like mirages.

Other experiments have also detected supermassive black holes. The most famous one was the detection M87’s Event Horizon Telescope, the first picture of a black hole ever taken. It was also made with the help of radio telescopes. They needed eight telescopes just to observe it. But what makes LOFAR unique is its ability to detect multiple objects — they may not be as detailed as with other telescopes, but there’s a lot of them. 

Future targets include observations in our galaxy to detect supernova remnants. The team also intends to detect magnetic fields which indicate the presence of exoplanets and their host stars. LOFAR are our new eyes, charting the sky with unprecedented objects will certainly bring important discoveries.

More information regarding the findings can be assessed in the preprint.