A series of ten articles to be published in the journal “Astronomy & Astrophysics” reports the results of the activity of the LoFar network with its 70,000 antennas with unprecedented details of various galaxies at radio frequencies. A team of astronomers has published these results consisting of astronomical images obtained by making the most of the LoFar network’s capabilities. This made it possible to obtain images twenty times sharper than the previous ones generated by LoFar.
Radio astronomy has made leaps forward also thanks to the use of antenna networks that work together as if they were a single radio telescope of sizes that can be truly enormous. The approach to this technique, called interferometry, normally consists in combining the signals of the various antennas in real time. However, it’s also possible to send the signals collected by every single antenna to a supercomputer that processes them and combines them to create an image. There are special cases such as the Event Horizon Telescope, which combines observations from different radio telescopes around the world, but for LoFar this approach was chosen for all of its operations.
In standard operations, the antennas present in the Netherlands are used, which make up the bulk of the network. This means using a virtual radio telescope with a diameter of about 120 kilometers. When all antennas are used, the virtual radio telescope has a diameter of almost 2,000 kilometers, which increases the resolution of the images by almost 20 times.
The images obtained using all LoFar antennas allowed to capture details never seen at radio frequencies of various galaxies. The top image (R. Timmerman; LoFar & Hubble Space Telescope) shows the galaxy Hercules A with the large lobes created by the activity of a supermassive black hole at its center. The new observations conducted with the entire LoFar network revealed that the jets emitted by the black hole become stronger or weaker over a few hundred thousand years. That variability produces the structures visible in the giant lobes.
The bottom image (From top left: N. RamÃrez-Olivencia et el. [radio]; NASA, ESA, the Hubble Heritage Team (STScI/AURA)-ESA/Hubble Collaboration and A. Evans (University of Virginia, Charlottesville/NRAO/Stony Brook University), edited by R. Cumming [optical], C. Groeneveld, R. Timmerman; LOFAR & Hubble Space Telescope,. Kukreti; LOFAR & Sloan Digital Sky Survey, A. Kappes, F. Sweijen; LOFAR & DESI Legacy Imaging Survey, S. Badole; NASA, ESA & L. Calcada, Graphics: W.L. Williams.) shows a series of images that combine observations conducted with the LoFar network with others conducted with other instruments.
The combination of various instruments that detect emissions in different bands of the electromagnetic spectrum has become common in astronomical studies. Radio telescopes are very useful because radio waves are among the few emissions that pass through clouds of dust and gas, so they’re an excellent complement to other observations in other bands. LoFar has already been used to study star-forming regions and areas around supermassive black holes, where the sensitivity of the entire network can offer details that are precious for astronomers.
The LoFar team made public the algorithms used for data processing to allow other teams of researchers to use the network having the software tools they need. The technologies developed for LoFar will also be implemented in the next generation SKA radio telescope. Meanwhile, LoFar, with its extensive low-cost antenna network, is already showing great results.
