An international research team led by the Observatory of Universität Hamburg has discovered four radio sources of gigantic size. These so-called Megahalos are up to ten million light years in size and could now be detected for the first time with the help of the radio telescope LOFAR. This discovery was published in the journal Nature.
Seen from a great distance, the mass in the universe is not evenly distributed, but resembles a net-like structure, the so-called cosmic web. At the nodes of the cosmic web, hundreds or even thousands of galaxies crowd together into clusters of galaxies. After the Big Bang, the collision of such galaxy clusters is one of the most powerful astronomical events ever. During such collisions, tiny charged particles are accelerated almost to the speed of light. These particles emit radio waves that can be measured with special telescopes.
Using the world’s largest radio telescope, the Low Frequency Array (LOFAR), an international team led by Dr. Virginia Cuciti of the Hamburg Observatory has detected four galaxy clusters surrounded by an envelope of weak radio radiation. Cuciti and colleagues have called this phenomenon “Megahalos.” They are about 30 times larger than any previously known radio sources. “We have discovered giant cosmic particle accelerators,” explains Cuciti, lead author of the study and Alexander-von-Humboldt-fellow at Universität Hamburg.
“There is a high probability that the four Megahalos discovered are just the tip of the iceberg of a widespread cosmological phenomenon,” says Dr. Cuciti. “This also means that further observations could reveal Megahalos in many more galaxy clusters,” adds Prof. Dr. Marcus Brüggen, co-author of the study. Megahalos suggest that most parts of the universe are filled with ultrafast electrons as well as with magnetic fields, and that there must be a mechanism to accelerate these electrons very efficiently.
LOFAR is a Europe-wide network of radio antennas, the core of which is located in the Netherlands. The telescope is designed to detect low-frequency radio waves in the 10-240 MHz range. It is operated by the Netherlands Institute for Radio Astronomy. France, Germany, Ireland, Italy, Latvia, Poland, Sweden, Bulgaria and the United Kingdom are partner countries.
Currently, LOFAR is undergoing a major upgrade to increase its sensitivity. This upgrade will allow researchers to explore the radio waves of the universe in unprecedented ways and discover more Megahalos.
Virginia Cuciti, Marcus Brüggen et al.: Galaxy clusters enveloped by vast volumes of relativistic electrons, Nature 609, 911–914 (2022).