The most detailed galaxy images ever seen with LOFAR

After nearly a decade of work, an international team of astronomers have released the most detailed images ever seen of galaxies beyond our own, revealing how they work in unprecedented detail. The images were created with data collected by the ASTRON built and operated Low frequency matrix (LOFAR), a radio telescope made up of a network of more than 70,000 small antennas in nine European countries, whose heart is in Exloo, the Netherlands. The results are the culmination of years of work by the team led by Dr. Leah Morabito of Durham University. The team was supported in the UK by the Scientific and Technological Facilities Council (STFC).

A compilation of scientific results. Credit from left to right from top: N. Ramírez-Olivencia et el. [radio]; NASA, ESA, 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 and 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: WL Williams.

In addition to supporting scientific exploitation, STFC also funds the UK subscription to LOFAR, including the costs of upgrading and operating the LOFAR station in Hampshire.

Unveil a hidden universe of light in HD

The universe is flooded with electromagnetic radiation, of which visible light is only a tiny part. From gamma rays and short wavelength x-rays to microwaves and long wavelength radio waves, every part of the light spectrum reveals something unique about the universe.

The LOFAR network creates images on FM radio frequencies which, unlike shorter wavelength sources such as visible light, are not blocked by clouds of dust and gas that can cover astronomical objects. Regions of space that appear dark to our eyes actually burn brightly in radio waves, allowing astronomers to see into star-forming regions or into the cores of galaxies themselves.

The new images, made possible by international collaboration, push the boundaries of what we know about galaxies and supermassive black holes. A special issue of the scientific journal Astronomy & Astrophysics is devoted to 11 research papers describing these images and the scientific results.

Radio systems detected by LOFAR. Credit: LK Morabito; LOFAR KSP surveys.

Better resolution through collaboration

The images show the interiors of near and far galaxies with a resolution 20 times sharper than typical LOFAR images. This was made possible by the team’s unique use of the bay.

The more than 70,000 LOFAR branches are spread across Europe, most of which are in the Netherlands. In normal use, only the signals from antennas located in the Netherlands are combined, creating a “virtual” telescope with a collecting lens with a diameter of 120 km. Using signals from all European antennas, the team increased the diameter of the “lens” to nearly 2,000 km, increasing the resolution by a factor of 20.

Unlike conventional array antennas which combine multiple signals in real time to produce images, LOFAR uses a new concept where the signals collected by each antenna are digitized, transported to a central processor and then combined to create an image to be created. Each LOFAR image is the result of the combination of signals from more than 70,000 antennas, allowing their extraordinary resolution.

The well-known Hercules A radio galaxy with its two huge jet streams, propelled by the central supermassive black hole. Credit: R. Timmerman; LOFAR and Hubble Space Telescope.

Make visible the jets of supermassive black holes

Supermassive black holes lurk at the heart of many galaxies, many of which are “active” black holes that devour falling matter and throw it back into the cosmos in the form of powerful jets. These jets are invisible to the naked eye, but they burn vividly in radio waves and it is these jets that the new high-resolution images have focused on.

dr. Neal Jackson of the University of Manchester said: ‘These high resolution images allow us to zoom in and see what is really going on when supermassive black holes launch radio jets, which was not previously possible at close frequencies. of the FM radio band.

The team’s work forms the basis of nine scientific studies that reveal new information about the internal structure of radio jets in a variety of different galaxies.

A ten-year challenge

Even before LOFAR became operational in 2012, the European team of astronomers began working on the enormous challenge of combining signals from over 70,000 antennas, up to 2,000 km apart. The result, a publicly accessible data processing pipeline detailed in one of the scientific papers, will allow astronomers around the world to use LOFAR to create high-resolution images with relative ease.

dr. Leah Morabito of Durham University said: “Our goal is for the scientific community to use the entire European LOFAR telescope network for their own science, without having to spend years becoming an expert. “

Super images require super computers

The relative ease of the end-user experience belies the complexity of the computational challenge that each image makes possible. LOFAR not only takes “pictures” of the night sky, but has to reconstruct the data collected by more than 70,000 antennas, which is a huge amount of computational work. To produce a single image, over 13 terabits of raw data per second – the equivalent of over 300 DVDs – must be digitized, transferred to a central processor and then combined.

Frits Sweijen from Leiden University: “To process such huge volumes of data, we have to use supercomputers. These allow us to convert terabytes of information from these antennas into several gigabytes of science-ready data in just a few days. Source: ASTRON.

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