LOFAR detects gigantic radio sources in the universe

Artistic representation of the large-scale structure of the Universe above the core of the LOFAR telescope. The inset shows a zoom into a galaxy cluster where a megahalo is observed (orange emission, from LOFAR observations).

An international research team, led by the Observatory of Universität Hamburg has, using LOFAR, discovered four radio sources of up to ten million light years in size: megahalos.

Seen from a great distance, the universe is not evenly distributed; it actually resembles a net-like structure, somewhat similar to the way neurons are connected to one another in the brain. At the nodes of this so-called cosmic web hundreds, sometimes even thousands of galaxies are crowded together into galaxy clusters. Sometimes, two galaxy clusters collide with each other and merge into a single cluster. In the process, they release enormous amounts of energy, so large that they are the most powerful events happening in our Universe after the Big Bang. During these collisions, tiny, charged particles are accelerated to near-lightspeed, emitting radio waves that can be detected with radio telescopes.

Using the Low Frequency Array (LOFAR), scientists have now discovered four galaxy clusters where a faint radio emission envelopes the entire clusters even reaching their outskirts. Dr. Virginia Cuciti led the international research team: “Megahalos extend up to ten million light years) in size, which means that they cover a volume that is about 30 times larger than the volume of the radio sources known so far in galaxy clusters. This implies that with megahalos we can now observe the peripheral regions of galaxy clusters which were previously almost inaccessible.”

Computer simulation of the large-scale structure of the Universe. The inset shows a zoom into a galaxy cluster where a megahalo is observed (orange emission, from LOFAR observations).

Cuciti’s team used LOFAR Two-metre Sky Survey (LoTSS) observations of these four galaxy clusters. While analysing the data of one of the clusters, she and her teammates saw some significant hints of radio emission on exceptionally large scales, Cuciti says. “So, we decided to re-inspect all the images of a sample of 310 clusters that we were studying with the aim of looking for similar emission. When we discovered that three other clusters of this sample showed emission on similar scales and with similar characteristics, it became clear that we discovered a new type of cosmic phenomenon that opens the possibility to explore the external region of galaxy clusters through radio observations.”

This discovery could not have been made without LOFAR, Cuciti says. “It is not by chance that megahalos have been discovered with LOFAR. They are very large, and their emission is very faint. Moreover, the synchrotron spectrum of megahalos is steep, which basically means that they are brighter at low radio frequency, therefore a sensitive radio telescope operating at low radio frequency, such as LOFAR, is the ideal instrument to detect them.”

But even then, it was not easy, co-author and astronomer at ASTRON Timothy Shimwell says: “Even in the very sensitive and wide area LOFAR surveys dataset these objects were very hard to find because they are so faint and a very careful analysis of large quantities of data was required to identify them.”

LOFAR 2.0
A region of the LOFAR core seen from above. The two antenna types of LOFAR are visible.

With LOFAR currently undergoing an upgrade to LOFAR2.0, making it an even more sensitive instrument, even more valuable information can be found about megahalos. Cuciti: “With more sensitive observations we could be able to detect megahalos in a much larger number of clusters. This is actually one of the most interesting aspects of this work, because it means that, if megahalos are present in a large fraction of clusters, if not all of them, we are opening a new field of research, a new way to systematically explore the periphery of galaxy clusters with radio observations. The LOFAR 2.0 upgrade will increase the sensitivity of LOFAR, especially in the LBA (at 50 MHz), and will therefore allow us to answer to the question: how many clusters host megahalos?"

The Nature-article Galaxy clusters enveloped by vast volumes of relativistic electrons can be found here.

Source: ASTRON-Netherlands Institute for Radio Astronomy

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LOFAR detects gigantic radio sources in the universe

Artistic representation of the large-scale structure of the Universe above the core of the LOFAR telescope. The inset shows a zoom into a galaxy cluster where a megahalo is observed (orange emission, from LOFAR observations).

An international research team, led by the Observatory of Universität Hamburg has, using LOFAR, discovered four radio sources of up to ten million light years in size: megahalos.

Seen from a great distance, the universe is not evenly distributed; it actually resembles a net-like structure, somewhat similar to the way neurons are connected to one another in the brain. At the nodes of this so-called cosmic web hundreds, sometimes even thousands of galaxies are crowded together into galaxy clusters. Sometimes, two galaxy clusters collide with each other and merge into a single cluster. In the process, they release enormous amounts of energy, so large that they are the most powerful events happening in our Universe after the Big Bang. During these collisions, tiny, charged particles are accelerated to near-lightspeed, emitting radio waves that can be detected with radio telescopes.

Using the Low Frequency Array (LOFAR), scientists have now discovered four galaxy clusters where a faint radio emission envelopes the entire clusters even reaching their outskirts. Dr. Virginia Cuciti led the international research team: “Megahalos extend up to ten million light years) in size, which means that they cover a volume that is about 30 times larger than the volume of the radio sources known so far in galaxy clusters. This implies that with megahalos we can now observe the peripheral regions of galaxy clusters which were previously almost inaccessible.”

Computer simulation of the large-scale structure of the Universe. The inset shows a zoom into a galaxy cluster where a megahalo is observed (orange emission, from LOFAR observations).

Cuciti’s team used LOFAR Two-metre Sky Survey (LoTSS) observations of these four galaxy clusters. While analysing the data of one of the clusters, she and her teammates saw some significant hints of radio emission on exceptionally large scales, Cuciti says. “So, we decided to re-inspect all the images of a sample of 310 clusters that we were studying with the aim of looking for similar emission. When we discovered that three other clusters of this sample showed emission on similar scales and with similar characteristics, it became clear that we discovered a new type of cosmic phenomenon that opens the possibility to explore the external region of galaxy clusters through radio observations.”

This discovery could not have been made without LOFAR, Cuciti says. “It is not by chance that megahalos have been discovered with LOFAR. They are very large, and their emission is very faint. Moreover, the synchrotron spectrum of megahalos is steep, which basically means that they are brighter at low radio frequency, therefore a sensitive radio telescope operating at low radio frequency, such as LOFAR, is the ideal instrument to detect them.”

But even then, it was not easy, co-author and astronomer at ASTRON Timothy Shimwell says: “Even in the very sensitive and wide area LOFAR surveys dataset these objects were very hard to find because they are so faint and a very careful analysis of large quantities of data was required to identify them.”

LOFAR2.0

A region of the LOFAR core seen from above. The two antenna types of LOFAR are visible.

With LOFAR currently undergoing an upgrade to LOFAR2.0, making it an even more sensitive instrument, even more valuable information can be found about megahalos. Cuciti: “With more sensitive observations we could be able to detect megahalos in a much larger number of clusters. This is actually one of the most interesting aspects of this work, because it means that, if megahalos are present in a large fraction of clusters, if not all of them, we are opening a new field of research, a new way to systematically explore the periphery of galaxy clusters with radio observations. The LOFAR 2.0 upgrade will increase the sensitivity of LOFAR, especially in the LBA (at 50 MHz), and will therefore allow us to answer to the question: how many clusters host megahalos?"

The Nature-article Galaxy clusters enveloped by vast volumes of relativistic electrons can be found here.

Source: ASTRON-Netherlands Institute for Radio Astronomy

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Gigapixel radio image of the Universe using Europe as a radio telescope

An illustration of the difference in resolving power between using only the Dutch LOFAR stations and all of the international stations throughout Europe, arranged in the formation of an HBA core stations. The animation fades from an angular resolution of 6" to a resolution of 0.3". Credit: Frits Sweijen

An international team of astronomers has created one of the largest and most detailed radio maps at megahertz frequencies thanks to Dutch supercomputers. This research, led by Frits Sweijen at Leiden University, has been published in Nature Astronomy on Thursday. Using the International LOFAR Telescope they have, in the wake of tremendous progress late last year, mapped an area of the sky the size of 25 full moons in great detail, with a resolving power comparable to optical telescopes on Earth. The resulting radio image contains nearly seven billion pixels and contains just shy of 2500 radio galaxies.

LOFAR

The sky is filled with radiation invisible to the naked eye, including radio waves at frequencies ten million times lower than red light. With tens of thousands of antennas across Europe, the LOFAR telescope listens to those cosmic radio waves at a frequency of 144 MHz, just above the FM radio band. Through these antennas the European continent transforms into an almost 2000 km big radio telescope. This tremendous size means that LOFAR can see exquisite and unprecedented detail at such low radio frequencies, with a resolving power high enough to make out the Great Pyramid if it were on the Moon. The combined area of all the antennas make it sensitive enough to detect a mobile phone ringing all the way out on Mars.

This resolving power is challenged by Earth's atmosphere however. Ultraviolet radiation from the Sun creates a layer of charged particles in the upper atmosphere. This so-called ``ionosphere'' distorts radio waves from space before they reach the telescope. For LOFAR it therefore is like looking at the sky from the bottom of the ocean. With advanced techniques these distortions can be corrected, focusing the telescope across its entire field of view, thus allowing it to be mapped.

Super computers

Determining these corrections and subsequently converting radio waves into an image, requires modern algorithms and a lot of compute power. Thanks to super computers this was not an issue. Locally, the Academic Leiden Interdisciplinary Cluster Environment (ALICE) lent its power to the scientists. Nationally, SURF in the Netherlands, provided early access to the new platform data processing platform named Spider. This platform is specifically designed for data-intensive projects like this. Lengthy calculations could be run in a massively parallel fashion thanks to these supercomputers. The final image was too large to be made in one go. To image the full field of view, it was processed in 25 smaller chunks each covering an area the size of a full moon. Each of these chunks was turned into an image over seven days, using software recently developed at ASTRON. Piece by piece, on a single computer, this process would have taken more than 175 days to complete. Thanks to the large scale compute infrastructure at Leiden and SURF, however, it only took seven days effectively.

The sharp eyes of the International LOFAR Telescope allow scientists to study the evolution of black holes and their host galaxies in more detail than before. Galaxies in the early Universe, for example, that would otherwise be too small to resolve due to their distance or young age, can have their spatial structure studied. The published results enable this for thousands of sources at once. With its near seven billion pixels this single image contains almost as many pixels as radio surveys from the past did covering the entire sky. These new results explore a tip of the ice berg with a detailed map of the entire Northern sky as the future goal.

This work made use of the Dutch national e-infrastructure with the support of the SURF Cooperative using grant no. EINF-251; the ERC Starting Grant ClusterWeb 804208; the Medical Research Council grant MR/T042842/1; the UK STFC ST/R000972/1 and ST/V000594/1 grants and the Academic Leiden Interdisciplinary Cluster Environment (ALICE) provided by Leiden University.

Article in Nature

Source:ASTRON-Netherlands Institute for Radio Astronomy/News

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Aurorae discovered on distant stars suggest hidden planets

Artist impression of a red-dwarf star’s magnetic interaction with its exoplanet
Credit to image: Danielle Futselaar (artsource.nl)

Using the world’s most powerful radio telescope, LOFAR, scientists have discovered stars unexpectedly blasting out radio waves, possibly indicating the existence of hidden planets.

Searching for red dwarfs

Leiden University’s Dr Joseph Callingham and his colleagues have been searching for aurorae from exoplanets using the Low Frequency Array (LOFAR), the world’s most powerful radio telescope. “We’ve discovered signals from 19 distant red dwarf stars, four of which are best explained by the existence of planets orbiting them,” Dr Callingham said. “We’ve long known that the planets of our own solar system emit powerful radio waves as their magnetic fields interact with the solar wind. This same process drives the beautiful aurorae we see at the poles of Earth.

“However, it is only with LOFAR have we had the sensitivity to find auroral emission outside our Solar System. This is an incredibly powerful tool to help find planets outside our Solar System and to determine their magnetic fields.” LOFAR was designed, built and is presently operated by ASTRON, the Netherlands Institute for Radio Astronomy, its core is situated in Exloo, the Netherlands.

A spectacle from lightyears away

Dr Harish Vedantham at ASTRON, the Netherlands Institute for Radio Astronomy, co-author of the paper, said that the team is confident these signals are coming from the magnetic connection of the stars and unseen orbiting planets, similar to the interaction between Jupiter and its moon Io. “Our own Earth has aurorae, commonly recognised here as the northern and southern lights. These beautiful aurorae also emit powerful radio waves – this is from the interaction of the planet’s magnetic field with the solar wind,” he said. “But in the case of aurorae from Jupiter, they’re much stronger as its volcanic moon Io is blasting material out into space, filling Jupiter’s environment with particles that drive unusually powerful aurorae.

“Our model for this radio light from our stars is a scaled-up version of Jupiter and Io, with an exoplanet enveloped in the magnetic field of a star, feeding material into vast currents that similarly power bright aurorae on the star itself.

“It’s a spectacle that has attracted our attention from lightyears away.”

The hunt for exo-aurora's
Video explaining aurorae on a star, video was made in 2020 when astronomers first detected aurorae on a star

Future observations with the Square Kilometre Array 

 

The team are now investigating the direct presence of the planets around the star using optical telescopes and searching for periodicity in the radio light. “The radio light should turn on and off like a lighthouse,” Dr Callingham said “and we hope to see that periodicity in new LOFAR data.” The discoveries with LOFAR are just the beginning, but the telescope only has the capacity to monitor stars that are relatively nearby, up to 165 lightyears away. With the next-generation Square Kilometre Array radio telescope finally under construction, switching on in 2029, the team predict they will be able to see hundreds of relevant stars out to much greater distances.

This work demonstrates that radio astronomy is on the cusp of revolutionising our understanding of planets outside our Solar System.

Scientific articles 

 

The population of M dwarfs observed at low radio frequencies. J.R. Callingham, H.K. Vedantham, T.W. Shimwell, B.J.S. Pope, I.E. Davis, P.N. Best, M.J. Hardcastle, H.J.A. Röttgering, J. Sabater, C. Tasse, R.J. van Weeren, W.L. Williams, P. Zarka, F. de Gasperin & A. Drabent. Accepted for publication in Nature Astronomy. https://www.nature.com/articles/s41550-021-01483-0

The TESS View of LOFAR Radio-Emitting Stars. Benjamin J.S. Pope, Joseph R. Callingham, Adina D. Feinstein, Maximilian N. Günther, Harish K. Vedantham, Megan Ansdell, & Timothy W. Shimwell. Accepted for publication in Astrophysical Journal Letters. https://doi.org/10.3847/2041-8213/ac230c

LOFAR

The International LOFAR Telescope is a trans-European network of radio antennas, with a core located in Exloo in the Netherlands. LOFAR works by combining the signals from nearly 110,000 individual antenna dipoles, located in ‘antenna stations’ across the Netherlands and in partner European countries. The stations are connected by a high-speed fibre optic network, with powerful computers used to process the radio signals in order to simulate a trans-European radio antenna that stretches over 2000 kilometres. The International LOFAR Telescope is unique, given its sensitivity, wide field-of-view, and image resolution or clarity. The LOFAR data archive is the largest astronomical data collection in the world.

LOFAR was designed, built and is presently operated by ASTRON, the Netherlands Institute for Radio Astronomy. France, Germany, Ireland, Italy, Latvia, the Netherlands, Poland, Sweden and the UK are all partner countries in the International LOFAR Telescope.

Source: ASTRON/LOFAR/News

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Most detailed-ever images of galaxies revealed using LOFAR

A compilation of the science results. Credit from left to right starting at the top: N. Ramírez-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.

After almost a decade of work, an international team of astronomers has published the most detailed images yet seen of galaxies beyond our own, revealing their inner workings in unprecedented detail. The images were created from data collected by the Low Frequency Array (LOFAR), a radio telescope built and maintained by ASTRON, LOFAR is a network of more than 70,000 small antennae spread across nine European counties, with its core in Exloo, the Netherlands. The results come from the team’s years of work, led by Dr Leah Morabito at Durham University. The team was supported in the UK by the Science and Technology Facilities Council (STFC).

As well as supporting science exploitation, STFC also funds the UK subscription to LOFAR including upgrade costs and operation of its LOFAR station in Hampshire.

Revealing a hidden universe of light in HD

The universe is awash with electromagnetic radiation, of which visible light comprises just the tiniest slice. From short-wavelength gamma rays and X-rays, to long-wavelength microwave and radio waves, each part of the light spectrum reveals something unique about the universe. The LOFAR network captures images at FM radio frequencies that, unlike shorter wavelength sources like visible light, are not blocked by the clouds of dust and gas that can cover astronomical objects. Regions of space that seem dark to our eyes, actually burn brightly in radio waves – allowing astronomers to peer into star-forming regions or into the heart of galaxies themselves.

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

Better resolution by working together

The images reveal the inner-workings of nearby and distant galaxies at a resolution 20 times sharper than typical LOFAR images. This was made possible by the unique way the team made use of the array.

The 70,000+ LOFAR antennae are spread across Europe, with the majority being located in the Netherlands. In standard operation, only the signals from antennae located in the Netherlands are combined, and creates a ‘virtual’ telescope with a collecting ‘lens' with a diameter of 120 km. By using the signals from all of the European antennae, the team have increased the diameter of the ‘lens’ to almost 2,000 km, which provides a twenty-fold increase in resolution.

Unlike conventional array antennae that combine multiple signals in real time to produce images, LOFAR uses a new concept where the signals collected by each antenna are digitised, transported to central processor, and then combined to create an image. Each LOFAR image is the result of combining the signals from more than 70,000 antennae, which is what makes their extraordinary resolution possible.

This shows real radio galaxies from Morabito et al. (2021). The gif fades from the standard resolution to the high resolution, showing the detail we can see by using the new techniques. Credit: L.K. Morabito; LOFAR Surveys KSP.

Revealing jets and outflows from super-massive black holes

Super-massive black holes can be found lurking at the heart of many galaxies and many of these are ‘active’ black holes that devour in-falling matter and belch it back out into the cosmos as powerful jets and outflows of radiation. These jets are invisible to the naked eye, but they burn bright in radio waves and it is these that the new high-resolution images have focused upon.

Dr Neal Jackson of The University of Manchester, said: “These high resolution images allow us to zoom in to see what’s really going on when super-massive black holes launch radio jets, which wasn’t possible before at frequencies near the FM radio band,”

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

Hercules A is powered by a supermassive black hole located at its centre, which feeds on the surrounding gas and channels some of this gas into extremely fast jets. Our new high-resolutions observations taken with LOFAR have revealed that this jet grows stronger and weaker every few hundred thousand years. This variability produces the beautiful structures seen in the giant lobes, each of which is about as large as the Milky Way galaxy. Credit: R. Timmerman; LOFAR & Hubble Space Telescope

A decade-long challenge

Even before LOFAR started operations in 2012, the European team of astronomers began working to address the colossal challenge of combining the signals from more than 70,000 antennae located as much as 2,000 km apart. The result, a publicly-available data-processing pipeline, which is described in detail in one the scientific papers, will allow astronomers from around the world to use LOFAR to make high-resolution images with relative ease.

Dr Leah Morabito of Durham University, said: “Our aim is that this allows the scientific community to use the whole European network of LOFAR telescopes for their own science, without having to spend years to become an expert.”

Super images require supercomputers

The relative ease of the experience for the end user belies the complexity of the computational challenge that makes each image possible. Because LOFAR doesn’t just ‘take pictures’ of the night sky, it must stitch together the data gathered by more than 70,000 antennae, which is a huge computational task. To produce a single image, more than 13 terabits of raw data per second – the equivalent of more than a three hundred DVDs – must be digitised, transported to a central processor and then combined.

Frits Sweijen of Leiden University, said: “To process such immense data volumes we have to use supercomputers. These allow us to transform the terabytes of information from these antennas into just a few gigabytes of science-ready data, in only a couple of days.”

Media

All images and video's belonging to this press release can be found in high resolution here.

Links to Arxiv (free) papers can be found here.

About LOFAR

The International LOFAR Telescope is a trans-European network of radio antennas, with a core located in Exloo in the Netherlands. LOFAR works by combining the signals from more than 70,000 individual antenna dipoles, located in ‘antenna stations’ across the Netherlands and in partner European countries. The stations are connected by a high-speed fibre optic network, with powerful computers used to process the radio signals in order to simulate a trans-European radio antenna that stretches over 1,300 kilometres. The International LOFAR Telescope is unique, given its sensitivity, wide field-of-view, and image resolution or clarity. The LOFAR data archive is the largest astronomical data collection in the world.

LOFAR was designed, built and is presently operated by ASTRON, the Netherlands Institute for Radio Astronomy. France, Germany, Ireland, Italy, Latvia, the Netherlands, Poland, Sweden and the UK are all partner countries in the International LOFAR Telescope.

Source: ASTRON/News

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Ultra-sensitive radio images reveal thousands of star-forming galaxies in early Universe

The deepest LOFAR image ever made, in the region of sky known as ‘Elais-N1’, which is one of the three fields studied as part of this deep radio survey. This image arises from a single LOFAR pointing observed repeatedly for a total of 164 hours. Over 80,000 radio sources are detected; this includes some spectacular large-scale emission arising from massive black holes, but most sources are distant galaxies like the Milky Way, forming their stars. Credit: Philip Best & Jose Sabater, University of Edinburgh.

An international team of astronomers has published the most sensitive images of the Universe ever taken at low radio frequencies, using the International Low Frequency Array (LOFAR). By observing the same regions of sky over and over again and combining the data to make a single very-long exposure image, the team has detected the faint radio glow of stars exploding as supernovae, in tens of thousands of galaxies out to the most distant parts of the Universe. A special issue of the scientific journal Astronomy & Astrophysics is dedicated to fourteen research papers describing these images and the first scientific results.

Cosmic star formation

Philip Best, University of Edinburgh (UK), who led the deep survey, explained: “When we look at the sky with a radio telescope, the brightest objects we see are produced by massive black holes at the centre of galaxies. However, our images are so deep that most of the objects in it are galaxies like our own Milky Way, which emit faint radio waves that trace their on-going star-formation.”

“The combination of the high sensitivity of LOFAR and the wide area of sky covered by our survey – about 300 times the size of the full moon – has enabled us to detect tens of thousands of galaxies like the Milky Way, far out into the distant Universe. The light from these galaxies has been travelling for billions of years to reach the Earth; this means that we see the galaxies as they were billions of years ago, back when they were forming most of their stars.”

Isabella Prandoni, INAF Bologna (Italy), added: “Star formation is usually enshrouded in dust, which obscures our view when we look with optical telescopes. But radio waves penetrate the dust, so with LOFAR we obtain a complete picture of their star-formation.” The deep LOFAR images have led to a new relation between a galaxy’s radio emission and the rate at which it is forming stars, and a more accurate measurement of the number of new stars being formed in the young Universe.

Exotic objects

The remarkable dataset has enabled a wide range of additional scientific studies, ranging from the nature of the spectacular jets of radio emission produced by massive black holes, to that arising from collisions of huge clusters of galaxies. It has also thrown up unexpected results. For example, by comparing the repeated observations, the researchers searched for objects that change in radio brightness. This resulted in the detection of the red dwarf star CR Draconis. Joe Callingham, Leiden University and ASTRON (NL), noted that “CR Draconis shows bursts of radio emission that strongly resemble those from Jupiter, and may be driven by the interaction of the star with a previously unknown planet, or because the star is rotating extremely quickly.”

Huge computational challenge

LOFAR does not directly produce maps of the sky; instead the signals from more than 70,000 antennas must be combined. To produce these deep pictures, more than 4 petabytes of raw data - equivalent to about a million DVDs – were taken and processed. “The deep radio images of our Universe are diffusely hidden, deep inside the vast amount of data that LOFAR has observed.” said Cyril Tasse from Paris Observatory, University PSL (France). “Recent mathematical advances made it possible to extract these, using large clusters of computers.”

Multi-wavelength data

Just as important in extracting the science has been a comparison of these radio images with data obtained at other wavelengths. “The parts of the sky we chose are the best-studied in the Northern sky” explained Philip Best. This has allowed the team to assemble optical, near-infrared, far-infrared and sub-millimetre data for the LOFAR-detected galaxies, which has been crucial in interpreting the LOFAR results.

LOFAR

LOFAR is the world’s leading telescope of its type. It is operated by ASTRON, the Netherlands Institute for Radio Astronomy, and coordinated by a partnership of 9 European countries: France, Germany, Ireland, Italy, Latvia, the Netherlands, Poland, Sweden and the UK. In its ‘high-band’ configuration, LOFAR observes at frequencies of around 150 MHz – between the FM and DAB radio bands. “LOFAR is unique in its ability to make high-quality images of the sky at metre-wavelengths”, said Huub Röttgering, Leiden University, who is leading the overall suite of LOFAR surveys. “These deep field images are a testament to its capabilities and a treasure trove for future discoveries”.

Additional images and videos are available at https://www.lofar-surveys.org/deepfields.html, which also hosts the papers, deep images and catalogues released today. A direct link to the special issue can be found here. 

 

Source:  ASTRON-Netherlands Institute for Radio Astronomy/News

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First direct detection of a brown dwarf with a radio telescope

Artist’s impression of Elegast. The blue loops depict the magnetic field lines. Charged particles moving along these lines emit radio waves that LOFAR detected. Some particles eventually reach the poles and generate aurorae similar to the northern lights on Earth. (Image credit: ASTRON / Danielle Futselaar)

Astronomers at ASTRON have used the LOFAR radio telescope to discover a “brown dwarf” – a faint object more massive than Jupiter, but significantly less massive than the Sun. The discovery of the object dubbed Elegast, opens up a new path that uses radio telescopes to discover faint objects that are close-cousins of Jupiter-like exoplanets. 

Radio waves emitted by brown dwarfs carry information about their magnetic field strength. Until now radio observations could only measure strong magnetic fields – about a hundred times the strength of a common fridge magnet. LOFAR’s low frequency of observation makes it sensitive to magnetic fields comparable to that of a fridge magnet, which is within the range postulated to exist on the coldest brown dwarfs and large exoplanets.

“Magnetic fields control the atmospheric properties and radiation environment around exoplanets and radio observations are our best hope of measuring them. With this discovery, we have taken an important step towards realising the promise of radio astronomy to exoplanet science,” said Dr. Harish Vedantham, ASTRON staff scientist and lead author of the study published today in the Astrophysical Journal Letters.

New discovery technique

The group used a new discovery technique to spot Elegast. Previously, astronomers pointed radio telescopes at known and catalogued brown dwarfs that were all found from their faint glow at infrared wavelengths. “With LOFAR, we want to go down the mass-ladder all the way to Jupiter-like planets that are too faint to have been found in existing infrared surveys, so we decided to search for these objects directly in our radio images,” said Dr. Joe Callingham, a VENI postdoctoral fellow at Leiden Observatory and co-author of the study.

Objects such as Elegast (and exoplanets) stand out in special “polarised” radio images because the electric field of the radio waves they emit rotates in a characteristic circular pattern as it propagates – a phenomenon called circular polarisation. “We could not have picked out Elegast in our standard radio images from among the crowd of millions of galaxies, but Elegast immediately stood out when we made circularly polarised images,” said Dr. Tim Shimwell, ASTRON staff and project scientist of the LOFAR survey that led to Elegast’s discovery. The group then used infrared follow-up observations from the Gemini telescope, a program of NSF's NOIRLab, and NASA’s Infrared Telescope Facility to confirm that Elegast was indeed a cold brown dwarf.

Elegast is the first object of its kind that has been directly identified in radio images. The group is now busy acquiring follow-up observations of Elegast to measure its magnetic field and compare the results with theory. They are also busy sifting through LOFAR data to identify more objects like Elegast.

“Our ultimate goal is to understand magnetism in exoplanets and how it impacts their ability to host life. Because magnetic phenomena of cold brown dwarfs like Elegast are so similar to what is seen on solar system planets, we expect our work to provide a vital datapoint to test theoretical models that predict the magnetic fields of extrasolar bodies,” said Vedantham.

The published journal article can be found here.

An open-access pre-print of the paper can be found here.

 

Source:  Astron/Astronomy/News

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Help to find the location of newly discovered black holes in the LOFAR Radio Galaxy Zoo project

As an example, take the case of the famous radio source 3C236. The upper image is the radio source, the middle one an optical image showing many stars and galaxies and the lower image an overlay of the radio and the optical image. In this case, for the human eye the origin of the radio emission is clear, it is the bright point-like radio source at the center of the radio image. This is the location of the massive black hole that is driving all the radio activity. From the overlay with the optical images the galaxy that hosts the black hole can then be identified. Image credit: Aleksandar Shulevski, Erik Osinga & The LOFAR surveys team. Hi-res image

Scientists are asking for the public’s help to find the origin of hundreds of thousands of galaxies that have been discovered by the largest radio telescope ever built: LOFAR. Where do these mysterious objects that extend for thousands of light-years come from? A new citizen science project, LOFAR Radio Galaxy Zoo, gives anyone with a computer the exciting possibility to join the quest to find out where the black holes at the centre of these galaxies are located.

Astronomers use radio telescopes to make images of the radio sky, much like optical telescopes like the Hubble space telescope make maps of stars and galaxies. The difference is that the images made with a radio telescope show a sky that is very different from the sky that an optical telescope sees. In the radio sky, stars and galaxies are not directly seen but instead an abundance of complex structures linked to massive black holes at the centres of galaxies are detected. Most dust and gas surrounding a supermassive black hole gets consumed by the black hole, but part of the material will escape and gets ejected into deep space. This material forms large plumes of extremely hot gas, it is this gas that forms large structures that is observed by radio telescopes.

The Low Frequency Array (LOFAR) telescope, operated by the Netherlands Institute for Radio Astronomy (ASTRON), is continuing its huge survey of the radio sky and 4 million radio sources have now been discovered. A few hundred thousand of these have very complicated structures. So complicated that it is difficult to determine which galaxies belong to which radio source, or in other words, which black hole belongs to which galaxy?

While the international LOFAR team consists of more than 200 astronomers from 18 countries, it is simply too small to take on this daunting task of identifying which radio structures belong to which host galaxy. Therefore, LOFAR astronomers are asking the public to help. In the context of the citizen science project ‘LOFAR Radio Galaxy Zoo’, the public is asked to look at images from LOFAR and images of galaxies and then associate radio sources with galaxies.

“LOFAR’s new survey has revealed millions of previously undetected radio sources. With the help of the public we can investigate the nature of these sources: Where are their black holes? In what kind of galaxies are the black holes located?’’ says Huub Röttgering from Leiden University (The Netherlands).

Tim Shimwell, ASTRON and Leiden University, explains why this is significant: “Your task is to match the radio sources with the right galaxy. This will help researchers understand how radio sources are formed, how black holes evolve, and how vast quantities of material can be ejected into deep space with such unprecedented amounts of energy”, he says.

Radio Galaxy Zoo: LOFAR is part of the Zooniverse project, the world’s largest and most popular platform for people-powered research. This research is made possible by volunteers — more than a million people around the world who come together to assist professional researchers.

Images

• More images can be found here
• The Radio Galaxy Zoo: LOFAR page is accessible here
• The tutorial video can be viewed here

Source: ASTRON-Netherlands Institute for Radio Astronomy/News

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Energy loss gives unexpected insights in evolution of quasar jets

 The radio jet of the quasar 4C+19.44, powered by a supermassive black hole lying in the center of its host galaxy and shining at long radio wavelengths as seen by the LOFAR radio telescope (magenta). The background image shows neighboring galaxies in the visible light highlighted thanks to the Hubble Space Telescope (cyan and orange) having the radio jet passing into the dark voids of intergalactic space (Harris et al. 2019). Image Credit: NASA/HST/LOFAR; Courtesy of J. DePasquale

An international team of astrophysicists observed for the first time that the jet of a quasar is less powerful on long radio wavelengths than earlier predicted. This discovery gives new insights in the evolution of quasar jets. They made this observation using the international Low Frequency Array (LOFAR) telescope, that produced high resolution radio images of quasar 4C+19.44 located over 5 billion light-years from Earth. 

 

Supermassive black holes, many millions of times more massive than our Sun reside in the central regions of galaxies. They grow even larger by attracting and consuming nearby gas and dust. If they consume material rapidly, the infalling matter shines brightly and the source is known as a quasar.

Some of this infalling matter is not digested, but instead is ejected in the form of so-called jets that punch through the surrounding galaxy and into intergalactic space for millions of light years. These jets, shining brightly at radio wavelengths, are composed of particles accelerated up to nearly the speed of light, but exactly how these particles achieve energies not attainable on the Earth is yet to be completely solved.

The discovery on quasar 4C+19.44 gives new insights to the balance between the energy in the field surrounding the quasar and that residing in the quasar jet. This finding indicates to an intrinsic property of the source rather than due to absorption effects. It implies that the energy budget available to accelerate particles and the balance between energy stored in particles and in the magnetic field, is less than expected.

"This is an important discovery that will be used for the years to come to improve simulations of jets. We observed for the first time a new signature of particle acceleration in the power emitted of quasar jets at long radio wavelengths. An unexpected behaviour that changes our interpretation on their evolution." Said Prof. Francesco Massaro from University of Turin. "We knew that this was already discovered in other cosmic sources but it was never before observed in quasars."

The international team of astrophysicists had observed the jet of the quasar 4C+19.44 at short radio wavelengths, in visible light, and X-ray wavelengths. The addition of the LOFAR images allowed astrophysicists to make this discovery. LOFAR is the first radio facility operating at long radio wavelengths, which produces sharp images with a resolution similar to that of the Hubble Space Telescope.

"We have been able to perform this experiment thanks to the highest resolution ever achieved at these long radio wavelengths, made possible by LOFAR." Said Dr Adam Deller, an astrophysicist of the Swinburne University of Technology who contributed to the LOFAR data analysis and imaging of 4C +19.44 while at ASTRON in the Netherlands, heart of the LOFAR collaboration.

Dr Raymond Oonk, an astronomer at ASTRON and Leiden University and Dr Javier Moldon, astronomer at the University of Manchester, explained that "We have developed new calibration techniques for LOFAR and this has allowed us to separate compact radio structures in the quasar jet known as radio knots, and measure their emitted light. This result was unexpected and demands to future deeper investigations. New insights and clues on particle acceleration will come soon thanks to the international stations of LOFAR."

The observation performed on the radio jet of 4C+19.44 was designed by Dr D. E. Harris, supervisor of Prof. Francesco Massaro, while working at the Harvard-Smithsonian Center for Astrophysics, several years ago. He performed the observation in collaboration with Dr Raffaella Morganti and his friends and colleagues at ASTRON. He only got the opportunity to see preliminary results as he passed away on 2015 December 6th. This publication, published in the first March issue of the Astrophysical Journal, is in memory of a career spanned much of the history of radio astronomy.

Source: ASTRON-Netherlands Institute for Radio Astronomy

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Swirling Electrons in the Whirlpool Galaxy

LOFAR radio map of the whirlpool galaxy M51 and its neighbourhood at a frequency of 150 MHz. The field covers 4 by 2.6 degrees. The observations were performed with the Dutch LOFAR high-band antennas. The map shows the distribution of hot electrons in M51 and also a large number of background galaxies.The inlay shows an enlarged view of M51 at 150 MHz (white contour lines) overlayed onto an optical image of M51 from the Digital Sky Survey (DSS). © David Mulcahy et al., Astronomy & Astrophysics 

The whirlpool galaxy Messier 51 (M51) is seen from a distance of approximately 30 million light years. This galaxy appears almost face-on and displays a beautiful system of spiral arms.

A European team of astronomers was able to observe M51 with the International LOFAR Telescope in the frequency range 115-175 MHz, just above the normal commercial FM radio frequency band of 88-108 MHz. The team obtained the most sensitive image of any galaxy at frequencies below 1 GHz so far.

With LOFAR's high sensitivity, the disk of M51 in the radio regime could be traced much further out than before. The astronomers detected cosmic electrons and magnetic fields 40,000 light years away from the center of M51. With LOFAR's high angular resolution, the spiral arms are clearly visible. Magnetic fields and cosmic rays are densest in spiral arms. Compared to higher radio frequencies, spiral arms appear broader due to the diffusion of cosmic electrons away from the spiral arms where they have been formed. 

The view of galaxies in the radio regime is different to their optical appearance. Whereas optical images show predominantly the visible light from stars, the radio waves unravel two constituents of galaxies that are invisible to optical telescopes: electrons, almost as fast as light, and magnetic fields. Their role for the stability and evolution of galaxies is increasingly under discussion. The electrons are "cosmic ray" particles produced in the shock fronts of giant supernova explosions. Magnetic fields are generated by dynamo processes driven by gas motions. When the electrons spiral around the magnetic field lines, radio waves are emitted, a process called synchrotron emission. Its intensity increases with the number and energy of the electrons and with magnetic field strength. 

For many decades, radio astronomy has been unable to explore low frequencies below 300 MHz because the ionosphere acts as a barrier of low-frequency radio waves (which are completely blocked below about 10 MHz). Sophisticated methods of data processing and superfast computers are needed to recover the emission. Due to these technical challenges, spiral galaxies have hardly been studied before at these very low radio frequencies. The only observations were of poor resolution and no details could be made out.

The target of investigation in David Mulcahy's PhD project was the beautiful spiral galaxy Messier 51 at a distance of about 30 million light years which is visible already in a small telescope in the constellation "Canes Venatici", not far away from the famous Big Dipper (in German: "Großer Wagen") in the sky.  

"Low-frequency radio waves are important as they carry information about electrons of relatively low energies that are able to propagate further away from their places of origin in the star-forming spiral arms and are able to illuminate the magnetic fields in the outer parts of galaxies", says David Mulcahy. "We need to know whether magnetic fields are expelled from galaxies and what their strength is out there." 

"This beautiful image, coupled with the important scientific result it represents, illustrates the fantastic advances that can be made at low radio frequencies with the LOFAR telescope", continues Anna Scaife from Southampton University, co-author of the paper. "Unravelling the mysteries of magnetic fields is crucial to understanding how our Universe works. For too long, many of the big questions about magnetic fields have simply been untestable and this new era of radio astronomy is very exciting." 

The Low Frequency Array (LOFAR), designed and constructed by ASTRON in the Netherlands, is a brand new radio telescope giving access to very low radio frequencies. 

LOFAR Stations in Europe.

© ASTRON, The Netherlands 

LOFAR explores the relatively unexplored frequency range below 240 MHz and consists of a multitude of small and simple antennas without moving parts. LOFAR consists of 38 stations in the Netherlands, 6 stations in Germany and one station each in the UK, France and Sweden. The novelty is the online combination of the signals from all stations in a powerful computing cluster located at the University of Groningen (Netherlands). 

Observations of M51 with LOFAR below FM radio frequencies (at 30-80 MHz) have already taken place. „This opens a new window to the Universe where we do not know how galaxies will look like", concludes Rainer Beck, who supervised David Mulcahy's PhD project. „Maybe we will see how galaxies are magnetically connected to intergalactic space. This is a key experiment in preparation for the planned Square Kilometre Array (SKA) that should tell us how cosmic magnetic fields are generated." 

Original paper:

The nature of the low-frequency emission of M51: First observations of a nearby galaxy with LOFAR, by D.D. Mulcahy, A. Horneffer, R. Beck et al., 2014, Astronomy & Astrophysics  (DOI: 10.1051/0004-6361/201424187).

Source: ASTRON Netherlands Institute for Radio Astronomy