“The Invisible Unveiled” –Hundreds of Thousands of Unknown Galaxies in the Distant Universe

galaxy cluster Abell 1314


Astronomers have recently discovered that the expanse of space-time within range of our telescopes—‘the universe’—is only a tiny fraction of the aftermath of the Big Bang. In a new, mind-boggling project, an international team of astronomers have mapped 300,000 previously unknown objects using the Low Frequency Array (LOFAR) telescope, almost all of which are galaxies in the distant universe; their radio signals traveling billions of light years to reach Earth.

We expect to find far more galaxies located beyond the horizon, unobservable to current optical telescopes, says the great British astrophysicist, Martin Rees, “each of which (along with any civilizations it hosts) will evolve rather like our own.”

An international team of more than 200 astronomers from 18 countries has published the first phase of a major new radio sky survey at unprecedented sensitivity using the Low Frequency Array (LOFAR) telescope. The survey revealed hundreds of thousands of previously undetected galaxies, shedding new light on many research areas including the physics of black holes and how clusters of galaxies evolve.

One of the most fundamental known unknowns in astronomy is just how many galaxies the universe contains. The Hubble Deep Field images, captured in the mid 1990s, revealed untold numbers of faint galaxies. It was estimated that the observable Universe contains between 100 to 200 billion galaxies.

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“It boggles the mind that over 90% of the galaxies in the Universe have yet to be studied. Who knows what we will find when we observe these galaxies with the next generation of telescopes,” says astronomer Christopher Conselice at the University of Nottingham, who led an earlier team that discovered that there are ten times more galaxies in the universe than previously thought, and an even wider space to ultimately search for extraterrestrial life.

“Maybe the universe has an edge just beyond the Hubble distance from us, and beyond that is sea monsters,” says Arthur B. Kosowsky, Professor, Physics, University of Pittsburgh, whose research focuses on cosmology and related issues of theoretical physics. “But since all of the universe we can observe looks relatively similar and uniform, this would be an extremely strange state of affairs.”

Radio astronomy reveals processes in the universe that cannot be seen with optical instruments. In this first part of the new sky survey, LOFAR observed a quarter of the northern hemisphere at low radio frequencies. At this point, approximately 10 percent of that data has been released to the public.

“If we take a radio telescope and we look up at the sky, we see mainly emission from the immediate environment of massive black holes,” says Huub Röttgering, Leiden University (The Netherlands). “With LOFAR, we hope to answer the fascinating question: Where do those black holes come from?” Researchers do know that black holes are messy eaters. When gas falls onto them, they emit jets of material that can be seen at radio wavelengths.

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“LOFAR has a remarkable sensitivity and that allows us to see that these jets are present in all of the most massive galaxies, which means that their black holes never stop eating,” says Philip Best, University of Edinburgh.

The galaxy cluster Abell 1314 shown above is located in Ursa Major at a distance of approximately 460 million light years from earth. It hosts large-scale radio emission that was caused by its merger with another cluster. Non-thermal radio emission detected with the LOFAR telescope is shown in red and pink, and thermal X-ray emission detected with the Chandra telescope is shown in gray, overlaid on an optical image. (Amanda Wilber/LOFAR Surveys Team/NASA/CXC)

Galaxy clusters are ensembles of hundreds to thousands of galaxies. It has been known for decades that when two clusters of galaxies merge, they can produce radio emissions spanning millions of light years. This emission is thought to come from particles that are accelerated during the merger process.

“With radio observations we can detect radiation from the tenuous medium that exists between galaxies,” says Amanda Wilber, University of Hamburg. “This radiation is generated by energetic shocks and turbulence. LOFAR allows us to detect many more of these sources and understand what is powering them.”

The image below shows how the LOFAR radio telescope opens a new view of the universe. The image shows galaxy cluster Abell 1314. In shades of grey, a piece of the sky can be seen as we know it in visible light. The orange hues show the radio emitting radiation in the same part of the sky. The radio image looks completely different and changes our assumptions about how galaxies arise and develop. These objects are located at a distance of approximately 460 million light years from Earth. In the middle of every galaxy there is a black hole. When matter falls into it, an unbelievable amount of energy is released and electrons are ejected like a fountain. These accelerated electrons produce radio emission that can extend over gigantic distances and is not visible at optical wavelengths. (Rafaël Mostert/LOFAR Surveys Team/Sloan Digital Sky Survey DR13)


LOFAR galaxy cluster Abell 1314


“What we are beginning to see with LOFAR is that in some cases, clusters of galaxies that are not merging can also show this emission, albeit at a very low level that was previously undetectable,” says Annalisa Bonafede, University of Bologna and INAF (Italy). “This discovery tells us that besides merger events, there are other phenomena that can trigger particle acceleration over huge scales.”

“Magnetic fields pervade the cosmos, and we want to understand how this happened. Measuring magnetic fields in intergalactic space can be difficult, because they are very weak. However, the unprecedented accuracy of the LOFAR measurements has allowed us to measure the effect of cosmic magnetic fields on radio waves from a giant radio galaxy that is 11 million light years in size. This work shows how we can use LOFAR to help us understand the origin of cosmic magnetic fields,” explains Shane O”Sullivan, University of Hamburg.


M51, also known as the Whirlpool Galaxy.

The image above shows M51, also known as the Whirlpool Galaxy. It is 15-35 million light years from Earth and around 60,000 light years in diameter. At the center of the spiral galaxy there sits a supermassive black hole. With the LOFAR data (yellow and red hues), we can see that the spiral galaxy and its companion are interacting because there is a bridge of emission joining them. Credit: Sean Mooney/LOFAR Surveys Team/Digitized Sky Survey

Creating low-frequency radio sky maps takes both significant telescope and computational time and requires large teams to analyse the data. “LOFAR produces enormous amounts of data—we have to process the equivalent of 10 million DVDs of data. The LOFAR surveys were recently made possible by a mathematical breakthrough in the way we understand interferometry,” says Cyril Tasse, Observatoire de Paris—Station de radio astronomie à Nançay (France).

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“We have been working together with SURF in the Netherlands to efficiently transform the massive amounts of data into high-quality images. These images are now public and will allow astronomers to study the evolution of galaxies in unprecedented detail,” says Timothy Shimwell, Netherlands Institute for Radio Astronomy (ASTRON) and Leiden University.

SURF’s compute and data center located at SURFsara in Amsterdam runs on 100 percent renewable energy and hosts over 20 petabytes of LOFAR data.

“This is more than half of all data collected by the LOFAR telescope to date. It is the largest astronomical data collection in the world. Processing the enormous data sets is a huge challenge for scientists. What normally would have taken centuries on a regular computer was processed in less than one year using the high throughput compute cluster (Grid) and expertise,” says Raymond Oonk (SURFsara).

The LOFAR telescope, the Low Frequency Array, is unique in its capabilities to map the sky in fine detail at meter wavelengths. LOFAR is operated by ASTRON in The Netherlands and is considered to be the world’s leading telescope of its type. “This sky map will be a wonderful scientific legacy for the future. It is a testimony to the designers of LOFAR that this telescope performs so well,” says Carole Jackson, Director General of ASTRON.

The next step: The 26 research papers in the special issue of Astronomy & Astrophysics were done with only the first two percent of the sky survey. The team aims to make sensitive high-resolution images of the whole northern sky, which will reveal 15 million radio sources in total.

“Just imagine some of the discoveries we may make along the way. I certainly look forward to it,” says Jackson. “And among these there will be the first massive black holes that formed when the universe was only a ‘baby,” with an age a few percent of its present age,” adds Röttgering.

The Daily Galaxy, Max Goldberg via Netherlands Institute for Radio Astronomy (ASTRON)

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