Chalmers University of Technology
Astronomers at Chalmers are part of the international team behind new, uniquely detailed images from the gigantic radio telescope Lofar which reveal the inner workings of galaxies. The images are the culmination of almost a decade of work in combining data from a network of over 70 000 antennas spread over nine European countries, among them Sweden.
Revealing a hidden universe in high definition
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 new research papers describing these images and the scientific results.
The international team of scientists, led by Leah Morabito at Durham University, UK, includes Chalmers astronomers John Conway and Eskil Varenius, and Deepika Venkattu, Ph.D. student at the Department of Astronomy, Stockholm University.
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 antennas are spread across Europe, with the majority being located in the Netherlands. In standard operation, only the signals from antennas located in the Netherlands are combined, and creates a "virtual telescope" equivalent to a dish with a diameter of 120 kilometres. By using the signals from all the European antennae, the team have increased this diameter to almost 2000 kilometres, which provides twenty-fold sharper resolution.
Unlike other radio telescope arrays 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 tens of thousands of antennas, which is what makes their extraordinary resolution possible.
- With its network of antennas over the whole of Europe, Lofar is showing us that it's possible to make astonishingly detailed images of universe as we have never seen it before", said John Conway, professor of radio astronomy at Chalmers, director of Onsala Space Observatory, and member of the team.
Jets and outflows from supermassive black holes
Supermassive black holes can be found lurking at the heart of many galaxies. Many of these are "active" black holes, which devour infalling 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.
"These high-resolution images allow us to zoom in to see what's really going on when supermassive black holes launch radio jets, which wasn't possible before at frequencies near the FM radio band", said team
member Neal Jackson, University of Manchester, UK.
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.
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 antennas located as much as 2000 km apart. The result, a publicly-available data-processing pipeline, which is described in detail in one of the scientific papers, will allow astronomers from around the world to use Lofar to make high-resolution images with relative ease.
"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", said Leah Morabito.
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. Lofar doesn't just take pictures of the night sky; it must stitch together the data gathered by more than 70 000 antennas, 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 every second - must be digitised, transported to a central processor and then combined.
"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", said team member Frits Sweijen, Leiden University, Netherlands.
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