The image above may look like a pretty typical picture of the night sky, but what you look at is much more special than just shiny stars. Each of these white dots is an active black dot.
And each of those black holes is throwing material at the heart of a galaxy millions of light-years away – that’s how they might be marked at all.
With 25,000 such dots, astronomers have created the most detailed map to date of black holes at low radio frequencies, an achievement that took years and a European-sized radio telescope to put together.
“This is the result of several years of work on very complex data,” explained astronaut Francesco de Gasperin of the University of Hamburg in Germany. “We had to devise new ways to turn the radio signals into images of the skies. “
(LOFAR / LOL check)
When they are just hanging out without doing much, black holes do not emit visible radiation, making them much harder to find. When a black hole actively collects material – spewing it in from a disc of dust and gas that circulates it as water circulates drainage – the intense forces involved generate radiation over many -wave that we can find across the vastness of space.
What makes the above image so special is that it covers the ultra-low radio waves, as found with the LOw Frequency ARray (LOFAR) in Europe. This interferometric network consists of approximately 20,000 radio antennas, distributed across 52 locations across Europe.
Currently, LOFAR is the only radio telescope network capable of producing deep, high-resolution images at frequencies below 100 megahertz, offering a view of the skies as nothing else. This data release, covering four percent of the Northern skies, is the first for the network’s ambitious plan to image the entire Northern sky in ultra-low frequencies, LOFAR LBA Air Survey (LoLSS).
Because it is Earth-based, LOFAR has a major hurdle to overcome that is not affected by location-based telescopes: the ionosphere. This is especially difficult for ultra-low frequency radio waves, which can be seen back into space. At frequencies lower than 5 megahertz, the ionosphere is unclear for this purpose.
The frequencies entering the ionosphere can vary depending on the position of the atmosphere. To overcome this problem, the team used supercomputers running algorithms to correct for ionospheric intervention every four seconds. Over the 256 hours LOFAR watched the skies, that corrects enough.
This is what gave us such a clear view of the ultra-low frequency sky.
“After many years of software development, it’s so amazing to see that this has now worked out,” said astronaut Huub Röttgering of the Leiden Observatory in the Netherlands.
Adjusting for the ionosphere also has another advantage: it allows astronauts to use LoLSS data to study the ionosphere itself. Ionospheric travel waves, scintillations, and the relationship of the ionosphere to solar cycles could be identified in much greater detail by the LoLSS. This will allow scientists to better inhibit ionospheric models.
And the survey will provide up-to-date data on all sorts of astronomical objects and onions, as well as perhaps unexplored or unexplored items in the 50 megahertz region.
“The final release of the survey will enable advances across a number of spatial research areas,” the researchers wrote in their paper.
“[This] it will allow the study of more than 1 million low-frequency radio spectra, providing unparalleled insights into physical models for galaxies, active nuclei, galaxy assemblages, and other areas of research. “
The results are expected to be published in Astronomy & Astronomy.