(ORDO NEWS) — The image above may look like a fairly ordinary image of the night sky, but what you’re looking at is much more special than just sparkling stars. Each of these white dots is an active supermassive black hole.
And each of these black holes is devouring matter in the heart of a galaxy that is millions of light-years away from us – that’s how they can generally be defined.
This image, released in 2021, contains 25,000 of these dots. It is the most detailed map of black holes at low radio frequencies to date, taking years and a Europa-sized radio telescope to complete.
“This is the result of years of work with incredibly complex data,” explained astronomer Francesco de Gasperin from the University of Hamburg in Germany back in February 2021.
“We had to invent new methods for converting radio signals into images of the sky.”
When they’re just hanging around, black holes don’t do anything, they don’t emit noticeable radiation, so they’re much harder to find.
When a black hole is actively accreting material winding it from a disk of dust and gas that spins around it just like water spins around a drain the intense forces involved generate radiation at multiple wavelengths that we can detect in the vastness of space.
What makes the above image so special is that it covers the ultra-low radio waves detected by Low Frequency ARray (LOFAR) in Europe.
This interferometric network consists of approximately 20,000 radio antennas located at 52 locations throughout Europe.
Currently, LOFAR is the only radio telescope network capable of capturing high-resolution deep images at frequencies below 100 MHz, offering an overview of the sky like no other.
Covering four percent of the northern sky, this data release was the first for the network’s ambitious plan to image the entire northern sky at ultra-low frequencies, the LOFAR LBA Sky Survey (LoLSS).
Because LOFAR is Earth-based, it needs to overcome a major hurdle that space telescopes don’t touch: the ionosphere.
This is especially important. problematic for ultra-low frequency radio waves, which can be reflected back into space. For this reason, at frequencies below 5 megahertz, the ionosphere is opaque.
The frequencies penetrating the ionosphere can vary depending on atmospheric conditions.
To solve this problem, the team used supercomputer algorithms to correct ionospheric interference every four seconds. During the 256 hours that LOFAR looked at the sky, many corrections were made.
This is what gave us such a clear view of the ELF sky.
“After many years of software development, it’s great to see that it’s actually worked now,” said astronomer Huub Röttgering of the Leiden Observatory in the Netherlands.
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