The image above is a normal picture of the night sky, but what you're seeing is more special than just stars. There is a black hole in those white dots.
Each of those black holes is consuming material at the center of a galaxy millions of light-years away, that's how they could be pinpointed.
Astronomers created the most detailed map to date of black holes at low radio frequencies in early 2021, an achievement that took years and a Europe-sized radio telescope to make.
"This is the result of many years of work on incredibly difficult data," said astronomer Francesco de Gasperin. We had to invent new ways to convert the radio signals into images.
The survey is called theLOFAR/LOL Survey.
Black holes don't give off any radiation when they're not doing much.
The LOw Frequency Array (LOFAR) in Europe can detect the ultra-low radio wavelength in the above image. Around 20,000 radio antennas are distributed throughout 52 locations across Europe.
LOFAR is the only radio telescope network that can provide a view of the sky at frequencies below 100 megahertz. The LOFAR LBA Sky Survey is a plan to image the entire Northern sky in ultra-low-frequencies.
LOFAR has a hurdle to overcome because it's based on Earth. It's problematic for radio waves that can be reflected back into space. The ionosphere is opaque at frequencies below 5 megahertz.
Depending on atmospheric conditions, the frequencies that penetrate the ionosphere can vary. The team used computers to correct for ionospheric interference every four seconds. LOFAR stared at the sky for a long time and made a lot of changes.
This has given us a clear view of the sky.
Huub Rttgering of the Leiden Observatory in the Netherlands said that it was wonderful to see that the software had worked out.
Having to correct for the ionosphere will allow astronomer to study the ionosphere itself. The relationship of the ionosphere with solar cycles could be characterized with greater detail with the LOLSS. Scientists will be able to better constrain ionospheric models.
The survey will provide new data on all sorts of objects and phenomena, as well as possibly undiscovered or unexplored objects in the region below 50 megahertz.
The researchers wrote in their paper that the final release of the survey will facilitate advances in astronomy.
This will allow for the study of more than 1 million low-frequency radio spectrum, providing unique insights on physical models for galaxies, active nuclei, and other fields of research. This experiment is an attempt to explore the ultra-low Frequency sky at a high resolution and depth.
The results have been published.
The first version of this article was published in February of 2021.
