A team of astronomers from different countries recently published a map which looks like a night sky full of stars but is in fact 25,000 supermassive black holes.

Black holes have fascinated various groups of people from school children to physicists and scientists, irrelevant of age. Yet we are still learning more and more about them with the passing time.

When we look at this map, we perceive numerous white dots where each dot is a black hole, situated in its own galaxy. The article released by University of Leiden on February 19 shared that it is the most detailed celestial map in the field of so-called low radio frequencies.

As many as 52 astronomers created the map using low radio frequencies as detected by the LOw Frequency ARray (LOFAR) in Europe and combining 256 hours of observations of the northern sky. LOFAR is said to be the largest combined radio telescope in the world, consisting of 52 stations spread over nine different countries: The Netherlands, Germany, Poland, France, the United Kingdom, Sweden, Ireland, Latvia and Italy.

This image currently shows 4 per cent of the northern half of the sky, and if the astronomers are successful, they will create the entire northern sky.

The article stated, "The radio emissions are emitted by matter that was ejected as it got close to the black hole."

According to the research leader Francesco de Gasperin, "This is the result of many years of work on incredibly difficult data. We had to invent new methods to convert the radio signals into images of the sky."

The process of creating the map included observations at long radio wavelengths, and because of the Earth's ionosphere, it is much difficult for the radio telescope to get a clear picture.

Co-author Reinout van Weeren explained this as "when you try to see the world while immersed in a swimming pool – when you look up, the waves on the water of the pool deflect the light rays and distort the view."

The map is relevant not only to get insight about the supermassive black holes but also about the large-scale structure of the universe.

The map is to be published in the journal Astronomy & Astrophysics soon.