By combining 256 hours of observations of the northern sky, astronomers have created a map showing 25,000 supermassive black holes. This is the most detailed celestial map in the field of so-called low radio frequencies.
The map covers 4 percent of the northern half of the sky. To create this map, scientists deployed supercomputers with new algorithms that correct the ionosphere’s effect every four seconds.
The astronomers, including Leiden astronomers, used 52 stations with LOFAR antennas spread across nine European countries.
Stars or black holes?
The map seems to have several thousand stars, but they are supermassive black holes located in separate, distant galaxies.
Research leader Francesco de Gasperin (formerly Leiden University, now Universität Hamburg, Germany) says about the study: “This results from many years of work on incredibly difficult data. We had to invent new methods to convert the radio signals into images of the sky.”
Co-author Reinout van Weeren (Leiden Observatory) explains, “Observations at long radio wavelengths are complicated by the ionosphere that surrounds the Earth. This layer of free electrons acts like a cloudy lens that constantly moves across the radio telescope. It’s similar to 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.”
Along with supermassive black holes, the map offers a window to the universe‘s large-scale structure, among other things.
- F. de Gasperin et al. The LOFAR LBA Sky Survey – I. survey description and preliminary data release. (Free preprint).