The above image may look like a somewhat normal image of the night sky, but what you are looking at is more special than just twinkling stars. Each of those white points is an active supermassive black hole.
And all of those black holes It consumes matter at the heart of a galaxy millions of light-years away – this is how it could ever be determined.
With a total of 25,000 such points, astronomers have created the most detailed map yet of black holes at low radio frequencies, a feat that took years and a European-sized radio telescope to assemble.
“This is the result of many years of working on very difficult data,” Explained astronomer Francesco de Gasperin From the University of Hamburg, Germany. “We had to devise new ways to convert radio signals into images of the sky.”
When black holes do not do much work, they do not emit any detectable radiation, which makes finding them much more difficult. When a black hole is actively forming matter – enveloping it from a disk of dust and gas that rotates around it as water circulates around a drain – the intense forces involved generate radiation across multiple wavelengths that we can detect across the expansion of space.
What makes the above image so special is that it covers very low radio wavelengths, as revealed by LOw Frequency ARray (Promises) in Europe. This interferometric network consists of about 20,000 wireless antennas, distributed in 52 locations across Europe.
Currently, LOFAR is the only radio telescope network capable of high-resolution deep imaging at frequencies below 100MHz, providing an unparalleled view of the sky. This data release, covering four percent of the northern sky, is the first for the network’s ambitious plan to photograph the entire northern sky at extremely low frequencies, the LOFAR LBA Sky Survey (LoLSS).
Since it is based on Earth, LOFAR has one big hurdle to overcome that doesn’t affect space telescopes: the ionosphere. This is Especially problematic for very low frequency radio waves, Which can be reflected back in space. At frequencies below 5 MHz, the ionosphere is opaque for this reason.
The frequencies that penetrate into the ionosphere can vary according to weather conditions. To get around this problem, the team used supercomputers that worked on algorithms to correct ionospheric interference every four seconds. Over the course of the 256 hours LOFAR stared at the sky, there are tons of corrections.
This gave us a clear view of the extremely low-end sky.
“After so many years of software development, it’s great to see that this has actually worked,” Astronomer Hope Rutgering said From the Leiden Observatory in the Netherlands.
Having to correct for the ionosphere has another benefit, too: it would allow astronomers to use LoLSS data to study the ionosphere itself. Ionospheric travel waves, flash, And the relationship of the ionosphere to solar cycles can be described in much more detail with LoLSS. This will allow scientists to better constrain the ionosphere models.
The survey will provide new data on all types of astronomical objects and phenomena, as well as undiscovered or undiscovered objects in the area below 50 MHz.
“The final version of the survey will facilitate progress across a range of areas of astronomical research,” The researchers wrote in their paper.
“[This] It will allow the study of more than a million low-frequency radio spectrums, providing unique insights into the physical models of galaxies, active nuclei, galaxy clusters, and other areas of research. This experience represents a unique attempt to explore extremely low-frequency skies with high resolution and angular depth. “
The results will be published at Astronomy and Astrophysics.