When we glance at the above image, we might think it is the night sky with a cluster of glittering stars, but these are not stars. Every white dot in this image represents an active supermassive black hole.
Blackholes, in general, don’t emit any detectable radiation, making it difficult for us to detect them. However, when they accrete materials from the nearby star or the spool of dust, they emit radiation across multiple wavelengths. We can detect these radiations and pinpoint the source.
Astronomers created this special low-frequency map consisting of around 25,0000 active supermassive blackholes using Low-Frequency Array (LOFAR).
The LOFAR is a large network of radio telescopes comprising around 20,000 fairly simple astronomical radio interferometers spread across 52 locations in Europe. LOFAR makes observations at radio frequencies between 10 and 250 MHz, and individual observations are combined using software to create a map of the sky. It is the only array capable of high-resolution imaging of deep space at frequencies below 100 MHz.
The ionosphere can reflect ultra-low-frequency radio waves into space. LOFAR, being a ground-based array, suffers from this ionospheric interference, and the frequencies that pass the ionosphere layer can be affected by the atmosphere. Hence, the team ran algorithms every four seconds on supercomputers to compensate for this interference.
Compensating for ionospheric interferences allows astronomers to study the ionosphere itself in detail. Ionospheric traveling waves, scintillations, and ionosphere – solar cycle relationship can be studied in detail with the LoLSS data.
The released survey data covers about four percent of the Northern sky and is part of the LOFAR LBA Sky Survey (LoLSS) to map the entire Northern sky in ultra low-frequencies.
The results will soon be published in Astronomy & Astrophysics.
New data from the survey can provide insights into all objects in the universe and help discover new objects and analyze unexplored objects.
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