Key takeaways
- An international team of researchers has created a groundbreaking map of the night sky revealing 25,000 supermassive black holes. Unlike traditional maps, this one is devoid of stars, focusing solely on these massive entities.
- Although black holes themselves are nearly invisible, the material they consume forms an accretion disk around them. This disk emits powerful radio waves as it spins at high speeds and occasionally ejects jets of particles, known as relativistic jets, from the black hole’s magnetic poles.
- The map was created using the Low Frequency Array (LOFAR), a network of 52 radio telescopes spread across Europe. LOFAR’s capabilities allowed astronomers to detect the low-frequency radio waves emitted by the jets from supermassive black holes.
- The new map captures low-frequency radio emissions from supermassive black holes in distant galaxies, covering about 4% of the northern hemisphere’s night sky. The researchers aim to eventually map the entire northern sky.
- Detecting these radio waves is challenging due to the Earth’s ionosphere, which distorts signals. To overcome this, researchers developed a supercomputer algorithm that adjusted for the ionosphere’s distortions every four seconds during 256 hours of observation.
An international team of researchers has recently unveiled a fascinating map of the night sky that contains 25,000 supermassive black holes but lacks any stars.
We know what you are thinking. How is that conceivable if black holes don’t emit light, you foolish gooses? That’s only half correct. The black hole itself is nearly invisible, but if it consumes a star or another object, the tidal forces of its gravity will tear it apart, forming a flattened accretion ring around it.
The material in the disk is spinning around the black hole’s event horizon at substantial fractions of the speed of light, and it is occasionally ejected by the black hole’s powerful magnetic field, resulting in jets of particles at the black hole’s magnetic poles.
These relativistic jets, as they are known, emit a large number of radio waves. Astronomers used the Low Frequency Array (LOFAR), a network of 52 radio telescopes spread across Europe, to survey the northern skies.
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“This is the result of many years of work on incredibly difficult data,” said lead researcher Francesco de Gasperin, who previously worked at Leiden University but is now at Universität Hamburg in Germany. “We had to invent new methods to convert the radio signals into images of the sky.”
The stunning map depicts low-frequency radio emissions from 25,000 supermassive black holes at the center of distant galaxies and takes up just approximately 4% of the northern hemisphere’s night sky. The researchers plan to eventually compile a full sky map of supermassive black holes visible in the northern hemisphere.
The map was part of a study accepted for publication in a future issue of the journal Astronomy & Astrophysics.
Analysis: computer algorithms help us see the universe
One of the challenges in detecting radio waves from supermassive black holes is that they frequently create low-frequency radio waves. Normally, this would not be an issue, but for Earth-based radio telescopes, the ionosphere entirely reflects radio waves below 3MHz and distorts signals beyond 30MHz.
“It’s similar to when you try to see the world while immersed in a swimming pool,” said study co-author Reinout van Weeren, of the Leiden Observatory. “When you look up, the waves on the water of the pool deflect the light rays and distort the view.”
To counteract this, researchers created a supercomputer algorithm that adjusted for the ionosphere’s distorting influence every four seconds over the course of 256 hours of observation.
“After many years of software development, it is wonderful to see that this has now really worked out,” stated research co-author Huub Röttgering, Scientific Director of the Leiden Observatory.
This isn’t the first time a computer algorithm has helped astronomers map the heavens. Katie Bouman is well known for developing the algorithm that combined data streams from the Event Horizon Telescope to produce the first image of a black hole’s event horizon.
Computer algorithms have long been instrumental in astronomy, and as our computers become even more powerful, the power of those algorithms to open our eyes to the universe will only grow.