Supermassive black holes are found in the largest galaxies in the universe and are billions of times more massive than our Sun. These black holes power active galactic nuclei, which emit light across the spectrum, including radio waves. The active galactic nucleus in Messier 87 is an incredibly powerful emitter of radio waves, far surpassing any radio transmitter on Earth. However, not all galaxies with supermassive black holes emit radio waves, leading to the question of whether they are silent or simply not switched on in the radio spectrum.
To investigate this, researchers searched for radio waves from the most massive galaxies in the nearby universe using the ASKAP radio telescope in Western Australia. Previous studies had detected radio waves from some massive galaxies, but it was unclear if all massive galaxies were radio sources. The new study found that all 40 of the most massive galaxies in their survey emitted radio waves.
While it appears that all very massive galaxies emit radio waves, not all of their black holes may be actively feeding. Some radio sources in massive galaxies may be afterglows from earlier activity, suggesting temporary pauses in feeding. Additionally, the power of radio emissions can vary greatly between galaxies of the same mass. The study found that galaxies that rotate the least tend to be the strongest radio wave emitters, although there are exceptions to this trend, such as galaxies that have undergone mergers with other galaxies.
The new generation of radio telescopes has provided valuable data on very massive galaxies and their black holes. However, there is still much to learn about how these systems work and why their radio power varies. Astronomers will continue to follow these clues to unravel the mysteries of supermassive black holes and their role in powering celestial objects.