We don't know the origins of the most energetic particles and light in the Universe.
Yes, we can trace some. But there is more gamma radiation than we can count and much more neutrinos flowing through the Universe. There are many more. Astronomers have now discovered a reason for some of these black holes: they are almost dormant.
They claim this can explain the excessive'soft' Gamma Rays in the Universe, without relying upon cold (nonthermal electrons), which has been problematic since electrons are thermalized on short timescales that are too short to produce high-energy particles.
It is not uncommon to see neutrinos and gamma rays. Gamma radiation, the most energetic form light in the Universe is detected at extremely high energies (teraelectronvolt range).
Neutrinos, also known as ghost particles, are nearly massless particles that flow through the Universe and interact with little or nothing. These, too, have been detected at high energies.
These energies can only be obtained if the cosmic accelerator is present in the photons or particles. These objects should have high energy, such as supernova remnants or a black hole actively consuming material.
Even after accounting for these high-energy sources we still have a gamma radiation excess in lower'soft energies as well as a neutrino surplus, which is hard to explain.
Shigeo Kimura, an astronomer at Tohoku University in Japan, led a team of researchers that discovered the excess could be due to supermassive black hole activity. These black holes are neither completely active nor almost dormant.
A supermassive blackhole is activated when it is surrounded by a vast disk of gas and dust that slowly siphons off the black hole. The black hole's immense forces heat the material within the disk, causing it to blaze across a variety of electromagnetic wavelengths including gamma radiation.
Additionally, material is siphoned from the black hole around its magnetic field lines. These act as an accelerator and propel it towards the poles. It is then launched into space at a significant fraction of the speed light.
Although every galaxy has a supermassive dark hole at its center, not all of them are active. For example, the supermassive black holes in our galaxy are pretty scary.
Kimura and his colleagues believe that the gamma radiation excess in the lower energy range megaelectronvolts, rather than the giga- or the teraelectronvolts, could be caused by supermassive dark holes that are accreting so low it is much less visible to Earth's telescopes.
They did calculations and came up with a solution. Although there's less material around non-active blackholes, it still exists and gets heated up.
This hot plasma could reach billions of degrees Celsius and generate gamma radiation in megaelectronvolts, which is what we call "soft" gamma.
Protons can be rapidly accelerated within this plasma. These high-energy protons can interact with radiation and matter to generate neutrinos, which is also explained by the neutrino excess. These quiet supermassive blackholes are sufficient to explain at most a small fraction of the excess signals.
It's a hypothesis at best, but it works mathematically. Astronomers will have a better understanding of the things to look out for in future observations, and the mystery surrounding those mysterious gamma radiations will be easier to solve.
Nature Communications published the research.
