Monday, October 3, 2022

Mystery gamma rays may originate from sleepy black holes, astronomers say

The most energetic light and particles in the universe represent an enduring mystery: We don’t know where they come from.

Sure, we can figure something out; But there may be more gamma radiation and neutrinos streaming through the universe than we can account for. Too much. And astronomers have found an explanation for some of them: nearly dormant black holes.

This, they say, can explain the abundance of ‘soft’ gamma rays in the universe without relying on cold (nonthermal) electrons – which has always been a problematic explanation, as electrons are thought to be too low-generating. Thermal is done on the go timetable. energy particle.

Gamma rays and neutrinos are not at all rare. Gamma radiation is the most energetic form of light in the universe, and has been detected in the extraordinarily high energy – teraelectronvolt range.

Neutrinos, or ghost particles, are nearly massless particles swirling through the universe, which barely interact with anything. Those too, we have detected higher energies.

To acquire these energies, the photons and particles within them require the presence of a cosmic accelerator. These must be high-energy objects, such as supernova remnants, or a black hole actively devouring material.

But once we account for these high-energy sources, we still have an excess of gamma-rays as well as neutrinos at lower ‘soft’ energies, which are difficult to explain.

According to a team of researchers led by astronomer Shigio Kimura of Tohoku University in Japan, the excess may come from an unexpected source: supermassive black holes that are nearly, but not quite, inactive — but neither are they completely active.

When a supermassive black hole is active, it is surrounded by a huge disk of dust and gas that is slowly being poured into the black hole. The immense forces at play in the space around the black hole heat the material in the disk so that it blazes across a range of electromagnetic wavelengths, including gamma radiation.

In addition, some material is carried outside the black hole along its magnetic field lines, which act as an accelerator, toward the poles, where it is launched into space at a significant percentage of the speed of light. Is.

Each galaxy is believed to contain a supermassive black hole at its center, but not all are active. For example, our galaxy’s supermassive black hole is pretty snoozy.

According to Kimura and his team, the excess of gamma-rays in the lower energy range – megaelectronvolts rather than giga- or teraelectronvolts – may be produced by supermassive black holes that are accumulating at such low levels that it is too small for our telescopes here. can be slow. on the earth.

The team did the calculations, and figured out how it would work. Although less material circulates around these non-active black holes, there is still some, and it still gets hot.

In fact, this hot plasma can reach billions of degrees Celsius – hot enough to generate gamma radiation in the megaelectronvolt range, or what we call ‘soft’ gamma rays.

Within this plasma, protons can be accelerated to high speeds. When these high-energy protons interact with radiation and matter, they can generate neutrinos – thus also explaining the abundance of neutrinos. And there are enough of these cool supermassive black holes in the universe to explain at least a significant proportion of these additional signals.

So far, it’s just a hypothesis, but the math checks. With this information, astronomers should have a better idea of ​​what to look for in future observations – and the mystery of those inexplicable gamma rays will be closer to being solved.

research has been published in nature communication.

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Nation World News Desk
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