Scientists may have found evidence that black vampire holes that feed on their victim stars – so-called microquasars – are the cosmic particle accelerators responsible for mysterious high-energy cosmic rays we see bombarding Earth.
These stellar-mass black holes exist in binary systems with a supergiant star from which they greedily strip material. Some of that stellar matter is then channeled to the black hole’s poles, where it is then blown away with high-speed relativistic jets. Microquasars get their name because they are similar to quasars, which are powered by giant supermassive black holes that feed on surrounding material, but not as extreme.
First discovered in 1912, cosmic rays can hit our planet with staggering energies that can reach 10²⁰ electron volts (eV). That is much more energetic than the particles accelerated by the Large Hardon Collider, Earth’s largest and most powerful particle accelerator.
To this end, supernovae and microquasars have been proposed as the powerful cosmic particle accelerators of our universe. Scientists therefore believe that these phenomena may be responsible for these high-energy cosmic rays. But evidence that microquasars accelerate particles to such high energies is so far scarce.
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The team made the connection between cosmic rays and microquasars when they used the High Energy Stereoscopic System (HESS) to detect extremely high-energy gamma rays coming from the jets of the most powerful microquasar in the Milky Way. It’s called SS 433.
These gamma rays are created when SS 433’s jets collide with surrounding matter, creating a shock front that accelerates electrons to speeds large enough to explain the particles observed in high-energy cosmic rays.
“The acceleration mechanism would be similar to that of a supernova remnant, although the shocks in SS 433 jets are faster than shocks from supernova remnants and can accelerate particles to higher energies,” says Valentí Bosch-Ramon, associate professor at the University from Barcelona. wrote in a perspective article discussing the research published in Science. “The highly energetic photons detected by SS 433’s large-scale jets are an indirect indicator that these types of objects should not be neglected when trying to explain the most energetic nuclei in galactic cosmic rays.”
The cosmic manatee
SS 433 was actually the first microquasar ever discovered; its existence was first revealed in 1975. It was given the name “SS 433” after it was included in a 1977 catalog of celestial objects, and subsequently became famous when science fiction author Arthur C. Clarke named it as one of his alternate “Seven Wonders of the Celestial Bodies”. World.”
SS 433 is at the heart of the supernova wreck called W50, located about 18,000 light-years from Earth and nicknamed the ‘Manatee Nebula’. Decades of intensive research have shown that SS 433 consists of a black hole with a mass about 10 to 15 times that of the Sun, and a white supergiant star. The two are about 15 million miles apart and orbit each other every 13 Earth days.
With no more than about a third of the distance between Mercury and the Sun between the two occupants of SS 433, the black hole’s enormous gravity can strip the outer layers of its stellar companion. This stripped material forms an accretion disk around the black hole, while some of it is actually carried into the black hole. Other parts of the material are guided to the poles of the black hole via powerful magnetic fields. From there, the funneled material is blown out at about 26% of the speed of light.
These jets rotate in a corkscrew-like pattern and are so powerful that they even form W50.
The W50 supernova wreckage was created when a massive star exploded some 20,000 years before the current situation. The microquasar inside has created two bulges or “bumps” that give W50 the appearance of a huge cosmic manatee, hence its colorful nickname.
SS 433’s jets can be seen in radio waves extending about 1 light-year on either side of their source. Eventually they lose energy and darken to the point where they are no longer visible. Curiously, however, these relativistic jets abruptly reappear in high-energy X-ray light about 75 light-years away from the microquasar’s origin.
According to the team, this indicates that something in each jet is accelerating particles to even higher energies, and therefore to greater speeds, than they had when they were blown around the black hole.
Using the five telescopes in Namibia that make up HESS, the scientists examined these strange jets from SS 433 in gamma-ray light, finding that more energetic gamma-rays originate further from the binary system.
The team found that the best explanation for this would be that fast, shock-accelerated electrons scatter infrared light particles and transform them into gamma rays.
The higher energy gamma rays found far from the feeding black hole indicate two points, about 75 light-years away from the central binary of SS 433, where shocks turn the jets back into a tight column and give the associated particles an energy boost .
This also explains the return of the jets in X-rays: accelerated electrons produce X-rays.
“This is the very first observation of energy-dependent morphology in the gamma-ray emission of an astrophysical beam,” Laura Olivera-Nieto, team leader and scientist at the Max-Planck-Institut für Kernphysik, said in a statement. “We were initially surprised by these findings. The concentration of such high-energy photons at the locations where the X-ray jets reappear means that efficient particle acceleration must be taking place there, which was not expected.”
There are still puzzles surrounding this intriguing microquasar that the team will now try to solve. This includes discovering what the jets are attacking to cause these shocks so far away from the binary system that launched them.
“We still don’t have a model that can uniformly explain all the properties of the jet, because no model has yet predicted this characteristic,” Olivera-Nieto said.
The team will also try to apply what they learned about the jets from microquasars to jets emanating from more powerful supermassive black hole-powered quasars.
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Moreover, while these findings suggest a source for high-energy cosmic rays, they do not close the book on the age-old cosmic mystery.
“SS 433 cannot be the source of the highly energetic, petaelectronvolt, cosmic ray protons detected on Earth because the source is too young for the particles to reach Earth once they escape the source,” Bosch wrote -Ramon. “However, microquasars that are closer and longer-lived, even if fainter and individually more difficult to detect, could make a non-negligible contribution to the local peta-electronvolt cosmic rays.”
The team’s research was published on Thursday, January 25 in the journal Science.