by Scientists may have found evidence that vampire black holes feeding on their victim stars – so-called microquasars – are the cosmic particle accelerators responsible for the mysterious high-energy cosmic rays we see bombarding the Earth.
These stellar mass black holes are in binary systems with supermassive stars from which they richly extract material. Some of that cosmic matter is then sent towards the poles of the black hole, where it is subsequently blasted out in high-speed relativistic jets. Microquasars get their name because they resemble quasars, which are powered by supermassive black holes that feed on the surrounding matter, but are less extreme.
First discovered in 1912, cosmic rays can hit our planet with enormous energies reaching 10²⁰ electronvolts (eV). That’s far more energetic than the particles accelerated at the Large Hardon Collider, which is the world’s largest and most powerful particle accelerator.
To that end, supernovae and microtremors have been suggested as powerful accelerators of cosmic particles for our Universe. Scientists therefore believe that these phenomena could be responsible for those high-energy cosmic rays. But the evidence that microquasars are accelerating particles to high energies is scant — so far, that is.
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The team made the link 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 Milky Way’s most powerful microquasar. It is called SS 433.
These gamma rays are created when SS 433’s jets slam into the surrounding material, creating a shock front that accelerates electrons to speeds great enough to account for the particles seen in high-energy cosmic rays.
“The acceleration mechanism would be similar to that in a supernova remnant, although the perturbations in SS 433’s jets are faster than supernova remnant perturbations and can accelerate particles to higher energies,” Valentí Bosch-Ramon , associate professor at the University of Barcelona, he wrote in a perspectives paper discussing the research published in Science. “The highly energetic photons detected from the large jets of SS 433 are an indirect indicator that the types should not be neglected these things when trying to explain the most energetic nuclei in Galactic cosmic rays.”
The cosmic manatee
SS 433 was the first microquasar ever discovered; Its contents were first revealed in 1975. It was named “SS 433” after being included in a 1977 catalog of celestial bodies, then rising to fame when science fiction author Arthur C. Clarke named it as one of his selections “Seven Wonders of the. World.”
SS 433 is at the heart of the supernova wreckage designated W50, located approximately 18,000 light-years from Earth and known as the “manatee nebula”. Many years of intensive study have revealed that SS 433 consists of a black hole with a mass of about 10 to 15 times the mass of the sun, and a white galaxy. The two are separated by about 15 million miles and orbit each other once 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 massive gravity can destroy its companion star’s outer strips. This stripped material forms an accretion disk around the black hole, some of which is actually sent to the black hole. Other parts of the matter are connected to the poles of the black hole by powerful magnetic fields. From there, the funnel material is blasted at about 26% of the speed of light.
These jets go in a corkscrew-like pattern and are so powerful that they even create a W50.
The W50 supernova wreckage was created when a massive star exploded around 20,000 years ago as we see it today. The microquasar created within two bulges or “humps” that cause W50 to take on the appearance of a giant cosmic manatee, hence its colorful nickname.
SS 433’s jets can be seen in radio waves that extend out for about 1 light year from either side of their source. Eventually, they lose energy and fade to the point where they are no longer visible. Curiously, however, these relativistic jets suddenly reappear in high-energy X-ray light about 75 light-years from the origin of the microquasar.
This, the team says, shows that something within each jet is accelerating particles to even higher energies, and therefore higher speeds than when they burst out of the black hole.
Using the five telescopes in Namibia that comprise HESS, the scientists investigated these strange jets from SS 433 in gamma-ray light, finding that more energetic gamma-rays come from further away from the binary system.
The team found that the best explanation for this was that high-speed, shock-accelerated electrons would scatter infrared light particles and transform them into gamma rays.
Higher-energy gamma rays detected from the two-point feeding black hole, about 75 light-years from the central binary SS 433, show where shocks are reshaping jets back into a tight column and giving the associated particles a boost of energy.
This also explains the emergence of X-ray jets: accelerated electrons produce X-ray emissions.
“This is the first ever observation of energy-dependent morphology in the gamma-ray emission of an astrophysical jet,” Laura Olivera-Nieto, team leader and scientist at the Max-Planck-Institut für Kernphysik, said in a statement. “We were initially surprised by these results. Due to the concentration of those high-energy photons at the re-emergence sites of the X-ray jets there must be an efficient acceleration of the particles, which was not expected.”
There are still puzzles regarding this interesting microquasar that the team will now do their best to solve. This will include finding out what the jets have hit to create those disturbances so far 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 feature,” said Olivera-Nieto.
The team will also try to apply what they learned about the microquasar’s jets to jets from more powerful black hole-powered supermassive quasars.
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Furthermore, although a source for high-energy cosmic rays is suggested, these results still do not close the book on the century-old cosmic mystery.
“SS 433 cannot be the source of the highly energetic, peta-electron, cosmic ray protons detected on Earth because the source is too young for its particles to reach Earth after escaping from the source ,” Bosch-Ramon wrote. “Nevertheless, closer and longer-lived microquasars, even if weaker and individually more difficult to detect, may be contributing non-illustratively to the local peta-electron of cosmic ray volts .”
The team’s research was published Thursday, January 25, in the journal Science.
