Vampire Black Holes: Unveiling the Cosmic Particle Accelerators
In a groundbreaking discovery, scientists have uncovered evidence suggesting that vampire black holes, known as microquasars, are responsible for the mysterious high-energy cosmic rays bombarding Earth. These stellar mass black holes exist in binary systems with supergiant stars, from which they greedily strip material. The stripped matter is then channeled towards the poles of the black hole, where it is blasted out in high-speed relativistic jets. This new finding sheds light on the long-standing question of what accelerates cosmic rays to such high energies.
Cosmic rays, first discovered in 1912, are particles that can hit our planet with energies reaching an astonishing 10²⁰ electronvolts (eV). To put this into perspective, these particles are more energetic than those accelerated at the Large Hadron Collider, which is Earth’s largest and most powerful particle accelerator. Supernovas and microquasars have been proposed as potential cosmic particle accelerators, but evidence of microquasars accelerating particles to such high energies has been scarce until now.
The breakthrough came when scientists used the High Energy Stereoscopic System (H.E.S.S.) to detect extremely high-energy gamma rays emanating from the jets of SS 433, the most powerful microquasar in the Milky Way. These gamma rays are produced when the jets of SS 433 collide with surrounding matter, creating a shock front that accelerates electrons to speeds capable of accounting for the particles observed in high-energy cosmic rays.
“The acceleration mechanism would be similar to that in a supernova remnant, although the shocks in SS 433 jets are faster than supernova remnant shocks and can accelerate particles to higher energies,” explained Valentí Bosch-Ramon, an associate professor at the University of Barcelona.
SS 433, the first microquasar ever discovered, sits at the heart of the supernova wreckage known as W50. Located approximately 18,000 light-years from Earth, W50 has earned the nickname “manatee nebula” due to its resemblance to the gentle sea creature. SS 433 consists of a black hole with a mass 10 to 15 times that of the sun and a white supergiant star. These two celestial bodies orbit each other every 13 Earth days, with a distance between them that is only about a third of the distance between Mercury and the sun.
The immense gravity of the black hole strips the outer layers of its stellar companion, forming an accretion disk around the black hole. Some of this material is fed to the black hole, while other parts are funneled to the black hole’s poles via powerful magnetic fields. From there, the material is blasted out at speeds of around 26% of the speed of light. These powerful jets shape W50 into its distinctive manatee-like appearance.
The jets of SS 433 can be observed in radio waves extending out for approximately 1 light-year from their source. However, they suddenly reappear in high-energy X-ray light around 75 light-years from the microquasar’s origin. This phenomenon indicates that something within each jet is accelerating particles to even higher energies and speeds than when they were initially expelled from the black hole.
Using H.E.S.S., scientists investigated these peculiar jets in gamma-ray light and discovered that more energetic gamma rays originate further from the binary system. The team concluded that high-speed, shock-accelerated electrons scatter infrared particles of light, transforming them into gamma rays. The higher energy gamma rays found away from the feeding black hole suggest two points, approximately 75 light-years from the central binary of SS 433, where shocks reshape the jets into a tight column and give the associated particles an energy boost. This also explains the reappearance of the jets in X-rays, as 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,” said Laura Olivera-Nieto, team leader and scientist with the Max-Planck-Institut für Kernphysik. “We were initially puzzled by these findings. The concentration of such high-energy photons at the sites of the X-ray jets’ reappearance means efficient particle acceleration must be taking place there, which was not expected.”
While this discovery provides valuable insights into microquasars and their role in cosmic particle acceleration, there are still many puzzles surrounding SS 433 that scientists aim to solve. They hope to determine what the jets are striking to create the shocks observed so far from the binary system.
The team also plans to apply their findings about microquasar jets to jets emerging from more powerful supermassive black hole-powered quasars. Additionally, while these findings suggest a potential source for high-energy cosmic rays, they do not fully explain the century-old cosmic mystery.
“SS 433 cannot be the source of the very energetic, peta-electronvolt cosmic-ray
