Four decades ago, researchers discovered a celestial oddity. There was an object inside the Milky Way that behaved just like a quasar, the active core of distant galaxies, but on a much smaller scale. This microquasar, called SS 433, has been studied in detail ever since. Now researchers have estimated that it shoots jets of material out at 26 percent of the speed of light.
The incredible speed is generated by the unusual setup of the system. A quasar is a supermassive black hole trying to gobble up gas too quickly and ending up shooting some of it back out in a huge jet. Microquasars are different in size but not in effect. The microquasar has a compact object at its center, likely a stellar-sized black hole or maybe a neutron star, stealing material from a companion star, and then throwing some of the plasma (electrons in particular) into a jet.
As reported in Nature, the electrons are accelerated by the object's magnetic field to energies thousands of times higher than what we can currently produce in our particle accelerators. These ultra-high-energy electrons interact with the cosmic microwave background, the light from the Big Bang, and produce gamma rays that were observed by the High-Altitude Water Cherenkov Gamma-Ray Observatory (HAWC).
“SS 433 is an unusual star system and each year something new has come out about it,” co-author Segev BenZvi, from the University of Rochester, said in a statement. “This new observation of high-energy gamma rays builds on almost 40 years of measurements of one of the weirdest objects in the Milky Way. Every measurement gives us a different piece of the puzzle, and we hope to use our knowledge to learn about the quasar family as a whole.”
HAWC is an unusual observatory because gamma-ray emissions are not studied with regular telescopes. HAWC is made up of 300 tanks of water and it doesn’t detect gamma rays directly. When a gamma-ray photon hits the atmosphere, it generates a shower of fast-moving particles. When they hit the water in the tanks, they are moving faster than light can move in water, and for this reason, they emit the so-called Cherenkov radiation. Cameras are in place to observe this radiation. By using the many tanks of the observatory, it is possible to study gamma-ray sources in detail.
“SS 433 is right in our neighborhood and so, using HAWC’s unique wide field of view, we were able to resolve both microquasar particle acceleration sites,” added the University of Maryland's Professor Jordan Goodman, US lead investigator and spokesperson for the HAWC collaboration. “By combining our observations with multi-wavelength and multi-messenger data from other telescopes, we can improve our understanding of particle acceleration in SS 433 and its giant, extragalactic cousins, called quasars.”
SS 433 is located 15,000 light-years from Earth and is one of the dozen microquasars that exist in the Milky Way.