Astronomers have discovered the universe’s most powerful winds: driven by supermassive black holes, they ripple across interstellar space bulldozing through material in galaxies, and are known as quasar tsunamis, we’re told.
“No other phenomena carries more mechanical energy,” said Nahum Arav, first author of a study into the winds, and a physics professor at the Virginia Polytechnic Institute and State University (Virginia Tech) in the US. “The amount of mechanical energy that these outflows carry is up to several hundreds of times higher than the luminosity of the entire Milky Way galaxy.” Move over, gamma-ray bursts, which are some of the most energetic events recorded in the universe: quasar tsunamis generate more energy in the long run, Arav explained. “Over the lifetime of ten million years, these outflows produce a million times more energy than a gamma-ray burst.” Quasars are extremely bright distant objects embedded deep within giant galaxies. As supermassive black holes gobble gas, the in-falling matter is compressed into a disk. This swirling structure is heated by frictional forces and it emits intense electromagnetic radiation. The subsequent radiation pressure pushes matter away from the galaxy’s center and drives winds that accelerate to velocities tens of millions of miles per hour. The team of researchers spotted one outflow that sped up from about 43 million miles per hour to 46 million miles per hour over three years. They reckon it’ll only get faster over time. The shock fronts from the ripples reach scorching temperatures as the wind hurls into the surrounding gas causing it to emit X-ray radiation that will gradually fade into visible and infrared light. The glow would light up the galaxy in different spots. “You’d get a huge light show – like Christmas trees all over the galaxy,” said Arav. Quasar tsunamis don’t just put on glittering light displays in space: they may explain longstanding cosmic mysteries such as why massive galaxies are so rare, and the strange link between the mass of a black hole in a galaxy and the mass contained in the galaxy. It’s possible that their destructive nature cuts off star formation, wiping out the resources needed to sustain a galaxy. The scientists discovered the phenomenon while studying 13 quasar winds: they were able to measure the speed of the outflows using NASA’s Hubble Space Telescope. The spectrograph instrument on-board measures the chemical signatures of gas molecules, and since the quasar wind accelerates the molecules, there is a doppler shift in the observations. That shift allows them to estimate the speed of these quasar tsunamis. “Hubble’s ultraviolet observations allow us to follow the whole range of energy output from quasars, from cooler gas to the extremely hot, highly ionized gas in the more massive winds,” said Gerard Kriss, co-author of the paper and a boffin at the Space Telescope Science Institute in Maryland. “These were previously only visible with much more difficult X-ray observations. Such powerful outflows may yield new insights into the link between the growth of a central supermassive black hole and the development of its entire host galaxy.” ®