Astronomers observing distant quasars have discovered something puzzling about a very rare class of these enigmatic objects — some appear to be sucking material inwards at relativistic speeds, whereas the vast majority of quasars do exactly the opposite.
Quasars dominated the early Cosmos, generating vast quantities of radiation that can be observed today right at the edge of our observable Universe. Consisting of an active supermassive black hole and a searing disk of plasma in the cores of young galaxies, the vast majority of quasars eject material from their energetic environments at high speed.
This may sound counter-intuitive; black holes consume matter after all, they don’t eject it. But in a quasar’s hot accretion disk — composed of a superheated soup of blended stars, gas and dust that strayed too close to the supermassive black hole’s gravitational wrath — the intense radiation blasts the surrounding material away from the black hole. Although some material inevitably gets fed from the accretion disk into the black hole, vast quantities are ejected at up to a significant fraction of the speed of light.
However, by taking a Doppler speed check of the motion of gas around known quasars, a team of researchers analyzing data from the Sloan Digital Sky Survey (SDSS-III) have discovered a very rare subset of quasars that don’t fit the norm.
“The gas in this new type of quasar is moving in two directions: some is moving toward Earth but most of it is moving at high velocities away from us, possibly toward the quasar’s black hole,” said Niel Brandt, study co-author and Distinguished Professor of Astronomy and Astrophysics at Penn State University. “Just as you can use the Doppler shift for sound to tell if an airplane is moving away from you or toward you, we used the Doppler shift for light to tell whether the gas in these quasars is moving away from Earth or toward these distant black holes, which have a mass from millions to billions of times that of the sun.”
“Matter falling into black holes may not sound surprising,” added team leader Patrick Hall of York University in Toronto, “but what we found is, in fact, quite mysterious and was not predicted by current theories.
“The gas in the disc must eventually fall into the black hole to power the quasar, but what is often seen instead is gas blown away from the black hole by the heat and light of the quasar, heading toward us at velocities up to 20 percent of the speed of light,” he said. “If the gas is falling into the black hole, then we don’t understand why it’s so rare to see infalling gas. There’s nothing else unusual about these quasars. If gas can be seen falling into them, why not in other quasars?”
So how rare are these objects? 1-in-10,000 rare. Of the tens of thousands of quasars known, only 17 such objects have been discovered so far.
For now, the researchers are baffled as to why these few distant supermassive black holes, which have masses millions to billions of times of the mass of our sun, appear to have more suck than the rest of their quasar cousins. Their work has been published in the journal Monthly Notices of the Royal Astronomical Society (doi: 10.1093/mnras/stt1012).
One explanation, says Hall, is that in actuality, the majority of gas is being ejected from the quasar, but it is moving in a peculiar fashion. Perhaps gas is rapidly orbiting around the black hole’s superheated accretion disk, sometimes traveling toward, sometimes away from us, but the Doppler measurements appear to show a bias toward the gas that is moving away. This may give the impression that the gas is being sucked into the black hole, when, in fact, it’s being ejected.
Regardless, these are strange objects that don’t appear to fit with current quasar theory, something astrophysicists will have to work on for a while yet.
Image credit: York University