Unknown radio structure detected around brightest known quasar
Astronomers have found two large, mysterious objects blasting out of the brightest black hole in the known universe. Discovered in a 1959 survey of cosmic radio wave sources, the supermassive black hole 3C 273 is a quasar – short for quasi-stellar object because the light emitted by these behemoths is bright enough to be mistaken for starlight. While black holes do not emit light, the largest ones are surrounded by gargantuan swirls of gas called accretion discs; as gas falls into the black hole, friction heats the disc and causes it to blaze with radiation, typically detected as radio waves.
3C 273 is the first quasar ever identified. It is also the brightest, shining more than 4 trillion times as bright as Earth’s Sun while sitting at a distance of more than 2.4 billion light years away. Over the decades, scientists have studied the blazing black hole nucleus extensively, but because the quasar is so bright, studying the surrounding galaxy that hosts it has been near impossible. That remarkable brightness has ironically left scientists largely in the dark about how quasars impact their host galaxies. However, recent research may finally change that.
A team of researchers calibrated the Atacama Large Millimeter/submillimeter
Array (ALMA) in Chile to separate the radiant glow of quasar 3C 273 from the light emitted by its host galaxy. They were left with just the radio waves emitted by the galaxy, revealing two massive and mysterious radio structures. One structure appears to be an enormous smudge of radio light that envelops the entire galaxy, then stretches on for tens of thousands of light years to the southwest. This radio fog overlaps with the second structure – a gargantuan jet of energy known as an astrophysical jet, which also stretches on for tens of thousands of light years.
Scientists aren’t exactly sure how or why astrophysical jets form. They do know, however, that jets are commonly seen around quasars and other supermassive black holes and likely arise from interactions between a black hole and its dusty accretion disc. Jets are typically made of ionised (electrically charged) matter and travel at near-light speed. The radiation released by these jets can appear brighter or dimmer depending on the radio frequency at which they’re viewed. However, the large radio structure surrounding 3C 273 showed a uniform brightness, regardless of its frequency. According to the researchers, this suggests that the two radio structures are created by separate, unrelated phenomena.
After testing several theories, the team concluded that the large radio fog around the galaxy comes from star-forming hydrogen gas that’s being ionised directly by the quasar itself. This is the first time that ionised gas has been seen stretching tens of thousands of light years around a supermassive black hole. This discovery touches on a longstanding mystery within astronomy: can a quasar ionise so much gas in its host galaxy that it prevents the formation of new stars? To answer this question, the researchers compared the galaxy’s estimated gas mass to other galaxies of the same type and size.
They found that while the quasar had ionised a truly mind-boggling amount of gas, rendering it useless for building new stars, star formation was not being visibly suppressed in the galaxy overall. This suggests that thriving, growing galaxies can still exist with radiation-belching quasars at their centres.
“This discovery provides a new avenue to studying problems previously tackled using observations by optical light,” said Shinya Komugi, an associate professor at Kogakuin University in Tokyo. “By applying the same technique to other quasars, we expect to understand how a galaxy evolves through its interaction with the central nucleus.”