A team of astrophysicists has found, for the first time ever, a really unique galaxy. It could change our perspective of how galaxies die.
In research presented Wednesday at the annual meeting of the American Astronomical Society in St. Louis, Allison Kirkpatrick, assistant professor of physics and astronomy at the University of Kansas, announced the detection of 22 objects she calls “cold quasars” — galaxies featuring an abundance of cold gas that still can produce new stars despite having a quasar at the center. This breakthrough discovery could change our understanding of how galaxies die. It may also represent a phase of every galaxy’s lifecycle that was unknown until now.
Quasars are basically supermassive black holes on steroids. Huge amounts of gas and dust surround these quasars, making them extremely bright — even brighter than a typical galaxy.
This gas and dust falls into the black hole and forms an “accretion disk.” That causes a mind-blowing amount of electromagnetic energy to blow out.
Typically, when a quasar forms at the center of a galaxy, it means the galaxy is retiring. This is a signal that the galaxy will stop producing new stars.
“All the gas that is accreting on the black hole is being heated and giving off X-rays,” Kirkpatrick said. “The wavelength of light that you give off directly corresponds to how hot you are. For example, you and I give off infrared light. But something that’s giving off X-rays is one of the hottest things in the universe. This gas starts accreting onto the black hole and starts moving at relativistic speeds; you also have a magnetic field around this gas, and it can get twisted up. In the same way that you get solar flares, you can have jets of material go up through these magnetic field lines and be shot away from the black hole. These jets essentially choke off the gas supply of the galaxy, so no more gas can fall on to the galaxy and form new stars. After a galaxy has stopped forming stars, we say it’s a passive dead galaxy.”
The discovery came during a survey of the brightest objects in the sky. Most such surveys examine X-rays produced by gas swirling toward a black hole at nearly the speed of light.
But Kirkpatrick also looked at these objects using infrared light, which emanates from much cooler phenomena, farther from galaxies’ violent cores.
“Infrared detections . . . suggest very, very cold dust. That’s not something you typically expect to see,” Kirkpatrick said.
The survey found 22 quasars at a distance of 6 to 12 billion light-years away showing unusual signatures. They looked like they were in the end stages of their life when viewed optically. However, they still emitted a bright, far infrared signature with a lot of dust and cold gas in them.
“These galaxies are rare because they’re in a transition phase,” said Kirkpatrick in a press release. “We’ve caught them right before star formation in the galaxy is quenched, and this transition period should be very short.”
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During the press conference, Kirkpatrick suggested if we could zoom in and see one of these quasars, it would be kind of like a donut. In the center of the galaxy, we’d see a dead zone. There, the quasar has blown away most of the gas and dust. Around the outside, we’d find a star-forming region still plentiful with the gas and dust.
Incredibly strong winds would be moving through the galaxy, so this period would only last for around 10 million years — a blink of an eye in the universe’s timelines.
That’s why these cold quasars are incredibly rare, and spotting one is an important step in understanding how galaxies mature, live and eventually die.
Kirkpatrick suggests the same thing could happen with our galaxy. However, we may face other problems before that happens, like an expanding sun ready to swallow the Earth as a whole.
Next, Kirkpatrick hopes to determine if the “cold quasar” phase happens to a specific class of galaxies or all of them.