This is what it looks like when galaxies are about to die

The beginning of the end of our galaxy is a few billion years old. That's when the sparkling disc of the Milky Way is projected onto its nearest neighbor, a spiral galaxy called Andromeda. The force of the collision will fuse the black holes at the center of the galaxies, producing a super-fast and ultra-fast light gas vortex called quasar.

Far from the galactic center, on a distant and unimportant planet called Earth, the quasar will initially appear as a brilliant blue halo in the sky, so bright that it will eclipse the stars. But quasars are subject to cataclysmic lightning, which sweeps gases and dust – the materials of which suns, the worlds and life are made – directly into the circumgalactic environment. Eventually, the galaxy will empty matter to make new stars.

This is how all galaxies die – at least, according to theories. But until now, no one has captured a galaxy in its transition phase, after forming a quasar, but before having lost all its stellar building blocks.

In a study presented Wednesday at the annual meeting of the American Astronomical Society in St. Louis, astrophysicist Allison Kirkpatrick announced the detection of 22 objects that she calls "cold quasars". but still contain dust clouds, suggesting that they have not yet lost the ability to create new stars.

They are right on the edge – oscillating between the time of creation and the expectation of death.

"One of the main questions we ask in astronomy is: how are galaxies dying?" Said Kirkpatrick, an assistant professor at the University of Kansas. "We know what they look like once they're dead. . . but the rest are only pieces that we have guessed. "

Now, she continued, "we have found a population that we can study in detail and map exactly how these galaxies are moving from the star-forming phase of their lives to the phase of their retirement."

The discovery took place during an investigation into the brightest objects of the sky. Most of these investigations look at the X-rays produced by the gas that travels to a black hole at a speed close to that of light – exactly the type of high-energy radiation that you would associate with a monstrously massive quasar.

But Kirkpatrick also examined these objects using infrared light, which emanates from much colder phenomena, further away from the violent nuclei of galaxies.

"Infrared detections. . . suggest a very very cold dust. It's not something you usually expect to see, "Kirkpatrick said.

His next step will be to try to measure the rate at which gases and dust are expelled from the galaxy, which will allow Kirkpatrick to calculate the time that galaxies spend in the "cold quasar" phase.

She will continue to search for more of these objects, which offer insights into a poorly understood phase of galactic stories.

"Astronomy is a unique science in that it is passive," she said. "We can not follow any process in real time, so we are limited by snapshots of different galaxies that we are trying to link together."

"The more we can complete this photo with snapshots, the better we can tell this story," she said. "And I think I found a new snapshot."

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