We have detected the most powerful microwave laser in the known universe

Astronomers have recorded a laser beam of microwaves produced by two galaxies smashing into each other, the brightest and most distant example of the phenomenon ever seen.

To produce a laser, the first atoms need to be stimulated into an unstable state with higher energy. Then particles of light or photons fired at these atoms cause them to break free and emit their own photons, causing a chain reaction that produces many more photons in the process. Since each atom emits identical photons, all the light produced is of the same frequency and forms a beam of coherent light.

The same process can occur when galaxies break apart. Gas from both galaxies compresses and produces more stars and light. After passing through dust clouds, this light can excite hydroxyl ions, which are composed of hydrogen and oxygen atoms, to higher energy states. When these excited ions are blasted with radio waves, for example from a supermassive black hole, they can suddenly break free and create a beam of extremely bright and focused microwave radiation, known as a maser.

Now, Roger Dean at the University of Pretoria in South Africa and his colleagues spotted the brightest and most distant maser to date in a galaxy nearly 8 billion light-years away called H1429-0028. Light from this galaxy is distorted by the massive galaxy between it and Earth, which acts like a magnifying glass, an effect called gravitational lensing.

Deane and his colleagues used the MeerKAT telescope in South Africa, which consists of 64 linked radio telescopes that act as one giant dish, to search for molecular hydrogen-rich galaxies that emit light at a telltale frequency. But when they turned MeerKAT toward H1429-0028, they saw light strongly emitted at a higher frequency that they knew was produced only by powerful masers.

“We had a quick look at 1667 megahertz [frequency]just to see if it was detectable at all, and it was a tremendous rumble [signal]. It was an instant record,” says Deane. “It was by accident.”

The light beam from the galaxy is so bright that the maser may have its own category, called a gigamaser, much more powerful than the megamasers that have been observed in galaxies closer to us. “That’s about 100,000 times the luminosity of a star, but in a distant galaxy, concentrated into a very, very small [electromagnetic] spectrum,” says Deane.

We should be able to detect similar masers at much greater distances when the Square Kilometer Array in South Africa, a much larger and more sensitive version of MeerKAT, is completed and online in the coming years, he says Matt Jarvis at Oxford University.

Such distant galaxy masers will come from some of the first galaxies formed in the universe and could give us precise information about how galaxies merged back in time, Jarvis says. “[Masers] it needs very precise conditions,” he says. To get these very specific physical conditions, to get a maser, you need a galaxy merger.”

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