Astronomers recently used a pair of powerful telescopes to zero in on a cosmic battle occurring some 11 billion light-years away from Earth. The combatants are a pair of galaxies charging at each other over and over again, at velocities upwards of 500 kilometers per second. According to one of the scientists studying the scene, one galaxy is cutting into the heart of the other with a blast of radiation. “We hence call this system the ‘cosmic joust,’” said study co-lead Pasquier Noterdaeme of the Institut d'Astrophysique de Paris.
This battle of the galaxies happened at a time when the Universe was less than 3 billion years old. It was a time when newly forming galaxies were colliding more frequently with each other. Our own Milky Way began forming around this time, itself the beneficiary of collisions with other galaxies over time. In fact, it's still gobbling up dwarf spheroidal galaxies as we speak.
This artist's impression shows a ‘cosmic joust’– a galactic merger in which the galaxy on the right hosts a quasar at its core. This quasar is powered by a supermassive black hole swallowing up material around it and emitting a powerful cone of radiation, piercing the other galaxy like a lance. As this radiation interacts with the galaxy on the left, it disrupts the clouds of gas and dust within, leaving behind only the smallest and densest regions. These regions are likely rendered incapable of star formation after the process. Credit: ESO/M. Kornmesser
The study of this battle began with a look at the quasar J 012555.11-012925.00. It's so bright in optical light that the presence of a jousting companion wasn't immediately obvious. Scientists had to use spectroscopic techniques to disentangle the quasar's emissions from those of its collisional partner. That's when they found evidence that the quasar was doing quite a bit of damage to the other galaxy. “Here we see for the first time the effect of a quasar’s radiation directly on the internal structure of the gas in an otherwise regular galaxy,” said researcher Sergei Balashev, of the Ioffe Institute in St. Petersburg, Russia.
Tracking the Damage
What's happening between these two early galaxies? It's helpful to look at the early history of galaxies. In general, galaxies form in a sort of hierarchical manner. That is, small "blobs" of galaxy material (gas, dust, stars) formed within the first few hundred million years after the birth of the Universe. Early galaxies began colliding, and if they had black holes, those likely merged together, too, giving rise to supermassive black holes some 400 million years after the Big Bang. Galaxy interactions have occurred throughout the rest of cosmic history. Scientists are particularly interested in the details of those early mergers and how the early quasars formed.
That brings us to J 012555.11-012925.00. It has an extremely active galactic nucleus. The "engine" in that nucleus is a supermassive black hole. It does what black holes usually do—consumes gas and material from the local neighborhood. As it does that, there's a huge release of electromagnetic radiation in the form of a jet. It's extremely bright radiation, particularly in radio emissions, which is why astronomers dubbed the first ones discovered as "quasi-stellar radio objects" or "quasars" for short. They are also bright in other wavelengths, making them thousands of times more luminous than a typical galaxy. In fact, the region of the nucleus often outshines the galaxy host.
This wide-field view shows the region of the sky around a pair of interacting galaxies, nicknamed the 'cosmic joust', in which one of them is piercing the other with intense radiation. The galaxies appear as a tiny white dot at the center of this image. The Atacama Large Millimeter/submillimeter Array (ALMA) resolved them in great detail, and ESO’s Very Large Telescope (VLT) studied the damage that one galaxy is inflicting on the other. Credit: DESI Legacy Survey
Scientists observed both the quasar and the regular galaxy at J 012555.11-012925.00 using the Atacama Large Millimeter Array (ALMA), as well as the European Southern Observatory's X-shooter spectrograph (both in Chile). ALMA was used to detect the millimeter-wavelength emissions from the scene. The X-shooter was used to study wavelengths of light from the objects, ranging from ultraviolet to near-infrared, streaming from both galaxies. The high resolution of these instruments allowed the team to study both galaxies in great detail and analyze their light. X-shooter's data gave scientists a good look at how badly the quasar's radiation is damaging its jousting partner galaxy.
Feeding the Black Hole
It turns out that J 012555.11-012925.00 is busy gobbling up material not just from its own environment, but also from its jousting partner. “These mergers are thought to bring huge amounts of gas to supermassive black holes residing in galaxy centers,” said Balashev. That effectively takes a lot of star-making material out of play. Contrast that with other galaxy mergers, where clouds of gas and dust within each galaxy collide and mingle, or are twisted around by the gravitational pull of the collision. Those interactions typically result in huge starburst knots in the participating galaxies. Not so in J 012555.11-012925.00, where the radiation from J 012555.11-012925.00 is destroying gas and dust clouds, leaving behind much smaller regions where starbirth could take place.
In this particular set of collisions, galactic feedback occurs. As the two galaxies get closer to one another, the one with the quasar reaches out and grabs material from the other galaxy. That feeds the black hole, releasing even more radiation to damage its companion and strip away much of its ability to make stars.
This study shows a fresh look at the action of galaxy mergers and collisions in the early Universe. It's not all cosmic dances and beautiful starbirth, but also contains scenes of radiation and destruction. What's needed now are more detailed observations with such telescopes as the ground-based VLT, the space-based JWST, or the upcoming Nancy Grace Roman orbiting observatory. These can all zero in on the heart of the action and suss out even more details of galactic mergers early in the history of the Universe.
For More Information
'Cosmic Joust': Astronomers Observe Pair of Galaxies in Deep-space Battle Quasar Radiation Transforms the Gas in a Merging Companion Galaxy
