For the first time, a relativistic jet has been detected from two colliding galaxies, traveling at speeds close to the speed of light!

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A Clemson University College of Science research team, in collaboration with an international team of astronomers, has unambiguously detected for the first time a relativistic jet emerging from two colliding galaxies. Essentially, this is the first photographic evidence that merging galaxies can produce jets of charged particles moving at nearly the speed of light. Additionally, scientists have previously discovered that these jets can be found in elliptical galaxies, which can form from the merger of two spiral galaxies. Now, for the first time, there is an unambiguous image of a jet forming from two younger spiral galaxies.

"For the first time, we have found two spiral or disk galaxies on a collision path that produce a gamma-ray emitting relativistic jet at the center of one of them," said Vaidehi Paglia, a former Clemson postdoctoral researcher and lead author of the study, published in the Astrophysical Journal. In addition to Paglia, who currently works at the Deutsches Elektronen Synchrotron in Germany, other Clemson authors include Associate Professor Marco Ajello, Professor Dieter Hartmann and Adjunct Professor Stefano Marchesi in the Department of Physics and Astronomy.

"The fact that the resulting jet was found to be so young allowed the researchers to clearly see the site of creation. "There have been many images of galaxy collisions taken by astronomers before, but this study is the first to capture two galaxies merging where there is a fully formed jet pointing towards us, albeit a very young jet, and therefore not bright enough. Normally, the light from a jet is so powerful that we cannot see the galaxy behind it. It's like someone shining a bright flashlight into your eye when trying to look at an object; all you can see is the flashlight."

The jet we discovered is relatively small, so we can actually see the galaxy where it was born. Jets are among the most powerful astrophysical phenomena in the Universe, and they can release more energy into the Universe in a single second than our Sun produces in its entire lifetime. This energy is in the form of radiation, such as intense radio waves, X-rays, and gamma rays. Jets are also the best accelerators in the Universe, much better than the supercolliders (accelerators used in high-energy physics research) we have on Earth.

The jets are thought to be born from older elliptical galaxies that have an active galactic nucleus (AGN), a supermassive black hole at their center. For reference, scientists believe that all galaxies have supermassive black holes at their centers, but not all galactic nuclei are AGNs. Our own Milky Way, for example, has a dormant black hole at its center. Scientists theorize that AGNs grow larger by gravitationally attracting gas and dust, in a process called accretion.

But not all of this matter accretes into the black hole, some of the particles are accelerated and ejected outward in narrow beams in the form of jets. It's difficult to expel gas from a galaxy and get it to the center, something needs to shake up the galaxy to get the gas there. Galaxy mergers or collisions are the easiest way to move gas, and if there's enough gas moving around, then this supermassive black hole will become extremely bright and potentially form jets. The research team's images captured these two galaxies, one of which is the Seyfert 1 galaxy known as TXS2116-077.

Another galaxy of similar mass as they collide a second time because of the amount of gas seen in the image. Eventually, all the gas will be expelled into space, and without gas, the galaxy can no longer form stars, and without gas, the black hole will shut down and the galaxy will lie dormant. Billions of years later, our Milky Way will merge with the Andromeda Galaxy. Scientists have performed detailed numerical simulations and predict that this event could ultimately lead to the formation of a giant elliptical galaxy.

Depending on the material conditions, relativistic jets may be produced, but that is in the distant future. The research team used one of the world's largest land-based telescopes, the Subaru 8.2-meter optical-infrared telescope located on a mountaintop in Hawaii to capture this image. Then it used the Gran Telescopio Canarias and William Herschel Telescopes on La Palma Island off the coast of Spain, and NASA's Chandra X-ray Observatory space telescope for observations.

Bo Ke Yuan | Research/From: Clemson University

Reference journal: Astrophysics

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