How are winged radio galaxies formed?

How are winged radio galaxies formed?

Observing the night sky with radio telescopes, the recurring vision is the elliptical radiogalaxieswhich feature twin jets that explode from both sides of their central super massive black hole.

In some cases, astronomers stumble upon something special and rare: an X-shaped radio galaxy, with four jets extending far into space. First discovered in 1992, X-shaped radio galaxies constitute less than 10% of all radio galaxies: the most famous is M87, one of the most massive galaxies in the universe, which was further popularized in 2019 when the Event Horizon Telescope immortalized its supermassive black hole central.

Now a new study, published on Astrophysical Journal Lettersdescribes the first simulation of growth of radio galaxies large scale that traces the galactic gas away from the supermassive black hole.

Using new simulation models, the astrophysicists of Northwestern of Chicago unexpectedly they discovered that the galaxy’s characteristic X shape (aka winged) is the result of the interaction between the jets and the gas falling into the black hole.

At the beginning of the simulation, the expanding gas ‘deflected’ the newly formed jets, which turned on and off, then forming a sort of X. Thus, the characteristic shape of these radio galaxies is explained.

Before this study it was thought that X-shaped radio galaxies could be the consequence of one collision between two galaxies in which the respective super-massive black holes merged, changing the direction of the jet. Another hypothesis was connected to the form of the jet that was altered, as it interacted with the large-scale gas enveloping an isolated supermassive black hole.

In my simulation, I tried not to assume anything. Usually, researchers place a black hole in the middle of a simulation grid and place a large, already formed gas disk around it, so they can add ambient gas to the outside of the disk. In this study, the simulation begins without a disk, but one soon forms as the rotating gas approaches the black hole. This disk then feeds the black hole and creates jets. I made the simplest assumptions possible, so the whole result was a surprise. This is the first time anyone has seen X-shaped morphology in simulations from very simple initial conditions. “He said Lalakosfirst author of the study.

But the things to observe in the universe are tied to questions of time: if the supermassive black hole has already formed, we cannot observe its evolution because human life is too short.

Lalakos plans to continue running simulations to better understand how these winged shapes are born and understand what happens near a black hole.

The study was supported by the National Science Foundation.

Top: a still image taken from the 3D simulation of the natural development of an X-shaped jet. The gas (bright red) falls into the black hole, which launches a pair of relativistic jets (blue). Jets propagate vertically and impact ambient gas (dark red) Older cavities (dark blue) dynamically rise at an angle to vertically propagating jets to form the X shape. Credit: Aretaios Lalakos / Northwestern University .

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