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The universe can be a bit like a magic trick. When you move around to observe the different wavelengths of light, you can see all kinds of objects, events and interactions that would otherwise be invisible to the human eye.
Using the Very Large Array telescope in New Mexico, astronomers led by Marie-Lou Gendron-Marsolais of the European Southern Observatory have peered into a gigantic cluster of galaxies. There, in low-frequency radio wavelengths, they saw the complex invisible halos that could be the result of intense galactic interactions.
There is much more to a galaxy than the visible light it emits. Many, including the Milky Way, have large-scale radio structures, vast bubbles or jets of radio emissions that extend far above and below the galactic plane. In many cases, these lobes and jets are well defined and more or less symmetrical.
In the cluster of Perseus, located in the constellation of Perseus about 240 million light years from the Milky Way, a different image emerges.
The Perseus Cluster is huge, one of the most massive objects in the known Universe. It contains thousands of galaxies enveloped in a huge cloud of hot gas. And the new VLA images – the first in high resolution in the mergahertz range from 230 to 470 at low frequency – reveal details never before seen in large-scale radio facilities.
The galaxy NGC 1275, also known as Perseus A, is located right in the center of the cluster and is the brightest galaxy within it. In its inner lobes, observations reveal new substructures: thin radio emission filaments and loop-like structures in the southern lobe. The observations also confirmed the presence of radio spurs in the outer lobes, first detected in 2002.
Meanwhile, the galaxy NGC 1265 has two long jets, but they are bent at 90-degree angles, which extend into a single comet-like tail that curves around. This structure is well known, but disconcerting; such tails are generally interpreted as tracers of movement through the intracluster medium, caused by ram pressure. Based on an analysis of the difference in brightness in the tail, the team interprets this shape as evidence of two separate electron populations.
They also identified new radio emission filaments in the tail, although at this stage it is difficult to say what created them. It could have been turbulence or magnetic fields; high resolution images will be needed for more detailed analysis.
Galaxy IC 310 is also a tailed galaxy, although its tail is straight, which is much more normal, consistent with a radio galaxy falling into the cluster. But recent research has revealed that this galaxy is a blazar, with a jet of material firing close to light from the galactic core in the direction of the observer (we are here on Earth).
Due to the viewing angle, the team was able to observe gamma radiation from the galactic center, as well as new structures in the tail jets: two distinct and closely collimated jets at the base of the tail. According to their analysis, the observations are consistent with a blazar, implying that bent jet radio galaxies and blazars are not mutually exclusive.
Galactic clusters are strange places, full of interactions and objects that we don’t understand at all well. These new observations are breadcrumbs on the learning path … but they also underscore the importance of getting there with the most powerful telescopes we can collect.
“These images,” said Gendron-Marsolais, “show us structures and details never seen before and this helps our efforts to determine the nature of these objects.”
The team’s research was accepted in Royal Astronomical Society Monthly Notices, and is available on arXiv.
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