(ORDO NEWS) — The rare merger of galaxy clusters has opened up an even rarer sight. Astronomers have discovered a low-frequency radio bridge between them stretching 6.5 million light years – evidence of a magnetic field connecting the clusters early in the fusion process.
Such a radio bridge between merging galaxy clusters was discovered only for the second time. But this already provides some important clues as to how these bridges are formed.
Clusters of galaxies are about 3 billion light-years away in a group called Abell 1758. As a result, four clusters are involved in an impending collision – two massive pairs of clusters coming together.
X-ray data last year showed that a tightly bound pair in the northern segment, dubbed Abell 1758N, had already collided and separated, and the cluster cores passed each other about 300-400 million years ago. Eventually they will return to get back together. A pair of clusters to the south, Abell 1758S, are still approaching each other.
Both of these pairs have a radio halo that is created by the acceleration of electrons as a result of fusion. And it is these pairs that are separated by a distance of 6 million light years, the gap is slowly closing.
This scenario is very similar to the collision of galaxies Abell 0399 and Abell 0401, which last year became the first merging galaxy clusters to have a low frequency radio bridge.
Using the LOFAR low-frequency radio telescope, which consists of 25,000 antennas, astronomers have detected a clear radio emission at 140 megahertz.
At 144 megahertz, they found radio emission extending between A1758N and A1758S, just like the radio bridge between Abell 0399 and Abell 0401.
“We confirm the presence of a giant radio-emitting bridge connecting the two systems. This is the second large-scale radio bridge observed in the cluster to date. The bridge is clearly visible in the 144 MHz LOFAR image and is tentatively detected at 53 MHz.”
This radiation is interpreted as evidence of a huge magnetic field connecting the two clusters. If this magnetic field acts like a synchrotron (particle accelerator), electrons must be accelerated along it to relativistic speeds, creating synchrotron radiation that is detected as low frequency radio emission.
These are some of the most gigantic structures currently observed in the Universe, and their origin is likely associated with turbulence that occurs in the intracluster environment at the initial stage of merger, which enhances both radio and X-ray emission between clusters.
There are quite a few merging galaxy clusters that have been identified in the universe. Searching for other radio bridges in them can help you figure out what gives rise to these huge structures.
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