Abell 2142, situated approximately 1.24 million light years away, is a luminous galaxy cluster.
Utilizing the LOw Frequency ARray (LOFAR), astronomers, primarily from the University of Bologna, Italy, observed the nearby galaxy cluster, Abell 2142. Their observations led to the discovery of a previously unidentified component within the cluster’s vast radio halo.
Galaxy clusters, bound by gravity, comprise up to thousands of galaxies. Representing the largest gravitationally bound entities known, they’re prime grounds for delving into galaxy evolution and cosmological studies.
Decoding the Radio Halo with LOFAR
Radio halos are expansive, diffuse radio-emission regions typically located at galaxy cluster centers. Given their low surface brightness, especially at GHz frequencies, they remain elusive. Yet, their brightness amplifies at lower frequencies. LOFAR’s prowess in capturing detailed, high-fidelity radio images at low frequencies is unparalleled.
Abell 2142, situated approximately 1.24 million light years away, is a luminous galaxy cluster. Housing over 900 galaxies within an 11.4-million light year radius, it boasts a hierarchical organization.
Historical radio observations disclosed Abell 2142’s dual-component giant radio halo—H1 and H2. Each showcases distinct properties. H1, the “core”, shines brighter with a compact, round form. Contrarily, H2, the “ridge”, exhibits an elongated shape, larger yet fainter than H1.
H3: The Latest Find
Under Luca Bruno’s leadership from the University of Bologna, an enhanced examination of Abell 2142’s radio halo was undertaken using LOFAR. Coupled with archival radio and X-ray data, they unearthed the halo’s third component—H3. This component mirrors the X-ray thermal distribution of the intracluster medium, spanning over 6.5 million light years. Displaying specific spectral and spatial properties, H3 earned its classification as a giant ultra-steep spectrum radio halo.
To decode H3’s origin, researchers proffer two theories: possibly emerging from an ancient energetic merger or less efficient turbulent re-acceleration induced by ongoing minor mergers. As they surmise, “H2 might have originally been H3’s inner section, later remolded by turbulence.”
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