Anytime astronomers figure out a new way of looking for magnetic fields in ever more remote regions of the cosmos, inexplicably, they find them.
These force fields — the same entities that emanate from fridge magnets — surround Earth, the sun and all galaxies. Twenty years ago, astronomers started to detect magnetism permeating entire galaxy clusters, including the space between one galaxy and the next. Invisible field lines swoop through intergalactic space like the grooves of a fingerprint.
Last year, astronomers finally managed to examine a far sparser region of space — the expanse between galaxy clusters. There, they discovered the largest magnetic field yet: 10 million light-years of magnetized space spanning the entire length of this “filament” of the cosmic web. A second magnetized filament has already been spotted elsewhere in the cosmos by means of the same techniques. “We are just looking at the tip of the iceberg, probably,” said Federica Govoni of the National Institute for Astrophysics in Cagliari, Italy, who led the first detection.
The question is: Where did these enormous magnetic fields come from?
“It clearly cannot be related to the activity of single galaxies or single explosions or, I don’t know, winds from supernovae,” said Franco Vazza, an astrophysicist at the University of Bologna who makes state-of-the-art computer simulations of cosmic magnetic fields. “This goes much beyond that.”
One possibility is that cosmic magnetism is primordial, tracing all the way back to the birth of the universe. In that case, weak magnetism should exist everywhere, even in the “voids” of the cosmic web — the very darkest, emptiest regions of the universe. The omnipresent magnetism would have seeded the stronger fields that blossomed in galaxies and clusters.
JULY 6, 2020!!!!
by European Space Agency!!!
A collection of intriguing images based on data from ESA’s Herschel and Planck space telescopes show the influence of magnetic fields on the clouds of gas and dust where stars are forming.
The images are part of a study by astronomer Juan D. Soler of the Max Planck Institute for Astronomy in Heidelberg, Germany, who used data gathered during Planck’s all-sky observations and Herschel’s ‘Gould Belt Survey’. Both Herschel and Planck were instrumental in exploring the cool Universe, and shed light on the many complexities of the interstellar medium – the mix of gas and dust that fills the space between the stars in a galaxy. Both telescopes ended their operational lifetime in 2013, but new discoveries continue to be made from their treasure trove of data.
Herschel revealed in unprecedented detail the filaments of dense material in molecular clouds across our Milky Way galaxy, and their key role in the process of star formation. Filaments can fragment into clumps which eventually collapse into stars. The results from Herschel show a close link between filament structure and the presence of dense clumps.
Herschel observed the sky in far-infrared and sub-millimetre wavelengths, and the data is seen in these images as a mixture of different colours, with light emitted by interstellar dust grains mixed within the gas. The texture of faint grey bands stretching across the images like a drapery pattern, is based on Planck’s measurements of the direction of the polarised light emitted by the dust and show the orientation of the magnetic field.
SUMMARY: We observed a ridge of radio emission connecting the merging galaxy clusters Abell 0399 and Abell 0401 with the Low-Frequency Array (LOFAR) telescope network at 140 megahertz. This emission requires a population of relativistic electrons and a magnetic field located in a filament between the two galaxy clusters. We performed simulations to show that a volume-filling distribution of weak shocks may reaccelerate a preexisting population of relativistic particles, producing emission at radio wavelengths that illuminates the magnetic ridge.
Galaxy clusters form at the intersections of the cosmic web filaments and grow by accreting substructures in a merging process, which converts most of the infall kinetic energy into thermal gas energy. A residual fraction of nonthermalized energy is expected to manifest itself in the form of turbulent gas motions, magnetic fields, and relativistic particles. Extended radio sources called radio halos and radio relics are found at the center and the periphery of galaxy clusters, respectively, visible through their emission of synchrotron radiation. Magnetic fields and relativistic particles in the large-scale structure of the Universe can be inferred from observations of these sources.
Observations show that magnetic fields are ubiquitous in galaxy clusters (1), whereas radio halos and relics are most common in merging clusters, suggesting that cluster mergers provide the acceleration of relativistic particles necessary for synchrotron emission (2). Collisions between nearly equal-mass clusters dissipate large amounts of energy within a few billion years. The merging galaxy clusters Abell 0399 and Abell 0401 are separated by a projected distance of 3 megaparsec (Mpc) and host a double radio halo (3). The presence of radio halos at the centers of both Abell 0399 and Abell 0401 was unexpected because radio halos are not common sources, and x-ray (4–7) and optical data (8) suggest that the two systems are still in the initial phase of a merger, before the bulk of kinetic energy of the collision has been dissipated. X-ray data show a hot (temperature T ≃ 6 to 7 keV) and nearly isothermal filament of plasma in the region between the two clusters (7).
There may be a weak shock (Mach number M < 2) in the outer part of the filament, at ~650 to 810 kiloparsec (kpc) from the collision axis (equivalent to an angular offset of 8 to 10 arc min). Observations with the Planck spacecraft (9, 10) detected a signal due to the Sunyaev–Zeldovich (SZ) effect, revealing a large-scale filament of gas connecting the two systems. The SZ effect is a spectral distortion caused by inverse Compton scattering of the cosmic microwave background radiation by hot electrons (T ∼keV), which is sensitive to the total thermal energy of the intervening medium.
We observed the region between Abell 0399 and Abell 0401 at radio wavelengths to investigate whether relativistic particles and magnetic fields exist on cosmic scales larger than those of galaxy clusters. Using the Low Frequency Array (LOFAR) telescope network at a central frequency ν = 140 MHz (corresponding to a wavelength λ = 2.14 m), we detected a filament of diffuse synchrotron emission connecting the two galaxy clusters.
The beautiful mess in Abell 2255!!!!
29 June 2020
An international team of astrophysicists led by Andrea Botteon from Leiden University, the Netherlands, has shed light on one of the most intricate objects of the radio sky: the galaxy cluster Abell 2255. Thanks to the incredible detailed images obtained with the European radio telescope LOFAR, the scientists have been able to observe details never seen before of the emission from the cluster. The halo in Abell 2255 is not smooth, but contains numerous filaments that have not been seen previously. The result has been presented today at the virtual annual meeting of the European Astronomical Society (EAS) and will be published in The Astrophysical Journal.
The observations carried out with the LOFAR radio telescope are changing the picture that astrophysicists had on galaxy clusters. Despite their name, clusters are not only composed by hundreds of galaxies spread over millions of light years that are bound together by gravity, but also contain particles moving at speeds close to the speed of light that are able to emit radiation in the radio band, when they interact with the cluster magnetic field. These radio emissions, that extend from cluster centers for millions of light years and are produced when two clusters of galaxies collide, have been called radio halos due to their generally spherical and smooth appearance.
The halo in Abell 2255 appears to be anything but smooth, though. First author Botteon: “We discovered the existence of numerous filaments within the halo emission that have not been seen previously. This was possible thanks to LOFAR, which has a sensitivity and angular resolution much higher than the radio telescopes that have observed galaxy clusters in the past, and also because the discovered filaments emit most of their radiation in long radio wavelengths, precisely those detected by the LOFAR antennas.”
Radio halos are still enigmatic sources for astrophysicists. One of the most accepted hypotheses on their origin is that they form due to the turbulent motions generated in the cluster gas, triggered when two clusters collide. In this framework, the new observations could provide valuable insights on radio halos.