The hidden magnetic Universe begins to come into view
The tireless search for magnetic fields in the Universe has led scientists to invent new ways to reach even more remote areas.
In 2019 astronomers were able to examine a more dispersed region of space, the spread between galaxy clusters.There the largest magnetic field up to that time was discovered, 1.00*10^7 light years of magnetized space spanning the entire length of the cosmic lattice. With the same exploration techniques, a second filament has been seen in another part of the cosmos, “We are probably looking at the tip of the iceberg” mentioned Federica Govoni, from the National Institute of Astrophysics, Cagliari Italy.
Franco Vazza, an astrophysicist at the University of Bologna, indicated “obviously it cannot be related to the activity of individual galaxies or individual explosions or, I don’t know, supernova winds, this goes much further than that.” One possibility is that cosmic magnetism is primordial, tracing all the way to the birth of the Universe, in that case weak magnetism should exist everywhere, even in the darkest and emptiest regions of the Universe, This omnipresent magnetism would have seeded the fields stronger that flourished in galaxies and clusters.
Primordial magnetism could also help solve another cosmological puzzle the Hubble tension, perhaps the hottest topic in cosmology, the problem is that the Universe appears to be expanding significantly faster than expected, in a Physical Review Letters article Karsten Jedamzik and Levon Pogosian argue that weak magnetic fields in the early Universe would lead to the fastest rate of cosmic expansion seen today.
The magnetic soul of the universe
In 1600, studies by English scientist William Gilbert on <lodestones>, which naturally magnetized the rocks that people had been forming on compasses for thousands of years, led him to believe that their magnetic force “mimics a soul “. He correctly assumed that the Earth itself is a “great magnet”, and that the stones charge “opposite the poles of the Earth.” Magnetic fields arise every time electrical charge flows. Earth’s field, for example, emanates from its inner “dynamo,” the stream of liquid iron churning at its core. The fields of refrigerator magnets and lodestons come from electrons that revolve around their constituent atoms.
However, once a “seed” magnetic field arises from moving charged particles, it can become larger and stronger by aligning the weaker fields with it. Magnetism “is a bit like a living organism,” said Torsten En-lin, a theoretical astrophysicist at the Max Planck Institute for Astrophysics in Garching, Germany, “because magnetic fields take advantage of all the free energy sources they can cling to and grow on. They can spread and affect other areas with their presence, where they also grow.”
Ruth Durrer, a theoretical cosmologist at the University of Geneva, explained that magnetism is the only force other than gravity that can shape the large-scale structure of the cosmos, because only magnetism and gravity can “get to you” at across great distances. Electricity, on the other hand, is local and short-lived, since the positive and negative charge in any region will generally neutralize. But you can’t cancel magnetic fields; they tend to add up and survive.
However, with all their power, these force fields maintain low profiles, they are immaterial, perceptible only when they act on other things. “You can’t just take a picture of a magnetic field — it doesn’t work like that,” said Reinout van Weeren, an astronomer at Leiden University who was involved in the recent magnetized filament detections.
Van Weeren and 28 co-authors in a 2019 paper inferred the presence of a magnetic field in the filament between galaxy clusters Abell 399 and Abell 401 from the way the field redirects high-speed electrons and other charged particles that pass through. of the. As their paths twist in the field, these charged particles release weak “synchrotron radiation.”
The synchrotron signal is strongest at low radio frequencies, so it is ripe for detection by LOFAR, an array of 20,000 low-frequency radio antennas spread across Europe.
The team actually collected data from the filament in 2014 for a single eight-hour stretch, but the data sat waiting as the radio astronomy community spent years figuring out how to improve the calibration of LOFAR measurements. The Earth’s atmosphere refracts radio waves that pass through it, so LOFAR sees the cosmos as if it were from the bottom of a swimming pool. The researchers solved the problem by tracking the wobbling of “beacons” in the sky — radio emitters with precisely known locations — and correcting that this wobble would undo all the data. When they applied the decompression algorithm to the filament data, they immediately saw the brightness of the synchrotron emissions.
ASTRON
The filament is magnetized everywhere, not just near galaxy clusters that are moving toward each other from either end. The researchers hope that a 50-hour data set they are now analyzing will reveal more details.
Additional observations have recently discovered magnetic fields that span the length of a second filament. The researchers plan to publish this work soon.
The presence of huge magnetic fields in at least these two filaments provides important new information. “It has stimulated a lot of activity,” van Weeren said, “because we now know that magnetic fields are relatively strong.”
A light through the voids
If these magnetic fields arose in the childhood universe, the question is: how? “People have been thinking about this problem for a long time,” said Tanmay Vachaspati of Arizona State University.
In 1991, Vachaspati proposed that magnetic fields could have undergone surgery during the transition from the electrodepression phase, the moment, a fraction of a second after the Big Bang, when the weak electromagnetic and nuclear forces became different. Others have suggested that the magnetism materialized microseconds later when the protons formed. Or shortly after: The late astrophysicist Ted Harrison argued in the first theory of primordial magnetogenesis in 1973 that turbulent proton-electron plasma may have had the first magnetic fields. Others have proposed that space become magnetized before all of this, during the cosmic critique, the explosive expansion of space that the Big Bang supposedly set in motion. It also may not have happened until the growth of structures a billion years later.
The way to test magnetogenesis theories is to study the pattern of magnetic fields in the most pristine patches of intergalactic space, such as the quiet parts of filaments and even more empty voids. Certain details, such as the field lines are smooth, helical, or “curved of all shapes, like a ball of string or something like that” (by Vachaspati), and how the pattern changes in different places and on different scales, carries a rich information that can be compared with theory and simulations. For example, if magnetic fields arose during the solenoid phase transition, as Vachaspati proposed, then the resulting field lines should be helical, “like a corkscrew,” he said.
The problem is that it is difficult to detect force fields that have nothing to press.
One method, started by the English scientist Michael Faraday in 1845, detects a magnetic field by the way the direction of polarization of light passing through it rotates. The amount of “Faraday rotation” depends on the intensity of the magnetic field and the frequency of the light. So by measuring polarization at different frequencies, you can infer the strength of magnetism along the line of sight. “If you do it from different places, you can make a 3D map,” Enlin said.
