“The Hunt is On” — For Elusive Magnetic Fields from the Big Bang (Weekend Feature)


Primordial Magnetic Fields


Scientists are on the hunt for primordial magnetic fields dating back to the Big Bang, which would transform our understanding of how the universe evolved and solve a major mystery of our Universe. The unsolved question is: where did these enormous magnetic fields — an invisible primordial ‘magnetic soul’ that pervades the Cosmos — come from, if they existed at all?

A Big Unknown for a Long Time

“The cosmology we know, leading to inflation, to the creation of elements and to the expansion of spacetime does not prescribe the production of magnetic fields,” astronomer Franco Vazza at the University of Bologna.wrote in an email to The Daily Galaxy. “However,” he adds, “if we discover that magnetic fields were actually also present at very primordial epochs, this would be a convincing sign of ‘new physics’, meaning that we will have to include new “pieces” to our cosmological models (i.e. equations). Finding evidence of magnetic fields on very large scales (tens of millions of lightyears) seems to be only compatible with such a primordial generation, hence there is more physics than we know in the current cosmological model.”

“One possibility is that cosmic magnetism is primordial, tracing all the way back to the birth of the universe,” writes Natalie Wolchover for Quanta. “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.”

“The Invisible Universe” –A Primordial ‘Magnetic Soul’ Pervades the Cosmos 

“It’s definitely been a big unknown for a long time and I think the tide is really turning,” says radio astronomer Tessa Vernstrom, who thinks they’re on the brink of such a breakthrough. Ventrom’s area of expertise is radio emission detections of cosmic filaments. “We’re starting to open the window on that part of the universe.”

Earlier this year, astronomers led by Vernstrom at the Commonwealth Scientific and Industrial Research Organisation (CISRO) in Perth, Australia, confirmed the detection of magnetic field lines stretching some 50 million light years between galaxy clusters — one of the first discoveries that magnetism exists at such gargantuan scales. But the real excitement is that the sheer size of the fields suggests they could be relics from the birth of the universe in the big bang.

“Cosmic Highways” –Gargantuan Filaments of Gas Fueled the Structure of the Universe 

Radio Emissions Link Directly to Underlying Magnetic Fields

In an email to The Daily Galaxy, Venstrom wrote that radio emissions that trace out the large-scale structure and filaments of the  Universe may lead to the breakthrough. “The radio emission,” she wrote, “is directly tied to underlying magnetic fields that cause it. When it comes to magnetic fields outside of and in-between galaxies they could have come from some primordial magnetic fields, or have been injected into the space from astrophysical processes inside galaxies like star formation (or some combination of these two). Simulations can predict what we might observe today under these different origin scenarios, for instance with a very weak primordial magnetic field but a strong contribution from stars and galaxies, we would not expect to see much radio emission (or strong magnetic fields today) inside filaments, rather only in more massive clusters of galaxies.”

“Thus by looking at these large-scale filaments as they have evolved now,” she continued, “and measuring how strong the radio emission is, and thus how strong the magnetic fields are today, we can use that with the theories or models to determine how strong the primordial field was that may have seeded these fields.” 

“We have this incredibly detailed picture of what happened in the universe, starting with a tiny fraction of a second after the big bang through to the point where galaxies and stars formed,” says Bryan Gaensler, director of the Dunlap Institute for Astronomy & Astrophysics at the University of Toronto in Canada. “But there are a few things we haven’t filled in yet, and I would argue that one of the biggest is where magnetic fields fit into this.”

The Hubble Tension –Resolved?

The biggest problem in modern cosmology is the Hubble tension. In 1929, Edwin Hubble discovered that nearby galaxies were moving away from our Milky Way galaxy with recession velocities proportional to their distance (v = H_o * d), demonstrating that the Universe is expanding. Current observations of galaxies in the local Universe place the Hubble constant at H_o = 73.5 +/- 1.6 km/s/Mpc. With each incremental one megaparsec (or 3.3 million light years) in distance, galaxies recede faster by 73.5 km/s.  

However, measurements of the cosmic microwave background — leftover radiation from the early Universe shortly after the Big Bang — imply H_o = 67.7 +/- 0.5 km/s/Mpc after accounting for the evolution in the expansion rate according to standard models of cosmology.

Either one of the measurements is wrong or there is some missing but necessary ingredient to cosmological models. 

“This problem,” writes Venstrom,  “is that the Universe seems to be expanding significantly faster than expected just based on what is known to exist so far.” However, recent work by cosmologists Karsten Jedamzik and Levon Pogosian argues that weak magnetic fields in the early universe would lead to the faster cosmic expansion rate seen today.

The Standard Model –”Plus Magnetic Fields”

“Currently, people do not take magnetic fields into account when they describe the evolution of the universe,” says Pogosian, a physicist at Simon Fraser University in Burnaby, Canada. What Pogosian and Jedamzik at the University of Montpellier in France, found, is that if you add magnetic fields to simulations of how the universe evolves under the standard model of cosmology, the prediction it makes for expansion today is much closer to the value we have actually measured rather than the one extrapolated from the standard model of cosmology. “It’s potentially a very exciting development,” says Pogosian.

“They state,” Ventrom told The Daily Galaxy “that primordial magnetic fields of strength ~0.1 nanGauss show promise to resolve the Hubble tension, thus confirming a strength of at least this much could support their argument, and so far observationally limits for the primordial magnetic field strength are within that range (current upper limits or estimates range from strengths of 0.1 to around 4 nanoGauss). The more observations we can make, the more accurately we can tweak this number.” 

The Daily Galaxy, Maxwell Moe, astrophysicist, NASA Einstein Fellow, University of Arizona via Tessa Vernstrom, Quanta and New Scientist

Image credit top of page: NASA/SOFIA; Star field image: NASA/Hubble Space Telescope


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