The world’s astronomers are increasingly probing the mystery of where the enormous magnetic fields that permeate our universe come from –from Earth to Mars to the Milky Way to intergalactic voids and beyond to the darkest, most remote regions of the cosmos.
The Death of Mars
A half a billion years ago, Mars magnetic field that protected an ocean as deep as the Mediterranean Sea was switched off. An impact basin deep enough to swallow Mount Everest in Valles Marineris reveals what might be the results of ancient asteroid the size of Pluto colliding with the Red Planet switching off its magnetic field, bathing the Red Planet in harmful radiation, and eroding its atmosphere by particles streaming from solar winds. Today, Mars is a frigid desert world with a carbon dioxide atmosphere 100 times thinner than Earth’s.
A strong magnetic field had probably played an important role in protecting the atmosphere from the solar wind and keeping the planet wet and habitable. “Venus and Mars have negligible magnetic fields and do not support life, while Earth’s magnetic field is relatively strong and does,” said Sarah McIntyre at Australia National University. “We find most detected exoplanets have very weak magnetic fields, so this is an important factor when searching for potentially habitable planets.”
An iconic new image of the Milky Way’s violent center (above) from the Murchison Widefield Array, a radio telescope in the Western Australian outback, shows huge golden filaments that indicate enormous magnetic fields –what our galaxy would look like if human eyes could see radio waves.
“An Unseen Magnetic Soul”
Anytime astronomers figure out a new way of looking for magnetic fields in ever more remote regions of the cosmos, inexplicably, they find them, observes Natalie Wolchover in Quanta about the invisible magnetic field lines that loop and swirl through intergalactic space like the grooves of a fingerprint, an unseen “magnetic soul”.
“Magnetism is primordial,’ she writes, “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.”
In 2019, astronomers discovered 10 million light-years of magnetized space spanning the entire length of a “filament” of the cosmic web, part of the massive web that fills much of space, connecting two galaxy clusters dubbed Abell 0399 and Abell 0401 that are slowly colliding with each other.
The Cosmic Web
“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 using the Low-Frequency Array (LOFAR) radio telescope to observe the bridge of radio-emitting plasma extending between the two galaxy clusters that are approaching a merger. The results imply that intergalactic magnetic fields connect the two clusters and challenge theories of particle acceleration in the intergalactic medium.
The cosmic web, shown here in a computer simulation, of massive filaments of galaxies separated by giant voids.
Primordial magnetism might also help resolve another cosmological conundrum known as the Hubble tension, observes Wolchover, pointing out that it is “probably the hottest topic in cosmology.”
“While the Hubble Constant is constant everywhere in space at a given time, it is not constant in time.” explains Chris Fassnacht, professor of physics at UC Davis about the current crisis in cosmology, or “tension”, in understanding the rate of expansion of the universe —known as the “Hubble Constant”—since the Big Bang, a central part of the quest to discover the origins of the universe.
“Dark Energy is Incredibly Strange”
Some physicists meanwhile propose dark energy is a ‘fifth’ force beyond the four already known – gravitational, electromagnetic, and the strong and weak nuclear forces. However, researchers think this fifth force may be ‘screened’ or ‘hidden’ for large objects like planets, making it difficult to detect.
“Dark energy is incredibly strange, but actually it makes sense to me that it went unnoticed,” said Noble Prize winning physicist Adam Riess, in an interview with The Atlantic. “I have absolutely no clue what dark energy is. Dark energy appears strong enough to push the entire universe – yet its source is unknown, its location is unknown and its physics are highly speculative.”
In a paper posted online in April and under review with Physical Review Letters, the cosmologists Karsten Jedamzik and Levon Pogosian, a professor of physics at Simon Fraser University in Canada, propose that weak magnetic fields in the early universe would lead to the faster cosmic expansion rate seen today.
“Like a Living Organism”
Astrophysicists at Johns Hopkins led by Nobel Laureate, Adam Riess, say researchers need to find conclusive evidence of primordial magnetism that appears to be everywhere, is the missing agent that shaped the universe.
“Everyone knows it’s one of those big puzzles,” said Pogosian. “But for decades, there was no way to tell whether magnetism is truly ubiquitous and thus a primordial component of the cosmos, so cosmologists largely stopped paying attention.”
Magnetism “is a little bit like a living organism,” said Torsten Enßlin, a theoretical astrophysicist at the Max Planck Institute for Astrophysics, “because magnetic fields tap into every free energy source they can hold onto and grow. They can spread and affect other areas with their presence, where they grow as well.”
The Daily Galaxy, Max Goldberg, via The Hidden Magnetic Universe Begins to Come Into View/Quanta and Science
Image credit: Combined radio/optical image of galaxy IC 342, using data from both the VLA and the Effelsberg telescope. Lines indicate the orientation of magnetic fields in the galaxy. R. Beck, MPIfR; NRAO/AUI/NSF; graphics: U. Klein, AIfA; Background image: T.A. Rector, University of Alaska Anchorage and H. Schweiker, WIYN; NOAO/AURA/NSF.