Synopsis: Cosmic Magnetism Revisited

An analysis of the polarized emission from some 3000 distant radio sources places a stringent upper limit on the strength of the cosmological magnetic field.

Magnetic fields are all over the place in the cosmos. Planets, stars, galaxies, and clusters of galaxies are all spanned by magnetic fields of known magnitude. A weaker field is also thought to permeate the Universe on larger, cosmological scales. But what is the strength of this cosmological field? To try to answer this question, Maxim Pshirkov from Lomonosov Moscow State University, Russia, and colleagues have turned to a large survey of distant radio sources whose radiation is affected by the magnetic field it passes through. The data allowed them to put a tight upper limit on the strength of the cosmological magnetic field.

When polarized radiation from a distant source crosses the space between the source and the Earth, the radiation’s polarization plane will be rotated by an angle that depends on the strength of the magnetic field that fills the space. The effect, known as Faraday rotation, therefore provides a means to estimate the field’s strength. Pshirkov and co-workers used existing rotation measurements from about 3000 radio sources spread over a large area of the sky, subtracting from the measurements the effect of the Milky Way’s magnetic field. By comparing the data with models of the expected rotation for a given cosmological-field strength, the researchers were able to derive an upper limit on the strength of about 1 nG, a fivefold improvement over the current one. A field as small as 1 nG implies, for example, that ultrahigh-energy cosmic rays will travel relatively unaffected on their way to Earth—a result that may help researchers find the sources of these particles.

This research is published in Physical Review Letters.

–Ana Lopes

Ana Lopes is a Senior Editor of Physics.


Features

More Features »

Announcements

More Announcements »

Subject Areas

CosmologyAstrophysics

Previous Synopsis

Biological Physics

Bacteria Create Own Swim Lane

Read More »

Next Synopsis

Atomic and Molecular Physics

No Vacancy for Tunneling

Read More »

Related Articles

Viewpoint: Neutron-Star Implosions as Heavy-Element Sources
Cosmology

Viewpoint: Neutron-Star Implosions as Heavy-Element Sources

A dramatic scenario in which a compact black hole eats a spinning neutron star from inside might explain a nearby galaxy’s unexpectedly high abundance of heavy elements. Read More »

Viewpoint: Spinning Black Holes May Grow Hair
Gravitation

Viewpoint: Spinning Black Holes May Grow Hair

A spinning black hole may lose up to 9% of its mass by spontaneously growing “hair” in the form of excitations of a hypothetical particle field with a tiny mass. Read More »

Synopsis: A Reionization Filter for the Cosmic Microwave Background
Cosmology

Synopsis: A Reionization Filter for the Cosmic Microwave Background

A new method of analyzing cosmic microwave background data could isolate signatures from the so-called reionization period that occurred a few hundred million years after the big bang. Read More »

More Articles