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Left-handed cosmic magnetic field could explain missing antimatter

Last Updated on Friday, 15 May 2015 08:23
Published on Thursday, 14 May 2015 05:01

The discovery of a 'left-handed' magnetic field that pervades the universe could help explain a long standing mystery – the absence of cosmic antimatter. A group of scientists, led by Prof. Tanmay Vachaspati from Arizona State University in the United States, with collaborators at Washington University and Nagoya University, announce their result in Monthly Notices of the Royal Astronomical Society.

fgst smallCaption: An artist’s impression of the Fermi Gamma ray Space Telescope (FGST) in orbit. Credit: NASA. Click for a full size imagePlanets, stars, gas and dust are almost entirely made up of 'normal' matter of the kind we are familiar with on Earth. But theory predicts that there should be a similar amount of antimatter, like normal matter, but with the opposite charge. For example, an antielectron (called a positron) has the same mass as its conventional counterpart, but a positive rather than negative charge.

In 2001 Prof. Vachaspati published theoretical models to try to solve this puzzle, which predict that the entire universe is filled with helical (screw-like) magnetic fields. He and his team were inspired to search for evidence of these fields in data from the NASA Fermi Gamma ray Space Telescope (FGST).

FGST, launched in 2008, observes gamma rays (electromagnetic radiation with a shorter wavelength than X-rays) from very distant sources, such as the supermassive black holes found in many large galaxies. The gamma rays are sensitive to effect of the magnetic field they travel through on their long journey to the Earth. If the field is helical, it will imprint a spiral pattern on the distribution of gamma rays.

Vachaspati and his team see exactly this effect in the FGST data, allowing them to not only detect the magnetic field but also to measure its properties. The data shows not only a helical field, but also that there is an excess of left-handedness - a fundamental discovery that for the first time suggests the precise mechanism that led to the absence of antimatter.

For example, mechanisms that occur nanoseconds after the Big Bang, when the Higgs field gave masses to all known particles, predict left-handed fields, while mechanisms based on interactions that occur even earlier predict right-handed fields.

gamma dis smallIllustration of the Fermi Gamma ray Space Telescope (FGST) map of the sky with the central band removed to block out gamma rays originating in the Milky Way. Gamma rays of different energies are represented by dots of various colors – red dots represent arrival locations of very energetic gamma rays, green dots represent lower energy, and blue dots represent lowest energy. The new analysis looks for spiral patterns in the distribution of gamma rays within patches on the sky, with the highest energy gamma ray at the center of the spiral and the lower energy gamma rays further along the spiral. A helical magnetic field in the universe gives an excess of spirals of one handedness - and FGST data shows an excess of left-handed spirals. Credit: Hiroyuki Tashiro. Click for a full size image

Prof. Vachaspati commented: "Both the planet we live on and the star we orbit are made up of 'normal' matter. Although it features in many science fiction stories, antimatter seems to be incredibly rare in nature. With this new result, we have one of the first hints that we might be able to solve this mystery."

This discovery has wide ramifications, as a cosmological magnetic field could play an important role in the formation of the first stars and could seed the stronger field seen in galaxies and clusters of galaxies in the present day.

 

Further information

The new work appears in W. Chen et al., "Intergalactic magnetic field spectra from diffuse gamma rays", Monthly Notices of the Royal Astronomical Society, vol. 450, pp. 3371-3380, 2015, published by Oxford University Press.

Details of the earlier theoretical models appear in T. Vachaspati, "Estimate of the Primordial Magnetic Field Helicity", Physical Review Letters, vol. 87, p. 251302, 2001.

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Media contact

Dr Robert Massey
Royal Astronomical Society
Tel: +44 (0)20 7734 7734 x214
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Science contact

Prof Tanmay Vachaspati
Director, Cosmology Initiative
Arizona State University
United States
Tel: +1 480 965 3587 (office; email preferred due to travel)
Mob: +1 609 964 6863 (email preferred due to travel)
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Notes for editors

The Royal Astronomical Society (RAS), founded in 1820, encourages and promotes the study of astronomy, solar-system science, geophysics and closely related branches of science. The RAS organizes scientific meetings, publishes international research and review journals, recognizes outstanding achievements by the award of medals and prizes, maintains an extensive library, supports education through grants and outreach activities and represents UK astronomy nationally and internationally. Its more than 3800 members (Fellows), a third based overseas, include scientific researchers in universities, observatories and laboratories as well as historians of astronomy and others. Follow the RAS on Twitter via @royalastrosoc.