Galaxy 5 billion light-years away shows we live in a magnetic universe
Galaxy 5 billion light-years away shows
we live in a magnetic universe
Gravitational lens
provides key opportunity
Date: August 28, 2017
Source: National Radio Astronomy Observatory
Summary: A chance combination of a gravitational lens
and polarized waves coming from a distant quasar gave astronomers the tool
needed to make a measurement important to understanding the origin of magnetic
fields in galaxies.
FULL STORY
Astronomers observed
the magnetic field of a galaxy five billion light-years away. The galaxy
provides important insight into how magnetism in the universe formed and
evolved.
Credit: Bill Saxton,
NRAO/AUI/NSF; NASA, Hubble Heritage Team, (STScI/AURA), ESA, S. Beckwith
(STScI). Additional Processing: Robert Gendler
With the help of a
gigantic cosmic lens, astronomers have measured the magnetic field of a galaxy
nearly five billion light-years away. The achievement is giving them important
new clues about a problem at the frontiers of cosmology -- the nature and
origin of the magnetic fields that play an important role in how galaxies
develop over time.
The scientists used
the National Science Foundation's Karl G. Jansky Very Large Array (VLA) to
study a star-forming galaxy that lies directly between a more-distant quasar
and Earth. The galaxy's gravity serves as a giant lens, splitting the quasar's
image into two separate images as seen from Earth. Importantly, the radio waves
coming from this quasar, nearly 8 billion light-years away, are preferentially
aligned, or polarized.
"The polarization
of the waves coming from the background quasar, combined with the fact that the
waves producing the two lensed images traveled through different parts of the
intervening galaxy, allowed us to learn some important facts about the galaxy's
magnetic field," said Sui Ann Mao, Minerva Research Group Leader for the
Max Planck Institute for Radio Astronomy in Bonn, Germany.
Magnetic fields affect
radio waves that travel through them. Analysis of the VLA images showed a
significant difference between the two gravitationally-lensed images in how the
waves' polarization was changed. That means, the scientists said, that the
different regions in the intervening galaxy affected the waves differently.
"The difference
tells us that this galaxy has a large-scale, coherent magnetic field, similar
to those we see in nearby galaxies in the present-day universe," Mao said.
The similarity is both in the strength of the field and in its arrangement,
with magnetic field lines twisted in spirals around the galaxy's rotation axis.
Since this galaxy is
seen as it was almost five billion years ago, when the universe was about
two-thirds of its current age, this discovery provides an important clue about
how galactic magnetic fields are formed and evolve over time.
"The results of
our study support the idea that galaxy magnetic fields are generated by a
rotating dynamo effect, similar to the process that produces the Sun's magnetic
field," Mao said. "However, there are other processes that might be
producing the magnetic fields. To determine which process is at work, we need
to go still farther back in time -- to more distant galaxies -- and make
similar measurements of their magnetic fields," she added.
"This measurement
provided the most stringent tests to date of how dynamos operate in
galaxies," said Ellen Zweibel from the University of Wisconsin-Madison.
Magnetic fields play a
pivotal role in the physics of the tenuous gas that permeates the space between
stars in a galaxy. Understanding how those fields originate and develop over
time can provide astronomers with important clues about the evolution of the
galaxies themselves.
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