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The Milky Way is not Just a Refrigerator Magnet --
presented by Science@NASA
Every person on Earth
lives inside a magnetic field.
Springing from the core of our planet,
lines of magnetic force wrap around the globe,
deflecting compass needles,
guiding pigeons,
protecting us from cosmic rays and solar storms.
Meanwhile, Earth moves through an even larger magnetic field-
that of the sun.
Massive currents flowing beneath the solar surface
give rise to a vast magnetic bubble
that envelopes every planet in the Solar System.
When NASA sent the Voyager probes
to find the edge of the sun's magnetic field,
it took them nearly 40 years to get there.
Turns out, that's nothing.
Researchers working with data
from the European Space Agency's Planck spacecraft
have mapped the magnetic field of the entire galaxy.
'The Milky Way's magnetic field
stretches across more than a hundred thousand light years,'
says Charles Lawrence,
the U.S. Planck project scientist
at NASA's Jet Propulsion Laboratory,
'and Planck has done a magnificent job mapping its structure.'
In late 2013,
Planck wrapped up a 4-year mission
to study the Cosmic Microwave Background Radiation,
the afterglow of the Big Bang.
To study the Cosmic Microwave Background,
Planck had to unravel everything in the foreground-
and that includes microwave emissions
from the Milky Way.
The Milky Way is made up not only of stars and planets,
but also of gas clouds
and dust grains floating between the stars.
Dust is the key:
Interstellar dust shines with a microwave light
that is polarized by galactic magnetism.
Tracing the polarization
allows researchers to map the Milky Way's vast magnetic field.
The Planck map,
which resembles a giant fingerprint,
is proof of a galactic dynamo at work.
'This dynamo operates in the interstellar medium
that pervades our galaxy,'
says Katia Ferriere,
a member of the Planck science team
at the Institut de Recherche
en Astrophysique et Planétologie in Toulosse, France.
'The motions of the interstellar gas,
which is an electric conductor,
generate electric currents,
which in turn generate magnetic fields.'
Similar currents move through the molten core of Earth
and in the interior of the sun-
except this is on a vastly larger scale.
'The main motion of interstellar gas in the Milky Way
is rotation about the galactic center,' continues Ferriere.
'This rotation
[not only generates the magnetic field but also]
stretches it in a circular direction,
wrapping magnetic field lines around the galactic core.
If we could see our galaxy from the top down,' she says,
'the magnetic field would have a spiral shape.'
Because Planck sees the Milky Way edge-on, however,
the spiral field appears to line up parallel to the galactic plane.
There are also many graceful arches
and loops that trace the shells of nearby supernova explosions.
Mapping these details is important.
For one thing, notes Ferriere,
'It helps us understand very high-energy cosmic rays.
These mysterious particles are deflected
by the Milky Way's magnetic field.
Tracing them back to their point of origin
requires knowing that field's morphology.'
Also, adds Lawrence,
'magnetic fields have a strong effect
on how clouds of gas collapse to form stars.
So this is telling us a lot about star formation, too.'
Work in this area is not done.
Later this year,
the Planck team plans to release a new map
based not on dust but rather on free electrons
spiraling through the magnetic field.
This could reveal new structures
in heretofore unexplored regions of the galaxy.
Says Lawrence,
'we still have some fingerprinting to do.'
For more news about the Milky Way's magnetic field,
and other results from Planck,
stay tuned to science.nasa.gov