Sky & Telescope - September 2021 - 24

Magnetogenesis
MAGNETIC GALAXY This composite image reveals strong magnetic
fields (lines) in the outflow created by abundant star formation in M82,
the Cigar Galaxy. The image combines observations of visible starlight
(gray), hydrogen gas (red), and infrared starlight and dust (yellow). Data
from the flying SOFIA telescope indicate that the magnetic field in M82's
center is 2-3×10−4 gauss - 10 to 100 times stronger than the largescale
fields in more sedate galaxies.
protons and neutrons (called hadrons) could exist. Before
this time, hadrons would have been ripped apart by the
motions of their constituent particles. This marks a transition
between an earlier universe composed mostly of these
subatomic particles to a later universe composed mostly of
hadrons, known as the quantum chromodynamic (QCD) phase
transition. The transition was similar to when water freezes.
It occurred in random places, stirring the plasma until it was
entirely converted into the new form. The stirring motions
mean that, in addition to the relativistic plasma dynamics,
the early universe was also turbulent. Although turbulence is
everywhere in our lives - from water pouring down a drain
to clouds moving through the sky - we still have yet to really
understand it physically.
Amazingly, when you go back even further, there was
This medium is referred to as a relativistic plasma, and it's not
something often seen on Earth or even in our Sun. It's the
state of matter that we expect to see inside a neutron star or
in the gas near a black hole. Like the plasmas that we observe
in the laboratory, the electrons and nuclei are unbound;
however, in relativistic plasmas, less-intuitive things - like
the mass increase, time dilation, and length contraction that
come with relativistic conditions - can significantly alter the
dynamics.
In addition, in a few-seconds-old universe, there was still
a significant amount of antimatter, which unleashed large
amounts of energy through collisions with normal matter. In
fact, there were near-constant, high-speed collisions between
all particles in the hot, dense environment: Every part of the
universe resembled the inside of the LHC, but with a much
higher density and more collisions. For this reason, protons
and neutrons had so much energy that they just couldn't
stick to each other.
When the average temperature in the universe was about
a trillion degrees, about 10 millionths of a second after the
universe began, we reach the earliest time that particles like
uMAGNETOGENESIS To understand where the universe's large intergalactic
magnetic fields came from, scientists use computer simulations
to explore the universe's earliest moments. These visualizations by
undergraduate student Catherine Wood track the creation of seed fields
within a fraction of a second after the Big Bang. Swirling motions generate
weak fields, which then coalesce in locations where the plasma's
characteristics are just right (blobs in left panel, fields are stronger in
cores). As time progresses (from left to right), the fields first increase due
to strong turbulence, then decrease as the fluid motions slow and the
universe expands and cools. Each cube translates into approximately 3
million light-years wide in today's universe (factoring in cosmic expansion),
and because of the expansion-induced scale changes, the panels
give the impression of watching an explosion in slow motion.
24 SEPTEMBER 2021 * SKY & TELESCOPE
another major phase transition. Today, four fundamental
forces govern our physical world (gravity, electromagnetism,
and the weak and strong nuclear forces), each transmitted
by different particles. For example, electromagnetism's
particle is the massless photon. But when the universe was
less than around a trillionth of a second old, the weak force's
2×10-11 second
3.6 x 10-27
2.1 x 10-27
1.5 x 10-28
M82 MAGNETIC FIELDS: MAGNETIC FIELD: NASA / SOFIA / E. LOPEZ-RODRIGUEZ,
INFRARED: NASA / SPITZER / J. MOUSTAKAS ET AL., VISIBLE AND HYDROGEN: KITT PEAK
OBSERVATORY; VISUALIZATIONS: CATHERINE WOOD

Sky & Telescope - September 2021

Table of Contents for the Digital Edition of Sky & Telescope - September 2021

Contents
Sky & Telescope - September 2021 - Cover1
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Sky & Telescope - September 2021 - 1
Sky & Telescope - September 2021 - Contents
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