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| A simulation of the cosmic web showing shock waves producing radio waves (pink) as they crash through magnetic fields (blue). (Image credit: F. Vazza/D. Wittor/J. West) |
Astronomers have detected enormous shockwaves rattling the cosmic web that
connects all galaxies in the universe, offering vital clues on how the largest
structures in space were shaped.
For the first time, astronomers have spotted enormous, galaxy-scale shock
waves rattling the "cosmic web" that connects nearly all known galaxies. These
cosmic waves could reveal clues about how the largest objects in the universe
were sculpted.
The discovery was made by stitching and stacking thousands of radio
telescope images together, which revealed the soft "radio glow" produced by
shock waves from colliding matter in our universe's biggest structures.
The cosmic web is a gigantic network of crisscrossing celestial
superhighways paved with hydrogen gas and dark matter. Galaxies tend to form
where multiple strands of the web intersect, often in clusters numbering in
the hundreds of thousands. Now a new study, published Feb. 15 in the journal
Science, could provide vital clues into the nature of the mysterious
magnetic fields that stretch beside these tendrils.
"Magnetic fields pervade the universe — from planets and stars to the largest
spaces in-between galaxies," lead author Tessa Vernstrom, an astronomer at the
International Centre for Radio Astronomy Research in Crawley, Australia, said
in a
statement. "However, many aspects of cosmic magnetism are not yet fully understood,
especially at the scales seen in the cosmic web."
Taking shape in the chaotic aftermath of the Big Bang, the cosmic web's
tendrils formed as clumps of matter from the roiling particle-antiparticle
broth of the young universe — whose rapid expansion pushed the filaments
outwards to form an interconnected soap-sud structure of thin films
surrounding countless, mostly empty voids.
Far from being completely frozen in place, the cosmic web's matter can
sometimes violently collide. When matter in the web merges, enormous shock
waves send charged particles ricocheting through the web's magnetic fields,
causing the particles to emit a faint radio wave glow. These shock waves
have been spotted around some of the universe's largest galaxy clusters, but
until now they were never observed around the web itself.
"These shock waves give off radio emissions which should result in the
cosmic web 'glowing' in the radio spectrum, but it had never really been
conclusively detected due to how faint the signals are," Vernstrom said.
To search for the faint signals, the researchers used data from the Global
Magneto-Ionic Medium Survey, the Planck Legacy Archive, the Owens Valley
Long Wavelength Array and the Murchison Widefield Array to stack radio
imaging from 612,025 galaxy cluster pairs, grouped together if they were
close enough to be directly connected by cosmic web tendrils. This stacking
helped boost the faint radio emissions from the shock waves beyond noisy
background effects.
Then, by looking only for polarized radio waves — whose rays vibrate at the
same angle as each other and were predicted in simulations to be emitted by
the shock waves — the researchers found the signal.
"As very few sources emit polarised radio light, our search was less prone
to contamination and we have been able to provide much stronger evidence
that we are seeing emissions from the shock waves in the largest structures
in the universe, which helps to confirm our models for the growth of this
large-scale structure," Vernstrom said.
Now that the shock waves' existence has been confirmed, they could be used
to probe the nature of the enormous magnetic fields that suffuse the web,
which play an unknown role in shaping the universe.
Reference:
T. Vernstrom et al. Polarized accretion shocks from the cosmic web. Science
Advances. Vol. 9, February 17, 2023.
DOI: 10.1126/sciadv.ade7233.
Tags:
Space & Astrophysics