This composite image shows a laser-produced shock wave on the left side. Brighter colors show the shock region of higher density or temperature. The right side shows a simulation of a shock wave collapsing, as it would have during the pre-galactic phase in the universe. Image: A. Ravasio (LULI), A. Pelka (LULI), J. Meinecke (Oxford), C. Murphy (Oxford), and F. Miniati (ETH). |
Why is the universe
magnetized? It’s a question scientists have been asking for decades. Now, an
international team of researchers including a University of Michigan
professor have demonstrated that it could have happened spontaneously, as the
prevailing theory suggests.
The findings are published
in Nature. Oxford University
scientists led the research.
“According to our
previous understanding, any magnetic field that had been made ought to have
gone away by now,” said Paul Drake, the Henry S. Carhart Collegiate
Professor of Atmospheric, Oceanic, and Space Sciences and a professor in
physics at U-M. “We didn’t understand what mechanism might create a
magnetic field, and even if it happened, we didn’t understand why the magnetic
field is still there.
“It has been a very
enduring mystery.”
With high-energy pulsed
lasers in a French laboratory, the researchers created certain conditions
analogous to those in the early universe when galaxies were forming. Through
their experiment, they demonstrated that the theory known as the Biermann
battery process is likely correct.
Discovered by a German
astronomer in1950, the Biermann process predicts that a magnetic field can
spring up spontaneously from nothing more than the motion of charged particles.
Plasma, or charged particle gas, is abundant in space.
Scientists believe that
large clouds of gas collapsing into galaxies sent elliptically shaped bubbles
of shockwaves through the early universe, touching off flows of electric
current in the plasma of the intergalactic medium.
Anyone who has built an
electromagnet in middle school science class is familiar with this concept,
Drake said.
“If you can make
current flow, you make a magnetic field,” Drake said.
The question in
astrophysics was what could have generated the current. This experiment
demonstrated that such asymmetrical shockwaves could do the job.
The results, Drake said,
aren’t particularly surprising. But it’s important for scientists to test their
theories with experiments.
“These results help
strengthen the understanding that we’ve taken from our interpretation of
astrophysical data,” Drake said. “And understanding the universe and
most definitely the origin of life is one of the great human intellectual
quests.”
