University of Oxford | 2012 Jan 26
Scientists have used a laser to create magnetic fields similar to those thought to be involved in the formation of the first galaxies; findings that could help to solve the riddle of how the Universe got its magnetism.
Magnetic fields exist throughout galactic and intergalactic space, what is puzzling is how they were originally created and how they became so strong.
A team, led by Oxford University physicists, used a high-power laser to explode a rod of carbon, similar to pencil lead, in helium gas. The explosion was designed to mimic the cauldron of plasma – an ionized gas containing free electrons and positive ions – out of which the first galaxies formed.
The team found that within a microsecond of the explosion strong electron currents and magnetic fields formed around a shock wave. Astrophysicists took these results and scaled them through 22 orders-of-magnitude to find that their measurements matched the ‘magnetic seeds’ predicted by theoretical studies of galaxy formation.
A report of the research is published in this week’s Nature.
‘Our experiment recreates what was happening in the early Universe and shows how galactic magnetic fields might have first appeared,’ said Dr Gianluca Gregori of Oxford University’s Department of Physics, who led the work at Oxford. ‘It opens up the exciting prospect that we will be able to explore the physics of the cosmos, stretching back billions of years, in a laser laboratory here on Earth.’
The results closely match theories which predict that tiny magnetic fields – ‘magnetic seeds’ – precede the formation of galaxies. These fields can be amplified by turbulent motions and can strongly affect the evolution of the galactic medium from its early stages.
Dr Gregori said: ‘In the future, we plan to use the largest lasers in the world, such as the National Ignition Facility at the Lawrence Livermore National Laboratory in California (USA), to study the evolution of cosmic plasma.’
A galactic magnetic field in a lab bolsters astrophysical theory
University of Michigan | Nicole Casal Moore | 2012 Jan 25
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 the Jan. 26 edition of 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."
Laser Tests Offer Clue to Magnetic Field Mystery
Discovery News | Irene Klotz | 2012 Jan 25
Laser first helps solve the puzzle of how the Universe got its magnetismWhy is the universe filled with magnetic fields? An experiment points to exploding stars as an explanation.
- A shock wave is the only thing needed to create a magnetic field, lab experiments show.
- An experiment using powerful lasers demonstrated what could happen when a star explodes.
- The test showed how an exploding star could lead to the creation of magnetic fields.
Science & Technologies Facilities Council, UK | 2012 Jan 26
World’s Most Powerful X-ray Laser Creates 2-Million-Degree Matter
SLAC | Stanford University | 2012 Jan 25
Generation of scaled protogalactic seed magnetic fields in laser-produced shock waves - G. Gregori et al
- Nature 481(7382) 480 (26 Jan 2012) DOI: 10.1038/nature10747