The double helix nebula appears on the left side of the reddish inset image; the larger-field greenish image is a shorter-wavelength infrared image made recently with the IRAC camera on the Spitzer Space Telescope by Susan Stolovy and her colleagues. Credit: NASA/JPL-Caltech/UCLA
Scientists expect to see a double helix while examining DNA, either via diagram or under an atomic force microscope. So, it's a little surprising to find that geometric shape at the end of a telescope, as a team of astronomers did recently. Apparently, near the center of our galaxy, is a nebula sharing the shape of our genetic material, the first one of its kind anybody has seen.
"[The nebula] made a lot of sense once we looked at it and started thinking about it, because it's oriented exactly along the galaxy's magnetic field as we would have expected, and yet nobody had predicted it," said Mark Morris, a UCLA astronomer and primary author of the paper that appeared in Nature on March 16th, announcing the finding.
Morris and his team used the spectrometer aboard NASA's Spitzer Space Telescope to analyze the nebula, which drifted across the screen while they were studying the galaxy's center. The cosmic double helix is probably made up of clouds of ionized dust hovering around a pair of magnetic field lines, Morris said, and a wave traveling up the field lines from the center of the galaxy created the twisting double helix shape.
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"The wave can carry charged dust particles with it, and it's those dust particles, very tiny dust particles, smaller than chalk dust, that inhabit our galaxy and can be carried aloft by such a wave," he said.
Morris compared the shape of the nebula to a rope held taut by two people, one of who rotates his end to create a twist that travels all the way down the line.
Like a rope attached at one end, magnetic field lines have tension, Morris said. "If there's something at the base of the magnetic lines twisting them, that twist wave will travel up the magnetic field and out of the galaxy."
Morris hypothesizes that the wave traveling up the magnetic field lines and creating the double helix nebula is a disk of gas at its base, made to spin by the gravity of the black hole at the center of our galaxy. The double strands of the nebula are created by the dumbbell-like structure of the spinning disk, which concentrates the magnetic field lines in two areas, he said—otherwise, the nebula would be cylindrical.
Gregory Benford, an astronomer at University of California, Irvine, agreed with Morris' disk theory for describing the nebula's shape.
"Two attracting filaments would naturally move helically, from their magnetic attraction."
Still, Morris cautions that his theory remains unproven, and one of the next steps for his team will be to run corroborating tests. He also plans to further analyze the content of the dust that constitutes the nebula's strands.