16 March 2006
DNA Shaped Nebula Observed At Center Of Milky Way
by Kate Melville
Astronomers using the Spitzer Space Telescope have observed an astonishing double helix shaped nebula near the center of our Milky Way galaxy. The astronomers, writing in Nature, estimate the nebula to be around 80 light years in length and situated only 300 light years away from the massive black hole at the center of the Milky Way.
The DNA shaped nebula stunned the astronomers involved. "We see two intertwining strands wrapped around each other as in a DNA molecule," said Mark Morris, a UCLA professor of astronomy, and lead author of the report. "Nobody has ever seen anything like that before in the cosmic realm. Most nebulae are either spiral galaxies full of stars or formless amorphous conglomerations of dust and gas. What we see indicates a high degree of order."
Morris believes that the magnetic field at our galaxy's center is responsible for the intriguingly shaped nebula. "We know the galactic center has a strong magnetic field that is highly ordered and that the magnetic field lines are oriented perpendicular to the plane of the galaxy," Morris explained. "If you take these magnetic field lines and twist them at their base, that sends what is called a torsional wave up the magnetic field lines. You can regard these magnetic field lines as akin to a taut rubber band. If you twist one end, the twist will travel up the rubber band," he added.
The magnetic field at the center of the Milky Way - although 1,000 times weaker than the magnetic field on the sun - occupies such a large volume of space that it has vastly more energy than the sun's field. Morris believes that all galaxies that have a well-concentrated galactic center may also have a strong magnetic field at their center.
Exactly what creates the torsional wave is still something of a mystery, but Morris doesn't believe the massive black hole at galactic central is the culprit. Orbiting the black hole, several light years away, is a massive disk of gas called the circumnuclear disk which Morris hypothesizes anchors the magnetic field lines. The disk orbits the black hole approximately once every 10,000 years. "Once every 10,000 years is exactly what we need to explain the twisting of the magnetic field lines that we see in the double helix nebula," Morris said.
Pic courtesy UCLA