"We see two intertwining strands wrapped around each other as in a DNA molecule," said team leader Mark Morris of the University of California, Los Angeles. "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 - space weather. What we see indicates a high degree of order."

The double-helix nebula is nearly 25,000 light-years away from Earth, but only about 300 light-years from the supermassive black hole occupying the center of the Milky Way.

Reporting in the March 16 issue of the journal Nature, the team said the Spitzer's unprecedented sensitivity and resolution in the infrared band was necessary to see the double-helix clearly.

"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 said. "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."

Morris said the magnetic field lines resembled a taut rubber band. "If you twist one end, the twist will travel up the rubber band," he said, adding that the wave also is like taking a long loose rope attached at its far end, throwing a loop, and watching the loop travel down the rope.

"That's what is being sent down the magnetic field lines of our galaxy," he explained. "We see this twisting torsional wave propagating out. We don't see it move because it takes 100,000 years to move from where we think it was launched to where we now see it, but it's moving fast - about 1000 kilometers per second - because the magnetic field is so strong at the galactic center - about 1,000 times stronger than where we are in the galaxy's suburbs."

A strong, large-scale magnetic field can affect the galactic orbits of molecular clouds by exerting a drag on them. It can inhibit star formation, and can guide a wind of cosmic rays away from the central region.

Astronomers think this strong field could be important for understanding quasars and violent phenomena in a galactic nucleus, and Morris said he will continue to study its qualities.

The magnetic field is strong enough to cause activity that does not occur elsewhere in the galaxy. The magnetic energy near the galactic center is capable of altering the activity of the galactic nucleus and, by analogy, the nuclei of many galaxies, including quasars, which are among the most luminous objects in the universe.

All galaxies that have a well-concentrated galactic center also could have a strong magnetic field at their center, Morris said, but so far, the Milky Way is the only galaxy where the view is good enough to study it.

Morris said he has argued for many years the magnetic field at the galactic center is extremely strong, and the new research supports that view.

The magnetic field at the galactic center, though 1,000 times weaker than the magnetic field on the Sun, occupies such a large volume that it contains vastly more energy than the Sun's field. It has the energy equivalent of 1,000 supernovae.

Regarding the wave's source, which is twisting the magnetic field lines near the center of the Milky Way, Morris thinks the answer is not the supermassive black hole - at least not directly. Instead, he said, it may be emanating from a massive disk of gas called the circumnuclear disk that orbits the black hole like the rings of Saturn, but from several light-years away. He hypothesizes that the magnetic field lines are anchored in this disk.

"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.

Co-authors of the Nature paper are Keven Uchida, a former UCLA graduate student and former member of Cornell University's Center for Radiophysics and Space Research; and Tuan Do, a UCLA astronomy graduate student. Morris and his team study the galactic center at all wavelengths.

Related Links
Spitzer at CalTech