Astronomers report an unprecedented elongated double helix nebula
near the center of our Milky Way galaxy, using observations from
NASA's Spitzer Space Telescope. The part of the nebula the
astronomers observed stretches 80 light years in length. The
research is published March 16 in the journal Nature.
"We see two intertwining strands wrapped around each other as in
a DNA molecule," said Mark Morris, a UCLA professor of physics and
astronomy, and lead author. "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 approximately 300 light years from the
enormous black hole at the center of the Milky Way. (The Earth is
more than 25,000 light years from the black hole at the galactic
The Spitzer Space Telescope, an infrared telescope, is imaging
the sky at unprecedented sensitivity and resolution; Spitzer's
sensitivity and spatial resolution were required to see the double
helix nebula 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.
"You can regard these magnetic field lines as akin to a taut
rubber band," Morris added. "If you twist one end, the twist will
travel up the rubber band."
Offering another analogy, he said the wave is like what you see
if you take a long loose rope attached at its far end, throw a loop,
and watch the loop travel down the rope.
"That's what is being sent down the magnetic field lines of our
galaxy," Morris said. "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 1,000 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; understanding this strong magnetic field is
important for understanding quasars and violent phenomena in a
galactic nucleus. Morris will continue to probe the magnetic field
at the galactic center in future research.
This 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 our 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 may also
have a strong magnetic field at their center, Morris said, but so
far, ours is the only galaxy where the view is good enough to study
Morris has argued for many years that the magnetic field at the
galactic center is extremely strong; the research published in
Nature strongly 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 has vastly more energy than the magnetic field on the
sun. It has the energy equivalent of 1,000 supernovae.
What launches the wave, twisting the magnetic field lines near
the center of the Milky Way? Morris thinks the answer is not the
monstrous black hole at the galactic center, at least not
Orbiting the black hole like the rings of Saturn, several light
years away, is a massive disk of gas called the circumnuclear disk;
Morris hypothesizes that the magnetic field lines are anchored in
this disk. The disk orbits the black hole approximately once every
"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 on the Nature paper are Keven Uchida, a former UCLA
graduate student and former member of Cornell
Center for Radiophysics and Space Research; and Tuan Do, a UCLA
astronomy graduate student. Morris and his UCLA colleagues study the
galactic center at all wavelengths.
NASA's Jet Propulsion Laboratory in Pasadena, Calif., manages the Spitzer Space
Telescope mission for the agency's Science Mission Directorate.
Science operations are conducted at the Spitzer
Science Center at the California
Institute of Technology. JPL is a division of Caltech. NASA funded