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Cosmic
'DNA': Double Helix Spotted in Space
By
Bjorn Carey
SPACE.com Staff Writer
posted:
15 March 2006
01:00 pm ET |
Magnetic forces at the center of the galaxy have twisted a nebula
into the shape of DNA, a new study reveals.
The
double helix shape is commonly seen inside living
organisms, but this is the first time it has been
observed in the cosmos.
"Nobody
has ever seen anything like that before in the cosmic
realm," said the study's lead author Mark Morris
of UCLA. "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."
These
observations, made with NASA's Spitzer Space Telescope,
are detailed in the March 16 issue of the journal
Nature.
Disk-driven
shape
The
DNA nebula is about 80 light-years long. It's about
300 light-years from the supermassive black hole at the center of the Milky Way. The nebula is nearly perpendicular
to the black hole, moving out of the galaxy at a quick
clip—about 620 miles per second (1,000 kilometers
per second).
Magnetic
field lines at the galactic center are about 1,000
times stronger than on Earth. They run perpendicular to the black hole,
but parallel through the nebula. Scientists think
that twisting of these lines is what causes the double
helix shape.
While
the black hole might be the first culprit to come
to mind, it's more likely that the magnetic field
lines are anchored to a giant gas disk that orbits
the black hole several light-years away, researchers
say.
It's
like having two strands of rope connected to a fixed
point, Morris said. As you spin the strands, they
braid around each other in a double helix fashion.
In this case the gas and dust of the nebula makes
up the strands.
"It's
as if there's a bar across the middle [of the black
hole], or a dumbbell shape, where the strands are
anchored, and as it spins around, it twists the strands
together," Morris told SPACE.com.
This
process takes a long time, though, since the disk
completes one orbit around the black hole roughly
every 10,000 years. But that's an important number.
"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.
The
recipe
The
recipe for a DNA nebula is strict but simple. It requires
a strong magnetic field, a rotating body, and a nebulous
cloud of material positioned just right.
Massive
central black holes are the best sources for both
the strong magnetic field and rotating body, and since
most large galaxies have them, Morris expects DNA-like
nebula may be common through out the universe.
"I
absolutely expect to see [this configuration] in gas-rich
galaxies with all these elements in place," Morris
said.
However,
these nebulas are tough to spot, and current technology
limits scientists' observations to our galaxy.