14 DAY TRIAL // The Spitzer Space telescope has made an unprecedented discovery: a nebula shaped as a double helix that stretches for more than 80 light years in length and which is located at only around 300 light years from the enormous black hole at the center of the Milky Way. By comparison, Earth is situated at more than 25 000 light years from the galactic center.
Nebulae are interstellar clouds of gas, dust and plasma that have resulted from the death of stars and where new stars are forming.
"We see two intertwining strands wrapped around each other as in a DNA molecule," said Mark Morris, a UCLA professor of physics and astronomy. "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."
Morris and his UCLA colleagues study the galactic center at all wavelengths. The Spitzer Space Telescope is an infrared telescope, and it is imaging the sky at unprecedented sensitivity and resolution. It is precisely Spitzer's sensitivity and spatial resolution that allowed astronomers to see the double helix nebula clearly.
Scientists now wonder what drives the formation of this unusual shape. Morris speculates that it might have to do with the magnetic fields:
"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. 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." "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."
Due to the fact that the nebula is made out of plasma - i.e. of ions and electrons - such magnetic fields influence the shape of the distribution of matter in space. Conversely, studying the distribution of matter - the shapes of such nebulae - one can obtain clues about the magnetic fields. Morris has argued for many years that the magnetic field at the galactic center is extremely strong - this new research, co-authored by Keven Uchida, a former UCLA graduate student, and Tuan Do, a UCLA astronomy graduate student, strongly supports his view.
The double helix nebula requires a strong magnetic field, a rotating body, and a nebulous cloud of material positioned just right. Massive central black holes are both sources of a strong magnetic field and are a rotating body. Morris expects that such nebulae may be relatively common through out the universe.
"I absolutely expect to see [this configuration] in gas-rich galaxies with all these elements in place," Morris said.
The magnetic field at the galactic center is 1 000 times weaker than the magnetic field on the sun, but it occupies such a large volume that it has vastly more energy than the magnetic field on the sun. Its energy is equivalent of that of 1 000 supernovae.
The magnetic field is important because it influences the formation of stars: the field exerts a "drag" force on the particles which can delay the formation of stars (the magnetic force is proportional to the velocity of the particle on which it acts).
Photo credit: M. Morris / UCLA; Spitzer telescope (NASA/JPL-Caltech)
