Galactic Center And The Pigtail Molecular Cloud
September 5, 2012

Astronomers Find ‘Pigtail’ Molecular Cloud In The Galactic Center

Lee Rannals for - Your Universe Online

Astronomers using a telescope at the National Astronomical Observatory of Japan have discovered a molecular cloud that has a peculiar helical structure.

The team, led by Shinji Matsumura, a second year Ph. D. candidate, named it a "pigtail" molecular cloud due to its morphology.

The pigtail molecular cloud is located in the galactic center, about 30,000 light years away from the solar system.

Giant molecular clouds found in this region are orbiting around the galactic center along two closed orbits. At the bottom of the pigtail molecular cloud, these two orbits intersect.

The team analyzed the multiple molecular spectral lines and revealed that the two molecular clouds collide with one another at exactly the bottom of the pigtail molecular cloud.

The astronomers say the discovery suggests that the helical structure of the "pigtail" molecular cloud formed when the two molecular clouds with different orbits collided and the magnetic tube was twisted.

Astronomers believe that the helical structure of gas is associated with twisted and coiled magnetic lines.

One member of the research team first noticed the existence of a helical molecular cloud when he examined the data of 115-GHz rotational spectral lines. The helical structure is about 60 light years by 60 light years.

After examination by the team, the astronomers immediately searched a similar structure in the data taken by Atacama Submillimeter Telescope Experiment (ASTE) that covers the same region.

They found that the same helical structure in the data of 346-GHz spectral lines was emitted by CO molecules. However, the structure in the data was not exactly clear.

"Therefore, I proposed that we should make additional observations to confirm the existence of the molecular cloud with the helical structure, and to uncover what made this peculiar, helical-structure molecular cloud," Tomoharu Oka, an Associate Professor and a researcher on the project, said.

The team followed up with more observations of the pigtail molecular cloud, which they named due to its shape.

"In order to solve the mystery of the pigtail molecular cloud, we carried out high-resolution spectroscopic observations of rotational spectral lines for six other molecules. Those molecules are clues to understanding the physical state," Matsumura said.

"We were amazed by the clear and beautiful helical structure of the 'pigtail' molecular cloud in the data taken by the follow-up observation. The data revealed that the pigtail molecular cloud has a huge volume of gas, several hundreds of thousands times greater than the Sun has."

The team said that the creation of this type of helical structure would be difficult when magnetic fields extend over the all Galactic central region.

"We emphasize two important points on our study," Matsumura said. "First, it proves that two orbit groups caused by the bar-like structure actually intersect at this point in the Galactic center. Second, it shows that the perpendicular magnetic field of approximately one milligauss is locally confined."

Two other helical structures have been found around the Galactic center so far. However, the pigtail molecular cloud has a clearer helical structure than all the others.

The team said the new molecular cloud is an important clue in probing molecular cloud dynamics in the Galactic disc.