Twisted Tale of our Galaxy's Ring

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Whitney Clavin 818-354-4673
Jet Propulsion Laboratory, Pasadena, Calif.
Whitney.clavin@jpl.nasa.gov

Feature: 2011-216 July 19, 2011

Twisted Tale of our Galaxy's Ring

The full version of this story with accompanying images is at:
http://www.jpl.nasa.gov/news/news.cfm?release=2011-216&cid=release_2011-216

New observations from the Herschel Space Observatory show a bizarre, twisted ring of
dense gas at the center of our Milky Way galaxy. Only a few portions of the ring, which
stretches across more than 600 light-years, were known before. Herschel's view reveals
the entire ring for the first time, and a strange kink that has astronomers scratching their
heads.

"We have looked at this region at the center of the Milky Way many times before in the
infrared," said Alberto Noriega-Crespo of NASA's Infrared Processing and Analysis
Center at the California Institute of Technology in Pasadena. "But when we looked at the
high-resolution images using Herschel's sub-millimeter wavelengths, the presence of a
ring is quite clear." Noriega-Crespo is co-author of a new paper on the ring published in a
recent issue of Astrophysical Journal Letters.

The Herschel Space Observatory is a European Space Agency-led mission with important
NASA contributions. It sees infrared and sub-millimeter light, which can readily
penetrate through the dust hovering between the bustling center of our galaxy and us.
Herschel's detectors are also suited to see the coldest stuff in our galaxy.

When astronomers turned the giant telescope to look at the center of our galaxy, it
captured unprecedented views of its inner ring -- a dense tube of cold gas mixed with dust,
where new stars are forming.

Astronomers were shocked by what they saw -- the ring, which is in the plane of our
galaxy, looked more like an infinity symbol with two lobes pointing to the side. In fact,
they later determined the ring was torqued in the middle, so it only appears to have two
lobes. To picture the structure, imagine holding a stiff, elliptical band and twisting the
ends in opposite directions, so that one side comes up a bit.

"This is what is so exciting about launching a new space telescope like Herschel," said
Sergio Molinari of the Institute of Space Physics in Rome, Italy, lead author of the new
paper. "We have a new and exciting mystery on our hands, right at the center of our own
galaxy."

Observations with the ground-based Nobeyama Radio Observatory in Japan
complemented the Herschel results by determining the velocity of the denser gas in the
ring. The radio results demonstrate that the ring is moving together as a unit, at the same
speed relative to the rest of the galaxy.

The ring lies at the center of our Milky Way's bar -- a bar-shaped region of stars at the
center of its spidery spiral arms. This bar is actually inside an even larger ring. Other
galaxies have similar bars and rings. A classic example of a ring inside a bar is in the
galaxy NGC 1097 (http://www.spitzer.caltech.edu/images/2687-ssc2009-14a-Coiled-Creature-of-the-Night),
imaged here by NASA's Spitzer Space Telescope. The ring glows brightly in the center of the galaxy's
large bar structure. It is not known if that ring has a kink or not.

The details of how bars and rings form in spiral galaxies are not well understood, but
computer simulations demonstrate how gravitational interactions can produce the
structures. Some theories hold that bars arise out of gravitational interactions between
galaxies. For example, the bar at the center of our Milky Way might have been
influenced by our largest neighbor galaxy, Andromeda.

The twist in the ring is not the only mystery to come out of the new Herschel
observations. Astronomers say that the center of the torqued portion of the ring is not
where the center of the galaxy is thought to be, but slightly offset. The center of our
galaxy is considered to be around "Sagittarius A*," where a massive black hole lies.
According to Noriega-Crespo, it's not clear why the center of the ring doesn't match up
with the assumed center of our galaxy. "There's still so much about our galaxy to
discover," he said.

An abstract and full PDF of the Astrophysical Journal Letters study is online at
http://arxiv.org/abs/1105.5486 .

Herschel is a European Space Agency cornerstone mission, with science instruments
provided by consortia of European institutes and with important participation by NASA.
NASA's Herschel Project Office is based at NASA's Jet Propulsion Laboratory, Pasadena,
Calif. JPL contributed mission-enabling technology for two of Herschel's three science
instruments. The NASA Herschel Science Center, part of the Infrared Processing and
Analysis Center at the California Institute of Technology in Pasadena, supports the
United States astronomical community. Caltech manages JPL for NASA.

More information is online at http://www.herschel.caltech.edu,
http://www.nasa.gov/herschel and
http://www.esa.int/SPECIALS/Herschel/index.html . Follow the NASA Herschel
Science Center and other related space missions on twitter at @Cool_Cosmos.

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