This image from Herschel reveals the ring with greater clarity than ever before. It can be seen as the yellow loop that appears to have two lobes (click through to see an annotated version). The ring is twisted so that part of it rises above and below the plane of our Milky Way galaxy.
Credit: ESA/NASA/JPL-Caltech
The ring can be seen as the yellow loop that appears to have two lobes, highlighted here with a white ribbon overlay.
Credit: ESA/NASA/JPL-Caltech
PASADENA: A bizarre, twisted ring of dense gas stretching more than 600 light-years at the centre of our Milky Way galaxy has been discovered by the European Space Agency's Herschel Space Observatory.
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 centre of the Milky Way many times before in the infrared," said Alberto Noriega-Crespo of NASA's Infrared Processing and Analysis Centre at the California Institute of Technology in Pasadena.
"But when we looked at the high-resolution images using Herschel's sub-millimetre wavelengths, the presence of a ring is quite clear." Noriega-Crespo is co-author of a new paper on the ring published in Astrophysical Journal Letters.
Giant infinity symbol
The Herschel Space Observatory sees infrared and sub-millimetre light, which can readily penetrate through the dust hovering between the bustling centre of our galaxy and us. Herschel's detectors are also suited to see the coldest phenomena in our galaxy.
A team of astronomers used Herschel to look at the Milky Way's inner ring and 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. They later determined the ring was torqued in the middle, so it only appears to have two lobes.
"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 centre of our own galaxy."
Ring moving as a unit
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 centre of our Milky Way's bar - a bar-shaped region of stars at the centre of its spidery spiral arms, and this bar is inside an even larger ring. 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 centre 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 centre of the torqued portion of the ring is not where the centre of the galaxy is thought to be, but slightly offset. The centre 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 centre of the ring doesn't match up with the assumed centre of our galaxy. "There's still so much about our galaxy to discover," he said.
That sounds too much like
That sounds too much like the end of CONTACT by Carl Sagan, where we can look at the sequence of pi a certain way and see a big circle.
"There's still so much about
"There's still so much about our galaxy to discover"
Always a good line when you are short of an explanation