Posted on 12/08/2005 3:16:16 PM PST by blam
Spiral arm of Milky Way looms closer than thought
19:00 08 December 2005
NewScientist.com news service
Maggie McKee
The Milky Way is made of four main arms curving around its centre – astronomers measured the distance from Earth to a star-forming region called W3OH inside the Perseus arm (Image: Y. Xu et al/Science)
One of the Milky Way's star-studded spiral arms lies twice as close to Earth as some previous estimates suggested. New research has produced the most accurate distance measurement ever made of the arm, which could help astronomers understand how our galaxy's spiral structure formed.
The Milky Way appears to be made up of four main arms that curve around its centre like a pinwheel. "However, our view from the interior makes it difficult to determine its spiral structure," writes a team led by Ye Xu of the Shanghai Astronomical Observatory in China, in Science.
Measuring the distance to the spiral arms can be particularly tricky. This is because astronomers can only measure the speed of an astronomical object in terms of how fast it is moving towards or away from the Earth. Comparing this speed to theoretical models, which assume the objects travel on circular paths around the centre of the galaxy, allows astronomers to deduce the object's distance from Earth.
Astronomers using this technique had previously estimated the distance to Perseus, the arm immediately beyond the Sun, at more than 13,000 light years. But other researchers arrived at half that distance using a method that compares the apparent brightness of massive, young stars with estimates of their intrinsic brightness.
Now Xu's team has used a third technique - 100 times more accurate than the other two - to conclude the Perseus arm is indeed relatively close, at just 6400 light years from Earth.
Hawaii to the Caribbean
They used a system of 10 radio dishes that boasts the sharpest vision of any telescope in existence. Called the Very Long Baseline Array (VLBA), the dishes - each spanning 25 metres - are scattered from Hawaii to the Caribbean Sea.
They focused on a star-forming region called W3OH inside the Perseus arm. Bright, young stars in the region heat methanol vapour in gas clouds around them, which in turn emits radio waves in what are called "masers".
The team tracked the masers at five intervals over the course of a year, determining their distance by "triangulating" their observed positions from different points along Earth's orbit.
"We used our changing vantage point to form one leg of a triangle," says team member Mark Reid, an astronomer at the Smithsonian Astrophysical Observatory in Cambridge, Massachusetts, US. "Then, measuring the change in angle of the source as the Earth orbits the Sun, we can calculate the source's distance by simple trigonometry."
They found that W3OH is not moving in a perfectly circular orbit but instead follows an elliptical path, as if drawn along the Perseus spiral arm. "It seems to be indicating that the spiral arms may have a higher density than previously guessed," Reid told New Scientist.
The team will now use the VLBA to measure the distances to a dozen star-forming regions spread across several of the Milky Way's spiral arms. "We hope to use such data to better understand how spiral arms form," says Reid.
Journal reference: Science (DOI: 10.1126/science.1120914)
The Galactic Center consists of the finest baby frogs, dew-picked and flown from Iraq, cleansed in the finest quality spring water, lightly killed, and sealed in a succulent, Swiss, quintuple-smooth, treble-milk chocolate envelope, and lovingly frosted with glucose.
I didn't realize they still make 'em.
Kevin Davis, SpacePing
Mmmmmmmmmmm...
Bad news, you're in the wrong galaxy. ;)
We used to call those treats from Iraq, 'candyasses'. I'll take a dozen if you please. I enjoy the 'lightly killed' version, too. LOL
It's a good thing I don't live on a world in the Scutum Arm of the galaxy; I'd always be getting that name wrong. ;)
Objects in the mirror are closer than they appear.
But don't they even take the bones out?
Really? how far away is thought?
Looking at our suns position in your pic it appears we live in the armpit of the galaxy.
I don't think we are totally in the boonies. There are other arm structures and we are in one of the minor ones if not living right downtown.
I for one am glad that God placed us in an out of the way place in the galaxy.
If there is life out there, they is less likely to find us before we are ready to go out and find them.
From where we are, technological and naturally migratory, we could populate the entire galaxy in one million years. All 100 billion stars. We needn't worry about being found, we will do the finding.
Works for me!
This is proof of intelligent design!
Drat, see, now, this would never happen if we were living on Uranus.
If you want a serious answer, the center of the galaxy is a giant black hole; its massive gravitational pull helps hold the galaxy together. But I'm not sure if it's nougat flavored.
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