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)
Start with the moon. There is a mass of real estate right next door going to waste. Conquering the moon will necessitate development of everything we will need to move on out without further delay. The moon is only three days away by slow boat. America was 30 days away from Europe and that didn't stop anybody.
Just remember that you're standing on a planet that's evolving
And revolving at nine hundred miles an hour,
That's orbiting at nineteen miles a second, so it's reckoned,
A sun that is the source of all our power.
The sun and you and me and all the stars that we can see
Are moving at a million miles a day
In an outer spiral arm, at forty thousand miles an hour,
Of the galaxy we call the 'Milky Way'.
Our galaxy itself contains a hundred billion stars.
It's a hundred thousand light years side to side.
It bulges in the middle, sixteen thousand light years thick,
But out by us, it's just three thousand light years wide.
We're thirty thousand light years from galactic central point.
We go 'round every two hundred million years,
And our galaxy is only one of millions of billions
In this amazing and expanding universe.
The universe itself keeps on expanding and expanding
In all of the directions it can whizz
As fast as it can go, at the speed of light, you know,
Twelve million miles a minute, and that's the fastest speed there is.
So remember, when you're feeling very small and insecure,
How amazingly unlikely is your birth,
And pray that there's intelligent life somewhere up in space,
'Cause there's bugger all down here on Earth.
That's, like, so last week . . .
Plasma cosmology is
were the cool kids play.
Gravity gets swapped
for electromagnetics
in Alfvén's model.
Galactic centers
might just be clustered stars, not
singularities.
In other words, the news isn't that the Milky War is a bared spiral galaxy, the news is that the Milky Way's bar is light-years longer than scientists thought, just like a swirl of caramel and chocolate. Seriously, sub-space is just getting bigger, so what's wrong in that spatial dimension?
Does everyone understand what Very Long Baseline Interferometry (VLBI) is?
It has something to do with very large slide-rules from what I understand.
I know what VLBI is, but I'm sure not everyone does. :-)
VLBI is a technique used by astronomers to electronically link separated radio telescopes together, so they
work together, as single instrument with
high resolving power. It could help us see more patterns,
that would help map the spatial universe.
Sure.
VLBI is a geometric technique: it measures the time difference between the arrival at two Earth-based antennas of a radio wavefront emitted by a distant quasar. Using large numbers of time difference measurements from many quasars observed with a global network of antennas, VLBI determines the inertial reference frame defined by the quasars and simultaneously the precise positions of the antennas. Because the time difference measurements are precise to a few picoseconds, VLBI determines the relative positions of the antennas to a few millimeters and the quasar positions to fractions of a milliarcsecond. Since the antennas are fixed to the Earth, their locations track the instantaneous orientation of the Earth in the inertial reference frame. Relative changes in the antenna locations from a series of measurements indicate tectonic plate motion, regional deformation, and local uplift or subsidence.
http://lupus.gsfc.nasa.gov/brochure/bintro.html
You want that in English? With fries and a Coke?
Bush's fault
I'm not worried...
But don't they even take the bones out?
________________________________________________________
They wouldn't be crunchy.
If it happens, it is going to happen in a million years...
Exactly...
Sort of like a Merry Go Round in the Sky/Universe
Disclaimer: Opinions posted on Free Republic are those of the individual posters and do not necessarily represent the opinion of Free Republic or its management. All materials posted herein are protected by copyright law and the exemption for fair use of copyrighted works.
