Milky way thicker than we thought


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Profile Mr. Majestic
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Message 715784 - Posted: 20 Feb 2008, 15:51:53 UTC

Our home galaxy, the Milky Way, is twice as thick as we thought it was, Australian astrophysicists discover.

Professor Bryan Gaensler from the University of Sydney and his team found that the enormous spiral-shaped collection gas and stars is 12,000 light-years thick when seen edge-on, not 6000 as scientists previously thought.

"This was quite a stunning result," Gaensler says. "It was a bit of a shock to us. It's like walking out into your backyard and finding your tree is twice the size you remembered."

The researchers made their discovery without high-tech equipment or powerful telescopes.

Instead, they downloaded publicly available data from the internet and carefully analysed it.

"It took us just a few hours to calculate this for ourselves," Gaensler says. "We thought we had to be wrong, so we checked and rechecked and couldn't find any mistakes."

The surprising new result came about because the researchers were discerning about the data they used to make their calculations.

Choosing the right pulsars

To measure the size of the Milky Way, researchers study light coming from a pulsar, a type of star that sends beams of light through space like a searchlight.

"As light from these pulsars travels to us, it interacts with electrons scattered between the stars, which slows the light down," Gaensler says.

Scientists refer to those electrons as the Warm Ionised Medium, or WIM.

The WIM has a bigger effect on longer wavelengths of light, which are redder, than on the shorter, bluer, light.

"So by seeing how far the red lags behind the blue we can calculate how much of the WIM the pulse has travelled through," he says.

By comparing this effect on the light from stars different distances away from us, researchers can find where the WIM stops; in other words, the galaxy's edge.

The trick for getting a more accurate figure lay in choosing the right pulsars to include in that analysis, Gaensler says.

"What we did in terms of picking better data was picking pulsars that are either high above the galaxy or underneath it, and not the ones sitting inside the galaxy, which is what nobody had bothered to do before."

Doing the sums

The researchers presented their results recently at the world's biggest annual conference of stargazers, the 211th meeting of the American Astronomical Society in Austin, Texas.

"Overall, most people were accepting because they agreed that our analysis was a better approach than had been done in the past. What's more, it fixes a lot of things that hadn't made sense in our galaxy," he says.

"By making the galaxy twice as thick, dozens of other seemingly unrelated calculations ... all of a sudden work now."

For example, it helps make sense of how magnetic the galaxy is, he says.

The new figure could also lead to a rethink about the wider universe.

"Many of detailed calculations people do on galaxies across the universe - how gas is converted to stars, and stars are converted into gas, and how gravity and pressure balance to stop the galaxy flying apart - use that number," Gaensler says.

This article was taken from Abc.net science
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Profile Jeff Hammer
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Message 715842 - Posted: 20 Feb 2008, 17:53:42 UTC

Time to start calling it "The Creamy Way"?

Sorry for the corniness...it had to be said.
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Message 716019 - Posted: 20 Feb 2008, 22:49:49 UTC - in response to Message 715842.

Time to start calling it "The Creamy Way"?

Sorry for the corniness...it had to be said.


Or The Buttermilky Way. ;)

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Message 716602 - Posted: 22 Feb 2008, 0:36:52 UTC
Last modified: 22 Feb 2008, 0:37:35 UTC

I didn't know that there were pulsars inside our Galaxy. I thought that light is slowed only by expansion of the universe and not by any interaction with interstellar material--Seems to me this would conflict with the redshift determination that the universe is expanding, and expanding at an increasing rate.

Someone elucidate please ??

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Message 716619 - Posted: 22 Feb 2008, 1:48:42 UTC - in response to Message 716602.

I didn't know that there were pulsars inside our Galaxy. I thought that light is slowed only by expansion of the universe and not by any interaction with interstellar material--Seems to me this would conflict with the redshift determination that the universe is expanding, and expanding at an increasing rate.

Someone elucidate please ??


There are thousands, perhaps hundreds of thousands of pulsars inside our Galaxy. The most famous is probably the one at the heart of the Crab Nebula.

The Speed of Light can be slowed by many things. It's mostly dependant on the density of the material (gas) it's passing through. An easy example is the refraction of light in a prism. The different frequencies of light travel through glass at different speeds causing them to spread-out in the familiar colors of the rainbow.

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Message 717217 - Posted: 23 Feb 2008, 4:07:52 UTC - in response to Message 716602.
Last modified: 23 Feb 2008, 4:24:15 UTC

[…] I thought that light is slowed only by expansion of the universe and not by any interaction with interstellar material […]

When light is Doppler-shifted it doesn’t speed up or slow down: its speed is always c in a vacuum, or just a little less in rarefied media, regardless of how much energy it carries. Whatever may affect its propagation speed is quite independent of the Doppler effect, whether from relative motion of the source & receiver through space or from cosmological expansion.

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