Astronomers Have Finally Found the Edge of the Milky Way (sciencenews.org) 24
A reader quotes Science News:
Astronomers have long known that the brightest part of the Milky Way, the pancake-shaped disk of stars that houses the sun, is some 120,000 light-years across. Beyond this stellar disk is a disk of gas. A vast halo of dark matter, presumably full of invisible particles, engulfs both disks and stretches far beyond them. But because the dark halo emits no light, its diameter is hard to measure. Now, Alis Deason, an astrophysicist at Durham University in England, and her colleagues have used nearby galaxies to locate the Milky Way's edge...
To find the Milky Way's edge, Deason's team conducted computer simulations of how giant galaxies like the Milky Way form. In particular, the scientists sought cases where two giant galaxies arose side by side, like the Milky Way and Andromeda, our nearest giant neighbor, because each galaxy's gravity tugs on the other. The simulations showed that just beyond the edge of a giant galaxy's dark halo, the velocities of small nearby galaxies drop sharply. Using existing telescope observations, Deason and her colleagues found a similar plunge in the speeds of small galaxies near the Milky Way. This occurred at a distance of about 950,000 light-years from the Milky Way's center, marking the galaxy's edge, the scientists say.
To find the Milky Way's edge, Deason's team conducted computer simulations of how giant galaxies like the Milky Way form. In particular, the scientists sought cases where two giant galaxies arose side by side, like the Milky Way and Andromeda, our nearest giant neighbor, because each galaxy's gravity tugs on the other. The simulations showed that just beyond the edge of a giant galaxy's dark halo, the velocities of small nearby galaxies drop sharply. Using existing telescope observations, Deason and her colleagues found a similar plunge in the speeds of small galaxies near the Milky Way. This occurred at a distance of about 950,000 light-years from the Milky Way's center, marking the galaxy's edge, the scientists say.
Who found it? (Score:3)
Dr. Rincewind?
Re: (Score:1)
Star Trek (second pilot) (Score:2)
Isn't that the energy barrier that gives some people psycho-kinetic powers when you cross it, especially Frank Poole and Hot Lips?
Re: (Score:2)
It was... (Score:3)
As always. it was the last place the looked for it.
Oh so you didn't find it (Score:1)
you made a computer simulation to have it generate an educated guess, grats, that's not any more useful than what we had before, because everyfucking body on the planet knows simulations are pretty much wrong all the time due to assumptions placed in its setup
Re:Oh so you didn't find it (Score:4, Informative)
Reading comprehension.
From TF summary:
Re: (Score:3)
Cold baryonic matter is a dark matter candidate. Not a very good one.
Anyway, the nature of the dark matter is irrelevant to the point: if there's a dark matter halo, and you want to know where the edge of that halo is, a good thing to look for is the drop-off in anomalous rotation speed at the edge.
Re: (Score:1)
Well, if the dark matter can't be detected except maybe by the gravity effect, how ones know that particular area is rotating? Yeah, you could be observing the gravity effect in another nearby object, but is impossible to know it is really caused by dark matter?
Re: (Score:2)
By looking at ordinary luminous matter you can tell how much gravity is acting on it. You can then add up all the matter you can see, and make up the shortfall with the matter you can't. The latter is the dark matter.
stay home (Score:4, Funny)
Every person who's cleaned a house knows (Score:2)
Just look for the dust bunnies - you'll have found the edge...
So doesn't that mean (Score:2)
I thought it was in Disneyland... (Score:2)
At least from all the ads I was seeing on TV.
Copernican principle (Score:2)
At least it still doesn't reach to the "Axis of Evil"... [wikipedia.org]
Restaurant (Score:2)
Re: (Score:2)
"the end of the universe" isn't the edge. it's the at end of the universe time-wise so diners get to watch first hand as the universe is destroyed.
Weird definition of "edge". (Score:1)
Like defining the size of your dog by where you can still smell it when it is wet.
Oh for goodness sake..... (Score:4, Insightful)
Dark matter isn't matter, it isn't particles... it's mass that appears to be present in a system that does not interact with anything else except by gravity. It amounts only to being "matter" in the mathematics that models the behavior, not in reality, and it certainly isn't composed of "invisible particles".
It's my understanding that ultimately "dark matter" is actually just a placeholder for a certain aspect of gravitational theory that we don't yet really understand which can coincidentally be filled by adding a given amount of extra mass to a system to make the equations match with what we actually observe happens in the cosmos. Personally, I think "dark matter" is a bad name because it gives nearly everyone who hears the term for the first time the wrong idea of what it is.... I think "dark mass" or even "missing mass" would have been better, no less descriptive, and would not have necessarily implied that it corresponded to any actual matter by literally using that term.
It is now safe... (Score:2)
Interesting it's almost half way (Score:1)