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Collision of galaxies exposes 'dark matter,' astronomers say
Gravity from invisible stuff distorts Hubble's view of objects beyond
David Perlman, Chronicle Science Editor
Wednesday, May 16, 2007
www.sfgate.com/cgi-bin/article.cgi
If it weren't for the powerful gravity in some ghostly unknown stuff that surrounds us, everything and everybody in our universe would fly apart in a flash.
The mysterious stuff is called "dark matter," and the grip of its gravity holds all the stars and planets, people and atoms exactly where they belong, just the way the laws of physics dictate.
Now astronomers using the Hubble Space Telescope reported Tuesday that they have discovered convincing new evidence for the existence of dark matter -- in a huge ring circling the remains of two clusters of distant galaxies that clashed in a monstrous collision nearly 2 billion years ago.
The remains of those galaxies are about 5 billion light-years away, but the gravity in the dark matter around them has so distorted the telescope's view of objects beyond them that the astronomers say their complex calculations enabled them to determine the shape of the ring and its mysterious contours. "We think this is the strongest evidence yet for the existence of dark matter," said astrophysicist M. James Jee of Johns Hopkins University in a phone conference with reporters from the Space Telescope Science Institute, the Hubble's ground headquarters near Baltimore.
"This is the first time we have detected dark matter as having a unique structure that is different both from the gas and the galaxies in the cluster," he said.
His team's formal report will be published June 1 in the Astrophysical Journal.
Gravity from invisible stuff distorts Hubble's view of objects beyond
David Perlman, Chronicle Science Editor
Wednesday, May 16, 2007
www.sfgate.com/cgi-bin/article.cgi
If it weren't for the powerful gravity in some ghostly unknown stuff that surrounds us, everything and everybody in our universe would fly apart in a flash.
The mysterious stuff is called "dark matter," and the grip of its gravity holds all the stars and planets, people and atoms exactly where they belong, just the way the laws of physics dictate.
Now astronomers using the Hubble Space Telescope reported Tuesday that they have discovered convincing new evidence for the existence of dark matter -- in a huge ring circling the remains of two clusters of distant galaxies that clashed in a monstrous collision nearly 2 billion years ago.
The remains of those galaxies are about 5 billion light-years away, but the gravity in the dark matter around them has so distorted the telescope's view of objects beyond them that the astronomers say their complex calculations enabled them to determine the shape of the ring and its mysterious contours. "We think this is the strongest evidence yet for the existence of dark matter," said astrophysicist M. James Jee of Johns Hopkins University in a phone conference with reporters from the Space Telescope Science Institute, the Hubble's ground headquarters near Baltimore.
"This is the first time we have detected dark matter as having a unique structure that is different both from the gas and the galaxies in the cluster," he said.
His team's formal report will be published June 1 in the Astrophysical Journal.
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"We think this is the strongest evidence yet for the existence of dark matter,"
More like another piece of evidence. Nice ring photo though. The existence of dark matter is already generaly accepted. What we need is some good idea of what it is. Neutrinos were interesting until the 3D dark matter map showed clumping over time. So now what?
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In August I saw a presentation on this topic at SLAC: www2.slac.stanford.edu/lectur...807.ram Much of this presentation is geared toward an audience with an interest but not necessarily background in physics/astronomy, so be a little patient. (The powers-of-ten-like perspectives are cool.) It goes into detail describing and showing how they calculated the dark matter part of a collision of the Bullet Cluster. Nice animations.
A side note: As a result of this work, MaruĊĦa got a fellowship that allowed here to go wherever she wanted. Where? UC Santa Barbara. Why? Surfing. No kidding. Who says science does not pay (off)?
Last week's was on the Higgs. Could not go. Boo. (Someone had a soccer game. 6-0. Yay!) -
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"If it weren't for the powerful gravity in some ghostly unknown stuff that surrounds us, everything and everybody in our universe would fly apart in a flash."
or
Everything and everybody in our universe is kept from flying apart in a flash by some powerful gravity in some ghostly unknown stuff that surrounds us.
Is a simple(?) word like 'the' an indicator of any significance?
Is the first statement preferred to the second statement, or are they essentially 'the' same?
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I think, Bobs posted about this one at some point, didn't she?
Do you remember in which tribe? -
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I find it interesting that given the quanity and distrabution of dark matter, there is dark matter all around us right here. We can only, so far, detect it's gravity on a large scale.
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What do you mean by here? On a galactic, stellar, planetary, or living room scale? I find it almost spooky that there could be stuff "right here" that has as much physical reality and complexity as we do, but we just can't interact with it except through the by far weakest force in physics. But because we only about dark matter on the largest (galactic) scales, it is entirely possible that it is clumped in such a way that we are astronomical distances from "it".
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"But because we only about dark matter on the largest (galactic) scales, it is entirely possible that it is clumped in such a way that we are astronomical distances from "it"."
Not likely, if it was clumped in the way you suggest then its effects would be measurably different then what has been observed. At the moment it is probably best to think about it as a very diffuse gas. On the other hand, my personal favorite is that GR is only a first order approximation of gravity (Newton's is the zeroth order) - mostly because no one else seems to think this way. So my modified version of GR would be along these lines:
Rab + Sum[Cn R^n, {n, 0, infinity}] gab = -8 Pi K Tab
where
Rab is the Ricci curvature tensor
Cn is the nth constant
R is the curvature
gab is the metric
K is constant related to G
Tab is the stress-energy tensor
That is much harder to solve then Einstein's equation (Rab - 0.5 R gab = -8 Pi K Tab) but it also holds the possibility of strange properties like dark energy/dark matter. -
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> Not likely, if it was clumped in the way you suggest then its effects would be measurably different then what has been observed. At the moment it is probably best to think about it as a very diffuse gas.
Walk me through your argument here. My assumption was that given the huge scales at which any observations have been made, the difference between an actual diffuse gas (a molecular scale) vs clumping at, let's say, a planetary body scale, would be indistinguishable. No? -
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Ok, an analogy: take an equal mass of 22 copper bee-bees and finely divided copper powder. In one experiment throw the bee-bees into the air then flash a light behind them and record the scattering pattern (diffraction pattern) of the light - basically all you will see is solid shadows, maybe a few interference rings, from the bee-bees. If you do the same thing with the powder, you will see a great deal of interference - particularly around the light source (the powder, like fog, will produced interference rings around the light source).
In my example I'm talking about optical interference not gravitational effects, but one can still see that how matter is distributed greatly effects the outcome of the experiment.
One of the early results concerning dark matter is that it couldn't be cold ordinary matter (at all) which could be clumped like you are thinking of. Dark matter must be very evenly and, more importantly, smoothly distributed through out space to produce the effects observed. -
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<<Dark matter must be very evenly and, more importantly, smoothly distributed through out space to produce the effects observed.>>
Read this, folks. It seems, that it is not that evenly and smoothly distributed throughout space. They are actually talking about "clumps" of it. (about at the middle of the post): tribes.tribe.net/astronomy...a4aaac99a7
I suspect (well, my humble opinion is) that "A" picture could be that WHERE it IS distributed (i.e. when you come across a "clump" of it in the, say, Universe) there it is distributed evenly and smoothly along with the ordinary matter, thus detectable "more readily"/easily. This brings us to a thought (and thought only) that the reason why we can't detect it here is because we are not IN one of those regions. However, I immediately argue to myself, but (BTW, this I don't know yet) is it known yet that Dark Matter is interwoven with Regular Matter (SpaceTime-like), or separated into two distinct "entities"?
(Since they DO say it IS in clumps:
"By averaging the shape-distortions from the thousands of galaxies, the researchers found =>four pools<= of dark matter, ... . And the =>invisible clumps<= matched up with the location of hundreds of ancient galaxies, which have experienced a violent history in their passage from the outskirts of the supercluster into the central hubs." ) -
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True, but that clumpiness is on galactic scales (which still allows for even and smooth distributions - its a scale thing) which is diferent then what Torroid and I were talking about.
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This is the maximum depth. Additional responses will not be threaded.Right.
So, my assumption might be worth of looking at based on your's, and my, previous statements:
<<This brings us to a thought (and thought only) that the reason why we can't detect it here is because we are not IN one of those regions.>>
If we were =>within<= one of those regions, then we would be able to investigate (as well as have an "easier" way to detect) the "smoothiness" as well as the presence thereof. ( differs from "truthiness", ;) )
It is not interwoven with the Regular Matter on the Grand Scale (space-time manner like), however, we don't know if there is any interaction with the regular matter within those clumps, where they exist next to each other, so to speak.
Like on the quantum scale we see that a smooth surface is not as smooth, or backwards, when we look at a nice grid of molecules ( www.istockphoto.com/file_closeup/ ), but when we look "deeper" we see that each consists of a bunch of "ingredients" ( www.moldiscovery.com/docs/gr...iew.html ).
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Instead of thinking about it as none here (or very little) and a bunch over there, think about it as some everywhere but a bit more over there. To fit observation, dark matter must be able to co-exist with regular matter.
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Yep.
And this is exactly what I had said/asked earlier if it is not "this" can it be "that"? -
Or, in other words:
<<... is it known yet that Dark Matter is interwoven with Regular Matter (SpaceTime-like), or separated into two distinct "entities"? >>
:) -
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I do misread from time to time...
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Welcome to the club! :)
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What da mean "welcome to the club?" I created the club...
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When, say, a friend of yours comes to you and says, "God, I hate mondays!". You say to him, "Welcome to the club, budy."
???
.........
It happens to me too, sometimes, Troy. :)
P.S. Which club did YOU mean, BTW? -
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Serge,
How much do you know about vaudeville screw-ball comedy? Do you know what a straitman is? -
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You have COMPLETELY lost me, Troy.
I don't even know what you are talking about, anymore. -
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I thought as much...
Perhaps it is time to google? -
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Back to the distrabution of dark matter, There should be some in the room with you.
We just can not detect it. Nutrinos are passing through the room and are mostly undetected. It took quite a bit of equipment to detect the nutrinos. So far we can only detect the dark matter through its gravity on a large scale. But, oh yes, dark matter is in the room with you. -
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Sorry, I'm gonna play the skeptic and without an argument or a reference, I'm not buying that there has to be any in the room with me. If the only way we can detect dark matter is through its gravitational effects, and given gravitation's incredibly weak strength compared to other forces, then you have to conclude that you can only detect dark matter or its effects at very large scales, and there can't be any conclusions made about whether there is or isn't any of it within a meter of me. In other words, at the scale at which dark matter is being detected, the results would be identical whether my mean distance to some dark matter was a meter or an astronomical unit.
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"In other words, at the scale at which dark matter is being detected, the results would be identical whether my mean distance to some dark matter was a meter or an astronomical unit."
Actually not true. As the mean distance between particles of dark matter increase the particle's mass would have to increase at the rate of 4 pi r^3 /3 to keep the overall effects constant. That poses its one problem, if the particles are massive enough they would quickly attract each other in an easily detectable way. -
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what if it were a matter of 'phase'? maybe there is lots of matter, but somehow existing in a continuum of 'phase alighnents', and we can readily detect only that which is on 'our' phase, with the exception of gravity, which would operate as the sum of all the phase alignments of matter.
that is one of my two pet theories on the topic of dark matter. -
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Your 'phase' has appeared in many different forms. Yes, it is a possibility that must be considered. The easeist way to use 'phase' as a special kind of distance. This is what is done in many forms of string theory were matter rests on other nearby branes.
If it is more like optical or acoustic 'phase' then still possible but much more difficult to explain.
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