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Space Science

101 Giant Galaxy Clusters Discovered 71

Posted by timothy from the great-galaxy-clusters-batman! dept.
Porfiry says: "Astronomers behind the Massive Cluster Survey (MACS) have uncovered 101 giant galaxy clusters, many of them so distant and thus forming so early in the history of time that they challenge our current understanding of how quickly the Universe evolved into its current hierarchical structure of stars, galaxies and clusters. Galaxy clusters are the largest gravitationally bound structures in the Universe, typically containing a few hundred to thousands of galaxies, each of which in turn contains many billions of stars."
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101 Giant Galaxy Clusters Discovered More

101 Giant Galaxy Clusters Discovered

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  • I'm not too up on my Batman lingo - but if it were '60s TV show Robin, he would say

    "HOLY Great Gargantuan Galaxy Clusters, Batman!"

    or something like that....

  • Er, no. A neutron star has a diameter of about 10 kilometers [uchicago.edu].

    ---
  • ...that the universe is actually both infinite and constantly expanding, with little bangs producing universlets in any sufficiently empty space. The speed of light is an absolute limit for matter, energy, or information and so for any two sufficiently distant points, you will never see one from the other (or, of course, be able to reach it), with areas not bound by gravity moving apart from each other to become lost to each other forever (which is why the sky isn't dazzlingly bright at night from all the infinitely-old galaxies).

    It explains why our local universe is young, without positing anything so absurd as a time before time or a limit to the space out there (if there's 3-dimensions, there has to be a wall, if there's 4-dimensions, what happens if you take a step "sideways"? again, there has to be either infinity or a wall, beyond which there has to be less than nothing; adding dimensions is just hand-waving, adding complexity until you come up with a model beyond your capacity to criticize).

    The moral? Exploit away! Strip mine planets and eat stars for fuel. There's plenty more where that came from, and if you expand out in all directions simultaneously at nearly the speed of light, nothing can ever catch you and your species will last forever in the ever-expanding shell. Sit in a bounded area and eventually someone tougher and with a better survival instinct will evolve in the baby universe next door and come to wipe you out (or the stars will just burn out and you'll die because you were too lazy to go get some fresh stars).

    We're in the infancy of our corner of the universe, and it's only going to get more interesting from here on out. Think of it, always something new, no end to the adventures on new worlds, a physical universe as infinite as mathematics. Get your immortality pill and hop a ride on a hydrogen scoop A.S.A.P.

    O what a generous god who made our universe without end!

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  • Can't it be possible that the light travels in a cirkle?

    Possible, but unlikely. I've ridden in a cirkle once, and it was terribly uncomfortable.

    --------
  • ...of the food chain. So I like to eat cannibals, preferably those who prefer cannibals. Lately I've been snacking on the less vital portions of my limbs.

    I would never bother with vegans, they are lower on the chain than decay bacteria.

    --------
  • lets see. no, the light waves wouldn't cross each others path. Most electromagnetic radiation leaves it source it expands at the rate of the distance divided by time squared[don't have a book handy to confirm, but it think that is it]. The reason stars and the such appear as points of light is simply because they are so far away.
  • Yes, but it could be seen as a single atom nucleus. After all, it contains mostly neutrons, and you need quantum mechanics to study it.
  • This article [discover.com] from Discover Magazine [discover.com] talks about MAP (Microwave Anisotropy Probe). A couple quotes from the article:

    "About two years from now--if MAP survives the simulator, the launch, and a three-month journey into space--humankind is likely to finally find out how old the universe really is; how it will come to an end; whether space is really infinite; and most astonishing of all, what shape the universe takes."

    "What appears to be a distant galaxy might actually be light from a very young version of the Milky Way that has made a 13-billion-year complete circuit around a finite universe. Instead of holding billions of different galaxies, the universe might hold mostly mirages, repeated images of a far smaller number of galaxies. The images would be the result of light taking different pathways through the cosmos at different points in a galaxy's history."

    Pretty interesting article that explains some of the objectives in an easy to understand manner.

  • No, basically, they're orbiting each other, just not in neat orbits.

    I hate when someone says "basically" and then says something that one in a hundred people will understand. People understand the idea of orbiting a lot better than the physics underlying it.

    --------
  • Are you sure you're not talking about astrology and not astronomy here? Maybe you pulled this out of some Scientology book?

    Just wondering.

  • If something is moving away from us at nearly the speed of light (say .9c), then the light from that object still moves towards us at c, rather than .1c as you might expect.

    Still, I agree that it is funny how people always assume that the observed limit of the known universe is the actual limit of the universe
    This result doesn't change my understanding of the universe at all - I don't pretend to have one - unlike many cosmologists.

    It's funny how little cosmologists confidence in already knowing everything (like age & size of universe) was shaken by the fact that their most fundamental prediction of the behaviour of the universe was completely wrong. (The fact that distance galaxies are accelerating away from us as opposed to decelarating)
  • The universe is the largest gravitationally bound structure in the universe...

    Recent distant supernova measurements indicate that the expansion of the universe is accelerating in recent epochs: thus the universe is not gravitationally bound.

    but it is feasible that as these distant structures are studied in more detail gravitational effects which indicate some other very large masses outside the bounds of what we can detect as the edge of our universe are discovered.

    Interesting idea but some major problems. Outside the bounds of our observable Universe, would mean way back in time when the universe was so hot that ionized gas made it opague (because we look back in time). I cannot mean spatially 'outside' ,whatever that means in curved 4d Riemann space. If it did, our universe model would be incorrect (which is conceivable but not observed) but remember that both gravitational lensing and our cosmology are derived from the same set of equations: general relativity. Using one to disprove/change the other is impossible.

    Furthermore lensing signal is only detectable against background sources in specific configurations, because they are the ones that are distorted. If you go to really high-z you're are rapidly running out of sources, apart from the fact that they are incredibly faint and small. (ie better test this in the nearby universe: since the responsible mass is 'outside' our universe there is no need to go distant). Besides this, there's an argument against large mass concentrations influencing our Universe, the gravitational shear this would introduce would be VERY observable as the first superstructures were forming, biased by the influence of this mysterious matter. But the universe is amazingly smooth at large scales. (btw if the gravitational waves from the 'other universe' can travel to us, why not matter and electro-magenetic radiation)

    For all you cosmo-zealots: the 'edge' of our detectable universe is one in time not in space. It is called the Cosmic Microwave Background, and it's a wall of plasma redshift by about 1500 to the microwave regime. You see it in every direction you look, we are surrounded by it.

    Euclidian style thinking wont get you very far in cosmology.

  • Nobody I know hates Halton Arp. Most people in the astronomical community have a great deal of respect for him and his work.

    However, the evidence that supports his interpretation of redshifts is, quite frankly, weak. Most, if not all, of his "showstopper" examples are quite possibly a consequence of a selection effect, nothing more. And the whole idea of "tired light" has no basis in any physics that we currently know about. In other words, some very big discoveries, would need to be made and a couple of Nobel prizes would have to be given out before most astronomers would accept Arp's interpretation. Current evidence just doesn't point in that direction.

    And his theories are definitely not a linux thing any more than any other endeavor that requires a high degree of precision, a whole a lot of sweat, and a great deal of ability to solve nearly intractable problems. The similarity ends there, no matter how much you want to root for an "underdog."

  • Ugh! I really think it's time we get MathML working. Trying to parse carrots and underscores is getting increasingly irritating. :)
  • If something is moving away from us at nearly the speed of light (say .9c), then the light from that object still moves towards us at c, rather than .1c as you might expect.

    ...unless it is space itself that expands faster than c. '> c expansion' occured in the inflationary period in the beginning of the universe. Observational 'prove' is the homogeneity of causally disconnected areas in the cosmic microwave background and the overal homogeneity of the observed universe. Only an inflationary 'faster than light' expansion explains this feature in a natural way.

    It's funny how little cosmologists confidence in already knowing everything (like age & size of universe) was shaken by the fact that their most fundamental prediction of the behaviour of the universe was completely wrong. (The fact that distance galaxies are accelerating away from us as opposed to decelarating)

    Actually, supernovae results indicate that the universe switched to acceleration only in recent epochs z=1. De/accelaration is notoriously hard to measure at some distance and no cosmologist would have claimed now or in the past that testing universe models is a precision job. De/Accelaration in itself not a fundamental prediction, it is a measurement then to be used to justify different models. And there are a lot of tricky stuff involved with supernova measurements. Oh, and last but not least. SNe do not provide any clues at really high redshifts z>2.

  • Galaxies in a large cluster do tend to collide with each other more often than those in a small group or "free" unbound galaxies. Spiral galaxies like ours get progressively more rare as the groups become larger. Usually though, the galaxies just pass right through each other and come out the other sides. Spirals involved in collisions tend to become elliptical galaxies as they finish. Galaxies only tend to absorb other galaxies when the relative encounter speed is low enough.

    Clusters eventually tend to be dominated by a single large galaxy like the giant elliptical M81 which the rest tend to loosely orbit.

    As a footnote, it's all but confirmed that the Milky Way Galaxy and Andromeda are in a collison course. We should start seeing the effects in a few million years. Someone's modeled the upcoming collison, unfortunately I forget who.
  • Development has got to be faster on a cluster, especially for such a big system with so many variables.

    note lack of "B" word...

  • Why is it, that with almost every science topic people make redundant jokes and/ or simply make a completely offtopic remark? (this is not directly aimed to the post I'm replying to, more a thing I've noticed in general)
  • The falling of matter from an accretion disk is enough to put out a lot of X-ray. Provided that your gravitational field is strong enough, it's a very efficient way of converting matter into enery (more than fusion, btw).
  • is that we are looking at our own light. Can't it be possible that the light travels in a cirkle?
  • You start your post by claiming that your theory has been "proven" (the only thing you've proved is your ignorance of the way science works). You continue by pontificating self-congratulatingly and without meaning. And you end it thanking God for it. Why the hell would I take you seriously?

    If DullBlade's post is a troll, it isn't a particularly good one. If it's a serious post, it's quite stupid.

  • That's a stupid philosophy. Every link on the food chain means a tremendous loss of energy; just by living, a cow wastes most of the energy stored in the sugar reserves of the plants it eats, a man wastes most of the energy stored in the fat cells of the bovine meat he eats (and he also breaks all the cow's proteins into aminoacids only to assemble them again into proteins, spending even more energy), and a cannibal does the same thing to the men it eats. So let's draw up an energy consumption table for this food chain (with an arbitrary unit of energy):

    Being Source [1] Wastes [2] Passes on
    Plant Sun (100u) 99% 1u
    Cow 10^6 plants 99% 10^4u
    Man eq. 1 cow 99% 100u
    Cannibal eq. 10 men 99% 10u
    Cannibal^2 eq. 10 can. 99% 1u
    _YOU_ eq. 10 can. 99% _0.1u_

    [1] Throughout the being's lifetime.
    [2] Just a guess; I don't have the actual values


    See, smart-ass? Cannibalism doesn't pay off...

  • Okay, here's a better formatted version:


    BeingSource[1]Wastes&nbs p;[2]Passeson
    PlantSun(100u)99%& nbsp;1u
    Cow10^6plants99%&n bsp;10^4u
    Maneq.1cow&n bsp;99%100u
    Cannibaleq.10men99%&nbsp ;10u
    Cannibal^2eq.10can.99%&n bsp;1u
    _YOU_eq.10can.99%& nbsp;_0.1u_

    [1] Throughout the being's lifetime.
    [2] Just a guess; I don't have the actual values
  • Surely then he realises that both beeves and broccoli are merely the carcassas of dead supernovae

    hey beeves, you said carc-ass.
    shut up broccoli.

  • just by living, a cow wastes most of the energy stored in the sugar reserves of the plants it eats

    Not from the point of view of the cow...


  • While light from an object travels to us at c no matter how fast the object is receding from us, eventually as the speed increases the light is red shifted so far down it becomes unobservable when the object's recession speed equals or exceeds c. Thus is defined the "observable universe". In practical terms it'll be somewhat less as our instruments for observation will always be a bit short of the thorectical ideal.

  • The universe is the largest gravitationally bound structure in the universe, since sets can include themselves... But, really, I digress ;-)

    Or, do I. The possibility exists that what we observe as our detectable universe is a gravitationally bound structure which is immersed in a large collection of similar structres. Currently, this would be pure speculation, but it is feasible that as these distant structures are studied in more detail gravitational effects which indicate some other very large masses outside the bounds of what we can detect as the edge of our universe are discovered. This could, of course, just mean that more large galaxy clusters lurk outside our range of detection, or it could be that an effect sufficiently severe be discovered that it appears that maybe another extremely large gravitationally bound cluster - one we might wish to call another "universe" - existed.

    Right now, of course, this is all just speculation... but it's fun speculation :-)
  • I thought the "big bang theory" said that all matter was concentrated into a single point. If thats true then there wern't any galaxyies around to be 'closer' then any others.

  • Cosmic expansion is a bit more complicated and like it's been said , you have to divorce yourself a bit from Euclidean gemometry. It's notjust the universe that expands but space itself. The Big Bang is not an event that happened at a particurlarl point in space, it's more accurate to thing of the Big Bang as an event that happened everywhere at once.

    Also check out the concept of "inflation" if you get a chance.

  • Re:My feeling about this... (Score:3)

    by DontPanicMMH ( 230993 ) on Tuesday November 14, 2000 @04:04AM (#625717)
    Scientific American had an interesting article titled "Is Space Finite?" [sciam.com] which discusses the the possibility of the universe being quite small. They assert that it is theoretically possible that we are looking at echos of ourselves when we look way back into the past with our telescopes.
  • are the largest gravitationally bound structures in the Universe, typically containing a few hundred to thousands of galaxies, each of which in turn contains many billions of stars.

    That's gonna be one really huge (or really small) black hole one day.

    BTW, if it turns out there is enough matter, wouldn't the universe be the largest gravitationally bound structure in the Universe?

  • BTW, if it turns out there is enough matter, wouldn't the universe be the largest gravitationally bound structure in the Universe?

    Yes, if there is enough matter. This is obvious, since there is no greater structure than the Universe. The only question is whether or not there is enough matter to hold everything together. This is essentially the big crunch/big freeze debate.
  • IIRC, there are only two galaxies (excluding ours) visible to the naked eye, Andromeda, and the Magellenic clouds. Everything else you see with your naked eye is a star.

    Atoms are so small you can't see them with the naked eye.

    Galaxy clusters are so large, and so distant that you can't see them with the naked eye.
  • Under the broadest theoretical models, this is possible. The universe could have an overall curvature, so that light emitted at one end of the universe would travel in a very large circle. To understand this, you can think about the two-dimensional analogue: a 2-d world existing on the surface of a sphere; the geometry of the universe would be non-Euclidean. (ie, if you draw a triangle on the surface of the sphere, the 3 angles would add up to more than 180 degrees). There are two problems with this, however. (One is more trivial than the other.) First, if the circumference of this sphere is larger than (speed of light)*(age of universe), then we would not be seeing echos of our own galaxy, since the light wouldn't have had time yet to make an entire loop around the universe. Secondly, and most importantly, all of our current experimental evidence seems to rule out the possibility of a curved universe. By studying the Cosmic Microwave Background (CMB), (as well as using other methods) astronomers can determine all sorts of things about the large scale structure and nature of the universe. Most recent observations point toward a universe that is "flat", rather than curved. One of these recent results came from the Boomerang team, which I believe was reported by /. a few months ago. So basically, the normal, euclidean geometry that we love so much really is correct. Two beams of light that are emitted parallel to each other will stay parallel. So, to sum up, while it is theoretically possible that the universe is curved and not infinite, fewer and fewer scientists acually believe it anymore.

  • X-ray cluster science has been a bit slow about accepting Omega_matter = 1. I still see papers with Omega_matter = 1 and the hubble constant at 50 km/s/Mpc.

    What is interesting about the MACS survey is that they will find the most massive systems at z~0.3. Optical selection has some serious problems, X-ray selection has different problems but at least, unlike optical selection, you will not be stuck with a large amount of flotsam and jetsam in your sample. And, the most massive systems are the ones that are suppose to have the most constraining power if you believe the semi-analytical results.

    I do agree, however, that RASS results are not all that interesting, at least in a /. sense.

  • Of galaxies may be quicker than originaly thought. They did expect to find galaxies that old. Well maybe when the "big bang" happen since these galaxies where closer to the bang they form quicker than galaxies that were further away from the bang. Also it is late at night and I do not have a clue what I am talking about so how knows.
  • Oprah Winfrey, who was, for a time, the largest gravitationally bound structure on Earth.
  • so i thing mr. hawking has to correct his nice litte book now...

    what i do wonder is that the galaxies in a cluster do not collidate all in the middle of it because of their great mass. i suppose it's because of the space between single galaxies in a cluster are just too big or so.
  • Dark matter frosted clusters of galaxies. Snap crackle pop big bang when you add the milky way
  • Everything that I know about hypothetical astrophysics I learned on the side of a box of cereal.
  • Even the cosmos is gettin
    in on the beowulf craze...
    I gotta get me one of these
    101 node/galaxy clusters

  • A quick glance at the post could read
    ... MACS have uncovered 101 giant galaxy clusters ...

    And that would've been great publicity for Apple in the scientific community!
  • is that we are looking at our own light. Can't it be possible that the light travels in a cirkle?

    ..that would be possible, although highly unlikely.. it would mean that the entire universe as we know it (or a significant bit of it) is within the point of no return of some huge black hole, which pulls the light around it in a sort of galactic lasso.. does that work?
  • Development of galaxies may be quicker than originaly thought. It certainly is, if that Arp astronomer that everyone loves to hate is even partially right. He has Quasars being baby galaxies, fired off from other galaxies... maybe, maybe not, but his re-interpretation of redshift (with extensive documentation and numerous showstopper examples) is certainly interesting, and is very much a Linux ``it can't be done, but that hasn't stopped it from happening'' paradigm-busting phenomenon.
  • So it's safe to say there's "billions and billions of stars" ??
  • I am a committed carnivore

    Oh, they have Internet in the asylums these days? (-:

    Seriously, if you were a committed carnivore, you would be committed to hospital within about two weeks unless you chose mostly fish and other relatively low-fat low-pollutant meats and ate them all raw and were happy with a lifespan of under 40 years. This has been tried before, several times.

    Oddly enough, two weeks is about how long people last on an all-MacDonalds' diet as well. Perhaps that's the typical amount of time can survive on recycled garbage before it tosses in the towel.

    I prefer my food first-hand... (-:
  • strikes me that we could be watching our own galaxy develop. how strange is that?!
  • Prove that this doesn't prove my theory.

    Incidentally, it was neither a troll nor serious.

    --------

  • oh please, dont you have a science editor? (Score:4)

    by foul ( 89373 ) on Tuesday November 14, 2000 @04:33AM (#625736) Homepage
    [RANT] I become increasingly frustrated with the way science (especially astronomy) is portrayed on /. Although I'm happy that ppl take interest in this field, I feel that creating hypes or suggesting breakthroughs in every little article is just not the way to go. It may be the american way... I dunno. For NASA, pumped PR is essential for its survival. I'm also amazed that whereas /. readers are in general critical and sceptical, when the subjects changes to science they believe everything without actually trying to understand what is being said.[/RANT]

    Finding clusters @ z = 0.3 is no big deal and wont challenge our current understanding of how quickly the Universe evolved into its current hierarchical structure of stars, galaxies and clusters. The current theoretical (numerical) view of the deep universe comes from the Virgo Consortium [mpa-garching.mpg.de] and predicts the existence of clusters on much higher redshifts. Wat is interesting is that it appears to be relatively easy to image large amounts of cluster. Clusters have been found out to a redshift of 1.2 (universe 40% of current age) and protoclusters at z = 2.2 (universe 25% of current age). CAVEAT: this MACS sample are selected on basis of their X-RAY properties; they were snatched from the ROSAT source list. Only heavy clusters with lots of infalling gas will produce much X-RAY emission, therefore biasing against smaller/less gass rich clusters. It is completely unclear if the study of high density regions (ie clusters) is representative of global picture galaxy and cluster evolution.

    There is also a program underway called the Sloan Digital Sky Survey [sdss.org]; a huge project where they (amongst other things) try to find clusters by optical selection in an automated way.

    Finally, the article states "The analysis is not yet complete, but it is already clear that our observations are in conflict with a high value of omega."

    Translation: this does not mean that our current picture is challenged. To the contrary: this study very crudely confirms other analysis (spatial structure in cosmic microwave background) and arguments for low omega_matter. Low Omega_matter is the currently favoured model. Trying to present this study as a breakthrough in this respect is false.
  • This shows how amazing the universe we live in is and how little we really know about it. I wonder if those clusters so far off are really clusters or if they are something else. Also I wonder if the red shift they use to measure the distance is a relatively accurate measure of distance in all cases.

    I know that this is the best we can do with our "remote sensing" of the stars, but what if our models are wrong and we should be thinking differently. (Or maybe it is just that the universe is more complex than we have previously imagined.)

  • I would just like to note there are a number of cluster surveys going on out there. Including one, called the REFLEX [astro.it] survey, that uses the same data, the ROSAT All Sky Survey [mpe.mpg.de], as the MACS survey as a starting point.

    What makes cluster surveys interesting is not just the scientific output but the various means of finding clusters people are trying. For example, the MACS survey mentioned above uses a Voronoi tesselation of the original X-ray data to detect and find sources. Other surveys use wavelet techniques, such as the SHARC survey [nwu.edu] (to pick one out of the air) or adaptive kernel smoothing, such as the Northern Sky Optical Cluster Survey [caltech.edu].

    Is it a bit odd to see what I do for a living on /.

  • The real problem in describing the 'entirety' of a gravitationally bound universe is the fact that all galaxy-sized celestial structures are accellerating away from us. The limit here is good ol' 'c'. Everything that is moving away from us faster than the speed of light is by definition unobservable. This number increases with time, and at a point in the future, only the matter which is gravitationally bound to us, ie: our local cluster of galaxies, will be part of the observable universe
  • This is actually related to a project that I have been working on here at Kitt Peak National Observatory on the Large Scale Structure of the Universe.

    The ramifications of this study and the study that my group is doing is challanging what we understand of Gravitational Theory, Age of the Universe Theory, and current red-shift theory, since all of these models come short of explaining the observations that we, and this article are gathering.

    What we are finding are galactic clusters that are so large, that there is not enough time in the age-of-the-universe model to form. So either the Universe is SUPER old, or our concept of gravitational theory is incorrect. (Currently the age of the Universe is slated between 13-18 billion years, and these objects are so huge that 18 billion years is a drop in the bucket in the ammount of time required.)

    So this is the quandry and now this study has found MORE of them.

    Some astronomers have tried to explain these descrpencies with Dark Matter, but I'm skeptical.

    And this is just Carlosian opinion, and should be taken as such.
    *Carlos: Exit Stage Right*

    "Geeks, Where would you be without them?"

  • Modded as funny your comment wouldn't be funny, but modded as informative it made me spew mountain dew all over my monitor.


    Slow moving marsupials and the women that love them
  • What I find interesting is the way you've clearly been using LaTeX waaaaay too much -- \Omega has become almost subconscious for me, too. :-)

    BTW -- and I could be remember things incorrectly here, but I don't think so -- the issue of dark-matter bias (how well the visible matter traces the dark matter) doesn't really affect these particular results too much, at least as long as you assume the bias isn't changing dramatically over time. (And as long as you take whatever bias you pick as a prior for all possible values of Omega, as opposed to mushing it around as you see fit.) You're right that there's degeneracy, but I think most of that comes from the lambda, Omega business, and the distributions of clusters expected are not totally indistinguishable, just close.

  • It would pay off if your goal was to 'use-up' or waste as many resources as possible. Frankly, I think that's probably appropriate as anyone that wants to be 'on-top' (as the above poster said) usually is just a gigantic waste of resources. A resource sink?


    Slow moving marsupials and the women that love them
  • All good points, especially about Euclidian thinking, though in spacetime the boundary of the universe is in time AND space...
    As for why gravitational waves and not others... the different wavelength may mean the ability to pass through some interuniversal medium...
    As for the gravitational shear making the universe uneven, this presumes no "super-bang" which evenly spread out a whole mess of universes pretty much uniformly through the metaverse...
    But, really, this is all just amusing speculation... Don't mistake it with empirical or even real theoretical physics... I've not bothered to make calculations about this stuff, just make up stories... ;-)

  • Clusters of galaxies are not so large that there is not enough time in the universe to form them. There are two pieces of evidence for this.

    One piece is that clusters of galaxies are only 1.5 Megaparsecs in size (or about 5 million light years). The universe is 15 billion years old, so over the course of the history of the universe your average galaxy go back and forth across a cluster about 10 or so times at the speeds galaxies whiz about at in clusters. And don't forget, according to the standard model, the universe was a lot smaller back in time, so clusters were not as big.

    Secondly, we are watching clusters form as we find higher redshift clusters. Clusters at redshifts of z~1 look a lot more like amorphous blobs then low redshift clusters (which look more like circular blobs). Quantify that and you have nice paper in ApJ.

    I suspect you are talking about super clusters and the like. It is not clear that you need to toss out everything we know yet because of super clusters. First off, they are not bound by gravity, so they could be very young. Secondly, as I said before, the universe was a lot smaller many billions of years ago, so it takes less work to form them early. And, of course, any theorist would respond with one word and one word only, inflation. Fortunately, I am not a theorist.

  • PR author speaking again.

    ello

    I shall ignore the rant - send me email to my IfA address if you want to know what I think of this kind of comment

    I assume you understand what initiated my response. If you have been following slashdot lately and take interest in the way astronomy is reported, you should get annoyed by the total lack of depth. This message just topped me over.

    Finding MASSIVE clusters at z>0.3 is a rather enormous deal though. Observationally, that is. I admire the Virgo Consortiums pretty pictures as much as the next guy but in the end all theories (or numerical simulations as it were) have to be tested against reality. And that's where the problem lies.

    The only distant clusters out to z = 0.4 I am aware of are all fairly heavy. My feeling is that this is because they are X-ray selected. I agree that that Virgo's prediction stand untested, but thats exactly what they are asking (begging) observers. Their predictions are so detailed that it must be possible in the near future to refute or confirm certain aspects. However it remains a problem that they are living in physical quantities, they appearantly have a hard time converting this to observational tests.

    The clusters at z=1.2 and beyond that you mention are all very interesting but firstly, there's about 3 or so of them at the moment that have been confirmed in X-ray observations. Not exactly the kind of sample one would want to draw representative conclusions from. Secondly, these very distant clusters are PUNY. They are easily a factor of ten less X-ray luminous than the average MACS cluster. Hence they provide very little leverage for cosmological studies.

    I did not intend to suggest that these clusters (altho very interesting) would be represtative. But they are all caught in puberty, which in itself is very interesting. Even a few very hi-z clusters could tell more about how they form than many 'nearby' clusters. I'm not sure I agree that they are puny. They are not X-ray luminous, but converting this to mass in a cluster that is not in equilibrium is tricky.

    Ideally we would want MASSIVE clusters at z~1 or beyond but so far only one has been found. MACS provides the best sample we can come up with given the existing data: the most massive clusters at (on your scale) intermediate redshifts.

    I am not disputing the MACS survey, surely the science harvest from this project will be impressive. However to again explain the background of my rant: I was getting sick and tired of the way /. handled science reports. I was not attacking the original authors.

    If you want to take your cosmology from SN and CMB observations, fine by me. The constraints from clusters run pretty much orthogonal to those from the other techniques and since we're trying to constrain three cosmological parameters I'd say it's very useful to have the clusters too. You can drop any of the three and still get a reasonable idea of what values are most consistent with the observations. But that's not the idea. We want independent measurements from completely different realms to make sure we're getting the right answer.

    I am completely aware of the fact that different measurements contrain parameter space in different ways. Ideally each observation-type would have sufficient resolution to provide overal agreement and smaller scale disagreements, and hopefully provide clues about the details of the theoretical predictions or more importantly observational biases. I did not suggest that one should prefer one observation over the other (altho i think that CMB has the best case sofar concerning cosmological parameters), rather to attack the suggestion in the article that this result challenges our view. I was under the impression that this study provided agreement.

    Please note that my critique was on the reporters, and the lassez-faire science culture in this tech-ezine.

    I find it difficult to consider this a shortcoming of our work. But of course you are free to find this boring...

    Shortcoming? I never said it would be. Boring? hardly. I'd wish there were more posts like this. Usually i'm replying to star trek zealots.

  • Re:Hooray for our side (Score:4)

    by the_other_one ( 178565 ) on Monday November 13, 2000 @08:41PM (#625747) Homepage

    I am a committed carnivore. I prefer to eat committed vegetarians.

  • Re:A Brief History of Time (Score:3)

    by astrophysics ( 85561 ) on Monday November 13, 2000 @08:41PM (#625748)
    Angular momentum creates a barrier in terms of the effective potential. Basically, unless the material can find a way to dissipate angular momentum, it can't fall to the center of the cluster.
  • > Not only is Harold Ebeling a professional astronomer, he's a committed vegetarian.

    Surely then he realises that both beeves and broccoli are merely the carcassas of dead supernovae?
  • I thought they were just fans of Apple computers?
  • Light can travel in circles, but only on event horizons of black holes. Hm... we're falling into a black hole! HELP!
    --

  • Very interesting (Score:3)

    by astrophysics ( 85561 ) on Monday November 13, 2000 @08:52PM (#625752)
    This is very interesting. Of course the popular article is short on details. Of interest to us astrophysicists is how many, how massive, and how large z, and how large a volume did they survey. We already know of a few clusters nearly 10^5 M_sol at z=0.5-0.8. I'll have to ask for details once they get back from the HEAD meeting...

    But, in any case, the claim of hundreds is very exciting. In a universe with a large \Omega (both matter and dark matter, but not lambda or quintesence), massive clusters become extremely rare at large redshifts. That's why the person claims this will help measure omega very accurately. Unfortunately, there is a degeneracey (I believe the primary degeneracey is how much the luminous matter distribution is representative of the dark matter distributions, but I'd have to check to be sure.) and this observation alone can not determine Omega. However, when combined with other observations (such as supernovae and CMB), Omega can indeed be tightly constrained. We're closing in...

  • This is of course a bit too subtle for a PR. So you are probably right in accusing us of presenting one aspect of this work in an overly dramatic fashion, and perhaps all of this is not sufficiently exciting for /.

    I understand. Thanx for taking the time to explain this and that. This type of stuff should have been modded +plenty informative in the ideal /.

    For now i'll spare my breath fo yet another round of replies to anyone who will post that this is yet another proof that there are infinite universes/big bangs/klingons.

  • Re:Very interesting (Score:3)

    by astrophysics ( 85561 ) on Monday November 13, 2000 @08:54PM (#625754)
    sorry, I meant nearly 10^15 M_sol, not 10^5 M_sol. Technically, it's 10^15 M_sol h^-1, where h = H_o/(100 km/s/Mpc).
  • ...a Galaxy cluster of these things!

  • I'm a theoretical chemist. I spend my time studying things on a scale of several atoms. I also enjoy quantum physics which deals with smaller stuff, so these atoms seem humungous. Now I step back and look at the stuff the organic chemists are doing, and wonder at the size of the molecules in amazement. But that's really nothing compaired to the biochemists and thier macromolecules. Then there are the structural engineers who deal with unimmagniable amounts of stuff; where the sheer number of atoms involved is unifathomable. But the geographers deal with masses; contenents; worlds! of this stuff. Then I look up at the sky and see white dots, some of which are galexy clusters containing thousands of galexies. And I fall down on the ground dizzy...

  • Take neutron stars, for example: entire solar masses compressed into a single neutron nucleus. See? It's still on an atomic scale.
  • I thought a neutron star had the density of an atomic nucleus, but was not compressed into one nucleus. Of course, this link [nasa.gov] doesn't seem to indicate whether I'm wholely correct or not. It does support my statement on the density, but doesn't say whether or not it's compressed into one nucleus.

    Of course, if it's compressed into one nucleus, it would help to explain the immense amount of x-rays this sucker is putting out.

    Kierthos

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