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Space Science

Astronomers Discover a Group of Quasars 4 Billion Light Years Across 106

New submitter mal0rd writes "NewScientist reports a 'collection of galaxies that is a whopping four billion light years long is the biggest cosmic structure ever seen. The group is roughly one-twentieth the diameter of the observable universe – big enough to challenge a principle dating back to Einstein, that, on large scales, the universe looks the same in every direction.' For reference, Andromeda is only 2.5 million light years away."
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Astronomers Discover a Group of Quasars 4 Billion Light Years Across

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  • by Anonymous Coward on Saturday January 12, 2013 @04:35PM (#42569583)

    I think that would depend a lot more on the exact definition of "structure" used by astronomer and the causal connection between the parts of the structure. If the structure were more of just a coincidence, a bunch of stuff that happens to line up, it would mean no change to inflation or the scales previous found for homogenization of structure in the universe. And given the nature of stuff in the universe to form around kind a foam shape, it wouldn't surprise me that you could find long strings where it seems things lined up. Although a quantitative approach would be needed instead, to see exactly what the chances of something they label as a structure appearing that much larger than the scale structures "should stop."

    If on the other hand, there is some sort of connection between the parts of the structure, such that it is clearly forming due to gravitational interaction between long distances part of it or due to some much earlier interaction at some point, that could change things. But that would be much harder to demonstrate than just seeing a bunch of dots lining up in a map.

  • by Anonymous Coward on Saturday January 12, 2013 @05:23PM (#42569905)

    That 13.5 billion years is simply the lowest possible lower bound for the age of the universe.

    The 13.7 billion year estimate is NOT a lower bound, but an actual estimate of time since the early part of the Big Bang, with its own error bars above and below that value. It is one thing to reject the theories that lead to that estimate, but if you do so, you can't treat it suddenly as a lower bound, you would have to reject it outright.

    We understand precisely nothing about the cosmic background radiation that allegedly provides us with the most accurate current estimate. That estimate is based on a model that was force-fitted to previous guesses.

    This seems to suggest you understand nothing about the models and theories applied to get those estimates, and what they take into account besides just the CMB.

    Are they seriously claiming that a black hole on the far rim of the cluster from us could have absorbed an entire galaxy worth of mass in a mere 9.5 billion years?

    No, because most estimates of quasar sizes range from a million to a billion solar masses, which would put it at a fraction of a less than 0.1% to almost a millionth of the mass of the Milky Way. So no one has claimed they absorbed a whole galaxy worth of mass when they are considered to be much less massive than full sized galaxies, and smaller than many dwarf galaxies even.

  • by bjorniac ( 836863 ) on Saturday January 12, 2013 @06:52PM (#42570491)

    It's a good question. I think you've gotten things a little backwards, though, with regars to the problem of propagation - inflation is a proposed explanation for propagation in the sense that it allows otherwise separate regions of the sky to have been in causal contact in the past. But this certainly does have impact upon the current inflationary paradigm in the following sense:

    If there were large structures or large inhomogeneities in the early universe (before inflation) then it would be hard to get inflation going. The basic models of inflation contain a field whose energy can be decomposed (and I'm playing very fast and loose here) into three parts: Potential, Kinetic and fluctuations. From these parts, we say that if the potential is large enough, the inflaton undergoes a "slow roll" down the potential during which our regular inflation happens. Fluctuations are treated as perturbations on this background, and it's from these that we expect to see the everyday structure in the universe. A warning though: We don't know the physics that causes these fluctuations to stop being quantum fluctuations and become classical perturbations in matter on this background.

    Now, if the fluctuations are too big, this model breaks down - the inflaton can't be high enough up its potential, and so slow roll can't happen. Hence before inflation we have to assume that the universe is largely homogeneous and isotropic, and fluctuations begin very small (technically in the "Bunch-Davies vacuum state).

    A big inhomogeneity AFTER inflation isn't too bad - it could well be that this is just the result of one of the longer wavelength fluctuations. Of course, one would then have to explain /why/ this wave in particular had such a large amplitude, but this really doesn't contravene inflationary models, it merely adds a new question about the initial conditions.

    Now, if we had been dealing with a serious overdensity (tons of quasars in the same spot) rather than a large strung-out structure, we would certainly have a problem with inflation, but so far as I know this isn't too big of an issue.

    Disclaimer: I work on the mathematical structure end of things, not the computation or observation, so there are certainly people more qualified than I, to whom I would happily defer if they want to post!

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