This new map of the universe charts out 1.2 million galaxies

Jul 15, 2016

By Andrew Liptak

In an attempt to better understand the nature of the expansion of our universe, scientists have created a 3D map plotting the locations of 1.2 million galaxies. This map may help give astronomers new details about how the universe has been expanding, which will help us learn more about the mysterious force that scientists believe has been driving the expansion.

Published in a new study, the 3D map shows 650 cubic billion light years, which is just a quarter of the known universe. Each point in this map isn’t a star: it’s an entire galaxy. The map was created by scientists working on the Baryon Oscillation Spectroscopic Survey (BOSS), a program of the Sloan Digital Sky Survey III (SDSS-III).

This survey examined fluctuations in the density of regular matter, which serve as a “robust standard ruler for measurements of cosmic distances.” Those fluctuations, called baryonic acoustic oscillations, are an ideal tool for plotting the relative positions of each galaxy. In the map, the purple dots mark the galaxies that are farthest away, while the yellow ones represent galaxies that are closer to us. This is important, because it allows scientists to figure out the relative motion of each object, which in turn lets them determine just how fast they’re moving away from one another.

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30 comments on “This new map of the universe charts out 1.2 million galaxies

  • @OP – Published in a new study, the 3D map shows 650 cubic billion light years, which is just a quarter of the known universe. Each point in this map isn’t a star: it’s an entire galaxy.

    Bbbbbuuutt the bronze-age middle-east on Earth, was still the central and predominant feature of the universe – (at least in some very small minds!)

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  • I’m somewhat puzzled as to which “quarter” of the “known” universe the OP is referring. Assuming he means that bit of the universe we can see it’s a sphere just over 13 billion light years in radius (or at least that’s how we perceive it, see below). A quick calc shows this has a volume of about 1 x 10^31 cubic light years or 10,000 cubic billions of light years (a cube one billion light years on each side. So a quarter of that would be about 2,500 cubic billion light years and not 650.

    People tend to find the matter of how big the universe is somewhat puzzling. We obviously can’t see anything that is more than 13.7 billion light years away, or at least anything that “was” more than 13.7 BLY away when its light sprang into existence because such light will not yet have reached us given the universe itself is 13.7 billion years old.

    However when we look at a distant object we see it as it was, and where it was, in the distant past. Where it is now, if it even still exists now, will be a lot further away than we perceive its light to be coming from because the universe has been busy expanding in the meantime and the object has been travelling away from us.

    What this actually means is the real radius of the observable universe at the present time is about 46 BLY and not 13.7 BLY. When we look at an image of the most distant galaxy that Hubble can see, just under 13.5 BLY away, that galaxy is actually now over 40 BLY away but we’re seeing it as it was, and where it was 13.5 billion years ago. Whether the universe is even bigger than 46 BLY in radius is unknown. It may actually be infinite and all we can see is a time distorted miniscule fraction of it.

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  • Arkrid Sandwich #5
    Jul 17, 2016 at 8:30 am

    I’m somewhat puzzled as to which “quarter” of the “known” universe the OP is referring.

    I think that is simply the fraction of the sky which the telescope has actually scanned an mapped so far.

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  • Alan4discussion #6
    Jul 17, 2016 at 8:46 am

    I think that is simply the fraction of the sky which the telescope has actually scanned an mapped so far.

    Even if that were the case then a quarter of the area of the sky would still still map a quarter of the volume of the sphere, which it apparently does not. I just get miffed when people don’t at least do a quick reasonableness check on any numbers they chuck into an article.

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  • Arkrid Sandwich #8
    Jul 17, 2016 at 9:56 am

    I don’t know, but the telescopes certainly don’t have the capability to map back all 13.7 billion light years, so perhaps they are just the nearby ones in some fraction of the sky.

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  • Arkrid Sandwich #5

    Right, well spotted. I think it is just bad science writing. This is unfortunately not unusual although in this case justifiably annoying to calculate. I took a look at the paper itself and it states the survey range was redshift 0.2 to 0.75 (this will give a radial distance) over a solid angle of 9300 square degrees.

    We can calculate the light travel time distance* from the redshifts given as 2.5 billion light years (Gly) to 6.77 Gly. So this is a huge chunk of space. To calculate the volume we have to convert the square degrees to steradians and multiply that by the difference in the cube of the radial distances. This gives 8.3×10^29 cubic ly or 830 cubic Gly. Close enough to whoever gave the writer the number of 650. It is certainly possible I have some rounding error or worse as I rushed through these calculations. Although I suspect the difference is because of the choice of Hubble parameter data needed for the calculation of distance.

    *light travel time distance is the easiest measure to use and it is the distance given in almost all astronomy articles/popular books. It is just the time it takes light to reach us multiplied by the speed of light.

    But even 830 cubic Gly is not nearly 1/4 of the volume of the observable universe. I think the answer is that when you convert the solid angular size of the survey area to steradians you get 2.83 which is about 23% of the whole sky. I think this is the number the writer was referring to.

    I think it is obvious someone handed these numbers to the reporter who wrote while not understanding.

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  • Hey, we’re so important that You-Know-Who flung out all them galaxies (on Day Two, wasn’t it?) just so we could eventually get to admire the Jackson Pollochness of them all.

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  • 16
    Pinball1970 says:


    830 cubic Gly is 0.2% of the volume of the Universe.

    How could the universe be infinite?

    Forget shapes and boundaries, if the universe had a starting point how can it ever be infinite unless it continues to infinity?

    14 billion years is a finite number yet I have read the universe could be infinite.

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  • Pinball1970 #16
    Jul 19, 2016 at 8:10 am

    @phil-rimmer – 830 cubic Gly is 0.2% of the volume of the Universe.

    How could the universe be infinite?

    The discussion is of the Observable Universe

    The Observable universe is governed by the time since the universe began and the speed of light. Light from anything beyond the boundary of the observable universe, has not yet reached us so is unobservable at the present time.

    There are also practicalities of what is actually observed with the current technology (as distinct from what could possibly be observed with appropriate advanced technology).

    Very distant observations using techniques such as gravitational lensing, only give patchy mapping, because they depend on there being large stars or galaxies in convenient places to facilitate this technique.

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  • Pin

    How could the universe be infinite?

    Or how could there be infinities?

    Going backwards, if it didn’t have a single starting point. The big bang may be just an event like others.

    Going inwards if the Planck Length doesn’t represent some lower limit to other possible physicses? Need it stop going down on ever tinier turtles and Horton to hear them?

    Going out into a multiverse of universes.

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  • A calculation of the physical volume of that space (how big that bit of space is now):

    A little more time a little more math: The proper distances (distance now) out to those redshift (called z) ranges used in the survey are: z=0.2 corresponds to a proper distance of 2.7 Gly. z=0.75 is a proper distance 8.9 Gly away.

    Note that each of these distances are larger than the light travel distances (2.5 Gly and 6.8 Gly) since the universe expanded in the time it took the light to travel to us. For the second distance the light took longer to travel and hence the larger expansion.

    This gives a physical volume of about 1900 cubic Gly. The proper distance radius of the observable universe is 46 Gly and this means the survey volume (now) is about 0.5% of the observable universe (now).

    The proper distances are maybe more meaningful than light travel distance but more annoying to calculate.

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  • Pinball1970 #16

    Adding a few points:

    When astronomers/cosmologists say infinite they mean spatially infinite. It does appear the future will be infinite in time.

    It seems likely the universe had a beginning but this is not known for certain. It is possible the universe is past eternal and there are reasonable models for that. There may be a multiverse but that is not likely to be past infinite either if most inflationary models are to be believed.

    14 (or 13.8) billion years is a finite number as before that the universe was in a state we have no good physics for describing. This may be because that was the beginning of our universe or it may be there is new physics there that we have yet to understand.

    The main point is at 13.8 billion years ago the equations we use to understand space and time do not work. It is a boundary beyond which we can only guess at approximations. The big bang should not be thought of as an event that happened but rather a boundary earlier than which we do not know anything–lots of quote mining potential for creationists there but then again when can a creationist not mangle a quote?

    This minute physics segment is nice on this topic: big bang

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  • 21
    Pinball1970 says:

    @#18 10 20

    Sorry that did not hit the spot.

    Do I have to understand general relativity (as in the maths ) to really understand what question I am asking?

    The Poincare conjecture is one of the hardest things I have ever read and dealt with possible shapes of the universe and needless to say my maths was not up to it.

    The question I am asking is at some point the universe was very small say 13.7999999 years ago.

    The radiation from the aftermath of the “event” is the CMBR, it is the wave length and temperature predicted by theory (just about) and has very slight variation, just enough to make galaxies.

    So, how is it possible to go from a small hot dense 13.799999 billion year old “shape” to an infinite shape? Do I mean shape? Am I asking the wrong question?

    I don’t understand the responses thus far from Phil or Northampton – sorry, perhaps I should have stuck with the numinous

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  • 22
    Pinball1970 says:


    I can get the observable part, some light for very distant parts of the universe might never reach us so we will never get a chance to interact with it.
    But..surely to be infinite in all directions? In a finite amount of time?? How can that be possible?

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  • Pin

    Sorry, I thought your question was about infinities from the get go.

    This is the best simple account of topological infinitude. (I misunderstood your question.) Note the 2D analogue of our 3D reality, the infinite sheet of paper (infinite area) rolled into a cylinder (of infinite area) then rolled again into a torus (of finite area, but appearing infinite if curiously repititious).

    We know space gets bent by gravity. The question is about the topology that could result.

    An “infinite universe” here means becomes infinite in infinite time, that is, it is not bounded to be finite in extent by its topological form. This does not mean it is infinite now or at any finite time in the future.

    Incidentally my fractional calculation of 0.2% was simply based on the currently accepted diameter of the “observable” universe 93Gly and the given volume supplied in the OP of 630 cubic Gly. Wiki Observable Universe for terms and conditions….

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  • Phil, my long lost brother,

    Yes, we do know that space gets bent by gravity. Everyone knows that. It should be replaced. (It can’t be bent back.) We need new space.

    Were you disheartened by my remark about Haidt? I apologize. I sent a couple of other less hateful comments on the BS thread since then, haven’t heard from you.

    By the way, Einstein distinguished between psychological time and what he called physical time. Can that distinction be applied to space?

    Danny Panny (The Republican convention is deeply unsettling. I feel unhinged.)

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  • Your muddling of the value of ideas with the (tenuously assumed) values of people that produce them is plain bizzare. I can’t handle this lack of emotional distance essential for rational thought. We can’t simply talk ideas because we must talk more about good and bad people, acceptable and shunned. Hopeless. I want none of this relentless groupism.

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  • 21: So, how is it possible to go from a small hot dense 13.799999 billion year old “shape” to an infinite shape? Do I mean shape? Am I asking the wrong question?

    No, I don’t think you’re asking the wrong question here. The short answer is if the universe is infinite in size then it was always infinite in size.

    Picture graph paper so big that the edges cannot be seen–infinite size graph paper–and the grid is expanding in size with time. The lines will get farther apart over time. If we picture what happened earlier the lines would be closer together. As we look further back in time (rewinding the film) the lines just get everywhere closer and closer until they are so close that we cannot distinguish individual lines. Because our graph paper is infinite in extent we never run out of lines so early enough the graph paper looks everywhere black, it is all ink. Not in one spot but everywhere. This corresponds to the singular state in GR cosmology.

    The big bang “happened” everywhere.

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  • 30
    Pinball1970 says:

    @phil Alan and Northampton
    The explanations are elegant and I like the vid- I have watched it twice now.
    I really dont think one can understand this fully without understanding the mathematics and structure of space time, general relativity and all the hyperbolic geometry that goes with it.
    Thanks chaps.

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