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NASA Space Earth Science Technology

Class of Large But Very Dim Galaxies Discovered (nature.com) 105

Posted by BeauHD from the great-unknown dept.
schwit1 writes from a report via Nature: Astronomers have now detected and measured a new class of large but very dim galaxy that previously was not expected to exist. Nature reports: "'[Ultradiffuse]' galaxies came to attention only last year, after Pieter van Dokkum of Yale University in New Haven, Connecticut, and Roberto Abraham of the University of Toronto in Canada built an array of sensitive telephoto lenses named Dragonfly. The astronomers and their colleagues observed the Coma galaxy cluster 101 megaparsecs (330 million light years) away and detected 47 faint smudges. 'They can't be real,' van Dokkum recalls thinking when he first saw the galaxies on his laptop computer. But their distribution in space matched that of the cluster's other galaxies, indicating that they were true members. Since then, hundreds more of these galaxies have turned up in the Coma cluster and elsewhere. Ultradiffuse galaxies are large like the Milky Way -- which is much bigger than most -- but they glow as dimly as mere dwarf galaxies. It's as though a city as big as London emitted as little light as Kalamazoo, Michigan." More significantly, they have now found that these dim galaxies can be as big and as massive as the biggest bright galaxies, suggesting that there are a lot more stars and mass hidden out there and unseen than anyone had previously predicted.
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Class of Large But Very Dim Galaxies Discovered More

Class of Large But Very Dim Galaxies Discovered

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  • Large but very dim, eh? I submit that these galaxies are composed primarily of your momma.

  • Re: (Score:2, Insightful)

    by account_deleted ( 4530225 )
    Comment removed based on user account deletion

    • Re: (Score:1, Funny)

      by DNS-and-BIND ( 461968 )
      We know we can't see it. That's why it's called "dark matter". Who knew building more sensitive detectors would reveal all this "matter" that was too "dark" to see before? Wow!
      • Comment removed based on user account deletion

        • Re:Take that dark matter! (Score:5, Informative)

          by wonkey_monkey ( 2592601 ) on Saturday July 30, 2016 @04:45AM (#52611133) Homepage

          Amazing! Dark matter is just regular matter that was dimmer than other galaxies according to you! Where's your nobel prize?

          Isn't that exactly what you just said before?

          Anyway, one of the things dark matter is hoped to explain is the rotation curves of galaxies we can already see. I don't see how these newly discovered ultra diffuse galaxies can do that.

          • Re: Take that dark matter! (Score:3, Informative)

            by Anonymous Coward

            But this discovery has nothing to do with dark matter. The 97% dark matter theory is the additional mass required to bind each galaxy together. These newly discovered galaxies would likely exhibit the same missing mass for their rotational speed.

          • This part may be explained by a competing theory ("complimentary"?) to Dark Matter most common models, that says that gravity behaves differently when it becomes very very low, which explains a large number of other things that Dark Matter only explains by using the right parameters (i.e. That Dark matter doesn't explain at all).

            • How is "only explains by using the right parameters" much different from "only explains by modifying an equation"?

              Admittedly I don't know what parameters of dark matter you're referring to, but if observations tell us they should have a certain value, what's the problem if they do?

        • Re: (Score:1)

          by Anonymous Coward

          The thing about dark matter- its main distinguishing feature- is it's dark. And the thing about space, the colour of space, your basic space colour, is dark. So how are you supposed to see it?

        • Amazing! Dark matter is just regular matter that was dimmer than other galaxies according to you! Where's your nobel prize?

          My point obviously was that dark matter was supposed to be some undetectable substance when it turns out our sensitivity just wasn't high enough. more 'regular matter' exists.

          Dark matter is a placeholder, not necessarily matter at all. It is a placeholder for physicists to shelve anomalies so we can continue work to find out what and why.

          Yes - physicists know that a certain amount of the anomalous effects are indeed actual matter that we haven't seen yet. But confusing the unfortunately named term "dark matter" for actual matter doesn't help. I prefer the less sophisticated but more accurate term - "Weird shit."

    • Re:Take that dark matter! (Score:5, Informative)

      by bruce_the_loon ( 856617 ) on Saturday July 30, 2016 @05:38AM (#52611207) Homepage

      The missing mass is at a galactic level, not at the universe level. Stars in the galaxies, including our own, are moving too fast in their orbits around the galactic core to not shoot off into the space between galaxies if only visible matter is assumed to account for the gravity of each galaxy holding the stars in their orbits.

      Other than the gravitation of each galaxy required to be 1000% of what the visible matter contributes, nothing we do to the existing formulas for gravity can account for it without changing the entire dynamics of the universe to something that doesn't match the observations.

      The source for the missing 90% gravity isn't visible as stars, dust, planets, gas etc and we've coined the term dark matter as a category to describe this source.

      These new dim galaxies cannot contribute to the dark matter as it is required in the structure of all galaxies. It might assist with understanding inflation as that is a universe-wide effect.

      • I guess the reason a black hole doesn't count as invisible mass is because of hawking radiation?

        • Re: (Score:1)

          by Anonymous Coward

          Mainly because of gravitational lensing. And because of the X-rays coming from clouds that get sucked into it. We can see the presence of a dark hole as soon as there are conventional matter and electromagnetic waves nearby.

          Black holes interact with conventional matter other than just gravitationally, and they interact with electromagnetic waves. Thus we can detect them. Dark matter does not. All we can see are rotation speeds of galactical objects in the outer regions of galaxies that are far higher than e

      • The missing mass is at a galactic level, not at the universe level. Stars in the galaxies, including our own, are moving too fast in their orbits around the galactic core to not shoot off into the space between galaxies if only visible matter is assumed to account for the gravity of each galaxy holding the stars in their orbits.

        It actually exists at both levels. We can determine how much matter there is in the universe based on how it expanded, and we can determine how much baryonic (i.e. non-dark) matter there is in the universe based on our observations of the cosmic microwave background and a few other things that tells us about the early universe. From that we know there must be invisible matter that interacts gravitationally and *maybe* through the weak force with ordinary matter. Dark matter would probably not be widely acce

      • It is also the universe level because DM is used to "explain" the background cosmic radiation.

        • Re: (Score:2)

          by Quirkz ( 1206400 )

          My understanding was the background cosmic radiation is the energy emitted from the big bang, diluted by the expansion of the universe. I don't think dark matter fits in there at all.

      • Planets aren't "visible" and if you find very dense (or extremely more prevalent) very dim objects, you indeed explain the missing Mass. The models that "call for" Dark Matter are based on observing light and then estimating mass, and finding out there's not enough mass to account for the orbits of things (which act as if unviable mass was there).

        All the Dark Matter theories are for crooks and incredibly ignorant scientists that will believe in that bs just as some people believe in paranormal that has neve

        • > Planets aren't "visible"

          They also don't account for enough of the missing mass.

          The principal component of the Solar System is the Sun, a G2 main-sequence star that contains 99.86% of the system's known mass and dominates it gravitationally. The Sun's four largest orbiting bodies, the giant planets, account for 99% of the remaining mass, with Jupiter and Saturn together comprising more than 90%. (https://en.wikipedia.org/wiki/Solar_System)

          Planets really are down in the noise of measurements by most stan

  • Actual discovery: Mass of one such galaxy (Score:5, Informative)

    by WoOS ( 28173 ) on Saturday July 30, 2016 @02:37AM (#52610959)

    RTFA (and Wikipedia) reveals that the discovery of the galaxies is actually one year old.
    What was discovered is that the mass of the brighest one found (1% light of milky way) is the same as the milky way (even if the nature summary talks about weight, tststs). The way they measured it is interesting:

    The more massive a galaxy is, the faster its stars move relative to one another. These motions broaden the spectral line through Doppler shifts, [...]. By combining six nights of data, the astronomers found that the stars’ typical movements relative to one another clocked in at 47 kilometres per second.

    What I would be interested in is how one is sure that one didn't simply misjudged the distance of the galaxy. If it was 10 times as far away as thought, it would also appear only 1% as bright as expected.

    • Re:Actual discovery: Mass of one such galaxy (Score:5, Informative)

      by Henriok ( 6762 ) on Saturday July 30, 2016 @06:29AM (#52611305)
      The are probably using mean red shift to measure the distance. The collective light of all the stars in the galaxy are together red shifted a certain amount that's a direct indication of how far away the galaxy is due to the expanding universe. The farther away the galaxy, the more red shift there is. And, one can measure speeds due to red shift very very accurately, down to tens of meters per second. The error bars here are that the far away galaxy can have a local movement that's unknown, but if the galaxy is a part of a cluster, that factor can be measured and accounted for. This is the most common and simplest way of measuring distance to galaxies, invented by Edwin Hubble in the 30s. The second most common is using Type 1A super novas, but they have to appear to be used, and.. that's a fluke incident, more commonly used to calibrate and confirm the red shift measurements.

    • Re: (Score:2)

      by ihtoit ( 3393327 )

      Because galactic forms follow known patterns, beyond certain sizes those patterns change, so knowing the size range of those types...) you can estimate the distance first by visual observation (simply measure its apparent width) then trig it. If that matches the redshift observations (which you can measure using spectroscopy), then you're there.

    • More here https://www.youtube.com/watch?... [youtube.com] ITC Luncheon April 14, 2016
      Harvard ITC hosted this years Sackler conference and Nicola Amorisco (ITC) gives a presentation "Ultra-diffuse Galaxies: the Low Surface Brightness Tail of the Abundant Dwarf Galaxy Population" for the first 15 minutes of this video. The conclusion is that UDGs are ubiquitous and numerous in both clusters and the field, Their formation is independent from the cluster environment, They are dwarf galaxies and represent the tail into the lo

  • Are there enough if these galaxies to account for the missing mass. I.e not so dark matter?

    • Re:Could this account for the missing mass? (Score:4, Insightful)

      by abies ( 607076 ) on Saturday July 30, 2016 @03:06AM (#52610983)

      I was under impression that dark matter was mainly to explain how galaxies work on 'small scale' (galaxy and galaxy cluster), rather than on entire universe scale. Having dim galaxies out there won't explain why other galaxies are spinning too fast and not falling apart.

      • Those galaxies that are spinning too fast are possibly full of dim witted matter also.

      • If we could miss entire huge galaxies like ours in the amounts predicted in these findings, I'd remain very skeptical that we can be sure we have accounted for all mass within a galaxy. Also, how galaxies move in relation to other galaxies would be slightly affected if the have huge amount of material between them, that we haven't detected yet other than "noticing some invisible mass must be within the to explain their interactions through gravity".

    • It's either Hillary's missing e-mail or Donald's missing clue.

    • Nope, but kudos to you for asking the question rather than leaping to conclusions, assuming it to be true, and having a condescending laugh at how stupid scientists have been all these years, as others have done.

      One of the things dark matter is hoped to explain is how the galaxies we already knew about rotate the way they do. We look at a galaxy, and we see stars at certain distances orbiting at certain speeds. But the distribution of rotational speeds doesn't make sense, given the amount of matter we can s

  • "Large but dim" - they need someone to be named after. The Donald has boasted about the size of his hands and his, ahem, stuff. The Donald Trump Galaxies is the best name.

  • They are so dim that they are still going to school, billions of years later - they keep failing their exams

  • I wonder if they are type 3 civilization controlling those Galaxies?

    • Re:Type 3s? (Score:4, Insightful)

      by Impy the Impiuos Imp ( 442658 ) on Saturday July 30, 2016 @05:49AM (#52611225) Journal

      It would still give off the same total energy, shifted into the IR...or much lower. I wonder if they detected longer wavelengths.

      I also wonder if thjs impacts the estimate for total number of galaxies at 100 billion.

      • Re:Type 3s? (Score:4, Informative)

        by careysub ( 976506 ) on Saturday July 30, 2016 @11:39AM (#52612343)

        It would still give off the same total energy, shifted into the IR...or much lower. I wonder if they detected longer wavelengths.

        I also wonder if thjs impacts the estimate for total number of galaxies at 100 billion.

        Good questions.

        No, this being a ground-based instrument, they could not look at the infrared wavelengths you are thinking of. The James Webb Telescope will be the perfect instrument to investigate this when it is launched in two years.

        Yes this will gave some impact on estimated galaxy counts.

  • To everyone stating that this is dark matter (Score:5, Informative)

    by Anonymous Coward on Saturday July 30, 2016 @07:03AM (#52611387)

    It's not. There are hree primary motivations for the belief that dark matter must exist:

    1) Galactic dynamics. Stars within galaxies are orbiting far too fast given the luminous matter in those galaxies -- far too fast. On the assumption of Newtonian mechanics, we need an overabundance of unobserved matter to matter of around four times, and this needs to be distributed spherically (regardless of the distribution of the galaxy itself). It is simply not possible for that matter to be normal matter; we would see, for instance, frequent microlensing events as the matter passes in front of distant stars. Note that this "dark matter" does not have to literally be dark matter in the form of a particulate matter; it could be anything that replicates the motion of stars within galaxies. MOND, for instance, does an admirable job of fitting practically all (if not all) galaxy rotation curves with a single parameter, which is a bit better than particulate theories can.

    2) Cluster dynamics. Galaxies within clusters are *also* orbiting far too fast given the luminous galaxies in the clusters. Here the "microlensing" issue is no longer micro -- galaxies lens rather more visibly. The dark matter distribution is no longer spherical. Note that we have observations, the Bullet Cluster being the most famous, where we can compare the mass distribution as recovered from lensing with the luminous matter and they're in very different places. In this instance, MOND doesn't work -- it breaks down entirely. That does not mean that the "dark matter" must be particulate, but it certainly can't actually be MONDian.

    3) Cosmology. Cosmology provides the strongest evidence that something behaving as dark matter has to exist. Cosmological observations tell us that the universe is flat, to within a percent or so. At the same time, we observe the abundances of primordial hydrogen, helium, lithium and the like. These abundances are exquisitely sensitive to the amount of normal matter in the universe. That is, the amount of standard model matter, not just "luminous matter". To fit the observations we're restricted to approximately 5% of the critical density being made up of normal, standard model matter. But to fit observations of the cosmic microwave background and of the large-scale distribution of matter we not only need to be at the critical density but we need around 25%-30% of the universe to be made up of matter that gravitates like normal matter does, and about 70%-75% in something that is beginning to act "anti-gravitationally". That is, entirely independently from galaxy observations, cosmology states we need between four and five times of the matter in the universe in the form of "dark matter". Again, this does not need to be particulate. The conclusions are predicated on a relatively naive interpretation of general relativity. Changing either the theory of gravity, or the way in which it is applied, can change the conclusions, but nothing is especially convincing and in particular little is more convincing than the possible existence of a lightest supersymmetric particle, which would fit observations across all scales.

    In each case it's useful to note that the galactic "dark matter" does not in fact have to be from the same source as the cosmological "dark matter". It's also important to note that in all cases its existence is deduced from comparing observations with a model explicitly based on a particular theory. As such, I would advise against taking either "dark" or "matter" as literal descriptions of what's going on. What we can say, with certainty, is that if you relatively naively apply Newtonian mechanics to galaxies or galaxy clusters, and if you relatively naively apply general relativistic dynamics to a universe which is smooth on extremely large scales, you independently come to the same conclusion: something in both cases acts as if there were an invisible distribution of gravitating matter, with an abundance about four or five times that of our normal, well-understood standard model m

  • Are they aware that the City of London is only one square mile, and where the fuck is Kalamazoo?

  • Did they check in infrared? Maybe most of the stars are surrounded by Dyson spheres as is what one would expect will happen to our galaxy in a few million years if we don't kill ourselves off first. If so these galaxies should be quite bright in the infrared.

    • Exactly what I thought. This is what a fully civilized galaxy would look like in the visible. Of course this isn't a likely explanation, but it is a fun one! Infrared, indeed.
  • possible. if galaxies with lots of stars are possible and galaxies with some stars are possible then galaxies with few or no stars must also be possible.
  • "The universe is a pretty big place. If it's just us, seems like an awful waste of space."

    - Carl Sagan, Contact

  • As an engineer, I have to do a lot of unit conversion.

    Anyone know how many Kalamazoos are in a London?

    And couldn't we just stick with SI units like the Paris?

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