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Dim Galaxy Could Give Clues to Dark Matter

Posted by michael on from the let-there-be-light dept.

chamblah writes "Reuters is reporting that the dimmest galaxy has been found. 'In fact, it is dimmest galaxy ever detected, which means it could give clues to the mysterious dark matter that appears to be pushing regular matter around.' Since this galaxy is '...100 times dimmer than the night sky', it could only be detected using 'instruments involved in the Sloan Digital Sky Survey, the sky-mapping project.' The galaxy is also part of the Andromeda galaxy, only 2 million light years from us. The article goes on to explain how finding these dim galaxies can be useful, 'Andromeda IX fits the profile for the small, dim galaxies that cosmic theorists predict should exist as leftovers from the formation of big galaxies.'"

40 comments

  1. Not really dim by Anonymous Coward · · Score: 5, Funny

    They're just eco-friendly and power saving.

    1. Re:Not really dim by SnoBall · · Score: 1

      It is dim because their bulbs aren't bright enough.

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    2. Re:Not really dim by Anonymous Coward · · Score: 0

      and not using nuclear power because the lack of a green glow

  2. If I read the article right ... by Daniel+Dvorkin · · Score: 5, Informative

    It's not "part of" Andromeda; it's a satellite galaxy, like the Magellanic Clouds are to the Milky Way. It wouldn't make a whole lot of sense to talk about a dim galaxy that's part of a regular galaxy, anyway ...

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    The correlation between ignorance of statistics and using "correlation is not causation" as an argument is close to 1.
  3. Yessir by Wylfing · · Score: 4, Funny
    The galaxy is also part of the Andromeda galaxy

    Exactly, just like I-90 is part of the Honda freeway!

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  4. OK ... by gstoddart · · Score: 1

    So ... I've R'd TFA, but I'm still not an astrophysicist ...

    Does one infer from this that the 'missing' dark matter is possibly just a bunch of stuff we haven't been able to see yet? Or is the magnitude of the dark matter just too big to be accounted for by dim structures in space?

    Just askin'.

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    Lost at C:>. Found at C.
    1. Re:OK ... by Jotaigna · · Score: 1

      thats right. Based on gravity pulls the astronomers are not able to explain, only with what we can see, the movements of stars and galaxies, on the other hand if there were dark things(which not emit, nor reflect enough light to be observed by us) hanging around, the whole puzzle would fit perfectly(or much better at least). So, finding a galaxy that faint, it means scientist would eventually find all that dark matter.

      If a tree falls in the forest and no one is near to hear it...does it still emits a sound?.

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    2. Re:OK ... by Too+Much+Noise · · Score: 1

      Well, technically dark matter IS 'just a bunch of stuff we haven't been able to see yet'. The speculation is that it might not be 'see-able' the way regular matter is.

      Anyway, this still does not seem to explain the first reason for coming up with the dark matter idea anyway. That being the way the galaxies rotate: spiral galaxies have a (visible) more or less discoidal disposition of matter (in a plane), but appear to rotate as if they were more like spheres (that is, the radial dependence of the speed corresponds to the one you'd expect in a galaxy with matter distributed inside a sphere, not on a disk). Satelite galaxies don't seem to provide enough matter to compensate for that.

    3. Re:OK ... by Aglassis · · Score: 3, Informative

      Tthe rotation of the Galaxies doesn't follow Kepler's Laws of planetary motion (which should apply if you consider all the stars in the galaxy to be planets). The easiest way to look at this is to compare the rotational velocities of the stars in the galaxy (which can be determined by taking the red/blue shift of the galaxy in general to determine its velocity relative to you and then taking the redshift of stars in the galaxy that are roughly parallel to your line of sight). Kepler's Third Law says that the orbital period squared is proportional to the long elliptical axis of the orbit cubed. Stars in galaxies don't do this so it is supposed that there is a dark matter halo surrounding the galaxy that corrects their motion to what is observed (of roughly ten time the mass of the galaxy). It is called dark matter because it can't be seen through electromagnetic radiation.

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  5. Dim by solarlux · · Score: 1

    > Reuters is reporting that the dimmest galaxy has been found

    Yeah, I always that galaxy wasn't too bright...

    1. Re:Dim by Anonymous Coward · · Score: 0

      Can I buy a verb, Pat?

  6. The News with a Different Twist.... by solarlux · · Score: 1

    Scientists have now found the brightest dark-sucker galaxy to date...

  7. Re:dimmer than night sky?? by Smallpond · · Score: 1

    From the article:

    "How dim is Andromeda IX? At least twice as faint as the previous record holder,"

    Obviously, they turned up the gain on their faintness detectors.

  8. What this means for dark matter by Pi_0's+don't+shower · · Score: 4, Informative

    Alright, I hope this doesn't come off as condescending, but IAAA (grad student, at least), and *one* dim, tiny dwarf galaxy will tell us very little about dark matter.

    You can measure its velocity dispersion to infer its total mass, and you can measure its light and spectra to attempt to infer its mass in baryons (protons, neutrons, and electrons), and you can measure the spectral lines to determine its metallicity, but this has nothing to do with inferring dark matter.

    Dark Matter is inferred, at least when it comes to galaxies and clusters of galaxies (to keep it simple), because the mass required to provide the galaxy/cluster with the internal velocities observed is much more than what we see in starlight. Therefore, some of the matter is non-luminous, or "dark". Dark matter exists, on AVERAGE, so that 1/7 of the total mass in a galaxy is in baryons, and 6/7 is in dark matter. This ratio varies widely for different galaxies, and I do not see how *one* galaxy is going to tell us anything?

    Also, if this satellite galaxy is less than ~100 kpc from Andromeda, the main galaxy's dark halo will envelop the satellite, too, further complicating the matter.

    1. Re:What this means for dark matter by M1FCJ · · Score: 1

      Sample size increased from zero to one?

    2. Re:What this means for dark matter by jc-mueee · · Score: 1

      Ok, well i'm only learning astrophysics now (as in this semester).

      Won't they be able to infer about the properties of dark matter due to the low density/mass of the observable ("bright") galaxy? As in there is a lower limit to the total mass and density of a clump (including the dark matter) before it is able to condense into a galaxy.

  9. Re:dimmer than night sky?? by M1FCJ · · Score: 1
    Twice as faint? It's only around one magnitude darker then. Not that much, is it?

    Of course I haven't read the article :-) I better go and have a look at it.

    Also I thought these days what mattered is the redshift, not faintness.

  10. Dark matter or dark energy by Anonymous Coward · · Score: 0

    the mysterious dark matter that appears to be pushing regular matter around

    Dark matter is all the matter in the universe that doesn't generate its own light. It is suposed to be at least 85% of the matter in the universe and therefore when we look up in the sky we are only seeing the 15% of the total matter at most.

    Because of dark matter and given that there is so much matter in so little space, astronomers think the universe should be collapsing, but instead it is expanding.

    Dark energy is an unkown source of energy that should be pulling all that matter apart. It is a theoretical explanation of why the universe is not collapsing. And a very bad at that. Very simmilar to the ether conjecture a century ago.

    So please get your facts straight.

    Also, since there is so much matter in the universe, and it was all in a very tiny place just after the big bang, we know for sure that we were inside a black hole. But nothing can escape a black hole, not even light. So we live inside a black hole. A gigantic black hole. Why don't we see the universe collapsing? Simply because time is a continuous and in the black hole event horizon, time doesn't flow. If you stay at the horizon, your clock doesn't go forward nor backward. Therefore as time is continuous, time must go backwards in the black hole, because it goes forward outside the black hole.

    Therefore the universe is collapsing, but we see it time reversed, because our time is going backwards, so we see the universe expanding. If astronomers get to see the big bang, what they will really see will be our heat death.

    1. Re:Dark matter or dark energy by Anonymous Coward · · Score: 0

      Are you kidding?

      We can't be inside a black hole, we would all be dead by now because of the strong tidal forces.

    2. Re:Dark matter or dark energy by bradkittenbrink · · Score: 2, Informative

      Also, since there is so much matter in the universe, and it was all in a very tiny place just after the big bang, we know for sure that we were inside a black hole. But nothing can escape a black hole, not even light. So we live inside a black hole. A gigantic black hole. Why don't we see the universe collapsing? Simply because time is a continuous and in the black hole event horizon, time doesn't flow. If you stay at the horizon, your clock doesn't go forward nor backward. Therefore as time is continuous, time must go backwards in the black hole, because it goes forward outside the black hole.

      To my knowledge, there are several mistakes in this description. However, I have never heard that reasoning before and after correcting these technical mistakes the reasoning as a whole may still be sound if it were phrased more accurately. First of all, matter can escape from a black hole, it gets radiated away in a thermal spectrum as described here. Secondly, if you're sitting on the event horizon, you would observe your clock to tick normally, time does flow. An observer far removed from the black hole would indeed observe your clock as stopped however. Thirdly, I don't think that you can simply say that time "flows backward" inside a black hole. Although I have never taken a GR course, I am familiar with special reletivity and I imagine the frame of reference inside the event horizon to be somewhat analagous to a frame of reference travelling faster than light (at least when comparing them to a traditional inertial frame). There's nothing theoretically wrong with such a coordinate system, but there is simply no way you can transform values measured there into a traditional frame of reference without getting nonsense for an answer. In other words, if you were sitting inside the event horizon, there is simply no way to translate the ticks you observe on your clock to what a far removed observer would observe.

    3. Re:Dark matter or dark energy by misterpies · · Score: 4, Interesting

      >>Simply because time is a continuous and in the black hole event horizon, time doesn't flow. If you stay at the horizon, your clock doesn't go forward nor backward. Therefore as time is continuous, time must go backwards in the black hole, because it goes forward outside the black hole.

      Well that sounds very neat and I'm sure any moderator with no knowledge of GR will mod you up. Unfortunately, though, if you do the maths you will discover that time does not run backwards inside a black hole. As someone pointed out, at the event horizon time does not stop for a local observer, but it appears to stop from the viewpoint of someone observing the horizon from outside.

      Inside the black hole, what happens is even stranger than time running backwards. As you are no doubt aware, spacetime has 4 dimensions: 3 of space and one of time. Inside the black hole, the time dimension is swapped with one of the space dimensions - the radial dimension pointing at the centre of the hole. (For a spherical black hole, the maths is easiest in polar coordinates so your spatial dimensions are radial, axial and azimuthal rather than x, y and z). Because it's now a time-like dimension, and time marches ever onwards, you are inevitably drawn along the radial direction into the centre of the black hole; you can no more escape it than you can stop time locally. On the other hand, time has now become a spatial dimension, so presumably you can move along the time axis freely (until you hit the centre of the black hole and are crushed into nothingness).

      That's what the maths says anyway. What it means philosophically (and biologically) to have your dimensions switched round is another question, and quite beyond my imagining.

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    4. Re:Dark matter or dark energy by Alsee · · Score: 1

      We can't be inside a black hole, we would all be dead by now because of the strong tidal forces.

      Aside from all of the errors in the original post, that is false as well. The more massive and larger a black whole gets the weaker the tidal forces become at the event horizon. Given a black hole equal to the mass of the entire universe, the tidal forces of entering the black hole would be essentially zero.

      Of course this really just brings us back to the fact that anying inside the event horizon is almost totally undefined by current physics.

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    5. Re:Dark matter or dark energy by Anonymous Coward · · Score: 0

      To my knowledge, there are several mistakes in this description. However, I have never heard that reasoning before and after correcting these technical mistakes the reasoning as a whole may still be sound if it were phrased more accurately. First of all, matter can escape from a black hole, it gets radiated away in a thermal spectrum as described here.

      Well sure, 1 atom per year, as almost undetected radiation. It is irrelevant.

      Secondly, if you're sitting on the event horizon, you would observe your clock to tick normally, time does flow.

      So do we, don't we? Time does flow normally for all observers, always. There is no point on saying that. Even if you were frozen, you would never realize you are frozen, nor would you ever realize time is flowing slowly.

      An observer far removed from the black hole would indeed observe your clock as stopped however.

      That's is exactly what is important. Now consider what would happen inside the black hole. Would time flow forward, backwards or would not flow, as in the horizon?

      Thirdly, I don't think that can simply say that time "flows backward" inside a black hole. Although I have never taken a GR course, I am familiar with special reletivity and I imagine the frame of reference inside the event horizon to be somewhat analagous to a frame of reference travelling faster than light (at least when comparing them to a traditional inertial frame). There's nothing theoretically wrong with such a coordinate system, but there is simply no way you can transform values measured there into a traditional frame of reference without getting nonsense for an answer.

      Time flowing backwards is nonsense? Can you elaborate?

      In other words, if you were sitting inside the event horizon, there is simply no way to translate the ticks you observe on your clock to what a far removed observer would observe.

      I never said I would do that transformation. We all know that 1 second for the observer at the event horizon would be the age of the universe for an outsider. The question is what happens when a second passes for somebody inside the event horizon? Since the outsider sees objects falling into the black hole, the insider sees objects getting far away from him.

    6. Re:Dark matter or dark energy by Anonymous Coward · · Score: 0

      Well that sounds very neat and I'm sure any moderator with no knowledge of GR will mod you up. Unfortunately, though, if you do the maths you will discover that time does not run backwards inside a black hole. As someone pointed out, at the event horizon time does not stop for a local observer, but it appears to stop from the viewpoint of someone observing the horizon from outside.

      Inside the black hole, what happens is even stranger than time running backwards. As you are no doubt aware, spacetime has 4 dimensions: 3 of space and one of time. Inside the black hole, the time dimension is swapped with one of the space dimensions - the radial dimension pointing at the centre of the hole. (For a spherical black hole, the maths is easiest in polar coordinates so your spatial dimensions are radial, axial and azimuthal rather than x, y and z). Because it's now a time-like dimension, and time marches ever onwards, you are inevitably drawn along the radial direction into the centre of the black hole; you can no more escape it than you can stop time locally. On the other hand, time has now become a spatial dimension, so presumably you can move along the time axis freely (until you hit the centre of the black hole and are crushed into nothingness).

      Nonsense of course. If all the universe collapses, your dimension gets reduced in exactly the same proportion, so you can't even notice it.

      That's what the maths says anyway. What it means philosophically (and biologically) to have your dimensions switched round is another question, and quite beyond my imagining.

      Very interesting, where did you read it? Why would coordinates swap? Just because one of the coordinates (time) got to zero?

    7. Re:Dark matter or dark energy by Anonymous Coward · · Score: 0

      Aside from all of the errors in the original post, that is false as well. The more massive and larger a black whole gets the weaker the tidal forces become at the event horizon. Given a black hole equal to the mass of the entire universe, the tidal forces of entering the black hole would be essentially zero.

      Of course this really just brings us back to the fact that anying inside the event horizon is almost totally undefined by current physics.

      So you say it would be possible to live inside a hugely massive black hole, right?

      The fact that current physics declares itself incompetent is not a reason for us to feel incompetent about it.

      Life inside a black hole should all be the same as outside it, because according to GR, you can't distinguish between the following two scenarios:

      1. You floating in space.
      2. You falling into another object.

      Therefore it is extremely hard (maybe impossible)to disprove that we are inside a gigantic black hole. In fact if the big bang theory is true, we can only be inside a black hole, because the whole universe was condensed in such a tiny space.

      Dark matter, which implies dark energy, is a proof that we must be inside a black hole, because all that matter should be shrinking and it is expanding, therefore it was very long ago in such a tiny space that obviously it would have formed a gigantic black hole.

      Dark energy is only a lame attempt to explain something that easily gets explained by living in a black hole.

      Do some calculations and you will see that escaping a black hole is impossible because you would need infinite energy, infinite time, and travel an infinite distance. In other words, once you enter a black hole is exactly the same as entering another universe in which you can travel all that you want in any direction, because inside the black hole the universe expands.

    8. Re:Dark matter or dark energy by Alsee · · Score: 1

      Sigh. I really meant this to be a "the first error is... type dismissal - in particular that event horizon tital forces must be destructive. But I don't like being missquoted:

      So you say it would be possible to live inside a hugely massive black hole, right?

      I don't know what post you were reading, but it wasn't anything I wrote. The closest thing I said to that was "anying inside the event horizon is almost totally undefined by current physics." That says nothing about the inside of a black hole, much less indicate it would be possible to live inside.

      Some major theories have everything going splat on the surface of the event horizon and a vacuum-like space inside. Most others have you rapidly going splat on the singularity or somesuch. There are many competing and contradictory theories, but not many that expect sustaining life.

      according to GR, you can't distinguish between the following two scenarios:
      1. You floating in space.
      2. You falling into another object.

      Right - within a sufficently narrow refference frame.

      However it's usually pretty easy to tell the difference later when you eventually go splat against that object.

      In fact if the big bang theory is true, we can only be inside a black hole, because the whole universe was condensed in such a tiny space.

      I can't even begin to address this properly. You are lookign at the ordinary behavior of ordinary lumps of matter and ordinary patch of space within the space of our universe, and trying to apply with the origin of universe itself. An origin that is no ordinary lump of matter and no ordinary patch of space, and which is *NOT* lying within space. You need to get into some really serious physics and equations to even begin to look at it.

      I'm going to wade in over my head and take a stab at it, hopefully I won't botch this too badly:

      The earliest moments of the universe are believed to have been characterized by hyper-inflation of space itself (don't ask me why), inflation vastly exceeding the speed of light. Normally it is impossible for mass or energy to escape the gravity of a black hole, but space itself expanding faster than the speed of light can carry that mass and energy outwards reguardless of any gravitational issues. After an instant of hyper-inflation the mass-energy density is below the black-hole threshhold, thus no black hole exists or is formed anywhere in the process.

      Sigh. I should have stuck with "Your first error is..." and quit. LOL.

      -

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    9. Re:Dark matter or dark energy by Anonymous Coward · · Score: 0

      The earliest moments of the universe are believed to have been characterized by hyper-inflation of space itself (don't ask me why), inflation vastly exceeding the speed of light. Normally it is impossible for mass or energy to escape the gravity of a black hole, but space itself expanding faster than the speed of light can carry that mass and energy outwards reguardless of any gravitational issues. After an instant of hyper-inflation the mass-energy density is below the black-hole threshhold, thus no black hole exists or is formed anywhere in the process.

      Yes, hyperinflation of space is pure mathematics at work, the same occurs inside the event horizon in a black hole. The fact that the space inflates is only because things get apart very fast and you notice this because it becomes times consuming and energy consuming to get to places you could easily before, namely outside the black hole.

    10. Re:Dark matter or dark energy by Alsee · · Score: 1

      I don't know where you get that space expands inside an event horizon. Toss up a link if you like. The "classical" view is that everything splats on the singularity. The recent suspicion is that everything may just splat on the event horizon without crossing it.

      Or maybe it just turns into blueberry pie, heh heh.

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    11. Re:Dark matter or dark energy by Anonymous Coward · · Score: 0

      I don't know where you get that space expands inside an event horizon. Toss up a link if you like. The "classical" view is that everything splats on the singularity. The recent suspicion is that everything may just splat on the event horizon without crossing it.

      Everything crosses the event horizon according to an observer that is outside the event horizon. The person who enters gets its time reversed, so instead of seeing that he is falling inside the black hole, he sees that he is farther and farther away from the center of the black hole, but now the event horizon is too far away for him to ever reach it.

      This is pure mathematics.

    12. Re:Dark matter or dark energy by Alsee · · Score: 1

      Everything crosses the event horizon according to an observer that is outside the event horizon.

      False. An outside observer NEVER sees anything cross the event horizon. He sees infinite time dilation as the object gets infinitely close to the horizon. This portion is not in dispute. Any google will confirm it. Here is the first Google result:

      to an outside observer any objects approaching the Schwarzschild radius appear to take an infinite time to penetrate toward the inside

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  11. Maybe there ain't no such thing as "dark matter" by mikula · · Score: 1

    Forgive the scepticism, but it may be worth noting that there are electrical discharge theories of the cosmos that do not need to invoke "dark matter" at all (though these theories are, for reasons unknown, not accepted by mainstream astrophysicists and cosmologists). The point being that maybe there ain't no such thing as "dark matter".

  12. Re:dimmer than night sky?? by TMB · · Score: 1

    You obviously don't live in a city.

    [TMB]

  13. Re:dimmer than night sky?? by beeplet · · Score: 2, Informative

    Any portion of sky which doesn't have a star/galaxy in it is black, black black!

    Not totally black... there is a fair bit of light that reflects off dust in the solar system (zodiacal light). So it's entirely possible for this galaxy to appear 101% as bright as the background sky.

    And just for general info... there are lots of low-surface brightness galaxies out there - Malin1 for example.

  14. Re:dimmer than night sky?? by meringuoid · · Score: 1
    Any portion of sky which doesn't have a star/galaxy in it is black, black black!

    Have you seen the Deep Field images? The Universe is positively thick with stars and galaxies. If you have a very dark object, you might well see it as a silhouette against a brighter background; cf. the Horsehead Nebula, or the Coal Sack.

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  15. Push me pull me by JohnPM · · Score: 2, Funny

    ...the mysterious dark matter that appears to be pushing regular matter around

    That must be the extra mysterious version of dark matter that works opposite to gravity (pushes).

    The normally mysterious version of dark matter is simply dark and mysterious. It pulls.

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  16. Re:Maybe there ain't no such thing as "dark matter by sethx9 · · Score: 1

    "there are electrical discharge theories of the cosmos that do not need to invoke "dark matter" at all" I was all ready to mod you up but, alas, no examples or links....

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  17. Re:Maybe there ain't no such thing as "dark matter by mikula · · Score: 1

    sorry, didn't have the links on-hand when I posted and just figured ppl would google for them. Here are a couple of good ones. http://www.catastrophism.com/texts/bruce/ http://www.catastrophism.com/texts/bruce/era.htm I bring up Electrical Discharge Theory at all just because too few ppl think to question basic assumptions. In this case, most everyone presumes there's "dark matter" just because most physicists and astronomers tell them so, but history tells us that physicists and astronomers have been wrong about a lot of things (think Ptolemy and epicycles). It's just human nature, it's rooted in uncertainty, yet humans presume to know things as fact when all they have are interpretations. A case in point is "dark matter". It is only an interpretation for the observable data, an interpretation backed by not that much data (I mean, we can't even see this stuff), and "dark matter" is certainly not the only interpretation for the observable data.