Dim Galaxy Could Give Clues to Dark Matter 40
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.'"
Not really dim (Score:5, Funny)
Re:Not really dim (Score:1)
Re:Dark matter or dark energy (Score:2)
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 tot
Re:Dark matter or dark energy (Score:2)
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 le
Re:Dark matter or dark energy (Score:2)
Or maybe it just turns into blueberry pie, heh heh.
-
Re:Dark matter or dark energy (Score:2)
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 [uoregon.edu]
-
Re:Dark matter or dark energy (Score:3, 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,
Re:Dark matter or dark energy (Score:5, Interesting)
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.
If I read the article right ... (Score:5, Informative)
What this means for dark matter (Score:5, Informative)
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.
Re:What this means for dark matter (Score:1)
Re:What this means for dark matter (Score:1)
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.
Yessir (Score:5, Funny)
Exactly, just like I-90 is part of the Honda freeway!
OK ... (Score:2)
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'.
Re:OK ... (Score:1)
If a tree falls in the forest and no one is near to hear it...does it still emits a sound
Re:OK ... (Score:2)
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 cor
Maybe there ain't no such thing as "dark matter" (Score:1)
Re:Maybe there ain't no such thing as "dark matter (Score:1)
Re:Maybe there ain't no such thing as "dark matter (Score:1)
Re:OK ... (Score:3, Informative)
Re:dimmer than night sky?? (Score:2)
"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.
Re:dimmer than night sky?? (Score:1)
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.
Re:dimmer than night sky?? (Score:2)
[TMB]
Re:dimmer than night sky?? (Score:3, Informative)
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 [cam.ac.uk] for example.
Re:dimmer than night sky?? (Score:2)
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.
Dim (Score:2)
Yeah, I always that galaxy wasn't too bright...
The News with a Different Twist.... (Score:2)
Push me pull me (Score:3, Funny)
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.