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Milky Way May Have Dark Matter Satellite Galaxies
rubycodez writes "Berkeley astronomer Sukanya Chakrabarti has detected perturbations in the gases surrounding our Milky Way and concludes there is a satellite 'Galaxy X' 250,000 light years away that is mostly dark matter, but that may contain dwarf stars visible in infrared. She expects many more such dark matter satellites to the Milky Way to be discovered using her technique."
"The creature from invisible Galaxy X"
Oliver's law of assumed responsibility: If you're seen fixing it, you will be blamed for breaking it.
How do you tell the difference between a blob of dark matter and a black hole? With all the small galaxies the Milky Way has swallowed over its lifetime, would it not be reasonable to find some relic black holes that have swung back out after being stripped of most of their surrounding gas/stars? Or, when "dark matter" is being talked about in this situation, is a black hole simply one of the possible candidates to supply the mystery mass?
What is the form of the dark matter? Does it coalesce into spherical bodies? Or does it homogenize into equidistant particles due to mutual repulsion? And if it is bound to the Milky Way by gravity, and itself bound to as a 'galaxy', does it exert cosmos expanding repulsion in an "inverse almost square" relationship? Is it 1/ (r- fudgeFactor)^2 or 1/ (r)^(2-fudgeFactor)?
Seriously. I'm a rocket scientist, and I'm baffled by the mixed properties of 'dark matter'. Can we land a probe on it, or would baryonic space probes pass right through it?
I don't think that's the case at all. The only reason we have "dark matter" is because of astronomical observations. That is classic science. Make an observation, and then come up with a theory to explain it. From observations we know that there is some type of mass out there affecting gravity. We call it 'dark matter' because we don't know what it is. This isn't an aether theory, it's based on real observations.
One day we'll find out why we're having to explain shit with "dark matter", and the stupid concept will be laughed at like the Luminiferous aether is now.
Yeah, like neutrinos and X-rays and all that other weird shit people made up to explain problems away.
Sheesh, evil *and* a jerk. -- Jade
Both interact with light solely through gravitation, but dark matter is constitutionally incapable of interacting with light. It's dark not because it holds onto light, but because light just passes through it the same way a piece of plastic ignores a magnetic field. (Actually, not quite the same, but it's close enough for the moment.)
Black holes may or may not interact with light; what's inside a black hole is undefined. But when light falls on it, it passes the point of no return and never leaves.
Light passing near either will be bent by the gravity, but you can tell the difference in light that falls directly on it.
In fact, because the inside of a black hole is unseeable, it's possible that you could have a black hole that condensed from a blob of dark matter. You couldn't see it, but you could infer it: if there's a black hole inside a dark matter blob, it might have fallen in that way. Unfortunately, our tools for detecting dark matter are poor, so we can't resolve them with that kind of precision.
It is possible that some of the evidence that caused us to deduce dark matter could have implied black holes instead. There are two competing theories, Weakly Interacting Massive Particles (dark matter) and Massive Compact Halo Objects (black holes). That these are called WIMPs and MACHOs is a sign that we have detected physicist humor. The MACHOs hypothesis has been largely ruled out by the failure to detect the kind of gravitational lensing that small, massive objects cause, so the suspected mass must be more diffuse. That leaves us with the WIMPs as the best hypothesis, but it leaves a lot of questions open.
One day we'll find out why we're having to explain shit with "dark matter", and the stupid concept will be laughed at like the Luminiferous aether is now.
I don't think that's the case at all. The only reason we have "dark matter" is because of astronomical observations. That is classic science. Make an observation, and then come up with a theory to explain it. From observations we know that there is some type of mass out there affecting gravity. We call it 'dark matter' because we don't know what it is. This isn't an aether theory, it's based on real observations.
I think we actually have enough evidence for dark matter but, to be fair, the luminiferous aether was also based on real observations. There used to be a great deal of controversy over whether light was a particle or a wave. If it was a particle, it didn't need a medium to travel through, but it became very hard to explain refraction and diffraction properties. If it was a wave, then it needs a medium. We know from experiments that the medium wasn't something we could normally interact with. You can pump air out of a glass container with something that is making noise inside it, and you will no longer be able to hear the noise, because the sound waves have no medium to travel through. You'll still be able to see the object, though. Therefore, it was easy to conclude, from experimental data, that if light was a wave, there had to be some medium for light to travel through, permeating through everything, but that we couldn't interact with (pump out).
We had a bunch of observations that really demanded the presence of the Aether, until Einstein came along with his photoelectric effect papers and came up with the real solution: you know what? Light is both a particle AND a wave. That was completely unlike what we normally experience, so it's not the interpretation people were coming up with to explain their observations. A whole lot of things happened in those years, between Einstein, Planck, and deBroglie that really enriched our understanding of the universe. None of them set out to disprove the aether, it's simply that when they finally had a theory which explained every observation, the aether was no longer necessary.
I think dark matter is probably real. We can measure mass via the dynamics of celestial objects, measure mass via gravitational lensing, and come up with similar results: there's more mass there. So it doesn't seem like it's a problem with our theories. That said, there's a lot of observations dark matter doesn't explain, so if it turned out that it doesn't exist after all, I wouldn't be entirely surprised, and it would be very much like the story of the aether. There's nothing wrong with that, and there was nothing wrong with introducing the aether back in those days. That really is what science is about. You make a theory that best fits your observation, and right now dark matter beats any other alternative. If someone comes up with a better alternative, scientists will drop dark matter as fast as they dropped the aether, but until then we need to go with what we have.
The difference between Dark Matter and Luminiferous Aether is they made something out of nothing. What's going on here is we have "something". We have gravity. This gravity is measurable and is out there, but we cannot find the matter associated with it.
Heck, based on the amount of gravity "Dark Matter" has, there is more of this unknown material than material we do see.
Something out there is creating a crap ton of gravity and we can't see it. Since mass is needed for gravity and matter is the only thing we know of that has mass, we figure we'll call it "Dark Matter" until we know more about it.
Dark Matter itself isn't something, Dark Matter is just the "idea" of something we don't know and we describe this unknown something as "Dark Matter".
The truth is out there..... LAWL.. had to.
I like to think of Dark Matter as a NULL value in a Database. It's a known unknown.
Properties: it has mass (bends space)... don't know of any others, except the trivial stuff like it can move and be scattered around.
Effects: explains galactic rotation curves, explains some instances of lensing, possibly explains the perturbations this article is about.
Yeah, it has exactly the one property that someone is missing: mass. But is conveniently free of any other property that could influence anything.
The explanations you refer to are all based on calculations that are ultimately based on our understanding of gravity. The least understood force, the one that just won't fit into the picture. What a real scientist should do was to better research and explain gravity instead of making up some magic invisible soup to fix it all.
Pseudoscience, I say.
Let's get this out of the way first:
And we don't have any way to test for matter whose only property is it brings our mathematical formulae in line with our physical observations.
The, "Gee, that's funny" observation is what drives all science.
Now:
Making observations and theories is part of science. But what sets science apart from superstition is rigorous testing of the theories.
Believe it or not, some scientists do real science.
There was a competing explanation for this family of "Gee, that's funny" observations called MOND - Modification Of Newtonian Dynamics. It was ruled out on the basis of evidence. (There may be a MOND v. 2.0 out there now - not sure.)
One candidate for dark matter is the sterile neutrino, which people - real scientists - are trying to detect right now. A few years ago they were almost ready to dismiss its existence, but more recent results suggest that it may actually exist.
So no, contrary to your majestic disbelief, dark matter is a Real Hypothesis (tm), investigated by Real Scientists (tm), doing Real Science (tm).
If you want to actually learn something about the topic rather than simply using Slashdot as an outlet for you whingeing about the universe not working the way you learned in fifth grade, Wikipedia is an easy place to get started.
Sheesh, evil *and* a jerk. -- Jade
Make an observation, and then come up with a theory to explain it. From observations we know that there is some type of mass out there affecting gravity. We call it 'dark matter' because we don't know what it is. This isn't an aether theory, it's based on real observations.
So, let me get this straight, all empty space is assumed to have the same "density" properties?
When we observe gravity as a warping of space, is it not reasonable to think that the warping of space might cause an effect similar to gravity, without requiring any mass at all?
My question is this: Why do we assume that all "empty space" is uniform?
Could it be that "dark matter" is simply "empty space" that is naturally "curved"?
One theory is that our universe exists on a "(mem)brane". What's to say that the membrane itself is perfectly smooth?
Perhaps it was, but the big bang (or other past universe-scale forces) caused ripples in the fabric of space-time itself.
Perhaps the variations in the space-time fabric density explain why energy/matter began to "clump" together, perhaps it just pooled into the valleys.
TL;DR: Dark matter may actually be nothing at all -- thus explaining: Why we can't observe dark matter; Why normal energy & matter pass right through it; Why the big bang's energy was not uniformly distributed.
Gravity does not work as we think over large distances.
The Pioneer Anomaly and the Flyby Anomaly are indicating that gravity actually works a bit different than we think. Maybe we will see a new formulation of gravity in the future, explaining these and removing the need for dark matter.
dark matter may interact with its own kind by forces other than the ones that cause normal matter to interact with its own kind. According to the musing (which the author rejects), dark matter operating under such forces could form complex systems, maybe even an unseen parallel universe where "people" live lives like ours, as unaware of us as we are of them. All undetectable, except by their gravitational attraction on us.
A plot for an SF story: every time the universe branches due to wavefunction collapse a copy of the universe is created which still interacts with the universe through gravitation but not through the other forces.
Local effects of this are extremely difficult to measure, but they can be perceived as a fifth force that appears, for instance in the Pioneer anomaly.
I wish my writing skills were good enough to write this story...
I prefer my women like dark matter: attractive, hard to catch, dark, and mysterious.
Actually, they do form gravitational lenses, and we've measured this.
Basically, the process is to find a galaxy cluster, measure the lensing to determine where the mass is, and subtract out the mass of the individual galaxies. What you're left with is the location of the dark matter.
http://news.discovery.com/space/hubble-3d-map-universe-dark-matter.html
Where you're wrong is that there's no "central galaxy." Dark matter is still closely associated with normal matter (after all, they do attract each other gravitationally). I think maps like this have shown that most galaxies actually have a "halo" of dark matter surrounding them.
Of course, the shape of this halo can vary quite a bit:
http://hubblesite.org/newscenter/archive/releases/2007/17/
Wow! Are those gorgeous pictures or what!
So no, contrary to your majestic disbelief, dark matter is a Real Hypothesis (tm), investigated by Real Scientists (tm), doing Real Science (tm).
So was the Luminiferous Aether. That didn't stop it from being "wrong" in the end.
Real Science (tm) as done by real Scientists (tm) produces as many wrong answers as right answers. This is a good thing and what differentiates it from Religion (tm).
Business/App ideas are like arseholes: everyone's got one, they're mostly shit, but very rarely they contain a diamond
laughed at like the Luminiferous aether is now.
Only ignorant idiots laugh at aether theories. It was a perfectly reasonable theoretical artifact given what was known at the time, and scientists did science: they publicly tested the idea that the universe was permeated with a fluid-like substrate responsible for mechanical transmission of light by publishing the results of controlled experiments and systematic observations.
The idea failed the tests, as so many do.
What's funny about that, excatly? Unless you're the sort of mean-spirited, small-minded asshat who laughs at people for being wrong.
Blasphemy is a human right. Blasphemophobia kills.
Could it be that "dark matter" is simply "empty space" that is naturally "curved"?
Sure, and this idea either has testable consquences, in which case I'm sure someone is working on testing them, or it doesn't, in which case it isn't interesting.
What you're proposing would appear in current theories as a parameterized cosmological constant. Of course, a scientist would then ask, "Why does the cosmological constant have that parameterization?"
The problem with that is that all else being equal, such distortions would tend to level themselves out. We don't assume flatness, it comes out of Einstein's equations as the lowest energy solution in the absence of matter. So when we see deviations from flatness, we think, "matter". And there is quite a lot of astronomical information now that suggests dark matter behaves in most respects like matter.
So, why assume a parameterized cosmological constant when it is known to be a poor fit to data we already have?
Blasphemy is a human right. Blasphemophobia kills.