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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.
Cue the chocolate milk and dark chocolate jokes. I'm too busy, otherwise I'd think of some. C'mon /., don't let us down!
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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?
Wouldn't dark matter galaxies so close to ours result in the occlusion of galaxies behind them?
Since a galaxy is mostly empty space -- wouldn't this result in a detectable degree of light variation?
------ The best brain training is now totally free : )
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.
Ahhhh, and me with no mod points! Some one should mod this up!
Tell me, what properties does dark matter have, save for explaining the factor 2-4 miscalculation of the universe's mass?
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
Dark matter is the fudge factor which explains the rotation of galaxies whose outer extents rotate too fast for known orbital mechanics. Applying Occums's razor, the explanation is missing mass. The alternative explanations:
Time is not as constant as we think. (Allowing for General Relativity)
Gravity does not work as we think over large distances.
Dark Energy (companion/alternative to DM)
Those first two are often dismissed as being too complicated because we've got plenty examples of our predictions being right based on those assumptions, and sort-of rule out Dark Energy. But be it Energy or matter it is some form of a quantifiable unknown.
Faced with revising our equations for reality on the small-medium scale, we'd rather say matter is escaping detection for the large scale.
Slashdot's rate-of-post filter: Preventing you from posting too many great ideas at once.
Disclaimer: 'The Elegant Universe' was a very entertaining science documentation. Easy to understand, fun to watch, but most likely got it totally wrong. Probably as wrong as my fun theory.
:-D
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.
Think of it this way: In day to day life, for everyday objects, x = 2y describes gravitational interaction. Test it over and over, and it works just fine.
.01 everything falls into place. And it works over and over.
.01 is, so we call it dark matter. Someday we'll figure out what it is, for now we call it dark matter. That's it.
Now, when we look way out into the universe at galaxies, x = 2y doesn't quite work, but if we use the formula x = 2y +
We don't know what the
it's based on real observations.
We can't see dark matter any more than our predecessors saw the Luminiferous aether.
Actually, we can via the gravitational effects of dark matter.
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.
The aether was exactly the same thing - an explanation for the real observation that light behaved like a propagating wave. It was perfectly legitimate science too. The situations are quite similar.
I am trolling
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
I'm not saying there's no such phenomenon as "dark matter" or "dark energy".
I'm agreeing with GP that our understanding of dark matter is no better than Huygen's or Boyle's understanding of the aether.
They didn't invent the aether for kicks. They had made physical observations of light and magnetism that known science could not account for. The "luminiferous aether" was an initial clumsy attempt to understand an emerging frontier in Science.
I think our successors will laugh at our clueless "dark matter" explanations for exciting phenomena we are on the cusp of discovering. But as long as our understanding is this vague, our "dark matter" is not much different than the "Luminiferous Aether" concept was three centuries ago.
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'm not an expert in astronomy by any stretch (engineering is my area of expertise) but my understanding of a lot of astronomy is a lot of what we observe is interpretation. Most of physics was determined by watching something move and producing a model. In astronomy we can't actually watch things move (much beyond our solar system anyway), instead we look at light and try to translate this into the motion that we can't see (primarily using red shift). What if red shift or our other ways of interpreting this light is wrong? Not so much about the whole theory (though has red shift ever been detected in an object we can also measure the actual velocity of?) but even if red shift is not linear or off by a certain factor, how much would that mess up the existing theories?
will sue the astronomers who found it over copyright violations. They've had "Mikey Way Dark' out for years.
It took me three seconds to realize I wasn't reading about a new dark chocolate milky way candy bar. I guess it's time to go home.
Obviously, there are gravitational distortions in space-time that current theories cannot explain. The idea that there is some sort of exotic matter creating those gravitational distortions is an untestable hypothesis (unless you know of a way to go out and collect the dark matter which may exist in these regions to run experiments on it).
It is equally likely that those regions of space are experiencing distortions due to some unknown natural distortion in space-time's structure itself or are caused by an interaction with another universe in the multiverse. It's also possible that our current model of how gravity works is incorrect at large scales due to other factors we don't yet understand. In any case, the distortions are at such a large scale and at such great distance from us that any hypothesis will be difficult to test.
"Dark Matter" is just a word for "something out there we can't see is causing gravitational distortions we can't account for." There's no reason the cause has to be some form of matter we haven't seen yet. Particle physicists haven't a clue what kind of a particle would have mass, but no interaction with light. People assume the distortions are caused by mass because all known distortions our theories work for are caused by mass, but all known normal mass particles also interact with light or emit light. So, people simply make up hypothetical particles with mass, but no interaction with light -- because they NEED for them to exist to fit their assumption that mass in our universe is causing the distortion.
I think it's far more likely we don't yet understand some aspect of gravity on galactic scales than there is some sort of magic form of matter that makes our current equations make sense in the areas that currently make no sense to us whatsoever.
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.
I think they're up to MOND 45.2 now. The problem with MOND is that it has yet to successfully predict anything. Every new set of data requires a refinement of the concepts in MOND, whereas general relativity has successfully predicted a lot of things that were later observed. That doesn't mean MOND can't be right, but there's no particular reason to think it's right.
"I zero-index my hamsters" - Willtor (147206)
Then why does dark matter, that is supposed to be in bigger amounts than bright matter (stars and junk) do not form gravitational lenses like normal galaxies do?
I should be able to spot a gravitational lens that has no visible source if this dark matter coalesces into "galaxies".
This should be the easy proof to get. If this stuff is so prevalent in the universe then we should have a scientific "metric buttload" of evidence in photographs of gravitational lenses without a central galaxy.
Do not look at laser with remaining good eye.
This is the case IF.....
you assume time works on a small scale exactly as it does on the large scale.
Physics falls apart when you go to small scale, thus the "fudge factor" quantum physics was created.
We are smaller than a quark compared to a single galaxy, thus the possibility that time operates differently on a macro scale are certainly plausible.
Do not look at laser with remaining good eye.
Then why does dark matter, that is supposed to be in bigger amounts than bright matter (stars and junk) do not form gravitational lenses like normal galaxies do?
You have evidence that it doesn't form gravitational lenses like normal galaxies? Then publish it and pick up a Nobel prize. My understanding is that we don't know enough to make claims like this.
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!
gravitational lensing that doesn't match the visible masses
This is a very interesting piece of evidence. It's not just that the gravity is stronger than we expect, is that the gravity is coming from locations where we don't see anything.
The obvious conclusion is that there is additional mass not producing any light for us to observe. But maybe our model for gravity is wrong. Occam's Razor points to the former, so let's start there with our investigations. If that doesn't pan out then we'll have to look for more exotic solutions.
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.
Not quite true. We have more observable gravity than our current understanding of gravity predicts, yes, but that doesn't necessarily mean there's an invisible gravity-pony out there causing all the 'extra' gravity.
The aether was created to solve the problem that light behaves as a wave, but waves must propagate through something. Once we had a better understanding of photons we could dispense with the aether.
The same holds true for our understanding of gravity. At the moment we are proposing that the universe is full of invisible gravity-ponies because 'something must be out there causing all this gravity'. We may come to a better understanding of gravity that allows us to dispense with the ponies.
Don't forget, after all, that we are also currently proposing that there are invisible inter-galactic gravity-ponies pushing the galaxies apart too.
Business/App ideas are like arseholes: everyone's got one, they're mostly shit, but very rarely they contain a diamond
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
> Occam's Razor points to the former
I'm not convinced invisibility is a simpler explanation than human error, nor that human error is more exotic than "dark matter."
Occam's Razor doesn't help here. Neither choice is obviously simpler than the other.
"Galaxy X could soon lead to Galaxies Y and Z, according to Chakrabarti". Phew, at least there could only be three of 'em.
Yes, I hear a lot of new research is looking into the quantization of space-time, in the order of Planck length.
Also, at small distances, gravity is weaker than all other forces, so it is less relevant.
Slashdot's rate-of-post filter: Preventing you from posting too many great ideas at once.
No. Real Science produces many, many more wrong answers.
Finally had enough. Come see us over at https://soylentnews.org/
In other news, lighting a stick on fire allows the wood to "express" the fire contained with in it, and people who weigh the same as ducks are witches.
Go Science!
Finally had enough. Come see us over at https://soylentnews.org/
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.
They are claiming that dark matter makes it's own galaxies which is what I am refuting.
Good info though, I'll use those for further discussion with astronomy friends.
Do not look at laser with remaining good eye.
I think his point is that the scientists are making the presumption that their current understanding and calculations are correct and that it is some unknown that is causing the whole problem labeling it "Dark Matter" as defined as WTF something I can't observe with a a lot of mass. So rather than looking for this magical element that is screwing up their mass calculations of the universe, perhaps they should take a harder look at a) the calculations they use to measure, b) the methodology used to test those calculations, or c) the foundations on which those calculations are based.
I would think that doing an experiment, finding results different than what you expect, and then blaming magical fairies, to be somewhat insane rather than scientifically rational. Anyway nothing wrong with giving the unknown a name and perusing that avenue of thought, only that it would be my last option. Needless to say I am not a big fan of the term "Dark Matter". It is something unknown and that is it. Perhaps the name itself simply has connotations I do not like...