Newly Discovered Satellite Galaxies: Another Blow Against Dark Matter?

by Nancy Atkinson on April 25, 2012

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Arp 302 consists of a pair of very gas-rich spiral galaxies in their early stages of interaction. Credit: NASA, ESA, the Hubble Heritage (STScI/AURA)-ESA/Hubble Collaboration, and A. Evans (University of Virginia, Charlottesville/NRAO/Stony Brook University)

A group of astronomers have discovered a vast structure of satellite galaxies and clusters of stars surrounding our Milky Way galaxy, stretching out across a million light years. The team says their findings may signal a “catastrophic failure of the standard cosmological model,” challenging the existence of dark matter. This joins another study released last week, where scientists said they found no evidence for dark matter.

PhD student Marcel Pawlowski and astronomy professor Pavel Kroupa from the University of Bonn in Germany are no strangers to the study – and skepticism — of dark matter. Together the two have a blog called The Dark Matter Crisis, and in a 2009 paper that also studied satellite galaxies, Kroupa declared that perhaps Isaac Newton was wrong. “Although his theory does, in fact, describe the everyday effects of gravity on Earth, things we can see and measure, it is conceivable that we have completely failed to comprehend the actual physics underlying the force of gravity,” he said.

While conventional cosmology models for the origin and evolution of the universe are based on the presence of dark matter, invisible material thought to make up about 23% of the content of the cosmos, this model is backed up by recent observations of the Cosmic Microwave Background that estimate the Universe is made of 4% regular baryonic matter, 73% dark energy and the remaining is dark matter.

But dark matter has never been detected directly, and in the currently accepted model – the Lambda-Cold Dark Matter model – the Milky Way is predicted to have far more satellite galaxies than are actually seen.

Pawlowski, Kroupa and their team say they have found a huge structure of galaxies and star clusters that extends as close as 33,000 light years to as far away as one million light years from the center of the galaxy, existing in right angles to the Millky Way, or in a polar structure both ‘north’ and ‘south’ of the plane of our galaxy.

This could be the ‘lost’ matter everyone has been searching for.

They used a range of sources to try and compile this new view of exactly what surrounds our galaxy, employing twentieth century photographic plates and images from the robotic telescope of the Sloan Deep Sky Survey. Using all these data they assembled a picture that includes bright ‘classical’ satellite galaxies, more recently detected fainter satellites and the younger globular clusters.

Altogether, it forms a huge structure.

“Once we had completed our analysis, a new picture of our cosmic neighbourhood emerged,” said Pawlowski.

The team said that various dark matter models struggle to explain what they have discovered. “In the standard theories, the satellite galaxies would have formed as individual objects before being captured by the Milky Way,” said Kroupa. “As they would have come from many directions, it is next to impossible for them to end up distributed in such a thin plane structure.”

Many astronomers, including astrophysicist Ethan Siegel in his Starts With a Bang blog, say the big picture of dark matter does a good job of explaining the structure of the Universe.

Siegel asks if any studies refuting dark matter “allow us to get away with a Universe without dark matter in explaining large-scale structure, the Lyman-alpha forest, the fluctuations in the cosmic microwave background, or the matter power spectrum of the Universe? The answers, at this point, are no, no, no, and no. Definitively. Which doesn’t mean that dark matter is a definite yes, and that modifying gravity is a definite no. It just means that I know exactly what the relative successes and remaining challenges are for each of these options.”

However, via Twitter today Pawlowski said, “Unfortunately the big picture of dark matter being reportedly fine only helps if looking from far away or with broken glasses.”

One explanation for how this structure formed is that the Milky Way collided with another galaxy in the distant past.

“The other galaxy lost part of its material, material that then formed our Galaxy’s satellite galaxies and the younger globular clusters and the bulge at the galactic centre.” said Pawlowski. “The companions we see today are the debris of this 11 billion year old collision.”

The team wrote in their paper: “If all the satellite galaxies and young halo clusters have been formed in an encounter between the young Milky Way and another gas-rich galaxy about 10-11 Gyr ago, then the Milky Way does not have any luminous dark-matter substructures and the missing satellites problem becomes a catastrophic failure of the standard cosmological model.”

“We were baffled by how well the distributions of the different types of objects agreed with each other,” said Kroupa. “Our model appears to rule out the presence of dark matter in the universe, threatening a central pillar of current cosmological theory. We see this as the beginning of a paradigm shift, one that will ultimately lead us to a new understanding of the universe we inhabit.”

Read the team’s paper.

Source: Royal Astronomical Society

About 

Nancy Atkinson is Universe Today's Senior Editor. She also works with Astronomy Cast, and is a NASA/JPL Solar System Ambassador.

StockportJambo April 25, 2012 at 4:37 PM

About time.

I’ve always thought that the whole “dark matter / dark energy” theory is a bunch of hocus pocus. Everyone just assumes it’s there, even though we can’t detect it, purely to fit some other theories.

Einstein’s cosmological constant has nothing on dark matter.

Olaf2 April 25, 2012 at 4:55 PM

When scientists quote things like this: “catastrophic failure of the standard cosmological model” the it is most likely that they are just quacks.

So let’s them present their research first before determining if they are quacks or real scientists.

StockportJambo April 25, 2012 at 5:37 PM

There is a link to their paper at the bottom of the article.

Jeff Boerst April 26, 2012 at 6:37 PM

Especially while touting their newly released theory… I mean, REALLY!? “Hey guys look at our paper! It proves you’re all wrong!” …”Oh, it does? OK… *grumble*”

Torbjörn Larsson April 25, 2012 at 5:50 PM

- About time for what? This won’t change anything, even if it were true. Which seems a very long shot, especially since the author’s only working theory is that DM has problems. See my previous comment on what a stretch they seem to make. (But I haven’t checked yet.)

DM has too much going for it that a single observation can unravel it. Modify it, possibly.

- Not “some other theories” but to predict characteristics of a lot of phenomena. We can detect it by many methods already, imaging is done by gravitational lensing for example.

It is rejecting a perfectly good theory for some vague assertions of “hocus pocus” that leads to hocus pocus. Compare with a magician, either you propose that stage magic is mundane manipulation which can, and has, been checked, or you leave it open to be magic.

MDK02026 April 25, 2012 at 6:20 PM

The ‘fat lady’ is is warming up

MDK02026 April 25, 2012 at 6:22 PM

The ‘Fat Lady’ is warming up…

MDK02026 April 25, 2012 at 1:24 PM

The “Fat Lady” is warming up for her finale…

StockportJambo April 26, 2012 at 12:44 AM

About time some proper scientists did some open-minded investigations on a subject that hasn’t sat right with me since the moment I heard about it.

I know you can infer the existence of dark matter, and that there are many theories and observations that can back this up, but you can’t actually see it. The only clue you have to it’s existence is a fairly wooly notion of how heavy the universe “ought” to be, and that something unknown is making the universe expand.

That to me is like cosmologists saying “It’s like magic”. No. It’s physics – and physics comes first & foremost from the physicAL. Because of that, I think it’s entirely plausible that someone has forgotten to carry the 1 somewhere & everything has been way off beam ever since.

Like I said, it’s possible. Not necessarily true, but when 95% of the universe is supposedly made up of substances we can’t see or directly detect, alarm bells need to be ringing somewhere.

Dark matter / dark energy may exist. Or it may not. I think it’s worth keeping an open mind on it and not limit your ideas either way, because the bottom line is, we don’t actually know one way or the other.

Jeff Boerst April 26, 2012 at 6:35 PM

a) we can see it’s effects per grav lensing and velocity distributions.
b) why do we need to see it to know it’s there?

Jeff Boerst April 26, 2012 at 6:35 PM

a) we can see it’s effects per grav lensing and velocity distributions.
b) why do we need to see it to know it’s there?

squidgeny April 26, 2012 at 9:18 PM

I think your last paragraph about keeping an open mind is absolutely right. But it seems to be counter to your belief that “dark matter is hocus pocus”…?

Zoutsteen from Holland April 25, 2012 at 6:05 PM

dark matter / dark energy refers to undefined … they looked at one possible solution and that solution doesn’t seem to explain it.
There is still a difference between calculation with known formula and observation. That difference, name it DELTA, is what scientists are looking for. What is DELTA? (What is dark matter)

lcrowell April 26, 2012 at 1:32 PM

I think there is confusion here. The cosmological constant does not determine dark matter content of the universe. This is a structure to the vacuum of spacetime or equivalently cosmology that determines the accelerated expansion of the universe. This is a property of a de Sitter spacetime, which has a pressure term associated with spacetime curvature that is the negative of the energy density of the vacuum, p = -?. The density is constant with respect to spatial coordinates or frame on a Hubble spatial frame.

Dark matter on the other hand is some gravitating form of mass-energy that is locally clumped with galaxies. The orbital velocity distribution with radius observed in galaxies and the data from Bullet Cluster clearly shows this exists based on gravitation. It is called dark because it does not appear to interact electromagnetically, and is thus not regarded as luminous matter.

The data reported here involves a polar distribution of globular clusters and mini-galaxies that are not predicted well by DM. Of course this may only mean that our understanding of how DM is distributed is not well understood. I doubt this rises to the level of falsifying the existence of DM.

LC

Jeff Boerst April 26, 2012 at 6:38 PM

Ya, I know what you mean… I don’t believe in Black Holes because of the word, “Black”.

Torbjörn Larsson April 25, 2012 at 5:45 PM

I don’t think last week’s result has been received as a “blow” by physicists. I’m not “in the know” but surely someone would have commented if it was a devastating problem.

As I commented at that time, it is an old problem for the Poisson model of our galactic neighborhood rather than dark matter as such. It is especially easy to see here, since it was a problem already when people thought dark matter included missing baryonic matter which has later been estimated as well.

The first self-consistent galaxy model (the Eris simulation) _needed_ DM to get the correct prediction of a spiral galaxy. DM was the missing key to understand galaxies in the first place.

So for all appearances, DM seems healthier for each passing year. It certainly has no competition left anywhere, not even MOND could do for galaxies what DM did recently.

I haven’t looked at the new paper yet, but a cursory glance says that 1) they have an old agenda (thanks for the info, Nancy!) and 2) they have constructed a tall tower of “what-ifs” to be able to claim a problem for DM. If anything, that shows how difficult it has become to reject it.

Finally, while this isn’t a nitpick I have come to understand that this may be an old “common sense” idea too uncritically accepted:

never been detected directly

We can never detect an object, its QM wavefunctions, “directly”. So this old idea becomes a judgment issue. Do we still need to see an object such as to be seeing reflected photons “directly”, would an UV camera see similar photons “directly”, and so on?

Since we now do observations by experiment the better description is, I would argue, that we do sufficiently constrained (and robust) observations to uniquely test a hypothesis. I.e. can we predict the observations alternatively? If not, we detect uniquely.

Atoms were hypothesized when chemical reactions were observed to follow stoichiometric (i.e. rational) ratios. But they were only accepted following Einsteins theory of Brownian motion, where they could be uniquely detected by looking at suspended dust particle’s motions. “Direct” photonic detection of atoms were made much later, AFAIK when isolated ions could be made to blink by photon absorption and emission in ion traps.

Dark matter has been uniquely detected by gravitational lensing in, say, cluster collisions. No alternative gravitation or matter theory can predict the same observation. So DM is at the very least as observed as atoms were then they were generally accepted.

TerryG April 25, 2012 at 6:57 PM

Thankfully, the ESA’s GAIA mission is only about about 14 months from launch. GAIA’s results will include a high precision 3-D map of billion stars and their proper motions throughout the Milky way and beyond.

Then we can really start testing these competing theories.

Good story UT.

Torbjörn Larsson April 25, 2012 at 7:03 PM

Having read the paper, it is a bit of a misdirection.

They propose tidal interactions, and those would according to some earlier models of theirs make DM non-existent and conveniently a common test of DM in dwarf galaxies (high mass, low luminosity) invalid. So it hinges on older results as well as this new prediction.

One really has to look at their old papers first. A little googling turned up this paper on tidal streams and dark matter:

“In the last decade stellar streams in and around the
Milky Way, which are possible debris from the disruption
of satellite galaxies during the hierarchical assembly
of our Galaxy, have become an active topic of investigation
for several reasons. Firstly, large scale CCD surveys
have provided unprecedented evidence of accretion and
tidal disruption of dwarf galaxies around large spirals in
the Local Group (Milky Way: see Majewski 2004; M31:
Ibata et al. 2002 and beyond: Pohlen et al. 2004). Secondly,
because tidal streams provide strong constraints
on the potential of host galaxies, it is possible to estimate
the shape of dark matter halos on large scales in contrast
to traditional tracers, such as HI or stellar kinematics
(see Sackett et al. 1999 for a review), which provide estimates
on relatively small scales.”

“Yet, the calculations mentioned above do not
take into account the evolution of the spatial distribution
nor the mass loss of substructures, which may weaken the
influence of substructures on the tidal stream evolution.
In this paper we focus on tidal streams in the Milky
Way simply because only for our Galaxy can streams be
resolved into stars and accurate phase-space information
gathered.”

“Thus, groundbased
observations already available for tidal streams
(basically providing distances and radial velocities along
the stream) and future satellite data covering the full
phase-space (making possible studies in the E–Lz plane)
can only constrain the present characteristics of the
Milky Way potential. As a direct consequence, Galaxy
evolution processes can be neglected when modeling tidal
streams, which clarifies one of the main caveats in current
N-body simulations and confirms that tidal stream
models computed under that hypothesis are appropriate
for tracing the distribution of dark matter around our
Galaxy.”

TL;DR: The MW and tidal streams have dark matter, but their respective structures aren’t informative on the history of MW. This, tidal streams having dark matter and not informative on MW history, are both in direct conflict with the claims of the paper under discussion here.

If the proposed structure exist it is then depicting DM concentration. Perhaps MW is simply trapped in a DM filament?

I’ll let them duke this out. Meanwhile, I wouldn’t hold my breath hoping DM is much erroneous a theory.

lcrowell April 26, 2012 at 12:55 AM

The motion of matter in a dark matter region should obey a force law similar to Hooke’s law ma = kx, where I have derived this here before. It is really an easy Gauss’ law exercise. So these streams would if immersed in DM dynamically evolve accordingly. This is not what the investigators found. However, the streams might be in a region that has a void of DM, or they are being attracted to a clump of DM along with the galaxy. In the first case the gravitational potential is constant if the void is symmetrically centered, which can be shown in an elementary Gauss’ law calculation. If the void is off to one side then the gravitational potential will not be constant. The DM in our galaxy may have a density distribution that sets up a gravitational potential that is not trivial. So there may be details in the distribution of DM which makes this observation.

LC

Aqua4U April 25, 2012 at 7:56 PM

Live and learn! I LIKE paradigm shifts… can you feel one approaching?

Ken Lord April 25, 2012 at 9:05 PM

As an interested layman, this is a difficult story to read.

No one but quacks claim Newton was wrong, just that his theory needed to be extended … which it was by Einstein.

From virtually one paragraph to the next we go from the current dark matter theory requiring that there be lots of satellite galaxies and material that has not been discovered, to the discovery of a vast network of apparently just such needed material, now breaking the same model. Which is it?

And why the assumption that just because the milky way’s satellites have a weird distribution (or at least the current catalog of known objects) that this is the way it is for all large galaxies?

How does this apply to the big examples? Have they considered the implications for the Bullet Cluster etc?

Ken Lord April 25, 2012 at 9:05 PM

As an interested layman, this is a difficult story to read.

No one but quacks claim Newton was wrong, just that his theory needed to be extended … which it was by Einstein.

From virtually one paragraph to the next we go from the current dark matter theory requiring that there be lots of satellite galaxies and material that has not been discovered, to the discovery of a vast network of apparently just such needed material, now breaking the same model. Which is it?

And why the assumption that just because the milky way’s satellites have a weird distribution (or at least the current catalog of known objects) that this is the way it is for all large galaxies?

How does this apply to the big examples? Have they considered the implications for the Bullet Cluster etc?

lcrowell April 26, 2012 at 12:42 AM

I have only read the abstract to their paper, given that it is 21 pages long abd I have 5 other papers on my stack to read I may not get to this. However, while what they observe may be accurate we may have an “assume a spherical cow problem.”

If one were to use acoustical waves to measure and compute the volume of a cow you would start out the problem by assuming a spherical cow. You then build up from there by deforming spherical symmetry. The same thing goes with models of galaxies and dark matter. We all have this basic model of a galaxy sitting in the middle of a spherical halo of dark matter. There are a few problems with this. Who is to say the dark matter halo is homogeneous? There might be voids inside a DM halo and denser regions as well. Further, the complexity in the evolution of galaxies and their dark matter might mean that you can have several galaxies in a DM halo, where one or more galaxies might in turn move around on orbits that take it outside the DM halo.

Dark matter has two things going for it. The first is the rotational profile of galaxies. There is the MOND theory, but it is simply too ad hoc and is failing observational tests for me to consider. The other is the Bullet Cluster, where it is clear that some non luminous matter has left the luminous matter behind So there must be “something” there, and because it does not emit light we call it dark matter. Some other galaxy collisions have been found not to support this as well, but we may be dealing with peculiar configurations of DM relative to those galaxies.

These data probably do not so much illustrate a problem with the existence of DM, but with how we model and understand how galaxies interact gravitationally with DM and the early evolution of galaxies and galactic clusters.

LC

Jeff Boerst April 26, 2012 at 6:30 PM

That’s amazingly lucid and well-put!

Dennis Patterson April 26, 2012 at 1:10 AM

Quote all your formulas and hypotheses and theories. . . . .I have always thought the idea of “dark matter” and “dark energy” as absurd and grasping at straws. Perhaps soon we will have information that will make sense. Waiting for the correct answer always beats jumping to conclusions. . . . . .

GregtheThird April 26, 2012 at 6:12 AM

I find the these authors findings to be very exciting in that it has the potential for important insights into the superstructure of the universe. There was a fairly recent article regarding the discovery of dark matter filaments feeding into galaxy clusters (*), and this finding seems to be something along the same lines. It is too bad that the authors had to bundle this along with other biased assertions of theirs in an attempt to bolster their previous arguments about the absence of dark matter. They certainly face an uphill battle there, but the larger point is that sometimes important discoveries are made out of a desperate quest to save a dying hypothesis or theory.

* http://www.universetoday.com/85927/australian-student-uncovers-the-universes-missing-mass/

GregtheThird April 26, 2012 at 7:03 AM

I will elaborate further about how I connect the dots from the referenced study to this one. To me the findings suggest that there are dark matter filaments left over from the big bang which naturally attracted surrounding dispersed gas to form the first proto-galaxies and the SMBHs that go with them. Galaxies are then anchored to these filaments like beads on a string and then over time accrete more gas dispersed in the intergalactic medium. If indeed the dark matter we are looking for is contrained to a narrow filament running perpendicular to the axis of rotation of he galaxy, then we will not see it in our immediate neighborhood, nor the halo, as a very recent study implies (*). It would follow then that all of the efforts to detect dark matter on Earth will fail. When you look at the concepts of invisible dark matter filaments spanning the universe leftover from the big bang that connect distant galaxies together, one can’t help but think how this sounds alot like what string theory would predict.

* http://news.nationalgeographic.com/news/2012/04/120419-dark-matter-sun-missing-stars-milky-way-space-science/

bruisedknee April 26, 2012 at 9:08 AM

love the idea that established theory is so fragile….. thats what science is all about. The thought that everything we know today could count for nothing in 50 years is what makes me come back again and again to this subject….. Blimey, next you’ll be telling us that the world is round!

Prism2Spectrum April 26, 2012 at 10:30 AM

“Our model appears to rule out the presence of dark matter in the universe, threatening a central pillar of current cosmological theory. We see this as the beginning of a paradigm shift, one that will ultimately lead us to a new understanding of the universe we inhabit.”

As one long skeptical of the “current cosmological theory”, I personally find this a very exciting prospect. It may be the turning prompt to refocus the hard lens of fixed view, and could just open-up a new, far more wonderful realization, one of awesome implication and panoramic sweep, of what our vast, highly Structured Universe actually shines so colorfully from its well-defined, organized systems of 300-Sextillion suns (and counting)!

Joel N April 26, 2012 at 3:42 PM

“While conventional cosmology models for the origin and evolution of the universe are based on the presence of dark matter, invisible material thought to make up about 23% of the content of the cosmos, this model is backed up by recent observations of the Cosmic Microwave Background that estimate the Universe is made of 4% regular baryonic matter, 73% dark energy and the remaining is dark matter.”

Uh, doesn’t the second model add up to 23% dark matter also?

Jason Kurant April 26, 2012 at 5:32 PM

I have always wondered if these models account for the time delay in the transmission of gravity. So, as the simulation calculates the affect of gravity on each particle by each other particle, it really needs to consider the affect of gravity on a particle by each other particle where it was when the first particle see it, based on its distance in time because of the fact that gravity also travels at the speed of light. Just as we see a star as it was back at the time the light left that star and started traveling to us, every particle sees every other particle as it was at the time that light or gravity left that other particle, not as it is or where it is at the current local time. I would think building this into the simulations would make them enormously more expensive to calculate. Does anyone know?

Bob Myers April 26, 2012 at 10:14 PM

“… luminous dark-matter substructures…” WTF?

hageljohn May 5, 2012 at 9:36 AM

Check out these very recent papers by the same team:
“Can filamentary accretion explain the orbital poles of the Milky Way satellites?”
http://adsabs.harvard.edu/abs/2012arXiv1204.6039P
and the major (long) review
“The dark matter crisis: falsification of the current standard model of cosmology”
http://adsabs.harvard.edu/abs/2012arXiv1204.2546K

So it seems the team has looked in much detail at all the possibilities, including the wider picture.

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