Dark matter in the Universe is distributed as a network of gigantic dense (white) and empty (dark) regions, where the largest white regions are about the size of several Earth moons on the sky. Credit: Van Waerbeke, Heymans, and CFHTLens collaboration.

Astronomers Witness a Web of Dark Matter

Article Updated: 24 Dec , 2015

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We can’t see it, we can’t feel it, we can’t even interact with it… but dark matter may very well be one of the most fundamental physical components of our Universe. The sheer quantity of the stuff – whatever it is – is what physicists have suspected helps gives galaxies their mass, structure, and motion, and provides the “glue” that connects clusters of galaxies together in vast networks of cosmic webs.

Now, for the first time, this dark matter web has been directly observed.

An international team of astronomers, led by Dr. Catherine Heymans of the University of Edinburgh, Scotland, and Associate Professor Ludovic Van Waerbeke of the University of British Columbia, Vancouver, Canada, used data from the Canada-France-Hawaii Telescope Legacy Survey to map images of about 10 million galaxies and study how their light was bent by gravitational lensing caused by intervening dark matter.

Inside the dome of the Canada-France-Hawaii Telescope. (CFHT)

The images were gathered over a period of five years using CFHT’s 1×1-degree-field, 340-megapixel MegaCam. The galaxies observed in the survey are up to 6 billion light-years away… meaning their observed light was emitted when the Universe was only a little over half its present age.

The amount of distortion of the galaxies’ light provided the team with a visual map of a dark matter “web” spanning a billion light-years across.

“It is fascinating to be able to ‘see’ the dark matter using space-time distortion,” said Van Waerbeke. “It gives us privileged access to this mysterious mass in the Universe which cannot be observed otherwise. Knowing how dark matter is distributed is the very first step towards understanding its nature and how it fits within our current knowledge of physics.”

This is one giant leap toward unraveling the mystery of this massive-yet-invisible substance that pervades the Universe.

The densest regions of the dark matter cosmic web host massive clusters of galaxies. Credit: Van Waerbeke, Heymans, and CFHTLens collaboration.

“We hope that by mapping more dark matter than has been studied before, we are a step closer to understanding this material and its relationship with the galaxies in our Universe,” Dr. Heymans said.

The results were presented today at the American Astronomical Society meeting in Austin, Texas. Read the release here.

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canderson
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canderson
January 9, 2012 7:13 PM

I would argue that inferring its location based on gravitational lensing still does not constitute a “direct” observation of dark matter.

Lawrence B. Crowell
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Lawrence B. Crowell
January 9, 2012 9:23 PM
The irony is that we don’t actually observe anything. Our eyes only have certain chemical receptors of photons (rhodopsins) which generate action potentials which along with others assemblies of action potential constructs some sort of virtual image in the brain we observe. These photons may scatter off some object, or be emitted by that object and so forth, but we do not actually perceive that object as it is, just as a representation of that object according to how photons interact with the eye and then ultimately the brain. Much the same holds for sound, olfaction, taste and tactile perception: Our brains ultimately construct a representation based upon a cascade of physiological processes. That representation is then something… Read more »
Torbjorn Larsson OM
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Torbjorn Larsson OM
January 9, 2012 10:40 PM

Nice exposition!

One could also add that we never observe here and now due to relativity. We can only observe and extrapolate or, better, theorize, while quantifying uncertainties.

Erik_F
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Erik_F
January 10, 2012 2:35 PM

Let alone the time it takes our brains to process input from “here and now” – we’re constantly living in the past. =)

Anonymous
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Anonymous
January 9, 2012 7:16 PM

Is dark matter all around us? I know (or think I know) that its mass is what keeps galaxies together but besides that matter and dark matter do not ‘interact’.

But it seems from what I have read that dark matter’s effects are only seen on very very large scales (galactic). We never see the orbit of a planet or moon disturbed by dark matter.

For something that make up an estimated 83% of the matter in the universe it certainly seems elusive.

Can someone shed some light on dark matter??

Anonymous
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Anonymous
January 9, 2012 7:44 PM

It if often suggested that dark matter is nothing more than ordinary matter, except that it doesn’t interact with ordinary matter in any way except through gravitation. But like you, I find it very curious that the effects of dark matter are only observed at the cosmic scale, whereas the effects of gravitation are observed at the planetary scale. Maybe such observations are forthcoming, or maybe our ideas of what this stuff is are completely wrong.

Peter
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Peter
January 9, 2012 11:14 PM
I liken it to trying to get your head around relativistic conundrums like looking behind your close-to-light-speed ship or watching someone fall into a black hole. Because we expect matter to be …well, matter, it seems to fly in the face of logic that we can’t feel it or bottle it or cough when we get too much up our noses. If it’s “everywhere” (and I’m speaking from human experience) as in all around us, and we can’t feel it, because it goes right through us, there really is no other way to register its existence. It’s like trying to figure out relativity without math. From our own, earthbound experiences, most of what relativity postulates is just too… Read more »
canderson
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canderson
January 9, 2012 7:53 PM
Matter and dark matter DO interact (that’s how we know the dark matter’s there) via gravity. What distinguishes them is the fact that dark matter interacts weakly (perhaps not at all) with electromagnetic energy (e.g. light)–in other words, photons are neither absorbed nor emitted by dark matter, and dark matter is not subject to the electromagnetic interaction. (While this may seem strange, consider that electrons are not subject to the strong nuclear force.) From a planet’s/moon’s perspective, dark matter is smoothly distributed as a halo surrounding the galaxy, and there’s as much in one direction as another (i.e. the planet’s/moon’s orbit is infinitesimal compared to the overall distribution of dark matter), so the effect on the orbit is… Read more »
Anonymous
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Anonymous
January 9, 2012 8:44 PM
Canderson, I did state that dark matter affected normal matter. My second sentence I stated that dark matter’s mass (hence gravity) affects matter on the galactic scale. The question I have is how could dark matter be unformly distributed? If dark matter does have mass then gravity should affect it like it affects normal matter. Should we not see dark matter ‘clump’ like regular matter does. I guess what I am asking in a nut shell is why don’t we see the effects of dark matter planets orbiting the sun? I understand we would see them directly but we sure should see dark matter interacting with regular matter on a smaller scale than galactic.
Kawarthajon
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Kawarthajon
January 9, 2012 9:05 PM
DM is not uniformly distributed. As mentioned in the articles, it is clumped together in a network of webs across the universe, which maybe helped to seed galaxies. It’s not that DM doesn’t interact with small scale objects (i.e. planets, moons, suns, etc…) – it still has a gravitational interaction with each of them. It is just that it is clumped around a galaxy in a halo such that it doesn’t differentially impact the various objects in our solar system. This might be compared to the impact the matter at the centre of our galaxy has on all the planets and moons and our sun, but they all feel a similar impact because they are all approximately the… Read more »
Anonymous
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Anonymous
January 9, 2012 9:27 PM
Kawarthajon, It does appear to be uniform within dwarf galaxies. In research published in The Astrophysical Journal scientists studied two of the most dark-matter dominated galaxies known and found a uniform distribution. University of Cambridge’s website reports the following from this link: http://www.cam.ac.uk/research/features/dark-matter-is-smoother-than-we-thought/ ) The standard cosmological model describes a universe dominated by dark energy and dark matter. Most astronomers assume that dark matter consists of “cold” (ie slow-moving) exotic particles that clump together gravitationally. Over time these dark matter clumps grow and attract normal matter, forming the galaxies we see today. Cosmologists use powerful computers to simulate this process. Their simulations show that dark matter should be densely packed in the centers of galaxies. Instead, new measurements… Read more »
Peter
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Peter
January 9, 2012 11:19 PM

For myself, I have assumed that dark matter can not “clump” past a certain limit. As in, there is likely no dark sand, dark dust, dark rock or dark foam. It’s a gas or a wavelike form of matter that doesn’t even interact with itself other than having antipathy to being lonely. So it doesn’t surprise me that it’s of uniform density in any galaxy. You can’t compress that which will not press on itself.

Anonymous
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Anonymous
January 10, 2012 12:14 AM

But even hydrogen clump (aka stars) do they not?

Peter
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Peter
January 10, 2012 1:18 AM

Yes of course. Sometimes, lots of loose hydrogen out there. However, you’re failing to recognize the “other” nature of dark matter. Hydrogen loves to interact ie: water. Dark matter acts totally unlike hydrogen, which is BTW, a singular. Its like you’re asking neutrinos to wake up and notice each other so they can start a big neutrino party. They’re loners and always will be.

Kawarthajon
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Kawarthajon
January 10, 2012 7:08 PM

Ok, but the article that we’re commenting on talks about how DM clumps into these networks and webs, with galaxies in them. I was talking about DM clumping on a large scale. If DM is clumped into a dwarf galaxy, then my point is secure, even if the distribution of DM is smooth within the galaxy. My point was that DM’s gravity operates on a grand scale and doesn’t have differential effects on comparatively little objects like planets, moons and stars.

AdrianTheRock
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AdrianTheRock
January 9, 2012 5:20 PM

Because it doesn’t interact electromagnetically, dark matter particles can’t easily slow down, so they just go on travelling round and round, in a halo.

Torbjorn Larsson OM
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Torbjorn Larsson OM
January 9, 2012 11:01 PM
Dark matter (DM) can’t clump, no electromagnetic interactions so no charges and no chemistry. DM particles are loosely associated with other gravitational masses such as stars. But pass through them like neutrinos, just more massive and likely then less speedy. As it happens, late last year the last unconquered territory of DM was laid to its feet. The Eris simulation modeled a spiral galaxy successfully for the very first time. The crucial component was – DM! The significance was that while alternative hypotheses could explain some particulars of precisely galaxies they were not successful anywhere else. And now they are kicked out by a more parsimonious model over a wide variety of scales. Earlier that year another large… Read more »
magnus.nyborg
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magnus.nyborg
January 10, 2012 8:25 AM
Assuming dark matter is composed of particles (wimps), then it seems the particles are moving randomly, i.e. they have a temperature. They can not be very cold, or they would simply collapse gravitationally. They can not be very hot, or DM would not contract at all. They can have an effective temperature that allows it to contract some, but at that point it behaves like a cloud of gas in an approximate hydrodynamic equilibrium. Each time two ‘galaxies’ with much DM collide, the effective temperature of the DM would increase slightly, causing the new DM-cloud to reach equilibrium in a slightly large size. Over time, this cloud would spread symmetrically unless otherwise disturbed. In effect, if the above… Read more »
Michal Rosa
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January 9, 2012 8:08 PM

It has not been observed in any way, shape or form, its existence so far has only been inferred. Dark matter, XXI-century science’s ether

Lights in the Dark
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January 9, 2012 8:21 PM

Not unlike black holes, wouldn’t you say? Yet we are fairly sure they are what they are, where we think they are.

Torbjorn Larsson OM
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Torbjorn Larsson OM
January 9, 2012 10:47 PM

I believe you mean aether, which was its time’s phlogiston. Hypotheses soundly rejected with time.

This is more like our neutrinos, hypotheses that successfully accrue tests and characteristics over time.

Note that neutrinos are quite difficult to observe too! Yet we can manage.

Anonymous
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Anonymous
January 9, 2012 8:30 PM

Wide-field weak lensing surveys like this one will be an important tool in our understanding of dark matter, as it gives us a way to directly map its distribution over a wide expanse of the cosmos.

Lawrence B. Crowell
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Lawrence B. Crowell
January 10, 2012 12:38 AM
As for clumping, DM does not generally clump because it does not interact by electromagnetism which dissipates away energy by radiating photons. Assume you were some super-observer who had super technology and you grabbed every particle of DM by some means and brought them all to a dead stop relative to the galaxy. These particles would be mutual gravitation begin to fall towards some relative center and implode into a huge black hole. The rub is that you have no catcher’s mitt to stop them, and their status as “cold” DM reflects the fact these particles are in motion and are in free orbits that are conservative and do not lose energy.. Do DM particles influence things like… Read more »
Peter
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Peter
January 10, 2012 12:49 AM

How do they know how the light coming to us has been bent? Is there something in the spectral signature that says, I was aligned like that but since passing by a huge glob of nothing, I look like this instead.? What tells us that what we’re detecting is an “after” picture?

DrFlimmer
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DrFlimmer
January 10, 2012 7:38 PM
The magic word here is “gravitational lenses”. We cannot infer it from “single” photons, but from distorted pictures of background galaxies. Since galaxies are not point sources their photons take a slightly different way into our telescopes depending on where they start in the galaxy. If there is no mass between the galaxy and us the photons travel on straight lines and the galaxy is seen as it is. However, if there is mass in between, then it becomes interesting. Now, it critically depends on the starting point how the way of the photon is affected by that mass. A photon from one side of the galaxy will be bent differently than a photon from the other side.… Read more »
Peter
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Peter
January 10, 2012 10:58 PM

Thanks, but I think you’re still suggesting that someone is making a value judgement about how “distorted” a galaxy might look. How do they quantify that level of distortion? Since we can’t see the galaxy from any other viewpoint, what have we to go on? There are lots of ACTUALLY distorted galaxies out there for which I would not want to be responsible to make that call.

DrFlimmer
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DrFlimmer
January 11, 2012 12:01 PM
Anonymous
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Anonymous
January 11, 2012 1:06 PM

As with other high-resolution images we’ve all seen ( almost unbelievable to me ), that Image of Galaxy Cluster Abell 2218 reveals such extreme distortions, it leaves little doubt SOMETHING has altered the original light-picture of the background galaxies — or gravity-lensed them, as by some impossibly huge glass lens! On such a gargantuan scale, yet ( out on another limb I go ), basically the same effect one could demonstrate with a curved glass lens in hand. Simply amazing!

I thought Peristoika’s questions were still good ones, as one off-stream observer of the grand planetarium show unfolding before us day by day, and week by week.

Anonymous
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Anonymous
January 11, 2012 4:40 PM

This study (and others like it) employed weak gravitational lensing to discern the distribution of dark matter. Weak lensing produces subtle distortions in the shapes of galaxies which, when studied statistically, can be used to infer the distribution of mass (in this case, dark matter). Wikipedia has a good description of the methodology behind weak lensing studies: http://en.wikipedia.org/wiki/Weak_lensing#Methodology

(btw, weak lensing rarely produces the long arcs and multiply-imaged galaxies as is seen in strong lensing, per Dr Flimmer’s awesome Abell 2218 image)

DrFlimmer
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DrFlimmer
January 11, 2012 10:26 PM

I had considered to talk about the differences of strong and weak lenses, but I decided that the general picture should be enough to start with (and I would have needed to look up the details of weak lensing wink ).

Peter
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Peter
January 10, 2012 12:49 AM

How do they know how the light coming to us has been bent? Is there something in the spectral signature that says, I was aligned like that but since passing by a huge glob of nothing, I look like this instead.? What tells us that what we’re detecting is an “after” picture?

Peter
Member
Peter
January 10, 2012 12:49 AM

How do they know how the light coming to us has been bent? Is there something in the spectral signature that says, I was aligned like that but since passing by a huge glob of nothing, I look like this instead.? What tells us that what we’re detecting is an “after” picture?

Anonymous
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Anonymous
January 10, 2012 3:01 PM
Gazing at the CFHT image, trying to picture it as a specially-dimensioned solid, its structure seems to have a familiar similarity to, mirror something seen in nature ( if true representation of how a solid version would appear ). No surprise would there be, though, as the mega-structure of galaxies in the Universe itself bears a remarkable resemblance to that of the inner human brain, and its neuron “web” – the folds within which intelligence is “fired”. ____________________________________________ These questions are more rhetorical, than anything else: Is “Dark Matter” matter? A quantifiable substance? That which “physicists have suspected helps gives galaxies their mass, structure, and motion, and provides the ‘glue’ that connects clusters of galaxies together in vast… Read more »
Torbjorn Larsson OM
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Torbjorn Larsson OM
January 10, 2012 7:37 PM

the overall structure of the Universe itself bears a remarkable resemblance to that of the inner human brain, and its neuron “web” – the folds within which intelligence is “fired”.

Not even close, unless you mean superficial likeness for rhetorical purposes. The cortex is very differentiated and even layered, these structures not so much.

A quantitative measure like a spatial FFT would testably show the difference.

As for the rest of the “rhetorical” comment it is way too many questions. The baseline is that DM is accepted fruitful theory on its own, it is an indelible part of standard cosmology as well, and you can study what scientists claim for example here on UT or here.

Anonymous
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Anonymous
January 11, 2012 10:54 AM
Sampling of images below ( a few main web-sites thereof ) that most closely support the comparison ( New York Times’ image comparison is a stunner! ): Surely, you cannot deny that some of the images of neurons, and “web” networks, along with others ( not all, to be sure ), do indeed resemble sections ( qualification – on a given scale, and in certain resolutions ) of the cosmic structure mapped-out by astronomers through super-computers: Filaments, intersecting knots ( absent sheets and walls, admittedly ) – neuron strands, cell junctures: You can almost picture the luminous galaxy-clusters strung along the “web”strands, around the “empty” inter-medium dark voids of the network – BRAIN STRUCTURE _________________________________________________ [] “Normal Neurons… Read more »
Anonymous
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Anonymous
January 11, 2012 3:11 PM
I am in the dark, lest I seek the light; so regarding link: [] “Remarkably, it turns out there is five times more material in clusters of galaxies than we would expect from the galaxies and hot gas we can see. Most of the stuff in clusters of galaxies is invisible and, since these are the largest structures in the Universe held together by gravity, scientists then conclude that most of the matter in the entire Universe is invisible. This invisible stuff is called ‘dark matter’, a term initially coined by Fritz Zwicky who discovered evidence for missing mass in galaxies in the 1930s.” – Goddard Space Flight Center on “Dark Matter” – http://imagine.gsfc.nasa.gov/docs/science/know_l1/dark_matter.html [] “We believe that… Read more »
weeasle
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weeasle
January 10, 2012 3:36 PM
Great amazing work by the CFHTLenS collaboration team, nice article Jason and some very interesting comments here too Especially like the discussion of clumping and action/interaction, lensing on galactic versus local scales…. In the past I have been a sceptic of DM and DE feeling somehome cheated that I was being asked to believe something not directly observable… Something about scientific models, etc… However, I may be a sceptic but do not wish to be contrarian for the sake of it. I am now accepting (thanks in large part to these UT articles and comments) that DM and DE are important substantial place-holders at the very least and starting to accept the validity of the concept as more… Read more »
Torbjorn Larsson OM
Member
Torbjorn Larsson OM
January 10, 2012 7:30 PM

Great! Now if you only can drop the misplaced “place holder” metaphor*, you can embrace the Dark side.

————
* We can observe DM by its characteristics of cold, particulate, mass and non-EM interaction, not so with theory place holders “insert remaining mass here”.

weeasle
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weeasle
January 11, 2012 1:46 AM

If I do join the dark side, will I end up like this ?

Torbjorn Larsson OM
Member
Torbjorn Larsson OM
January 11, 2012 3:14 PM

Actually we go more light on the booze-ons (having them on the “darks”, as we may refer to the preferred mix).

I dunno about the bad case of helmet hair. Of course, with no static clinging and less mechanisms to end up at the bottom of a gravity well you can have any hair style and it will look the same old burr. I never said there wasn’t disadvantages!

wjwbudro
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wjwbudro
January 10, 2012 4:19 PM

If the Higgs mechanism is supposed to give rise to mass and normal baryonic matter seems to aggregate around dark matter clumps and filaments, is a connection possible?

Torbjorn Larsson OM
Member
Torbjorn Larsson OM
January 10, 2012 7:23 PM
Mass is complicated. More generally it is a local conservation of energy (that gravity can feel as mass by its curving of spacetime), so it takes many forms. As for Higgs, 3 out of 4 different standard Higgs give mass to W & Z and hence themselves by such bootstrapping. But the remaining one gets its mass from symmetry breaking. Yet other different mechanisms makes Higgs give masses to matter and force particles. And the different cases continue to accrue as we look at additional mass contributions from conserved energies as we go to composite particles (say, nucleons, getting energies from both quarks and gluons), atoms (energies from electron shells), molecules (bonding energies), and so on. Surely though,… Read more »
wjwbudro
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wjwbudro
January 10, 2012 10:05 PM

Thanks T.L. for your reply and ref. to the past article on the Higgs, I forgot about that. It’s getting harder to keep all the various proposals in my aged short term memory. I never really understood this Higgs thing anyway. Old school says energy gives rise to mass. Oh well, time for another Excedrin.

wjwbudro
Member
wjwbudro
January 10, 2012 7:43 PM

I should have added, connection at post bb matter genesis?

Dilip G Banhatti
Member
January 11, 2012 7:33 AM

What is inferred by gravitational lensing is intervening gravitating matter. Only due to the current fashion it is called dark matter!
-Dilip G. Banhatti / Madurai (India)

Ivan3man_At_Large
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Ivan3man_At_Large
January 11, 2012 1:20 PM

Well, dude, how do you account for the gravitational lensing observations that show the presence of considerably more mass than is indicated by the clusters’ light alone?

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