Dark matter detected

Killjoy

Killjoy

Propelling The Farce!!
Valued Senior Member
Evidently, astronomers have finally been able to detect the presence of dark matter...

https://www.space.com/dark-matter-detected-cosmic-web-filaments-universe-evolution-subaru-telescope

For the first time, astronomers have detected dark matter hanging from massive filaments that stretch across the universe and form a "cosmic web" that trap galaxies like morning dew on a spiderweb.

Researchers from Yonsei University in Seoul, South Korea, used the Subaru Telescope — an 8.2-meter optical-infrared telescope near the summit of Maunakea in Hawaii — and an effect that gravity has on light to indirectly observe dark matter sitting on cosmic web filaments in the Coma Cluster.

This marks the first-ever detection of dark matter on the cosmic web, and could help confirm how this structure — with strands that run for tens of millions of light-years — has influenced the evolution of the universe.
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Interesting technique used to observe the unobservable...
"Seeing" the location of dark matter around these cosmic web strands is a completely different story, however.

That's because, despite making up an estimated 85% of all the matter in the universe, dark matter is invisible because it doesn't interact with light like everyday matter that comprises stars and dust does.

Dark matter's dominance over everyday matter also means it dominates the filaments of the cosmic web, forming an invisible scaffold along which the universe's structure takes shape.

However, even though dark matter doesn't interact with light, it does interact with gravity — and this interaction impacts the movement of everyday matter and light that we can see.

The team behind this research took advantage of this concept, using it to detect dark matter on cosmic web filaments threaded throughout the Coma Cluster.
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I wonder if the actual dark matter is responsible for the gravitational lensing.
 
It sounds like the researchers infer the existence of dark matter from gravitational lensing. The lensing of the light implies that mass must be in the way, but if no other source of mass makes sense and we can't directly see the mass, we call it "dark matter".

In other words, this isn't a direct observation of dark matter. It is an inference.
 
James R said:
It sounds like the researchers infer the existence of dark matter from gravitational lensing. The lensing of the light implies that mass must be in the way, but if no other source of mass makes sense and we can't directly see the mass, we call it "dark matter".

In other words, this isn't a direct observation of dark matter. It is an inference.
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Not if they can measure the deviations and make a (rough?) map of the objects causing the deviations.

That is what I assumed they might be at the start of.

Wasn't it said when gravitational waves were detected that this would be a way of detecting objects that have been undetectable till now?(regions from where light could not reach us ,perhaps)
 
James R said:
It sounds like the researchers infer the existence of dark matter from gravitational lensing. The lensing of the light implies that mass must be in the way, but if no other source of mass makes sense and we can't directly see the mass, we call it "dark matter".

In other words, this isn't a direct observation of dark matter. It is an inference.
Click to expand...
I suppose that's why they claimed to have detected, rather than observed it. Presumably we'll never be able to see it.


geordief said:
Not if they can measure the deviations and make a (rough?) map of the objects causing the deviations.

That is what I assumed they might be at the start of.

Wasn't it said when gravitational waves were detected that this would be a way of detecting objects that have been undetectable till now?(regions from where light could not reach us ,perhaps)
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I'm wondering how much matter comprises these filaments of the cosmic web. (first I've read of that, I must say)
Are they themselves sufficiently massive to produce the effect attributed to dark matter ?
 
Killjoy said:
I suppose that's why they claimed to have detected, rather than observed it. Presumably we'll never be able to see it.



I'm wondering how much matter comprises these filaments of the cosmic web. (first I've read of that, I must say)
Are they themselves sufficiently massive to produce the effect attributed to dark matter ?
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I thinkI have heard of those (massive) filaments before.

They don't sound as if they could be massive enough to me ,but I certainly have exponentially zero expertise in this area.

Doe it sound like the dark matter is somehow attached to these massive filaments?

Gravitational attraction?
 
geordief said:
Not if they can measure the deviations and make a (rough?) map of the objects causing the deviations.
Click to expand...
It sounds like that's approximately what they have done. They have identified some places near "cosmic filaments" where there's more mass than we can see.
Wasn't it said when gravitational waves were detected that this would be a way of detecting objects that have been undetectable till now?(regions from where light could not reach us ,perhaps)
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Yes, but there are very few gravitational wave detectors in existence right now. I doubt they have very good resolution (but I don't know).
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Killjoy said:
I'm wondering how much matter comprises these filaments of the cosmic web.
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Lots and lots. The "cosmic web" they are talking about is looking at the universe at the largest scales. These are galaxy-sized objects or larger.

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geordief said:
Doe it sound like the dark matter is somehow attached to these massive filaments?

Gravitational attraction?
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Dark matter only appears to interact gravitationally. We can't see it because it doesn't emit light (hence "dark matter") or interact electrically with anything, as far as we can tell.

Dark matter seems to be found in association with other matter, as far as I'm aware. It makes some sense: dark matter and ordinary matter must attract one another gravitationally. The dark matter just "adds" the "extra" mass necessary to produce the measured gravitational attraction that acts on the ordinary matter we can actually see.

Really, at present "dark matter" is just a place holder for "some source of mass that we haven't yet identified, but which seems to be necessary to generate 'extra' gravity".
 
DM already inferred by the properties of galaxies but there are problems with it.
If there is a particle associated, they have not found evidence of that either.

Interesting though, I'll catch up with the articles. Thanks Killjoy
 
I'm no astronomer but to me it looks as if the journalist has no idea what he is writing about, with all this crap about dark matter "dangling" from a "spider's web" that "traps" galaxies. It's a silly attempt to invoke the imagery of a spider's web when it does not fit the science. What the hell does "dangling" even mean in the context of objects in space?

My understanding of cosmic filaments is that it is the galaxies themselves that seem to be strung out so as to form filaments of matter, with voids between them. So it's just a description of how galaxies are spatially distributed at very large scale, not some feature, distinct from galaxies, that "traps" them in some undefined way.

If my understanding of that is correct, then we would obviously expect dark matter to be present, since it seems to be present in all galaxies. So what these astronomers have done, it seems to me, is to detect the presence of dark matter at a new scale of observation, viz. when looking at far off entire filaments of galaxies, as opposed to individual ones. They have done this by making use of gravitational lensing.

So it's not a new feature of the cosmos, and it's not direct observation of dark matter. It's managing the feat of observing lensing at the scale of entire filaments, for the first time.

That is how it looks to me. However I'll be happy to be corrected.
 
James R said:
Really, at present "dark matter" is just a place holder for "some source of mass that we haven't yet identified, but which seems to be necessary to generate 'extra' gravity".
Click to expand...

The concept of dark matter always sounded a bit funky to me. I guess it's no weirder than, say, a black hole, but somehow it seemed like a notion devised to explain away the apparently incomprehensible evidence that there's "not enough" matter in the Universe. I mean - what could comprise matter which behaves unlike any that we can observe directly ?
 
Killjoy said:
The concept of dark matter always sounded a bit funky to me. I guess it's no weirder than, say, a black hole, but somehow it seemed like a notion devised to explain away the apparently incomprehensible evidence that there's "not enough" matter in the Universe.
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My point is: dark matter is not yet an explanation of anything. It's just a term we use to label the mystery.

A lot of observational evidence suggests that galaxies contain a lot more mass than we can account for in terms of ordinary matter made up of things like protons, electrons and neutrons, apparently even if we use very generous estimates of the potential amounts of ordinary matter that we can't see directly.

As I see it, there are three possibilities:
  1. The observational data is flawed for some reason we aren't aware of yet. This one seems unlikely because there seems to be a lot of corroborating evidence using different techniques.
  2. There is some new type of matter, possibly something that "breaks" the Standard Model of particle physics, whose properties are yet to be discovered. This is thought to be the most likely explanation at the moment, and it is why the problem gets the name "dark matter". A lot of money is being spent on experiments to try to directly detect dark matter particles which have the necessary properties. If dark matter is real, then the particles involved must be weakly interacting - e.g. they have mass and respond to gravity, but they don't interact electromagnetically.
  3. Something is wrong with our theory of gravity on large scales (galaxies and above). Some tweaks and alternatives have been suggested. I'm not up to date on how the alternatives are going, when compared to the various data.
 
Killjoy said:
The concept of dark matter always sounded a bit funky to me. I guess it's no weirder than, say, a black hole,
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Black holes exist and have been observed. Dark Matter as James said, is a place holder for phenomena that is as yet not explained.
 
Killjoy said:
The concept of dark matter always sounded a bit funky to me. I guess it's no weirder than, say, a black hole, but somehow it seemed like a notion devised to explain away the apparently incomprehensible evidence that there's "not enough" matter in the Universe. I mean - what could comprise matter which behaves unlike any that we can observe directly ?
Click to expand...
You are just asking the same question that cosmologists and particle physicists are wrestling with. We need more observations, in various fields, to get an answer.
 
I have an idea for what dark matter is. I've been studying an alternative form of relativity put forward by Osiak. He suggests that relativistic energy is properly E = (gamma)^2 m c^2/2 instead of (gamma) m c^2 from Einstein. This is for reasons I find convincing. There are a lot of interesting consequences of an extra relativistic factor in the energy. One of them is that inertial mass can be less than gravitational mass, if ordinary matter is a composite of matter and antimatter. Also, there are the Shupe-Harari preon models where ordinary matter is about half antimatter and half matter, but not exactly. This means the gravitational mass of ordinary matter might be on the order of five or ten or more times its inertial mass. (I got 6 for the dark-to-visible matter ratio in a rough estimate, for deuterium.) Since the gravitational constant is measured by measuring the attraction between two masses based on their inertial mass assuming it's equal the gravitational mass, then the G we are using is too big. Hence there seems to be a lot of missing matter, but there isn't really.

It makes some testable predictions. One is that the measurement of G will depend on the composition of the test bodies. Basically, depending on the neutron proportion. So different isotopes of the same element would give different G values in a predictable way. I am looking at a G measurement review article and it seems to be saying there is an unexpectedly large variance in the different measurements. If these variations can be related in a way that can be derived from the model, it could support both Osiak relativity and the preon model of particles. They both have to be true for this explanation to work.

Osiak relativity also doesn't conserve energy relativistically and there's a lot more of it in the hot early universe than assuming Einstein relativity, which might drive cosmic inflation. Also unconserved energy can become gravitational potential energy a.k.a. dark energy.

I suspect Einstein got the same result as Osiak but threw it away because it didn't conserve energy. Osiak just said it's more faithful to the relativity principle, didn't realize it breaks energy conservation. I connected some dots.
 
Dave Lush said:
This means the gravitational mass of ordinary matter might be on the order of five or ten or more times its inertial mass.
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I realize you've posted a simplified view of your idea so I might be interpreting it wrong but wouldn't these effects you mention be just as detectable at the human-scale as at the cosmological scale? i.e. wouldn't this inertial/gravitational discrepancy be apparent in any object we observed in a lab?
 
Nice question, fellow Dave C. I had a similar kind of thought, initially, but then I realized that the Einsteinian equivalence principle is about the indistinguishability of acceleration in an elevator and the force of gravity. So it's saying that measuring the weight of something is measuring its inertial mass, not its gravitational mass. Gravitational mass is just about how strong of a gravitational field a body creates, not inertia.

I posted a draft paper on researchgate:

There is another paper there I posted about Osiak relativity. It used to be all one paper, but I decided to split it out.

The math in the dark matter paper is basically arithmetic. When I say I got 6, it's not a rounding.
 
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