Fermi and dark matter

[DazzaD]

For all you and I know "dark matter" is simply composed of more suns and more ISM than we realize. Unless you have evidence that some other form of matter exists and could be involved, I have no evidence that "Dark matter" is anything other than "ordinary matter" that you simply can't account for.

Ok.. I will bite.

Nucleosynthesis
http://www.astro.ucla.edu/~wright/BBNS.html

WMAP
http://wmap.gsfc.nasa.gov/universe/uni_matter.html

 

[Michael Mozina]

I think I'll take that quote apart, claim by claim and see where we end up....

Some normal matter is packed together in tight, dense little clumps. Good examples of this are stars and galaxies. When you run two large clusters (spanning millions of light years) into each other, these little clumps hardly ever hit each other, and move with a lot of momentum. What does this mean? They tend to miss one another, and they hardly get slowed down by the friction of moving through the other cluster. In other words, they behave like the little metal balls in a game of "Crossfire". They mostly just pass straight through to the other side.

So far, so good. Now of course that this "pass straight through" effect would mean that the "cores" and stars and the planets and asteroids and such would tend to "pass straight through'.

Those cores and basic infrastructure (and any ISM that passed through) are your two primary (blue) "blobs".

That leaves us with the gas, which is where most of the normal matter is,

Well, let's start by noting we made an "assumption" that most of the matter is in the form of a "gas".

and the dark matter.

"Dark matter" or more accurately "unidentified mass". It could be "clumpy" like the first example, or a MACHO type of "dark matter".

For all intents and purposes, these are distributed over the entire cluster, so they're very diffuse, but also omnipresent. The gas is still made up of protons, neutrons, and electrons, and these tiny particles interact with one another very easily.

Now we've made another assumption. We *assumed* that there are charged particles when in fact some of the material could be found in neutral atoms, not necessarily charged particles.

When they run into each other, they behave similarly to running two jets of water into each other:

Er well, sort of, but unless they have the density of water they won't necessarily directly interact with an any particular atom/particle in the other ISM. If they are "bound" in any way, due to say "local cloud density", they may be less likely to interact with other particles in the other ISM.

There is a lot of friction between them, which (if you remember) both slows them down and also heats them up. The slowing down is why the X-ray-emitting gas is always in the middle of these clusters (in all three cases), and the heating is why the gas becomes energetic enough to emit X-rays! In other words, the gas goes "SPLAT!"

Of course the other way to explain "x-rays" involves "electrical current". It just so happens that these are million mile per hour, fast moving charged particles, IOW "current flow' sheets flying past each other at millions of miles per hour relative to one another. That is bound to create "current flow" inside the "plasma sheets" of the ISM of each galaxy.

But what of the dark matter?

What about it? You mean like those neutral atoms in the ISM that this author never mentions?

Although it obeys the same gravitational laws of physics, it's missing the main source of friction -- electric charge!

Ah, then he *IS* talking about those neutral atoms in the ISM he never mentioned.

In fact, we're pretty sure that dark matter has practically no electromagnetic interactions at all.

Er, well neutral atoms interact with the EM field but not like a charged particle. They do tend to "absorb light" and make things seem darker than the really are.

The friction between dark matter particles (as well as between dark matter and gas) is so small it might as well not even be there at all. Colliding dark matter with itself is as futile as colliding light beams with one another; they might as well not even be there!

Well, unless two neutral atoms slam into each other, ya, I guess they'd just whiz by each other at millions of miles an hour.

I'm afraid this quote is based upon several assumptions that do not seem to be justified. Most plasma is 'dusty' meaning it's not fully ionized. There will be neutral atoms in the ISM of each galaxy, not simply proton and electrons and other charged ions.

 

[Michael Mozina]

Baryon fraction is well constrained in several ways - none of which you would approve of though, I'm sure.

Try me.

It's actually quite a straightforward calculation - the collision cross-sections are pretty well known and basically no stars or planets collide in a galaxy merger. Gas does though.

Well, surely some gas collides, but it wouldn't all collide.

It's straightforward laboratory-founded kinetic theory of gases. You can calculate the gas density and figure it out simply enough. There's no weird physics at all.

I'm sure that there is nothing weird about the physics of plasma interactions, but the relative speeds and charges of the particles are going to make any "guestimations" pretty difficult at best. How much of the ISM is actually "charged" and how much of it is contained in neutral atoms?

 

[Michael Mozina]

Ok.. I will bite.

Nucleosynthesis
http://www.astro.ucla.edu/~wright/BBNS.html

Welcome to the conversation. Nice link. I liked the graphs and such. Here an example of how they account for "normal matter' in the BB.

The mass fraction in various isotopes vs time is shown at right. Deuterium peaks around 100 seconds after the Big Bang, and is then rapidly swept up into helium nuclei. A very few helium nuclei combine into heavier nuclei giving a small abundance of Li7 coming from the Big Bang. This graph is a corrected version of one from this LBL page. Note that H3 decays into He3 with a 12 year half-life so no H3 survives to the present, and Be7 decays into Li7 with a 53 day half-life and also does not survive.

Never once did they mention any of the half-life expectations of "dark matter", or explain how it is composed and how it was created or destroyed. Pure oversight or did these calculations predate any 'dark matter" discussions? How would dark matter change anything in these calculations?

WMAP
http://wmap.gsfc.nasa.gov/universe/uni_matter.html

Perhaps you could elaborate/explain some of the 'claims' of this link?

You, this computer, the air we breathe, and the distant stars are all made up of protons, neutrons and electrons. Protons and neutrons are bound together into nuclei and atoms are nuclei surrounded by a full complement of electrons. Hydrogen is composed of one proton and one electron. Helium is composed of two protons, two neutrons and two electrons. Carbon is composed of six protons, six neutrons and six electrons. Heavier elements, such as iron, lead and uranium, contain even larger numbers of protons, neutrons and electrons. Astronomers like to call all material made up of protons, neutrons and electrons "baryonic matter".

So far, so good. All the things mentioned show up in 'empirical physics'.

Until about thirty years ago, astronomers thought that the universe was composed almost entirely of this "baryonic matter", ordinary atoms.

So in other words, when I was in college the universe was based on "empirical physics". Right or wrong, there was nothing "mystical" about it.

However, in the past few decades, there has been ever more evidence accumulating that suggests there is something in the universe that we can not see, perhaps some new form of matter.

Perhaps, or perhaps not? What makes them think there is any need for a new form of matter? How do they know they didn't underestimate the amount of ordinary material in a distant galaxy?

http://www.space.com/scienceastronomy/080515-galactic-dust.html
http://www.sciencedaily.com/releases/2009/08/090819145846.htm

 

[edd]

Try me.

DazzaD has already posted BBN constraints. Baryon fraction also affects the CMB power spectrum. I'm sure there's at least one other method I've forgotten (perhaps looking at X-ray emission from clusters?)

 

[Michael Mozina]

DazzaD has already posted BBN constraints. Baryon fraction also affects the CMB power spectrum. I'm sure there's at least one other method I've forgotten (perhaps looking at X-ray emission from clusters?)

You don't find it even the least bit odd that no one says a word about what's going on with "dark matter' during this process? We have all this technical discussion about baryonic matter, and not a single peep about how "dark matter" was created and/or destroyed in the "creation event"? Isn't that a wee "fishy" to say the least?

 

[edd]

You don't find it even the least bit odd that no one says a word about what's going on with "dark matter' during this process? We have all this technical discussion about baryonic matter, and not a single peep about how "dark matter" was created and/or destroyed in the "creation event"? Isn't that a wee "fishy" to say the least?

No. We don't know much about dark matter but we do know it doesn't interact much with normal matter, and it doesn't decay fast - or it wouldn't be here for us to measure today.

 

[Michael Mozina]

No. We don't know much about dark matter

Except you evidently know that it decays and emits gamma rays in quantity x (that is curve fitting exercise to match the Fermi data)? From a skeptics point of view it sure seems like you "know" things about "dark matter" when it's convenient for the purposes of a paper, yet plead ignorance when it's less convenient (like where it comes from, how it's made, etc).

but we do know it doesn't interact much with normal matter, and it doesn't decay fast - or it wouldn't be here for us to measure today.

All of these beliefs you have about this theoretical "abnormal (dark) matter" seems to be predicated upon the premise that we originally estimated the "normal matter" correctly in the first place. I have no confidence in that assessment, particularly based on recent revelations.

 

[DeiRenDopa]

Επιτέλους!

"Finally!" - did iGoogle get it right? What would a rough transliteration of the sound of the word be? (Epitelo??)

 

[edd]

Except you evidently know that it decays and emits gamma rays in quantity x (that is curve fitting exercise to match the Fermi data)? From a skeptics point of view it sure seems like you "know" things about "dark matter" when it's convenient for the purposes of a paper, yet plead ignorance when it's less convenient (like where it comes from, how it's made, etc).

No actually, I don't - as you can perfectly well tell from the posts I made at the start of this thread. You would do well not to misrepresent my views when you've obviously read what I said on the matter before.

I said there are theoretical reasons to think it might and that therefore it is a good idea to go and look for that, in order to test those theories.

 

[Perpetual Student]

"Finally!" - did iGoogle get it right? What would a rough transliteration of the sound of the word be? (Epitelo??)

At last! or Finally!

epi-teloos

 

[Reality Check]

Please read it again RC and look for the term "blob". Better yet, do a "Find" and locate the word "blob". You were talking about blobs way back then and I "dealt" with it then too.

The only "blobs" in the post are in text you quote from me.
The question is about blobs of gas, i.e. the inter-cluster medium (ICM) in colliding galactic clusters.
You continue display your ignorance of the actual question by talking about galaxies (not ICM and not blobs) and solar systems (not ICM and not blobs)

It's not my "ability to understand" you, it's my "ability to believe" that statement that I'm having trouble with. What else is there to "collide" other than stars and ISM?

For umpteenth time:
The intercluster medium (ICM) is doing the colliding. They are the blobs of gas in the question.



This is your failure to understand simple English:

• The ICM is not the interstellar medium (it is the plasma between galaxies). THE ISM may collide but is a tiny part of the gas in the clusters.
• The ICM is not stars (it is the plasma between galaxies).
• The ICM is not galaxies (it is the plasma between galaxies).
• The ICM is not solar systems (it is the plasma between galaxies).

 

[Reality Check]

Why would all "normal matter" be expected to "collide' rather than just "pass through' in your opinion? Here's where the wheels seem to come off your argument. There no way it's all going to interact with matter in the other galaxy. Much of the solar system infrastructures might pass through intact. The density and composition of the ISM will determine how much material might actually be expected to "collide".

I think I'll devote a separate post to your quote.

The usual "the solar system infrastructures" rant with the usual answer.
In colliding galactic clusters:

• Galaxies rarely collide since they are quite small compared to a cluster.
• Stars collide even more rarely than galaxies sine they are really tiny compared to a galaxy.

Can you understand this and that it has nothing to do with the question?

The quote gives the reason that normal matter is expected to collide - it interacts electromagnetically.

In this case we have clouds of ICM colliding where the mean free path of the atoms is about a lightyear. This means that even if the ICM was not colliding the atoms will travel about a lightyear before colliding. I would expect that the collision would double the density of the ICM, halve the mean free path and so an atom will collides every 0.5 lightyears.

Thus in order for an atom to "pass through" the 1 megaparsec thickness of the ICM it will collide and interact with other atoms at least 3 million times and possibly 6 million times. Scientist know a lot about what happens when atoms of normal matter collide.

• In general they slow down.
• They also heat up and emit radiation.

That is what astronomers see for some of the ICM

• The ICM slows down and forms a blob at the center of the collision.
• The ICM is already emitting X-rays (it is a plasma). The collision produces more X-rays allowing astronomers to map the position of this part of the ICM and see the shock-waves as the galactic clusters collide.

But most of the ICM

• Does not slow down.
• Has not heated up.

According to you this is normal matter that has magically avoided over 3 million possible collisions and just passed through the rest of the ICM. You might have a point if only a millionth part of the ICM passed through. But that is not the case - most of the ICM managed to pass through the rest of the ICM.

A normal person will conclude that the reason that most of the ICM passed through the rest of the ICM is because most of the ICM does not interact electromagnetically with the rest of the ICM. This means that this part of the ICM is made up of something we have not seen before - weakly interacting massive particles (WIMPs).

 

[Reality Check]

I think I'll take that quote apart, claim by claim and see where we end up....

So far, so good. Now of course that this "pass straight through" effect would mean that the "cores" and stars and the planets and asteroids and such would tend to "pass straight through'.

Those cores and basic infrastructure (and any ISM that passed through) are your two primary (blue) "blobs".

Wrong. The "cores" and stars and the planets and asteroids and such would stay as galaxies. The blobs are not galaxies. They are gas.

Well, let's start by noting we made an "assumption" that most of the matter is in the form of a "gas".

Wrong.

1. Astronomers observe that the ICM (a "gas" or plasma") exists by looking at the X-rays emitted by it.
2. Astronomers observe that most of the matter in galactic clusters is in the ICM.

Now we've made another assumption. We *assumed* that there are charged particles when in fact some of the material could be found in neutral atoms, not necessarily charged particles.

No assumption: Plasmas are are quote well understood.

Er well, sort of, but unless they have the density of water they won't necessarily directly interact with an any particular atom/particle in the other ISM. If they are "bound" in any way, due to say "local cloud density", they may be less likely to interact with other particles in the other ISM.

More of your "ISM" stupidity". It is the ICM (or IGM).
It is also a plasma. The atoms are not "bound" in any way, due to say "local cloud density".
The atoms in the ICM will interact less often than the atoms in water. You though have forgotten what the scale of galactic cluster collisions means. Millions of lightyears = millions of interactions.

Of course the other way to explain "x-rays" involves "electrical current". It just so happens that these are million mile per hour, fast moving charged particles, IOW "current flow' sheets flying past each other at millions of miles per hour relative to one another. That is bound to create "current flow" inside the "plasma sheets" of the ISM of each galaxy.

More of your ISM stupidity.
Citation please or is this just another of your unsupported assertions pulled out from some unknown recess?

What about it? You mean like those neutral atoms in the ISM that this author never mentions?

More of your ISM stupidity.
Like those neutral atoms in the ICM that do not exist.

Ah, then he *IS* talking about those neutral atoms in the ISM he never mentioned.

No he "IS NOT*. He is stating that dark matter does not have any electric charge otherwise it would interact electromagnetically.

Er, well neutral atoms interact with the EM field but not like a charged particle. They do tend to "absorb light" and make things seem darker than the really are.

And they are really easy to detect because of the absorption, e.g neutral hydrogen.

Well, unless two neutral atoms slam into each other, ya, I guess they'd just whiz by each other at millions of miles an hour.

That is right - two neutral atoms can miss each other. The thing you do not know is that there are a lot of atoms (neutral and otherwise).
Even at the small density of the ICM, a neutral atom will collide with another atom (or electron or ion) every lightyear (over 3 million times to get to the other side of the cluster).

I'm afraid this quote is based upon several assumptions that do not seem to be justified. Most plasma is 'dusty' meaning it's not fully ionized. There will be neutral atoms in the ISM of each galaxy, not simply proton and electrons and other charged ions.

More of your ISM stupidity.
The ISM does contain neural atoms (mostly hydrogen). But...
For umpteenth time:
The intercluster medium (ICM) is doing the colliding. They are the blobs of gas in the question.

 

[Reality Check]

Can Micheal Mozina answer a simple question about intercluster medium

Since MM is obsessed with the interstellar meduim, stars and solar systems for some reason, I have emphasised that this question is about the intercluster medium (ICM) (original question in this thread here).

First asked 18 July 2009
Here is the question about the intercluster medium in colliding galactic clusters:

1. A is a big blob of gas with the same size and density of the ICM in a galactic cluster.
2. B is a bib blob of gas with the same size and density of the ICM in a galactic cluster..
3. Blob A hits blob A.
   • If the gas is all the same stuff then the result will be another blob of gas.
     It is probable that some of the gas will not not collide. In that case there will be blobs of gas to each side. The size of these outlying blobs will reflect the amount of gas that did not collide. See the point below about why insignificant amounts of normal (baryonic) matter will not collide.
   • If the gas is a mixture of two kinds of gas , one of which interacts weakly with the other, then the result will be 3 blobs since the weakly interacting gas passes through the other gas.
     The size of these outlying blobs will reflect the amount of gas that did not collide plus the amount of weakly interacting gas.
4. We see 3 blobs.
   The outlying blobs contain most of the matter in the bolbs A and B.
5. Thus the gas is made of two kinds of gas, one of which interacts weakly with the other.

Any problems with this analysis with what is going on with the majority of the matter (i.e. ICM) in the Bullet Cluster and MACS J0025.4-1222 (and even Abell 520)?

Remember that astronomers can calculate the probability of atoms in the ICM colliding as they travel millions of light years through each cluster. I do not know the exact number but expect it to be high (an atom travels millions of light years through a medium containing about 1 atom per cubic meter - you do the math!).



It has become obvious that you cannot do the math so here is it:

• The intracluster medium (or intergalactic medium):
  

  Although the ICM on the whole contains the bulk of a cluster's baryons, it is not very dense, with typical values of 10-3 particles per cubic centimeter. The mean free path of the particles is roughly 1016 m, or about one lightyear

• The Bullet cluster is at least 1 megaparsec in width 3,261,6366 lightyears.
• That means that normal baryonic particles collide over 3 million times to pass from one side to the other.
• Normal baryonic particles that collide heat up. Normal baryonic particles that heat up in the ICM produce X-rays that can be detected as in the rest of the Bullet Cluster.

Thus the amount of gas that did not collide is tiny (less than one part in a million and that is being generous). The outlying blobs are thus mostly weakly interacting gas, i.e. particles that collided but did not interact strongly.

If you cannot find any problems then you agree that these three observations are evidence that there is matter that does not interact like baryonic matter. This we call nonbaryonic matter.

 

[Michael Mozina]

No actually, I don't - as you can perfectly well tell from the posts I made at the start of this thread. You would do well not to misrepresent my views when you've obviously read what I said on the matter before.

My apologies ed. I was a little loose with the term 'you' (yet again).

I said there are theoretical reasons to think it might and that therefore it is a good idea to go and look for that, in order to test those theories.

I hear you.

The skeptic senses in me start twitching when we move from "I'm not sure how to explain that unidentified mass" to "dark matter emits gamma rays". There's no logical correlation that I can observe between the two, other than a pure leap of faith. There are many things that "might" cause gamma rays from distant objects in space. The most logical option to explain these types of emissions is the sun and the planets of the galaxy.

*If* these known sources come us short in explaining the gamma rays, it could be that we simply underestimate the number of stars in galaxies and we underestimate the number of smaller stars in particular. It "might' be caused by lots of things.

IMO "jumping to the conclusion" that a "new form of matter" is responsible for gamma rays from space is simply an "act of faith". It's never been seen before in our solar system to the best of our knowledge. If we observe the Fermi images however, one very obvious source of gamma rays that passes through the images is our own sun.

With all that "missing mass" to explain out there, I'm a lot more inclined to believe that we simply underestimate the number of light sources in a given galaxy due to the dust that tends to absorb a lot of the light.

 

[Michael Mozina]

Wrong. The "cores" and stars and the planets and asteroids and such would stay as galaxies. The blobs are not galaxies. They are gas.

OMG RC, you sure relied on the personal insult a lot in that post. I'll skip the line by line response and cut to the chase.....

Even if we assume that everything you said is 'true' as it relates to where "most" of the mass is located, you still have never resolved the core problem with your assumption.

*Some* of that "plasma' might indeed be "ionized" in some way. Most "plasmas" however are quite "dusty", meaning the protons and ions picked up an electrons somewhere and now it's a neutral hydrogen or helium or oxygen atom. Some of the "dust" may in fact be "charged" or ionized in some way, but surely not all of it.

There's no particular "great surprise" that neutral atoms that are sparsely spread out would "pass through" neutral atoms and even charged particles in the other plasma sheet. There's nothing that will move them off course short of a direct "hit" with another atom in the oncoming plasma sheet.

Now "some" of the "ions" will indeed "pick up electrons" and become attracted to charged particles in the oncoming stream, but not all the material is going to 'glow" in "x-ray", a relatively *high energy* part of the EM spectrum. It's really no great surprise that *some* material 'interacts' and some material "passes right on through". Much will depend on the charge of the particle and the trajectory of oncoming traffic. You really don't have any legitimate way to distinguish 'ordinary neutral particles" from any other type of "dark matter". In fact you don't need anything other than neutral ions to explain "dark matter" that will not necessarily "glow' in an x-ray spectrum unless it actually "collides" with an oncoming particle.

 

[Reality Check]

The skeptic senses in me start twitching when we move from "I'm not sure how to explain that unidentified mass" to "dark matter emits gamma rays".

The real problem is that you seem to interpret "dark matter emits gamma rays" as "dark matter does emit gamma rays".

What scientists are stating is that it may be possible to detect dark matter if it decays or annihilates to electron/positron pairs and these will emit gamma rays. Nobody is saying that dark matter will emit gamma rays (indirectly) and so might be detected.
Since it is possible that gamma rays may come from dark matter, it is a viable if small area of scientific research, e.g.
Possible Evidence For Dark Matter Annihilation In The Inner Milky Way From The Fermi Gamma Ray Space Telescope.
and
The Fermi Haze: A Gamma-Ray Counterpart to the Microwave Haze

 

[Michael Mozina]

http://chandra.harvard.edu/photo/2005/felines/

One more point RC....

The core of almost every galaxy containing a black hole will tend to contain fairly large quantities of iron. Such ions, even if charged, contain a *lot* of kinetic energy. Unless they directly interact with something in the oncoming traffic, they'll likely "pass on through" due to their mass and momentum.

You really can't tell from light years away what "dark matter" might be made of. It could be many things, including neutral iron atoms for all you know.

 

[Michael Mozina]

The real problem is that you seem to interpret "dark matter emits gamma rays" as "dark matter does emit gamma rays".

Unless it does, the cited papers you handed me are utterly meaningless and a great waste of time.

What scientists are stating is that it may be possible to detect dark matter if it decays or annihilates to electron/positron pairs and these will emit gamma rays.

If, if, if?????? If I have to "have faith" in a half dozen "properties" of "dark matter" which you cannot demonstrate, how is that not a "religion"?

Nobody is saying that dark matter will emit gamma rays (indirectly) and so might be detected.

Well, if they don't, what's the point of those papers?

Since it is possible that gamma rays may come from dark matter,

Anything is possible, but how "likely" is it? If you can't show it happened even one time on Earth, it's certainly not nearly as likely as say "electrical discharges" which emit gamma rays on Earth every single day, day in and day out.

it is a viable if small area of scientific research, e.g.
Possible Evidence For Dark Matter Annihilation In The Inner Milky Way From The Fermi Gamma Ray Space Telescope.
and
The Fermi Haze: A Gamma-Ray Counterpart to the Microwave Haze

What's the point of these papers if you aren't claiming that "dark matter" emits gamma rays? If that doesn't happen, your papers are pointless, and that's exactly what I think of them. Look at the assumptions and how they turned the whole thing into a curve fitting exercise with imaginary friends.....

We study the gamma rays observed by the Fermi Gamma Ray Space Telescope from the direction of the Galactic Center and find that their angular distribution and energy spectrum are well described by a dark matter annihilation scenario.

Well described by dark matter annihilation? Well described mathematical lipstick on a big time metaphysical pig. What annihilation?

In particular, we find a good fit to the data for dark matter particles with a 25-30 GeV mass, an annihilation cross section of ~9x10^-26 cm^3/s, and that are distributed with a cusped halo profile within the inner kiloparsec of the Galaxy.

In other words they simply "assumed" that some number would fit and they tinkered around with the numbers until they found one. Big deal. The whole thing is one giant *assumption* about dark matter being a "new" form of matter, and they made up the numbers to make the curve fit right. All that works fine and dandy when you never have to empirically demonstrate a word of it. What "annihilation" did we ever observe from such an even here on Earth? How many times does it happen in a solar system compared to say the times that Fermi is able to see gamma rays from the sun, or from Earth due to electrical discharges?

The whole thing was "made up" from imaginary matter, with imagined 'properties' and a lot of mathematical lipstick. Not a single word of it can be demonstrated via empirical physics. It's all one big "act of faith" on the part of the "believer" and the only thing even attractive about the whole thing is the mathematical lipstick. IMO you guys are "suckers" for any dizzy blond theory as long as it has bright red mathematical lipstick. It's still a metaphysical pig because never once did anyone demonstrate that.

A) new forms of matter exist.
B) new forms of matter exist at that energy state.
C) new forms of matter remain stable at that energy state for longer than a half millisecond
D) new forms of matter annihilate at all
E) new forms of matter annihilate at the rate specified.

The authors made at least 5 claims that they can't empirically demonstrate and I'm just supposed to ignore them because it has pretty lipstick?