So we've found the missing "dark matter"?

[fizzy]

Hubble Reveals Observable Universe Contains 10 Times More Galaxies Than Previously Thought

http://hubblesite.org/newscenter/archive/releases/2016/39/full/Change the data to fit model ?

 

[phinds]

Hubble Reveals Observable Universe Contains 10 Times More Galaxies Than Previously Thought
http://hubblesite.org/newscenter/archive/releases/2016/39/full/
Change the data to fit model ?

This has nothing to do with dark matter. Why do you think it does?

 

[Charles Kottler]

This has nothing to do with dark matter. Why do you think it does?

I'll admit, my first thought on seeing the article was "well there's at least some of the missing matter". On reflection though, I guess the 'missing' matter is within galaxies rather than between or beyond them.

 

[phinds]

I'll admit, my first thought on seeing the article was "well there's at least some of the missing matter". On reflection though, I guess the 'missing' matter is within galaxies rather than between or beyond them.

Exactly. Galaxies, as far as is currently known/believed, formed BECAUSE dark matter clumped somewhat in the early universe and thus became the seeds of galaxies.

I did not find the article convincing, but it SEEMS to be fact-based so maybe that's just me.

 

[fizzy]

I'll admit, my first thought on seeing the article was "well there's at least some of the missing matter". On reflection though, I guess the 'missing' matter is within galaxies rather than between or beyond them.

who said dark matter could not be between galaxies? I thought that this was basically proposed as a fix for the expansion of the universe not matching models.

 

[phinds]

who said dark matter could not be between galaxies? I thought that this was basically proposed as a fix for the expansion of the universe not matching models.

I've not heard anyone say dark matter does not exist in intergalactic space any more than normal matter not existing in intergalactic space, but the density of dark matter (and normal matter as well) is believed to be MUCH higher around/inside galaxies.

I was not aware that the expansion model needs any fixing, but I,m no expert on the subject.

 

[Charles Kottler]

who said dark matter could not be between galaxies? I thought that this was basically proposed as a fix for the expansion of the universe not matching models.

Dark matter was initially proposed to explain the rotational speed of stars within a galactic plane, but shortly after was applied to galactic clusters exhibiting similar properties. The version of the article I read did not go into enough detail to say whether the 'new' galaxies are inside clusters, which would count against dark matter, or not.

 

[fizzy]

So if we invent 10x more galaxies there will a lot less need to invent dark matter. That is what I meant about "finding" dark matter. I did not mean we had detected the undetectable, more like we found alternative frig factor.

Hypothetical galaxies instead of hypothetical dark matter.

 

[phinds]

Dark matter was initially proposed to explain the rotational speed of stars within a galactic plane, but shortly after was applied to galactic clusters exhibiting similar properties.

yes.

The version of the article I read did not go into enough detail to say whether the 'new' galaxies are inside clusters, which would count against dark matter, or not.

no, it would NOT count against dark matter, as far as I can see. You still need dark matter as the seeds of galaxies.

 

[phinds]

So if we invent 10x more galaxies there will a lot less need to invent dark matter. That is what I meant about "finding" dark matter. I did not mean we had detected the undetectable, more like we found alternative frig factor.

Hypothetical galaxies instead of hypothetical dark matter.

I disagree. New galaxies have nothing to do with dark matter. How would new galaxies explain the Bullet Cluster?

 

[fizzy]

I disagree. New galaxies have nothing to do with dark matter. How would new galaxies explain the Bullet Cluster?

So if we keep the dark matter plus the 10x more unseen galaxies we'll need 10x more dark energy to accelerate it outwards.

 

[phinds]

So if we keep the dark matter plus the 10x more unseen galaxies we'll need 10x more dark energy to accelerate it outwards.

Don't know if that's true or not. Also, as I said in post #4 I'm still not convinced that this report of 10X is correct.

 

[Chalnoth]

So if we keep the dark matter plus the 10x more unseen galaxies we'll need 10x more dark energy to accelerate it outwards.

No. Not at all.

This report, no matter how accurate it is, says nothing at all about the average density of matter/energy in the universe, which has already been measured to within a few percent through CMB observations.

 

[phinds]

Don't know if that's true or not. Also, as I said in post #4 I'm still not convinced that this report of 10X is correct.

Now that I think about it, I realize that my having any doubt at all about that (needing more dark energy) not being the case was very misplaced and basically brain dead.

We have an existing amount of dark energy and it is known to within a fair degree of accuracy that it is causing the existing expansion, so REGARDLESS of the amount of matter, we obviously have exactly the right amount of dark energy to cause the observed expansion for the existing amount of matter.

 

[awcrowe]

i just read the article in space.com. It says in the last pararaph 10x more in the distant past. the first thought i had was. Is this 10x more matter also. It does not seem this is the case. only that there were more galaxies that merged into the same amount of mass that we know there is in the universe today.
Need to reaed more thought.

 

[patmurris]

I'm not sure what they revealed... and how to interpret it.

"In analyzing the data, a team led by Christopher Conselice of the University of Nottingham, U.K., found that 10 times as many galaxies were packed into a given volume of space in the early universe than found today. Most of these galaxies were relatively small and faint, with masses similar to those of the satellite galaxies surrounding the Milky Way. As they merged to form larger galaxies the population density of galaxies in space dwindled."

Sounds like in the early universe there were more smaller galaxies which then gradually merged to form the larger ones we see 'today'. That does not mean more matter - only its distribution changed over time.

Edit: How this discovery does affect current matter/energy estimates is unclear to me.

 

[fizzy]

Thanks for all the replies. It seems rather unclear what they are proposing to have modeled but if it is just 10x the number but smaller bits, without changing the overall mass, it seems rather an empty claim that is being misrepresented because it seems like a dramatic change to existing ( alleged ) knowledge .

There are also press articles claiming "up to 20x" which is starting to just look like clickbait. The term "up to" is usually a good indicator or sensationalism and not science.

We have an existing amount of dark energy and it is known to within a fair degree of accuracy that it is causing the existing expansion,

Isn't the expansion the reason for the hypothesised existence of DM, thus by definition it is the "right" amount?

so REGARDLESS of the amount of matter, we obviously have exactly the right amount of dark energy to cause the observed expansion for the existing amount of matter.

... and so, if we change the amount of matter we believe is there, we will need to change the hypothesised amount of DE. No?

I'm inclined to agree with more small bits because if they were saying 10x more mass it would be causing a lot of ( gravity ) waves in the community.

 

[Chalnoth]

Thanks for all the replies. It seems rather unclear what they are proposing to have modeled but if it is just 10x the number but smaller bits, without changing the overall mass, it seems rather an empty claim that is being misrepresented because it seems like a dramatic change to existing ( alleged ) knowledge .

There are also press articles claiming "up to 20x" which is starting to just look like clickbait. The term "up to" is usually a good indicator or sensationalism and not science.

Yes, essentially. This is the norm with science reporting in the popular media.

Isn't the expansion the reason for the hypothesised existence of DM, thus by definition it is the "right" amount?

Not exactly. The expansion rate can be used to determine the total matter density (dark + normal), but isn't sensitive to dark matter alone. Dark energy is primarily detected through the rate of expansion of our universe over time.

Dark matter is primarily detected through its effect on structure in the universe. Our most sensitive measurements of the overall dark matter density come from the CMB.

... and so, if we change the amount of matter we believe is there, we will need to change the hypothesised amount of DE. No?

It's not really possible. At this point, we have too many independent measurements of the expansion rate across a broad range of redshifts. The estimated dark matter density might shift by a few percent in one direction or the other, but not by any large amounts.

 

[fizzy]

Thanks for those explanations.

Our most sensitive measurements of the overall dark matter density come from the CMB.

But CMB is an incredibly noisy measurement and results derived therefrom seem to be crude fits to a sparse number of data points huge error bars.

How do we conclude results to within 'a few percent' from that kind of data?

 

[phinds]

But CMB is an incredibly noisy measurement and results derived therefrom seem to be crude fits to a sparse number of data points huge error bars.

That is exactly the opposite of what I have always understood to be the case. Do you have a reference for that statement?

 

[Chalnoth]

But CMB is an incredibly noisy measurement and results derived therefrom seem to be crude fits to a sparse number of data points huge error bars.

It's the complete opposite. Because the CMB is so incredibly bright, and because the physics that are relevant to the production of the CMB are so simple, it's an incredibly accurate probe of certain features of our universe.

In this specific instance, as of the latest Planck results the CMB determines the average dark matter density of our universe to within about 2%.

For example, most astronomical observations are plagued by the fact that there's a lot that we're not seeing: do we not see certain galaxies because they aren't there, or because they were too dim for detection? Incidentally, this is what motivated the news post in the OP: a model of how many galaxies are there that are too dim to see.

The CMB doesn't have this problem, because it has nearly uniform brightness in every direction on the sky. There's no worry that there might be parts of the CMB we're not seeing. Plus, at certain frequencies, the small differences in temperature from place to place on the sky are brighter than anything else across more than 90% of the sky. To get very accurate measurements, we can use measurements of the CMB across a range of frequencies to subtract these foreground signals, in addition to just not using data from the small area where the foregrounds are really bright (e.g. the center of our galaxy, radio quasars).

The physics that produced the CMB are also really simple: you can use simple integrals to model what the temperature differences should be (a modern computer can calculate the predicted statistical properties of the CMB given a model to very high accuracy within just a couple of seconds). This is as opposed to galaxy formation, which is a monstrously complicated phenomenon that is often modeled using complex N-body simulations and lots of questionable approximations.

 

[Drakkith]

But CMB is an incredibly noisy measurement and results derived therefrom seem to be crude fits to a sparse number of data points huge error bars.

The error bars for the CMB spectrum are extraordinarily small. The sources I've seen consistently say that they are too small to see on a graph unless greatly exaggerated.

 

[Drakkith]

Thread unlocked.

 

[Igael]

Could you please tell me what does mean the word confidence in page 10 in the Planck 2013 results. XVI. Cosmological parameters

We give best fit parameters (i.e. the parameters that maximise the overall likelihood for each data combination) as well as 68% confidence limits for constrained parameters.
​

 

[Vanadium 50]

Could you please tell me what does mean the word confidence

https://en.wikipedia.org/wiki/Confidence_interval

 

[Igael]

https://en.wikipedia.org/wiki/Confidence_interval

Thank you very much.