90% of the Universe Found Hiding In Plain View 279
The Bad Astronomer writes "As much as 90% of previously hidden galaxies in the distant Universe have been found by astronomers using the Very Large Telescope in Chile. Previous surveys had looked for distant (10 billion light years away) galaxies by searching in a wavelength of ultraviolet light emitted by hydrogen atoms — distant young galaxies should be blasting out this light, but very few were detected. The problem is that the ultraviolet light never gets out of the galaxies, so we never see them. In this new study, astronomers searched a different wavelength emitted by hydrogen, and voila, ten times as many galaxies could be seen, meaning 90% of them had been missed before."
I RTFA... (Score:4, Informative)
Re:Dark stuff? (Score:5, Informative)
Does this account for any missing mass and/or dark matter?
FTFA: "...this has nothing to do with dark matter."
Re:Implications for dark matter estimates? (Score:5, Informative)
From TFA:
"I'll note: this has nothing to do with dark matter. As it happens, 90% of the matter in the Universe is in a form that emits no light, but affects other matter through gravity. We know it exists ... locally, in nearby galaxies and clusters of galaxies, too. This new result doesn't affect that, since the now un-hidden galaxies are very far away, like many billions of light years away. They can't possibly affect nearby galaxies, so they don't account for dark matter."
Re:90%, not so coincidentally... (Score:3, Informative)
Actually, it is just a coincidence. This has nothing to do with dark matter or dark energy.
This is an observation of distant galaxies. The theory of dark matter comes from observations much closer to home, within this galaxy. It's designed to explain why the galaxy doesn't fall apart; it has too little matter for gravity to do it on its own.
Since then, other independent observations have confirmed that galaxies have more matter than we can see.
Dark energy is also completely different. It comes from the observation that the far-away galaxies appear to be accelerating. What they're observing here is mass, not motion. (Yeah, same thing, but only at really high speeds, and this isn't that, either.)
They're finding a lot more galaxies, which is great, but it doesn't in and of itself radically change anything about how we view the fundamental theories of physics.
Re:Implications for dark matter estimates? (Score:5, Informative)
Absolutely wrong. TFA even states this means nothing for dark matter, we knew that these galaxies were out there, we just hadn't spotted them yet. Besides, we've seen dark matter much closer to home. When galaxies collide, the gas pressure stops the regular matter, while the dark matter keeps moving along at the same speed. The dark matter has mass, so it creates a gravatic lens. We have seen these lenses, with no visible matter to create them, when galaxies collide.
Redshift? (Score:5, Informative)
Re:Implications for dark matter estimates? (Score:5, Informative)
Dark matter isn't just matter that isn't lit up (that was one of the original theories, but has since fallen to the wayside), it is matter that is fundamentally different and doesn't appear to interact with regular matter at all, except gravitationally.
Re:Dark stuff? (Score:2, Informative)
Because estimates of the density of galaxies in the universe have been based on the volume that is closer to us and therefore relatively more visible, and did not suffer from the problem described. The assumption had been that the universe far away is, in a general manner, similar to the universe nearby, on the usual principle that there is nothing special about the place that we are. When the density of remote (and very early) galaxies fell off, it was assumed to be more likely to be an observational artefact than a genuine falling off. Which is what the article says has now been proved to be the case. Estimates of the number of galaxies were based on the bits we can see easily, not the bits we can hardly see.
Re:Deez Nuts are Hiding in Plain View (Score:2, Informative)
Re:Implications for dark matter estimates? (Score:4, Informative)
it is matter that is fundamentally different and doesn't appear to interact with regular matter at all, except gravitationally.
More specifically, it doesn't appear to interact electromagnetically. Which just happens to exclude all of our direct detection methods (i.e. telescopes).
One candidate for dark matter is the neutralino, which is predicted by Supersymetric Theory and is basically a neutrino but heavier, and like a neutrino interacts through the Weak Interaction which allowed us to find neutrinos, and maybe even actual dark matter [arstechnica.com].
Re:Next step: a better name (Score:4, Informative)
Re:Implications for dark matter estimates? (Score:5, Informative)
I knew about the fudge factor we needed to get the equations to work - I didn't know we have actually seen something like that.
It was never a "fudge factor" to make the equation of gravity "work". It was a prediction of the already extremely well-working equation. Not "Oh noes gravity is broken, we need 'dark matter' to fix it." Rather "Huh, gravity implies there is a mass here that we can't see with our electromagnetic detection devices".
Think of it this way. You're walking around a room blindfolded with a cane that has a pressure sensor on the end that uses a voice synthesizer to tell you the readings. You notice that all along a large flat plane the pressure sensor detects pressure equal to that with which you push. Newton's 3rd Law tells you that for this to happen, something must be pushing back with equal force. Something like a wall.
Now, do you say that the wall is a fudge to make Newton's 3rd Law work?
Or do you say that Newton's 3rd Law implies that there is a wall there?
I mean you might as well say that the existence of the Sun is a fudge to make electromagnetic and gravitational equations work.
I'm not trying to rag on you or anything (I mean you said 'thank you' for evidence after all), just trying to clear up a misconception that I think has lead to a lot of unnecessary skepticism of dark matter.
Re:A Nice Step (Score:2, Informative)
So they found the dark matter? If so, this is astounding.
No. This is making the dark-matter theorists look bloody foolish. All those convoluted theories and reality distorting models are now rubbish.
Re:Implications for dark matter estimates? (Score:3, Informative)
Those observations actually *ARE* scientific evidence for dark matter. Unfortunately, they don't constrain what it could be very tightly. The current dark matter theory can shift to something else without changing it's name (and has in the past).
E.g., what is the temperature of the dark matter? For awhile there was argument between the hot dark matter interpretation and the cold dark matter interpretation...but both camps agreed it wasn't made of protons or neutrons and didn't radiate in the infrared.
What is it?? Who knows. I'm not really convinced it's particulate. But I don't know what the alternative could be.
(Caution: IAMNAAP [I am not an AstroPhysicist])
Re:Next step: a better name (Score:5, Informative)
Actually it's the Overwhelmingly Large Telescope. [owlpages.com]
Re:I Smell Another Apple Ad (Score:5, Informative)
There's a big fat gap between what the calculations say the rate of galaxy formation should be, and what it is actually observed to be. This new observation accounts for 90% of that rate.
Re:A Nice Step (Score:4, Informative)
No, I meant quantum leap as in literally a quantum leap.
An electron dropping from orbital L3 to L2 instead of L2 to L1 is exactly what sends out photons of a more detectable temperature.
Re:Way to go (Score:5, Informative)
I’ll note: this has nothing to do with dark matter. As it happens, 90% of the matter in the Universe is in a form that emits no light, but affects other matter through gravity. We know it exists, and you can find out why here. We know it exists locally, in nearby galaxies and clusters of galaxies, too. This new result doesn’t affect that, since the now un-hidden galaxies are very far away, like many billions of light years away. They can’t possibly affect nearby galaxies, so they don’t account for dark matter.
This will change the ratio of luminous matter:dark matter but not eliminate dark matter entirely.
Not that you said that it would necessarily get rid of dark matter, but it was a conclusion that suggested itself from the summary's wording.
Re:Implications for dark matter estimates? (Score:3, Informative)
No, its neither an assertion, nor a fact in the observational sense, it is a statement that is true by definition. If something can interact with things in our universe then it is in our universe, in the same sense that if you can add 1 to a number and get an integer, that number is also an integer.
Re:A Nice Step (Score:3, Informative)
Re:Implications for dark matter estimates? (Score:2, Informative)
And here's the thing about scientific theories - they come with varying degrees of confidence. Being a scientific theory does not infer we are necessarily as sure as we can possibly be - it's just perhaps the best current explanation for the evidence (and facts) we have.
And it's entirely possible (and indeed healthy) that we have multiple ones at the same time.
Re:Implications for dark matter estimates? (Score:3, Informative)
Weakly interacting does not mean that it interacts via the weak interaction.
That's right that is a possible English interpretation of "weakly", which is why what I quoted explicitly explained that the acronym "Weakly Interacting" came from their "expectation of the weak interaction" at the Electro-weak [wikipedia.org] scale, to make it clear they don't mean "weak interaction" as in "not very strong", but rather the Weak Force, one of the unified fundamental forces of the Standard Model.
That is why direct detection experiments look for elastic interactions between a dark matter particle and a nucleus in the experiment. This is why you have to minimize the background as much as possible.
It's because the weak interaction is relevant only at such a close distance between particles that a neutrino-like particle has to basically directly impact a nucleus, which is a ridiculously tiny target in ordinary matter where nuclei are held apart by the electromagnetic force. It's mostly empty space to uncharged particles. That's why the probability of an interaction in an object the size of one of our detectors is so low that it takes years of measurement to be sure you've really seen one, and a deep hole to make sure it's not overwhelmed by noise.
Read the Ars and the Berkeley article, they explain all the findings there. Yes the actual discovery is still only a modest probability, but it's clear the theory it's based on is a mass-full particle that interacts through the Weak Force.
Re:Mod parent down (Score:4, Informative)
It is imprecise to say physicists indicate there should be much more mass in the universe. What they say is that there is mass missing in every galaxy which implies it is missing from the universe but only on a galaxy by galaxy basis. Dark matter is necessary to explain why galaxies form. In other words the "missing" matter is in each and every galaxy. Discovering more galaxies doesn't affect that issue.
When I was a physics major in the dark ages they were just beginning to notice that computer simulations based on observed stellar quantities and masses had the annoying property of never resulting in galaxies. In subsequent years it was computed that the needed mass for galaxy formation wasn't off by a little but actually by a huge factor.
Eventually some observations of gravitational lensing have provided more evidence that there was huge amounts of mass measured in this indirect fashion that was simply not seen by exhaustive charting of the observed stars.