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Astronomers Make Important Dark Matter Discovery
Posted by
Zonk
on Tue Aug 15, 2006 12:26 PM
from the matter's-goth-sister dept.
from the matter's-goth-sister dept.
saudadelinux writes "To quote a press release on NASA's site, astronomers using the Chandra X-ray Observatory have discovered 'how dark and normal matter have been forced apart in an extraordinarily energetic collision.' There will be a briefing at noon, August 21 ET, on this discovery, with streaming media provided by NASA, and some details of the research posted on Harvard's Chandra site just beforehand."
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Dark Matter — "Alternative Gravity" Team Responds 215 comments
An anonymous reader writes, "Following previous results, an international team of astronomers answers, defending the case for a modification of the theory of gravity. This article presents an alternative to dark matter and states constraints on the neutrino mass. In short, dark matter is still not a necessity, provided that neutrinos weigh 2eV. This is allowed by what we currently know and should be tested in the KATRIN experiment in 2009."
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Nothing to see, move along (Score:5, Insightful)
Re:Nothing to see, move along (Score:5, Funny)
Not at all. It's got plenty of mass, it's just dark.
Parent
Re:Nothing to see, move along (Score:5, Funny)
Like Oprah.
Parent
NOOooo...!!! (Score:5, Insightful)
I can't count how many times I've read something on Slashdot about something cool that's already happened, just barely, and said "Once again, information I could have put to much better use YESTERDAY!!!
Zonk, pay no attention to the criticism; I for one WELCOME some in-advance info (might even vote for it for "overlord"...)
Parent
Together again (Score:4, Funny)
Measure DM (Score:5, Funny)
Please record (Score:5, Funny)
Warp 1 Mr. Sulu (Score:4, Funny)
Cool! Now I can get started on my warp engine!
Yours, Zephram Cochrane
Re:Warp 1 Mr. Sulu (Score:4, Funny)
Parent
The importance (Score:4, Funny)
It's not "dark" matter (Score:5, Funny)
We like to refer to it as "matter of color."
Dark Matter (Score:4, Funny)
Nice visual demonstration that dark matter exists (Score:5, Informative)
I would assume this is the Bullet Cluster (1E 0657-56) combined X-ray and weak lensing results that Maxim reported [harvard.edu] at the Six Years of Science with Chandra Symposium [harvard.edu] last November. The interesting bit is that in this merging galaxy cluster the hot gas (~ 30%) has collided and been brought to a stop while the dark matter (~ 70%) haloes which are collisionless have passed through each other and are offset from the gas. By plotting the weak lensing image (which shows the total mass) over the X-ray image (which shows the baryons/gas) you can therefore see the existance of dark matter, since the mass is in a totally different place from the gas you can see in the X-ray. This isn't a fundamentally new result but it is a very nice visual demonstration of the existance of dark matter. Rotation curves of galaxies and the temperatures of galaxy clusters had proved it already but with this you don't need to do any maths you can just see it. Page 25 of this 6.5 MB pdf [harvard.edu] is the one you want for the image.
Re:Question. (Score:5, Informative)
Parent
Re:Question. (Score:5, Funny)
Humans, at least alive ones, are not at zero degrees K, and therefore radiate energy, not much, but some. We might be said to be dim matter.
http://en.wikipedia.org/wiki/Dark_matter [wikipedia.org]This link will tell you more.
Parent
Re:Question. (Score:5, Informative)
In cosmology, dark matter refers to matter particles, of unknown composition, that do not emit or reflect enough electromagnetic radiation (light) to be detected directly, but whose presence may be inferred from gravitational effects on visible matter such as stars and galaxies.
It's a blanket term used for stuff in the universe we think is there but haven't seen because we can not detect it's presence.
Parent
Re:Question. (Score:5, Insightful)
We look for explanations of what's going on, not just saying "it's God. Don't go there." Think of dark matter as a placeholder, not the end product. Over time, we should find a reasonable explanation of what's causing the discrepancy, at which point it will just become part of the "normal" physics.
Parent
Re:Question. (Score:4, Funny)
Apparently, when you seperate dark matter from normal matter you get an extraordinarily energetic collision, whereas when you seperate a Christian from God you get a rational thinking being.
Parent
Re:Question. (Score:5, Insightful)
Religionists, OTOH, believe in a Supreme Being a priori, and attribute whatever they cannot otherwise explain to the "mysterious ways" of the divine. The edifice of cosmology would withstand the discovery that there is no dark matter. Would religion be able to withstand the discovery that there is no God?
Parent
Re:The whole day? (Score:5, Funny)
August 21 Eastern Time? Wow, great.
This is news to announce there will be news at a later date.
the future will be here, any day now
Parent
Re:Typo in title (Score:4, Funny)
Parent
Not at all (Score:5, Insightful)
It's, in a nutshell, about science: attempting to actually classify and understand the universe. Just proclaiming "ok, I hereby do dub Pluto a planet" is ok for everyday life, but a bit too vague for science. It's like you can talk generically about "radiation" in casual conversation or in super-hero comics, but to a scientist that's uselessly vague. A scientist will be more interested in what _kind_ of radiation (i.e., the exact particle), at what energies, etc.
The same happens in astrophysics. You can't just say "ooh, that's a pretty star", because that doesn't give you much to work with. Is it a planet? An asteroid? A comet? A star? A nova? A white dwarf? What? There are very good reasons to split hairs there, because out of such splitting hairs comes the understanding of what they are and how they work.
E.g., from the splitting of hairs as to how we classify stars came such categories as "white dwarf." In turn, that let us wonder about how big a white dwarf can be, which gave us the Chandrasekhar limit. In turn that told us that when a star goes over (actually it later it turned out that when it's just right under) that limit, it goes *KABOOM* in a spectacular Type Ia supernova. Since it happens at the exact same point, it tells us that every Type Ia supernova is exactly the same as any other one. Which in turn lets us use them to measure distances and velocities in distant galaxies. And from those came a bunch of other astrophysics stuff.
_That_ is why for science it's important to worry about such distinction. Sure, you can get through your everyday life without ever worrying about the difference between Pluto and an asteroid, or between a Type Ia and a Type 1b supernova. But for scientists, it's an entirely different situation.
The informal proclaiming which is what also doesn't scale. When you deal with a whole universe worth of stuff, you have a continuum of things, ranging from individual nuclei all the way to the super-massive black holes in the centre of galaxies. And there are trillions of trillions of them. You can't just go proclaiming for each and every single one of them if it's a planet, an asteroid, or what. You need some rule you can apply there.
Parent
**SPOILER** (Score:5, Informative)
Dark Matter is collionless, i.e. the DM from the smaller system hasn't been slowed down by the collion and just zooms through. The gas is slowed down. So, the DM and gas are no longer in the same place. We can see the gas in an X-ray telescope (Chandra) and detect the mass by the gravitational lensing effect on the background galaxies.
This is the first time that this has been shown, and it basically disproves the entire category of theories that DM is an illusional caused by us not understanding the action of gravity at long ranges (MOND).
Abstract from a conference talk about this. [cosis.net] (PDF)
Parent
Re:**SPOILER** (Score:5, Informative)
The most relevant is probably http://arxiv.org/abs/astro-ph/0309303 [arxiv.org] .
Parent
Re:Think that's bad? (Score:5, Informative)
"Mordehai Milgrom never wanted to be a heretic. Twenty-five years ago, while poking around for a meaty research problem, he found one that changed the course of his career--and that might yet transform our most fundamental understanding of the universe. His ideas, long relegated to the fringes of physics, where all but cranks fear to tread, have finally become too intriguing for his mainstream colleagues to ignore. Milgrom's heresy? He denies the existence of dark matter, the shadowy and thoroughly hypothetical stuff generally held to make up 80 percent or more of all matter in the universe. Even though dark matter has eluded all attempts at detection, most cosmologists are convinced it must be out there."
So potentially there may not be any dark matter and the vast money being spent on it's pursuit is being wasted. For the record I don't believe in string theory either. I have to say that I would love to subscribe to the simplicity of Milgroms ideas, but it's just a gut check that fitting the theory to the data is better than creating a fudge factor - which dark matter ultimately seems to be.
Parent