Astronomers Make Important Dark Matter Discovery

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."

Re:Question.

[dreamchaser]

A small portion of it is rocks, dust, etc. Prevailing theories hold that much (most) of it is made up of non-baryonic matter which has yet to be observed.

Re:Question.

[SupremoMan]

Not at all sir. http://en.wikipedia.org/wiki/Dark_matter [wikipedia.org]This should enlighten you a bit.

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.

Re:Question.

[Anonymous Coward]

yes, dark matter is the unilluminated matter in the universe. It supposedly consists of both "normal matter" (i.e. protons, neutrons, electrons) which you could "shine a torch at" such as dead stars and planets which dont give off light and "other matter" such as neutrinos and as of yet undiscovered particles. This "other matter" would interact very weakly except through gravity, so if you were to "shine a torch at it" you wouldn't see anything. that's a brief answer, theres more info here: http://en.wikipedia.org/wiki/Dark_matter#Dark_matt er_composition [wikipedia.org] ("normal matter" is baryonic(i.e. contains protons and neutrons), "relativistically" refers to near-light speeds)

Think that's bad?

[jd]

In recent studies of deuterium in the galaxy, they're finding less than 1/25th of what they're expecting, and almost entirely in the wrong places. They therefore conclude that there must be MORE than what they expect, but in a place/form that is invisible.

Will Hannibal Lector please stop eating the brains of astrophysicists.

**SPOILER**

[drxray]

They're referring to the Bullet Cluster. It's a merging system where a small cluster is passing through a large cluster leaving a shockwave that looks like a bullet's wake, hence the name.
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)

Re:Question.

[wanerious]

By "not seen", we just mean that it doesn't *glow* like stars, not that it can't be detected at all. In fact, we detect it by the gravitational influence it has on neighboring luminous matter as well as lensing the light of background objects. We can study its large-scale nature and distribution fairly well, just not the composition or small-scale structure yet.

Re:Think that's bad?

[The Great Pretender]

There was a recent article in Discover [discover.com] that profiled a physist (Mordehai Milgrom) who had come up with modification on Newtons law to explain the planets orbits (forgive me, I'm a layman in this but it seems that dark matter started as a way to explain the weird plant orbits in extended galaxies - I encourage you all to correct me).

"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.

Re:**SPOILER**

[whitehatlurker]

Hmmm. That does make sense (after translation :-). The cluster [nyud.net]'s name (1E0657-56) is also used in the url on the NASA site (chandra.harvard.edu/photo/2006/1e0657/)

Nice visual demonstration that dark matter exists

[riptalon]

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:**SPOILER**

[mako1138]

Thanks for the explanation. I just looked at arXiv, and there are several relevant papers [arxiv.org] to be found.

The most relevant is probably http://arxiv.org/abs/astro-ph/0309303 [arxiv.org] .

Re:Think that's bad?

[bla]

yes, sir. i am not the parent, nor am i an astrophysicist, but i just saw it this afternoon on cnn.com

clicky [cnn.com]

Re:Not at all

[Alsee]

Congratulations, you have just argued that there are Ten planets. That Ceres should be a planet "because it already has years of tradition in the cultures".

Ceres was assigned a planetary symbol, and remained listed as a planet in astronomy books and tables for about five decades, until several other asteroids were discovered. You are arguing that Pluto should continue to be listed as a planet for the SOLE reason that it has the same "tradition in the cultures" for about seven decades.

[Ceres/Pluto] is merely the first known and most famous [asteroid/Kuiper object]. [Ceres/Pluto] was called a planet for a few deecades because at the time there was no better catagory to lump it into. [Ceres/Pluto] was considered an oddball misfit amongst planets for several very good reasons. However we then discovered that there are thousands more [asteroids/Kuiper object], and that rather than being some ill fitting oddball planet, [Ceres/Pluto] is actually a perfectly fit member of a different non-planet group. That [Ceres/Pluto] is actually a a perfect fit meber of the [asteroid/Kupier object] group in the [asteroid belt / Kuiper belt].

Just because [you/they] learned in elemantary school that [Pluto/Ceres] was a planet, and [you/they] never heard of [Kuiper objects /asteroids] at the time, is not a valid reason to teach the next generation of kids a blatantly incorrect grouping.

Just imagine if your teacher has taught you that there are planets and there are asteroids, and that Ceres clearly belongs in the asteroid group, but that we are going to test you and require you to say that Ceres is a planet simply because we inadvertantly taught that incorrect information to kids last year and we don't want to fix the tests or the text books?

The only difference is that new we need to teach kids taht there are planets, plus the asteroid belt with thousands of asteroids, and there's the Kuiper belt with thousands of Kuiper objects. Teach kids that *ALL EIGHT* planets were formed in, and all orbit in, a strict planetary plane. Teach kids that Kuiper objects are ALL snowballs of frozen gas, and that they did NOT formed in the planetary disk with the planets, and that they do NOT lie in the planetary plane (except perhaps by sheer chance). That Pluto is a Kupier object because it lies out in the Kuiper belt, and because it is a snowball of frozen gas, because it did not form in the planetary disk with the planets and that it does not orbit in the disk of planets.

Pluto is not an oddball off kilter snowball of a planet outside the planetary disk, Pluto is simply an ordinary Kuiper object. The only noteable think about Pluto is that it is the first and most famous Kupir object, just as Ceres was the first and most famous asteroid.

"We know that dolphins are really mammals, but we 'grandfathered in' dolphins as an honourary member of fish".

-

Re:Think that's bad?

[TrekkieGod]

I'm not an astrophysist, nor was I involved in the conversation before now, but I did read your linked article :)

Thanks for posting it, btw. I was taking what the parent said for granted, and it sounded pretty bad, but now it looks like it was a combination of bad reading comprehension and badly worded writing. The article you linked to at least, doesn't claim scientists are finding less deuterium than they expected and therefore expect more. Quite the contrary, they're finding a lot more than they expected, and thus are deciding that their theories need to be changed. I quote:

scientists had assumed that at least a third of the primordial deuterium present in the Milky Way was destroyed over time as it cycled through the stars...but FUSE found deuterium exists in amounts less than 15 percent below what was there originally.

So, they thought there were massive amounts of deuterium was "destroyed" and that not as much was left. Destroyed is a pretty bad way of describing it, but they allude to it in the article that what they mean by it is, "was transformed into heavier elements by stellar fusion." Instead, they're finding out that the amount of deuterium in the galaxy now is only about 15% less than what they thought was the original amount available. They also mention it being in unexpected places, or rather, not distributed evenly, which they find unusual according to current theories.

Nothing to complain about here. Seems to me that the astrophysicists still have their brains intact, and realize their theory needs to be tweaked if it doesn't match the evidence.