Slashdot Mirror
Dark Matter Discovered
sebFlyte writes "Wired is reporting that scientists have come up to a solution as to where all the matter in the universe actually is. Experiments being done with Chandra, NASA's X-ray telescope have shown up a likely candidate for the solution of the dark matter problem. There are massive quantities of Baryons in a super-heated gas cloud several hundred million light years away."
There are massive quantities of Baryons in a super-heated gas gloud several hundred million light years away."
Which, IMHO, is a damn fine place for them to be, rather than here.
The absorption pattern, as detected by Chandra, is consistent with interference caused by carbon, neon, nitrogen and oxygen ions -- in other words, baryons.
It's really a neon sign on Frogstar World B announcing the construction of a restaurant to be constructed on this location in several billion years and reservations are welcome.
"Assuming that what we see is a standard portion of the universe, we extrapolated the data and derived the volume density (of baryons in all the clouds) -- and it's consistent with 50 percent," said astronomer Fabrizio Nicastro, of the Harvard-Smithsonian Center for Astrophysics and lead author of the study.
Later a two-headed, three-armed man entered and ate a piece of fairycake and destroyed their model.
Whereas baryons account for 4 percent of the total matter and energy in the universe, dark matter is thought to make up 23 percent. The remaining 73 percent of the so-called matter-energy budget consists of what scientists call "dark energy." This energy acts like an anti-gravitational force that, in theory, is causing the universe to expand rather than contract.
And here I thought it all existed somewhere along Lucas Valley Road and explained the Jar Jar character and Episodes I-III...
A feeling of having made the same mistake before: Deja Foobar
And would this "superheated gas pocket" perchance reside in Nibbler's lower intestinal tract? ;D
In case anyone's wondering what a baryon is...
http://en.wikipedia.org/wiki/Baryon
I don't see anything??
Here's a picture.
They found some of the ordinary matter that has gone unaccounted for, not dark matter. Read the article.
CDE open sourced! https://sourceforge.net/projects/cdesktopenv/
"There are massive quantities of Baryons in a super-heated gas gloud"
Google wants to know if you mean "gas cloud".
Wired is reporting that scientists have come up to a solution as to where all the matter in the universe actually is.
WIRED also said that "Push is the next Big Thing."
In physics we don't call it dark matter. We call it "make the theory fit the data" matter.
The summary is not correct (big surprise there) in that this is a confirmation of a long-suspected theory as to where the missing ordinary (baryonic) matter in the universe is. This does not solve the dark matter problem at all.
9
Read more at the press release from the Chandra team at Marshall: http://www.spaceref.com/news/viewpr.html?pid=1604
Dark matter is yet another topic altogether, as is the even more elusive dark energy.
They are extremely interesting for anyone fascinated with physics.
Creative Demolition
This should be "Missing Matter Discovered" not "Dark Matter Discovered"
They HAVE NOT found dark matter, they've found the 'missing matter' as the article says. They have found a clue as to the dark matter, as a result of the discovery.
Although discovering the dark matter would be much cooler, (yeah I was excited when I read the title).
[rant] Why is it the only 3 times I've 'emailed the on duty editor' before publishing, I've been ignored and the mistakes gone through?? [/rant]
Windows in 6 Bytes (IA-32) : 90 90 90 90 CD 19
"Baryons, along with mesons, belong to the family of particles known as hadrons, meaning they are composed of quarks. Baryons are fermions composed of three quarks, while mesons are bosons composed of a quark and an antiquark."
Wikipedia cleared that one up nicely!
-=test-sig_0.1.5(NoWhitespaceVersion)=-
In other words, if regular stuff is about 5% of the energy density of the universe, with dark matter at about 20%, and dark energy at about 75% -- the stuff in this story comes into that 5%, ie, regular stuff and not dark matter.
Here's what I do: Bitty Browser & Andromeda
Tachyons are in fact hypothesized faster-than-light-particles, appearing for instance in certain string theory scenarios.
:-)
But baryons are by no means the counterpart to tachyons. All known elementary particles in the universe are either fermions (particles with spin in integer multiples of 1/2) or bosons (particles with integer spin). Bosons include the photon, the gluon and many others. The fermions are further subdivided into leptons and quarks. Leptons include the electron and the electron neutrino among others. Baryons are particles made up of three quarks, and are fermions and include among others, the proton and neutron, which are the most commonly found baryons in nature, since all heavier baryons normally decay.
Two quarks (fermions) can combine to form mesons, which are in fact bosonic in nature (since two quarks with spin half combine to form a particle with integer spin).
Hope that confused the issue a little
A bit more on-topic: Finding baryons in this amount is a big deal, since baryon has previously been suspected to primarily exist in galaxies, and only in small amounts outside galaxies. While it by no means doesn't solve all problems of cosmology, it is a big help.
So they say they've found the missing matter, but nowhere in the article do they actually tell us where all the missing socks went. Sure sounds like a scam to me!
> > In case anyone's wondering what a baryon is...
> > http://en.wikipedia.org/wiki/Baryon
> In case anyone's wondering what slashdot is...
> http://www.slashdot.org/
In case anyone's wondering why the hell am I wasting my time so pointlessly.... I have no life.
They reversed the anti-proton to tachyon ratio in the main deflector array after flooding it with a plasma burst diverted from the warp core and then polarising it by reinforcing the nucleon field.
Drill baby drill - on Mars
Assuming that what we see is a standard portion of the universe
An astrophysicist, a physicist, and a mathematician are attending a conference in Scotland. During a break, they take a walk through some of the countryside, and come upon a black sheep.
"Aha," exclaims the astrophysicist. "I had no idea that all sheep in Scotland are black."
The physicist looks at her colleague in disbelief. "All sheep in Scotland are black? Are you nuts? We've only seen one sheep!"
The mathematician interrupts. "And only one side of that sheep."
Which is what they're constantly doing. I heard the theories in my astronomy class. There's plenty of them, such as brown dwarves just drifting around out there. How do you explain them? Well some star has a vector or some light appears bent (lens effect) and it's figured there's some large enough object out there not emitting light which is doing it. And who's to say it isn't large amounts effectively of bits the size of pea gravel drifting around?
In other words, if regular stuff is about 5% of the energy density of the universe, with dark matter at about 20%, and dark energy at about 75% -- the stuff in this story comes into that 5%, ie, regular stuff and not dark matter.
Dark matter is, as I understood, matter which isn't emitting some radiation, i.e. visible light or gamma rays. It's predicted, because without something being somewhere a number would be +0.0000150 instead of +0.0000146 and we can pretty much drop the old Intel Pentium jokes.
A feeling of having made the same mistake before: Deja Foobar
Turns out it was behind the sofa cushions all along.
"Win treats sysadmins better than users. Mac treats users better than sysadmins. Linux treats everyone like sysadmins."
Obviously that's where the bulk of all the Univere's matter is. Each pound of the stuff weighs 10,000 pounds.
First, I had to look up "tachyon". You are right, tachyons are apparently particles that travel faster than the speed of light. I've only heard the term from Star Trek, and for the time being that's where these particles are from - the realm of (science) fiction. I've certainly never had them mentioned in class!
Baryons are not the counterpart to tachyons. Baryons are simply particles that are made up of quarks. The two best known examples are neutrons and protons, which make up virtually all of the stuff you own. Yes, baryonic matter is pretty much everything we interact with.
Two examples of particles that are very common and all around us are electrons and neutrinos. You're familiar with electrons (which are not baryons!), and the nuclear reactions in the Sun are constantly producing a mind-boggling number of neutrinos. Generated in the centre, they travel at nearly the speed of light which means that the ones passing through your body right now are about 8 minutes old. By comparison, the light from the Sun (photons, also not baryons) bounces off all the photons there, so by the time it actually reaches you it's about a million years old.
Finally, and most importantly, dark matter has not been discovered. You are also right in that the reporter is very much out of his depth. The article states that there is evidence for baryons to be found in places where we have not seen them before. What's one theory as to how they got there? Dark matter.
Not correct, there are two classes of elementry particles (that we know about) Bosons and Fermions.
Bosons are things like :
- Photons
- Gluons
- W and Z Bosons
- Higgs Bosons
Bosons don't have anti-particles, and are less likely to form stable structures.Fermions are things like :
- Quarks
- Electrons
- Neutrons
- Protons
Fermions do have anti-particles, and form the everyday matter that you interact with.IANAP, but two photons cannot cancel each other out, however two beams can (assuming they are co-axial and anti-phased).
As for the flashlight, general light is not regular so you certainly can't make one using interference.
Windows in 6 Bytes (IA-32) : 90 90 90 90 CD 19
At least there were, several hundred million years ago.
slashdot broke my sig
"Dark" matter is regular stuff. Forget all the hyperbole about "exotic" new forms of unpredictable Star Trek technobabble with physics-defying properties. It's called "dark" matter because it's not "bright" matter, like stars, conveniently radiating bazillions of units of energy for us to easily spot them.
It seems perfectly reasonable that there exists matter that's not formed into glowing plasma balls and is thus harder to spot.
But that presentation is kind of prosaic, and wouldn't sell lots of issues of the World Weekly News.
Dark matter might yet prove to be baryonic, but since about 70% of the universe is the even weirder dark energy, why is it so impossible to believe that 25% could be a new type of matter that interacts gravitationally, but not in other expected ways?
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That paper you linked did not sway me, in part because it was clearly written without an open mind. It uses phrases like "the only way to do X if you rule out Y is to theorize something clearly unreasonable" to make its points. If observations disprove one theory, it does not prove the only known alternative. It simply means that you should question some more of your assumptions to figure out what you missed.
Clearly not all matter is in stars, so if that is your definition, then some dark matter must exist. My BS subject refered to the theories that dark matter must be something undiscovered, because we can't seem to find enough to fit the Big Bang theory's predictions. I remain convinced that the percentage of dark matter necessary to make Omega equal to 1 does not fit with observation.
I don't pretend to know what the correct theory is, but I am convinced that the Big Bang is not accurate, and that there are forces/processes at work in the cosmos that are being thrown out prematurely because they contradict the Big Bang, thus preventing the most accurate theory from surfacing. Ned Wright's defenses and criticisms are not the open-minded evaluation that I was looking for.
--Sandy
Hi --
Distinguishing between baryonic matter -- stuff that bears any resemblance to everything around you, whether it is visible or not -- and other "dark" matter that does not fall into that category, is actually pretty commonplace in astrophysics. This seems like semantics, but turns out to be an important distinction.
The point is that the fraction of baryonic matter in the universe is, we think, reasonably well constrained (by both observations of light element abundances in conjunction with Big Bang nucleosynthesis models, and by measurements of fluctuations in the cosmic microwave background) to be only about 5% of the total mass/energy density. Yet there's an additional matter component (accounting for about 25% of the total density) that we know little about -- this is what most astronomers mean when they say "dark matter" these days.
This article says nothing at all about that 25%. It does, however, provide some clues towards a more complete accounting of the 5% that is "normal" (i.e. baryonic) matter. This is a very significant result, but the slashdot writeup and most of the comments to this article are completely distorting it.
The puzzle regarding the "normal" 5% was this: in the local universe (redshifts less than 2), only 10% or so of it is luminous matter, stars and galaxies and the like. More (40% or so) has been accounted for by studies of cool clouds of gas residing between stars, but this still left 50% in an unknown reservoir of baryons. Theory/simulation had suggested that one such reservoir might be the "warm/hot intergalactic medium" -- gas that is heated to millions of K.
The problem is that detecting low-density gas at that temperature is quite difficult, partly since most bound electrons have been lost. Only the more massive elements retain any electrons, and so can be visible in absorption in the FUV or X-rays.
What the paper discussed here (published today in Nature) does is to describe a plausible-looking detection of such filaments of "warm-hot" gas, through X-ray absorption. They use this detection to extrapolate a matter density of this WHIM component, and find that it could account for 30-50% of the baryonic mass, and so constitute the "missing" baryonic matter.
Note that this says nothing at all new about the 25% of truly "dark" non-baryonic matter.
One fairly large quibble is that the 30-50% number represents an extrapolation from just two absorbers, over a comparatively short distance, to infer the WHIM density in the whole universe. That's sort of a big jump, in case that part wasn't obvious. But you can't do this sort of analysis for very many sightlines -- you need a really bright emitting object on the other side of the WHIM clouds if you're going to see them, and such objects are few and far between -- so for right now that's what you get.
If you happen to be somewhere that has a subscription to Nature (most universities do), you can check out the two articles related to this in today's edition:
There's a "news and views" article by Mike Shull that's a nice summary of the issues involved. And there's the full research article by Nicastro et al.
Hope that clears at least a few things up. If I have time later tonight, I'll try to come back and respond to some of your other points.
cheers.
2. Several ways --- rotation, motion of a number of satellite galaxies, mass/light ratio, Tully-Fisher relation, and, if it's a spiral, simply by the size if we know the distance (this is pretty rough, but a decent indicator)
3. Within a galaxy, I don't think so. But intra-galactic dark matter is just one type. There is also non-luminous matter in between galaxies in clusters to account for their motion. Hot X-ray gas is one candidate, but I thought I remembered that there didn't seem to be enough of that stuff to account for cluster dynamics. Maybe this new stuff will help out, though the mass deficit was much more than this 2% if I recall correctly, and is probably non-baryonic.
3. Yes, they should. That's the problem. Outer stars and globular clusters are orbiting way to fast if all the mass in the galaxy is traced by luminous matter. A good model to account for the rotational behavior is a spherical halo (not just a disk) of non-luminous matter. This is the intra-galactic dark matter, and not relevant to the article.
First, this result only applies to BARYONIC dark matter, which is only a fraction of all the dark matter out there. Second, we already knew that a lot of it at the epochs in question was in the form of hot intercluster gas.
The current work is an improvement over previous studies, and is good work. But the headline rather sucks. I thought we'd detected axions or something, even though I'd already read about this result.
I teach techniques to estimate cluster masses based on X-ray emission, and have used the Chandra X-ray Observatory myself. A headline about such work shouldn't trick me.
Professor of Astronomy, Author of Spider Star & Star Dragon (Tor)
If you just think astrophysics is math, you'd flunk the heck out of my astronomy exams no matter your mathematical sophistication. Probably every level of astronomy, from non-major to graduate level. At least the way I teach it.
Math is a very useful tool in astrophysics, but there's a reason that math is a separate department from any physical science.
Professor of Astronomy, Author of Spider Star & Star Dragon (Tor)
Actually, it is well established that the dark matter is NOT baryonic.
The story is a bit about dark matter, because there is a dark matter presence implied by the newly discovered gas clouds. But that's no surprise - the observed structure of ordinary galaxies already implies that they as well are permeated with dark matter.
Cosmologists, primarily based on data from the Wilkinson Microwave Anisotropy Probe, are now willing to put pretty hard numbers on the ratios of baryonic and non-baryonic matter (about 1:7 or so). ALL of the non-baryonic matter is dark. A good fraction of the baryonic matter is dark, in the sense that it doesn't emit much light (e.g., very cool stars, non-accreting black holes, planets, etc.).
There sure is dark matter out there that we don't understand well at all, and probably more than one kind. Neutrinos are one form, since recent experiments indicate they do have some mass. Neutrinos are pretty exotic compared to normal baryonic matter. There may well be weirder stuff.
Agree with you though, that Star Trek overdoes it.
Professor of Astronomy, Author of Spider Star & Star Dragon (Tor)
Yeah, at least part of them. You can go to my website above, hit "Astronomy Work" link on the left, and be taken to http:physics.uwyo.edu/~mbrother where you'll find links to three recent courses I've taught. The intro astronomy course (1050) is currently in session and so the slides for that one are incomplete. These are slides, meant to accompany lecture, so they aren't enough on their own, but you might enjoy looking anyway.
Professor of Astronomy, Author of Spider Star & Star Dragon (Tor)
Wayne Hu at the university of Chicago has a great set of webpages that explain these results. If you don't have much of a background, start with the lowest level and work up. To get to the hard numbers (two significant figures), check out the "experiments and data" link. They're based on the relative amplitudes of the acoustic peaks in the microwave background.
The page can be found here.
Professor of Astronomy, Author of Spider Star & Star Dragon (Tor)