Dwarf Galaxies Dim Hopes of Dark Matter

An anonymous reader writes Once again, a shadow of a signal that scientists hoped would amplify into conclusive evidence of dark matter has instead flatlined, repeating a maddening refrain in the search for the invisible, omnipresent particles. The Fermi Large Area Telescope (LAT) failed to detect the glow of gamma rays emitted by annihilating dark matter in miniature "dwarf" galaxies that orbit the Milky Way, scientists reported Friday at a meeting in Nagoya, Japan. The hint of such a glow showed up in a Fermi analysis last year, but the statistical bump disappeared as more data accumulated. "We were obviously somewhat disappointed not to see a signal," said Matthew Wood, a postdoctoral researcher at Stanford University who was centrally involved the Fermi-LAT collaboration's new analysis, in an email.

Comments

Aether

[frovingslosh]

Dark Matter is the Aether of the 21st century. Eventually we'll stop wasting money on finding it.

Re:Aether

[Attila the Bun]

Dark Matter is the Aether of the 21st century. Eventually we'll stop wasting money on finding it.

...and the enlightened explanation for galactic rotation curves will be, what?

There's strong evidence for the presence of unseen stuff in galaxies. It shows itself in its gravitational effects on the way stars orbit around galaxy centres. Either our understanding of gravity is wrong (an option on which money has also been "wasted"), or there is some invisible "dark" matter out there. Figuring out what that matter is will mark a huge advance in cosmology and likely determine the future direction of particle physics too.

If you feel that understanding our universe and our origins is wasted effort, then we will never see eye to eye.

Re:Aether

[Anonymous Coward]

In particular, it is like the Luminiferous Aether because it is a hastily invented answer to something we've observed when the problem is we don't properly understand the question.

The three most beautiful letters

[Intrepid imaginaut]

WTF

I love it when science can't explain something yet, it means we have so much more to learn.

Re:statistically

[Bengie]

Then we need someone else to explain the excessive spacial distortion. We assume it's matter, but no matter what it is(pun), it does not fit anything we currently know about. I guess something other than matter could distort space time like matter, but we'd not quite sure yet. But as it stands currently, the only thing that can distort space is something that has mass, and anything with mass is "matter".

Dwarf Galaxies Dim Hopes of WIMPS

[mbone]

The Dark Matter is still there, as something (we don't know what). This doesn't "dim" the existence of DM as an effect* at all. What this does is (again) dim some faint hopes it might be WIMPS. It doesn't constrain other models / theories at all.

* : even if the DM is MOND, or some other gravity correction, it might not be matter, but the effect would still exist.

We don't know anything is weird here

[fyngyrz]

Dark Matter and Dark Energy are not terms that should conjure up weirdness in your mind. Not at this point, anyway.

Neither concept has a shred of evidence behind it indicating that anything exotic is going on. If you really want a good handle on the terms, just think of them as "We hope some sources of energy and matter we can't detect are out there because otherwise, the math behind our hypotheses doesn't work."

It's a limitation of trying to figure out what's going on incredible distances -- and times -- from us with a combination of barely functional tools, our (decent, I'm guessing) grasp of science, and the participant's intuitions.

Re:We don't know anything is weird here

[Artifakt]

I suspect we should have avoided terms like "Dark X', in favor of something that sounds more neutral and less dramatic. (I know, 'dramatic' sells research programs, especially to congress...).

            Linguistic problems have happened frequently in Physics and particularly Cosmology. After all, "Big Bang" was a term made up to poke fun at the idea it described, coined by Fred Hoyle, who wanted to defend the alternative ""Steady State" theory and thought "Big Bang" would sound rediculous. The phrase "Collapse of the state vector" in Quantum Mechanics has a similar problem, in that 'collapse' itself has a negative connotation, and makes it sound to some people like the Quantum state is superior to the Classical state, like some sort of 'fall from heaven' occurs when the vector reifies. "Reification" was a more neutral term that many people such as Dirac and Minkowski liked, but which died out in use by the 1970's. A lot of the Depak Chopra sort of writing on QM seems to stem from seeing the process of quantum probabilities becoming classical events as a fundamentally negative thing, and the Quantum "Realm" as somehow closer to God than the regular realm we experience, and calling it a collapse certainly encourages that view.

              Dark Matter and Dark Energy may be causing something of the same effect, where a more neutral term, such as "Undetected Matter", or "Unknown Force" might not.

Re:We don't know anything is weird here

[Roger W Moore]

Neither concept has a shred of evidence behind it indicating that anything exotic is going on.

It depends on what you mean by 'exotic'. In physics we usually reserve this term for 'new physics that we do not yet understand'. In these terms Dark Matter is "exotic". There is a huge amount of evidence (from galaxy rotation curves, cosmic microwave background and gravitational lensing) indicating that there some sort of mass which is not made of atoms. Since all the matter we have a handle on is made of atoms (or, if a plasma, parts of atoms) 'exotic' seems like an appropriate description at least until we figure out what it is exactly.

Your suggestion that the "maths does not work" has been tried. Modified Newtonian Dynamics (MOND) models essentially died with the Bullet Cluster because this showed that there was a gravitational field (it lensed the galaxies behind it) where there was no atomic matter. Effectively when this pair of galaxies collided the atomic matter in each interacted with each other and slowed down and the Dark Matter passed through each other without interacting. It is very hard to explain this with anything other than some type of 'exotic' form of matter not made of atoms.

Re:We don't know anything is weird here

[PvtVoid]

There is a huge amount of evidence

IANAP but wouldn't you phrase this somewhat differently?

Why should he phrase it differently? There is a huge amount of evidence. As in, multiple, independent measurements that all point in exactly the same direction:

- Galactic rotation curves
- Gravitational lensing
- Cosmic Microwave Background acoustic oscillations
- Cluster baryon fractions from X-ray measurements
- Large-scale structure

All of these things require something like dark matter to make any sense at all.

Re:Scientists obsessed with exotic explainations

[aXis100]

Plenty of scientists have tried to use simpler explanations but there is evidence that rules them out. The best example is the bullet cluster - two galaxies collided and the various components of the cluster - stars, gas and dark matter - all behaved differntly during the collision. The gravitational lensing effects cannot be explained by theories that dont include dark matter.

http://en.wikipedia.org/wiki/B...