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back to article Astronomers map largest ever zone of dark matter

An international research team has presented the largest ever map of dark matter at the 219th American Astronomical Society conference in Austin, Texas. The team used a 340 megapixel camera, dubbed MegaCam, to take one degree by one degree shots for five years from the Canada-France-Hawaii Telescope (CFHC) on Mauna Kea mountain …

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Thank you Star Ship Science

And all who sail within her!

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Coat

No, no, no .......

that's just a bit of dirt on the lens !

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Science in reverse is not science

"The map shows largely what you’d expect, given the current state of theoretical thinking about dark matter"

Which says it all, unfortunately.

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Anonymous Coward

It all depends on your gear, I suppose.

You mean having a hypothesis which you then demonstrate with observation and experiment isn't science? What do they teach them at these schools?

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But on the other hand...

...is it not bad science to have a theory, and look for *evidence that supports* your theory, rather than looking at all the evidence and *modifying* your theory accordingly ?

Though to be fair, when you're an astro-boffin, there's an AWFUL lot of evidence to look at. Like, all of it.

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FAIL

No. That's called science. You come up with theories based upon what you've seen in experiments, and then try to do experiments which will provide evidence for/against the theory. Things in Astrophysics are just a bit messed up because we've evidence for things that act in certain ways (for example dark matter and dark energy) but we've not got much evidence yet for what they are. By thinking what makes sense from what we do know you can hopefully come up with ways to test it.

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Coat

Clouds

"Astrophysics are just a bit messed up because we've evidence for things that act in certain ways (for example dark matter and dark energy) but we've not got much evidence yet for what they are"

Galactic dust clouds without an illuminating source.

/mines the one with the flashlight in the pocket

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Perfectly good science

What's wrong with observations that fit within the current best theory? Bad science would be if nobody bothered to look.

Of course it's much more exciting on the occasions when observation shows something not accounted for by the theory, but the scientific merit of the observation is no different.

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I think that Isaac Asimov summed up that second para perfectly. Something like:

"Contrary to popular belief, most important discoveries do not start with 'Eureka', but with 'That's interesting.......'."

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Pint

Yup

Just ask Captain Jack Sparrow. The character has a lot of confidence in his ability to observe and correctly perceive what he observes. Most people don't say, "That's interesting..." when they observe something completely different. They dismiss it as impossible and immediately drop it from their memories because if they followed up on why they probably hallucinated the observation they would not want to have to deal with any conclusions reached.

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Anonymous Coward

I don't believe there is enough information in such a short article for me to understand what they have done. Which disappoints me. But that's a nice set of photos on the universe, blobs of light and all. By the way has anyone seen the canals on Mars ? I'm sure we can interpret that to mean there is a civilisation there struggling to survive againt the odds.

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Alien

They are there, they're just hiding. You know that Spirit got eaten by a Sarlacc.

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Boffin

Roughly what they've done

This is a weak-lensing survey. The idea is that the shapes of galaxies seen from Earth are changed by gravitational lensing from mass concentrations that the light has passed through on the way; so you produce an enormous sample of galaxies which you're reasonably confident are at about the same, large distance (by looking at their colours in several infra-red bands: 'photometric Z' is the term, Z being the symbol for red-shift), and the map plots roughly the extent to which the galaxy images in each patch of space are elongated.

The galaxies are small and the variations in their shapes are comparable to all sorts of other systematic effects caused by (for example) the presence of the atmosphere, so there are several statistical steps in there, which is why the maps look so blobby; the confirmation is at least in part that the brightest blobs turn out actually to contain foreground galaxy clusters, though a bright blob without a galaxy cluster would be a much more exciting result.

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Meh

So let me get this right

1. Work out how the light should bend based on known mass of a galaxy

2. Measure how much light is actually bent by the galaxy

3. Announce that the difference is due to dark matter, a mass force that's not coming from normal stuff in the galaxy.

Is this what they have done?

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Alien

No, not really

"dark matter" is postulated to exist because the observed rotation rate of galaxies doesn't match up with what we would expect to see based on our observations of where the mass appears to be and our understanding of how gravity works.

Multiple hypotheses have been proposed to explain this discrepancy (in fact, pretty much every combination of possibilities has been suggested). Many experiments have since been conducted in an attempt to eliminate one or more of those possibilities. The hypotheses include:

1. The effect is caused by Baryonic dark matter (ie regular matter that we just can't see because it's dark)

2 .The effect is caused by one of at least two different kinds of non-Baryonic dark matter (ie exotic particles, either of a type that we know about already or which we don't know about yet and might find in one of the ongoing supercollider experiments)

3. Our understanding of how gravity works is just wrong. A detailed proposal called MOND (Modified Newtonian Dynamics) adjusts gravity at long distances to explain the rotation rate discrepancy.

The thing about experiments like this is that they pretty much eliminate option 3. According to option 3, we shouldn't see light bend gravitationally around where the dark matter would need to be, because according to that hypothesis it doesn't exist.

There's much more you can find online. Google for terms like "MOND" and "non-baryonic dark matter".

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