Gaseous Galaxies a Problem for Dark Matter Theory

BY STEVEN SPARKMAN
Anchor: Jennifer Meckles

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Dark matter theory is the most widely accepted explanation for how galaxies behave. But a new study shows an alternative theory explains things dark matter doesn’t. BBC News has more.

“Instead of calling upon dark matter, the Modified Newtonian Dynamics (MoND) theory says that the effects of gravity change in places where its pull is very low. A new paper suggests that MoND better predicts the relationship between gassy galaxies’ rotation speeds and masses.”

For a little background, the difference between the two theories is how they account for the way galaxies move. Galaxies don’t seem to have enough gravity to keep from flying apart.

One explanation is that five times more dark matter, stuff we can’t detect, exists than regular matter, accounting for the missing gravity. MOND theory, the other explanation, predicts that gravity changes. (Image Source: NASA Planetquest)

The study’s author looked at the mass and rotation of some easy-to-analyze gaseous galaxies, and plotted it against MOND’s prediction. He told Science Magazine how the test worked out.

“The MOND line went right through the data. ‘You draw the line and the data fall right on it... No muss, no fuss.’ ”

The data matched so well, and dark matter theory’s predictions on the line above did so poorly, dark matter proponents have had to sit up and take notice. (Image source: Cornell University Library)

But even though MOND seems to work well at describing single galaxies, dark matter theory is still king of galaxy clusters.

For instance, it accurately describes the Bullet Cluster, where most of the matter, in red, can’t account for most of the gravity, shown in blue. MOND theory wasn’t able to compete. (Image source: Chandra Observatory)

It’s a tricky problem, but before we abandon or modify dark matter, a writer from io9 reminds us that even a wrong theory can get the right answer sometimes.

"So what does this mean? It definitely doesn't mean we have to throw out dark matter - this is just one very specific result that suggests - but doesn't prove - that in one particular circumstance, MOND seems to describe things better than the dark matter model can."

So is most of our universe invisible or were Newton and Einstein wrong about gravity? Share your theories in our comments section.

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4. Added :28-Feb-11
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