Monday, February 5, 2007

Now if only we could do something about that name....

Geez.... Scientists have created a map of dark matter distribution in the universe:
Dark matter, the ubiquitous yet ethereal stuff filling the cosmos, has been mapped three-dimensionally for the first time by a team of astronomers using a fleet of orbiting and ground-based telescopes. Implementing techniques not even dreamed of when dark matter was first postulated, they have created a map two degrees on a side (roughly 15 times the area of the full Moon) and 6 billion light years deep. The Cosmic Evolution Survey, or COSMOS, reveals the spatial distribution of dark matter stretching back to a time when the Universe was half its present age.


The COSMOS team made their map of dark matter by exploiting a peculiar characteristic of gravity: its ability to warp space. Einstein postulated that gravity bends space like a bowling ball placed in the middle of a bed distorts the mattress. Light moving through empty space travels in a straight line, but if it passes by a mass, the gravity will bend the light's path. How much the path bends depends on how much mass there is and how it's distributed.

That is how scientists can detect dark matter. Mass (both visible and invisible) twists, bends, and warps the light from distant galaxies on its way from there to here. The visible mass can be measured in several ways, and by subtracting the visible component from the total mass, researchers are able to find the location and quantity of dark matter.


The result is nothing less than profound: a three-dimensional map millions of light years across and billions deep, showing the location of trillions of solar masses of invisible ethereal stuff that only decades ago was a complete mystery.

Even glancing at the map reveals insights into the Universe. The left hand side represents matter that is close to us, and the right side is farther away. We see more distant matter as it was farther in the past, so in a sense we have a time machine that lets us understand the Universe as it was 6 billion years ago. In the past, dark matter formed huge structures spanning hundreds of millions of light years across. But in more recent history, these enormous blobs have broken into smaller, scattered clumps. This shows that over time, the gravity of the big structures made them collapse into an array of smaller ones—just as modern theories of cosmology have predicted.

COSMOS verifies theory's next prediction, too: Once dark matter condensed into smaller blobs, its gravity would increase, drawing in more dark matter and normal matter. Eventually, the normal matter would gather near clumps of dark matter, so wherever we see large amounts of dark matter today, we should also see normal matter. The survey confirms this; the visible matter detected lies roughly along the same positions as the dark matter.

Of course, as the article points out, this only covers around 1/10,000th of the sky, and it still doesn't tell us what dark matter is.

But still... wow.

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