One of the brilliant things about astrophysics is being able to take pictures of invisible stuff.
Infrared telescopes, for example, allow astronomers to see "dark" nebulas (picture), clouds of dust and gas that weakly reflect light from nearby stars, glowing mostly in thermal emissions.
Similarly, high-energy x-rays and gamma rays let scientists "see" black holes, objects that by definition are so dense not even light can escape their gravitational pull.
OK, to be fair, we don't see the black hole directly, but rather the radiation from infalling material. But still, what we do see is pretty good proof of objects that once existed only in theory.
Dark matter is another substance drawn from theory that astrophysics is starting to make visible—although the trick to finding dark matter is a bit more complicated.
For starters, dark matter doesn't absorb or emit light, and so far we have no proof of it interacting directly with normal matter.
We know dark matter is there based solely on gravity. Stars move within galaxies, and galaxies rotate on their axes, in ways that suggest there must be more matter present than what we can see.
In addition, clusters of galaxies bend light from objects behind them (an effect known as gravitational lensing) more than they should based on the visible matter present.
The galaxy cluster Abell 1689 is among the most powerful gravitational lensing clusters ever observed, according to NASA, making it a great place to map the distribution of dark matter.
Now, a new picture of this lens-filled cluster from the Hubble Space Telescope has allowed astronomers to create one of the sharpest and most detailed maps yet of dark matter.
