Islands in the sky

Dwarf galaxies have stood star-to-star with celestial thugs for more than a billion years. Astrophysicists want to know what's holding them together.

Where we see black sky, astonomers see mass - but what's tipping the scales?

spiral-shaped galaxies. Now, however, an ordinary and long-neglected piece of the universe - the humble dwarf galaxy - promises rich insights into our place in the cosmos. "These common and durable galaxies are the cosmic equivalent of rocks," says John "Jay"Gallagher III, a professor of astronomy and a current explorer of miniature galaxies. "There are 10 times as many dwarf galaxies as giants, but for the most part they've been ignored." These galaxies, which contain just a million or so stars, have become important because they seem to be jam-packed with dark matter, the hypothesized missing mass of the universe. Astrophysicists have long been trying to account for the chunk of the universe's supposed mass that does not exist as stars, planets or other directly detectable phenomena. In dwarf galaxies, they might have found it. "The smallest ones seem to be absolutely loaded with dark matter," says Gallagher. Because dwarf galaxies have so few stars, they could easily be ripped apart by the gravitational pull of nearby giant galaxies, such as our own Milky Way, around which orbits a constellation of dwarf galaxies. But something, says Gallagher, is holding them together, and recent observations by Wisconsin astronomers and others point to dark matter as the celestial glue whose gravity keeps the small galaxies intact. Dwarf galaxies pose another puzzle: They apparently are very old, but they seem to have changed little over billions of years. "We call it the Hollywood effect," says UW-Madison astronomer Eric M. Wilcots, another scholar of dwarf galaxies. One idea, he says, is that the early universe may have been dominated by these small galaxies and, all of a sudden, many of them coalesced to form more familiar giant galaxies, such as the Milky Way. If that's the case, it would be like finding a cosmic time capsule in our backyard. Astrono-mers hope it holds answers to the questions of the earliest moments of the cosmos.

Now you see it

Engineers have long known they could make materials stronger if they could get a good look at their atomic structure. Now they can.

"Companies and researchers developing new materials need much more precise information about how improvements are made and performance is enhanced."

The 3DAP is able to make atomic-scale maps of the position and identity of millions of atoms. There are just a handful of these microscopes in the world at this point. Kelly has specialized in making a very high-speed 3DAP that will ultimately record 1 million atoms per second. Just how much faster is that than current methods? To study material contain-ing 1 billion atoms, over a distance of about one micrometer, takes more than a year. Kelly's 3DAP would only take about 17 minutes. That's a quantum leap for the study of many critical materials, says Kelly. The 3DAP will play a role in greatly improv-ing the development and manufacture of a number of high-tech materials. For example, it will help design and create stronger structural metals like steels and aluminum alloys. "Compa-nies and researchers developing new materials need much more precise information about how improvements are made and performance is enhanced," Kelly says. One could liken current methods to a nearly hit-and-miss proposition - "You can make changes in the process which improve the material, but you don't have any way of knowing why it improved," Kelly says. That makes further improvements more difficult to predict and make. "But if you can see the interface more sharply, at the atomic level, you can see what's better. You may find that what you've done is the best so far achieved - but not necessarily the best there could be." Other types of scientific studies will find 3DAP a revolutionary tool as well. For example, scien-tists (including Sue Babcock, assistant professor of materials science and engineering) are studying why impurities in materials often segregate to form a weak point, potentially leading to failures in the high-strength metals and ceramics that make up bridges or aircraft. Other researchers are anxious to get a look at very small-scale nucle-ation and growth phenomena. "It has not been possible to study these kinds of processes down towards the atomic scale which is where every-thing is happening," says Kelly. The 3DAP has already produced three-dimensional images. The development team, which includes both graduate and undergraduate students, has almost completed installation of a new stage called the Local Electrode Atom Probe (LEAP), which will make it much easier to analyze planar structures like semi-conductors. LEAP will also make it much easier to achieve the high pulsing rates 3DAP needs to see that revolutionary million atoms per second.