University of Wisconsinâ€Madison
She probes black holes to fathom the early days of our universe.
If you can see a star with your naked eye, Amy Barger probably isn't interested in it. What gets her going are the faraway objects invisible to anything but the most powerful instruments. I'm just really fascinated by what's going on at the edge," she says. The farther out, the better."
By the mid-1990s, researchers figured they had most of the universe's history tied up. The early universe was speckled with a few intensely bright objects called quasars, whose cores are thought to contain black holes billions of times as massive as the sun. These supermassive" black holes gulped down the surrounding dust and gas, heating it and making it blast light at all frequencies. Measurements indicated that black hole activity peaked around 11 billion years ago, three billion years after the big bang.
But these conclusions were based primarily on visible light. Barger was among the first crop of scientists to monitor multiple wavelengths by combining data from many telescopes. As a just-
minted Ph.D. working at the University of Hawaii, she was awarded time on SCUBA, a far-infrared camera, and discovered a previously unknown population of quasars. Next Barger, 34, led a team that surveyed a small section of sky using NASA's orbiting Chandra X-Ray Observatory. Only x-rays would reveal certain dust-enshrouded black holes.
The team matched those objects to visible galaxies, painstakingly extracting each one's redshift, a measure of its distance. The lower the redshift, the more recent the black hole activity. I suddenly realized the average redshift was astonishingly low. â€Whoa, what's going on?' " Barger recalls thinking. Her conclusion: Active black holes abound in relatively nearby galaxies, which means that they were active much more recently than previously thought. And although the newly discovered black holes are weaker than quasars, their combined glow actually outshines their older counterparts.
The discovery raises fresh uncertainties. Why are nearby black holes so plentiful? How does their activity relate to star formation? These are just the sort of questions Barger likes. I want to see how things within the universe evolve," she says. Ultimately, it leads to us."
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