Astronomers have the most amazing jobs in the world. They regularly peek out at the universe, digging up more things than the eye can see. Oh sure, our eyes can detect amazing things in what astronomers call "visible" or "optical" light -- what you see when you look at planets, stars and galaxies. But there's more than meets the eye, as we've been finding out this week at the American Astronomical Society meeting. There are hundreds of papers and talks, all reporting on observations made in all the wavelengths of light: gamma rays, X-rays, ultraviolet, radio, infrared, microwave, and, of course, visible light.
For example, there are places in space that glow in infrared light. You really can't see this form of light, but you feel it as warmth on your skin in sunlight. NASA's Stratospheric Observatory for Infrared Astronomy, which is mounted into the side of a modified 747 aircraft, recently used infrared detectors to peer into a region of the sky called the Orion Nebula. SOFIA looked at gas and dust being heated by nearby stars embedded in the nebula. That warmed-up interstellar material gives off heat in the form of infrared radiation, which SOFIA's detectors "see." As a result of the study, astronomers learned that the nebula is filled with interstellar dust made up of silicon, carbon and other metals, and a mix of ice and organic molecules. This stuff is the seed material for stars and planets in the nebula.
Another image presented at this week's meeting, taken using the Hubble Space Telescope, shows the nearby Andromeda Galaxy. It was taken in visible and ultraviolet wavelengths of light and is centered on a 100-million-solar-mass black hole at the hub of Andromeda. Hubble focused on a tightly packed cluster of hot, young blue stars that probably formed near the black hole, which now raises questions about how they survive in such a dangerous environment.
There's other "stuff" out there in the universe that we can't see with any kind of telescope. Its gravitational pull is so strong that it can cause a beam of light to swerve from its path. Every galaxy has so much of this mysterious matter stuffed into it that its motions are affected. But this material remains hidden, invisible ... and dark. That's why it's called "dark matter." It fascinates astronomers so much that it is taking center stage in advanced astronomy observations.
Sukanya Chakrabarti, is an assistant professor of physics for the Charles E. Schmidt College of Science at Florida Atlantic University, and she specializes in searching out this dark matter. "Most of the mass in the universe is dark," she said during a presentation where a group of astronomers were showing off their latest observations of the effects of dark matter in the cosmos. Knowing where that dark matter is, and how much there is presents astronomers with a big challenge.
People who search for dark matter have known for a long time that galaxies have dark matter throughout them. Chakrabarti looks at specific parts of galaxies called "gas disks" to see how they are affected by this unseen substance. And she has found ripples in those disks. What caused the ripples? She suspects the dark matter haloes of nearby galaxies could be distorting those gas disks. It's similar to what happens when you throw a rock into a pond and ripples flow out across the surface of the water. The amount of rippling Chakrabarti sees in the disks can be used to figure out how much dark matter there is in the area. "The idea is that the ripples in outer gas disks are like a gravitational mirror that let us to see how the dark matter is distributed," said Chakrabarti.
Dark matter studies are becoming more and more important in studies of the early universe, where it played a role in shaping the matter we can see -- particularly the galaxies. It may be dark, but it's an integral part of the universe.
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