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A photo of the Pinwheel Galaxy.

This image of the Pinwheel galaxy, a close neighbor of the Milky Way, was made with the new NASA Spitzer Space Telescope. The telescope--orbiting the sun--is helping U of M researchers study how galaxies assemble, destroy, and recycle the building blocks of stars and planets.

Pinwheel galaxy may hold secrets

U researchers study the building blocks of planets

By Deane Morrison

Published on June 4, 2004

Astronomers are a nosy lot. They like to know exactly what their neighbors are up to. Lately, a couple of U of M astronomers have been using NASA's Spitzer Space Telescope to see what's doing in the Pinwheel galaxy, a resident of the Milky Way neighborhood a mere three million light-years away. The Pinwheel is known by its catalog name, M33. About half the diameter of the Milky Way, M33 appears in the northern sky not too far from the famous Andromeda galaxy. Andromeda, M33, and the Milky Way are the "Big Three" of what astronomers call the Local Group of about 35 galaxies. This week Elisha Polomski, a postdoctoral fellow in the astronomy department, unveiled a series of infrared pictures taken by the Spitzer at a meeting of the American Astronomical Society in Denver. The work is the first in a planned series of observations of M33.

The iron in Earth's core was forged in the bellies of large, luminous stars, and the heavier elements were created in supernova explosions. The deaths of those stars sprayed interstellar space with dust and gas, some of which clumped together in a disk that coalesced to form the sun and its planets, including Earth.

"M33 is a gigantic laboratory where you can watch dust being created in exploding stars called novae and supernovae, being distributed in the winds of giant stars, and being reborn in new stars," says Polomski. "You can see the universe in a nutshell." Along with researchers from the Harvard-Smithsonian Center for Astrophysics and the University of Arizona, Polomski and U of M astronomy professor Robert Gehrz will examine the M33 galaxy in detail for the next two and a half years. They'll study the processes that circulate energy and chemical elements through the galaxy to build up, destroy, and recycle the building blocks of stars and planets. Because it operates at infrared wavelengths--outside the visible part of the spectrum--the Spitzer Space Telescope finds details hidden from the human eye. It works on the principle than any object that is warmer than its surroundings tends to give off heat in the form of infrared radiation; the cooler the object, the longer the wavelength of infrared light it emits. The Minnesota-Smithsonian-Arizona team is observing M33 at wavelengths ranging from 10 to 30 times longer than visible light, giving them a window on objects that are much colder than stars or even the human body. The new pictures were taken in light at wavelengths ranging from 3.5 to 24 microns (millionths of a meter). "At 3.5 microns we see stars," says Gehrz, leader of the M33 observation team. "At eight, we see warm dust that's about 100 degrees Fahrenheit. At 24 microns we're picking up cool dust that's between minus 100 and minus 190 degrees Fahrenheit." Observations of M33's cool components are expected to reveal much about the "metabolism" of galaxies. A galaxy is akin to a living body, in which food substances are broken down to build the body, and the waste and decomposition products of a body are recycled to feed new life. For example, the iron in Earth's core was forged in the bellies of large, luminous stars, and the heavier elements--all the way to uranium, the heaviest naturally occurring element--were created in supernova explosions. The deaths of those stars sprayed interstellar space with dust and gas, some of which clumped together in a disk that coalesced to form the sun and its planets, including Earth. Polomski, Gehrz, and the other researchers expect to map out the evolutionary process of the birth, old age, and death of stars in M33 and compare it to the process in our own galaxy. The team has assembled thousands of images from the telescope and is now planning follow-up studies of four objects in M33: the remnant of a supernova explosion, two star-forming regions, and a mysterious dust-shrouded object visible at the long wavelengths only Spitzer can see. Gehrz was instrumental in focusing the mirrors of the Spitzer Telescope. As a scientist with the team that oversaw the fabrication and testing of the telescope's optics, he had to make sure there were no more incidents like the one that befell the Hubble Space Telescope, whose focus was initially blurry. Getting the focus right was imperative because the Spitzer circles the sun in the same orbital path as Earth, but millions of miles behind. Therefore, no astronauts could ever be sent on a repair mission. All that hard work is now paying off. Spitzer was launched in August 2003, and astronomers everywhere are giving it rave reviews for clarity. For more on the M33 galaxy, see ftp.seds.org/messier/m/m033.html. For more on the Spitzer Space Telescope, see spitzer.caltech.edu.

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