Messier 81

This Spitzer Space Telescope composite image shows the primary components of galaxy Messier 81 (top), in Ursa Major. Old stars predominate in the central portion of the galaxy, while the graceful spiral arms are dominated by infrared emission from dust. Massive stars are being born in the bright clumps within the spiral arms. The composite picture is made from images in 3.6, 8.0, and 24 microns, which are colored red, green, and blue, respectively (below).

Courtesy NASA/JPL/Caltech/K. Gordon (University of Arizona) and S. Willner (Harvard-Smithsonian Center for Astrophysics), N.A. Sharp (NOAO/AURA/NSF).

Astronomers have embarked upon a new era brimming with never-before-seen celestial objects and new views of classic astronomical marvels. That was the message sent to the public on December 18th as NASA released the first scientific images from the Space Infrared Telescope Facility (SIRTF), now called the Spitzer Space Telescope. As one principal investigator remarked, "We can expect a flood of discoveries over the next five years."

Unlike the Hubble Space Telescope, which is tuned to see the cosmos in visible light (with some spillover into the near-infrared and near-ultraviolet), Spitzer is an infrared-only telescope. This affords it the opportunity to see things never seen before in astronomy. Most notably, dust clouds are often opaque to visible or near-infrared light. But Spitzer, looking in lower-energy wavelengths, can see through the dusty cloak, unveiling the mysteries that lie beneath. These treasures include newly forming planets and the shrouded birthing rooms of stars and galaxies.

Spitzer will detect and discern the feeble heat coming from objects vast distances away. To do so the entire instrument is cryogenically cooled with liquid helium to 5.5° Kelvin (–268°C). Unfortunately, the spacecraft carries only a fixed amount of coolant on board, thus limiting its expected lifetime to just 5.8 years — double the expected lifespan at launch. Moreover, Spitzer cannot be serviced. It resides in an Earth-trailing orbit, slowly drifting from our planet with each passing day. As such, space shuttles can't reach it.

The last of NASA's four Great Observatories (its sister scopes are the Hubble Space Telescope, Compton Gamma-Ray Observatory, and Chandra X-ray Observatory), the Spitzer Space Telescope hosts a trio of powerful instruments: the Infrared Array Camera (IRAC) will observe simultaneously in four wavelengths centered at 3.6, 4.5, 5.8, and 8.0 microns; the Multiband Imaging Photometer for Spitzer (MIPS) can do both photometric mapping and high-resolution imaging at 24, 70, and 160 microns; and an Infrared Spectrograph (IRS) that will take spectral images from 5.3 to 40 microns.

IC 1396

In early November the Spitzer Infrared Array Camera observed the Elephant's Trunk Nebula, a dark globule within the emission nebula IC 1396 in the constellation Cepheus. The infrared image (right) pierces through the opaque cloud seen in visible light (left) to show the birth of embryonic stars and young stars not seen before.

Courtesy NASA/JPL/Caltech/W. Reach (SSC/Caltech).

Since its launch, the spacecraft has been exceeding expectations, both operationally and scientifically. Some initial results from images received primarily during the science verification phase include:

  • The capability of "dissecting" a galaxy into its component parts in images provided by IRAC. Seeing galaxy components like what we see in Messier 81 (above) "will change the way we classify galaxies," says IRAC's principal investigator Giovanni Fazio (Harvard-Smithsonian Center for Astrophysics).
  • Evidence for organic molecules in a distant galaxy. Spitzer's infrared spectrograph has already returned IRAC data showing polycyclic aromatic hydrocarbons — a molecule found in soot and burnt toast — in HH46/47 in the constellation Vela.
  • The structure of a protoplanetary disk around Fomalhaut in Piscis Austrinus. The finding was based on Spitzer's multiband-imaging photometer examination of the dust disk around the star. "What we see around this star is the debris from the process by which the planetary system evolves," says principal investigator George Rieke (University of Arizona).

    SIRTF was renamed yesterday in honor of the late Lyman Spitzer, Jr. In 1946 Spitzer suggested placing a large telescope in space as a way to eliminate disturbances caused by Earth's atmosphere. Project officials said the announcement of the new name was withheld until it was certain the observatory was operating properly.

    With Spitzer, infrared astronomy has "crossed a new threshold," says project scientist Michael W. Werner (Jet Propulsion Laboratory).

  • Comments

    You must be logged in to post a comment.