NASA Creates Portrait of Life and Death in the Universe

photo: March 8, 2004

In a small nearby galaxy lies a luminous cloud of gas and dust, called a nebula, which houses a family of newborn stars. If not for the death of a massive star millions of years ago, this stellar nursery never would have formed.The nebula, Henize 206, and the remnants of the exploding star that created it, are pictured in superb detail in a new image from NASA's Spitzer Space Telescope. Henize 206 sits just outside our own galaxy, the Milky Way, in a satellite galaxy 163,000 light-years away called the Large Magellanic Cloud. It is home to hundreds and possibly thousands of stars, ranging in age from two to 10 million years old.

"The image is a wonderful example of the cycle of birth and death that gives rise to stars throughout the universe," said Dr. Varoujan Gorjian, a scientist at NASA's Jet Propulsion Laboratory, Pasadena, Calif., and principal investigator for the latest observation.As in other stellar nurseries, the stars in Henize 206 were created when a dying star, or supernova, exploded, shooting shock waves through clouds of cosmic gas and dust. The gas and dust were subsequently compressed, gravity kicked in, and stars were born. Eventually, some of the stars will die in a fiery blast, triggering another cycle of birth and death. This recycling of stellar dust and gas occurs across the universe. Earth's own Sun descended from multiple generations of stars.

The new Spitzer picture provides a detailed snapshot of this universal phenomenon. By imaging Henize 206 in the infrared, Spitzer was able to see through blankets of dust that dominate visible light views. The resulting false-color image shows embedded young stars as bright white spots, and surrounding gas and dust in blue, green and red. Also revealed is a ring of green gas, which is the wake of the ancient supernova's explosion."Before Spitzer, we were only seeing tantalizing hints of the newborn stars peeking through shrouds of dust," Gorjian said.

These observations provide astronomers with a laboratory for understanding the early universe, and stellar birth and death cycles. Unlike large galaxies, the Large Magellanic Cloud has a quirk. The gas permeating it contains roughly 20 to 50 percent of the heavier elements, such as iron, possessed by the Sun and gas clouds in the Milky Way. This low-metallicity state approximates the early universe, allowing astronomers to catch a glimpse of what stellar life was like billions of years ago, when heavy metals were scarce.NASA's Spitzer Space Telescope has used its infrared eyes to poke through the cosmic veil to reveal a striking nebula where the entire lifecycle of stars is seen in splendid detail.

The LMC is a small satellite galaxy gravitationally bound to our own Milky Way. Yet the gravitational effects are tearing the companion to shreds in a long-playing drama of 'intergalactic cannibalism.' These disruptions lead to a recurring cycle of star birth and star death.

Astronomers are particularly interested in the LMC because its fractional content of heavy metals is two to five times lower than is seen in our solar neighborhood. [In this context, 'heavy elements' refer to those elements not present in the primordial universe. Such elements as carbon, oxygen and others are produced by nucleosynthesis and are ejected into the interstellar medium via mass loss by stars, including supernova explosions.] As such, the LMC provides a nearby cosmic laboratory that may resemble the distant universe in its chemical composition.

The primary Spitzer image, showing the wispy filamentary structure of Henize 206, is a four-color composite mosaic created by combining data from an infrared array camera (IRAC) at near-infrared wavelengths and the mid-infrared data from a multiband imaging photometer (MIPS). Blue represents invisible infrared light at wavelengths of 3.6 and 4.5 microns. Note that most of the stars in the field of view radiate primarily at these short infrared wavelengths. Cyan denotes emission at 5.8 microns, green depicts the 8.0 micron light, and red is used to trace the thermal emission from dust at 24 microns. The separate instrument images are included as insets to the main composite.

An inclined ring of emission dominates the central and upper regions of the image. This delineates a bubble of hot, x-ray emitting gas that was blown into space when a massive star died in a supernova explosion millions of years ago. The shock waves from that explosion impacted a cloud of nearby hydrogen gas, compressed it, and started a new generation of star formation. The death of one star led to the birth of many new stars. This is particularly evident in the MIPS inset, where the 24-micron emission peaks correspond to newly formed stars. The ultraviolet and visible-light photons from the new stars are absorbed by surrounding dust and re-radiated at longer infrared wavelengths, where it is detected by Spitzer.

This emission nebula was cataloged by Karl Henize (HEN-eyes) while spending 1948-1951 in South Africa doing research for his Ph.D. dissertation at the University of Michigan. Henize later became a NASA astronaut and, at age 59, became the oldest rookie to fly on the Space Shuttle during an eight-day flight of the Challenger in 1985. He died just short of his 67th birthday in 1993 while attempting to climb the north face of Mount Everest, the world's highest peak.