June 2, 1999 CHICAGO - Like a collage of photographs showing a human being from infancy to old age, a striking new picture unveiled today by a University of Washington astronomer shows various stages in the life cycle of stars, all occurring at one time.
The photograph clearly shows structures that will develop into stars, a starburst cluster featuring young massive stars, and a blue supergiant in its last stage before the death throes of becoming a supernova. This single view, believed to be the first of its kind, illustrates the entire stellar life cycle, said Eva Grebel, a Hubble postdoctoral fellow in the UW astronomy department.
A huge gas cloud that includes two giant gaseous pillars is the most dominant part of the image. However, the starburst cluster stands out because winds from its massive stars cleared away the surrounding gas, giving scientists a much better view of what is occurring inside.
"We even see stars that are currently being formed in the surroundings of this very massive cluster," Grebel said.
She and her colleagues, Wolfgang Brandner of NASA's Jet Propulsion Laboratory in Pasadena, Calif., and You-Hua Chu of the University of Illinois at Urbana-Champaign, presented the image at the centennial meeting of the American Astronomical Society.
The photograph of the giant galactic nebula NGC 3603 was taken March 5 using the Wide Field Planetary Camera 2 on the Hubble Space Telescope. The nebula is about 20,000 light years from Earth (a light year is about 5.88 trillion miles) and about 26,000 light years from the center of the galaxy, the same distance as our solar system.
Bok globules, which appear as small dark masses in the upper right corner of the photo, could contain one or several forming stars. When such globules evolve and are near an ionizing source, such as the giant cluster, they can begin to look like proplyds.
The term proplyd comes from protoplanetary disk, which is the material around a forming star that eventually could form a planetary system. It is believed proplyds consist of a central disk of neutral gas. In the photo, two proplyds appear as bright yellow objects slightly separated from the gas cloud in the lower center of the image.
"By studying these in greater detail, we hope to learn a lot more about the early life of a star," Grebel said.
Brandner said the proplyds are 560 billion to 1.7 trillion miles in size. But he said it is doubtful these developing stars ever will harbor planets because simulations indicate that within a few tens of thousands of years the disk of protoplanetary material will be completely ionized and dispersed because of its closeness to the cluster.
The central starburst cluster has at least two dozen massive stars, including O3 stars that, at about 120 times the mass of our sun, are the most-massive stars known. The massive stars stand out because of their brightness, but that makes it much less certain how many low-mass stars are in the cluster because they are hard to see. It is estimated there are tens of thousands of them.
Just to the left and slightly above the cluster is the blue supergiant known as Sher 25. The star is in its last stages before going supernova, though it could be thousands of years before that happens, Grebel said. A visible ring around Sher 25 has a diameter of a little more than one light year.
Also visible in front of the gas cloud are two giant pillars, formed as gas is beginning to be blown away by powerful winds from massive stars and from supernova explosions. Eventually the pillars are expected to dissolve, along with the rest of the gas cloud, Grebel said.
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