September 15, 1999

Life Cycle of Stars Captured in HST Image

Image of NGC 3603*, an interstellar cloud of gas and dust in the southern constellation Carina, the Keel. The cloud lies at a distance of about 20,000 light-years from Earth. This stunning image shows in one single view many of the key stages in the evolution of stars, as explained in the text below. The image was taken with the Wide Field and Planetary Camera 2 of NASA's Hubble Space Telescope (HST) on March 5, 1999.

Please click on the image for a larger view and the numbered labels referenced in the text below.

Image Credits: Wolfgang Brandner (Jet Propulsion Laboratory/Infrared Processing and Analysis Center), Eva K. Grebel (University of Washington), You-Hua Chu (University of Illinois, Urbana-Champaign), and NASA.

The above image of a section of the interstellar cloud NGC 3603 shows in one single view many of the key stages in the life cycle of stars: The birth of stars and star clusters, the formation of protoplanetary disks, the impact on the cloud material by radiation and winds from young, hot stars, and the rapid evolution of the most massive of these stars to the point where they are about to explode as supernovae.

Here are some of the most interesting of the features visible in this image:

1. Cluster of Young, Hot Stars

Just above the center of this image lies a compact cluster of young, hot, and bright stars (identified in the enlarged image by the number "1"). These stars were born from the gas and dust of NGC 3603. The stars' intense radiation and the fast, gaseous winds blowing from them have pushed away the nebular gas in their vicinity, giving us an unobstructed view of the star cluster.

Within a million to a few million years, the most massive of these hot and bright stars evolve to the point where they explode as supernovae, expelling the matter outside their compact cores into space. The stars' cores collapse into neutron stars or, possibly, black holes.

2. Supergiant Star Sher 25

Just above and to the left of the central region of the star cluster just described, one finds the blue supergiant Sher 25. The star is surrounded by a ring of glowing gas that it ejected roughly 7,000 years ago (2a). Perpendicular to and on opposite sides of the ring are blobs of gas ejected by Sher 25 (2b). The blobs are rich in nitrogen and other elements produced by nuclear reactions in the interior of Sher 25.

Sher 25 is reminiscent of the precursor star of supernova 1987A, which exploded in February of 1987 in the Large Magellanic Cloud. Sher 25, too, is expected to explode as a supernova. However, astronomers cannot predict the precise timing of this event.

3. Star Birth

The small, dark patches visible in the upper- and lower-right sections of the image are very dense, cold, and light-absorbing cloud structures called Bok globules (3), after the Dutch-American astronomer Bart J. Bok (1906-1983). In these globules, gravity is pulling dust and molecules together to form new stars.

Astronomers believe that the stars forming in Bok globules are rather different from the hot, bright stars in the cluster described under heading 1 above. The stars forming in Bok globules have masses comparable to that of the Sun or less, while the hot, bright cluster stars have masses of up to 20 times that of the Sun, and a few may be even more massive. The low-mass stars born in Bok globules will take many billions of years to evolve before ending their lives by becoming white dwarfs, while many of the cluster stars will race through their evolutions in a few millions of years and explode as supernovae.

4. Emerging, Recently Formed Stars

Newly formed, as well as still-forming, stars are present not just in the Bok globules, but are scattered about at many places throughout NGC 3603. Some lie at the tips of the pillars of gas and dust (4) that characterize the edges of the cavity surrounding the star cluster described above. The radiation and winds emanating from the hot, bright cluster stars scour away the gas and dust of the wall of the cavity they have created, sculpting the pillars and exposing the newly formed stars.

The formation of these pillars of gas and dust and the freeing of newly formed stars from the surrounding cloud material occur by the same process that created the pillars seen in the famous Hubble image of the Eagle Nebula.

5. Protoplanetary Disks

The two bright, compact, tadpole-shaped nebulae in the lower-left section of the image (5) are probably gas and dust blown off from protoplanetary disks. Protoplanetary disks surround some very young stars and are believed to be places where concentrated dust and gas coalesce to form planets.

Protoplanetary disks were also found by Hubble in the Orion Nebula. However, those in NGC 3603 are 5 to 10 times larger in size than those in Orion, and correspondingly more massive.

* The acronym "NGC" refers to the New General Catalogue of Nebulae and Clusters of Stars, compiled at the end of the nineteenth century by the Danish astronomer Johan L. E. Dreyer.

More Cool Stuff

We obtained the above image from press release 99-20 of June 1, 1999, of the Space Telescope Science Institute (STScI):

http://oposite.stsci.edu/pubinfo/pr/1999/20/index.html

To learn more about the birth, evolution, and death of stars, go to:

http://observe.ivv.nasa.gov/nasa/exhibits/stellarbirth/opening1.html
http://observe.ivv.nasa.gov/nasa/space/stellardeath/stellardeath_opening.html

To view the famous Hubble image of the gaseous pillars in the Eagle Nebula, go to our Observation of the Week of December 20, 1995:

http://observe.ivv.nasa.gov/nasa/ootw/1995/ootw_951220/ob951220.html

As part of its Learning Technologies Project (LTP), NASA supports a number of educational Web sites that have excellent material on the space sciences:

http://observe.ivv.nasa.gov/nasa/education/edu/edudocs/topic_space.html