On the Life Cycle of Stars

In honor of the 400th anniversary of Galileo Galilei's (and humankind's) first observations with a telescope, 2009 has been declared the International Year of Astronomy. I thus thought it only appropriate to devote at least one post to the heavens.


"Although stars are frequently assumed to be constant and unchanging features of the firmament, they are in fact evolving dynamic systems. New stars condense out of gaseous nebulae, and old stars evolve through planetary nebulae and supernovae into white dwarfs, neutron stars and black holes. These processes—star formation and evolution—are critical to understanding many features of the Universe, including the evolution of galaxies, the dispersal of chemical elements and the distribution and energetics of gas.

Some of the [Hubble Space Telescope's] HST's most lasting (and beautiful) contributions to stellar astronomy have been its studies of star-forming regions like the Orion nebula [see figure, above]. In these regions, luminous massive stars ionize the gas cloud from which they coalesced, causing the cloud to glow brightly in various emission lines. The HST's earliest observations of the Orion nebula revealed that it was peppered with a remarkable population of young stars surrounded by dense disks of gas and dust. These disks are undoubtedly remnants of the late accretion phase during which the stars condensed. Although the presence of such disks had been inferred from theory and from observations with the Very Large Array, the HST's superior image resolution revealed the first true pictures of the disks' structures and physical properties."¹

References:
1. Dalcanton JJ. 18 years of science with the Hubble Space Telescope. Nature 457: 41-50, 2009.