Stars, like our Sun, can be thought of as "basic particles" of the Universe, just as atoms are "basic particles" of matter. Groups of stars make up galaxies, while planets and ultimately life arise around stars. Although stars have been the main topic of astronomy for thousands of years, we have begun to understand them in detail only in recent times through the advent of powerful telescopes and computers.
A hundred years ago, scientists did not know that stars are powered by nuclear fusion, and 50 years ago they did not know that stars are continually forming in the Universe. Researchers still do not know the details of how clouds of gas and dust collapse to form stars, or why most stars form in groups, or exactly how planetary systems form. Young stars within a star-forming region interact with each other in complex ways. The details of how they evolve and release the heavy elements they produce back into space for recycling into new generations of stars and planets remains to be determined through a combination of observation and theory.
The stages of solar system formation, starting with a protostar embedded in a gas cloud (upper left of below diagram), to an early star with a circumstellar disk (upper right), to a star surrounded by small "planetesimals" which are starting to clump together (lower left) to a solar system like ours today.
Astronomers know that a large number of stars that are like our Sun have gas-giant planets. The number of confirmed planets and candidate planets is now in the thousands. Many of these exoplanets are very large (like Jupiter), but smaller planets nearer to Earth's size are also being discovered.
The continual discovery of new and unusual planetary systems has made scientists re-think their ideas and theories about how planets are formed. Scientists realize that to get a better understanding of how planets form, they need to have more observations of planets around young stars, and more observations of leftover debris around stars, which can come together and form planets.
To unravel the birth and early evolution of stars and planets, we need to be able to peer into the hearts of dense and dusty cloud cores where star formation begins. These regions cannot be observed at visible light wavelengths as the dust would make such regions opaque and must be observed at infrared wavelengths.
The James Webb Space Telescope's superior imaging and spectroscopy capabilities will allow us to study stars as they are forming in their dusty cocoons. It will also be able to image disks around stars and study organic molecules that are important for life to develop.
Image credits: Star-forming region in Carina - NASA, ESA, and M. Livio and the Hubble 20th Anniversary Team (STScI), solar system formation graphic - Shu et al. 1987, Kepler 22b, the first confirmed extrasolar planet found by NASA's Kepler Space Telescope to orbit within the habitable zone of a Sun-like star - NASA/Ames/JPL-Caltech, Infrared Spitzer image of a star-forming region - NASA/JPL-Caltech/ Harvard-Smithsonian CfA
Want to know more? Visit the James Webb Space Telescope project home page.