We think we know how stars live and die, but our picture of how stars form to begin with is incomplete. Although astronomers have discovered more than 1000 planets in other solar systems, we do not really know what conditions actually produce life.
In 1925, Cecilia Payne first applied the new science of quantum mechanics to the analysis of stellar spectra. Besides relating stellar spectral types to photospheric temperatures, Payne showed that stars - and hence most of the observable universe - are composed mostly of hydrogen. Today, SSP scientists and other astronomers analyze spectra to measure chemical abundances and other physical properties of stellar atmospheres. In addition to providing information on the structure and evolution of stars, these measurements constrain the ages and masses of the oldest stars in the galaxy.
Many stars are in binary or multiple star systems, where two or more stars orbit a common center of mass. Because the stars in a multiple star system have the same age, widely separated binaries and multiple stars provide good tests of stellar evolution theory. In close binary systems, the two stars often exchange mass and angular momentum, which changes their evolution compared to single stars. SSP scientists study the physical processes associated close and wide binary stars.
Asteroseismology applies seismology to stars. On Earth, seismologists measure motions and waves in the crust and mantle to learn about their structure and composition. In the Sun and other stars, asteroseismologists measure changes in the brightness and velocity to learn about the structure of the atmosphere and interior of a star. Because the changes are small (velocities of meters per second), CfA scientists use special purpose instruments to study the structure of nearby bright stars.
Stars form in the cold dense cores of giant molecular clouds. All newly-formed stars are surrounded by a circumstellar disk containing enough material to make a planetary system. SSP scientists use observations and theoretical data to understand how the central star and the surrounding disk evolve with time.
Many stars form in clusters. The clusters range in size from small groups of 5-10 times to dense clusters of thousands of stars. SSP scientists study the origin, structure, and evolution of young star clusters.
Every planetary system forms in a thin disk of gas and dust orbiting a young star. Small dust grains, a micron or two in size, collide and merge into large aggregates that settle into the midplane of the disk. In the midplane, aggregates grow into planetesimals with diameters of roughly 1 km. Collisions between planetesimals produce planets. SSP scientists use theoretical calculations to understand how dust grains evolve and how planetesimals become planets.
The Giant Magellan Telescope consortium has begun to design and build the first of the next generation, extremely large telescopes. The Giant Magellan Telescope (GMT) is based firmly on the heritage of the highly successful Magellan telescopes, which, thanks to their superb site and excellent design, routinely produce the best images of the current generation of ground-based large telescopes. The GMT will continue in this tradition, and will offer sharp images over wide fields in natural seeing, and with seeing enhanced by ground layer adaptive optics.
Open stars clusters are collections of stars with similar ages, chemical compositions, and distances from the Sun. These qualities make open clusters important cosmic laboratories for studies of fundamental astrophysics such as: the formation of stars, stellar evolution, dynamical interactions between stars, and the chemical and dynamical evolution and structure of the disk of our Galaxy. Nearby open clusters play a key role in calibrating our measure of cosmic distances.
Supernovae are exploding stars. These stellar explosions are responsible for creating all the elements heavier than iron and for distributing the elements synthesized throughout the star's lifetime to the interstellar medium. The CfA Supernova Group uses various telescopes (Mount Hopkins, MMT, Magellan) to study supernovae of all types, both in nearby and distant galaxies.
The Spitzer Space Telescope is providing astronomers with an unprecedented view of the birth of stars in our Galaxy. Using the Spitzer's IRAC instrument, developed at Cfa, we can probe deep inside of the gas and dust that enshrouds stellar nurseries.
In 2005 Smithsonian astronomers discovered the first "hypervelocity star:" a massive star whose 2 million mph velocity can be explained only by ejection from the Galaxy's massive black hole. This "outcast" star has been thrown out of the Milky Way and is destined to drift in the emptiness of intergalactic space. Smithsonian astronomers are leading the discovery of new hypervelocity stars. Hypervelocity stars tell us about the types of stars orbiting near the central black hole, and the history of stellar interactions with the central black hole.