Dr. John Bally
Colorado
University of Florida Astronomy Colloquium - Apr. 25th, 2008
Star and Planet Formation in Nearby Regions
I will review the lessons learned from studies of the closest star forming regions in
Perseus and Orion. The Orion complex contains the nearest on-going sites of both high
and low mass star formation, making it an ideal laboratory. The expanding Gould Belt
of stars and gas may have led to the formation of the proto-Orion clouds about 15 to 20
Myr ago. The first sub-group of the Orion OB association was born about 10 to 15 Myr
ago. Dozens of massive stars and a sequence of expanding OB association sub-groups
have been forming in Orion ever since. More than a dozen supernova explosions within
the last 5 to 10 Myr created the 100 by 300 pc diameter Orion-Eridanus bubble. The
bubble overran and compressed the Orion A and B molecular clouds, triggering the birth
of massive stars and clusters including the Orion Nebula, NGC 1977, NGC 2024, and
other groups throughout the Orion complex. Thus, Orion provides compelling evidence
for triggered star formation.
Massive (and low-mass) stars continue to form in the dense molecular ridge immediately
behind the Orion Nebula. Some of these massive stars have large space velocities,
indicating that they were recently ejected from their birth environment by the decay of a
non-hierarchical multiple massive star system. Radial velocity and proper motion
measurements indicate that the Orion OMC1 outflow and the ejection of thee massive
stars, the BN object and radio sources I and n, may have had a common origin. I will
discuss a specific model for this event that may shed light on the theory of massive star
formation, prompt mass segregation in forming clusters, the origin of runaway massive
stars, and the high multiplicity fraction at the upper end of the stellar mass distribution.
Detailed studies of the young star population in Orion have shown that massive stars have
a profound impact on the formation and evolution planetary systems, and on the outflows
that young stars often produce. Finally, I will comment on several unsolved mysteries
regarding Orion's massive stars. Where did Betelgeuse and Rigel form? Are they part of
the Orion OB association? Or, do they represent a previously unrecognized region of
recent massive star formation located between us and Orion?