Max Planck Institute for Astronomy  

Markus Feldt

PSF Seminar
Massive YSOs

The Formation of Massive Stars

       Stars are born in clouds of gas and dust,  and they are most probably born in the centres of particularly  cool and dense regions, sometimes referred to as  cores.  These cores are quasi-stable. They may  survive for many times their free-fall collapse timescales,  but at some time they begin to fall under the force of their self gravity and collapse to create new star.  The more massive such a core is, the faster the collapse and the evolution of the resulting young (proto-)star. And the more massive the core, the more massive the new star will be.  Because these massive stars (M > 8Msun) form so quickly, they are embedded inside the dense clouds for a considerable fraction of their lifetime and are thus hard to observe by astronomers during their childhood.  And because these stars are also very hot, they are doing rather violent things to the dense cloud around them:  The dust gets molten and/or blown away, the gas becomes ionized. Sometimes they even start destroying accretion disks around neighbouring (lower-mass) stars.  By these means, such young massive stars create the objects that I am most interested in: Ultracompact HII Regions.