Tuesday, Feb 14th: Are galaxies foggy?

Event Date: 

Tuesday, February 14, 2017 - 4:00pm

Event Date Details: 

Refreshments will be served at 3:40pm.

Event Location: 

  • Broida 1640
  • Physics Colloquium

The stellar disks of galaxies are enormous, but they are only the tip of the iceberg: galaxies are embedded in much larger structures known as halos, roughly ten times as big and ten times as massive as the galaxy disk.  Galaxy halos are expected to be filled with hot, diffuse plasma; this hot plasma plays a crucial role galaxy formation, and fundamentally determines the mass-scale of galaxies.  As new observational techniques begin to probe halo gas, however, they have found that their halos are also full of cold gas.  This cold gas is unexpected because it cannot be supported against gravity.  Moreover, these observations typically indicate a relatively modest total fraction of cold gas (~0.01% by volume), yet find it in essentially every sightline through the galaxy... it's hard to understand how so little gas manages to be present everywhere.  I will show that cold gas clouds are prone to "shattering" into fragments, producing a mist of tiny, distributed cloudlets which naturally reproduces these unexpected observations.  This same effect dramatically enhances the drag force coupling the dynamics of cold and hot gasses, with potentially dramatic consequences for galaxy formation; I will discuss ongoing research into this effect.