My current Research

 

StAr Formation

Following the Trail of Water and Organics

Sample of observational results from the dark cloud B68.

Plot shows dust absorption (top right) and emission (top left) and molecular emission maps shown at bottom.  Figure taken from Bergin & Tafalla 2007, ARAA

Spectrum from the HEXOS key program using the HIFI instrument on board Herschel.  Spectrum is from a star forming region in Orion (called Orion KL) centered near 1.1 THz and illustrate the rich molecular spectrum that is dominated by organics and water.

Stars are born inside giant clouds composed of gas and tiny solid particles that astronomers call dust grains. These clouds contain enough mass to create of millions of stars like the Sun and are predominantly molecular in composition. These regions can be observed with emission arising from gaseous molecules which are effective probes of the birth sites of star and planetary systems.

With collaborators I have explored the chemical changes associated with stellar birth.   These are summarized in a review article: Bergin & Tafalla 2007

To understand the origin of Earth’s water I have been involved in several observational and theoretical efforts.  In the previous decade I was associated with NASA's Submillimeter Wave Astronomy Satellite (SWAS) which was in operation from 1998 through 2003. During this time SWAS found the surprising result that water vapor in the interstellar medium was not as abundant as had been previously theorized. Water is likely present, but mainly in the form of water ice coating tiny solid silicate grains. With the launch of the Herschel Space Telescope in 2009 I have been working with international teams through the Herschel Key Programs WISH, DIGIT, and HOPS.   Our initial results from WISH observations have provided clear confirmation of the previous results.  The ice-covered grains could collide, stick together and form increasingly larger objects, eventually becoming the building blocks of planets in a new solar system.  

My theoretical efforts have explored the major formation and destruction paths for water in all phases.   One example is shown above where with my post-doctoral fellow Tom Bethell, I have theorized that water can rapidly form in abundance at the surface of the planet-forming disk.   We suggested that water itself is capable of shielding the planet-forming gas from the destructive effects of stellar radiation.  This is analogous to the way the Earth’s ozone layer protects life; here this layer protects the chemistry of planet formation.

The emerging field of astrobiology seeks to explore possible links between chemistry in space and the origins of life. While the exact nature of this connection is uncertain, the presence of water and complex organics in the interstellar medium, in comets within our own solar system, and on the Earth (Mars?) provides the clearest relation.  My research focuses on deciphering the clues on how water and organics form and following the trail though towards the stage of planetary birth.

To explore the origins of organics I have been leading the Hershel Guaranteed Time Key Program “Herschel observations of EXtra-Ordinary Sources (HEXOS)”.  HEXOS has surveyed the spectrum of molecular emission in the richest molecular sources in the galaxy.  A small sample of the rich spectrum is shown to the right.  In our entire spectrum we have likely detected over 100,000 molecular emission lines that can be used to identify new molecules and explore the full extent of molecular chemistry in space.


Schematic of the structure of the terrestrial planet-forming region within a disk near a young Sun as envisaged by Bethell and Bergin 2009.   Our model suggests that water vapor on the surface of the planet-forming disk can provide a protective shield that allows for a rich chemistry deep inside where planets are born.