How
soon after the Big Bang could water have existed? Not right away,
because water molecules contain oxygen and oxygen had to be formed in
the first stars. Then that oxygen had to disperse and unite with
hydrogen in significant amounts. New theoretical work finds that despite
these complications, water vapor could have been just as abundant in
pockets of space a billion years after the Big Bang as it is today.
"We looked at the chemistry within young molecular clouds containing a
thousand times less oxygen than our Sun. To our surprise, we found we
can get as much water vapor as we see in our own galaxy," says
astrophysicist Avi Loeb of the Harvard-Smithsonian Center for
Astrophysics (CfA).
The early universe lacked elements heavier than hydrogen and helium.
The first generation of stars are believed to have been massive and
short-lived. Those stars generated elements like oxygen, which then
spread outward via stellar winds and supernova explosions. This resulted
in "islands" of gas enriched in heavy elements. Even these islands,
however, were much poorer in oxygen than gas within the Milky Way today.
The team examined the chemical reactions that could lead to the
formation of water within the oxygen-poor environment of early molecular
clouds. They found that at temperatures around 80 degrees Fahrenheit
(300 Kelvin), abundant water could form in the gas phase despite the
relative lack of raw materials.
"These temperatures are likely because the universe then was warmer
than today and the gas was unable to cool effectively," explains lead
author and PhD student Shmuel Bialy of Tel Aviv University.
"The glow of the cosmic microwave background was hotter, and gas
densities were higher," adds Amiel Sternberg, a co-author from Tel Aviv
University.
Although ultraviolet light from stars would break apart water
molecules, after hundreds of millions of years an equilibrium could be
reached between water formation and destruction. The team found that
equilibrium to be similar to levels of water vapor seen in the local
universe.
"You can build up significant quantities of water in the gas phase even without much enrichment in heavy elements," adds Bialy.
This current work calculates how much water could exist in the gas
phase within molecular clouds that will form later generations of stars
and planets. It doesn't address how much water would exist in ice form
(which dominates within our galaxy) or what fraction of all the water
might actually be incorporated into newly forming planetary systems
This work has been accepted for publication in the Astrophysical Journal Letters and is available online.
The authors are Shmuel Bialy & Amiel Sternberg (Tel Aviv
University) and Avi Loeb (CfA). This joint project was carried out as
part of the Raymond and Beverly Sackler Tel Aviv University - Harvard
Astronomy Program.
Headquartered
in Cambridge, Mass., the Harvard-Smithsonian Center for Astrophysics
(CfA) is a joint collaboration between the Smithsonian Astrophysical
Observatory and the Harvard College Observatory. CfA scientists,
organized into six research divisions, study the origin, evolution and
ultimate fate of the universe.
For more information, contact:
Christine Pulliam
Public Affairs Specialist
Harvard-Smithsonian Center for Astrophysics
617-495-7463
cpulliam@cfa.harvard.edu
Christine Pulliam
Public Affairs Specialist
Harvard-Smithsonian Center for Astrophysics
617-495-7463
cpulliam@cfa.harvard.edu
