Water in our Universe
Water in our Universe
Where Does Water in our Universe Come From?
The strange thing about the abundance of Water in our Universe is not the fact that there is so much of it – but rather the fact that is has taken as long as it has for the sheer amount of water in interstellar space to be confirmed.
The Universe is literally awash with water, and although water in its liquid state is yet to be discovered outside of the solar system, there are huge reservoirs of water in its gaseous and frozen states in the molecular clouds out of which stars are forming as far as the (aided) eye can see.
Until comparatively recently, astronomers believed that the abundance of Water in our Universe arose relatively late in the Universe’s evolution, but recent research suggests that the first water molecules formed as early as one billion years after the Big Bang.
This of course means that much of the Water in our Universe (and by extension, in the solar system), is older than our Solar System, which begs this question – “Where does all the water come from?” Let us explain:
The Origin of Water in our Universe
The story of the Big Bang is a complicated one, and it need not be rehashed here, but suffice to say that the creation of the Universe led to the formation of hydrogen and helium, in the ratio of about 3:1, in favor of hydrogen. Of course, some other, and heavier elements also formed but only in trace amounts, and they do not concern us at this point.
The young Universe was of course very hot, but within a few hundred million years, the first, massive first generation of stars started popping into existence. Although the first stars were not quite as massive as they were once thought to have been, they were massive enough to burn through their supply of hydrogen very quickly.
The life span of the first generation of stars is thought to have been only a few tens of millions of years old, and when they died in massive supernova explosions, their heavier elements synthesis started seeding the Universe with the material for the second generation of stars.
This is admittedly a gross over simplification of the process, but the fact is that relatively large quantities of oxygen were created in this way. Nonetheless, water did not start forming through the combination of oxygen and hydrogen straight away. The Universe was still too hot for this to happen, and besides, the amounts of oxygen required for large-scale water formation only existed in the then very hot nebula that resulted from the deaths of the first stars, and then only in amounts a few thousand times smaller than what we see in “modern” nebulae.
Another complicating factor was the presence of very strong UV radiation that prevented the coming together of oxygen and hydrogen on the one hand, and the fact that UV radiation broke apart the oxygen/hydrogen bond in regions where temperatures were favorable for water to form.
UV Radiation vs. Water Formation
Although it is generally accepted today that water started forming somewhat less than a billion years after the Big Bang, this water was strictly in the gaseous phase, and it occurred only in areas that offered the right conditions.
Nevertheless, although the early nebula were oxygen poor, water formation did not depend on, or need a complex chemical environment. All that was required was hydrogen, oxygen, and a temperature of 800F (26.60C), or 299K- and of course, no UV radiation.
During this early stage in the Universe’s evolution, the ambient temperature was relatively high, which offered the ideal conditions for water to form, but during this time, water formation faced the challenge of the high levels of UV radiation emitted by very energetic young stars that existed in very large numbers.
However, as the first generation stars died out, their places were taken by second generation stars that “sucked up” larger quantities of material per star than existed in their predecessors, and one effect of this was that the spatial separation between stars increased.
This process would have decreased the effect of UV radiation on water molecules, which increased at a rate commensurate with the reduction in UV radiation, and the more water formed, the bigger its cooling effect on the gas clouds in which it existed became.
The Advent of Frozen Water in the Universe
During the first billion years or so of the Universe’s existence, all the water that had formed was in the form of water vapor, and astronomers surmise that water in its frozen state only came about sometime after the process of galaxy formation began.
The early universe was relatively free of dust, which meant that there was nothing for water vapor to condense onto, just like it would not have rained on Earth if there were no dust grains in the atmosphere for water vapor to condense onto to form water droplets, but where did the dust in the early universe come from?
There is much that remains unclear about how the first galaxies formed, but suffice to say that the gravitational effects of the first galaxies collected immense amounts of gas, stars, and whatever else was floating about, to concentrate this material in relatively small volumes of space. The inevitable result of this was collisions between objects – objects that formed from the material around proto-stars that were then forming at a very much higher rate than happens today.
This process is roughly analogous to what happens in the asteroid belt today, where rocky bodies are continuously being ground into dust by asteroids colliding, reforming, and getting crushed into dust by subsequent collisions.
However, stars also emit, or lose some of their heavier elements through normal processes, such as their solar winds, or eruptions from their surfaces, with these particles being about the size of particles found in cigarette smoke, and these processes are by far the largest contributor to space dust.
In practical terms, the dust that resulted from collisions and normal stellar processes in nascent galaxies remained within the nascent galaxies, where the individual grains eventually became coated with condensed water, which then froze.
All of the above was theory, and until very recently, nobody was quite sure what the ratio between water ice and water vapor in space was. New research by Italian and Spanish astronomers have found that most of the water in the Milky Way Galaxy occurs in solid ice crystals, with only about 1% of water being in the gaseous phase.
Moreover, water ice occurs mostly in cold spots within the Galaxy. These cold spots have temperatures as low as -4410F (-163oC) which is only 100C above absolute zero, and which results from large volumes of space being shielded from the heat of nearby stars by dense clouds of dust.
These cold spots are suspected to number in the millions in the galaxy, and although it has been relatively easy to detect ice crystals within these clouds with ground-based telescopes, finding water vapor presented some challenges.
All elements emit light in very specific frequencies that can be seen within the overall spectrum of light emitted by an object, but the water vapor in earth’s atmosphere tends to absorb the light signature emitted by water vapor, which effectively renders water vapor in space invisible.
The image below is a color enhanced version (blue represents water) of the largest known reservoir of water vapor in the Universe – at about 100,000 times as big as the Sun, it contains enough water to fill the oceans on earth a staggering 140 trillion times.
This made it impossible to compare the amount of water vapor with the amount of visible water ice in the galaxy, but a new method developed by Italian astronomer Andrea Moneti has made it possible to detect water vapor semi-directly.
Moneti realized that it might be possible to find the characteristic finger print of water vapor by analyzing the light that had passed through clouds of water vapor on its way to Earth.
Using this method, and comparing his findings with archived data, Moneti and his collaborators have found that the cold regions in the Galaxy contain as much total water (vapor and ice), as warmer regions where stars are actively forming, but where water only exists in its gaseous phase.
Water and Life in Space
Although water vapor has been detected in the discs of gas and clouds that surround proto-stars, the exact role that water plays in the formation of planetary atmospheres is not yet fully understood.
At the risk of under-stating the process, it appears that some of the water is incorporated into gas planets in a modified form; however, as rocky planets form, some of the water is incorporated into the planets themselves, but a large part of the water in the original cloud seems to end up in comets, and it appears that there are some similarities between the water in cold molecular clouds, and the water that goes into the formation of comets.
Comets are essentially dirty ice balls, and they contain many of the same organics that occur in molecular gas clouds, which could mean that comets played, or still play a crucial role in the distribution of life throughout the universe.
It is known, for example, that much of the water we have on earth today was delivered by comets, and it is just possible that the seeds of life were delivered along with the water.
Of course, there is no proof of the latter notion, but the facts that water occurs all over the Universe in vast quantities, and that many of the building blocks of life also occur universally, it is just possible that life on earth may have had its origins in deep space.
*This is a special post, written by one of the greatest astronomy authors of our time. It’s with my most esteemed pleasure to present and thank the great Reinier Breytenbach
Author credit: Reinier Breytenbach