Our Exhibition

The exhibition includes:

 

 

Figure 1: The standard layout of the Stars 'r' Us! posters which form part of our exhibit.

 

Figure 2: The "Life of a Star" poster. To see a larger version, click on the image above.

 

Life of a Star

The cosmos evolves through a continual cycle of star birth, life and death. Stars are formed from vast clouds of gas and dust. They age and then they die either by simply cooling down or in the spectacular brilliance of an exploding star. In dying, old stars release atoms into the cosmos, perpetuating the cycle. We are the products of such cycles. The very atoms from which we are formed were forged in the nuclear furnaces of ancient stars even before our own Sun was born.  Today, astronomers have realised that chemistry plays a crucial part in controlling this evolutionary cycle. With the help of chemists, they have created a new scientific discipline, astrochemistry, which seeks to understand the important role played by chemistry in our cosmos.

 

Poster Summary

Stars may seem eternal but they are not. They grow old and die but the stuff they are made from lives on...

 

Stars in Colour

The cosmos was originally formed from atomic hydrogen with a splash of helium and a pinch of lithium. The first generation of stars took these elements and in their brief lives began a process of chemically enriching the cosmos that continues today. Much of our current periodic table was, and continues to be, born in the nuclear furnaces of stars. Nuclear synthesis takes hydrogen nuclei and fuses them into heavier and heavier atoms. Spectacular supernova events ensure that the energetically unfavoured fusion processes leading to heavy atoms fill out the remainder of the table. We can see this process going on in our own star - the Sun. Atoms absorb and emit light that is characteristic of their structure. For example, neon emits characteristic red light and argon emits a characteristic blue green light. You can see these emission lines using a simple spectroscope as in our Exhibit 1 - Seeing Stars. Astronomers use basically the same tools to look at stars, linking spectrographs to their telescopes to measure the spectra of distant objects. Some objects, such as our Sun, produce relatively simple spectra showing the range of atoms present in the star. Other objects, such as low mass stars and "failed stars" or brown dwarfs (which are the missing link between gas giant planets like Jupiter and small, low-mass stars), are so cool that their spectra are full of molecular fingerprints. However, the spectra of all objects, as they grow older, become richer. We see evidence for the formation of molecules in the cooler parts of the stellar envelope. These molecules can be released from the stars into the vast gulfs of space between the stars (the interstellar medium) only to be reduced to their constituent atoms by the harsh radiation environment to be found there. However, some molecules such as SiO and TiO can condense in the outflows from old stars to form dust resistant to the ravages of the interstellar medium.

 

Poster Summary

Just by looking at the colour of a star it is possible to work out how old it is, how hot it is and what it is made of…

 

 

Figure 2: The "Stars in Colour" poster. To see a larger version, click on the image above.

 

Exhibit 1: Seeing Stars.

 

 

Figure 3: The "Chemical Fingerprints" poster. To see a larger version, click on the image above.

 

 

Exhibit 2: Seeing the Unseen.

 

 

 

 

Chemical Fingerprints

Molecules, in contrast to atoms, exhibit a much more complex spectroscopy. They can rotate (observed in the radio and microwave regions of the electromagnetic spectrum). They can vibrate (observed in the infrared). Observations tell us that in certain regions of the space between the stars, we can find dense clouds rich in molecules (See our Exhibit 2 - Seeing the Unseen). Over 150 molecules have been identified in these regions. Somewhat fewer, but still a significant number, have been identified in less dense regions. But how did they get there? If the interstellar medium only contains atoms and dust then chemistry is the answer.

 

Poster Summary 

Every atom or molecule has a unique ‘fingerprint’, which is formed from ‘electromagnetic radiation’…

 

 

 

Chemistry in the Cold

But how is this rich chemical soup that we observe in dense clouds formed? At first this might sound like a trivial question until we realise how extreme the conditions in these dense clouds really are. First of all, let us consider the temperature. As we know chemical reactions get slower as we reduce the temperature. This is simply because we have to put energy into most reactions to get them going. They must overcome an activation barrier. At low temperatures fewer molecules can cross that barrier and the reaction slows. At the temperatures of dense clouds (more than 250 degree C below zero), chemistry involving activated processes effectively stops. There are virtually no molecules with sufficient energy to cross the barrier. Chemical reactions also tend to get slower as we reduce the pressure. We can think of a chemical reaction as a collision. Many important reactions require that such reactive collisions to occur in the presence of a third collision partner to help stabilise the reaction product by removing some of its excess energy. Such three-body collisions are important in processes in the chemistry of our atmosphere and in combustion reactions for example. However, as we lower the pressure, the likelihood of such processes occurring is rapidly reduced. At the pressures we observe in the densest clouds the likelihood of a three- body collision is so small as to be negligible even on the timescale of billions of years.

How then do we get any chemistry at all in these clouds? We need reactions with no activation barriers that can proceed via simple two body processes. Reactions involving ions, molecules and reactive molecular fragments in the gas phase can go a long way to explaining the chemical richness of these environments. However, such processes cannot account for all of the complexity we observe. Indeed they cannot even account for the amount of molecular hydrogen that is observed. Yet molecular hydrogen is the most abundant molecule in the cosmos. We need something more than just gas phase chemistry. That something is the interaction of the gas with the dust found in these clouds and it is now accepted that the gas- dust interaction plays a key role in the chemistry of the interstellar medium.

But why are these molecules so important? The dense regions in which we see molecules are also the regions of our cosmos in which new stars and their planetary systems are being formed. As a small clump of cold dense gas starts to collapse under the influence of gravity it will warm up. The pressure of the warming gas will oppose the collapse unless that thermal energy can be removed from the clump. Molecules provide the means of radiating that energy away on rotational and vibrational transitions. Indeed this is how we detect most of the molecules – by their emission in the radio and microwave region. So it becomes very important to know how quickly molecules are formed in the gas phase and on the grain surfaces and how quickly they can be released from their icy mantles into the gas phase as a gas clump warms.

Poster Summary

In order to react, atoms must collide with one another but it is so cold in space, and with such low pressures. It’s a wonder any chemistry goes on at all…

 

 

Figure 4: The "Low Temperature" and "Low Pressure" posters. To see a larger versions, click on the images above.

 

Figure 5: The "Chemistry in the Cold" poster. To see a larger version, click on the image above.

 

 

Figure 6: The "Reproducing Space in the Laboratory" poster. To see a larger version, click on the image above.

 

Exhibit 3: Laboratory Ultrahigh Vacuum Apparatus.

Reproducing Space in the Laboratory

In studying the chemistry and physics of grain surfaces we employ complex laboratory apparatus that allows us to mimic the conditions in a cold, dense cloud. Our ultrahigh vacuum apparatus reproduces pressures close to those observed in the dense regions where stars and planets are being formed. Helium refrigerators then allow us to cool a model surface to colder than 250 degrees C below zero to reflect the temperatures in such environments. We can then create beams of atoms and molecules to shine on the cold surfaces and use infrared spectroscopy to investigate the growing ices and the interaction of simple atoms and molecules with such ices. In parallel, we use mass spectrometry to study the low-pressure gas phase. As an illustration of this work, we have studied how carbon monoxide interacts with water ice grown from water vapour at relevant temperatures. Our combination of experiments tells us that the interaction is much more complex that previously thought. The key goal to achieve in the next couple of years is to understand the actual processes by which molecules are formed on the cold grain surfaces themselves. We need to understand the formation of not just molecular hydrogen but more complex molecules such as water, ammonia, methane, methanol etc. and even the molecules that are the precursors to life.

 

 

Poster Summary

Our research involves looking at the processes that occur on the surfaces of dust grains and ice in space…

 

Creating Life

The icy grains found in the cold, dense clouds have more than one role to play in the evolution of the cosmos. Bathed in cosmic radiation (ultraviolet light, protons and electrons), chemical transformations can occur in these chemical nanofactories that convert the simple ices of water, ammonia, carbon monoxide etc. into more complex carbon containing molecules. Evidence suggests that such processing may even produce the molecular precursors to life such the amino acids, nucleic acid bases, and simple sugars. The recent observation of glycine by radio astronomy supports this idea. Laboratory experiments are also in progress, to explore how such precursor molecules may have been transformed into those necessary for the development of biological molecules. Such research in turn is providing a new concept of the evolution of the early chemistry on Earth and the conditions for the origins of life, conditions that may be common on other planets in other solar systems. The basic ingredients of life are transported to a planet by comets and meteorites (the latter having been shown to contain over 20 amino acids from which life may develop). They seed the primordial oceans and atmosphere of any young planet associated with a new star and provide a vital ‘kick start’ to the development of life on that planet. This is exogenous delivery.

Alternatively, life may begin by forming the prebiotic molecules in situ within the energetic environment of the oceans and atmosphere of a young planet, for example lightening may trigger chemistry that combines simple molecules compounds into amino acids, sugars and other important species. This is endogenous synthesis.

if exogenous delivery is true, it suggests that since comets and meteorites are likely to be common to any new solar system in the galaxy then the conditions for life may be common throughout the universe. However, if prebiotic compounds have to be formed in the atmosphere/oceans of a planet then life may only arise when a strict set of conditions are met making the successful development much less likely. Miller and Urey first investigated the hypothesis that prebiotic compounds could be formed in the early Earth’s atmosphere/oceans some 50 years ago. We can add a modern twist to this famous experiment by utilising modern analytical tools to look at how quickly complexity arises in a simple primordial broth.

 

Poster Summary

We now know how complex molecules are formed in the stars but how do chemicals become life?

 

 

Figure 7: The "Creating Life" poster. To see a larger version, click on the image above.

Exhibit 4: Life in a Jar

Summary

How life developed and whether the conditions for life are universal is one of the major unsolved scientific questions and is now the subject of a new scientific discipline - astrobiology! However, it is important to realise that unless the basic chemistry occurs, which we need to observe, understand and demonstrate in the laboratory, then biology might never occur. With the growing number of observations of planets around distant stars (exoplanets), we must use our knowledge of chemistry to seek out characteristic markers for life within the spectral signatures of these planets. Then perhaps one day we will learn if we are unique or whether we are just one variation in a large number of life forms throughout the universe!

 

 

Built and Maintained by Members of the SRU Consortium