The birth of stars and planets

Which molecules are found in the space where new stars and planets form? And how exactly do these celestial bodies form? Ewine van Dishoeck uses the most powerful telescopes in the world, in locations such as the mountains of Chili and Hawaii, to study this. These telescopes can detect the radiation of molecules in gas clouds. Van Dishoeck and her colleagues use these ‘fingerprints’ to determine which molecules are present in the gas clouds and how likely it is that a star or planet will form there. The molecules also provide information on the physical conditions in the clouds, for example how hot or thin the cloud is.

The birth process works as follows. Sooner or later, the gas cloud, which contains all sorts of molecules and dust particles, collapses under its own gravity. As the cloud collapses, a young star forms in its centre. Often, some of the molecules continue to rotate in a disc around this young star, the ‘sun’ of the new system. Such a disc is roughly equal in diameter to our own solar system. While the sun grows, dust particles in the disc clump together, thus forming new planets in the system. However, we do not know exactly how these planets form and why the solar systems that have been discovered differ so greatly from ours. Ewine van Dishoeck and her colleagues hope that by researching the formation process of large numbers of young stars in different stages of evolution they will be able to answer this question.

Van Dishoeck is also trying to answer the question of how molecules that are already present in the original gas cloud end up on the young planets. ‘One of the theories is that this is caused when comets and asteroids strike that have molecules “stuck” to them, but we don’t know for sure,’ explains Van Dishoeck. ‘Once we can answer this question, we will know more about whether the earth might have a little brother or sister somewhere that can sustain life. We will also know more about how our own earth, and life on it, developed.’

The hunt for water

14 May 2009 is a date that Ewine van Dishoeck will never forget. It is the day when the Herschel Satellite was launched with the mission: seek water! Van Dishoeck was involved in the preparations for decades, before everything suddenly speeded up. Herschel did manage to find an excess of water in space in 2010.

The discovery of water is important, because ice in the clouds where new stars and planets form plays an important role in the development of these new celestial bodies. It is also interesting to see how much of that water ends up on the young planet itself, because the presence of water is an important condition for life to  develop.

You cannot observe these processes from the ground, because our own atmosphere contains too much water. Herschel therefore measures which thin gas clouds contain high concentrations of water. The images that the telescope sends enable Ewine van Dishoeck and her Leiden colleague Michiel Hogerheijde to see what happens to that water as planets form and how much water is in the zone of the disc where planets form. They also search for ‘heavy’ water (water that has had one hydrogen atom replaced by a heavier deuterium atom), because the data could tell us about the origins of water on our own planet. The research bears the evocative name: WISH (Water In Star-forming regions with Herschel).

Herschel represents a once-in-a-lifetime opportunity for this research. The telescope exhausted its supply of coolant in 2013 and ceased to operate, and there will be no such mission in the next 20 to 30 years. Van Dishoeck and her colleagues therefore seized the opportunity to gather as much data as possible. Although Herschel is ‘exhausted’, the data will still some take five years to collate.

Read more on the project WISH here.

The space laboratory

For Ewine van Dishoeck space is an exotic laboratory, because thin gas clouds in the cosmos contain molecules that are not present on earth and that could never become part of our daily lives. As regards the molecules that are commonplace for us, such as water, the question is how they could have developed in that thin space: how can hydrogen and oxygen atoms ever find each other in all that empty space?

Scientists suspected that dust particles had an important role to play in this, but you cannot simply bring the molecules and compounds that you observe in space back to earth to test this theory.

In a special lab that Van Dishoeck developed with funding from American philanthropists, astronomers led by her colleague Harold Linnartz reproduce the special conditions in space in order to answer such questions and test their theories. They grow ice mantles on dust particles before bombarding them with UV light and particles, and have demonstrated that water really can develop on dust particles if you bombard them with hydrogen atoms. Complex organic molecules such as alcohol can also be formed.

Ewine van Dishoeck is also fascinated by the question of how to break down certain compounds again. ‘UV radiation from stars can destroy molecules in space. I study that process.’

The research into molecules in space has turned our standard terrestrial chemistry upside down. ‘You really need to start from the beginning when doing chemical research in space,’ says Van Dishoeck. She therefore also works a lot with standard ‘terrestrial’ chemists, who set to work on this wonderful new world in the lab or at their computers.

Super telescopes

Without state-of-the-art telescopes, it would be impossible for astronomers to conduct further research. This also applies for Ewine van Dishoeck and her colleagues, if they wish to study the formation of new galaxies in thin clouds. ‘Ten years ago, telescopes could look into the middle of a cloud, but you can now zoom in with a factor of ten to a hundred. I often compare viewing such a cloud to an aerial photo of a city. First we saw the city as a big patch with a few roofs and now we can see the market stalls.’

Over the years, Ewine van Dishoeck has been involved in the development of different telescopes: the Herschel telescope, for example. She attended the first meeting on this back in the 1980s. ‘As an astronomer you are always dealing with the science of the future. It is extremely important to involve astronomers in the initial phases.’ Another large project in which Van Dishoeck has been involved is ALMA or the Atacama Large Millimeter Array. This is a collection of 66 telescopes that are being built at a height of 5000 metres in Chile close to its borders with Argentina and Bolivia. There are currently 39 telescopes. This super battery of telescopes allows astronomers to make very detailed recordings of gas in space. ALMA enables Van Dishoeck to take a closer look at the formation of stars and planets, and may even see the fingerprints of complex molecules that they have reproduced in the lab but this time ‘live’.

Van Dishoeck spent years raising money and enlisting people for ALMA as well as organising and supervising its construction. ‘Alma means “soul” in Spanish. And I think that I have sold a small piece of my soul to ALMA.’

A third project in which she is involved is the James Webb Space Telescope. This successor to the Hubble Telescope will be launched in around 2018. The telescope will have a mid-infrared camera on board (parts of which were built in the Netherlands) that is so sensitive that you could see a burning candle on Jupiter through it. The telescope will be used for further research into planet formation.