Star Clouds

Wonder was exhibited at Moores Building Contemporary Art Gallery, Fremantle, Western Australia in 2014.

Wonder is an inquiry into locating the individual in the context of the universe. After all, we are all made from stardust.

These paintings, drawings and knitted installations are inspired by a certain type of star, R Coroner Borealis stars (RCBs), which occasionally eject clouds of carbon rich dust, obscuring them from view and decreasing their apparent magnitude. Once this exhalation of dust dissipates, the star regains its former brightness – dimming and brightening with slow, irregular breaths. The RCBs Clouds are knitted imaginings of these carbon rich clouds. The crocheted Star Graphs, catalogue the changes in brightness. Starting from the centre, you can count the number of stitches to ascertain the time period, while the colour represents the brightness of the star. The repeated motif of the oval references images of the Cosmic Microwave Background (echoes of early light, dating back to the Big Bang).

This exhibition features a number of collaborations with good friends, with out whom, these artworks would not have been created. The artworks are all based on the research of astrophysicist Melanie Hampel, and feature elements that have been created by artist/engineer Daniel Macnish and musician Owen Elliott.

WONDER – The RCB Type Star

Melanie Hampel

Only a small fraction of the universe is composed of the normal matter we are familiar with. Physicists call this ‘baryonic matter’. But which material is the most common one? The simplest atom there is, is the hydrogen atom. It is also the most abundant one with ca. 74% of all baryonic matter being hydrogen.

Hydrogen is followed by the noble gas helium which makes up about 24% of the matter. This means that all other elements altogether only contribute up to 2%. Usually the composition of stars is similar to this distribution. The star that has been studied best is our sun. Not surprisingly it is also composed mainly of hydrogen, with a quarter of helium and only a tiny amount of heavier elements, which astronomers refer to as ‘metals’. But there are some kinds of stars that deviate from this expected composition. One of these are the R Coronae Borealis stars, or short: RCBs. Although hydrogen is so common in our universe, the atmospheres of RCB stars do not show any signs of hydrogen! Instead, their main element is helium, which makes up about 99% of their material. RCBs are also classified as so called carbon stars, because they contain a relatively big amount of carbon. But what does relatively mean? In this case it means, that carbon is more abundant than oxygen. The composition of RCBs is quite remarkable, but what really makes them so fascinating and rare objects can only be seen when they are observed over a longer period: They disappear unexpectedly! Just as randomly, they might reappear!

Of course they don’t really disappear, we can just not observe them anymore because suddenly their brightness decreases immensely. This can be as severe as the star getting a few thousands times dimmer over the course of just a few weeks (stars are very old objects that evolve over the time of millions of years, so weeks usually don’t mean anything in the life of a star). It is more than 200 years ago, that the English astronomer Edward Pigott observed in 1795 that the prototype of the RCB-class R CrB was missing from the sky. It reappeared later that year only to disappear again and has been showing this behavior in irregular intervals ever since.

In July 2007 it started another one of its decline phases but it has not reappeared to normal brightness yet. Even for RCB stars this marks an unusually long decline. To visualise the variations in the brightness of a star, one can create a light curve. It shows the intensity of the light (measured in magnitudes) as a function of time. Here you can see the light curve of the prototype R CrB. It shows the variability over the last 27 years. One can clearly see the dips in the curve when the starlight was blocked by a dust cloud. These dips are irregular and one can also see the last decline from 2007 onwards that is much longer than the other ones. Untitled Since then the search for more stars with this unusual behavior has been ongoing. They are still rare objects and only about 100 of them are known today. Since 1795, not only have the number of discovered RCBs increased, the understanding of RCBs and their declines has also improved.

We now know that RCBs produce clouds which are made up of carbon dust. The star randomly ejects a puffy cloud in any direction. This is the reason for the unpredictable declines: If such a cloud gets into the line of sight it obscures the star and blocks its light. As a consequence it seems like the star has disappeared because the light we receive from it is much fainter than usual. Such a cloud might then just dissipate so that the star reappears slowly until it shines at its maximum brightness again.


Melanie Hampel is an Astrophysicist who currently lives, works and studies in Bonn, Germany. Her research on RCBs brought her to Australia in 2012 to study at the Australian National University, examining the mass distribution of RCBs. References: Clayton, G. C. 1996, PASP, 108, 225 Tisserand, P., Clayton, G. C., Welch, D. L., et al. 2013, A&A, 551, A77 We acknowledge with thanks the variable star observations from the AAVSO International Database contributed by observers worldwide and used in this research.

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