Caroline Herschel was a famous astronomer. She discovered eight comets, and made observations of nearby stars and distant galaxies. She did all this 200 years ago, during a time when women didn’t usually have jobs in science, and she was the first woman to be paid for her scientific work.

Scientists today

Dr Mark SullivanCaroline Herschel catalogued huge numbers of nebulae (galaxies and clusters of stars) whilst hunting for comets. Dr Mark Sullivan is an astrophysicist working at the University of Oxford, who also studies objects deep in space, specialising in supernovae - exploding stars.

Can you briefly describe your research?

I'm trying to answer the question "What is the Universe made of?".

This question has inspired generations of scientists - so perhaps surprisingly the nature of over two thirds of the Universe is a complete mystery to us. The galaxies, stars and planets that we can see make up less than 5% of the Universe. About a quarter of the Universe is in the form of Dark Matter - material that we cannot see (it does not shine like stars), but which we know must be there because of its gravitational effect on the stars that we can see. The remaining 70% that I study is even more mysterious.

We know that the Universe is getting bigger, an expansion driven by a "Big Bang" nearly 14 billion years ago.  As the Universe contains objects like stars and planets, gravity should pull everything together and slow down this expansion. However, experiments in the last decade have come to a quite different and startling conclusion: our Universe is expanding at an ever faster speed, the opposite to the effect of gravity. This is an astonishing result, and there is now feverish research into trying to discover what is causing this accelerating expansion.  We call the substance responsible "dark energy" (astronomers are not original at naming things!), and we think that it makes up about 70% of the Universe with an incredibly low density - equivalent to less than a speck of dust in a volume of space the size of the Earth. Beyond that, there are only theories. Find out more about Dark Energy here.

I use cosmic explosions known as supernovae to study this dark energy.

SupernovaSupernovae, like the one in the picture on the left, are stunning objects in their own right, the dramatic and violent endpoints of a star's life, thermonuclear explosions (caused by atomic nuclei fusing at high temperatures) which can outshine galaxies.  A particular type are unique as they always explode with nearly the same brightness. Such objects are "standard candles", immensely useful to astronomers, the equivalent of cosmic rulers which can measure vast intergalactic distances. I hunt out these explosions billions of light-years away, and measure their brightness as they appear to us on Earth. When we compare the level of brightness we perceive with  a knowledge of their actual brightness we can infer their distance, and, from that, information about the geometry and history of the Universe.

Who or what inspired you to become a scientist?

I've always liked and enjoyed science: the idea of being able to explain the everyday world around us has always been attractive to me.

NebulaAstronomy has always been my favourite. I remember a holiday as a young teenager where some local amateur astronomers had set-up a telescope and pointed it at various objects in the sky. When I looked through it, it was pointed at a nebular (a region of space where new stars are formed, see right). While it wasn't as beautiful as images taken with the Hubble Space Telescope, it was still stunning: something completely invisible to the naked eye was easily revealed through only a small telescope. The following Summer, in the warm evenings and nights (much better than on cold Winter nights) I learnt the basic constellations, and my way around the night sky. I never became expert at it (I still don't know all the constellations), but just lying and looking at the sky was enough to inspire me to take astronomy further.

Of course, professional astronomy is a serious science that requires a significant level of training. But, the great thing is that it is also a science that anyone can get involved in: from just looking up at night, to using binoculars to see faint galaxies, to participating in citizen science projects like Galaxy Zoo (or Supernova Zoo!). It's one of the most accessible sciences.

What subjects did you study at A-level [or equivalent] and what did you do your degree in?

My A-levels were in Physics, Chemistry, Maths and Geography. The geography is perhaps a surprise (rather than, say, further maths) but I wanted something a little different from pure science.


What do you love about your job?

I like knowing that when I come into work in the morning, there is a chance that by the time I go home at night, I will have discovered something that nobody knew about before. Perhaps a new supernova at some mind-boggling distance from the Earth, or perhaps some new constraint on the nature of Dark Energy. This doesn't happen every day of course - my job is like many others in that some days you wonder what you've really achieved. But those days are usually few in number.

Studying supernovae is particularly fun in this regard. When I go observing (maybe 3-4 times per year), I'm almost guaranteed to observe something new - because the supernovae are found only a few days before I arrive at the observatory (sometimes just the previous night) it's always organised chaos at the telescope, getting the right observations of the best targets. But, somehow, it all comes together, and I usually leave the observatory armed with new supernova discoveries for my research.


What are your hobbies?

ObservatoryI like sport (especially cricket), and travel. One privilege of being an astronomer is that travel to distant places is common. Professional observatories tend to be located on top of mountains, above the clouds and away from big cities and towns, the light from which could drown out the stars and galaxies that we study. There aren't any places in the UK which are like that! And the mountain tops themselves seem like nothing on Earth - very dry and very high, with landscapes like something from Mars. (Of course, it's not all fun - the travel can be exhausting, with long plane rides for just a few nights observing!)


If you could go back in time and meet Caroline Herschel, what would you like to ask her?

Caroline Herschel lived in a very different age - one where there were no computers, electronic cameras, or even photographic plates to assist with her observations. Making accurate observations of the sky would have been incredibly laborious and difficult, without the benefit of the clear skies typically enjoyed by modern day astronomers (observing from Slough is not quite the same as observing from La Palma!). And, of course, at the same time she would have inevitably been living in the shadow of her brother, William Herschel, the discoverer of Uranus and after whom a large telescope on La Palma is named. Nonetheless, she made significant contributions to astronomy, discovering numerous comets, and publishing accurate catalogues of stars (and even has a poem dedicated to her).

I would like to ask her what inspired her to dedicate her life to science, astronomy and cataloguing the sky, at a time when women scientists in general (and women astronomers in particular) were so rare? What motivated her during her long scientific studies? And, how difficult was it for her to gain the recognition that she deserved? It would be fascinating to hear if there are any parallels between life as a scientist then, and life as a scientist today.