Research focus: Sara Motta on the mysteries of black holes

9th September 2015

News, Student news, Alumni news

A desire to improve our understanding of black holes is driving research by Junior Research Fellow Sara Motta.

  • An artist's impression of a black hole. Source:

    Artist's impression of a black hole. Source:

  • Junior Research Fellow, Sara Motta

    Junior Research Fellow, Sara Motta


“Although we think we understand how a star dies we don’t know exactly how it becomes a black hole and how it behaves afterwards,” said Sara, and this is something she hopes to make clearer through her research.

Originally from Italy, Sara joined Wadham in March, leaving Spain where she had been working as a post-doctoral researcher at the European Space Astronomy Centre in Madrid, to work in the Astrophysics Sub-Department of the University of Oxford. Her fascination with space began as a child; a combination of a book about constellations and a desire to understand how such things as clouds, rainbows and the universe came about. She went on to study Physics then specialised in Astrophysics.
Sara explains her research: “Galactic objects such as black holes and neutron stars are what remain from a normal star larger than the our Sun, at the end of its life. When a star dies it becomes a neutron star or a black hole depending on how big it was at the beginning. They are also known as star relics and they are normally observable when found in in binary star systems.”  

To study black holes Sara analyses data collected with x-ray satellites which data register the radiation from black holes using instruments similar to a ‘Geiger Counter’.

“If you have a binary system and one of the two stars is a compact object, because of gravity, the compact object will start eating the mass from the other star. The material from the other star forms a hot, bright, shiny disc around the compact object. It is this disk that shows up brightly in x-rays and it is this disk that we can observe with an x-ray telescope. Such potentially damaging x-rays are blocked by the earth’s atmosphere thus they cannot be studied from the ground so are studied by satellites launched out of the atmosphere where they can freely observe the x-ray sky.”

Sara was part of the LOFT consortium, hoping to persuade the European Space Agency to launch a satellite, LOFT, devoted to the study of neutron stars, black holes and other compact objects by means of their very rapid x-ray variability. Although the satellite did not gain ESA approval this time, Sara is hopeful that it will in the future.

“This will give us precise information about what happens to matter when it falls into the black hole. We know the matter spirals down onto the disc and then it disappears in the black hole, but before getting there it emits a lot of light. From this light we can understand what is going on billions of light years away.” find something. And then you feel like you understand a piece of the universe and that is amazing.

Sara Motta

Because of the expense involved in building a satellite, getting it into orbit and operating it afterwards, the proposals and ideas for investigation have to be carefully researched by experts collaborating internationally. The project is then evaluated by the space agency and has to be found to be in the interests of humanity. 

“It is a long process. From the moment you have an idea to the moment that you can launch the satellite, easily 20 years can pass. It is kind of scary that you have to put together the technology which will be useful 20 years from now. As a result, space science incorporates many innovations and breakthroughs in technology, which when you build a satellite are extremely costly, but years later, have an indirect result on the more accessible costs of technology. For example, smart phones can take high quality photos thanks to the same technology used on-board satellites launched 20 years ago. Much of the technology we use in daily life has comes from space science,” said Sara

Sara’s current research investigates data from existing satellites. “I use the predictions of Einstein’s theory of relativity to try to understand what happens to the matter around the black hole. You need to have a clear theory of what you hope to see, what you predict is happening in order to focus your research. As an observational astronomer I work with real light data from real sources, which I compare with the predictions of general relativity.”

“I can work out the velocity of the particles that are orbiting the black holes, because their movement is well predicted by the theory of general relativity and is associated to a certain frequency that I can see in the data using Fourier analysis. This technique allows you to decompose the light from your astrophysical source into many waves, each with a certain frequency. For the past couple of years I have been looking for the specific frequency of particles orbiting black holes and comparing this with my theoretical predictions. For me this is all very exciting – I feel I am contributing to the knowledge of humanity. However it can be incredibly confusing as we have so much data and so many theories that it is often very difficult to create order and decide if a theory is correct or not. But when you find something it is much more rewarding! Then you feel like you understand a piece of the universe and that is amazing.”

Sara admits to bias, but believes that in Astrophysics, the expansion of our general knowledge progresses really fast, probably faster then in many other fields. “Each time you have a good idea and design a new instrument, you expand your knowledge so quickly, discovering new things every day. Think of how much we have learned about Pluto from the New Horizon mission, and from the Philae Lander probe from the Rosetta mission to safely land on a comet only a few months ago!”

More about LOFT

The Large Observatory for X-ray Timing (LOFT) is a proposed ESA space mission originally slated to launch around 2022, and now proposed to launch around 2025.

The mission will be devoted to the study of neutron stars, black holes and other compact objects by means of their very rapid X-ray variability. LOFT is supported by a large international collaboration, led by researchers spread over most of the European countries, including Italy, Switzerland, Germany, Denmark, United Kingdom, Greece, Ireland, the Netherlands, Poland, Czech Republic, Spain, and with contributions from Brazil, Canada, Israel, United States and Turkey. SRON Netherlands Institute for Space Research acts as principal investigator.