Alessandra Buonanno is a theoretical physicist working in the field of gravitational waves. She is at present a Director at the Max Planck Institute for Gravitational Physics, (Albert Einstein Institute) in Potsdam, Germany. On a recent visit to ICTS-TIFR, Bengaluru to participate in the Future of Gravitational-Wave Astronomy program held between 19- 22 August 2019, she spoke to us on her journey as a scientist and the exciting work on gravitational waves being done in India.

IH: Please tell us about your current research interests.

AB: I work on modelling gravitational waves from binary systems composed of black holes and neutron stars. Our team routinely provides LIGO and Virgo with accurate waveform models, that are used to search for gravitational-wave signals in the data and infers the properties of the astrophysical sources. As the detectors become more and more sensitive, we need to include more physics in the waveform models, in order to detect more signals and interpret them. For example, we would like to know whether the signals were coming from binary black holes or from other astrophysical objects and whether the black holes were spinning, or whether they were moving on eccentric or quasi-circular orbits. To interpret the gravitational signals, we need to understand how the shape of the waveforms changes over time, as the two bodies steadily and speedily approach merger. Otherwise, signals might be mis-identified. Also, since LIGO and Virgo use several hundred thousand waveform models to carry out analyses, the waveforms need to be accurate and fast.

Our team uses a synergistic approach that improves approximate, but fast waveforms using highly accurate, but slow waveforms produced by supercomputers. This exercise is repeated many times. We are also working on developing novel ideas to solve the two-body problem in General Relativity in an approximate but quick way, which may reduce the production of many time consuming numerical simulations. I am also interested in developing analyses that can extract precise signatures (smoking-guns) of the nature of remnant objects formed after the merger of two compact objects, such as black holes and/or neutron stars. Indeed, we expect that two black holes merge into a new black hole. But, how can we prove it? In the field of General Relativity, black hole solutions with zero intrinsic rotation (or spin) were found by Schwarzschild in 1916. There also exists a solution for black holes with non-zero intrinsic rotation, found by Roy Kerr in the mid-1960s. But the question to address is whether the merger of two black holes forms a Schwarzschild/Kerr black hole or something else?

Black holes newly formed through merger are expected to go through a phase called ring-down, during which slight distortions cause the black hole to vibrate emitting gravitational radiation in the form of quasi-normal modes. A black hole is like a bell; if you perturb it, it rings spacetime emitting a superposition of quasi-normal modes. Like in atom spectroscopy, if the quasi-normal modes are extracted, one can identify the nature of the object and test if it agrees with the Schwarzschild or Kerr solution in Einstein’s theory of General Relativity. These tests will be possible with LIGO and Virgo in the future, with better sensitivity and higher signal-to-noise ratios.

IH: How did you get interested in the field of gravitational waves?

AB: I started studying gravitational waves by chance. I was initially trained as a theoretical physicist and a particle physicist. My Ph.D. thesis was on cosmology of the early universe. I worked on models of cosmic inflation inspired by string theory. Cosmic inflation is a phenomenon that we believe occurred at very early times in the history of the universe, within a miniscule fraction of a second after it was born.

After my Ph.D. thesis, I spent nine months at CERN, and then I started a postdoctoral fellowship at the Institute des Hautes Etudes Scientifiques (IHES) in France, outside Paris. It was there that I began working on gravitational waves from binary systems with Dr. Thibault Damour, after spending the first year working with him on cosmology and cosmic strings.

After finishing my time at IHES, I had to choose between joining Dr. Kip Thorne’s group at Caltech to study gravitational waves and Fermilab outside Chicago to study cosmology. After a lot of thinking, I chose the former as during the late 90s, gravitational waves were still an unexplored and new field, and it seemed promising and exciting to me. Experiments were still being built and no-one knew when gravitational waves would be first detected on Earth. Caltech also hosted a very large group of scientists working on theoretical, experimental and data-analysis aspects of gravitational waves. I took advantage of this unique opportunity and learned a lot of science related to gravitational waves, and I also acquired new skills.

IH: Share with us your journey as a woman in science?

AB: I am very much aware of the issues that many women encounter in science and academia. But I have been very fortunate to have not experienced them first-hand. During my training as a postdoctoral scholar or even previous to that, I cannot recall of any experience where I felt I was being discriminated because of my gender. I have always been very focused on my work and I have worked hard to achieve my goals. Perhaps because I was very self-critical of my work and very determined to not be distracted from my goals, it didn’t occur to me that such discrimination did exist around me.

Growing up I always had the support of my family in whatever I chose to do and I was never discriminated or treated differently for being a girl. No one at home told me I couldn’t do research because I was a girl. I also have been very lucky to have had excellent mentors and colleagues. I had fruitful and pleasant collaborations with other graduate students and post-docs, and I have very fond memories of my post-doc days. My Ph.D. supervisor Dr. Michele Maggiore, Dr. Gabriele Veneziano my post-doc supervisor at CERN, Dr. Thibault Damour at IHES, and Dr. Kip Thorne at Caltech, have all inspired me and have provided me with invaluable advice during my professional career. All I can say is that I have been very lucky and am very grateful to them. But I do know there exists a gender gap in academia. Many women quit research after their Ph.D. thesis or post-docs, and the numbers reduce as one goes higher up in the academia ladder. And of course, I see this pattern in the Max Planck Society also. The number of women directors is still small. Also, the area in which I work, that is theoretical physics, has very few women scientists - even lesser than other areas such as astrophysics. That’s something I have noticed here at ICTS too. But yes, there is a lot to be done to retain more women in science and it has to start much before women enter university. It should begin much earlier in life; both at school and at home. Boys and girls have to be treated equally since early on in their childhood, and young girls should be encouraged to be confident, to believe in themselves, and take up science, if that is what they wish to do.

At the Max Planck Institute we have researchers and scientists from all over the world. The work we do goes beyond geo-political boundaries. There are many countries that are still not economically strong enough to support world class research facilities and infrastructures, and the people of these countries have less opportunities to take up science as a career. Science should have no boundaries and as scientists, we should ensure it is done that way. It is true that we need more women in science, but we must also work towards increasing diversity that goes beyond the gender category.

IH: Gravitational waves is a new and emerging topic in Indian science. What is your opinion on the work that is being done here in India?

AB: It’s a very exciting time for science in India. The interest on gravitational waves has gone up in the last decade and of course India has a long history related to this field. Dr. Sanjeev Dhurandhar (IUCAA, Pune) spoke about this during the workshop. There are also decades of excellent work done by Prof. Bala Iyer (ICTS, Bangalore) and many other Indian colleagues.

Soon, work will begin on building a new gravitational-wave detector in India. It is called LIGO-India and is funded by the Government of India. We hope that it will functional by 2025. I am really happy and thrilled at the support and attention the gravitational-wave community has received in India.

Dr. Alessandra Buonanno was one of the key speakers at the Future of Gravitational Waves program, recently held at ICTS -TIFR. Photo - Ipsita Herlekar © ICTS-TIFR.

In science, big discoveries like the detection of gravitational waves from merging black holes, don’t happen every day. But the few times such opportunities come, one has to grab it and act on it fast. Scientists from India have been able to contribute significantly to this field because they have done just that. Now what is important, but also challenging is that they build an interferometer, and if it is planned and managed well, there is no reason why it will not succeed. Having an interferometer in India will be of great help, for accurately localizing the source that produces the gravitational waves. Precise localization is a very important aspect of multi-messenger astronomy, because astronomers will be able to find the electromagnetic counterparts of a gravitational wave more easily. This will allow scientists to shed light on the most energetic and mysterious phenomenon in the universe. For example, two years ago we were able to associate the gravitational wave dubbed GW170817 to a short gamma-ray burst, proving that this energetic astrophysical event was due to the collision of two neutron stars. Thus, multi-messenger astronomy is very important, and the science enabled by LIGO-India will contribute immensely to this newly born area of research.

Click here to view Dr. Alessandra Buonanno’s talk at ICTS as a part of the Future of Gravitational Waves program.

Ipsita Herlekar

is the Science Communication Coordinator at ICTS