SCIDEV | Q&A: India rides the gravitational waves (Interview)
Karan Jani, doctoral candidate at the Center for Relativistic Astrophysics, Georgia Tech, explains to SciDev.Net the Indian contribution to current theoretical understanding of how the universe began.
Jani explains the role of LIGO — giant detectors that helped discover gravitational waves — that may earn the Nobel prize in physics for the physicists who conceived it 32 years ago.
What is the next step after the detection of gravitational waves?
We detected gravitational waves from two black holes that had collided. Both had very different mass systems. My main role with the Laser Interferometer Gravitational Wave Observatory (LIGO) — a large scale physics experiment to detect cosmic gravitational waves and develop gravitational-wave observations as an astronomical tool to find black holes of larger and larger masses.
As we understand the universe, black holes that LIGO can see are formed from the death of the stars, and there is only a fundamental limit as to how big a star can be. And if I detect two black holes which are 300 times the mass of the Sun, then our whole understanding of how the earliest stars and black holes form in the universe gets a paradigm shift. That is one of my personal goals.
What is the larger goal for science?
The larger goal of the community is to find every astrophysical object from which gravitational waves can be detected. So let’s say if I have two neutron stars, (the collapsed core of a large star of 10–29 solar masses), or a black hole and neutron star collide then we can see both gravitational waves and electromagnetic waves from them.
Now, the next step in this whole field is to take an instrument into space, where I can see, say, the collision between two galaxies, or even how the universe started. The very first release of gravitational waves was led right after the Big Bang.
This ‘window to the universe’ might lead to more findings?
Yes. But there are a lot of things for which the models are not perfect. For instance we do not have a precise understanding of how two black holes are together. Or why the large-scale structure of the universe is the way it is, why there are gaps. If the universe had a perfect structure, then it would have been a flat plane. There is a star and then there is a huge gap and then another star. And even larger gaps between galaxies. So we need to know why things are as they are. The very first instance of fluctuation of the universe is recorded in gravitational waves. We have detected one type of fluctuation which is the cosmic microwave background (CMB). But the light of CMB was released when the universe was 380,000 years ago and hence limits our quest to understand the birth of our universe. The cosmic gravitational wave background we will eventually see will give us information about the when the universe was born.
What has been the historical contribution of Indian scientists in the field?
Vishweswara, a graduate student at Caltech in the late 1950s wrote three seminal first author papers in the field of general relativity. His first paper analyzed for the first time the structures of both spinning and non-spinning black holes. This was before the term ‘black hole’ was coined. The second paper proved for the first time that a black hole is a stable solution, hence guaranteeing that it can indeed exist in our real universe. The third paper, which was cited by us (LIGO team), proved that gravitational-waves will be emitted in a process known as “ringdown of black holes”.
Sanjeev Dhurandhar was the first to work in the field of gravitational wave data analysis in India. He worked out a method for accurately detecting gravitational waves from the expected noisy data of LIGO. The method was developed jointly by him and B. Sathyaprakash (now at Penn State University). Dhurandhar’s greatest contribution was to produce PhD students from India in the field of gravitational waves and it is solely because of him that we remained one of the leading nations in the field.
Where do you see India in the next step of the journey?
India had agreed to build one gravitational wave detector, which is LIGO, in coordination with the US and India is one of the very few countries doing this. We have already seen the universe in radio telescope and in optical telescope. But we don’t know the universe in gravitational waves. So the more the observatories, the better will be our collective understanding of this. India has a very strategic geographical location, where if you build such an observatory, your understanding of precisely which galaxy the wave came from is tremendously improved.
Will this help strengthen India’s human capital in science?
We have a fair amount of historical legacy of scientists working on relativity, starting from S Chandrashekhar, P.C. Vaidya, A. K. Raychaudhuri to C. V. Vishweshara, right down to Sanjeev Dhurandhar. They all have been working in the fields of gravity and gravitational waves. So it seems fitting that India has invested in this field because we already have a lot of scientific minds working in the field.
Detector construction will lead to strong partnership with the industries. Those industries would have to invest in technical support staff. That will go a long way in building R&D expertise in Indian industries. Besides, this scale of scientific work across multiple government departments is a big step.
What is the locational advantage India has that you are speaking of?
If you have two detectors close by, that means the signal is approaching them pretty much at the same time. If these are farther from each other, there would be a difference. If the signal comes to India first and then reaches the US, that means it came from the direction that is joining India to the US. And it is important to know where gravitational-waves come from because then I can tell my colleagues with telescopes to point them at that particular patch in the sky. If they see an X-ray coming from that same patch in sky, that’s a breakthrough. Then we will know that the universe has Black Holes that have gas around them, that creates the X-ray or something… things we do not know right now.
Will the LIGO project help India in capacity building?
If India wants to seriously invest in this whole field of science, it would need so many PhDs, and have a technical staff of hundreds, which we aim to achieve in ten years. While we will take ten years to construct this detector, the job of a scientist like me would be to have PhD students, then train Masters and Bachelors students and so forth, who will later go for doing their PhDs. So that is how you put a human capital for this project.
How will it build technical capacity?
There are many areas that go beyond astrophysics. Ultimately you are building the detector for the astrophysicist community which wants to detect Black Holes and answer these questions. But in the process, you have to learn how to make precise lasers, you have to learn about quantum optics, a big chunk is instrumentation, and you have to even learn geology, because the seismic noise in the detector is coming from the geology around it. And all this requires a set of people who are interested in the project and not just in the astrophysics.