Fr Richard D’Souza's findings are likely to upset a major paradigm in our understanding of galaxy evolution

Once upon a time, there were three galaxies in the Local Group – Andromeda (M31), the Milky Way and its sibling, the M32p galaxy. About two billion years ago, Andromeda cannibalised and destroyed M32p, leaving behind a trail of cosmic debris as evidence.

It was the perfect crime, till now.

Scientists Fr Richard D’Souza SJ and Eric Bell at the University of Michigan used computer models and simulations to show Andromeda’s dark past. Their research suggests that Andromeda’s M32 compact satellite galaxy is actually the stripped core of the destroyed M32p. Their findings were published in Nature Astronomy last week.

D’Souza, the lead author on the paper, was born in Mapusa (Goa), studied at St Xavier’s College, Mumbai and did most of his priestly studies in India. In an email interview, the Jesuit and scientist tells us about his work and the intersection of science and faith in his life.

Tell us about your new findings and their significance.

My research centers on how galaxies grow through mergers. A galaxy like Andromeda, our nearest big neighbour, is thought to have merged with hundreds of smaller galaxies. These smaller galaxies are destroyed in the process due to tidal forces of gravity leaving behind a trail of stellar debris (like ‘crumbs’) around the main galaxy called its stellar halo.

By studying the stellar halo of a galaxy, I have developed a technique of inferring the size of the largest galaxy that was destroyed in the process. This is similar to guessing what a small child has eaten after looking at the ‘crumbs’ and mess scattered on the floor around it. Observations over the last decade have shown that Andromeda has the largest stellar halo for any galaxy its size. We realised that to build such a large stellar halo, Andromeda must have merged with a really large galaxy (one-fourth its size) not too long ago.

How is the discovery of this decimated galaxy going to help future research and study?

It was traditionally thought that such large mergers would destroy the disks of galaxies, converting them to spheroidal elliptical galaxies. We now know that the disk of the Andromeda galaxy survived this particularly large merger, though we don’t know exactly why. So, this finding upsets a major paradigm in our understanding of galaxy evolution. One thing we can take away is that the disks of galaxies are more resilient than previously thought. We hope that this finding motivates further studies to understand what circumstances lead to the disks of galaxies surviving such large interactions.

The next part of my research involves studying the stellar halos and the merger histories of other more distant galaxies, to try and understand which of the galaxy’s properties are caused by merging.

Will this help solve the mystery formation of Andromeda’s M32 satellite galaxy?

We think so. We have only proposed a model and it needs to be tested and verified. While everyone agrees that Andromeda had a large collision two billion years ago, some scientists doubt whether this collision resulted in M32. Such disagreement is good. Science is a conversation, a back and forth, and we will iteratively come to the truth.

Speaking of disagreement, how does faith and science intersect for you?

For me, they are two very fundamental ways of knowing the same reality. Humanity needs both these ways of knowing, to understand reality and to move forward in life. Science is based on assumptions and faith. Especially in astronomy, where it is very difficult to prove something exactly, it surprises me how much really goes on assumptions and beliefs.

Taking a cue from philosophy, meaning cannot be found within a system, it can only be found external to it. Science cannot offer us meaning in life, only something that is totally transcendental, like the divine, can. Without meaning, we will not move forward, we will not have hope, we will not strive to do the things we do, and without hope, people have nothing to look forward to. Religion and faith gives us meaning, and it often gives us a pretty good reason to do good science, because it becomes an expression of reaching out to this transcendent, that is God.

Is this what attracted you to science?

I was always interested in science. As a kid, I loved building things and computers. In college, I got a taste for research in physics. My Jesuit superiors encouraged me to take up astronomy as there was a rich tradition of Jesuits studying astronomy and doing research in it. After my ordination and my time in Goa, I returned to the sciences and went back to do a PhD in astronomy.

My general field of study is galaxy formation and evolution. This field tries to understand the rich diversity of galaxies we see in the Universe. Where and how did it all start? What path did the Universe take to get here?

How did you start working for the Vatican Observatory?

The Jesuits manage and run the Vatican Observatory. As soon as I started my Master's in Physics in Heidelberg, Germany, they reached out to me. After my PhD in 2016, I formally joined the staff of the Vatican Observatory. Although I am associated with them, I went for a post-doc to the University of Michigan, and make occasional short visits back to the Observatory in Rome or their offices in Tucson.

Most of the astronomers at the Vatican Observatory are Jesuits, if not Catholic Priests and Brothers. The place has the right combination of science and faith. Moreover, the members have such good connections and friends all over the world; it has opened a lot of doors for me.

Does your work and research enhance your spiritual life?

Normally, I aim to keep the two apart but it does not actually work out. I often find myself preaching about the hard process of research and the spiritual lessons one can draw from it. When I am down and disappointed in my research, I find myself praying for inspiration and for God’s help. My spiritual life and my research work interweave seamlessly.

In an interview, you mentioned that most people misunderstand the Catholic Church’s stance towards science and creation. How so?

Most people misunderstand the Catholic Church’s present teaching of creation. It teaches us that God created the world but does not insist on how. The Church agrees with modern Biblical scholarship that while the first few chapters contain many major theological truths about the human person and the relation to the world and to God, it is not to be taken literally or historically.

The Church’s idea of creation is not in complete contrast with science and history. Fr George Lemaitre, a Belgian Catholic priest, was the originator of the idea of the Big Bang in the 1930s, after applying Einstein’s equations of relativity to the Universe. The ‘big bang’ is a very Catholic idea!

The knowledge of the faith in the average Christian is quite limited. We were taught a couple of things as children and then our religious education stopped after the age of 13 or 14. Our religious knowledge remains at the level for children. On the other hand, we spend a lot of time and energy in educating ourselves professionally. I only wish Catholics would do the same and remain up to date with their faith education.