s one of the many students at St Britto’s High School, Mapusa and St Xavier’s Higher Secondary school, Mapusa, little did young Richard D’Souza know that one day he would be teaching the world about the ways of our galaxy – the Milky Way.
A study published in the journal Nature Astronomy, for which he was lead author, shed light on the discovery that the long-lost sibling of the Milky Way galaxy was shredded and devoured by the our closest large galactic neighbour—the Andromeda galaxy, about 2 billion years ago. The massive galaxy, although mostly shredded, left behind a rich trail of evidence, an almost invisible halo of stars larger than the Andromeda galaxy itself, and a separate compact galaxy, M32.
This disrupted galaxy was the third-largest member of the Local Group of galaxies, after the Milky Way and Andromeda galaxies.
Using computer models, Richard D’Souza and Eric Bell of the University of Michigan in the US were able to piece together this evidence, revealing this long-lost sibling of the Milky Way.
“It was a ‘eureka’ moment. We realised we could use this information of Andromeda’s outer stellar halo to infer the properties of the largest of these shredded galaxies,” says Richard.
“I would like to think that it a step towards progress. The data already existed, but we could not explain it and it appeared a mystery. We provided a new model, which could explain this data as well as a way forward to apply this same technique to other galaxies. This allows us, for the first time, to unravel a galaxy’s past history, especially in terms of at least the largest galaxy it disrupted in the course of its lifetime! The logical next step is to get more data and to apply it to other galaxies, “ says Richard, while speaking to Herald about this achievement and what it means for the future.
And this achievement has not only grabbed international headlines but it has also grabbed the attention of Goans, who have praising his achievement.
“I have been very busy the last week, and hardly had any time to respond to personal messages. But I would like to thank everyone for their support and love down the years. I remember them all fondly,” he says, reacting to the response he has been receiving.
Asked to elaborate on his fond memories, he said that he particularly enjoyed teaching theology and scripture during those days (when he was in Goa).
“For me, it was not only about trying to give people information about the newest findings of theology, but it also involved being creative in communicating these ideas and concepts in a way that people could understand and relate to,” says Richard.
He was referring to the program at the Pedro Arrupe Institute, in Raia, which he had started along with his Jesuit companion, Fr Shannon Pereira.
“Our aim was to educate the Catholic laity in Goa in matters of faith, theology and scripture. We realised that the knowledge of the faith for the average Catholic in Goa was quite limited. We were taught catechism as children, and then our religious education pretty much remained stagnant after the age of 13 or 14. We were never taught to theologise about the present problems we face in Goa. Yet today, people in Goa are professionally very well educated. There is a huge yearning among the faithful to know more about their faith and to take a more active role in the running of the Church in Goa. We wanted to help such people,” says Richard.
When asked if he visits Goa often, he informs us that he comes down regularly, once a year, to visit his parents who have settled in Mapusa. Richard’s father, Joseph D’Souza, is originally from Pilerne, while his mother, Mary, is originally from Siolim, but grew up in Pune.
Richard spent his initial years in Kuwait. After the Gulf war in 1990, his family came back to Goa. He studied in St Britto’s from Std 8 to 10, and went on to St Xavier’s, Mapusa. He then, joined the Jesuits, heading to its Novitiate in Belgaum for two years. After a year of Humanities in Pune, he went to St Xavier’s Mumbai to do his Bachelor’s degree in Physics. After that, he completed his Master’s degree in Physics at the University of Heidelberg, Germany. He then returned to India, continued with his studies of philosophy and theology and got ordained as a priest. Later on, he went back to Germany to pursue his Doctorate in Astronomy at the Max Planck Institute of Astrophysics in Garching, Munich. As soon as he was done, he joined the staff of the Vatican Observatory.
His latest achievement has done the Vatican Observatory proud.
“I enjoy doing research, and luckily, this is also the job given to me by my Jesuit superiors. I am glad that my present research has received wide media coverage. After all, this is what the Vatican Observatory is set up for. As Pope Leo XIII in refounding the Vatican Observatory in 1891 wanted ‘that everyone might see clearly that the Church and her Pastors are not opposed to true and solid science… but that they embrace it, encourage it, and promote it.’ Over the years, the Vatican Observatory had tried to do this. My research and the publicity it is getting will go a long way to demonstrating that the Church is not opposed to good and true science, but actively supports it,” says Richard.
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Richard explaining his achievement
The Andromeda and the Milky Way galaxies are relatively close by, and are the largest members of the ‘Local Group’ of galaxies. Astronomers have long studied the Local Group, including its smaller members, and thought they knew their local neighbourhood pretty well. We now realise that there was another galaxy out there (which we call M32p) that was almost half the size of the Milky Way and which was destroyed by Andromeda. This comes as a complete surprise! It makes M32p the third largest member of the Local Group. The next smallest member, the Triangulum galaxy, is at least 8 times smaller than the Milky Way. So indeed, M32p was a long-lost sibling finally found.
My research centres around how galaxies grow through mergers. Over the course of its lifetime, a galaxy like Andromeda, our nearest big neighbour, is thought to have merged with hundreds of smaller galaxies, due to the attractive forces of gravity. 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.
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 significantly large galaxy (quarter its size) not too long ago.
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 that previously thought. We hope that this finding motivates further studies to understand in what particular circumstances do the disks of galaxies survive such large interactions.
