Jesuit Father Richard D'Souza finds halos mesmerizing.

Galactic halos, that is. Not the angelic variety.

It's enthralling to the Vatican Observatory astronomer that those halos of stars that have fallen into one galaxy from another during collisions and mergers can provide clues to a galaxy's multibillion-year history.

Father D'Souza, a post-doctoral researcher at the University of Michigan since 2016, studies the evolution of galaxies. His focus largely has been on the Milky Way's neighbor, the Andromeda galaxy, designated as M31 in French comet hunter Charles Messier's catalog of astronomical objects.

Through months of meticulous research, Father D'Souza, 40, believes he has helped uncover a key part of Andromeda's past.

In a paper published last July in the journal Nature Astronomy, Father D'Souza and fellow University of Michigan astronomer Eric Bell hypothesized that M31 cannibalized what until about 2 billion years ago was the third largest member of the Local Group -- a clump of galaxies, including our Milky Way and Andromeda, traveling through the universe together and interacting over time.

The two astronomers -- who share a warm friendship as well as a professional relationship that dates to the early 2000s when they studied at Heidelberg University in Germany -- suggested that Andromeda's halo shows signs that another Messier object, M32, was devoured by the more massive M31 over a period of about 3 billion to 4 billion years.

Father D'Souza uncovered clues in Andromeda's halo, finding stars that had a higher proportion of metallicity -- elements heavier than hydrogen and helium -- that matched the chemical composition of stars in the remnants of M32.

Accessing simulations of galaxy collisions and analyzing data for months, Father D'Souza and Bell developed a paper outlining the likelihood that the massive M31 essentially ate the smaller M32 -- which they designated as M32p, meaning the progenitor -- spitting out its galactic core, which continues to orbit Andromeda.

The idea caught the imagination of the mainstream media, which reported their hypothesis widely, but not so much in the astronomical community, Father D'Souza told Catholic News Service in an interview in the office he shares with other researchers. Some astronomers studying M31 liked the idea and understood the research that led to the hypothesis; others resoundingly disapproved.

"I have been going around actually giving talks on this at various (astronomy) departments," Father D'Souza said. "Once they see the evidence, they say, 'Wow, this is great.' Up until then they don't see it."

Bell said the reaction doesn't matter, but that the process of developing the paper offered an opportunity to work closely with Father D'Souza, while learning much along the way, that was the best outcome of collaborating.

Whatever the reaction, the paper served to spread Father D'Souza's name more widely. That's good for an astronomical career, said Jesuit Brother Guy Consolmagno, director of the Vatican Observatory.

"Now he's well enough established in research that he could do it anywhere," Brother Consolmagno said.

That's exactly what's ahead for Father D'Souza, who is nearing the end of his three-year stint in Michigan. In June he will head to Vatican Observatory headquarters in Castel Gandolfo, Italy, to join a small team of astronomers. He plans to learn Italian while he continues his work on galactic evolution.

Father D'Souza as a young student in India was interested in the sciences and at one point even mentioned to his Jesuit superiors guiding his novitiate that he wanted to work at the Vatican Observatory. That dream wouldn't become realized until 2016 when Brother Consolmagno named him to the staff and offered to support his post-doctoral work in Michigan.

"He's someone we've known for 20 years," Brother Consolmagno told CNS. "He's brilliant. He's one of the smartest guys we've had come along in a long time."

Despite his love of astronomy, Father D'Souza has found it's his pastoral duties as a priest that feed his soul.

While in Ann Arbor, Father D'Souza celebrates Mass on weekends at St. Mary Student Parish a few blocks from campus. He said he has immersed himself in preparing for the liturgy, spending hours writing meaningful homilies.

"I learned here in Ann Arbor that my biggest support system was actually the parish," Father D'Souza said. "What I found, at least in St. Mary's for me, it was very challenging to preach on Sundays because you couldn't just do your run-of-the-mill homily. You had to think, you had to enthuse, you had to make sense of reality: what's happening in the world, what's happening in American politics."

Born to a Catholic family in Pune, India, in the western state of Goa in 1978, Father D'Souza grew up in Kuwait, where his parents, Joseph and Mary, had emigrated for work. They raised their sons, Christopher and Richard, in an Indian neighborhood where parents kept tight reins on their children because the Indians' freedom was restricted.

In 1990, as the U.S.-led Gulf War approached, the D'Souzas fled Kuwait with thousands of other Indians, spending three weeks in a refugee camp in Jordan before returning to their homeland. "It was a bit traumatic. You lose everything. You take two, three bags," Father D'Souza said.

He enrolled in Jesuit-run St. John de Britto High School, named for a Portuguese missioner and martyr. There, the future priest was introduced to the Jesuit charism and became captivated by the order's missionary history. He joined the Jesuit novitiate at 17 after graduation.

Young D'Souza soon realized that many of the Jesuits were involved in the mundane of everyday ministry rather than the excitement he imagined being a missionary might be. "(Soon though) I realized they didn't lie in their history," he told CNS. "I realized there was the potential to do the extraordinary."

Three months into his novitiate, Father D'Souza's older brother died after contracting an uncommon form of malaria. "I felt the pain of my parents," he said. But they insisted that he continue on his chosen path.

Throughout his formation that led to his ordination in December 2011, Father D'Souza pursued studies in physics at St. Xavier's University in Mumbai, India, and at Heidelberg University in Germany. He also holds bachelor's degrees in philosophy and theology, which helped prepare him for the priesthood, plus a doctorate in astronomy, earned in 2016.

Part of his work preparing for becoming a priest involved time in India where he founded and directed a short-lived community college in Belgaum, India, and established a theology program for parishioners in Goa.

Father D'Souza sees his upcoming appointment to the Vatican Observatory as a great complement to his priestly vocation. In both areas, he sees a call to search for meaning and understanding of God's creation, he said.

And he sees no conflict in both roles he has been called to fill.

"We're looking for something beyond us," he said, citing Jesuit Father Karl Rahner. "The most transcendental thing you can have is God. ... Astronomy is the most transcendental of the sciences and yet most physical, and that is the reason perhaps it has long fascinated everyone in history."