Feb. 8, 2013
Ph.D. Student Discovers Galaxy’s True Size
This image of NGC 6872 is a composite of ultraviolet from GALEX (in blue), optical from the Very Large Telescope (VLT) (in green), and infrared from the Spitzer Space Telescope (in red).
Glowing clouds of interstellar gas and dust appear to swirl and tumble across a thick veil of billions of stars flung like blue and white diamonds on black velvet. It’s a galaxy that’s visible from Earth by a small telescope, but it takes a telescope that detects ultraviolet (UV) light to see its real size.
Using NASA’s GALEX satellite-space telescope, Rafael Eufrasio, a physics Ph.D. student at Catholic University, showed that the spiral galaxy — NGC 6872 — is much bigger than previously thought. In fact, the galaxy, which has been cataloged since 1959, turned out to be the largest spiral galaxy in the known universe.
The discovery that NGC 6872 is five times (about 520,000 light-years in diameter) the size of the Milky Way galaxy made international news in January after Eufrasio announced it at the American Astronomical Society meeting in California.
Eufrasio has been working on a team of astrophysicists including Duilia de Mello, CUA associate professor of physics; Eli Dwek at the NASA Goddard Space Flight Center in Greenbelt, Md.; and other international members from Brazil and Chile.
As part of his research, he investigated the interaction of the galaxy NGC 6872 with a much older galaxy in its vicinity known as IC 4970.
Eufrasio explains that the galaxy looks red (light from old stars) in the center and then bluer and bluer (light from younger and younger stars) as one moves to the outskirts of the disk, further from the nucleus. Light more energetic (or bluer) than human eyes can detect is ultraviolet, while light that can be seen is called visible or optical.
A collision between the two galaxies happened around 130 million years ago and triggered star formation throughout NGC 6872's disk (out of the gas in the disk), first near the nucleus and later on in more distant regions in the arms, he says. The full size of the galaxy is only revealed by the UV radiation given off by those young stars formed after IC 4970 passed through the disk of NGC 6872.
Stars are where all the elements of the periodic table are forged from the simplest atoms (mostly hydrogen and helium) by nuclear fusion, he says.
The UV light of galaxies comes mostly from stars much more massive than Earth’s sun, the ones burning fuel much faster and dying young, at about 10 million years, in explosions known as supernovae. These explosions enrich interstellar space with all the elements the exploding stars forged during their lives.
Eufrasio also says that at the end of the spiral arm of NGC 6872, the team found a long-sought tidal dwarf galaxy, a ‘baby galaxy’ in the process of formation, resulting from the forces generated by the collision.
Eufrasio holds a master’s degree in physics from CUA (2010) and two undergraduate degrees from Brazilian universities. Before coming to the United States in 2008, he was a high school teacher in Brazil for five years, preparing Brazilian students for the International Olympiads of Physics.
Physics was always his vocation but then, he says, fate stepped in. He applied to CUA in response to an ad that de Mello sent to the Brazilian Physics Society for students to pursue a Ph.D. in physics at the University and to work at NASA. “Despite having a strong background in physics, I had almost no previous knowledge in astrophysics,” he notes.
The spiral galaxy research is part of a project that de Mello started in 2008 — searching for stars formed outside colliding galaxies, nicknamed “blue blobs.” In 2011, Eufrasio joined her team in its quest for more blue blobs. NGC 6872 showed some unusual features in the ultraviolet spectrum, says de Mello.
Last summer, Eufrasio worked with a visiting Ph.D. student, Fernanda Urrutia-Viscarra from the University of Sao Paulo, and they produced measurements of NGC 6872. At the end of the summer, Eufrasio attended a conference in China to present the results and came back, according to de Mello, “full of great ideas that led us to realize that we had discovered the largest spiral galaxy.”
“Rafael's curiosity and great knowledge of physics makes him a very unique young researcher. It is a pleasure to see CUA Ph.D. students blossoming like he is right now,” she adds.
Eufrasio says he expects to defend his dissertation next year.
“The connection between CUA and NASA Goddard was essential to my past five years as a graduate student,” he says. “Goddard is the perfect environment for graduate students to learn astrophysics by exploiting all the data, instruments, and expertise from world experts.”