Arthur Congdon

NASA researcher focuses on bringing dark matter to light

Bringing darkness to light: That’s the result that Arthur Congdon seeks to achieve in his research as he probes galaxies for evidence and understanding of elusive “dark matter.”

Congdon began an assignment in October 2008 at the Jet Propulsion Laboratory (JPL) at California Institute of Technology in Pasadena, Calif. He is a participant in the NASA Postdoctoral Program, which is administered by Oak Ridge Associated Universities.

Congdon is engaged in leading-edge research at JPL, using what’s known as strong gravitational lensing (SGL) to unveil secrets of the universe.

Scientists have long known that if galaxies and clusters of galaxies were only made up of observable stars and gases, there wouldn’t be enough gravity to keep them from flying apart. Thus, these stars and gases must be being held together with more than just the “normal” gravity contained in those systems.

“The ‘extra gravity’ is most likely caused by the presence of dark matter,” Congdon said. “Its properties have been extremely difficult to pin down because dark matter interacts with normal matter almost exclusively through gravity. Scientists have put a lot of ingenuity into finding ways around this problem.”

And that’s where Congdon’s research with lensing comes in.

“Einstein’s general theory of relativity shows that gravity can bend light in a way that’s similar to how optical lenses do,” he said. “Observing the way that distant galaxies bend the light coming from even more distant quasars [or the centers of very, very distant galaxies] can tell us how the mass in those galaxies is distributed.

If a quasar is almost directly behind a galaxy, an observer from earth will see multiple images of the quasar. Seeing where those multiple images are, and how bright they are, tells us a lot about the galaxy that’s acting as a lens.”

SGL is especially useful for studying dark matter, since lensing is sensitive to all mass in galaxies, not just to visible material such as stars and gas.

By learning about the small-scale distribution of dark matter in galaxies, we can, in principle, find out what dark matter is made of. Since most of the mass in the universe is dark matter, understanding it, as Congdon is working to help us do, will tell us much more about the universe on many scales.

Lensing is not a new concept, but it has gained new interest in recent years.

“Thanks to the creativity and persistence of generations of scientists and engineers, we now have instruments like the Hubble Space Telescope, which can gather data precise enough to study the effects of gravitational lensing. This observing capability was inconceivable in Einstein’s time,” Congdon said.

Already, Congdon’s findings are aiding scientists in their quest to sort through the many theories about dark matter’s location, origins and role in forming our Milky Way and other galaxies.

For a researcher focused on trying to “see” the unseen in our galaxies, it might be considered noteworthy that Congdon is himself visually impaired, uses a wheelchair and does not have the use of his hands. However, he spends little time dwelling on that. He considers himself no more gifted or challenged than any other researcher. For him, it’s all about enjoying his quest and advancing knowledge of the unknown.

“The universe is what it is and does what it does, and it’s our great challenge—and our great opportunity—to observe it carefully and try to describe it in a way that both makes sense of it and acknowledges its amazing beauty,” he said.

When he isn’t exploring the wonder of the universe, Congdon focuses on other forms of structured beauty and intricacy—from baseball to classical music.

“I’ve been following the Dodgers now that they’re my new home team,” said the Philadelphia native. “Another longstanding interest is classical music. I find beauty in the structure and order that both music and astronomy strive for. My favorite music is from the Romantic era, especially Brahms, because it has an emotional quality that I often find moving.”

Congdon’s career is also on a melodious trajectory. Looking ahead, he hopes to continue his work on “understanding the formation and evolution of galaxies using strong lensing and other techniques. The NASA Postdoctoral Program has given me a wonderful opportunity to pursue my research under the guidance of an expert in the field.”

That “expert” is Congdon’s advisor at the JPL—Leonidas Moustakas—an accomplished research scientist who, for his part, credits Congdon with making rock-solid contributions during his first year at the lab.

“Art is an expert on the theory of the extraordinary phenomenon of strong gravitational lensing,” Moustakas noted. “A new direction in his work will map how dark matter and normal matter interplay within galaxies, predictions which will be very important in future observational work.”

Clearly, Congdon’s observational skills will continue to uncover galactic secrets, bringing more “darkness” into the light of understanding.