Spatial Relations
Adaptive optics enabled the first direct observation of exoplanets, including the three seen here orbiting planetary system HR 8799, in 2008. Deformable mirrors designed by Thomas Bifano are advancing this technology for next-generation telescopes.
Image courtesy of W. M. Keck Observatory
How do you see the invisible? Four hundred years ago, Galileo Galilei used a little help. Improving on telescope designs by Hans Lippershey, he turned his telescope to the sky and observed for the first time the cratered surface of the moon, discovered four satellites of Jupiter, and resolved nebular patches into stars.
With lenses and mirrors, Galileo’s design allowed the human eye to see into space. This year, the International Year of Astronomy marks the anniversary with a global appeal by the International Astronomical Union and UNESCO to expand our understanding of our place in the universe by viewing the day- and night-time sky.
Eyes on the Skies
Since Galileo’s time, telescopes have focused on faint blobs and splotches, but Thomas Bifano, director of the Photonics Center at Boston University, has helped fine-tune those discoveries, making them a little clearer. Bifano’s research with silicon microelectromechanical (MEMS) deformable mirrors allows for high-resolution, high-contrast astronomical telescope compensation with adaptive optics. Using a semiconductor fabrication process, Bifano’s foundry made the technology accessible to the scientific community.
Thomas Bifano
Astronomers were able to find massive black holes at the merger of two distant galaxies with adaptive optics, and in our own solar system, deformable mirrors have shown the rings of Uranus, and allowed BU professors Jeffrey Baumgardner, Jody Wilson, and Michael Mendillo to see the sodium tail of Mercury.
“One of the big goals for astronomy is to not only peer deeper into the universe, but also more precisely, so that I could see a tiny, Earth-like planet around a bright star,” says Bifano, a member of the University’s Center for Space Physics and the Fraunhofer Center for Manufacturing Innovation. Bifano, with College of Engineering alumnus Paul Bierden, co-founded Boston Micromachines Corp., a business leader in the production of deformable mirrors for astronomy, defense, and bio-imaging. “And if I can see an Earth-like planet around a bright star, then I can measure the light coming back from that and say, ‘Oh, there’s carbon dioxide, or oxygen there, and there might be people living there.’”
Last year, scientists had the first direct observation of exoplanets—planets circling other stars, including Fomalhaut, a bright star 25 light-years from Earth—and a star called HR 8799, 128 light-years from Earth. Instead of launching a telescope into space to avoid Earth’s messy atmosphere, which tends to meld the light of far-flung planets with its nearby star, astronomers used adaptive optics. The precisely controlled warping of the deformable mirror straightens out distorted light.
“We had found exoplanets, but we’d found them by watching a star ‘wobble,’ as a planet orbits the star. But the star’s so bright, and the planet’s so dim, you can’t see the planet,” says Bifano. “It would be like trying to see someone holding a match, behind someone holding a floodlight. The way you see the planet is to make the telescope’s optics perfect, and the deformable mirror helps with that.”
This February, Bifano’s career-long research in micro-deformable mirrors for astronomical telescopes earned him the prestigious Bepi Colombo Prize. After a week of competing with four other finalists from around the world, he received the prize during a daylong ceremony at the University of Padua in Italy—the same university where Galileo chaired the mathematics department from 1592 to 1610.
“It was thrilling to win,” says Bifano, “and deeply rewarding to be a finalist presenting my research about telescopes in a room named for Galileo, on the 400th anniversary of his first pointing a telescope toward the sky in Padova.”
Left: A hexagonal deformable mirror comprised of 331 ultraflat silicon mirror segments.
Right, clockwise from lower right: one of Jupiter’s moons, Io, as seen from Earth without adaptive optics; two images of Io taken at the UCO/Lick Observatory by a telescope outfitted with adaptive optics, which provide a level of detail comparable to the fourth image, taken by the Galileo spacecraft orbiter.
Image of deformable mirror courtesy of Thomas Bifano
Images of Io courtesy of F. Marchis/Center for Adaptive Optics/University of California at Berkeley
Mapping the Final Frontier
Nathan Schwadron’s work with the Interstellar Boundary Explorer (IBEX) is expanding the realm of astronomical discovery a little closer to home—mapping the edges of our solar system. Because the solar system lacks clear definition—unlike, say, a room with four distinct walls—finding out where it ends and the rest of the Milky Way begins is less straightforward than it sounds.
Nathan Schwadron
Schwadron, now an associate professor of astronomy at BU, was at the Southwest Research Institute in San Antonio, Texas, when he and Dave McComas, NASA’s principal investigator for IBEX, wrote the original IBEX proposal.
Launched into space in October 2008 on the back of a Pegasus-XL rocket, the IBEX satellite is designed to detect where the solar wind, the outward flow of ionized solar gas that creates the heliosphere, collides with the interstellar medium, an accumulation of material released from the stars in our galaxy and dispersed through stellar winds, novae, and supernovae. The mission is led by the Southwest Research Institute, Los Alamos National Laboratory, and Lockheed Martin Advanced Technology Center.
Schwadron’s lab collects and processes images and other information sent back about the interstellar medium, revealing global properties of the termination shock that separates our heliosphere from the local interstellar medium.
The IBEX satellite launched in October 2008 is now beginning to send back data about the termination shock, one of several plasma boundaries that surround and protect our solar system from the harsh radiation environment of the local galactic medium. Outside the termination shock, a fast supersonic flow of solar wind (shown here in green) abruptly changes into a much slower hot plasma (orange), which is then deflected back and into the Sun’s tail. Beyond that is the heliopause, which separates the solar wind from the galactic plasma, and perhaps also a bow shock or bow wave, where the galactic plasma is first deflected around the heliosphere.
Image courtesy of NASA
“For years we’ve built astronomy on photons,” says Schwadron. “In our case, we’re actually not looking at photons, we’re looking at energetic neutral atoms that are born on the edge of our solar system.”
In space, charged particles interact with electromagnetic fields. But when a particle is neutral and has no charge, it has no way to interact with those fields so it moves in straight lines, much like a photon. The IBEX team uses the energetic neutral atoms to measure the energetic particles in the medium around the solar system to image plasmas, just like light.
“Whereas people have been sending probes out to image individual sections of the cocoon around Earth, the Earth’s magnetosphere, now with these neutral atoms, we can actually image the whole thing,” says Schwadron. “For the first time, images showed us that these are global boundaries surrounding us, these are global dynamics, and suddenly the field completely changed.”
While Schwadron was developing the IBEX proposal in 2004, Voyager I, an individual probe launched in 1977, hit the termination shock of the heliosphere, entering the heliosheath. Voyager II hit the termination shock in 2007. The measurements that each Voyager sent back recorded only one specific location and time—two pinpricks in the fabric of the interstellar boundary.
“Voyager I made the first measurements of the termination shock, which was amazing, because it was the actual discovery of it,” he says. “But at the end of the day, it was just the measurement of those two points, and that’s all you get. With IBEX, we get to see the whole thing.”
The astronomy department at BU is shaping the future by merging astronomy and space science, says Schwadron. “IBEX is pushing the frontier of space science, of what we can detect locally, into the realm of what we know about the galaxy. IBEX is about bringing the two worlds of astronomy and space science together.”
“Astronomy is all about seeing what we haven’t seen before, discovering what we haven’t discovered,” he says, likening IBEX to Dr. Seuss’s classic children’s book Horton Hears a Who. “You have little Whos sitting in their part of the universe, and they know about the Sun, and that there’s a region outside them. But all they know is kind of the most distant properties, they’ve forgotten there’s this intermediate environment. Horton is also there, and they don’t realize it. With IBEX, there’s a discovery of how we fit in with our own cosmic environment.”