For many people, a career award is the perfect occasion for looking back – and taking stock of all you’ve accomplished over years of effort in a field.
Not so for John Monnier. The professor of astronomy and winner of the 2014 Michelson Prize for outstanding work in interferometry has his sights firmly on the future. He’s just sought funding for a new instrument called MYSTIC, which he calls “the next big thing in interferometry,” and is already looking 10-20 years down the road at the real game-changer: a proposed Planet-Formation Imager, for which he is leading the international charge.
Interferometry combines light from several small, distantly spaced telescopes to create an image with the resolution of a much larger telescope.
This is not to suggest he isn’t grateful for the recognition. Quite the contrary. “It was a surprise and an honor to be chosen,” he says. “It’s a new award so there’s a real backlog of qualified and deserving scientists out there.”
It’s just that, like the award’s namesake, Nobel laureate and interferometry pioneer Albert Michelson, Monnier is always looking to break new ground.
A History of Pushing the Limits
It’s been that way since the beginning. Even in graduate school at the University of California, Berkeley, Monnier was involved in ground-breaking interferometry instrumentation. One of the projects used aperture masking to turn Keck, the world’s largest optical and infrared telescope, into an interferometer equivalent to 21 smaller telescopes. He also worked on a long-baseline project, combining two telescopes at Berkeley’s Infrared Spatial Interferometer Array. This facility was the brainchild of Nobel Laureate Charles Townes, Monnier’s PhD advisor.
During a postdoc at the Harvard-Smithsonian Center for Astrophysics, Monnier proceeded to combine three telescopes. He then joined the faculty at U-M, intent on taking things further. To do this, he looked to Georgia State University’s Center for High Angular Resolution Astronomy (CHARA), which operates a six-telescope optical/infrared interferometric array on Mount Wilson, California.
“With CHARA, I wanted to bridge the two worlds I had worked on, one where you’re truly combining individual telescopes and the other where you have enough collecting apertures to really do imaging, like at Keck,” says Monnier. “With only two or three telescopes, you can take measurements but not produce images. But CHARA has six telescopes, which is the most available right now – and enough to do imaging. Combining all six was my goal.”
Monnier's Michigan InfraRed Combiner (MIRC). The world's most advanced instrument for infrared imaging, it combines all six telescopes at the CHARA Array. Inset: Monnier peers through an alignment telescope during MIRC's commissioning.
After only a little more than a decade, he’s achieved that goal. With U-M funding, he built the Michigan InfraRed Combiner (MIRC), the world’s most advanced instrument for infrared imaging. Used first in four- and later in six-telescope mode, MIRC was refined through the years by several talented graduate students and postdoctoral researchers to improve the observing precision and sensitivity, allowing it to achieve a number of scientific breakthroughs.
These include a series from Monnier’s own group, such as the first images of the surfaces of main-sequence stars other than the Sun; the first resolved images of interacting binaries, clearly showing how the gravity of a nearby companion can distort the actual shape of the stars; and a strict upper limit on the mass of hot Jupiter Upsilon Andromedae b. The group's images of several rapid rotators revealed these stars’ oblate shapes and uneven surface brightness, overturning the 1924 von-Zeipel law for gravity darkening. Recently, MIRC was used to image the exploding star Nova Delphinus, revealing both its expansion rate and its slightly elliptical shape.
Some of MIRC's breakthrough images: Several rapidly rotating stars (top), the exploding star Nova Delphinus (bottom left), and interacting binary Beta Lyrae.
Looking Ahead: MYSTIC & PFI
While MIRC has facilitated a number of breakthroughs, Monnier is eager to use interferometry to probe a longstanding interest and one of the field’s declared “priorities of the decade”: planet-formation.
“Over the past decade, we’ve come to realize that the rather simple picture we had of how planets form in disks of dust and gas around young stars is much more complex than we first thought,” he says. “My colleagues and I were the first to measure the sizes of these disks in the infrared, and we could see even then that something was fishy because the disks appeared actually many times bigger than the models predicted.”
While additional measurements have since helped refine the models, Monnier is eager to see a big leap forward. “Right now we can image the surface of stars, but we need to be able to image the fainter things around those stars like the disks and the planets forming within them,” he says
And he’s proposed just the instrument to do it. Called MYSTIC, the Michigan Young STar Imager for CHARA, it takes advantage of detector and integrated optics technologies originally developed for the telecommunications industry. With them, Monnier says, CHARA can become 10 to 40 times more sensitive, generating a “huge impact” on the field.
“One of the issues with our current models is that they are based on information we have from disks around stars that are quite a bit more massive than the Sun,” says Monnier. “But it’s not clear that the planet-formation process around these stars is the same as what’s happening around smaller stars like ours, which produced Earth. MYSTIC’s increased sensitivity could allow us to gather this data.”
Looking even further ahead, Monnier is leading the charge for a completely new facility that would move infrared interferometry from milli-arcsecond to sub-milli-arcsecond resolution.
“The dream is to be able to image all the important stages of planet formation by looking at the whole planet-forming disk as this process is unfolding,” he says. “That requires a very large boost in our ability to image the warm dust and gas that are being pushed around by and accreting onto the young planets. To do this, we’ll need an interferometer many kilometers in size.”
He’s working to catalyze just such an instrument. He co-founded and now serves as the project director for the Planet-Formation Imager (PFI), leading an international consortium to define the instrument’s architecture and science goals.
He acknowledges the project is ambitious but knows it pays to aim high. “PFI is a dream today,” he says, “but so was the Atacama Large Millimeter Array (ALMA) just 30 years ago. And now ALMA is a billion-dollar international facility revolutionizing astronomy.”
Click here to learn how you can support Monnier’s work with MYSTIC and PFI.