Capturing the invisible

Astrophysicist Charles Hailey is building instruments to examine dark matter, black holes and more

Capturing the invisible
Charles Hailey with a prototype of his GAPS dark matter detector

Above his desk at Columbia University, astrophysicist Charles Hailey has pinned up a colored photograph of the super-massive black hole at the center of our galaxy. The black hole is hidden by hot gas and dust, and is so dense that light itself cannot escape its gravitational pull. “There are only about ten people in the world who have seen this,” Hailey says.

The image comes from NASA’s newly launched Nuclear Spectroscopic Telescope Array, or NuSTAR satellite telescope. Hailey led the team that designed and built NuSTAR’s optics, the first ever to scan our galaxy with high resolution in the so-called “hard” or high-energy X-ray spectrum of light. “The hard X-ray band is the last frontier of the light spectrum that has not yet been studied with high sensitivity,” says Steven Kahn, an astrophysicist at Stanford University. These hard X-rays are among the only kinds of light that escape the center of the galaxy. And until now, no satellite was able to focus them into clear images. Hard X-rays are produced by the matter around a black hole and a variety of other ultra-hot stellar bodies.

In the past, high resolution satellite telescopes like NuSTAR have been created by meticulously polishing metallic or glass surfaces that are used to reflect light. But the polishing is “extremely expensive and time consuming,” says Hailey. The Chandra X-Ray Observatory, a low-energy X-ray telescope launched in 1999, cost $1.65 billion to construct, and the Hubble Space Telescope, launched in 1990, cost over $2.5 billion.

But by using a technique — pioneered by Hailey and advanced by NASA — called ‘glass slumping’ to build NuSTAR’s optical device, Hailey avoided polishing altogether. Instead Hailey and his team took smooth glass panels, heated by his colleagues at NASA to the right curvatures, and pressed them onto a perfectly smooth, machined surface. This eliminated both the painstaking polishing process and the need to align the glass by hand. The result was that NuSTAR cost only $165 million to produce, a fifteenth of the cost of Hubble.

Wiry and wry, Hailey is animated as he describes NuSTAR and his other experiments, eagerly jumping to his chalkboard to illustrate glass slumping and drive a point home. Hailey traces his interest in science and astrophysics back to his early childhood. Now 57, he was given his first telescope in 5th grade, and built his own at age 16. Today he is, as Kahn explains, “one of the leading astrophysicists in the country.” But what separates Hailey from many of his colleagues is how many different areas of physics he has contributed to.

Before NuSTAR, Hailey worked as an atomic physicist developing methods to detect nuclear materials at Lawrence Livermore National Lab. And before that he was employed by a now-defunct company, KMS Fusion, working with plasmas and building X-ray detectors. “Most scientists, particularly experimentalists, get channeled into a narrow part of the field that they try to become more and more of an expert on,” says Kahn, who has worked with Hailey in the past. “But Dr. Hailey has always had very broad interests.” Even now, NuSTAR is not the only project Hailey is working on.

Hailey also leads the General Antiparticle Spectrometer (GAPS) project at the University of California, Los Angeles, which seeks to detect dark matter, the unseen force which makes up more than 90 percent of the known universe’s mass. “Dark matter is the most outstanding mystery in particle physics,” says Stefano Profumo, an astro-particle physicist at the University of California, Santa Cruz. “It’s the clearest evidence that we don’t understand the whole of particle physics.”

GAPS, which completed its first test-run in northern Japan last summer, uses a large balloon to lift a five-foot cube of detectors into the earth’s upper atmosphere. The detectors, like a giant Geiger counter, attempt to capture a type of antimatter particle called antideuterons, which some physicists think are the debris created when dark matter collides with itself.

Hailey thinks that GAPS will be key to narrowing down the possible candidates for dark matter’s composition. But he concedes that due to dark matter’s unknown nature, nobody knows for sure. “Depending on the exact nature of dark matter, you may or may not produce antideuterons,” says Hailey. But Profumo agrees that the antimatter particle is a likely byproduct. “In the best models that have a dark matter candidate, you should produce antideuterons.”

GAPS has other limitations too. Some exotic cosmic sources, such as evaporating black holes, are hypothesized to be originators of antideuterons and could give a false reading. “But I think it’s a fantastic experiment,” says Profumo. “The production of antideuterons wouldn’t conclusively point to dark matter, but it would add a very important piece to the puzzle.”

Though Hailey is investigating crucial questions in physics, his work, he says, is far from glamorous. He talks about the endless days he spent doing tedious measurements, helping to design and build the telescope optics for NuSTAR over 14 years. “It’s hard, dirty business,” says Hailey. “You’re slumping glass, putting it together with epoxy, taking measurements, and you’re not doing any astrophysics.”

Even circumventing the polishing-problem, he says, building NuSTAR required an exasperating level of detailed precision and time. By the final stages of developing NuSTAR’s optics, “the work was so painful and so hard to do.” But Hailey gestures, smiling, toward his photograph of the galactic center. “But after two months of NuSTAR’s flight, I said to myself, my God, this was worth 14 years of my life.”

The payoff for Hailey is the new data pouring in every day from NuSTAR, which includes newly discovered black holes, information on recent supernovae and images of the galactic center. “Every time I look at a piece of data, I look at something that nobody has ever seen before,” says Hailey. “It’s like pure heaven to go after this.”

Posted in: Physical Science

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