X-Ray Specs

Columbia astrophysicist Chuck Hailey is building a telescope to view stars so hot they’ve never been seen.

by David J. Craig Published Spring 2010
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NuSTAR telescope labI

t may look like a polished artillery canister, but it’s as fragile as an eggshell. Peer inside and you’ll see 133 cylinders, all made of paper-thin glass. The cylinders are arranged concentrically so that, when viewed from either end, they resemble the rings of a halved onion.

Astronomers call this type of optic device a “light bucket,” because when it’s pointed at a star it will collect every bit of light offered. But this light bucket, designed by Columbia astrophysicist Chuck Hailey, is different from others. Most telescopes today use a dish-shaped mirror to collect light and to reflect the beams back, at slightly different angles, toward a focal point. When Hailey’s optic gets launched into space next year, as part of a new NASA satellite telescope, light beams will shoot in one end, through tiny spaces in between its glass cylinders, and exit out the back. In the process, something unprecedented will occur: Extremely high energy light beams known as hard X-rays, which would penetrate straight through the components of any other telescope, will get reflected slightly, and set on paths to converge at a focal point 30 feet away — at the far end of the satellite, called the Nuclear Spectroscopic Telescope Array (NuSTAR). There, digital sensors will receive the X-rays and transmit their properties down to scientists who will generate computer images of the stars from which the X-rays came.

This elegant instrument is the first ever capable of focusing hard X-rays. (Hard X-rays vibrate at higher frequencies than the so-called soft X-rays used in medical imaging, which in turn are “stronger” than visible light.) It is a technological centerpiece of NuSTAR, which is scheduled to launch into Earth’s orbit in late 2011.

“We want to focus hard X-rays because some celestial phenomena emit no other type of light,” says Hailey, who oversees a team of 15 scientists and engineers building the optic at Columbia’s Nevis Laboratories in Irvington, New York. “Neutron stars, for instance, can produce flares so hot that we can’t see them.”

The NuSTAR telescope should lead to spectacular discoveries. For starters, scientists will gain a deeper understanding of the extreme physics that occur on ultrahot bodies like neutron stars, which can be invisible altogether. They’ll also get a peek inside gigantic clouds of space dust. The center of our own galaxy, for example, is shrouded by gas and debris generated by the deaths of many stars. Only hard X-rays (and even stronger gamma rays) typically escape the maelstrom that lingers around collapsed stars for billions of years. To glimpse a neutron star inside this region, and to track its movement, will be of great value to scientists. Most notably, it will help them spot black holes, which are identifiable by the circular patterns that celestial bodies chart around them.

“I can’t wait to see into the center of the Milky Way,” says Hailey ’83GSAS, who earned his PhD in physics at Columbia. “The galactic center is the real zoo. That’s where the black holes have to be, because black holes are born where stars collapse. Only a couple of dozen black holes have ever been discovered within our galaxy. This is our chance to discover literally thousands of them and to really study their properties. We’re about to lift the curtain.”

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Keep up the great work, Chuck!


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