Image courtesy CXC/SAO/ESA/ASU/Caltech/U.Minn/NASA
A carrier plane releases a Pegasus rocket. Photograph courtesy Orbital Sciences Corporation.
Published June 12, 2012
Tomorrow NASA is slated to launch its newest orbiting observatory, which will peer into the mysterious high-energy x-ray universe with unprecedented detail.
Used on Earth for medical imaging and in airport security machines, high-energy x-rays are naturally produced by some of the most exotic objects in the universe. (Also see related pictures: "X-Ray History—Hidden Kitten, Quackery, and More.")
The Nuclear Spectroscopic Telescope Array, or NuStar, will seek out these rays to capture images of black holes, neutron stars, and other cosmic bodies with a hundred times more sensitivity and ten times better resolution than previous spacecraft.
Current x-ray telescopes—such as NASA's Chandra X-ray Observatory and the European Space Agency's XMM-Newton—can get clear looks at objects that emit lower energy x-rays, but due to technical challenges, these craft have trouble bringing higher energy wavelengths into focus.
NuStar will use a row of 133 fingernail-thin mirrors stacked like Russian dolls to focus light onto state-of-the-art detectors, producing crisp pictures in high-energy wavelengths.
"We're going to look at the remnants of stars that exploded long ago and also be poised to respond quickly—within a day—to any new explosions like supernovae or gamma-ray bursts," said NuStar's principal investigator Fiona Harrison, an astrophysicist at the California Institute of Technology (Caltech).
By extending our view of the x-ray universe, the NuStar team is "almost guaranteed to make new and exciting discoveries," said MIT's Jeffrey Hoffman, an astronomer and former NASA astronaut who's not affiliated with the mission.
"The experience of astronomy says that every time you open a new wavelength region with much greater clarity—in the infrared, or gamma rays, or now high-energy x-rays—you'll have exciting discoveries," he said.
"Which ones will turn out to be the real superstars, we don't know yet."
Folded up for flight, the refrigerator-size NuStar is scheduled to launch at 11:30 a.m. ET from the U.S. Army's Ronald Reagan Ballistic Missile Defense Test Site on Kwajalein Atoll, about midway between Hawaii and Australia.
Attached to a Pegasus XL rocket, NuStar will use what's known as an air-launch system.
On launch day, a carrier plane will cruise over the Pacific and drop the rocket at about 40,000 feet (12,000 meters). After a five-second fall, the rocket's engines will ignite, and Pegasus will lift the satellite into an equatorial orbit.
Once in space, NuStar will extend its 33-foot-long (10-meter-long) mast and begin collecting data for its two-year primary mission phase.
Among its science goals, NuSTAR is designed to seek out and study black holes in our Milky Way galaxy and beyond.
Researchers hope the craft's data will help improve our understanding of how black holes form during the violent collapses of dying stars and how the objects grow as they consume nearby matter, from dust and gas to whole planets and stars.
Black holes are often defined as objects so massive that nothing, not even light, can escape their grasp. But matter falling into a black hole gets so hot that it emits huge amounts of radiation, helping scientists pinpoint the otherwise invisible objects.
With NuSTAR's increased sensitivity, "you'll be able to see further in toward the surface of a black hole, because as you get closer, the energy of the radiation that's coming out gets higher and higher," MIT's Hoffman said.
"Being able to focus on these higher energies is all new, and it will really help us to probe the structure of black holes."
NuSTAR will also explore the strange behavior of extreme black holes, such as the supermassive monsters at the centers of most large galaxies.
Actively feeding galactic black holes, also called blazars, act like cosmic particle accelerators, cranking out jets of high-energy radiation at nearly the speed of light.
Studying x-rays from these jets can give scientists a better picture of their structure and composition, helping them to figure out why some supermassive black holes are feeding while others remain dormant.
Expecting the Unexpected
NuSTAR's extreme x-ray vision will also help scientists decipher how star explosions seed the universe with ingredients for galaxies, stars, planets—and even life.
When a supermassive star runs out of hydrogen in its core, it starts fusing atoms into progressively heavier elements. Eventually the dying star collapses and explodes as a supernova, which litters the cosmos with atoms of oxygen, carbon, iron, and more.
NuStar will be able to see the high-energy x-rays from radioactive nuclei initially produced in the explosions.
"Elements like iron and the calcium in our bones are forged in stars and expelled out into the galaxies [by supernovae]. We are 'star stuff,'" mission leader Harrison said.
"The material in our bodies was forged in the stars, and by being able to study the explosions and the material that gets expelled, we can learn a lot about how these explosions happen and how these elements are created."
NuStar will also collect information on the ruins of dead stars, such as the variety of ultradense neutron stars left over by some supernovae, including highly magnetic magnetars and rapidly rotating pulsars.
This stellar graveyard can serve as a laboratory for observing the unique physics of matter at gravitational extremes.
In addition to these well-defined science objectives, Harrison said, the mission team is ready to explore the unknown.
"I'm expecting that some of our greatest scientific highlights won't be the things we've predicted," she said.
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