http://www.nustar.caltech.edu

Hefty telescope to float

Assuming all goes well this April, a high-altitude balloon flight in New Mexico will help to demonstrate whether an innovative telescope is ready to launch into space.

If chosen by NASA, the telescope, called the Nuclear Spectroscopic Telescope Array, or NuSTAR for short, should be orbiting Earth by the end of the decade, taking the first focused high-energy X-ray pictures of matter falling into black holes and shooting out of exploding stars. In addition, it will give scientists an unprecedented look at the origins of the heavy elements we’re all made of.

The high-altitude balloon flight in New Mexico will help to demonstrate whether the advanced sensors invented and built at Caltech are ready for space. The balloon phase of the project sports the intuitive acronym HEFT (for High-Energy Focusing Telescope), and will mark the first time that focused pictures at high-energy X-ray wavelengths will have been returned from high altitudes. High-energy X rays tend to penetrate the gas and dust of galaxies much better than the soft X rays observed by NuSTAR’s forerunners. In fact, even the HEFT data from the balloon is expected to be superior to any data returned so far from satellites at high X-ray energies.

NuSTAR will be much better than the balloon experiment, says Caltech astrophysicist Fiona Harrison, NuSTAR’s principal investigator, because it’s necessary to get above Earth’s atmosphere for extended periods to get a good view of the X-ray sky. NuSTAR will orbit Earth at an altitude of about 300 miles or so for at least three years. “With this mission, we’ll open the hard X-ray frontier and look at things never seen before,” says Harrison, who is also associate professor of physics and astronomy at Caltech.

NuSTAR has three basic science goals:

• The taking of a census of black holes at all scales. NuSTAR will not only count them, but will also measure the rate at which material has fallen into them over time, and the rate at which supermassive black holes have grown.

• The detecting and measuring of radioactive material in recently exploded stars. These remnants of supernovae will provide a better idea of how elements are formed in supernova explosions and then mixed in the interstellar medium (the space between stars).

• The observing and imaging of the highly energetic jets that stream out of certain black holes at nearly the speed of light.

NASA will give NuSTAR an up-or-down decision by next year for launch in 2009. The proposed telescope is part of the agency’s Small Explorer Program (SMEX), which seeks out new technologies and proposals for space missions that can be launched at low cost.

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