February 7, 2005
Researchers hope to break new ground in high-energy
astrophysics with hard x-ray telescope, now up for final NASA
By Tim Stephens
Researchers at UCSC and their collaborators at other institutions
anticipate new insights into the mysteries of high-energy astrophysics
as plans for an innovative x-ray telescope progress toward final
approval by NASA.
The NuSTAR hard x-ray telescope is
depicted here in an intermediate stage during its deployment
in space, expected to take place in 2009. Photo
courtesy of the NuSTAR team
If all goes well with a technical study approved by NASA for
this year, the telescope should be orbiting Earth by the end
of the decade and taking the first focused high-energy x-ray
pictures of matter falling into black holes and shooting out
of exploding stars.
Named the Nuclear Spectroscopic Telescope Array (NuSTAR), the
project has just been pegged by NASA for detailed study in the
competitive Small Explorer Program, which seeks out new technologies
and new proposals for space missions that can be launched at
Pending a final NASA review next year, NuSTAR will be scheduled
for launch in 2009.
"This is a real explorer mission. There has never been
a sharp focusing telescope in this part of the spectrum before,
so there is a very broad range of exploration science that needs
to be done," said Stephen Thorsett, professor and chair
of astronomy and astrophysics at UCSC.
Thorsett chairs the science team of 11 co-investigators from
seven institutions who have been planning the science goals
for NuSTAR. Stan Woosley, also a professor of astronomy and
astrophysics at UCSC, is another of the co-investigators. Supermassive
black holes, gamma-ray jets, and the birth of new elements in
supernovae are the three main areas of investigation planned
for NuSTAR. But Thorsett said the most interesting results are
likely to be the unexpected ones.
"We're almost certain to be surprised. Even in the first
calibration observations, when we plan to look at local neutron
stars, I expect the results will provide a thesis worth of work
for a graduate student," he said.
According to Fiona Harrison, a California Institute of Technology
astrophysicist and principal investigator of the NuSTAR project,
an April high-altitude balloon flight in New Mexico should help
to demonstrate whether the telescope's advanced sensors, invented
and built at Caltech, are ready for space. The balloon test
will mark the first time that focused pictures at high-energy
("hard") x-ray wavelengths will have been returned
from high altitudes.
Focusing hard x-rays the way an optical telescope focuses light
is technically very challenging, but well worth the effort,
Thorsett said. Hard x-rays tend to penetrate the gas and dust
of galaxies much better than the soft x-rays observed by existing
x-ray satellites. NuSTAR will be 1,000 times more capable of
finding new black holes than anything previously launched into
"Black holes that have large amounts of matter falling
into them shine very brightly in this part of the spectrum,
and the signal can get out of the cores of galaxies because
hard x-rays are very penetrating. So this telescope will give
us a very direct way to see and measure the growth of supermassive
black holes, which we think are very common in the cores of
galaxies," Thorsett said.
Studying black holes is one of three basic science goals for
NuSTAR. The telescope will be used to take a census of black
holes at all scales, and will also measure the "accretion
rate" at which matter has fallen into them over time.
Another goal is to detect and measure radiation emitted in
the aftermath of stellar explosions, or supernovae. The remnants
of supernovae that exploded centuries ago still emit signals
that can shed new light on how elements are formed and ejected
in supernovae. NuSTAR will be especially good at observing the
radioactive decay of titanium to calcium, which tends to be
produced in the region of a supernova where material either
is ejected forever from the explosion or falls back inward to
form a compact remnant of some sort. NuSTAR will provide a direct
test of theories developed by Woosley and others to explain
how the elements are formed.
"We can look at these newborn elements in supernova remnants
and compare the observations with the predictions from computer
models," Thorsett said.
The third goal is to observe the highly energetic jets that
stream out of certain black holes at nearly the speed of light.
Coupled with observations from the Gamma-Ray Large-Area Space
Telescope (GLAST), NuSTAR will provide data to help scientists
explain this still-enigmatic but powerful phenomenon.
UCSC scientists are also involved in the GLAST project, which
will use detectors designed and built by UCSC physicists in
the Santa Cruz Institute for Particle Physics.
"NuSTAR is another step in the development of a strong
program in high-energy astrophysics at UCSC. Together with our
partner institutions in the Bay Area and southern California,
and other national and international partners, we are looking
forward to a very active future for high-energy astrophysics
research," Thorsett said.
In addition to UCSC and Caltech, the other participating organizations
and universities in the NuSTAR project are the Jet Propulsion
Laboratory (managed by Caltech for NASA), Columbia University,
Stanford Linear Accelerator (SLAC), the Lawrence Livermore National
Laboratory, Sonoma State University, and the Danish Space Research Institute. NuSTAR's
spacecraft will be built by General Dynamics Spectrum Astro.
The Small Explorer Program is designed to provide frequent,
low-cost access to space for physics and astronomy missions
with small to midsized spacecraft. NASA has successfully launched
six SMEX missions since 1992. The missions include the Reuven
Ramaty High Energy Solar Spectroscopic Imager, launched in February
2002, and the Galaxy Evolution Explorer, launched in April 2003
and led by Caltech physics professor Chris Martin.
The selected proposals were among 29 SMEX and eight mission-of-opportunity
proposals submitted to NASA in May 2003. They were in response
to an Explorer Program Announcement of Opportunity issued in
February 2003. NASA selected six proposals in November 2003
for detailed feasibility studies. Of these, NASA has now selected
the International Boundary Explorer for launch in 2008 and NuSTAR
for a possible launch in 2009.
NASA's Goddard Space Flight Center, Greenbelt, Md., manages
the Explorer Program for the Science Mission Directorate.
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