A type of celestial object that has long stumped
astronomers has been found to emit X-rays, thus proving a
theory of how the objects form.

Dr. Steven Pravdo of NASA’s Jet Propulsion Laboratory,
Pasadena, Calif., and other scientists have concluded that
these objects, called Herbig Haro objects, are produced by
high velocity shocks. Pravdo is the lead author of a paper
published in the Oct. 18 issue of the journal Nature.

Herbig Haro objects are found in regions where new stars
are forming. They are nebulae, or dust and gas clouds. They
form when high-velocity gas emitted from young stars collides
with clouds of interstellar material. The collision heats the
gas in the surrounding nebula to sufficiently high
temperatures to produce X-rays.

Observations for the past 20 years showed no evidence of
X-ray emission from these objects, which are named for
astronomers George Herbig and Guillermo Haro. Previous
instruments lacked the resolution and sensitivity necessary to
‘see’ these X-rays. The discovery of the X-ray emissions was
possible through the very powerful Advanced CCD Imaging
Spectrometer on NASA’s Chandra X-ray Observatory, which has
been in orbit since 1999.

On Oct. 8, 2000, astrophysicists used the instrument to
study HH 2, one of the brightest and closest Herbig Haro
objects in the Orion Nebula. They determined that HH2
contains shock-heated material with a temperature of about 1
million degrees Kelvin (about 1 million degrees Fahrenheit).
Pravdo and his team used three criteria to rule out the
possibility that the emissions came from any other source.
First, Chandra’s high spatial resolution pinpointed the
location of the X-rays at HH 2. Second, the X-rays appeared to
be covering a region bigger than a star. Third, the
temperature of the X-rays was about 1 million degrees, cooler
than nearby X-ray stars. One million degrees is about the
temperature expected if material moving at about 300
kilometers per second (about 600,000 miles per hour) collides.
At this speed, you could go from Los Angeles to San Diego and
back in one second.

The principal investigator of the Advanced CCD Imaging
Spectrometer, Dr. Gordon Garmire of Pennsylvania State
University, University Park, is a co-author of the paper.
Other co-authors include Drs. Yohko Tsuboi, Yoshitomo Maeda
and Eric Feigelson, all from Pennsylvania State University,
and Dr. John Bally from the University of Colorado, Boulder.
The Advanced CCD Imaging Spectrometer X-ray camera was
developed for NASA by Pennsylvania State University and the
Massachusetts Institute of Technology, Cambridge, Mass. NASA’s
Marshall Space Flight Center in Huntsville, Ala., manages the
Chandra program. TRW, Inc., Redondo Beach, Calif., is the
prime contractor for the spacecraft. The Smithsonian’s Chandra
X-ray Center controls science and flight operations from


Images associated with this release are available online



http://chandra.harvard.edu .

The Chandra X-ray Observatory is managed for NASA by the
Smithsonian Astrophysical Observatory, Cambridge, Mass. JPL
is managed for NASA by the California Institute of Technology
in Pasadena.