A very massive star collapsed to form a neutron star and not a black
hole as anticipated, according to new results from NASA’s Chandra X-ray
Observatory. This discovery shows that nature has a harder time making
black holes than previously thought.

Scientists found this neutron star – a dense whirling ball of neutrons
about 12 miles in diameter – in an extremely young star cluster.
Astronomers were able to use well-determined properties of other stars
in the cluster to deduce that the parent star of this neutron star was
at least 40 times the mass of the sun.

“Our discovery shows that some of the most massive stars do not collapse
to form black holes as predicted, but instead form neutron stars,” said
Michael Muno, a University of California, Los Angeles, postdoctoral
Hubble fellow. He is lead author of a paper to be published in an
upcoming edition of The Astrophysical Journal Letters.

When very massive stars make neutron stars and not black holes, they
will have a greater influence on the composition of future generations
of stars. When the star collapses to form the neutron star, more than 95
percent of its mass, much of which is metal-rich material from its core,
is returned to the space around it.

“This means that enormous amounts of heavy elements are put back into
circulation and can form other stars and planets,” said J. Simon Clark
of the Open University in the United Kingdom.

Astronomers do not completely understand how massive a star must be to
form a black hole rather than a neutron star. The most reliable method
for estimating the mass of the parent star is to show that the neutron
star or black hole is a member of a cluster of stars, all of which are
close to the same age.

Because more massive stars evolve faster than less massive ones, the
mass of a star can be estimated if its evolutionary stage is known.
Neutron stars and black holes are the end stages in the evolution of a
star, so their parent stars must have been among the most massive stars
in the cluster.

The work described by Muno was based on two Chandra observations on May
22 and June 18, 2005. NASA’s Marshall Space Flight Center, Huntsville,
Ala., manages the Chandra program for NASA’s Science Mission
Directorate. The Smithsonian Astrophysical Observatory controls science
and flight operations from the Chandra X-ray Center in Cambridge, Mass.

Additional information and images are available on the Web at:
http://chandra.harvard.edu or http://chandra.nasa.gov