Neutron Star Found Where a Black Hole was Expected

A star 40 times themass of the Sun collapsed to form a neutronstar instead of a blackhole, researchers said today.

When a massive starburns out, its outer layers crash down on the star's core, creating a denseball of matter from which nothing could escape. Scientists previously thoughtthat when a massive star died and collapsedon itself, it had no choice but to create a black hole.

Now, new data fromNASA's Chandra X-ray Observatory suggests that massive stars have a little wiggleroom, and sometime produces a neutron star instead.

"Our discoveryshows that some of the most massive stars do not collapse to form black holesas predicted, but instead form neutron stars," said study lead author Michael Muno of University California, Los Angeles.

Researchersdiscovered this neutron star, a dense neutron ball about 12 miles in diameter,in the midst of an extremely young cluster of stars. By estimating the age andmass of the other stars in the cluster, the scientists were able to determinethat this neutron star's parent was at least 40 times the mass of the Sun.

Very massive starsevolve faster than smaller massive stars, so a star's mass can be estimated ifits evolutionary stage is known. Neutron stars and black holes are the endstages of a star's life, so the stars that produced them must have been amongthe most massive stars in the cluster.

When very massivestars shirk convention and turn into neutron stars instead of black holes, theyhave a greater influence on the composition of future generations of stars.Instead of having most of its mass gobbled up by a black hole, the star sendsmore than 95 percent of its mass - mostly metal-rich material from its core -into the surrounding space.

"This means thatenormous amounts of heavy elements are put back into circulation and can formother stars and planets," said J. Simon Clark of the Open University in theUnited Kingdom.

Althoughresearchers now know that the death of a massive star can produce a neutronstar, they don't completely understand the mechanism that determines a star'sfate. Most likely it depends on how massive the star is, but astronomers don'tknow how massive a star must be to form a black hole instead of a neutron star.

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• Birth of a Black Hole is Messy, New Observations Suggest
• Collapse or Collision: The Big Question in Star Formation