At more than 200 times sun’s mass, giant sets new record

By Ron Cowen

Web edition: July 23, 2010

Astronomers have discovered the most massive star known in the universe. The hefty body weighs in at about 265 times the mass of the sun and at birth tipped the scales at the equivalent of 320 suns, more than twice the generally accepted limit for a newborn.

Paul Crowther of the University of Sheffield in England and his colleagues describe the findings in an upcoming Monthly Notices of the Royal Astronomical Society. Science News previewed the discovery in May, when scientists met for a symposium on star formation and evolution.  

Crowther and his collaborators examined massive stars within two clusters, one in the Milky Way and the other in the Large Magellanic Cloud, a satellite galaxy of the Milky Way some 165,000 light-years from Earth. The team scanned the regions using the European Southern Observatory’s Very Large Telescope atop Cerro Paranal in Chile and looked at archival data from the Hubble Space Telescope. Four stars in the Large Magellanic Cloud star cluster, dubbed R136, had temperatures more than seven times hotter than the sun and were several million times brighter and tens of times larger.

Those properties, combined with the age of the stars, indicate that each of the four weighed more than 150 suns at birth. One of the stars, R136a1, was more than twice that mass when it formed, the researchers calculate.

The findings suggest it’s possible for individual stars in the present-day universe to become as heavy as 300 suns. Theoretical studies had previously suggested that such heavyweights might have formed only during the first few hundred million years of the universe, when the chemical composition of the cosmos favored the production of massive stars.

Less massive, but still hefty, stars ranging from 8 to 150 suns eventually die as supernovas and leave behind dense cinders — either black holes or neutron stars. Heavier stars, between 150 and 300 suns, may end their brief lives in exceptionally brilliant explosions known as pair-instability supernovas, once thought to have occurred only in the early universe. The new report lends support to claims that pair-instability supernovas have already been observed in the universe today.