Astrophysics

A diamond heavier than the Sun

Pierre Bergeron, a Professor in the Department of Physics at Université de Montréal, and a team of researchers from the United States , have just discovered a very massive white dwarf star named LHS 4033 which confirms a hypothesis put forward more than 70 years ago by the American astrophysicist Subrahmanyan Chandrasekhar, winner of the 1983 Nobel Prize for physics. “What makes this discovery important is that the mass of the object we discovered is below the limit between a white dwarf and a neutron star,” the Québec astronomer explains.

To achieve these results, published in the April 2004 issue of The Astrophysical Journal, Mr. Bergeron used data he had gathered himself in an observing session in Arizona last October. He compared his calculations with photometric data obtained by his colleagues in three series of observations in Arizona and Hawaii .

The large majority of white dwarfs observed to date have a mass equivalent to 60% of the Sun’s mass. Back in the 1930s, the Indian-born scientist had predicted that if a white dwarf reached 1.4 times the mass of the Sun, the balance between its pressure and gravity would be upset. The modern value of this limit mass is 1.36 times the mass of the Sun. The mass of the star discovered by the astrophysicists is 1.33 times the mass of the Sun, still within the mass range corresponding to a white dwarf. The existence of LHS 4033 would appear to provide confirmation of the “Chandrasekhar mass.”

The discovery is especially meaningful for the Québec researcher, since he used a method for analyzing spectroscopic observations of his own invention. Published in his 1992 after his post-doctorate, the “Bergeron method” is now widely used.

This white dwarf also exhibits a feature that makes it even more exotic, the researcher points out. “Physical models of this star tell us that matter will reorganize itself, at very low temperature and very high pressure. As a result, a gigantic crystalline network of carbon seems to be forming—a veritable diamond in the sky! Warning to prospectors: in case you are thinking of mining it, the mass of this diamond is larger than the Sun’s mass!