Pulsating star puzzle solved by scientists in Chile

A team of researchers, led by Grzegorz Pietrzyński from Universidad de Concepción, have measured the mass of a very large and bright star with high accuracy, providing new insight into distances in the universe.


An international team of scientists led by researchers from Universidad de Concepción have found the answer to a vital astronomical question at observatories in the north of Chile.

Using a ‘high accuracy radial velocity planet searcher’ (HARPS) instrument on the 3.6 meter telescope at the European Southern Observatory in La Silla, about 160 km north of the city of La Serena and the 6.5 m Magellan telescope at the Las Campanas Observatory on the border of Chile’s Atacama and Coquimbo regions, the team, led by the university’s Grzegorz Pietrzyński, have measured the mass of a cepheid star within 1 percent accuracy.

Cepheid stars are extremely important for astronomists as they are the primary objects used for measuring distances to nearby galaxies, and hence for mapping out the universe.

“Based on cepheids we measure the whole universe, so our knowledge of the current status and of the future of the universe are based on cepheids,” Pietrzyński said. “If we know very well the evolution of those stars, we are more confident about our measurements of distances in the universe.”

Since the 60s scientists have been trying to resolve a discrepancy in the predicted mass of cepheids, with two important theories providing different results, said Wolfgang Gieren, another member of the project team at the Universidad de Concepción. One theory, the ‘pulsating star’ theory, predicted a mass up to 30 percent less than that predicted by the other, the ‘evolution of stars’ theory.

Now, according to the researchers, their first observation through Chile’s clear skies of a double star – where a pulsating cepheid and another star pass in front of one another – has supported the prediction of the ‘pulsating star’ theory, settling the important debate and confirming how to calculate the masses of cepheid stars.

“Now we know where we stand. We know what the masses are and that is really a breakthrough,” said Gieren.

The rare occurrence was spotted among the stars in the Large Magellanic Cloud, where the Cepheid and another star orbit each other in 310 days.

The scientists hope to find other examples of these pairs of stars and believe that using these systems they will eventually be able to measure the distance to the Large Magellanic Cloud to 1 percent, a large improvement of the cosmic distance scale.

The study appears in the Nov 25 2010 edition of the journal Nature.