Thermonuclear Blasts Yield Breakthrough on Structure of Neutron Star

Mo Xinhai

PureInsight | January 6, 2003

Three superimposed photographs of a moving neutron star taken by the Hubble space telescope.
NASA and F.M. Walter (State University of New York at Stony Brook)

[] According to NASA's official website, on November 7, amidst the fury of 28 thermonuclear blasts on a neutron star's surface, scientists using the European Space Agency's (ESA) XMM-Newton X-ray satellite obtained a key measurement revealing the nature of matter inside these enigmatic objects.

A neutron star is composed of densely packed neutrons. The objects we see on this earth are usually composed of molecules, which consist of atoms. Compared to neutrons, there is an enormously large space not only between molecules or atoms, but also inside molecules and atoms. Therefore, compared to the objects that we normally see during our daily lives, neutron stars have strikingly high densities. The density of a typical neutron star is about 100 trillion times higher than that of the earth. A neutron star the size of a small matchbox can weigh as much as a couple of billion tons.

The neutron star measured by the ESA is part of a binary star system named EXO 0748-676, located in the Volans, or Flying Fish. Scientists estimate that neutron stars contain a mass of about 1.4 Suns compacted into about a 10-mile-wide sphere (16 kilometers). Dr. Jean Cottam of NASA's Goddard Space Flight Center in Greenbelt, Md., leads the international effort to use the gravitational red shift to study the internal structure of a neutron star. The result, capturing for the first time the ratio between such an ultra-dense star's mass and its radius in an extreme gravity environment, was featured in the November 7 issue of Nature.

"It is only during these bursts that the region is suddenly flooded with light and we were able to detect within that light the imprint, or signature, of material under extreme gravitational forces," said Cottam.

The extent of the gravitational red shift depends directly on the neutron star's mass and radius. The mass-to-radius ratio, in turn, determines the density and nature of the star's internal matter, called the equation of state. The results from such measurments are thus very important in understanding the characters of neutron stars. By understanding the precise ratio of mass to radius, and thus pressure to density, scientists can determine the nature of this superfluid and speculate on the presence of exotic matter and forces within -- the type of phenomena that particle physicists search for in earthbound particle accelerators. These results also prove for the first time that neutron stars do exist in nature.

"Unlike the Sun, with an interior well understood, neutron stars have been like a black box," said co-author Dr. Frits Paerels of Columbia University in New York. "We have bored our first small hole into a neutron star. Now theorists will have a go at the little sample we have offered them," he said.

More importantly, said co-author Dr. Mariano Mendez of SRON, the National Institute for Space Research in the Netherlands, "We have now established a new means to probe the interior neutron stars (by studying the gravitational red shift). We can use it to measure the mass-to-radius ratios of other neutron stars, perhaps uncovering a quark star."

New discoveries by modern science, especially the phenomena observed in astrophysics, have greatly broadened the view of human beings. As recently as the past few decades, people doubted the existence of matter such as neutron stars, black holes, and the like, because they are far beyond people's everyday life experiences. But now they have been proven one after another by phenomena observed in research laboratories. Because of their strong preconceptions obtained in everyday society, people tend to disagree or scoff at anything that cannot be seen or that modern science has not recognized or uncovered. It has been proven again and again that such notions themselves are not scientific. Some phenomena that our science cannot currently observe or explain will undoubtedly become common knowledge in the future.

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