Massive star mystery: Do they explode?

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Overblown claims?
Other astrophysicists, however, said these claims were exaggerated, raising questions about the assertion that very massive stars don't go supernova.

"My main concern is whether they have enough statistics yet to confirm this," said Adam Riess, an astrophysicist at Johns Hopkins University and at the Space Science Telescope Institute in Baltimore, which oversees Hubble's science operations. "It's a little like concluding that there cannot be a much more advanced civilization than ours because they have not contacted us yet. An argument by absence. But it's very plausible."

Crockett said it is possible that massive stars do actually produce supernovae that have simply gone unobserved as yet, "but as the number of events in our sample increases this possibility becomes increasingly unlikely."

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Weidong Li, a research astronomer at the University of California, Berkeley, agreed that almost all supernova precursors have a mass lower than 25 solar masses (25 times the mass of the sun), so many groups have questioned the ultimate fate of very massive stars.

"However, very massive stars are much rarer than less massive stars, so the fact that we detect about a dozen less massive progenitors doesn't mean that stars more massive than 25 solar mass will go to black holes without a supernova explosion, or too faint to observe," Li said.

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In fact, supernovae that likely come from very massive stars have already been observed, Li said, though their precursor stars have not (because the supernova sites have not been observed with the Hubble Space Telescope or big ground-based telescopes). He noted SN 2006gy, as an example, an object that he and his colleagues have published research on.

"This supernova is likely the result of a supernova explosion of a very massive star, with greater than 60 solar mass," Li told SPACE.com.

Image details
The Hubble image showing supernova SN2006bc is part of a sharp view of the spiral galaxy NGC 2397. This classic spiral galaxy has long prominent dust lanes along the edges of its arms, seen as dark patches and streaks silhouetted against the starlight. Hubble's resolution allows the study of individual stars in nearby galaxies.

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Located nearly 60 million light-years from Earth, the galaxy NGC 2397 is typical of most spirals, with mostly older, yellow and red stars in its central portion, while star formation continues in the outer, bluer spiral arms. The brightest of these young, blue stars can be seen individually in a high-resolution view from the Hubble's Advanced Camera for Surveys (ACS).

The images were obtained on Sept. 14, 2006, with the ACS.

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