Stars Missing In Action Now Counted

Almost one in five exploding stars in nearby galaxies is simply not seen, astronomers have determined.

For galaxies further out, that fraction doubles. This finding clears the way for these stellar beacons to be used as a good measure of how fast galaxies made stars earlier in the universe's history.

Key evidence for this "body count" of missing supernovae has come from detailed studies of the galaxy Arp 299, made with the 8.2-m Gemini North telescope.

The work is reported in a paper, "Core-Collapse Supernovae Missed by Optical Surveys", published online in the Astrophysical Journal last month.

Massive stars live fast and die young, going out in a blaze of glory as "core-collapse supernovae".

"Because they don't live long, only about 10 million years, the number of massive stars that we can see being born should be essentially identical to the number we see exploding," said the study's lead author, Dr. Seppo Mattila of the University of Turku in Finland.

"The trouble has been, lots of these supernovae just seemed to have gone missing," he said.

"We expected to see more."

Our own Milky Way Galaxy is a case in point.

Two to three supernovae should explode in our galaxy every century. But the last time anyone might - just might - have seen one directly was in 1680.

In 2008, however, NASA's Chandra X-ray Observatory and the Very Large Array radio telescope of the US National Radio Astronomy Observatory found a supernova remnant about 140 years old near the center of our galaxy.

"That's where the supernovae are mostly hiding - in the dusty central parts of galaxies," said Dr. Stuart Ryder of the Australian Astronomical Observatory, one of the new paper's authors.

"That's where most stars in a galaxy congregate, and where most of them die."