Scientists glimpse 'lens' that made star brighter

Monday, December 17, 2001

For the first time, scientists say they've glimpsed a mysterious object in the Milky Way galaxy that acts like a lens to make a distant star appear brighter.

Such objects, called microlenses, are part of the unseen "dark matter" that accounts for perhaps 90 percent of matter in galaxies, and even a bigger portion of matter in the entire universe. Nobody knows what all this dark matter is.

For all that mystery, however, the newly glimpsed object turns out to be just what scientists had expected: an ordinary but very faint star.

The work was reported in the Dec. 6 issue of the journal Nature by scientists at Lawrence Livermore Laboratory in Livermore, Calif., and elsewhere.

Researchers say the star, about 600 light-years from Earth, acted like a lens seven years ago to magnify the brightness of a star in the Large Magellanic Cloud, a clump of stars some 150,000 light-years away. The cloud lies in the direction of the constellation Doradus in the southern hemisphere.

In early 1993, the researchers say, the newly glimpsed star lay exactly between that distant star and Earth. Its gravity bent the light from the distant star, just as a lens does. The result was to make the distant star appear brighter for a while, until the two stars roamed out of alignment with Earth.

The researchers used images taken in 1999 by the Hubble Space Telescope to identify the Milky Way star.

Bohdan Paczynski of Princeton University, an expert in gravitational lensing, said it's about 80 percent likely that the star identified in the new study really was the lensing object. "In a couple of years we shall know for sure," after follow-up work is done, he said.

The new work is part of a project to look for what scientists call MACHOs -- massive compact halo objects, which include not only stars but also starlike objects that never "turned on," and black holes. Scientists want to know how much dark matter is accounted for by MACHOs.

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