UBC scientists may be a step closer to finding the answer to one
of astronomy’s most perplexing questions: What is the galaxy made
of?
“We may have identified a component of the unknown dark matter
in the galaxy — the 90 per cent of the mass of the galaxy which
we thought was invisible,” says Prof. Harvey Richer, an astronomer
in UBC’s Physics and Astronomy Dept.
Research released by a four-member team which included Richer and
fellow UBC astronomer Asst. Prof. Douglas Scott, indicates that
ancient white dwarf stars — the burned-out remains of normal stars
like the Sun — may make up more than half of the invisible “dark
matter” in the Milky Way Galaxy.
The team of researchers, which also included Rodrigo Ibata from
Germany and Roland Gilliland from the Space Telescope Science Institute
in Baltimore, arrived at the conclusion after they compared images
of the Hubble Deep Field — the deepest optical image of the sky
— from the Hubble Space Telescope in 1995 and 1997. They found
that five objects moved slightly in the foreground between the two
images. The scientists believe that the objects may be old white
dwarf stars.
“If this picture is correct, there will be an enormous rethinking
of how galaxies formed and evolved,” says Richer.
In the past, white dwarf stars have been suggested as a possible
explanation of the missing matter in the galaxy but this may be
the first time anybody has seen them, he says.
The team’s results will be published in the October issue of The
Astrophysical Journal Letters. Meanwhile, the team has plans
to check their work this December when they will again use the Hubble
Space Telescope to look at the same field and see if the previously
detected motion in the five objects is confirmed.
A large consortium including astronomers from UBC, Victoria, Princeton
University and Germany are also using the Canada-France-Hawaii Telescope
in Hawaii to search for more local examples of these ancient white
dwarfs.
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