MORE EVIDENCE FOR AN ACCELERATING UNIVERSE

For Immediate Release

Contact: Science News

202/872-5119

Two teams of astronomers say their observations of distant supernova

support the bizarre notion that the universe will not only expand

forever but will do so at an ever increasing rate. Details appear in

the Oct. 31 issue of Science News, a weekly news magazine. The article

is attached.

Saul Perlmutter of the Lawrence Berkeley (Calif.) National Laboratory

and Alex V. Filippenko of the University of California, Berkeley

announced the findings on Oct. 29 at a workshop on supernovas at the

University of Chicagol's Enrico Fermi Institute. The workshop continues

through Saturday, Oct. 31, and both Perlmutter and Filippenko can be

reached through the Institute at 773/834-2057.

Please credit Science News in stories including this information.

Studies Support an Accelerating Universe

by Ron Cowen

New findings support the bizarre notion that the universe will not

only expand forever but will do so at an ever increasing rate. Early

this year, two teams studying the brightness of a collection of

distant, exploded stars--called type Ia supernovas--reported

preliminary evidence that the expansion of the cosmos is accelerating

(SN: 3/21/98, p. 185).

Although his team has only begun analysing a dozen or so new

supernovas, "the additional data set is reinforcing our conclusion

that the acceleration [of the universe] appears to be nonzero," says

Alex V. Filippenko of the University of California, Berkeley.

Filippenko and his colleagues had initially studied 16 other

supernovas.

"We have found no systematic errors that could explain why it is that

it looks like we have an accelerating universe," notes Saul Perlmutter of

the Lawrence Berkeley (Calif.) National Laboratory, a member of the

second team, which has analyzed 42 supernovas. Both Filippenko and

Perlmutter reported their latest results on Oct. 29 at a meeting at

the University of Chicago on type Ia supernovas.

Type Ia supernovas can illuminate the universe's expansion rate

because they all have roughly the same luminosity. The astronomers

record each supernovas brightness and redshift, the amount by which

cosmic expansion has stretched the wavelength of the light it emits.

Redshift also indicates how many billions of years ago the light now

reaching Earth left a supernova. The most distant supernovas studied

by the astronomers come from a time when the universe was half its

current age.

If the universe has revved up its rate of expansion, a supernova at a

given redshift would lie farther away than expected, and so it would

appear dimmer. That's exactly what both teams continue to find. The

supernovas examined are about 15 percent fainter than astronomers can

account for in a standard model of the universe with no acceleration.

Because gravity always acts to slow expansion, the findings are

forcing theorists to grapple with the existence of an antigravity

force or some other exotic source of energy in the cosmos (SN:

2/28/98, p. 139) .

Caveats about the findings abound. Astronomers worry that masking by

dust, rather than an accelerating cosmos, may explain the supernova

results. Another concern is that supernovas in the distant past may

not have been as bright as they are now. Perlmutter reports that his

team did an additional analysis in which they discarded the reddest

supernovas. Red coloration can be a signpost of fine dust, which

absorbs more blue light than red. The scientists still found evidence

of an accelerating universe.

Surprisingly, because dust seems to be ubiquitous, Filippenko's group

finds that some of the distant supernovas in their survey are less red

than those nearby. This doesn't rule out the possibility that large

particles of dust, which absorb all wavelengths of light uniformly,

cause some of the dimming, critics say.

"I'm reaching the point that I'm beginning to believe the two teams,"

says Jeremiah P. Ostriker of Princeton University. "In another year,

we will know much more, but they've come a long way in the last year."