EMBARGOED
FOR RELEASE UNTIL 12:30 P.M. EDT
MONDAY, JUNE 5 - TIME OF PRESS CONFERENCE
AT THE MEETING OF THE AMERICAN ASTRONOMICAL
SOCIETY
Rochester,
N.Y. - The world's most successful
automated search for nearby supernovas,
conducted by the University of California,
Berkeley, has found 70 of these
exploding stars in its first two
years of operation, providing valuable
information about the evolution
and physics of stellar explosions.
The
data also are giving cosmologists
greater confidence in conclusions
about the structure of the universe
gleaned from studies of distant
supernovas. These include recent
findings that the universe is flat,
its expansion is accelerating, and
that some two-thirds of the universe's
mass is made up of strange matter
called dark energy or "vacuum
energy."
"Our
study of distant supernovas depends
entirely on a reliable calibration
of nearby ones," said Alex
Filippenko, a professor of astronomy
at UC Berkeley and leader of the
Lick Observatory Supernova Search
(LOSS) conducted by the Katzman
Automatic Imaging Telescope (KAIT).
"We want to understand the
basic physics of supernovas going
off in galaxies, and KAIT is so
important because it finds essentially
all the supernovas in the galaxies
we monitor."
Filippenko
summarized the operation of the
robotic telescope and results to
date at a media briefing Monday,
June 5, during the national meeting
of the American Astronomical Society
in Rochester, N.Y. His formal talk
at the meeting takes place at 2
p.m. on Monday in a session on automated
telescopes. More details will be
presented by recent UC Berkeley
graduate Maryam Modjaz in a display
paper the same day.
UC
Berkeley's robotic telescope scans
about 1,000 galaxies a night looking
for new points of light, generally
within about 500 million light years
(3 billion trillion miles) of Earth.
Put into operation in late 1996,
it was fully programmed to conduct
the supernova search by the middle
of 1998. By the end of 1998 the
KAIT had found 19 new supernovas,
and in 1999 it found 40 - nearly
three times the number found in
a calendar year by any previous
robotic supernova search. This year
it already has discovered 11 new
nearby supernovas.
Because
the telescope catches almost every
supernova in the galaxies it monitors,
the data give astronomers a better
idea of how common supernovas are
and of their variety.
Filippenko
and post-doctoral fellow Weidong
Li have found, for example, that
so-called Type Ia supernovas are
less uniform than once thought.
This may have major implications,
since Type Ia supernovas are used
as a "standard candle"
to estimate galactic distances.
If there are several common types,
conclusions based on an assumption
of uniformity may be incorrect.
Type
Ia supernovas are thought to occur
in binary star systems. One of the
stars, a white dwarf, is thought
to steal matter from a larger companion
until its mass exceeds a certain
limit, at which point the star becomes
unstable and is consumed in a gigantic
thermonuclear explosion.
"This
is the process by which we are made
of star stuff," Filippenko
said. "Iron and oxygen and
other heavier elements are produced
in supernovas. This is where we
came from."
Based
on their supernova data, he and
Li have concluded that more than
one-third of Type Ia supernovas
are peculiar, in that they are brighter
or dimmer than the "average"
Type Ia, or that their spectra show
unusual chemical composition.
They
and their colleagues have submitted
a paper to the Astrophysical Journal
documenting the high percentage,
about 36 percent, of peculiar supernovas,
and speculating on what this implies
about what is creating the explosion.
It may be, for example, that some
Type Ia supernovas result from the
merger of two white dwarf stars
into an unstable mass that quickly
explodes. Thus, Filippenko said,
Type Ia supernovas may be produced
in multiple ways.
Filippenko
and his colleagues also have found
possible differences between the
pattern of brightening of nearby
supernovas and the pattern typical
of distant supernovas. He doubts
this is a significant problem for
cosmologists who have concluded,
from analysis of the distance and
recession speed of distant supernovas,
that the universal expansion is
accelerating. Nevertheless, he said,
it is important to verify that supernovas
which exploded billions of years
ago look the same - in particular,
that they have the same peak power
output - as those which exploded
more recently.
"When
we say some supernovas are further
away then we expect, we are making
an assumption that they aren't dimmer
than we expect," said Filippenko.
"Confidence in our conclusions
can only get better with a fair
comparison of distant and nearby
supernovas."
Filippenko
is part of an international crew
of astronomers - the High-Z Supernova
Search Team - that in 1998 concluded
from a study of Type Ia supernovas
that the expansion of the universe
is accelerating. That information,
combined with new data on the cosmic
background radiation, recently led
cosmologists to even more amazing
findings about the universe: not
only is it accelerating, but its
geometry is flat. For this to be
the case, the normal matter we see
and the dark matter we infer to
be present from other studies comprise
only one-third of all the matter
in the universe.
"Our
earlier work on supernovas showed
some weird stuff in the universe,
essentially a 'vacuum energy' that
is accelerating the expansion,"
he said. "Now the MAXIMA and
BOOMERANG cosmic microwave background
radiation experiments have given
us high quality data that complement
the supernova data, and create a
greater acceptance of this weird
stuff in the universe. This will
create a revolution in the next
decade."
To
boost confidence in their analysis
of distant supernovas, Filippenko
and his team have secured time this
fall on the Hubble Space Telescope
to obtain accurate color measurements
of seven distant supernovas. They
hope that by comparing the colors
of distant and nearby supernovas,
they can determine if there is any
intervening dust that would dim
the light from distant supernovas
and make them appear farther away,
thus throwing their conclusions
into question.
Filippenko
and Li also have embarked on a study
of the motion of nearby supernovas
to get an idea of the bulk flow
of galaxies and clusters of galaxies
through the universe. This will
provide a measure of the amount
of normal and dark matter in the
universe, Filippenko said.
The
recent successes of KAIT are largely
due to Li, placed in charge of telescope
operations in 1997 after arriving
from the Beijing Astronomical Observatory,
where he had directed their automated
supernova search. UC Berkeley engineer
and astronomer Richard Treffers
made significant additional improvements
in the hardware.
Every
night computers check the weather
at Lick Observatory on Mt. Hamilton
outside San Jose, Calif., open the
dome, point and focus the telescope
and take digital pictures. The images
are sent via the internet to Li's
computer at UC Berkeley, where they
are compared automatically to earlier
pictures of the same region of sky.
Images with new points of light
are flagged so that, the next morning,
a crew of several undergraduates
can double-check them and identify
the best candidates. In winter,
the KAIT can take as many as 1,200
images a night. Li is working to
increase this number, and so far
has reduced the time per image from
40 seconds to 30 seconds.
When
a supernova is discovered, spectra
of the star often are obtained at
the Shane three-meter telescope
at Lick Observatory, and photometry
is carried out by KAIT itself.
KAIT construction
and operations have been supported by the Sylvia and Jim Katzman
Foundation, which donated funds at a critical time in the
telescope's development, as well as by the National Science
Foundation, the National Aeronautics and Space Administration,
the University of California, the Hewlett-Packard Company,
Sun Microsystems, Photometrics Ltd., AutoScope Corporation,
and Lick Observatory.