This deep view of the universe reveals a plethora of galaxies in
visible and infrared light. The image by NASA's Hubble Space
Telescope revealed many more than expected. (R. Williams
[STScI], the HDF-South team, and NASA)
The new number was based on observations by the orbiting
telescope’s Deep Field camera last October, when it looked at a
speck-sized area of the southern sky, taking what amounts to a
visual core sample of the heavens.
The Hubble telescope took a similar view of the northern sky in
1995, and then estimated that there might be 80 billion galaxies
in existence.
Harry Ferguson of the Space Telescope Science Institute, which
studies Hubble findings, said the southern observations looked a
bit further into the past than the northern ones, and managed to
detect dimmer objects in space, which accounts for the higher
galactic count.
12 Billion Light Years Away The Deep Field-South project looked
12 billion light years away in distance, back in time to a
period perhaps one billion years after the theoretical big bang
that astronomers believe created the universe.
Hubble’s glimpse of the southern sky took in an area that would
appear to be “about the size of a grain of sand held at arm’s
length,” Ferguson told reporters at the American Astronomical
Society meeting in Austin.
But in that small segment of the sky, the telescope spied 620
galaxies.
Scientists extrapolated from that sample to theorize that there
might be 125 billion galaxies over the whole sky.
"Anybody could have predicted it", Ferguson said, stressing that
by looking further back in time, it was expected that more
galaxies would turn up.
Weird-Shaped Galaxies
Ferguson and other astronomers at a news conference acknowledged
that some of the newly detected galaxies were oddly shaped,
unlike the symmetrical Milky Way that contains Earth and other
more familiar galaxies that are shaped like spirals and
ellipses.
These newly-spied galaxies appeared to be a disorganized
collection of loosely-bound lumps. One astronomer likened their
shape to a Danish pastry with raisins and another called one
group of these galaxies “a pastry shop.”
The notion that there might be more galaxies than originally
thought is grist for astronomers trying to figure out how the
universe developed, especially in its earliest stages, Ferguson
said.
Perhaps Ghost Galaxies, Too
Because these observations by Hubble could see very faint
objects whose light made its journey toward Earth billions of
years ago, it probably counted so-called ghost galaxies in its
estimate.
Ghost galaxies are tiny, and consist of large amounts of
mysterious dark matter. Since astronomers believe that 90
percent of the universe may be made up of dark matter, that
makes the ghosts worth studying and new astronomical instruments
make this possible.
A light year is the distance light travels in a year, about 6
trillion miles.
By John Noble Wilford
AUSTIN, Tex. -- In a stunning run of discoveries over the last
three years, astronomers have observed 17 nearby stars that
appear to be orbited by planets more or less the size of
Jupiter. The most recent detection of a planet around a star
other than the Sun was described here Saturday.
But while astronomers continue the search for more such objects,
they have now seen enough to be puzzled by an emerging pattern:
None of these extrasolar planetary systems seems to resemble the
Sun's family of planets. Is this an observational fluke? Or is
the solar system a cosmic oddball?
At a meeting of the American Astronomical Society, scientists
reviewed the mystifying evidence. All of these objects are found
in orbits much closer to their parent stars than Jupiter, the
solar system's giant, is to the Sun. Astrophysicists could only
speculate how such large planets, ranging in mass from one-half
to 10 times the mass of Jupiter, can orbit so close to a star
and survive what must be destabilizing gravitational stresses.
Other studies reveal that many of the stars orbited by large
bodies typically have two to three times more heavy elements
than exist in the Sun. And except for the extrasolar planets
extremely close to their host stars, most of these objects
appear to travel in orbits unlike those of planets around the
Sun.
"For the first time, we have enough extrasolar planets out there
to do some comparative study," said Dr. Geoffrey W. Marcy of San
Francisco State University, who is the leading discoverer of
these objects. "We are realizing that most of the Jupiter-like
planets far from their stars tool around in elliptical orbits,
not circular orbits, which are the rule in our solar system."
Dr. Marcy noted that 9 of the 17 detected extrasolar planets
sweep relatively close to their stars and then swing far out
again, giving an oval shape to their orbital paths. The others
travel in more circular orbits, presumably because they are even
closer to their stars and are regulated by gravitational tides.
One of these is only four million miles from its star and takes
only 4.2 days to complete its revolution, or "year."
An elliptical orbit was observed for the most recently
discovered extrasolar planet, around the star HD 168443 in the
constellation Serpens, the Snake. This new planet, Dr. Marcy
reported Saturday, orbits its star once every 58 days at an
average distance that is nearer to the star than Mercury, with
an 88-day orbit, is to the Sun.
The eccentricity of the newly discovered planet -- the degree
that it deviates from a circular path -- is 0.54, about 10 times
the eccentricity in the orbit of most solar system planets.
Theorists have proposed several possible explanations for such
eccentric orbits. When enough large planets orbit a star in
proximity, perhaps they generate a gravitational slingshot that
projects the planets into elongated orbits. Or perhaps a passing
star has upset the delicate balance of these planetary systems.
In some cases, the planets could be perturbed because their star
is part of a binary system, where two stars are locked in
gravitational embrace.
If elliptical orbits appear to be common for other planets as
massive as Jupiter, astronomers are wondering what different
circumstances in the solar system keep mighty Jupiter and Saturn
in circular orbits. It is not a trivial question, for the
emergence of life on Earth probably depended on the answer.
Jupiter-size bodies plunging toward and away from their stars
are likely to sweep aside smaller worlds, sending them crashing
into the star or flying out of orbit into interstellar space.
Current technology is incapable of detecting Earth-size planets
around other stars, but they almost certainly could not exist
near their star's warmth in a system so unsettled by large
planets in wrecking orbits, Dr. Marcy said.
"The implications are also profound for the search for
extraterrestrial life," Dr. Marcy said.
Yet of the all the Sun-like stars that have been studied so far
by planet seekers, only 5 percent have been found to have
Jupiter-mass planets in such eccentric orbits. Taking an
optimistic view, Dr. Marcy said that leaves 95 percent of stars
that may be free of these influences and could harbor habitable
planets.
Although nearly all astronomers agree that these detected
objects are extrasolar planets, a few holdouts are not so sure.
They have raised the possibility that these are brown dwarfs,
objects that formed like stars but lacked sufficient mass to
support nuclear fusion in their cores.
Dr. William D. Cochran, an astronomer at the University of Texas
here, said that too many of the objects had masses comparable to
Jupiter's for them to be brown dwarfs. But at the meeting, he
cautioned that they may not be planets, particularly because so
many of them have eccentric orbits and are so close to their
stars. They might be some new type of object unlike anything in
the solar system.
"To find a new type of object would be an extremely exciting
result," Dr. Cochran said. "Right now, we are still going to
call them 'planets,' even though they may really be something
slightly different."
http://news.bbc.co.uk/low/english/sci/tech/newsid_251000/251318.stm
BBC News Online: Sci/Tech
Friday, January 8, 1999 Published at 18:30 GMT
In the groove
By BBC News Online Science Editor Dr David Whitehouse
*
Astronomers using the Hubble Space Telescope have observed dust disks
around two stars that may indicate the presence of planets.
The immense disk of dust surrounding one of the stars has a dark band
separating two lighter regions, "like a wide groove in a phonograph
record."
The scientists speculate that an unseen planet may have gravitationally
carved out this 3.7 billion mile-wide gap. The star, a fairly ordinary
one known as HD 141569, lies about 320 light-years away in the
constellation of Libra.
Hubble shows that the disk is in two parts. A bright inner region and
a
fainter outer region separated by a dark band. Superficially, it
resembles the largest gap in planet Saturn's rings.
"The most obvious way to form a gap in a disk is with a planet," says
astronomer Alycia Weinberger. "The planet does not have to be in the
gap, however. It could either be sweeping up the dust and rocks from
the disk as it travels in its orbit around the star, or the gravity
of
the planet could knock the dust out of one part of the disk."
The vast disk is 75 billion miles across, or about 13 times the
diameter of Neptune's orbit. The inner edge of the gap is 21 billion
miles from the star.
Though already a fully formed star, HD 141569 is relatively young,
probably only 1% through its lifetime as a stable star. It is nearly
three times more massive and 22 times brighter than our Sun.
HD 141569 was first suspected of having a dust disk in 1986. Thermal
radiation from it was observed earlier this year. At the distance of
HD
141569, the crisp resolution of the Hubble Space Telescope shows
structures as small as 1 billion miles across.
Held in place
The other star around which a dust ring has been detected is called
HR
4796A. It likewise offers clues into the possible presence of young
planets.
"The rings surrounding the giant planets in our own solar system are
held in place by the gravitational force of moons orbiting nearby,"
explains Brad Smith of the University of Hawaii.
"The narrow width of the HR 4796A ring implies that it also is held
in
place by unseen bodies, most probably planets or protoplanets."
HR 4796A is about 70% larger than the Sun and probably less than 10
million years old. "Considering our own solar system to be middle aged,
HR 4796A would be a mere infant," says Smith.
"It is especially interesting this stellar ring is so young, indicating
planetary bodies have already formed in less than 10 million years."
Just visible to the naked eye, HR 4796A is located 220 light-years
away
in the southern constellation of Centaurus.
To image the rings, Hubble scientists had to use a coronagraphic camera
on Hubble's Near Infrared Camera and Multi-Object Spectrometer
(NICMOS).
A coronagraph blocks out the glare of a star's light (just as the Moon
blocks the Sun's light during a solar eclipse) so that much fainter
surrounding material can be seen. These images add to the growing body
of evidence that there may be planetary systems around many, if not
most, stars similar to our Sun.
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http://www.bergen.com:80/morenews/science0419990104c.htm
Monday, January 4, 1999
By DIEDTRA HENDERSON
Special from The Seattle Times
**
Don't expect too much romance from a statistician like Amir Aczel, a
man whose career is rooted in the cool certainty of numbers.
Once Aczel had established, using probability theory, that there's a
100-percent chance that intelligent life exists elsewhere in the
universe, the brief romance of the moment evaporated.
Rationality reared its familiar head.
"My next question was, 'Well, what do you do with that?' " said Aczel,
an associate professor of statistics and mathematics at Bentley College
in Massachusetts. "You can't talk to them. You can't meet them. It
will
take thousands of years to get a message across -- if they're even
listening. It was more of a concept, rather than something practical."
That's the difference between Aczel, son of a cargo-boat captain who
routinely navigated beneath the stars, and the late Carl Sagan, who
often wondered which stars might provide warmth and produce the
chemical building blocks necessary for life to thrive.
Sagan originally approached the publisher with the idea that turned
into Aczel's newest book, "Probability 1: Why There Must be Intelligent
Life in the Universe" (Harcourt Brace, $22). Sagan, author of "Contact"
and co-founder of a society devoted to the search for extraterrestrial
life, didn't get a chance to write the book before his death.
"If I had to guess," Sagan did write in "Pale Blue Dot: A Vision of
the
Human Future in Space," ". . . I would guess that the Universe is
filled with beings far more intelligent, far more advanced than we
are.
But of course I might be wrong. Such a conclusion is at best based
on a
plausibility argument, derived from the numbers of the planets, the
ubiquity of organic matter, the immense time scales available for
evolution, and so on."
Or, as Aczel says via mathematical equation, probability, expressed
by
an upper-case P, is one, meaning there's a 100-percent chance that
intelligent life exists elsewhere.
His mathematical equation takes into account the number of planets that
contain life and are in orbit around at least one star in the known
universe. (So far, Earth is the only planet to fit the criteria.)
It also factors in the extremely remote chance that DNA has developed
and continues to thrive elsewhere and quantifies planets that orbit
a
nurturing star that is neither too hot nor too frigid.
To some, the notion that intelligent life exists elsewhere, in some
galaxy so far away it's beyond the reach of our telescopes, is the
stuff of science fiction. Physicist Enrico Fermi's skeptical question
-- "Where are they?" -- still stands, 47 years after Fermi uttered
it
and despite 22 years of eavesdropping using the world's most
sophisticated radio telescopes to listen for the signals generated
by
beings light years away.
Aczel, who also wrote "Fermat's Last Theorem," began his foray into
the
realm of outer space while walking around Orlando, Fla. He saw a sign
for Harcourt Brace and wandered in, explaining to the book publisher
that he was an author in need of an editor.
An executive editor who phoned back liked none of his book ideas. But
she wondered whether he would write about the probability of
extraterrestrial life.
"My initial reaction was, 'No, I don't want to do that.' I never really
thought about that. I'm a statistician -- we believe in data. How am
I
going to prove that? How am I even going to consider such a
possibility?" he recalled. "She said, 'Why don't you try?' "
A question that had never before occurred to him -- What else exists
in
space? -- now haunts him, the search for its answer occupying five
or
six hours of his day. "We were put on this planet to solve this puzzle
of what is out there. It's a fascinating puzzle," he said.
January 1999
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