Dark Energy: Astronomers Hot on Trail of Mysterious Force

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HeXp£Øi±

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PHILADELPHIA -- At first there was disbelief. Then widespread befuddlement. Then a period of quantification. Now, five years after discovering that the universe is expanding at an ever-faster pace, scientists know exactly how much mysterious "dark energy" is behind the acceleration and have turned to figuring out what it is.

The task may eat up a lifetime, researchers admit. Or perhaps some new Einstein will figure it out next year in a light-bulb moment. The reward will be a far more complete understanding of the history and fate of the cosmos.

At a meeting of the American Physical Society (APS) here this week, front-line observational astronomers and big-thinking theorists said important clues to one of the most vexing mysteries of modern science are already rolling in. Cautious optimism infused the gathering.

Much important but unpublished data are already collected, SPACE.com has learned, and by the end of this year the history of the universe's expansion could become a bit clearer, further illuminating the path toward understanding dark energy.

Change of pace

Our universe has always been expanding, with practically all galaxies receding from each other, except for those bound in clusters.

The expansion was decelerating until about 6.3 billion years ago, however. Then an important switch to acceleration occurred. Something caused the universe to step on the gas, driving a growth that now speeds up each day. It is like a rocket whose speed increases 100 mph in the first mile, then by the same amount the next half-mile, then in a quarter-mile, and so on.

Scientists admit they've made almost zero progress in understanding dark energy. They have no idea what it is or how it works.

Various researchers describe the phenomenon as a repulsive force, as vacuum energy, as anti-gravity, and as possibly no more than a different manifestation of gravity over large distances. Some say the repulsion could be a response to dark matter, unseen stuff that is known to make up nearly a quarter of the universe, but such a link has never been established.

All that's clear is that dark energy comprises 73 percent of the mass-energy budget of the universe, and that it is no longer an arguable point for theorists but instead is a viable quarry for astronomers.

Surprise finding

While not even trying, the Hubble Space Telescope (news - web sites) just spotted two very distant exploding stars that represent baby steps ahead of a footrace of expected observations.

The so-called supernovae, announced this morning, are 5 billion and 8 billion light-years away and were found serendipitously by Hubble's new Advance Camera for Surveys, installed a year ago, while it was making a calibration run. Hubble officials, who have been saying the new camera would turn Hubble into a supernova hunting machine, offered the discoveries as proof of that claim.

The supernovae bracket the presumed time of the switch from deceleration to acceleration, and examination of them has helped build the observational case that the shift occurred. Two other groups have used Hubble to purposely collect data on several more supernovae and results will likely be reported by the end of the year, researchers told SPACE.com.

Hubble is but one tool being used to probe dark energy.

Scientists are also exploring so-called cosmic microwave background radiation that carries an imprint of the baby universe's structure. Just two months ago, that effort led to the first firm determination of the age of the universe, a solid estimate for when the first stars were born, plus undisputed confirmation of dark energy's expansive role.



Other teams are examining the structure of the space through time by noting how interstellar hydrogen absorbs light. Still other researchers are pushing back the frontier of time, finding galaxies that formed when the universe was less than 10 percent its present age.

For the first time in history, experts suggest, cosmological data is accumulating faster than the wild theories that try to describe it all.

"By far the best is yet to come," said Max Tegmark, a cosmologist at the University of Pennsylvania. "We're not even halfway through this avalanche of data in cosmology."

Going back in time

Theorists have known since the 1920s that the universe was expanding. They wondered if that expansion would go on forever, or if common gravity might eventually win out and pull everything back together in a sort of Big Crunch.

Then in 1998 two separate groups hunting faraway supernovae found several that were dimmer than they should have been, indicating that the universe is not just expanding, but accelerating.

The supernovae are of a particular variety, known as Type IA, that all shine with the same intrinsic brightness. Astronomers use them as "standard candles," their observed brightness revealing their distance. Light from the objects is analyzed to determine how much the waves have stretched, which bears an exact relationship to how much the universe has expanded since the light left its source -- the exploded star.

The 1998 finding of an accelerating universe was initially met with disbelief by its discoverers. Once digested -- in some cases only in the last couple of years by skeptics -- its profound implications for the composition and fate of the cosmos brought the term dark energy into common use.

Meanwhile, theorists had already figured out that an accelerating universe would necessarily be preceded by a period of deceleration, which would have followed an initial phase of rapid inflation associated with the Big Bang.

Here is why things must have slowed down:

"Early on the universe had lots of mass in a small volume," explains John Blakeslee of Johns Hopkins University. "The pull from gravity must have been enormous." As the universe expanded, gravity would have become less effective over the larger distances, and dark energy would have taken over.

One previously detected supernova, at about 10 billion light years away, supported this idea when reported in 2001, but the object proved difficult to study. The Hubble observations presented today also support the switch, said Blakeslee, lead author of a paper on the findings that will be published in the June Astrophysical Journal.

Had the universe always been accelerating, the supernova that's 8 billion light-years distant would have been dimmer, Blakeslee said in a telephone interview.

"It's not conclusive at all," Blakeslee said of his work. Another 20 or so very distant supernova are needed to make a strong case, he added.

Those 20, and then some, will not take long.

Hubble's new eyesight "should allow astronomers to discover roughly 10 times as many of these cosmic beacons as was possible with Hubble's previous main imaging camera," Blakeslee said.

Already in the bag

A separate Hubble project, led by Adam Riess of the Space Telescope Science Institute, has already bagged several distant supernovae. Riess, who worked on one team that made the 1998 acceleration breakthrough, reported preliminary results of his latest work at the APS meeting and is expected to publish a paper soon, possibly later this year.

Eleven other distant supernovae have been examined by Hubble in another study headed up by Saul Perlmutter of the Lawrence Berkeley National Laboratory. Perlmutter led the other team involved in the 1998 discovery of acceleration.

Perlmutter was not involved in the two new Hubble discoveries, but he told SPACE.com they are among many important steps that could lead to a firm determination of when acceleration began. Many of the discoveries are coming from ground-based telescopes, he noted, but Hubble "is really becoming a key for everybody in terms of follow-up" to glean the necessary detail.

By building a strong historical timeline of the universe, astronomers and cosmologists hope to answer a pressing question: Do the properties of dark energy change over time?

The answer would help them determine what dark energy is and would allow refined predictions about the origin and fate of the universe. No one expects a quick resolution, however.

Michael Turner, one of the world's foremost cosmologists from the University of Chicago, said solving the dark energy problem "is going to require a crazy idea." While most leading theories project the universe will accelerate forever, perhaps even to the wild point that it rips all matter apart, the notion that it might eventually collapse has not been ruled out, Turner said at the APS meeting.

"The destiny question is wide open," Turner said

http://story.news.yahoo.com/news?tm..._astronomers_hot_on_trail_of_mysterious_force
 
J.B.S. Haldane said:
My own suspicion is that the universe is not only queerer than we suppose,
but queerer than we can suppose.
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I've been following this story some too. Interesting, to say the least. The universe is a very strange place, isn't it?:headbang:
 
So much for that idea.

Leaking Gravity May Explain Cosmic Puzzle
By Sara Goudarzi
Special to SPACE.com
posted: 28 February 2005
06:28 am ET


WASHINGTON, D.C. - Scientists may not have to go over to the dark side to explain the fate of the universe.

The theory that the accelerated expansion of the universe is caused by mysterious "dark energy" is being challenged by New York University physicist Georgi Dvali. He thinks there's just a gravity leak.

Scientists have known since the 1920s that the universe is expanding. In the late 1990s, they realized that it is expanding at an ever-increasing pace. At a loss to explain the stunning discovery, cosmologists blamed it on dark energy, a newly coined term to describe the mysterious antigravity force apparently pushing galaxies outward.

This repulsive, unknown force is believed to make up more than 70 percent of the mass-energy budget of the universe.

But the existence of dark energy is far from proven, and some researchers believe they and their colleagues simply don't understand gravity at larger scales. The gravitational pull between any two objects becomes less with distance. But in Dvali's view, it weakens more than standard theory predicts.

Dvali would modify the theory of gravity so that the universe becomes self-accelerating, eliminating the need for dark energy. He presented his work here earlier this month at the annual meeting of the American Association for the Advancement of Science.

Dvali borrows from string theory, which states that there are extra, hidden dimensions beyond the four we are familiar with: three directions and time. String theory suggests that gravitons -- hypothetical elementary particles transmitting gravitational forces -- can escape to other dimensions. Dvali says this would cause "leaks" in gravity over cosmic proportions, reducing gravitational pull at larger distances more than expected.

"The gravitons behave like sound in a metal sheet," says Dvali. "Hitting the sheet with a hammer creates a sound wave that travels along its surface. But the sound propagation is not exactly two-dimensional as part of the energy is lost into the surrounding air. Near the hammer, the loss of energy is small, but further away, it's more significant."

The effect is to alter the space-time continuum, speeding up universal expansion.

"Virtual gravitons exploit every possible route between the objects," Dvali said, "and the leakage opens up a huge number of multi-dimensional detours, which brings about a change in the law of gravity."

The speeding up of the universe suggest that Einstein’s laws of General Relativity, describing the interaction of space and matter, must be modified at large cosmic distances.

"It is this modification, and not dark energy, that is responsible for the accelerated expansion of the universe," Dvali concludes.

The idea might be testable.

Gravity leakage should create minor deviations in the motion of planets and moons. Astronauts on the Apollo 11 mission installed mirrors on the lunar surface. By shooting lasers at the mirrors, a reflected beam can be monitored from Earth to measure tiny orbital fluctuations. Dvali said deviations in the Moon's path around Earth might reveal whether gravity is really leaking away.
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I never was one for a theory that has to invent 70% of the universe out of whole cloth to work.
 
Funny how these ideas, once the truth is fully known,
will all seem like crack-pipe dreams.
 
Dark Matter: Invisible, Mysterious and Perhaps Nonexistent

Galaxies don't have enough regular matter to keep them from flying apart, scientists have been telling us for years. So there must be a bunch of unseen "dark matter" lurking in every galaxy.

But dark matter has never been directly detected, and nobody knows what it might be made of. A few scientists remeain skeptical. To a lay person, it might sound downright crazy.

Now a new study suggests there may be no such thing as dark matter.

Fred Cooperstock of Northeastern University and Steven Tieu at the University of Victoria say Einstein's theory of general relativity can explain the cohesiveness of individual galaxies including our Milky Way.

Here's the thinking:

Newton's laws of physics explain why our solar system stays together. But the planets are negligible in the overall gravitational scheme, with the Sun being the total ruler and containing 99.86 percent of all the mass.

The same Newtonian physics were long ago applied to galaxies, and the rotation of stars couldn't be explained, so dark matter was invented to make theory work.

But a galaxy is much different than the solar system, Cooperstock explains. The conglomeration of all the matter -- stars, black holes, gas, and dust -- is collectively the source of the galactic gravity. Even a black hole at a galaxy's center typically packs less than 1 percent of the galaxy's overall mass.

The overall galaxy's gravity "feeds its own motion ... unlike the case of the solar system," Cooperstock told SPACE.com.

The science of the new argument is complex, but here goes:

"In the galaxy case, having rotation, we have found that general relativity provides a very important potential that is connected to the density of the galactic matter in what we call a 'nonlinear' manner,'" Cooperstock says. "This is unlike Newtonian physics."

This nonlinear effect has been noted before. "The interesting twist is that this holds also for the simpler steady rotational motion under gravity as in the galaxy," he said.

The upshot: The motions of stars in galaxies "is realized in general relativity's equations without the need to invoke massive halos of exotic 'dark matter' that nobody can explain by current physics," Cooperstock said.

A small percent of what used to be considered dark matter is made of burned-out stars that are hard to see. Predictions for how much of that material exists would not change.

Also, the new idea does not yet explain how large clusters of galaxies bind together. Further research by other theorists might solve that problem too, however, Cooperstock said. The new analysis has been submitted to the Astrophysical Journal but has yet to be reviewed by other scientists.

If it is right?

"This would remove about 25 percent of the mass of the universe, the ultimate weight-reduction program," Cooperstock said.
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It's a real shame they wasted all those years and all those dollars on fantasies about dark matter, instead of on real science, where you work with reality.
 
Nah. You have to have the whack-job cutting edge theories percolating through the system. Its a given that 19 out of 20 of 'em turn out to be poo ... but that 1 ... oh that 1... turns out to be one that turns the establishment on its ear.
 
Astronomers Had it Wrong: Most Stars are Single

For more than 200 years, astronomers thought that most of the stars in our galaxy had stellar companions. But a new study suggests the bulk of them are born alone and never have stellar company.

Since planets are believed to be easier to form around single stars, the discovery could mean planets are more common as well.

Conventional wisdom on double star systems, called binaries, goes as far back as the late 1700s. More sophisticated observations made in the 20th century seemed to confirm the numerical dominance of pairs.

Stellar surveys found that more than half of all Sun-like stars were part of multiple systems. For more massive stars, like O- and B-type stars, the number was estimated to be as high as 80 percent.

A few stars, like the North Star, Polaris, have two or more companions.

"If you go out and look at the all visible stars in the night sky and ask, ‘How many of those are binary?’ the answer is, ‘Most of them,’" said study author Charles Lada of the Harvard-Smithsonian Center for Astrophysics (CfA). "The assumption was that because most bright stars were binaries, all stars would tend to be binaries."

The catch, however, is that most stars in the Milky Way are not bright stars like our Sun, but dim, low-mass stars called red dwarfs.

Red dwarfs

Scientists estimate that red dwarfs make up to 85 percent of the stars in our Galaxy. These stars are about one-fifth as massive as the Sun and up to 50 times fainter.

Red dwarfs are so dim that it’s only been in the past decade or so that technology has improved to the point where astronomers can study them in detail. And they’ve found that only about 25 percent of red dwarfs have stellar companions.

Lada concludes that upwards of two-thirds of all star systems in the galaxy are single, red dwarf stars. His finding, announced today, was detailed in a recent online edition of Astrophysical Journal Letters.

"It’s an important realization," said Christopher McKee, an astronomer from the University of California, Berkeley who was not involved in the study. "The facts that [Lada] points out were available for a long time and people just hadn’t put them together."

The skew towards singleness only applies to red dwarfs, however. It’s still true that more than half of the brighter, more massive stars in the galaxy have companions.

Star birth

Recent observations show that half a dozen new stars are produced each year in the Milky Way, but many of the details surrounding their births remain unclear. According to the classical theory, stars form when large clouds of dust and gas in space collapse under the force of gravity. If these dense cores of matter reach a critical limit, internal nuclear fires ignite and new stars are born.

However, this theory doesn’t explain why most large stars tend to have companions.

"There are theories that can form binary stars and theories that can form single stars, but there none that explain why you form more singles than binaries," Lada told SPACE.com.

Astronomers have some ideas though. Observations have shown that the large clouds that serve as stellar nurseries for massive stars are more turbulent than small clouds where red dwarfs are thought to typically come from. It could be that this turbulence causes massive stars to form in groups of two or more.

"If the [large clouds] have some initial turbulent motions, then as they collapse, they will tend to split up," Lada explained.

Forming planets

Lada’s finding could be good news for planet-hunters. Although some studies suggest that planet formation around binary star systems is more common than previously thought, most astronomers believe that making planets is still easier around single stars. It’s thought that when there are two or more stars, the gravitational forces between them hinder matter from clumping into cores dense enough to form planets.

If single stars are the rule and not the exception, as the new finding suggests, then extrasolar planets may be more common as well.

"Red dwarfs may be a fertile new hunting ground for finding planets, including ones similar in mass to the Earth," Lada said.

One such planet may have already been found. Astronomers recently discovered a cold, rocky planet that is about 5.5 times the mass of Earth around a red dwarf 28,000 light-years away.
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Yet another case of blind assumptions.
 
Missing Gas Found in Milky Way
By Robin Lloyd
Special to SPACE.com
posted: 21 August 2006
05:59 am ET

The true abundance in the Milky Way of a heavy, primordial form of hydrogen has eluded scientists for decades, but it turns out that huge quantities of it have been hidden in the dust that is scattered between stars.

The new finding relied on satellite measurements of a type of hydrogen called deuterium and found that its distribution in our galaxy is patchy rather than uniform. It will force big changes in theories about star and galaxy formation, astronomers say.

"Since the 1970s we have been unable to explain why deuterium levels vary all over the place," said Jeffrey Linsky, an astrophysicist at the University of Colorado at Boulder. "The answer we found is as unsettling as it is exciting."

Heavy hydrogen

Deuterium is a type, or isotope, of hydrogen that is a bit heavier than regular hydrogen. Deuterium has one proton and one neutron while regular hydrogen has no neutrons and one proton.

Scientists think deuterium is burned and destroyed during a star's lifetime, which theoretically means the amount of deuterium present in the universe can be used as a measure of star creation and galaxy building over billions of years.

Still, previous deuterium measurements varied so much that some scientists thought the measurements were wrong or that there was something wrong with their instruments. The instruments were fine. The results were right. It was the explanation of the results that was lacking.

New data

New data from NASA's Far Ultraviolet Spectroscopic Explorer (FUSE) satellite, launched in 1991 to study the origin and evolution of hydrogen and deuterium in the universe, allowed Linsky and his colleagues to confirm previous patchy deuterium findings and take it big step further.

The deuterium shows up in patches because it tends to clump with solid dust grains and therefore becomes invisible. This explains why along certain sight lines, satellites detect a lot of deuterium in interstellar gas but very little in other directions, Linsky said.

The patchy distribution of deuterium especially made sense to Princeton University's Bruce Draine, one of Linsky's co-authors on a research paper on the new deuterium findings. Three years ago, he proposed that the patchiness has to do with the chemistry of dust grains found in the space between stars, the interstellar medium. These regions of space consist mostly of gas but there is a small fraction of material in the form of very small particles, usually less than 1 micron in size (one particle of flour is about 60 microns wide).

Strong bond

The basic idea is that the chemical bond between carbon atoms and deuterium atoms in the interstellar medium is slightly stronger, due to that extra neutron, than the chemical bond between carbon and hydrogen atoms. Over time then, deuterium atoms replace hydrogen atoms in dust grains made primarily of carbon. This process occurs when dust grains are very cold and undisturbed, which is typical in the interstellar medium.

However the shock wave of a nearby supernova shock or hot star can suddenly zap the solid-phase, deuterium-carbon bond in dust grains and send the deuterium back into the gas phase.

The FUSE spacecraft only measures deuterium in the gas phase so it finds low quantities of deuterium when no supernova or star is or was recently nearby and high quantities when a nearby hot star or supernova shock wave has evaporated the deuterium back into a detectable phase.

FUSE not only found patchy deuterium. It found more deuterium than scientists predicted. Scientists thought at least a third of the deuterium created during the Big Bang would have been destroyed over time as a result of stellar formation, leaving much less than the amount FUSE detected.

What it means

If the peak levels of deuterium are correct, either a lot less material has been converted to elements in stars or more primordial gas rained down onto our galaxy over its lifetime than previously thought.

"My guess is that the second scenario is the more likely answer," Linsky told SPACE.com. "We know very little about the rate at which deuterium-rich gas is raining down on the galaxy today and in the past."

The paper by Linsky, Draine and their colleagues was published in the Astrophysical Journal.
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So much for dark matter, eh?
 
Pfft... Just follow inky into the bathroom right after meat pizza and BBQ wings night. You'll quickly believe in dark matter... and hell.
 
unclehobart said:
Pfft... Just follow inky into the bathroom right after meat pizza and BBQ wings night. You'll quickly believe in dark matter... and hell.
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Gee willikers... did I stink up your house that bad? :(
 
But... but... the fantasticness of his toilet PREVENTED the leaving behind of dark matter...
 
Inky didn't stink up the bathroom...we have good air fresheners!

Just ask Prof's baby how long he smelled like apple cider ;)
 
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