The solar wind - the stream of charged particles billowing away from the Sun - is at its weakest for 50 years.
Scientists made the assessment after studying 18 years of data from the Ulysses satellite which has sampled the space environment all around our star.

They expect the reduced output to have effects right across the Solar System.

Indeed, one impact is to diminish slightly the influence the Sun has over its local environment which extends billions of kilometres into space.
Confirmation of that prediction should come from the far-distant Voyager spacecraft which were launched in the 1970s and are now bearing down on the edge of the heliosphere - the great "bubble" of wind material that surrounds the Sun.

Scientists now predict the Voyagers will hit the edge and cross over into interstellar space - that region considered to be "between the stars" - sooner than anticipated.

Space age
The solar wind, which originates in the Sun's hot outer atmosphere known as the corona, gusts and calms with the star's familiar 11-year cycle of activity (but also over its less well known longer cycles, too).

Calmer wind conditions would be expected to prevail right now, but the Ulysses data indicates circumstances unprecedented in recent times.
"This is a whole Sun phenomenon," said Dave McComas, Ulysses solar wind instrument principal investigator, from Southwest Research Institute, San Antonio, US.

"The entire Sun is blowing significantly less hard - about 20-25% less hard - than it was during the last solar minimum 10-15 years ago.

"That's a very significant change. In fact, the solar wind we're seeing now is blowing the least hard we've see it for a prolonged time, since the start of those observations in the 1960s at the start of the space age."

In addition to being calmer, the wind measured at Ulysses is 13% cooler.

However, judging from Sun activity data collected by non-satellite methods over the past 200 years, the current behaviour is thought to be well within the long-term norm.

Nonetheless, scientists expect the weakened wind to have a wide range of impacts.

Energetic rays
The charged wind particles also carry with them the Sun's magnetic field, and this has a protective role in limiting the number of high-energy cosmic rays that can enter the Solar System.

More of them will probably now make their way through.

Many of these rays, which include electrons and atomic nuclei, originate in exploding stars and at black holes, and move at colossal speeds.
They pose no major risk to people on Earth because our atmosphere also works to reduce their intensity; but they are a consideration for space operations.

The rays can damage satellite electronics, and if current solar wind conditions persist, engineers would have to take this into account when deciding how to "harden" their spacecraft. Astronauts, too, are at risk from the higher doses of radiation associated with cosmic rays.

"The Sun also puts out cosmic rays in the form of bursts and these bursts are much less frequent at solar minimum. However, when they do occur at solar minimum, they are more lethal, so this is not a good time to be travelling in space owing to both kinds of cosmic rays," explained Professor Nancy Crooker, from Boston University, Massachusetts, US.

"Reduced solar activity also leads to the cooling of Earth's upper atmosphere and if Earth's upper atmosphere is cooler then there is less drag up there on satellites and this means we are left with much more debris up there - which is also something astronauts have to look out for."

Some researchers have attempted to link the intensity of cosmic rays at Earth to cloudiness and climate change. Current conditions may be a good opportunity to test these ideas further.
The Ulysses mission is a co-operative venture between the US space agency and the European Space Agency (Esa). Launched by the shuttle in 1990, it was the first satellite to study the space environment above and below the Sun's poles.

It samples the solar wind and solar magnetic field as it circles the star in a six-year orbit that also carries it out to Jupiter and back.

But the harsh conditions of space are now slowly taking their toll on the spacecraft.

Ulysses' main transmitter no longer works and it is struggling to put enough power into its heating systems. With the satellite currently moving away from the Sun, it is gradually getting colder; and engineers expect the hydrazine fuel used in its thrusters to freeze very soon.

When this happens, Ulysses will no longer be able to orientate itself and its antenna, and contact will be lost with Earth.

"Even though the end is now in sight, every day's worth of new data is adding to our knowledge of the Sun and its environment; and it's been a great and exciting mission," said Richard Marsden, Esa's Ulysses project scientist and mission manager.
source :http://news.bbc.co.uk/

Paul Steinhardt's universe is a lot like the workaday world of many people, a cycle of early vigor, spent energy, exhausted return, and new beginnings. However, in Steinhardt's universe, there is absolutely no end to the cycle.

The Princeton physicist and his colleague, Neil Turok of Cambridge University, have developed a whole new theory for how the universe came to be. Their proposal seeks to explain recently uncovered flaws in the scientifically accepted model for the origin and evolution of all known things. It describes a series of big bangs and equally significant crunches that form a never-ending cycle of rejuvenation and destruction.

In this universe -- our universe -- time never ends.

The current leading theory for the universe holds that it emerged from a single Big Bang sometime around 12 billion to 15 billion years ago, undergoing an early and rapid period of inflation. That much remains widely accepted.

"However, the standard model has some cracks," Steinhardt and Turok write in a paper published today in the online version of the journal Science.

Astronomers have in recent years learned that the universe is not just expanding, but is doing so at an ever-increasing pace. This can't be explained given the known matter and energy that exists. To account for the acceleration, theorists have conjured a product they call dark energy, which supposedly repels things rather than attracting, as gravity does.

No one has seen this dark energy, and scientists don't even know what it is. But they say it's all around us.

More important, it shouldn't be there.

"The recent discoveries of cosmic acceleration and gravitationally self-repulsive dark energy were not predicted and have no particular role in the standard model," Steinhardt and Turok argue. "Furthermore, the standard model does not explain the beginning of time,' the initial conditions of the universe, or what will happen in the long-term future."

So to patch some of the theoretical cracks, Steinhardt and Turok envision a universe based on perpetual expansion and contraction.

Here's how it works, and keep in mind we're jumping into the middle of the explanation: A big bang sends everything outward. Matter and radiation develop. Dark energy drives an expansion -- as is presently underway -- that lasts trillions of years. Finally, the matter, radiation, and even black holes are "diluted away," leaving the universe smooth, empty, and flat.

Then everything contracts in a so-called big crunch, and a fresh cycle begins.

"In this picture, space and time exist forever, Steinhardt says. "The big bang is not the beginning of time. Rather, it is a bridge to a pre-existing contracting era."

Curiously, the cyclic universe, as it is called, puts the origin of some present-day structures and events prior to the Big Bang.

While existing theory states that galaxies and large clusters of galaxies developed from lumps and filaments that formed in the otherwise smooth fabric of space and time shortly after the Big Bang, Steinhardt thinks the seeds of galaxy formation were created by instabilities that arose during the last contraction, before the crunch that led to "our" bang.

The new model "turns the conventional picture topsy-turvy," he says.

The cyclic universe has roots in even more complex thoughts like so-called superstring theory, which suggests there are as many as 10 spatial dimensions, not just the three we know of. The seemingly inexplicable physics of a big crunch and a big bang might be explained with the aid of these extra dimensions, which are otherwise invisible to us, several theorists believe.

In fact, Steinhardt, Turok and others proposed last year that our universe might have sprung from the collapse of an extra dimension, an idea they called the Ekpyrotic Universe. The cyclic universe builds on this former work but, Steinhardt says, does a better job explaining observations of our present universe.

Other theorists are not quick to give up their standard model, so the concept of a cyclic universe faces an uphill battle for prominence. Even Steinhardt acknowledges that the prospect of unseating a well established cosmological theory "would seem extremely dim."

Meanwhile, the new concept is not free of cracks, either: Even the cyclic universe does not address when the cycles began, so "the problem of explaining the beginning of time remains," the researchers say.
Source :http://www.space.com/

ScienceDaily (Sep. 11, 2008) — Eta Carinae, the galaxy's biggest, brightest and perhaps most studied star after the sun, has been keeping a secret: Its giant outbursts appear to be driven by an entirely new type of stellar explosion that is fainter than a typical supernova and does not destroy the star.

Reporting in the Sept. 11 issue of Nature, University of California, Berkeley, astronomer Nathan Smith proposes that Eta Carinae's historic 1843 outburst was, in fact, an explosion that produced a fast blast wave similar to, but less energetic than, a real supernova. This well-documented event in our own Milky Way Galaxy is probably related to a class of faint stellar explosions in other galaxies recognized in recent years by telescopes searching for extragalactic supernovae.

"There is a class of stellar explosions going off in other galaxies for which we still don't know the cause, but Eta Carinae is the prototype," said Smith, a UC Berkeley postdoctoral fellow.

Eta Carinae (η Car) is a massive, hot, variable star visible only from the Southern Hemisphere, and is located about 7,500 light years from Earth in a young region of star birth called the Carina Nebula. It was observed to brighten immensely in 1843, and astronomers now see the resulting cloud of gas and dust, known as the Homunculus nebula, wafting away from the star. A faint shell of debris from an earlier explosion is also visible, probably dating from around 1,000 years ago.

Presumably blown off by the star's fierce wind, the shells of gas and dust are moving slowly - at speeds of 650 kilometers per second (1.5 million miles per hour) or less - compared to the blast shell of a supernova.

Smith's recent observations using the international Gemini South 8-meter telescope and the Blanco 4-meter telescope at Cerro Tololo Inter-American Observatory in Chile reveal something new: Extremely fast filaments of gas moving five times faster than the debris in the Homunculus nebula were propelled away from Eta Carinae in the same event. The amount of mass in the relatively slow-moving Homunculus was already at the edge of plausibility in terms of what an extreme stellar wind could do physically, Smith said. The much faster and more energetic material he discovered poses even harsher difficulties for current theories.

Instead, the speeds and energies involved are reminiscent of material accelerated by the fast blast wave of a supernova explosion.

The fast speeds in this blast wave could roughly double earlier estimates of the energy released in the 1843 eruption of Eta Carinae, an event that Smith argues was not just a gentle surface eruption driven by the stellar wind, but an actual explosion deep in the star that sent debris hurtling into interstellar space. In fact, the fast-moving blast wave is now colliding with the slow-moving cloud from the 1,000-year-old eruption and generating X-rays that have been observed by the orbiting Chandra Observatory.

"These observations force us to modify our interpretation of what happened in the 1843 eruption," he said. "Rather than a steady wind blowing off the outer layers, it seems to have been an explosion that started deep inside the star and blasted off its outer layers. It takes a new mechanism to cause explosions like this."

If Smith's interpretation is correct, supermassive stars like Eta Carinae may blow off large amounts of mass in periodic explosions as they approach the end of their lives before a final, cataclysmic supernova blows the star to smithereens and leaves behind a black hole.

Much fainter than a supernova, the explosion that generated the fast-moving blast wave around Eta Carinae would have been similar to faint stellar explosions, sometimes called "supernova imposters," now being discovered in other galaxies by Earth-based robotic telescopes and other supernova searches. Such searches have been looking primarily for Type Ia supernovae that could help astronomers understand the accelerating expansion of the universe, but they also find other gems along the way, Smith said.

"Looking at other galaxies, astronomers have seen stars like Eta Carinae that get brighter, but not quite as bright as a real supernova," he said. "We don't know what they are. It's an enduring mystery as to what can brighten a star that much without destroying it completely."

Eta Carinae is a rare supermassive star in our galaxy, probably once having had a mass 150 times that of the sun. Such large stars burn brightly for only a few million years, all the while shedding mass as the intense light pushes the outer layers of the star away in a stellar wind. After 2 to 3 million years of this, Eta Carinae now weighs about 90 to 100 solar masses, having shed about 10 solar masses in its most recent 1843 eruption alone.

"These explosions may be the primary way by which massive stars can shed their outer hydrogen layers before they die," Smith said. "If Eta Carinae is able to shed 10 solar masses every thousand years or so, that's an efficient mechanism for peeling off a large fraction of the star."

Astronomers now believe that Eta Carinae and other luminous blue variable stars are nearing the end of their lives, having burned hydrogen in their cores into helium. If they explode at the stage where they still have an envelope of hydrogen shrouding the helium core, the resulting supernova will look vastly different from one that results from a star that sloughs off all its hydrogen before exploding.

Smith suggests that it is still unclear if supernova impostors are scaled-down versions of supernovae, failed supernovae, precursor events or entirely different kinds of explosions.

"This could be an important clue for understanding the last violent phases in the lives of massive stars," he said, noting that astronomers still cannot accurately predict the fate of stars that are 30 or more times the mass of the sun.

The observations reported in the Nature paper included visible spectra from the Blanco telescope, which is part of the U.S. National Optical Astronomy Observatory (NOAO), and near-infrared spectra taken with the Gemini South telescope. Both telescopes are in Chile's Andes mountains near an elevation of 9,000 feet. NOAO and the Gemini Observatory are operated by the Association of Universities for Research in Astronomy.

The research was supported in part by the National Aeronautics and Space Administration and the National Science Foundation.