Svarbu / Important

Prasidėjo tinklapio pertvarkymas: keičiamos kategorijos, nauji puslapiai, išvaizda, ir pan.

Beginning of the reorganisation: the categories are being changed, new pages created, the appearance changed.

CERN announces start-up date for LHC

Source/šaltinis: CERN

Geneva, 7 August 2008. CERN1 has today announced that the first attempt to circulate a beam in the Large Hadron Collider (LHC) will be made on 10 September. This news comes as the cool down phase of commissioning CERN’s new particle accelerator reaches a successful conclusion. Television coverage of the start-up will be made available through Eurovision.

The LHC is the world’s most powerful particle accelerator, producing beams seven times more energetic than any previous machine, and around 30 times more intense when it reaches design performance, probably by 2010. Housed in a 27-kilometre tunnel, it relies on technologies that would not have been possible 30 years ago. The LHC is, in a sense, its own prototype.

Starting up such a machine is not as simple as flipping a switch. Commissioning is a long process that starts with the cooling down of each of the machine’s eight sectors. This is followed by the electrical testing of the 1600 superconducting magnets and their individual powering to nominal operating current. These steps are followed by the powering together of all the circuits of each sector, and then of the eight independent sectors in unison in order to operate as a single machine.

By the end of July, this work was approaching completion, with all eight sectors at their operating temperature of 1.9 degrees above absolute zero (-271°C). The next phase in the process is synchronization of the LHC with the Super Proton Synchrotron (SPS) accelerator, which forms the last link in the LHC’s injector chain. Timing between the two machines has to be accurate to within a fraction of a nanosecond. A first synchronization test is scheduled for the weekend of 9 August, for the clockwise-circulating LHC beam, with the second to follow over the coming weeks. Tests will continue into September to ensure that the entire machine is ready to accelerate and collide beams at an energy of 5 TeV per beam, the target energy for 2008. Force majeure notwithstanding, the LHC will see its first circulating beam on 10 September at the injection energy of 450 GeV (0.45 TeV).

Once stable circulating beams have been established, they will be brought into collision, and the final step will be to commission the LHC’s acceleration system to boost the energy to 5 TeV, taking particle physics research to a new frontier.

‘We’re finishing a marathon with a sprint,’ said LHC project leader Lyn Evans. ‘It’s been a long haul, and we’re all eager to get the LHC research programme underway.’

CERN will be issuing regular status updates between now and first collisions. Journalists wishing to attend CERN for the first beam on 10 September must be accredited with the CERN press office. Since capacity is limited, priority will be given to news media. The event will be webcast through http://webcast.cern.ch, and distributed through the Eurovision network. Live stand up and playout facilities will also be available.

A media centre will be established at the main CERN site, with access to the control centres for the accelerator and experiments limited and allocated on a first come first served basis. This includes camera positions at the CERN Control Centre, from where the LHC is run. Only television media will be able to access the CERN Control Centre. No underground access will be possible.

For further information and accreditation procedures: http://www.cern.ch/lhc-first-beam

New Study Finds Clumps and Streams of Dark Matter in the Milky Way (UT)

One of the leading theories for how the universe evolved after the Big Bang is the Cold Dark Matter Theory (CDM). This theory proposes that chilly dark matter moved slowly in the early universe, allowing matter to clump together to form the clusters of galaxies that we see, instead of matter being distributed evenly across the universe. Using the properties of the CDM theory, astronomers recently ran an intensive computer program using one of the world’s most powerful supercomputers to simulate the halo of dark matter that envelopes our galaxy. The simulation revealed dense clumps and streams of the mysterious dark matter lurking within our Milky Way galaxy, including the region of our solar system.

“In previous simulations, this region came out smooth, but now we have enough detail to see clumps of dark matter,” said Piero Madau, professor of astronomy and astrophysics at the University of California, Santa Cruz.

This simulation, detailed in an article in the journal Nature, may help may help scientists figure out what dark matter actually is. So far, it has been detected only through its gravitational effects on stars and galaxies. Another part of the CDM theory says that dark matter consists of weakly interacting massive particles (WIMPs), which can annihilate each other and emit gamma rays when they collide. Gamma rays from dark matter annihilation could be detected by the recently launched Gamma-ray Large Area Space Telescope (GLAST).

“That’s what makes this exciting,” Madau said. “Some of those clumps are so dense they will emit a lot of gamma rays if there is dark matter annihilation, and it might easily be detected by GLAST.”

If so, it would be the first direct detection of WIMPS.

Although the nature of dark matter remains a mystery, it appears to account for about 82 percent of the matter in the universe. The clumps of dark matter created “gravitational well” that draws in ordinary matter, giving rise to galaxies in the centers of dark matter halos.

Using the Jaguar supercomputer at Oak Ridge National Laboratory, the simulation took about one month to run and simulated the distribution of dark matter from for 13.7 billion years – from near the time of the Big Bang until the current epoch. Running on up to 3,000 processors in parallel, the computations used about 1.1 million processor-hours.

Evidence of dark energy found (A)

A team of astronomers at the University of Hawaii Institute for Astronomy (IfA) led by Istvan Szapudi has found direct evidence for the existence of dark energy. Dark energy works against the tendency of gravity to pull galaxies together and so causes the universe’s expansion to speed up. The nature of dark energy (what precisely it is, and why it exists) is one of the biggest puzzles in modern science.

This is arguably the clearest detection to date of dark energy’s stretching effect on vast cosmic structures: there is only a one in 200,000 chance that the detection would occur by chance.

“We were able to image dark energy in action, as it stretches huge supervoids and superclusters of galaxies,” Szapudi says. Superclusters are vast regions of space, half a billion light-years across, that contain an unusually high concentration of galaxies, while supervoids are similarly sized regions with a below-average number of galaxies. They are the largest structures known in the universe. The team made the discovery by measuring the subtle imprints that superclusters and supervoids leave in microwaves that pass through them.

“When a microwave enters a supercluster, it gains some gravitational energy, and therefore vibrates slightly faster,” explains Szapudi. “Later, as it leaves the supercluster, it should lose exactly the same amount of energy. But if dark energy causes the universe to stretch out at a faster rate, the supercluster flattens out in the half-billion years it takes the microwave to cross it. Thus, the wave gets to keep some of the energy it gained as it entered the supercluster.”

“Dark energy sort of gives microwaves a memory of where they’ve been recently,” says team member Mark Neyrinck. The team also includes Benjamin Granett, the first author on the paper, which will be published in the Astrophysical Journal Letters in August or September.

The team compared an existing database of galaxies with a map of the cosmic microwave background radiation (CMB), the faint hiss of microwaves left over from the Big Bang. As predicted, they found that the microwaves were a bit stronger if they had passed through a supercluster, and a bit weaker if they passed through a supervoid.

“With this method, for the first time we can actually see what supervoids and superclusters do to microwaves passing through them,” Granett says.

The signal is difficult to detect, since ripples in the primordial CMB are larger than the imprints of individual superclusters and supervoids. To extract a signal, the team averaged together patches of the CMB map around the 50 largest supervoids and the 50 largest superclusters that they detected in extremely bright galaxies drawn from the Sloan Digital Sky Survey, a project that mapped the distribution of galaxies over a quarter of the sky.

The UH team compared directions in the sky where they found superclusters (red circles) and supervoids (blue circles) with the strength of the CMB. Superclusters are more likely to coincide with directions where microwaves are unusually strong (red or orange coloring) and supervoids with directions where the microwaves are unusually weak (blue coloring). Granett, Neyrinck, Szapudi

Electrical Activity on Titan Confirmed (UT)

Research has just been published proving Saturn’s moon is sparkling with electrical activity. Scientists are in general agreement that organic molecules, the precursors to life on Earth, are a consequence of lightning in the atmosphere. Now, using data from the Huygens probe that descended through Titan’s atmosphere in 2005 and continued transmitting for 90 minutes after touchdown, Spanish scientists have “unequivocally” proven that Titan has electrical storms too. The presence of electrical activity in the atmosphere is causing much excitement as this could mean that organic compounds may be found in abundance on the Titan surface.

The fruits from the Cassini-Huygens mission are coming thick and fast. Only yesterday, Nancy reviewed the discovery of liquid hydrocarbon lakes by Cassini’s Visual and Infrared Mapping Spectrometer (VIMS). Although possible lakes have been theorized, it is only now that there is observational proof of the existence of such features. Now, three years after the Huygens probe dropped through Titan’s atmosphere, scientists have made another crucial discovery: Titan experiences electrical activity in its atmosphere. Now Titan has all the necessary components for life; it has an atmosphere with electrical activity, increasing the opportunity for prebiotic organic compounds to form, thus increasing the possibility for life to evolve.

According to Juan Antonio Morente from the University of Granada, Titan is already considered a “unique world in the solar system” since the early 20th Century when Spanish astronomer José Comas y Solá made the discovery that the Saturn moon had an atmosphere. This is what makes Titan special, it has a thick atmosphere, something that is not observed on any other natural satellite in the Solar System.

“On this moon clouds with convective movements are formed and, therefore, static electrical fields and stormy conditions can be produced. This also considerably increases the possibility of organic and prebiotic molecules being formed, according to the theory of the Russian biochemist Alexander I. Oparín and the experiment of Stanley L. Miller [who managed to synthesise organic compounds from inorganic compounds through electrical discharges] That is why Titan has been one of the main objectives of the Cassini-Huygens joint mission of NASA and the European Space Agency” - Juan Antonio Morente.

Morente and his team analysed data from Huygens’ Mutual Impedance Probe (MIP) that measured the atmospheric electrical field. The MIP instrument was primarily used to measure the atmosphere’s electrical conductivity but it also acted as a dipolar antenna, detecting the natural electric field. The MIP was therefore able to detect a set of spectral peaks of extremely low frequency (ELF) radio signals (known as “Schumann resonances”). These ELF peaks are formed between the moon’s ionosphere and a huge resonant cavity in which electromagnetic fields are confined.

The detection of these signals have led the Spanish researchers to state that it is “irrefutable” evidence of electrical activity on Titan, not dissimilar to static charge that builds up in the terrestrial atmosphere, leading to electrical storms.

“We Have Water” on Mars, TEGA Test Confirms (UT)

The Phoenix Mars lander finally was successful in delivering a fairly fresh sample of Martian soil to the Thermal and Evolved Gas Analyzer (TEGA) oven on Wednesday and a “bake and sniff” test identified water in the soil sample. “We have water,” said William Boynton of the University of Arizona, lead scientist for TEGA. “We’ve seen evidence for this water ice before in observations by the Mars Odyssey orbiter and in disappearing chunks observed by Phoenix last month, but this is the first time Martian water has been touched and tasted.”

The soil sample came from a trench approximately 2 inches deep. When the robotic arm first reached that depth, it hit a hard layer of frozen soil. Two attempts to deliver samples of icy soil on days when fresh material was exposed were foiled when the samples became stuck inside the scoop. Most of the material in Wednesday’s sample had been exposed to the air for two days, letting some of the water in the sample vaporize away and making the soil easier to handle.

“Mars is giving us some surprises,” said Phoenix principal investigator Peter Smith of the University of Arizona. “We’re excited because surprises are where discoveries come from. One surprise is how the soil is behaving. The ice-rich layers stick to the scoop when poised in the sun above the deck, different from what we expected from all the Mars simulation testing we’ve done. That has presented challenges for delivering samples, but we’re finding ways to work with it and we’re gathering lots of information to help us understand this soil.”

Also at the press conference announcing the results, NASA also announced a mission extension for Phoenix, through Sept. 30. The original prime mission of three months ends in late August. The mission extension adds five weeks to the 90 days of the prime mission.

“Phoenix is healthy and the projections for solar power look good, so we want to take full advantage of having this resource in one of the most interesting locations on Mars,” said Michael Meyer, chief scientist for the Mars Exploration Program at NASA Headquarters in Washington.

During the mission extension, the science team will attempt to determine whether the water ice ever thaws enough to be available for biology and if carbon-containing chemicals and other raw materials for life are present.

A full-circle, color panorama of Phoenix’s surroundings was recenlty completed by the spacecraft.

“The details and patterns we see in the ground show an ice-dominated terrain as far as the eye can see,” said Mark Lemmon of Texas A&M University, lead scientist for Phoenix’s Surface Stereo Imager camera. “They help us plan measurements we’re making within reach of the robotic arm and interpret those measurements on a wider scale.”

Phoenix's Workspace on Mars

Liquid Lake on Titan Confirmed (UT)

NASA’s Cassini mission has detected liquid hydrocarbons on Saturn’s moon Titan, in a large, glassy lake near the moon’s south pole. Before the Cassini mission began, scientists thought Titan would have global oceans of methane, ethane and other light hydrocarbons. But after more than 40 close flybys of Titan by Cassini, data showed no global oceans exist. However hundreds of dark, lake-like features are present. Until now, it was not known whether these features were liquid or simply dark, solid material. Using Cassini’s Visual and Infrared Mapping Spectrometer (VIMS), which identifies the chemical composition of objects by the way matter reflects light, a liquid ethane lake 235 kilometers (150 miles) long was detected. This makes Titan the only body in our solar system beyond Earth known to have liquid on its surface.

“This is the first observation that really pins down that Titan has a surface lake filled with liquid,” said Bob Brown of the University of Arizona, Tucson, leader of the VIMS instrument.

Scientists had deduced through earlier observations that there was likely liquid on Titan, but this is the first incontrovertible evidence. (Emily Lakdawalla at the Planetary Society explains this excellently.)

“Detection of liquid ethane confirms a long-held idea that lakes and seas filled with methane and ethane exist on Titan,” said Larry Soderblom, a Cassini interdisciplinary scientist with the U.S. Geological Survey. “The fact we could detect the ethane spectral signatures of the lake even when it was so dimly illuminated, and at a slanted viewing path through Titan’s atmosphere, raises expectations for exciting future lake discoveries by our instrument.”

Titan’s hazy, nitrogen and methane atmosphere makes it difficult to study the moon’s surface. The liquid ethane was identified using a technique that removed the interference from the atmospheric hydrocarbons.

The VIMS instrument observed a lake, called Ontario Lacus, in Titan’s south polar region during a close Cassini flyby in December 2007. The lake is roughly 20,000 square miles (7,800 square miles) in area, slightly larger than North America’s Lake Ontario.

The ethane is in a liquid solution with methane, other hydrocarbons and nitrogen. At Titan’s surface temperatures, approximately 300 degrees Fahrenheit below zero, these substances can exist as both liquid and gas. Titan shows overwhelming evidence of evaporation, rain, and fluid-carved channels draining into what, in this case, is a liquid hydrocarbon lake.

Earth has a hydrological cycle based on water and Titan has a cycle based on methane. Scientists ruled out the presence of water ice, ammonia, ammonia hydrate and carbon dioxide in Ontario Lacus. The observations also suggest the lake is evaporating. It is ringed by a dark beach, where the black lake merges with the bright shoreline. Cassini also observed a shelf and beach being exposed as the lake evaporates.

“During the next few years, the vast array of lakes and seas on Titan’s north pole mapped with Cassini’s radar instrument will emerge from polar darkness into sunlight, giving the infrared instrument rich opportunities to watch for seasonal changes of Titan’s lakes,” Soderblom said.

More information is available at NASA’s Cassini site, JPL’s Cassini site, and the Univeristy of Arizona’s VIMS site.

Ontario Lacus

Astronomers Discover a Supernova/Gamma Ray Burst Hybrid (UT)

Astronomers have just uncovered the true nature of what they thought was a regular supernova observed in January. At the time, it looked like a supernova emitting a 5-minute long burst of X-rays. But these X-rays were of a lower energy (known as “soft” X-rays) than expected leading some to believe this was a normal emission from a supernova explosion that was being observed during detonation (astronomers don’t usually get the chance to observe a star as it explodes and usually have to make do with analysing the supernova remnant). However, it is now believed this strange supernova event may have been emissions from a dying star at an intermediate mass, neither producing a supernova nor a gamma ray burst, but a combination of both…

Orbiting above Earth on January 9th 2008, the NASA/STFC/ASI Swift telescope caught a rare glimpse of what seemed to be a “normal” supernova at the precise moment of detonation. This observation was completely by luck, as Swift was already observing a supernova remnant (SN 2007uy) in spiral galaxy NGC 2770 that had exploded the previous year (90 million light-years away near the Lynx constellation). Then, as Swift was retrieving data from the SN 2007uy remnant, SN 2008D blasted a 5-minute long burst of X-rays in the same galaxy making this the first supernova to be directly observed.

However, looks can be deceiving. Researchers from a host of institutions including Italian National Institute for Astrophysics (INAF), the Max-Planck Institute for Astrophysics (MPA) and the European Southern Observatory (ESO) have analysed the supernova data thoroughly and at first agreed with the original assessment that it was indeed “normal.”

“What made this event very interesting is that the X-ray signal was very weak and ’soft’, very different from a gamma-ray burst and more in line with what is expected from a normal supernova.” - Paolo Mazzali, INAF’s Padova Observatory/MPA, research leader.

However, astronomers at the Asiago Observatory in Northern Italy had designated the event as a Type 1c supernova, more commonly associated with long-period gamma-ray bursts. Type 1c supernovae are generated by hydrogen-poor progenitor stars with helium-rich outer layers prior to exploding at the end of their lives. But SN 2008D generated soft X-rays more associated with smaller stellar explosions. Therefore SN 2008D was probably produced by a star that was massive at birth (approximately 30 solar masses), rapidly using up its hydrogen fuel in its short life until it was only 8-10 solar masses. At this point it exploded, probably creating a remnant black hole. This chain of thought has led Paolo Mazzali and his team to think SN 2008D was produced by an object of a mass at the boundary of a normal supernova and gamma-ray burst.

“Since the masses and energies involved are smaller than in every known gamma-ray burst related supernova, we think that the collapse of the star gave rise to a weak jet, and that the presence of the Helium layer made it even more difficult for the jet to remain collimated, so that when it emerged from the stellar surface the [X-ray] signal was weak.” - Massimo Della Valle, co-investigator.

Researcher and co-author Stefano Valenti points out that this discovery indicates that all black hole-producing supernovae have the potential to be gamma-ray burst progenitors. “The scenario we propose implies that gamma-ray burst-like inner engine activity exists in all supernovae that form a black hole,” he added.

The Cosmic Void: Could we be in the Middle of it? (UT)

On large scales, the Universe is homogeneous and isotropic. This means that no matter where you are located in the cosmos, give or take the occasional nebula or galactic cluster, the night sky will appear approximately the same. Naturally there is some ‘clumpiness’ in the distribution of the stars and galaxies, but generally the density of any given location will be the same as a location hundreds of light years away. This assumption is known as the Copernican Principle. By invoking the Copernican Principle, astronomers have predicted the existence of the elusive dark energy, accelerating the galaxies away from one another, thus expanding the Universe. But say if this basic assumption is incorrect? What if our region of the Universe is unique in that we are sitting in in a location where the average density is a lot lower than other regions of space? Suddenly our observations of light from Type 1a supernovae are not anomalous and can be explained by the local void. If this were to be the case, dark energy (or any other exotic substance for that matter) wouldn’t be required to explain the nature of our Universe after all…

Dark energy is a hypothetical energy predicted to permeate through the Cosmos, causing the observed expansion of the Universe. This strange energy is believed to account for 73% of the total mass-energy (i.e. E=mc2) of the Universe. But where is the evidence for dark energy? One of the main tools when measuring the accelerated expansion of the Universe is to analyse the red-shift of a distant object with a known brightness. In a Universe filled with stars, what object generates a “standard” brightness?

Type 1a supernovae are known as ’standard candles’ for this very reason. No matter where they explode in the observable universe, they will always blow with the same amount of energy. So, in the mid-1990’s astronomers observed distant Type 1a’s a little dimmer than expected. With the basic assumption (it may be an accepted view, but it is an assumption all the same) that the Universe obeys the Copernican Principle, this dimming suggested that there was some force in the Universe causing not only an expansion, but an accelerated expansion of the Universe. This mystery force was dubbed dark energy and it is now a commonly held view that the cosmos must be filled with it to explain these observations. (There are many other factors explaining the existence of dark energy, but this is a critical factor.)

According to a new publication headed by Timothy Clifton, from the University of Oxford, UK, the controversial suggestion that the widely accepted Copernican Principle is wrong is investigated. Perhaps we do exist in a unique region of space where the average density is much lower than the rest of the Universe. The observations of distant supernovae suddenly wouldn’t require dark energy to explain the nature of the expanding Universe. No exotic substances, no modifications to gravity and no extra dimensions required.

Clifton explains conditions that could explain supernova observations are that we live in an extremely rarefied region, right near the centre, and this void could be on a scale of the same order of magnitude as the observable Universe. If this were the case, the geometry of space-time would be different, influencing the passage of light in a different way than we’d expect. What’s more, he even goes as far as saying that any given observer has a high probability of finding themselves in such a location. However, in an inflationary Universe such as ours, the likelihood of the generation of such a void is low, but should be considered nonetheless. Finding ourselves in the middle of a unique region of space would out rightly violate the Copernican Principle and would have massive implications on all facets of cosmology. Quite literally, it would be a revolution.

The Copernican Principle is an assumption that forms the bedrock of cosmology. As pointed out by Amanda Gefter at New Scientist, this assumption should be open to scrutiny. After all, good science should not be akin to religion where an assumption (or belief) becomes unquestionable. Although Clifton’s study is speculative for now, it does pose some interesting questions about our understanding of the Universe and whether we are willing to test our fundamental ideas.

arXiv:0807.1443v1

Finding the weight of black holes (A)

How do you weigh the biggest black holes in the universe? One answer now comes from a completely new and independent technique that astronomers have developed using data from NASA’s Chandra X-ray Observatory.

By measuring a peak in the temperature of hot gas in the center of the giant elliptical galaxy NGC 4649, scientists have determined the mass of the galaxy’s supermassive black hole. The method, applied for the first time, gives results that are consistent with a traditional technique.

Astronomers have been seeking out different, independent ways of precisely weighing the largest supermassive black holes, that is, those that are billions of times more massive than the Sun. Until now, methods based on observations of the motions of stars or of gas in a disk near such large black holes had been used.

“This is tremendously important work since black holes can be elusive, and there are only a couple of ways to weigh them accurately,” says Philip Humphrey of the University of California at Irvine, who led the study. “It’s reassuring that two very different ways to measure the mass of a big black hole give such similar answers.”

NGC 4649 is now one of only a handful of galaxies for which the mass of a supermassive black hole has been measured with two different methods. In addition, this new X-ray technique confirms that the supermassive black hole in NGC 4649 is one of the largest in the local universe with a mass about 3.4 billion times that of the Sun, about a thousand times bigger than the black hole at the center of our galaxy.

The new technique takes advantage of the gravitational influence the black hole has on the hot gas near the center of the galaxy. As gas slowly settles towards the black hole, it gets compressed and heated. This causes a peak in the temperature of the gas right near the center of the galaxy. The more massive the black hole, the bigger the temperature peak detected by Chandra.

This effect was predicted by two of the coauthors—Fabrizio Brighenti from the University of Bologna, Italy, and William Mathews from the University of California at Santa Cruz—almost 10 years ago, but this is the first time it has been seen and used.

“It was wonderful to finally see convincing evidence of the effects of the huge black hole that we expected,” says Brighenti. “We were thrilled that our new technique worked just as well as the more traditional approach for weighing the black hole.”

The black hole in NGC 4649 is in a state where it does not appear to be rapidly pulling in material towards its event horizon, nor generating copious amounts of light as it grows. So, the presence and mass of the central black hole has to be studied more indirectly by tracking its effects on stars and gas surrounding it. This technique is well suited to black holes in this condition.

“Monster black holes like this one power spectacular light shows in the distant, early universe, but not in the local universe,” says Humphrey. “So, we can’t wait to apply our new method to other nearby galaxies harboring such inconspicuous black holes.”

These results will appear in an upcoming issue of The Astrophysical Journal.