The proof is in the pudding only if you concede the fact of the pudding
By Steve Mirsky | Wednesday, November 23, 2011 | 30
The leaves are turning as I write in early October. Also turning is my stomach, from the accounts coming out of something called the Values Voter Summit in Washington, D.C. According to Sarah Posner writing online in Religion Dispatches, talk-radio host Bryan Fischer went out of his way to attack me. And probably you. Anybody, really, who accepts science as an arbiter of reality. Fischer told the assembled that America needs a president who will “reject the morally and scientifically bankrupt theory of evolution.”
Evolution is a strange process indeed, to cobble together organisms who so completely and emotionally reject it. Well, evolution concerns itself only with differential survival, and brainpower may not be a crucial factor. Fischer may as well have gotten out of a car at the convention center and proclaimed that the car had not brought him there and did not in fact exist. To thunderous applause. One’s only reasonable response to this whole scene is to bring forefinger to mouth and rapidly toggle the lips while humming, so as to produce a sound roughly in accord with a spelling of “Blblblblblblblblblb.”
A few days before the summit, over in the rational world, Saul Perlmutter won a share of the 2011 Nobel Prize in Physics. He and his fellow laureates, Adam Riess and Brian Schmidt, showed that the universe is not only expanding, the expansion is accelerating. (On hearing this news, my brother asked me if there was a limit. I told him yes, no more than three people can share any one Nobel Prize.)
Perlmutter’s Nobel led to an additional, highly coveted prize. His University of California, Berkeley—home to 22 Nobelists over the years—gives newly minted laureates a campus-wide parking permit. And, if asked, every time Perlmutter exits his car he will no doubt respond that he arrived in it and that it exists.
Perlmutter the driver also surely has the good sense to know that alcohol impairs judgment and neuromuscular skills. Contrast that mind-set with Miami Herald reporter Jose Cassola—well, former Miami Herald reporter now—who ran a stop sign shortly before Perlmutter was getting news of his Nobel and then told the cop who pulled him over, “You can’t get drunk off of vodka.”
As Cassola explained to the arresting officer: “I’m fat, I won’t be able to get drunk from only seven shots.” He later expounded on his unique theories about alcohol and its effects to media-watch reporter Gus Garcia-Roberts of the Miami New Times: “Dude, I go to Chili’s all the time and have two-for-one margaritas, and then I get in my car. Am I drunk? No!”
The disoriented mind pronouncing itself whole is always a wonder to behold. Which brings us back to the Values Voter Summit. Oddly, Fischer’s enraptured audience may have been morphologically identifiable. That notion appears in an article in the June 25, 1885, issue of the journal Nature by Charles Darwin’s half cousin Francis Galton. (It’s probably a good example of our information inundation that less than an hour after I discovered this 126-year-old article, I cannot re-create the steps by which I wound up reading it. E-mail? Twitter? Link within a link? It’s all part of the mystery.)
Galton found himself at a boring lecture and decided to study the sea of heads in front of him. He noted that “when the audience is intent each person ... holds himself rigidly in the best position for seeing and hearing.” In other words, they sit up straight. When the talk got tedious, “the intervals between their faces, which lie at the free end of the radius formed by their bodies, with their seat as the centre of rotation varies greatly.” In other words, they lean.
By all accounts, the audience at the Values Voter Summit was sitting ramrod straight, indicating great engagement with the material being presented. Although a scientific mind-set requires a consideration of another possibility: that x-rays would reveal in each attendee a stick responsible for the vertical attitude and in desperate need of removal.
Source...Scientific American
Permanent Address: http://www.scientificamerican.com/article.cfm?id=respect-for-evidence
viernes, 25 de noviembre de 2011
Hunt for Higgs Particle Enters Endgame
Large Hadron Collider could soon deliver a clear verdict on missing boson.
November 18, 2011 | 12 Nature and reproduced by Scientific America
----------------------------------------------------------------------------------
By Geoff Brumfiel of Nature magazine
Bill Murray is a man with secrets. Along with a handful of other scientists based at CERN, Europe's particle-physics facility near Geneva, Switzerland, Murray is one of the few researchers with access to the latest data on the Higgs boson -- the most sought-after particle in physics.
Looking at his laptop, he traces a thin black line that wiggles across a shaded area at the centre of a graph. This is the fruit of his summer's labours. "It's interesting, actually, looking at this again," he muses. A tantalizing pause. "But no, I can't say..."
Despite Murray's coyness, there are few places left for the Higgs to hide. Billed as the particle that helps to confer mass on other matter, and the final missing piece in the `standard model' of particle physics, the Higgs would be a huge prize for CERN's Large Hadron Collider (LHC), the world's most powerful particle accelerator. But so far, the two massive detectors there--ATLAS, where Murray works, and the Compact Muon Solenoid (CMS) -- have not seen any convincing signals of the elusive particle.
At a conference in Paris on November 18, teams from ATLAS and the CMS experiments presented a combined analysis that wipes out a wide swathe of potential masses for the Higgs particle. Gone is the entire mass range from 141 to 476 gigaelectronvolts (GeV; energy and mass are interchangeable in particle physics). Together with earlier results from the 1990s, the analysis leaves a relatively narrow window of just 114-141 GeV in which the Higgs could lurk (see `Cornering the Higgs').
Analysis of the very latest data from this autumn--which Murray isn't yet ready to share -- will scour the range that remains. If it turns out to be empty, physicists may have to accept that the particle simply isn't there. Working around the clock, the detector teams hope to have this larger data set analysed before the end of December. "We'll know the outcome within weeks," says Guido Tonelli, spokesman for the CMS detector.
Waiting for God
The quest for the Higgs boson, often called the `God particle' after the title of a 1993 book by Nobel prizewinner Leon Lederman, is the public face of science at the LHC. Most high-energy physicists wince at the deistic designation, but they hold a near-religious devotion to the boson. Contrary to the popular view, their belief has less to do with mass than with fundamental forces.
Four fundamental forces are at work in nature: gravity, the strong nuclear force, the weak nuclear force and electromagnetism. Since the mid-1960s, physicists have strongly suspected that the weak and electromagnetic forces are actually different aspects of a single `electroweak' force. This is partly because the photon, the force-carrying particle of electromagnetism, is highly similar to the force-carrying particles of the weak force -- the W and Z bosons. Moreover, a single electroweak theory successfully predicts the interactions of fundamental particles.
There is one problem, however: the W and Z bosons are extremely heavy, nearly 100 GeV, whereas the photon is massless. To explain the difference, a number of physicists (including Peter Higgs in 1964) proposed a new field and particle. The eponymous Higgs mechanism would interact with the W and Z bosons, giving them mass, but would ignore the photon, allowing it to remain massless. Relatively straightforward tweaks to the Higgs machinery allow it to endow other particles, such as quarks, with their observed masses as well.
"The Higgs now sought at CERN is expected on the basis of the simplest picture" for the electroweak theory, says Steven Weinberg, a theorist who won a Nobel prize in 1979 for his work unifying electromagnetism and the weak force. "But there are other possibilities," he adds, reckoning the odds that the LHC's detectors will find the Higgs at 50/50 (see `Do you believe?').
If there is no Higgs, then what? Gian Giudice, a theorist at CERN, recently published work suggesting that giant clusters of W bosons might serve the same purpose, but even he admits that "it would be a great surprise if it were true". Other models without the Higgs boson invoke extra dimensions of space, but they are not yet sufficiently developed to guide experiments.
Perhaps the most likely alternative is that the Higgs is not a single particle, but rather a class of particles, which together do the job of unifying the two forces. Such a concept might appeal theoretically if a single Higgs is not found, but it would be a major headache for experimentalists to check. Theorists believe that the conventional Higgs boson would leave only a subtle mark on the detectors as it decays into W and Z bosons, high-energy photons and other particles. If there were two Higgs-like particles instead of one, the signal of each would be weaker still, says Murray. "It starts to get quite messy to do the analysis," he says.
The answer to the Higgs question lies in the data now being crunched at CERN and other academic-computing centres around the world. The first 70 trillion or so collisions turned up intriguing Higgs-like decays in the ATLAS and CMS experiments, hinting at a particle of around 140 GeV (see Nature 475, 434; 2011). But the second batch of collisions showed nothing. If the collisions now being analysed show further evidence of Higgs decays, then the teams on the two experiments are likely to announce that they have found a tentative signal, to be firmed up in 2012. If not, the search will probably continue until the LHC is shut down for an upgrade at the end of next year.
Even if that continued search shows no evidence for a Higgs or anything else, the LHC will push on. Without a unified electroweak force, the standard model is unable to predict how certain particles and forces interact inside the collider, says Matthew Strassler, a theorist at Rutgers University in Piscataway, New Jersey. The LHC will gather data on exactly those processes, and that information could potentially be used to find a way in which electromagnetism and the weak force fit together. That process, Strassler adds, is likely to take many years.
This article is reproduced with permission from the magazine Nature. The article was first published on November 18, 2011. Source Scientific American
November 18, 2011 | 12 Nature and reproduced by Scientific America
----------------------------------------------------------------------------------
By Geoff Brumfiel of Nature magazine
Bill Murray is a man with secrets. Along with a handful of other scientists based at CERN, Europe's particle-physics facility near Geneva, Switzerland, Murray is one of the few researchers with access to the latest data on the Higgs boson -- the most sought-after particle in physics.
Looking at his laptop, he traces a thin black line that wiggles across a shaded area at the centre of a graph. This is the fruit of his summer's labours. "It's interesting, actually, looking at this again," he muses. A tantalizing pause. "But no, I can't say..."
Despite Murray's coyness, there are few places left for the Higgs to hide. Billed as the particle that helps to confer mass on other matter, and the final missing piece in the `standard model' of particle physics, the Higgs would be a huge prize for CERN's Large Hadron Collider (LHC), the world's most powerful particle accelerator. But so far, the two massive detectors there--ATLAS, where Murray works, and the Compact Muon Solenoid (CMS) -- have not seen any convincing signals of the elusive particle.
At a conference in Paris on November 18, teams from ATLAS and the CMS experiments presented a combined analysis that wipes out a wide swathe of potential masses for the Higgs particle. Gone is the entire mass range from 141 to 476 gigaelectronvolts (GeV; energy and mass are interchangeable in particle physics). Together with earlier results from the 1990s, the analysis leaves a relatively narrow window of just 114-141 GeV in which the Higgs could lurk (see `Cornering the Higgs').
Analysis of the very latest data from this autumn--which Murray isn't yet ready to share -- will scour the range that remains. If it turns out to be empty, physicists may have to accept that the particle simply isn't there. Working around the clock, the detector teams hope to have this larger data set analysed before the end of December. "We'll know the outcome within weeks," says Guido Tonelli, spokesman for the CMS detector.
Waiting for God
The quest for the Higgs boson, often called the `God particle' after the title of a 1993 book by Nobel prizewinner Leon Lederman, is the public face of science at the LHC. Most high-energy physicists wince at the deistic designation, but they hold a near-religious devotion to the boson. Contrary to the popular view, their belief has less to do with mass than with fundamental forces.
Four fundamental forces are at work in nature: gravity, the strong nuclear force, the weak nuclear force and electromagnetism. Since the mid-1960s, physicists have strongly suspected that the weak and electromagnetic forces are actually different aspects of a single `electroweak' force. This is partly because the photon, the force-carrying particle of electromagnetism, is highly similar to the force-carrying particles of the weak force -- the W and Z bosons. Moreover, a single electroweak theory successfully predicts the interactions of fundamental particles.
There is one problem, however: the W and Z bosons are extremely heavy, nearly 100 GeV, whereas the photon is massless. To explain the difference, a number of physicists (including Peter Higgs in 1964) proposed a new field and particle. The eponymous Higgs mechanism would interact with the W and Z bosons, giving them mass, but would ignore the photon, allowing it to remain massless. Relatively straightforward tweaks to the Higgs machinery allow it to endow other particles, such as quarks, with their observed masses as well.
"The Higgs now sought at CERN is expected on the basis of the simplest picture" for the electroweak theory, says Steven Weinberg, a theorist who won a Nobel prize in 1979 for his work unifying electromagnetism and the weak force. "But there are other possibilities," he adds, reckoning the odds that the LHC's detectors will find the Higgs at 50/50 (see `Do you believe?').
If there is no Higgs, then what? Gian Giudice, a theorist at CERN, recently published work suggesting that giant clusters of W bosons might serve the same purpose, but even he admits that "it would be a great surprise if it were true". Other models without the Higgs boson invoke extra dimensions of space, but they are not yet sufficiently developed to guide experiments.
Perhaps the most likely alternative is that the Higgs is not a single particle, but rather a class of particles, which together do the job of unifying the two forces. Such a concept might appeal theoretically if a single Higgs is not found, but it would be a major headache for experimentalists to check. Theorists believe that the conventional Higgs boson would leave only a subtle mark on the detectors as it decays into W and Z bosons, high-energy photons and other particles. If there were two Higgs-like particles instead of one, the signal of each would be weaker still, says Murray. "It starts to get quite messy to do the analysis," he says.
The answer to the Higgs question lies in the data now being crunched at CERN and other academic-computing centres around the world. The first 70 trillion or so collisions turned up intriguing Higgs-like decays in the ATLAS and CMS experiments, hinting at a particle of around 140 GeV (see Nature 475, 434; 2011). But the second batch of collisions showed nothing. If the collisions now being analysed show further evidence of Higgs decays, then the teams on the two experiments are likely to announce that they have found a tentative signal, to be firmed up in 2012. If not, the search will probably continue until the LHC is shut down for an upgrade at the end of next year.
Even if that continued search shows no evidence for a Higgs or anything else, the LHC will push on. Without a unified electroweak force, the standard model is unable to predict how certain particles and forces interact inside the collider, says Matthew Strassler, a theorist at Rutgers University in Piscataway, New Jersey. The LHC will gather data on exactly those processes, and that information could potentially be used to find a way in which electromagnetism and the weak force fit together. That process, Strassler adds, is likely to take many years.
This article is reproduced with permission from the magazine Nature. The article was first published on November 18, 2011. Source Scientific American
Another Origin for Cosmic Rays
Some superfast particles arriving at Earth may originate from shock waves in turbulent stellar clusters, a gamma-ray study published in the November 24th issue of Science suggests. The observations are the first firm direct evidence of a longstanding theory for the origin of these particles, called cosmic rays, but they don’t do anything for another, even longer-standing theory in favor of supernova remnants.
Cosmic rays were first discovered in 1912 by Victor Hess, who won a Nobel Prize for his detection of this strange source of radiation entering the atmosphere from space. Until the 1930s scientists thought cosmic rays were some sort of electromagnetic wave — hence their name. But the deceptively dubbed “rays” are actually speedy charged particles whizzing through the universe. They’re mostly protons from hydrogen atoms stripped of their electrons, but they can also be heavier atomic nuclei, electrons, and other subatomic particles.
Gamma rays detected by the Fermi LAT (top image) are emitted by freshly accelerated cosmic rays traveling through the stormy Cygnus X region (in infrared, bottom image). The cosmic ray "cocoon" fills the cavities carved out around and between two star clusters, Cyg OB2 and NGC 6910.
NASA / DOE / Fermi LAT / I. Grenier / L. Tibaldo
Yet even after 99 years, astronomers still don’t know for sure where cosmic rays receive their energy boost. The problem with figuring out where cosmic rays come from is that they appear to come from everywhere. Because they’re charged particles, cosmic rays react to whatever magnetic fields they encounter, and there are a lot of magnetic fields in galaxies, whether from stars or planets or even the galaxy itself. By the time the particles reach Earth, they’re hitting us from all sides.
Gamma rays don’t have this problem. The most energetic photons in the universe, gamma rays basically travel in straight lines from their sources to us. And because cosmic rays are stupendously energetic, they produce gamma rays when they run into stuff.
Astronomers have used gamma rays to probe likely sites of cosmic ray acceleration. For several decades researchers have suspected that our galaxy’s rays come from supernova remnants, and X-ray and gamma-ray observations do indicate that electrons are being accelerated to high energies at remnants’ shock fronts as they slam into surrounding gas and dust, sending the electrons surfing in and out of the blast wave. But there’s no conclusive evidence of proton and nuclei acceleration, and these heavier particles make up 99% of cosmic rays, says Isabelle Grenier (Paris Diderot University and CEA Saclay), a coauthor on the new study. “We have no smoking gun,” she says. “We have very strong hints, but no proof.”
To hunt for cosmic rays’ origin, Grenier and her colleagues turned the Fermi Gamma-ray Space Telescope’s Large Area Telescope to point at the star-forming region Cygnus X, a tumultuous section of space about 4,500 light-years away filled with billows of thousand-mile-per-second stellar winds and strong ultraviolet radiation from young stars. The team detected a diffuse gamma-ray glow from inside a superbubble blown out by the young, massive members of two of the region’s star clusters, Cyg OB2 and NGC 6910. What’s more, the radiation looks like it’s coming from protons, not electrons.
The average energies Grenier’s team observed are much higher than the energies of cosmic rays near Earth. Add that higher energy to the emission’s confinement (meaning, the particles haven’t had a chance to move very far from their energizing source), and the fact that the gamma rays come from protons, and it looks like the team’s caught, as they put it, “freshly accelerated cosmic rays” that haven’t slowed down to near-Earth energy levels yet.
To find the source, the team focused at first on a strong gamma-ray-emitting supernova remnant called γ Cygni that appears in the same part of the sky. The remnant’s distance isn’t pinned down, so it’s not clear if it’s actually associated with Cygnus X. But that it might be there, in the same place as cosmic rays, sparked the researchers’ interest. “We were so excited,” says Grenier. “And I must say that, several months after, I’m not convinced that it’s the best scenario anymore.” The diffuse gamma-ray emission showed no sign of any connection with the remnant.
But the astronomers discovered something else intriguing: the diffuse gamma-rays are completely confined to the superbubble created by the stars’ strong winds, even edged by an infrared-emitting shell of dust grains heated by the intense starlight.
That made the researchers turn to a second theory for cosmic ray production, one involving exactly this kind of environment. Astronomers have suspected since the 1980s or so that cosmic rays may also come from clusters of massive, young stars called OB associations, where the O and B stand for the two hottest, most massive types of the family of stars that fuse hydrogen in their cores. The suspicion stems from the cosmic rays’ composition. Many of the common heavier elements, such as carbon and silicon, are about as abundant among the particles as they are in the solar system, but there are some elements that are overrepresented. Particularly, a heavy isotope of neon, neon-22, is about five times as abundant in cosmic rays as it is in the solar system. But Ne-22 is seen in the outer layers thrown off by really massive, young, windy stars called Wolf-Rayet stars. Overall, the cosmic rays’ chemical makeup suggests that about 20% are created by WR stars, while the rest are other particles found in the interstellar medium, the stuff between the stars.
A sizable fraction of cosmic rays may be born in WR stars’ massive outflows, but that’s not necessarily where they gain their energy. In 1999 Richard Mewaldt (Caltech) and his colleagues reported the presence in cosmic rays of the cobalt isotope cobalt-59. Co-59 is a daughter isotope, an atom formed by the radioactive decay of nickel-59 when that atom captures an electron and shoves it together with one of its proton to make a neutron. Such a snatch can’t happen when the nickel atom’s nucleus is accelerated to high energies and stripped of its electrons, as cosmic ray particles are. That means that the nuclei that make up cosmic rays aren’t born with their high energies: they hang around a while — about 100,000 years, the team concluded — before being sped up and out into interstellar space.
“This rules out a supernova accelerating its own ejecta,” Mewaldt says, although some of the heavier cosmic ray nuclei probably first formed in supernova explosions. “But [it] is consistent with accelerating cosmic rays from a region where massive stars are born, a region that will be enriched in WR material because of the high-velocity winds of these stars.”
Grenier’s team didn’t measure specific chemical composition, so they don’t know what the cosmic rays are made of. Whatever the ingredients — and they’re probably a combination of interstellar medium, old supernova ejecta, and outflows from an earlier batch of Wolf-Rayet stars — it looks like they’re now being accelerated by the current stellar clusters’ winds.
“This is a very important paper,” says Mewaldt of Grenier’s study, “because it provides the first direct evidence for the distributed acceleration of cosmic rays in OB associations.”
The cosmic rays are still confined in a “cocoon” because they can’t spread out fast in the torrid environment inside the superbubble, Grenier says. The massive stars are only a few million years old, and their powerful winds and ultraviolet radiation create a maelstrom inside the cavity, twisting magnetic fields into tangles that trap the cosmic rays. Over time the particles will escape into quieter regions, but what happens to their energies while inside the cocoon remains a mystery.
It’s a mystery that’s particularly intriguing to Grenier. Low-energy cosmic rays (at least, lower energy than the ones the team observed) “are very, very important for the structure of the clouds of the gas from which we form stars,” she explains. Dense clump of clouds eventually collapse under their own gravity to make stars. While the clouds are pretty opaque to light, cosmic rays can sneak inside, bringing with them heat and catalyzing the formation of molecules. How that heat and chemistry influence star formation isn’t known, and Grenier is pursing the question with her colleagues. What is clear is that “if you radiate those clouds with more cosmic rays or [fewer] cosmic rays, you change the game.”
Fuente...SKY AND TELESCOPE
Posted by Camille Carlisle, November 23, 2011
related content: News Topics, Cosmology news, Milky Way news, Stellar science
links: + digg | + del.icio.us | + reddit | + permalink | + rss
Cosmic rays were first discovered in 1912 by Victor Hess, who won a Nobel Prize for his detection of this strange source of radiation entering the atmosphere from space. Until the 1930s scientists thought cosmic rays were some sort of electromagnetic wave — hence their name. But the deceptively dubbed “rays” are actually speedy charged particles whizzing through the universe. They’re mostly protons from hydrogen atoms stripped of their electrons, but they can also be heavier atomic nuclei, electrons, and other subatomic particles.
Gamma rays detected by the Fermi LAT (top image) are emitted by freshly accelerated cosmic rays traveling through the stormy Cygnus X region (in infrared, bottom image). The cosmic ray "cocoon" fills the cavities carved out around and between two star clusters, Cyg OB2 and NGC 6910.
NASA / DOE / Fermi LAT / I. Grenier / L. Tibaldo
Yet even after 99 years, astronomers still don’t know for sure where cosmic rays receive their energy boost. The problem with figuring out where cosmic rays come from is that they appear to come from everywhere. Because they’re charged particles, cosmic rays react to whatever magnetic fields they encounter, and there are a lot of magnetic fields in galaxies, whether from stars or planets or even the galaxy itself. By the time the particles reach Earth, they’re hitting us from all sides.
Gamma rays don’t have this problem. The most energetic photons in the universe, gamma rays basically travel in straight lines from their sources to us. And because cosmic rays are stupendously energetic, they produce gamma rays when they run into stuff.
Astronomers have used gamma rays to probe likely sites of cosmic ray acceleration. For several decades researchers have suspected that our galaxy’s rays come from supernova remnants, and X-ray and gamma-ray observations do indicate that electrons are being accelerated to high energies at remnants’ shock fronts as they slam into surrounding gas and dust, sending the electrons surfing in and out of the blast wave. But there’s no conclusive evidence of proton and nuclei acceleration, and these heavier particles make up 99% of cosmic rays, says Isabelle Grenier (Paris Diderot University and CEA Saclay), a coauthor on the new study. “We have no smoking gun,” she says. “We have very strong hints, but no proof.”
To hunt for cosmic rays’ origin, Grenier and her colleagues turned the Fermi Gamma-ray Space Telescope’s Large Area Telescope to point at the star-forming region Cygnus X, a tumultuous section of space about 4,500 light-years away filled with billows of thousand-mile-per-second stellar winds and strong ultraviolet radiation from young stars. The team detected a diffuse gamma-ray glow from inside a superbubble blown out by the young, massive members of two of the region’s star clusters, Cyg OB2 and NGC 6910. What’s more, the radiation looks like it’s coming from protons, not electrons.
The average energies Grenier’s team observed are much higher than the energies of cosmic rays near Earth. Add that higher energy to the emission’s confinement (meaning, the particles haven’t had a chance to move very far from their energizing source), and the fact that the gamma rays come from protons, and it looks like the team’s caught, as they put it, “freshly accelerated cosmic rays” that haven’t slowed down to near-Earth energy levels yet.
To find the source, the team focused at first on a strong gamma-ray-emitting supernova remnant called γ Cygni that appears in the same part of the sky. The remnant’s distance isn’t pinned down, so it’s not clear if it’s actually associated with Cygnus X. But that it might be there, in the same place as cosmic rays, sparked the researchers’ interest. “We were so excited,” says Grenier. “And I must say that, several months after, I’m not convinced that it’s the best scenario anymore.” The diffuse gamma-ray emission showed no sign of any connection with the remnant.
But the astronomers discovered something else intriguing: the diffuse gamma-rays are completely confined to the superbubble created by the stars’ strong winds, even edged by an infrared-emitting shell of dust grains heated by the intense starlight.
That made the researchers turn to a second theory for cosmic ray production, one involving exactly this kind of environment. Astronomers have suspected since the 1980s or so that cosmic rays may also come from clusters of massive, young stars called OB associations, where the O and B stand for the two hottest, most massive types of the family of stars that fuse hydrogen in their cores. The suspicion stems from the cosmic rays’ composition. Many of the common heavier elements, such as carbon and silicon, are about as abundant among the particles as they are in the solar system, but there are some elements that are overrepresented. Particularly, a heavy isotope of neon, neon-22, is about five times as abundant in cosmic rays as it is in the solar system. But Ne-22 is seen in the outer layers thrown off by really massive, young, windy stars called Wolf-Rayet stars. Overall, the cosmic rays’ chemical makeup suggests that about 20% are created by WR stars, while the rest are other particles found in the interstellar medium, the stuff between the stars.
A sizable fraction of cosmic rays may be born in WR stars’ massive outflows, but that’s not necessarily where they gain their energy. In 1999 Richard Mewaldt (Caltech) and his colleagues reported the presence in cosmic rays of the cobalt isotope cobalt-59. Co-59 is a daughter isotope, an atom formed by the radioactive decay of nickel-59 when that atom captures an electron and shoves it together with one of its proton to make a neutron. Such a snatch can’t happen when the nickel atom’s nucleus is accelerated to high energies and stripped of its electrons, as cosmic ray particles are. That means that the nuclei that make up cosmic rays aren’t born with their high energies: they hang around a while — about 100,000 years, the team concluded — before being sped up and out into interstellar space.
“This rules out a supernova accelerating its own ejecta,” Mewaldt says, although some of the heavier cosmic ray nuclei probably first formed in supernova explosions. “But [it] is consistent with accelerating cosmic rays from a region where massive stars are born, a region that will be enriched in WR material because of the high-velocity winds of these stars.”
Grenier’s team didn’t measure specific chemical composition, so they don’t know what the cosmic rays are made of. Whatever the ingredients — and they’re probably a combination of interstellar medium, old supernova ejecta, and outflows from an earlier batch of Wolf-Rayet stars — it looks like they’re now being accelerated by the current stellar clusters’ winds.
“This is a very important paper,” says Mewaldt of Grenier’s study, “because it provides the first direct evidence for the distributed acceleration of cosmic rays in OB associations.”
The cosmic rays are still confined in a “cocoon” because they can’t spread out fast in the torrid environment inside the superbubble, Grenier says. The massive stars are only a few million years old, and their powerful winds and ultraviolet radiation create a maelstrom inside the cavity, twisting magnetic fields into tangles that trap the cosmic rays. Over time the particles will escape into quieter regions, but what happens to their energies while inside the cocoon remains a mystery.
It’s a mystery that’s particularly intriguing to Grenier. Low-energy cosmic rays (at least, lower energy than the ones the team observed) “are very, very important for the structure of the clouds of the gas from which we form stars,” she explains. Dense clump of clouds eventually collapse under their own gravity to make stars. While the clouds are pretty opaque to light, cosmic rays can sneak inside, bringing with them heat and catalyzing the formation of molecules. How that heat and chemistry influence star formation isn’t known, and Grenier is pursing the question with her colleagues. What is clear is that “if you radiate those clouds with more cosmic rays or [fewer] cosmic rays, you change the game.”
Fuente...SKY AND TELESCOPE
Posted by Camille Carlisle, November 23, 2011
related content: News Topics, Cosmology news, Milky Way news, Stellar science
links: + digg | + del.icio.us | + reddit | + permalink | + rss
martes, 22 de noviembre de 2011
Astrónomos reconstruyen la historia de un agujero negro
Tres equipos de astrónomos han logrado determinar la masa, la rotación y la distancia a la Tierra de un agujero negro especialmente famoso, Cygnus X-1, y con esos parámetros han reconstruido su historia. El objeto tiene casi 14,8 veces la masa del Sol, gira 800 veces por segundo y está a 6.070 años luz de aquí. Fue identificado como candidato a agujero negro hace casi cuatro décadas, pero entonces el gran especialista Stephen Hawking no estaba convencido y, en 1974, apostó con un colega y amigo, el físico teórico estadounidense Kip Thorne, a que no se trataba de tal objeto. Perdió. En 1990, cuando ya se habían hecho más observaciones de Cygnus X-1, el físico británico aceptó la derrota. Fue una de las varias apuestas que Hawking y Thorne han hecho sobre cuestiones científicas.
Una vez aceptado como tal, el objeto no perdió interés, al contrario. Cygnus X-1 es un agujero negro estelar, es decir, que se ha formado por el colapso de una estrella masiva, y forma un sistema doble con otro astro. Ahora, los tres grupos de astrónomos, que han trabajado con telescopios en tierra y en el espacio, presentan sus conclusiones complementarias en tres artículos publicados en The Astrophysical Journal. "La nueva información nos proporciona pistas sólidas acerca de cómo se formó el agujero negro, su masa y su velocidad de rotación, y es emocionante, porque no se sabe mucho acerca del nacimiento de un agujero negro", señala Mark Reid, líder de uno de los equipos, en un comunicado del Harvard-Smithsonian Center for Astrophysics (EE UU). El horizonte de sucesos (la frontera de no retorno de la materia que cae en un agujero negro) gira en este más de 800 veces por segundo, muy cerca del máximo calculado.
Otro dato importante es la edad: tiene unos seis millones de años, según estudios de la estrella compañera y modelos teóricos. Por tanto, es relativamente joven en términos astronómicos, y no ha tenido mucho tiempo para tragarse suficiente materia de su entorno como para acelerar su rotación, por lo que Cygnus X-1 debió nacer ya girando muy rápido. Además, debió formarse prácticamente con la misma masa que tiene ahora, 14,8 veces la del Sol. "Ahora sabemos que es uno de los agujeros negros estelares más masivos de la galaxia y gira más rápido que cualquier otro que conozcamos", afirma Jerome Orosz (San Diego State University). El telescopio espacial de rayos X Chandra, de la NASA, ha sido clave en esta investigación.
"Como no puede escapar de un agujero negro más información, su masa, rotación y su carga eléctrica supone la descripción completa", dice Reid. "Y la carga de este agujero negro es casi cero".
Un tercer equipo, gracias a los radiotelescopios sincronizados del sistema VLBA, ha logrado precisar la distancia de Cygnus X-1 (dato esencial para determinar la masa y la rotación), así como el desplazamiento del objeto en el espacio. Resulta que el agujero negro se mueve muy despacio respecto a la Vía Láctea, lo que significa que no recibió impulso al formarse. Este dato apoya la hipótesis según la cual este objeto no se formó en una explosión de supernova (cuando una estrella supermasiva ha consumido todo su combustible), que habría dado ese impulso y llevaría mucha más velocidad. Debió ser un colapso estelar, sí, pero sin explosión, lo que dio origen al agujero negro en cuestión. En cuanto a la distancia, antes de estas nuevas medidas que la han fijado en 6.070 años luz, se estimaba entre 5.800 y 7.800 años luz, indican los expertos del National Radio Astronomy Observatory (que opera el VLBA).
Fuente EL PAÍS - Madrid - 21/11/2011
Una vez aceptado como tal, el objeto no perdió interés, al contrario. Cygnus X-1 es un agujero negro estelar, es decir, que se ha formado por el colapso de una estrella masiva, y forma un sistema doble con otro astro. Ahora, los tres grupos de astrónomos, que han trabajado con telescopios en tierra y en el espacio, presentan sus conclusiones complementarias en tres artículos publicados en The Astrophysical Journal. "La nueva información nos proporciona pistas sólidas acerca de cómo se formó el agujero negro, su masa y su velocidad de rotación, y es emocionante, porque no se sabe mucho acerca del nacimiento de un agujero negro", señala Mark Reid, líder de uno de los equipos, en un comunicado del Harvard-Smithsonian Center for Astrophysics (EE UU). El horizonte de sucesos (la frontera de no retorno de la materia que cae en un agujero negro) gira en este más de 800 veces por segundo, muy cerca del máximo calculado.
Otro dato importante es la edad: tiene unos seis millones de años, según estudios de la estrella compañera y modelos teóricos. Por tanto, es relativamente joven en términos astronómicos, y no ha tenido mucho tiempo para tragarse suficiente materia de su entorno como para acelerar su rotación, por lo que Cygnus X-1 debió nacer ya girando muy rápido. Además, debió formarse prácticamente con la misma masa que tiene ahora, 14,8 veces la del Sol. "Ahora sabemos que es uno de los agujeros negros estelares más masivos de la galaxia y gira más rápido que cualquier otro que conozcamos", afirma Jerome Orosz (San Diego State University). El telescopio espacial de rayos X Chandra, de la NASA, ha sido clave en esta investigación.
"Como no puede escapar de un agujero negro más información, su masa, rotación y su carga eléctrica supone la descripción completa", dice Reid. "Y la carga de este agujero negro es casi cero".
Un tercer equipo, gracias a los radiotelescopios sincronizados del sistema VLBA, ha logrado precisar la distancia de Cygnus X-1 (dato esencial para determinar la masa y la rotación), así como el desplazamiento del objeto en el espacio. Resulta que el agujero negro se mueve muy despacio respecto a la Vía Láctea, lo que significa que no recibió impulso al formarse. Este dato apoya la hipótesis según la cual este objeto no se formó en una explosión de supernova (cuando una estrella supermasiva ha consumido todo su combustible), que habría dado ese impulso y llevaría mucha más velocidad. Debió ser un colapso estelar, sí, pero sin explosión, lo que dio origen al agujero negro en cuestión. En cuanto a la distancia, antes de estas nuevas medidas que la han fijado en 6.070 años luz, se estimaba entre 5.800 y 7.800 años luz, indican los expertos del National Radio Astronomy Observatory (que opera el VLBA).
Fuente EL PAÍS - Madrid - 21/11/2011
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