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Tuesday, 7 August 2012
Physicists unveil plans for 'LEP3' collider at CERN - physicsworld.com
Physicists unveil plans for 'LEP3' collider at CERN - physicsworld.com
A group of physicists from Switzerland, Japan, Russia, US and the UK has proposed using the tunnel that currently houses the Large Hadron Collider (LHC) at the CERN particle-physics lab near Geneva for a dedicated machine to study the Higgs boson. The facility, dubbed LEP3, is named after CERN's previous accelerator, the Large Electron–Positron Collider (LEP), which used to exist in the LHC tunnel before being shut down in 2000. In a preliminary study submitted to the European Strategy Preparatory Group, LEP3's backers say that the machine could be constructed within the next 10 years.
The plans for LEP3 come just weeks after physicists working at CERN reported that they had discovered a new particle that bears a striking resemblance to a Higgs boson, as described by the Standard Model of particle physics. The ATLAS experiment measured its mass at around 125 GeV and the CMS experiment at 126 GeV.
LEP3 would operate at 240 GeV and comprise two separate accelerator rings that would smash electrons and positrons rather than protons and protons, as with the LHC. In their study, the 20 authors call the concept for LEP3 "highly interesting" and that it deserves more detailed study. "Now is the right moment to get this on the table," says theorist John Ellis from Kings College London in the UK, who is an author of the preliminary study and hopes that it will trigger debate among physicists as to how to study the new boson in detail.
Which collider is built to succeed the LHC will depend on what the LHC discovers in the next couple of years after it has run at its full design energy of 14 TeV. If it turns out that the LHC finds only the Higgs, then Ellis says there would be a strong case for LEP3. But if more particles are discovered by the LHC – such as supersymmteric particles – it would make sense to consider the other two proposals. "LEP3 could be a more secure option than the ILC if only a Higgs is discovered," Ellis told physicsworld.com. "But, of course, it would be foolish to choose anything now, given that the LHC has not hit full energy yet."
CERN plans to run the LHC into the 2030s after it has undergone a major upgrade in energy and luminosity in the coming decade. However, Ellis thinks that it may even be possible for the LHC and LEP3 to cohabit for a short time. "It would not be ideal, but it could be something to think about," says Ellis. "If the LHC does not discover anything beyond the Higgs, then would you keep running it for years?"
That view is shared by linear-collider director Lyn Evans, who told physicsworld.com that he thinks it is unlikely that the proposal for LEP3 will get very far. "The first job is to fully exploit the LHC and all its upgrades," says Evans, who led the construction of the LHC. "This is at least a 20 year programme of work, so I think that it is very unlikely that the LHC will be ripped out and replaced by a very modest machine with little scope apart from studying the Higgs."
A group of physicists from Switzerland, Japan, Russia, US and the UK has proposed using the tunnel that currently houses the Large Hadron Collider (LHC) at the CERN particle-physics lab near Geneva for a dedicated machine to study the Higgs boson. The facility, dubbed LEP3, is named after CERN's previous accelerator, the Large Electron–Positron Collider (LEP), which used to exist in the LHC tunnel before being shut down in 2000. In a preliminary study submitted to the European Strategy Preparatory Group, LEP3's backers say that the machine could be constructed within the next 10 years.
The plans for LEP3 come just weeks after physicists working at CERN reported that they had discovered a new particle that bears a striking resemblance to a Higgs boson, as described by the Standard Model of particle physics. The ATLAS experiment measured its mass at around 125 GeV and the CMS experiment at 126 GeV.
LEP3 would operate at 240 GeV and comprise two separate accelerator rings that would smash electrons and positrons rather than protons and protons, as with the LHC. In their study, the 20 authors call the concept for LEP3 "highly interesting" and that it deserves more detailed study. "Now is the right moment to get this on the table," says theorist John Ellis from Kings College London in the UK, who is an author of the preliminary study and hopes that it will trigger debate among physicists as to how to study the new boson in detail.
Tunnel vision
LEP3 is designed to be installed in the LHC tunnel and serve the two LHC's general-purpose detectors – ATLAS and CMS. If LEP3 is to be built, it will have to fight off two rival proposals for a future collider to study the Higgs – the International Linear Collider (ILC) and the Compact Linear Collider (CLIC). But Ellis says that one advantage of LEP3 is that the tunnel to house it is already built and the collider would use the existing infrastructure, such as cryogenics equipment, thus making LEP3 more cost-effective. LEP3 would also use conventional electromagnets to accelerate particles rather than the accelerating superconducting cavities that will be employed by the ILC.Which collider is built to succeed the LHC will depend on what the LHC discovers in the next couple of years after it has run at its full design energy of 14 TeV. If it turns out that the LHC finds only the Higgs, then Ellis says there would be a strong case for LEP3. But if more particles are discovered by the LHC – such as supersymmteric particles – it would make sense to consider the other two proposals. "LEP3 could be a more secure option than the ILC if only a Higgs is discovered," Ellis told physicsworld.com. "But, of course, it would be foolish to choose anything now, given that the LHC has not hit full energy yet."
CERN plans to run the LHC into the 2030s after it has undergone a major upgrade in energy and luminosity in the coming decade. However, Ellis thinks that it may even be possible for the LHC and LEP3 to cohabit for a short time. "It would not be ideal, but it could be something to think about," says Ellis. "If the LHC does not discover anything beyond the Higgs, then would you keep running it for years?"
"Little scope"
Yet some disagree that LEP3 represents the best way to study the Higgs, adding that a decision would have to be made between building LEP3 and running the high-luminosity upgrade to the LHC in the 2020s. "They both have an excellent physics case, but somehow LEP3 presents less chance of a huge breakthrough," says one leading CERN researcher who prefers not to be named. "[The LHC upgrade] has precision measurements as well as discovery reach to offer."That view is shared by linear-collider director Lyn Evans, who told physicsworld.com that he thinks it is unlikely that the proposal for LEP3 will get very far. "The first job is to fully exploit the LHC and all its upgrades," says Evans, who led the construction of the LHC. "This is at least a 20 year programme of work, so I think that it is very unlikely that the LHC will be ripped out and replaced by a very modest machine with little scope apart from studying the Higgs."
Thursday, 5 April 2012
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Sunday, 11 July 2010
What makes the LHC tick?
GENEVA--The Large Hadron Collider is a marvel of both brute-force and sophisticated engineering.
To start, look at the mostly circular cavern, 27 kilometers in circumference, that houses the accelerator. It's got an average depth of 100 meters, but in fact it's actually horizontal: its plane is tilted 1.4 percent to keep it as shallow as possible to minimize the expense of digging vertical shafts while placing the cavern in a subterranean sandstone layer.
Tidal forces from the moon cause the Earth's crust to rise about 25cm, an effect that increases the LHC's circumference by 1mm. That may not sound significant, but it must be factored into calculations.
The cavern itself is recycled from an earlier accelerator, the LEP (Large Electron-Positron) accelerator, to cut costs.
"You get the biggest tunnel you can afford. It's the one thing you can't change after the fact," said said Tom LeCompte, physics coordinator for one of the major LHC experiments, ATLAS. Bigger accelerators are desirable because the more the path of charged particles curves, the more energy they lose through what's called synchrotron radiation.
There's something of a tension between those who operate the LHC and those who are running its experiments. In this earlier stage of its real work, a lot of time is devoted to working out the kinks and understanding the LHC.
"It's a machine in its very youth," said Mirko Pojer, a physicist and the engineer in charge of LHC operations. "Most of the things are not routine."
To get protons and lead ions up to full speed, the particles travel through some of CERN's history as a center of nuclear physics research. Two previously state-of-the-art accelerators, the Proton Synchrotron that started operation in 1959, and the Super Proton Synchrotron that started in 1976, are now mere LHC stepping stones on the way to higher energies.
The LHC has two beams that circulate in opposite directions on separate paths. At four locations, the two beams collide, producing the showers of particles researchers study. The nature of the particles is inferred from characteristics such as how much energy they release when they are absorbed at the edges of the detector; other detectors track the particles as they travel, letting physicists gauge their properties by how much their path is curved by an electric field, for example.
One of the standout features that lets the LHC reach such tremendous energy is its collection of magnets, supercooled to 1.9 Kelvin, or -456.25 degrees Fahrenheit. At this temperature, the magnets and the cables that connect them are superconducting, meaning that electrical current can travel within them without losing energy.
A total of 1,232 magnetic dipoles are responsible for steering the beams around the LHC's curve, and separate devices called a radiofrequency cavity accelerate the ions and group them into bunches.
These bunches pass through each other like two swarms of very tiny bees, and sometimes the protons actually collide. So far, the LHC operators haven't filled the accelerator to capacity. Eventually each beam will consist of 2,808 bunches, each with 100 billion protons, spaced about 7 meters apart, traveling around the ring 11,245 times per second, and producing 600 million collisions per second.
Maxed out today, the LHC produces collisions of two protons with a total energy of 7 tera-electron volts, or TeV, but after a coming shutdown period to upgrade the LHC, it's planned to reach a total energy of 14TeV.
That's actually kind of a feeble amount of energy by one view--a flying mosquito has about 1TeV worth of energy. What makes it impressive is that energy is confined to the very tiny volume of a proton collision. To attain it, the LHC consumes about the same amount of electrical power as all Geneva.
Pojer was off duty on September 19, 2008, when the LHC hit its roughest patch. The LHC had done well just days earlier when researchers fired it up with its first beam. Pojer had just sat down to a congratulatory glass of champagne when a colleague called: "Run here, immediately. It's urgent."
It turns out a faulty electrical connection between two magnets had heated up, causing an explosive helium leak. The helium used to cool the LHC's magnets is so cold it's what's called a superfluid, and heating it up so it turns into a gas causes big problems with gas pressure. Some of the massive magnet structures of the accelerator shifted by a half a meter by the forces involved.
"Everybody was depressed and astonished," Pojer said of the problem. "Slowly we recovered," though, and a happier day came on March 30, 2010, when he was the engineer in charge of ramping the LHC up to 3.5TeV energy level.
"It was amazing and exciting," Pojer said, and indeed there was jubilation among the crews and researchers. Now, when the engineers in charge running LHC aren't working on refinements such as a tighter beam that increases the chances of collisions, the LHC is used for its scientific mission.
The LHC's hardware is largely located underground, but on the surface are several control rooms, each festooned with large monitors, for overseeing the operations and the experiments. But a significant part of the LHC's effective operation actually takes place far from CERN.
That's because a worldwide grid of computers is used to process the data that actually comes from the experiments. CERN maintains a primary copy of the data produced, but several tier-one partners have copies of parts, and about 130 to 150 tier-two partners keep their own copies many scientists actually use in their research.
That's not to say CERN's computers aren't central. A data center with hundreds of machines churns night and day to process the data. "It never stops, not even at Christmas," said Ian Bird, worldwide LHC computing grid project leader, with a million computing jobs in the center in flight at any given moment.
That's because LHC experiments don't lack for data. "Experiments have a knob," a way to adjust how much data is captured. Collectively, the LHC experiments produce about 15 petabytes of raw data each year that must be stored, processed, and analyzed.
Data processing is needed to sift the interesting unusual events out from the sea of background noise, to find enough of them to prove they aren't flukes, and to offer precise measurements. There was a day when individual events at particle accelerators were observed in bubble chambers or recorded on film, but computers are an essential component in the LHC's scientific investigations.
http://news.cnet.com/8301-30685_3-20009671-264.html
To start, look at the mostly circular cavern, 27 kilometers in circumference, that houses the accelerator. It's got an average depth of 100 meters, but in fact it's actually horizontal: its plane is tilted 1.4 percent to keep it as shallow as possible to minimize the expense of digging vertical shafts while placing the cavern in a subterranean sandstone layer.
Tidal forces from the moon cause the Earth's crust to rise about 25cm, an effect that increases the LHC's circumference by 1mm. That may not sound significant, but it must be factored into calculations.
The cavern itself is recycled from an earlier accelerator, the LEP (Large Electron-Positron) accelerator, to cut costs.
"You get the biggest tunnel you can afford. It's the one thing you can't change after the fact," said said Tom LeCompte, physics coordinator for one of the major LHC experiments, ATLAS. Bigger accelerators are desirable because the more the path of charged particles curves, the more energy they lose through what's called synchrotron radiation.
There's something of a tension between those who operate the LHC and those who are running its experiments. In this earlier stage of its real work, a lot of time is devoted to working out the kinks and understanding the LHC.
"It's a machine in its very youth," said Mirko Pojer, a physicist and the engineer in charge of LHC operations. "Most of the things are not routine."
To get protons and lead ions up to full speed, the particles travel through some of CERN's history as a center of nuclear physics research. Two previously state-of-the-art accelerators, the Proton Synchrotron that started operation in 1959, and the Super Proton Synchrotron that started in 1976, are now mere LHC stepping stones on the way to higher energies.
The LHC has two beams that circulate in opposite directions on separate paths. At four locations, the two beams collide, producing the showers of particles researchers study. The nature of the particles is inferred from characteristics such as how much energy they release when they are absorbed at the edges of the detector; other detectors track the particles as they travel, letting physicists gauge their properties by how much their path is curved by an electric field, for example.
One of the standout features that lets the LHC reach such tremendous energy is its collection of magnets, supercooled to 1.9 Kelvin, or -456.25 degrees Fahrenheit. At this temperature, the magnets and the cables that connect them are superconducting, meaning that electrical current can travel within them without losing energy.
A total of 1,232 magnetic dipoles are responsible for steering the beams around the LHC's curve, and separate devices called a radiofrequency cavity accelerate the ions and group them into bunches.
These bunches pass through each other like two swarms of very tiny bees, and sometimes the protons actually collide. So far, the LHC operators haven't filled the accelerator to capacity. Eventually each beam will consist of 2,808 bunches, each with 100 billion protons, spaced about 7 meters apart, traveling around the ring 11,245 times per second, and producing 600 million collisions per second.
Maxed out today, the LHC produces collisions of two protons with a total energy of 7 tera-electron volts, or TeV, but after a coming shutdown period to upgrade the LHC, it's planned to reach a total energy of 14TeV.
That's actually kind of a feeble amount of energy by one view--a flying mosquito has about 1TeV worth of energy. What makes it impressive is that energy is confined to the very tiny volume of a proton collision. To attain it, the LHC consumes about the same amount of electrical power as all Geneva.
Pojer was off duty on September 19, 2008, when the LHC hit its roughest patch. The LHC had done well just days earlier when researchers fired it up with its first beam. Pojer had just sat down to a congratulatory glass of champagne when a colleague called: "Run here, immediately. It's urgent."
It turns out a faulty electrical connection between two magnets had heated up, causing an explosive helium leak. The helium used to cool the LHC's magnets is so cold it's what's called a superfluid, and heating it up so it turns into a gas causes big problems with gas pressure. Some of the massive magnet structures of the accelerator shifted by a half a meter by the forces involved.
"Everybody was depressed and astonished," Pojer said of the problem. "Slowly we recovered," though, and a happier day came on March 30, 2010, when he was the engineer in charge of ramping the LHC up to 3.5TeV energy level.
"It was amazing and exciting," Pojer said, and indeed there was jubilation among the crews and researchers. Now, when the engineers in charge running LHC aren't working on refinements such as a tighter beam that increases the chances of collisions, the LHC is used for its scientific mission.
The LHC's hardware is largely located underground, but on the surface are several control rooms, each festooned with large monitors, for overseeing the operations and the experiments. But a significant part of the LHC's effective operation actually takes place far from CERN.
That's because a worldwide grid of computers is used to process the data that actually comes from the experiments. CERN maintains a primary copy of the data produced, but several tier-one partners have copies of parts, and about 130 to 150 tier-two partners keep their own copies many scientists actually use in their research.
That's not to say CERN's computers aren't central. A data center with hundreds of machines churns night and day to process the data. "It never stops, not even at Christmas," said Ian Bird, worldwide LHC computing grid project leader, with a million computing jobs in the center in flight at any given moment.
That's because LHC experiments don't lack for data. "Experiments have a knob," a way to adjust how much data is captured. Collectively, the LHC experiments produce about 15 petabytes of raw data each year that must be stored, processed, and analyzed.
Data processing is needed to sift the interesting unusual events out from the sea of background noise, to find enough of them to prove they aren't flukes, and to offer precise measurements. There was a day when individual events at particle accelerators were observed in bubble chambers or recorded on film, but computers are an essential component in the LHC's scientific investigations.
http://news.cnet.com/8301-30685_3-20009671-264.html
The Incredible Shrinking Proton That Could Rattle the Physics World
It wasn’t supposed to be like this. The Higgs boson, dark matter, neutrinos—weird or poorly understood phenomena like these seemed the likely candidates to provide a surprise that changes particle physics. Not an old standby like the proton.
But the big story this week in Nature is that we might have been wrong all along in estimating something very basic about the humble proton: its size. A team from the Paul-Scherrer Institute in Switzerland that’s been tackling this for a decade says its arduous measurements of the proton show it is 4 percent smaller than the previous best estimate. For something as simple as the size of a proton, one of the basic measurements upon with the standard model of particle physics is built, 4 percent is a vast expanse that could shake up quantum electrodynamics if it’s true.
If the [standard model] turns out to be wrong, “it would be quite revolutionary. It would mean that we know a lot less than we thought we knew,” said physicist Peter J. Mohr of the National Institute of Standards and Technology in Gaithersburg, Md., who was not involved in the research. “If it is a fundamental problem, we don’t know what the consequences are yet” [Los Angeles Times].
Simply, the long-standing value used for a proton’s radius is 0.8768 femtometers, (a femtometer equals one quadrillionth of a meter). But the study team found it to be 0.84184 femtometers. How’d they make their measurement? First, think of the standard picture of electrons orbiting around a proton:
According to quantum mechanics, an electron can orbit only at certain specific distances, called energy levels, from its proton. The electron can jump up to a higher energy level if a particle of light hits it, or drop down to a lower one if it lets some light go. Physicists measure the energy of the absorbed or released light to determine how far one energy level is from another, and use calculations based on quantum electrodynamics to transform that energy difference into a number for the size of the proton [Wired.com].
That was how physicists derived their previous estimate, using simple hydrogen atoms. But this team relied on muons instead of electrons. Muons are 200 times heavier than electrons; they orbit closer to protons and are more sensitive to the proton’s size. However, they don’t last long and there aren’t many of them, so the team had to be quick:
The team knew that firing a laser at the atom before the muon decays should excite the muon, causing it to move to a higher energy level—a higher orbit around the proton. The muon should then release the extra energy as x-rays and move to a lower energy level. The distance between these energy levels is determined by the size of the proton, which in turn dictates the frequency of the emitted x-rays [National Geographic].
Thus, they should have seen the specific frequency related to the accepted size of a proton. Just one problem: The scientists didn’t see that frequency. Instead, their x-ray readings corresponded to the 4-percent-smaller size.
Now the task at hand is to check whether this study is somehow flawed, or is in fact a finding that will shake up physics.
In an editorial accompanying the report in the journal Nature, physicist Jeff Flowers of the National Physical Laboratory in Teddington, England, said there were three possibilities: Either the experimenters have made a mistake, the calculations used in determining the size of the proton are wrong or, potentially most exciting and disturbing, the standard model has some kind of problem [Los Angeles Times].
But the big story this week in Nature is that we might have been wrong all along in estimating something very basic about the humble proton: its size. A team from the Paul-Scherrer Institute in Switzerland that’s been tackling this for a decade says its arduous measurements of the proton show it is 4 percent smaller than the previous best estimate. For something as simple as the size of a proton, one of the basic measurements upon with the standard model of particle physics is built, 4 percent is a vast expanse that could shake up quantum electrodynamics if it’s true.
If the [standard model] turns out to be wrong, “it would be quite revolutionary. It would mean that we know a lot less than we thought we knew,” said physicist Peter J. Mohr of the National Institute of Standards and Technology in Gaithersburg, Md., who was not involved in the research. “If it is a fundamental problem, we don’t know what the consequences are yet” [Los Angeles Times].
Simply, the long-standing value used for a proton’s radius is 0.8768 femtometers, (a femtometer equals one quadrillionth of a meter). But the study team found it to be 0.84184 femtometers. How’d they make their measurement? First, think of the standard picture of electrons orbiting around a proton:
According to quantum mechanics, an electron can orbit only at certain specific distances, called energy levels, from its proton. The electron can jump up to a higher energy level if a particle of light hits it, or drop down to a lower one if it lets some light go. Physicists measure the energy of the absorbed or released light to determine how far one energy level is from another, and use calculations based on quantum electrodynamics to transform that energy difference into a number for the size of the proton [Wired.com].
That was how physicists derived their previous estimate, using simple hydrogen atoms. But this team relied on muons instead of electrons. Muons are 200 times heavier than electrons; they orbit closer to protons and are more sensitive to the proton’s size. However, they don’t last long and there aren’t many of them, so the team had to be quick:
The team knew that firing a laser at the atom before the muon decays should excite the muon, causing it to move to a higher energy level—a higher orbit around the proton. The muon should then release the extra energy as x-rays and move to a lower energy level. The distance between these energy levels is determined by the size of the proton, which in turn dictates the frequency of the emitted x-rays [National Geographic].
Thus, they should have seen the specific frequency related to the accepted size of a proton. Just one problem: The scientists didn’t see that frequency. Instead, their x-ray readings corresponded to the 4-percent-smaller size.
Now the task at hand is to check whether this study is somehow flawed, or is in fact a finding that will shake up physics.
In an editorial accompanying the report in the journal Nature, physicist Jeff Flowers of the National Physical Laboratory in Teddington, England, said there were three possibilities: Either the experimenters have made a mistake, the calculations used in determining the size of the proton are wrong or, potentially most exciting and disturbing, the standard model has some kind of problem [Los Angeles Times].
Black Holes - What Are Black Holes and How Do They Form?
Often the subject of science fiction novels, black holes are mysterious objects that, while very real, have a certain mythology that surrounds them. Some of these myths actually arise out of scientific truth, while others are the result of wild imagination. So what is fact and what is fiction? And where do black holes come from anyway?
What Is a Black Hole?
Simply put, a black hole is a region of space that is so incredibly dense that not even light can escape from the surface. However, it is this fact that often leads to miss-understanding. Black holes, strictly speaking, don't have any greater gravitational reach than any other star of the same mass. If our Sun suddenly became a black hole of the same mass the rest of the objects, including Earth, would be unaffected gravitationally. The Earth would remain in its current orbit, as would the rest of the planets. (Of course other things would be affected, such as the amount of light and heat that Earth received. So we would still be in trouble, but we wouldn't get sucked into the black hole.)
There is a region of space surrounding the black hole from where light can not escape, hence the name. The boundary of this region is known as the event horizon, and it is defined as the point where the escape velocity from the gravitational field is equal to the speed of light. The calculation of the radial distance to this boundary can become quite complicated when the black hole is rotating and/or is charged.
For the simplest case (a non-rotating, charge neutral black hole), the entire mass of the black hole would be contained within the event horizon (a necessary requirement for all black holes). The event horizon radius (Rs) would then be defined as Rs = 2GM/c2.
How Do Black Holes Form?
This is actually somewhat of a complex question, namely because there are different types of black holes. The most common type of black holes are known as stellar mass black holes as they are roughly up to a few times the mass of our Sun. These types of black holes are formed when large main sequence stars (10 - 15 times the mass of our Sun) run out of nuclear fuel in their cores. The result is a massive supernova explosion, leaving a black hole core behind where the star once existed.
The two other types of black holes are supermassive black holes -- black holes with masses millions or billions times the mass of the Sun -- and micro black holes -- black holes with extremely small masses, perhaps as small as 20 micrograms. In both cases the mechanisms for their creation is not entirely clear. Micro black holes exist in theory, but have not been directly detected. While supermassive black holes are found to exist in the cores of most galaxies.
While it is possible that supermassive black holes result from the merger of smaller, stellar mass black holes and other matter, it is possible that they form from the collapse of a single, extremely high mass star. However, no such star has ever been observed.
Meanwhile, micro black holes would be created during the collision of two very high energy particles. It is thought that this happens continuously in the upper atmosphere of Earth, and is likely to happen in particle physics experiments such as CERN. But no need to worry, we are not in danger.
How Do We Know Black Holes Exist If We Can't "See" Them?
Since light can not escape from the region around a black hole bound by the event horizon, it is not possible to directly "see" a black hole. However, it is possible to observe these objects by their effect on their surroundings.
Black holes that are near other objects will have a gravitational effect on them. Going back to the earlier example, suppose that our Sun became a black hole of one solar mass. An alien observer somewhere else in the galaxy studying our solar system would see the planets, comets and asteroids orbiting a central point. They would deduce that the planets and other objects were bound in their orbits by a one solar mass object. Since they would see no such star, the object would correctly be identified as a black hole.
Another way that we observe black holes is by utilizing another property of black holes, specifically that they, like all massive objects, will cause light to bend -- due to the intense gravity -- as it passes by. As stars behind the black hole move relative to it, the light emitted by them will appear distorted, or the stars will appear to move in an unusual way. From this information the position and mass of the black hole can be determined.
There is another type of black hole system, known as a microquasar. These dynamic objects consist of a stellar mass black hole in a binary system with another star, usually a large main sequence star. Due to the immense gravity of the black hole, matter from the companion star is funneled off onto a disk surrounding the black hole. This material then heats up as it begins to fall into the black hole through a process called accretion. The result is the creation of X-rays that we can detect using telescopes orbiting the Earth.
Hawking Radiation
The final way that we could possibly detect a black hole is through a mechanism known as Hawking radiation. Named for the famed theoretical physicist and cosmologist Stephen Hawking, Hawking radiation is a consequence of thermodynamics that requires that energy escape from a black hole.
The basic (perhaps oversimplified) idea is that, due to natural interactions and fluctuations in the vacuum (the very fabric of space time if you will), matter will be created in the form of an electron and anti-electron (called a positron). When this occurs near the event horizon, one particle will be ejected away from the black hole, while the other will fall into the gravitational well.
To an observer, all that is "seen" is a particle being emitted from the black hole. The particle would be seen as having positive energy. Meaning, by symmetry, that the particle that fell into the black hole would have negative energy. The result is that as a black hole ages it looses energy, and therefore loses mass (by Einstein's famous equation, E=Mc2).
Ultimately, it is found that black holes will eventually completely decay unless more mass is accreted. And it is this same phenomenon that is responsible for the short lifetimes expected by micro black holes.
What Is a Black Hole?
Simply put, a black hole is a region of space that is so incredibly dense that not even light can escape from the surface. However, it is this fact that often leads to miss-understanding. Black holes, strictly speaking, don't have any greater gravitational reach than any other star of the same mass. If our Sun suddenly became a black hole of the same mass the rest of the objects, including Earth, would be unaffected gravitationally. The Earth would remain in its current orbit, as would the rest of the planets. (Of course other things would be affected, such as the amount of light and heat that Earth received. So we would still be in trouble, but we wouldn't get sucked into the black hole.)
There is a region of space surrounding the black hole from where light can not escape, hence the name. The boundary of this region is known as the event horizon, and it is defined as the point where the escape velocity from the gravitational field is equal to the speed of light. The calculation of the radial distance to this boundary can become quite complicated when the black hole is rotating and/or is charged.
For the simplest case (a non-rotating, charge neutral black hole), the entire mass of the black hole would be contained within the event horizon (a necessary requirement for all black holes). The event horizon radius (Rs) would then be defined as Rs = 2GM/c2.
How Do Black Holes Form?
This is actually somewhat of a complex question, namely because there are different types of black holes. The most common type of black holes are known as stellar mass black holes as they are roughly up to a few times the mass of our Sun. These types of black holes are formed when large main sequence stars (10 - 15 times the mass of our Sun) run out of nuclear fuel in their cores. The result is a massive supernova explosion, leaving a black hole core behind where the star once existed.
The two other types of black holes are supermassive black holes -- black holes with masses millions or billions times the mass of the Sun -- and micro black holes -- black holes with extremely small masses, perhaps as small as 20 micrograms. In both cases the mechanisms for their creation is not entirely clear. Micro black holes exist in theory, but have not been directly detected. While supermassive black holes are found to exist in the cores of most galaxies.
While it is possible that supermassive black holes result from the merger of smaller, stellar mass black holes and other matter, it is possible that they form from the collapse of a single, extremely high mass star. However, no such star has ever been observed.
Meanwhile, micro black holes would be created during the collision of two very high energy particles. It is thought that this happens continuously in the upper atmosphere of Earth, and is likely to happen in particle physics experiments such as CERN. But no need to worry, we are not in danger.
How Do We Know Black Holes Exist If We Can't "See" Them?
Since light can not escape from the region around a black hole bound by the event horizon, it is not possible to directly "see" a black hole. However, it is possible to observe these objects by their effect on their surroundings.
Black holes that are near other objects will have a gravitational effect on them. Going back to the earlier example, suppose that our Sun became a black hole of one solar mass. An alien observer somewhere else in the galaxy studying our solar system would see the planets, comets and asteroids orbiting a central point. They would deduce that the planets and other objects were bound in their orbits by a one solar mass object. Since they would see no such star, the object would correctly be identified as a black hole.
Another way that we observe black holes is by utilizing another property of black holes, specifically that they, like all massive objects, will cause light to bend -- due to the intense gravity -- as it passes by. As stars behind the black hole move relative to it, the light emitted by them will appear distorted, or the stars will appear to move in an unusual way. From this information the position and mass of the black hole can be determined.
There is another type of black hole system, known as a microquasar. These dynamic objects consist of a stellar mass black hole in a binary system with another star, usually a large main sequence star. Due to the immense gravity of the black hole, matter from the companion star is funneled off onto a disk surrounding the black hole. This material then heats up as it begins to fall into the black hole through a process called accretion. The result is the creation of X-rays that we can detect using telescopes orbiting the Earth.
Hawking Radiation
The final way that we could possibly detect a black hole is through a mechanism known as Hawking radiation. Named for the famed theoretical physicist and cosmologist Stephen Hawking, Hawking radiation is a consequence of thermodynamics that requires that energy escape from a black hole.
The basic (perhaps oversimplified) idea is that, due to natural interactions and fluctuations in the vacuum (the very fabric of space time if you will), matter will be created in the form of an electron and anti-electron (called a positron). When this occurs near the event horizon, one particle will be ejected away from the black hole, while the other will fall into the gravitational well.
To an observer, all that is "seen" is a particle being emitted from the black hole. The particle would be seen as having positive energy. Meaning, by symmetry, that the particle that fell into the black hole would have negative energy. The result is that as a black hole ages it looses energy, and therefore loses mass (by Einstein's famous equation, E=Mc2).
Ultimately, it is found that black holes will eventually completely decay unless more mass is accreted. And it is this same phenomenon that is responsible for the short lifetimes expected by micro black holes.
Extra Dimensions Ten Billion Times Smaller Than An Atom
From the quest for the most fundamental particles of matter to the mysteries of dark matter, supersymmetry, and extra dimensions, many of nature’s greatest puzzles are being probed at the Large Hadron Collider. Results from the LHC is expected to rewrite physics textbooks. Below are some of the questions to which scientists are seeking fundamental answers about the nature of the Universe, including are there dimensions that we cannot yet detect.
What is the form of the universe?
Physicists created the Standard Model to explain the form of the universe—the fundamental particles, their properties, and the forces that govern them. The predictions of this tried-and-true model have repeatedly proven accurate over the years. However, there are still questions left unanswered. For this reason, physicists have theorized many possible extensions to the Standard Model. Several of these predict that at higher collision energies, like those at the LHC, we will encounter new particles like the Z', pronounced " Z prime." It is a theoretical heavy boson whose discovery could be useful in developing new physics models. Depending on when and how we find a Z' boson, we will be able to draw more conclusions about the models it supports, whether they involve superstrings, extra dimensions, or a grand unified theory that explains everything in the universe. Whatever physicists discover beyond the Standard Model will open new frontiers for exploring the nature of the universe.
What is the universe made of?
Since the 1930s, scientists have been aware that the universe contains more than just regular matter. In fact, only a little over 4 percent of the universe is made of the matter that we can see. Of the remaining 96 percent, about 23 percent is dark matter and everything else is dark energy, a mysterious substance that creates a gravitational repulsion responsible for the universe’s accelerating expansion. One theory regarding dark matter is that it is made up of the as-yet-unseen partners of the particles that make up regular matter. In a supersymmetric universe, every ordinary particle has one of these superpartners. Experiments at the LHC may find evidence to support or reject their existence.
Are there extra dimensions?
We experience three dimensions of space. However, the theory of relativity states that space can expand, contract, and bend. It’s possible, therefore, that we encounter only three spatial dimensions because they’re the only ones our size enables us to see, while other dimensions are so tiny that they are effectively hidden. Extra dimensions are integral to several theoretical models of the universe; string theory, for example, suggests as many as seven extra dimensions of space. The LHC is sensitive enough to detect extra dimensions ten billion times smaller than an atom. Experiments like ATLAS and CMS are hoping to gather information about how many other dimensions exist, what particles are associated with them, and how they are hidden.
(Editor's note: the most powerful microscopes now in existence can see into the upper picometer range (trillionths of a meter; nanotechnology is measured in nanometers or billionths of a meter about the size of a hydrogen atom.)
What are the most basic building blocks of matter?
Particle physicists hope to explain the makeup of the universe by understanding it from its smallest, most basic parts. Today, the fundamental building blocks of the universe are believed to be quarks and leptons; however, some theorists believe that these particles are not fundamental after all. The theory of compositeness, for example, suggests that quarks are composed of even smaller particles. Efforts to look closely at quarks and leptons have been difficult. Quarks are especially challenging, as they are never found in isolation but instead join with other particles to form hadrons, such as the protons that collide in the LHC. With the LHC’s high energy levels, scientists hope to collect enough data about quarks to reveal whether anything smaller is hidden inside.
Why do some particles have mass?
Through the theory of relativity, we know that particles moving at the speed of light have no mass, while particles moving slower than light speed do have mass. Physicists theorize that the omnipresent Higgs field slows some particles to below light speed, and thus imbues them with mass. We can’t study the Higgs field directly, but it is possible that an accelerator could excite this field enough to "shake loose" Higgs boson particles, which physicists should be able to detect. After decades of searching, physicists believe that they are close to producing collisions at the energy level needed to detect Higgs bosons.
What is the form of the universe?
Physicists created the Standard Model to explain the form of the universe—the fundamental particles, their properties, and the forces that govern them. The predictions of this tried-and-true model have repeatedly proven accurate over the years. However, there are still questions left unanswered. For this reason, physicists have theorized many possible extensions to the Standard Model. Several of these predict that at higher collision energies, like those at the LHC, we will encounter new particles like the Z', pronounced " Z prime." It is a theoretical heavy boson whose discovery could be useful in developing new physics models. Depending on when and how we find a Z' boson, we will be able to draw more conclusions about the models it supports, whether they involve superstrings, extra dimensions, or a grand unified theory that explains everything in the universe. Whatever physicists discover beyond the Standard Model will open new frontiers for exploring the nature of the universe.
What is the universe made of?
Since the 1930s, scientists have been aware that the universe contains more than just regular matter. In fact, only a little over 4 percent of the universe is made of the matter that we can see. Of the remaining 96 percent, about 23 percent is dark matter and everything else is dark energy, a mysterious substance that creates a gravitational repulsion responsible for the universe’s accelerating expansion. One theory regarding dark matter is that it is made up of the as-yet-unseen partners of the particles that make up regular matter. In a supersymmetric universe, every ordinary particle has one of these superpartners. Experiments at the LHC may find evidence to support or reject their existence.
Are there extra dimensions?
We experience three dimensions of space. However, the theory of relativity states that space can expand, contract, and bend. It’s possible, therefore, that we encounter only three spatial dimensions because they’re the only ones our size enables us to see, while other dimensions are so tiny that they are effectively hidden. Extra dimensions are integral to several theoretical models of the universe; string theory, for example, suggests as many as seven extra dimensions of space. The LHC is sensitive enough to detect extra dimensions ten billion times smaller than an atom. Experiments like ATLAS and CMS are hoping to gather information about how many other dimensions exist, what particles are associated with them, and how they are hidden.
(Editor's note: the most powerful microscopes now in existence can see into the upper picometer range (trillionths of a meter; nanotechnology is measured in nanometers or billionths of a meter about the size of a hydrogen atom.)
What are the most basic building blocks of matter?
Particle physicists hope to explain the makeup of the universe by understanding it from its smallest, most basic parts. Today, the fundamental building blocks of the universe are believed to be quarks and leptons; however, some theorists believe that these particles are not fundamental after all. The theory of compositeness, for example, suggests that quarks are composed of even smaller particles. Efforts to look closely at quarks and leptons have been difficult. Quarks are especially challenging, as they are never found in isolation but instead join with other particles to form hadrons, such as the protons that collide in the LHC. With the LHC’s high energy levels, scientists hope to collect enough data about quarks to reveal whether anything smaller is hidden inside.
Why do some particles have mass?
Through the theory of relativity, we know that particles moving at the speed of light have no mass, while particles moving slower than light speed do have mass. Physicists theorize that the omnipresent Higgs field slows some particles to below light speed, and thus imbues them with mass. We can’t study the Higgs field directly, but it is possible that an accelerator could excite this field enough to "shake loose" Higgs boson particles, which physicists should be able to detect. After decades of searching, physicists believe that they are close to producing collisions at the energy level needed to detect Higgs bosons.
Sunday, 25 April 2010
Dark matter may give neutron stars black hearts
DARK matter may be prompting black holes to appear spontaneously in the hearts of distant exotic stars. If so, this could hint at the nature of dark matter.
Arnaud de Lavallaz and Malcolm Fairbairn of King's College London wondered what would happen when dark matter - which makes up most of the mass of galaxies - is sucked into the heart of neutron stars. These stars, the remnants of supernova explosions, are the densest known stars in the universe. It turns out that the outcome depends on the nature of dark matter.
Most of the favoured theories of dark matter suggest each particle of the stuff is also an antiparticle, meaning that they should annihilate each other when they meet. But Fairbairn and de Lavallaz considered a dark matter particle of a different type, which is not also its antiparticle.
The pair calculated what would happen if dark matter particles like these were attracted by the intense gravity of neutron stars. Because they would not annihilate each other, the dark matter particles would end up forming a smaller, dense star at the heart of the neutron star. If the neutron star were near the centre of the galaxy, for example, and surrounded by an abundance of dark matter, then it would continue to accrete dark matter.
Eventually, the mass of the dark matter star would exceed its "Chandrasekhar limit" - beyond which a star cannot withstand gravitational pressure. The dark matter star would collapse into a black hole. "Then the neutron star won't be able to survive anymore, and it'll collapse too," says Fairbairn. "It would be pretty catastrophic."
Their calculations show that if a neutron star collapsed in this way the result would be a burst of gamma rays, which could be spotted from Earth (arxiv.org/abs/1004.0629).
Various underground experiments back on Earth have been trying to detect dark matter, using different techniques. While none of the major experiments have seen anything yet, physicists running the Dark Matter (DAMA) experiment inside the Gran Sasso mountain in Italy have been saying for some time that dark matter particles are hitting their detector. Most physicists are sceptical of the DAMA results because it doesn't sit well with favoured theories on the nature of dark matter.
Fairbairn says that the DAMA experiment could be sensitive to dark matter particles that do not self-annihilate, which might explain why it is seeing something and others are not.
Dan Hooper of Fermilab in Batavia, Illinois, agrees the pair's scenario is plausible because the existence of dark matter particles that do not self-annihilate cannot be ruled out. "We could look for evidence that neutron stars don't live very long in regions with a lot of dark matter," he says. "I find exciting the prospect of using exotic stars as dark matter detectors."
http://www.newscientist.com/article/mg20627564.900-dark-matter-may-give-neutron-stars-black-hearts.html?DCMP=OTC-rss&nsref=physics-math
Physicists find a particle accelerator in the sky
The first evidence that thunderstorms can function as huge natural particle accelerators has been collected by an international team of researchers.
In a presentation at a meeting of the Royal Astronomical Society in Glasgow last week, Martin Füllekrug of Bath University described how the team detected radio waves coinciding with the appearance of "sprites" – glowing orbs that occasionally flicker into existence above thunderstorms. The radio waves suggest the sprites can accelerate nearby electrons, creating a beam with the same power as a small nuclear power plant.
"The discovery of the particle accelerator allows [one] to apply the knowledge gained in particle physics to the real world, and put the expected consequences to experimental testing," Füllekrug told physicsworld.com.
An old idea
The idea of natural particle accelerators existing just kilometres above our heads first came in 1925, when the UK physicist and Nobel laureate Charles Wilson investigated the effects of a thundercloud's electric field. Wilson claimed that the electric field would cause an electrical breakdown of the Earth's atmosphere above the cloud, leading to transient phenomena such as sprites.
These sprites, physicists suggested, would do more than just light up the sky. As highly energetic particles or "cosmic rays" from space bombard our atmosphere, they strip air molecules of their outer electrons. In the presence of a sprite's electric field, these electrons could be forced upward in a narrow beam from the troposphere to near-Earth space. Moreover, the changing electron current would, via Maxwell's equations, produce electromagnetic waves in the radio-frequency range.
In 1998 Füllekrug's colleague Robert Roussel-Dupré of Los Alamos National Laboratory in New Mexico, US, used a supercomputer to simulate these radio waves. The simulations predicted they would come in pulses with a fairly flat spectrum – contrary to the electromagnetic spectrum of the lightning itself, which increases at lower frequencies.
Predictions confirmed
In 2008, while a group of European scientists timed the arrival of sprites from a mountain top in the French Pyrenées, Füllekrug was on the ground with a purpose-built radio-wave detector. The signals he detected coincided with the sprites and matched the characteristics of Roussel-Dupré's predictions.
"It's intriguing to see that nature creates particle accelerators just a few miles above our heads," says Füllekrug, adding: "They provide a fascinating example of the interaction between the Earth and the wider universe."
Füllekrug notes that he has no particular applications in mind for a sky-based particle accelerator, although he believes there may be wider implications for science. Researchers have many questions about the middle atmosphere because it is so difficult to set up observational platforms there. But by employing what physicists have learned about how such electron beams interact with matter, researchers could use this phenomenon to study this part of the atmosphere.
Indeed, we might be hearing a lot more about natural particle accelerators in the near future. The IBUKI satellite from Japan could soon be looking at the movement of charged particles in the atmosphere. In the next few years several missions – including CHIBIS from Russia and TARANIS from France – should provide more data about these accelerators.
http://physicsworld.com/cws/article/news/42368
Dwarf planets are not space potatoes
In 2006 there was an outcry from many astronomers when Pluto was stripped of its planetary status and renamed as a dwarf planet. The aggrieved feel that the distinction is rather arbitrary, especially as it is difficult to distinguish dwarf planets from other bodies in the solar system. Now, however, a pair of researchers are offering a more rigid definition by calculating the lower limit on the size of dwarf planets for the first time.
The IAU's definition of a planet is a celestial body that meets three strict criteria. First, it must be in orbit around the Sun. Second, it must have sufficient mass that its self-gravity overcomes other forces in the rigid body so that it assumes a nearly round shape. Finally, it must also have cleared the neighbourhood around its orbit by drawing in other space material with its gravitational field.
A dwarf planet meets all of these criteria except the last. Indeed, this was the downfall of Pluto, whose orbital path overlaps with other objects such as asteroids and the planet Neptune.
This categorization, however, does not sit happily with many astronomers who point out that Neptune also fails the test because of its overlap with Pluto. Furthermore, there is no agreement on how small dwarf planets can be, making it difficult to estimate the number of dwarf planets in the solar system.
Potato radius
In this latest research, Charles Lineweaver and Marc Norman at the Australian National University address this issue by deriving from first principles a lower limit on the radius of protoplanets. They calculate, using their new equation, that asteroids must have a radius of at least 300 km and icy moons must have a radius above 200 km for self-gravity to dominate and create spherical bodies. Below this radius, a balance between gravitational and electronic forces can create all sorts of shapes referred to as rounded potatoes.
The new categorization increases the number of bodies orbiting beyond those that should now be classified as "dwarf planets". Previously, astronomers had known the size of a lot of these bodies, but not whether they were spherical. "Measuring the shape of objects as a function of size can help us determine how hot these objects were when their shapes were set early in their formation," says Lineweaver.
Decaying beauty spied for first time by LHC
A rare, fleeting "beauty" particle has been spotted in the first run of the Large Hadron Collider (LHC).
The LHC started work on 30 March, and one of its four large detectors detected evidence of a beauty quark – also, less poetically, known as a bottom quark – on 5 April.
The find should be the first of many beauty decays that LHCb, the LHC's beauty experiment, will observe, and demonstrates the detector is working as planned.
This first recorded particle is a meson composed of an anti-beauty quark – the beauty quark's antiparticle – and an up quark – one of the two common quarks that make up protons and neutrons. While up quarks last for billions of years, the large beauty quarks swiftly decay into lower-energy particles in about 1.5 x 10-12 seconds.
After travelling only 2 millimetres in the accelerator, the beauty quark decayed to a lighter quark – still paired with the original up quark – and the extra energy was carried off in the form of electron-like particles called muons.
Extremely rare
"It's a very rare event – it's like a needle in a haystack," says Andreas Schopper, a spokesperson for LHCb. "In these 10 million data or so we find this one event."
The particle was detected by LHCb's automatic trigger system, which is designed to recognise unusual events or particles but to ignore the vast majority of proton collisions. Less than 1 per cent of the collisions will be of interest to LHCb scientists.
Once an event is recorded, the details of detector signals are sent out to computing centres on five continents, where over a few days software reconstructs particle tracks. "It is the teamwork of the collaboration," says Schopper. "This is the first time we have really detected and reconstructed such a big particle."
Back to the big bang
LHCb will look at many such decays in order to shed light on what happened to the antimatter that should have been created alongside the matter that makes up our universe.
The experiment is designed to examine what happens to beauty quarks, which form in high-energy explosions – not least the big bang. By comparing the decay products of beauty quarks, LHC researchers hope to find clues as to why our universe seems to favour matter over antimatter.
"While precision measurements will need many millions of beauty particles, as with kisses, the first is always very special," says Jürgen Schukraft, spokesperson for the LHC's ALICE experiment. "It shows that the detector is up to its task, performing very well in identifying the complex decay pattern."
The LHC started work on 30 March, and one of its four large detectors detected evidence of a beauty quark – also, less poetically, known as a bottom quark – on 5 April.
The find should be the first of many beauty decays that LHCb, the LHC's beauty experiment, will observe, and demonstrates the detector is working as planned.
This first recorded particle is a meson composed of an anti-beauty quark – the beauty quark's antiparticle – and an up quark – one of the two common quarks that make up protons and neutrons. While up quarks last for billions of years, the large beauty quarks swiftly decay into lower-energy particles in about 1.5 x 10-12 seconds.
After travelling only 2 millimetres in the accelerator, the beauty quark decayed to a lighter quark – still paired with the original up quark – and the extra energy was carried off in the form of electron-like particles called muons.
Extremely rare
"It's a very rare event – it's like a needle in a haystack," says Andreas Schopper, a spokesperson for LHCb. "In these 10 million data or so we find this one event."
The particle was detected by LHCb's automatic trigger system, which is designed to recognise unusual events or particles but to ignore the vast majority of proton collisions. Less than 1 per cent of the collisions will be of interest to LHCb scientists.
Once an event is recorded, the details of detector signals are sent out to computing centres on five continents, where over a few days software reconstructs particle tracks. "It is the teamwork of the collaboration," says Schopper. "This is the first time we have really detected and reconstructed such a big particle."
Back to the big bang
LHCb will look at many such decays in order to shed light on what happened to the antimatter that should have been created alongside the matter that makes up our universe.
The experiment is designed to examine what happens to beauty quarks, which form in high-energy explosions – not least the big bang. By comparing the decay products of beauty quarks, LHC researchers hope to find clues as to why our universe seems to favour matter over antimatter.
"While precision measurements will need many millions of beauty particles, as with kisses, the first is always very special," says Jürgen Schukraft, spokesperson for the LHC's ALICE experiment. "It shows that the detector is up to its task, performing very well in identifying the complex decay pattern."
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