Physics Archives

November 2, 2009April 26, 2016 by Nancy Atkinson

Solving the Mystery of Cosmic Rays’ Origins

What accelerates cosmic rays to nearly the speed of light? Astronomer have pondered that question for nearly 100 years, and now new evidence supports a theory held for two decades that cosmic rays likely are powered by exploding stars and stellar winds. “This discovery has been predicted for almost 20 years, but until now no instrument was sensitive enough to see it,” said Wystan Benbow, an astrophysicist at the Smithsonian Astrophysical Observatory who coordinated this project for the Very Energetic Radiation Imaging Telescope Array System (VERITAS) collaboration.

Nearly 100 years ago, scientists detected the first signs of cosmic rays, which are actually not rays or beams but subatomic particles (mostly protons) that zip through space at nearly the speed of light. The most energetic cosmic rays hit with the punch of a 98-mph fastball, even though they are smaller than an atom. Astronomers questioned what natural force could accelerate particles to such a speed.

The rarest cosmic rays carry over 100 billion times as much energy as generated by any particle accelerator on Earth. Astronomers have devised ingenious methods for detecting cosmic rays that hit Earth’s atmosphere. However, detecting cosmic rays from a distance requires much more effort.

This representative-color figure shows the very-high-energy gamma-ray emission observed by VERITAS coming from the Cigar Galaxy, also known as Messier 82. The black star is the location of the active starburst region. The emission from M82 is effectively point-like for VERITAS, and the white circle indicates the size of a simulated point source. The entire galaxy would be contained within the circle. Credit: CfA/V.A. Acciari

VERITAS has found new evidence for cosmic rays in the “Cigar Galaxy,” also known as Messier 82 (M82), which is located 12 million light-years from Earth in the direction of the constellation Ursa Major, which strongly support the long-held theory that supernovae and stellar winds from massive stars are the dominant accelerators of cosmic-ray particles.

Galaxies with high levels of star formation like M82, also known as “starburst” galaxies, have large numbers of supernovae and massive stars. If the theory holds, then starburst galaxies should contain more cosmic rays than normal galaxies. The VERITAS discovery confirms that expectation, indicating that the cosmic-ray density in M82 is approximately 500 times the average density in our Galaxy, the Milky Way.

“This discovery provides fundamental insight into the origin of cosmic rays,” said Rene Ong, a professor of physics at the University of California, Los Angeles, and the spokesperson for the VERITAS collaboration.

Using gamma rays to infer cosmic rays

VERITAS could not detect M82’s cosmic rays directly because they are trapped within the Cigar Galaxy. Instead, VERITAS looked for clues to the presence of cosmic rays: gamma rays. Gamma rays are the most energetic form of light, far more powerful than ultraviolet light or even X-rays. When cosmic rays interact with interstellar gas and radiation within M82, they produce gamma rays, which can then escape their home galaxy and reach Earthbound detectors.

It took two years of dedicated data collection to tease out the faint signal coming from M82.

“We knew that the detection of M82 would have important scientific implications. As a result, we scheduled an exceptionally long exposure immediately after the experiment became fully operational” said Benbow. “The data needed to be meticulously analyzed to extract the gamma-ray signal, which is over a million times smaller than the background noise. Although the signal is only a tiny fraction of the data, we made many checks for possible bias and we are confident that the signal is genuine.”

“The detection of M82 indicates that the universe is full of natural particle accelerators, and as ground-based gamma-ray observatories continue to improve, further discoveries are inevitable.” said Martin Pohl, a professor of physics at Iowa State University who helped lead the study. A next-generation VHE gamma-ray observatory, the Advanced Gamma-ray Imaging System (AGIS), is already under development.

VERITAS is operated by a collaboration of more than 100 scientists from 22 different institutions in the United States, Ireland, England and Canada. Click here for more information on VERITAS.

Lead image caption: A composite of multi-wavelength images of the active galaxy M82 from Hubble, Chandra, and Spitzer. Credit: NASA, ESA, CXC, and JPL-Caltech

Source: Harvard Smithsonian Center for Astrophysics

October 28, 2009December 24, 2015 by Nancy Atkinson

Particles Injected into Large Hadron Collider

The first ion beam entering point 2 of the LHC, just before the ALICE detector (23 October 2009). Credit: CERN

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The Large Hadron Collider reached an important milestone last weekend as a beam of ions was injected into the clockwise beam pipe. This is the first time particles have been inside the collider since September, 2008 when physicists were forced to shut down the system because of a massive failure. According to a CERN press release, lead ions were placed in the clockwise beam pipe on Friday October 23, but did not travel along the whole circumference of the LHC. CERN officials still hope for a restart in 2009, with the first circulating beam likely to be injected in mid-November, and the first high energy collisions occurring around mid-December.

CERN said that later last Friday the first beam of protons followed the same route — and then on Saturday protons were sent through the LHCb detector.

They reported all settings and parameters showed a perfect functioning of the machine. In the coming weeks, physicists hope to have the first circulating beam. Then hunt for the elusive Higgs particle will recommence.

Here is an interview with CERN director general Rolf-Dieter Heuer about the switch-on of the LHC.

Sources: CERN, Physics World

October 23, 2009December 24, 2015 by Nancy Atkinson

Your CCD Camera Just Won a Nobel Prize

Charged Coupled Devices (CCD) for Ultra-Violet and Visible Detection. Credit: NASA

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Well, actually, the people who invented the first successful imaging technology using a digital sensor, called a CCD (Charge-Coupled Device), have been awarded the Nobel Prize in Physics. In 1969 Willard S. Boyle and George E. Smith came up with the idea “from their own heads,” Smith said, and CCDs revolutionized photography, as light could now be captured electronically instead of on film, and became an irreplaceable tool in astronomy, providing new possibilities to visualize the previously unseen. The device also made it possible for amateur astronomers to rival the professionals in terms of quality astrophotography. CCD technology is also used in many medical applications, e.g. imaging the inside of the human body, both for diagnostics and for microsurgery. Sharing the prize with Boyle and Smith is Charles K. Kao, who in 1966 made a discovery that led to a breakthrough in fiber optics.

Both achievements helped shape the foundations of today’s networked societies.

September 1, 2009December 24, 2015 by Nancy Atkinson

New Way to Measure Curvature of Space Could Unite Gravity Theory

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Einstein’s general theory of relativity describes gravity in terms of the geometry of both space and time. Far from a source of gravity, such as a star like our sun, space is “flat” and clocks tick at their normal rate. Closer to a source of gravity, however, clocks slow down and space is curved. But measuring this curvature of space is difficult. However, scientists have now used a continent-wide array of radio telescopes to make an extremely precise measurement of the curvature of space caused by the Sun’s gravity. This new technique promises to contribute greatly in studying quantum physics.

“Measuring the curvature of space caused by gravity is one of the most sensitive ways to learn how Einstein’s theory of General Relativity relates to quantum physics. Uniting gravity theory with quantum theory is a major goal of 21st-Century physics, and these astronomical measurements are a key to understanding the relationship between the two,” said Sergei Kopeikin of the University of Missouri.

Kopeikin and his colleagues used the National Science Foundation’s Very Long Baseline Array (VLBA) radio-telescope system to measure the bending of light caused by the Sun’s gravity to within one part in ~~30,000~~ 3,333 (corrected by NRAO and updated here on 9/03/09 — see this link provided by Ned Wright of UCLA for more information on deflection and delay of light). With further observations, the scientists say their precision technique can make the most accurate measure ever of this phenomenon.

Bending of starlight by gravity was predicted by Albert Einstein when he published his theory of General Relativity in 1916. According to relativity theory, the strong gravity of a massive object such as the Sun produces curvature in the nearby space, which alters the path of light or radio waves passing near the object. The phenomenon was first observed during a solar eclipse in 1919.

Though numerous measurements of the effect have been made over the intervening 90 years, the problem of merging General Relativity and quantum theory has required ever more accurate observations. Physicists describe the space curvature and gravitational light-bending as a parameter called “gamma.” Einstein’s theory holds that gamma should equal exactly 1.0.

“Even a value that differs by one part in a million from 1.0 would have major ramifications for the goal of uniting gravity theory and quantum theory, and thus in predicting the phenomena in high-gravity regions near black holes,” Kopeikin said.

To make extremely precise measurements, the scientists turned to the VLBA, a continent-wide system of radio telescopes ranging from Hawaii to the Virgin Islands. The VLBA offers the power to make the most accurate position measurements in the sky and the most detailed images of any astronomical instrument available.

Sun's Path in Sky in Front of Quasars, 2005. Credit: NRAO

The researchers made their observations as the Sun passed nearly in front of four distant quasars — faraway galaxies with supermassive black holes at their cores — in October of 2005. The Sun’s gravity caused slight changes in the apparent positions of the quasars because it deflected the radio waves coming from the more-distant objects.

The result was a measured value of gamma of 0.9998 +/- 0.0003, in excellent agreement with Einstein’s prediction of 1.0.

“With more observations like ours, in addition to complementary measurements such as those made with NASA’s Cassini spacecraft, we can improve the accuracy of this measurement by at least a factor of four, to provide the best measurement ever of gamma,” said Edward Fomalont of the National Radio Astronomy Observatory (NRAO). “Since gamma is a fundamental parameter of gravitational theories, its measurement using different observational methods is crucial to obtain a value that is supported by the physics community,” Fomalont added.

Kopeikin and Fomalont worked with John Benson of the NRAO and Gabor Lanyi of NASA’s Jet Propulsion Laboratory. They reported their findings in the July 10 issue of the Astrophysical Journal.

Source: NRAO

July 19, 2009May 8, 2017 by John Carl Villanueva

What is Entropy?

After some time, this cold glass will reach thermal equilibrium

Perhaps there’s no better way to understand entropy than to grasp the second law of thermodynamics, and vice versa. This law states that the entropy of an isolated system that is not in equilibrium will increase as time progresses until equilibrium is finally achieved.

Let’s try to elaborate a little on this equilibrium thing. Note that in the succeeding examples, we’ll assume that they’re both isolated systems.

First example. Imagine putting a hot body and a cold body side by side. What happens after some time? That’s right. They both end up in the same temperature; one that is lower than the original temperature of the hotter one and higher than the original temperature of the colder one.

Second example. Ever heard of a low pressure area? It’s what weather reporters call a particular region that’s characterized by strong winds and perhaps some rain. This happens because all fluids flow from a region of high pressure to a region of low pressure. Thus, when the fluid, air in this case, comes rushing in, they do so in the form of strong winds. This goes on until the pressures in the adjacent regions even out.

In both cases, the physical quantities which started to be uneven between the two bodies/regions even out in the end, i.e., when equilibrium is achieved. The measurement of the extent of this evening-out process is called entropy.

During the process of attaining equilibrium, it is possible to tap into the system to perform work, as in a heat engine. Notice, however, that work can only be done for as long as there is a difference in temperature. Without it, like when maximum entropy has already been achieved, there is no way that work can be performed.

Since the concept of entropy applies to all isolated systems, it has been studied not only in physics but also in information theory, mathematics, as well as other branches of science and applied science.

Because the accepted view of the universe is that of one that is finite, then it can very well be considered as a closed system. As such, it should also be governed by the second law of thermodynamics. Thus, like in all isolated systems, the entropy of the universe is expected to be increasing.

So what? Well, also just like all isolated systems, the universe is therefore also expected to end up in a useless heap in equilibrium, a.k.a. a heat death, wherein energy can no longer be extracted from anymore. To give you some relief, not everyone involved in the study of cosmology is totally in agreement with entropy’s so-called role in the grand scheme of things though.

You can read more about entropy here in Universe Today. Want to know why time might flow in one direction? Have you ever thought about the time before the Big Bang? The entire entropy concept plays an important role in understanding them.

There’s more about entropy at NASA and Physics World too. Here are a couple of sources there:

Here are two episodes at Astronomy Cast that you might want to check out as well:

Source:
Hyperphysics

June 4, 2009December 24, 2015 by Brian Ventrudo

What If There Is Only One Universe?

When it comes to universes, perhaps one is enough after all.

Many theories in physics and cosmology require the existence of alternate, or parallel, universes. But Dr. Lee Smolin of the Perimeter Institute for Theoretical Physics in Waterloo, Canada, explains the flaws of theories that suggest our universe is just one of many, and which also perpetuate the notion that time does not exist. Smolin, author of the bestselling science book ‘The Trouble with Physics’ and a founding member of the Perimeter Institute, explains his views in the June issue of Physics World.

Smolin explains how theories describing a myriad of possible universes, or a “multiverse”, with many dimensions and particles and forces have become more popular in the last few years. However, through his work with the Brazilian philosopher Roberto Mangabeira Unger, Smolin believes that multiverse theories, which imply that time is not a fundamental concept, are “profoundly mistaken”.

Smolin says a timeless multiverse means our laws of physics can’t be determined from experiment. And he explains the unclear connection between fundamental laws, which are unique and applicable universally, and effective laws, which hold based on what we can actually observe.

Smolin suggests new principles that rethink the notion of physical law to apply to a single universe. These principles say there is only one universe; that all that is real is real in a moment, as part of a succession of moments; and that everything real in each moment is a process of change leading to future moments. As he explains, “If there is just one universe, there is no reason for a separation into laws and initial conditions, as we want a law to explain just one history of one universe.”

He hopes these principles will bring a fresh adventure in science.

If we accept there is only one universe and that time is a fundamental property of nature, then this opens up the possibility that the laws of physics evolve with time. As Smolin writes, “The notion of transcending our time-bound experiences in order to discover truths that hold timelessly is an unrealizable fantasy. When science succeeds, we do nothing of the sort; what we physicists really do is discover laws that hold in the universe we experience within time. This, I would claim, should be enough; anything beyond that is more a religious urge for transcendence than science.”

Source: Institute of Physics

May 14, 2009December 24, 2015 by Nancy Atkinson

Is Everything Made of Mini Black Holes?

In 1971 physicist Stephen Hawking suggested that there might be “mini” black holes all around us that were created by the Big Bang. The violence of the rapid expansion following the beginning of the Universe could have squeezed concentrations of matter to form miniscule black holes, so small they can’t even be seen in a regular microscope. But what if these mini black holes were everywhere, and in fact, what if they make up the fabric of the universe? A new paper from two researchers in California proposes this idea.

Black holes are regions of space where gravity is so strong that not even light can escape, and are usually thought of as large areas of space, such as the supermassive black holes at the center of galaxies. No observational evidence of mini-black holes exists but, in principle, they could be present throughout the Universe.

Since black holes have gravity, they also have mass. But with mini black holes, the gravity would be weak. However, many physicists have assumed that even on the tiniest scale, the Planck scale, gravity regains its strength.

Experiments at the Large Hadron Collider are aimed at detecting mini black holes, but suffer from not knowing exactly how a reduced-Planck-mass black hole would behave, say Donald Coyne from UC Santa Cruz (now deceased) and D. C. Cheng from the Almaden Research Center near San Jose.

String theory also proposes that gravity plays a stronger role in higher dimensional space, but it is only in our four dimensional space that gravity appears weak.

Since these dimensions become important only on the Planck scale, it’s at that level that gravity re-asserts itself. And if that’s the case, then mini-black holes become a possibility, say the two researchers.

They looked at what properties black holes might have at such a small scale, and determined they could be quite varied.

Black holes lose energy and shrink in size as they do so, eventually vanishing, or evaporating. But this is a very slow process and only the smallest back holes will have had time to significantly evaporate over the enter 14 billion year history of the universe.

The quantization of space on this level means that mini-black holes could turn up at all kinds of energy levels. They predict the existence of huge numbers of black hole particles at different energy levels. And these black holes might be so common that perhaps “All particles may be varying forms of stabilized black holes.”

“At first glance the scenario … seems bizarre, but it is not,” Coyne and Cheng write. “This is exactly what would be expected if an evaporating black hole leaves a remnant consistent with quantum mechanics… This would put a whole new light on the process of evaporation of large black holes, which might then appear no different in principle from the correlated decays of elementary particles.”

They say their research need more experimentation. This may come from the LHC, which could begin to probe the energies at which these kinds of black holes will be produced.

Original paper.

Source: Technology Review

May 4, 2009December 24, 2015 by Nancy Atkinson

Is a Nearby Object in Space Beaming Cosmic Rays at Earth?

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Data from several different space and ground based observatories imply the presence of a nearby object that is beaming cosmic rays our way. Scientists with the Fermi Space Telescope say an unknown pulsar may be close by, sending electrons and positrons towards Earth. Or another more exotic explanation is that the particles could come from the annihilation of dark matter. But whatever it is, the source is relatively close, surely in our galaxy. “If these particles were emitted far away, they’d have lost a lot of their energy by the time they reached us,” said Luca Baldini, a Fermi collaborator.

Comparing data from the Fermi space telescope with results from the PAMELA spacecraft and the High Energy Stereoscopic System (H.E.S.S.) ground-based telescope, the three observatories have found surprisingly more particles with energies greater than 100 billion electron volts (100 GeV) than expected based on previous experiments and traditional models.

Fermi is primarily a gamma ray detector, but its Large Area Telescope (LAT) is also tool for investigating the high-energy electrons in cosmic rays.

Video of the LAT detecting high energy particles.

Cosmic rays are hyperfast electrons, positrons, and atomic nuclei moving at nearly the speed of light. Unlike gamma rays, which travel from their sources in straight lines, cosmic rays wend their way around the galaxy. They can ricochet off of galactic gas atoms or become whipped up and redirected by magnetic fields. These events randomize the particle paths and make it difficult to tell where they originated. But determining cosmic-ray sources is one of Fermi’s key goals.

Using the LAT, which is sensitive to electrons and their antimatter counterparts, positrons, the telescope looked at the energies of 4.5 million cosmic rays that struck the detector between Aug. 4, 2008, and Jan. 31, 2009 and found more of the high-energy variety than expected, those with more than 1 billion electron volts (eV).

A spokesman from the Goddard Space Flight Center said the exact number of how many more is not currently available, due to peculiarities of the data.

But results from Fermi also refute other recent findings from a balloon-borne experiment. The Advanced Thin Ionization Calorimeter (ATIC) captured evidence for a dramatic spike in the number of cosmic rays at energies around 500 GeV from its high atmospheric location over Antarctica. But Fermi did not detect these energies.

“Fermi would have seen this sharp feature if it was really there, but it didn’t.” said Luca Latronico, a team member at the National Institute of Nuclear Physics (INFN) in Pisa, Italy. “With the LAT’s superior resolution and more than 100 times the number of electrons collected by balloon-borne experiments, we are seeing these cosmic rays with unprecedented accuracy.”

“Fermi’s next step is to look for changes in the cosmic-ray electron flux in different parts of the sky,” Latronico said. “If there is a nearby source, that search will help us unravel where to begin looking for it.”

Source: NASA

April 21, 2009December 24, 2015 by Nancy Atkinson

Do We Need a New Theory of Gravitation?

Draco satellite dwarf galaxy. Credit: Mischa Schirmer, University of Bonn

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A group of physicists say that the distribution of satellite galaxies that orbit the Milky Way, as well as the apparent dark matter within them, presents a direct challenge to Newton’s theory of gravitation, as the galaxies are not where they should be. “There is something odd about their distribution,” said Professor Pavel Kroupa from the University of Bonn in Germany. “They should be uniformly arranged around the Milky Way, but this is not what we found.” Standard cosmological models predict the presence of hundreds of these companions around most of the larger galaxies, but up to now only 30 have been observed around the Milky Way. The physicists say that Newton’s theory of gravitation should be modified.

The astronomers from Germany, Austria and Australia looked at the small dwarf galaxies that orbit the Milky Way and discovered that the eleven brightest of the dwarf galaxies lie more or less in the same plane – in a kind of disk shape – and that they revolve in the same direction around the Milky Way (in the same way as planets in the Solar System revolve around the Sun). Some of these contain only a few thousand stars and so are relatively faint and difficult to find.

Professor Kroupa and the other physicists believe that this can only be explained if today’s satellite galaxies were created by ancient collisions between young galaxies. Team member Dr. Manuel Metz said, “Fragments from early collisions can form the revolving dwarf galaxies we see today, but this introduces a paradox. Calculations suggest that the dwarf satellites cannot contain any dark matter if they were created in this way. But this directly contradicts other evidence. Unless the dark matter is present, the stars in the galaxies are moving around much faster than predicted by Newton’s standard theory of gravitation.”

Metz added, “The only solution is to reject Newton’s theory. If we live in a Universe where a modified law of gravitation applies, then our observations would be explainable without dark matter.”

With this evidence, the team share the convictions of a number of groups around the world who believe that some of the fundamental principles of physics have been incorrectly understood. If their ideas are correct, it will not be the first time that Newton’s theory of gravitation has been modified. In the 20th century it happened when Einstein introduced his Special and General Theories of Relativity and again when quantum mechanics was developed to explain physics on sub-atomic scales. The anomalies detected by Dr. Metz and Professor Kroupa and their collaborators imply that where weak accelerations predominate, a ‘modified Newtonian dynamic’ may have to be used. If the scientists are right then this has far-reaching consequences for our understanding of the Universe we live in.

The two studies will appear in papers in Monthly Notices of the Royal Astronomical Society and the Astrophysical Journal.

Source: RAS

Category: Physics