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Aurora

An aurora, sometimes referred to as a polar light or northern light, is a natural light display in the sky, predominantly seen in the high latitude 

Most auroras occur in a band known as the auroral zone, which is typically 3° to 6° wide in latitude and between 10° and 20° from the geomagnetic poles at all local times (or longitudes), most clearly seen at night against a dark sky. A region that currently displays an aurora is called the auroral oval, a band displaced towards the nightside of the Earth. Early evidence for a geomagnetic connection comes from the statistics of auroral observations. Elias Loomis (1860), and later Hermann Fritz (1881) and S. Tromholt (1882) in more detail, established that the aurora appeared mainly in the auroral zone. Day-to-day positions of the auroral ovals are posted on the internet.

A geomagnetic storm causes the auroral ovals (north and south) to expand, and bring the aurora to lower latitudes. It was hardly ever seen near the geographic pole, which is about 2000 km away from the magnetic pole. The instantaneous distribution of auroras ("auroral oval")[3] is slightly different, being centered about 3–5 degrees nightward of the magnetic pole, so that auroral arcs reach furthest toward the equator when the magnetic pole in question is in between the observer and the Sun. The aurora can be seen best at this time, which is called magnetic midnight.

Auroras seen within the auroral oval may be directly overhead, but from farther away they illuminate the poleward horizon as a greenish glow, or sometimes a faint red, as if the Sun were rising from an unusual direction. Auroras also occur poleward of the auroral zone as either diffuse patches or arcs, which can be sub-visual.

Causes of auroras

A quiescent solar wind flowing past the Earth’s magnetosphere steadily interacts with it and can both inject solar wind particles directly onto the geomagnetic field lines that are ‘open’, as opposed to being ‘closed’ in the opposite hemisphere, and provide diffusion through the bow shock. It can also cause particles already trapped in the radiation belts to precipitate into the atmosphere. Once particles are lost to the atmosphere from the radiation belts, under quiet conditions new ones replace them only slowly, and the loss-cone becomes depleted. In the magnetotail, however, particle trajectories seem constantly to reshuffle, probably when the particles cross the very weak magnetic field near the equator. As a result, the flow of electrons in that region is nearly the same in all directions ("isotropic"), and assures a steady supply of leaking electrons. The leakage of electrons does not leave the tail positively charged, because each leaked electron lost to the atmosphere is replaced by a low energy electron drawn upward from the ionosphere. Such replacement of "hot" electrons by "cold" ones is in complete accord with the 2nd law of thermodynamics. The complete process, which also generates an electric ring current around the Earth, is uncertain.

Colors of auroras

1. Red: At the highest altitudes, excited atomic oxygen emits at 630.0 nm (red); low concentration of atoms and lower sensitivity of eyes at this wavelength make this color visible only under more intense solar activity. The low amount of oxygen atoms and their gradually diminishing concentration is responsible for the faint appearance of the top parts of the "curtains". Scarlet, crimson, and carmine are the most often-seen hues of red for the auroras.

2. Green: At lower altitudes the more frequent collisions suppress the 630.0 nm (red) mode: rather the 557.7 nm emission (green) dominates. Fairly high concentration of atomic oxygen and higher eye sensitivity in green make green auroras the most common. The excited molecular nitrogen (atomic nitrogen being rare due to high stability of the N2 molecule) plays a role here, as it can transfer energy by collision to an oxygen atom, which then radiates it away at the green wavelength. (Red and green can also mix together to produce pink or yellow hues.) The rapid decrease of concentration of atomic oxygen below about 100 km is responsible for the abrupt-looking end of the lower edges of the curtains. Both the 557.7 and 630.0 nm wavelengths correspond to forbidden transitions of atomic oxygen, slow mechanism that is responsible for the graduality (0.7 s and 107 s respectively) of flaring and fading.

3. Blue: At yet lower altitudes, atomic oxygen is uncommon, and molecular nitrogen and ionized molecular nitrogen takes over in producing visible light emission; radiating at a large number of wavelengths in both red and blue parts of the spectrum, with 428 nm (blue) being dominant. Blue and purple emissions, typically at the lower edges of the "curtains", show up at the highest levels of solar activity. The molecular nitrogen transitions are much faster than the atomic oxygen ones.

4. Ultraviolet: Ultraviolet light from auroras (within the optical window but not visible to virtually all humans) has been observed with the requisite equipment. Ultraviolet auroras have also been seen on Mars, Jupiter and Saturn.
Infrared: Infrared light, in wavelengths that are within the optical window, is also part of many auroras.

5. Yellow and pink are a mix of red and green or blue. Other shades of red as well as orange may be seen on rare occasions; yellow-green is moderately common. As red, green, and blue are the primary colours of additive synthesis of colours, in theory practically any colour might be possible but the ones mentioned in this article comprise a virtually exhaustive list.

Standard Model

The Standard Model explains how the basic building blocks of matter interact, governed by four fundamental forces

The theories and discoveries of thousands of physicists since the 1930s have resulted in a remarkable insight into the fundamental structure of matter: everything in the universe is found to be made from a few basic building blocks called fundamental particles, governed by four fundamental forces. Our best understanding of how these particles and three of the forces are related to each other is encapsulated in the Standard Model of particle physics. Developed in the early 1970s, it has successfully explained almost all experimental results and precisely predicted a wide variety of phenomena. Over time and through many experiments, the Standard Model has become established as a well-tested physics theory.
Matter particles

All matter around us is made of elementary particles, the building blocks of matter. These particles occur in two basic types called quarks and leptons. Each group consists of six particles, which are related in pairs, or “generations”. The lightest and most stable particles make up the first generation, whereas the heavier and less stable particles belong to the second and third generations. All stable matter in the universe is made from particles that belong to the first generation; any heavier particles quickly decay to the next most stable level. The six quarks are paired in the three generations – the “up quark” and the “down quark” form the first generation, followed by the “charm quark” and “strange quark”, then the “top quark” and “bottom (or beauty) quark”. Quarks also come in three different “colours” and only mix in such ways as to form colourless objects. The six leptons are similarly arranged in three generations – the “electron” and the “electron neutrino”, the “muon” and the “muon neutrino”, and the “tau” and the “tau neutrino”. The electron, the muon and the tau all have an electric charge and a sizeable mass, whereas the neutrinos are electrically neutral and have very little mass.

Forces and carrier particles


There are four fundamental forces at work in the universe: the strong force, the weak force, the electromagnetic force, and the gravitational force. They work over different ranges and have different strengths. Gravity is the weakest but it has an infinite range. The electromagnetic force also has infinite range but it is many times stronger than gravity. The weak and strong forces are effective only over a very short range and dominate only at the level of subatomic particles. Despite its name, the weak force is much stronger than gravity but it is indeed the weakest of the other three. The strong force, as the name suggests, is the strongest of all four fundamental interactions.
Three of the fundamental forces result from the exchange of force-carrier particles, which belong to a broader group called “bosons”. Particles of matter transfer discrete amounts of energy by exchanging bosons with each other. Each fundamental force has its own corresponding boson – the strong force is carried by the “gluon”, the electromagnetic force is carried by the “photon”, and the “W and Z bosons” are responsible for the weak force. Although not yet found, the “graviton” should be the corresponding force-carrying particle of gravity. The Standard Model includes the electromagnetic, strong and weak forces and all their carrier particles, and explains well how these forces act on all of the matter particles. However, the most familiar force in our everyday lives, gravity, is not part of the Standard Model, as fitting gravity comfortably into this framework has proved to be a difficult challenge. The quantum theory used to describe the micro world, and the general theory of relativity used to describe the macro world, are difficult to fit into a single framework. No one has managed to make the two mathematically compatible in the context of the Standard Model. But luckily for particle physics, when it comes to the minuscule scale of particles, the effect of gravity is so weak as to be negligible. Only when matter is in bulk, at the scale of the human body or of the planets for example, does the effect of gravity dominate. So the Standard Model still works well despite its reluctant exclusion of one of the fundamental forces.

So far so good, but...


...it is not time for physicists to call it a day just yet. Even though the Standard Model is currently the best description there is of the subatomic world, it does not explain the complete picture. The theory incorporates only three out of the four fundamental forces, omitting gravity. There are also important questions that it does not answer, such as “What is dark matter?”, or “What happened to the antimatter after the big bang?”, “Why are there three generations of quarks and leptons with such a different mass scale?” and more. Last but not least is a particle called the Higgs boson, an essential component of the Standard Model.
On 4 July 2012, the ATLAS and CMS experiments at CERN's Large Hadron Collider (LHC) announced they had each observed a new particle in the mass region around 126 GeV. This particle is consistent with the Higgs boson but it will take further work to determine whether or not it is the Higgs boson predicted by the Standard Model. The Higgs boson, as proposed within the Standard Model, is the simplest manifestation of the Brout-Englert-Higgs mechanism. Other types of Higgs bosons are predicted by other theories that go beyond the Standard Model.
On 8 October 2013 the Nobel prize in physics was awarded jointly to François Englert and Peter Higgs "for the theoretical discovery of a mechanism that contributes to our understanding of the origin of mass of subatomic particles, and which recently was confirmed through the discovery of the predicted fundamental particle, by the ATLAS and CMS experiments at CERN's Large Hadron Collider."
So although the Standard Model accurately describes the phenomena within its domain, it is still incomplete. Perhaps it is only a part of a bigger picture that includes new physics hidden deep in the subatomic world or in the dark recesses of the universe. New information from experiments at the LHC will help us to find more of these missing pieces.

XJ1500+0154: Black Hole Meal Sets Record for Duration and Size

• A supermassive black hole in a small galaxy 1.8 billion light years away has been partaking in a decade-long binge of a star.


• This is known as a tidal disruption event and happens when an object gets too close to a black hole and is torn apart by gravity.


• Other similar events have been seen before but this one is much longer, representing an unusually massive meal.


• A trio of orbiting X-ray telescopes, including Chandra, was used to make this discovery.

XJ1500+0154 Black Hole

A trio of X-ray observatories has captured a remarkable event in their data: a decade-long binge by a black hole almost two billion light years away. This discovery was made using data from NASA's Chandra X-ray Observatory, Swift Observatory, and ESA's XMM-Newton, as reported in our press release.

This artist's illustration depicts what astronomers call a "tidal disruption event," or TDE. This is when an object, such as a star, wanders too close to a black hole and is destroyed by tidal forces generated from the black hole's intense gravitational forces. During a TDE, some of the stellar debris is flung outward at high speeds, while the rest (shown as the red material in the illustration) becomes hotter as it falls toward the black hole, generating a distinct X-ray flare. A wind blowing away from this infalling material is shown in blue.

Among observed TDEs, this event involved either the most massive star to be completely ripped apart and devoured by a black hole or the first instance where a smaller star was completely ripped apart. The resulting X-ray source is known as XJ1500+154 and is located in a small galaxy about 1.8 billion light years from Earth. The optical image in the left inset shows this galaxy and a cross to mark the location of XJ1500+0154. This image reveals that XJ1500+0154 is found in the center of the galaxy, implying that the source likely originates from a supermassive black hole that resides there. The image on the right shows XJ1500+0154 in the Chandra image covering the same field.

The source was not detected in a Chandra observation on April 2, 2005, but was detected in an XMM-Newton observation on July 23, 2005, and reached peak brightness in a Chandra observation on June 5, 2008. These observations show that the source became at least 100 times brighter in X-rays. Since then, Chandra, Swift, and XMM-Newton have observed it multiple times.

The X-ray data also indicate that radiation from material surrounding this black hole has consistently surpassed the so-called Eddington limit, defined by a balance between the outward pressure of radiation from the hot gas and the inward pull of the gravity of the black hole.

This TDE may help answer the question as to how supermassive black holes in the early universe grow. If supermassive black holes can grow, from TDEs or other means, at rates above those corresponding to the Eddington limit, this could explain how supermassive black holes were able to reach masses about a billion times higher than the sun when the universe was only about a billion years old.

A paper describing these results appears in the February 6th issue of Nature Astronomy. The authors are Dacheng Lin (University of New Hampshire), James Guillochon (Harvard-Smithsonian Center for Astrophysics), Stefanie Komossa (QianNan Normal University for Nationalities), Enrico Ramirez-Ruiz (University of California, Santa Cruz), Jimmy Irwin (University of Alabama), Peter Maksym (Harvard-Smithsonian), Dirk Grupe (Morehead State University), Olivier Godet (CNRS), Natalie Webb (CNRS), Didier Barret (CNRS), Ashley Zauderer (New York University), Pierre-Alain Duc (CEA-Saclay), Eleazar Carrasco (Gemini Observatory), and Stephen Gwyn (Herzberg Institute of Astrophysics).

NASA's Marshall Space Flight Center in Huntsville, Alabama, manages the Chandra program for NASA's Science Mission Directorate in Washington. The Smithsonian Astrophysical Observatory in Cambridge, Massachusetts, controls Chandra's science and flight operations.

Wormhole

A wormhole is a theoretical passage through space-time that could create shortcuts for long journeys across the universe. Wormholes are predicted by the theory of general relativity. But be wary: wormholes bring with them the dangers of sudden collapse, high radiation and dangerous contact with exotic matter.

In 1935, physicists Albert Einstein and Nathan Rosen used the theory of general relativity to propose the existence of "bridges" through space-time. These paths, called Einstein-Rosen bridges or wormholes, connect two different points in space-time, theoretically creating a shortcut that could reduce travel time and distance.

Wormholes contain two mouths, with a throat connecting the two. The mouths would most likely be spheroidal. The throat might be a straight stretch, but it could also wind around, taking a longer path than a more conventional route might require.

Einstein's theory of general relativity mathematically predicts the existence of wormholes, but none have been discovered to date. A negative mass wormhole might be spotted by the way its gravity affects light that passes by.

Certain solutions of general relativity allow for the existence of wormholes where the mouth of each is a black hole. However, a naturally occurring black hole, formed by the collapse of a dying star, does not by itself create a wormhole.

Further, "A wormhole is not really a means of going back in time, it's a short cut, so that something that was far away is much closer," NASA's Eric Christian wrote.

The equations of the theory of general relativity have valid solutions that contain wormholes. The first type of wormhole solution discovered was the Schwarzschild wormhole, which would be present in the Schwarzschild metric describing an eternal black hole, but it was found that it would collapse too quickly for anything to cross from one end to the other. Wormholes that could be crossed in both directions, known as traversable wormholes, would only be possible if exotic matter with negative energy density could be used to stabilize them. Wormholes are also a very powerful mathematical metaphor for teaching general relativity.

The Casimir effect shows that quantum field theory allows the energy density in certain regions of space to be negative relative to the ordinary vacuum energy, and it has been shown theoretically that quantum field theory allows states where energy can be arbitrarily negative at a given point. Many physicists, such as Stephen Hawking, Kip Thorne and others, therefore argue that such effects might make it possible to stabilize a traversable wormhole. Physicists have not found any natural process that would be predicted to form a wormhole naturally in the context of general relativity, although the quantum foam hypothesis is sometimes used to suggest that tiny wormholes might appear and disappear spontaneously at the Planck scale, and stable versions of such wormholes have been suggested as dark matter candidates. It has also been proposed that, if a tiny wormhole held open by a negative mass cosmic string had appeared around the time of the Big Bang, it could have been inflated to macroscopic size by cosmic inflation.

HIGGS BOSSON PARTICLE(AKA GOD PARTICLE)

The UNIVERSE is supposed to originate from an event called "Big Bang". All the particles including the sub-atomic particles are supposed to be originated from the same event. In layman’s terms, different subatomic particles are responsible for giving matter different properties. One of the most mysterious and important properties is mass. Some particles, like protons and neutrons, have mass. Others, like photons, do not. The Higgs boson, or “God particle,” is believed to be the particle which gives mass to matter. The “God particle” nickname grew out of the long, drawn-out struggles of physicists to find this elusive piece of the cosmic puzzle.

The “standard model” of particle physics is a system that attempts to describe the forces, components, and reactions of the basic particles that make up matter. It not only deals with atoms and their components, but the pieces that compose some subatomic particles. This model does have some major gaps, including gravity, and some experimental contradictions. The standard model is still a very good method of understanding particle physics, and it continues to improve. The model predicts that there are certain elementary particles even smaller than protons and neutrons. As of the date of this writing, the only particle predicted by the model which has not been experimentally verified is the “Higgs boson,” jokingly referred to as the “God particle.”

Each of the subatomic particles contributes to the forces that cause all matter interactions. One of the most important, but least understood, aspects of matter is mass. Science is not entirely sure why some particles seem mass-less, like photons, and others are “massive.” The standard model predicts that there is an elementary particle, the Higgs boson, which would produce the effect of mass. Confirmation of the Higgs boson would be a major milestone in our understanding of physics.

The “God particle” nickname actually arose when the book The God Particle: If the Universe Is the Answer, What Is the Question? by Leon Lederman was published. Since then, it’s taken on a life of its own, in part because of the monumental questions about matter that the God particle might be able to answer. The man who first proposed the Higgs boson’s existence, Peter Higgs, isn’t all that amused by the nickname “God particle,” as he’s an avowed atheist. All the same, there isn’t really any religious intention behind the nickname.

Currently, efforts are under way to confirm the Higgs boson using the Large Hadron Collider, a particle accelerator in Switzerland, which should be able to confirm or refute the existence of the God particle. As with any scientific discovery, God’s amazing creation becomes more and more impressive as we learn more about it. Either result—that the Higgs boson exists, or does not exist—represents a step forward in human knowledge and another step forward in our appreciation of God’s awe-inspiring universe. Whether or not there is a “God particle,” we know this about Christ: “For by him all things were created: things in heaven and on earth, visible and invisible . . . all things were created by him and for him” 

FRB 1221102(continued)

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Astronomers have for the first time pinpointed the location of a "fast radio burst" - a type of short-duration radio flash of unknown astrophysical origin - and have used this to identify its home galaxy. The galaxy, located over 3 billion light years away, is small, a so-called dwarf galaxy, and very different to our own Milky Way. Also, a persistent, compact radio source is close to the source of the bursts, which provides important insights into its astrophysical origin. The results from an international team, including Laura Spitler from the Max-Planck-Institute for Radio Astronomy in Bonn, Germany, appear today in three publications in Nature and the Astrophysical Journal Letters.

Zoom Image

A number of radio telescopes were used within the European VLBI Network (EVN) to observe FRB 121102 (artist’s impression).

A number of radio telescopes were used within the European VLBI Network (EVN) to observe FRB 121102 (artist’s impression).

Fast Radio Bursts (FRBs) are visible for only a fraction of a second, and have puzzled astronomers since their discovery a decade ago.  Precise localization of an FRB requires radio telescopes separated by large distances, which allow high resolution images to be made when these telescopes are used in combination with each other. Such follow-up observations were made possible with the first discovery of a repeating source of fast radio bursts, FRB 121102, using the 305-m Arecibo Radio Telescope in Puerto Rico, USA.

Prior to this discovery, astronomers had only indirect evidence that fast radio bursts come from far outside our Milky Way galaxy, because poor localization has prevented them from uniquely identifying their galaxy of origin. The new finding is critical because it has also allowed astronomers to precisely measure the distance to the source, and hence how much energy it is producing.

The Very Large Array in New Mexico, USA detected a total of nine radio bursts from FRB 121102. This determined its sky position to a fraction of an arc second, over 200 times more precise than previous measurements. “Near this position, astronomers found both steady radio and optical sources, which pointed the way to the galaxy hosting the FRB,” says Shami Chatterjee from Cornell University, the first author of the paper in “Nature”.

The team was able to zoom-in on the radio sources with a factor of 10 more precision using the Arecibo Radio Telescope and the European VLBI Network (EVN), which links telescopes spread across the world.  "With a bit of luck, we were able to detect bursts from FRB 121102 with the EVN and now we know that the origin of the bursts is right on top of the persistent radio source", says Benito Marcote from JIVE in the Netherlands.  The 100-m radio telescope in Effelsberg, Germany, is the largest and most sensitive member of the EVN. "Bursts from this source are faint, and Effelsberg played a key role in making this discovery possible," says Laura Spitler, postdoctoral researcher at the Max-Planck-Institute for Radio Astronomy (MPIfR), who discovered FRB 121102.

The team used one of the world's largest optical telescopes, the 8-m Gemini North on Mauna Kea in Hawaii, to discover that the bursts originate from a host galaxy, and use its measured spectrum to obtain a redshift value which places the source at a whopping distance of over 3 billion light-years. "This gives us incontrovertible confirmation that this FRB originates very deep in extragalactic space,” says co-author Cees Bassa (ASTRON). Though the mystery of the FRB’s distance is now solved, astronomers have a new puzzle on their hands. The galaxy hosting the FRB is surprisingly small - a so-called dwarf galaxy.

The fact that FRB 121102 is hosted by a dwarf galaxy may be a vital clue to its physical nature.  Such galaxies contain gas that is relatively pristine compared to that found in the Milky Way.  "The conditions in this dwarf galaxy are such that it may be possible to form much more massive stars than in the Milky Way, and perhaps the source of the FRB bursts is from the collapsed remnant of such a star," suggests co-author Jason Hessels (ASTRON, University of Amsterdam).

Alternatively, astronomers are considering a very different hypothesis in which the FRB bursts are generated in the vicinity of a massive black hole that is swallowing surrounding gas, a so-called active galactic nucleus.

To try and differentiate between these two scenarios, astronomers are continuing to study FRB 121102 using the world's premier radio, optical, X-ray and gamma-ray telescopes.  "For example, if we can find a periodicity to the arrival of the bursts, then we will have strong evidence that it originates from a rotating neutron star", says Laura Spitler.

Deciphering the origin of the FRBs will also depend on localizing more such sources, and astronomers are debating whether all FRBs detected to date are of a similar physical origin or whether there are multiple classes of this new cosmic phenomenon.

The 100-m Effelsberg Radio Telescope of the Max Planck Institute for Radio Astronomy is located in a valley approximately 40 kilometers southwest of Bonn, Germany.

The European VLBI Network (EVN) is a collaboration of the major radio astronomical institutes in Europe, Asia and South Africa and performs high angular resolution observations of cosmic radio sources.

The 305-m William E. Gordon Telescope of the Arecibo Observatory is located close to Arecibo in Puerto Rico, USA.

The Karl G. Jansky Very Large Array consists of 27 radio antennas in a Y-shaped configuration on the Plains of San Agustin fifty miles west of Socorro, New Mexico, USA. Each antenna is 25 meters (82 feet) in diameter.