Physics Archives

July 27, 2008December 24, 2015 by Ian O'Neill

IBEX Mission Will View the Final Frontier of the Solar System

The heliopause is the frontier between the Solar System and the interstellar medium. Credit: NASA/JPL

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Space is far from empty. The Solar System can be viewed as a “bubble” of solar matter – filled with particles emitted by the Sun as the solar wind – extending well beyond the orbit of Pluto. The solar wind velocity is supersonic for most of this distance (exceeding a million miles per hour), but the point at which it begins to interact with the interstellar medium (ISM), the solar wind drops to subsonic velocities, creating a region of compression known as the termination shock. After 26 years of flight, the Voyager 1 deep space probe entered this bizarre, turbulent region of space, where solar particles build up and magnetic fields become twisted. Now a new mission has been designed to watch this region of space from afar to begin to understand the boundary of our solar system, where violent turbulence rules and high-energy atoms are generated…

In 2004, Voyager 1 hit it and in 2006, Voyager 2 hit it. The first probe flew through the termination shock at around 94 AU (8 billion miles away); the second measured it at only 76 AU (7 billion miles). This result alone suggests that the termination shock may be irregularly shaped and/or variable depending on solar activity. Before the Voyager missions, the termination shock was theorized, but there was little observational evidence until the two veteran probes traversed the region. The termination shock is of paramount importance to understanding the nature of the outer reaches of the solar system as, counter-intuitively, the Sun’s activity increases, the region beyond the termination shock (the heliosheath) becomes more efficient at blocking deadly cosmic rays. During solar minimum, it becomes less efficient at blocking cosmic rays.

Artist impression of Voyager 1, the first probe to traverse the heliosheath (NASA)

In an effort to map the location and characteristics of the termination shock and heliosheath beyond, NASA scientists are preparing the Interstellar Boundary Explorer (IBEX) for launch in October. IBEX is part of NASA’s Small Explorer program (SMEX), where inexpensive, small probes are used to efficiently observe particular cosmic phenomena. IBEX will be orbiting beyond the influence of the Earth’s magnetic field (the magnetosphere) at a 200,000 mile distance from the Earth. This is because the phenomenon IBEX will be observing can be generated by our own magnetic field. So what will IBEX be measuring? To understand the interaction between solar wind ions and the interstellar medium, IBEX will use two sensors to detect energetic neutral atoms (ENAs) being blasted from the outermost reaches of the solar system.

How are ENAs generated and how are they a measurement of the interaction between the heliosphere and the ISM? Out there in the ISM exists neutral atoms and ions. As the solar system passes through interstellar space, the strong magnetic field generated around the heliosphere deflects the charged ions, pushing them out of the way. However, slow-moving neutral atoms are not affected by the magnetic field and penetrate deep into the heliosheath. When this happens, these neutral atoms from the ISM interact with energetic protons (which do have charge) rapidly spiralling along the magnetic field embedded in the solar wind. When this interaction occurs (known as charge exchange), an electron is stripped from the ISM atom and attracted to the energetic solar wind proton, thus making it neutral. When this exchange occurs, an energetic hydrogen atom (electron and proton) is ejected. An ENA is born.

Now, this is where the clever bit comes in. As mentioned before, neutral atoms do not “feel” magnetic fields, so when ENAs are created they are ejected in a straight line. Some of these atoms will be directed toward the Earth. IBEX will then measure these ENAs and work out where they came from. As they will have travelled directly to IBEX, the location of the termination shock may be deduced. Over a period of time, IBEX will be able to build up a picture of the locations of these atomic interactions and relate them the characteristics of the boundary of our Solar System.

But the best thing is, we won’t need to send a probe into deep space and wait for decades before it traverses the boundary layer, we will be able to make these measurements from Earth orbit. Such an exciting mission. Roll on the Pegasus rocket launch October 5th, 2008!

Source: Physorg.com

July 10, 2008December 24, 2015 by Ian O'Neill

Particle Physicists Discover Lowest Energy “Bottomonium” Particle

During particle collisions, hadrons split into quarks and bosons (University of Oregon)

Particle physicists working with the BaBar detector at Stanford Linear Accelerator Center have discovered a new particle in the bottomonium family of “quarkonium” particles. Technically it isn’t a “new particle” it is a previously unobserved state of particle, but when we are talking about subatomic particles, their energy states become a big deal (and their names get very cool). We are in the realms of the vanishingly small and the discovery of the lowest energy bottomonium particle may not seem very significant. But in the world of quantum chromodynamics, this completes the long quest to find experimental evidence for this elusive meson and may help explain why there is more matter than anti-matter in the Universe…

Quarkonia are types of mesons containing two quarks: one quark and its anti-quark (they are therefore “colourless”). They belong to one of two families: “bottomonium” or “charmonium”. As the names suggest, bottomonium contains a bottom quark and anti-bottom quark; charmonium contains a charm quark and anti-charm quark. Groups of three quarks (interacting via the strong force) are baryons (i.e. protons and neutrons) whereas groups of two quarks are mesons. Mesons are all thought to be made from a quark-antiquark pair and are therefore of huge importance when studying why there is more matter than anti-matter in the Universe.

This is where the BaBar detector at the Stanford Linear Accelerator Center (SLAC), CA, comes in. The BaBar international collaboration investigates the behaviour of particles and anti-particles during the production of the bottomonium meson (bottom-antibottom quark pairs) in the aim of explaining why there is an absence of anti-particles in everyday life.

For each particle of matter there exists an equivalent particle with opposite quantum characteristics, called an anti-particle. Particle and anti-particle pairs can be created by large accumulations of energy and, conversely, when a particle meets an anti-particle they annihilate with intense blasts of energy. At the time of the big-bang, the large accumulation of energy must have created an equal amount of particles and anti-particles. But in everyday life we do not encounter anti-particles. The question, therefore, is “What has happened to the anti-particles?” – From the BaBar/SLAC collaboration pages.

All matter has a “ground state”, or the lowest energy the system is trying to attain. As particles for instance try to reach this ground state, they lose energy, often in the form of electromagnetic radiation. Once reached, the ground state determines the baseline at which measurements can be made for higher energy states of those particles. And this is what the BaBar team has done, they have been able to isolate the lowest possible energy state for the bottomonium particle (which is far from easy). So what have they named the ground state of bottomonium? Quite simply: Î·b, pronounced “eta-sub-b“.

The bottomonium particle was generated during a collision between an electron and positron. The energy generated by this collision created a bottom quark and an anti-bottom quark bound together. At this point, the bottomonium particle was of too high an energy, but it very quickly decayed, emitting a gamma ray leaving the Î·b behind. However, Î·b’s are highly unstable and will quickly decay into other particles, plus they are very rare and difficult to detect. This particular decay event only occurs once in every two or three thousand higher energy bottomonium decays, so many collisions had to be measured and a huge amount of data had to be gathered by the BaBar detector before a precise measurement of the Î·b ground state could be gained.

“This very significant observation was made possible by the tremendous luminosity of the PEP-II accelerator and the great precision of the BaBar detector, which was so well calibrated over the BaBar experiment’s 8-plus years of operation. These results were highly sought after for over 30 years and will have an important impact on our understanding of the strong interactions.” – Hassan Jawahery, BaBar Spokesperson, University of Maryland.

If you want to find out more, you can check out the BaBar team’s publication (with the longest list of co-authors I’ve ever seen!) or the SLAC press release.

Source: SLAC

July 9, 2008December 24, 2015 by Ian O'Neill

Large Hadron Collider Could Generate Dark Matter

One of the biggest questions that occupy particle physicists and cosmologists alike is: what is dark matter? We know that a tiny fraction of the mass of the universe is the visible stuff we can see, but 23% of the Universe is made from stuff that we cannot see. The remaining mass is held in something called dark energy. But going back to the dark matter question, cosmologists believe their observations indicate the presence of darkmatter, and particle physicists believe the bulk of this matter could be held in quantum particles. This trail leads to the Large Hadron Collider (LHC) where the very small meets the very big, hopefully explaining what particles could be generated after harnessing the huge energies possible with the LHC…

The excitement is growing for the grand switch-on of the LHC later this summer. We’ve been following all the news releases, research possibilities and some of the more “out there” theories as to what the LHC is likely to discover, but my favourite bits of LHC news include the possibility of peering into other dimensions, creating wormholes, generating “unparticles” and micro-black holes. These articles are pretty extreme possibilities for the LHC, I suspect the daily running of the huge particle accelerator will be a little more mundane (although “mundane” in accelerator physics will still be pretty damn exciting!).

David Toback, professor at Texas A&M University in College Station, is very optimistic as to what discoveries the LHC will uncover. Toback and his team have written a model that uses data from the LHC to predict the quantity of dark matter left over after the Big Bang. After all, the collisions inside the LHC will momentarily recreate some of the conditions at the time of the birth of our Universe. If the Universe created dark matter over 14 billion years ago, then perhaps the LHC can do the same.

Should Toback’s team be correct in that the LHC can create dark matter, there will be valuable implications for both particle physics and cosmology. What’s more, quantum physicists will be a step closer to proving the validity of the supersymmetry model.

“If our results are correct we now know much better where to look for this dark matter particle at the LHC. We’ve used precision data from astronomy to calculate what it would look like at the LHC, and how quickly we should be able to discover and measure it. If we get the same answer, that would give us enormous confidence that the supersymmetry model is correct. If nature shows this, it would be remarkable.” – David Toback

So the hunt is on for dark matter production in the LHC… but what will we be looking for? After all dark matter is predicted to be non-interacting and, well, dark. The supersymmetry model predicts a possible dark matter particle called the neutralino. It is supposed to be a heavy, stable particle and should there be a way of detecting it, there could be the opportunity for Toback’s group to probe the nature of the neutralino not only in the detection chamber of the LHC, but the nature of the neutralino in the Universe.

“If this works out, we could do real, honest to goodness cosmology at the LHC. And we’d be able to use cosmology to make particle physics predictions.” – Toback

Source: Physorg.com

June 30, 2008December 24, 2015 by Ian O'Neill

Forget Neutron Stars, Quark Stars Might be the Densest Bodies in the Universe

The difference between a neutron star and a quark star (Chandra)

So neutron stars may not be the densest exotic objects in the cosmos after all. Recent observations of ultra-luminous supernovae suggest that these explosions may create an even more exotic remnant. Neutron stars can form after a star ends its life; measuring only 16 km across, these small but massive objects (one and a half times the mass of the Sun) may become too big for the structure of neutrons to hold it together. What happens if the structures of the neutrons inside a neutron star collapse? Quark stars (a.k.a. “Strange” stars) may be the result, smaller and denser than neutron stars, possibly explaining some abnormally bright supernovae observed recently…

Three very luminous supernovae have been observed and Canadian researchers are hot on the trail as to what may have caused them. These huge explosions occur at the point when a massive star dies, leaving a neutron star or black hole in their wake. Neutron stars are composed of neutron-degenerate matter and will often be observed as rapidly spinning pulsars emitting radio waves and X-rays. If the star was massive enough, a black hole might be formed after the detonation, but is there a phase between the mass of a neutron star and a black hole?

It appears there might be a smaller, more massive star on the block, a star composed not of hadrons (i.e. neutrons), but of the stuff that makes up hadrons: quarks. They are thought to be one step up the star-mass ladder, the point at which the mass of the supernova remnant is slightly too big to be a neutron star, but too small to form a black hole. They are composed of ultra-dense quark matter, and as neutrons break down it is thought some of their “up” and “down” quarks are converted into “strange” quarks, forming a state known as “strange matter.” It is for this reason that these compact objects are also known as strange stars.

Quark stars may be hypothetical objects, but the evidence is stacking up for their existence. For example, supernovae SN2005gj, SN2006gy and SN2005ap are all approximately 100 times brighter than the “standard model” for supernova explosions, leading the Canadian team to model what would happen if a heavy neutron star were to become unstable, crushing the neutrons into a soup of strange matter. Although these supernovae may have formed neutron stars, they became unstable and collapsed again, releasing vast amounts of energy from the hadron bonds creating a “Quark-Nova”, converting the oversized neutron star into a quark star.

If quark stars are behind these ultra-luminous supernovae, they may be viewed as super-sized hadrons, not held together by the nuclear strong force, but by gravity. Now there’s a thought!

Source: NSF

June 21, 2008December 24, 2015 by Ian O'Neill

Newsflash: The LHC Won’t Punch a Hole in the Earth After All…

Particle Collider — Today, CERN announced that the LHCb experiment had revealed the existence of two new baryon subatomic particles. Credit: CERN/LHC/GridPP

Its official: We’re not going to be blown up, smothered in stranglets, sucked into a black hole or turned into ooze by the Large Hadron Collider (LHC). To put any concerns to rest, CERN (the European Organization for Nuclear Research) has concluded in another approved safety report that the LHC is harmless and will not hurt us, our planet or the Universe. This new investigation builds on previous findings that the LHC is safe, reiterating what scientists have been telling us for years. Besides, the LHC isn’t doing anything that nature isn’t already doing every second…

I actually thought the LHC safety reports were done and dusted (the original report was actually completed in 2003), but it seems, to be thorough, CERN wanted to re-confirm their previous conclusions that the LHC was safe and ready for use later this year.

The LHC is understandably under intense scrutiny and will be subject to a range of audits from safety to environmental impact. This new report commissioned to investigate whether any of the theoretical particles created in the LHC collision chamber could pose a threat, not only to the cows and sheep in the Swiss countryside, but to the Earth and the Cosmos. Strengthened with experimental and observational research, the new report prepared by a team of physicists at CERN, UC Santa Barbara and the Institute for Nuclear Research of the Russian Academy of Sciences, has covered all the factors from previous safety investigations, and again concluded that the LHC is… safe.

As with any high-energy experiment, scientists and governments are under increased pressure to ensure every step is being taken to safeguard against any catastrophic accident. The LHC, soon to be the world’s most powerful particle accelerator, has seen more criticism than most physics experiments. For one, it is expensive (Â£2.4 billion or $4.7 billion), so collaborating governments and institutions want to know where their money is going, but second, CERN wants to avoid public misconceptions about what harm the LHC could do. This is epitomised in a recent lawsuit a Hawaiian man filed against CERN, citing the new accelerator might generate a black hole (that the Earth would get sucked into) or create a chain reaction, unleashing exotic “stranglets” on the planet. This is an extreme case of a misconception about what the LHC is capable of, so it seems essential that in-depth studies into LHC safety must be carried out continuously.

Listed is the safety reports perceived LHC threats (with likelihood of occurrence in parentheses):

Microscopic black holes (not very likely): Although it would be pretty cool if micro-black holes were generated, the report concludes that this event will be unlikely, although theoretically possible. If a micro-black hole was produced by an LHC collision, it is very likely that it would evaporate very quickly (via Hawking Radiation), making it difficult for any observation attempt. If a micro-black hole was produced but it didn’t evaporate (which isn’t possible, in theory), depending on its charge, it would behave differently. Charged, the micro-black hole could interact with matter and get stopped as it tries to pass through the Earth. Un-charged, the micro-black hole will pass straight through the Earth and into space (as it will be weakly interacting) or simply hang around inside our planet. We know collisions between cosmic rays and the Earth’s atmosphere happen naturally, often at higher energies than the LHC. Therefore, if micro-black holes are possible, the only option would be that they evaporate very quickly.. Besides, even if they were stable, they cannot suck in any matter and grow because they will have minimal gravitational influence over matter. Boring really…
Strangelets (practically impossible): This hypothetical “strange matter” (containing up, down and strange quarks) could theoretically change ordinary matter into strange matter in a thousand-millionth of a second. This possibility was raised in 2000 before the opening of the Relativistic Heavy Ion Collider (RHIC) in the US. This collider uses heavier particles than most of the LHC tests and therefore more likely to produce stranglets. In fact some of its experiments are set up to detect this strange matter. No stranglets have been found in eight years; not only that, but the chain reaction theorized (turning the world into a clump of strangeness) has no experimental foundation. Stranglets do not exist, and the LHC will not produce them.
Vacuum bubbles (practically impossible): Perhaps the Universe is not in its most stable configuration. Perturbations generated by the LHC could push it into a more stable state (a vacuum bubble), destroying the Universe as we know it. Not very likely. Again, collisions of higher energies happen throughout the cosmos, let alone in our own atmosphere, we’re still here, our Universe is still here (or is it?).
Magnetic monopoles (practically impossible): Hypothetical particles with a single magnetic pole, either north or south. If they could exist, they might mess around with protons possibly causing them to spontaneously decay. There is no reason to suspect they can exist, and even if they did, they could not be produced by the LHC as they are too heavy. Again, cosmic rays come to the rescue; as the high energy natural particle hit the atmosphere, their collisional energy is higher than the LHC. No magnetic monopoles, not end of the world.

Is that all there is? Surely there are more new and inventive ways to destroy the planet? Oh well…

So, it looks like we are in the clear for the grand switch on of the LHC! And now, you can have a ring-side seat, watching all the operations at the LHC via the array of webcams CERN has up and running:

Source: CERN

June 7, 2008April 26, 2016 by Ian O'Neill

Can a Wormhole Generate its Own Magnetic Field?

Artist impression of what it could look like when entering a wormhole (http://en.wikipedia.org/wiki/Image:FY221c15.png)

Wormholes are a strange consequence of Einstein’s theory of general relativity. These “shortcuts” through the fabric of space and time may link two different locations in the universe; they may even connect two different universes together. This also leads to the possibility that wormholes can allow travel between two points in time. These strange entities have provided science fiction stories with material for many years, but there is credible physics behind wormholes. Now it seems that in theory slowly-rotating wormholes may be able to generate their own magnetic field. Could this be used to detect the presence of wormholes in our observable Universe?

In a previous Universe Today article, I found some interesting research about the possibility of observing a wormhole using sensitive radio telescopes. What’s more, an observer may be able to see the light from another part of the Universe that has travelled along the wormhole and then emitted through the wormhole’s mouth. An observer could expect to see a bubble-like sphere floating in space, with emitted light intensifying around the rim.

In a publication last month, Mubasher Jamil and Muneer Ahmad Rashid from the National University of Sciences and Technology in Pakistan investigates the properties of a slowly rotating wormhole and the effect this would have on a surrounding volume of space. Their calculations assume a cloud of charged particles (i.e. electrons) are gravitationally attracted to the entity, and as the wormhole rotates, it drags the cloud of electrons with it. This approach had already been carried out when considering the effects of a slowly rotating compact star on surrounding stellar plasma.

This gravitational effect is known as “frame-dragging”. As the wormhole is predicted to have a gravitational influence on the space surrounding it, Einstein’s general relativity predicts that space-time will be warped. The best way to visualize this is to imagine a heavy ball on an elastic sheet; the ball causes the sheet to stretch downward, in a cone-shape. If the ball is spun on the sheet, friction between the ball and elastic will cause the sheet to distort in another way, it will begin to twist out of shape. If you apply this idea to space-time (the elastic sheet), and you have a slowly rotating wormhole (the ball), distortions in space-time will have a dragging effect on the surrounding particles, causing them to spin with the wormhole.

This is where Jamil and Rashid’s paper steps in. If you have a rotating mass of charged particles, a magnetic field may be generated (as a consequence of Maxwell’s equations). Therefore, in theory, a slowly-rotating wormhole could have its own magnetic field as a consequence of the electromagnetic field set up by the motion of charged particles.

So could a wormhole be detected by instrumentation? That depends on the magnitude of the warping of space-time a rotating wormhole has on local space; the smaller the wormhole, the smaller the density of rotating charged particles. As theorized natural wormholes are expected to be microscopic, I doubt there will be a large magnetic field generated. And besides, you’d have to be very close to the mouth of a wormhole to stand the chance of measuring its magnetic field. The possibility of detecting a wormhole may remain in the realms of science-fiction for a while yet…

Source: arXiv preprint server

June 2, 2008December 24, 2015 by Ian O'Neill

How do you Model the Earth’s Magnetic Field? Build your own Baby Planet…

The model Earth, can a magnetic field be modelled in the lab? (Flora Lichtman, NPR)

The Earth’s magnetic field is quite a mystery. How is it generated? How does it remain so stable? We have known of the Earth’s magnetic field for hundreds of years and the humble compass has been telling us the direction of magnetic North Pole since the 12th Century. Animals use it for navigation and we have grown dependent on its existence for the same reason. What’s more, the magnetosphere gives us a powerful shield against the worst solar storm. Yet we still have little idea about the mechanisms generating this field deep in the core of the Earth. In the hope of gaining a special insight to the large-scale, planetary magnetic field, a geophysicist from the University of Maryland has built his very own baby Earth in his laboratory, and it will be spinning (liquid metal included) by the end of the year…

This story reminds me of a classic experiment carried out by Norwegian Kristian Birkeland at the turn of the 19th Century. In an attempt to understand the dynamic Aurora Borealis (Northern Lights), Birkeland experimentally proved that electrical currents could flow along magnetic field lines (a.k.a. Birkeland, or “field-aligned” currents, pictured left). This can be observed in nature as charged particles from the solar wind interact with the Earth’s magnetosphere and are then guided down to the Earth’s magnetic poles. As the particles flow into the upper polar atmosphere, they collide with atmospheric gases, generating a colourful light display called aurorae. However, this early experiment simulated a magnetic field; it did not model how the Earth generates it in the first place.

Now, in a laboratory in the University of Maryland, geophysicist Dan Lathrop is pursuing this mystery by building his very own scale version of the Earth (pictured top). The model is set up on apparatus that will spin the 10-foot diameter ball to an equatorial speed of 80 miles per hour. To simulate the Earth’s molten outer core, Lathrop will fill the sphere with molten metal. The whole thing will weigh in at 26 tonnes.

This is Lathrop’s third attempt at generating a scale model of the Earth’s magnetic field. The last two attempts were much smaller, so this large experiment had to be constructed by a company more used to engineering heavy-duty industrial equipment.

It is believed that the Earth’s molten outer core, starting 2,000 miles below the Earth’s crust, generates the global magnetic field. This “dynamo effect” is somehow created through the interaction of turbulent liquid iron flow (which is highly conductive) with the spin of the planet. In Lathrop’s model, he will be using another conductive liquid metal, sodium. Molten iron is too hot to maintain in this environment, sodium exists at a liquid phase at far lower temperatures (it has a melting point close to that of the boiling point of water, nearly 100°C), but there are some serious hazards associated with using sodium as an iron analog. It is highly flammable in air and is highly reactive with water, so precautions will have to be taken (for one, the sprinkler system has been disabled, water in the case of a sodium fuelled fire will only make things worse!). This whole experiment, although risky, is required as there is no direct way to measure the conditions in the outer core of the Earth.

“The conditions of the core are more hostile than the surface of the sun. It’s as hot as the surface of the sun but under extremely high pressures. So there’s no way to probe it, no imaginable technique to directly probe the core.” – Dan Lathrop

Spinning this heavy sphere should cause sustained turbulence in the flow of the liquid sodium and it is hoped a magnetic field can be generated. There are many puzzles this experiment hopes to solve, such as the mechanics behind magnetic polar shift. Throughout the Earth’s history there is evidence that the magnetic poles have switched polarity, prolonged spinning of the model may cause periodic magnetic pole reversal. Testing the conditions in the conductive liquid metal may shed some light on what influences this global pattern of polar shift.

This kind of experiment has been done before, but scientists have directed the flow of liquid metal through the use of pipes, but this model will allow the metal to naturally organize itself, creating its own turbulent flow. Whether or not this test generates a magnetic field it is unknown, but it should aid our understanding about how magnetism is generated inside the planets.

See the video at National Public Radio »

Source: National Public Radio

May 31, 2008December 24, 2015 by Ian O'Neill

Warm Coronal Loops May Hold the Key to Hot Solar Atmosphere

Coronal loops as imaged by TRACE at 171 Angstroms (1 million deg C) (NASA/TRACE)

Coronal loops, the elegant and bright structures threading through the solar surface and into the solar atmosphere, are key to understanding why the corona is so hot. Yes, it’s the Sun, and yes, it’s hot, but its atmosphere is too hot. The puzzle as to why the solar corona is hotter than the Sun’s photosphere has kept solar physicists busy since the mid-twentieth century, but with the help of modern observatories and advanced theoretical models, we now have a pretty good idea what is causing this. So is the problem solved? Not quite…

So why are solar physicists so interested in the solar corona anyway? To answer this, I’ll pull up an excerpt from my first ever Universe Today article:

…measurements of coronal particles tell us the atmosphere of the Sun is actually hotter than the Suns surface. Traditional thinking would suggest that this is wrong; all sorts of physical laws would be violated. The air around a light bulb isn’t hotter than the bulb itself, the heat from an object will decrease the further away you measure the temperature (obvious really). If you’re cold, you donâ€™t move away from the fire, you get closer to it! – from “Hinode Discovers Sun’s Hidden Sparkle“, Universe Today, December 21st, 2007

This isn’t only an academic curiosity. Space weather originates from the lower solar corona; understanding the mechanisms behind coronal heating has wide-ranging implications for predicting energetic (and damaging) solar flares and forecasting interplanetary conditions.

So, the coronal heating problem is an interesting issue and solar physicists are hot on the trail of the answer to why the corona is so hot. Magnetic coronal loops are central to this phenomenon; they are at the base of the solar atmosphere and experience rapid heating with a temperature gradient from tens of thousands of Kelvin (in the chromosphere) to tens of millions of Kelvin (in the corona) over a very short distance. The temperature gradient acts across a thin transition region (TR), which varies in thickness, but can be only a few hundreds of kilometers thick in places.

These bright loops of hot solar plasma may be easy to see, but there are many discrepancies between the observation of the corona and coronal theory. The mechanism(s) responsible for heating the loops have proven to be hard to pin down, particularly when trying to understand the dynamics of “intermediate temperature” (a.k.a. “warm”) coronal loops with plasma heated to around one million Kelvin. We are getting closer to solving this puzzle which will aid space weather predictions from the Sun to the Earth, but we need to work out why the theory is not the same as what we are seeing.

Solar physicists have been divided on this topic for some time. Is coronal loop plasma heated by intermittent magnetic reconnection events throughout the length of a coronal loop? Or are they heated by some other steady heating very low in the corona? Or is it a bit of both?

I actually spent four years wrestling with this issue whilst working with the Solar Group at the University of Wales, Aberystwyth, but I was on the side of “steady heating”. There are several possibilities when considering the mechanisms behind steady coronal heating, my particular area of study was AlfvÃ©n wave production and wave-particle interactions (shameless self-promotion… my 2006 thesis: Quiescent Coronal Loops Heated By Turbulence, just in case you have a spare, dull weekend ahead of you).

James Klimchuk from the Goddard Space Flight Center’s Solar Physics Laboratory in Greenbelt, Md., takes a different opinion and favours the nanoflare, impulsive heating mechanism, but he is highly aware that other factors may come into play:

“It has become clear in recent years that coronal heating is a highly dynamic process, but inconsistencies between observations and theoretical models have been a major source of heartburn. We have now discovered two possible solutions to this dilemma: energy is released impulsively with the right mix of particle acceleration and direct heating, or energy is released gradually very close to the solar surface.” – James Klimchuk

Nanoflares are predicted to maintain warm coronal loops at their fairly steady 1 million Kelvin. We know the loops are this temperature as they emit radiation in the extreme ultraviolet (EUV) wavelengths, and a host of observatories have been built or sent into space with instruments sensitive to this wavelength. Space-based instruments such as the EUV Imaging Telescope (EIT; onboard the NASA/ESA Solar and Heliospheric Observatory), NASA’s Transition Region and Coronal Explorer (TRACE), and the recently operational Japanese Hinode mission have all had their successes, but many coronal loop breakthroughs occurred after the launch of TRACE back in 1998. Nanoflares are very hard to observe directly as they occur over spatial scales so small, they cannot be resolved by the current instrumentation. However, we are close, and there is a trail of coronal evidence pointing to these energetic events.

“Nanoflares can release their energy in different ways, including the acceleration of particles, and we now understand that the right mix of particle acceleration and direct heating is one way to explain the observations.” – Klimchuk.

Slowly but surely, theoretical models and observation are coming together, and it seems that after 60 years of trying, solar physicists are close to understanding the heating mechanisms behind the corona. By looking at how nanoflares and other heating mechanisms may influence each other, it is very likely that more than one coronal heating mechanism is at play…

Aside: Out of interest, nanoflares will occur at any altitude along the coronal loop. Although they may be called nanoflares, by Earth standards, they are huge explosions. Nanoflares release an energy of 10²⁴-10²⁶ erg (that is 10¹⁷-10¹⁹ Joules). This is the equivalent of approximately 1,600 to 160,000 Hiroshima-sized atomic bombs (with the explosive energy of 15 kilotonnes), so there is nothing nano about these coronal explosions! But on the comparison with the standard X-ray flares the Sun generates from time to time with a total energy of 6×10²⁵ Joules (over 100 billion atomic bombs), you can see how nanoflares get their name…

Original source: NASA

May 29, 2008December 24, 2015 by Ian O'Neill

Temperature Conditions of a Supernova Recreated in UK Laboratory

A scientist cleans a vacuum spatial filter for the Vulcan Petawatt Facility during construction (Rutherford Appleton Laboratory)

Scientists are one step closer to attaining the ultimate goal: producing temperatures high enough to sustain fusion, the reaction that powers our Sun and the possible future for global energy production. Researchers at the Rutherford Appleton Laboratory in Oxfordshire, UK, have attained temperatures higher than the surface of the Sun, 10 million Kelvin (or Celsius), by using a powerful one petawatt laser called Vulcan. This experiment goes beyond the quest for fusion power; generating these high temperatures recreates the conditions of cosmological events such as supernova explosions, and astronomical bodies like white dwarfs and neutron star atmospheres…

This is some awesome research. An international collaboration of researchers from the UK, Europe, Japan and the US have succeeded in harnessing an equivalent of 100 times the world energy production into a tiny spot, measuring a fraction of the width of a human hair. That’s a whopping one petawatt of energy (one thousand million million watts, or enough to power ten trillion 100W light bulbs) focused on a volume measuring about 0.000009 metres (9Âµm) across (I took the value of the diameter of a human hair to be 90Âµm, as measured by Piezo Technology, in case you were interested). This is a vast improvement on previous tests, where the volume heated measured 20 times smaller than this new experiment. This feat was achieved through the use of Rutherford Appleton’s Vulcan laser.

The petawatt laser was able to attain this vast power by delivering a very short-period pulse onto the target. After all, the planet didn’t experience a black out as the laser was switched on, the laser is able to amplify the amount of power available by focusing on a microscopic volume for a short period of time. Vulcan blasted its target with the one petawatt laser beam for a mere 1 picosecond (one millionth of a millionth of a second). This may seem miniscule, but this microscopic period of time allowed the target material to be heated to the 10 million Kelvin.

These tests not only allow scientists to study what happens when matter is heated to such extremes, it also paves the way to more powerful lasers fusing the nuclei of hydrogen, deuterium and tritium. Self-sustaining nuclear fusion may then be possible, unlocking a gateway into a huge source of energy. It is conceivable that a future fusion reactor will use a powerful, focused laser to start fusion events, allowing the energy produced by each reaction to power the next. This is the basis of self-sustaining nuclear fusion.

“This is an exciting development – we now have a new tool with which to study really hot, dense matter” – Prof. Peter Norreys, STFC funded researcher and Vulcan scientist.

The Vulcan has some stiff competition though. In the US, the Texas Petawatt laser broke the record for most powerful laser a few days ago, reaching energies in excess of one petawatt. But plans for a bigger UK laser, the Hiper (High Power laser Energy Research), will be even more powerful and is intended to investigate fusion power.

Source: Telegraph

May 8, 2008December 24, 2015 by Ian O'Neill

Stars Orbiting Close to Black Holes Flattened like Hot Pancakes

Playing with black holes is a risky business, especially for a star that is unlucky enough to be orbiting one. Assuming an unfortunate star hasn’t already had all of its hydrogen fuel and other component elements stripped from its surface, the powerful tidal forces will have some fun with the doomed stellar body. First the star will be stretched out of shape and then it will be flattened like a pancake. This action will compress the star generating violent internal nuclear explosions, and shockwaves will ripple throughout the tormented stellar plasma. This gives rise to a new type of X-ray burst, revealing the sheer power a black hole’s tidal radius has on the smaller binary sibling. Sounds painful…

It is intriguing to try to understand the dynamics near a supermassive black hole, especially when a star strays too close. Recent observations of a distant galaxy suggests the material pulled from a star near the center of a galactic nucleus caused a powerful X-ray flare which echoed from the surrounding molecular torus. The infalling stellar gas was sucked into the black hole’s accretion disk, generating a huge quantity of energy as a flare. Whether or not the star stayed intact for the duration of its death-spiral into the supermassive black hole it is unknown, but scientists have been working on a new model of a star orbiting a black hole weighing in at a few million solar masses (assuming the star can hold it together for that long).

Matthieu Brassart and Jean-Pierre Luminet of the Observatoire de Paris-Meudon, France, are studying the effects of the tidal radius on a star orbiting close to a supermassive black hole. The tidal radius of a supermassive black hole is the distance at which gravity will have a far greater pull on the leading edge of the star than the following edge. This massive gravitational gradient causes the star to be stretched beyond recognition. What happens next is a little strange. In a matter of hours, the star will swing around the black hole, through the tidal radius, and out the other end. But according to the French scientists, the star that comes out isn’t the same as the star that went in. The star deformation is described in the accompanying diagram and detailed below:

(a)-(d): Tidal forces are weak and the star remains practically spherical.
(e)-(g): Star falls into the tidal radius. This is the point at which it is destined to be destroyed. It undergoes changes in its shape, first “cigar shaped”, then it gets squeezed as the tidal forces flatten the star in its orbital plane to the shape of a pancake. Detailed hydrodynamical simulations of shock wave dynamics have been carried out during this “crushing phase”.
(h): After swinging around the point of closest approach in its orbit (perihelion), the star rebounds, leaving the tidal radius and begins to expand. Leaving the black hole far behind, the star breaks up into clouds of gas.

As the star is dragged around the black hole in the “crushing phase” it is believed that the pressures will be so great on the deformed star that intense nuclear reactions will occur throughout, heating it up in the process. This research also suggests powerful shock waves will travel through the hot plasma. The shock waves would be powerful enough to produce a short (<0.1 second) blast of heat (>10⁹ Kelvin) propagating from the star’s core to its deformed surface, possibly emitting a powerful X-ray flare or gamma-ray burst. Due to this intense heating, it seems possible that most of the stellar material will escape the black holes gravitational pull, but the star will never be the same again. It will be transformed into vast clouds of turbulent gas.

This situation wouldn’t be too hard to imagine when considering the dense stellar volume in galactic nuclei. In fact, Brassart and Luminet have estimated that there may be 0.00001 event per galaxy, and although this may seem low, future observatories such as the Large Synoptic Survey Telescope (LSST) may detect these explosions, possibly several per year as the Universe is transparent to hard X-ray and gamma-ray emissions.

Source: Science Daily