Scoperto il "motore" del vento solare. Forse può aiutarci ad avere energia da fusione.

Questa è bellissima. Una sonda NASA, Wind, lanciata nel lontano 1994 e dotata di una strumentazione i cui dati vengono registrati su nastro per essere ogni volta riprodotti e trasmessi a terra, contiene forse i dati che spiegano perché il vento solare soffi tanto veloce e tanto caldo. Un perché che i ricercatori della fusione nucleare sono molto interessati a capire, perché da questa spiegazione possono a loro volta ricavare un metodo che renderà più efficienti i futuri reattori a fusione.

Il sole è un po' come una pentola che bolle, rilasciando in tutte le direzione un "vapore" costituito da un gas magnetico ricco di particelle. Al contrario della pentola, però, questo vapore non diventa più freddo e lento man mano che si allontana dal sole. Al contrario: il vento solare accelera fortemente e si riscalda attraversando l'atmosfera solare, la corona. Secondo gli scienziati alle origini del fenomeno ci sarebbero le onde di ciclotrone ionico (ione cyclotrone waves), un effetto di risonanza che coinvolge gli ioni pesanti del plasma solare e li accelera come una fionda, conservandone l'energia e quindi il calore. Forse sfruttando questo stesso meccanismo, si potrebbero intercettare e eliminare gli ioni pesanti che staccandosi dalle pareti delle camere di reazione di fusione emettono calore togliendolo alla reazione stessa, e causandone l'interruzione.

Solar Wind Energy Source Discovered

March 8, 2013: Using data from an aging NASA spacecraft, researchers have found signs of an energy source in the solar wind that has caught the attention of fusion researchers. NASA will be able to test the theory later this decade when it sends a new probe into the sun for a closer look.

The discovery was made by a group of astronomers trying to solve a decades-old mystery: What heats and accelerates the solar wind?

The solar wind is a hot and fast flow of magnetized gas that streams away from the sun's upper atmosphere.  It is made of hydrogen and helium ions with a sprinkling of heavier elements.  Researchers liken it to the steam from a pot of water boiling on a stove; the sun is literally boiling itself away.

“But,” says Adam Szabo of the NASA Goddard Space Flight Center, “solar wind does something that steam in your kitchen never does.  As steam rises from a pot, it slows and cools.  As solar wind leaves the sun, it accelerates, tripling in speed as it passes through the corona. Furthermore, something inside the solar wind continues to add heat even as it blows into the cold of space."

Finding that "something" has been a goal of researchers for decades.  In the 1970s and 80s, observations by two German/US Helios spacecraft set the stage for early theories, which usually included some mixture of plasma instabilities, magnetohydrodynamic waves, and turbulent heating.  Narrowing down the possibilities was a challenge. The answer, it turns out, has been hiding in a dataset from one of NASA's oldest active spacecraft, a solar probe named Wind.

Launched in 1994, Wind is so old that it uses magnetic tapes similar to old-fashioned 8-track tapes to record and play back its data.  Equipped with heavy shielding and double-redundant systems to safeguard against failure, the spacecraft was built to last; at least one researcher at NASA calls it the "Battlestar Gallactica" of the heliophysics fleet. Wind has survived almost two complete solar cycles and innumerable solar flares.

"After all these years, Wind is still sending us excellent data," says Szabo, the mission’s project scientist, “and it still has 60 years' worth of fuel left in its tanks.”

Using Wind to unravel the mystery was, to Justin Kasper of the Harvard-Smithsonian Center for Astrophysics, a "no brainer." He and his team processed the spacecraft's entire 19-year record of solar wind temperatures, magnetic field and energy readings and ...

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Tsunami e suoni della corona solare

Giorni fa su Repubblica.it è stato pubblicato un pezzo sugli esperimenti condotti dal gruppo di fisica solare della Sheffield University, che tra l'altro ha "trasposto" l'effetto acustico - quello di una corda di chitarra pizzicata - collegato alle osservazioni di fenomeni quali le Eziezioni di massa coronale (CME). Una registrazione audio di questo effetto è presente su SoundCloud:

Sound of the Sun (courtesy Richard Morton) by University of Sheffield

Questa pagina sul sito dell'ufficio stampa della università contiene altre spiegazioni e filmati su questo esperimento di "astrofisica acustica".

Sono andato a guardarmi la fonte originale di queste storie sul sito del Media Center dell'ateneo britannico. Il gruppo di scienziati è lo stesso che nel marzo scorso ha addirittura partecipato a una udienza parlamentare a Londra per spiegare le sue teorie sulla enorme differenza di temperatura che nelle stelle come il Sole sussiste tra superficie e atmosfera (corona). Gli astrofisici della Sheffield ritengono che questo gradiente sia correlato alla presenza di una gran quantità di scosse di tipo sismico, dei veri e propri tsunami, che agitano gli strati della coronosfera.

Ecco un comunicato che spiega a grandi linee queste teorie, che secondo il team guidato da Robertus von Fay-Siebenburgen potrebbero essere alla base di nuovi approcci interdisciplinare allo studio della fisica solare, anche ai fini di un diverso modo di sfruttarne qui a terra l'energia, prevenendo al tempo stesso gli effetti negativi dei dirompenti fenomeni che si verificano sul Sole e all'interfaccia tra questo e il campo magnetico del nostro pianeta.

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3 March 2010

Mega-tsunami hits House of Commons

A breakthrough discovery by experts at the University of Sheffield, which sheds light on mega-tsunamis on the Sun, is set to be revealed at the House of Commons next week (Monday 8 March 2010).

Solar physicists from the University will discuss their discovery of solar Transition Region Quakes to an audience of MPs both from the House of Commons and the House of Lords at the House of Commons Marquee, after being selected by the Parliamentary and Scientific Committee. It is hoped their findings hold the key to understanding the long-standing secret of solar coronal heating.

The solar transition region is located about 2000km above the Sun´s visible surface. It is the narrow layer of sharp transition in density and temperature between the relatively cool solar chromosphere, which reaches temperatures of about 10-20,000 Kelvin, and the very hot upper corona, which sees temperature hit 1-10 Megakelvin.

The way in which the solar corona is heated to temperatures of over a million degrees has so far remained a long-standing puzzle of solar and space physics, especially as this region of the Sun is even further away from the centre of energy production than the underlying solar surface.

But the team of experts at the University, including Professor Robertus von Fay-Siebenburgen, postdoctoral research associate Dr Victor Fedun and postgraduate student Eamon Scullion, all from the University´s Department of Applied Mathematics and members of the Solar Wave Theory Group and the Solar Physics and Space Plasma Research Centre, (SWAT/SP2RC), have addressed this enigma by discovering that Transition Region Quakes power the lower base of the solar corona.

The quakes take the form of mega-tsunamis generated by narrow (a few 100 km radius), long (10-40,000 km) rapidly rising (10-100 km/s) plasma jets. When these jets hit the transition region, they excite a wealth of Transition Region Quakes that have now been observed and modelled for the first time.

The breakthrough has allowed the experts to estimate that at any moment of time there are about 60,000 of these mega-tsunamis splashing and crashing around the Transition Region.

Colleagues at SP2RC, and in SWAT, devoted many years of research to understand this energy balance and wave processes of the solar atmosphere, using a combined approach of analytical theory, numerical modelling using a supercomputer Iceberg in Sheffield and the UKMHD Cluster in St Andrews, as well as joint satellite observations involving more than one spacecraft simultaneously.

The next step for the team will be to investigate the properties of this torrential sea and focus on the details of transferring the tsunami energy into plasma heat.

The news comes as the University of Sheffield launches a unique venture entitled Project Sunshine, led by the Faculty of Science. The Project aims to unite scientists across the traditional boundaries in both the pure and applied sciences to harness the power of the sun and tackle the biggest challenge facing the world today: meeting the increasing food and energy needs of the world´s population in the context of an uncertain climate and global environment change. It is hoped that Project Sunshine will change the way scientists think and work and become the inspiration for a new generation of scientists focused on solving the world´s problems.

Professor Robertus von Fay-Siebenburgen from the University of Sheffield´s Department of Applied Mathematics and Head of SP2RC, said: "This is indeed a very promising and fantastic result. We may now get a step closer to resolve one of the greatest puzzles of astrophysics - why the atmosphere of stars, like the Sun, is so much hotter than its surface.

"A number of international space missions are devoted to studying the heating of the solar atmosphere. With the Japanese-lead Hinode satellite on board the high-resolution UK-built EIS camera that we have used in this research, we were very lucky to observe these massive and energetic waves. This leap forward will certainly help us reveal the secrets of the Sun."

Dinamica solare in HD: piccole variazioni, grandi effetti

Continuano ad arrivare copiosi i risultati delle osservazioni del Solar Dynamics Observatory. Questa volta il protagonista è l'Atmospheric Imaging Assembly, uno dei tre strumenti a bordo del satellite SDO. Consente una visuale ad alta risoluzione e su un amplissima gamma di temperature della corona solare.

Dalle prime immagini gli scienziati riescono a capire meglio perché una variazione su minuscola scala sul Sole finisca per avere enormi ripercussioni anche sul nostro pianeta, dove le perturbazioni solari si fanno sentire sui cavi dell'alta tensione e sui sistemi di comunicazione satellitare. A corredo dell'articolo che segue, trovate una quantita di immagini, filmati e presentazioni a questo indirizzo.

La presentazione sull'AIA la potete trovare qui, in Pdf, mentre qui trovate un incredibile database di eventi solari, l'interfaccia di ricerca SolSearch che estrae i dati dalla Heliophysics Events Knowledgebase (HEK), uno dei servizi del Solar and Astrophysics Laboratory della Lockheed Martin.

Spacecraft Reveals Small Solar Events Have Large Scale Effects

05.25.10

NASA's Solar Dynamics Observatory, or SDO, has allowed scientists for the first time to comprehensively view the dynamic nature of storms on the sun. Solar storms have been recognized as a cause of technological problems on Earth since the invention of the telegraph in the 19th century.

The Atmospheric Imaging Assembly (AIA), one of three instruments aboard SDO, allowed scientists to discover that even minor solar events are never truly small scale. Shortly after AIA opened its doors on March 30, scientists observed a large eruptive prominence on the sun's edge, followed by a filament eruption a third of the way across the star's disk from the eruption.

"Even small events restructure large regions of the solar surface," said Alan Title, AIA principal investigator at Lockheed Martin Advanced Technology Center in Palo Alto, Calif. "It's been possible to recognize the size of these regions because of the combination of spatial, temporal and area coverage provided by AIA."

The AIA instrument also has observed a number of very small flares that have generated magnetic instabilities and waves with clearly-observed effects over a substantial fraction of the solar surface. The instrument is capturing full-disk images in eight different temperature bands that span 10,000 to 36-million degrees Fahrenheit. This allows scientists to observe entire events that are very difficult to discern by looking in a single temperature band, at a slower rate, or over a more limited field of view.

The data from SDO is providing a torrent of new information and spectacular images to be studied and interpreted. Using AIA's high-resolution and nearly continuous full-disk images of the sun, scientists have a better understanding of how even small events on our nearest star can significantly impact technological infrastructure on Earth.

Solar storms produce disturbances in electromagnetic fields that can induce large currents in wires, disrupting power lines and causing widespread blackouts. The storms can interfere with global positioning systems, cable television, and communications between ground controllers and satellites and airplane pilots flying near Earth's poles. Radio noise from solar storms also can disrupt cell phone service.

Launched in Feb. 2010, the spacecraft's commissioning May 14 confirmed all three of its instruments successfully passed an on-orbit checkout, were calibrated and are collecting science data.

"We're already at five million images and counting," said Dean Pesnell, the SDO project scientist at NASA's Goddard Space Flight Center in Greenbelt, Md. "With data and images pouring in from SDO, solar scientists are poised to make discoveries that will rewrite the books on how changes in solar activity have a direct effect on Earth. The observatory is working great, and it's just going to get better."

Goddard built, operates and manages the SDO spacecraft for NASA's Science Mission Directorate in Washington. SDO is the first mission of NASA's Living with a Star Program. The program's goal is to develop the scientific understanding necessary to address those aspects of the sun-Earth system that directly affect our lives and society.

Un telescopio spaziale per il nostro sole mutevole

Non ce ne accorgiamo, dicono gli scienziati della NASA, ma il nostro sole è una stella variabile, una continua fabbrica di fenomeni misteriosi, un vero e proprio laboratorio di astrofisica. Per studiarla, per cercare di capire tutte le conseguenze della sua dinamicità sulla nostra atmosfera e probabilmente il nostro clima, sta per essere lanciata, il 9 febbraio l'ambiziosa missione del Solar Dynamics Observatory. Che ha anche aperto un fantastico canale su You Tube.

Solar Dynamics Observatory: The 'Variable Sun' Mission
02.05.2010

February 5, 2010: For some years now, an unorthodox idea has been gaining favor among astronomers. It contradicts old teachings and unsettles thoughtful observers, especially climatologists. "The sun," explains Lika Guhathakurta of NASA headquarters in Washington DC, "is a variable star." But it looks so constant... That's only a limitation of the human eye. Modern telescopes and spacecraft have penetrated the sun's blinding glare and found a maelstrom of unpredictable turmoil. Solar flares explode with the power of a billion atomic bombs. Clouds of magnetized gas (CMEs) big enough to swallow planets break away from the stellar surface. Holes in the sun's atmosphere spew million mile-per-hour gusts of solar wind. And those are the things that can happen in just one day.
Over longer periods of decades to centuries, solar activity waxes and wanes with a complex rhythm that researchers are still sorting out. The most famous "beat" is the 11-year sunspot cycle, described in many texts as a regular, clockwork process. In fact, it seems to have a mind of its own.
"It's not even 11 years," says Guhathakurtha. "The cycle ranges in length from 9 to 12 years. Some cycles are intense, with many sunspots and solar flares; others are mild, with relatively little solar activity. In the 17th century, during a period called the 'Maunder Minimum,' the cycle appeared to stop altogether for about 70 years and no one knows why."
There is no need to go so far back in time, however, to find an example of the cycle's unpredictability. Right now the sun is climbing out of a century-class solar minimum that almost no one anticipated.
"The depth of the solar minimum in 2008-2009 really took us by surprise," says sunspot expert David Hathaway of the Marshall Space Flight Center in Huntsville, Alabama. "It highlights how far we still have to go to successfully forecast solar activity."
That's a problem, because human society is increasingly vulnerable to solar flare ups. Modern people depend on a network of interconnected high-tech systems for the basics of daily life. Smart power grids, GPS navigation, air travel, financial services, emergency radio communications—they can all be knocked out by intense solar activity. According to a 2008 study by the National Academy of Sciences, a century-class solar storm could cause twenty times more economic damage than Hurricane Katrina.
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Morse dalle stelle per l'anno dell'astronomia

Ieri sul sito Spaceweather.com è apparsa questa divertente foto ottenuta dal fotoastronomo del Colorado, Jimmy Westlake, puntando l'obiettivo centrato sulla stella Sirio e manovrando l'otturatore, a mano, a intervalli regolari (Jimmy ci ha messo un paio d'ore, con 15 gradi sottozero). In questo modo il fotografo ha modulato in codice Morse la traccia luminosa delle stelle, ottenendo una serie di punti e linee che compongono la scritta IYA2009. E' il suo personale omaggio a una manifestazione molto importante, l'International Year of Astronomy che l'Unesco celebra in questi giorni a Parigi con un convegno intitolato The role of astronomy in society and culture.

GRB, quando le stelle trasmettono gravitoni

La NASA sta dedicando una serie di articoli affascinanti sull'astrofisica dei raggi gamma, in occasione del sesto simposio internazionale sui "brillamenti gamma" (Gamma Ray Burst), un fenomeno raro ed elusivo associato alla formazione dei buchi neri e a (ipotetiche) dinamiche tra stelle estremamente dense. L'ente spaziale americano nel 2004 ha messo in orbita un satellite dedicato allo studio dei GRB, una missione chiamata SWIFT cui hanno collaborato anche l'Agenzia Spaziale Italiana e il "nostro" Osservatorio di Brera.

Come viene spiegato in questo primo articolo, ci sono due tipi di GRB, uno di lunga, l'altro di breve durata. Il primo è il "sintomo" di una stella ultramassiva che sta collassando in un buco nero. Il secondo... Il secondo non si sa. Ma gli scienziati sospettano che possa avere a che fare con lo scontro tra stelle di neutroni, oggetti astronomici di densità fuori del comune: se potessimo raccoglierne un campione con un cucchiaino, una punta peserebbe qualche migliaio di miliardo di tonnellate. Il problema non sta tanto nel rilevare i GRB di breve durata (per quello c'è SWIFT), ma verificare la teoria dello scontro tra stelle neutroniche. Se l'ipotesi regge la traccia misurata con i raggi gamma potrebbe essere accompagnata da un fenomeno di tipo non elettromagnetico: lo scontro tra questi corpi produce una increspatura gravitazionale, un fenomeno mediato da particelle diverse. Per queste onde ci vogliono antenne gravitazionali come quella che gli italiani hanno costruito vicino a Pisa o come il Gravitational-wave Observatory (LIGO), una duplice struttura (stato di Washington e stato della Louisiana) basata, come quella di Cascina, sull'interferometria laser. In questo tipo di osservatori le "antenne" sono costituite da una complessa geometria lineare di raggi laser che viene perturbata dalle impercettibili variazioni di massa indotte, in un sistema di specchi, dalle famose increspature gravitazionali.
Potete leggere la serie di articoli sui GRB a questi indirizzi.

http://science.nasa.gov/headlines/y2008/20oct_briefmystery.htm
http://science.nasa.gov/headlines/y2008/21oct_oddballs.htm
http://science.nasa.gov/headlines/y2008/22oct_missinggrbs.htm
http://science.nasa.gov/headlines/y2008/17oct_gammaraypulsar.htm

A Brief Mystery: What are Short Gamma-ray Bursts?
10.20.2008

October 20, 2008: For decades it was baffling. Out of the still night sky, astronomers peering through their telescopes would occasionally glimpse quick bursts of high-energy light popping off like flashbulbs at the far side of the universe.
These bursts seemed impossibly powerful: to appear so bright from so very far away, they must vastly outshine entire galaxies containing hundreds of billions of stars. These explosions, called gamma ray bursts (GRBs), are by far the brightest and most energetic phenomena in the known universe, second only to the Big Bang itself. Scientists were at a loss to imagine what could possibly cause them.
Astronomers now know what the longer-lasting GRBs are: the collapse and explosion of an ultra-massive star to form a black hole at its core, an explanation first proposed by Stan Woosley of the University of California in San Diego. But there’s a second category of GRBs that still remains a mystery.
"The short-lived ones are very poorly understood. It's where the frontier [of research] is now," says Neil Gehrels, principal investigator for the GRB-detecting Swift satellite at NASA's Goddard Space Flight Center.
Gehrels and other researchers have gathered this week at the Sixth Huntsville Gamma Ray Burst Symposium in Huntsville, Ala., to discuss progress on this and other mysteries surrounding GRBs.

Princeton: le stringhe cosmiche trasmettono in Banda L

Si sta stranamente affollando la porzione di spettro degli 1,4 GHz, allocata al DAB terrestre ma anche ai servizi DAB satellitari. Per fortuna non c'è rischio che l'ultima sorgente interferenziale scoperta recentemente danneggi i pochi servizi radiofonici che utilizzano tali frequenze. PhysOrg.com rivela che un fisico della prestigiosa università di Princeton, Tanmay Vachaspati, ha ipotizzato la possibilità di dare la caccia alle stringhe cosmiche attraverso il monitoraggio di emissioni radio impulsive a 1,4 GHz. In questa porzione dello spettro elettromagnetico, i misteriosi "oggetti" teorizzati dai cosmologi potrebbero emettere un flebile scintillio radio. Detta in maniera grossolana (molto grossolana ma direi di evitare di mettersi a disquisire su RP delle differenze tra bosoni e fermioni), le stringhe cosmiche (da non confondersi con le superstringhe cosmiche) sono sottili incrinature, vere e proprie smagliature del continuum che percorrono la struttura fine dell'universo fin dai primissimi istanti del Big Bang. Sarebbero insomma i resti di un universo che passa rapidamente, espandendosi, da una fase all'altra, un po' come accade con le imperfezioni nei materiali che si raffreddano troppo in fretta dopo la fusione. La teoria dice che queste smagliature sono più sottili di un protone - per cui vengono a tutti gli effetti considerate monodimensionali . E sono soprattutto lunghe, perché attraversano l'universo "da un capo all'altro". Queste strutture dinamiche contorcendosi dovrebbero generare onde gravitazionali, ma a questo punto sarebbe davvero un bel problema andarle "intercettarle". Ma essendo oggetti superconduttori, il loro spasmi dovrebbero provocare, al fluire della corrente, delle scintille. O almeno questo è quanto afferma Vachaspati, che ha studiato il rapporto relativo alle osservazioni di un altro cosmologo, Dunc Lorimer. Quest'ultimo nel 2007 avrebbe registrato uno strano burst radio, una scarica brevissima (un millisecondo), senza tuttavia riuscire a stabilire una precisa corrispondenza tra questa scarica e una fonte radio galattica. L'anomalia è stata studiata a Princeton, dove Vachaspati ha stabilito una compatibilità teorica con la distribuzione spettrale del burst (centrato appunto sugli 1,4 GHz) e una possibile stringa cosmica "caricata" con una corrente di centomila GeV (gigaelettronvolt). Tutti all'inseguimento di nuove scariche da stringa cosmica? Il vero problema, per i fisici dei primi picosecondi dell'universo è stabilire se le stringhe esistono davvero. Dalla loro eventuale presenza, afferma Tanmay Vachaspati, si potrebbe trarre conclusioni importanti sui modelli fondamentali della teoria delle particelle. Inclusa la remota possibilità che le particelle, la materia, sia intimamente legata a questo impercettibile reticolo, la maglia che tiene insieme tutto e verso cui tutto va a confluire. Nuove osservazioni ricevute fuori dal raggio di copertura dei "trasmettitori" galattici, potrebbero aiutarci a decidere, una volta per tutte, se queste benedette stringhe si siano formate o meno.

Cosmic strings might emit cosmic sparks, answer cosmological questions

By Lisa Zyga,

(PhysOrg.com) -- For astronomers, understanding what happened in the early moments of the universe could answer many questions in physics and astronomy. One possible player in the early universe is cosmic strings, which arise naturally in particle physics models. However, cosmic strings are quite strange hypothetical entities: they’re thinner than a proton, but can be as long as the universe. Cosmic strings might have formed as imperfections when the early universe was undergoing drastic phase changes.
“If cosmic strings were found to exist, it would tell us that the universe was very hot (trillion trillion degrees) in the first fraction of a nanosecond,” physicist Tanmay Vachaspati told PhysOrg.com. “It would tell us that the fundamental theory must admit string solutions. Further studies of the properties of the strings could tell us if string theory may be correct. So the discovery of cosmic strings would be truly remarkable for a wide cross-section of physicists and astronomers.”
Cosmic strings are also superconducting, and can be viewed as elastic, current-carrying wires that permeate the cosmos as closed loops and infinitely long curves. The strings oscillate under their own tension, giving off very strong electromagnetic radiation.
Possibly, a recent observation of a radio burst, or spark, could have been caused by such a superconducting cosmic string. That’s the idea being suggested by Vachaspati, from the Institute for Advanced Study in Princeton, New Jersey, and Case Western Reserve University in Cleveland, Ohio.
Vachaspati has developed a prediction that cosmic strings could produce potentially observable radio sparks, and recently published his study in Physical Review Letters. Previous attempts to observe cosmic strings have focused primarily on high-energy emission such as gamma rays, rather than lower-energy radio waves.
The recent radio spark was observed by Dunc Lorimer and colleagues, and reported in 2007. No host galaxy has been identified for the spark, which lasted only a millisecond, and had a high central frequency of 1.4 GHz. Vachaspati found that the radio spark’s properties, such as its duration, fluence, spectrum, and event rate, match well with a superconducting cosmic string that carries a current of about 100,000 GeV.
“Lorimer et al’s result is the first radio burst to be detected at cosmological distances,” Vachaspati said. “Their observation triggered the idea that radio bursts may be a good way to search for strings.”
Such a spark could come from a point called a “cusp” on an idealized, one-dimensional cosmic string. For a brief instant, a cusp reaches the speed of light, and this localized region emits a very strong electromagnetic radiation. Vachaspati found that an observer located at a large distance and slightly off the beam direction could see this radiation as a spark similar to the one observed by Lorimer’s group.
Whether this particular radio spark was caused by cosmic strings or something else, Vachaspati explains that the important thing is how his predictions could influence particle physics. For example, the existence or absence of cosmic strings could be used to constrain various fundamental models.
He explained that the superconducting cosmic string model may be tested in a variety of ways, such as looking for signatures of decaying particle emission, looking for unusual “fanlike” radiation patterns from kinks on the strings, and finding more radio sparks located outside of galaxies.