Scientists Shed Light on How Solar Flares Accelerate Particles to Nearly the Speed of Light

Shedding light on particle acceleration in solar flares

From the NEW JERSEY INSTITUTE OF TECHNOLOGY:

solar-flare-vla

This image shows the speed of fast plasma outflows produced by the flare. The termination shock is shown as a transition layer where the colors change abruptly from red/yellow to blue/green. At bottom is the Karl G. Jansky Very Large Array, which captured the termination shock in action using radio observations. CREDIT SDO/AIA data is from NASA. VLA image courtesy of NRAO/AUI. Image prepared by Chen, Jibben, and Samra.

For scientists studying the impacts of space weather, one of the central mysteries of solar flares – the colossal release of magnetic energy in the Sun’s atmosphere that erupts with the force of millions of hydrogen bombs – is the means by which these explosions produce radiation and accelerate particles to nearly the speed of light within seconds. The most powerful blasts dispatch energized particles that can penetrate Earth’s atmosphere within an hour, disrupting orbiting satellites and electronic communications on the ground.

In an article published in Science magazine this week, “Particle acceleration by a solar flare termination shock,” solar scientists at several institutions, including NJIT, have shed light on an elusive structure known as a termination shock that is believed to play a key role in converting released magnetic energy from flares into kinetic energy in accelerated particles. Through a recent set of observations captured by a large radio telescope, the Jansky Very Large Array, they have imaged a shock and its time evolution during a long-lasting solar flare and demonstrated its role in accelerating particles.

“Although predicted by theoretical models, this is the first time we have had direct images and movies showing the repeated formation, disruption, and reformation of a termination shock, enabling us to link it directly to particle acceleration,” said Dale Gary, distinguished professor of physics at NJIT and one of the authors of the article. Bin Chen, an astrophysicist at the Harvard Smithsonian Center for Astrophysics who will join NJIT next January, is the article’s lead author.

The powerful shocks occur when high-speed jets expelled from the explosive energy-release site of a solar flare collide with stationary plasma below. One surprising result is that, occasionally, some jets can disrupt the shock, after which the shock takes time to reform. During the disruptions, radio and X-ray emission due to accelerated particles is observed to decrease not just at the shock, but throughout the emitting region, showing that the shock is at least partly responsible for accelerating those particles.

The observations were made possible by the ability of the newly enhanced Karl G. Jansky Very Large Array in New Mexico to acquire the more than 40,000 individual images per second of observation needed to resolve the rapidly varying emission features produced by the termination shock. This level of resolved detail allowed the firm identification of the radio source as a shock and revealed its dynamic evolution. Chen developed the technique to visualize the shock dynamics from the millions of images taken during the event.

“Radio emission is an excellent means to study highly energized particles, because the particles emit radio waves very readily without losing much energy in the process. High-energy particles are not directly visible through optical solar telescopes, while they produce higher-energy X-ray photons mainly when the particles hit the surface of the Sun and release all of their energy,” Gary said. “To better understand flares, it is important to detect the particles where they are produced, which is done through radio observations, in addition to where in the solar environment their energy is deposited, which is the role of optical, ultraviolet, and X-ray observations.”

Solar flares erupt when stored magnetic energy is suddenly released and converted to other forms, such as high-energy particles, hot plasma at millions of degrees, intense electromagnetic radiation and plasma eruptions called coronal mass ejections (CMEs). Solar radiation from the primary flare and that generated secondarily from CMEs can affect Earth in many ways. The high-energy particles can destroy the electronic systems in satellites used in telecommunications, weather forecasting and navigation systems, among other services. The electromagnetic radiation can interfere directly with communication and navigation signals, ionize the atmosphere, and cause short-wave radio black-outs. Associated magnetic disturbances can also affect devices on the ground such as power transformers.

The study of flares began in 1859 following what is known as the Carrington Event, a solar flare and associated geomagnetic storm so powerful that it electrified telegraph wires, causing spark discharges that caught paper on fire, caused world-wide magnetic disturbances, and was visible across the globe in the form of auroras. That storm was by some estimates four orders of magnitude stronger than the flare described in the Sciencearticle.

“A flare the size of the Carrington event would pose real danger today because of our increasing reliance on susceptible technology,” Gary said. “Big events are difficult to predict, however. We have ways of measuring energy build-up, but sometimes when we think a large flare will occur, the energy dissipates quietly or in a series of smaller events instead. Studies like ours provide better understanding of the fundamental processes occurring in flares, and may one day lead to better predictions.”

NJIT is expanding its own, solar-dedicated radio telescope, the Expanded Owens Valley Solar Array, to observe the Sun every day with many of the same observational capabilities. Multi-frequency imaging with high frequency and time resolution will become a standard method of studying solar flares in the near future.


 

Particle acceleration by a solar flare termination shock

Abstract:

Solar flares—the most powerful explosions in the solar system—are also efficient particle accelerators, capable of energizing a large number of charged particles to relativistic speeds. A termination shock is often invoked in the standard model of solar flares as a possible driver for particle acceleration, yet its existence and role have remained controversial. We present observations of a solar flare termination shock and trace its morphology and dynamics using high-cadence radio imaging spectroscopy. We show that a disruption of the shock coincides with an abrupt reduction of the energetic electron population. The observed properties of the shock are well reproduced by simulations. These results strongly suggest that a termination shock is responsible, at least in part, for accelerating energetic electrons in solar flares.

http://www.sciencemag.org/content/350/6265/1238.short

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69 thoughts on “Scientists Shed Light on How Solar Flares Accelerate Particles to Nearly the Speed of Light

    • Models … are good when they both forecast and backcast observed system dynamics. The opposite is also probably true: models that neither forecast nor backcast well are poor approximations of reality.
      You, Dear Leif, are a proponent of both conventional and your own empirical models; would you rate them as “good” or “modestly predictive” or “not great” because of the chaotic nature of the underlying systems?
      Or, if you prefer not to take that on, would you say that most long term climate modeling is rather poor due to the influence of the same chaotic mathematical relationships of the dynamical system called “the real world”?
      I am impressed with virtually everything coming out of the scientific community regarding the past, present and possible future of the environment. My only real disappointment stems from the seemingly-refuted predictions cast by “the models” in the last 20+ years, compared to the present. With “the models” being so clearly out-of-whack, what are we missing?
      Might it be as simple as that fellow a few days or week past, that promoted the idea that global instrumental warming most closely tracks with an equally global seasonal variance on the ozone layer, and its ability to pass through or absorb the particularly energetic portion of the Sun’s spectrum known as UV-A, UV-B and UV-C? His is perhaps not a model with a long track record of having good predictive correlation, but one thing’s for sure: the time constants seem consistent, the scaling seems consistent, the attribution seems rational, and it has the merit of allowing for the Sun’s own fairly substantial 22 year cycle of heightened and lowered UV output synchronous with its magnetic-pole reversal events.
      I may not have presented a comment-able question or point, but I’m hopeful that you might have a response anyway.
      GoatGuy

      • What you are missing GoatGuy, is that the models that miss the mark in climate change/warming have political, not scientific.goals. They are trying to claim that the models are scientific and thus reliable when they are not, because regardless of the outcome, the funding gravy train is based on trying to get the “right” results for political policy goals. The goals of the models used to discover what this post are covering are scientific and therefore it matters much more to the scientists that it match reality. Not all models are bad. The models used for building new airliners are so good, they can actually build a plane from them that will match reality. In the case of this post, however, the models do not appear to have a forecast ability, but can show at least that what we are seeing fits with particular theories currently being researched. I will be excited to see when they can actually predict what we observe before the fact. It is good to see they are making progress.

    • I thought that ( n ) stood for ‘ nano ‘ , in the SI units system, rather than for ‘ nearly ‘.
      So just how nearly does this accelerator get to the value of ( c ) ??
      Is it close enough to detect particle mass increases; or are we just talking 75% of top speed ??
      g

  1. These models are based on less information than climate models and should be treated with even more skepticism. Charged particles are accelerated by the sun the same as they on earth, by electric and magnetic fields. That’s why they keep accelerating past the Earth.

    • Charged particles are accelerated by the sun the same as they on earth, by electric and magnetic fields
      That is precisely what also the Standard Model posits as the laws of physics are the same. What is different is that the solar atmosphere is a very good electrically conductor, while the Earth’s is not.

      • So I looked at the wiki you referenced.
        Seems like they left out a curve.
        So they had M = 1 at the throat.
        It sure would have been nice if they had also plotted what the M=1 velocity is from end to end of the whole nozzle.
        Obviously highway engineers don’t understand de laval nozzles; nor do highway drivers.
        When they choke down the freeway to fewer lanes, the traffic is supposed to speed up, in order to get everybody through the choke point.
        Instead, everybody slams on the brakes.
        g
        Still not sure I understand the gravity acceleration part, although I do get the falling gravity with distance part. It would seem that the particle deceleration, would diminish, in the sun’s frame of reference; but how the velocity increases in the sun’s reference, I don’t get.
        Under that notion, those particles would keep accelerating forever, up to umpteen nines percent of c in the sun’s frame.
        So the whole expanding universe would have particles of immense mass travelling at (c) or extremely close to it.

  2. Article: “…these explosions produce radiation and accelerate particles to nearly the speed of light within seconds. The most powerful blasts dispatch energized particles that can penetrate Earth’s atmosphere within an hour.”
    When someone says something is “nearly” something else, I assume it means at least 75%. But one hour transit time from Sun to Earth would be (8.33/60) = 13.8% of the speed of light.
    That’s very, very fast — 93 million mph — but it’s not what I’d call “nearly the speed of light,” which would be about 670 million mph.

    • The devil is in the details. Individual particles will spiral locally around magnetic field lines and most are trapped. The bulk of the energetic particles that escape generally follows the curved field lines and will be slower in traversing the actual distance. The heated corona escapes even slower taking 1-4 days to reach the Earth.

      • Again, daveburton’s comment was my first thought. 93 million miles in an hour is not “nearly” 93 million miles in 8 minutes, irrespective of the mechanism. A significant percent of C would be a better descriptor.

        • Again: the details. The light electrons are easy to accelerate, but they have to drag the much heavier protons with them when getting to the Earth. There are no discrepancies. You just have to actually read the post.

      • One also needs to read and understand the comment. No discrepancies noted only criticism of the use of the descriptor of “nearly the speed of light”.

        • Nearly the speed of light is quite correct for the electrons at the time and place where they are accelerated. But they cannot get here that fast because they are dragged down by the protons.

      • Dragged down by protons .. electrostatically? I would like to read the article, but it is paywalled. What prevents electrons from just taking off at their relativistic speed?

      • Yes, the post says that the particles are eccerated to near the speed of light “within seconds”. It doesn’t say they retain that velocity by the time they reach the Earth.

      • Thanks for the link. I’ll need some time to read it. Meanwhile, my difficulty with a proton-electron “very strong” attraction is that it only takes some 15eV to completely tear an electron from a hydrogen atom.

        • To tear the electron away takes 2*10^(-18) Joule. This seems small, but there are a LOT of electrons. Another way of putting it: the electric attraction is some 1000,000,000,000,000,000,000,000,000,000,000 times stronger than the gravitational attraction binding the particles to the Sun.

  3. Still thinking how weird it is that with the universe 95% Hydrogen and Helium our sun should be flinging the entire periodic table with only 5% He in the mix.

  4. ‘As matter approaches the speed of light, it approaches infinite mass.” – Einstein
    I assume “particles” have mass. Hence, they are exaggerating.

  5. It’s commendably selfless of Dr. Svalgaard to teach science hobbyists like myself here and at his website. I appreciate his gift of sharing, along with all the other fine minds who participate here, and offer my thanks.

    • I agree. Thanks Leif, and all.
      And I’ll quote the next one up: I just got to understand nature a bit better.

      • He gets flak because when someone suggests that the sun affects climate he points to a time in the past when solar activity was the same as at present and insists that nothing has changed.

        • insists that the Sun hasn’t changed. If you then claim that the climate has, you must look elsewhere for an explanation, and there are lots of places to look.

    • I agree as well. Thank you for your participation Dr. Svalgaard. I do have a question, or – rather – I don’t really understand what this paper is saying. “The powerful shocks occur when high-speed jets expelled from the explosive energy-release site of a solar flare collide with stationary plasma below.”
      So, does that mean the highly accelerated particles are “bouncing: off and that’s what accelerates them?

      • The electric fields in the reconnection region and a host of waves in the plasma accelerate the particles and they rush down into the underlying plasma. The collision [as any high-speed collision – think rifle bullets hitting their target] generates heat and diverse havoc.

  6. It seems that the Alfven electric double-layer shock can accelerate paarticles as well as the Petschek slow-mode hydromagnetic shocks associated with magnetic reconnection events. The termination shock papers do not seem to integrate these although the termination shock may be the same at the slow-mode shocks.

      • It looks like the process described does not invoke Alfven double layers. Bratenahl and I worked for years on magnetic reconnection so I can appreciate their flare process focus. However, Alfven always chided us for not including his double layer effect. Finally we invoked the magnetic reconnection process but included a double layer as a trigger for fast solar flare reconnection which we called an “Impulsive Flux Transfer Event”.

        • The Double Layer is not where causes the [repeated] acceleration of the particles [the electric field points the wrong way]. There are good reasons the DLs are not considered to be the ‘be all and end all’ of astrophysical processes. For one, the charge separation that is a necessary condition for formation of the DL needs a different explanation.

      • Dr Baum,
        Please help me out with reconnection. It seems to me that electrons spiraling around the flux tubes will cause the tubes to repel until the tubes move closer until the relative velocities of the electrons are high enough to overcome the repulsion. Then, the flux tubes will snap together and a large portion of their combined energy will be released. Can it be that simple?

      • “A [somewhat] accessible explanation is here
        http://www.leif.org/EOS/Plasma-Reconnection.pdf
        This paper references the experiment I worked on and cites Bratenahl and Yeates as observing anomalous resistivity in that reconnection experiment. Later I replaced Yeates and then Bratenahl and I called it a conduction mode instability which was consistent with a double layer since decreasing current carrier density was observed in the presence of increasing reconnection current.
        Again, we did not consider the double layer as the primary acceleration mechanism but rather as the trigger which destabilized steady reconnection making the reconnection impulsively flare-like. Before the conduction instability flare-like impulsive activity was not observed in our experiments.

        • we did not consider the double layer as the primary acceleration mechanism
          “It seems that the Alfven electric double-layer shock can accelerate particles”…
          precision in expression helps…

      • “lsvalgaard
        December 7, 2015 at 12:15 pm
        we did not consider the double layer as the primary acceleration mechanism
        “It seems that the Alfven electric double-layer shock can accelerate particles”…
        precision in expression helps…”
        Precision in measurements helps even more. So far as I know solar measurements can’t determine the local level of conductivity or the presence of double layers. If I knew the relative importance of double layers vs hydromagnetic shocks in acceleration I would tell you. But I am certain that neither is of zero importance.

        • solar measurements can’t determine the local level of conductivity or the presence of double layers.
          The local level of conductivity is nearly infinite [depending on the temperature and pressure which are known]. Double Layers are not observed. The point of the paper was to present observational evidence that support the Standard Model [now more than 50 years old].

        • If I knew the relative importance of double layers vs hydromagnetic shocks in acceleration I would tell you. But I am certain that neither is of zero importance
          The modern understanding of Reconnection does not operate with or refer to ‘Double Layers’:
          http://www.leif.org/EOS/Yamado-Reconnection-2007.pdf
          Neither in the laboratory nor in Space Plasmas.
          As far as I am concerned, Alfven’s ideas on DLs are not applicable. I have discussed this with him several times in the past, but he was even more stubborn than I am.

      • Leif says,”As far as I am concerned, Alfven’s ideas on DLs are not applicable. I have discussed this with him several times in the past, but he was even more stubborn than I am.” Semi-infinite?

      • “lsvalgaard December 7, 2015 at 5:59 pm
        The modern understanding of Reconnection does not operate with or refer to ‘Double Layers’:
        http://www.leif.org/EOS/Yamado-Reconnection-2007.pdf
        Neither in the laboratory nor in Space Plasmas.”
        For example we said:
        On flares, substorms, and the theory of impulsive flux transfer events
        A. Bratenahl, P. J. Baum
        Solar Physics, March 1976, Volume 47, Issue 1, pp 345-360
        “Current flow along the reconnection line increases with magnetic flux storage. When flux build-up exceeds the level corresponding to a critical limit on the current, instabilities induce a sudden transition in the mode of conduction.’
        In our earliest publications we called it anomalous resistivity as do the authors of modern solar flare theories.
        Indeed, modern papers call anomalous resistivity the trigger for the flare. But whether the conduction is upset by the fusion term ‘anomalous resistivity’ or the cosmic electrodynamic term ‘double-layer’ seems to be largely a matter of personal choice:
        Double layers and anomalous resistivity in symbiotic relationships
        http://ntrs.nasa.gov/search.jsp?R=19860063247

  7. On Solarham.com they will show ( when it happens) the effects of CME’s. They show the rapid arrival of various particles like protons I am not an expert but visit the site to find out about recent Solar activity and the various videos of events as they are recorded by a number of Solar satellites. It is an interesting site with a ton of links to more Solar info.

  8. I don’t think it can be that simple. One scientist from Sandia suggested to me that the mutual inductance of two-current carrying rods would disappear as the rods snapped together. I played with flexible conductors and an inductance meter and found that such a process never happened.

  9. While this thread is full of intelligent humans with near-orgasmic feeling for this “discovery,” how about using your superior IQs to advance genetics? Organisms (humans) can live forever with the right genetic manipulations. You’ll all be dead in 50-100 years. Why not advance humans instead of human knowledge?

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