Erupting Prominences

Jupsat Pro Astronomy Software

Secrets of the Deep Sky

Get Instant Access

Looping arches of magnetism hold up, suspend and insulate elongated structures filled with material at a temperature of about 10,000 kelvin, which is hundreds of times cooler and denser than the surrounding million-degree corona, ttese structures are called prominences when seen in hydrogen-alpha photographs taken at the apparent edge of the Sun, perhaps because they prominently stand out against the dark background,

FIG. 7.12 Solar flare model A solar flare is powered by magnetic energy released from a magnetic interaction site above the top of the loop shown schematically here. Electrons are accelerated to high speed, generating a burst of radio energy as well as impulsive loop-top hard X-ray emission. Some of these non-thermal electrons are channeled down the loop and strike the chromosphere at nearly the speed of light, emitting hard X-rays by electron-ion bremsstrahlung at the loop footpoints. When beams of accelerated protons enter the dense, lower atmosphere, they cause nuclear reactions that result in gamma-ray spectral lines and energetic neutrons. Material in the chromosphere is heated very quickly and rises into the loop, accompanied by a slow, gradual increase in soft X-ray radiation. This upwelling of heated material is called chromo-spheric evaporation.

resembling arched viaducts or bridges, like the Pont Neuf in Paris, ttey appear as dark, snaking features, called filaments, when projected against the bright chromosphere disk. So, prominence and filament are essentially two words that describe different perspectives of the same thing, tteir long sinuous forms trace out a region of magnetic neutrality that separates large areas of opposite magnetic direction, or polarity, in the underlying photosphere.

Coronal loops that are anchored within individual active regions are about ten times smaller than the total length of the largest prominences or filaments. Active regions sometimes appear underneath a prominence, and a coronal streamer is often found above it. In such a helmet streamer, a low-density cavity surrounds the prominence with a dense helmet dome overlying the cavity.

Prominences and filaments can remain suspended and almost motionless above the photosphere for weeks or months, but there comes a time when they cannot bear the strain, tten, without warning, the supporting magnetism becomes unhinged (Fig. 7.13), most likely because it got so twisted out of shape that it snapped. And a surprising thing happens! Instead of falling down under gravity, the stately, self-

FIG. 7.13 Filament lifts off A filament is caught at the moment of erupting from the Sun. The dark matter is relatively cool, around 20,000 kelvin, while the bright material is at a temperature of about a million kelvin. The structure extends 120,000 kilometers from top to bottom. This image was taken from the Transition Region And Coronal Explorer, abbreviated TRACE, on 19 July 2000 at a wavelength of 17.11 nanometer, emitted by eight and nine times ionized iron, denoted Fe IX and Fe X, at a temperature of about 1.0 million kelvin. (Courtesy of the TRACE consortium and NASA; TRACE is a mission of the Stanford-Lockheed Institute for Space Research, ajoint program of the Lockheed-Martin Solar and Astrophysics Laboratory, or LMSAL for short, and Stanford's Solar Observatories Group.)

contained structures erupt, often rising as though propelled outward through the corona by a loaded spring (Fig. 7.14).

It's as if the lid had been taken off the caged material. Cool gas is then flung outward in slingshot fashion, tearing apart the overlying corona and ejecting large quantities of matter into space.

ttese eruptive prominences, as they are called when viewed at the Sun's apparent edge, are hurled outward at speeds of several hundreds of kilometers per second, releasing a mass equivalent to that of a small mountain in just a few hours. Such an event is sometimes called a disparition brusque for its sudden disappearance (Fig. 7.15). Eruptive prominences can be larger, longer lasting and more massive than solar flares.

Prominences, or filaments, often re-form in the same shape and place after an explosive convulsion. It is as if some minor irritation builds up beyond the limit of tol-

FIG. 7.14 A prominence erupts Rapid, sequential hydrogen-alpha photography catches an erupting prominence, which had not been detected as a filament during previous days. It suddenly rose from an active region and expanded at an apparent velocity of 375 kilometers per second, hurling material far away from the Sun. Here the magnetic loops rise to a maximum visible extent of 360,000 kilometers injust 16 minutes. This sequence of hydrogen-alpha images was taken on the west edge, or limb, of the Sun using the automatic flare patrol heliograph at the Meudon Station of the Observatoire de Paris; the solar disk has been occulted to give a better view of the event. (Courtesy of Madame Marie-Josephe Martres, and observer Michel Bernot, Observatoire de Paris, Meudon, DASOP.)

FIG. 7.14 A prominence erupts Rapid, sequential hydrogen-alpha photography catches an erupting prominence, which had not been detected as a filament during previous days. It suddenly rose from an active region and expanded at an apparent velocity of 375 kilometers per second, hurling material far away from the Sun. Here the magnetic loops rise to a maximum visible extent of 360,000 kilometers injust 16 minutes. This sequence of hydrogen-alpha images was taken on the west edge, or limb, of the Sun using the automatic flare patrol heliograph at the Meudon Station of the Observatoire de Paris; the solar disk has been occulted to give a better view of the event. (Courtesy of Madame Marie-Josephe Martres, and observer Michel Bernot, Observatoire de Paris, Meudon, DASOP.)

FIG. 7.15 Disparition brusque A prominence shines brightly at the south-east edge of the Sun in the red light of hydrogen alpha, printed here as a negative image for contrast. It had been observed as a dark filament for weeks at a time during several previous rotations of the Sun. Then, in less than 40 hours after this picture was taken, the prominence was no longer visible. It probably rose and disappeared high in the corona withinjust a few hours. The French astronomers use the term disparition brusque to describe this sudden disappearing act of a large prominence rooted in a quiet region of the Sun. (Courtesy of Madame Marie-Josephe Martres, Observatoire de Paris, Meudon, DASOP.)

FIG. 7.15 Disparition brusque A prominence shines brightly at the south-east edge of the Sun in the red light of hydrogen alpha, printed here as a negative image for contrast. It had been observed as a dark filament for weeks at a time during several previous rotations of the Sun. Then, in less than 40 hours after this picture was taken, the prominence was no longer visible. It probably rose and disappeared high in the corona withinjust a few hours. The French astronomers use the term disparition brusque to describe this sudden disappearing act of a large prominence rooted in a quiet region of the Sun. (Courtesy of Madame Marie-Josephe Martres, Observatoire de Paris, Meudon, DASOP.)

erance, and the magnetic structure tosses off the pent-up frustration, like a dog shaking off the rain. Long, dark filaments rise and disappear, replaced by an elongated arcade of bright X-ray loops across the initial filament position, so their magnetic backbone regroups as before beneath the erupting prominence.

Closed magnetic loops apparently support the long filament, like parallel hammocks, at heights that are about ten times the diameter of the Earth, ttis arcade of closed loops is anchored in the Sun, but is opened up at the top by the rising filament, like removing the top of a jack-in-the-box. tte magnetism subsequently reconnects and closes up again beneath the erupting filament or prominence, forming a new arcade of closed loops that shines in X-rays and resembles a giant's rib cage.

tte disappearing prominences are strongly correlated with another form of energetic solar activity, the coronal mass ejections, that play an important role in solar-terrestrial interactions.

Was this article helpful?

0 0
Telescopes Mastery

Telescopes Mastery

Through this ebook, you are going to learn what you will need to know all about the telescopes that can provide a fun and rewarding hobby for you and your family!

Get My Free Ebook


Post a comment