Tag Archives: solar flares

Sun’s coronal loops could be optical illusions

An active region of the sun just rotating into the view of NASA’s Solar Dynamics Observatory gives a profile view of coronal loops over about a two-day period, from Feb. 8-10, 2014. (Image credit: NASA/Solar Dynamics Observatory)

Everyone knows the picture of the sun. A bright orange ball with jets of fire spewing out thousands of miles into space with temps soaring above a million degrees. However, a new study from the National Center for Atmospheric Research (NCAR) brings into question coronal loops existence at all.

The report, published in The Astrophysical Journal, found that these may actually be optical illusions. While the researchers were able to pinpoint some of the coronal loops they were looking for, they also discovered that in many cases what appear to be loops in images taken of the Sun may in fact be wrinkles of bright plasma in the solar atmosphere. As sheets of bright plasma fold over themselves, the wrinkles look like bright thin lines, mimicking the look of distinct and self-contained strands of plasma.  

“I have spent my entire career studying coronal loops,” said NCAR scientist Anna Malanushenko, who led the study. “I was excited that this simulation would give me the opportunity to study them in more detail. I never expected this. When I saw the results, my mind exploded. This is an entirely new paradigm of understanding the Sun’s atmosphere.”

Coronal loops are found around sunspots and across active regions of the Sun. These structures are associated with the closed magnetic field lines that connect attractive regions on the solar surface. Many coronal loops last for days or weeks, but most shift quite rapidly. The assumption that they exist is a normal one for scientists because it suits the most basic understanding of magnetism.

The findings, which have been coined the “coronal veil” hypothesis, could have substantial implications for solar research. These coronal loops have been used for decades as a way to garner info about density, temperature, and other physical characteristics of the solar atmosphere.

“This study reminds us as scientists that we must always question our assumptions and that sometimes our intuition can work against us,” Malanushenko said.

The research relied on a realistic 3D simulation of the solar corona produced by MURaM, a radiative magnetohydrodynamic model that was extended to replicate the solar corona in an effort led by NCAR several years ago. The model allowed the researchers to slice the corona in distinct sections in an effort to isolate individual coronal loops.

Since there is a significant magnetic field in the Sun, the existence of magnetic field lines that could trap a rope of plasma between them and create loops seems like an obvious explanation. And in fact, the new study confirms that such loops still likely exist.

However, the loops seen on the Sun have never really behaved exactly as they should, based on the knowledge of magnets. As an example, scientists would assume the solar magnetic field lines to expand as they move higher in the corona. Therefore, the plasma trapped between the field lines should also spread out between the boundaries, creating thicker, dimmer loops. But images of the Sun do not show this. Instead, they show the opposite. The loops further out still appear thin and bright.

The possibility that these loops are instead wrinkles in a coronal veil help explain this and other inconsistencies with scientists’ expectations of coronal loops. It also brings into question new mysteries such as what determines the shape and thickness of the folds and how many of the apparent loops in images of the Sun are actually real strands, and how many are optical illusions.

For the first time, the research group was also able to capture the entire life span of a solar flare, from the build-up of energy below the solar surface to the emergence of the flare at the surface, and finally to the fiery release of energy.

Malanushenko said that understanding the number of coronal loops which are actually optical illusions will require continued observations that probe the corona and new data analysis techniques.

“We know that designing such techniques would be extremely challenging, but this study demonstrates that the way we currently interpret the observations of the Sun may not be adequate for us to truly understand the physics of our star.”

Illustration by Wendy Kenigsberg/Matt Fondeur/Cornell University

Biofluorescence shining light on the search for alien life

The use of ultraviolet flares from red suns and biofluorescence may provide astronomers with vital life signs in the universe

Illustration by Wendy Kenigsberg/Matt Fondeur/Cornell University
Illustration by Wendy Kenigsberg/Matt Fondeur/Cornell University

A new method of searching for life in the cosmos has been pioneered by astronomers from Cornell University.

The team propose that astronomers could utilise harsh ultraviolet radiation flares from red suns — once thought to destroy surface life on planets — to assist in the discovery of hidden biospheres. The team’s study — published in the journal Monthly Notices of the Royal Astronomical Society — suggests that ultraviolet radiation could trigger biofluorescence — a protective glow — from life on exoplanets.

Jack O’Malley-James, a researcher at Cornell’s Carl Sagan Institute and the study’s lead author, says: “This is a completely novel way to search for life in the universe.

“Just imagine an alien world glowing softly in a powerful telescope.”

Biofluorescence, similar to that found in coral, could be used by astronomers to search for life (S.E.A. Aquarium)

Some undersea coral on Earth use a similar form of biofluorescence that the team intend to utilise in the search for life. The coral does this in order to render the sun’s harmful ultraviolet radiation into harmless visible wavelengths, in the process, creating a beautiful radiance.

“Maybe such life forms can exist on other worlds too, leaving us a telltale sign to spot them,” points out Lisa Kaltenegger, associate professor of astronomy and director of the Carl Sagan Institute.

She points out that in our search for exoplanets, we have searched for ones which look like our own planet. This research plays off the idea the biofluorescence may not have evolved on Earth exclusively.

In fact, as this is a form of defence from harsh UV radiation, logic suggests that its usefulness — and thus, the chance of development — would be increased around stars where UV flares are commonplace.

A large fraction of exoplanets — planets beyond our solar system — reside in the habitable zone of M-type stars. This type of star — the most commonly found in the universe — frequently flare, and when those ultraviolet flares strike their planets, biofluorescence could paint these worlds in beautiful colours.

The next generation of Earth- or space-based telescopes can detect the glowing exoplanets — should they exist.

Ultraviolet rays are transformed into less-energetic and therefore less harmful wavelengths through a process called “photoprotective biofluorescence.” This should leave a very specific signal which astronomers can search for.

Kaltnegger continues: “Such bio fluorescence could expose hidden biospheres on new worlds through their temporary glow when a flare from a star hits the planet.”

The astronomers used emission characteristics of common coral fluorescent pigments from Earth to create model spectra and colours for planets orbiting active M stars to mimic the strength of the signal and whether it could be detected for life.

Proxima b — a potentially habitable world found orbiting the active M star Proxima Centauri in 2016 could qualify as a target for such a search. The rocky exoplanet has been one of the most optimal space travel destinations due to the proximity of the star it orbits — although such jaunts are a concern for the far-future.

Jack O’Malley-James, continues: “These biotic kinds of exoplanets are very good targets in our search for exoplanets, and these luminescent wonders are among our best bets for finding life on exoplanets.”

Large, land-based telescopes that are being developed now for 10 to 20 years into the future may be able to spot this glow.

Kaltenegger concludes: “It is a great target for the next generation of big telescopes, which can catch enough light from small planets to analyze it for signs of life, like the Extremely Large Telescope in Chile.”


Original research: Biofluorescent Worlds II: Biological Fluorescence Induced by Stellar UV Flares, a New Temporal Biosignature. Jack T O’Malley-James, Lisa Kaltenegger.