Next-generation lens provides unparalleled, accurate pictures of the solar surface
A next-generation optical device developed by the New Jersey Institute of Technology (NJIT) has allowed scientists to view the Sun in unparalleled detail.
Developed at NJIT’s Big Bear Solar Observatory (BBSO), the lens corrects images of the Sun that are typically distorted by multiple layers of atmospheric turbulence.
It is providing scientists with the most precisely detailed, real-time pictures to date of solar activity occurring across vast stretches of the Sun’s surface.
The observatory’s 1.6-meter New Solar Telescope can now produce simultaneous images, for example, of massive explosions such as solar flares and coronal mass ejections that are occurring at approximately the same time across large structures such as a 20,000-mile-wide sunspot in the Sun’s photosphere.
“To understand the fundamental dynamics of the Sun, such as the origin of solar storms, we need to collect data from as wide a field of view as possible,” said NJIT’s Professor Philip Goode.
“During large flares, for example, magnetic field changes appear to occur at many different places with near simultaneity,” he explained.
“Only by seeing the comprehensive array of eruptions all at once will we be able to accurately measure the size, strength and sequencing of these magnetic events and also analyse the forces that propel the star’s magnetic fields to twist around each other until they explode, spewing massive amounts of radiation and particles that, when directed earthward, can cause disruptive space weather.”
The multi-conjugate adaptive optics (MCAO) device sits downstream of the aperture of the BBSO telescope, currently the world’s highest-resolution solar telescope.
The system is composed of three mirrors that change shape to correct the path of the incoming light waves, guided by a computer attached to ultra-fast cameras that take more than 2,000 frames per second to measure aberrations in the wave path.
The system is called multi-conjugate because each of the three mirrors captures light from a different altitude - near the ground and at about three and six miles high - and the three corrected images together produce a distortion-free picture that eliminates the effects of turbulence up to about seven miles.
The MCAO system has tripled the size of the corrected field of view now available with the current technology, known as adaptive optics, which employs a single shape-shifting, or deformable, mirror to correct images.
“The gain of using three deformable mirrors instead of one is easily visible. The images are crisp in a much larger area,” said researcher Dirk Schmidt. “After many years of development, this is an important milestone for the new, wide-field generation of solar adaptive optics.”
Turbulent airflows at different layers of the Earth’s atmosphere, from the ground up to the jet stream, change the path of the Sun’s light faster than the human eye can compensate, blurring the images captured by conventional telescopes in a similar fashion to how hot exhaust creates a haze on highways.
The blurring occurs when air masses at different temperatures mix, distorting the propagation of the light and causing it to take an ever-changing, random path from the distant object, arriving at the observer with a randomized angle of incidence. That same atmospheric turbulence causes the twinkling of stars.
The MCAO team, which includes researchers from NJIT, NSO and the Kiepenheuer Institute for Solar Physics in Germany, has been working together for more than a decade on the next generation of adaptive optics to correct these distortions.
“Over the years, we had reconfigured the mirrors scores of times, waiting for that ‘Wow!’ moment,” Goode said. “Finally, late last July, we saw what we had long sought - a continuous stream of sharp, wide-field corrected, but essentially identical images.
“There was stunned silence, followed by applause. We then repeated the test several times by looking at various places on the Sun to prove we had succeeded. The final trick was narrowing the field to get a deeper-focused correction with each mirror, much like you would adjust a camera to have the near and far field in focus.”
The new technique provides a clearer, more comprehensive view of solar activity that could eventually allow researchers to understand some of the Sun’s more mysterious dynamics.
For example the means by which explosions emanating from its surface produce magnetic explosions and radiation that accelerate particles to nearly the speed of light within seconds.
In addition, the greater the understanding of the Sun’s physical processes, the better policymakers will be able to predict and prepare for solar storms which often disrupt communications satellites, knock out GPS systems and shut down air travel.