There's a (Magnetic) Hole in the Sun
Yes, that's right, there's a hole in the sun, but it's not a sign of anything scary, it's actually a wonderful insight to some pretty 'cool' solar dynamics.
Yes, that's right, there's a hole in the sun, but it's not a sign of anything scary, it's actually a wonderful insight to some pretty "cool" solar dynamics.
Imaged by NASA's Solar Dynamics Observatory through filters that are sensitive to extreme ultraviolet light, this huge dark spot in the center of the sun's disk is a low density region of plasma in the sun's corona (the sun's multimillion degree magnetized atmosphere).
The solar corona is a magnetically-dominated region, populated with "open" and "closed" magnetic field lines, that protrude from the sun's interior and into the corona, along which the super-heated plasma is guided. The bright regions in this image are locations of closed field lines, known as coronal loops. Dense plasma is trapped in these elegant loops, being heated, generating intense radiation.
However, in this observation of the sun, an obvious dark patch has rotated into view, a sign that density is low and the hot plasma is escaping from the corona into interplanetary space.
Coronal holes are the source of the fast solar wind that can impact space weather at Earth, and this coronal hole shows that a stream of high-velocity plasma (highly-energetic particles composed mainly of protons) is headed our way. The magnetic field in coronal holes act like a fire-hose, spraying coronal plasma away from the sun as it rotates, spiraling through the solar system.
According to Spaceweather.com, plasma from this coronal hole will reach Earth orbit on Oct. 8-9. It's possible that, depending on magnetic conditions, arrival of this stream of fast solar wind may intensify auroral activity in high latitudes.
Like solar flares and coronal mass ejections (CMEs), intense bursts of solar wind activity can increase the radiation environment surrounding Earth, impacting sensitive electronics in satellites and spacecraft. The SDO and armada of other solar observatories such as the NASA/ESA Solar and Heliospheric Observatory (SOHO) and Japanese Hinode space telescopes are on constant watch for explosive events in the corona and the presence of coronal holes so space weather can be better predicted before it impacts Earth.
A composite image of the sun's corona on Oct. 4 using filters sensitive to 3 different wavelengths of EUV emissions from the sun's corona. Bright regions in the lower corona highlight "active regions" where flares and coronal mass ejections are likely to be triggered over sunspots in loops of magnetic fieldlines. Dark regions highlight areas of "open" fieldlines where plasma is escaping to space as the fast solar wind.
The sun may be an average star when compared to the menagerie of stars that exist in our galaxy, but to Earth and all life on our planet, the sun is the most important object in the Universe. However, regardless of its importance and close proximity, our nearest star holds many mysteries that continue to fox solar physicists after decades of modern studies with cutting-edge observatories. One of the biggest mysteries surrounding the sun is the underlying mechanisms that drive solar flares and coronal mass ejections (CMEs). Monday evening (EST), the sun reminded us that it hasn't quite finished with the current solar maximum (of solar cycle 24), unleashing a powerful X4.9 solar flare -- the biggest of 2014. An armada of space telescopes witnessed the event, including NASA's Solar Dynamics Observatory that can spy the sun's temper tantrums in astounding high definition. Shown here, 5 of the 10 filters from the SDO's Atmospheric Imaging Assembly (AIA) instrument are featured, showing the sun's lower corona (the solar multimillion degree atmosphere) through 5 wavelengths; each wavelength of extreme ultraviolet light representing a different plasma temperature and key coronal features -- such as coronal loops (highlighted here in the 'yellow' 171A filter) and ejected plasma that formed a CME.
At 7:13 p.m. EST (00:13 UT, Feb. 25) -- pictured here on the far left -- the active region (AR) 1990 was crackling with activity. Then, as magnetic field lines from the sun's interior forced together and through the solar photosphere, large-scale reconnection events occurred. Reconnection is a magnetic phenomena where field lines "snap" and reconnect, releasing huge quantities of energy in the process. At 7:44 p.m. EST (00:44 UT) -- second frame from the right -- a kinked coronal loop can be seen rising into the corona. At 7:59 p.m. EST (00:59 UT) -- far right -- solar plasma contained within the magnetic flux is accelerated to high energy, generating powerful x-rays and extreme ultraviolet radiation, creating the X-class flare.
The X4.9 flare was caught through the range of SDO fliters, including this dramatic view as seen through the 131A filter. The flare was so bright that photons from the flare overloaded the SDO's CCD inside the AIA instrument, causing the signal to "bleed" across the pixels. This bleeding effect is common for any optical instrument observing powerful solar flares.
Intense coronal activity is often associated with active regions -- the active lower corona is pictured here, left. In this case, the flare erupted from AR1990, at the limb of the sun. Also associated with active regions are sunspots, dark patches observed in the sun's photosphere (colloquially known as the sun's "surface") -- pictured right. The sun's cooler photosphere has been imaged by a different SDO instrument called Helioseismic and Magnetic Imager (HMI), which detects the intensity of magnetic fields threading though the sun's lower corona and photosphere.
In the case of AR1990, a large sunspot can be seen at the base of the coronal loops that erupted to generate the powerful flare. This is a prime example of how sunspots can be used to gauge solar activity and how they are often found at the base of intense coronal activity and flares.
The HMI monitors magnetic activity across the disk of the sun and can also generate a picture on the direction of the magnetic field polarity. In this observation of the sun's magnetic field around the time of the recent X-class flare, other active regions can be easily seen -- intense white and black regions highlighting where magnetic field lines emerge and sink back into the sun's interior in active regions.
The joint NASA/ESA Solar and Heliospheric Observatory (SOHO), which has been watching the sun since 1996, also spotted the flare, tracking a CME that was generated shortly after. Seen here by SOHO's LASCO C2 instrument, that monitors the interplanetary environment surrounding the sun for CMEs and comets, a growing bubble of solar plasma races away from the sun.
Approximately an hour after the flare, the CME grew and continued to barrel into interplanetary space. Space weather forecasters don't expect that this CME will interact with the Earth's atmosphere as it is not Earth-directed. This observation was captured by SOHO's LASCO C3 instrument -- an occulting disk covers the sun to block out any glaring effect. By combining observations by the SDO, SOHO and other solar observatories, the connection between the sun's internal magnetic "dynamo", the solar cycle, flares and CMEs, solar physicists are slowly piecing together what makes our nearest star tick, hopefully solving some of the most persistent mysteries along the way.