September 17, 2014

03.03.11: The Riddle of the Blank Sun: Solved?

A spotless Sol… (Photo by Author).

   Researchers At the Indian Institute of Science and Education and the Harvard-Smithsonian Center for Astrophysics may have shed light on an enduring mystery from the past decade. In an article due to be published today in Nature, Dibyendu Nandi and co-author Andre Munoz-Jaramillo have come up with convincing evidence as to why the past solar minimum of 2008-09 was such a persistent one. During this minimum, over 600 spotless days occurred, the most since the great minimum of 1913. As a result, the outer magnetic sheath of the sun that we reside in shrunk, the Earth’s upper atmosphere cooled due to lower ultraviolet levels and contracted, and an increase of cosmic ray activity was seen in the inner solar system. This subsequently affected the usual drag that is induced on satellites, slowing down the rate of orbital decay and causing a buildup of space junk… just what’s up with our nearest star?

   Now, researchers have built a model of the solar interior that fits a description of what has actually occurred; and the trouble started back at the peak of cycle #23 with a speeding up of the “Great Conveyor Belt” of plasma in the suns interior. This magnetic dynamo sub-ducts sunspot activity towards the poles, only to have them “well up” as these conveyors turn in opposite directions in both hemispheres. Paradoxically, a slowing down leads to a relaxing and expansion of the belt, allowing magnetic activity to surface; speeding up meant the activity never had a chance to surface. Sunspot activity usually begins at high latitudes at the beginning of a cycle, a hallmark that the new cycle is indeed underway. As the sunspot cycle progresses, sunspot activity tends to progress to lower latitudes. The model suggested by Nandi and Munoz is built on the buoyant evolution of sunspots versus the interplay of the magnetic dynamo and the meridional flows in the solar interior. This theory may also explain two other lingering mysteries; why are sunspots never seen at polar solar latitudes? Does the sun have longer cycles juxtaposed over the known 11 year one, such as the 70 year cycle that occurred in the 17th century known as the Maunder Minimum?

   Researchers will soon have a chance to put all of these models to the test. NASA’s Solar Dynamics Observatory is on solar vigil, and the twin STEREO spacecraft have reached a vantage point giving scientists 360° coverage of the Sun. Solar cycle #24 will see the sun scrutinized as never before. Even today, two new sunspot groups have emerged, and a large prominence looking like an acacia tree can be seen on the limb of the sun from Astroguyz HQ via our trusty PST… the approaching 2013-14 solar maximum may prove to mark a renaissance in solar science.      

 

26.10.09:Seeing Starspots.

A simulation of Corot-2a with transiting hot Jupiter and starspots. (Simulation and phot by author).

A simulation of Corot-2a with transiting hot Jupiter and starspots. (Simulation and photo by author).

We know more about our Sun than any other star because it gives us the opportunity to study solar activity up close. But just how normal is it? Recently, astronomers have been able to spy activity on other suns, teasing the data out of exoplanet transits. These are planets that happen to cross the tiny visible face of their parent star as seen from our line of sight and thus exhibit a tiny but measurable dip in their apparent brightness. Earlier this year, a team at the Hamburg Observatory has been refining this technique by monitoring the star Corot-2a. A younger Sun-like star, Corot-2a spins once every 4.5 earth days and possesses a transiting “hot Jupiter” which orbits once every 1.74 days. Examining a statistical analysis of the light curve as seen by the European Space Agencies’ (ESA) prolific Corot space observatory has yielded “notches” in the smooth curve, a tell-tale sign of “starspot” activity. This was conducted over 80 successive transits. The goal is to begin puzzling together a “butterfly diagram” for alien suns, much like the familiar 11 year cycle diagram yielded by Sporer’s Law for our own Sun. Doubtless, other suns follow different cycles, and this data will add to our understanding of stellar evolution. This will also answer such questions about our own Sun, such as; why do sunspots never form above a particular latitude? Are there larger interwoven cycles? And just what was our Sun like in its juvenile days?