The sun is not the perfect sphere

Scientists recently used the RHESSI spacecraft (NASA) to test the sun's roundness with unprecedented accuracy. They discovered that the sun was not the perfect sphere. In years of intense activity, the sun formed a "red melon skin" that gradually increased its flatness: the sun's equatorial radius was slightly larger than its polar radius.

Results are published in Science Express on October 2.

Co-author Hugh Hudson of the University of California Berkeley said: 'The sun is the largest object and therefore the smoothest object in the solar system. Because of its strong gravitational force, its perfection reaches 99.999%. Determining the exact shape of the sun is not a simple thing. '

The team completed the work by analyzing data from high-energy solar spectrophotometer lenses Reuven Ramaty or RHESSI, which is an X-ray space telescope launched in 2002 with a mission to explore. the fire of the sun. Although RHESSI is not created for the purpose of determining the sun's roundness, it is actually ideal for this purpose. RHESSI observed the solar disk through a narrow cut, and turned at 15 rpm. The rapid rotation with the spacecraft model sampling data (necessary to capture the image of the sun's flame) has enabled researchers to trace the shape of the sun with little systematic errors than previous studies. Their technique is particularly sensitive to small differences in equatorial radius and polar radius or 'flatness'.

Hudson describes: 'We found that the surface of the sun has a rather rugged structure: bright lines are arranged in a grid pattern, much like the shell of a cantaloupe but much more subtle. During the active phases of the sun, these lines appear around the equator, brighter and larger than the 'waist of the star'. At the time of the 2004 observation of RHESSI, the lanes increased the equator's radius to an angle of 10.77 + 0.44 milli arcsecond , or the width of a human hair when viewed from a mile away.

Ripple lines like red melon skin on the surface of the sun.The white glowing magnetic network has made the sun flatter during periods of strong activity.Amateur astronomer Gary Palmer took this picture in July 2005 thanks to the purple-K calcium filter.(Photo: Gary Palmer)

Alexei Pevtsov, a scientist at the RHESSI program at NASA, said: 'It sounds like a very small angle, but in fact it has great significance.' Small deflection from perfect roundness can affect the sun's pulling force on Mercury; at the same time altering Einstein's theory of relativity. Einstein's relativity depends on careful calculations of the orbits of the planets. Small bulges are also signs that reveal the mysterious movement inside the sun. For example, if the sun has a fast moving core after the first stage of the star formation process, it will cause the surface to expand. 'The exact calculations of RHESSI give strict conditions for such models'.

The lines like melon peel are actually magnetic. They form huge bubbles of convection on the surface of the sun and are called 'super particles'. Super particles are bubbles in a boiling pot of water that is magnified to the size of a star, in the sun they can reach 30,000 km (twice the width of the Earth), and are created a magnetized magnetization. The magnetic field at the center of these bubbles spreads to the edge, where they form magnetic lines. The lines appear most clearly in the years near the Solar Max time - the time when the solar cell inside the sun "increased rotation speed" to create the strongest magnetic field. Solar physicists have known super particles and magnetic networks that they have created for years, but only now RHESSI can reveal the unexpected relationship between super particles and degrees. flattening of the sun.

Hudson said: 'When we exclude the effect of magnetic networks, we get the exact parameters of the sun's shape under the influence of gravitational forces and motion. The corrected flatness of the non-magnetic sun is 8.01 + - 0.14 milli arcsecond, close to the predicted value of a simple rotation '.

Additional analysis from the flatness data obtained by RHESSI can help researchers detect a seismic form of seismic wave that has long been resounding inside the sun: is the gravitational oscillation itself. Also called 'g-mode'. The discovery of g-mode will open a new boundary for solar physics - the science that studies the inner core of the sun.

Martin Fivian, Hugh Hudson, Robert Lin and Jabran Zahid wrote an article announcing the findings with the title 'A large excess in apparent solar balance due to surface magnetism' (roughly translated as' Sun is flatter than normal due to magnetic surface '); The article is published in the October 2 issue, Science Express.