Holes in the Sun

Not too long ago, photos appeared on the Internet that showed a huge hole in the sun. What the heck are these big black holes, some of which are large enough to swallow at least 50 Earths?

First of all, these are usually photos from NASA's orbiting Solar Dynamics Observatory, and they're just large dark areas in the X-ray part of the spectrum. One of these appeared on January 1, 2015 when the sun was in its active period. These events are called coronal holes. The corona is the sun's atmosphere. In order to see these, one must image the sun in a spectral limited exposure using extreme ultraviolet light and X-rays. They are not visible in the visible region of the spectrum. Astronauts on the Skylab space station first saw coronal holes in 1973, but the first observations in X-ray go back to the 1960's.

Actually, coronal holes are caused by magnetic field lines of the sun that come out of the photosphere (the surface) and instead of arcing back they leave the sun. This causes the particles (high energy protons) to heat up and glow. Normally, the coronal magnetic lines loop back, but in a coronal hole, they don't. The overall effect is to eject stronger (higher energy) solar winds than in the other parts of the sun. Keep in mind that the corona of the sun is heated to 1 to 2 million degrees K. The cooler black area is also a bit cooler as far as UV and X-rays emissions are concerned. That's why they appear to be black.

A coronal hole isn't really a hole. It's just a region of the sun's atmosphere that's lower in density. They're different than sunspots, which are lower temperature zones on the photosphere of the sun. Coronal holes appear at the polar areas of the sun. The higher energy solar winds from these holes cause very spectacular auroras, but they can also disrupt satellites and communications. This means that coronal holes are a factor in space weather.

The sun's magnetic field is very strong and varies all over the place from the poles to the equator. The polar field is 1 - 2 gauss and in sunspots the fields hits 3,000 gauss. It's obvious that something goes wrong with the magnetic lines to form these coronal holes. The sun's magnetic field is complicated and the lines often twist and tangle to cause coronal mass ejections, which are a much more serious event that could cause serious consequences for Earth's electronic driven communication array.

This is just another danger to Earth, but other wise it's spectacular artifact in size and area on the sun.

Thanks for reading.