The Internet’s Virtual Galaxy Trip

How would the galaxy look in the eyes of those who travel to it from distant space? “SPACE.com,” a space science web site, can show you in its virtual galaxy trip.

The first stop for those who travel to the galaxy is the “halo.” The halo, which consists of stars and gas surrounding the galaxy, measures approximately 100,000 light years in radius and 1,000 light years in thickness. There are 170 groups of permanent stars and more than 10 small galaxies contained within.

The next stop would be the spiral disc. Scientists have estimated that there are about 100 billion stars in the galaxy. But it was recently reported that there are an additional one billion stars which are very old and almost invisible.

Most of the stars in the galaxy are concentrated in the main disc. The largest disc is flat and moves spirally motion, like the swirl of a hurricane. Our 4.6 billion-year-old sun is in a spiral arm of the galaxy and is 26,000 light-years away from the center of the galaxy.

If a spacecraft goes nearer to the expanded part, which is the densest and the brightest part at the center of the galaxy, it would feel a stronger gravity force. There is a bar- shaped group of stars in the expanded part of space. There are approximately 30 million stars spread over a distance of 27,000 light years in the “galaxy bar.” Those stars are easily visible since most of them are old red stars.

The final destination would be a black hole. One black hole which is estimated to be located in our galaxy is called “Sagittarius A” or “Sgr A.” Most black holes are formed when stars with great mass collapse. But large black holes like “Sgr A” in the galaxy seem to have been born along with their galaxies. They not only swallow materials around them, but also have the force to arrange stars in the correct positions.

Yi-Young Cho lycho@donga.com