Like Sand Through the Hourglass, So Go the Galaxies

patch of sky covered by grain of sand contains 10,000 galaxies

If you want to obscure your view of something, a grain of sand is probably not the first thing that you would choose. It is so small that it is hard to think of too many things it could cover.

Would you believe that a single grain of sand is sufficient to block out your view of 10,000 galaxies? The Hubble Space Telescope has proven there are over 100 billion galaxies. Even though you can’t see them, the sky is simply lousy with galaxies — each containing about 1,000,000,000,000 stars.

Next time you might feel tempted to dismiss a grain of sand of insignificant, hold it out at arm’s length and contemplate what might be behind it. The patch of sky it covers contains more stars than you could count in your lifetime.

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Singular Facts About Singularities

The regions around supermassive black holes shine brightly in X-rays. Some of this radiation comes from a surrounding disk, and most comes from the corona, pictured here as the white light at the base of a jet. This is one possible configuration for a corona -- its actual shape is unclear.
The regions around supermassive black holes shine brightly in X-rays. Some of this radiation comes from a surrounding disk, and most comes from the corona, pictured here as the white light at the base of a jet. This is one possible configuration for a corona — its actual shape is unclear.

Black holes — also known as “singularities” — can be big or small. Scientists think the smallest black holes are as small as just one atom. These black holes are very tiny but have the mass of a large mountain. Mass is the amount of matter, or “stuff,” in an object.

Another kind of black hole is called “stellar.” Its mass can be up to 20 times more than the mass of the sun. There may be many, many stellar mass black holes in Earth’s galaxy. Earth’s galaxy is called the Milky Way.

The largest black holes are called “supermassive.” These black holes have masses that are more than 1 million suns together. Scientists have found proof that every large galaxy contains a supermassive black hole at its center. The supermassive black hole at the center of the Milky Way galaxy is called Sagittarius A. It has a mass equal to about 4 million suns and would fit inside a very large ball that could hold a few million Earths.