Just How Small You Are

On my Google homepage I have the NASA Image of the Day and today's image struck me as particularly interesting. First, the image:


Here is the description that goes along with it:

Cosmic Heavyweights in Free-for-All

The most crowded collision of galaxy clusters has been identified by combining information from three different telescopes. This result gives scientists a chance to learn what happens when some of the largest objects in the universe go at each other in a cosmic free-for-all.

Using data from NASA's Chandra X-ray Observatory, Hubble Space Telescope and the Keck Observatory on Mauna Kea, Hawaii, astronomers were able to determine the three-dimensional geometry and motion in the system MACSJ0717.5+3745 (or MACSJ0717 for short) located about 5.4 billion light years from Earth.

The researchers found that four separate galaxy clusters are involved in a triple merger, the first time such a phenomenon has been documented. Galaxy clusters are the largest objects bound by gravity in the universe.

In MACSJ0717, a 13-million-light-year-long stream of galaxies, gas and dark matter -- known as a filament -- is pouring into a region already full of galaxies. Like a freeway of cars emptying into a full parking lot, this flow of galaxies has caused one collision after another.

Image Credit: X-ray (NASA/CXC/IfA/C. Ma et al.); Optical (NASA/STScI/IfA/C. Ma et al.)

If you look at the image you will see several galaxies and a few foreground stars. I should point out that if you look closely enough you will notice that many, and as a matter of fact most of those spots and smudges are galaxies. Of the several hundred points of light in the image only a small fraction are foreground stars in our own galaxy. From my count there are only ~26 foreground stars in the image. The rest are galaxies. (I should say that it is hard to differentiate some galaxies from foreground stars by sight, but foreground stars in images like this typically have diffraction lines.)

So think about the number of galaxies in the picture and then think that the Milky Way has ~100-200 billion stars in it, and the Milky Way is only a medium or even a small galaxy. Now look at the picture and consider how many galaxies there are and that every smudge, every discoloration and point of light is a galaxy. And each galaxy has as many or more stars than the Milky Way. That is just how small you are.