Further Away Table of Contents The Human Body

5. And even further


Our Milky Way contains more than 100 billion stars, has a diameter of 100.000 ly and a thickness of 1000 ly. Big enough to be the Universe, one would say. And that was the opinion of many scientists in the beginning of the twentieth century. There was a discussion going on about a special kind of nebula, the Spiral Nebula's, whether they belonged to the Milky Way, or that they were located outside the Galaxy. For example the Andromeda Nebula, clearly visible on a clear night for the unarmed eye as a small fuzzy cloud.
Around 1925 it became convincingly clear that the Andromeda nebula was a separate "island universe". Suddenly the Universe became much larger.

Really a lot bigger!
We know now that the Andromeda Galaxy is located at a distance of about 2.5 million ly from the Milky Way. Actually it is a close neighbor, because there are many more, often much further away. How many? Of course not easy to count them, but the present estimate is many hundreds of billions!
And how far away?
In 2008 a galaxy has been discovered at a distance of 12.8 billion ly. Keep in mind that looking at far away objects, we see them as they were in the past! We observe this galaxy, as it was 12.8 billion years ago, when the Universe was only a few hundred million years old.

Here are a few beautiful pictures of nearby galaxies. Some of them got nicknames. NGC stands for New General Catalogue, and M for the Messier Catalogue.

M104 (Sombrero) (29 million ly)

NGC 4414 (62 million ly)

M101 (Pinwheel) (27 million ly)

M51 (Whirlpool) (23 million ly)

NGC 1300 (61 million ly)

M81 (Bode's Galaxy) (12 million ly)

The images above may suggest that galaxies are isolated, "quiet" islands, but that is far from the truth. The Whirlpool is aleady an example of two interacting galaxies, and the Antennae galaxies show a real collision. The Universe contains clusters of galaxies, while other regions are remarkably void. And M87 shows a 5000 ly long "jet" probably originating in a black hole in the center of the galaxy.

NGC 4038 & 4039 (Antennae) (45 million ly)

Seyfert Sextet (190 million ly)

M87 (55 million ly)

With powerful telescopes, numerous galaxies can be found everywhere in the night sky.
The left picture below, taken with the Hubble Telescope in 2004, shows a part of the deep sky. The size of the picture corresponds to about one-tenth of the diameter of the Moon, as seen from the Earth. The picture contains an estimated 10.000 galaxies. The right image below shows a detail.

Billions of galaxies, each with billions of stars. How many stars are there in the (observable) Universe?
A recent estimate gives 71022

Hubble Ultra Deep Field Image


One more important discovery by Hubble must be mentioned here.
Have you ever heard the siren of an approaching ambulance? How the pitch of the siren is higher, and then, after passing you, lower? It is called the Doppler effect and it works not only for sound, but also for light. When a light source approaches you the color will be a little bit more blue, when it moves away, it will be a bit more red.
The effect can only be noticed when the relative speed is high, hundreds or even thousands of km/s.
Hubble discovered that almost all galaxies had a "red shift", meaning that they are moving away from us. Even more interesting, the larger the distance of a galaxy, the larger this red shift. It looked like the Universe had exploded, with the remnants (the galaxies) moving outward. When would this explosion have taken place? At present the astronomers are pretty sure, that this Big Bang took place about 13.7 billion years ago.
Later more about this Big Bang. Let us first return to the Human Realm.

Further Away Table of Contents The Human Body