This week’s winner of the Clark Planetarium, KUTV-2 Cosmic Quiz is Zachary Griffin. He wants to know, “What is the farthest known galaxy?”
There are several galaxies that are good candidates for the farthest-known galaxy, but what they all have in common is they’re roughly 13 billion light years distant. That means that when astronomers see these galaxies they’re seeing light that has been traveling for about 13 billion years.
It’s amazing to see something that far away because the universe itself is only 13.7 billion years old. We’re seeing the way this galaxy looked less than a billion years after the universe began. These photons of light have been in transit for 95% of the age of the universe.
A quick note about galaxies: We live in a galaxy called the Milky Way. It’s a giant, slowly spiraling collection of about 200 billion stars and it measures about 100,000 light years in diameter.
Our Sun is an ordinary star located about 30,000 light years from our galaxy’s center.
Our nearest galactic neighbor is the Andromeda Galaxy. It’s slightly larger than the Milky Way Galaxy and is located 2.5 million light-years from us. It’s a favorite target for amateur astronomers and is the most distant object visible to the unaided eye. You’ll notice a lot of stars surrounding the Andromeda Galaxy in the image below. Those stars are the stars of our Milky Way Galaxy in the foreground, only a few hundred or thousand light years distant.
Not all galaxies are beautiful spirals, but the Milky Way and Andromeda Galaxies are.
To appreciate how far away the most distant observed galaxy is, it will help to make a scale model.
If you shrunk the Milky Way Galaxy down to about the size of a salad plate (about 7 inches), then the Andromeda Galaxy becomes the size of a dinner plate roughly 12 feet away.
2.5 million light years shrunk down to 12 feet. Intergalactic distances within a small room. Wow, that’s quite a cosmic crunch.
Now that you’ve got that kind of scale in mind, you can begin to appreciate just how far away the “farthest” galaxies are.
At the scale we’ve just created, the farthest galaxies are twelve miles away. That’s the distance from downtown Salt Lake City to Sandy.
And what’s in between?
To answer that question – try thinking about this:
Imagine you’re looking at a region of space as empty as any you’ve been able to detect. You’ve chosen a tiny black bit of the night sky near the Big Dipper that’s only the size of a grain of sand held at arm’s length.
Now imagine that you’ve got the Hubble Space Telescope available to you, and you ask it to stare at that tiny speck of empty space for about ten days, non-stop.
What does the Hubble Telescope see in that “empty” bit of space the size of a grain of sand at arm’s length?
Everything you see in this image is a galaxy, each containing billions of stars. Some of these galaxies are only a few hundred million light-years distant. Some are billions of light-years from us.
One more time, that’s an image of a piece of “empty” sky the size of a grain of sand held at arm’s length. It turns out that deep space looks like this in all directions. Galaxies everywhere. The current estimate is that there are something on the order of 100 billion galaxies in the universe.
So, does it really matter how far away the farthest galaxy is?