How do scientists determine the age of galaxies in pics taken by Hubble space telescope?
Raymond asked:
I don’t quite understand how they determine that the galaxies in some ultra-deep-field pictures are billions of years old… How do they determine that? How do they know that they are looking into the past of the universe? If they determine that the distance of the galaxies is, for example, 13 billion light years, that means that the light the telescope is able to capture has been traveling for 13 billion years, right? But then how is it that they determine that those are the early galaxies in the universe and that those galaxies were formed soon after the Big Bang? Can someone please explain with simple and easy-to-understand terms? Maybe some examples? Thanks!
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I don’t quite understand how they determine that the galaxies in some ultra-deep-field pictures are billions of years old… How do they determine that? How do they know that they are looking into the past of the universe? If they determine that the distance of the galaxies is, for example, 13 billion light years, that means that the light the telescope is able to capture has been traveling for 13 billion years, right? But then how is it that they determine that those are the early galaxies in the universe and that those galaxies were formed soon after the Big Bang? Can someone please explain with simple and easy-to-understand terms? Maybe some examples? Thanks!
January 13th, 2010 at 11:00 pm
By their colour. SpaceBoy360*
January 16th, 2010 at 4:08 am
The current distance of galaxies and the rate of their expansion makes extrapolation of the age of the universe possible. For example, if you know the distance between to objects, and know how fast they are moving away from each other, it is easy to determine how long ago they were in the same place. The Hubble telescope was instrumental in actually determining the exact distance to far-away galaxies. Using the red-shift of those galaxies, it is also possible to determine how fast they are expanding away from each other. So determining the age of the universe at that point is easy. eelfins
January 18th, 2010 at 9:30 am
The rate of recession (going away from us) is so high (as shown by the Doppler shift of the light of the galaxies) as to give us idea that the galaxies are 13 billion LY away. That means the light is 13 billion years old when it reaches us now. If those galaxies existed 13 billion years ago, and the universe has been expanding only 13.4 billion years, and the first stage (inflation) of the universe after the Big Bang and the formation of matter (protons, electrons, neutrons) took 100 million years, those galaxies were made only 300 million years after the origin of the universe. They are among the first galaxies to form. They were very young when light began the journey. Starrysky
January 19th, 2010 at 2:19 am
They make the assumption that the laws of physics here are the same as the laws of physics there. You’ll want to look at “Hubble’s Law,” and I won’t go into detail here. In cosmology, there’s really no difference between time and distance. When you look at something that appears to be 13 billion light years away, you’re looking at something that “was” 13 billion years ago. At least, that’s a good way of thinking of it. The math is actually that all times and all distances exist en bloc, and our perspective of what’s “now” is quite personal, not absolute. But that gets confusing, so I’d stick with the simpler viewpoint. John de Witt