Viewing size of Galaxies 7 Billion light years away?

In summary, scientists say that the galaxy would appear to be twice the expected size (angular size) as a consequence of the expansion of the universe. This is because the space between galaxies expands, and so does the space within a galaxy. However, the angular size of a galaxy at a certain distance will not change as a result of the expansion of the universe.
  • #1
Remo Aviron
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Would a galaxy 7 billion LY away appear to be twice the expected size (angular size) as a consequence of the expansion of the universe? (Assuming the universe is 14 Billion years old). My math says yes. But of course, I am just using trig and geometry. Just curious.
 
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  • #2
I'm not sure how you are using that math, but the galaxy isn't expanding, just the distance between it and here. It would appear a size dictated by the actual size and distance to it.
 
  • #3
Update and correction

Sorry, I messed up the math. It wouldn't be double. I know the Galaxies are not expanding. But the Universe is. Space is.

The question is how does the expansion of universe affect the preceived angular size of the galaxy? For example, if the galaxy were 100,000 ly across, you would expect it to occupy an angle of 0.0008 degrees. Does it occupy this angle, a smaller angle or a larger angle.
 
  • #4
The space between galaxies expands so does the space within a galaxy, so probably you will not see the difference in angular size of that distance galaxy.
 
  • #5
I think Remo Aviron is talking about the 'turn over' in the angular size vs redshift relation which occurs at about a redshift of ~1.65. If he/she is, then if we consider a standard ruler which has physical size 1kpc at a comoving distance of 1Mpc (0.003 billion LY), it will have an apparent angular size = 200 arcsecond. Moving this object to 7 billion LY (redshift =0.6), it will have apparent angular size = 0.15 arcsec, but moving it to reshift 6 (27.468 billion LY) it will actually have a larger apparent angular size when compared to the object at 7 billion LY, ie. apparent angular size = 0.17.

See http://www.atlasoftheuniverse.com/redshift.html" link for more information.
 
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  • #6
Well done, matt, I had a less delicate reply in mind. Scientists excel at discerning facts, politicians excel at manipulating them.
 

1. How do scientists determine the size of galaxies that are 7 billion light years away?

Scientists use a variety of methods to determine the size of galaxies, including measuring their brightness and using mathematical models. However, for galaxies that are 7 billion light years away, the most common method is to measure their angular size, which is the apparent size of the galaxy as seen from Earth. This is done using telescopes and taking into account the distance and expansion of the universe.

2. Can we see the actual size of galaxies that are 7 billion light years away?

No, we cannot see the actual size of galaxies that are 7 billion light years away. Due to the finite speed of light, the light we receive from these galaxies is from 7 billion years ago. This means we are seeing the galaxies as they were 7 billion years ago, and their actual size may have changed since then.

3. What is the average size of galaxies that are 7 billion light years away?

The average size of galaxies that are 7 billion light years away varies greatly, as there are many different types of galaxies in the universe. However, on average, these galaxies tend to be smaller than those closer to us, as they are being observed at an earlier stage in their development.

4. Can the size of galaxies change over time?

Yes, the size of galaxies can change over time. Galaxies are constantly evolving and changing, and their size can be affected by various factors such as interactions with other galaxies, gas and dust dynamics, and the growth of their central black holes. However, these changes may not be observable in a human lifetime.

5. Is there a limit to how large a galaxy can be 7 billion light years away?

There is no known limit to how large a galaxy can be 7 billion light years away. The observable universe is estimated to be around 93 billion light years in diameter, so it is possible for galaxies to be much larger than that. However, the largest known galaxies are typically found closer to us, as they have had more time to grow and merge with other galaxies.

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