The telescope image at the right was taken of the Andromeda Galaxy, which is loc
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Question
The telescope image at the right was taken of the Andromeda Galaxy, which is located about 2.5 million ly away from us. Is this an image showing how the Andromeda Galaxy looks right now, how it looked in the past, or how it will look in the future? Explain your reasoning.
Imagine that you are observing the light from a distant star that was located in a galaxy 100 million ly away from you. By analysis of the starlight received, you are able to tell that the image we see is of a 10-million-year-old star. You are also able to predict that the star will have a total lifetime of 50 million years, at which point it will end in a catastrophic supernova.
How old does the star appear to be to us here on Earth?
How long ago was it that the star was actually 10 million years old? Explain.
How long will it be before we receive the light from the supernova event? (Note that we have already received the light from the star as it was at age 10 million.)
Has the supernova already occurred (at the time we first observed the star)? If so, how long ago did it occur?
9. Imagine that you take images of two main sequence stars that have the same mass. From your observations, both stars appear to be the same age. Consider the following possible interpretations that could be made from your observations. For each one, explain why the interpretation does or does not make sense. (HINT: Go back to your answers regarding the photographs in questions 2-6)
Both stars are the same age and the same distance from you.
Both stars are the same age but at different distances from you.
The stars are actually different ages but at the same distance from you.
The star that is closer to you is actually the older of the two stars
The star that is farther from you is actually the older of the two stars.
Explanation / Answer
The image is actually showing how the Andromeda galaxy looked in the past, precisely 2.5 million years ago. It is because the galaxy is 2.5 Millin light years away and hence the light received for the image is what it emitted 2.5 million years before.
How old does the star appear to be to us here on Earth?
The star appears to be of 10 million years old, as stated.
How long ago was it that the star was actually 10 million years old? Explain.
The star is 100 million light years away and therefore, the star was 10 million years old at 100 million light years ago.
How long will it be before we receive the light from the supernova event? (Note that we have already received the light from the star as it was at age 10 million.)
The total lifetime of the star is 50 million years and already we have received the light as it was at 10miilion year old. Therefore, it would be another 40 million years before we receive the light from the supernova event.
Has the supernova already occurred (at the time we first observed the star)? If so, how long ago did it occur?
Yes, as stated, the star was 10 million years old at 100 million light years ago. The lifetime of the star was 50 million years. Therefore, the supernova occurred (100-50-10) 60 million years ago.
9. Imagine that you take images of two main sequence stars that have the same mass. From your observations, both stars appear to be the same age. Consider the following possible interpretations that could be made from your observations. For each one, explain why the interpretation does or does not make sense. (HINT: Go back to your answers regarding the photographs in questions 2-6)
Both stars are the same age and the same distance from you.
Not possible to have stars of same mass at the same distance and of the same age.
Both stars are the same age but at different distances from you.
Possible as the observations support it.
The stars are actually different ages but at the same distance from you.
Not possible as explained earlier.
The star that is closer to you is actually the older of the two stars
No, the light of the star which is closer will be seen earlier and hence it will be newer.
The star that is farther from you is actually the older of the two stars.
Yes, the light from the farther star will be seen later and hence might be the older.
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