Twin Super Nova spaced many LY apart

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emc
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Twin Super Nova spaced many LY apart

Post by emc » Thu Feb 11, 2010 10:12 pm

Would two identical Super Nova spaced (hey, that could be a pun!) many light years apart appear to flare at different rates? (Identical in every way except for “spacing” from our vantage point) I've read the more distant Super Nova would appear to brighten and dim at a slower rate but I don’t understand why.

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Chris Peterson
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Re: Twin Super Nova spaced many LY apart

Post by Chris Peterson » Thu Feb 11, 2010 10:46 pm

emc wrote:Would two identical Super Nova spaced (hey, that could be a pun!) many light years apart appear to flare at different rates? (Identical in every way except for “spacing” from our vantage point) I've read the more distant Super Nova would appear to brighten and dim at a slower rate but I don’t understand why.
I've not heard of any relationship between the timing of a supernova light curve and its distance. Do you happen to have any references? I looked around a bit and didn't find anything.
Chris

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emc
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Re: Twin Super Nova spaced many LY apart

Post by emc » Thu Feb 11, 2010 11:30 pm

This is what I read… the subject is cosmic expansion

... If the universe indeed has been continuously expanding for billions of years, the most distantly observed objects would be moving away at extreme velocities (close to the speed of light). Einstein’s relativity theory predicts that these distant “clocks” will thus run about 10-60% more slowly (due to relativistic effects) than equivalent clocks in the vicinity of the Milky Way. Observations show that in the Milky Way, an exploding star (supernova) takes about seven months to transition from maximum to minimum brightness, and a typical gamma-ray burst takes an average of about 15 seconds to undergo this same transition. However, at great distances these transitions take longer by the exact amounts consistent with their distance in an expanding universe…

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Chris Peterson
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Re: Twin Super Nova spaced many LY apart

Post by Chris Peterson » Fri Feb 12, 2010 5:56 am

emc wrote:If the universe indeed has been continuously expanding for billions of years, the most distantly observed objects would be moving away at extreme velocities (close to the speed of light). Einstein’s relativity theory predicts that these distant “clocks” will thus run about 10-60% more slowly (due to relativistic effects) than equivalent clocks in the vicinity of the Milky Way.
Okay, that makes sense. I wouldn't have thought the most distant supernovas were far enough away for there to be significant time dilation, but I guess that's not true. The most distant supernova is around z=2.4, which means an apparent recession velocity of 0.8 c, and a time dilation of 1.7. I think that only a tiny fraction of detected supernovas are far enough away for time dilation to be apparent, but there are some that have been reported on. Check out The High-Z SN Search Team's list of publications; several are related to the observation of time dilation effects.
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emc
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Re: Twin Super Nova spaced many LY apart

Post by emc » Fri Feb 12, 2010 12:19 pm

Thanks for responding Chris. My question was poorly worded. I appreciate your help.

When I read the listed paragraph, I wondered at the fact that time dilation occurs at great distances due to the objects velocity relative to our position (and that we could observe the phenomena), and I also realized that I would need to be able to understand GR in order to comprehend why. It seemed to me that when two widely spaced supernovas ignited at the same time, the more distant flare would simply be observed some time after the closer one. That it appears to flare at a slower rate is fascinating and puzzling. So I wondered further if it’s kind of like Doppler shift. Since sound changes gradually as the sound source recedes. Is that a good analogy?