- 3786 - SUPERNOVAE - prove the universe is expanding. Measuring cosmic distances using Supernovae 1A starting in the 1990’s has greatly changed our views of the Universe. The measurements were in two parts. The redshift of the light spectrum is measured. This can be thought of as the “Doppler effect“.
---------------- 3786 - SUPERNOVAE - prove the universe is expanding
- The Universe is expanding, so galaxies are moving away from us, the further away they are the faster they are moving away, and the greater the redshift of the light that is measured.
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- The further away the star the dimmer it appears. With Supernovae 1A we have a particular type of supernova explosion that has a standard amount of brightness, or intensity of light. We can calculate distance knowing that amount of dimness is the inverse square is of it distance.
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- Supernovae 1A come from binary systems where one of the stars is a White Dwarf, which by definition must be less than 1.4 Solar Mass, because if it were more massive than 1.4 Solar Mass it would explode as a supernova and if it remains more than 1.4 Solar Mass after that it becomes a Neutron Star.
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- What happens in the binary system is that the White Dwarf is gradually pulling mass from its sister star until it reaches this 1.4 Solar Mass limit. Therefore, astronomers know that the mass at the time of the supernova explosion is exactly 1.4 Solar Mass and therefore they know its “Intrinsic Brightness“. Next, we measure the “Apparent Brightness” from here on Earth. The amount of dimness can than be used to calculate the distance to the supernova light source.
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- Since we know exactly the mass of the star before it exploded we can calculate the intensity of the light that the explosion created. This is the intrinsic, or absolute, or original brightness.
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- Now when we measure the Apparent Brightness we know that it has decreased by the inverse of the radius squared. The light is expanding in a sphere. The area of a sphere is 4*pi*r^2. That tells us mathematically how much the light is diluted in its expansion. In equation form this is:
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-------------- Apparent Brightness = Original Brightness / 4*pi*r^2
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--------------- r^2 = Original Brightness / 4*pi* Apparent Brightness.
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- If we plot the redshift of the wavelength of the light versus the distance calculated by the dimness of the light we get a graph that is nearly a straight line. Especially for distances from 100 to 300 million lightyears it is a straight line with a slope of 0.67% shift / 100 million lightyears.
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- The 0.67% shift is the percentage the Universe has expanded in the length of time of 100 million years. The Apparent Brightness would be exactly the inverse square of distance if the Universe was not expanding during the time the light is traveling here. The light is traveling through progressively larger volumes of space in order to reach us. Therefore, the supernovae will appear dimmer than we would expect from our Apparent Brightness calculation.
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- Consequently, in the graph of redshift versus luminosity the plot is curved. At 40% of the Universes’ current size the distance calculated due to Apparent Brightness would be 35 billion lightyears.
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- However, if we correct for the expansion induced dimming we get another plot that is nearly a straight line. The corrected distance back to when the Universe was 40% its current size gives us a distance of 14 billion lightyears.
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- This corrected distance is the distance between galaxies TODAY. Back with the light first began its journey to us the galaxies were closer together. Therefore, the total distance the light traveled is somewhat less than the corrected distance.
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- With this last correction the Supernovae distance plot in a straight line with a slope of 60% / 8 billion lightyears at the time the Universe was 40% its current size. Therefore:
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-------------- 60% / 8 BLY = 100% / x
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------------- x = 13.3 billion lightyears and put the age of the Universe at 16 billion years.
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- In addition to the space expansion, as the wavelengths of the photons are stretched out, the light progressively looses energy, which further reduces the Apparent Brightness. Adding this correction the plots of redshift versus distance calculate suggests that the expansion of the Universe has been nearly constant for the past 10 billion years at 8% / billion lightyears. ( 60% per 8 BLY). This would put the current age of the Universe at 14.5 billion years.
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- The Cosmic Microwave Background Radiation measurements have allowed more accurate calculating of the age of the Universe putting it at 13.7 billion years. Measured brightness of Supernovae 1A have been an excellent rough cut. Today’s best calculations are telling us that the expansion of the Universe is indeed accelerating.
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- This is not what astronomers expected from the data. They expected that gravity would eventually be slowing down the expansion of the Universe. On the contrary, it is speeding up. Therefore, there must be an anti-gravity force in the Universe that we do not understand. Let’s call it “Dark Energy” that exists it the vacuum of space and we are determined to learn what it is.
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December 14, 2022 SUPERNOVAE - prove the universe is expanding 890 3786
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--------------------- --- Thursday, December 15, 2022 ---------------------------
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