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------------ 1884 - What we know about the expansion of the Universe?
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- We know the Universe is expanding at an ever faster rate. What is causing this expansion? We don’t know. We call it the repulsive pressure of “Dark Energy“. What is it expanding in to? We don’t know. We call it “past the edge of the Observable Universe“. This review is about how we know what we think we know about the expanding Universe.
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- It was in the 1920’s that Henrietta Leavitt discovered that some stars pulsate and the faster they pulsate the brighter they are. Knowing their distance we could calculated their intrinsic brightness. Once intrinsic brightness is known we can calculate other unknown distances:
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--------------------- Apparent Brightness = Intrinsic Brightness / 4 * pi * (distance)^2
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--------------------- Distance ^2 = Intrinsic Brightness / Apparent Brightness * 4 * pi
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- Space is expanding between those galaxies that are close enough together to be gravitationally locked. If galaxies are separated by enough space then Dark Energy overpowers gravity and their separation accelerates. The Milky Way Galaxy and the Andromeda Galaxy are gravitationally locked and these two galaxies will merge in about 5 billion years from now. Galaxies further away will be flying away from us.
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- Gravity is a force that falls off, weakens, with the square of the distance of separation
( r ).
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------------------------ F = G *m*M / r^2
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- Dark Energy is a repulsive force that remains constant with distance. Or, possibly even increases with distance. The Universe is expanding and may be even be expanding at an ever increasing acceleration of expansion.
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- How do we know this?
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- We are saying that the faster galaxies are away the faster they are moving away. Eventually all these galaxies will be so far away their constant speed of light will never reach us. Unless galaxies are gravitationally locked and merging they will all disappear from sight.
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- How do we measure these distances and the receding velocity of these stars? We measure the brightness of exploding stars.
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- Since 1995 observations of distant supernovae have convinced astronomers that galaxies are speeding away from us at an accelerating rate. Edwin Hubble taught us in 1923 that galaxies were receding. The further away the faster they were receding, but we did not know that this rate was accelerating. Empty space is growing in volume. The more volume the faster space grows.
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- Astronomers calculate distances by measuring the brightness of a “ known “ light source residing in the galaxy. Astronomers measure the receding velocity by the redshift ( Doppler shift) of the wavelengths of a known light element. The acceleration conclusion came from the discovery that exploding stars are dimmer than expected and therefore more distant than expected.
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- Could this conclusion be incorrect? Could it be that the supernovae themselves are not as “ bright “ as expected?
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- This scenario happened to astronomers once before: In 1923 Edwin Hubble measuring “spiral nebulae” thought to be inside our Milky Way galaxy. At the time we thought everything , the universe, was inside our galaxy alone. Hubble was studying “ nova’ , variable stars, and these spiral nebulae not realizing they were actually other galaxies outside our own.
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- The variable stars were Cepheid stars. An astronomer , Henrietta Leavitt, discovered that Cepheids get brighter- and -dimmer with a certain “period”. If we measure the period we know the Intrinsic brightness of the Cepheid. By measuring several Cepheids we can develop an ( Apparent Brightness / Distance) relationship.
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- Hubble used this relationship to calculate the distances to these “spiral nebulae”. Hubble used his distance measurements combined with “ redshifts” of light to derive the rate of expansion, the more distant the galaxies the faster they were moving away.
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- His calculations were correct in theory but incorrect in magnitude. His problem was there were two types of Cepheids and he was only using the type Henrietta was studying. This made his calculations for the rate of expansion to be far too high. Hubble later corrected his mistake and the rate of expansion is today known as the “ Hubble Constant”
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-------------------- Hubble Constant = h = 50,245 miles per hour per million light years.
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- Today’s Constant comes from measuring Type 1a Supernovae explosions, not only Cepheid variable stars because they get too dim in distant galaxies. Supernovae shine brighter, for a short time, than their entire galaxy. They can be observed over billions of light years distance. ( Cepheids are able to be seen over only millions of lightyears distance)
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- Our distance measurements depend on the light-curve ( brightness versus time) of a Type 1a Supernovae , that is a fusion reaction of a White Dwarf star exploding at 1.4 Solar Mass.
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- By 1995 enough of these measurements were made of supernovae that astronomers were convinced the universe is expanding at an ever increasing acceleration. They do not know what or how but there is a “Dark Energy” of repulsive force that dominates the Universe.
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- These distance conclusions depend on a White Dwarf star accreting matter from a companion star. But, could the same supernovae explosion occur by the collision and merger of two White Dwarf stars? Are there two different brightness’s to take into account just like the different Cepheids?
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- Could the distant supernovae be a different composition than those measured closer where distances are well known. Earlier stars did not have the heavier elements in their composition because these heavier elements are only created in supernovae explosions.
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- Could the enormous distances of light travel be dimming the light. Intergalactic dust or some other light dimming property could cause this. ( photon-axion interactions).
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- Could there be two types of Type 1a Supernova. One a little brighter in the blue, ultraviolet side of the spectrum. The other a little brighter in the red, infrared side of the spectrum. Are these two light curves slightly different? Higher redshifts could be intrinsically fainter and not farther away?
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- Never the less, astronomers have looked at every angle and concluded the Universe is expanding 7% faster than previously calculated. It was 47,000 miles per hour per million lightyears. The new calculation is 50,245 miles per hour per million lightyears, +or - 2.4% uncertainty.
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- The 50,245 mph is the calculation using 2,400 Cepheids measured in 19 galaxies and 300 Type 1a supernovae. To add to this there is a totally different measurement using the “ Cosmic Microwave Background” radiation. Recognizing the pattern in the radiation background to be the result of quantum fluctuations occurring in the plasma shortly after the Big Bang. That pattern has expanded into the pattern we see today.
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- The CMB calculations are that the Universe is 68% repulsive Dark Energy accelerating the expansion of the Universe. Gravity needed to reverse this comes from only 5% Normal Matter and 27% Dark Matter. The Supernovae calculations listed above have the composition of the Universe at 75% repulsive Dark Energy.
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- One more angle for these distance calculations comes from the discovery that there are clusters of galaxies occurring 500 million lightyears apart. The theory is that Normal Matter gets pushed out by radiation while Dark Matter does not. The result is cosmic waves called “ Baryon Acoustic Oscillations” ( BAO). Baryons are the name given for protons and neutrons combined.
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- The 500 million lightyear pattern becomes a “ standard ruler” to measure cosmic distances. Using this measurement astronomers calculate that the Universe is 70% Dark Energy.
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- All three methods of distance measurements are approaching the same answer, the Universe is accelerating its expansion due to Dark Energy repulsive force occupying all free space. More accurate measurements will bring these percentages closer together, 68%, 70%, 75% ( CMB, BAO, Supernovae ).
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- OK, regardless, what is causing this repulsive force? Here are 3 theories:
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--------------- Could it be undiscovered hyper-fast particles called “ sterile neutrinos”? These particles could have a greater effect in early expansion and a lesser value in local expansion.
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--------------- Could gravity not always follow the General Theory of Relativity? Do we need to modify Einstein’s equations for gravity and the warping of space-time?
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---------------- Could we just be dealing with systematic errors and wider uncertainties in our distance measurements? 95% of the Universe emits zero light. Its existence is only surmised by its gravitational influence on visible galaxies. What we are observing took 13.77 billion years to get here. A lot of things could have happened in that amount of time.. We are still learning. Stay tuned, an announcement will be made shortly.
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- Request these Reviews to learn more about Dark Energy and Cepheids and Type 1a Supernovae.:
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- #1864 - How is Dark Energy expanding the Universe? Listing 7 other Reviews on this topic.
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- #1055 - Cepheids used to discover America.
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- #1881 - Supernovae are like snow flakes. Listing 9 other Reviews about supernovae.
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--- Some reviews are at: -------------- http://jdetrick.blogspot.com -----
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----- 707-536-3272 ---------------- Saturday, June 11, 2016 -----
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