An Accelerating Universe? Not So Fast
By: News Notes
Summarized by: Jacob A. Hawkins
Some of the most interesting and pivotal information about our universe was released recently. Much to the despair of many astronomers everywhere, who thought that the ex 959y242j pansions of the universe would be slowing down, the expansion rate of the universe seems to be speeding up. This reiterates Albert Einstein's "cosmological constant". It supposedly measured accounts beautifully for the "missing" energy that the universe ought to have in order to make the inflationary theory of the early Big Bang come out just right. This new discovery depends heavily on one factor, thought. That factor is the measurements of the universe's past expansion rate using the apparent brightnesses of Type Ia supernovae. Type Ia supernovae should result from the same, precisely metered amount of explosive material going off in the same manner. The exploding stare is a massive whit dwarf comprised of oxygen and carbon, onto which matter slowly pours from a close companion star. At a point when the star gains enough mass to detonate it does in a nuclear fusion reaction, which yields the same energy in every case. This is why they would make excellent basis' for comparison. Yet a recent study by one of the leading supernova search teams is casting a shadow of doubt over this belief. The leader of this study is Adam Riess of the University of California, Berkeley. He and several of the High-Z Supernova Search Team are comparing their observations with those of the rival Supernova Cosmology Project. They have found that nearby Type Ia supernovae take anywhere from 10 to 15 percent longer to reach maximum brightness than do very distant Type Ia supernovae. This could be from the distant, old stellar systems not being quite the same as the newer ones. This then opened the idea that when the universe was younger, massive white dwarfs formed with different amounts of carbon and oxygen than now. If the rise times are different then this could affect the intrinsic brightnesses of the supernovae. A dimming of only 30 percent in these standard supernovae would make the cosmological constant go away. Riess and his colleagues suggest that this might be a simpler explanation than invoking a mysterious new cosmic force.
One of the differences that is certain is that no white dwarfs were formed from the low-mass stars back when the universe was young. This is because low-mass stars hadn't had time to evolve to white-dwarfhood.
Some of the explanations of these differences are that gray dust is dimming the brilliant light of the supernova. However Riess says "There's a signature of a cosmological constant that can't be forged by gray dust of by evolutionary effects if you go back to redshifts of one or more. The two groups are now doing supernova hunts to find two Type Ia events at about that distance.
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