Acceleration of the expansion of the universe

[heyo]

Can somebody tell me what is the mechanism by which they proved that the expansion of the universe is actually accelerating? I know it has something to do with a certain type (type 1a?) of supernovae in distant galaxies, but I never really understood how they came to the definitive conclusion that the universe is accelerating outward ever faster.<br /><br />Heyo

 

[newtonian]

Heyo - For starters, note this link concerning more recent confirmation of the earlier evidence from type 1A Supernovae:<br /><br />http://www.space.com/scienceastronomy/dark_energy_040518.html<br /><br /><br />The article by Roy Britt explains evidence gathered by the Chandra X-ray observatory from a study of 26 galaxy clusters.<br /><br />The point of proof involves the distances these clusters are at- greater than would be from ordinary expansion, and implying some sort of dark energy.<br /><br />Here is an excerpt:<br /><br />Chandra looked at 26 galaxy clusters, each surrounded by a cloud of hot gas and held together by dark matter, another unknown thing invoked to explain why the galaxies don't just fly apart, as they would if left to gravity from regular matter alone.<br /><br />The clusters are about 15 percent visible matter. The rest of the regular matter is hot gas only visible in X-rays. Chandra allowed the researchers to determine the masses of the cluster and thereby learn how far away each one is.<br /><br />"The distances to the clusters are all significantly larger than if there were no dark energy," said Steve Allen of the Institute of Astronomy in Cambridge, U.K.<br /><br />Allen and colleague Andy Fabian presented their findings today at a NASA press conference.<br /><br />Fabian explained that the clusters they studied are spread across time and space, throughout the decelerating phase and the acceleration phase.<br />End quote.<br /><br />The space.com article is dated 5/18/04.<br /><br />I'll research further if no one else gets to it first.

 

[newtonian]

Heyo - OK, on the original supernovae evidence discovered in 1998, see this link:<br /><br />http://www.space.com/scienceastronomy/astronomy/cosmic_darknrg_020115-1.html<br /><br />The 1/15/02 space.com article showed it was the greater than expected distance supernovae were at which indicated acceleration of expansion.<br /><br />An excerpt:<br /><br />These researchers found that the supernovas were dimmer than they should have been, and that meant they were farther away than they should have been. The only way for that to happen, the astronomers realized, was if the expansion of the universe had sped up at some time in the past.<br /><br />End quote.<br /><br />Btw, the universe apparently accelerated, slowed down and then accelerated again.<br /><br />See the articles for estimates on the time-line.<br /><br />

 

[heyo]

Thanks ya'll..<br /><br />But when they say "the galaxies were farther away than they were supposed to be" how do they know how far there were supposed to be?<br /><br /><img src="/images/icons/laugh.gif" /><br /><br />Heyo

 

[newtonian]

Heyo - Your welcome.<br /><br />I don't have the numbers, however:<br /><br />Expansion at a certain rate would lead to certain distances.<br /><br />It was assumed the rate was slowing due to gravitation, and the expected distances based on that assumption would be the distances the galaxies were supposed to be at.<br /><br />However, in recent billions of years it has not been slowing - according to present interpretations of the new observations from Chandra (x-ray) and Hubble (type 1-A supernovae).<br /><br />Therefore, these galaxies are further away than expected.

 

[mooware]

I understand the universe expansion is accelerating!