Unifying Concept: S.C.E.2.4.5 know various scientific theories on how the universe wasformed.THE BIG BANGPHOTO RELEASE NO....
in this columnare a few tens of millions of light-years away, and therefore represent ourcurrent stage of the universe s e...
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Unifying concept

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Unifying concept

  1. 1. Unifying Concept: S.C.E.2.4.5 know various scientific theories on how the universe wasformed.THE BIG BANGPHOTO RELEASE NO.: STScI-PR94-52CEMBARGOED UNTIL: 1:00PM (EST) DECEMBER 6, 1994Original image located @ http://oposite.stsci.edu/pubinfo/gif/GalaxEvC.gifGALAXIES: SNAPSHOTS IN TIMEThis sequence of NASA Hubble Space Telescope (HST) images of remotegalaxies offers tantalizing initial clues to the evolution of galaxies in theuniverse.These are traditional spiral and elliptical-shaped galaxies that make up the twobasic classes of island star cities that inhabit the universe we see in our currentepoch (14 billion years after the birth of the universe in the Big Bang). Ellipticalgalaxies contain older stars, while spirals have vigorous ongoing star formationin their dusty, pancake-shaped disks. Our Milky Way galaxy is a typical spiral,or disk-shaped galaxy, on the periphery of the great Virgo cluster. Both galaxies
  2. 2. in this columnare a few tens of millions of light-years away, and therefore represent ourcurrent stage of the universe s evolution.These galaxies existed in a rich cluster when the universe was approximatelytwo-thirds its present age. Elliptical galaxies (top) appear fully evolved becausethey resemble todays descendants. By contrast, some spirals have a frothierappearance, with loosely shaped arms of young star formation. The spiralpopulation appears more disrupted due to a variety of possible dynamicaleffects that result from dwelling in a dense cluster.Distinctive spiral structure appears more vague and disrupted in galaxies thatexisted when the universe was nearly one-third its present age. These objects donot have the symmetry of current day spiralsand contain irregular lumps of starburst activity. However, even this far backtoward the beginning of time, the elliptical galaxy (top) is still clearlyrecognizable. However, the distinction between ellipticals and spirals grows lesscertain with increasing distance.These extremely remote, primeval objects existed with the universe was nearlyone-tenth its current age. The distinction between spiral and elliptical galaxiesmay well disappear at this early epoch. However, the object in the top frame hasthe light profile of a mature elliptical galaxy.This implies that ellipticals formed remarkably early in the universe while spiralgalaxies took much longer to form.Credit: A. Dressler (Carnegie Institutions of Washington),M. Dickinson (STScI), D. Macchetto (ESA/STScI), M. Giavalisco(STScI), and NASA

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