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Many astronomers have long assumed that by an age of about 5 billion years, disk galaxies had come to look nearly the same as they appear today. “It’s almost like a mantra,” Kassin said. “Many astronomers say that the Hubble sequence is in place by a redshift (which astronomers denote with the letter z) of 1,” using astronomical shorthand for two important concepts. The Hubble sequence is a diagram—originally devised by Edwin Hubble in 1926—for classifying the visible shapes of galaxies. Because looking far out into the depths of space is the equivalent of looking back in time to earlier eras in the universe, the redshift z is how astronomers measure both age and distance in the universe; a redshift of z = 1 corresponds to approximately 8 billion years ago, when the universe was only about 5 billion years old.
A very massive object – or collection of objects – distorts the view of faint objects beyond it so much that the distant images are smeared into multiple arc-shaped images around the foreground object. According to Rogier Windhorst, one of the letter’s authors and a professor at the School of Earth and Space Exploration in Arizona State University’s College of Liberal Arts and Sciences, this effect is analogous to looking through a glass coke bottle at a light on a balcony and noticing how it is distorted as it passes through the bottle. Cosmologists such as Windhorst believe that gravitational lensing likely distorted the measurements of the flux and number density of the most distant galaxies seen in the recent deep near-IR surveys with the Hubble Space Telescope Wide Field Camera 3.
When you look back to when the universe was young, you are seeing extremely early objects (also known as ``First Light’’ objects) that are very far away. The older and farther away the object, the more foreground universe there is to look through, which means the greater the chance that there will be something heavy in the foreground to distort the background image. This research suggests that gravitational lensing is likely to dominate the observed properties of very early galaxies, those that are at most 650-480 million years old (now seen with Hubble at redshifts of z > 8-10, respectively). The halos of foreground galaxies when the universe was in its heydays of star formation (about 3-6 billion years old and at a lower redshift of z=1-2) will gravitationally distort most of these very early objects.