Seeing the Universe

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Seeing the Universe with New Eyes

Contemporary understanding of the cosmos developed quite recently, aided by ever more sophisticated and sensitive instruments. The prevailing view of a static universe comprised only of the Milky Way was shattered in the 1920s, when Edwin Hubble showed that not only are there galaxies beyond our own, but that they are rushing away from us. Also, the further away from the Milky Way, the faster they move. The universe is expanding, implying that it began in an infinitely dense and incredibly energetic state--the "Big Bang."

The Big Bang theory was bolstered in 1964 with the discovery of the cosmic background radiation (CBR), the remnants of the radiation released in the first second of the life of the universe. But the theory contained no solution to the "horizon" and "flatness" problems until 1979, when Alan Guth came to the rescue by adding inflation to the Big Bang. At only 10^-35 seconds following the Big Bang, cosmologists theorize that he universe underwent a critical phase transition that caused space to expand exponentially (i.e. inflate), flattening out any pre-existing curvature of space and thrusting once-intimately connected matter billions of light years apart.

Minute fluctuations in the CBR--footprints of the small ripples in the density of matter that led to the formation of today's galaxies and clusters--were only discovered in 1992, and new ground and space-based telescopes and X-ray satellites continue to reveal new information about the age, composition and structure of the universe.

Seeing Further Out and Back

Bigger, more sensitive and far-seeing telescopes will provide us with a more complete picture of the universe on vaster scales and further back into time than presently possible. A new study, The Sloan Digital Sky Survey, will map the redshift of 100,000 galaxies--some ten times the current count--permitting the construction of a comprehensive 3-D map of the distribution of galaxies in the universe to a distance of 1000 Megaparsecs.

With such a large volume of the universe mapped, cosmologists will be able to make firm quantitative measurements about the nature of large scale structure which any successful model must reproduce. The Sloan survey will also increase the sample of known quasars a hundred-fold to over one hundred thousand. Since quasars are the oldest and nost distant astronomical objects known, and thought to represent an early phase of galaxy evolution, the increased sample will allow astronomers to pin down the epoch of galaxy formation with more precision.

The Hubble Space Telescope, with its superb imaging capabilities, will continue to collect images of distant galaxies and clusters of galaxies. Because of the finite speed of light, the more distant the galaxy, the further into the past we are peering. Hubble can see what galaxies and clusters looked like many billions of years ago, providing astronomers with the essential data to say how galaxies evolve over time.

A particularly important key program of the HST is the measurement of the Hubble constant, which is a key parameter in cosmological theories and presently unknown to within a factor of two. By making careful distance measurements to a "ladder" of increasingly distant galaxies, the HST is expected to measure the Hubble constant to a precision of about 10 percent.

Peering through the X-Ray Window

The Advanced X-Ray Astronomical Facilility (AXAF) to be launched by NASA in 1998 will image the cosmos in the X-ray bands of the electromagnetic spectrum with unprecedented clarity. Both galaxies and clusters of galaxies emit in the X-ray because of various evolutionary processes brought to light with previous generations of X-ray satellites.

AXAF will be able to survey a large volume of the universe comparable to the Sloan Digital Sky Survey, thus providing cosmologists with an independent and complimentary way to map the large scale structure of the universe. Models of structure formation will therefore be double constrained to predict where the galaxies form, but also the thermal properties of the gas out of which they form--a much harder challenge!

Revisiting the Footprints of Creation

One of the most exciting prospects is a follow-on to the COBE satellite which map the cosmic microwave background (CMB) with high angular resolution over the entire sky. Both the European and American space agencies are conducting studies on the design of such a satellite which might be launched by 2005. A high resolution CMB image would be able to map the "seeds of structure" on length scales corresponding to clusters and superclusters of galaxies, and thus provide direct measurements of the primordial density fluctuations required as input to numerical models. Such an instrument may also be able to distinguish between the gaussian and non-gaussian classes of models for the origin of the primordial fluctuations which give rise to structure. A variety of ground-based experiments are already measuring small portions of the sky to the precision that an all-sky satellite will eventually have.

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NCSA. Last modified 11/9/95.