Bringing the Universe into Better Focus


Cosmologists, astronomers who study the universe as a whole, believe they are making significant progress toward the Holy Grail of their profession -- determining the age and size of the melange of stars, supernovas, galaxies and other stuff beyond the beyond.

A tall order to be sure, but a goal that may be achievable in the lifetimes of many alive today. The successful repair of the Hubble Space Telescope, which despite its flawed equipment has been collecting volumes of useful information since its launching, is a major step toward this once unimaginable achievement.

In fact, the National Aeronautics and Space Administration was moved to observe optimistically in one of its press releases this year that the Earth-orbiting Hubble was "closing in on the age of the universe," which astronomers now estimate to be somewhere between 12 billion and 20 billion years. Last week's repairs on the Hubble telescope's faulty vision should enhance that optimism.

Cosmology is a wonderful science: Almost anyone can participate, given a nagging curiosity about the big bang, black holes, dark matter and all the other words that have found their way into everyday speech. Of course, to play on cosmology's first team people must be university-trained and conduct informative research.

One element of cosmologists' work, seemingly simple but frustratingly elusive, has been the quest for an accurate yardstick to measure the immense distances of the universe. Determining the distance to the moon (238,000 miles) involves elementary mathematics; not so trying to determine the distance of a star that could be 10 million light years away. (A light year is the distance light travels in a year, or 5.9 trillion miles.)

The brightness, or magnitude, of the star should be some indication of its distance, but some stars are intrinsically brighter than others. So, the question arises: Is bright star "A" closer than dim star "B" or vice versa? Cosmology is replete with this kind of question, and the answers, long in coming, are worth waiting for.

Among this century's cosmic measurers have been Henrietta S. Leavitt of the Harvard College Observatory; Vesto M. Slipher of the Lowell Observatory; Edwin P. Hubble, for whom the telescope is named; his colleague, Milton L. Humason; and Hubble's brilliant successor in this field of research, Allan Sandage of the Observatories of the Carnegie Institution of Washington.

In 1912, Miss Leavitt was studying objects called variable stars at the Harvard observatory. The stars varied in brightness as they spun around, just like the revolving lamp in an old-fashioned lighthouse.

She determined that so-called Cepheid variables with longer periods (the time it took the star to make one complete revolution) were brighter than their sisters with shorter periods. These studies led to the conclusion that the stars' periods predict their intrinsic brightness.

"By simply measuring the periods, she could determine the magnitude of one star relative to another; each period uniquely corresponds to a magnitude," Jay M. Pasachoff of Williams College has noted in his book "Contemporary Astronomy."

This determination was an important clue in solving the distance problem, but it was not a total solution. Recent work with the Hubble telescope by Jeremy Mould of the California Institute of Technology and Wendy Freedman of the Carnegie Institution of Washington and their colleagues has greatly expanded these data by observing Cepheid variable stars in a galaxy designated M81.

"In our two observed fields in M81 we have found a total of 32 Cepheids," Dr. Freedman said. "Decades of previous work from the largest ground-based telescopes have only succeeded in measuring two Cepheids. The Hubble Space Telescope's superior resolution and its ability to schedule observations when and where they are required give HST a special advantage in this work."

Dr. Mould has said: "This is the first step in a major program of measuring distances of galaxies with the Hubble Space Telescope."

With the improvements in the telescope's optics, Dr. Mould added, "we plan to use the same technique on galaxies up to 50 million light years away, which will allow us to measure the Hubble Constant, the rate of expansion of the universe."

For the amateur cosmologist, the late Edwin Hubble's work is certainly one of the two or three most interesting aspects of the science. Building on Slipher's earlier studies, Hubble devised a simple formula for measuring cosmic expansion after confirming the theory that galaxies are moving away from us at uniform velocities. The more distant the galaxies the faster they are moving, he explained.

This is the sort of concept that makes cosmology fascinating to curious lay people.

It defies earthly experience. For instance, a sharply-hit baseball loses speed as it heads over the outfield. A bullet's velocity diminishes in proportion to its distance from the gun.

Specifically, Hubble wrote that the velocity of recession (moving away from us) of a galaxy is proportional to its distance. Put another way, the more distant the galaxy, the faster it is traveling away from the observer. This axiom is called "the constant of proportionality."

Hubble's simple equation for these thoughts states that velocity is equal to the constant of proportionality times distance.

There is one problem with this equation. Nobody knows what the constant is.

Last year, a team of scientists that included Carnegie's Dr. Sandage working with Abhijit Saha, Nino Panagia and F. Duccio Macchetto (all of the Space Telescope Science Institute in Baltimore) reached what has been called "a most probable value of the Hubble constant." It is 45. But maybe it's 50 or even 80.

If it's 50, said Holland Ford, a professor in the department of physics and astronomy at the Johns Hopkins University and an astronomer at the Space Telescope Science Institute on the Hopkins campus, that number indicates that the universe is about 20 billion years old.

If the constant's correct number is 80, it would mean that the universe is 12 billion years old.

"But," Dr. Ford added, "12 billion years is younger than some of our best estimates of the age of some of our oldest stars."

For the present, the layman might well take refuge in Dr. Ford's mercifully watered-down explanation of the constant's meaning.

He summed it up this way: "If you know how fast you're moving and how far you've come, you know how long you've been going."

And when you know that?

You are on your way to knowing the age of the universe.

Albert Sehlstedt, a retired science writer for The Sun, has covered the space program since its inception.

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