Rambling on about our Expanding Universe
In this International Year of Astronomy, 400 years after Galileo's turned his telescope to systematic study of the heavens, it's good to reflect on a few landmarks of how what we now accept as common knowledge was once terra incognita, where not even the questions were considered let alone possible answers. The power of the mind, and of technical advances (telescopes, cameras, CCDs, satellites) to expand our knowledge is ever surpris-ing. Here are few discoveries that provided definitive an-swers of what were previously often tentative hypothesis. In so doing, these expanded the minds of people, which is what I meant by our expanding universe--I mean expand-ing ideas, not just expanding space.
1610-The power of systematic observation is powerfully exemplified by Galileo with the publication of Sidereus Nuncius. He notes the movement of 4 'stars' around Jupiter, and after systematic observation, realizes that these are moons circling the planet. He noted mountains and valleys on the moon, and that Venus' phases further supported a Copernican solar system.
1687-Newton publishes the Principia, describing among other things a rigorous mathematical treatment of the motions of heavenly bodies, and a theory of gravity. And beyond invention of calculus, he invents the reflector design of telescopes using a curved mirror to collect light, the prin-ciple on which modern large scopes are based.
1785-Herschel deduces the space of the Milky Way, assumed the sun was near the center.
1905-Einstein introduces relativity and further develops the concept of space-time and general relativity in additional papers.
1908-Henrietta Leavitt discovers that Cepheid variables are standard candles among stars. These were used to determine interstellar distances and show that the stars lay at tremendous distances.
Early 1920's-Edwin Hubble identifies Cepheids in some 'spiral nebula' and their dis-tances show these to be extremely distant, far outside our Milky Way. Later, he and Milton Humason formulated "Hubble's Law" relating red shifts to distance, and estab-lished the principle of an expanding universe.
Early 1930's-Jansky invents radio astronomy, mounts his an-tenna on Model T wheel, detects emissions from the cen-ter of our galaxy in direction of Sagittarius. The power of radio and extra-radio astronomy has answered many ques-tions, but maybe the most basic of these is surely the Pen-zias and Wilson discovery of the microwave background as evidence of a 'big bang' birth of our universe. Descrip-tions of black holes were mathematically described by Chandrasekhar, Oppenheimer, Penrose, and x-ray astron-omy found Cygnus X as the first object accepted as a black hole. Today, super-massive holes are widely ac-cepted to be at the core of most large galaxies.
1990-The Hubble Space Telescope launches, with a 2.5 meter mirror this was the first of the large orbiting observatories. Be-yond its discoveries and importance to professional scien-tists, it has been a prominent face of modern astronomy, and as much as any other instrument, fired the imagination and awe of a grateful public.
1988-onward-Another set discoveries that have fascinated the public has been the discovery of extra-solar planets. From 51 Pegasi orbit a firey G-type star in a 4-day orbit, to Gliese-581 orbiting a red dwarf, currently 344 confirmed extra-solar planets are known.
1988-Riding the bus home while at Penn State in the 80s, I was relating to a friend how galaxies had been recently detected with red shifts more than 3. A fellow passenger interjected himself to tell us how this was im-possible, because it was incompatible with theories of galactic evolution. He represented himself as an expert , astrophysics grad student. In 2009, we hear of galaxies at red shifts higher than 7, that must have formed shortly af-ter the big bang.
Today, in 2009, new observations are made all the time that point to answers to tough questions. An example: Black holes are found in almost all galaxies. The black holes in this era of the universe typically have a mass around 1/200 to 1/700 the galaxies, a tight relation that im-plies a fundamental relation between the two. One hy-pothesis has been that primordial gas clouds underwent collapse, formed stars, while a black hole in the cloud grew by accretion of gas, emitting vast amounts of radiative en-ergy as a quasar or active galactic nucleus (AGN). The radiation of emitted would eventually heat the galactic gas so much it would arrest further infall, clearing the center of the galaxy of gas, and stopping growth of the black hole. There has been question of which formed first, the black hole or the galaxy is key, but how can this be answered? It sounds like a chicken-or-egg problem: which came first there? Well this spring a group reported that when galaxies at the earliest age of the universe, around a billion years post big-bang, the black holes were around 1/30th the mass of the galaxy. Because the difference between then and today, they hypothesize that galaxies grow by accretion around the black hole 'pit'. Note that the difference shouldn't be because the black hole was somehow getting smaller, because nothing can escape and their mass should only grow, never shrink.
Some questions once ridiculed as foolish are now enter-tained seriously scientifically. What came before the be-ginning of our universe, and did it affect us? (If interested, read Neil Turok's research for example on some thinking on this problem.) What is the fate of our universe, and how will it evolve? Will physical laws and constants evolve? Is it easy for life to form, or hard? Observations in the next few years or decades on Mars and watery or icy moons like Europa or Ganymede in our solar system may help answer this. Looked at this way, some of today's 'un-askable' questions may ultimately be reliably answered in the future. We only need stay tuned in.Published in the May 2009 issue of the NightTimes