Jan
27
Stellar Burning and the Age of the Universe
“From straightforward physics — gas laws, gravitational laws, thermodynamics, and nuclear physics — come secure estimates of the age of stars, galaxies, and the cosmos itself.” — Dr. Hugh Ross, astrophysicist, pastor, and Christian apologist
I had planned on doing a politics-oriented post this week. But, honestly, I’m just sick of hearing/reading about the current big stories, and I couldn’t bring myself to delve into one. So, change of plan…
Last week, I cited an excerpt from the book A Matter of Days: Resolving a Creation Controversy
“When we light a fire in a wood-burning stove, smoke without flames tells us that an infant fire is struggling to ignite. As the fire catches and grows hotter, the smoke clears and bright yellowish-orange flames appear. As the remaining wood burns, the flames begin to die, leaving charred black chunks and glowing embers, indicators that the fire is going out. With good information about the characteristics of the wood, ambient humidity, air pressure, air temperature, and air circulation, a crude estimate can be made (based on the color, brightness, and temperature of the fire) about how long the fire has been burning.
The duration of stellar burning can be measured with far greater precision. A star’s composition is much simpler than that of wood. A star is 97 to 98 percent hydrogen and helium and contains no molecules. It is 100 percent gas — no liquids or solids. A star’s external environment is a near-perfect vacuum. Its burning mechanism (nuclear fusion) is well understood and experimentally confirmed. Unlike a piece of burning wood, stars strictly obey thermal and hydrostatic equilibrium. Because stars are such simple systems, if astronomers know the mass of a star, they can determine its age with high precision based on measurements of the star’s color and brightness.
Astronomers have measured the colors and brightness of millions of stars. Through these observations, they’ve found the range of ages for stars from the youngest to the oldest. With straightforward determination of how long the universe would need to expand before stars could begin to form, astronomers add the age of the oldest stars to the time necessary for the onset of star formation (95-470 million years, depending on the star mass and the local gas density) to discover the universe’s age. The latest cosmic age determination based on stellar burning alone is 13.7 +/- 0.4 billion years. The largest uncertainty in this cosmic age figure lies in the measurements of distances to the relevant star clusters. An observing program is under way to reduce this uncertainty.
A significant clue that the universe must be much older than several thousand years comes from the instability of young stars. A star begins when a gas cloud collapses under gravity’s influence. During the collapse phase, the star at times accretes (gathers) gas and dust and at other times loses gas and dust to outer space. During this time, certain nuclear reactions can turn on and off at different places on and within the star. Also, large unstable spots can form on the star’s surface. Thus, in this infant period (which for a star as massive as the Sun lasts 50 million years), the star’s luminosity remains highly unstable. During the next few hundred million years, a solar-type star’s luminosity variability substantially subsides but still persists. Also, its ionizing radiation (hard UV and soft X-rays) remains at a deadly level — 50 times higher than that of a middle-aged star. (The extreme instability of the infant Sun’s luminosity and the intensity of the juvenile Sun’s ionizing radiation are two of several reasons why life could not have survived on Earth until the Sun was at least a few hundred million years old.
Some young-earth creationist leaders argue that God must have created all stars in a mature state. This concept manifests two problems. First, it insinuates that God created stars already partly burnt with all the ashes and decay characteristics of stars hundreds of millions of years old. God would thus be deceiving us into thinking the universe is old when in fact it is young. Second, astronomers observe stars in various stages of infant and juvenile development throughout our galaxy and in other galaxies. In fact, astronomers observe the entire range of star development — from newborn to infant, to juvenile, to middle-aged, to old, to completely burnt out — with ages ranging from a few days to nearly 13.5 billion years. They even see preborn stars.
Another indicator that the universe is older than a few thousand years is that all the galaxies astronomers see, adding the look-back times, fall within the same relatively narrow age range: 9 to 13 billion years old. (The universe is slightly older than the oldest galaxies because it took those galaxies some time to form.) Nearly 30 years ago, American astronomer Donald Hamilton determined that all the galaxies formed in roughly the same era. Except for the aftermath of collisions between mature galaxies, astronomers see no newborn or young galaxies nearby (corresponding to the recent era). Neither do they see any extinct galaxies.”
