Today’s New Reason To Believe

by Jeff Zweerink

Twinkle, twinkle little star,
My, oh my, how large you are.
How’d you get to be so big? When gas pressure and magnetic fields should have prevented you from forming?

Okay, so my poem doesn’t rhyme, but it does communicate two important issues regarding stars. First, astronomers have detected many stars with masses ranging from 20 times the mass of the Sun to around 150 times. Second, astronomers struggled to understand how such massive stars form.

Gravity, radiation pressure, gas pressure, and magnetic fields constitute the dominant processes in star formation. The basic process starts when a gas cloud becomes sufficiently dense that it begins to collapse under its own gravity. As the cloud collapses, the radiation pressure and rotational energy of the gas and the magnetic fields permeating the cloud grow larger. In relatively simple formation models, these three effects halt the collapse of clouds larger than roughly 20 solar masses. The existence of stars more massive than this limit means that some process must overcome this difficulty, or that the model is oversimplified.

It turns out that these older models assumed that star formation occurred in a spherically symmetrical manner. In other words, the only direction in which things changed was the distance from the center of the gas cloud. These models were one-dimensional in that the radius represented the only variable. More sophisticated, two-dimensional models accounted for the fact that the gas would begin rotating about an axis. They revealed that energy from the cloud’s collapse could dissipate though jets emitted along the rotation axis. Nonetheless, rotational and magnetic effects still stunted growth of stars beyond 40 solar masses.

A team of U.S. scientists recently generated a fully three-dimensional model of stellar formation. Their model showed that gravitational instabilities form in the cloud and in the disk that surrounds the cloud. These instabilities serve to channel gas onto the star while the radiation escapes through optically thin parts of the cloud. Furthermore, the instabilities cause the disk to fragment and form companion stars. Not only does this model demonstrate how stars up to 100 solar masses can form, it also explains why massive stars tend to form in binary systems.

Why is this important? First, it is these massive stars that produce the bulk of elements heavier than helium. At the end of their “lives,” the stars undergo catastrophic explosions that distribute the heavy elements through space for future stars to use. They also live very short lives—a few million years for the most massive stars—so they inject these heavy elements into other stars that are forming from the same gas cloud. A growing body of evidence indicates that our solar system formed in such a chaotic environment. It’s good to know that the laws of physics permit these life-essential processes to occur in the universe. Seems like they might even be designed for that purpose.

by Hugh Ross

One of the most extraordinary features of the solar system is that it contains adequate abundances of all the elements essential for advanced life. What makes it so exceptional is that the elements must come from different sources: asymptotic giant branch stars, a Type I supernova (see here and here), Type II supernovae of at least two different types, white dwarf binary stars, and now, according to a new study also from a “faint supernova with mixing fallback.”¹

A team of six Japanese astronomers, plus an American astronomer, carefully recorded the amounts of decay products from the following short-lived radionuclides (SLRs): beryllium-10, aluminum-26, chlorine-36, calcium-41, manganese-53, iron-60, palladium-107, iodine-129, and hafnium-182. In their calculations the team demonstrated that ejection of heavy-element material into the primordial solar system’s protoplanetary disk came from all but the last source mentioned above. However, none of these astrophysical sources can account for the early solar system’s abundances of SLRs with half-lives less than five million years, namely aluminum-26, calcium-41, manganese-53, and iron-60.

The astronomers’ calculations revealed that a rare kind of supernova could explain the solar system’s abundances of these particular SLRs. This supernova type is a low-luminosity (that is, faint) supernova where, during the star’s explosion, the inner region of the star experiences mixing. A small fraction of the mixed material is ejected into the interstellar medium and the remainder falls back into the core. In the words of the research team, “The modeled SLR abundances agree well with their solar system abundances.”

They also calculated the time interval between the explosion of the faint supernova and the formation of solar system’s oldest solid materials. That interval is approximately equal to one million years. The faint supernova eruption would need to be quite near the solar system forming region but not so close as to disturb its formation. Likewise, the timing and the proximity for the other sources (asymptotic giant branch stars, Type I supernova, Type II supernovae of at least two different types, white dwarf binary stars) of the heavy elements would need to be similarly fine-tuned.

SLRs make two important contributions to the solar system. One, they are heat sources for primordial asteroidal metamorphism and/or differentiation. Primordial asteroids are the building blocks for the solar system’s rocky planets (Mars, Earth, Venus, and Mercury). Thus, Earth’s exceptional interior differentiation (a crucial factor for establishing its strong, long-lasting magnetic field) is due, in part, to the primordial solar nebula’s exceptional abundances of SLRs.

Two, they provide high-resolution chronometers for events that took place during the first few million years of the solar system’s formation. Continuing studies could potentially yield a detailed history for early solar system events with a timing precision of better than a hundred thousand years for the different occurrences. Such historical accuracy could deliver much more evidence for the supernatural design of the solar system for life’s, and humanity’s, benefit.

1. A. Takigawa et al., “Injection of Short-Lived Radionuclides into the Early Solar System from a Faint Supernova with Mixing Fallback,” Astrophysical Journal 688 (December 1, 2008): 1382-87.

by Jeff Zweerink

Does the universe end at the farthest reaches we can observe? If it doesn’t, then what characteristics does this realm beyond the observable universe exhibit? While science fiction authors have written in depth about alternate universes, many scientists want to bring these questions into their arena. To do so, they must posit explanations that account for existing data and predict what future experiments and observations might reveal. The most expedient avenue for such investigations involves inflation and its effect on the cosmic microwave background (CMB) radiation .

A team of Caltech cosmologists recently developed an inflationary model that predicts that the universe is far larger than the region we can see (a Level I multiverse in more technical lingo). Their research seeks to explain a possible asymmetry of the amplitudes of the CMB fluctuations observed by WMAP. Hailed in the popular press as chance to “glimpse before the big bang”, this model makes predictions that will allow cosmologists to better understand the mechanism responsible for the important inflationary era early in the history of the universe.

The pertinent feature of their model utilizes two different scalar fields, instead of one, during the inflationary epoch. One field, the inflaton, drives the inflationary expansion. A second field called the curvaton produces the density fluctuations. Using a two-field approach allows the model to explain the possible asymmetry in the fluctuation amplitudes without disrupting the uniformity seen in the CMB.

Large-scale modes of the curvaton extend beyond the region that inflated to become our observable universe. Thus, different sections of the observable universe can have different values for the curvaton field. These variations lead to different amplitudes for the CMB fluctuations. If this model proves true, it implies that our observable universe represents a small fraction of the total size of the universe. More importantly, this model makes detailed predictions that will be tested by future measurements of the CMB by missions like Planck.

In an earlier TNRTB, I described another piece of data that indicates the universe is much larger than what we can see. Exciting times lay ahead as scientists try to find out just how big the universe is. Regardless of what future results reveal about the physical extent of the universe, RTB expects those results to also provide further demonstration that a supernatural Creator stands as the ultimate cause of this universe.

If you would like to see a question about the multiverse addressed in this forum, send it to multiverse@reasons.org.