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.

Previously Posted on Feb 8th, 2008 by David H. Rogstad, Ph.D.

Ever since childhood I have been fascinated with the idea that there are other intelligent beings living in outer space. At the age of seven, I heard about the crash of a flying saucer recovered on a ranch near Roswell, New Mexico. While my dad thought the whole thing was a bunch of foolishness, my friends and I had great fun imagining “Martinis” coming from Mars to visit our planet. We later learned they were called Martians.

In the course of my research in radio astronomy, I worked with a graduate student who was so fascinated with the possibility of intelligent life in outer space that he would spend any spare time on the telescopes searching for signals that might have been sent from distant stars. Needless to say, he didn’t discover anything. I suggested to him that whoever he might hear from out there would have been made by the same creator who made us. So, I asked, why doesn’t he also spend some time investigating the existence of this creator? So far as I know, he didn’t follow up on my recommendation. However, he did later become very active in SETI (Search for Extraterrestrial Intelligence) research.

SETI work based at the University of California, Berkeley’s Space Sciences Laboratory has received a boost recently with the upgrade of the 1,000-ft diameter antenna at the Arecibo Observatory in Puerto Rico. This instrument is the largest single-dish radio telescope in the world, and some of its time has been made available for SETI. With its additional frequency coverage from new and more sensitive receivers, the capability of this system can generate 500 times more data than before in its search for extraterrestrial intelligence.

Interestingly, this project makes use of private home computers to do the processing. Referred to as SETI@home, the Berkeley researchers invite anyone who has a home computer attached to the Internet to contribute its unused time to process the data. Those interested can download a screensaver that works on the SETI task when the computer is in screensaver mode. This has little or no impact on the volunteer, but provides huge amounts of computer time for the project. The SETI@home boasts a community that provides as many as 320,000 computers. They are now asking for more in order to process the new level of data-taking.

Researchers in this project mention that despite the fact UC Berkeley has been analyzing radio signals from space since 1978 on various telescopes, no telltale signals from an intelligent civilization have yet been found. However, with the new upgrades they have great hope that the future will vastly improve the possibility of success. While many SETI researchers acknowledge the low probability for discovering an intelligent signal, they are convinced that such a discovery would be so profound that it merits the effort.

Researchers at RTB, on the other hand, have a different view as expressed in their creation model. Essentially, conservative estimates of the probability of another site beyond the Earth having the necessary conditions for advanced life are zero. There are no “others” out there with whom we can communicate. For further discussion of this conclusion, see here for a secular perspective, and here for the RTB perspective.