Regner I've highlighted the bits that that demonstrate accepted and assumed fuzziness and without real substance.
Jack Regner Trampedach wrote:
James,I did notice your question first time around, and I am sorry I haven't replied until now. The "Answers in Genesis" (AIG) page your posted got the numbers right, but theirconclusions are, well, - hopefully based on ignorance.Down through the first paragraph of the section "Stars Were of Supernatural Origin" (strange to have that in past tense...) they are quite right and I have no objections towhat they write. But then they state (about gas clouds collapsing to form stars) "However, such compression would be very difficult to accomplish because gas has a tendency to expand, not contract."Here they appeal to your everyday experiences with gases in the Earth's atmosphere - they disperse and often rise in our atmosphere. Now, this is a very poor analogy to the case of giant molecular clouds which host star formation. Being millions of times heftier than the Sun they are self-gravitating - they produce their own gravitational field, which is very different from the circumstances here on Earth. The densities in these clouds can be lower than the best vacuums we can produce here on Earth, but the vast size of these clouds means they can still pack a lot of mass. The clouds are turbulent and some parts will have much larger densities and can start to collapse.They continue:"In fact, if a gas cloud were to begin to be compressed, it would drastically increase its pressure, magnetic field, and rotation speed. All of these factors would strongly resist any further compression. The compression of a nebulawould be stopped long before any star could form."The main show-stopper is pressure, whereas rotation and magnetic fields scale in a way that makes them minor players in this game. So it is mainly a balance between gravity and pressure. This balance will be struck at some radius of the contracting sub-cloud, and contraction will stop. As you compress a gas adiabatically (without adding or removing energy from the gas) the temperature will increase, as well as the density, thereby increasingthe pressure: pressure = constant * density * temperature (approximately)If we could lower the temperature, the balance would hapen at a smaller radius - morecompact sub-cloud.Enters atomic physics: The electrons of an atom can populate a great number of states or orbitals that all have different energies. The one with the lowest energy, is the ground- state. If you excite an atom to one of those higher energy states, the atom will spontaneously decay into the ground-state, emitting a photon that carries away the energy difference between the two states. In our gas-cloud the most likely excitation mechanism is collisions between particles - another one is excitation by photons (since the gas has a finite temperature the gas will glow with a specific spectrum) - the important part is that there is only one decay mechanism. This means that more photons will be emitted than were absorbed and the difference will be extracted from the motions of the particles between each other - the temperature of the gas. This is called radiative cooling, and it can be very efficient. In fact our models indicate that the collapse will take place in less than a million years (in contrast to normal stellar evolution taking billions of years). We don't have strong observational evidence for the speed of this phase since it is still slow on a human scale, and since we have seen too few to be able to do the statistical analysis to obtain lifetimes ofproto-stars.AIG further states: "And despite claims to the contrary, we've never seen a star forming."I have several issues with that statement:a) Observing stars is like taking a photo of a busy pedestrian street and from such a single snapshot find out how people change during their lives. The relevant question here, ishow many births have you witnessed while shopping, or commuting to work?We have just recently found the maternity ward and made instruments (space-based infrared telescopes) to peer into the maternity ward (cold, dense, dusty gas-clouds). b) There is no sign at the surface of a proto-star turning into a proper star, and the process is gradual anyway, with the nuclear fusion at the centre, slowly ramping up. ^ c) We have seen the pregnant mothers and the newborn babies being carried away to the nursery. Still assuming there is no birth taking place in between seems a bit silly to me.But we are of course still observing to cover the full process. To be continued (soon). Regner
