2.2 A Star is Born (and Dies)
13
Spirals are ubiquitous. We will encounter this form in completely different contexts, created by totally different mechanisms, from galaxies down to hurricanes and
on to molluscs and plants. Rotation is ubiquitous in a different way, prevailing on
the cosmic level, and downscaled only by humans inventing the wheel. Rotation is
robust due to the law of momentum conservation, but spirals are fragile: when two
galaxies collide, the result is commonly a globular galaxy. Even though the volume
within a galactic disk is almost totally void, gravitational interaction between stars
disrupts the ordered structure.
2.2 A Star is Born (and Dies)
The intragalactic volume is almost as void as intergalactic space because gravitational instability did not stop at the formation of galaxies, but went on to the birth
of the first stars hundreds of million of years after the Big Bang. Gas clouds were
never quiet, swept by supersonic turbulence, shaped by shock waves into intermittent filaments and sheets enhancing density contrasts and seeding the cores of future
stars.
Although stars lie outside the course of this narrative, they are of the utmost
importance for further morphogenesis. They are not just the source of energy for
life, but kilns where the chemical elements necessary for life have been forged. Stars
have a life of their own, from birth, to maturity, old age, and death, and generations
of stars evolve not unlike population cohorts. Before the first stars were born, matter
consisted solely of hydrogen and helium atoms. The principal elements of living
matter – carbon, nitrogen, and oxygen – are a product of nuclear synthesis within
mature stars. Still heavier elements, like most metals, are formed when massive stars
explode.
Generations of stars differ because the chemical composition of the Universe
evolved as a result of nucleosynthesis in earlier stars. The birth of early stars was
the most difficult. Counterintuitively, matter needs to cool before heating up, since
internal pressure preventing gravitational collapse grows with temperature, leading
to a larger critical mass. The weakly interacting lighter elements of the early Universe cool more slowly, so early stars had to be more massive. The compaction
stopped when the temperature had risen enough to ignite nuclear reactions. How
could this have happened? We have reproduced nuclear fusion here on the Earth (a
potential cause of our own annihilation) by using nuclear fission to ignite it. But
there were no heavy nuclei to split in the compressing gas clouds. We are trying
to create a tiny artificial sun in a more delicate and manageable way, an endeavor
long hoped to come to fruition within the next twenty years (the time span in which
Nasreddin Hodja had promised to teach a donkey to talk). Pierre-Gilles de Gennes
once said: “We want to put a sun in a box, a nice idea. The problem is how to make
the box”. So far, all attempts at confining plasma while heating it to attain net energy
gain have failed.
13
Spirals are ubiquitous. We will encounter this form in completely different contexts, created by totally different mechanisms, from galaxies down to hurricanes and
on to molluscs and plants. Rotation is ubiquitous in a different way, prevailing on
the cosmic level, and downscaled only by humans inventing the wheel. Rotation is
robust due to the law of momentum conservation, but spirals are fragile: when two
galaxies collide, the result is commonly a globular galaxy. Even though the volume
within a galactic disk is almost totally void, gravitational interaction between stars
disrupts the ordered structure.
2.2 A Star is Born (and Dies)
The intragalactic volume is almost as void as intergalactic space because gravitational instability did not stop at the formation of galaxies, but went on to the birth
of the first stars hundreds of million of years after the Big Bang. Gas clouds were
never quiet, swept by supersonic turbulence, shaped by shock waves into intermittent filaments and sheets enhancing density contrasts and seeding the cores of future
stars.
Although stars lie outside the course of this narrative, they are of the utmost
importance for further morphogenesis. They are not just the source of energy for
life, but kilns where the chemical elements necessary for life have been forged. Stars
have a life of their own, from birth, to maturity, old age, and death, and generations
of stars evolve not unlike population cohorts. Before the first stars were born, matter
consisted solely of hydrogen and helium atoms. The principal elements of living
matter – carbon, nitrogen, and oxygen – are a product of nuclear synthesis within
mature stars. Still heavier elements, like most metals, are formed when massive stars
explode.
Generations of stars differ because the chemical composition of the Universe
evolved as a result of nucleosynthesis in earlier stars. The birth of early stars was
the most difficult. Counterintuitively, matter needs to cool before heating up, since
internal pressure preventing gravitational collapse grows with temperature, leading
to a larger critical mass. The weakly interacting lighter elements of the early Universe cool more slowly, so early stars had to be more massive. The compaction
stopped when the temperature had risen enough to ignite nuclear reactions. How
could this have happened? We have reproduced nuclear fusion here on the Earth (a
potential cause of our own annihilation) by using nuclear fission to ignite it. But
there were no heavy nuclei to split in the compressing gas clouds. We are trying
to create a tiny artificial sun in a more delicate and manageable way, an endeavor
long hoped to come to fruition within the next twenty years (the time span in which
Nasreddin Hodja had promised to teach a donkey to talk). Pierre-Gilles de Gennes
once said: “We want to put a sun in a box, a nice idea. The problem is how to make
the box”. So far, all attempts at confining plasma while heating it to attain net energy
gain have failed.