Astronomers have known for 70 years that an analysis of a star’s spectra can suggest some mysterious absorptions throughout interstellar space when viewed at specific wavelengths. These are termed diffuse interstellar bands (DIBs). DIBs are attributed to complex organic molecules that the American astrophysicist, Dr. Theodore Snow of the University of Colorado, believes may compose the largest known reservoir of organic matter in the Universe. This interstellar organic material is normally discovered in the same proportions. However, extremely dense clouds of matter like presolar nebulae are exceptions. In the heart of these nebulae, where matter is even denser, DIB absorptions plateau or even plummet. This happens because the organic molecules that are responsible for the formation of DIBs clump together. The clumps of matter absorb less radiation than when it flowed freely through interstellar space.
Such primitive, primordial nebulae frequently contract to create a solar system like our own–hosting planets, moons, asteroids, and comets. Stars like our Sun are born in the secretive depths of these extremely dense blobs embedded within the billowing, swirling folds of giant, dark, cold molecular clouds that inhabit our Milky Way Galaxy in huge numbers. Even though it may seem counter intuitive, things have to get very cold in order for a searing-hot baby star to be born. This is because stars are born tucked within relatively dense concentrations of gas and dust, and these regions are extremely frigid, with temperatures of only 10 to 20 Kelvin–only a bit above absolute zero. At these temperatures, gases become molecular, causing atoms to merge together, thus making the gas clump to very high densities. When this density reaches a certain point, stars are born.
All stars are huge spheres composed of searing-hot, glaring, roiling, gas. The billions upon billions of stars that dwell in the observable Universe are all primarily composed of hydrogen–which is both the most abundant atomic element listed in the familiar Periodic Table, as well as the lightest. Stars transform hydrogen fuel deep within their hot nuclear-fusing cores into progressively heavier and heavier atomic elements. The only atomic elements that formed in the Big Bang birth of the Cosmos about 13.8 billion years ago, were hydrogen, helium, and small quantities of beryllium, and lithium (Big Bang nucleosynthesis). All of the other atomic elements listed in the Periodic Table were formed deep within the seething, secretive hearts of the stars, their glaring-hot interiors progressively fusing the nuclei of atoms into heavier and heavier things (stellar nucleosynthesis).
Even though giant molecular clouds are mainly composed of gas, with smaller quantities of dust, they also contain large populations of sparkling, newborn stars. The material within the ghostly, billowing, dark clouds clumps together in an assortment of sizes, with the smaller clumps extending approximately one light-year across. The dense clumps eventually collapse to form protostars. The entire star-birthing process lasts for about 10 million years.
The sparkling myriad of stars inhabiting the Cosmos are kept bouncy and fluffy as a result of the energy that is manufactured by the process of nuclear fusion that is occurring within their cores. The stars are able to maintain a necessary–and very delicate–equilibrium between the powerful squeezing crush of their own relentless gravity–which tries to pull everything in–and their enormous energy output, which churns out radiation pressure, that tries to push everything out and away from the star. This immense production of energy is the result of stellar nucleosynthesis that creates heavier atomic elements out of lighter ones. The precious balance between gravity and radiation pressure is maintained from the “birth” of the star until its “death”–the entire “lifetime” of the star–which it spends on the hydrogen-burning main sequence of the Hertzsprung-Russell Diagram of Stellar Evolution. Alas, the inevitable comes when the star has finally managed to burn its necessary supply of hydrogen fuel–and gravity wins the ancient battle against pressure. At this tragic point, the star’s core collapses, and the star perishes. Small stars, like our own Sun, meet their doom with relative peacefulness, as well as great beauty–puffing off their varicolored outer gaseous layers into the space between stars. Larger, heavier stars, on the other hand, do not go gentle into that good night. More massive stars end their stellar “lives” by blasting themselves to pieces in the catastrophic and violent rage of a supernova explosion, which effectively destroys the star. Where there was once a star, there is a star no more. Therefore, the mass of a star is what determines its fate.
The Rosetta mission taught astronomers that comet nuclei form as the result of gentle accretion of grains progressively larger and larger in size. First, small particles bump into one another and then stick together to create larger grains. These then go on to combine to form ever larger chunks–and so on, and on, until a comet nucleus forms that is a few miles wide. The frozen comet nucleus, in this way, becomes one of the multitude icy inhabitants of the Kuiper Belt, Scattered Disc, or Oort Cloud –where it will remain unless some gravitational interaction evicts it from its frigid, twilight home and sends it screaming towards the melting fires of our Sun.
The comet’s organic molecules, that once drifted throughout the primordial, primitive solar nebula–and are responsible for DIBs–were probably not destroyed, but instead were incorporated into the grains composing cometary nuclei, where they have remained for 4.6 billion years. A sample return mission would allow laboratory analysis of cometary organic material and, at long last, uncover the hidden identity of the mysterious interstellar matter causing the observed strange patterns in stellar spectra. mkv movies 2019