Thursday, July 13, 2017

The most comprehensive course ever

kw: book reviews, nonfiction, science, astrophysics, cosmology, physical universe, galaxies

As a student of geophysics, I occasionally remarked that the subject's bailiwick was "from the center of the Earth to the end of the Universe." The same could be said for astrophysics. Geophysics and astrophysics are a kind of tag team, covering the same realm from different perspectives. Astrophysics deals in part with how stars forge the elements that wind up in planets, while geophysics deals in the main with what happens to those elements once they form a solid or semisolid body (e.g. a gas giant planet).

I have great interest in both subject areas, so it was a real treat to read Welcome to the Universe: An Astrophysical Tour by Neil deGrasse Tyson, Michael A. Strauss, and J. Richard Gott. The book is a distillation of material from a course taught by these three men at Princeton University, to non-astronomy students.
  • Part I: Stars, Planets and Life, was written (and I presume taught) primarily by Dr. Tyson with certain sections by Dr. Strauss.
  • Part II: Galaxies, was written (and presumably taught) entirely by Dr. Strauss.
  • Part III: Einstein and the Universe, was written (and presumably taught) entirely by Dr. Gott.
You could say that Tyson deals with stellar and condensed matter, Strauss with galaxies and their formation, and Gott with the gamut of cosmological theories. For me, given my lifelong love of reading astrophysical books, both popular treatments and texts and monographs, there was little I would call "new to me." But these scientists are writing at the top of their form, and present their subjects in a most enjoyable way. I had certain take-away's from each author:
  • Chapters 7 and 8 [Tyson], "The Lives and Deaths of Stars", parts I and II, are a good summary of the different types of stars based on their masses, certain features of their internal dynamics that are a result of their mass, and the fate of each type. I did not note a discussion of the first stars, those that were entirely metal-free (Astronomers call all elements heavier than helium "metals", which is understandable from a statistical viewpoint: of the 88 natural elements beginning with lithium, and also the two synthetic elements among the first 92, all but 18 are metals). Perhaps it would have been confusing, because such "zero-metallicity stars" could not have had "careers" that fit well into the Hertzsprung-Russell Diagram that does such a good job classifying all known stars in the present universe.
  • Chapter 16 [Strauss], "Quasars and Black Holes", provides a clear summary of the spectral evidence that led firstly to the discovery that quasars are receding at phenomenal rates and are thus very distant (up to more than 90% of the way to the Big Bang some 13.8 billion years ago) and thus extremely luminous; and secondly that they must be powered by matter streaming into enormous black holes at the centers of galaxies. Nearly all quasars are more distant than a few billion light years. The closest is 600 million l-y. Quasars are the highest energy "active galactic nuclei" (AGN's), and since it seems that every galaxy hosts a supermassive black hole (from millions to billions of solar masses), any galaxy could host an AGN whenever a clump of matter finds its way to the galactic center.
  • Chapter 24 [Gott], "Our Future in the Universe", discusses what has happened to the whole universe since the Big Bang, and what is expected to happen, according to current theories. It is on a sort of super-logarithmic scale, highlighting 15 events ranging from the first 10-44 second to (very approximately) 10100 years in the future. In the text other possible events are mentioned, and one is as far off as a number of years described by a number with 1034 zeroes! That number of zeroes equals the number of hydrogen atoms in about 17 billion kilos of hydrogen. There will never be enough paper to "write" it down.
I was eager to see how Dr. Gott discussed Dark Energy and the (alleged) accelerating expansion of the universe. In the seven chapters he wrote, from time to time he discusses one or another mathematical principle that seems to require cosmic inflation (near the very beginning) or accelerating expansion (ongoing). I have yet to see an explanation of accelerating expansion that makes sense to me. The "evidence" for such acceleration is the anomalous brightness of some very distant supernovae. I have read recent articles that question both the data and the interpretation.

For my own part, I have yet to see an analysis of Type 1a supernovae that originate with a C-O white dwarf that accretes material of very low metallicity, as we would expect of very ancient objects at very great distances. Accretion, however, is not certain as a mechanism; WD-WD collisions are thought to produce the more prevalent type of supernova. The mass limit that must be crossed to yield a supernova is 1.44 solar masses. Thus the product of a collision will momentarily have a mass in the range 1.44 (plus a little) to 2.88 (minus a little). So, how "standard" is the standard candle known as a Type 1a supernova?

Well, that question did not get addressed, but for now that is OK. Astrophysicists and cosmologists are not single "voting bloc" in this regard, and I continue to read with interest the work being reported in this area.

Fascinating subjects, excellent writing: I expect this book to become a classic in its field.

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