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Decoding the Cosmos

Judith Ann Irwin

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eBook - ePub


Decoding the Cosmos

Judith Ann Irwin

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About This Book


The new edition of the popular textbook for undergraduate astronomers, covers the "how" of astrophysics

Astrophysics: Decoding the Cosmos, Second Edition, describes how information about the physical nature of stars and other celestial bodies is obtained and analyzed to gain a better understanding of the universe. This acclaimed introductory textbook makes the complex principles and theories underlying astrophysics accessible to students with basic knowledge of first-year calculus-based physics and introductory astronomy. Reader-friendly chapters explore physical processes using relevant examples and clear explanations of how radiation and particles are analyzed. Such analysis leads to the density, temperature, mass, and energy of astronomical objects.

In the time since the first publication of Astrophysics, the power of telescopes has increased considerably. Reflecting advancements in the field, this new edition includes carefully reviewed and updated material throughout, including recent GAIA satellite results, new information from subatomic particles, neutrinos, and cosmic rays, and brand-new case studies on Gamma-ray bursters, soft repeaters, fast radio bursts, exoplanets, and signals from exoplanetary atmospheres. Retaining its focus on electromagnetic radiation, the second edition now covers more of the ways that information about the universe is acquired, such as particles, gravitational radiation, and meteoritics. This textbook:

  • Describes complex processes in a clear and accessible manner
  • Provides relevant background information on the physics and examples of the theory in practice to place the subject into context
  • Includes new figures, case studies, examples, further readings, end-of-chapter problems of varying difficulty levels, and open-ended "Just for Fun" problems
  • Features a companion website containing information required to solve the designated web-based problems in the text and a range supplementary learning material

Astrophysics: Decoding the Cosmos, Second Edition, is the ideal intermediate textbook for second- and third-year undergraduate students in Astrophysics courses, as well as a useful resource for advanced undergraduate and graduate students looking to refresh their knowledge in basic concepts.

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The Non-electromagnetic Signal

Here, we consider signals that are not electromagnetic (EM) in nature. Historically, these have provided us with limited knowledge about our universe in comparison to EM radiation. This is still the case, but knowledge gleaned from such signals is increasing and it is useful to understand how information can be extracted from these non-EM messengers. The signals are also quite diverse, including particles, from the subatomic to larger meteoritic material, sound waves as detected from incoming meteors, and now gravitational waves (GWs) as well. In Chapter 1 , we will look at a variety of particulate matter. Chapter 2 is devoted to GWs whose recent discovery has opened up a brand new window on our Universe.

Chapter 1
The Particles: Macroscopic to Subatomic: Macroscopic to Subatomic

It's not safe out here. It's wondrous, with treasures to satiate desires both subtle and gross, but it's not for the timid.
–Star Trek, The Next Generation, Episode Q Who?
Before we look at signals that are coming to us in the form of electromagnetic (EM) radiation, let us consider the particles. The Earth is moving constantly through a stream of particles as it orbits the Sun, from the subatomic to the macroscopic. All together, these ‘signals’ have given us only a tiny amount of information compared to EM radiation, but as instrumentation and analysis improve, the particles are finding an important niche in the lexicon of astronomical information. The striking contrast in size between particulate matter is illustrated in Figure 1.1. Let us start with the most tangible of these messengers – the meteoritic1 particles.
Photos depict (Left) Early photograph of cosmic ray tracks in a cloud chamber. (Right) The 1.8 km diameter Lonar meteorite crater in India.
Figure 1.1 (Left) Early photograph of cosmic ray tracks in a cloud chamber. (Right) The 1.8 km diameter Lonar meteorite crater in India.
Source: Cairns et al. [13], Judith A. Irwin.


Of order 2 × 106 kg of meteoritic particles in the mass range, 10−5 to 102 mg, descend upon the Earth each year [43, 48]. The incoming particulate material covers an even wider mass range (10−12 to 1 g) with the largest contribution on a daily basis coming from particles with masses ≈10−2 mg. Thus, the total mass influx is likely an order of magnitude higher [47]. These values are uncertain because there is no single method of determining a mass influx over such a large range of masses. Small particles are swept-up interplanetary debris typically from asteroids or comets, called interplanetary dust particles (IDPs) or micrometeorites. Incoming meteors also produce smoke during ablation, called meteoric smoke particles (MSPs) which contribute to the mix. It is estimated that, if all of the dust in the Solar System between the Sun and Jupiter were rolled into a ball, the resulting sphere would be 25 km in diameter [47].
In the higher mass range of 0.01–109 kg, the cumulative number of particles, N, impacting the Earth per year (i.e. the total number that are greater than some energy, E) is shown in Figure 1.2. The corresponding diameter and mass are shown at the top [55] assuming a typical incoming velocity of 20.3 km s−1 and a density of 3 g cm−3. The adopted density is typical of chondrites, which represent more than 90% of known meteorites. Chondrites are stony-type meteorites containing chondrules (Figure 1.3) which are spherical-appearing inclusions.
Graph depicts the cumulative number of atmospheric impacts per year, N, for bolides in the 0.01–100 m size range from a variety of ground-based and space-based observations (symbols). Mass and size are shown at the top of the figure, and bolide kinetic energy, E, is shown at the bottom in units of kT TNT equivalent (1kT TNT equivalent = 4.185 × 1012 J). For comparison, the atomic bomb that was dropped on Nagasaki on 9 August 1945, exploded with an energy of about 20 kT TNT equivalent. The long solid black line is a fit to satellite fireball data and has the form, N = 3.7 E-0.90 (for E in kT TNT), and the dashed line is from lunar cratering estimates.
Figure 1.2 Cumulative number of atmospheric impacts per year, N, for bolides in the 0.01–100 m size range from a variety of ground-based and space-based observations (symbols). M...

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