Astrophysics

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Early 1900s comparison of elemental, solar, and stellar spectra

Astrophysics is a science that employs the methods and principles of

extrasolar planets, the interstellar medium and the cosmic microwave background.[4][5] Emissions from these objects are examined across all parts of the electromagnetic spectrum, and the properties examined include luminosity, density, temperature, and chemical composition. Because astrophysics is a very broad subject, astrophysicists apply concepts and methods from many disciplines of physics, including classical mechanics, electromagnetism, statistical mechanics, thermodynamics, quantum mechanics, relativity, nuclear and particle physics, and atomic and molecular physics
.

In practice, modern astronomical research often involves a substantial amount of work in the realms of

.

History

Astronomy is an ancient science, long separated from the study of terrestrial physics. In the Aristotelian worldview, bodies in the sky appeared to be unchanging spheres whose only motion was uniform motion in a circle, while the earthly world was the realm which underwent growth and decay and in which natural motion was in a straight line and ended when the moving object reached its goal. Consequently, it was held that the celestial region was made of a fundamentally different kind of matter from that found in the terrestrial sphere; either Fire as maintained by Plato, or Aether as maintained by Aristotle.[6][7] During the 17th century, natural philosophers such as

natural laws.[11] Their challenge was that the tools had not yet been invented with which to prove these assertions.[12]

For much of the nineteenth century, astronomical research was focused on the routine work of measuring the positions and computing the motions of astronomical objects.

chemical elements in the Solar atmosphere.[17]
In this way it was proved that the chemical elements found in the Sun and stars were also found on Earth.

Among those who extended the study of solar and stellar spectra was Norman Lockyer, who in 1868 detected radiant, as well as dark lines in solar spectra. Working with chemist Edward Frankland to investigate the spectra of elements at various temperatures and pressures, he could not associate a yellow line in the solar spectrum with any known elements. He thus claimed the line represented a new element, which was called helium, after the Greek Helios, the Sun personified.[18][19]

In 1885,

Edward C. Pickering undertook an ambitious program of stellar spectral classification at Harvard College Observatory, in which a team of woman computers, notably Williamina Fleming, Antonia Maury, and Annie Jump Cannon, classified the spectra recorded on photographic plates. By 1890, a catalog of over 10,000 stars had been prepared that grouped them into thirteen spectral types. Following Pickering's vision, by 1924 Cannon expanded the catalog to nine volumes and over a quarter of a million stars, developing the Harvard Classification Scheme which was accepted for worldwide use in 1922.[20]

In 1895,

James E. Keeler, along with a group of ten associate editors from Europe and the United States,[21] established The Astrophysical Journal: An International Review of Spectroscopy and Astronomical Physics.[22] It was intended that the journal would fill the gap between journals in astronomy and physics, providing a venue for publication of articles on astronomical applications of the spectroscope; on laboratory research closely allied to astronomical physics, including wavelength determinations of metallic and gaseous spectra and experiments on radiation and absorption; on theories of the Sun, Moon, planets, comets, meteors, and nebulae; and on instrumentation for telescopes and laboratories.[21]

Around 1920, following the discovery of the Hertzsprung–Russell diagram still used as the basis for classifying stars and their evolution, Arthur Eddington anticipated the discovery and mechanism of nuclear fusion processes in stars, in his paper The Internal Constitution of the Stars.[23][24] At that time, the source of stellar energy was a complete mystery; Eddington correctly speculated that the source was fusion of hydrogen into helium, liberating enormous energy according to Einstein's equation E = mc2. This was a particularly remarkable development since at that time fusion and thermonuclear energy, and even that stars are largely composed of hydrogen (see metallicity), had not yet been discovered.[25]

In 1925 Cecilia Helena Payne (later Cecilia Payne-Gaposchkin) wrote an influential doctoral dissertation at Radcliffe College, in which she applied Saha's ionization theory to stellar atmospheres to relate the spectral classes to the temperature of stars.[26] Most significantly, she discovered that hydrogen and helium were the principal components of stars, not the composition of Earth. Despite Eddington's suggestion, discovery was so unexpected that her dissertation readers (including Russell) convinced her to modify the conclusion before publication. However, later research confirmed her discovery.[27][28]

By the end of the 20th century, studies of astronomical spectra had expanded to cover wavelengths extending from radio waves through optical, x-ray, and gamma wavelengths.

gravitational waves
.

Observational astrophysics

Supernova remnant LMC N 63A imaged in x-ray (blue), optical (green) and radio (red) wavelengths. The X-ray glow is from material heated to about ten million degrees Celsius by a shock wave generated by the supernova explosion.

celestial objects by using telescopes
and other astronomical apparatus.

The majority of astrophysical observations are made using the electromagnetic spectrum.

Other than electromagnetic radiation, few things may be observed from the Earth that originate from great distances. A few gravitational wave observatories have been constructed, but gravitational waves are extremely difficult to detect. Neutrino observatories have also been built, primarily to study the Sun. Cosmic rays consisting of very high-energy particles can be observed hitting the Earth's atmosphere.

Observations can also vary in their time scale. Most optical observations take minutes to hours, so phenomena that change faster than this cannot readily be observed. However, historical data on some objects is available, spanning

pulsar deceleration
studies). The information obtained from these different timescales is very different.

The study of the Sun has a special place in observational astrophysics. Due to the tremendous distance of all other stars, the Sun can be observed in a kind of detail unparalleled by any other star. Understanding the Sun serves as a guide to understanding of other stars.

The topic of how stars change, or stellar evolution, is often modeled by placing the varieties of star types in their respective positions on the Hertzsprung–Russell diagram, which can be viewed as representing the state of a stellar object, from birth to destruction.

Theoretical astrophysics

Theoretical astrophysicists use a wide variety of tools which include analytical models (for example, polytropes to approximate the behaviors of a star) and computational numerical simulations. Each has some advantages. Analytical models of a process are generally better for giving insight into the heart of what is going on. Numerical models can reveal the existence of phenomena and effects that would otherwise not be seen.[30][31]

Theorists in astrophysics endeavor to create theoretical models and figure out the observational consequences of those models. This helps allow observers to look for data that can refute a model or help in choosing between several alternate or conflicting models.

Theorists also try to generate or modify models to take into account new data. In the case of an inconsistency, the general tendency is to try to make minimal modifications to the model to fit the data. In some cases, a large amount of inconsistent data over time may lead to total abandonment of a model.

Topics studied by theoretical astrophysicists include stellar dynamics and evolution; galaxy formation and evolution; magnetohydrodynamics; large-scale structure of matter in the universe; origin of cosmic rays; general relativity and physical cosmology, including

gravitational waves
.

Some widely accepted and studied theories and models in astrophysics, now included in the

cosmic inflation
, dark matter, dark energy and fundamental theories of physics.

Popularization

The roots of astrophysics can be found in the seventeenth century emergence of a unified physics, in which the same laws applied to the celestial and terrestrial realms.[11] There were scientists who were qualified in both physics and astronomy who laid the firm foundation for the current science of astrophysics. In modern times, students continue to be drawn to astrophysics due to its popularization by the Royal Astronomical Society and notable educators such as prominent professors Lawrence Krauss, Subrahmanyan Chandrasekhar, Stephen Hawking, Hubert Reeves, Carl Sagan and Patrick Moore. The efforts of the early, late, and present scientists continue to attract young people to study the history and science of astrophysics.[32][33][34] The television sitcom show The Big Bang Theory popularized the field of astrophysics with the general public, and featured some well known scientists like Stephen Hawking and Neil deGrasse Tyson.

See also

References

  1. .
  2. ^ "astrophysics". Merriam-Webster, Incorporated. Archived from the original on 10 June 2011. Retrieved 2011-05-22.
  3. PMID 17796068
  4. ^ a b "Focus Areas – NASA Science". nasa.gov.
  5. ^ "astronomy". Encyclopædia Britannica. 29 May 2023.
  6. .
  7. ^ Cornford, Francis MacDonald (c. 1957) [1937]. Plato's Cosmology: The Timaeus of Plato translated, with a running commentary. Indianapolis: Bobbs Merrill Co. p. 118.
  8. ^ Edward Slowik (2013) [2005]. "Descartes' Physics". Stanford Encyclopedia of Philosophy. Retrieved 2015-07-18.
  9. ^
  10. Academy of Sciences of the Czech Republic. Retrieved 2015-07-18. {{cite journal}}: Cite journal requires |journal= (help
    )
  11. , The great majority of astronomers working in the early nineteenth century were not interested in stars as physical objects. Far from being bodies with physical properties to be investigated, the stars were seen as markers measured in order to construct an accurate, detailed and precise background against which solar, lunar and planetary motions could be charted, primarily for terrestrial applications.
  12. .
  13. ^ Hetherington, Norriss S.; McCray, W. Patrick, Weart, Spencer R. (ed.), Spectroscopy and the Birth of Astrophysics, American Institute of Physics, Center for the History of Physics, archived from the original on September 7, 2015, retrieved July 19, 2015
  14. ^
  15. ^ The Astrophysical Journal. 1 (1).
  16. PMID 17747682
  17. .
  18. . Eddington had realized that there would be a mass loss if four hydrogen atoms combined to form a single helium atom. Einstein's equivalence of mass and energy led directly to the suggestion that this could be the long-sought process that produces the energy in the stars! It was an inspired guess, all the more remarkable because the structure of the nucleus and the mechanisms of these reactions were not fully understood.
  19. , retrieved July 19, 2015
  20. ^ Steven Soter and Neil deGrasse Tyson (2000). "Cecilia Payne and the Composition of the Stars". American Museum of Natural History.
  21. ^ D. Mark Manley (2012). "Famous Astronomers and Astrophysicists". Kent State University. Retrieved 2015-07-17.
  22. ^ The science.ca team (2015). "Hubert Reeves – Astronomy, Astrophysics and Space Science". GCS Research Society. Retrieved 2015-07-17.
  23. Hayden Planetarium
    . 2015. Retrieved 2015-07-17.

Further reading

External links