Astrophysics

Astrophysics uses the already understood theories of physics (the study of matter and energy) to describe astronomical (universal) phenomena or events. Astrophysicists try to understand the processes that cause our universe and everything in it to behave the way it does.

Background

For thousands of years, humans observed phenomena in the sky, but had no physical explanation for what they saw. Scientists in the twentieth century, however, have been able to explain many astronomical phenomena in terms of detailed physical theories, relating them to the same chemistry and physics at work in our everyday lives.

Whereas experiments in many other scientific fields can be performed under controlled conditions in a laboratory, astrophysical experiments cannot: the energies and distances involved are simply too great. Even though conditions vary greatly throughout the universe, astrophysicists can observe events in the sky and then develop theories about those events based on the laws that govern our day-to-day experiences on Earth. It is common belief that the laws of physics are consistent throughout the universe.

Processes in the universe

The first astrophysical concept or law to be recognized was the law of gravity. Although it is a very weak force compared to the other fundamental forces of nature, gravity is the dominant factor determining the structure and the fate of the universe. The force of gravity acted over vast distances of space to bring together large structures, such as galaxies, and smaller ones, such as stars and planets. However, scientists generally hold the view that the understanding of the interaction and behavior of atoms marks the true beginning of astrophysics. Indeed, even such enormous objects as stars are governed by the action of atoms.

Importance of instrumentation

Recent advances in space instrumentation have allowed astrophysicists to observe astronomical phenomena that previously had been too far away to see. Large space-based observatories, such as the Hubble Space Telescope, continually lead to major advances in astrophysics by exploring parts of the universe with a sensitivity never before imagined. Space probes, such as the Voyagers, which visited most of the outer planets of our solar system, have provided detailed measurements of the physical environment throughout our solar system. Spectroscopes, optical devices that analyze electromagnetic radiation (energy in the form of waves or particles), have enabled astrophysicists to determine the chemical composition of distant stars or galaxies.

[See also Cosmology; Galaxy; Infrared astronomy; Quasar; Relativity, theory of; Solar system; Star; Sun; Telescope; Ultraviolet astronomy; X-ray astronomy ]

astrophysics The study of the physical nature of the Universe and the objects in it, notably stars, galaxies, and the composition of the space between them. Astrophysics originated in the application of spectroscopy to the study of starlight in the 19th century. It complements the traditional branches of astronomy, astrometry and celestial mechanics, which are concerned with the positions and motions of objects. Observational astrophysics interprets the electromagnetic and gravitational radiation emitted by celestial objects. Theoretical astrophysics attempts to explain the processes involved, which can lead to new understanding of the behaviour of matter under conditions not encountered on Earth. For example, nuclear physics had to develop before energy generation inside stars could be understood, and study of objects such as white dwarfs and neutron stars has helped confirm predictions about the behaviour of matter under extreme compression and intense gravitational fields. Astrophysics can also probe the extremely tenuous gas between the stars, where complex molecules are formed and high-energy particles called cosmic rays move close to the speed of light. It also addresses ultimate questions about the origin of the Universe, the conditions shortly after its creation, and the origin of the chemical elements, are dealt with by astrophysics. Closer to home, astrophysics deals with matters such as the environment of the planets and the effects of the solar wind, which could explain short-term changes in our weather and long-term changes in climate. Many areas of physics are involved in such studies, including spectroscopy, plasma physics, atomic physics, and relativity. In recent years, astrophysical advances have resulted from observations by satellites in space, which allow astronomers to study the Universe at all wavelengths from radio waves to gamma rays.

Astrophysics

Astrophysics is the analysis of the physical structure and evolution of objects studied by means of astronomical observations (e.g., stars, galaxies, radio sources, X-ray sources, quasi-stellar objects). The physical structure of such objects depends on a balance of gravitation, radiation pressure, and centrifugal forces, while their evolution depends on their initial composition and the reactions that take place between matter and radiation. In particular, nuclear reactions create new elements in the interior of stars and provide their major energy source. Detailed analysis discloses important relations between the color of light emitted by a star and its total radiation output; this relation changes with the age of the star. At its life's end, a star may die in a supernova explosion, or it may end up as a white dwarf star, neutron star, or black hole, depending on its mass.

See also Astronomy; Black Hole; Cosmology, Physical Aspects; Gravitation

george f. r. ellis

astrophysics Branch of astronomy that studies the physical and chemical nature of celestial bodies and their evolution. Many branches of physics, including nuclear physics, plasma physics, relativity, and spectroscopy, are used to predict properties of stars, planets, and other celestial bodies. Astrophysicists also interpret the information obtained from astronomical studies of the electromagnetic spectrum, including light, X-rays, and radio waves.

as·tro·phys·ics / ˌastrōˈfiziks/ • n. the branch of astronomy concerned with the physical nature of stars and other celestial bodies, and the application of the laws and theories of physics to the interpretation of astronomical observations. DERIVATIVES: as·tro·phys·i·cal / -ikəl/ adj. as·tro·phys·i·cist / -isist/ n.

astrophysics application of the theories and methods of physics to the study of stellar structure , stellar evolution , the origin of the solar system , and related problems of cosmology . The distinction between astrophysics and modern astronomy is disappearing in scientific usage.

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