Astrophysics | Research & Encyclopedia Articles

Astrophysics

Astrophysics is the field of science that combines astronomical observations with physical principles. It may be argued that the first true astrophysicist was Sir Isaac Newton, who explained the orbits of the planets, which had been known from antiquity, from his laws of motion and his universal law of gravity. As a field, astrophysics first began to mature in the latter half of the nineteenth century. This was due primarily to several key technical innovations that revolutionized the field of astronomy.

First, as the nineteenth century progressed, so did the sizes of the largest telescopes, and hence the furthest distances, as well as the smallest and dimmest features astronomers could observe. Whereas earlier astronomers usually worked in relative isolation using small telescopes, increased support from both governments and private individuals led to the founding of more observatories (like the U.S. Naval Observatory in 1844, the Lowell Observatory in 1894, the Yerkes Observatory in 1897, and the Mount Wilson Observatory in 1904) with improved equipment and larger telescopes.

Next was the invention of the photograph plate in the first half of the nineteenth century by Louis Daguerre. The first known astronomical application of the photographic plate was a Daguerrotype of the Moon taken by the American J. W. Draper in 1840. The impact of photographic plates on the field of astronomy was tremendous--images of the sky could be taken and stored for years, and accurate positions and brightnesses could be inferred from analyzing the plates at leisure afterwards.

Last was the invention of the diffraction grating for use in analyzing spectra from astronomical bodies. Seminal work on the diffraction grating was done by Joseph von Fraunhofer beginning in 1821, who demonstrated that the gratings could produce spectra of unprecedented quality. Although the grating was invented by an American astronomer, David Rittenhouse, in 1785, it was von Fraunhofer who first used it to study absorption lines in the spectrum of the Sun, and who derived equations governing their behavior. Scientists began to use the diffraction grating in their research after other instrument makers began to produce them in bulk after 1850. Accurate spectra of astronomical bodies would have an even greater impact on astrophysics than the photographic plate: by comparison with spectra obtained in gases in terrestrial laboratories, scientists could deduce the composition of vastly distant astronomical bodies by using the unique spectral "fingerprints" left by atomic and molecular species. Moreover, under the right conditions, the density, temperature, velocity (along the line of sight), and the magnetic field of the emitting gas, as well as similar properties for absorbing gas along the line of sight, could all be inferred from a spectral measurement. The impact which the advent of spectroscopy would have on astrophysics cannot be overemphasized: whereas previously stars and other astronomical bodies were simply lights in the sky, afterwards they were physical systems whose properties could be measured, modeled, and understood.

The advent of quantum mechanics, relativity theory, and nuclear physics during the first half of the twentieth century led to some of the most impressive strides in modern astrophysics. Although late nineteenth century astronomers had cataloged and archived volumes of data, they often lacked the understanding of basic physical principles to comprehend their observations. With a deeper understanding of fundamental physical principles, enormous strides were made in all branches of astrophysics during the first half of the 20th century. In cosmology, Einstein's theory of general relativity was able to explain Edwin Hubble's observation that galaxies seemed to recede from us in all directions: in Einstein's theory, the universe itself was dynamic, and expanding in time. Building on a century of work in stellar physics, Hans Bethe finally cracked the riddle of how stars like our Sun shine by drawing from terrestrial knowledge of nuclear reactions. The list of such contributions of physical principles with astronomical observations goes on and on: the union of the two has been quite successful indeed.

The period from the 1950s to today has been one of unprecedented expansion in astrophysics, by any standard of measurement: volumes of data, numbers of papers published, and numbers of researchers in the field. Just as in the birth of modern astrophysics during the period after 1850, the reasons are primarily technological. The space age led to the launching of new satellites and missions to other planets and the Sun opening up entirely new frontiers in our knowledge of the universe. Also from space, astronomers can gaze through many bands of the electromagnetic spectrum not visible from the ground because the earth's atmosphere blocks them out. Indeed, only radio waves and optical light are easily transmitted through the earth's atmosphere. Finally, the invention of the modern computer, which is ideally suited to storing and manipulating enormous volumes of data, was absolutely crucial in assisting astronomers in their capacity to deal with the ever-increasing tide of information from their observations. Indeed, the modern computer has led to a third branch of astrophysics, alongside observation and theory: computational astrophysics, which uses the computer to simulate nature under the model conditions put forth by a scientist.

Today, astrophysicists delve deeper into the discoveries of previous generations, seeking to understand the myriad of new questions that surface with every discovery. Cosmologists are narrowing in on the lifetime, geometry, and future of the universe itself. Extragalactic astrophysicists puzzle over the nature of fantastically energetic bursts of gamma radiation, which are now known to sometimes originate in galaxies far away from our own. Scientists studying our own galaxy seek to understand how it formed, and whether it has a supermassive black hole at its center as do many other galaxies. Other scientists studying the physics of the interstellar medium (ISM) try to comprehend the vastly complicated processes by which the tenuous ISM eventually forms stars, and how those stars replenish the ISM with energy and new material from their nuclear forges through winds and explosions. Experts on very compact white dwarfs, neutron stars, and black holes study the enormously energetic and fascinatingly rich array of phenomena that these systems exhibit. Still others try to make sense of revolutionary discoveries of planets around other stars, which are quite unlike those in our own solar system. At the dawn of the new millennium, astrophysicists are learning how the universe works, and the end is still nowhere in sight.