A molecular cloud, sometimes called a stellar nursery (if star formation is occurring within), is a type of interstellar cloud, the density and size of which permit absorption nebulae, the formation of molecules (most commonly molecular hydrogen, H2), and the formation of H II regions. This is in contrast to other areas of the interstellar medium that contain predominantly ionized gas.
Timeline of knowledge about the interstellar medium and intergalactic medium:
Radio astronomy is a subfield of astronomy that studies celestial objects at radio frequencies. The first detection of radio waves from an astronomical object was in 1933, when Karl Jansky at Bell Telephone Laboratories reported radiation coming from the Milky Way. Subsequent observations have identified a number of different sources of radio emission. These include stars and galaxies, as well as entirely new classes of objects, such as radio galaxies, quasars, pulsars, and masers. The discovery of the cosmic microwave background radiation, regarded as evidence for the Big Bang theory, was made through radio astronomy.
The Karl G. Jansky Very Large Array (VLA) is a centimeter-wavelength radio astronomy observatory in the southwestern United States. It lies in central New Mexico on the Plains of San Agustin, between the towns of Magdalena and Datil, approximately 50 miles (80 km) west of Socorro. The VLA comprises twenty-eight 25-meter radio telescopes deployed in a Y-shaped array and all the equipment, instrumentation, and computing power to function as an interferometer. Each of the massive telescopes is mounted on double parallel railroad tracks, so the radius and density of the array can be transformed to adjust the balance between its angular resolution and its surface brightness sensitivity. Astronomers using the VLA have made key observations of black holes and protoplanetary disks around young stars, discovered magnetic filaments and traced complex gas motions at the Milky Way's center, probed the Universe's cosmological parameters, and provided new knowledge about the physical mechanisms that produce radio emission.
Jan Hendrik Oort was a Dutch astronomer who made significant contributions to the understanding of the Milky Way and who was a pioneer in the field of radio astronomy. The New York Times called him "one of the century's foremost explorers of the universe"; the European Space Agency website describes him as "one of the greatest astronomers of the 20th century" and states that he "revolutionised astronomy through his ground-breaking discoveries." In 1955, Oort's name appeared in Life magazine's list of the 100 most famous living people. He has been described as "putting the Netherlands in the forefront of postwar astronomy."
The hydrogen line, 21 centimeter line, or H I line is a spectral line that is created by a change in the energy state of solitary, electrically neutral hydrogen atoms. It is produced by a spin-flip transition, which means the direction of the electron's spin is reversed relative to the spin of the proton. This is a quantum state change between the two hyperfine levels of the hydrogen 1 s ground state. The electromagnetic radiation producing this line has a frequency of 1420.405751768(2) MHz (1.42 GHz), which is equivalent to a wavelength of 21.106114054160(30) cm in a vacuum. According to the Planck–Einstein relation E = hν, the photon emitted by this transition has an energy of 5.8743261841116(81) μeV [9.411708152678(13)×10−25 J]. The constant of proportionality, h, is known as the Planck constant.
Hendrik Christoffel "Henk" van de Hulst was a Dutch astronomer.
Bartholomeus Jan "Bart" Bok was a Dutch-American astronomer, teacher, and lecturer. He is best known for his work on the structure and evolution of the Milky Way galaxy, and for the discovery of Bok globules, which are small, densely dark clouds of interstellar gas and dust that can be seen silhouetted against brighter backgrounds. Bok suggested that these globules may be in the process of contracting, before forming into stars.
Onsala Space Observatory (OSO), the Swedish National Facility for Radio Astronomy, provides scientists with equipment to study the Earth and the rest of the Universe. The observatory operates two radio telescopes in Onsala, 45 km south of Gothenburg, and takes part in several international projects. Examples of activities:
Venkataraman Radhakrishnan was an Indian space scientist and member of the Royal Swedish Academy of Sciences. He retired from his career as professor emeritus of the Raman Research Institute in Bangalore, India, of which he had previously been director from 1972 to 1994 and which is named after his father. He served on various committees in various capacities including as the vice president of the International Astronomical Union during 1988–1994. He was also a Foreign Fellow of both the Royal Swedish Academy of Sciences and the U.S. National Academy of Sciences. He was an Associate of the Royal Astronomical Society and a Fellow of the Indian Academy of Sciences, Bangalore.
The Dwingeloo Radio Observatory is a single-dish radio telescope near the village of Dwingeloo in the northeastern Netherlands. Construction started in 1954, and the telescope was completed in 1956. The radio telescope has a diameter of 25 m. At the time of completion it was the largest radio telescope in the world, but it was overtaken in 1957 by the 250 foot (76 m) Lovell Telescope.
ASTRON is the Netherlands Institute for Radio Astronomy. Its main office is in Dwingeloo in the Dwingelderveld National Park in the province of Drenthe. ASTRON is part of the institutes organization of the Dutch Research Council (NWO).
Associated Universities, Inc. (AUI) is a research management corporation that builds and operates facilities for the research community. It is a not-for-profit 501(c)(3) corporation headquartered in Washington, D.C., United States. The current president is Adam Cohen. The corporation's major current operating unit is the National Radio Astronomy Observatory, which it operates under a Cooperative Agreement with the National Science Foundation.
Gart Westerhout was a Dutch-American astronomer. Well before completing his university studies at Leiden, he had already become well-established internationally as a radio astronomer in the Netherlands, specializing in studies of radio sources and the Milky Way Galaxy based on observations of radio continuum emissions and 21-cm spectral line radiation that originates in interstellar hydrogen. He emigrated to the United States, became a naturalized citizen, and held a number of important scientific and management positions in academic and government institutions.
Gale Bruno van Albada was a Dutch astronomer, known for his orbital observations of binary stars and studies on the evolution of galaxy clusters.
Smith's Cloud is a high-velocity cloud of hydrogen gas located in the constellation Aquila at Galactic coordinates l = 39°, b = −13°. The cloud was discovered in 1963 by Gail Bieger, née Smith, who was an astronomy student at Leiden University in the Netherlands.
Splatalogue is a database for astronomical spectroscopy which contains information on nearly six million spectral lines and is maintained by the National Radio Astronomy Observatory (NRAO). The name is a portmanteau of "spectral line catalogue".
High-velocity clouds (HVCs) are large collections of gas found throughout the galactic halo of the Milky Way. Their bulk motions in the local standard of rest have velocities which are measured in excess of 70–90 km s−1. These clouds of gas can be massive in size, some on the order of millions of times the mass of the Sun, and cover large portions of the sky. They have been observed in the Milky Way's halo and within other nearby galaxies.
In radio astronomy, a fast radio burst (FRB) is a transient radio pulse of length ranging from a fraction of a millisecond, for an ultra-fast radio burst, to 3 seconds, caused by some high-energy astrophysical process not yet understood. Astronomers estimate the average FRB releases as much energy in a millisecond as the Sun puts out in three days. While extremely energetic at their source, the strength of the signal reaching Earth has been described as 1,000 times less than from a mobile phone on the Moon.
Harold Irving "Doc" Ewen was an American physicist, radio astronomer, and business executive. He served in the United States Navy in World War II as a second lieutenant. As a graduate student under Edward M. Purcell, he was the first to detect the galactic 21-cm hydrogen line.
