- 3668 - ASTROPHYSICS - a timeline of discovery? “What is Astrophysics”? Astrophysics is defined as the branch of astronomy that employs the principles of physics and chemistry to ascertain the nature of the astronomical objects, rather than their positions or motions in space.
--------------------- 3668 - ASTROPHYSICS - a timeline of discovery?
- Astrophysicists use the principles of physics to study the sun, stars and their evolution, galaxies and their evolution, the exoplanets, intergalactic medium, and the cosmic microwave background radiation.
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- The most important tool to decode the universe is the “electromagnetic spectrum“. So astrophysicists analyze the spectrum of these systems and thus understand their dynamics. Topics such as dark energy, dark matter, and gravitational waves fall under modern astrophysics.
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------------------------ Timeline of Astrophysics
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- Dark Lines found in the Solar Spectrum (1802 and 1814). Astrophysics began when Sir William Wollaston (in 1802) and Joseph Fraunhofer discovered dark lines (now known as Fraunhofer Lines) in the spectrum of the Sun .
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- When sunlight is passed through a prism, it splits into the colors of the rainbow. These colors are known as the spectrum of the Sun. But when observed, there are many dark lines in it. These are absorption lines caused by impurities such as calcium, sodium, magnesium, iron, etc.
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- The chief element present in the Sun is hydrogen, and the impurities in minuscule quantities absorb the light coming from the inside at specific wavelengths, resulting in the dark features.
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- Classification of stars ere made into 7 types by Pickering (1885). Pickering and his team included women such as Annie Jump Cannon and Antonia Maury, classified 400,000 stars into 7 major categories based on their spectrum. The system, known as the “Harvard Classification Scheme“, changed astrophysics and is still used today. It again showed the importance of the field of spectroscopy in astrophysics.
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- Back around 1920, the source of stellar energy was a complete mystery. Arthur Eddington used Einstein’s mass-energy equivalence to show that stars produce energy by fusing hydrogen into helium in their core.
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- Doctoral Thesis of Cecilia Payne (1925) is described as one of the most remarkable doctoral thesis in astrophysics, Payne hypothesized that hydrogen and helium are the stars’ major constituents.
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- Hubble’s Law and the expanding Universe proposed in 1929. For a long time, it was believed that the universe contains only one galaxy: the Milky Way. Of course, we had images of other galaxies such as the Andromeda galaxy, the Magellanic clouds, etc… They were believed to be stellar systems inside our own Milky Way.
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- But soon, it was realized that there are many more galaxies in the universe. Astrophysics took yet another important turn with the work of Edwin Hubble. Hubble’s law states that the farther a galaxy in deep space, the faster it moves away from us. This was solid proof of the fact that the universe is expanding.
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- The field of radio astronomy was pioneered by Karl Jansky in August 1932. At Bell Telephone Laboratories Jansky built an antenna designed to receive radio waves at a frequency of 20.5 MHz.
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- After recording signals from all directions for several months, Jansky eventually categorized them into three static types: nearby thunderstorms, distant thunderstorms, and a faint, steady hiss of unknown origin. He spent over a year investigating the source of the third type of static. The maximum intensity rose and fell once a day, leading Jansky to surmise that he was detecting radiation from the Sun initially.
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- After a few months of following the signal, however, the brightest point moved away from the position of the Sun. Jansky also determined that the signal repeated on a cycle of 23 hours and 56 minutes, the period of the Earth’s rotation relative to the stars (sidereal day), instead of relative to the sun (solar day).
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- By comparing his observations with optical astronomical maps, Jansky concluded that the radiation was coming from the Milky Way and was strongest in the direction of the center of the galaxy, in the constellation of Sagittarius. Today radio astronomy is a very important branch of research. It is used to study high energy sources such as quasars.
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- The Discovery of the first Black Hole occurred in 1971. The black holes theory can be traced back to Einstein’s general relativity in the second decade of the 20th century. However, the first clues of these exotic objects from the sky came in 1971 from the constellation of Cygnus.
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- The constellation is the home to Cygnus X-1, one of the most powerful X-ray sources seen from Earth. It was discovered in 1964. In 1971, two groups of astronomers working independently detected radio emissions from Cygnus X-1, and their accurate radio position pinpointed the X-ray source to the star.
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- It is a supergiant star that is, by itself, incapable of emitting the observed quantities of X-rays. Hence, the star must have a companion that could heat the gas to the millions of degrees needed to produce the radiation source for Cygnus X-1.
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- After 2 years of detailed analysis, astronomers surmised that the companion is indeed a black hole. Cygnus X-1 has since been studied extensively using observations by orbiting and ground-based instruments.
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- The first evidence of exoplanets, planets orbiting the stars other than the Sun, came way back in 1917 but wasn’t confirmed. On 9 January 1992, radio astronomers Aleksander Wolszczan and Dale Frail announced two planets orbiting the pulsar PSR 1257+12. There are over 5,000 confirmed exoplanets, over 3,139 systems, with 691 systems having more than one planet.
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- The discovery of gravitational waves ushered in a new era in astrophysics. Gravitational waves are produced when two compact objects such as black holes collide with each other.
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- April 10, 2019, The Event Horizon Telescope released the first-ever image of the black hole at the heart of the M87 galaxy. Along with detecting the gravitational waves, it was the most remarkable event in astronomy so far in this century.
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- “Astronomy” is the branch of science that talks about motion and relative positions of heavenly bodies. This includes predicting the positions of planets, eclipses, meteor showers, etc. Astronomy mainly focuses on celestial mechanics and optics to learn the positions and composition of some celestial objects.
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- “Cosmology” is the study of the origin, evolution, and ultimate fate of the universe. Cosmology studies the universe on a larger scale. It studies the universe as a whole. Cosmology differs from astronomy in that the former is concerned with the Universe as a whole while the latter deals with individual celestial objects.
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August 30, 2022 ASTROPHYSICS - a timeline of discovery? 3663
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