Quasars are one of the most interesting and mysterious objects in the visible universe. These immensely bright and distant sources of radiation were first discovered in the 1960s and have challenged astronomers to explain their origin, nature and behaviour. In this blog, we will explore the most-asked question, "What exactly are quasars?", their origin and history, properties and significance of quasars and what is the future of quasar research.
Quasars emit radiation from a small, but extremely energetic region called an accretion disk, which surrounds a supermassive black hole. The black hole's gravitational pull causes gas and dust to spiral towards it, heating up and emitting light and other forms of radiation. This process releases more energy than entire galaxies of stars, making quasars some of the most energetic objects in the universe.
The true nature of quasars was finally revealed in the late 1960s, when astronomers discovered that some of these sources were associated with faint, diffuse galaxies. The first quasar was discovered in 1963 by radio astronomers Maarten Schmidt and Bev Oke. They were studying a radio source known as 3C 273, which was much smaller and brighter than any known star. Later observations showed that this object also emitted intense light across the electromagnetic spectrum, including visible light, X-rays, and gamma rays. The discovery of 3C 273 marked the birth of quasar astronomy.
The redshift of quasars is another important property that has provided clues to their nature and distance. Redshift is a measure of how much the light emitted by an object has been shifted towards longer wavelengths, or lower frequencies, due to the expansion of the universe. Quasars have redshifts ranging from about 0.06 to 7.5, which corresponds to distances of up to 10-20 billion light-years away. This means that the light we observe from quasars today has been travelling through space for billions of years and provides a glimpse into the early universe.
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| Depiction of a quasar |
What are Quasars?
Quasars, short for quasi-stellar objects, are extremely luminous and compact regions in the centers of galaxies that emit vast (unimaginable) amounts of energy, including radio waves, X-rays, and visible light. Quasars appear as point sources in the sky and were originally classified as stars, but their spectra revealed features which were unusual and it was concluded that they were not ordinary stars.Quasars emit radiation from a small, but extremely energetic region called an accretion disk, which surrounds a supermassive black hole. The black hole's gravitational pull causes gas and dust to spiral towards it, heating up and emitting light and other forms of radiation. This process releases more energy than entire galaxies of stars, making quasars some of the most energetic objects in the universe.
Quasar Discovery
Quasars were first detected in the late 1950s and early 1960s, when radio astronomers noticed that some radio sources were extremely bright and varied in intensity over short timescales. Subsequent optical observations revealed that these sources had peculiar spectra, consisting of broad emission lines that were unlike those of any known star or galaxy. The term "quasi-stellar object" was coined to describe these enigmatic sources, which appeared star-like but were clearly not stars.The true nature of quasars was finally revealed in the late 1960s, when astronomers discovered that some of these sources were associated with faint, diffuse galaxies. The first quasar was discovered in 1963 by radio astronomers Maarten Schmidt and Bev Oke. They were studying a radio source known as 3C 273, which was much smaller and brighter than any known star. Later observations showed that this object also emitted intense light across the electromagnetic spectrum, including visible light, X-rays, and gamma rays. The discovery of 3C 273 marked the birth of quasar astronomy.
.jpg "3C 273 Quasar") |
| 3C 273 Quasar |
The implication was that quasars were not isolated stars, but rather were located at the centers of distant galaxies. The discovery of the association between quasars and galaxies helped to establish the modern understanding of the structure and evolution of the universe.
Properties of Quasars
Quasars are characterized by their extreme brightness, variability, and redshifts. The most luminous quasars emit energy at rates of up to 10^13 times that of the sun, making them some of the most energetic objects in the universe. Quasars are also highly variable, with their brightness changing by factors of up to a few percent on timescales of days to weeks. This variability is thought to be due to changes in the accretion disk around the central black hole. |
| Artist’s impression of quasar J0313-1806 |
The redshift of quasars is another important property that has provided clues to their nature and distance. Redshift is a measure of how much the light emitted by an object has been shifted towards longer wavelengths, or lower frequencies, due to the expansion of the universe. Quasars have redshifts ranging from about 0.06 to 7.5, which corresponds to distances of up to 10-20 billion light-years away. This means that the light we observe from quasars today has been travelling through space for billions of years and provides a glimpse into the early universe.
Significance of Quasars
Quasars are important objects for studying the formation and evolution of galaxies and the large-scale structure of the universe. The discovery of quasars helped to establish the existence of supermassive black holes at the centers of galaxies and the role they play in regulating the growth and activity of galaxies. Quasars also provide a powerful tool for studying the intergalactic medium and the epoch of reionization, when the first stars and galaxies ionized the neutral hydrogen that pervaded the universe after the Big Bang.In addition to their scientific importance, quasars are also fascinating objects in their own right. They emit enormous amounts of energy across a wide range of wavelengths, and their light has traveled for billions of years across the vast expanse of space to reach us. By studying quasars, we can learn about the extreme conditions that exist in the universe, such as the intense gravitational and magnetic fields near black holes, and the processes that drive the growth and evolution of galaxies.
Studying Quasars
Astronomers use a variety of techniques to study quasars, including observations with ground-based and space-based telescopes, and computer simulations. One of the most powerful tools for studying quasars is spectroscopy, which allows astronomers to analyze the light emitted by quasars and determine their chemical composition, temperature, density, and other properties. Spectroscopy has revealed that quasars contain a variety of elements, including hydrogen, helium, carbon, nitrogen, oxygen, and iron, and that they emit radiation across a wide range of frequencies.
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| Artist’s impression of the quasar 3C 279 |
Another important technique for studying quasars is gravitational lensing, which occurs when the light from a quasar is bent and distorted by the gravitational field of a massive object, such as a galaxy or a cluster of galaxies, that lies between the quasar and Earth. Gravitational lensing can amplify the brightness of quasars and provide insights into the distribution of dark matter and the structure of the universe.
Future of Quasar Research
Quasar research is a rapidly evolving field that is likely to yield many exciting discoveries in the coming years. New telescopes, such as the James Webb Space Telescope and the Square Kilometer Array, will provide unprecedented views of quasars and their environments, allowing astronomers to study their properties in even greater detail. In addition, theoretical models of quasar formation and evolution are constantly being refined and updated, as scientists seek to understand the complex processes that govern the behavior of these enigmatic objects.
Conclusion
Quasars are some of the most fascinating and mysterious objects in the universe, emitting vast amounts of energy from the centers of distant galaxies. Their discovery has revolutionized our understanding of the cosmos and provided important insights into the structure and evolution of the universe. By studying quasars, astronomers can learn about the properties of matter and radiation under extreme conditions, and explore the history and fate of the universe.
