Quasar

Artistic representation of the quasar GB1508.

A quasar or quasar (acronym for quasariestelar”, translation of the English quasi-stellar radio source) is defined as either a newborn galaxy or well that source of energy that occurs in the black hole at the center of said newborn galaxies, characterized by being an astronomical source of electromagnetic energy, which includes radio frequencies and visible light.

General information

Quasars occur in a huge black hole, which sucks in all matter in its vicinity. When this occurs, due to the enormous speed of rotation of the formed accretion disk, a gigantic amount of energy is produced, released in the form of radio waves, infrared, light, ultraviolet and X-rays, which turns quasars into the brightest and hottest objects in the known universe.

Originally it was assumed that quasars were white holes, although progress in the study of their formation and characteristics has ruled out this assumption.

In optical telescopes, most quasars appear as simple points of light, although some appear to be the centers of active galaxies. Most quasars are too far away to be seen by small telescopes, but 3C273, with an apparent magnitude of 12.9, is an exception. At a distance of 2.44 billion light-years, it is one of the farthest objects that can be directly observed with amateur equipment.

Some quasars show rapid changes in luminosity, which implies that they are small, since an object cannot change faster than the time it takes light to travel from one end to the other. The highest known redshift of a quasar is z=7.54 ULAS J1342+0928, although one was recently detected at z=7.52 and it is being studied whether it is even further away.

Quasars are thought to be powered by the accretion of matter from supermassive black holes into the nuclei of distant galaxies, turning them into highly luminous versions of a general class of objects known as active galaxies. The mechanism that causes the emission of the large amount of energy and its rapid variability is not known. Knowledge of quasars has advanced very rapidly, although there is no clear consensus on their origins.

Properties of Quasars

More than 200,000 quasars are known, and all observed spectra have a significant redshift, ranging from 0.06 to a maximum of 7.08. Therefore, all quasars are located at great distances from Earth, the closest being 240 Mpc (780 million light-years) and the furthest 6 Gpc (13 billion light-years). Most quasars are more than 1 Gpc away; Since light must take a very long time to travel the entire distance, quasars are observed as they were long ago, in the universe as it was in its distant past.

Although they appear faint when viewed through optical telescopes, their high redshift means these objects lie at great distances, making quasars the most luminous objects in the known universe. The brightest quasar in the sky is 3C 273 in the constellation Virgo. It is at a distance of ~670 million parsecs, that is, around 2.2 billion light-years. It has an apparent magnitude of 12.8, bright enough to be seen with a small telescope, but its absolute magnitude is -26.7. At a distance of 10 parsecs (about 33 light-years), this object would shine brighter in the sky than the Sun. The luminosity of this quasar is about two trillion (2 × 10¹²) times greater than that of the Sun, or a hundred times more than the total light of an average galaxy like the Milky Way.

The hyperluminous quasar APM 08279+5255 had, when discovered in 1998, an absolute magnitude of -32.2, although high-resolution images from the Hubble Space Telescope and the Keck telescope revealed that this system was gravitationally lensed. A study of the gravitational lensing phenomenon in this system suggests that it has increased by a factor of 10. It is, however, a brighter object than the closest quasars like 3C273. HS 1946+7658 is thought to have an absolute magnitude of -30.3, but it has also been magnified by gravitational lensing.

Quasars have been found to vary in luminosity on various time scales. Some vary their brightness every few months, weeks, days, or hours. This evidence has allowed scientists to theorize that quasars generate and emit their energy from a very small region, since each part of the quasar would have to be in contact with the others on that time scale to coordinate the luminosity variations. That is, a quasar that varies on a time scale of a few weeks cannot be larger than a few light weeks across.

Quasars exhibit many of the same properties as active galaxies: the radiation is not thermal, and some have been observed to have jets and lobes like radio galaxies. Quasars can be observed in many areas of the electromagnetic spectrum such as radio frequency, infrared, visible light, ultraviolet, X-rays, and even gamma rays. Most quasars are brightest in the near-ultraviolet reference frame, near the Lyman-alpha hydrogen emission line of 1216 Å or (121.6 nm), but because of their redshift, that point of luminosity is observe as far as 9000 Å (900 nm) in the near infrared.

Broadcast Generation

Since quasars display properties in common with all active galaxies, many scientists have compared the emissions from quasars to those of small active galaxies due to their similarity. The best explanation for quasars is that they are powered by supermassive black holes. To create a luminosity of 10⁴⁰ W (the typical brightness of a quasar), a supermassive black hole would have to consume the equivalent of ten stars of matter per year. The brightest known quasars should devour 1,000 solar masses of matter each year. Quasars are thought to "turn on" and "off" depending on their environment. One implication is that a quasar would not continue to feed at that rate for 10 billion years, which would satisfactorily explain why there are no nearby quasars. In this framework, after a quasar had just consumed the gas and dust, it would become a normal galaxy.

Quasars also provide some clues about the end of Big Bang reionization. Older quasars (z > 4) show a Gunn-Peterson effect and have absorption zones in front of them indicating that the intergalactic medium at that time was neutral gas. The most recent quasars do not show absorption zones, but instead their spectra show a spiky part known as the Lyman-alpha forest. This indicates that the intergalactic medium is undergoing reionization towards plasma and that neutral gas only exists in small clusters.

Another interesting feature of quasars is that they show evidence of elements heavier than helium. This means that these galaxies underwent a massive phase of star formation creating Population III stars between the time of the Big Bang and the first observed quasars. The light from these stars may have been observed by NASA's Spitzer Space Telescope, although as of late 2005 this interpretation awaited confirmation.

History of Quasar Observation

3C 273.

The first quasars were discovered with radio telescopes in the late 1950s. Many were recorded as radio sources that had no corresponding visible object. Using small telescopes and the Lovell telescope as an interferometer, the objects were shown to have a very small angular size. Hundreds of these objects were recorded by 1960 and the Third Cambridge Catalog of Radio Sources was published. (3C) while astronomers scanned the sky with optical telescopes. In 1960, the 3C 48 radio source was finally linked with an optical object. The astronomers detected what looked like a faint blue star at the position of the radio source and obtained its spectrum: Containing many unknown emission lines, the anomalous spectrum resisted interpretation.

In 1962 an outstanding breakthrough was achieved. Another radio source, 3C 273, was estimated to suffer five occultations by the Moon. The measurements obtained by Cyril Hazard and John Bolton during one of the occultations using the Parkes Observatory allowed Maarten Schmidt to optically identify the object and obtain its visible spectrum with the Hale telescope on Mount Palomar. This spectrum revealed the same strange emission lines. Schmidt realized that these were the lines of the hydrogen spectrum with a redshift of 15.8%. This discovery showed that 3C 273 was receding at a speed of 47,000 km/s. This discovery revolutionized quasar observation and allowed other astronomers to search for redshifts in the emission lines of other radio sources. 3C 48 was shown to have a redshift of 37% of the speed of light.

The term quasar (in English, quasar) was coined by Chinese-American astrophysicist Hong-Yee Chiu in 1964 in Physics Today , to describe these foreign objects:

So far, the name, clumsy and long, of 'quasi-stellar radio sources' has been used to describe these objects. Because their nature is completely unknown, it is difficult to prepare a short and appropriate nomenclature for them, as their essential properties are implied in their name. For convenience, the abbreviated form ‘quasar’ will be used during this article

Hong-Yee Chiu in Physics TodayMay 1964

It was later discovered that not all quasars, but only about 10%, had high radio emissions (radio-intense ones). Therefore, the name QSO (Quasi-stellar object) is used to refer to these objects, including the radio-intense (RLQ) and radio-quiet (RQQ) classes.

A topic of debate during the 1960s was whether quasars were near or far objects as their redshift implied. It was suggested that the redshift of quasars was not due to the Doppler effect but to light escaping from a gravitational wall. However, it was believed that a star of sufficient mass to form such a wall would be unstable. Quasars also displayed unusual emission lines previously only seen in nebulae of low density of hot gas, which would be too diffuse to detect. generate the observed energy and stay within the gravitational wall. There were also serious concerns regarding the cosmological idea of distant quasars. A strong argument against this is that the energies involved in quasars exceeded all known energy conversion processes, including nuclear fusion. At the time, there were some suggestions that quasars were some unknown form of stable antimatter and that this could influence their brightness. This objection was removed with the proposal of the accretion disk mechanism in the 1970s, and today the cosmological distance of quasars is accepted by scientific consensus.

In 1979, the gravitational lensing effect predicted by Einstein's General Theory of Relativity was confirmed by observing for the first time images of the double quasar 0957+561.

By the 1980s, unified models were developed in which quasars were viewed as a class of active galaxies, and a general consensus had emerged that in most cases it was the angle of view that distinguished one from another. kinds of others, like blazars and radio galaxies. The high luminosity of quasars was believed to be the result of friction caused by gas and dust falling into the accretion disks of supermassive black holes, which could convert 10% of an object's mass into energy, unlike the 0.7% obtained in nuclear fusion processes that dominate energy production in solar stars.

This mechanism is also thought to explain why quasars were more common at the beginning of the universe, as this energy production ends when the supermassive black hole consumes all the gas and dust nearby. This means that it is possible that most galaxies, including the Milky Way, have passed through an active stage, appearing as a quasar or other class of active galaxy depending on the black hole's mass and accretionary rotation, and which are inactive now due to a lack of matter to power their radiation-generating central black holes.