Quasar GB1508

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Quasar is an astronomical source of electromagnetic energy, which includes radio frequencies and visible light.

The luminosity of a quasar is equivalent to that of a trillion suns. This allows that, despite the enormous distance at which the quasars are, they can be observed with the appropriate telescopes.

Quasars were only discovered in the 20th century

In the 1930s, Karl Jansky (one of the forerunners of modern radio astronomy) discovered that static interference on transatlantic telephone lines came from nothing less than the Milky Way.

Jansky
Karl Jansky (1905 – 1950) was an American radio engineer. Credit: Wikipedia

Twenty years later, in the 1950s, astronomers could already use radio telescopes.

With them, they discovered that there was a powerful source of radio emission; but, in the image of the sky they could not find a star or something similar that could be the emitter of that energy.

These emission sources had no equivalent in the visible field.

Explanation of the strange name quasar

At the beginning, when the existence of other objects similar to Jansky’s was discovered, because the nature of these energy sources was completely unknown, it was difficult to come up with an appropriate name.

So, they were given a descriptive name. But, this one was very long: “near stellar radio sources“.

To use a shorter name, as of May 1964, they are called “quasars”, to indicate that they are “almost star-like” objects.

History of the discovery of quasars

The first quasars were discovered with radio telescopes in the late 1950s.

Hundreds of these objects were registered around 1960, as radio sources that did not have a corresponding visible object.

The astronomers continued to tirelessly explore the sky, with optical telescopes, trying to visualize some of these objects, without obtaining any results.

In order to systematize the new findings, the “Third Cambridge Catalog of Radio-Sources” (3C) was published.

Only in 1960, it was possible to link a radio source (3C 48), with an object visible by optical means.

In 1962, a breakthrough was made, predicting that another radio source, 3C 273, would soon have five occultations, when the Moon came between them and Earth.

What happened during the occultations of 3C273 behind the Moon was observed with a radio telescope.

The source of emissions was quickly associated with a counterpart at the Monte Palomar optical telescope.

In 1963, several articles were published in the journal Nature, reporting that the object exhibited a large redshift, in the hydrogen spectrum. This implied that this source was very far from the Milky Way, several billion light years away.

Quasar 3C273
Image of quasar 3C273 obtained with one of the cameras of the Hubble Space Telescope. Credit: NASA, Wikipedia.

This quasar 3C273 is probably the oldest and brightest. It is located in a giant elliptical galaxy, in the constellation Virgo.

The quasar is so far away that its light has taken about 2.5 billion years to reach us. Furthermore, the quasar 3C273 was found to be moving away from the Milky Way at a speed of 47,000 km / s.

It is currently believed that quasars can generate an amount of energy similar to the energy released by more than a hundred medium-sized galaxies.

Quasars are extremely far from the solar system

The luminosity of a quasar is equivalent to that of a trillion suns. But, it is at such a great distance that it can hardly be seen from Earth.

The quasar that is closest to our planet is 780 million light years away.

Quasars are extraordinarily bright

Astronomers claim that quasars are the most luminous objects in our entire universe.

The high luminosity of the quasars is supposed to be the result of friction caused by gas and cosmic dust falling into the disks of supermassive black holes.

This friction mechanism would explain that quasars were more common at the beginning of the universe.

Later, when the supermassive black hole had already consumed all the gas and dust that was nearby, the energy production ended.

The brightest known quasars should devour matter the equivalent of 1,000 solar masses each year.

It is currently believed that quasars can release an energy level similar to the sum of energy released by more than a hundred medium-sized galaxies.

In this assumption, after a while, the quasar would have turned into a normal galaxy.

quasar jet
Illustration of ejectad jets you by a quasar. Credit: NASA

Quasars are like powerful beacons that can help you investigate what happened in the past. when the first stars and galaxies formed.

ULAS
ULAS J1120 is the farthest quasar, and it was discovered in 2011. Credit: Wikipedia.

This quasar must have originated 770 million years after the great explosion of the Big Bang, approximately 13 billion years ago.

The discovery of ULAS J110 was made with the Hawaiian infrared telescope. The news was published in June 2011.

ULAS J110 is home to a black hole, and its luminosity is greater than 10 trillion times the luminosity of the Sun. It is the brightest quasar discovered so far.

Finding this quasar involved a painstaking search, but it was worth the effort as it will help unravel some of the mysteries of the early universe, and understand how supermassive black holes grew, a few hundred million years after the Big Bang.

The observations showed that the mass of the black hole at the center of ULAS J1120 is equal to 2 billion times the mass of the Sun.

It is difficult to explain the existence of such a large mass, at such an early stage after the Big Bang.

Recent discoveries

Thanks to the radiation emitted at different frequencies, quasars are observed in different places on the electromagnetic spectrum: X-rays, gamma rays, ultraviolet rays, etc.

Among the most exhaustive, interesting and significant recordings and observations of quasars that have been carried out so far, those made using three telescopes stand out:

  •  the Submillimeter Telescopte (Arizona),
  •  the Atacama Pathfinder Experiment (Chile) and
  •  the Submillimeter Array (Hawaii).

Scientists have so far discovered about two hundred thousand quasars.

Possible quasars that are more distant cannot be detected by tracing in visible light, because their light, stretched by the expansion of the universe, has shifted almost completely towards the infrared part of the spectrum by the time it reached Earth. .

How quasars form

Quasars are believed to arise when a huge black hole, located in the nucleus of a galaxy, begins to absorb all the matter it finds in its vicinity.

When this happens, a disk is formed that acquires an enormous speed of rotation.

This produces a gigantic amount of energy, released in the form of radio waves, light, infrared, ultraviolet and X-rays. In this way, quasars become the brightest objects in the known universe.

Current theories about the growth of supermassive black holes predict a slow increase in mass as the compact object attracts matter from its surroundings.

There are serious doubts regarding the formation of distant quasars. One hypothesis is that the energies involved in quasars exceeded all known energy conversion processes, including nuclear fusion.

For now, the mechanism that causes the emission of the large amount of energy and its rapid variability is not known.

Properties of quasars

Among the many investigations and studies undertaken in this regard, there is one that establishes that quasars have elements heavier than hydrogen; for example, helium.

In the 1980s, models were developed in which quasars were viewed as a class of active galaxies.

Small in size, quasars are distinguished by the emission of radiation at all frequencies.

Quasars are said to be very luminous distant galaxies, powered by a supermassive black hole at their center.

More than 200,000 quasars are known, and all observed spectra have considerable redshift.

All quasars are located at great distances from Earth; the closest, 780 million light years. The farthest, 13,000 million light years.

APM08279
The hyperluminous quasar APM 08279. Credit: ESA

Most quasars are more than 2 billion light-years away; Since light takes all this time to reach the Earth, the quasars that are observed now do not look as they can be now, but as they were millions of years ago.

The hyperluminous quasar APM 08279 was discovered in 1998. High-resolution images from the Hubble space telescope and the Keck telescope revealed that this system was a gravitational lensing.

It is a more luminous object than the closest quasars. Its luminosity may have been increased by the gravitational lensing effect.

Quasars display many properties identical to those of active galaxies: radiation is not thermal.

Another interesting feature of quasars is that they show evidence that they contain elements heavier than helium.