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Quasars

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Quasars

The name quasar is derived from the expression 'quasi-stellar', which means star-like. This is due to the fact that quasars were first discovered from a high amount of radio-wave emission. When these objects were observed they looked like faint, star-like points. However, these objects seemed to have a very large redshift compared to stars, which indicates that they were not stars, but something else entirely.

What is a quasar?

A quasar was believed to be a star since it was recorded emitting a very large amount of radiation, at star-like levels. However, the standard characteristics indicating a star is present, like hydrogen deposits, were missing.

Distant quasars in distant galaxies were then studied. The debris and gas particles in orbit around the black holes were colliding with each other, superheating due to friction, and accelerating to very high speeds due to the huge gravitational fields. When matter falls into supermassive black holes, it releases a tremendous amount of energy. This energy is what is known as a quasar (shown below).

Quasars, Quasar, StudySmarter

A quasar.

What is the redshift of quasars?

When the light from objects in the universe is observed, it can indicate several features. The light of each object has a particular range of the electromagnetic spectrum. Redshift is when the spectrum is shifted towards the red end of the spectrum where the wavelengths are larger. According to the Doppler effect, the wavelength is shortened towards the direction of motion. In this case, the wavelength is lengthened. In the case of quasars, this further indicates that the object is moving away from the observer (on Earth). In fact, the more distant the object, the faster it moves.

Quasars were found with a dramatic redshift, implying they were moving very fast. This means that they must be at the very edge of the expanding universe moving away from us, thus explaining the shift in the wavelength.

Redshift is the stretched appearance of light when an object is moving away from an observer. The wavelength of light appears to be increased while the frequency of the wave appears smaller. Hence the wave appears to be closer to the red end of the electromagnetic spectrum, as shown below.

Quasars Electromagnetic spectrum StudySmarter.

Electromagnetic spectrum.

When the opposite happens and the objects are moving towards the observer, the wavelength of the light wave decreases while the corresponding frequency appears to be increased. Hence the wave appears to be closer to the blue end of the spectrum, and the light is said to be blueshifted.

The creation of a Quasar

A quasar is created by the interaction of matter around supermassive black holes. Supermassive black holes are created when the mass of a star is contracted so much that it fits into the Schwarzschild radius or gravitational radius. This is the minimum radius where the gravitational attraction between the particles of the star causes it to collapse. The mass is contracted into a very small space that bends spacetime irreversibly, so that even light cannot escape.

Inside the Schwarzschild radius, particles would need to exceed the speed of light to escape the gravitational pull of the supermassive black hole. Outside this radius is the black hole diameter, also called the event horizon (seen below).

The debris gases and particles around the black hole in the accretion disk are attracted by the very large gravitational forces, causing them to accelerate with speeds close to the speed of light and collide with each other, releasing huge amounts of energy.

The energy emitted from the accretion disc is known as a quasar. It is in the form of electromagnetic radiation that travels at the speed of light. Since the emitted energy is around the event horizon, it can actually escape and be detected.

Quasars Event horizon of a black hole StudySmarterThe event horizon of a black hole - StudySmarter Originals

How are quasars discovered?

This light released by a quasar is very bright. Sometimes a stream of jet is also emitted from the centre of the quasar in the form of radio waves, which can then be detected by radio telescopes or other telescopes. However, the jet's emission is only active when there is matter in the accretion disk.

When matter around the accretion disk is consumed the quasar will be inactive, causing them to be very faint. They can be very hard to detect once they become inactive. There are hundreds of thousands of known quasars to date. The oldest neon quasar known to date is P172+18; it is 780 million years old, which provides clues about the earliest stages of the universe.

Relation of quasars to black hole size

Quasars can only form when supermassive black holes are present. The larger the size of the black hole, the larger the gravitational field will be around the black hole. Therefore, the collisions of matter will be greater and more violent, resulting in quasars.

The sizes of the black hole and quasars are an indication of their age, as supermassive black holes can only exist in the distant areas of the universe, as they must have existed and consumed matter for a long time.

Quasars - Key takeaways

  • Quasars are large amounts of energy being released from the collision of debris around a black hole.

  • Quasar means star-like. They were named as such as they were detected emitting a huge amount of energy, like stars.

  • Redshift is a phenomenon where light is shifting towards the red end of the electromagnetic spectrum, indicating that the object is moving away from the observer.

  • Quasars are discovered by radio telescopes detecting the radio waves emitted from the quasars’ jets.

Frequently Asked Questions about Quasars

A quasar is energy in the form of electromagnetic radiation being released from the collision of matter (particles, gases, stars) orbiting supermassive black holes near the event horizon.

Quasars were first detected using radio telescopes that detected tremendous energy being released, which resembled star-like energy emission.

The brightest quasar known is called 3C 273 and is in the constellation of Virgo.

A quasar is not a black hole, but the energy that is released from the collision of matter around a black hole.

A quasar is caused from the matter that surrounds a black hole in an accretion disk experiencing gravitational forces and heating up, resulting in collisions, which releases energy in the form of electromagnetic radiation.

Final Quasars Quiz

Question

What is the difference between a star and a quasar?

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Answer

A star is made from hydrogen atoms undergoing fusion and a quasar is the energy released from collisions of matter.

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Is a quasar a black hole? Yes or no.

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No

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Is a quasar a star? Yes or no.


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No.

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What is the difference between a black hole and a quasar?


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Answer

A black hole is a collapsed star and quasar is the energy that is emitted from the collision of matter around a black hole.

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 How are quasars detected?


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Answer

Using the telescopes that detect radio waves and x-rays.

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Where are quasars located in the universe?


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Answer

 Quasars are located at the edge of the universe.

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How do we know of quasars moving far away?


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Answer

The red shift phenomenon.

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How do quasars relate to the big bang theory?


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Due to redshift, indicating that quasars are moving away with increasing acceleration, validating the theory of an expanding universe.

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What evidence shows that quasars are located at the edge of the universe?


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The black holes fueling the quasars must have existed and consumed matter for a long time.

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Are quasars some of the oldest discovered objects in the universe? Yes or no.


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Answer

Yes

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Why are quasars some of the oldest objects in the universe?


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 Because they are located at the edge of an expanding universe.

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Are quasars an indication of the younger universe?


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Yes

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Are quasars some of the brightest objects in the universe?


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Yes


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What did the EM radiation of quasars reveal?


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Answer

Redshift.

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What does redshift mean?


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Answer

The EM wavelength increases when objects are moving away from the observer.

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Is the Redshift phenomenon and doppler effect the same?


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Answer

No, the doppler effect applies in both sound and EM radiation and the redshift is the effect of the Doppler effect for EM radiation.

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Question

Which is the oldest quasar?


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Answer

The quasar named P172+18 is the oldest quasar found.

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