Quasar and Blazar: The Brightest Object in the Universe

At night, a lot of stars scattered in the sky. From the obvious to the very difficult to see. The stars are actually very bright, it’s the distance that makes them all look dim. However, have you ever wondered which star is the brightest? Or even, what is the brightest object of the universe? Quasar and blazar are the answers.

quasar
Copyright: ESO/M. Kornmesser

But before that, we must know first, how the heck do we judge how bright a celestial object is? The answer is to look and measure the brightness. Let’s discuss the brightness of celestial objects first.

Brightness of Celestial Objects

Celestial objects have varying brightness, from those that are easily seen with the naked eye, to those that need special telescopes such as the Hubble Space Telescope. Therefore, we need a scale or measurement system for that. In this case, the most common are Apparent Magnitude and Absolute Magnitude.

The apparent magnitude is the level of how bright the object is from the earth. While absolute magnitude is the level of how bright the object is from a distance of 10 parsecs (3.26 light-years).

The two measurement scales are logarithmic scales, and the smaller the value, the greater the brightness. One level down means brighter ± 2.5 times the previous level.

sky object magnitude
Brightness of some objects that are easily found in the sky.

Note:
Because of the distances in outer space are very, very large, special units are used in distance measurements, including the AU (Astronomical Units), Ly (Light years / light years), and Parsec (Parallax Second).

1 AU ≈ 1.496 × 108 km (earth-sun distance)
1 ly ≈ 63,241.1 AU ≈ 9,461 × 1012 km
1 Parsec ≈ 3,26 ly ≈ 206,265 AU ≈ 3,086 × 1013 km


After knowing the basics of measuring the brightness of celestial objects. But before discussing quasars and blazes, we must first know the main ingredients and origins of the quasars and blazars themselves, it’s black holes.

Begins With a Black Hole

black-hole
The first image of a black hole
Copyright: Event Horizon Telescope Collaboration

Stars with mass 20 times the mass of the sun or more, there will be a supernova explosion or hypernova at the end of its life. The explosion left the star’s core. If the core of the star has more than 3 solar masses, a black hole will form.

During his life, a black hole will ‘eat’ the surrounding material which is generally in the form of stars. The most common mistake is that a black hole will suck these objects. When in fact, the term ‘sucking’ is incorrect. Objects such as stars that are ‘eaten’ by black holes are only caused by the same force found in stars, planets, and other objects, it’s the gravitational force.

The thing that made these surrounding stars are eaten is that they were too close to the black hole. This causes a significant difference in the gravitational force on the near and far surface of the star. This makes the star become elongated. In this event, star matter can be detached from the star and circling the black hole.

black hole
A simulation when a star passing near a black hole
Copyright: NASA; S. Gezari (Johns Hopkins University); dan J. Guillochon (University of California Santa Cruz)

These materials revolve around black holes at very, very high speeds. The high speed makes the material hot and emits electromagnetic radiation, including visible light. This event is more common in supermassive black holes in the galactic core, which are then called quasars. The material that rotates around the black hole is called an accretion disk.

After learning about the black hole and its behavior in ‘eating’ stars, we can enter into the following discussion on quasars and blazars.

Quasar and Blazar

Quasar

Quasars are very bright nuclei of active galaxies, which are supermassive black holes (millions to billions of solar masses) surrounded by rotating cosmic material called the accretion discs. The accretion disk rotates at such a high speed that it becomes very hot and emits electromagnetic radiation including visible light. This makes the quasar very, very bright.

About 10% of quasars emit laser-like jets on both poles. This jets speed is near the speed of light, which consists mainly of subatomic particles (such as electrons) and electromagnetic radiation. This jet is also called the Relativistic Jet or Astrophysical Jet. At first glance, this jet is similar to GRB (Gamma Ray Burst).

You can also read more about GRB (Gamma Ray Burst) in the following source.

Gamma Ray Burst: Natural ‘Sniper’ From Space

Note:
Quasar was originally called Quasi-Stellar Object (QSO) which means “star-like object”. This is because the appearance of the quasar at a glance resembles a star.

Blazar

On the other hand, the blazar is a quasar which its relativistic jets are aimed right towards the earth. The explanation is in accordance with the following illustration of the quasar and blazar.

blazar quasar
Quasars (left) and blazar (right)
Copyright: Sophia Dagnello, NRAO/AUI/NSF

Then How Bright Are They?

In short, they are very, very bright. They shine thousands of times brighter than the combined lights of billions of stars in a galaxy put together. Consider the following picture.

blazar quasar
Stars (right) and quasars (left)
Copyright: Charles Steidel (California Institute of Technology, Pasadena, CA) dan NASA

The bright object on the right is a star in our galaxy, hundreds of light-years away. And the bright object right in the middle is a quasar within 9 billion light years away. Both look equally bright.

The quasar is in a galaxy that we cannot see because it is covered by the light of the quasar itself. Have you imagined how bright it is?

One of the brightest Blazars ever found was 3C 273. It has an absolute magnitude of -26.7. This means that if the quasar is 32.6 light years from us, the light will be the same as the sun we now feel, which is only 8 minutes light from the earth.

Another bright blazar found was 3C 454.3. It has an absolute magnitude of -31.4. That is, the blazar is 260 trillion brighter than our sun.

Conclusion

Quasars are phenomena where a black hole is surrounded by cosmic matter from stars that are too close to the black hole. About 10% of quasas emit relativistic jets of subatomic particles and electromagnetic radiation. If the jet is right toward us, this quasar is called a blazar. Quasar and blazar are very bright. It is so bright that it generally makes its parent galaxy invisible.

“The interesting is, the brightest object in the universe actually starts from the darkest object in the universe (black hole).”

– Informasains

Stay curious.

Sources and References:

  1. Apparent Magnitude: Definition & Formula – Study.com
  2. Mars Fact Sheet – NASA
  3. The 26 Brightest Stars – University of Wisconsin
  4. Black hole – Wikipedia
  5. Quasar – Wikipedia
  6. List of Quasars – Wikipedia
  7. A Giant Quasar Jet – Smithsonian Astrophysical Observatory
  8. Hubble’s 100,000th Exposure Captures Image of Distant Quasar – Hubblesite

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