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Quasar

A quasar is the brightest objects in the Universe. They exist at the center of galaxies and draw from energy from supermassive black holes.

An x-ray image of a quasar.

Image credit: X-ray: NASA/CXC/Univ of Michigan/R.C.Reis et al; Optical: NASA/STScI

 
Have you ever wondered what lies at the center of a galaxy? If you peer at the very center of some galaxies, you may find a curious object called a quasar. These objects are extremely bright. They are often brighter than the entire galaxy they’re in! Though they are very luminous, scientists did not discover quasars until the 1960’s.
 
At that time, astronomers were pointing their radio telescopes toward the sky. They noticed radio waves coming off of celestial bodies they expected, like the sun. They also noticed radio waves coming from places they couldn’t explain. The astronomers called these mysterious objects “quasi-stellar radio sources”. This term was later shortened to quasar. Quasars are usually found billions of light-years away from Earth! 
 
We now know a lot more today about quasars than ever before. The astronomy community has many thousands of quasars cataloged. 
 

What does a quasar look like?

A quasar is made up of two key parts. The first is the supermassive black hole. A supermassive black hole is a black hole that is over a billion times the mass of our Sun. Black holes have very strong gravitational pulls, so they draw in objects around them. As material falls near the black hole, it surrounds it and becomes an accretion disk. The supermassive black hole and accretion disk are the two parts of the quasar.
 
This accretion disk heats up due to the friction caused by the pull of the black hole. How hot does the quasar get? Recent estimates suggest that quasars can reach over 18 trillion degrees Fahrenheit! Now that’s hot!
 

As the material heats up, it emits massive amounts of radiation. The magnetic field of the black hole causes two streams of material to flow away from the quasar. This material travels for millions of light years across the universe.

An artists rendition of what a quasar might look like.

Image credit: NASA/ESA/ESO/Wolfram Freudling et al. (STECF)

What is an example of a quasar?

An image of a quasar with the light split by gravitational lensing.

Image Credit & Copyright: J. Rhoads (Arizona State U.) et al., WIYN, AURA, NOAO, NSF

A famous example of a quasar is the Einstein Cross. Take a look at the image above – what do you see? It may look like there are five objects here, but this image is actually of just one quasar! How can this be?
 
The true quasar is at the center of this image. The other four light sources around it are not actually there. This famous picture is the composite of four separate images of the exact same quasar. Why do four extra entities appear?
 
This is due to a phenomenon called gravitational lensing. As light travels from the quasar to earth, it bends around a galaxy in between the two objects. This is because gravity can bend light, just like the lenses on a pair of glasses. As the light bends around the galaxy, it arrives at different points relative to the observer. This is how those extra points of light pop up!

Other Great Resources

What is a Quasar? – Universe Today: https://www.youtube.com/watch?v=fThGKOgSo5I

Quasars: Brightest Objects in the Universe – Space: https://www.space.com/17262-quasar-definition.html

Focus on Einstein’s Cross: A Gravitational Lens – Skyhound:  http://observing.skyhound.com/archives/sep/Q2237+0305A.html

Written By: Francis Aguisanda