Astronomy and Astrophysics 101: Quasar

quasar planes

Illustration of the quasar. Credit: NASA/CXC/M. Weiss

What is a quasar?

A quasar is a highly active and luminous type of active galactic nucleus (AGN). While all quasars are active galactic nuclei, not all active galactic nuclei are quasars.

Quasars are a subclass of active galactic nuclei (AGNs), which are highly luminous galactic nuclei where gas and dust fall into a supermassive mass.[{” attribute=””>black hole emit electromagnetic radiation across the entire electromagnetic spectrum. The gas and dust become luminous as a result of the extreme gravitational and frictional forces exerted on them as they fall into the black hole.

Quasar 3C 273

Optical image of the quasar 3C 273 (the bright stellar-like object in the center) obtained with the Hubble Space Telescope. It was the first quasar ever to be identified. Credit: NASA

Quasars are some of the most luminous objects in the known Universe, typically emitting thousands of times more light than the entire
A quasar is a highly active and luminous type of active galactic nucleus (AGN). All quasars are active galactic nuclei, but not all active galactic nuclei are quasars. Credit: ESA/Hubble,[{” attribute=””>NASA
, M. Kornmesser

In 1996 Hubble’s 100,000th exposure was celebrated by capturing an image of a quasar located 9 billion light-years from Earth.

Quasar Hubble 100,000th Exposure

The Hubble Space Telescope achieved its 100,000th exposure on June 22, 1996, with a snapshot of a quasar that is about 9 billion light-years from Earth. The Wide Field and Planetary Camera 2 captured this image of the quasar, the bright object in the center of the photo. The fainter object just above it is an elliptical galaxy. Although the two objects appear to be close to each other, they are actually separated by about 2 billion light-years. Located about 7 billion light-years away, the galaxy is almost directly in front of the quasar. Credit: Charles Steidel (California Institute of Technology, Pasadena, CA) and NASA/ESA

In 2019 it was announced that Hubble had observed the brightest quasar in the early Universe. After 20 years of searching, astronomers identified the ancient quasar with the help of strong gravitational lensing. A dim galaxy is located right between the quasar and Earth, bending the light from the quasar and making it appear three times as large and 50 times as bright as it would be without the effect of gravitational lensing.

Even still, the lensed quasar is extremely compact and unresolved in images from optical ground-based telescopes. Only Hubble’s sharp vision allowed it to resolve the system, and this unique object provides an insight into the birth of galaxies when the Universe was less than a billion years old. Hubble’s study of gravitationally lensed quasars has also contributed to our understanding of the rate of expansion of the Universe.

Word Bank Quasar

Credit: NASA & ESA

Hubble has also imaged quasar ghosts — ethereal green objects which mark the graves of these objects that flickered to life and then faded. These unusual structures orbit their host galaxies and glow in a bright and eerie green hue, and offer insights into the pasts of these galaxies.

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