Double Quasars [UPSC Notes]

In April 2023, astronomers made a rare discovery using NASA’s Hubble Space Telescope and other observatories. They found a pair of quasars that were bound together by gravity, inside two galaxies that were merging. This happened when the universe was only 3 billion years old. This discovery is significant as it sheds light on the progenitor population of black holes in the early universe and the emergence of supermassive black holes through mergers.

Know more about this discovery in this article where this important science and technology topic is covered for the IAS exam.

What are Quasars?

Image source: skyandtelescope.org

Quasars, short for “quasi-stellar objects,” are extremely bright and distant objects in space that emit huge amounts of energy. 

• They are powered by supermassive black holes at the centres of galaxies, which pull in gas and dust from their surroundings. 
• The material heats up as it falls toward the black hole, emitting intense radiation and creating the bright glow of a quasar. 
• Quasars are among the most luminous objects in the universe and can be seen billions of light-years away.

Finding Close Binary Quasars:

• Scientists have only started studying close binary quasars recently, in the last 10 to 15 years. 
• Modern observatories are strong enough to spot instances where two quasars are active at the same time and will merge eventually. 
• Researchers have found more and more proof that big galaxies form when smaller ones combine. 
• As they come together, supermassive black holes should be created in the merging galaxies.

Significance of the Discovery:

• The discovery of two quasars that are closely bound together is important because it shows that there may be more pairs like this in the early universe.
• This discovery can help researchers understand how black holes form and how often they merge.
• Scientists now have a way to identify these binary quasars that are very close together.
• This finding can help us better understand how the universe evolved.

Also read: Runaway Black Holes

The Search for Binary Quasars:

• Scientists had to use advanced technology from different observatories to find these two quasars. 
• NASA’s Hubble Space Telescope and W.M. Keck Observatories in Hawaii were used to locate the quasars, while International Gemini Observatory in Hawaii, NSF’s Karl G. Jansky Very Large Array in New Mexico, and NASA’s Chandra X-ray Observatory helped with the study. 
• Additionally, ESA’s Gaia space observatory initially identified the double quasar.

Using Gaia to Identify Binary Quasars:

• Scientists used a new method with the Gaia space observatory to find possible double-quasar candidates. 
• Gaia is good at measuring the positions, distances, and motions of nearby objects. But researchers found a way to use Gaia’s database to explore the distant universe. 
• They looked for quasars that looked like nearby stars. The quasars appeared as single objects in the data because they were so close together. 
• But Gaia was able to detect a small, unexpected “jiggle” that made it look like some of the quasars were moving.

Challenges in Identifying Binary Quasars:

• It’s hard to find binary quasars because a nearby galaxy could make a faraway quasar look like two objects. This can create a false impression of a binary pair. 
• Scientists used the Keck telescope to ensure that there were no galaxies between the suspected double quasar and us.
• Additionally, gravity can distort space, which can also create the illusion of a binary pair.

Conclusion:

• The discovery of binary quasars in the early universe is an exciting development for astronomers studying the evolution of the universe. 
• The upcoming NASA’s Nancy Grace Roman Space Telescope is expected to provide significant improvements in this research area, enabling researchers to identify more binary quasars.

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