The Most Mysterious Phenomena in Existences - Quasars

Ever looked up at the sky and wondered, what's the most mysterious thing in existence? 

Today, we are looking at something we know very little about. In the modern world, we've been used to knowing that humanity has found, or known the majority of the things we observe in the world, and in the universe, but it's important to realize that there are many many more things in the world and in the universe alike that humanity has a whole still doesn't know about, and quasars are amongst them.

What is a Quasar?

A quasar, or quasi-stellar object (QSO) for short, is basically an extremely "luminous active galactic nucleus (AGN) in which a supermassive black hole with a mass ranging from millions to billions of times the mass of the sun is surrounded by a mostly gaseous accretion disk" [1]. Now, what does this all mean? In simple terms, a quasar is a black hole with a gaseous accretion disk of gas, dust, and other materials, which sits in the middle of super active galaxies. This phenomenon is very interesting because being such a simple idea, and a complex activity at the same time, these quasars can sometimes as bright, or ten to a hundred times brighter than normal galaxies themselves! To go into detail into these huge powerhouses, we need to define a few terms, so first, let's start with back holes. 

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What are Black Holes?

Simply put, a black hole is exactly like a planet or a star, but unlike a planet or a star, black holes have unimaginably large amounts of matter, resulting in substantial amounts of mass. They basically fold into themselves and become a simple point in space, which bends space-time to the extent that nothing can escape it, even something like a light going in the absolute fastest speeds possible. To understand them in more detail let's take a look at spacetime. Spacetime is what scientists have come up with to explain the concept of gravity and spacetime, so let's first start with spacetime. Think of spacetime as the fourth's dimension, a dimension with length, width, height, and time, yes time also. To make visualizing this easier, think of spacetime as a sheet of fabric, I know it doesn't make sense, but let's just roll with it. Now, if you put an object on to a piece of fabric, it bends the fabric, and that's what you can think of when something sits in the universe. Just like an object is placed on the fabric will bend the fabric a little, objects on the 4D fabric of spacetime will bend it, either it is a planet, a star, or a galaxy. This is important because anything with mass bends spacetime, therefore has gravity, because the literal bending of spacetime is the definition of gravity! Indeed, everything, including you, a book, or a pencil has gravity, you just don't feel it to the same extent at the earth's gravity since it's so negligible compared to astronomical objects. And now to connect all of these back to black holes, just as planets bend spacetime a little, and stars and galaxies bend spacetime quite a bit, black holes, as they have a huge mass, bend spacetime to the extent that it basically goes it to create a huge, extremely deep well. If you put something inside a hole and pull it hard enough, the object comes back, right? if you put something inside a place home and pull or push it away, no matter how hard you pull or push on it, it's impossible to get it back, even light, since it becomes one with the black hole's mass. Below, you can see an image to help visualize things a little. 

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Connecting Spacetime and Black Holes back to Quasars

Now that we have a little more understanding of black holes, we can start talking about the actual phenomena of quasars. As mentioned before, quasars are basically really active black holes, with a gaseous accretion disk around them. It is important to know that quasars are one of the oldest phenomena to ever have existed, thought to have been formed just mere millions of years after the formation of the universe, after the so-called "Dark Ages" of the universe. When the universe was forming, as the oldest planets and then starts began to form, these black holes also begin to form, when billions of the time the mass of these earliest stars came together and began to form these black holes. Since there was still a vast amount of dust and debris in the universe very close to each other, some black holes began to suck up some of these gaseous particles, and as the black hole started to suck up more and more of the gas around it, it slowly but steadily began to form an accretion disk. As the gas fall towards the black hole, tons and tons of energy in the form of electromagnetic radiation start to shoot up perpendicularly from the edges of the black hole. The power radiated by quasars can be absolutely enormous, which is partly the reason why we first detected them to be closer than they actually are. As these quasars need gas and dust to be close to forming in the first place, most quasars are thought to be formed at the very beginning of the universe, as mentioned before. This partly explains the massive redshifts measured from quasars. Because the quasar system can be extremely bright and powerful, when we first detected them, we thought of them as galaxy-like objects, based on their perceived size, brightness, and radiation strength, but soon from the redshift of then, and their spectra, realized that they are not at all like galaxies and that they are much much farther and older that we thought of them as. They are also called quasi-stellar (star-like) radio sources because when quasars were first detected, they were detected through radio-wave emissions. In fact, these objects are detectable with any of the electromagnetic spectrum's waves since they are so powerful and energetic that they produce radiation from all of the electromagnetic spectrum. Sometimes, when we see these quasars, we see them as many different objects because of phenomena such as gravitational lensing (Learn about this on the "Black Hole" post), which result in interesting pictures such as the famous "Enstine's Cross." To talk about the unknowns about these interesting things in the night sky, to be honest, they are a lot we don't know about. Pretty much everything mentioned in this post is mostly the things we know about these quasars, and there are much much more to be learned about these, including what types of gases are in these accretion disks, whether they need host galaxies to form or maintain the strength, or how long they can even exist for.

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Summary

Just to recap, quasars, or quasi-stellar object (QSO) for short, is basically an extremely "luminous active galactic nucleus (AGN) in which a supermassive black hole with a mass ranging from millions to billions of times the mass of the sun is surrounded by a mostly gaseous accretion disk. Quasars are extremely fascinating objects of the night sky and scientists and researchers are still trying to figure out more about them, and hopefully in the future, maybe will find more about these interesting objects, and maybe even visit one of them, even though that might be a long stretch into the future. 

Anyways, guys, it has been a long and amazing journey into the world of quasars and I hope each and every one of you guys enjoyed learning about these wonderful objects of the universe. Wishing all of you guys a great rest of your days and hope to see you guys in the next article!

Aadhav JaiMurugesh

[1] https://en.wikipedia.org/wiki/Quasar

[2] https://www.eso.org/public/images/eso1122a/

[3] https://qph.fs.quoracdn.net/main-qimg-c9356b9737a4f5cc55f15be3884cd36a.webp

[4] https://www.youtube.com/watch?v=MDtOFhQ0Ll8&t=325s&ab_channel=ProfessorDaveExplains