The Yin and Yang of the Universe

Let’s start with a sort of unrelated topic: what do you think is the brightest thing in the universe? Maybe the sun? The Milky Way galaxy? What is the largest galaxy in the universe, (IC 1101)? Discord light mode? Those are good guesses, but the true brightest object is in a place that nobody would expect: black holes, the darkest object in the universe.

In this photo, there are two seemingly bright objects; they must be stars, right? Well, the one on the right is a star, a few hundred, maybe around 200 light-years away, but the one on the left is a Quasar, about 8.7 billion light-years away. If the distance between the Earth and the sun were to be scaled down to 1cm, the distance between us and the star would be roughly equivalent to the distance from San Francisco to Sacramento in real life. In contrast, the distance between the quasar and us would be farther than the distance between the Sun and Neptune in real life. 

But what are Quasars? Quasars are very intense AGN, or active galactic nuclei. They occur when the supermassive black hole in the center of a galaxy is consuming so much mass that the accretion disk, the huge cloud of matter that surrounds the black hole, moves near the speed of light, gets so hot and so bright from the friction and collisions that the light emitted can be seen millions to billions of light-years away. The temperature of the accretion disk can reach millions of degrees Kelvin (at this scale, Celsius and Kelvin are basically identical). 

Quasars also emit massive jets of matter that could stretch up to thousands to even millions of light-years in length, making them longer than their own host galaxy, and our galaxy and most other galaxies. These jets are some of the hottest phenomena in the universe, reaching temperatures between 10 and 18 trillion degrees Kelvin.

A black hole can maintain a bright accretion disk without absorbing all surrounding objects immediately with its immense gravity because black holes are spinning extremely fast. The reason they spin is that black holes are formed from the core of dying stars, including the massive ones at the center of galaxies (quasi-stars are only hypothetical, but are one proposed explanation for how supermassive black holes formed so early in the universe). When a star collapses, its core retains angular momentum. Since a black hole is extremely compact, an object as huge as a star turning into a very tiny point would mean that black holes are spinning ridiculously fast due to the conservation of angular momentum. Some black holes can spin so fast that they approach the speed of light. 

When these black holes are absorbing a massive amount of matter, material that is too close gets pulled past the event horizon, the inescapable boundary of a black hole, while matter farther away enters the orbit of the black hole. Since the black hole has an immense gravitational pull and is spinning near the speed of light, the orbiting matter would get tugged along and accelerated, approaching the speed of light and heating up due to friction, causing the accretion disk to emit the intense light that makes quasars detectable billions of light-years away. 

What we are seeing when we observe quasars today is what they looked like billions of years ago, when the universe was much smaller and denser, and the conditions to create these behemoths were far more common.

References:

• https://www.astronomy.ohio-state.edu/ryden.1/ast162_8/notes36.html

• https://futurism.com/scientists-discover-quasar-that-emits-jets-reaching-18-trillion-degrees#:~:text=We've%20always%20thought%20there,Kovalev%20said%20in%20a%20statement.

• https://nustar.caltech.edu/news/nustar230525#:~:text=The%20team%20used%20the%20data,the%20surface%20of%20the%20Sun.

• https://www.psu.edu/news/research/story/recipe-powerful-quasar-jets