As of now, there are still many unknowns and uncertainties regarding the characteristics and behavior of quasars.
When discussing the most frightening objects in the universe, many may first think of black holes. Black holes are extreme objects with such strong gravitational forces that not even light can escape them.
However, you may not know that there exists an entity in the universe that is even more terrifying, powerful, and mysterious than black holes: the quasar.
A quasar is a class of very bright active galactic nuclei, which contain a supermassive black hole surrounded by a rotating accretion disk. The material in these accretion disks is drawn in by the immense gravitational pull of the black hole, creating an extremely compressed and hot environment. In this process, the material is heated to incredibly high temperatures, releasing a tremendous amount of energy that makes quasars some of the brightest objects in the universe.
Quasars are extremely distant and bright entities, characterized by significant redshift. (Image: Zhihu).
The formation process of quasars is not fully understood, but some theories suggest they may be created by the collapse of primordial clouds or the merger of galaxies.
These objects were first discovered in the 1950s. At that time, humans could only observe their faint and star-like light in the visible spectrum, without understanding their true nature.
It wasn’t until 1963 that Dutch-American astronomer Maarten Schmidt accidentally discovered the extreme redshift phenomenon while observing the spectrum of quasar 3C-273, indicating that quasars are objects moving at very high speeds and great distances. Since then, more in-depth studies and observations of quasars have been conducted, revealing various types and characteristics of these phenomena. So, why are quasars scarier than black holes?
In visible light, a quasar looks like a normal star, meaning a point source of light. In reality, this light comes from dense material halos surrounding the nuclei of active galaxies (young galaxies), usually containing supermassive black holes. (Image: Grunge)
The size of a black hole is determined by its mass, typically measured by its event horizon radius. The event horizon is the boundary of a black hole beyond which matter and light cannot escape. According to general relativity, we can calculate the event horizon radius of black holes with different masses.
Using the mass of the Sun as a reference, the event horizon radius for a black hole with a mass equal to that of the Sun is about 3 km. The black hole at the center of the Milky Way has a mass approximately 4 million times that of the Sun, resulting in an event horizon radius of about 12 million km.
However, the supermassive black holes at the centers of quasars far exceed these numbers. The largest known supermassive black hole currently resides in the quasar TON-618. Its mass is about 66 billion times that of the Sun, and its event horizon radius is approximately 190 billion km. If this black hole were placed at the center of the Solar System, its event horizon would cover the outer part of the Kuiper Belt.
The first quasar, designated 3C 273, was discovered by Dutch-American astronomer Maarten Schmidt in 1963 in the constellation Virgo, from the Palomar Observatory. By 2005, over 100,000 quasars had been discovered. (Image: USGS).
Black holes themselves do not emit light, but when a black hole accretes surrounding material, it generates extremely powerful radiation. This radiation can be observed across many electromagnetic spectrum ranges, including radio waves, infrared light, visible light, ultraviolet, X-rays, and gamma rays.
Observing this radiation is crucial for our understanding of the nature of black holes and the behavior of material around them. However, despite their extremely powerful radiation, even the brightest black holes cannot compare to quasars.
Quasars are active galactic nuclei controlled by supermassive black holes. They have higher accretion rates and larger accretion disks than ordinary black holes. As gas in the accretion disk falls toward the black hole, it releases an enormous amount of energy, forming radiation and extreme rays. The radiation power of quasars is enormous, with the brightness of the brightest quasars exceeding 10^41 watts, thousands of times brighter than ordinary galaxies. Quasars can even outshine the galaxy clusters they reside in, allowing them to be observed from vast distances.
Quasars are more terrifying than black holes, as they formed in the early stages of the universe and have a significant impact on the structure and evolution of the cosmos. (Image: Zhihu).
Although black holes can consume surrounding material, they do not absorb everything indefinitely. When material is drawn into a black hole and begins to accumulate, a hot and high-pressure accretion disk is formed. This accretion disk releases enormous energy during the accretion process, creating radiation pressure. This radiation pressure arises from the intense friction experienced by the material in the accretion disk under the influence of immense gravity, leading to strong thermal radiation. This radiation pressure can counteract the black hole’s gravitational force to a certain extent and limit the rate of material accumulation.
This is known as the radiation pressure equilibrium limit, which defines the maximum brightness a black hole can achieve. However, the supermassive black holes at the centers of quasars can surpass this limit and achieve brightness beyond the Eddington limit.
This is due to the complex physical conditions at the center of quasars. In addition to the presence of accretion disks, there are factors such as strong magnetic fields, turbulence, and outflows that affect the transport of material and energy. These complex factors lead to the formation of multi-level, multi-dimensional, and multi-band mechanisms at the center of quasars.
In this complex system, some of the material is expelled at extremely high speeds, creating radiation and high-intensity shock waves. The expelled material can carry away some energy and angular momentum, thereby reducing the radiation pressure of the accretion disk. This phenomenon allows more material to accrete into the black hole.
Quasars are also an important tool for exploring the history and physical laws of the universe. By understanding quasars, we can not only gain deeper insights into the universe but also reflect more on ourselves. (Image: Zhihu).
Black holes are extreme entities in the universe, and their characteristics and behaviors can be described and predicted using existing physical theories. According to general relativity, we can calculate the size, shape, temperature, entropy, and Hawking radiation characteristics of black holes.
Through quantum mechanics, we can explore phenomena such as the quantum states of black holes, information paradoxes, and the evaporation process. Thermodynamics allows us to analyze the thermodynamic laws, thermodynamic equilibrium, phase transitions, and other processes related to black holes.
In contrast, quasars present many unknowns and uncertainties regarding their characteristics and behaviors, requiring us to continuously observe and explore them. For example, we still do not know how quasars form and develop, how they influence the structure and chemistry of the universe, how they interact with surrounding matter and energy, and how they generate radiation and extreme rays.
Thus, while the characteristics and behaviors of black holes can be relatively clearly described by physical theories, many unanswered questions remain regarding the properties and behaviors of quasars. For quasars, we need to continuously observe and study them to clarify their formation and evolution mechanisms, as well as their impacts on the universe.
