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Mobile App Chapter 19: Problem 14
What accounts for the differences among various types of AGNs? a. the type of the host galaxy b. the size of the central black hole c. the amount of dark matter in the galaxy's halo d. our viewing angle
Short Answer
Expert verified
d. our viewing angle
Step by step solution
01
Understand AGNs
Active Galactic Nuclei (AGNs) are extremely bright central regions of galaxies, powered by material falling into supermassive black holes. There are different types of AGNs, including quasars, Seyfert galaxies, and blazars.
02
Identify Key Factors
The differences among various types of AGNs can be attributed to several factors including the type of host galaxy, the size of the central black hole, the amount of dark matter in the galaxy's halo, and our viewing angle.
03
Assess Viewing Angle
One prominent factor is our viewing angle. For example, quasars are seen when the viewing angle allows a direct view of the accretion disk and jet, whereas Seyfert galaxies are seen at different angles where the visibility of the central region is partially obscured by the surrounding material.
04
Comparison to Other Factors
While the type of host galaxy, the size of the black hole, and the amount of dark matter are important aspects of galaxies with AGNs, they do not as consistently determine the type of AGN observed.
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
supermassive black holes
In the heart of every Active Galactic Nucleus (AGN) lies a supermassive black hole. These black holes are millions to billions of times the mass of our Sun. They possess such strong gravitational pulls that not even light can escape once it crosses the event horizon. Supermassive black holes grow by pulling in nearby gas, dust, and even stars, forming what is known as the accretion disk around them. As material falls into the black hole, it heats up and emits enormous amounts of energy, which makes AGNs some of the brightest objects in the universe.
quasars
Quasars are a particular class of AGNs. They are incredibly luminous, with light that can outshine entire galaxies. Quasars are often so distant that they appear as bright point sources, resembling stars when viewed from Earth. These distant objects provide insight into the early universe, as their light has traveled billions of years to reach us. Quasars generate their immense energy from the accretion disk around their supermassive black holes. Observing furthest quasars can help astronomers study the universe's history and evolution.
Seyfert galaxies
Seyfert galaxies are another form of AGNs, known for their bright, compact nuclei. Unlike quasars, Seyfert galaxies are relatively closer to us and belong to spiral galaxies. They exhibit strong emission lines in their spectra, indicating highly energetic processes in their cores. Seyfert galaxies are named after Carl Seyfert, who first identified them in the 1940s. These galaxies are divided into Seyfert Type 1 and Type 2, depending on the visible characteristics of their emission lines and the viewing angle from Earth.
blazars
Blazars are among the most energetic and variable types of AGNs. They are characterized by their strong jet activities pointing directly towards Earth. This orientation results in phenomena such as rapid and dramatic variability in brightness, polarization, and powerful emissions across the electromagnetic spectrum. Blazars are thought to be a subset of quasars, where one of the relativistic jets is aligned with our line of sight, magnifying their observed strength through a process called relativistic beaming.
viewing angle
The viewing angle plays a crucial role in the appearance of AGNs. Depending on how we observe the accretion disk and jets around a supermassive black hole, an AGN can appear as a quasar, Seyfert galaxy, or blazar. For instance, when viewed edge-on, the dense dust and gas may obscure the nucleus, as seen in Seyfert Type 2 galaxies. Conversely, when looking directly at the jet, the AGN appears as a blazar. This concept highlights how the orientation affects what we observe and how we classify these fascinating objects.
accretion disk
The accretion disk around a supermassive black hole is a swirling mass of gas and dust pulled in by the black hole's gravity. The material in the accretion disk orbits the black hole, gradually spiraling inward due to friction and gravitational interactions. As it moves closer to the black hole, it heats up and emits vast amounts of energy, primarily in the form of X-rays and ultraviolet light. This glowing disk is a key feature of AGNs and provides much of their observed luminosity.
jet
Jets are narrow, high-speed streams of plasma ejected from the regions around supermassive black holes. These jets are formed when magnetic fields in the accretion disk accelerate particles to near-light speeds. They extend for thousands to millions of light-years, often reaching far beyond the host galaxy. Jets emit strongly across the electromagnetic spectrum and can influence the intergalactic medium. They are important in understanding AGNs, as they contribute significantly to their visibility and energy output.
host galaxy
The type of host galaxy housing an AGN can influence its characteristics. Typically, AGNs are found in large galaxies with substantial central bulges. While quasars often reside in elliptical galaxies, Seyfert galaxies are commonly found in spirals. The evolution of the host galaxy and its interaction with neighboring galaxies can affect the material available for accretion, thus impacting the activity of the supermassive black hole. Studying the host galaxies provides context for understanding the lifecycle of AGNs and their environments.
