Quasars vs. Seyferts

Attribute	Quasars	Seyferts
Definition	Extremely luminous and distant celestial objects powered by supermassive black holes	Galaxies with very bright nuclei powered by accretion onto supermassive black holes
Distance	Located at extreme distances from Earth	Relatively closer to Earth compared to quasars
Luminosity	Extremely high luminosity	High luminosity, but lower than quasars
Size	Can be larger in size compared to Seyferts	Smaller in size compared to quasars
Redshift	Higher redshift values	Lower redshift values

Introduction

Quasars and Seyfert galaxies are both types of active galactic nuclei (AGN) that emit large amounts of energy. They are characterized by their high luminosity and variability in brightness. While they share some similarities, such as being powered by accretion onto supermassive black holes, there are also key differences between the two types of objects.

Physical Characteristics

Quasars are extremely luminous objects located at the centers of galaxies, emitting energy across the electromagnetic spectrum. They are among the most powerful sources of energy in the universe, outshining entire galaxies. Seyfert galaxies, on the other hand, are spiral galaxies with an active nucleus that emits strong emission lines. They are less luminous than quasars but still exhibit high levels of activity.

Size and Scale

Quasars are typically much smaller in size compared to Seyfert galaxies. They are thought to be powered by supermassive black holes with masses ranging from millions to billions of times that of the Sun. In contrast, Seyfert galaxies have smaller black holes at their centers, typically with masses on the order of millions of solar masses. The size of the region emitting the energy in quasars is also much smaller than in Seyfert galaxies.

Emission Properties

Quasars are known for their broad emission lines, which are indicative of high velocities and extreme conditions near the black hole. These lines are often blueshifted or redshifted due to the Doppler effect caused by the motion of the emitting gas. Seyfert galaxies, on the other hand, exhibit narrower emission lines, suggesting lower velocities and less extreme conditions in their nuclei.

Variability

Both quasars and Seyfert galaxies show variability in their brightness over time. Quasars can vary in luminosity on timescales ranging from days to years, with some exhibiting rapid fluctuations in brightness. Seyfert galaxies also show variability, but typically on longer timescales compared to quasars. The variability in both types of objects is thought to be related to changes in the accretion rate onto the central black hole.

Host Galaxies

Quasars are often found in massive elliptical galaxies, which are thought to have undergone significant mergers in the past. The presence of a quasar at the center of a galaxy is indicative of a recent or ongoing merger event. Seyfert galaxies, on the other hand, are typically found in spiral galaxies, which are less massive and have a more ordered structure compared to elliptical galaxies. The presence of a Seyfert nucleus in a spiral galaxy is not necessarily linked to a recent merger event.

Obscuration

Quasars are known for being highly luminous and visible across the electromagnetic spectrum, with little to no obscuration by dust and gas. Seyfert galaxies, on the other hand, often exhibit significant obscuration in the form of dust lanes and gas clouds in their host galaxies. This obscuration can make it challenging to observe the central regions of Seyfert galaxies at certain wavelengths, leading to differences in the observed properties of quasars and Seyferts.

Conclusion

In conclusion, quasars and Seyfert galaxies are both fascinating objects that provide valuable insights into the processes occurring at the centers of galaxies. While they share some similarities, such as being powered by accretion onto supermassive black holes, they also exhibit distinct differences in terms of physical characteristics, size, emission properties, variability, host galaxies, and obscuration. Studying these differences can help astronomers better understand the diversity of AGN and the role they play in shaping the evolution of galaxies.