Question

List four characteristics of quasars that distinguish them from ordinary stars.

Short answer

Quasars are extremely bright, distant, have redshifted emission spectra, and are powered by supermassive black holes.

Step-by-step solution

Brightness

Quasars are some of the brightest objects in the universe and can outshine entire galaxies. Unlike ordinary stars, their luminosity is exceptionally high due to the energy they emit from the accretion of material around supermassive black holes at the centers of distant galaxies.

Distance

Quasars are located at much greater distances from us compared to ordinary stars. They often reside billions of light-years away, indicating that they existed in the early universe, whereas ordinary stars can be relatively close.

Emission Spectra

Quasars have very distinct emission lines in their spectra. These lines show a significant redshift, which indicates their rapid movement away from us and their location in the distant universe, as opposed to the spectra of ordinary stars, which are much less redshifted.

Energy Source

The energy source of quasars differs from ordinary stars. While stars generate energy through nuclear fusion, quasars derive their tremendous energy from the gravitational pull and infall of material into supermassive black holes, leading to high-energy processes and radiation.

Key concepts

Brightness of Quasars

Quasars, short for quasi-stellar objects, are renowned for their extraordinary brightness. They are among the most luminous objects in the universe. To visualize their brilliance, imagine a single quasar outshining an entire galaxy filled with billions of stars! This immense brightness isn't due to nuclear fusion like in ordinary stars. Instead, it stems from the accretion process around supermassive black holes.
As matter spirals into these black holes, it heats up and emits massive amounts of energy. This energy release makes quasars visible even from billions of light-years away. Their bright shine has allowed astronomers to study these distant cosmic beacons, despite their vast distances.

Distance of Quasars

Quasars are not just bright, but they are also incredibly distant. Often located billions of light-years away, quasars give us a glimpse into the early universe. This incredible distance suggests that quasars formed during the universe's infancy, making them ancient relics that help scientists understand cosmic history.
Unlike most stars we see in the night sky, which can be relatively close to Earth, quasars reside at such great distances that they are considered to be among the oldest observable objects we can study. Their remoteness is one of their defining features, offering a unique look into the past.

Emission Spectra of Quasars

The emission spectra of quasars are unique and reveal a lot about their nature and movement. These spectra contain distinct emission lines that are significantly redshifted. Redshift happens because quasars are moving away from us at high speeds, a consequence of the expanding universe. This redshift is more pronounced in quasars than in ordinary stars, indicating their position in the distant universe.
By studying these emission lines, astronomers can learn about the composition, temperature, and speed of quasars. This information helps scientists unravel the mysteries surrounding these powerful cosmic objects.

Energy Source of Quasars

Unlike ordinary stars that rely on nuclear fusion to generate energy, quasars have a completely different energy source. Their power comes from the gravitational forces at play around supermassive black holes. As vast amounts of material get drawn toward these black holes, the material heats up and accelerates, emitting immense radiation as it spirals inward.
This process of accretion is fantastically efficient, converting gravitational energy into light and other forms of radiation, making quasars incredibly bright. By understanding this process, scientists can study how black holes interact with and influence their cosmic environment, shedding light on some of the most extreme conditions in the universe.