Quasar

Some spots in space are very bright.

They look like tiny stars. But they are very far away.

These spots are in the center of galaxies. They have a huge black hole. This black hole is very heavy.

Gas falls toward the black hole. This gas spins in a big ring. The gas gets very hot. It lets out a lot of light.

These spots have a lot of power. They are brighter than whole galaxies. Some are very far from Earth.

Quasars were more common long ago. They help us learn about space. Do you want to look up?

Some spots in space shine very brightly. We call these spots quasars. They look like tiny stars in photos.

But they are actually in the center of galaxies.

A quasar is powered by a supermassive black hole. This is a black hole with a huge mass. It can be millions or even billions of times heavier than our Sun. Gas spins around the black hole in a ring. We call this ring an accretion disc. As the gas falls toward the black hole, it heats up. This process lets out a lot of light and energy.

Quasars are very powerful. Some are thousands of times brighter than our Milky Way galaxy.

They are often very far away. The nearest one is 600 million light-years from Earth. Some are even 31.6 billion light-years away! Quasars were more common in the distant past. They were most active about 10 billion years ago. This happened when there was more gas nearby for the black holes to use.

A quasar is an incredibly bright spot in the center of a galaxy. These objects are also called active galactic nuclei, or AGN for short. They are some of the most luminous things in the entire universe. Some quasars shine thousands of times brighter than our own Milky Way galaxy.

Because they are so far away, they often look like tiny, faint stars in photos. Scientists sometimes call them quasi-stellar objects because of this star-like appearance.

How does a quasar make so much light? The power comes from a supermassive black hole at the center. This black hole has a huge mass, often millions or billions of times that of our Sun. Around the black hole, gas spins in a flat ring called an accretion disc. As this gas falls toward the black hole, it heats up very quickly. This heat releases massive amounts of energy as electromagnetic radiation. This includes light that we can see and X-rays that we cannot.

Astronomers first found these strange objects during the 1950s. They noticed them using radio telescopes before they could see them with regular light. In 1963, Allan Sandage and Thomas A. Matthews identified a radio source called 3C 48 as a visible object. Later, Maarten Schmidt made a huge discovery using the Hale Telescope on Mount Palomar. He looked at the radio source 3C 273 and saw strange patterns in its light. He realized the light was redshifted, which means it was stretched by the expansion of space.

There are many different facts about where quasars live and how many exist. About one million quasars have reliable measurements of their distance. There are also between 2 and 3 million identified in other catalogs. The closest known quasar is about 600 million light-years from Earth. Some are much further, reaching a distance of 31.6 billion light-years.

These distant quasars show us what the universe was like 13.2 billion years ago. Quasar activity was most common about 10 billion years ago.

Quasars help us understand how galaxies grow and change over time. We know they live in the centers of galaxies. Sometimes, the host galaxies are crashing into each other or merging.

This movement can help push more gas into the center. When there is plenty of gas, the black hole can eat more and shine brightly. Eventually, the gas runs out and the quasar becomes an ordinary galaxy. This shows us that the bright quasars of the past are related to the galaxies we see today.

A quasar is an extremely luminous active galactic nucleus (AGN). You might also hear them called quasi-stellar objects, or QSOs. These objects are among the most powerful energy sources in the entire universe. In fact, some quasars are thousands of times more luminous than a whole galaxy like our Milky Way.

Because they are so incredibly far away, they often appear as tiny, faint points of light in photographs. This star-like appearance is why the name "quasi-stellar" was originally used.

The immense energy of a quasar comes from a specific physical process. At the center of the quasar sits a supermassive black hole. These black holes have a mass ranging from millions to tens of billions of solar masses. Around the black hole, gas forms a structure called an accretion disc. As the gas in this disc falls toward the black hole, it heats up. This process releases massive amounts of energy as electromagnetic radiation. This radiation includes visible light and high-energy X-rays.

Many different factors can change how a quasar looks to us. The observed properties depend on the mass of the central black hole. The rate of gas accretion, or how much matter is falling in, also matters. The orientation of the accretion disc relative to the observer can change the view. Some quasars also feature a jet of energy. Finally, the amount of gas and dust in the host galaxy can obscure the light.

Astronomers began discovering these mysterious objects in the 1950s. They were first detected as radio-wave sources of unknown origin. In 1963, Allan Sandage and Thomas A. Matthews identified the radio source 3C 48 with an optical object. They found a faint blue star-like object with a very strange spectrum. Later, in 1963, Maarten Schmidt made a major breakthrough. He studied the radio source 3C 273 using the Hale Telescope on Mount Palomar. He discovered that the spectral lines were redshifted by 15.8%.

This redshift was a revolutionary discovery for science. Redshift occurs when light is stretched by the expansion of the universe. Schmidt's work suggested that 3C 273 was not a nearby star. Instead, it was a very distant and incredibly powerful active galactic nucleus. While many scientists were skeptical at first, evidence grew throughout the 1960s and 1970s. They realized that the high energy output was possible if the objects were very far away. This helped confirm that quasars are indeed cosmological in origin.

We have identified many quasars throughout our surveys. About one million quasars have reliable spectroscopic redshifts. Between 2 and 3 million more have been identified in photometric catalogs. The nearest known quasar is approximately 600 million light-years from Earth. Some are much further away. The most distant known AGN has a redshift of 10.1. This corresponds to a distance of 31.6 billion light-years. Looking at these distant objects is like looking back in time 13.2 billion years.

Quasar activity tells us a story about the history of our universe. Surveys show that quasar activity was much more common in the distant past. The peak epoch of this activity was approximately 10 billion years ago. This is likely because there was more matter available to fuel the black holes. As a quasar consumes the gas in its accretion disc, the fuel eventually runs out. Once the gas is gone, the energy production falls off. The quasar then becomes an ordinary galaxy.

Quasars also help us understand how large-scale structures form. Some quasars are found in concentrations known as large quasar groups. These groups may be some of the largest known structures in the universe. They can act as tracers for how mass is distributed across space. Studying quasars connects our understanding of black holes, galaxy evolution, and the expansion of the cosmos. They remain a vital tool for exploring the deep history of the universe.