Quasars

Hubble discovered that supermassive black holes lurk at the hearts of most galaxies. But not all black holes are equal.

Orange, spiral debris disk swirls around a black hole. A jet of material blasts from the vicinity of the black hole.

Picture a region about the size of the solar system, pouring out 100 to 1,000 times as much light as an entire galaxy containing a hundred billion stars, generating a glow that outshines its host galaxy and everything in it.

These objects are called quasars. They are distant galaxies whose incredibly bright cores are powered by supermassive black holes. Quasars have been found with luminosities between 10 to 100,000 times that of our Milky Way galaxy, generated from an area just a few light-days to a few light-years across.

Quasars occur when immense amounts of matter fall into a supermassive black hole, spiraling around it in the form of a disk before entering. This “accretion disk” is subjected to extreme gravitational and frictional forces, causing the gas and dust to heat up to millions of degrees and become luminous, blasting out dazzling jets of material into the universe. Together, the jets and glowing disk outshine their host galaxies.

illustration of a dusty swirl of particles spiraling in, with streams of glowing material spewing outward from the center
This artist's concept depicts a distant galaxy with an active quasar at its center. Hubble found that the radiation pressure from the vicinity of the black hole pushes material away from the galaxy's center at a fraction of the speed of light. The "quasar winds" are propelling hundreds of solar masses of material outward into the galaxy disk each year. This affects the entire galaxy as the material snowplows into surrounding gas and dust.
NASA, ESA and J. Olmsted (STScI)

The closest quasars to Earth are hundreds of millions of light-years away. Because of how much time it takes light to travel across the vastness of space, this means that we see these galaxies as they were in the earlier universe. Because quasars require so much matter to spark their extraordinary radiation, astronomers think they occur when galaxies merge, which happened much more frequently in the early universe.

A multii-panel image of 10 quasars, which resemble blurry, star-like objects.
The top row of this image shows a selection of photos from a Hubble survey of 11 ultra-bright quasars that existed at the peak of the universe's star-formation era, 12 billion years ago. Despite their brightness, these quasars are actually dimmed by dusty gas around them. Hubble used infrared observations to probe deeply into the material around the quasars. The bottom row shows the Hubble observations with the glare of the quasar subtracted, revealing evidence for collisions between galaxies that fuel the supermassive black holes at their centers.
NASA, ESA, and E. Glikman (Middlebury College, Vermont)

Quasars were first found in the 1950s and 60s and labeled “quasi-stellar radio sources,” because they looked like stars but emitted radio waves. Hubble’s sharp vision was used to identify the shapes of galaxies containing quasars. The telescope found quasars in both spiral and elliptical galaxies, colliding and ― surprisingly ― seemingly undisturbed, which may indicate a subtler mechanism for feeding a supermassive black hole than galaxy collision.

Six panels of somewhat indistinct, small, orange-colored galaxies with blobs of bright light within or nearby.
When seen through ground-based telescopes, quasars resemble stars, yet they are billions of light-years away. Though they aren’t much bigger than Earth's solar system, they emit 100 to 1,000 times as much light as an entire galaxy. These Hubble images, captured early in the telescope’s history, revealed some of the galactic homes of these dazzling objects.
John Bahcall (Institute for Advanced Study, Princeton), Mike Disney (University of Wales), and NASA

Today quasars are classified as a type of object known as an Active Galactic Nucleus (AGN), a galaxy with an extremely bright core caused by the light emitted as matter falls into a central supermassive black hole. Quasars are the most powerful type of AGN.

A Hubble photograph of two, closely spaced, white objects, one above and to the left of the other. Each is surrounded by a diffuse orange ring with small orange rays. Black background with very faint brownish orange splotches.
A Hubble Space Telescope photograph of a pair of quasars that existed when the universe was just 3 billion years old. They are embedded inside a pair of colliding galaxies. The quasars are separated by less than the size of a single galaxy. Quasars are powered by voracious, supermassive black holes blasting out ferocious fountains of energy as they engorge themselves on gas, dust, and anything else within their gravitational grasp. The black holes will eventually merge.
NASA, ESA, Yu-Ching Chen (UIUC), Hsiang-Chih Hwang (IAS), Nadia Zakamska (JHU), Yue Shen (UIUC)
This artist's conception shows the brilliant light of two quasars residing in the cores of two galaxies that are merging.
This artist's concept depicts the brilliant light of two quasars residing in the cores of two galaxies that are in the chaotic process of merging. The gravitational tug-of-war between the two galaxies stretches them, forming long tidal tails and igniting a firestorm of starbirth.
NASA, ESA, and J. Olmsted (STScI)

Among its quasar observations, in 2019 Hubble found the brightest quasar known in the early universe by using a combination of its sharp vision and a natural gravitational lens in space to see the distant object. Gravitational lenses occur when the gravity of a massive object ― in this case another galaxy ― warps and magnifies the light of an object behind it. The quasar’s brightness is equivalent to about 600 trillion Suns and the supermassive black hole powering it is several hundred million times as massive as our Sun, but even with gravitational lensing making it three times as large and 50 times as bright, only Hubble had the ability to resolve it.

Hubble continues to explore quasars and their galactic homes, helping refine our understanding of these cosmic beacons.

bright quasar "dots" against black backgrounds of space
Each of these Hubble snapshots reveals four distorted images of a background quasar and its host galaxy surrounding the central core of a foreground massive galaxy. The gravity of the massive foreground galaxy is warping and multiplying the quasar’s light in an effect called gravitational lensing. Such quadruple images of quasars are rare because of the nearly exact alignment needed between the foreground galaxy and background quasar to produce the images.
NASA, ESA, A. Nierenberg (JPL) and T. Treu (UCLA)
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