3C 273
First identified quasar and brightest in the sky.
3C 273 sits at the core of a giant elliptical galaxy in Virgo. It holds the distinction of being the first quasar ever identified, and it remains the visually brightest one in Earth’s sky, shining at an apparent magnitude of 12.9—over 16 times brighter than its host galaxy. The object lies about 749 megaparsecs (2.4 billion light-years) away, and its central supermassive black hole weighs in at roughly 900 million solar masses.
Visible from March to July in both hemispheres, 3C 273 is bright enough to be spotted with a 6-inch amateur telescope. Because of its radio brightness and its status as the first recognized quasar, its position in the FK5 catalog serves as a reference point for 23 extragalactic radio sources that define the International Celestial Reference System. For amateur astronomers, it is the most distant celestial object they are likely to see through their scopes.
Optically, 3C 273 is the sky’s brightest quasar, with an apparent magnitude of about 12.9, and one of the closest, with a redshift of 0.158. Its luminosity distance works out to 749 megaparsecs (2.4 billion light-years). Using the Very Large Telescope interferometer, parallax measurements give an angular distance estimate of 1.80 +0.32 −0.28 billion light-years. The quasar’s absolute magnitude is −26.7—if it were as close as Pollux (about 10 parsecs), it would appear nearly as bright as the Sun. Since the Sun’s absolute magnitude is 4.83, 3C 273 is over 4 trillion times more luminous than the Sun at visible wavelengths.
Its brightness varies across the electromagnetic spectrum, from radio to gamma rays, on timescales from days to decades. Radio, infrared, and optical light from a large-scale jet show polarization with a consistent orientation, pointing to synchrotron radiation. That radiation comes from a jet of charged particles moving at relativistic speeds. VLBI radio observations reveal proper motion in some radio-emitting regions, further evidence of relativistic jets. 3C 273 is a prototype active galactic nucleus, demonstrating that its energy comes from accretion onto a supermassive black hole—no other astrophysical source could produce such output. Reverberation mapping of broad emission lines puts the black hole’s mass at 886 ± 187 million solar masses.
The quasar’s visible jet stretches about 200,000 light-years (61 kiloparsecs) and appears 23 arcseconds across. Such jets are thought to arise from interactions between the black hole and its accretion disk. In 1995, Hubble Space Telescope images revealed a structured jet with bright knots separated by faint regions. The jet’s viewing angle from Earth is about 6°, and in 2003 it abruptly changed direction by an intrinsic angle of 2°—larger than its intrinsic opening angle of 1.1°. The jet is generating an expanding cocoon of heated gas, possibly impacting a tilted gas disk within the central 6 kiloparsecs.
The host galaxy is a giant elliptical with an apparent magnitude of 16 and an apparent size of 29 arcseconds. Its morphological classification is E4, meaning it is moderately flattened. The galaxy’s mass is estimated at about 2 × 10¹¹ solar masses.
The name “3C 273” comes from the Third Cambridge Catalog of Radio Sources (1959), where it was the 273rd entry by right ascension. After Cyril Hazard used lunar occultation at Parkes Radio Telescope to get an accurate position, the radio source was quickly matched to an optical counterpart—an unresolved star-like object. In 1963, Maarten Schmidt and Bev Oke published papers in *Nature* showing that 3C 273 has a redshift of 0.158, placing it billions of light-years away. Before this, other radio sources had been linked to optical objects (like 3C 48), and many active galaxies had been mistaken for variable stars (such as BL Lac, W Com, and AU CVn). But their spectra didn’t match any known stars. 3C 273 was the first object recognized as a quasar—an extremely luminous source at a vast distance. It is a radio-loud quasar and was also one of the first extragalactic X-ray sources, discovered in 1970. As of 2006, the mechanism behind its X-ray emissions remained debated, even after new observations with the Spitzer Space Telescope.
- type
- Quasar
- constellation
- Virgo
- apparent_visual_magnitude
- 12.9
- host_galaxy_type
- Giant elliptical galaxy (E4)
Verified Timeline
Lore & Background
After accurate positions were obtained using lunar occultation by Cyril Hazard at the Parkes Radio Telescope, the radio source was quickly associated with an optical counterpart, an unresolved stellar object. In 1963, Maarten Schmidt and Bev Oke published a pair of papers in Nature reporting that 3C 273 has a substantial redshift of 0.158, placing it several billion light-years away. Its spectrum did not resemble that of any normal stars with typical stellar elements, leading to its identification as the first quasar.
Reader's Guide
It is one of the most luminous quasars known, with an absolute magnitude of −26.7, meaning that if it were only as distant as Pollux (~10 parsecs) it would appear nearly as bright in the sky as the Sun. Since the Sun's absolute magnitude is 4.83, it means that the quasar is over 4 trillion times more luminous than the Sun at visible wavelengths. Its luminosity is variable at nearly every wavelength from radio waves to gamma rays on timescales of a few days to decades. It is the most distant celestial object average amateur astronomers are likely to see through their telescopes, visible from March to July in both the northern and southern hemispheres. Situated in the Virgo constellation, it is bright enough to be observed by eye with a 6-inch (150 mm) amateur telescope.
Did You Know?
- 3C 273 outshines its entire host galaxy by more than 16 times.
- The quasar's jet measures about 200,000 light-years long, roughly twice the diameter of the Milky Way.
- If 3C 273 were as close as Pollux (~10 parsecs), it would appear nearly as bright in the sky as the Sun.
- The mass of its central supermassive black hole is approximately 900 million times the mass of the Sun.
- 3C 273 was one of the first extragalactic X-ray sources discovered, in 1970.
The Identification That Redefined the Sky
For decades, astronomers had catalogued radio sources and linked some to faint optical smudges, but nobody could explain what they actually were. Objects like BL Lac, W Com, and AU CVn had been misread as variable stars, and their spectra bore no resemblance to any known stellar composition. After accurate positions were obtained using lunar occultation by Cyril Hazard at the Parkes Radio Telescope, the radio source was quickly associated with an optical counterpart, an unresolved stellar object. In 1963, Maarten Schmidt and Bev Oke published a pair of papers in Nature reporting that 3C 273 has a substantial redshift of 0.158, placing it several billion light-years away. That single number placed the object billions of light-years away, far beyond any star. 3C 273 was the first object to be identified as a quasar—an extremely luminous object at an astronomical distance.
A Luminosity Beyond Stellar Imagination
The true energy output is staggering: with an absolute magnitude of −26.7, the quasar is over 4 trillion times more luminous than the Sun at visible wavelengths. The quasar's output is not steady; it fluctuates across nearly the entire electromagnetic spectrum, from radio waves all the way to gamma rays, on timescales ranging from a few days to several decades. Polarization with coincident orientation has been observed with radio, infrared, and optical light being emitted from a large-scale jet; these emissions are therefore almost certainly synchrotron in nature. The radiation is created by a jet of charged particles moving at relativistic speeds. VLBI radio observations of 3C 273 have revealed proper motion of some of the radio emitting regions, further suggesting the presence of relativistic jets of material.
The Jet and Its Elliptical Home
The quasar has a large-scale visible jet, which measures ~200,000 light-years (61 kpc) long, having an apparent size of 23″. In 1995, optical imaging of the jet using the Hubble Space Telescope revealed a structured morphology evidenced by repeated bright knots interlaced by areas of weak emission. The viewing angle of the jet is about 6° as seen from Earth. The jet was observed to abruptly change direction by an intrinsic angle of 2° in 2003, which is larger than the jet's intrinsic opening angle of 1.1°. An expanding cocoon of heated gas is being generated by the jet, which may be impacting an inclined disk of gas within the central ~ 6 kpc. All of this sits at the heart of a giant elliptical galaxy with an apparent magnitude of 16 and an apparent size of 29 arcseconds. The morphological classification of the host galaxy is E4, indicating a moderately flattened elliptical shape. The galaxy has an estimated mass of ~ 2×10¹¹ M☉.
A Prototype That Anchors the Sky
This is a prototype of an Active Galactic Nucleus, demonstrating that the energy is being produced through accretion by a supermassive black hole (SMBH). No other astrophysical source can produce the observed energy. The mass of its central SMBH has been measured to be 886±187 million solar masses through broad emission-line reverberation mapping. Due in part to its radio luminosity and its discovery as the first identified quasar, 3C 273's right ascension in the Fifth Fundamental Catalog (FK5) is used to standardize the positions of 23 extragalactic radio sources used to define the International Celestial Reference System (ICRS).
Frequently Asked Questions
How bright does 3C 273 appear from Earth?
Despite its staggering intrinsic output, it presents an apparent visual magnitude of roughly 12.9, so it is far beyond naked-eye reach but accessible to modest amateur telescopes. It still ranks as the brightest quasar in our night sky by visual magnitude.
Why is 3C 273 historically significant in astronomy?
It was the first object ever recognized as a quasar, proving that a point of light could be powered by a black hole at cosmological distances. That identification opened the door to the entire field of active-galactic-nucleus research and reshaped how we understand the universe.
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