3C 273
First identified quasar and brightest in the sky.
It was the first quasar ever to be identified and is the visually brightest quasar in the sky as seen from Earth, with an apparent visual magnitude of 12.9.
- type
- Quasar
- constellation
- Virgo
- apparent_visual_magnitude
- 12.9
- host_galaxy_type
- Giant elliptical galaxy (E4)
Lore & Background
After accurate positions were obtained using lunar occultation at the Parkes Radio Telescope, the radio source was quickly associated with an optical counterpart, an unresolved stellar object. Its spectrum did not resemble that of any normal stars, 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 it would appear nearly as bright as the Sun. 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 hemispheres.
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. That single number placed the object billions of light-years away, far beyond any star. Crucially, accurate sky positions had first been secured by Cyril Hazard using lunar occultation at the Parkes Radio Telescope, which allowed the radio signal to be matched to an unresolved stellar-looking optical counterpart.
A Luminosity Beyond Stellar Imagination
The true energy output is staggering: with an absolute magnitude of −26.7, the quasar is over four 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.
The Jet and Its Elliptical Home
The outflow carves a growing shell of superheated gas that may be colliding with an inclined disk of material within the innermost six kiloparsecs. Polarization measurements across radio, infrared, and optical bands confirm that the emission is synchrotron radiation, while VLBI radio observations have detected proper motion in the emitting regions, further confirming relativistic speeds. All of this sits at the heart of a giant elliptical galaxy classified as E4—a moderately flattened shape with an apparent magnitude of 16, an angular size of 29 arcseconds, and a total stellar mass estimated at around two hundred billion solar masses.
A Prototype That Anchors the Sky
It demonstrates, more clearly than any other source, that the prodigious energy output can only be explained by accretion onto a supermassive black hole—no other known astrophysical mechanism can match the observed power.
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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