3C 273
What is 3C 273?
Black holes & quasars· Distance 2.4 billion ly. The object whose light Maarten Schmidt decoded in 1963, revealing a new kind of object: the quasar. Although it is 2.4 billion light-years away it shines at about magnitude 13, making it one of the most distant things an amateur telescope can show.
📍 Visible from where you are right now — computed in your browser
Its place in the sky
A black hole, in the direction of Virgo.
Mass, distance, nature
| Mass | ~890 million Suns |
|---|---|
| Distance | ~2.4 billion ly (z = 0.158) |
| Apparent magnitude | 12.9, the brightest quasar |
| Jet | ~200,000 ly long |
| How the mass is measured | reverberation mapping gives ~890 million Suns; in 2018 the GRAVITY interferometer measured the gas rotation directly and found ~260 million |
Figures are representative approximations. Source: compiled from NASA and IAU public data.
Discovery and name
In 1963 Schmidt decoded its spectrum and found it 2 billion ly away — the first quasar identified.
Sizing 3C 273's engine from its flickering
Once 3C 273 had been identified, scientists noticed that its brightness changes over days to years. That is a clue to the size of the region giving off the light. If the region were very large, light from its near and far sides would reach us at different times, blurring any change. So the faster the brightness changes, the smaller the glowing region must be.
The calculation showed that 3C 273's light must come from a region tiny compared with a whole galaxy. Producing the light of roughly a hundred Milky Ways in so small a space is hard to explain with stars. This puzzle was an important reason the explanation “gas falling into a giant black hole makes the light” came to be accepted. The same principle is still used to estimate the size of quasar cores.
The black hole in depth
3C 273 is number 273 in the third catalogue of radio sources made at the University of Cambridge. In 1962 its exact position was found by timing the moment the Moon passed in front of it, and at that spot sat an ordinary-looking 13th-magnitude star. In 1963 Maarten Schmidt realised that the pattern in the star's spread-out light matched the pattern of hydrogen, only shifted as a whole about 16 percent toward the red.
A shift toward the red means the object is moving rapidly away from us as the universe expands. A shift this large puts it about 2.4 billion light-years away. To look like a bright star from so far away, it must be far brighter than an ordinary galaxy — and indeed 3C 273 shines with more than four trillion times the Sun's light. Objects like this, which look like stars but are not, came to be called quasi-stellar objects, or quasars.
This enormous light comes from a black hole of about 890 million solar masses at the centre, as gas falling into it heats up and glows. A jet of gas about 200,000 light-years long also stretches out from the core. At about magnitude 13 it shows as a star-like point in a telescope of 15 cm or more. In the Sky view it appears in western Virgo on spring evenings.
Frequently asked
- What is the mass of 3C 273?
- The mass of 3C 273 is ~890 million Suns.
- How far is 3C 273 from Earth?
- The distance of 3C 273 is ~2.4 billion ly (z = 0.158).
- How bright is 3C 273 (apparent magnitude)?
- The apparent magnitude of 3C 273 is 12.9, the brightest quasar.
- Where in the sky is 3C 273?
- 3C 273 lies in the direction of Virgo.
Related
Figures are representative approximations. Simulated positions use J2000 mean elements.