3C 273
What is 3C 273?
Black holes & quasars· Distance 2.4 billion ly. The object whose spectrum Maarten Schmidt decoded in 1963, giving birth to the idea of quasars. At 2.4 billion light-years it still shines at magnitude 12.9, one of the most distant things an amateur telescope can show. Check its position in spring's Virgo in the Sky view.
📍 Visible from where you are right now — computed in your browser
bearing · altitude · rise time · best time tonight
Where 3C 273 is in your sky right now: https://nowsky.org/solar/sky?sel=3c 273 — location and time set automatically, no login.
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 |
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.
Frequently asked
- What is the mass of 3C 273?
- ~890 million Suns.
- How far is 3C 273 from Earth?
- ~2.4 billion ly (z = 0.158).
- How bright is 3C 273 (apparent magnitude)?
- 12.9, the brightest quasar.
- Where in the sky is 3C 273?
- In the direction of Virgo.
- Where is 3C 273 in the sky right now?
- Open the sky view for your location and time and it shows the position in the sky right now.
Brightness changing in weeks — the paradox that sized a quasar
A paradox followed soon after 3C 273 was identified. Photographic records from the 1960s showed its brightness changing noticeably within weeks. A source larger than a few light-weeks cannot vary that fast, so light equal to thousands of Milky Ways had to come from a region no bigger than the solar system — a density impossible for hundreds of billions of stars. That paradox pushed forward the explanation that matter falling onto a black hole produces the light.
The reasoning is still the basic way of sizing active galactic nuclei: the timescale of brightness changes sets an upper limit on the source's size. 3C 273 has Harvard plate records back to 1887, making it one of the few quasars with a 130-year light curve, and a quasi-period of about 13 years found in that curve is discussed in terms of a binary black hole or a precessing disk. The first quasar ever identified is also the longest observed.
The black hole in depth
3C 273 is entry 273 in the third Cambridge catalogue of radio sources, pinned down precisely in 1962 by timing its disappearance behind the Moon. The spot held an unremarkable thirteenth-magnitude star, but in 1963 Maarten Schmidt realised its strange spectral lines were hydrogen lines stretched by 16 percent. That redshift meant a distance of 2.4 billion light-years, and to look star-like from so far it had to outshine hundreds of galaxies. The quasi-stellar radio source, the quasar, was born.
At its core sits a black hole of about 890 million solar masses, whose accretion disk radiates thousands of times the light of the entire Milky Way. A jet 200,000 light-years long has been imaged by Hubble in visible light and by Chandra in X-rays. As the brightest quasar known, 3C 273 serves as the benchmark of its class, and its brightness changes over months revealed early on that the central engine is no larger than the solar system.
At magnitude 12.9 a 15-centimetre telescope shows it as a star-like point, which makes it a favourite candidate for the most distant object amateurs can see; the light on view left before multicellular life appeared on Earth. Select 3C 273 in the Sky view to see its spot in western Virgo between Spica and Denebola, best on spring evenings.
Related
Figures are representative approximations. Simulated positions use J2000 mean elements.