The "quasi-stellar radio source" 3C 273 and its jet. It is the 273rd object in the Third Cambridge Catalog of Radio Sources.
Fifty-two years ago yesterday, February 5, 1963, Maarten Schmidt figured out a key property of quasars, namely that it was receding from the Earth at 47,400 km/s. Assuming that this recession velocity was due to the expansion of the universe (and not that it was an object within our own Milky Way galaxy that was just moving really fast), and assuming that the Hubble constant was about 95 km/s/Mpc (today, the best value from WMAP is 71.0 ± 2.5 km/s/Mpc ), he estimated the distance to the quasar to be 500 Mpc (a parsec is the distance of an object that has a parallax of one arc second, which is about 30 million million km, or in scientific notation 3 × 1016 m), or 1.5 × 1025 m, or 15 trillion trillion meters. At the time, it was the furthest known object in the universe.
How did he do it? By realizing that the spectral lines observed in the spectrum of this star were redshifted by such an amount that no one had recognized that they were actually the spectral lines of hydrogen. In 1868, Anders Ångström had measured the wavelengths of the hydrogen lines in the visible portion of the spectrum to have the following values.
(It's amazing how accurate he was!) From Schmidt's published paper (which you can read here), he showed that there were not only the three lines in the 4000-5000 Ångström range, but also a magnesium line and a mercury line. But dividing the observed wavelengths (first column, l) by a factor 1.158 (second column, l/1.158) Schmidt obtains the well-known wavelength values (third column, l0). Comparing this third column with Ångström's original measurements above, you can see that they match.
What does the factor 1.158 signify? This is a Doppler redshift that translates into a recessional velocity of 47,400 km/s.
What are quasars? They are now thought to be bright young galaxies, powered by massive black holes at their centers. You can read more about this here.
Update: A detailed history of this historic discover can now be found here. It's interesting to note that the authors were aided by the fact that in 1963 most scientific communication was by letter, and thus has been preserved. It will be interesting for future historians to deal with the almost ubiquitous email communication, and the fact that it is unclear how 'archival' these will turn out to be.
Update: A symposium in honor of Fifty Years of Quasars was held at CalTech. Most of the talks can be watched online here. The talk by Maarten Schmidt is especially interesting - a first hand recollection.
What does the factor 1.158 signify? This is a Doppler redshift that translates into a recessional velocity of 47,400 km/s.
What are quasars? They are now thought to be bright young galaxies, powered by massive black holes at their centers. You can read more about this here.
Update: A detailed history of this historic discover can now be found here. It's interesting to note that the authors were aided by the fact that in 1963 most scientific communication was by letter, and thus has been preserved. It will be interesting for future historians to deal with the almost ubiquitous email communication, and the fact that it is unclear how 'archival' these will turn out to be.
Update: A symposium in honor of Fifty Years of Quasars was held at CalTech. Most of the talks can be watched online here. The talk by Maarten Schmidt is especially interesting - a first hand recollection.
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