Why did a star look like a powerful radio source?
A source called 3C 273 looked like a point of light in a telescope, but it also emitted radio waves. Its optical spectrum contained broad bright bands at puzzling wavelengths. Finding a pattern in those bands could reveal something about the object. A spectrum spreads the incoming light by wavelength, much as a prism separates colours. An emission line is a bright feature at a characteristic wavelength; its pattern can act like a fingerprint of the emitting atoms.
A familiar pattern, shifted
Schmidt compared the bands with known lines from hydrogen. A useful rough check is to compare a line near 5,632 ångströms with the hydrogen H-beta line near 4,861 ångströms. The ratio minus one is about 0.159. This classroom calculation is illustrative: the original paper uses several lines and reports a common redshift of about 0.158. One matching line would not be decisive: the test becomes more persuasive when several features match the same fractional shift. The original table lists four lines identified with the hydrogen Balmer series, alongside other possible identifications and measurement uncertainty.
Why would that matter?
If the shift is mainly cosmological, the object is very far away; for it to look so bright from Earth, it must be extraordinarily luminous. That interpretation helped open the study of quasars, sources that can look star-like despite their enormous luminosity. Apparent brightness alone is not the source’s total output: a weak nearby lamp and a powerful distant lamp can look equally bright. A distance interpretation therefore changes the estimated luminosity, the amount of energy emitted per unit time.
What did the paper not settle?
Schmidt also considered a gravitationally redshifted nearby star and argued that it was difficult to reconcile with the observations. The radio localization by Hazard, Mackey and Shimmins was a separate related investigation. The 1963 spectrum did not itself establish the modern black-hole explanation for quasars. The paper discussed why the proposed nearby-star explanation faced difficulties; it did not turn one observation into a complete account of the object’s energy source.
Try a source check
Ask your agent to locate Schmidt’s line table, reproduce one approximate wavelength ratio, and explain why the distance conclusion depends on interpreting the redshift. Then compare the separate lunar-occultation paper to identify who contributed the radio position. For a second check, compare another line in the table and state how closely its fractional shift agrees. Treat differences as measurement and identification questions, not as an excuse to replace the observed values.
Scientific scope
The 1963 paper regarded an extragalactic interpretation as most plausible but also discussed a gravitationally redshifted nearby star. Its distance and luminosity inference depends on the cosmological interpretation. The radio-localization investigation of Hazard, Mackey and Shimmins is a related separate contribution, not part of Schmidt’s byline. The paper did not establish the modern black-hole engine.
Read the original work
- 3C 273: A Star-Like Object with Large Red-Shift
- Investigation of the Radio Source 3C 273 By The Method of Lunar Occultations
Sources and reading locations for this explanation
- 3C 273: A Star-Like Object with Large Red-Shift
Original 1963 paper: spectral lines, redshift and competing interpretations.
- Investigation of the Radio Source 3C 273 By The Method of Lunar Occultations
Separate 1963 radio-localization contribution and authors.
This English explanation is an editorial reading view. It does not replace the complete original work or certify its science.
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People and systems
M. Schmidt
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Research locations and affiliations
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Documented countries / regions: United States
Mount Wilson and Palomar Observatories and California Institute of Technology, Pasadena, US. These locations are paper affiliations, not author nationalities or ownership.