4C 05.34 is a quasar located in the constellation of Canis Minor. The 4C in the name refers to the Fourth Cambridge Catalog, which, as it sounds, is the fourth in a series of astronomical catalogs from Cambridge University. The objects in the various Cambridge Catalog are sources of radio emission. The most famous of these catalogs is the Third Cambridge Catalog, sort of like how Grand Theft Auto III is the most famous game in the Grand Theft Auto series. In that case, the Fourth Cambridge Catalog is like Grand Theft Auto IV. The Fourth Cambridge Catalog was published in the 1960s [1, 2], and it includes both the identification of radio emission from astronomical objects previously identified at other wavelengths as well as objects never seen before in any other part of the electromagnetic spectrum, and that includes 4C 05.34.
4C 05.34 is a quasar, which is a type of galaxy with an active galactic nucleus (AGN). To briefly review, a typical AGN consists of a supermassive black hole millions or billions of times the mass of the Sun, a disk of gas falling into the black hole, and jets above the poles of the black hole that form from hot gas from ther disk that was deflected away from the black hole itself by its magnetic fields. These jets typically produce a lot of radio emission, which is why lots of astronomers use radio telescopes to identify and study AGN. Quasars are a subset of galaxies with AGN where the jets are pointed nearly but not quite directly towards the Earth, so the radio emission from quasars looks like it comes from very small regions in the sky.
One of the most interesting things about 4C 05.34 is that it was, in 1970, the number one most distant astronomical object that anyone knew about [3]. This makes 4C 05.34 the equivalent of the number one song from 1970, Simon & Garfunkel's Bridge Over Troubled Water. Both 4C 05.34 and Simon & Garfunkel would go on to win several Grammys, and that included Bridge Over Troubled Water winning Best Song of the Year [4] and 4C 05.34 winning Best Performance by a Supermassive Black Hole, but despite these numerous achievements, 4C 05.34 could not prevent the break-up of one of the greatest creative duos in music history.
Anyway, let's get back to science. As I said before, 4C 05.34 was the most distant object in the universe that anyone knew about in 1970. However, to describe the distance to this object, I'm going to spend some time reviewing how professional astronomers talk about distances to other galaxies. I've actually briefly covered some of this material in previous episodes, but I'm going to do a deep dive in this episode.
For objects within our galaxy and for nearby galaxies, astronomers can use various techniques to determine the actual physical distances to these objects in one way or another, and these distances are expressed in units such as light years or parsecs, which are equivalent to about 3.26 light years, or kiloparsecs or megaparsecs. When astronomers first starting measuring distances to other galaxies, they discovered that most galaxies appear to be moving away from ours, which stretches out the light waves and makes them redder (or, in other words, the light is redshifted). The astronomers also discovered that galaxies that are located further away appear to be moving faster than galaxies that are closer. These discoveries demonstrated that the universe was expanding and led to the Big Bang theory (the scientific theory and not the TV show), but these discoveries also allowed astronomers to use the redshifting of light as a proxy for distance.
For galaxies within a couple hundred million light years of Earth, the redshifting of light corresponds to velocities of hundreds or thousands of kilometers per second, and these velocities can be multiplied by a constant called the Hubble constant (named after Edwin Hubble) to convert them to distances. For more distant galaxies, though, the light is so redshifted that the velocities would be equivalent to fractions of the speed of light, so astronomers like to describe the distances in terms of the quantity z, which describes how much the lightwaves are stretched out. More specifically, 1+z is equal to the ratio of the observed (or redshifted) wavelength of light to the original wavelength of light.
In the case of 4C 05.34, the value of z is equal to 2.873 [5], which means that the quasar is moving so quickly away from us that the wavelengths of light are stretched out to 3.873 times their original size. When average professional astronomers talk to each other, they would say that the z for 4C 05.34 is 2.873, and all of them would understand what they are talking about. However most other people who aren't professional astronomers want to know actual distances to these astronomical objects, and in fact, professional astronomers usually get asked, "How far away is that?" Also, people want these distances in some sort of units like light years, or kilometers, or miles (because they are American), or furlongs (because they think other people will think that they are clever for choosing furlongs), or maybe inches or fathoms or Angstroms or cubits or nautical miles (because they are either biblical scholars, professional mariners, or truly abnormal human beings).
In this podcast series, I have almost always tried to state the distances to other astronomical objects because, as I said earlier, people really want to know how far away things are. I also normally try to describe distances using at least light years, although I also include parsecs because professional astronomers use parsecs. Light years and parsecs work for things in our galaxy and for nearby galaxies, but they don't work well for things as far away as 4C 05.34, where the physics gets weird (or, to use the technical term, relativistic). The light from 4C 05.34 would have spent about 11.25 billion years to get to Earth, but most professional astronomers would not say that this is equivalent to a distance of 11.25 billion light years. One reason is because relativity effects have caused 4C 05.34 to decrease in brightness so much that it looks like it is actually about 79 billion light years away. This is called the luminosity distance. (By the way, current estimates are that the universe is about 13.5 billion years old.) However, relativity also affects the size of the quasar as it is seen from Earth so that it seems like it's only about 5.25 billion light years away. This is called the angular size distance. These different distances and the general weirdness make everything confusing, and this is why professional astronomers just like to use z and ignore using light years or megaparsecs for things that are really far away.
So, at a z of 2.873, 4C 05.34 was the most redshifted object and therefore the most distant object that professional astronomers knew about in 1970. It would continue to be the most distant object that astronomers knew about until 1973, when astronomers discovered the quasar OH 471 at a z of 3.408 [6]. However, 4C 05.34 would continue to be interesting for other reasons, and one of those reasons was that astronomers discovered multiple gas clouds between us and the quasar.
Hot hydrogen gas clouds in space will emit light at very specific wavelengths, and when astronomers make spectra of things that contain hot hydrogen gas, these specific wavelengths of light look like very narrow lines, so astronomers call them spectral lines. However, cold hydrogen gas clouds in space will absorb light at those same wavelengths. In spectra of light that passes through such clouds, these specific wavelengths of light will look like dark lines against the bright rainbow-like backgrounds.
Astronomers measured the redshift (or z) of 4C 05.34 using light emitted in the form of bright hydrogen spectral lines at multiple specific wavelengths. However, multiple gas clouds sit between us and the quasar, and because those gas clouds are closer to us (or, because those galaxies are at lower z), those cold gas clouds do not appear to be moving as quickly away from us as the quasar itself. As seen from Earth, the hydrogen gas in these cold gas clouds absorb light at slightly shorter or bluer wavelengths than the wavelengths at which hydrogen emits light from the quasar, and these clouds create dark lines in the spectrum of 4C 05.34 [7, 8, 9]. These days, this phenomenon is actually a well-known way for astronomers to search for hidden clouds of hydrogen gas in space and to study the structure of the universe. However, back in the 1970s, when people were just beginning to understand quasars, this was revolutionary. Astronomer were really surprised to find lots of dark spectral lines in the spectrum of 4C 05.34. The analysis of 4C 05.34's spectrum turned out to be way ahead of its time, and that is why astronomers still reference these old science results.