00:00:00.000 In 1969, man first walked on the moon, and we saw these images.
00:00:13.360 Of course they needed to be beamed to the earth from the moon, but at that time the United
00:00:19.020 States was not facing the moon, so what happened?
00:00:23.600 Well this telescope collected the signal, it is called the Parks Radio Telescope, and
00:00:34.240 The telescope is huge, but small by the standards of some of the larger telescopes around
00:00:40.240 Affectionately, in Australia, it is known as The Dish, in part because of this movie which
00:00:48.040 It's worth watching, it's an Australian comedy classic by some of our most prominent
00:00:51.520 comedians, and it's broadly historically accurate.
00:00:55.080 What is even less known than the fact this dish was used to collect those signals coming
00:01:00.680 from the moon, was that seven years earlier, just after it was constructed, the dish found
00:01:06.920 that a certain radio source, which had already been designated, 3C273, it was pinpointed
00:01:13.800 by the Parks Radio Telescope dish, when the moon passed in front of the source.
00:01:19.200 This was in 1962, and allowed the Parks Astronomers to inform other astronomers at Mount Palomar
00:01:25.480 to use their 200-inch telescope to look for an optical counterpart.
00:01:32.080 People with radio telescopes notice something strange using radio waves, and they communicate
00:01:36.360 with the people who operate other kinds of telescope, the ones you think of when you think
00:01:43.520 And then the optical astronomers are able to more closely pinpoint the object.
00:01:48.760 The thing about radio waves is that they have long wavelengths, and long wavelengths means
00:01:53.200 low resolution, which also means it's harder to tell exactly on the sky where the signal
00:02:00.320 This is why that moon, oculation as we call it, oculation of the object behind the moon,
00:02:06.720 That process allows you to pinpoint the position of the radio object a little more precisely.
00:02:12.240 If you notice the radio waves disappear just as the moon passes a certain region of the sky,
00:02:17.160 then you can more precisely determine where in the sky those radio waves are coming from.
00:02:21.880 And that then helps astronomers who use the optical telescopes to move their telescopes
00:02:25.320 to exactly where they need to be to see the object in the regular wavelengths that
00:02:31.840 Anyways, when they did this with the 3C273 object, they saw a faint star, and they wish
00:02:40.640 The spectra was analyzed by astronomer Martine Schmidt and its collaborators, but it was Schmidt
00:02:46.280 who first suggested this object had a large redshift, but before we get to him, let's go
00:02:54.360 When the moon was passing in front of the object in 1962, the radio telescope had to be
00:03:01.800 The director of the telescope, John Bolton, was worried about being able to see the object
00:03:06.480 in the radio band, and so dug a trench around the telescope so the dish could dip below
00:03:12.480 Not only that, but he asked for local radio stations to be switched off during the observations.
00:03:16.960 This was the same John Bolton who, 13 years earlier in 1949, suggested that some radio
00:03:22.160 sources detected in the sky could be, from outside the galaxy.
00:03:28.240 No doubt in part this was the motivation for going to some quite extraordinary lengths
00:03:32.480 to ensure the radio telescope in Australia would not miss this opportunity to further
00:03:36.640 constrain some properties of this radio object that the moon was passing in front of.
00:03:41.560 By the way, Sam Neill's character in the movie The Dish was based on John Bolton.
00:03:46.440 In 1960 and 1961, there were already astronomers reporting the existence of so-called
00:03:53.760 These were stars that were quite unusual in putting out a lot of radio waves, but also
00:04:01.560 This is curious because of course later we would learn they were indeed from outside the galaxy.
00:04:07.240 But who cares that they called them radio stars?
00:04:09.800 Well, the significance for, let's say, the philosophy of science is that stars need to
00:04:15.840 be within about 120,000 light years of where we are.
00:04:18.840 In fact, that is the diameter of the Milky Way galaxy.
00:04:22.640 But quite as a typically more than 10 billion light years away, some are much more than
00:04:28.080 this, which means astronomers just a few decades ago were underestimating their distance
00:04:39.600 The history of science, the history of correcting some rather large errors in our initial
00:04:48.720 Also, and this is key, the evidence was there in the spectra in these early observations.
00:04:57.680 The astronomers could easily, if they had the right knowledge, have interpreted the
00:05:04.720 And some later on did indeed claim, as I'll come to soon, that they did interpret it
00:05:09.880 this way, but were unwilling to go out on a limb for fear of ridicule.
00:05:14.840 An issue of sky and telescope in 1961, that's the magazine for astronomers, the popular
00:05:19.160 magazine, even reported that there is a remote possibility that one of these objects,
00:05:24.960 not 3C273 but 3C48, may be a distant galaxy of stars, but there is general agreement
00:05:32.520 among the astronomers concerned that it is a relatively nearby star with most peculiar
00:05:38.280 And before I get to the nature of and the physics of quasars, I'd like to talk a little
00:05:42.800 bit more about the history, namely who could be credited with actually discovering quasars.
00:05:48.760 As we'll see, the answer to that question is not very simple, and for all intents and purposes
00:05:53.640 in science, it's entirely unimportant as well, but some of us, myself included, like
00:05:58.480 to trace the history of science, just to see what kind of fits and starts we've had
00:06:03.320 along the way to the knowledge that we've got now, what kind of errors and missteps
00:06:07.480 have been made in the past, is it possible that we won't make that error in the future?
00:06:12.760 Probably not, but it might at least broaden our way of thinking about certain areas of science
00:06:18.440 in physics, for example, where we rule out certain observations as not possibly being
00:06:23.960 able to indicate what, in fact, they do indicate.
00:06:27.400 Anyways, in terms of the history, of course, just as in history anywhere else, you can
00:06:31.840 emphasise and de-emphasise certain things and that can colour what you think is the answer
00:06:37.160 to a simple question, a seemingly simple question like who discovered the first quasar.
00:06:42.280 Now in this case, we have the astronomer John Bolton who suggested that some objects
00:06:47.680 might be outside the galaxy, namely these quasars, does he deserve the credit or is it
00:06:52.360 Martin Schmitt, who first looked at the spectra from 3c273 and determined that it had
00:06:58.840 a very large redshift, which is suggestive of the fact that it might be outside of the
00:07:03.360 galaxy, or was it hungry chew of NASA's Goddard Institute for Space Studies, who coined
00:07:09.360 the term quasar in a May 1964 article for Physics Today in Biologism at How Things Work,
00:07:15.960 if you name something, then you get the credit for having discovered it.
00:07:19.360 Now I tend to think it might have been both Bolton, who seemed to be convinced the object
00:07:24.000 was outside of the galaxy, and therefore went to these extraordinary lengths with his radio
00:07:28.480 telescope in Australia to gather the evidence that was needed, which then led Schmitt
00:07:33.360 to being able to have the spectra and interpret the spectra as, in fact, having a higher
00:07:38.800 redshift, which was the clincher for how far away this object was, and later on how bright
00:07:46.360 And even all of this story is a little bit dubious, because there are many others who contributed
00:07:53.360 And lots of ideas were being thrown around, apparently, in late night discussions, and
00:07:56.840 in Schmitt's case, certainly it's something like a party of astronomers where shots
00:08:00.360 of alcohol being consumed late at night, so who knows what was said and where the conjectures
00:08:05.760 Whatever the case, there is a history of the discovery of quasars, a paper by K.I. Kellerman
00:08:11.880 from the National Radio Astronomy Observatory in Charlottesville, which runs her 14 pages
00:08:16.240 and then an additional three pages, which is a list of all the references that are used.
00:08:22.160 So it's a comprehensive account, and if you're interested in more of this, of course,
00:08:26.640 I've put the link to that paper in the description.
00:08:29.520 Now, a part of this history that is interesting is that quasars seem to have absolutely
00:08:34.480 been discovered in 1963 by who exactly is a matter of debate, but in 1963, four very important
00:08:42.000 papers, scientific papers, were published at that time, all converging on the nature of quasars,
00:08:49.280 and in the history of quasars document that I was talking about, there's a paragraph about
00:08:53.440 this period, and it's worth reading the beta because, well, it's interesting to me.
00:08:58.360 And it says, and I'll quote, the four now classic papers by Hazard et al. 1963, Schmitt 1963,
00:09:05.840 Okie 1963, and Greenstein and Matthews 1963 were published as consecutive papers in the March 16,
00:09:16.000 Whether by error or intentionally, Hazard's name appeared in nature with a CSIRO radio physics
00:09:21.840 laboratory affiliation, although Hazard was affiliated with the University of Sydney,
00:09:26.400 relations between the University of Sydney and the radio physics laboratory,
00:09:30.000 where at the time already strained, and this incident further exacerbated the existing tensions.
00:09:36.160 Hazard had been invited by John Bolton, Taffy Bowen, and Joe Porsy to use the park's telescope
00:09:44.960 As a non-staff member, Hazard was not familiar with the operation of the telescope,
00:09:49.280 nor the receivers, and so following standard practice for non-radio physics observers,
00:09:53.680 John Schimens and Brian McKee were added to the observing team to provide telescope and receive
00:09:59.760 a support respectively, Bolton 1990, characteristically, Bolton declined to put his name on the paper,
00:10:07.440 claiming that he was just doing his job as director.
00:10:11.040 Haynes and Haynes, 1993, attribute the error to an unintentional mistake on the part of the
00:10:17.440 journal due to the change from a letter format as submitted to an article format as published,
00:10:23.600 although the manuscript submitted by the radio physics publications office has the word
00:10:28.320 delete, handwritten, next to Hazard's University of Sydney address end quote.
00:10:34.640 Now, the CSIRO is Australia's Commonwealth Science and Industry Research Organization.
00:10:41.120 It is our premier government-funded research body for science. And so the fact that
00:10:48.720 that institution was having an argument or didn't like the University of Sydney at the time
00:10:54.240 is a matter of historical interest. Whatever the case, the message here is that despite
00:11:00.880 sociological effects, the truth wins out, errors do indeed get corrected in science.
00:11:06.240 Whatever the politics is, that is not the main driver of science or of discoveries in science,
00:11:12.800 the science makes its way regardless. And all the coony and sociological musings
00:11:18.960 have very little impact, ultimately upon what we do discover. It may have an effect on the
00:11:23.840 history of science and who gets credit, but the fact is, quasars are there and we know about them
00:11:30.080 despite Sydney University fighting with the government science agency and they're apparently
00:11:34.880 being some jealousy around Bolton or some such. Science makes progress anyway,
00:11:40.400 objective progress. This is a point David Deutsch makes in his critique of coon in the fabric
00:11:46.160 of reality. Sociology is not a primary driver of scientific discoveries, not at all.
00:11:52.720 Error correction is the identification of problems are and the creation of their solutions are.
00:11:58.400 As this example of quasars shows, so that's the history except for one more remark,
00:12:03.920 these discoveries I will talk about. We're all really sparked in England and Australia and one
00:12:09.360 may well ask, why? Well, it seems to be a combination of two things. First, the English had broadly
00:12:15.120 speaking the best radio technology because this was just after World War II and it was military
00:12:20.560 technology that was first used or a form of military technology that was first used to detect
00:12:26.400 objects from the sky. As a result, they were able to begin doing radio astronomy better and
00:12:30.960 earlier than most others. Although even before this, there was Carl Jansky who was an American
00:12:37.040 astronomer after which the unit, the Jansky, is named the Jansky unit. Carl Jansky is probably
00:12:44.160 the most famous radio astronomer because he was one of the first and the Jansky is roughly speaking a
00:12:49.040 unit of radio wave intensity. So how strong the signal is. You measure it in Jansky's and Jansky
00:12:57.280 was interested in pointing radio telescopes. So he's radio telescope at the Milky Way and realized
00:13:04.000 that it's putting out that the center of the Milky Way is putting out radio waves. Anyway,
00:13:08.560 this explains why England was good at radio astronomy. They had lots of the early military technology,
00:13:14.560 but why was Australia so good? Australia is so good because the place is empty. It is quiet.
00:13:20.720 If you want to do astronomy, you need somewhere away from noise. Many people think of light
00:13:25.360 pollution when you're looking at the sky, but there's also, of course, radio pollution.
00:13:29.200 So if there are too many radio stations or if there are otherwise any other sources of radiation
00:13:33.600 around you, then this is going to interfere with the radio signal. So trying to stick a radio
00:13:38.800 telescope, a really good radio telescope, somewhere near Los Angeles or London is much harder to do
00:13:44.240 than to go way out in the middle of Australia somewhere. In fact, we're building some of the
00:13:49.920 largest radio telescopes in the world here in Western Australia at the moment as well. And parks
00:13:56.240 is quite a long way. The parks radio telescope is quite a long way from any built-up area.
00:14:02.480 But let's now move on to some more of the science. And all of this is essentially motivated by
00:14:07.920 remarks I made in my Nexus video, where I said our understanding of what a quasar really is
00:14:13.920 as I described, a black hole consuming stars. And as a consequence, the accretion disk,
00:14:22.080 which is the disk of material that is falling into the black hole, is rotating so quickly that it
00:14:28.480 creates magnetic fields. The reason it creates magnetic fields is because this gas that is spiraling
00:14:34.640 into the black hole is ionized, ionized gas. Ionized gas means you have an electrical current
00:14:42.000 to the kind. And ion is a charged particle. So lots of them moving together constitute an electric
00:14:47.760 current. And all the way back in the 1800s, we had people like Michael Faraday explaining how
00:14:54.560 moving charges, like electrons, or in this case, ions, can generate magnetic field. These
00:15:00.480 magnetic fields that are generated caused a production of jets of material that head in all
00:15:06.720 directions, but in our case towards the earth, which we can see, which we can detect. So in that
00:15:12.480 Nexus video, I presume to explain what we know of quasars in an approximately two minute clip.
00:15:19.360 Of course, that would be a very crude low resolution explanation. And so in part what I said was,
00:15:25.520 the jet head in all directions, but in our case towards the earth. Now there's ambiguity in this,
00:15:32.160 this is a kind of sloppy way of explaining what's going on. What I meant there, my intention was
00:15:37.840 that we are not privileged. If you were to take a thousand quasars at random from a god's
00:15:43.200 eye view of the universe, you would notice the jets oriented in all possible directions.
00:15:48.560 Some tiny portion of them are pointed right towards the earth. And these are the ones that we can see.
00:15:55.520 We are in the beam, so to speak. Now this is only partially correct and there's an important way
00:15:59.920 in which it's incorrect that the overwhelming majority of quasars are not ones where we're directly
00:16:05.760 in the beam. And as we'll come to, these in fact have a different name. We can still call them
00:16:10.480 quasars for reasons that I'll come to, but generally they get the name blazars. That's where we
00:16:15.760 are head on into the beam. But in fact, the mechanism whereby we can see quasars is generally
00:16:22.880 somewhat more complicated than this. And I'll come to this. But anyway, this is the motivation for
00:16:28.000 today's video. And I'm using a number of sources for this, not least of which is
00:16:34.640 this book, which is titled an introduction to modern astrophysics by Carolyn Ostley,
00:16:40.240 affectionately called Bob by the people that I went to university with. Bob standing for big
00:16:46.320 orange book. It runs for something close to 1,300 and something pages. And the frustrating thing
00:16:54.880 for us as students I recall was a running jerk of sorts, which was that every time we were expected
00:17:01.200 to get a new text, even at the graduate level, it was titled something like an introduction to
00:17:08.400 something or other. And so that's an introduction to modern astrophysics. It didn't matter how
00:17:13.280 many years we studied or how senior we became, we were always just at the introductory level.
00:17:18.480 And we always wondered when were we going to ever move beyond an introduction to? Presumably
00:17:22.720 after we did a PhD, which I never did. And incidentally, you can get texts called advanced astrophysics.
00:17:29.920 A well-known one is this one, nebduerics advanced astrophysics, which is basically just a lot more
00:17:35.920 physics than it is astronomy, but the content isn't necessarily anymore complicated than the one
00:17:41.280 that I've got here. In fact, I find the explanations in the one that I have far better than the ones
00:17:46.800 that are in this advanced astrophysics one. I think in a lot of cases these titles come down to
00:17:52.000 marketing more than anything else. What our best theory is now tell us. Lots of galaxies are what
00:17:57.280 are known as active galaxies, which just means galaxies that are brighter than normal if you observe
00:18:03.600 them using radio telescopes. Among the first of these noticed were noticed by an astronomer
00:18:09.360 Carl Safert, and they are called Safert galaxies or seafood galaxies even to this day. Some of
00:18:15.200 these galaxies also emit a lot of x-rays. Seafoods, along with quasars, are all now classed as
00:18:22.000 AGNs, which is the acronym for Active Galactic Nuclear Eye because we know they are all part
00:18:28.160 of the same kind of thing. Basically the nuclear eye or the center of the galaxies are the active
00:18:34.240 parts, the energetic parts, the particularly bright parts that are sending out the radiation that
00:18:39.280 we can then detect. An interesting thing here is the taxonomy of these objects,
00:18:44.560 because they were not all originally known to be the same. But now we do kind of know that they
00:18:49.360 are the same thing. The classic kind of AGN is pretty much encapsulated by the first one that was
00:18:56.160 discovered, Cygnus A shown here. It's moving in about 16,600 kilometers a second away from us,
00:19:03.920 that's quite fast. And we've calculated its luminosity to be 4.8 times 10 to the power of 37 watts
00:19:11.840 in the radio band alone. This is several million times brighter than a normal galaxy,
00:19:18.640 and is about three times more energy than the Milky Way puts out across all of its wavelengths,
00:19:24.800 which is absolutely astonishing because well radio waves are the least energetic of all of the
00:19:31.120 wavelengths of electromagnetic radiation. Now at the center of this image of Cygnus A, that
00:19:36.960 rather little dot, is a whole galaxy. It's a galaxy according to Bob, the big orange book,
00:19:43.440 a CD galaxy, which is a giant elliptical galaxy, or it could be a type of e galaxy if I go
00:19:48.400 looking on the internet at other sources. It depends on who I consult him out this. In any case,
00:19:53.600 it's huge, which means those lobes are even more stupendously large, and it is those lobes of gas
00:20:01.520 that are illuminated by the jet, and what makes the galaxy so bright. Now, my textbook here
00:20:09.040 says that a quasar's radio emission may come from either, radio lobes, or from the central source
00:20:15.680 in its core, quasar's are so far away that in optical images, most appear as overwhelmingly bright,
00:20:22.960 star-like nuclei, surrounded by faint fuzzy halos, in some cases a fuzzy halo can be resolved
00:20:29.520 into a faint parent galaxy. To be visible from such great distances, quasars must be exceptionally
00:20:37.040 powerful. Now, just a note on the terminology, quasar. Today, the term quasar has come to be used
00:20:45.280 almost universally for both things that put out a lot of radio waves, called QSRs, which is
00:20:52.640 quasi-stellar radio sources, and much quieter QSOs, which are quasi-stellar objects. So, this bit of
00:21:04.320 terminology is rather confusing. As a result, it's come into encounter the descriptions,
00:21:09.120 radio-loud quasars, and radio-quiet quasars. However, it is sometimes the case that QSO is used
00:21:16.240 as an abbreviation for quasar. The terminology, as I said, can be confusing in the literature,
00:21:21.840 and, indeed, its contradictory, to say that a particular quasar is radio-quiet is equivalent to
00:21:28.400 saying that we are discussing radio-quiet, quasi-stellar radio sources based on the original definition
00:21:35.120 of what a quasar is. And so, as time went on after this first one was discovered, many others
00:21:41.280 were discovered that were similar but which had important differences, and they all were extremely
00:21:48.560 bright and, aside from the radio-quiet ones, putting a lot of energy in the radio part of the
00:21:54.880 spectrum. They had high-red shifts, but they could be seen like stars, which is rather unusual
00:22:02.720 because if they're on the other side of the universe, they must be putting out a heck of a lot
00:22:08.160 of energy, and no one could really figure out what the source of this energy was. After all,
00:22:13.680 if they were like a star, that would mean they're putting out the energy in all directions
00:22:19.040 evenly, which is a mystery because no such physical process would have enabled them to put out
00:22:25.040 quite so much energy in such a small volumus space. They were putting out more energy than many,
00:22:31.760 many galaxies, and yet they appear to be like a star. Could they have been a star? That seemed to
00:22:37.360 be physically impossible. Whatever the case, people started to develop a, started to develop a
00:22:43.200 taxonomy, a way of naming these things. And so we have these kinds here, and this table here
00:22:49.680 is from the textbook that I use. So we've got seafood galaxies, we've got quasars, radio galaxies,
00:22:57.040 blazars, blazars of these things where, as we will see, the jet that illuminates the lobes
00:23:04.320 is pointed directly at us, at least for a short time. Now, what happened much later was the
00:23:12.800 creative theory that in fact all of these objects were essentially the same kind of thing.
00:23:18.720 They were a black hole with an accretion disk, and the accretion disk caused the production
00:23:24.720 because it was spinning so rapidly in the way that I described in that other episode that I did.
00:23:30.240 The accreted material spinning so rapidly that it ionizes the gas, and this ionized gas
00:23:37.280 constitutes an electric current. And the electric current generates a magnetic field and the
00:23:42.240 magnetic field can cause signetron radiation. The signetron radiation rather like the kind of
00:23:48.720 radiation that comes out of a particle accelerator generates these jets of material. The jets of
00:23:53.760 material go streaming out at right angles from the disk of material, eventually that jet of
00:23:59.360 material encounters the interstellar medium. So other bits of gas, very diffuse gas, but bits of
00:24:05.440 gas that are out there, and slow down and eventually are collected as huge clouds of gas. And so
00:24:12.000 where did these huge lobes come from? Well, that's just the material coming out of the center
00:24:16.640 via those jets. And so then the jet is colliding in with remnants of itself. And those remnants
00:24:21.760 are being illuminated by the new stuff that's colliding into it. And that causes the extremely
00:24:26.800 bright light that is coming from these things. Now, the way in which we say this is a unified
00:24:33.440 model is that all of them are exactly the same thing. The difference is the major differences,
00:24:38.480 the orientation between our vantage point here on Earth and the object. So if the object is
00:24:45.200 side onto us, we might call it a quasar. But if we're in the beam, we're a blazer. And various
00:24:50.880 other factors like the accretion rate, you know, how quickly the black hole at the center is
00:24:55.840 consuming stars. Has an effect on whether or not it's called a seafood galaxy, a radio galaxy,
00:25:02.080 a quasar or a blazer. But as the text has already said, the light that is coming from the quasar,
00:25:10.080 in most cases, is indeed coming from the brightness of the lobes. In some cases, it's also from
00:25:15.680 the central disk as well. And in some cases, it's from us being the direct path of the jet.
00:25:22.560 And the jet might itself be moving around. It might be processing in a certain sense. And so
00:25:28.240 that is why a lot of these blazers are particularly variable in their brightness. Sometimes we're in
00:25:33.440 the path of the jet and sometimes we're not. As the jet moves backwards and forwards,
00:25:37.680 such that we can either see it very clearly and brightly or not. Now it's worth going over a little
00:25:43.200 bit more detail about how these jets are generated. So the generation of jets according to
00:25:49.040 my text, which says quote, the radio lobes are produced by jets of charged particles ejected
00:25:54.880 from the central nucleus of the active galactic nuclei at relativistic speeds. These particles
00:26:00.560 are accelerated away from the nucleus in two opposite directions powered by the energy of a
00:26:06.000 creation and awe by the extraction of rotational kinetic energy from the black hole. The jet must
00:26:12.640 be electrically neutral overall, but it is not clear whether the ejected material consists of
00:26:17.680 electrons and ions or an electron positron plasma. The latter being less massive would be more
00:26:24.320 easily accelerated. The disk's magnetic field is coupled or frozen in to this flow of charged
00:26:31.200 particles. The resulting magnetic torques may remove angular momentum from the disk, which would
00:26:36.960 allow the accreting material to move inward through the disk. The incredible narrowness and
00:26:43.040 straightness of some jets means that a collimating process must be at work very near the central
00:26:49.280 engine powering the jet. A thick, hot, accretion disk around the black hole could provide
00:26:56.240 natural collimation by funneling the outflowing particles. Because the accreting material
00:27:01.440 retains some angular momentum as it spirals inward through the disk, it will tend to pile up at
00:27:07.040 the smallest orbit that is compatible with its angular momentum. Inside this centrifugal barrier,
00:27:13.120 there may be a relatively empty cavity that can act as a nozzle directing the accreting gases
00:27:18.880 outward along the walls of the cavity. However, producing highly relativistic jets, as frequently
00:27:24.240 observed, appear to be difficult to accomplish with this nozzle mechanism. Now as the jet of
00:27:31.280 material travels outwards, its energy primarily resides in the kinetic energy of its particles.
00:27:37.760 However, the jet encounters resistance as it penetrates the interstellar medium within the host
00:27:44.000 galaxy and the intergalactic medium beyond. As a result, the material at the head of the jet
00:27:49.680 is slowed and a shock front forms there. The accumulation and deceleration of the particles at
00:27:55.920 the shock front causes the directed energy of the jet to become disordered as the particles
00:28:00.800 splash back to form a large lobe in which the energy may be shared equally by the kinetic
00:28:06.880 and magnetic energy. The problem of calculating the motion of a jet through the intergalactic
00:28:11.280 medium is so complicated that extensive numerical simulations are required to model the process.
00:28:16.320 The motion of the charged particles and the magnetic fields within the lobes of radio-allowed
00:28:21.040 objects contain an enormous amount of energy. For Cygnus A, the energy of each lobe is estimated
00:28:26.320 to be approximately 10 to the power of 53 to 10 to the power of 54 joules equivalent to the
00:28:32.000 energy liberated by 10 to the power of 7 supernovae. Okay, end quote for the textbook there.
00:28:38.960 And so this is why David Deutsch makes that wonderful quip in his TED Talk about. It's a bit
00:28:45.200 difficult to explain exactly what it would be like in one of those jets. It would be a bit like
00:28:50.960 experiencing a supernova explosion but at point blank range and for millions of years at a time.
00:29:00.240 And so that's where we get at this. A single jet there has the energy liberated by 10 to the
00:29:05.520 power of 7 supernovae which is quite remarkable. And so the thing about quasars is they are luminous.
00:29:13.600 They're really bright. This means that they can be seen at distances much greater than other
00:29:18.240 objects like stars or regular galaxies. And it's this quality of being so luminous and so much
00:29:23.840 easier to detect at large distances that makes them important probes, so we say, in astronomy,
00:29:30.240 of the early universe. If a quasar is observed at a redshift of 2.0, this means the age of the
00:29:37.280 universe is only about 3.5 billion years at the time when we're observing the quasar or a quarter
00:29:42.560 of what it is now. And of course, because the quasars become more numerous, the more distant that
00:29:47.680 you look, they're a good record of how the universe is evolving over time. The ones that are closest
00:29:54.160 to us are behaving in a certain way, perhaps having a redshift or a moving with space at a certain
00:30:00.160 velocity and others that are much further away are moving with a different velocity. And this,
00:30:04.720 of course, is what led to the discovery of dark energy, this accelerating expansion of the universe
00:30:11.120 by looking at these very distant quasars. Now today, the most distant quasars that are out there
00:30:17.920 have a redshift of more than 7, according to Wikipedia, at the moment the most distant quasar yet
00:30:25.440 seen lies 29.36 billion light years away from Earth. As it says there, these distances are much
00:30:32.720 larger than the distance light could travel in the universe as 13.8 billion year history,
00:30:36.640 because space itself has also been expanding. So this one quasar that's mentioned there, it's got a
00:30:42.560 funky name J1342 plus 0.0928. It's got a redshift of 7.54, which is less than a billion years,
00:30:54.240 well less than a billion years after the big bang. So this is looking back very close to the
00:31:00.320 origin of the universe. The universe was indeed much, much smaller back then. Now if you look
00:31:05.760 up on the internet again, if you look if you Google, you'll find that the brightest quasar,
00:31:09.840 the apparently brightest quasar, so the apparent magnitude of the apparent brightness,
00:31:13.840 is indeed three, seven, two, seven, three, which is one I've been talking about the first one
00:31:17.600 I've ever discovered. And if you know where to look, apparently a medium-sized amateur telescope will be
00:31:22.080 able to resolve that. It'll look just like a star. We're pretty boring to look at. In fact,
00:31:25.920 but hey, you could say you're observing a quasar. But this is not the most powerful quasar, of
00:31:32.480 course. This is just the one that happens to be closest to us, easiest to see. And so therefore
00:31:37.600 was the first to be discovered and any amateur astronomer with a good enough bit of equipment
00:31:42.240 can indeed see it. The most powerful quasar known as of 2021, apparently is something that's got a
00:31:51.520 funky name, which I won't read out. It's just a long list of letters. It doesn't have a popular name.
00:31:56.560 You can Google this, of course. But its luminosity is 2.66 times 10 to the power 41 watts,
00:32:03.600 which is something of the view order of 10,000 times more than the other quasars that I've mentioned
00:32:08.880 here, such as three and three, that first one. So it's even brighter than those ones. And according
00:32:16.080 to one of the more prestigious journals, the notices of the Royal Astronomical Society,
00:32:24.000 the black hole associated with that quasar is 34 billion solar masses. It's number,
00:32:32.240 it's just astonishing. So the black hole alone is 34 billion times the mass of the sun. And so
00:32:39.200 it's producing this vast amount of energy. So that's as of today, the most powerful one that we
00:32:45.360 can see. And clicking a few more links, I find that Phil Plait, who is the bad astronomer. He's
00:32:53.040 written an article and I'll just take it on face value, where he says that this new quasar
00:33:00.400 found, I think it was found back in 2018, the brightest one, the most or rather the most powerful
00:33:05.200 one, the most luminous one with the 34 billion solar mass black hole. Apparently in order to do
00:33:11.920 the maths, probably, it must be eating a star, a day, a star, a day, not a star a year as most
00:33:19.520 other quasars apparently do. Now this to me raises questions about something called the Eddington
00:33:24.720 limit. And this Eddington limit is, well, it's just a consequence of the laws of physics
00:33:31.920 that you can't have more luminosity than this, given how quickly things can fall into a black
00:33:39.440 hole under gravity and then heat up and thus cause the brightness that you can see. But there
00:33:46.000 could be other physics going on here that we aren't aware of, of course. Okay, so that's where
00:33:51.280 I'll end this episode for today just to point out I had some misconceptions in that original
00:33:57.920 Nexus video there. The misconceptions being about how the light reaches us from a quasar. Are we
00:34:04.960 directly in the beam? Generally not in some cases we are, but usually we call these things blazers
00:34:11.040 or something else more exotic. There's a b-lack objects as well for what it's worth.
00:34:14.560 But usually what we're seeing is the jets of material are in fact perpendicular to us. They're
00:34:24.160 not necessarily being pointed straight at us. They can be pointed at some sort of angle towards us,
00:34:29.360 very rarely, as I say, directly towards us, but in most cases they're not oriented that way.
00:34:34.000 And instead are going perpendicular to where we are and they're then illuminating these big lobes,
00:34:40.480 these big gas clouds. And we can see the big gas clouds. And because they're so huge that's why
00:34:45.840 they're so bright, so luminous and we can detect them here on earth. And the process, the
00:34:52.480 exotic processes that are going on there are producing the radio waves. And those exotic processes
00:34:57.920 are also causing the illumination of these large lobes, which are then the things that we can detect
00:35:02.480 here from the other side of the universe to where it's all going on. And all of this explanation
00:35:07.760 as I like to link things back to the way in which knowledge is constructed and what we've talked
00:35:14.160 about throughout topcast is the idea of self-similarity. But over time, our understanding of these
00:35:20.320 quasars becomes ever better. And the models of these things in our minds come to more closely
00:35:27.520 resemble the actual physics that's going on there on the other side of the universe, that one
00:35:33.920 structure resembles the other over time. And this is the story of people. For more on that,
00:35:40.560 see my episode called The Nexus. Until next time, bye bye.