About science; About quasi stellar objects

This is about science produced by the California Institute of Technology and originally broadcast by station KPCC in Pasadena California. The programs are made available to the station by national educational radio. This program is about quasars stellar objects with host Dr. Robert McGregor Leean and his guest Dr. Beverly oak professor of astronomy. Here now is Dr. McGrath. We read more and more frequently in the press and other news media. The discovery of a new and unique objects in space and one that we've heard a good deal about lately are these quasi star objects. Beth would you tell us about our earliest discovery of these objects and our experience developed. Many years ago it was when radio astronomy began. It was quickly realized that there were many so-called sources in the sky these were very tiny regions

where which were radiating in the radio spectrum. And these were quite bright objects and people were doing a lot of work trying to identify these these were radio stars as we call us. These were so-called radio stars yes. They you know a few cases they were able to look at photographs taken with ordinary telescopes they were able to discover what the object was the Crab Nebula for instance was one such object which was discovered. And during the years they discovered or identified perhaps 30 or 40 percent of these objects that remained however quite a number of. Like the majority of these radio sources which there seem to be no identification whatsoever for if you looked on a photograph there were nothing particularly there which would catch your eye then. But nothing was

visible in that light. Nothing was visible when you looked at it with ordinary light. The first identification was made. So three or four years ago now when it was found that there was a very faint star a star like object at least which could perhaps be identified with one of these radio sources. When the light from this was studied in more detail it was found that this was not a Nord Neri star but it was some strange sort of object which. Persuaded people that this must be the source the next source which was found objects received 273. This was discovered by means of occultation by the mone. This was able to pinpoint the radio position extremely accurately and with this accurate position then the optical source could be

identified this again turned out to be a relatively bright star like object. Since they are there have been identified perhaps 100 of the radio sources with these stellar objects. These are referred to usually as quality stellar sources or quality stellar objects are the majority the majority of these identified with bright objects in the light. Most of them not 3C 273 which I mentioned before is a British one is by far the brightest one which has been found most of them are quite faint stars. They have can be photographed only with quite large telescopes. They also most of them are radio sources of one sort or another. The original ones were all radio sources this is the way in which they were discovered. Sandridge out what Wilson and Palmer observatories found within the last two years that there were a number of similar

objects which had rather similar characteristics but which were not radio sources. Some are light character similar light characteristics. I think there is some discussion as to what you identify as the unusual characteristics which prescribe a quasi stellar object. What makes it different from other star objects. The main difference and the one which we usually use as our criterion for identifying them is the spectrum. If you break up the light into the various component colors you find that the quasi stellar objects have a rather smooth appearance and superimposed on these are very broad strong emission lines which are produced by atoms such as hydrogen helium carbon things of the sort.

When you say a smooth appearance we mean that the amount of light emitted at the different wavelengths or colors is more or less uniformly distributed. Yes it's quite uniformly distributed if you look at a star on the other hand ordinary star and ordinary star you find that the so-called spectrum is caught up very much with strong absorption lines. Occasionally you Sharky emission lines but the whole appearance of the spectrum is entirely different. So this is one of the characteristics which set the quasi stellar objects apart. Yes yes you mentioned that a certain emission lines were recognized. Is this unusual in itself. Certainly there are emission lines that are seen in an ordinary star and. You vary in ordinary stars this is very rarely the case you are seeing only very special stars which have emission line stars normally have absorption lines. If you look at nebulae those glowing gas in the space between the stars. This material also has emission lines and

in many cases it's the same emission lines which we see in the quasi stellar objects. However most of the objects of this sort the nebula we do not have a continuum which goes with them so again there is a striking difference between me cause the stellar objects on the one hand and nebulae on the other in spite of the fact that they both have the mission lines present. So in terms of the spectra then the two distinguishing features are one the more uniform nature of the continuous light emission Plus the emission lines which you identify with certain constituents. Yes you mentioned a couple of these earlier. The constituents of the Green Line. Yes the main one which is seen in most objects at least the closer objects is hydrogen. Occasionally we think we can see Helium of a lot rather surprisingly weak. One would expect the helium lines

to be stronger than they are. The other elements which we do see are big Nazeem for instance. We sometimes see oxygen carbon things of this fact. These are just the elements which we would expect to be have the strongest lines these are the most abundant elements in the sun for instance. Can you say anything from what has already been seen with regard to the relative abundance of these species. One can say a little bit the to analyze the spectrum thoroughly requires a minimum knowledge of the processes which go on inside the object. And these we still don't know very much about the engine in a general sort of way the emission lines which are observed are the ones which we would expect to see if the diamond were normal abundance of hydrogen which you expect. Yeah and so on. Yes the we don't see we don't see strange things for instance

and. This sort of thing the How about in addition to the spectral features of these objects. Something about the structure. Is there anything unique about the structure or singular in some way or another the structure is something probably the most difficult thing to get out. We are these just because they are stellar in appearance cannot be resolved in a telescope if you look at them they look like a point source as far as we just a little speck a line to speck of light so that any anything that we can determine from the above the structure has to come from a study of what the object is doing or see some of the characteristics of the object for instance its temperature and its density. Various things of this sort these are all inferences they're not direct observations. One of the ways in which we have recently been able to get some idea of

the size is to look at the rate at which the object is fluctuating in brightness. There are several of these quasi stellar sources which are observed to change in brightness. What kind of frequency is this that the until recently. It could mean more in a few years. Recently it was thought to be perhaps a few a year or two perhaps likely last observations which we have made during the last approximately one year indicate now that the fluctuations are in fact happening within an interval of about one day and the implication of this is that the diameter size of these objects cannot be much larger than the time it takes light to go across the object and the length of time which is which the fluctuation seen. What would that represent in a way of actual distance than this what is a light day.

A light day is well to begin with. The distance from the earth to the sun is about 90 million miles and light will travel this distance in 8 minutes there for its distance is 8 light minutes. If you go to a somewhat larger distance for instance the size of our planetary system to Pluto for instance then you get something which is a fraction of a light day so that we are now looking at an object apparently which is not much larger than our solar system about the size of a solar system. What else can you say about the unique characteristics of these quasi stellar sources. Perhaps in terms of the spectra of their number distribution the one of the I think one of the unique characteristics which perhaps the most important one is the very large red shift which is observed. The way that you know you

are going to have to explain. OK if you look at a star like the sun or a neighboring star you find that the lines are shifted very slightly by the Doppler effect and if you listen to a train going past the whistles you reach the frequency of the sound at the West pitch pitch changes and light behaves in exactly the same way. So if the source of light is moving away from you the pitch changes. Down down yes. Or in wavelength increase. Yes and the same thing happens with light. If you look at most stars for instance the shift is extremely small. It can be measured but. That is about all. To suggest that the starter object is moving away then it should be going down. And if if you move down in pitch or if the wave length increases be in the characteristic of all the quasi stellar objects so far observed is that the wavelengths are increased. And

surprisingly enough they are increased by a very very large amount large compared to anything that's been seen. We have no one we knew about galaxies of course 30 or 40 years ago it was realized that these had also had red shifts and the redshifts again were quite large in terms of what we normally like to think about. But it turns out that the quasi stellar objects of red shifts which are almost an order of magnitude larger still the red shifts are in fact approaching to a sizable fraction of the velocity of light. If you are to say that we object itself as moving relative to us at a loss it is approaching that of the speed of light. This is right yes. Had there been any developments in terms of explanations for these quasi star sources there have been some suggestions.

The first thing which has to be decided is whether the sources are relatively close to us or whether they are very distant. And if they are very distant Then we must think of them as being analogous to very distant galaxies perhaps even related to very distant galaxies. It has also been suggested that these may be very small objects which are relatively close to our own galaxy but they would have to move very fast if they were close to our own galaxy they would have to be to be moving extremely fast and they have to be presumably ejected from either center of our own galaxy or the center of some other galaxy. They don't seem to be a reasonable explanation at this point. I personally don't think so the main trouble was such an explanation is that the amount of energy required. Is having down to such a law bringing them to such high velocities is an extremely large amount of energy and we still have no idea as to

how we can get this money much energy the energy problem unfortunately isn't solved even if these objects are very distant. That is if they're at distances comparable with very distant galaxies we still have to think in terms of lots of energy which are almost impossible to conceive of. You arrive at this because of what their brightness. Yes there are. If you compare one of these tiny objects with a normal galaxy you find that it is now radiating energy at a rate which is perhaps 100 times larger than what now then for instance our own whole Milky Way see into my Milky Way the entire Milky Way system which consists of something like a hundred thousand million stars like the sun. This tiny object which is perhaps not much larger than our solar system is radiating 100 times as much energy as this whole conglomeration. So just trying to explain that is in itself a tremendous task. Yes and many attempts have been made in

principle. The amount of energy is available and it's rather interesting to see if one estimates the total amount of energy which can be associated with a galaxy like our own Milky Way system. You find that the amount of energy which is needed is just about this amount. The if this is where the energy comes from then the remaining problem is how do you manage to extract all of this energy. What is the physical process slows the physical process which caused the first release converts this potential energy into actual radiation which we eventually see. And this is still I think a complete mystery. So the possibility that these objects might be things that are emitted from our own galaxy or from immediate proximity appears to be not as attractive. How about the notion that they are very distant objects moving away from us at a high speed.

This is attractive at least to me because we don't know all of that. There are normal galaxies or slightly peculiar galaxies which in fact do just this. We have not observed look falsities as large as the quasi stellar objects display. And the reason this redshift business in terms of the redshift the reason for this is only that the objects are relatively much fainter. We cannot see them as far away and since the objects move faster the farther away they are. We just have not been able to probe deep enough into space to see these large velocities. But it seems attractive to have a hypothesis where at least we which has which can be interpreted much the same way as other observations which we have been studying for many years. Aha how do you connect these objects with great distance. There's a

so-called double law which was discovered by Hubble at my Wilson Observatory many years ago now. He found it among fairly distant ordinary galaxies that the size of the red shift. This change of wavelength from us was proportional to the distance of the object the farther away the distance the distance of the object the larger the redshift and this is one independent way of determining this distance so that the correlation was a precise one. Or at least the correlation was moderately precise it was about and it was done by a completely independent technique so you can make this connection that of redshift with distance. Yes and so you like to think that perhaps these objects can be identified on the same scale. The hope is that eventually we can find the connection between one of these quasi stellar objects and another object or objects which

we know something more about this. This still has not been done but at least it's possible. You indicated the enormous amounts of energy being radiated by these objects. In fact you've connected it or associated with the total energy associated with a complete galaxy such as the Milky Way. At that rate of energy production. Can one expect these objects to have existed for long periods of time. Almost certainly not. The if you look at some of the data which one finds from the radio observations there is quite a bit of evidence which suggests that these objects cannot have lifetimes which are more than perhaps a million years. In other words these are whatever these objects are this is a very trendy and very short lived in terms of the total age of the universe. Yes the age of the universe is perhaps 10 billion

years. These are objects which are tens 10000 times shorter in their lifetime. So that this must be a process which goes on for a short period of time. You indicated great distances how great are the distances for example. Based on this Hubble loss the closest object 3C 273 is at a distance of 500 million parsecs or fifteen hundred million light years. This is by far the closest of these when you go to the very distant ones. The method by which you calculate distance becomes involved with cosmology and unless one knows how the universe is made it's not possible to calculate directly what the distance is or what you want the distance means. Can you give some indication is there some spread of possibilities here. I mean is it a few billion light years away are it certainly

in terms of light years I mean it's certainly several billion light years away perhaps. We are looking at objects which go back about half the age of the universe. When we look at these very distant ones. Does this suggest then that these are objects which we are now beginning to see which we are in a state of evolution very early in their development. This I think is certainly possible. The one of the attractive pictures which has been proposed for these objects is that they are actually galaxies like our Milky Way system again which are in the process information so that when we were a very early galaxy galaxy something of that art. That we're seeing them and that very early stage of development. Are there any other objects with similar properties. Yes there. Are a small class of

galaxies called Seaford galaxies which have some of the properties of quasi stellar sources these are galaxies which are overall very normal in appearance. They have however at the center a very tiny bright nucleus which is almost as bright as the whole galaxy in some cases this nucleus. If you look at the spectrum has very many of the characteristics of quasi stellar sources and certainly very very possible what the nuclei of these particular very special galaxies may be related directly in some way with quasi stellar objects. And are these objects also very far away. Most of them are not. The one of these the fact the brightest of these is one of the relatively close galaxies. And it's one where we can actually photograph the whole galaxy we can. We can see it is a more or less

normal galaxy so that we know that in the center of this object something very strange is going on. And it seems to be something quite analogous to the causes to other sources is the energy production rate comparable. It's not as large as a quasi stellar source by perhaps a factor of 100. But again it's rather difficult to see where the energy even this amount of energy comes from. And in this case we know we can measure the diameter of these to some extent even just looking at them. We know that these again are very tiny objects. Well the discovery of these crazy star objects has been an important event in the last few years in astronomy. Can you speak in terms of the analogy of other events in astronomy that might be comparable. Probably the most directly comparable event was the discovery that some 40 years or 50

years ago now that the some of the objects which people called nebulae in those days were not in fact associated with our own Milky Way but that they must be in fact very large Milky Way systems themselves. That was a major step and it was a major step it was realized that there were these very large systems very much like our Milky Way that were at distances of millions of light years this is fact or distances 10 or 20 or 30 times larger than any distances which astronomers had been contemplated up to that time. And this led to the whole concept of the. The evolving universe at that time and great progress was made from that time onward soon probing deeper and deeper into space this in a sense provides a similar technique it

doesn't perhaps carry us into space. A great deal farther but it does give us the tools to probe very much deeper into space we can infer some of these qualities stellar objects we can program it to probably almost to the edge of the known universe. So they represent these objects represent that and measuring our relating to the total universe. Do you think that perhaps they are suggestive. Well there is certainly the question of the part of the energy source itself which seems to be unexplained. Yes in principle you say that energy can be developed. We have no way of explaining it. This in itself can lead to entirely new frontier of understanding. I think this is right. Yes and in another provokes it gets me another way in which it provokes a lot of activities that is makes us realize perhaps for the first time that our universe is

something which is very dynamic. We used to think that galaxies did nothing for billions of years but more or less just sat there slowly revolving we know that very violent events can happen in me to these galaxies or to similar galaxies when they are forming perhaps even later on in their lifetime so that we have to think of the universe as being something which is evolving and develop all the where things are happening in fact in times. Which are relatively short times of millions of years or very very short lengths of time. From the standpoint of astronomy certainly that's connected with your earlier remarks that these production energy production rates that the objects could not persist for any lengthy period. Yes on the scale of the universe's age where then we see these objects as instruments to probe further and further into the universe and out to the reaches we see them as perhaps provoking

new thoughts and developments and ideas as to explain the sources of energy. And this means then much more excitement in the field of astronomy for a good many years to come. I'm sure this will be the case. Thank you very much for that. This was about science with host Dr. Robert McGregor Leanne and his guest Dr. Beverly oke join us again for our next program when Dr. Peter listen men will lead a discussion about space exploration about science is produced by the California Institute of Technology and is originally broadcast by station KPCC in Pasadena California. The programs are made available to this station by national educational radio. This is the national educational radio network.