Tag: quasars

The supernova and the quasar: the hungriest guy in the universe followed the ultimate toaster

Keith S. Taber

Communicating astronomical extremes

I was recently listening to a podcast of an episode of a science magazine programme which included two items of astronomy news, one about a supernovae, the next about a quasar. I often find little snippets in such programmes that I think work making a note of (quite a few of the analogies, metaphors and similes – and anthropomorphisms – reported on this site come from such sources). Here, I went back and listened to the items again, and decided the discussions were rich enough in interesting points to be worth taking time to transcribe them in full. The science itself was fascinating, but I also thought the discourse was interesting from the perspective of communicating abstract science. 1

I have appended my transcriptions below for anyone who is interested – or you can go and listen to the podcast (episode 'Largest ever COVID safety study' of the BBC World Service's Science in Action).

Space, as Douglas Adams famously noted, is big. And it is not easy for humans to fully appreciate the scales involved – even of say, the distance to the moon, or the mass of Jupiter, let alone beyond 'our' solar system, and even 'our' galaxy. Perhaps that is why public communication of space science is often so rich with metaphor and other comparisons?

When is a star no longer a star (or, does it become a different star?)

One of the issues raised by both items is what we mean by a star. When we see the night sky there are myriad visible sources of light, and these were traditionally all called stars. Telescopes revealed a good many more, and radio telescopes other sources that could not detected visually. We usually think of the planets as being something other than stars, but even that is somewhat arbitrary – the planets have also been seen as a subset of the stars – the planetary or wandering stars, as opposed to the 'fixed' stars.

At one time it was commonly thought the fixed stars were actually fixed into some kind of crystalline sphere. We now know they are not fixed at all, as the whole universe is populated with objects influenced by gravity and in motion. But on the scale of a human lifetime, the fixed stars tend to appear pretty stationary in relation to one another, because of the vast distances involved – even if they are actually moving rather fast in human terms.

Wikipedia (a generally, but not always, reliable source) suggests "a star is a luminous spheroid of plasma held together by self-gravity" – so by that definition the planets no longer count as stars. What about Supernova 1987A (SN 1987A) or quasar J0529-4351?

"This image, taken with Hubble's Wide Field and Planetary Camera 2in 1995, shows the orange-red rings surrounding Supernova 1987A in the Large Magellanic Cloud. The glowing debris of the supernova explosion, which occurred in February 1987, is at the centre of the inner ring. The small white square indicates the location of the STIS aperture used for the new far-ultraviolet observation. [George Sonneborn (Goddard Space Flight Center), Jason Pun (NOAO), the STIS Instrument Definition Team, and NASA/ESA]" [Perhaps the supernova explosion did not actually occur in February 1987]

Supernova 1987A is so-called because it was the first supernova detected in 1987 (and I am old enough to remember the news of this at the time). Stars remain in a more-or-less stable state (that is, their size, temperature, mass are changing, but, in proportional terms, only very, very slowly2) for many millions of years because of a balance of forces – the extremely high pressures at the centre work against the tendency of gravity to bring all the matter closer together. (Imagine a football supported by a constant jet of water fired vertically upwards.) The high pressures inside a star relate to a very high temperature, and that temperature is maintained despite the hot star radiating (infra-red, visible, ultraviolet…) into space 3 because of the heating effect of the nuclear reactions. There can be a sequence of nuclear fusion reactions that occur under different conditions, but the starting point and longest-lasting phase involves hydrogen being fused into helium.

The key point is that when the reactants ('fuel') for one process have all (or nearly all) been reacted, then a subsequent reaction (fusing the product of a previous phase) becomes more dominant. Each specific reaction releases a particular amount of energy at a particular rate (just as with different exothermic chemical reactions), so the star's equilibrium has to shift as the rate of energy production changes the conditions near the centre. Just as you cannot run a petrol engine on diesel without making some adjustments, the characteristics of the star change with shifts along the sequence of nuclear reactions at its core.

These changes can be quite dramatic. It is thought that in the future the Earth's Sun will expand to be as large as the Earth's orbit – but that is in the distant future: not for billions of years yet.

Going nova

Massive stars can reach a point when the rate of energy conversion drops so suddenly (on a stellar scale) that there is a kind of collapse, followed by a kind of explosive recoil, that ejects much material out into space, whilst leaving a core of condensed nuclear matter – a neutron star. For even more massive stars, not even nuclear material is stable, as there is sufficient gravity to even collapse nuclear matter, and a black hole forms.

It was such an explosion that was bright enough to be seen as a 'nova' (new star) from Earth. Astronomers have since been waiting to find evidence of what was left behind at the location of the explosion – a neutron star, or a black hole. But of course, although we use the term 'nova', it was not actually a new star, just a star that was so far away, indeed in another galaxy, that it was not noticeable – until it exploded.

Dr. Olivia Jones (from the UK Astronomy Technology Centre at The Royal Observatory, Edinburgh) explained that neutron stars form from

"…really massive stars like Supernova 1987A or what it was beforehand, about 20 times the mass of a Sun…

So, what was SN 1987A before it went supernova? It was already a star – moreover, astronomers observing the Supernova were studying

…how it evolves in real time, which in astronomy terms is extremely rare, just tracing the evolution of the death of a star…

So, it was a star; and it died, or is dying. (This is a kind of metaphor, but one that has become adopted into common usage – this way of astronomers talking of stars as having births, lives, careers, deaths, has been discussed here before: 'The passing of stars: Birth, death, and afterlife in the universe.') What once was the star, is now (i) a core located where the star was – and (ii) a vast amount of ejected material now "about 20 light years across" – so spread over a much larger volume than our entire solar system. The core is now a "neutron star [which] will start to cool down, gradually and gradually and fade away".

So, SN 1987A was less a star, than an event: the collapse of a star and its immediate aftermath. The neutron star at is core is only part of what is left from that event (perhaps like a skeleton left by a deceased animal?) Moreover, if we accept Wikipedia's definition then the neutron star is not actually a star at all, as instead of being plasma (ionised gas – 'a phase of matter produced when material is too hot to exist as, what to us seems, 'normal' gas) it comprises of material that is so condensed that it does not even contain normal atoms, just in effect a vast number of atomic nuclei fused into one single object – a star-scale atomic nucleus. So, one could say that SN 1987A was no so much a star, as the trace evidence of a star that no longer existed.

And SN 1987A is not alone in presenting identity problems to astronomers. J0529-4351 is now recognised as being possibly the brightest object in the sky (that is, if we viewed them all from the same distance to give a fair comparison) but until recently it was considered a fairly unimpressive star. As doctoral researcher Samuel Lai (Research School of Astronomy and Astrophysics, Australian National University) pointed out,

this one was mis-characterised as a star, I mean it just looks like one fairly insignificant point, just like all the other ones, right, and so we never picked it up as quasar before

But now it is recognised to only appear insignificant because it is so far away – and it is not just another star. It has been 'promoted' to quasar status. That does not mean the star has changed – only our understanding of it.

But is it a star at all? The term quasar means 'quasi–stellar object', that is something that appears much like a star. But, if J0529-435 is a quasar, then it consists of a black hole, into which material is being attracted by gravity in a process that is so energetic that the material being accreted is heated and radiates an enormous amount of energy before it slips from view over the black hole's event horizon. That material is not a luminous spheroid of plasma held together by self-gravity either.

This video from the European Southern Observatory (ESO) gives an impression of just how far away (and so how difficult to detect) the brightest object in the galaxy actually is.

These 'ontological' questions (how we classify objects of different kinds) interest me, but for those who think this kind of issue is a bit esoteric, there was a great deal more to think about in these item.

"A long time ago, in a galaxy far, far away"

For one thing, it was not, as presenter Roland Pease suggested, strictly the 37th anniversary of the SN 1987A – at least not in the sense that the precursor star went supernovae 37 years ago. SN 1987A is about 170 000 light years away. The event, the explosion, actually occurred something like 170 000 years before it could be detected here. So, saying it is the 37th anniversary (rather than, perhaps, the 170 037th anniversary 4) is a very anthropocentric, or, at least, geocentric take on things.

Then again, listeners are told that the supernova was in "the Large Magellanic Cloud just outside the Milky Way galaxy" – this is a reasonable description for someone taking an overview of the galaxies, but there is probably something like 90,000 light-years between what can be considered the edges of our Milky Way galaxy and this 'close by' one. So, this is a bit like suggesting Birmingham is 'just outside' London – an evaluation which might make more sense to someone travelling from Wallaroo rather than someone from Wolverhampton.

It is all a matter of scale. Given that the light from J0529-4351 takes about twelve billion years to reach us, ninety thousand light years is indeed, by comparison, just outside our own galaxy.

But the numbers here are simply staggering. Imagine something the size of a neutron star (whether we think it really is a star or not) that listeners were informed is "rotating…around 700 times a second". I do not think we can actually imagine that (rather than conceptualise it) even for an object the size of a pin – because our senses have not evolved to engage with something spinning that fast. Similarly, material moving around a black hole at tens of thousands of kilometres per second is also beyond what is ready visualisation. Again, we may understand, conceptually, that "the neutron star is over a million degrees Celsius" but this is just another very big number way that is outside any direct human experience.

Comparisons of scale

Thus the use of analogies and other comparisons to get across something of the immense magnitudes involved:

  • "If you think of our Sun as a tennis ball in size, the star that formed [SN] 87A was about as big as the London Eye."
  • "A teaspoon of this material, of a neutron star, weighs about as much as Everest"
  • the black home at the centre of the quasar acquires an entire Sun worth of mass every single day
  • the black hole at the centre of the quasar acquires the equivalent of about four earths, every single second
  • the quasar is about five hundred trillion times brighter than the Sun, or equivalent to about five hundred trillion suns

Often in explaining science, everyday objects (fridges, buses – see 'Quotidian comparisons') are used for comparisons of size or mass – but here we have to shift up to a mountain. The references to 'every single day' and 'every single second' include redundancy: that is, no meaning is lost by just saying 'every day' and 'every second' but the inclusion of 'single' acts a kind of rhetorical decoration giving greater emphasis.

Figurative language

Formal scientific reports are expected to be technical, and the figurative language common in most everyday discourse is, generally, avoided – but communication of science in teaching and to the public in journalism often uses devices such as metaphor and simile to make description and explanations seem more familiar, and encourage engagement.

Of course, it is sometimes a matter of opinion whether a term is being used figuratively (as we each have our own personal nuances for the meanings of words). Would we really expect to see a 'signature' of a pulsar? Not if we mean the term literally, a sign made by had to confirm identify, but like 'fingerprint' the term is something of a dead metaphor in that we now readily expect to find so-called 'signatures' and 'fingerprints' in spectra and D.N.A. samples and many other contexts that have no direct hand involvement.

Perhaps, more tellingly, language may seem so fitting that it is not perceived as figurative. To describe a supernova as an 'evolving fireball' seems very apt, although I would pedantically argue that this is strictly a metaphor as there is no fire in the usual chemical sense. Here are some other examples I noticed:

  • "we have been searching for that Holy Grail: has a neutron star formed or has a black hole been left behind"
  • "the quasar is not located in some kind of galactic desert"
  • there is a "storm, round the black hole"
  • "the galaxies are funnelling their material into their supermassive black hole"
  • "extraordinarily hot nuclear ember"
  • "a dense dead spinning cinder"
  • "the ultimate toaster"

Clearly no astronomer expects to find the Holy Grail in a distant galaxy in another part of the Universe (and, indeed, I recently read it is in a Museum in Ireland), but clearly this is a common idiom to mean something being widely and enthusiastically sought.5

A quasar does exist in a galactic desert, at least if we take 'desert' literately as it is clearly much too hot for any rain to fall there, but the figurative meaning is clear enough. The gravitational field of the black hole causes material to fall into it – so although the location, at the centre of a galaxy (not a coincidence, of course), means there is much material around, I was not sure how the galaxy was actively 'funnelling' material. This seems a bit light suggesting spilt tea is being actively thrown to the floor by the cup.

A hot ember or cinder may be left by a fire that has burned out, and one at over a million degrees Celsius might indeed 'toast' anything that was in its vicinity. So, J0529-4351 may indeed be the ultimate toaster, but not in the sense that it is a desirable addition to elite wedding lists.

Anthropomorphism

Anthropomorphism is a particular kind of metaphor that describes non-human entities as if they had the motivations, experiences, drives, etc., of people. The references to dying stars at least suggest animism (that the stars are in some sense alive – something that was once commonly believed 6), but there are other examples (that something is 'lurking' in the supernova remnant) that seem to discuss stellar entities as if they are deliberate agents like us. In particular, a black hole acquiring matter (purely due to its intense gravitational field) was described as feeding:

  • quasars are basically supermassive black holes just swallowing up all the stars and rubbish around
  • a quasar is feeding from the accretion disc
  • a monstrous black hole gobbling up anything within reach
  • just sat [sic] there, gobbling up everything around it
  • it has to have been feeding for a very, very long time
  • it will eat about four of those earths, every single second
  • in a particularly nutritious galaxy
  • a quasar that has been declared the hungriest object in the universe

There is clearly some kind of extended metaphor being used here.

Feeding frenzy?

The notion of a black hole feeding on surrounding material seems apt (perhaps, again, because the metaphor is widely used, and so familiar). But there seems a lot more 'negative analogy' than 'positive analogy: that is the ways in which (i) a black hole acquires matter, and (ii) an organism feeds, surely have more points of difference than similarity?

  • For advanced animals like mammals, birds, fish, snails and the like, feeding is a complex behaviour that usually involves active searching for suitable food, whereas the black hole does not need to go anywhere.
  • The animal has specialist mouth-parts and a digestive system that allows it to break apart foodstuff. The black-hole just tears all materials apart indiscriminately:"it's just getting chopped up, heated up, shredded".
  • The organism processes the foodstuff to release specific materials (catabolism) and then processes these is very specific ways to support is highly complex structure and functioning, including the building up of more complex materials (anabolism). The black hole is just a sink for stuff.
  • The organism takes in foodstuffs to maintain equilibrium, and sometimes to grow in very specific, highly organised ways. The black hole just gets more massive.

A black hole surely has more in keeping with an avalanche or the collapse a tall building than feeding?

One person's garbage…?

Another feature of the discourse that I found intriguing was the relative values implicitly assigned to different material found in distant space. There is a sense with SN 1987A that, after the explosion, the neutron star in some sense deserves to be considered the real remnant of the star, whilst the other material has somehow lost status by being ejected and dispersed. Perhaps that makes sense given that the neutron star remains a coherent body, and is presumably (if the explosion was symmetrical) located much where the former star was.

But I wonder if calling the ejected material – which is what comprises the basis of "an absolutely stunning supernova [which is] beautiful" – as 'debris' and 'outer debris"? Why is this material seen as the rubbish – could we not instead see the neutron star as the debris being the inert residue left behind when the rest of the star explored in a magnificent display? (I am not suggesting either should be considered 'debris', just playing Devil's advocate.)

Perhaps the reference to being able to "isolate the core where the explosion was from the rest of the debris" suggests all that is left is debris of a star, which seems fairer; but the whole history of the universe, as we understand it, involves sequences of matter changing forms quite drastically, and why should we value one or some of these successive phases as being the real product of cosmic evolution (stars?) and other phases as just rubbish? This is certainly suggested by the reference to "supermassive black holes in the middle of a galaxy … swallowing up all the stars and rubbish".

Let's hear it for the little guys

Roland Pease's analogy to "the muck at the bottom of your sink going down into the blender" might also suggest a tendency to view some astronomical structures and phenomenon as intrinsically higher status (the blender/black hole) than others (clouds of dust, or gas or plasma – the muck). Of course, I am sympathetic to the quest to better understand "these guys" (intense quasars already formed early in the universe), but as objectively minded scientists we should be looking out for the little guys (and gals) as well.

Appendix A: "the star hidden in the heart of [the] only supernova visible from Earth"

"If you are listening to this live on Thursday, then you're listening to the 37th anniversary of the supernova 1987A, the best view astronomers have had of an exploding star in centuries, certainly during the modern telescope era. So much astrophysics to be learned.

All the indications were, back then, that amidst all the flash and glory, the dying star should have given birth to a neutron star, a dense dead spinning cinder, that would be emitting radio pulses. So, we waited, and waited…and waited, and still there's no pulsing radio signal.

But images collected by the James Webb telescope in its first weeks of operation, peering deep into the ejecta thrown out by the explosion suggest there is something powerful lurking beneath.
Olivia Jones is a James Webb Space Telescope Fellow at Edinburgh University and she helped in the analysis."

"87A is an absolutely stunning supernova , it's beautiful, and the fact that you could see it when it first exploded with the naked eye is unprecedented for such an object in another galaxy like this.

We have been able to see how it evolves in real time, which in astronomy terms is extremely rare, just tracing the evolution of the death of a star. It's very exciting."

"I mean the main point is the bit which we see when the star initially explodes , we see all the hot stuff which is being thrown out into space, and then you've got this sort of evolving fireball which has been easiest to see so far."

"Yes, what see initially is the actual explosion of the star itself right in the centre. What happens now is then we had a period of ten years when you couldn't actually see very much in the centre. You needed these new telescopes like Webb and JWST to see the mechanics of the explosion and then, key to this is what was left behind, and we have been searching for that Holy Grail: has a neutron star formed or has a black hole been left behind at the centre of this explosion. And we've not seen anything for a very long time."

"And this neutron star, so this is the bit where the middle of the original star which at the ends of its life is mostly made of iron, just gets sort of crushed under it's own weight and under the force of the explosion to turn itself entirely into this sort of ball of neutron matter."

"Yeah, it's the very, very core of the star. So the star like the Sun, right in the centre is a very dense core, but really massive stars like Supernova 1987A or what it was beforehand, about 20 times the mass of a Sun.

If you think of our Sun as a tennis ball in size, the star that formed 87A was about as big as the London Eye. So it's a very massive star. The pressure and density right in the centre of that star is phenomenal. So, it creates this really, really, compact core. A teaspoon of this material, of a neutron star, weighs about as much as Everest. So, it's a very, a very dense, very heavy, core that is left behind."

"These were the things which were first detected in the 1960s, because they have magnetic fields and they rotate, they spin very fast and they cause radio pulsations and they're called pulsars. so When the supernova first went off I know lots of radio astronomers were hoping to see those radio pulsations from the middle of this supernova remnant."

"Yes. So, we know really massive stars will form a black hole in the centre, 30, 40, 50 solar masses will form a black hole when it dies. Something around 20 solar masses you'd expect to form a neutron star, and so you'd expect to see these signatures, like you said, in the radiowaves or in optical light of this really fastly rotating – by fastly rotating it can be around 700 times a second – but you would expect to see that signature or some detection of that. But even with all these telescopes – with the radio telescopes, X-ray observatories, Hubble – we've not seen that signature, before and so we are wondering, has a black hole been formed? We've seen neutrinos, so we thought the neutron star had formed, but we've not had that evidence before now."

"So, as I understand it, what your research is doing is showing that there's some unexplained source of heat in the middle of the debris that's been thrown out, and that's what your associating which what ought to be a neutron star in the middle, is that roughly speaking the idea?"

"So, the wonderful thing thing about the Webb telescope, you can see at high resolution both the ring, the outer debris of the star, and right at the very centre where the explosion was, but it's not just images we take, so it's not just taking a photograph, we also have this fantastic instrument or two instruments, called spectrographs, which can break down light into their individual elements, so very small wavelengths of light, it's like if you want to see the blue wavelength or the red wavelength, but in very narrow bands."

"And people may have done this at school when they threw some salt into a Bunsen burner and saw the colours, it's that kind of analysis?"

"Yes. And so what we see where the star was and where it exploded was argon and sulphur, and we know that these needed an awful lot of energy, to create these, and I mean a lot, of energy. And the only thing that can be doings this, we compared to many different kinds of scenarios, is a neutron star."

"So this is basically an extraordinarily hot nuclear ember, that's sort of sitting in the middle."

"Yes, right in the middle and you can see this, cause Supernova 1987A is about 20 light years across, in total, and we can isolate the core where the explosion was from the rest of the debris in this nearby galaxy, which I think is fantastic."

"Do you know how hot the surface of this star is and is it just sort of the intense heat, X-ray heat I imagine, that's coming off, that's causing all this radiation that you're seeing."

"I hope you are ready for a very big number."

"Go on."

"The neutron star is over a million degrees Celsius."

"And so, that's just radiating heat, is it, from, I mean this is like the ultimate toaster?"

"Yes, so what eventually will happen over the lifetime of the universe is this neutron star will start to cool down, gradually and gradually and fade away. But that'll be many, many billions of years from now.

What we currently have now is one of the hottest things you can imagine, in a very small location, heating up all its surroundings. I would not want to be anywhere nearby there."

Roland Pease interviewing Dr. Olivia Jones (Edinburgh University)
Appendix B: "possibly the brightest object in our universe"

"Now 1987A was, briefly, very bright. Southern hemisphere astronomy enthusiasts could easily spot it in the Large Magellanic Cloud just outside [sic] the Milky Way galaxy. But it was nothing like as bright as JO529-4351 [J0529-4351], try memorising that, its a quasar twelve or so billion light years away that has been declared the brightest object in the universe and the hungriest. At first sight, it's an anonymous, unremarkable spot of light of trillions on [sic] an astronomical photo. But, if you are an astronomer who knows how to interpret the light, as Samual Lai does, you will find this is a monstrous black hole gobbling up anything within reach. Close to the edge of all that we can see."

"So this quasar is a record breaking ultra-luminous object, in fact it is the most luminous object that we know of in the universe. Its light has travelled twelve billion years to reach us, so it's incredibly far object, but it's so intrinsically luminous that it appears bright in the sky."

"And as I understand it, you identified this as being a very distant and bright object pretty recently though you have gone back through the catalogues and its was this insignificant speck for quite a long time."

"Yes, indeed. In fact we were working on a survey of bright quasars, so we looked at about 80% of the sky using large data sets from space satellites. Throughout our large data sets, this one was mis-characterised as a star, I mean it just looks like one fairly insignificant point, just like all the other ones, right, and so we never picked it up as quasar before. Nowadays we are in the era of extremely astronomical, pardon the pun, data sets where in order to really filter thorough them we have these classification algorithms that we use. So, we have the computer, look at the data set, and try to learn what we are looking at, and pick out between stars and quasars."

"Now, is it also interesting, they were discovered about sixty years ago, the first quasars. These are basically supermassive black holes in the middle of a galaxy that's just swallowing up all the stars and rubbish just around it, and that's the bit that for you is quite interesting in this instance?"

"Yes, exactly, and the quasar owes its luminosity to the rate at which it is feeding from this accretion disc, this material that's swirling around, like a storm, with the black hole being the eye of the storm."

"I mean, I think of it as being a bit like the muck at the bottom of your sink going down into the blender at the bottom, it's just getting chopped up, heated up, shredded, and, I mean what sort of temperatures are you talking about? What, You know, what kind of energy are you talking about being produced in this system?"

"Yes ,so the temperatures in the accretion disc easily go up to tens of thousands of degrees, but talking about brightness, the other way that we like to measure this is in terms of the luminosity of the Sun, which gives you are sense of scale. So, this quasar is about five hundred trillion times brighter than the Sun, or equivalent to about five hundred trillion suns."

"And it's been doing this sort of constantly, or for really for a long time, I mean it's just sat there, gobbling up everything around it?"

"Yeah, I mean the mass of the quasar is about 17 billion solar masses, so in order to reach that mass it has to have been feeding for a very, very long time. We work it out to be about one solar mass per day, so that's an entire Sun worth of mass every single day. Or if you like to translate that to more human terms, if you take the Earth and everybody that's on it, and you add up all of that mass together, it will eat about four of those earths, every single second."

"I suppose what I find gob-smacking about this is (a) the forces, the gravitational forces presumably involved in sweeping up that amount of material, but (b) it must be an incredibly busy place – it can't be doing this in some kind of galactic desert."

"Yes, indeed, I mean these quasars, these super-massive black holes are parts of their galaxies, right, they're always in the nuclear regions of their host galaxies, and in some way the galaxies are funnelling their material into their supermassive black hole."

"But this one must be presumably a particularly, I don't know, nutritious galaxy, I guess. It is so far away, you can't make out those kinds of details."

"We can however make out that some of that material moving around, inside the storm, round the black hole, their dynamics are such that their velocities reach up to tens of thousands of kilometres per second."

"Why are you looking for then? Is it because you just want to break records – I'm sure it's not. Or is it, that you can see these things a long way away? Is it, it tells you about the history of galaxies?"

"I mean we can learn a lot about the universe's evolution by looking at the light from the quasars. And in fact, the quasar light it tells you a lot about not just the environment that the quasar resides in, but also in anything the quasar light passes through. So, you can think of this, lights from the quasar, as a very distant beacon that illuminates information about everything and anything in between us and the quasar."

"I mean the thing that I find striking is, if I've read the numbers right, this thing is so far away that the universe was about a billion years old. I mean I suppose what I'm wondering is how did a black hole becomes so massive so early in the universe?"

"Ah see, I love this question because you are reaching to the frontier of our current understanding, this is science going as we speak. We are running into an issue now that some of these black holes are so massive that there's not enough time in the universe, at the time that we observe them to be at, in order for them to have grown to such masses as they are seen to be. We have various hypotheses for how these things have formed, but at the moment we observe it in its current state, and we have to work backwards and look into the even older universe to try to figure out how these guys came to be."

Roland Pease interviewing Dr. Samuel Lai (Australian National University)

Notes

1 Having been a science teacher, I find myself listening to, or reading, science items in the media at two levels

  • I am interested in the science itself (of course)
  • I am also intrigued by how the science is presented for the audience

So, I find myself paying attention to simplifications, and metaphors, and other features of the way the science is communicated.

Teachers will be familiar with this. Curriculum selects some parts of science and omits other parts (and there is always a debate to be had about wither the right choices are made about what to include, and what to omit). However, it is rare for the selected science itself to be presented in 'raw' form in education. The primary science literature is written by specialists for other specialists, and to a large extent by researchers for other researchers in the same field – and is generally totally unsuitable for a general audience.

Curriculum science is therefore an especially designed representation of the science intended to be accessible to learners at a particular stage in their education. Acids for twelve years olds or natural selection for fifteen year olds cannot be as complex, nuanced and subtle as the current state of the topic as presented in the primary literature. (And not just because of the level f presentation suitable for learners, but also because in any live field, the work at the cutting edge will by definition be inconsistent across studies as this is just where the experts are still trying to make the best sense of the available evidence.)

The teacher then designs presentations and sequences of learning activities to engage particular classes of learners, for often teaching models and analogies and the like are needed as stepping stones, or temporary supports, even to master the simplified curriculum models set out as target knowledge. Class teaching is challenging as every learner arrives with a unique nexus of background knowledge, alternative conceptions, relevant experiences, interests, vocabulary, and so forth. Every class is a mixed ability class – to some extent. The teacher has to differentiate within a basic class plan to try and support everyone.

I often think about this when I listen to or read science journalism or popular science books. At least the teacher usually knows that all the students are roughly the same age, and have followed more-or-less the same curriculum up to that point. Science communicators working with the public know very little about their audience. Presumably they are interested enough in the topic or science more generally to be engaging with the work: but likely of a very diverse age, educational level, background knowledge: the keen ten year old to the post-doctoral researcher; the retired engineer to the autistic child with an intense fascination in every detail of dinosaurs…

I often find myself questioning some of the simplifications and comparisons used on science reports in the media – but I do not underestimate the challenge of reporting on the latest findings in some specialist area of science in an 'academically honest' way (to borrow a term from Jerome Bruner) in a three minute radio slot or 500 words in a magazine. So, in that spirit, I was fascinated by the way in which the latest research into Supernova 1987A and J0529-4351 was communicated, at least as much as the science itself.

2 That is, the flux of material emitted by our Sun, for example, is quite significant in human terms, but is minute compared to its total mass. Our sun has cooled considerably in the past few billions of years, but that's long time for it to change! (The Earth's atmosphere has also changed over the same time scale, which has compensated.)

3 Some very basic physics (Isaac Newton's law of cooling) tells us that objects radiate energy at a rate according to their temperature. Stars are (very large and) very hot so radiate energy at a high rate. An object will also be absorbing radiation – but the 'bath' of radiation it experiences depends on the temperature of its surroundings. A hot cup of coffee will cool as it is radiating faster than it is absorbing energy, because it is hotter than its surroundings. Eventually it will be as cool as the surroundings and will reach a dynamic equilibrium where it radiates and absorbs at the same rate. (Take the cooled cup of coffee into the sauna and it will actually get warmer. But do check health and safety rules first to see if this is allowed.)

The reference to how

"what eventually will happen over the lifetime of the universe is this neutron star will start to cool down, gradually and gradually and fade away. But that'll be many, many billions of years from now"

should be understood to mean that the cooling process STARTED as soon as there was no internal source of heating (form nuclear reactions or gravitational collapse) to maintain the high temperature; although the process will CONTINUE over a long period.

4 That weak attempt at humour is a variant on the story of the museum visitors who asked the attendant how old some ancient artefacts were. Surprised at the precision of the reply of "20 012 " years, they asked how the artefacts could be dated so precisely. "Well", the attended explained, "I was told they were twenty thousand years old when I started, and I've worked here for twelve years."

Many physics teachers will not find this funny at all, as it is not at all unusual for parallel mistakes to be made by students. (And not just students: a popular science book suggested that material in meteors can be heated in the atmosphere to temperatures of up to – a rather precise – 36 032 degrees! (See 'conceptions of precision').

5 The Holy Grail being the cup that Jesus is supposed to have used at the last supper to share wine with his disciples before he was arrested and crucified. Legend suggests it was also used to collect some of his blood after his execution – and that it was later brought to England (of all places) by  Joseph of Arimathea, and taken to Glastonbury. The Knights of King Arthur's Round Table quested to find the Grail. It was seen as a kind of ultimate Holy Relic.

6 Greek and Roman cultures associated the planets (which for them included the Sun and Moon) with specific Gods. Many constellations were said to be living beings that have been placed in the heavens after time on earth. Personification of these bodies by referring to them in gendered ways ('he', 'she') still sometimes occurs.

Read about personification

In his cosmogony, Plato had the stars given a kind of soul. Whereas Aristlotle's notion of soul can be understood as being something that emerges from the complexity of organisation (in organisms), Plato did imply something more supernatural.