Episode: 829
Title: HPR0829: Interview with Prof Jocelyn Bell-Burnell
Source: https://hub.hackerpublicradio.org/ccdn.php?filename=/eps/hpr0829/hpr0829.mp3
Transcribed: 2025-10-08 03:09:21

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Today's show is from the John Cast Podcast and is released under a creative commons attribution
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carry out all over the earth and beyond.
In today's show, aired in June 2000 and 7, they interview Joslyn Bellburnel on the 40th anniversary
on her discovery on pulsars.
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Enjoy!
This interview with Professor Joslyn Bellburnel is part of the John Cast for the full show
go to www.jodcast.net.
Well, please start us off with if you wouldn't mind a quick history about the discovery that you made of pulsars.
Right, so the discovery of pulsars, which was 40 years ago this year, 1967, scary.
I was a grad student in Cambridge working for my doctorate, and my thesis project was to identify quasars,
which are very distant, very energetic objects.
Still quite mysterious, newly discovered then and very mysterious, very sexy things.
So I was supposed to be finding quasars and having a stab at measuring how compact they were,
measuring their angular diameter.
And in fact, that's what my thesis was on, because by the time the pulsars came along,
it was too late to change the title of the thesis, and the pulsars went in appendix.
The technique we were using involved scanning the sky regularly,
and we were scanning it using a short time constant, a short integration time,
like taking a rapid exposure in photography.
So you see things that are changing quite fast.
And after running this survey for a month or so, I started very occasionally picking up a curious signal
that I couldn't make sense of.
It didn't seem to be one of the quasars I was looking for, didn't look right.
The other thing one picks up in abundance with a radio telescope is artificial interference,
badly suppressed equipment, sparking thermostats, things like that.
That signal didn't look really like artificial interference either for some reason.
And I think the first few times I saw what I simply logged it with a question mark.
But your brain remembers things that you don't realise it remembers.
And by about the fourth or fifth time I came across this signal, my brain said,
you've seen something like this before.
And that's actually quite remarkable, because that signal occupied about a quarter inch
on the chart recording paper.
And each scan of the sky took 400 feet, or each day of operation produced 100 feet of chart paper.
So I was remembering the odd quarter inch in hundreds of feet of chart paper.
Presumably all the rest of what you were recording, the rest of the 400 feet of chart paper was right.
It was what you were interested in.
It was the raw data of your experiment that you were trying to achieve.
It was just that one little niggling remote.
That one little niggling bit amongst all the other stuff that was understood reasonably.
Yes, one didn't like the interference, but it's a fact of radio astronomers' lives.
And there were the quasars that we were meant to be looking for.
So that was very reassuring.
But yeah, it negled.
And my brain actually did a double take.
It didn't just say, you've seen this signal before somewhere, haven't you?
It said, you've seen this signal before, haven't you from that bit of sky?
Was it not?
And then it's quite easy, because you go back to the chart recordings that cover that bit of sky.
And you search them all.
And you find that, yeah, just once or twice, we're looking at that bit of sky.
There was this signal that I couldn't make sense of.
So it couldn't be coincidence that the interference only occurred when you were looking at that one pet of sky.
Well, that was something we had to consider.
It looked like something cosmic, because it seemed to go right in with the constellations.
But you couldn't be absolutely sure.
Now, one of the problems was all that signal was jammed into a quarter inch.
We had the chart paper running slowly.
And what we actually needed was the equivalent of a photographic enlargement, blow it up,
so you could actually see what the signal was.
And if you're using chart recorders, that means running the paper faster through the chart recorder and spreading out the signal.
But the snag was you couldn't just switch the chart recorder to high speed and leave it,
because it would run through all the paper in 20 minutes.
And it was tour enough going out to the observatory each day to change paper,
putting in the ink wells and so on.
So I discussed this with my supervisor, and we decided that I'd go out to the observatory each day
at the appropriate time, switch to high speed chart recording for the relevant five minutes,
you know, be generous with the time, switch off the high speed recording back to normal speed,
back to the normal survey.
And I did that for a month, and there was absolutely nothing except the standard hiss, the receiver noise,
the kind of hiss you get on a radio when it's not properly tuned to a station.
And that wasn't what I was there for.
But that's very much life as a research student.
There's a lot of patient non-results, it's doggedness.
I was surprised you lasted a month of finding no signal.
Well, I lasted a month, and then one day there was a very interesting lecture in Cambridge
that coincided with when I should be at the observatory.
And I thought, stuff this, I'm going to the lecture.
So I went to the lecture, which I still remember very clearly.
It was a lecture about aging.
It was a lunchtime, you know, bring your own lunch in a brown bag kind of thing and listen to a speaker.
Very good talk.
It gets more relevant as you get older.
And next morning when I went out to the observatory for the routine paper change,
I discovered that the source had reappeared and the business funny, scrappy signal again.
And I'd missed it.
My supervisor was already jumping down my throat because he was frustrated by this month of no signal.
And he thought maybe it had been some kind of flair star that had erupted and died down.
And that I'd gone and missed it.
So I didn't dare tell him that I had actually missed the thing that had reappeared and I hadn't been there.
So I didn't dare go back for lunch or anything.
I stayed out at the observatory until that relevant time of day came and switched to the high speed chart recording.
Unfortunately, the thing was still strong.
With hindsight, we can now see that it was very weak.
It was close to the threshold of detection.
And for many days it was just below the threshold and it only poked its head up above the threshold occasionally.
For it to do it two days running was pretty lucky.
But I got it that second day and it turned out to be a string of pulses.
It was quite clear as the paper flowed under the pen that this thing was pulsing.
It looked as if it was pulsing regularly.
And as soon as it had finished and was over for the day,
it took the paper off the chart recorder and spread it out on the floor.
It didn't have any rulers, but I made a makeshift ruler by taking a strip of paper
and putting little tick marks on it and then sliding the strip of paper along
and seeing that the tick marks kept coinciding with the pulses.
So it was keeping constant pulse period to within the accuracy of my quotes ruler.
I didn't know what the hell it was.
It was a period of one and one third seconds.
You train as a physicist to do all this undergraduate work.
And you know that you've got to do some sort of test.
And I thought, what kind of test can I do on this?
The source had transit it.
It wasn't going to come back for almost 24 hours.
What do you do?
I decided I'd test the time constant of the pen recorder.
The only thing I think of to test.
So I got a little battery and put it across the pen recorder
and of course the pen went flick.
And it was a very good pen recorder and you couldn't measure the time constant of it.
It was so good.
What do you mean by a time constant?
It's response to an incoming signal.
How rapidly it responds to a sharp signal, yes.
Does it respond sharply or does it gradually wake up to the fact that a sharp signal has hit it?
So I decided I'd better phone my supervisor who was working in one of the undergraduate laboratories
in Cambridge teaching students.
And he'd probably been dealing with some not-so-bright Cambridge student under graduate.
And then his grad student who's supposed to be brighter but doesn't at that point sound it.
Phones him up and says, hey Tony, you know that funny signal.
It's a string of pulses, one and a third seconds apart.
And it's nothing to do with the time constant of the pen recorder either.
And Tony says, well that settles it.
Must be man-made.
Because Tony knew what I didn't know.
And that is that if you've got something repeating a period of one and a third seconds,
it can only be one and a third light seconds across or less, which makes it pretty small for an astronomical object.
And to have something pulsing at one and a third seconds sound awfully artificial.
It's somebody in the next oral laboratory and they've set a signal generator to a period of one and a third seconds or something like that.
Tony was interested enough to come out to the observatory the next day.
And this is really pushing our luck because now it's been strong for two days in a row.
And he stood looking over my shoulder as I switched the high speed recorder.
And fortunately it performed for a third day in the row and in came a string of pulses.
So Tony sought for his own eyes.
And people say was it great fun? Was it exciting?
And no, it was worrying.
Tony was quite convinced there was something wrong with the equipment.
And we spent the next month trying to find out what was wrong.
And we gradually eliminated things.
We established that to a degree of accuracy it went round with the stars.
Which meant it wasn't Joe Bloggs driving down the road home from work in a badly suppressed car.
Because Joe Bloggs was getting off work four minutes earlier each day.
Half an hour a week.
He was keeping a Sunday or your time.
He was keeping a Sunday or your time.
In fact the only humans who keeps a Sunday or your time are other astronomers.
So Tony wrote to all the astronomical observatories.
Have you had a program going since last August which could conceivably cause radio interference?
Of course you ask a question like that and they'll deny or not interference.
So the answers were no.
But we did ask.
Then we asked a colleague with his research student who had a separate radio telescope,
separate radio receiver to see if their telescope could pick up the signal.
That was scary.
The telescopes were slightly misaligned and the signal appeared in my telescope first.
And I saw it with my telescope so we knew it was strong and performing that day.
And it should have appeared in the other telescope maybe 20 minutes half an hour later.
And we all stood by the pen recorder for that telescope and nothing happened.
And nothing happened.
And Tony and colleague started walking down this very long laboratory,
saying now what could it be that appears in our telescope but not yours?
Could it be this? Could it be that?
I was pattering along behind them trying to keep up with them in every sense of the word.
And the other research student Robyn stayed by his pen recorder.
And we got away down this long lab and suddenly there was a strangle cry.
Here it is.
And we went charging back up the lab.
And there it was pulsing beautifully, exactly like it showed in mine.
We had miscalculated by five minutes when it would show in the second radio telescope.
Right.
Fortunately the miscalculation had only been five minutes.
If it had been 25 minutes, we'd have given up and gone home.
Yes.
That was close.
So there were things like that that we were doing for this first month to try and find out what the trouble was.
Because I suppose at this time you were still treating it as a form of interference.
You were worried that this signal could be screwing up the rest of your observations
that you were interested in for the quasar observations.
But you're slowly narrowing it down to, well, if it's interference,
it's a very odd kind of interference.
Yes.
We really wanted to know what it was to be sure that we understood our equipment,
particularly if it was a fault with the equipment.
We had to know about it sooner rather than later because my whole thesis was in jeopardy then.
And we were tackling it quite hard, but we were also being discreet
because if it was something darn stupid, we didn't want to advertise it.
That we picked up this funny signal and watched it was because we didn't have the switch on the receiver set right.
Yes.
So we were being circumspect, but not unduly secretive, just quietly trying to find out what was wrong.
Keep it to ourselves the time being and getting it sorted out.
So we established it wasn't anything wrong with the equipment, which I was very relieved about
because I had wired up that radio telescope and I was afraid I had literally got some wires crossed.
And this is what was doing it.
You know, I was going to be out on my ear without a PhD from Cambridge.
Not good on the CV.
So it wasn't a fault with the equipment.
It didn't seem to be interference because it kept siderial time.
Wasn't other astronomers.
And then we managed to establish that it was from beyond the Earth, indeed, beyond the solar system.
It was out in the Milky Way about 200 light years away.
So how did you establish that?
That's a little tricky to explain.
It's using a technique called dispersion.
It's something that radio amateurs may be familiar with.
Because if you're a radio amateur, you'll have come across things called whistlers, which sound a bit like this.
So descending whistling note starts with a high frequencies, ends up with the low frequencies.
And that's caused by a lightning strike in New Zealand.
The lightning strike generates a sharp radio wave.
The radio signal propagates round to Britain, but it does a big loop following the magnetic field lines.
And as it travels through near Earth space, the higher frequencies get less affected than the lower frequencies.
The lower frequencies get delayed, and they arrive a little bit later.
And so you get this descending signal.
The same thing would happen if there were a lightning strike somewhere away out in space.
If you get a sharp radio signal, and as it travels to Earth, it would get dispersed.
The high frequencies would arrive first, the low frequencies later.
So we did this test on some of the pulses.
And we established that indeed the high frequencies did arrive before the low frequencies.
Basically, what we had was two radio receivers tuned to slightly different frequencies.
And you could see the pulse arrive first in the high frequency radio receiver, and then the low frequency.
And the time delay between the two, along with a guestimate of very rough finger in the wind estimate of how many electrons there were in free space,
gives you an estimate of how far the signals come to give that amount of dispersion.
And it turned out to be a couple of hundred light-years.
So the source is way beyond the Earth, way beyond the solar system, but quite close within our galaxy.
And very small.
And very small.
We not only had established it was very small, we'd also, by that stage, established that it kept pulsing very, very, very accurately.
1.3372795 seconds or something like that.
Now, if something is going to keep pulsing very regularly, it's not getting tired, it's not flagging.
So it's got to have big energy reserves. So it's got to be big.
So it's big, and it's small.
And it's 200 light-years away.
Boing!
Actually, you sharpen up those statements. It's a good example of science at work.
When we say it's big, it's got big energy reserves.
We actually mean it's massive, lots of mass.
When we say it's small because of the rapid repetition rate, we're saying it's small in diameter.
And we now know these things are neutron stars, which are very dense.
There's a lot of mass in a very small volume.
So, yeah, they are massive, and they're small in dimension.
But, of course, that's hindsight.
Our best developed faculty, as they say.
At the time, we were having trouble making sense of this.
Radio astronomers are aware at the back of their minds that if there are other civilizations out there in space,
it may be the radio astronomers that first pick up the signal.
They'd probably communicate using the hydrogen line at 21 centimeters.
Not obvious why they'd communicate at 80 megahertz, which frequency we were at.
But, just possibly, maybe, it's some of the civilization.
Not a very intelligent civilization, if it is, because the frequency of there,
the repetition rate of the signal is dead constant.
So, if they're sending us a signal, it's in the amplitude of the pulses.
And that's a daft way to communicate across space.
You use FM, not AM.
So, it didn't make total sense, but, you know, just faintly possibly.
And this is where the nickname Little Green Men came from.
So, we nicknamed that source, Little Green Men.
Subsequently, became Little Green Men, number one, when I find numbers 2, 3, and 4.
But, Little Green Men.
And we argued that if it was Little Green Men, they were probably on a planet
going round their sun.
And as their planet went round their sun, we might see some small changes in the pulse period due to Doppler effect.
So, we started, well, we started, we were already making the measurements necessary.
We continued carefully monitoring that pulse period over about three, four months, something like that.
And we actually found some change in the pulse period.
But it turned out to be due to the motion of the earth round the sun,
not the motion of a Little Green Men's planet round their sun.
So, we proved that the earth went round the sun.
Probably didn't need proving, but reassuring.
It's always a good theory.
So, we were doing the right sums.
And after about a month of all these various tests, we were beginning to wonder just what to do.
We really ought to publish this result, but we had awfully little clue what it was.
We didn't really want to say it was Little Green Men.
And we had a discussion one evening, just before Christmas, about how we were going to publish this.
It was a high-level discussion with the head of the group in Tony and another senior member of staff.
And since I happened to stumble in on the meeting, they invited me in as well.
And we didn't resolve it.
And I went home for supper that evening, really very, very fed up.
I had six months of grant money left in which to finish observations, write a thesis and get another job.
And some silly lot of Little Green Men apparently had decided to use my frequency and my area to sing them to earth.
Because of all the special observations of this funny signal, the routine data analysis was falling behind.
The system was still churning out 100 feet of chart paper every day and had been doing it now for four or five months.
Which you would have to analyze by eye by hand.
And my logbook is full of plaintive comments.
Now a thousand feet behind with the chart analysis.
Now a two thousand feet behind with chart analysis.
Falling behind.
Yes, measuring the laser feet.
And after some supper, I decided to go back into the lab to do some more of this routine chart analysis.
You could get in a few hours work before they shut the lab at 10 o'clock at night.
At that point, we didn't have keys.
You were shut in or you were shut out and it was your choice.
At about quarter to ten, I was analyzing a piece of chart, another bit of sky.
For those who are into astronomy, it was 12 hours away from Cassiopeia A.
And the radio telescope was such that it could see Cassiopeia A through the back of the telescope.
And it was a strong and messy signal with a lot of ionospheric scintillation.
And in amongst all that garbage, I thought I saw a quarter inch of this sort of scruffy signal.
It was by now about 13 minutes to ten.
I got out all the chart recordings that covered that bit of the sky through the mouth over the floor.
And ascertained that on occasion, when the garbage from your Cass wasn't too bad,
you could see another piece of scruff.
That piece of scruff went through the telescope beam at about two o'clock in the morning.
And at about nine o'clock the next morning, I was going off for Christmas,
to Ireland with my fiancee to be, to announce our engagement.
I kind of had to be there.
I see a decision is in front of you.
So I bundled up all the paper on the desk, rushed out of the lab just as the janitor was closing the doors.
And two o'clock in the morning went out to the observatory.
It was dead cold, 21st of December.
On occasion, when it was very cold, the radio telescope refused to work at full belt.
Never discovered what the problem was.
But sure enough, when I got out there that night, the telescope was working at about half power.
No way was it going to see a weak signal.
So I swore at it and breathed on it and I flicked switches and I did everything I could think of.
Standard experimental technology.
Yep, yep, that's right.
And I got it to work for five minutes.
And it was the right five minutes and it was the right beam setting.
And I switched on the high speed recorder and in came blip, blip, blip, blip.
This time one and a quarter seconds apart.
The first one had been one and a third seconds.
But clearly of the same ilk.
A relative.
But in a different part of the sky.
Totally different part of the sky.
And that was great.
That was the sweet moment.
That was Eureka.
They must have been incredible.
Because now it's little green men too.
It's not no longer your first observation.
It was no longer isolated.
Right.
But it can't be little green men either.
Because there's unlikely to be two lots of little green men on opposite sides of the universe.
Both deciding to signal to a rather inconspicuous planet Earth.
Both deciding to use a rather silly frequency and a very daft technique.
It had to be some new kind of source.
And to the end we'd worked out that being TV broadcasts in and around the VHF band.
For about 40 years at that stage.
40 years max.
So anything within 40 light years of the Earth might have known that Earth was inhabited.
But our first source was 200 light years away.
So they had no inkling that we existed.
But anyway, discovering the second one really killed that.
I piled the chart recording on Tony's desk with a note saying,
Hey Tony, think I've got a second one disappeared off to Ireland for Christmas.
Got Julie engaged, reappeared after Christmas.
Tony had kindly kept the survey running,
which meant he put fresh paper in the chart recorders and fresh ink in the ink wells.
And he popped all the charts on my desk, neatly rolled up for me to analyse.
And when I got back from Christmas, sporting and engagement ring,
which was the daftest thing I ever did,
found this pile of charts on my desk.
Couldn't find Tony, but it was quite clear what I had to do.
So I sat down and started doing some chart analysis.
And I was looking at a third totally different part of the sky.
And suddenly realised I could see two lots of this scruffy type of signal,
about two foot apart on the same strip of chart recording.
And at that point, Tony turned up out of his meeting.
I said, Tony, look at this.
I think by that stage I'd got out some previous charts from that area
and established that there was signal there.
And Tony said, how many more have you missed?
Go back through all your old recordings and check.
And there were about two miles.
And this was months before you were presumably supposed to finish your PhD.
Yes, that's right. Yes.
And the money runs out.
We subsequently confirmed the third and the fourth ones.
And I went back through all the chart recordings and found no more likely candidates.
And in fact, that radio telescope, I think, only found one or maybe two more pulsars in Tokyo.
The fourth pulsar that we found was very interesting.
It had a period of only one quarter of a second.
And could, on occasion, be very strong, like Penn hit the end stops.
And it became a bit of a tourist attraction amongst the research students in the group.
They'd say, when is 0950 transiting Jocelyn?
And I'd tell them.
And they'd say, I want to go out to the observatory then.
And I'd say, why?
I'd say, I want to see a pen banging across the end stops four times a second.
People went out just to...
It was also important because it was clearly stretching what rudimentary theories we had.
It was that much faster. Instead of one and a quarter, it was a quarter second period.
So that's how the first four pulsars were discovered.
Oh, fantastic story. That's spectacular.
That's science and action.
It's science and action, yeah.
And a question though.
You mentioned that this last poll show that you mentioned had such a strong signal.
Yeah.
Did you not occur to you at the time that this, you know, this very strong sort of, you know, banging of this needle backwards and forwards was something strange?
Or is this...
You thought it's pharma-jogo in person as attractive or something like that?
It looked like interference. It was so strong.
It was only on occasion when it dropped its strength that I could see.
It was one of those regular, scruffy signals.
Yeah.
What happened then?
So presumably there was a happy end of the story.
You got your PhD finished.
But these observations were published in the appendix.
Yeah.
Why was this because it was 100% sure or there was no explanation or what?
No. Tony told me that it was too late to change the title of my thesis.
I was halfway through my third year at the stage.
Right.
From what I know of university systems now, I'm not sure he was right.
But of course I believed him at the time.
And it was a pretty black day because I had spent a lot of time on these pulsing signals.
And I'd rather neglected the quasars.
And I had to get back up to speed on them and write a thesis and defend it.
I did that.
But I put the pulsars in in appendix because I thought there ought to be some contemporary account of the discovery of this signal.
So you had to go back through all those thousands of data to analyze for pulsars.
Yes.
So it took the place else.
Yes. That's right.
And what was the next step then?
You published your PhD.
There was a, as you say, a contemporary record of these interesting new objects.
Yeah.
What happened then?
Well, the results had also been published in nature by then.
We wrote the first one up.
And it was published at the end of February.
So by that stage, we knew that there were a few others, but we haven't really sussed them out properly.
We put the next three in another paper.
The publication of the first paper was interesting.
Martin Ryle phoned up John Maddox, who was editor of Nature.
And more or less said, we've got something interesting. Hold the presses.
Really?
I think John Maddox probably refereed the paper himself.
Just a check.
I've asked him this and he didn't answer the question directly, but he turned the paper round in two weeks.
And it came out at the end of February.
Tony held a colloquium in the Cavendish just a few days before nature was published.
And we kept fairly quiet about these results because we still weren't 100% sure what we were dealing with.
So we were only at that stage prepared to go public.
And Tony gave the colloquium a pretty titillating title and everybody in Cambridge came.
And Fred Hoyl came and sat in the front row.
And Tony gave this colloquium and announced this discovery and said we found a few others and, you know, that it or done.
At that stage, we weren't too sure what we were dealing with.
We knew it wasn't little green men.
One possibility it was white dwarfs with oscillations in their atmosphere,
somehow launching shockwaves, although the quarter-second pulsar was pushing that.
And for some reason you'd have to be seeing some of the harmonics and not the fundamental and it was all a bit iffy.
And the other possibility was a rotating thing called a neutron star, which nobody'd really come across before.
Some math theoreticians had proposed their existence 30 years beforehand, but, you know, they were tiny, you'd never see them.
And so we had these two models kicking around of a rotating neutron star or an oscillating white dwarf.
And we weren't too sure what.
And at the end of the colloquium and it just shows the power of Fred's brain.
Fred said in his best Yorkshire accent, I don't think it's a white dwarf.
I think it's a supernova remnant.
And Fred was right.
But just think of the physics that had been going on in his brain.
He started by saying he hadn't heard of these things before, which we were quite relieved about,
because we didn't want word out too widely.
So he was doing this from cold in the course of a 40-50 minute talk and homing in on the right conclusion.
It was amazing.
Amazing.
So now we've gone from the three or four original pulsars that you discovered to...
How many have we got now?
It's over 1,600.
1,700 or 1,760 or something.
Yeah, maybe even 1,800.
And they show us we're taking a variety going from the second period pulsars,
sort of that you've discovered through to these incredibly fast ones, the many second pulsars.
And the very first interview, I think, that the John Cast presented was with Michael Kramer,
a general bank about the double pulsar, which is an amazingly exquisitely sensitive test
of Einstein's theory of general relativity.
So I feel what you've started has become a fascinating field of physics in its own right.
And isn't it interesting that it's still a very exciting, dynamic, rapidly changing field?
You'd think after 40 years it would have settled into an interesting but mature phase.
Blow me, is it heck?
It's still rolling in all sort of staggering discoveries.
Yeah, it's fascinating.
What is the most interesting part of pulsar study now as you see it?
There's a lot of interest in the high magnetic field end of pulsars, neutron stars,
with X-ray and gamma-ray astronomy also contributing to that.
So there's some interesting things going on there.
And some of the transient pulsars, the ones that once in the blue moon and then shut up for 25 pulsars
and then do another pulsar, shut up for 13 pulsars.
Those, they're also up in that same sort of area.
So there's quite a lot of attention focused there.
There's interesting questions around whether there are some high mass pulsars, some high mass neutron stars,
which we really strain our theories of gravity if it's true.
So what do we mean by high mass?
The canonical mass for a pulsar is about 1.3 or 1.4 times the mass of the Sun.
There's hints or maybe even more than hints of some around about two solar masses.
So that's very interesting.
But why is it a problem for us?
Why should a heavier mass neutron star be a problem?
They shouldn't exist if the Einsteinian theory of gravity is right, put crudely.
I mean, there's a few ifs and buts and caveats on that, but that's broadly what the thrust is.
So they're interesting to people who are interested in the theory of gravity.
And breaking it.
And then there's also the question of how fast can a neutron star rotate?
How fast can a pulsar spin?
The suggestions that the fastest is about 700 revolutions per second.
And the fastest one discovered is jolly close to that.
If they get a faster one, still again, we're going to be pushing on some understandings of what these things are.
Is that because if it rotates too quickly, you'll just throw itself apart.
There is that, but even before it gets to that stage, it's reckoned that the inside gets a bit wobbly and turbulent.
It sends out gravitational radiation, which effectively stops it spinning as fast as it wants to and puts a natural limit on it.
That's the theory. Watch this space. Maybe broken quite quickly.
Like exciting times.
Thank you very much indeed.
My pleasure.
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