Ladies and Gentlemen:
Before you discover for yourselves
let me tell you that I am no expert at after dinner speeches.
The nearest I have come was writing a Ph.D. thesis; my
supervisor kindly read a draft of it and advised me that it read
more like an after-dinner speech than a Cambridge University
dissertation. He was right, of course, but it has taken me years
to see the funny side of his remark.
There has been a lot of interest shown in the discovery of
pulsars, and also some misunderstanding. I would like to take
this opportunity of setting the record straight. However, it all
happened 8 or 9 years ago, and after such a time there is some
difficulty in remembering it all accurately.
The story began in the mid-1960's, when the technique of
interplanetary scintillation (IPS) was discovered.
IPS is the apparent fluctuation in intensity of the radio
emission from a compact radio source. It is due to diffraction
of the radio waves as they pass through the turbulent solar wind
in interplanetary space. Compact radio sources, e.g. quasars,
scintillate more than extended radio sources. Professor Tony
Hewish realized this technique would be a useful way of picking
out quasars, and designed a large radio telescope to do this. I
joined him as a Ph.D. student when construction of this
telescope was about to start.
The telescope covered an area of 41/2 acres - an area that would
accommodate 57 tennis courts. In this area we put up over a
thousand posts, and strung more than 2000 dipoles between them.
The whole was connected up by 120 miles of wire and cable. We
did the work ourselves - about five of us - with the help of
several very keen vacation students who cheerfully
sledge-hammered all one summer. It took two years to build and
cost about E15,000, which was cheap even then.
We started operating it in July
1967, although it was several months more before the
construction was completely finished.
I had sole responsibility for operating the telescope and
analyzing the data, with supervision from Tony Hewish. We
operated it with four beams simultaneously, and scanned all the
sky between declinations +50' and -10' once every four days. The
output appeared on four 3-track pen recorders, and between them
they produced 96 feet of chart paper every day. The charts were
analyzed by hand by me. We decided initially not to computerize
the output because until we were familiar with the behavior of
our telescope and receivers we thought it better to inspect the
data visually, and because a human can recognize signals of
different character whereas it is difficult to program a
computer to do so.
After the first few hundred feet of chart analysis I could
recognize the scintillating sources, and I could recognize
interference. (Radio telescopes are very sensitive instruments,
and it takes little radio interference from nearby on earth to
swamp the cosmic signals; unfortunately, this is a feature of
all radio astronomy.)
Six or eight weeks after starting
the survey I became aware that on occasions there was a bit of
"scruff' on the records, which did not look exactly like a
scintillating source, and yet did not look exactly like man-made
interference either. Furthermore I realized that this scruff had
been seen before on the same part of the records - from the same
patch of sky (right ascension 1919).
The source was transiting during the night - a time when
interplanetary scintillation should be at a minimum, and one
idea we had was that it was a point source. Whatever it was, we
decided that it deserved closer inspection, and that this would
involve making faster chart recordings as it transited.
Towards the end of October when we
had finished doing some special test on 3C273, and when we had
at last our full complement of receivers and recorders, I
started going out to the observatory each day to make the fast
recordings. They were useless. For weeks I recorded nothing but
receiver noise. The "source" had apparently gone.
Then one day I skipped the
observations to go to a lecture, and next day on my normal
recording I saw the scruff had been there. A few days after that
at the end of November '67 I got it on the fast recording. As
the chart flowed under the pen I could see that the signal was a
series of pulses, and my suspicion that they were equally spaced
was confirmed as soon as I got the chart off the recorder. They
were 11/3 seconds apart. I contacted Tony Hewish who was
teaching in an undergraduate laboratory in Cambridge, and his
first reaction was that they must be manmade.
This was a very sensible response in
the circumstances, but due to a truly remarkable depth of
ignorance I did not see why they could not be from a star.
However he was interested enough to come out to the observatory
at transit-time the next day and fortunately (because pulsars
rarely perform to order) the pulses appeared again. This is
where our problems really started. Tony checked back through the
recordings and established that this thing, whatever it was,
kept accurately to sidereal time.
But pulses 11/3 seconds apart seemed
suspiciously manmade. Besides 11/3 seconds was far too fast a
pulsation rate for anything as large as a star. It could not be
anything earth-bound because it kept sidereal time (unless it
was other astronomers).
We considered and eliminated radar
reflected off the moon into our telescope, satellites in
peculiar orbits, and anomalous effects caused by a large,
corrugated metal building just to the south of the 41/2 acre
telescope.
|
"Were these pulsations
man-made, but by man from another civilization?" |
Then Scott and Collins observed the pulsations with another
telescope with its own receivers, which eliminated instrumental
effects. John Pilkington measured the dispersion of the signal
which established that the source was well outside the solar
system but inside the galaxy.
So were these pulsations man-made,
but made by man from another civilization?
If this were the case then the
pulses should show Doppler shifts as the little green men on
their planet orbited their sun. Tony Hewish started accurate
measurements of the pulse period to investigate this; all they
showed was that the earth was in orbital motion about the sun.
Meanwhile I was continuing with routine chart analysis, which
was falling even further behind because of all the special
pulsar observations. Just before Christmas I went to see Tony
Hewish about something and walked into a high-level
conference about how to present these results. We did not really
believe that we had picked up signals from another civilization,
but obviously the idea had crossed our minds and we had no proof
that it was an entirely natural radio emission.
It is an interesting problem - if
one thinks one may have detected life elsewhere in the universe
how does one announce the results responsibly? Who does one tell
first?
We did not solve the problem that afternoon, and I went
home that evening very cross here was I trying to get a Ph.D.
out of a new technique, and some silly lot of little green men
had to choose my aerial and my frequency to communicate with us.
However, fortified by some supper I returned to the lab that
evening to do some more chart analysis.
Shortly before the lab closed for
the night I was analyzing a recording of a completely different
part of the sky, and in amongst a strong, heavily modulated
signal from Cassiopea A at lower culmination (at 1133) I thought
I saw some scruff. I rapidly checked through previous recordings
of that part of the sky, and on occasions there was scruff
there. I had to get out of the lab before it locked for the
night, knowing that the scruff would transit in the early hours
of the morning.
So a few hours later I went out to the observatory. It was very
cold, and something in our telescope-receiver system suffered
drastic loss of gain in cold weather. Of course this was how it
was! But by flicking switches, swearing at it, breathing on it I
got it to work properly for 5 minutes - the right 5 minutes on
the right beam setting.
This scruff too then showed itself
to be a series of pulses, this time 1.2 seconds apart. I left
the recording on Tony's desk and went off, much happier, for
Christmas. It was very unlikely that two lots of little green
men would both choose the same, improbable frequency, and the
same time, to try signaling to the same planet Earth.
Over Christmas Tony Hewish kindly kept the survey running for
me, put fresh paper in the chart recorders, ink in the ink
wells, and piled the charts, unanalyzed, on my desk. When I
returned after the holiday I could not immediately find him, so
settled down to do some chart analysis.
Soon, on the one piece of chart, an
hour or so apart in right ascension I saw two more lots of
scruff, 0834 and 0950. It was another fortnight or so before
1133 was confirmed, and soon after that the third and fourth,
0834 and 0950 were also. Meanwhile I had checked back through
all my previous records (amounting to several miles) to see if
there were any other bits of scruff that I had missed.
This turned up a number of faintly
possible candidates, but nothing as definite as the first four.
|
"It is an interesting
problem..... if one thinks one may have detected
life elsewhere..... how does one announce the
results responsibly?" |
At the end of January the paper announcing the first pulsar was
submitted to Nature.
This was based on a total of only 3
hours' observation of the source, which was little enough. I
feel that comments that we kept the discovery secret too long
are wide of the mark. At about the same time I stopped making
observations and handed over to the next generation of research
students, so that I could concentrate on chart analysis,
studying the scintillations and writing up my thesis.
A few days before the paper was published Tony Hewish gave a
seminar in Cambridge to announce the results. Every astronomer
in Cambridge, so it seemed, came to that seminar, and their
interest and excitement gave me a first appreciation of the
revolution we had started. Professor Hoyle was there and I
remember his comments at the end.
He started by saying that this was
the first he had heard of these stars, and therefore he had not
thought about it a lot, but that he thought these must be
supernova remnants rather than white dwarfs. Considering the
hydrodynamics and neutrino opacity calculations he must have
done in his head, that is a remarkable observation!
In the paper to NATURE we mentioned that at one stage we had
thought the signals might be from another civilization. When the
paper was published the press descended, and when they
discovered a woman was involved they descended even faster. I
had my photograph taken standing on a bank, sitting on a bank,
standing on a bank examining bogus records, sitting on a bank
examining bogus records: one of them even had me running down
the bank waving my arms in the air - Look happy dear, you've
just made a Discovery! (Archimedes doesn't know what he missed!)
Meanwhile the journalists were
asking relevant questions like was I taller than or not quite as
tall as Princess Margaret (we have quaint units of measurement
in Britain) and how many boyfriends did I have at a time?
|
"Look happy dear, you've
just made a Discovery." |
That was how my part in the proceedings ended. I finally
finished the chart analysis, measured the angular diameters of a
number of radio sources, and wrote my thesis. (The pulsars went
in an appendix.)
Then I moved out of the field to
another part of the country, to get married. It has been
suggested that I should have had a part in the Nobel Prize
awarded to Tony Hewish for the discovery of pulsars. There are
several comments that I would like to make on this: First,
demarcation disputes between supervisor and student are always
difficult, probably impossible to resolve. Secondly, it is the
supervisor who has the final responsibility for the success or
failure of the project.
We hear of cases where a supervisor
blames his student for a failure, but we know that it is largely
the fault of the supervisor. It seems only fair to me that he
should benefit from the successes, too. Thirdly, I believe it
would demean Nobel Prizes if they were awarded to research
students, except in very exceptional cases, and I do not believe
this is one of them. Finally, I am not myself upset about it -
after all, I am in good company, am I not!
All this happened 8 or 9 years ago, and to show that I operate
in real time I would like to end by telling you what it is like
to be on the inside in x-ray astronomy at the moment.
When I left radio astronomy and went into gamma-ray astronomy I
told myself firmly that I had already had more than a lifetime's
share of excitement and good luck and that I must settle down
now and do some reliable and solid, undramatic science, though
hopefully it would be interesting science. And certainly
gamma-ray astronomy was suitably unspectacular (although I
cannot help noticing how it has improved since I left the field
three years ago).
Then I went to MSSL and into x-ray
astronomy, still telling myself that I had already had more than
a lifetime's share....... I had not appreciated that x-ray
astronomy was about to boom, and had not reckoned on the
excitement of participating in a satellite project in those
sorts of circumstances.
Life with a satellite is hectic: it
never stops, nor takes holidays or weekends off - it keeps
going, day in, day out. If you are not careful it runs you
instead of you running it. If somebody could invent a Lord's Day
Observance satellite, I would be pleased to work on it. I
mentioned earlier the 31/2 miles of chart recordings from the
radio telescope that I analyzed. The data from our experiments
on Ariel V now cover 12 miles of computer printout, and the bird
is still flying.
One hears about information explosions, but it is only when one
happens all around you that you appreciate what it is.
Within the lifetime of Ariel V - the
last two years new, dramatic results have been rolling in thick
and fast. X-ray transients have come to stay; many x-ray sources
are found to be highly variable; periodicities on a time-scale
of minutes have been discovered; more recently still x-ray
bursts have opened our eyes to yet another type of phenomenon;
and x-ray emission from galaxies and clusters of galaxies is now
well established.
What will the Universe throw at us
next?
There is now a thirteenth
commandment:
"Thou shalt not make predictions
in x-ray astronomy, lest the Lord thy God reveal the
folly of thy ways unto all."
