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ScienceWeek
2004 11 June C1 PULSARS AND WOMEN IN ASTRONOMY
Jocelyn Bell, now known as S. Jocelyn Bell Burnell, was the de facto discoverer of the first pulsar in 1967. She was a graduate student at that time, and although her supervisor Antony Hewish later received a Nobel Prize for the discovery, Jocelyn Bell was not included.
The following points are made by S. Jocelyn Bell Burnell (Science 2004 304:489):
1) Pulsars are phenomenal objects: rapidly rotating neutron stars that send out beams of radio waves which, like lighthouse beams, sweep around the sky as the star rotates. They are amazingly precise timing devices that can be used as clocks for testing relativity theory and may be used for timekeeping and navigation. With a diameter of only about 15 kilometers and a density comparable to that of the nucleus of an atom, they also provide a laboratory for some extreme physics.
2) In the fall of 1967, I was conducting a routine mapping project studying the radio scintillation of quasars for my doctoral thesis at Cambridge University, under the direction of my adviser, Antony Hewish. Investigation of a puzzling weak signal showed it to be a string of pulses, 1.33 seconds apart. We spent a month trying to find out what was wrong, so unexpected was the signal; and we nicknamed it "Little Green Men" (LGM). At the end of that month, I found a second pulsar, killing the LGM hypothesis and indicating a new kind of astronomical source.
3) Being a research student, I had time to understand the instrument, recognize real and spurious signals, and investigate the anomalous or unexpected. Arguably, my student status and perhaps my gender were also my downfall with respect to the Nobel Prize, which was awarded to Professor Antony Hewish and Professor Martin Ryle. At that time, science was still perceived as being carried out by distinguished men leading teams of unrecognized minions who did their bidding and did not themselves contribute other than as instructed! Although I was not included, I celebrated that first award in 1974 of the Physics Prize for an astronomical discovery. Now I celebrate the fact that we have a better understanding of the teamwork necessary for scientific progress.
4) It took a relatively long time to recognize the first pulsar. However, once that happened, pulsar research rapidly advanced, although often in unexpected ways and in sudden spurts. Following the developments in pulsar research over the past 36 years has given me immense pleasure. More disappointing have been the developments in the recognition and advancement of women in astronomy. In December 2003, the International Astronomical Union (IAU) published an analysis of its membership. With only 10% of their membership female, the UK and the US fall well below the international average. The only thing that has changed since a similar survey about 5 years ago is that the proportion in most countries has gone up a few percent. Admittedly, it tends to be the more senior astronomers who are IAU members, and there tend to be more women in the junior ranks, but at this rate it will take 50 years until 50% of senior astronomers are female.
Science http://www.sciencemag.org
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ON PULSARS
The following points are made by Martin Rees (citation below):
1) Priority for the discovery of pulsars went to Anthony Hewish and Jocelyn Bell, Cambridge radio astronomers, whose discovery of "pulsars" constituted one of the most remarkable pieces of serendipity in modern science.
2) Hewish built a special instrument with an important special feature: it was sensitive enough to record rapid changes in the intensity of the radiation from distant sources. And he found what he was looking for: just as stars twinkle because their light passes through turbulent air, so some radio sources "scintillate" because the radio waves pass through an irregular medium on the way toward us. But his research student, Jocelyn Bell, found variations of a quite distinctive kind -- sporadic series of regular pulses, each pulse lasting a fraction of a second, coming from specific points in the sky. A frantic few months of effort ensued. The Cambridge radio astronomers had to check whether the signals had a terrestrial origin (maybe some secret space project?). Three more of these mysterious sources were soon found, each ticking at a well-defined rate. Could they perhaps be signals from intelligent extraterrestrials? This idea was never taken very seriously, but the sources were jocularly referred to as LGM 1, 2, 3, and 4 (for "little green men").
3) When this discovery was announced in the journal Nature, even the other astronomers in Cambridge were astonished. Hewish and his colleagues had not shared their excitement with anyone outside a tight-knit group. This concealment annoyed some of us at the time, but in retrospect I think Hewish was no more than prudent. Only a few months elapsed between Jocelyn Bell's first intimations and the actual publication, so nobody's chance of follow-up work was seriously delayed. And, for most of those months, Hewish and Bell weren't completely confident that the signals were "real". If the sporadic radio pulses had turned out to have a mundane interpretation, or to arise from some fault in their equipment, a premature announcement would not only have been embarrassing, but might have wasted the efforts of many other astronomers who would undoubtedly have followed up any rumor of this kind.
4) What could these objects be? An ordinary star like the Sun would fly apart if it pulsed or rotated much faster than once per hour. Bodies that turned on and off in a fraction of a second plainly had to be much more compact. Were they white dwarfs, or maybe neutron stars? Were they pulsing or spinning? All these options (and many others) had their advocates. The Cambridge group originally favored pulsating white dwarf stars. (A naive inquirer at a press conference was perplexed about how, at such a great distance, white dwarfs could be distinguished from little green men!)
5) The case for rotating neutron stars was first clearly argued by Thomas Gold. There were good reasons for expecting neutron stars to form when the cores of heavy stars collapsed, triggering supernova explosions. They would be so small, and have such strong gravity, that they could spin as fast as a thousand revolutions per second without flying apart. The spin rate would provide a natural stable clock; a "lighthouse beam" anchored to the star would send an intense pulse toward us once per revolution.
6) Only a year later, the debate was settled in Gold's favor. A very fast pulsar was found at the center of the Crab Nebula, transmitting 30 pulses per second: a white dwarf could neither rotate nor pulsate as fast as that, but such rapid spin was no problem for a neutron star. Moreover, careful timing showed that the pulse rate was gradually slowing down: this was natural if energy stored in the star's spin was being gradually converted into radiation, and into a wind of particles that keep the Crab Nebula shining in blue light.
Adapted from: Martin Rees: Before the Beginning: Our Universe and Others. Perseus Books 1997, p.71. More information at: http://www.amazon.com/exec/obidos/ASIN/0738200336/scienceweek
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Editor's Note:
It is generally agreed that [Susan] Jocelyn Bell, who was 24 years old and Hewish's graduate student at the time (1967), made the actual discovery of the first pulsar by noticing unexplained pulses in radio telescope data contained in 100-foot lengths per day of paper charts, and that her discovery was instrumental in Hewish winning his Nobel Prize in Physics in 1974, which he shared with Martin Ryle (1918-1984), a prime figure in the development of radio-telescope astronomy.
The Bell discovery was made while Bell, Hewish, and Ryle were at Cambridge University (UK), and the astronomer Martin Rees, who was of the faculty at Cambridge at that time, writes of Jocelyn Bell as follows: "Jocelyn Bell received less than her fair share of credit for the discovery of pulsars. This happened, I think, because of the social pressures which (then even more than now) impeded women's careers, and lowered their scientific aspirations. After getting her PhD, Jocelyn Bell left active research for several years -- giving priority to her husband's career seemed at that time the "natural" thing to do. Had she instead continued, and acquired "visibility" by joining the small cohort of radio astronomers who, over the next few years [after 1967] consolidated our knowledge of pulsars and discovered many more -- as, almost certainly, a /man/ with her extraordinary initial record would have done -- it is hard to believe her achievements would have been slighted to the same extent." [Martin Rees: Before the Beginning, (1997) p.263].
It has been suggested that in an earlier age CP-1919, the first observed pulsar, would have been called "Bell's Star". No matter the name of the first observed pulsar, it was discovered by Susan Jocelyn Bell (now Susan Jocelyn Bell Burnell), and there are many who believe that the Nobel Prize in Physics of 1974 should read Ryle, Hewish, and Bell. Bell Burnell, however, disagrees, and she has stated: "Nobel prizes are based on long-standing research, not on flash-in-the-pan observation by a research student. The award to me would have debased the prize."
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