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Ilya
2010-Mar-15, 08:57 PM
This is really a history question, not astronomy question.

Right up until Jocelyn Bell discovered pulsars, all astronomers AFAIK dismissed neutron stars as essentially unfindable. It never occurred to anyone what fireworks one would put out in close orbit around a main sequence star. Or for that matter, what an enormous magnetic field a neutron star would have, with rather drastic effects. Why not?

korjik
2010-Mar-15, 09:29 PM
Sir Arthur Eddington said they did not exist, so they did not.

Until someone found one.

JohnD
2010-Mar-15, 09:55 PM
I don't think that a pulsar needs to be paired with a normal star, does it? Or rather that only one type of pulsar (of three) may be energised by accretion from a nearby companion.

And I fear, Ilya, that the retrospectoscope is a very useful instrument with which to poke ridicule at the omissions of those who went before. How could they have been so stupid? Very easily, just as easily as their succesors.

Einstein used a "cosmological constant" to explain why the Universe had not collapsed under gravity. He later called it his "greatest mistake", so if Einstein could berate himself in that way, who are we to criticise the mistakes of others?

John

slang
2010-Mar-16, 12:01 AM
And I fear, Ilya, that the retrospectoscope is a very useful instrument with which to poke ridicule at the omissions of those who went before. How could they have been so stupid? Very easily, just as easily as their succesors.

Personally, I don't see ridicule or stupidity implied in the question. I think the question "why didn't they think of X earlier, was there an identifiable reason for it?" is valid. An opportunity might have been missed, is there anything that can be learned from that to avoid missing other opportunities?

tdvance
2010-Mar-16, 01:16 AM
I have wondered myself--I know it's largely "emergent physics" rather than fundamental physics (like frame dragging) and thus harder to predict. Still, given a star with its magnetic field, one that's even more powerful on larger stars that give rise to pulsars (was that known then?), and take that same field and compress it from star-sized to about 10 miles diameter approx. and you have one very intense field. From there, one would think one could guess it would shine like a beacon out of those poles, while rotating fast because of conservation of angular momentum.

01101001
2010-Mar-16, 02:17 AM
American Institute of Physics: A Pulsar Discovery (http://www.aip.org/history/mod/pulsar/pulsar1/01.html)


[PHILLIP] MORRISON: In '68 January or February of that year—I remember myself meeting at the airport a friend who just returned from Great Britain, an astronomer. And he said, "Have you heard the latest?" And I said, "Well, what's that?" He said, "They've got something that pulses every second—a stellar signal that pulses every second." I said, "Oh, that couldn't be true!" "Yes," he said, "it's absolutely true. They announced it recently. They've studied it for about five or six months. It's extraordinary."


[MIKE] DISNEY: And the reason why everybody was excited was because it looked as if pulsars were the first actual sight of something which people had been prognosticating for thirty years—namely neutron stars.

10 pages.

korjik
2010-Mar-16, 02:25 AM
Actually, what I said what pretty much the whole story. The Chandrasekar limit was figured out in the 1930s, but Eddington did not like the thought of a stars mass stuck in a package even smaller than the Earth.

This suppressed any research into the field.

The properties of a neutron star arent all that odd once you consider conservation of angular momentum and energy. A star large enough to make a neutron star will spin really fast when shrunk down to around 10 km across, and the freezing in of the magnetic fields will give you an immense field for the same reason.

If Eddington hadnt been such a driving force in astronomy at the time, someone would have thought it through and hypothesized pulsars a couple decades before they were found. As it was, it didnt take very long at all to figure out what pulsars were once they were found.

Ilya
2010-Mar-16, 12:41 PM
And I fear, Ilya, that the retrospectoscope is a very useful instrument with which to poke ridicule at the omissions of those who went before. How could they have been so stupid? Very easily, just as easily as their succesors.
I was not making fun of, or ridiculing anybody. OP was a genuine question. Once you accept that neutron star is a possibility, figuring out its spin and magnetic field SHOULD have been very easy. Much less obvious properties of many other theoretical objects (in astronomy and otherwise) had been figured out prior to experimental discovery. The fact that nobody did implied to me there was some good reason for it. And Korjik just told us what that reason was.

Tensor
2010-Mar-16, 11:25 PM
I was not making fun of, or ridiculing anybody. OP was a genuine question. Once you accept that neutron star is a possibility, figuring out its spin and magnetic field SHOULD have been very easy. Much less obvious properties of many other theoretical objects (in astronomy and otherwise) had been figured out prior to experimental discovery. The fact that nobody did implied to me there was some good reason for it. And Korjik just told us what that reason was.

In Kip Thorne's book "Black Holes and Time Warp's, Einstein's Outrageous Legacy" there is a very good description of Chandra's and Eddington's disagreement. Chandra had been doing the calculations and was using an analytic calculator of Eddington's (I think Eddington was a mentor to Chandra). As a result, Eddington was well aware of Chandra's calculations.

At the meeting where Chandra presented his results, Eddington asked for and received permission to speak for 15 minutes after Chandra. He basically handwaved away Chandra's facts and calculations. As most of the calculations were pretty esoteric for the time (combining GR and Equations of State) and Eddington was recognized as one of the few who understood relativity, Eddington's opinion held sway for quite a while.

It first began to crumble within the Quantum Mechanical folks and then finally the GR folks. But it took until his death until it was seriously discussed. Chandra was crushed and pretty much left England and kept to himself. Although Chandra and Eddington remained friends.

Thorne argues that Eddington's attitude and tactics were a sign of respect for Chandra. Eddington was used to the rough and tumble, attack, give and take of the academic world and his attack was a sign that he accepted Chandra as an equal. Chandra, of course, was young and not used to this sort of treatment and thought his work had been somehow been subverted.

ngc3314
2010-Mar-17, 04:31 AM
Baade and Zwicky had discussed neutron stars in the 1940s; Zwicky in particular, was not one to let his ideas be swayed by authority. But in the mid-1960s, astrophysics seems so placid by our current standards. Magnetic fields were known in sunspots, but little measured in other stars. Radio astronomy had unveiled high-energy processes, understood to be mostly connected to magnetic acceleration of charges. The total cumulative exposure time of X-ray detectors for nonsolar astronomy was measured in minutes. Accretion onto white dwarfs was pretty well understood to account for dwarf novae, and maybe others - but magnetic white dwarfs were understood only later. Most of the theoretical pieces were there, but no one was looking in that direction. Would that I knew how to apply the analogy to astrophysics today...

Cougar
2010-Mar-17, 02:57 PM
But it took until [Eddington's] death until it was seriously discussed.

I always generally disagreed with Planck's comment about how scientific ideas came to be accepted. This may be a case where it is applicable.



"A new scientific truth does not triumph by convincing its opponents and making them see the light, but rather because its opponents eventually die, and a new generation grows up that is familiar with it." - Max Planck

Ken G
2010-Mar-17, 05:02 PM
But it wasn't Eddington's death that ushered in neutron stars, it was the pulsar discovery (Eddington died in 1944). I think we have something rather simpler here-- extraordinary claims require extraordinary evidence. It is similar with black holes-- they were predicted over 200 years ago, but no evidence for them existed, and they just seemed too bizarre to consider (it's true that Eddington didn't like them, and neither did Einstein for that matter, but their real problem was the absence of evidence). It wasn't until pulsars were discovered that the door was opened for such bizarre objects, and the term "black hole" came into common usage. I have no idea how much longer it would have taken had pulsars not been strong radio sources, but by now we'd see the X-rays from their accretion disks.

I do echo the sentiment in the OP though-- if black holes and neutron stars can form, they can form in binaries, and the mass accretion should (in 20-20 hindsight) have been anticipated to create some fireworks. But no one anticipated supermassive black holes, and the fireworks come in the X-rays for stellar mass black holes, and those have only been recently observable. So I think it all comes down to the observations we've been able to do in the last few decades, moreso than any particular personalities (though I don't dispute the influence of Eddington-- that certainly didn't help!). No matter what Eddington said, both neutron stars and black holes were found pretty much as soon as it was technologically possible to find them. But like ngc3314 says-- the real question is who will find them, and that requires being clever enough to know what "current wisdom" to ignore, or else just waiting to get lucky (as seems more often the case)!

Nereid
2010-Mar-17, 06:40 PM
Baade and Zwicky had discussed neutron stars in the 1940s; Zwicky in particular, was not one to let his ideas be swayed by authority. But in the mid-1960s, astrophysics seems so placid by our current standards. Magnetic fields were known in sunspots, but little measured in other stars. Radio astronomy had unveiled high-energy processes, understood to be mostly connected to magnetic acceleration of charges. The total cumulative exposure time of X-ray detectors for nonsolar astronomy was measured in minutes. Accretion onto white dwarfs was pretty well understood to account for dwarf novae, and maybe others - but magnetic white dwarfs were understood only later. Most of the theoretical pieces were there, but no one was looking in that direction. Would that I knew how to apply the analogy to astrophysics today...
(bold added)

My €0.02's worth: astrophysics is in a somewhat odd state today, and a rather uncomfortable one at that.

Just about every theoretical idea around has either been, or is being, vigorously prodded and squeezed, to see what sort of novel observables there might be. And when some such even half-way decent ones are published, telescopes get to work (or, in some cases, entirely novel observatories are built, e.g. LIGO, IceCube). However, most sexy theoretical ideas seem to produce observables that are observable only with new observatories far, far beyond the current technological or, more pertinent, financial resources available.

That leaves us with what must surely be the observational astronomer's delight: the near certainty of making serendipitous discoveries, some of which will earn someone a Nobel Prize or three.

It gets better.

With almost all the best astronomical observations now available to everyone, 'at the click of a mouse', these discoveries can be made by anyone, PhD in astronomy or not. Let's see who can come up with the best, recent, examples! :)

My vote: RRATs (http://www.atnf.csiro.au/news/press/rrats.html)

peteshimmon
2010-Mar-17, 07:45 PM
I was munching my morning sandwiches during
teabreak while reading the Daily Telegraph
story about pulsating radio sources in the
heavens. Neat. Over the next 18 months the
subject exploded (so to speak) until the
moment in WH Smiths when the magazine showed
television pictures of a pulsar going on and
off. It was a time when everything was being
found out!

The real story is the thinking, funding,
building and operation of the Pulsar aerial.
Such things as feeder lines, baluns,
insulators and sheep. That story needs to
be told properly.

ngc3314
2010-Mar-17, 07:49 PM
(bold added)

With almost all the best astronomical observations now available to everyone, 'at the click of a mouse', these discoveries can be made by anyone, PhD in astronomy or not. Let's see who can come up with the best, recent, examples! :)

My vote: RRATs (http://www.atnf.csiro.au/news/press/rrats.html)

Hanny's Voorwerp (http://www.astr.ua.edu/keel/research/voorwerp.html)? (So I'm biased).

To follow up Ken G, history has shown that the Universe is so full of unexpected things that new technology has been a surer path of discovery than previous ideas. It's a fairly big dal when theory predicts a new phenomenon that someone goes out to discover - Einstein's predictions, neutron stars after a long time, black holes, pulsating He white dwarfs. Was it Eddington who claimed that if we had never seen a star, we should be obliged to infer their existence? Permit me an observer's laugh at that...

Nereid
2010-Mar-17, 08:13 PM
Let the nominations continue to roll in!

A recent example of how no (theoretical) stone is being left unturned: The effect of neutrinos on the matter distribution as probed by the Intergalactic Medium (http://arxiv.org/abs/1003.2422).

An example of a bit of an anomaly that was NOT immediately pounced on: Richard Lieu and the unexpectedly weak Sunyaev-Zel'dovich effect seen in WMAP data (recently confirmed, by the WMAP team, in one of their Seven-Year papers). IIRC, the SZ effect is also key to 'Dark Flows'.

A longer-standing puzzle: the estimated primordial abundance of lithium. Sure it's a messy issue (for example, who can claim to have a good handle on all relevant physical processes between the BBN and the formation of the oldest stars whose atmospheric Li abundances are used to estimate the primordial abundance?), but that should be a theorist's delight!

Another one: the relative luminosity (magnification) of lensed quasars.

But these are few and far between; much more common are the 'pulsars' (an older example: GRBs).

Tensor
2010-Mar-17, 09:01 PM
Let the nominations continue to roll in!

Snip...

But these are few and far between; much more common are the 'pulsars' (an older example: GRBs).

Talking to a neighbor who is working on her PhD, she provided some nice perspective. What is really nice about these new discoveries are the opportunities for PhD subjects. If it's new, just about any answer is good for a PhD.

Nereid
2010-Mar-17, 09:20 PM
Why did it take so long for this particular penny to drop?

Detection of a Large Scale Structure of Intracluster Globular Clusters in the Virgo Cluster (http://arxiv.org/abs/1003.2499)

And talking of Nobels, surely James Gunn richly deserves one, doesn't he? Look at all the great things SDSS has produced (maybe I should start a thread, calling for nominations of your faves)! Not to mention the Gunn-Peterson trough, the ...