Scientific utility of computer detection of pulsars?
26 Dec 2018 10:23:11 UTC
Topic 217707
(moderation:
It appears that we are hunting for pulsars in order to study gravity waves. And it further appears that it requires hundreds, if not thousands of hours of computer time (on fast GPUs) to even detect the pulsars using long time-scale integration (or whatever technique it is).
So I am wondering how you can extract useful information from a passing gravity wave if you can barely detect the pulsar signals at all? Would you not need a pulsar that can be detected in real-time in order to measure the fine differences in timing required for gravity wave work?
Quote:It appears that we are
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A pulsar once detected can have it's signal fully characterised (sky position, frequency, frequency derivative .. ), and thus can be listened to at leisure regardless of how long it took to find it first time. This is more difficult for the gamma ray pulsars where we only detect off Earth, and for that matter most of their rotations do not yield a photon detectable hereabouts.
That's indeed one application of radio pulsar knowledge : high time resolution observation of pulsars. If you are aware of principles of synthetic aperture radar then that is the right idea as, for instance, The Square Kilometer Array when built will satisfy. You have an array of receivers, each one with very tightly known position plus excellent knowledge of time delays between them. The array 'looks' at a source by use of deliberate delays b/w receiver signals. If that is done digitally and in parallel then one can listen to pulsars in real-time, and as you say observe a gravity wave passing by because of a coherent pattern of timing changes across the pulsars.
Some pulsars are so well known and observed over decades so, for example, the number of rotations since discovery to some given moment in the present day is known exactly : so & so full rotations ( an integer ) plus a phase value ( fraction of a rotation ). If some areas of the sky have all the known pulsar signals appearing to be arriving late/early, with corresponding early/lates elsewhere then you have a prima facie case for the passage of a gravitational wave going past Earth. Here upon one attributes this early/late-ness to changes in spacetime around Earth's neighbourhood and not some conspiracy of pulsar behaviour at source that just happens to make it look that way.
Cheers, Mike.
I have made this letter longer than usual because I lack the time to make it shorter ...
... and my other CPU is a Ryzen 5950X :-) Blaise Pascal
Very good. I hope the
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Very good. I hope the Einstein people will list in their publications anything that comes out of our pulsar detections (other than they are found at all). That is where the payoff comes.
By the way, it appears that the Australians have cornered the market in really good explanations of extraordinarily complex science in a way that ordinary people can more or less get some glimpse of.
https://www.youtube.com/watch?v=JDmKLXVFJzk
https://www.youtube.com/watch?v=IhpGdumLRqs
I guess it comes from living upside down; it must allow the ideas to flow more freely.
Jim1348 wrote:I hope the
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E@H project management has always been very gracious in mentioning this community based supercomputer when it comes to published results. For instance with the gravitational wave analysis, while we have yet to detect a continuous wave source, E@H has placed bounds on certain parameters for neutron stars. This has in turn fed back to models that describe NS properties. The science done here is real and validated ie. hardcore stuff.
BTW : Occasionally the question arises : what if ( after careful diligence ) E@H finds no continuous waves down to some threshold and degree of accuracy ? Would we have then failed ? The correct answer is NO ! We would have discovered the way that this Universe behaves and hence trigger a change in our thinking accordingly. One putative mechanism for continuous waves is 'pimples' on neutron stars that cause a 'wobble' that generates said waves. Maybe such pimples don't/can't form due to the material properties of neutron star surfaces. That's a valid scientific outcome. At this point I'll mention the ( probably ) most famous 'null result' of them all : The Michelson & Morley experiment which ultimately directed thinking towards General Relativity that has passed all experimental tests yet thrown at it.
Cheers, Mike.
( edit ) ASIDE : There are many areas of modern study with the title of 'science' that crucially miss out on the bit of methodology "discovered the way that this Universe behaves and hence trigger a change in our thinking accordingly". I won't mention them specifically so as to avoid food fights. I'm sure you can think of some. If you want to test a theory try applying it to a data set from which it was not originally derived/induced. Always suspect a physical theory that fails in the worst way possible : it can't match tomorrow's data set.
I have made this letter longer than usual because I lack the time to make it shorter ...
... and my other CPU is a Ryzen 5950X :-) Blaise Pascal
On the NASA home page I have
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On the NASA home page I have read that the fastest traveling gamma ray pulsar known, J0002 was found by Einstein@home after 10000 years of computer time, along with other 22 gamma ray pulsars. It travels at 4 million km/hour, which would take it from the Earth to the Moon in six minutes.
Tullio
tullio wrote:On the NASA home
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Link?
Zalster wrote:tullio wrote:On
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https://www.nasa.gov/feature/goddard/2019/nasa-s-fermi-satellite-clocks-cannonball-pulsar-speeding-through-space
Go to the NASA Home page and
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Go to the NASA Home page and in the Search label search for cannonball pulsar. It is no longer visible on the home page and I am unable to make a link.
Tullio
tullio wrote:Go to the NASA
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could just click on the link I posted above
I also posted a YT Video of
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I also posted a YT Video of the same topic.