Space.com article
6 Jan 2010 9:15:51 UTC
Topic 194707
(moderation:
Interesting article on Space.com today about a large new set of 'millisecond pulsars' that has been found by using the Ferme Space Telescope that could help in the search for gravitational waves.
http://www.space.com/scienceastronomy/100105-fermi-pulsars.html
Space.com article
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Here is a NASA article:
pulsars
Tullio
Let me try to understand. If
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Let me try to understand. If there is a double pulsar system it will lose energy by emission of gravitational waves and then it will emit radio waves with a longer wavelength. Example: the Hulse-Taylor pulsar. If instead the companion star is a normal star, not a collapsed one, this will transfer material to the pulsar which will increase its rotation rate and hence its radio frequency. Then it will be used like a clock in a GPS satellite. But how this can be used to detect GW?
Tullio
RE: Let me try to
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You have a large group of dispersed and distant objects which are believed to be pretty stable frequency wise ( however they arrive at that state ). If over a long period of time we notice that they all ( well mostly, it's a statistical thing ) speed up and slow down to some common pattern, then we might deduce that it's our clocks running slow/fast and not a change in the source behaviours. That would reasonably mean that a gravitational wave is passing by us hereabouts. It would be a very low frequency gravitational wave with a period of the order of months to years ....
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
Thanks.Mike. Then we could
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Thanks.Mike. Then we could use pulsars instead of LISA to detect very low frequency GW, such as those generated in the Big Bang.
Tullio
RE: Thanks.Mike. Then we
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IIRC there is some overlap, but LISA looks at lower frequencies than this radio-telescope/pulsar trick. With very long wavelength GW's one views quite extensive sources - like the whole universe for instance! :-)
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
RE: LISA looks at lower
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This is incorrect.
Millisecond pulsar timing arrays look for GWs at frequencies of nHz (10e-9 Hz). LISA is sensitive in the frequency range of mHz (10e-3) Hz.
So LISA looks at higher frequencies than the radio-telescope/pulsar trick.
Director, Einstein@Home
RE: RE: LISA looks at
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Whoops, wrong way round. Thanks Bruce. :-)
Nano Hz, that makes the wavelength 3 x 10^(+8) x 10^(+9) ~ 10^(+17) meters = 10^(+14) km. Now what's 10^(+14) km in size, or equivalently how far does light travel in a billion seconds? I make that 10^(+9) / ( 60 * 60 * 24 * 365 ) ~ 317 light years. I found that Canopus ( the really bright one in Carina ) is about 310 light years away and Antares ( the bright red one in Scorpius ) is about 330 light years.
Or inverting the problem : you won't get a single investigator who will live long enough to see even one wavelength pass by. Halley's Comet would come and go about 4 times. You might make a quarter of a wavelength if you start young enough! I suppose that begs the question of error, in our lifetimes, given we only catch a fraction of the wave? Normally we count waves as they go past and divide by some clocked interval etc. Wow, we'd want real good accuracy here. In fact the more precise one is the lower one can go in frequency, and be confident, and thus the longer the wave. The longer the wave the bigger the thing that caused it.
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
RE: Let me try to
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Each pulsar is part of an 'all-sky array' which then forms a detector that is sensitive to events not necessarily related to the specific system of any particular pulsar, although the effects you mentioned will surely have to be taken into account as they will certainly change the timing of any pulsar that happens to be part of such a binary system.
To detect a general background of GWs would require very accurate measurements of the timing of about twenty individual millisecond-pulsars for a period of five to ten years. The required accuracy of the timing measurements has to be within about 100 nanoseconds. To detect the GWs from merging supermassive black holes requires only five pulsars, but measurement of arrival times of their pulses requires a greater degree of accuracy – within 10 nanoseconds. See this article from ScienceNews.