As far as I know, pulsar-based navigation has been intensively investigated. I wonder are there any other natural bodies in the universe that can emit stable signals like pulsars?
You would need to essential physical conditions in natural bodies
1. Ability to collimate (beam) electro magnetic radiation - there are other
processes that do this.
2. Ability to "pulse" that beam at regular intervals. Neutron stars obviously do this via rotation.
These other sources of collimated radiation do not have natural mechanisms to "pulse" it
A fascinating question.
Yes. there are at least two other cosmic phenomena that are cyclical.
In the electromagnetic spectrum (EM), the output of a Cepheid variable star is the first thing that comes to mind with regards to a regular 'signal'. Other EM 'sources' with a variable nature might be the line of sight brightness of a binary star system - occultation in a preferred direction will give rise to a cyclical signal.
Postulated gravitational signals might also be cyclical - again, a binary system , perhaps with neutron stars in it (!), might be such a source.
Novae aren't, probably, *that* regular as a signal source, but they are repeat 'performers' and so depending on your criterion of 'regular' they could be considered as being a stable signal source.
Hello Bothun, thank you very much for your answer. Although I am just interested in this field, your answer gives me some precious advice.
Hello Garry, your answer is very useful for me. Actually, I am not major in this field. I just wonder if there are any other natural bodies can be used as navigation beacons just like pulsars. You have given me a clear and primary understanding of the problem. Thank you very much.
For cepheids the pulsation period is of order days
the only "star" that would have a rapid "ringing" period would
be a white dwarf but there i no known mechanism to get a degenerate
core to ring (ringing basically means hitting it with a sledgehammer and
watch the energy dissipate through resonant waves)
It depends on what you want a reference for, time, linear momentum or angular momentum.
The Cosmic Microwave Background can be used as a velocity reference. Closer to home, the orbit of the Moon was at one time the most accurate clock available, and it, plus the orbits of the planets were used to construct, "ephemeris time". These orbits, plus the orbits of artificial satellites such as LAGEOS, are still used as references for a non-rotating frame. The best non-rotating frame is, however, derived today by VLBI from the quasars, and that is purely on the basis of their enormous distances.
Of course, the entire Doppler technique of finding exoplanets is based on stars emitting very precise spectral lines, which can be used as velocity references, good to a fraction of a meter per second.
If we could ever get a good signal to noise in gravitational radiation the normal modes of a nearby black hole could also be used as a time reference.
Thank you Mr. Bothun. I'll try to refer more background information in this field.
Thank you Mr. Eubanks, The concept of using black hole as time reference is very interesting.
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