Can my spaceship figure out its position using Cepheid Variables?
In my story, reasonably far in the future, an intrepid group of explorers are on the first manned mission to the Andromeda galaxy, travelling close to the speed of light. They slumbered in suspended animation for thousands of years, in their frame of reference (to a stationary observer, it would have been much longer), but were awakened by the ship's systems after an error somewhere in the bowels of the computer sent the ship off course. The main computers are down, and the crew don't know what year it is or where exactly they are. They can make some basic distance measurements by looking at the angular sizes of Andromeda and the Milky Way, but not to great precision.
Fortunately, the ship is equipped with a telescope, and the main engineer happens to be an ex-astronomer. The backup navigational system relies on manual observations of Cepheid variables, stars that have a fixed relationship between their pulsational periods and their absolute magnitudes. The ship has a database of the positions of nearby dwarf galaxies, and by observing Cepheids in four of these galaxies (using multiple Cepheids in each galaxy, to reduce measurement error), and determining their periods and apparent magnitudes, the crew can calculate the distance to each galaxy. Using trilateration, these measurements can then help them figure out where exactly they are, to greater precision.
Eventually, they'll discover that they are, fortunately, still in in the Local Group, about 500,000 parsecs from the Milky Way and 400,000 parsecs from Andromeda, placing them off course. However, they're still firmly within the galaxy group.
This is my current proposal for an ad-hoc improvised navigational system for when something goes wrong on the ship. I'm not looking for other options at the moment, but I'd like to know whether or not this is plausible, and what problems I haven't thought about.
To be explicit, here are some of the things I'm concerned about (although there may be other problems):
- The speed of the ship means that light from the stars would be highly red-shifted (if $v=0.99c$, then $z=13.11$, which is enormous). I would hope this could be corrected for, but it's still fairly extreme.
- I really don't know for sure how much metallicity variations in the Cepheid populations would affect the observations.
- We've detected extragalactic Cepheids from Earth; Edwin Hubble used them to measure the distance to Andromeda. This makes me think that detecting Cepheids from intergalactic space is possible, but it's highly dependent on the telescope being used.
Is my method realistic, or are there some major problems I haven't thought of, like the points I raised above?
Note: I'm not asking for general methods for how to find the location of my ship. That's been discussed quite a lot (at least for interstellar travel) in How can I know where to point my spaceship?, Stellar Navigation for Dummies - Finding your way home, and other related questions. This means I'm not interested in answers involving alternative methods such as triangulation or networks of pulsars - just Cepheids, as the question says. Please don't digress into these!
0 answers
0 comment threads