# Mapping the far side of the galaxy

Humans got a one time ticket to the other side of the galaxy, traveling $2r$ in just a few days (where $r$ is the distance from earth to the super massive black hole: 28,000 lightyears)

The stars we see are roughly 56,000 years old; now, that's not really that old compared to the grand scheme of things.

How plausible would it be for us to predict what stars would be there (considered the stars orbital period is roughly 225 million years, so that would give the stars movement a 0.08 degree movement.) Also predicting the age of the stars in terms of what star would be gone, and what new stars would have been born.

And could we, before we launch, make a map that would be usable from the other side of the galaxy?

The means of travel is of no interest to this question, the question is, can we as humans with the technology we have today and the knowledge about stars and with the predictions we can do (about star nebulae and star lifespan) make a usable map (You don't need to have EVERY star to make a map just a few "big enough" to be distinct - or am i wrong?)

Lets assume for all purposes whom ever gave us the means of travel will us nothing bad. (eg. place us inside a star), and lets also assume that it has been a one way communication, so no asking questions.

• Did you really mean to tag this both science-based and reality-check? It would be better to pick one. – a CVn Aug 16 '16 at 13:30
• @MichaelKjörling Are you sure? The two tags are complements, in my view (albeit a bit superfluous). – TylerH Aug 16 '16 at 14:09
• @TylerH Yes, because [reality-check] is for "asking whether or not a particular concept is realistic in a given context" whereas [science-based] indicates that the OP wants "answers based in hard science, not magic or pseudo-science, but do not require scientific citations". All three of the triad reality-check/science-based/hard-science also suggest alternatively the other two tags of the triad. – a CVn Aug 16 '16 at 14:12
• I edited the title because mapping while moving into a region is a very different question. You specificwlly need to know what’s there before jumping. – JDługosz Aug 16 '16 at 21:43
• vmrob brings up a good point in a comment to Jimmery's answer. Who is calling the time periods "days"? – a CVn Aug 17 '16 at 6:45

Quoting Wikipedia for a moment, we notice that

The Milky Way contains between 200 and 400 billion stars (...). The exact figure depends on the number of very-low-mass stars, which are hard to detect, especially at distances of more than 300 ly (90 pc) from the Sun.

So we're having trouble detecting "very-low-mass stars" (which might be as much as half of them) if they're more than 300 lightyears away - and the milky way's diameter (the distance we want to travel) is...

usually considered to be about 100,000–120,000 light-years but may be 150,000–180,000 light-years

So, for at least 99.8% of the distance we won't be able to know whether there's a "low-mass star" (which is still, you know, a STAR. So "low-mass" is pretty relative) in the way. Pretty risky - though we might still want to take that risk, most of space is fairly empty after all and that kind of Opportunity won't come again very soon.

The other issue is predicting where the stars will be - it might be possible for us to compute the position of all KNOWN stars... but since we might be missing as much as half of them, the uncertainity there will be rather high.

"what stars would be gone, what new stars" - new stars would be hard to predict, but we can make some educated guesses at how long a star of a certain class has to live, and how old it was when the light reaching us right now was sent out. So that at least should be doable.

As I said, we should still definitely take the opportunity - but it'll be more like "setting out into (mostly) uncharted waters" than "this cluster of stars looks promising, set a course" ;)

/edit: My numbers are a bit off since they assume a trip through the entire diameter rather than just 2x the distance from the center, sorry about that. The general points stand though :)

• If the destination is on the opposite side of the galaxy, the percentage of stars we can see is probably much lower because all the stars in the center will obscure our view of what's there. – Cyrus Aug 16 '16 at 13:12
• @cyrus Yes. Between us and the opposite side of the galaxy are other stars, nebulae, and all sorts of obstructions. I don't think we can see ANY stars on the opposite side of the galaxy. We can reasonably speculate that they are probably similar in type, number, and distribution to what we can see on our side, but that's a long way from specifics. It's like, I've never been to Berlin. I can guess that there must be streets and houses and cars and so on, but that's a long way from drawing a map. – Jay Aug 16 '16 at 13:41
• Why should will take the opportunity? If it's about being in a random unknown spot in the universe, we basically already are. If there was an imminent threat here, why not but otherwise, as you said, you're pretty much sure to end up in the middle of nowhere with billions kilometers to the closest celestial body which, most certainly, won't be able to support life anyway. – spectras Aug 16 '16 at 13:49
• @spectras basic curiosity. Sure, most people will not want to leave friends, family, home, and a pretty high chance at living to old age behind for a trip into the unknown - but I bet we wouldn't have any trouble finding enough people to fill whichever size of spaceship we're offered for this trip. Young people feeling immortal, old and/or sick people wanting to go out with a bang, anyone in between with either not enough ties to earth to be bothered by (probably) no return trip, or able to bring all their ties with them... – Syndic Aug 17 '16 at 5:59
• @spectras well, we are destroying earth right now and that probably won't change in the near future. Also overpopulation. Why are trips to Mars planned, what is there to be found? And in that case we KNOW it doesn't support life. It's an adventure and humanity is curious, that's all the reason there needs to be. – Otto Abnormalverbraucher Aug 17 '16 at 13:46

We don't know a whole lot about the far side of the galaxy. We assume it's generally similar to the parts we can see, but we have little in the way of observations of it. The galactic bulge, with its messes of stars, clouds of gas and dust, and so on, blocks our view quite thoroughly.

So we can't specify where we want to go, because we don't know. Would the nice aliens care to trade our tickets for the long-distance flight in for a few shorter journeys? They'd be much more useful.

• Or maybe travel 2r in a big circle bringing us back where we started, then use the miles for something else? – Steve Jessop Aug 16 '16 at 17:45
• @SteveJessop you need ~3,14r to get back, 2r in a big circle will only get you about 60% of the way :) – Magic-Mouse Aug 17 '16 at 10:05
• @Magic-Mouse: yeah, might have to carefully phrase how big of a circle you want. Excellent opportunity to directly test whether the universe is flat on that scale, the only disadvantage being that if it isn't you're nowhere near home. – Steve Jessop Aug 17 '16 at 10:14

# For the parts we can see

We think we could. Astronomers and astrophysicists are pretty sure that star evolution is pretty well known and we can predict what will happen in billions of years. Just google for "what will happen to the sun" and you'll see. Given that, 56 thousands years seems trivial.

On the other hand, we amassed only few hundreds years of observations of scientific value, and few thousands indirect archeological tips. All that from only one point of view - Earth. So no one could actually see anything we think we know happening.

If such journey would be possible, astronomers and physicist from all over the world would insist that it's main concern would be to verify. And no one would be surprised, if map was pretty accurate. Every little inaccuracy would be treated like finding of great scientific value.

# For the parts we cannot see

No base for predictions.

Astronomers seem to have already done a reasonable amount of mapping of the galaxy. See here, here and here. Admittedly locations on the far side will have moved. On average everything will have shifted 37.333 light years over the 56,000 year time difference between our observations and what is on the far side now. That's enough to make easy ball part corrections.

If humans did have a one-way ticket to the far side of the galaxy, provided there was sufficient time before their departure it is very promising that good approximate maps could be made. Either by conducting extensive surveys, compiling existing information about the galaxy, and integrating this into useful galactic maps. Remember the use of maps would be supplemented by interstellar navigation.

Also, if it becomes too difficult we might be able to ask those who issued the one-way ticket about to find our way around (assuming they're familiar with the galaxy's far side).

As your question asks about what "stars" would be there the answer is that we could give you a rough estimate of the composition of the stars and their densities on average as well as a rough idea of the super structure of their galactic positioning (because it should be roughly the same as what we see on this side of the galaxy so we can estimate that there will be x% of stars we see with the y type of stars of z number of stars and towards some given region that will likely be more or less densely packed), but we would not be able to say there will be star x at coordinate y or a cluster here or there, because how could we? We're blocked from seeing stars easily within our galaxy after a certain distance towards the center of our galaxy via conventional methods of viewing stars...

However, given say 50 to 100 years we may have ways to get past these problems to see where and how dense stars are as far out as we can, using Gravitational(? this may be a wrong but close to correct term) waves which we can then use to create mathematical models of the galaxy which should be fairly accurate, and should be able to even predict a rough classing of those stars based on the mass of a star being correlated to it's class.

So presently the images that a4android is about the best you'd get for a prediction, but move up 50 to 100 years (maybe even sooner) and we might be able to predict and have models that are very highly accurate.

Ok, you want to travel the distance of 56,000 light years in a few days.

As you put the "reality check" tag on your question, I am going to say this now: this is not possible.

If you traveled at the speed of light itself (which AFAIK is impossible for anything with mass) it would take you 56,000 years to reach your destination (or 20,440,000 days). And you are proposing to travel there in a few days (lets say 5 days for arguments sake).

So you are proposing to travel at over 4 million times the speed of light.

Even if you had the most accurate maps of the galaxy ever produced, traveling at that speed would destroy you, your ship, the planet Earth and anything in the nearby vicinity. Possibly even the galaxy itself.

However if you wanted to utilize some form of "Faster Than Light" (FTL) travel, then navigation becomes a different beast altogether. All methods of FTL travel are theoretical at best, but most of them involve jumping across space.

In this case navigating your way to a point 56,000 light years away is relatively easy. You find a point (or series of points) that is empty and then jump/warp/appear there.

All depends on the method of FTL travel you are employing.

EDIT:

You said that Humans got a one time ticket to the other side of the galaxy, which makes me think that this is something that affects the entire human race, and not one individual.

Who produced this ticket? And assuming the ticket is a metaphor, how did we encounter this opportunity to travel to the other side of the galaxy?

I can think of two possibilities. The first is that a more advanced race is giving us this opportunity and the second is a freak phenomena, similar to a wormhole or stargate appears within a reachable distance.

In either case the position of stars on the other side of the galaxy and whether we need to navigate around them is irrelevant.

In the first possibility it will be the advanced race that does the navigating for us, and undoubtedly they will have accurate maps of the other side of the galaxy. So we don't need the maps.

In the second possibility, we will get spat out randomly on the other side of the galaxy. Due to the interference caused by the super massive black hole in the center of the galaxy we have no way of finding out the position of stars on the other side. So the wormhole could put us within the close vicinity of a star, but more likely it will put us somewhere safe.

I think you need to provide us with more information on how you are getting to the other side of the galaxy in such a short time. This will then determine how navigation can be made and whether we can make maps of the other side of the galaxy.

• Note that "reality-check" only requires internal consistency. The combination of faster-than-light and reality-check is entirely reasonable, and in some very specific cases, even faster-than-light and science-based can make sense together. – a CVn Aug 16 '16 at 13:31
• Okay, but that's all irrelevant when answering the question as asked. You seem to have a contention about how the travel works, and then a dispute about why we'd need the maps, but you haven't provided an answer to the question. You could perhaps leave a comment or try and catch @Magic-Mouse on chat if you believe the question should be edited, but an answer is not the place for such disputes. – Azuaron Aug 16 '16 at 18:29
• In my answer I do say Due to the interference caused by the super massive black hole in the center of the galaxy we have no way of finding out the position of stars on the other side. - but the OP does ask if we could make a map before we launch - and to answer that I think we need more information on the method of travel - for instance if we were getting help from a more advanced race perhaps we could collaborate with them to make a map - or if its a wormhole maybe we could make a map by sending instruments down the wormhole before we go ourselves... – Jimmery Aug 16 '16 at 18:38
• Which is a great thing to put in a comment on the question, wait for a response, then write an answer incorporating OP's response. You have approximately 2 lines actually answering the question, which I missed because they're embedded among 28 lines that are not answering the question. – Azuaron Aug 16 '16 at 21:11
• Travel in the desired timeframe most definitely is possible if we use the traveler's frame of reference for the passage of time. Due to length contraction of everything that isn't the traveler, the distance between source and destination would be reduced. No need to travel FTL, just travel close and there will be no violations of physics. Be wary, however, as the passage of external time would be immense. You would need to travel ~99.999999999999% of the speed of light to get there in a day. – vmrob Aug 17 '16 at 3:34