Aliens exist on the other side of the nearby wormhole, but we don't know wormhole exists yet. How might they be detected and communicated with?

Question

Scenario: Humans have setup an observation/research station close enough to study the super blackhole Sagittarius A*, which in this world is a wormhole. Aliens exist on the other side. (I am flexible whether its a civilization, reserach station, Alien Joe Schmoe's pet radio project, or whatever) Neither civilizations learned/proved wormholes exist yet. Neither civilizations know about each other in any way. The technology to actually travel through the wormhole is decades if not centuries away from this scenario, but some form of information or signal "leaks" through both ways.

This "thing" that leaks through will be at first remain undetected, or thought of as background noise/random natural occurrances. Eventually after decades? centuries? of study they realize it's not random at all, its potential sign of alien life.

Both sides will eventually notice the "leakage" from the other side, albiet perhaps decades apart. Currently, I'm agnostic as to whether the humans or aliens were first. They will naturally try to study it, decipher it, then try to communicate by sending some kind of communcation back.

Question: What might this "leakage" be, how might they gather useful data from it, and how can this lead to eventual communication and have the scenario play out?

Additional Details:

• The alien civilization uses a duodecimal system. Any language or computer protocols or deciphering/communication challenges will be influenced accordingly.
• Without changing the scope of the main question, the human observation station is actually unmanned. It is constructed by self-replicating nanorobots fired from an "Alcubierre catapult" (No manned FTL yet. Not to be discussed in this question) with a quantum entangled communication capability to send information back to Humans. (Not to be discussed in this question, will likely just handwave it in) The relevance of this detail to the scope of this question might be whether or not that creates an additional layer of challenge to the scenario, for example, the necessity to build any instruments that wouldn't already be part of the existing blackhole observation/research setup.
• Discussion of anything directly related to the handwaved quantum communication is outside of the scope of this question. Discussion on any effects due to the wormhole such as time difference/lag and its impact on alien contact/communication is within the scope.

Answer 1

For the moment, both sides currently see this as the same black hole, and only that, right? So if one side starts tossing in very large masses periodically to test gravitational theories, both sides can notice it. You'll need hypersensitive gravitational instruments, but hey, you didn't get into orbit around Sagittarius A* using a grade-school yardstick, and you didn't want to show up with a bathroom scale. Any gravitational/mass changes (and subsequent Hawking radiation changes) could be detected from either side.

Since we're watching everything that's going into the black hole on our side (as are they), we'll know it's weird when all our sensors start indicating sharp, unexpected, periodic rises in the black hole's mass. We might even catapult in massive objects of our own, to double-check our current gravitational theories. And once both sides are tossing in planets or hyperspeed (high relativistic mass) projectiles at routine intervals, both sides will know something's up that they don't understand. Cue trying to understand it by altering our patterns, studying the distributions of return signals, imitating them, statistically analyzing the distribution of gravity spikes, and generally determining that there is intelligent life on the other side. (One easy way would be a simple game. We throw in one object, you throw in two, we throw in three, you throw in four (or 1, 1, 2, 3, 5, 8, 11, or whatever).

After that, it's just a tedious matter of building and decoding communication protocols, blind. But if we apply enough computing power and brilliant minds, we might be able to pull it off.

Answer 2

Charge

The way black holes are often envisioned is as singularities with only three properties: mass, charge, and spin. Changing the mass or spin of a galactic black hole significantly involves dumping tremendous amounts of material.

That leaves charge. If you shoot a proton beam at relativistic speeds (generated with a standard particle accelerator), you can charge up the galactic black hole until it can repel your protons from falling in despite their velocity. This would seem like a basic high priority experiment for any civilization studying a black hole. The process can be reversed by beaming in cathode rays (electrons), and all charges will fade away naturally quite quickly (I have no idea how quickly) because there are lots of ions floating around in space, and the opposite charge is pulled in.

If we can study the hole even from Earth we might be able to measure its charge somehow (I don't know how) based on the effects on material in the vicinity. Certainly a robot probe in orbit could feel the charge moving the hairs on its little nanotechnological arm. If we see the hole has a strong charge, despite our expectation it naturally tends to be neutral, we would be interested how the charge accumulates. If we find a positively charged black hole with positive charge streaming away from it, that's a huge red flag, because charge is conserved - it has to come from somewhere. And if we find the hole is going from positive to negative and back again without explanation, that's going to invite full-on speculations of alien involvement.

Answer 3

The aliens could detect an Alcubierre bubble crashing into our side of the black hole.

The Alcubierre Warp Drive: On the Matter of Matter

Meanwhile the region of space infront of a ship decelerating from superluminal velocity to subluminal velocity is blasted with a concentrated beam of extremely high energy particles.

You mention in passing an Alcubierre catapult. Suppose your nanobots bail out the back of the bubble at a distance from the black hole. The bubble continues on its way, eventually winding up in the black hole. The above linked article made some stir in the lay science press because of its prediction that a decelerating Alcubierre bubble would unload a huge birst of very blueshifted light and very energetic particles, obliterating anything in front of it. More of my musings here

It is clear that particles can enter a moving superluminal warp bubble and then later exit either faster or slower than when they went in. Whether the particles are in interstellar space, or a planet, or a black hole is just a matter of density.

In any case, your nanobots are used up by the environment around the black hole and so new ones are sent on a repeating schedule. The warp bubble they arrive in continues on after the nanobots exit, eventually plowing into the black hole. "Safest place for it. How can we hurt something like that?" reason the engineers in typical Man vs Nature fashion.

It turns out that compressing the stuff of a black hole into a warp bubble does definitely have effects that are detectable on the far side of the hole. "Detectable" does not do justice to the scale of these effects. These effects occur with a predictable frequency corresponding to the new nanoprobes arriving.

Once they figure it out, the aliens reply by interacting with the wormhole to produce a countdown to the next probe. The countdown of course is in duodecimal.

Answer 4

Nobody at either end will 'see' anything

Sagittarius A is thought to be approximate 25000 light years from Earth. Even if the alien civilization is parked right next to the other end of the wormhole (which would be unfortunate for them assuming their 'end' of the wormhole is as energetic as our end appears to be) it would still take 25000 years for any signal from Earth to reach the wormhole entrance. Doesn't matter if it's passive signal like reflected light showing our planet's atmospheric (life bearing) composition or an artificial man made 'hello' it's still going to take 25000 years to get there. And assuming they're equally distant from their end of the wormhole as we are from ours your talking 50,000 years!

Then on top of that assuming both societies are more or less at the same level of technological development there's no way either will be able to produce a man made/alien made/artificial signal with the power output needed to be detectable at that range. The most powerful radio broadcasts ever generated on Earth would be undetectable by any alien radio astronomer with our level of technology beyond our local stellar neighborhood (Don't have an exact range. Someone else may be able to provide one but think tens of light years not thousands!)

So we're effectively invisible to each other. Sol is just one utterly ordinary star amongst thousands of millions of others stars the aliens might observe and vice versa. Our signals vanish into the galactic background long before they get anywhere near the wormhole as do theirs. And unless both civilizations make it to the stars chances are both will be extinct long before any trace of their existence reaches the other, even if they could detect it.

The lesson? put your both ends of your wormhole a lot closer to each civilization (i.e. a few light years away not thousands).