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Warning: this review has a lot of astronomy and physics in it!
As the episode opens, we see a nice special-effects view of a binary star system, with a red giant transferring mass onto a companion star. There is a bridge of gas connecting the stars and an accretion disk around the companion. The companion star brightens suddenly and an apparent shell of gas (or is it just light) explodes off of the companion star. Suddenly, there's nothing in the location of the companion star and only the accretion disk continuing to fall into...a black hole.
We pan to a planet orbiting the red giant, where SG-10 is frantically running toward the stargate - apparently they are well aware of the black hole that has just formed and know that it's going to be bad news for them. Their voices and motions are oddly distorted toward slow motion, due to the gravitational time dilation caused by their proximity to the black hole. While they do manage to dial the stargate, they never make it back to the Earth.
OK, so here's the first of what will probably be many astronomy interludes. The binary system that the writers have created is only marginally realistic. At first, I thought of the most typical binary system that has a red giant donating mass to a companion, and in that typical system, the companion would be a white dwarf. However, when a white dwarf explodes in a supernova, it is destroyed completely and doesn't leave a black hole behind, so that doesn't work.
Black holes are generally created by a high-mass star reaching the end of its life and dying in a supernova explosion, where the star's core is left behind as a neutron star or black hole. However, the stars in a binary system typically form at the same time, so the higher-mass star will die first, and it would be the one to explode in the supernova. But, the star that does NOT explode is a red giant, so it is in the process of dying first and thus should be more massive. For that reason, it didn't make sense to me initially that the companion star would explode in a supernova. However, in unusual cases, if the red giant donates enough mass to the companion star, then this can "artificially" accelerate the aging of the companion star (because it's becoming a more massive star), so in principle, this would speed it along to a supernova death. (An alternate case would be a neutron star companion turning into a black hole, but in that case, there would be no explosion, so I'm disregarding that.)
Either way, the problem with the supernova set-up in this case is that a lot of the dying star's mass is blown away in the supernova explosion. The star has to have a minimum of 8 solar masses to explode in a supernova, but only about 3 solar masses will be left behind in the black hole. That's a lot of mass exploding outward! Because of this outward explosion of hot gas, it's likely that the planet's surface would be devastated. Even if not, since the black hole suddenly has a lot less mass than its progenitor used to, the orbit of the binary system will change drastically. The orbit will become much larger, and it's even possible that the two stars will separate and no longer be a bound binary system. All this goes to say that the planet orbiting the red giant should not end up being anywhere near the black hole and so it shouldn't be affected as dramatically as the show depicts. Contrary to what O'Neill says later on, black holes don't "suck" things in arbitrarily, any more than the Earth or the Sun "sucks" things in with their gravitational forces.
OK, so I'll accept the black hole set up. At least the writers were trying to be authentic, and probably for anyone but an astronomer, these issues would be negligible details.
Back at the SGC, they know that SG-10 opened a wormhole home but never returned. Also, their radio signal containing their identification had a much smaller frequency than normal. (Of course, Carter realized on the fly what was happening and had the signal increased in frequency until they recognized it.) General Hammond orders them to dial up SG-10's planet and send a MALP through to assess the situation. O'Neill is oddly very eager to lead SG-1 through on a rescue mission. I have no doubt he would be the first to volunteer to lead a rescue, but I thought he was way too eager, given that nothing was known about the situation. I felt like the writers just set this up so O'Neill would realize later they would've all died if the rescue had proceeded immediately.
The MALP's return signal is also strange - the image looks red, and they are getting the signal at a very slow rate. When they figure out how to correct the image, they see that SG-10 seems to be frozen in position, running toward the stargate and screaming. The accretion disk around the black hole is visible in the sky. As Carter will soon deduce, the light has been redshifted due to the gravitational time dilation caused by the black hole.
There are two issues here, and in my thinking, they got one right and one wrong. First, they find out that they've only gotten a few frames of video from the MALP instead of the hundreds or thousands of frames they would get per second. This is correct - time on the planet is progressing much more slowing than time in the SGC, so on the planet, there's only been time for a few frames of video to be taken.
But, the image shouldn't appear "red" to the SGC. To the MALP on the planet, everything seems normal: the speed of time, color, sound, etc. The MALP should record normal-looking video. What is distorted is the frequency of the radio signal transmitted to the SGC, just like SG-10's GDO signal originally was distorted. Once the SGC corrects for this, the video should appear normal.
In short order, everyone realizes that they cannot rescue SG-10. Anyone that goes to the planet will instantly be stuck in the same predicament. I liked how O'Neill knew this immediately - it was established was back in the first episode "Children of the Gods" that he is an astronomy buff.
Now the real problem appears: they can't turn the stargate off and disengage the wormhole. At first, this is only an annoyance that they can't dial any other systems or bring back teams that are away. (Incidentally, Daniel is off-world with another SG team and is absent for most of the episode.) They try some pretty standard methods for turning off the stargate, like disconnecting power and so on. There's no real urgency and they are just working the problem.
But on the surface above the SGC, we see that there is more going on than we realized. The surface guards have lost contact with the SGC inside the mountain, and so they've followed their protocol to notify a special forces team and other contingencies. Since the SGC is obviously a very critical operation, this is taken as an emergency situation and even the president is involved.
A special forces team goes down an access tunnel to ascertain the situation in the SGC. Meanwhile, Hammond is coming up to the surface because he can't reach the president on his special red phone. When Hammond encounters the operation on the surface, he's quickly briefed and whisked off to talk to the joint chiefs and the president about what to do.
And what is the big problem? When the special forces team gets down below and encounters the rest of the SGC personnel, we find out that the SGC is experiencing time dilation from the wormhole connection to the vicinity of the black hole. Time in the SGC is progressing more slowly than at the surface, hence the cut-off in communications.
I liked how the writers kept Carter too busy up to this point trying to disconnect the stargate, which explains why she hadn't noticed any signs of this happening. Once she is briefed, she quickly figures out that the time dilation effects are strongest closest to the stargate and that they lessen farther out. But, the effect is increasing and spreading. She also notes, which I appreciated, that the gravitational effects of the black hole are also being transmitted through the black hole, but in defiance of physics, the gravitational effects are delayed compared to the time dilation effects.
She's completely correct: that does defy physics. It's the curvature of spacetime by the black hole that causes both what we perceive as gravitational force and time dilation. They can't be decoupled, at least, not if General Relativity is correct. (The implication here by Carter is that our Theory of General Relativity must not be correct, or not in this situation.) But they don't have time to ponder theory - they have to figure out how to turn off the stargate. Otherwise, as the gravitational effects DO spread, the Earth will be shredded and pulled into the black hole through the stargate.
Here is where the episode's writers take advantage of the time dilation effects. At the surface above the SGC, time is progressing normally, faster than within the SGC, so the people there have "more time" to figure out a solution. For example, Hammond goes to Washington, DC, and back over 18 hours but seems to return to the SGC in something like a few minutes or an hour. Hammond's orders: activate the self-destruct for the SGC, hoping this will destroy the stargate and cut off the connection to the black hole. Carter worries that the stargate is too indestructible for that and would survive the blast, only to stay buried in the mountain and enable the black hole to gradually pull the Earth in.
Hammond doesn't think Carter's instinct is enough to counteract the orders from the joint chiefs, so he orders the SGC to be evacuated except for two volunteers to set off the self-destruct before leaving. O'Neill volunteers of course. As does Colonel Cromwell, the leader of the special forces team and apparently former comrad of O'Neill's. Everyone leaves, while O'Neill and Cromwell wait for 5 minutes before setting off the self-destruct.
While O'Neill and Cromwell are waiting, they finally bring up why O'Neill obviously doesn't like Cromwell: O'Neill and Cromwell were on a mission together in Iraq. During the mission, O'Neill got shot and Cromwell thought he was dead, so Cromwell ordered the evacuation of the team. O'Neill obviously did not die, but instead spent four months in an Iraqi prison. Clearly O'Neill holds it against Cromwell for leaving him behind.
But 5 minutes in the SGC is some 6 hours at the surface. Carter, Teal'c, Hammond and the rest go to the surface to wait to see what happens. Carter continues to work through the problem. Eventually she realizes that a better solution is not to blow up the SGC overall, but to set off an explosion at a certain position near the stargate. This won't destroy the stargate, but would cause the stargate connection to "jump" to another planet, similar to what happened to O'Neill and Carter in season 1 in "Solitudes" that caused them to go to the buried stargate in Antarctica.
This plan apparently gets approval, because Carter, Teal'c, and Sargeant Siler appear down in the SGC with 1 minute left before O'Neill is supposed to set off the self-destruct. Now, O'Neill and Cromwell will take the special explosive close to the stargate and set off the timer to detonation.
This is where things get really tricky and the special effects get really fun. By this point, the gravitational effects of the black hole have spread enough into the SGC that things are starting to "fall" toward the stargate. The big picture window between the control room and the stargate room has shattered because of too much pull from the black hole on the window. Carter, Teal'c, and Siler set up a pulley system to "lower" O'Neill, Cromwell, and the bomb on three separate ropes. Why can't they just use a timer on the bomb? They aren't sure exactly what the difference is in the time dilation between their location and near the stargate, so they might set it off at the wrong time. I feel like this is actually pretty reasonable.
O'Neill, Cromwell, and the bomb start going down. Pretty soon, they start feeling the extreme gravity - they feel like they weigh a lot and moving is difficult. This is quite accurate.
Of course, we need something to add suspense. A window separating the control room from the stargate room shatters, and the shards of glass fall toward the stargate. Since the gravitational force gets stronger closer to the stargate, the shards become like daggers and injure them. One of the shards ends up being poised to cut one of the ropes. O'Neill and Crowell star setting the bomb to explode. Cromwell's rope breaks, but he is able to grab O'Neill to save himself. But O'Neill isn't going to be able to hold Cromwell and manipulate the bomb, so Cromwell lets go and falls into the stargate. O'Neill starts the bomb and starts climbing back up his rope. Teal'c and Carter start pulling as well, and O'Neill manages to get far enough away to survive.
When O'Neill regains consciousness in the infirmary, the situation has been resolved. The stargate jumped to another planet, as planned, and they turned it off. The Earth is saved. Daniel is back.
This was a really fun episode. Even though I picked apart the black hole physics, I thought the fact that they even tried to put in the correct physics and make a story out of it was great! The physics that they did include was correct in spirit, even if not literally, and which viewers are ever going to be in the situation where they need to know the literal correctness of black hole physics?
In the long term of the series, though, this episode doesn't have many ramifications. Obviously the SG teams will never go back to the black hole planet. This episode does establish the idea that effects from the other side of the wormhole can come through the wormhole.
We didn't get much character development in this episode. The bit of history between O'Neill and Cromwell felt pretty forced into the episode, and it seemed obvious that Cromwell was going to redeem himself in O'Neill's eyes by dying in some way.