Another week, another roundup of your questions. This week listeners asked: are we all going to die in 2012 when the solar system passes through the galactic plane? Did Venus make the Moon? And what will extraterrestrials see when the Sun is dead and gone? And there’s even more. If you’ve got a question for the Astronomy Cast team, please email it in to email@example.com and we’ll try to tackle it for a future show.
Are we all going to die in 2012 when the solar system passes through the galactic plane?
Did Venus crash into the Earth and create the Moon?
What will extraterrestrials see in our solar system when the sun is dead and gone?
If nothing can escape a black hole, why do images show jets of high speed particles shooting off black holes?
Do black holes attract objects gravitationally from all angles?
Has the universe already expanded so much that we’re only seeing the “local group” of larger universe?
Download the transcript
Fraser Cain: Welcome to AstronomyCast’s Question Show. This is where we answer your questions about Space and Astronomy. Hey Pamela, are you ready for the various ways the Universe is trying to kill us question show? [Laughter]
Dr. Pamela Gay: Of course. Isn’t that my favorite topic?
Fraser: It is. Although I think it’s like every second episode is going to be the various ways the Universe is trying to kill us.
Pamela: Well that’s because the Universe is trying to kill us.
Fraser: I know. The Universe really doesn’t like us. This week listeners asked: “Are we all going to die in 2012 when the Solar System passes through the Galactic Plane?” “Did Venus smash up the Earth and make the Moon?” “And what will Extraterrestrials see when the Universe has killed the Sun?” And there are even more and they’re not all about death.
So if you’ve got a question for the AstronomyCast team, please e-mail it in to firstname.lastname@example.org and we’ll try and tackle it for a future show. Alright, let’s get on with the first question.
Whitney Venter asked “I was watching a particularly interesting video (I’m guessing on like youtube or something) and it discussed the alignment of our Solar System with the Plane of the Milky Way Galaxy and how the gravitational pull of the Super Massive Black Hole in the center will pull our Planet and cause major global catastrophes…strangely timed with 2012. Do we have any proof that this is going to affect us at all?”
Pamela, are we all going to die in 2012?
Pamela: No, no.
Fraser: No, of course we’re not.
Pamela: The Mayan calendar is ending but it also restarts. It’s a cyclic kinda thing. And, really our orbit through the Galaxy it takes oh, 200 to 250 million years depending on who you talk to. And we are oscillating in and out of the disc of the Galaxy.
I’m not sure quite when that happens, but we think we’re at least several million years away from going through a troubled zone again. So again, no problems there.
Fraser: Right. So let’s just clarify this. The Milky Way is kinda like a warped record. A little bit.
Fraser: And our Sun, as it is going around the Milky Way also kinda bobs up and down in the discs.
Fraser: Sometimes it’s above the plane of the Milky Way, sometimes it’s below the Milky Way, and sometimes it goes right through the middle. So, I guess the first question is: are we going through the middle? Exactly, precisely in 2012 will we go right…perfectly?
Pamela: No. We can roughly calculate but it is always going to be rough. And the whole thing is our Universe, is kinda foamy. Not our Universe, our Galaxy is kinda foamy, and so how do you define the exact middle of foam?
Fraser: Right. So, you know that calculation will be off by several million years. And there is no way to calculate that exact moment to within a couple of years.
Pamela: Right. And so, yeah, we’re going around, we’re going up and down, but this is a process that takes millions and millions of years.
The Milky Way, it’s about 7,000 light years thick. That’s a lot and so as we’re going through this, it’s going to take us time to pass all the way through and, yeah, we’re not worried, we’re fine, really.
Fraser: Okay, but then I guess the second part of that question is once we pass through the exact perfect alignment with these Super Massive Black Holes, then will we die? [Laughter] Is this an accident waiting, death waiting to happen?
Pamela: There’s no perfect alignment with the Super Massive Black Hole in the center. It’s just sitting there. It’s a blob of mass. It is changing in no way. WE are happily far away from it. We’re going to stay happily away from it.
Fraser: But what is the significance of passing through the Plane of it? Passing right in perfect alignment with the very middle of the disc so that there’s 45 hundred light years of Milky Way above us, and 45 hundred light years of Milky Way below us, is that dangerous?
Pamela: No, not really. The only thing that we’re really worried about is that there seems to be this record in the fossils of every 26 to 32 – depending on whose papers you read – million years there’s a mass extinction here on the Planet Earth.
Some people have postulated maybe it’s because we’re going through overly dense parts of the Milky Way. Maybe it’s because there’s a Brown Dwarf Star orbiting our Solar System that disturbs the Ort cloud.
Maybe there is something else that we haven’t thought of yet. But, even that is again many million years from happening again. So, no matter what different period you look at, nothing bad is set for 2012.
Fraser: Right. And I’m gonna do some shameless self promotion here as well. We have a whole series of articles on Universe Today about 2012 written by Ian O’Neal, who is one of our writers there.
He has done a great series of covering Gravitational Solar Flares, Galactic Alignment, all that stuff so it’s great. So if you are worried about 2012, you should have no reason to be. Come check it out.
Alright, so Mel Dunkly asks: “When listening to the Earth, Venus and Moon episodes, I noticed it was mentioned that Venus and Uranus are reverse to the rest of the Planets and then heard that something smashed into the Earth to create our Moon. Is it possible that it was a collision with Venus that created the Moon and caused its strange spin?”
Now, before we do that, I think we should clarify what’s weird about Venus and what’s weird about Uranus.
Pamela: Okay. So when you look out at our Solar System, all the Planets are orbiting the Sun going in the same direction around the Sun.
It is actually counterclockwise if you are looking down at the North Pole of the Earth from above the Solar System. And, then if you look at most of the Planets, they’re also rotating in a counterclockwise direction with various amounts of tilt to the Rotation Axis.
Fraser: I think if you could imagine, if you close your eyes and imagine the Earth rotating the way you’ve always seen it, you could replace all the Planets with that.
Pamela: Except for Uranus and Venus. And they’re both problem children. Uranus is turned over pretty much exactly on its side so that it’s Rotational Axis is in the Plane of where all the rest of the Planets are. So its North Pole is occasionally pointed straight at the Sun and that doesn’t happen with any of the other Worlds.
Fraser: Right. I think one analogy is if you imagine all of the Planets spinning like tops as they go around the Sun, Uranus is on its side rolling around the Sun.
Pamela: Right. It’s the top that already fell over.
Pamela: Now, Venus is the top that flipped over and is spinning on its head. Venus is just screwed up. It somehow and there is various different models for how this happened, it either got hit with something large, or it slowly got torqued over through interactions with the other Planets gravitationally.
So there is a lot of different ways that you can get it there. None of them involve hitting the Earth.
Fraser: Well, that was the question, right? So, it’s turning backwards, right?
Fraser: Yeah. So if you look at it, while all of the Planets are going counterclockwise, Venus is going clockwise. It’s just going the wrong way. And it takes almost like a year to complete one turn.
Pamela: And, so it has this really slow rotation rate. It’s going in the wrong direction. Something happened. It either got hit or it got torqued.
You can do mathematical models that make both work. And whatever hit it was not the Planet Earth.
Fraser: Well, so how do we know, I mean you say that but how do we know that it didn’t hit the planet earth?
Pamela: [Laughter] Well, we know the mass of Venus. And if something the size of Venus had hit the Earth more than just creating the Moon would have happened.
To get the right ratio of masses to produce the Moon you have to basically make the Earth smaller and hit the earth with something the size of Mars. So whatever hit Earth was the size of Mars which is much smaller than Venus and we kept it.
So the mass that came into the collision with the Planet Earth it got redistributed so you had Planet Earth, you had Mars sized object. The two objects combined and they splashed off the Moon in the process.
Fraser: Right. And I guess you can imagine some really complicated billiards to have Venus smash into Earth and then get back close to the Sun in a nice circular orbit.
Pamela: Yeah. There is no particularly easy way to do that and there is no particularly easy way to get the right ratios of Masses. It’s, you can’t get there from here.
Fraser: Right. Now if we saw Venus in a really strange elliptical orbit careening near the Earth every few million years…
Pamela: And, Earth itself also had a crazy orbit…
Fraser: And if the Earth had a crazy orbit and it clearly looked like the two had both been bashed with something, then maybe. But Earth has an elliptical orbit that is roughly circular, and I believe Venus has actually a very circular orbit.
So, it’s just like the two have been going in their orbits the same way they have for billions of years.
Pamela: While there are changes in the orbits over time, you couldn’t have created something the size of the Moon, kept the size of the Earth, and have something the size of Venus. The three masses, there is just no way to collide and get what we see.
Fraser: Right, right. So something hit Venus, turned it backwards. Something hit Earth, created the Moon, just completely separate unhappy accidents.
Fraser: Or happy accidents. I like the moon.
Pamela: Yeah, we do, we kinda need it.
Fraser: So let’s move on. This one comes from Kyle Novak. “After the Sun completely burns out, and the Planets are left orbiting a very dense rock, or the largest diamond in the universe, what is left of the Solar System that is detectable from another Star System? What is to prevent some future spaceship from crashing into an unseen dead Solar System? Have Astronomers accounted for this unseen Mass in the models of the Galaxy?”
Alright, let’s kinda crack this open. So when the Sun burns out, what would we see or, let me put it another way, for a Star that has already done this, what do we see from here?
Pamela: Well, in general what we just see is a very small, very hot object – White Dwarf. The Universe hasn’t been around along enough for White Dwarfs to really cool off so that they’re small infrared red objects.
They’re hot. Over time they’re gonna get colder, and colder and colder, and eventually they are going to become objects that can only be seen in the infrared.
Fraser: But that’s hundreds of billions of years.
Pamela: Yeah, so we’re not worried about that right now. Right now you look out and you just see a small hot compact object. We haven’t detected any yet, but it’s possible that we could detect the Planets around or whatever Planets are left around these White Dwarfs by looking for Eclipses.
The thing is most of the Stars that have had the time to become White Dwarfs at this point they formed so long ago that they probably didn’t have enough metals for them to have had Planets. So we may not be able to find any objects like this right now.
But in the future as people are out exploring, they will be able to see Planets around the White Dwarf that will be our Sun by looking for Eclipses. They also if there happen to be any observable lines in the White Dwarf they are not ideal lines but you can if someone tries hard enough and gets lucky, they might be able to see slight shifting. That tells them there could be something there but probably not enough shifting to get a Doppler Shift to make definite detection of Planets. White Dwarfs weren’t really designed to do that.
Fraser: Right, it would take some pretty fancy, or kinda crazy flying to say, hey you know the closest way from point A to point B is right past that White Dwarf.
Pamela: Right. The Universe is mostly empty space. And so the probability of it at any point accidentally running into a Planet in the Solar System is pretty low.
Fraser: Yeah. And even so for the next hundred, several hundred billion years, even you know mediocre infrared telescopes will be able to spot the cooling down White Dwarfs. They are never going to be invisible.
Pamela: Now, the other part of this question is actually kinda cool. Have Astronomers accounted for this unseen Mass in their models of the Galaxy? Yeah, we’re trying to. That’s the cool part.
There are these two projects: Oogle and Macho, which are out there trying to find the blobs of Mass that don’t want to be seen. We’re looking for Rogue Planets. We’re looking for White Dwarfs. We’re looking for little tiny Brown Dwarf Stars. Stars that just might otherwise go unnoticed because they are too far away or they are too faint or we just can’t see them.
But if they happen to line up perfectly with the background Galaxy as they orbit around the Milky Way, they can gravitationally lens that brighter background object and make it suddenly appear a lot brighter.
So what happens is we’ll go outside and for instance using very precise telescopes watch the large and small Magellanic Clouds and look for changes in brightness in individual Stars in these two nearby Galaxies.
There’s a characteristic brightening and faintening of an object that you get with a Gravitational Lens. So if some distant Star that we otherwise couldn’t see passes right in front of one of those bright stars in the Magellanic Clouds, we’ll see a characteristic brightening and faintening and we can go, oh, there’s something there. Then we can start to figure out when we do this long enough, just how much stuff is out there that we’re otherwise not detecting.
They’ve been doing these couple of projects for about 10 years now, over 10 years now. We can say well there’s really not that much that we didn’t account for. It was kind of hoped that maybe we’d find enough Rogue Planets, enough Rogue Brown Dwarfs that Dark Matter wouldn’t be quite as worrisome of a problem that it is. But now we’re looking at less than a percent is random, otherwise unanticipated stuff.
Fraser: Right. So this is actually a very important question that Astronomers have been wondering and they’ve done a pretty detailed survey. The answer seems to be no. It does not account for Dark Matter.
Fraser: Okay. Good question. Let’s move on. This comes from Joseph, no last name. “I always hear that nothing can escape a Black Hole; not even light. When I see diagrams or animations of Black Holes, they have giant extragalactic jets of high speed particles coming away from them. I’m sure that has something to do with the Black Hole’s Magnetic Field, but if nothing can escape the Black Hole, wouldn’t that include the Magnetic Fields as well?
So, is this true or does it only apply to things that have crossed the Event Horizon? So I know what Joseph is talking about…you have a Black Hole and you have this great big disc sprayed out on either side of it and then these jets that are coming up from top to bottom. So, are those caused by the Magnetic Field?
Pamela: Yes. But it’s not the Black Hole’s magnetic field. It’s the Accretion Disc’s Magnetic Field.
Fraser: Right. So that disc of material is generating the Magnetic Field and so it’s not escaping from the Black Hole itself.
Pamela: Right. The Accretion Disc is outside the Event Horizon.
Fraser: So if the Magnetic Field was coming from the Black Hole, would that be able to escape a Black Hole?
Pamela: This sort of starts to get back into the can Gravitons escape Black Holes question.
Fraser: But isn’t a Magnetic Field part of Electromagnetism? Isn’t it just the same thing as Photons in another form?
Pamela: Right. And here’s where you start getting into weird things. I was looking at some Web sites earlier that were talking about how Black Holes can have Static Electric Fields and you’re working with Virtual Photons that aren’t really real, and so they are able to communicate information.
It starts getting really confusing. This is where I have to say I just don’t know. We’re still trying to build coherent models because Gravity and Quantum Mechanics don’t work together.
Fraser: Right. Well I think that’s probably going to be another week. Because we’ve actually got about 10 questions like can Gravitons escape a Black Hole?
Pamela: And I’m looking for a Particle Physicist to hold hostage and explain this to me. The one in my department keeps hiding.
Fraser: Alright, well then…
Pamela: I’ll bribe him with cookies.
Fraser: That makes sense. So why don’t we tackle that separate part then for a future question show, promise. [Laughter]
Pamela: We’ll probably do a whole show on it: How Forces escape Black Holes.
Fraser: Our next question is quite related to that. This comes from Jason Wood. “I’ve noticed in illustrations that Black Holes appear to have a front and a back and a disc swirling around them. Shouldn’t the Black Hole be gravitationally attracting objects from all angles?”
Once again, you imagine that you know it’s like a plate spinning with these the jets coming off the top and bottom. Wouldn’t you just have like a ball with blobs just coming in directly straight down? Why do you have that shape?
Pamela: That actually comes down to Conservation of Angular Momentum. Pretty much everything in the Universe is spinning in one way or another. The only way you can get two objects not spinning is if they happen to collide exactly center to center. And that’s hard to do.
Pretty much any other collision is going to introduce rotation into the System. And over the course of the Universe everything has had a chance to interact and end up spinning. Once you start getting Preferential Dynamics, I mean look at the Spiral Galaxy you have a nice flat pancake of material that is all collectively rotating in one direction.
As material falls into a Black Hole it generally isn’t heading straight toward the center of the Black Hole, but is off to one side. That allows it to set up in a disc. Even if something tries to fall in counter to the rotation of the disc, as it hits that spinning disc it’s going to get caught up in the momentum of the spinning disc and end up rotating as well. So we end up with this rotating disc of material around a Black Hole. Disc is the natural structure that rotating bodies fall into.
When you start looking at anything that you throw up in the air and rotate, you end up with what we call a Fictional Force. There’s a great XKCD cartoon on this.
When you spin something it feels like it’s experiencing an outward Force and it actually ends up flattening. The math gets ugly. You start looking into different frames of references. The result is you spin something it flattens out.
Fraser: But I think a good analogy for that is you’re sitting in a bathtub and you pull the drain why doesn’t all of the water just go straight down the drain? It’s like, it doesn’t fit. It’s too much, right?
Pamela: It’s too much. It can’t all get in there at once. And the reason you don’t end up with a stationary backlog is there is always some sort of little instability that makes the right side move forward faster than the left or the left side faster than the right. This slight difference in the way the water is flowing on either side of the drain ends up getting accerlated and creating this spinning action.
Fraser: Right. And so the same with the Black Hole. If a Black Hole wasn’t getting very much material and it was all coming straight in it would just plunge in and just go fip, fip, fip and just disappear into the Black Hole.
In some cases there is just too much material to all fit in at once or it doesn’t quite hit. It just gets caught up into this disc and so it spins. That’s why we get it. And that’s why we get the Solar System, and that’s why we got the Milky Way, and that spinning, that material coming together, as the material comes together it spins.
Pamela: Angular Momentum. It’s the bane of everything in the Universe and what makes it all flat.
Fraser: Alright, let’s move on to the next and last question. This comes from William Berry. “So in the ‘End of the Universe part II’, you mentioned that they won’t have any evidence that we live in the Universe larger than the Local Group. It will seem as if the Local Group is all there is. And then that will crash into itself from Gravity. How do we know that this isn’t currently the case?”
So, I think what William is talking about is the episode II of our ‘End of the Universe’ we talked about how because of the expansion of the Universe because of Dark Energy there will come a time when the distant other Galaxy Clusters will go below the horizon where they will be going away from us faster than the speed of light.
Light from those objects will never reach us so we won’t even know that they are there. If we look out into Space all we’ll see are the Galaxies of the Local Group. So the question then is how do we know that this hasn’t already happened?
How do we know that the Universe that we see isn’t just the remnants of some bigger Universe that is accelerating away faster than the speed of light so we can’t see it?
Pamela: Well the answer is it is actually that Universe as well. There are, depending on how large the Universe actually is (and this is the thing, we don’t know how big our universe actually is we probably only see a small fraction of it) there are probably parts of the distant Universe that are accelerating away from us faster than the speed of light due to the expansion of the Universe.
It’s not things moving faster than the speed of light. It’s the stuff between us and them. When you add up all of the expansion bits you end up with the expansion of the Universe carrying those things away faster than the speed of light.
So there are already parts in the Universe we’ll never be able to see. And the parts that we’ll never be able to see are getting closer every day as more and more stuff is carried far enough away that it’s beyond our reach.
We’re basically in this shrinking bubble of Universe that we have the potential to see. And well every day we’re sort of kind of able to see a little bit more of the Universe. There’s also more stuff that is getting carried away such that we’ll never be able to see it.
Fraser: But don’t we know that the Universe did start at a specific point and time? I mean we know of the Big Bang Cosmology because we see several lines of evidence, but one is that we see the cause of Microwave Background Radiation.
Pamela: Right now we are able to see things that go 13.7 billion light years away in time. And so we’re able to understand the Universe. It is expanding. We can see things that are moving away from us at different rates so we can see how the expansion rate is changing over time. We can see the Cosmic Microwave Background.
Eventually all of that stuff is going to be gone. We won’t be able to see any of those parts of the Universe. So yeah, there’s already stuff we’ll never be able to see. But some of the stuff we can see today is going to disappear as well given enough time.
Fraser: Right. And a good example is with the Background Radiation. We see it in microwave because the Photons have been stretched out so far already.
I mean they started out as visible light and now we see them as microwaves and the problem is that in the far, far future, they are going to stretch out to be radio waves. They are going to be Cosmic Radio Background Radiation.
Fraser: And then eventually they will stretch out so far that the wavelength of those radio waves will be bigger than the Solar System; bigger than the Galaxy. There is no way to detect them.
And so we just won’t see them anymore. We will still be hit by Photons from the Background, but we just won’t be able to detect it. So the fact that we can see it today tells us where and when and how it happened.
Pamela: And we’re going to lose all of that information. It’s a kinda sad future.
Fraser: Yeah. Okay. Good, well I’m glad we could do another death episode.
Fraser: And I’m sure it’ll be every second episode is going to be the death episode. And, yeah, alright, and next week back to our regular show.
Pamela: Sounds great. I’ll talk to you later.