We think of space as a vacuum, but there are regions of different density. There are winds blowing from stars and other objects that clear out vast bubbles in space, and look absolutely fantastic in pictures. And might have been critical for Earth to even exist in the first place.
Bubble Nebula (NGC 7635) (Hubblesite)
The Horsehead Nebula (NASA)
The Pillars of Creation (NASA)
HII Region (Swinburne University)
Solar Wind (NOAA)
V838 Monocerotis (Hubblesite)
Hubble Space Telescope (NASA)
Planetary Nebula (ESA Hubble)
NGC 2392 (Hubblesite)
Supernova 1987A (AAVSO)
Molecular Cloud (Swinburne University)
What is a quasar? (EarthSky)
Active Galaxies (NASA)
Galaxy Clusters (Harvard | Smithsonian CfA)
Dynamo Effect (University of Oregon)
Transcriptions provided by GMR Transcription Services
Fraser: Astronomy Cast, episode 636, Blowing bubbles in space. Welcome to Astronomy Cast, your weekly facts-based journey through the cosmos where we help you understand not only what we know, but how we know what we know. I’m Fraser Cain, publisher of Universe Today. With me as always is Dr. Pamela Gay, a senior scientist for the Planetary Science Institute and the director of CosmoQuest. Hey, Pamela, how are you doing?
Pamela: I am doing as good as one can do when spring is in high pollination. I’m having fantasies of being out in one of these vacuous bubbles in space.
Fraser: Right, where there’s no pollen?
Pamela: Where there are no trees. Yeah, yeah.
Fraser: No pollen, yeah. Yeah, again, every year, it gets a little worse for me. Every year, as allergy season arrives, I have to remind myself that I have… that I do suffer from seasonal allergies, because I didn’t when I was younger, and now I do. And to just take my Claritin and move on. So, yeah, but I definitely am a little gurgly right now.
Pamela: We apologize for any sniffles that make it through to the final recording.
Pamela: We’re sorry, folks.
Fraser: We’re counting on our editors to clean up the final audio. So, hopefully, it’ll be better. All right, we think of space as a vacuum. But there are regions of different density. There are winds blowing from stars and other objects that clear out vast bubbles in space and look absolutely fantastic in pictures. And they might have been critical for earth to even exist in the first place. So, we’re recording the show right now. And I’ve set one of these bubbles. I think it’s the Bubble Nebula, but one of these incredible bubbles in space, and many of them had been seen before.
And so hopefully, people are sort of remembering these cool photographs, and like the Hubble space telescope that really looks like a bubble, like someone has blown a soap bubble in middle of space. What is it?
Pamela: So, they are a variety of different things, the one that is behind you, the one that I’m currently showing up on the screen, these are what are called H II regions. That means there are areas where hydrogen has been ionized, that a little electron has been heated up and blown away. And these regions are created by extremely hot stars giving off ultraviolet ionizing light that over the distance where that light is intense enough to ionize the hydrogen, you get these amazing spheres of glowing gas. And the reason they look like bubbles is these spheres we see the thickest amount of the sphere around the edges. So, that’s where, well, we see these cool red areas.
Fraser: So, I just sort of imagined that you had like the solar winds and the radiation was pushing material away from the stars. But you’re saying that the intense radiation from the star itself is ionizing the hydrogen in this area and causing it to glow in a way that’s different from the I guess the background nebula?
Pamela: So, it’s a little bit of all of the above. And looking at regions like the Helix Nebula which is formed from a variety of different hot stars where you can start to see the structures, what you have is the winds from the hot stars are pushing material out. The ultraviolet light from the hot stars is creating that ionizing radiation that is creating glowing spheres around the stars. So, you have regions that are glowing brightly due to the ionizing radiation, and you have these filamentary structures that are created by the winds from the stars.
Fraser: And I guess what are the implications? Like you’ve got a young hot star that is blowing out this intense radiation, what happens to this region around it beyond it looking pretty in our telescopes? Does it stop star formation? Does it cause extra star formation? What does it do?
Pamela: So, the awesome thing about this is really big blobs of material collapse the fastest, form hot stars that create all of this amazing structure as the first thing that gets created in a star-forming region. Once these hot stars are out there doing their bubble-blowing thing blasting out the material around them, they can shock other clouds of material to collapse and form additional solar systems. So, this is part of a chain reaction of star formation that just starts with something knocking on the side of a giant molecular cloud getting that biggest thing forming, and it just all collapses down from there.
Fraser: So, you’ve got these stars, they’re blowing up these winds, they’re causing overdense regions out at the limits around them, and those overdense regions are still I guess, cold hydrogen, and so they can start collapsing –
Fraser: Into new stars. And eventually, you’re going to get overlapping stars blowing their bubbles and you’re going to run out of material that is capable of collapsing.
Pamela: Exactly. And when we look out at regions like the Horsehead Nebula, the Pillars of Creation, those not bubble-shaped areas are the remnants of material that got knocked around into the shape they are through the combination of massive stars pushing out, and then the gravity of what’s inside of them pulling in.
Fraser: Like when you look at the Pillars of Creation, and you see those tentacles, like a tentacle hand reaching up. And you can see other examples of these same kinds of nodules, it looks very familiar, very similar to what we talked about these other Bubble Nebula, but the things are kind of enshrouded in gas and dust and we can’t really see what’s going on inside of them.
Pamela: Those are just protostars. So, when they’re still enshrouded like that, those are either proplyds, protostars, it all depends on what stage in their evolution they’re in. And they haven’t fully ignited, their nuclear reactions haven’t fully turned on yet. And so they don’t have that light pressure to push everything out from around them. Over time, those pillars are going to get eaten away by the light of the stars forming inside of them. They are literally going to cannibalize themselves to form new stars.
Fraser: And then we would see the bubble?
Pamela: Well, it depends on how much material is left around and what the shape of the material is. So, I have to admit, I’ve picked and choose which H II regions to show to you because these happen to look like bubbles. What’s amazing about the H II regions is as you get different pockets of star formation, you can end up with these incredible filamentary structures of the pockets colliding together to blow a series of bubbles that you get more of a froth in that kind of a situation.
Fraser: It’s amazing to me that all of this is essentially driven by gravity. That –
Fraser: That gravity is what triggers the star formation in the first place, that the gravity pulls in these stars into denser and denser regions, pulls the gas and dust into denser regions, which turns them into stars. And then the stars because of their gravity ignite with their fusion and then are pushing out with the radiation and their own stellar winds that are causing gravity to make other parts collapse down and continue this cycle. And this isn’t necessarily what has to do with today’s episode, but literally, gravity just is just writing the rules of the whole universe.
Pamela: But light is the other side of this, and that’s the thing that always gets me is our universe is a balance between gravity pulling things together and light pushing things apart. Stars support themselves in light. Our Solar System is largely protected from the interstellar medium by the bubble that our own Sun has cleared out around us. It’s light versus gravity.
Fraser: Right, so that actually transitions into the next part of this conversation that I wanted to have. So, you were starting to go into this idea, and I had sort of mentally wanted to cover this, as well as that when we look at these beautiful bubbles, nebulae, they’re young stars, they’re hot stars.
Fraser: But we’ve got spacecraft out there examining the bubble, that the solar system, that our own Sun four and a half billion years old, is continuing to blow.
Pamela: Yes. And, so here, it’s our solar wind is the driving process. And it is thin enough, and at a temperature where it’s not really something that we can go out and just look at. But as the Voyager probes have gone on their escape trajectory out of our solar system, they’ve been able to see the kinds of particles that they’re experiencing, the kinds of fields that they’re experiencing, are varying on their journey outwards so that now they’re starting to see more and more and more interstellar medium as they leave that protective bubble.
Fraser: And I mean, I guess every star has one of these bubbles, and you call it protective, what is this protecting us against?
Pamela: There’s a lot of high-energy particles out there that get somewhat deflected. And radiation is really just not a good thing for the human body. So, I think it is safe to say that less cosmic rays is always a good thing.
Fraser: More better.
Fraser: So it’s like the Earth has a magnetosphere and then the solar system has a magnetosphere.
Pamela: Exactly. And there’s beyond the magnetosphere, literally, the solar wind is pushing out and moving the material around us. And while we don’t get to see this with our own solar system, it’s the kind of thing that we’ve had the opportunity to see in other systems. V838 Mon is my favorite example. This star for unknown reasons led off two different flashes of light, and a flash of light has a width to it. And as these expanding bubbles of light with width move away from the surface of the star, they are illuminating the structure of the material around the star allowing us to see that bubble that has been cleared out by the stars’ solar winds in the past and perhaps even enhanced through mass loss of that star.
Fraser: That’s crazy. Yeah, it’s one of these dramatic images, and especially because it’s a sequence that Hubble has been observing this star for decades now we can actually see the light echoes moving through this region, we can see how the shape of the bubbles that it has blown out or changing over time. It’s unbelievable that you sort of imagined things to work at astronomical amounts of time. And yet every now and then there are these things that are unfolding in front of us in vastly faster time periods.
Pamela: Yes, the speed of light, literally the speed of light.
Fraser: The speed of light. Now we’ve talked about young stars creating bubbles, but as stars die, they can as well.
Pamela: Yeah, and this is where on the low energy side of death we get to the planetary nebula. This is the ultimate fate of our own star. And it’s how a lot of stars out there are going to, well, eventually end their lives. What happens is the outer layers of the star during its red giant phase and beyond get let go as the star expands, and the material goes past the point that gravity can hold on to it.
We don’t fully understand the pulsation mechanism of these massive stars but stars like Mira can breathe in and out over the period of roughly a year in a rather irregular manner. And on the way back in they always bring everything with them.
Fraser: I’m sort of imagining you’ve got this star that’s pulsing and like the mere variables, the scale to which they pulse is mind-blowing that they can change on their brightness and their size, like at one point, they’re way out beyond the orbit of, say Jupiter. And then the next moment, or weeks later they’re now down –
Pamela: Several months down.
Fraser: Yeah, months later, now they’re down vastly smaller. And then they do this again at a very regular rate. And I guess each time as they are expanding outward, they’re accelerating this material away from the star, and then the star stops and pulls back in but a lot of that material is still coasting away from the star on an escape velocity. And so you get these just shells of dead star sloughed off into space, around the star.
Pamela: And exactly how they get sloughed off is going to be determined through a combination of what stuff is inside that solar system that can block the expansion of that material. So, you can end up with systems that have areas that clearly have less material or more material within them. Planetary nebulae are something we’re still working very, very hard to figure out because they come in detail where the more and more and more resolution we get on our telescopes, the more crazy structures are revealed in these planetary nebulae.
These structures are that combination of a star getting puffed out by light pressure, coming back in as best it can, and just letting go of the light eventually, as the core just stops producing more energy, collapses down to become a white dwarf. Now, the star that was expanding and contracting is doing this in an irregular matter. It’s doing it while gravitationally interacting with perhaps a binary star, perhaps planets within the system. It’s doing it while having whatever interstellar media is surrounding it.
And to understand the structure, we have to understand what was there in the first place? What influences might have changed the symmetry of the stellar wind, and everything inside that might have been adding that little extra kick is perhaps a massive planet went past.
Fraser: Right. It seems like the magnetic field of the sun, perhaps the interactions of the planets, these all play a part of the mix to create the planetary nebula. And it’s still like, we don’t even know if the sun is going to turn into a planet. Maybe the sun doesn’t have the right, raw ingredients to create a planetary nebula like we see out there. Or maybe it does. It’s funny that it used to be assumed but now it’s a bit up in the air.
Pamela: I still remain firmly in the camp of it’s going to be a planetary nebula.
Fraser: You just want one?
Pamela: Yeah, I do. It may not last very long. They don’t all last the same amount of time. But –
Fraser: Yeah. All right, we’re gonna talk about this some more in a second, but it’s time for a break.
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Fraser: And we’re back. All right, so what happens if we need a bubble and we need it fast?
Pamela: The best way to do that is to just explode a giant star, just explode it. Yeah, it’s going to release a massive kick of energy that is going to include remaindary bits of the former star and also collide with violence into any surrounding material and shock it into doing its own glowing kind of thing.
Fraser: I think my favorite example of this is the Supernova 1987 A, which was really the closest supernova that has been recorded in modern history while we had really good telescopes, and you can see this debris cloud again, year after year expanding outward with blobs of fiery material.
Pamela: And it’s a figure eight.
Fraser: Yeah, yeah.
Pamela: There’s a central bit, and then these two expanding rings that there’s literally a dumbbell of Shockwave out there.
Fraser: And this ties back to the first part of the show when we were talking about how you’ve got some triggering event that causes the collapse of star formation in a nebula in the first place. And it’s often these supernovae, these bubbles are the ones that actually get the whole process rolling.
Pamela: And they can be amazingly energetic events that are giving off gamma rays, X rays, ultraviolet light, they are heating the area around them, they are shocking them and compressing the gas around them. And if one of these goes off near a giant molecular cloud, it can be just enough force to set that giant molecular cloud out of balance between gravity in and just gas pressure out. So, the nudge of a supernova is thought to be part of what triggers this entire process in the first place.
Fraser: And that’s interesting, when you sort of imagine that you’ve got like the supernova first is just a big shock to the system that begins the process, but then afterwards this more gentle, roiling star formation continues the process until all of the fuel in the solar nebula has been used up. It’s absolutely fascinating to think about.
Pamela: And it’s really this bubble-blowing process that seems to be at the core of moving a whole lot of things around. So, at the very center of our galaxy, our supermassive black hole appears to periodically blow bubbles as well. And these are also shockers that, well, have radio bands, and these bubbles giving off high energy light, it looks currently like there are two different sets of bubbles. Again, we have that figure-eight structure where something fell to its doom in the center of the Milky Way galaxy and the high energy light that was given off while the thing was being destroyed blew out bubbles in the interstellar medium above and below that black hole. And that too can trigger star formation.
Fraser: And so this is where I was going to take this next as we talked about just stars themselves and fairly small phenomena, but these can exist at this much greater scale. These bubbles blowing out of the supermassive black hole are tens of thousands of light-years long. They’re enormous.
Fraser: And yet, it’s weird, or isn’t it interesting that they kind of fall, they’re perpendicular to the spin of this supermassive black hole that has something to do with the way this magnetic field is wrapped up around and the way it’s rotating. This material is falling in, and then it’s being thrown out in both directions. And it happened a long time ago. It happened tens of thousands, millions of years ago, and we’re still seeing the repercussions. Is it a time when the supermassive black hole might have been a quasar, might have been very bright?
Pamela: I think going all the way to quasar is a few steps too far.
Pamela: But it definitely was active at that point. And we see, essentially, they appear to expand as the shockwave moves through space. This is at a much more energetic level, similar to when an explosion goes off, and the sound waves propagate through the air creating this wind that pushes things out, and the light goes far faster. But then that shock follows behind. And there are some really cool concerts and stuff where you can see the sound propagating through the crowd as they react.
Pamela: And here what we’re seeing is the energy propagating well through the galactic region as it travels through space.
Fraser: Can we scale this up one more notch? Do we see bubbles at the galaxy cluster scale?
Pamela: I am reluctant to say the word bubble. What we do see in galaxy clusters is the region in the center of the galaxy is extremely hot, it’s giving off X-ray radiation. It’s that level of hot. But this is gravity pulling everything together and heating it up. Not some central Dynamo heating it up. We do have jets in the centers of a lot of these systems. But that’s different physics that we talked about last week.
Fraser: Right, right, right. So, you can definitely get wins at a galactic scale, coming from these collisions and interactions and so on, but not necessarily these nice, clean bubbles blowing in all directions in the same way. Well, it’s absolutely fascinating and they’re wonderful to look at. And now when you see one of those pictures, maybe you’ll know a little more about what’s going on. Thanks, Pamela.
Pamela: Thank you so much, Fraser. And thank you so much to everyone out there who makes this show possible week after week. This week I want to say thank you to a group of our Patreon over on patreon.com/astronomy cast. Thank you to Ninja Nick, Janelle Duncan, Michelle Cullen, Mark H. Widick, J. Alex Anderson, Benjamin Carryer, Frode Tennebø, Matt Rucker, and Anitusar, Schercm, Moose and Deer, Abraham Cottrill, Father Prax, Kimberly Rieck, Philip Grand, Mark Steven Rasnake, Jim McGihon, Dwight Illk, Bruce Amazeen, Jen Greenwald, Andrew Stephenson, Brent Kreinop, Dustin A Ruoff, Planetar, Gfour184, Kseniya Panfilenko, Gabriel Gauffin, Cemanski, The Mysterious Mark, Rachel Fry, Steven Coffey, Peter, Sean Martz, Joe Wilkinson, Glen McDavid, John Öiseth, The Air Major, and Benjamin Davies. Thank you all so very much.
Fraser: Thanks, everyone. And we’ll see you next week.
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