It’s been a while since we checked to make sure the Universe was still expanding. Yeah, apparently, that’s still a thing. But in the last few years powerful new telescopes and expansive surveys have given us much more knowledge about what’s happening.
What is the Big Bang? (EarthSky)
Supermassive Black Hole (Swinburne University)
Dark matter (CERN)
What is a neutrino? (Scientific American)
Dark Matter (show) (IMdB)
James Webb Space Telescope (NASA)
The Hydrogen 21-cm Line (Georgia State University)
Formation of Spectral Lines (Lumen Learning)
Giant Space Bubbles (NASA Goddard)
Epoch of Reionization (MIT Haystack Observatory)
Transcriptions provided by GMR Transcription Services
Fraser: Astronomy Cast, Episode 597: The Expansion of the Universe Revisited. 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?
Dr. Gay: I am doing well. How are you doing, Fraser?
Fraser: Okay. There’s been a big outbreak of COVID here on the Vancouver Island.
Dr. Gay: Yeah.
Fraser: It’s pretty bad. My son’s high school had, I think, eight cases and they had to quarantine about 90 people.
Dr. Gay: Oh, God.
Fraser: It got into a nursing home here in the region, another couple of schools. So, it’s like the worst case of COVID. I know I’ve been glad to be living on an island far away from everything, but we still have to keep our defenses up. Clearly, it broke through the defenses and has been having a party, here, in my part of Vancouver Island.
Dr. Gay: Yeah.
Fraser: Yeah. It’s kind of a pain.
Dr. Gay: It seems like this is going around. I’m personally – we’re trying to quarantine our different segments of our house. My husband got some stomach something last weekend. Not the one that was yesterday, but the one that was a week before and ended up in the ER and they had him unmask and they admitted him to the ward and they transferred him between sections of the hospital unmasked. They weren’t testing people for COVID before putting them on the ward. So, in the utter fullness of precaution, we’re doing – okay. This is your quadrant of the house. This is my quadrant of the house.
Dr. Gay: And be masked everywhere else because, unfortunately, you have to walk down the hallway to use the bathroom in my house.
Fraser: Right. So, you’re looking at two weeks of caution. Yeah.
Dr. Gay: Yeah.
Fraser: Because, for both of you – neither of you want to get this.
Dr. Gay: No. No. Absolutely not.
Fraser: All right.
Dr. Gay: Oh, but we’re here to discuss science, which is far more exciting. Before we do, this your reminder: newest guidelines are – my dog just took my headphones off.
Fraser: Those are not the newest guidelines. She can’t hear me because her dog took her headphones off.
Dr. Gay: I have…
Fraser: There’s no way those headphones are staying on. That dog is going to take them off every time.
Dr. Gay: So, I have an emotional support dog quite by accident. I got her the day I quit a job and she learned, because I picked her up every time I was upset, how to be an emotional support dog and she could tell I was upset talking about COVID and was simply trying to do her job. But, what I was going to say is the latest guidelines are: wear an N95 mask or a K95 mask with a surgical or cloth mask over it. So, all of you out there, stay safe, double mask. We’re going to get through this somehow, eventually, but before we get through it, we’re going to talk about science because the science keeps going.
Fraser: Yeah. It’s been a while since we checked in to make sure the universe was still expanding. Yeah. Apparently, that’s still a thing. But, in the last few years, powerful new telescopes and expansive surveys have given us much more knowledge about what’s happening, especially at the earliest times. We’ll talk about that in a second. But, first, let’s have a break.
And we’re back. All right, Pamela. Now, we, of course, have talked about the expansion of the universe. The inevitable, ongoing expansion of the universe at the largest scales.
Dr. Gay: The heat death.
Fraser: Yeah. The eventual heat death that the time when all matter in the universe was compressed incredibly close together. But, every single part of this process is constantly being analyzed and as it does, more questions pop up. New studies have to be made. New experiments are launched. New instruments go up. So, although we know, roughly, the universe is expanding, there’s little pieces of this puzzle – hundreds, thousands of little pieces of the puzzle and scientists have been making really interesting incremental discoveries and advances across the board. So, there’s some really interesting new advances that you wanted to talk about.
Dr. Gay: Right. So, I want to assure everyone. At the biggest, broadest scales of understanding the universe, we have it. We’ve got this.
Fraser: The universe is expanding.
Dr. Gay: The universe is expanding. We see the cosmic microwave background that tells us that the universe came from this thing that we have termed The Big Bang. We understand that cosmo-nucleosynthesisoccurred. We get the correct ratios of the elements coming out of The Big Bang. Where we run into trouble is anything involving detailed understanding of structure or what has happened since that cosmic microwave background was released.
Fraser: Mm-hmm. So, let’s talk about what – again, in broad strokes, we know you have the universe, the universe was a hot, dense state, cooled down to the point that, in the beginning, it was opaque because it was so hot. It was like the interior of a star. Cooled down to the point, roughly the temperature of a red, giant star, red dwarf star, that light could finally escape out into the universe. What came next?
Dr. Gay: So, at this point, our universe was a neutral gas, for the most part. It was more or less of constant density, but the slightest variations between that more and less constant density, created places where dark matter and regular matter, the stuff we’re made of, that our tables are made of, could gravitationally collapse into a density capable of forming stars and galaxies.
Now, the timescales that that happened on is our first point of confusion because really hot gas, you can’t collapse it down. Really hot dark matter, not going to collapse down simply because the energies of the individual particles ricocheting off of each other, through interactions, are going keep things expanded out against gravity trying to collapse things down.
But, somehow, at a timescale we’re still figuring out, things did collapse down and this is where the chicken and the egg problem comes up.
Fraser: Right. And just to put a finer point on this, we have this situation in the Milky Way where you’ve got clouds of gas, cold gas left over from The Big Bang, but it doesn’t turn into a star because it’s just hanging out there in perfect balance.
Dr. Gay: Yeah.
Fraser: It takes some kind of kick, some kind of event. Hot gas, forget it. There’s no turning that into a star. So, what do we think, now, was the way this all got kicked in to place?
Dr. Gay: So, when we first discussed this many, many years ago, I said that we were trying to figure out exactly how galaxies scaled up, how soon small galaxies formed, how quickly small galaxies merged into ever larger and larger galaxies. Then, we got the big telescopes built and we started looking back at the earliest moments in the universe with the Atacama Large Millimeter Array, with the MeerKAT facilities out in South Africa, with all the radio telescopes in Australia and we discovered that at the point that we thought the smallest galaxies would have just started to be forming; a few hundred million years, 600 million years, after The Big Bang. There’s already perfectly formed massive galaxies hanging out, doing their massive galaxy thing. So, we hit the timescales wrong.
Dr. Gay: Yeah.
Dr. Gay: So, it appears that dark matter plays a slightly different role than we thought. The original thinking had been that luminous matter would fall into these big, diffuse dark matter halos and form little, tiny systems because there was no easy way to channel enough material into these dark matter halos that it could form galaxies. Well, apparently, turbulence, when material falls in and it’s churning as it goes, is able to give off enough energy that you can have turbulent collapse to form that massive galaxy. Okay. So, we’ve figured out the massive galaxy. And what’s cool is we can actually see the cooling filaments from this in new images that have just been published in the past few weeks. But, then comes the problem of, how do you get a supermassive black hole to form fast enough? Here, we’re starting to think either more turbulence, or there are theories that are showing you could do it with dark matter. For years…
Fraser: Whoa. Whoa. Whoa.
Dr. Gay: Yeah.
Fraser: Okay, I’ve got about a thousand questions and we’ll get to them in a second.
Dr. Gay: Okay.
Fraser: But, first, let’s have a break.
Dr. Gay: Okay.
Fraser: And we’re back. All right. Okay. Supermassive – okay.
Dr. Gay: Yeah.
Fraser: So, supermassive black holes.
Dr. Gay: Yes.
Fraser: Which are enormous black holes, millions of times of the mass of the Sun at the heart of every galaxy. Blah blah blah. You’ve heard that a million times.
Dr. Gay: Yeah. Yeah. Yeah.
Fraser: And dark matter, we don’t know what that is.
Dr. Gay: Right.
Fraser: Can it turn into a black hole? Well, probably, sure, because everything goes into black holes.
Dr. Gay: It’s stuff.
Fraser: How would you get dark matter, which we don’t even know what it is, turn into black holes, which we kind of don’t even really know what they are, what’s inside them. How would this work?
Dr. Gay: Well, according to some of the latest theories, if you take, say, a billion solar masses of dark matter particles that have a mass similar the mass of a neutrino, and we’re starting to think that dark matter is probably pretty similar to neutrinos in whatever configuration it is in. If you pile all of the mass together, it will naturally collapse. The gravity will overcome whatever kind of pressure is supporting dark matter and allow it to collapse down into that supermassive black hole on timescales that match these youngest massive galaxies that we’re seeing.
Fraser: Right. I just want to have a tangent, here, for one second.
Dr. Gay: Okay.
Fraser: That is that when we talk about dark matter, we talk about this weird, invisible particle that only interacts with regular matter through its mass. It doesn’t give off any light and people have this – I don’t know. They have this response. This immediate, knee-jerk response, like, “That’s impossible. I don’t like it. Science wrong.” But, look at the neutrino.
Dr. Gay: Yeah.
Fraser: The neutrino is – fits the bill for dark matter in almost every single way. That it is essentially invisible, on average, a neutrino will go through a lightyear of lead. I call that not interacting with regular matter.
Dr. Gay: Yeah. It fits.
Fraser: In theory, pack enough of them together – have enough neutrinos and you’ll have yourself some gravity. If you’re okay with being fine with the idea of neutrinos…
Dr. Gay: …Which we detect on a regular basis.
Fraser: Which we detect on a regular basis, but were very difficult and were only detected fairly recently with enormous experiments and up until that point, they were just entirely theoretical. Just the math predicted them. That if you have a problem with dark matter, but you’re okay with neutrinos, it’s really – they’re almost the same thing. It’s funny. It’s just that one has been detected and the other hasn’t and…
Dr. Gay: And the one has a name that sounds like a particle and the other sounds like it was made up.
Fraser: That sounds like a particle. Yeah. So, is that the problem?
Dr. Gay: I think so.
Fraser: That we just – that dark matter just doesn’t have a really cool name?
Dr. Gay: Yeah. I’m willing to go with that. It sounds like a sci-fi show. In fact, the name was for a sci-fi show.
Fraser: I know. I know. So, okay. I feel like I’m finally – I just developed a new way to talk about this. So, I guess, the point being we know that dark matter doesn’t interact with regular matter and it doesn’t interact with itself either.
Dr. Gay: Yes.
Fraser: So, the only way that you could make this happen is if it was just in the same region at the same time with enough density to create a black hole.
Dr. Gay: That is exactly what it is. Any time you get enough mass together that the gravitational attraction in towards the center can overcome whatever form of pressure is supporting the material, it will collapse into, potentially, a black hole. In this case, it does it on the correct timescales, in the correct amounts of mass, and it just makes sense. The idea is that dark matter, which is the bulk of the universe, was able to fall into a dense enough halo that it could collapse into a black hole faster than all that luminous stuff that’s coming in from way further away was able to collapse down.
Fraser: Right. And would be getting pushed back based on the heat.
Dr. Gay: Exactly.
Fraser: Right. Really interesting.
Dr. Gay: It all comes down to the density of the stuff throughout the universe.
Fraser: Right. What else have you got for us?
Dr. Gay: So, we’ve also been trying to work out the details of, how do you take a universe made of neutral gas, which is pretty opaque, you can’t look through it, and you turn it into this transparent universe that allows us to look billions and billions of years across space and time to see all this stuff happening? We tried blaming quasars, we tried blaming star formation, but we needed data to do it. The amazing this is, we’re finally starting to be able build the telescopes, that work from them surface of our planet, to figure this out. This was supposed to be done by the JWST which has refused to launch for the last 11 years.
Fraser: October. October 31st. It’s gonna happen. We’re only nine months away now. Not even. Seven months away. Seven and a half.
Dr. Gay: And how long will it take to be fully commissioned and working?
Fraser: A day.
Dr. Gay: It’s gonna take longer than that to get from the surface of the Earth to its orbit.
Fraser: All right. All right. Fine.
Dr. Gay: So, all this really cool science was supposed to be done with the James Webb Space Telescope and we’re an impatient lot, us astronomers. When you refuse to finish building our space telescope, we start finding other ways, apparently. I haven’t. I bear no responsibility for this.
People far better at engineering than I am have figured out how to build ground-based telescopes working in radio waves, submillimeter waves, and as they ply these longer wavelengths of light, they’re looking back to the beginning of the universe and they’re starting to be able to measure massive star formation. They’re starting to be able to see how it literally was, those first stars lighting up that made our universe transparent, but what was also really cool is you end up with bubbles of material getting pushed out by early supernovae. So, it’s this one-two punch of material getting pushed out as well as the illumination from the stars.
Fraser: All right. We’ll talk about that some more in a second, but first, it’s time for another break.
And we’re back. So, I do love this idea that astronomers find a way. That even if the telescope that they’re depending on to peer into the dark ages of the universe takes, I don’t know, a decade longer than expected, that they come up with an entirely new technique using Earth-based, fairly inexpensive radio telescopes. Just a large array of them sitting in the desert of South Africa to see this time. So, what is the technique that they’re using?
Dr. Gay: It’s interferometry. It’s a way of taking the light of multiple different small scopes and combining it together to create a much more high-resolution ability to look at things. The amount of detail you can see in anything is determined by how big it is from edge to edge, but it doesn’t have to be complete from edge to edge. So, you can take a mirror and turn it into a honeycomb and its ability to detect details will be exactly the same as when it was a solid piece of glass. It’s going to weigh a lot less and take up a lot less space. With optical telescopes, we don’t generally do that, but with radio, we will scatter telescopes all over an entire continent. Sometimes all over…
Fraser: Sometimes a planet.
Dr. Gay: Yeah. Exactly. You don’t want to cover that much ground with radio equipment. So, to get these very high-resolution images, they’re combining telescopes spread out over miles and kilometers, and kilometers and miles. Each telescope is able to gather a certain amount of light and because there’s enough of them, they can also detect very faint signals. So, you have the amount of collecting area gives them faint, the edge-to-edge size gives amazing resolution. Put it all together, find a tunnel that is mostly empty between here and some distant object and, finally, you can see that distant object.
Fraser: I want to talk just a little bit about the technique that they’re using. Are they going after the 22-centimeter line specifically? Or…
Dr. Gay: No. So, what they’re actually doing is they’re looking for some of the ionization lines that come from star formation. So, we start seeing the Hydrogen 21-centimeter line that’s the wavelength of the light we see that’s coming from hydrogen gas and large, diffuse clouds. We’re not interested in those clouds in the early universe. We know those are there. We’re interested in figuring out what ionizes them and makes it so that we can see through everything. This is where understanding how the light comes off of bright stars really starts to matter.
When we look at starlight, we can divide it out into a rainbow. We’re going to see dark spots in that rainbow, which is where light is getting absorbed out by the atmosphere of the star, but we’re also going to see bright lines, either from nearby gas that is getting ionized or, in some cases, actually, from some of the stars who have ionization lines. It’s those bright lines, those emission lines that we’re looking for because, well, first of all, they’re brighter. So, they’re easier to see at these kinds of distances, but they’re also specifically signifying this kind of star formation is going on.
Dr. Gay: This is what is illuminating the universe. Come look at me.
Fraser: Right. Okay. So, that’s the technique, what have they been able to find in? What are the new discoveries they’ve been able to make in this period?
Dr. Gay: Well, what we’re finding is: there is complex structure around these galaxies of how the gas is getting made transparent. We have exploding stars that are able to shock the gas and create bubbles, essentially blowing bubbles. So, that’s one way you get a lower density area that is much more easy to ionize. This can also blow bubbles that clear out passages from the galaxies. Essentially escape routes. Then, we’re also seeing that the star formation, itself, is so hot and so bright that it can push the material out around it.
Now, over time, we’re also going to get the cores of the galaxies going where a disc of material around supermassive black holes, it will also get very hot and bright. It clears out the region around it as well. So, we have all these different mechanisms coming together.
This is one of those amazing cases of both and. All these different things keep happening and the crazy thing is, when you read the papers, a lot of times, it comes across as, “And we have shown that the universe was re-ionized by star formation. And we have shown the universe is re-ionized by active galaxies.” It’s all these things. The universe refuses to take limits. It has no boundaries. It’s going to do amazing things its way.
Fraser: Right. It’s just our job to uncover it. What are some interesting experiments or observatories that are coming up in the near future that will continue to push our knowledge of this early time?
Dr. Gay: Well, a lot of these radio telescopes are pathfinders to the eventual Square Kilometre Array, which is divided across two continents with some of its dishes at some wavelengths. Dishes is a bit of a stretch for the Square Kilometre Array. It looks more like spiky bits out in the desert.
Some of the detectors are going to be put in South Africa, and other southern African nations, others are going to be put in Australia. These two sets of arrays are going to be working at slightly different wavelengths and they’re going to have a massive collection area, and a massive resolution, and they’re working at these extremely long wavelengths that, with these objects being very redshifted, will give us the ability to see further back than we’re currently able to see a lot of the time.
Fraser: Yeah. I think we’ll be doing, eventually, dozens of shows on discoveries made about the Square Kilometre Array. It’s going to be amazing. All right. Did you have some names for us this week?
Dr. Gay: I do. So, as always, we’re here thanks to the generous contributions of people like you. Rich, Ally, Nancy, all the people behind the scenes. Beth Johnson. Everything they do is because of your contributions. This week, I would, specifically, like to thank brand new, paid a year in advance sponsor Kevin Lyle, Dave, Nate Detwiler, Phillip Walker, Elad Avron, Matt Rucker, Joshua Adams, Dave Lackey, Gregory Singleton, Paul D Disney, Karthik Venkatraman, Cooper, Lew Zealand, Sarah Turnbull, Chris Scherhaufer, Gfour184, Matt Newbold, Father Prax, Steven Shewalter, Dean McDaniel, and planetar. So, thank you all so much for everything you’ve done to keep us going.
Fraser: Thank you, Pamela.
Dr. Gay: My pleasure. Astronomy Cast is a joint product of Universe Today and the Planetary Science Institute. Astronomy Cast is released under a Creative Commons Attribution license. So, love it, share it, and remix it, but please credit it to our hosts, Fraser Cain and Dr. Pamela Gay. You can get more information on today’s show topic on our website, astronomycast.com. This episode was brought to you thanks to our generous patrons on Patreon. If you want to help keep this show going, please consider joining our community at patreon.com/astronomycast. Not only do you help us pay our producers a fair wage, you will also get special access to content right in your inbox and invites to online events. We’re so grateful to all of you who have joined our Patreon community already. Anyways, keep looking up. This has been Astronomy Cast.