Universe of Learning: Science Briefing 12/5/19 – Chemistry of the Early Universe - 1 - Dr. Quyen Hart 0:00 [Slide 1] Hello everyone, this is Dr. Quyen Hart from NASA's Universe of Learning. Welcome today's science briefing. Thanks to all of you for joining us and to anyone listening to the recording in the future. For this December science briefing, our panel will talk about how astronomers use novel observations to understand the formation of the first stars and of primordial molecules. Slides for today's presentation can be found on the Museum Alliance and NASA Nationwide sites, as well as NASA's Universe of Learning site. All the recordings from previous talks should be up on the websites as well. As always, if you have any issues or questions now or in the future, you can email Jeff Nee at [email protected]. Again, that's [email protected]. Or Museum Alliance members can contact him through their new team chat app and the info is on the website. Dr. David Neufeld 1:02 So, thanks everyone very much for joining us. Today we're going to be talking about a period long ago. First of all, before there were any stars, in the first briefing, and then, in the second part, we'll hear about the formation of the very first stars. Dr. David Neufeld 1:23 [Slide 2] If we could advance the slides, please. Dr. David Neufeld 1:26 [Slide 3] And one more. So, I'm David Neufeld, and I'll talk to you about what we believe was the very first type of molecule ever to form in the history of our universe. And I'll discuss how this molecule has been detected recently in the present-day universe in a nebula that is shown on the left of this slide, and using NASA's, and the German space agency, DLR's, SOFIA Airborne Observatory to observe this very first molecule, the helium hydride ion. Dr. David Neufeld 2:09 [Slide 4] So we could go to the next slide, please, slide four. Let me just say a few words about the very early history of our universe. And in fact, for the first, roughly, 100 million years after the universe began with the Big Bang, there were no stars or galaxies at all. Initially, the universe was very uniform, smooth, and very hot. And there were no atoms, there were just atomic nuclei, which formed within the first few minutes, and then free electrons, filling up the universe. In fact, there were only three chemical elements at that time: hydrogen, helium, and lithium. And as you may know, all of the other elements including, of course, the main constituents of the Earth and our bodies, were produced only later by the nuclear reactions that power the stars, or the supernova explosions that end the lives of stars. Before there were any stars, we just had these three chemical elements. Universe of Learning: Science Briefing 12/5/19 – Chemistry of the Early Universe - 2 - Dr. David Neufeld 3:27 [Slide 5] If we can go now to slide five, the next slide. We can continue the story by saying that as the universe expanded, it also cooled as it grew older. And eventually, about 100,000 years after the Big Bang, the first atoms formed. So, what I mean here is that the negatively charged electrons and the positively charged nuclei of hydrogen, helium, and lithium, started to combine together to form atoms. In fact, first helium atoms formed, and then, a little later, hydrogen atoms. Dr. David Neufeld 4:09 [Slide 6] So if we could go to the next slide please, number six. We can now see that the very first molecules to form actually involved the combination of the helium atoms that had formed in the cooling universe with the hydrogen, still a nuclei. And the hydrogen nucleus is just a proton. So, this helium hydride ion was the first molecule to form, and so the first chemical bond in the history of our universe was between a helium atom and a hydrogen ion to form the helium hydride molecule, which is sort of shown in this picture on the right where you'll see it has two electrons, sort of in between the two nuclei pulling them together in a molecule. And then there were subsequent chemical reactions produced other molecules, and in particular, hydrogen molecules, H2, so two protons and two electrons shown in the bottom right hand panel. And the formation of these molecules was actually quite important, we believe, because molecules are very efficient, more so than atoms, in radiating away energy. And that allows the gas to cool faster. And once the gas became cool enough, it could collapse under its own weight to form the first stars and galaxies, and this will be discussed in the next part of the briefing. Dr. David Neufeld 5:48 [Slide 7] So if we could move on now to seven Thank you. Sorry, back one. Yeah. Helium hydride ions, they contain the very first bond in the universe. We consider this as the very first step on a pathway leading to more and more complexity in our universe, starting with the formation of atoms, and then molecules, and then of course, more and more complicated molecules and more and more complicated things in the universe, like DNA, and our brains, but this was sort of the first step on the path to complexity. Now, the story I've just told you, is based on very well-informed theoretical models, but we're actually very far from being able to detect helium hydride ions, this first type of molecule in the early universe that I'm talking about now. Dr. David Neufeld 6:47 [Slide 8] But it is possible, and it's recently happened that we've detected helium hydride ions in our own galaxy in the present-day universe, in a nearby planetary nebula known as NGC 7027. And a Hubble Space Telescope image of this is shown in the right panel of slide eight. These planetary nebulae actually have nothing to do with planets, or nothing directly to do with planets, they were so named, because in a small telescope, they looked a little bit like the disk of the planet. But they're obviously not planets, what they are, in fact, are stars that are at a more advanced aged stage of evolution than our Sun that have shed an envelope, and all that's left in Universe of Learning: Science Briefing 12/5/19 – Chemistry of the Early Universe - 3 - the middle of the star is a very hot white dwarf star that is then illuminating, with very strong ultraviolet radiation, this envelope, which is lit up and glows as you can see. Dr. David Neufeld 8:00 [Slide 9] We could go to slide nine please. We can say that this shell, then, has very abundant helium ions and hydrogen atoms. The helium ions are produced when the ultraviolet radiation from the central star strips away the electrons, and in that shell that surrounds the star, reactions can take place to form the helium hydride ion. Dr. David Neufeld 8:27 [Slide 10] Next slide please slide 10. So, the helium hydride ions emit radiation at a very characteristic wavelength. It's about 0.149 millimeters, and this is known to many more decimal places. But unfortunately, this radiation cannot be detected from the ground. It's in a part of the spectrum we call the "far infrared." It's actually blocked by water vapor in Earth's atmosphere. So, in order to observe it, we need to get either out of the atmosphere with a space observatory, or at least above most of the water vapor. And in fact, we can do the second of those things with an airborne observatory. And so, my colleagues and I, and particularly, this effort was led by Rolf Güsten at the Max Planck Institute for Radio Astronomy in Germany, we used the SOFIA Airborne Observatory, which is a heavily modified Boeing 747 operated by NASA, and its German counterpart, DLR. And you can see in the upper right panel, a picture of Sofia, and you can see there's a door there on the left side of the aircraft and sticking out, or pointing out ,is a two-and-a-half-meter diameter telescope. This is an incredible technical feat to get this thing to work. And then inside the aircraft, there's a pressurized cabin where various different instruments can be used to analyze the infrared radiation that this telescope can see. And we're above about 99% of the water vapor. And so, we have a clear view of some of the wavelengths that would be completely blocked, even from a mountaintop observatory. And one of the instruments is a high-resolution spectrometer capable of splitting up the infrared radiation into its constituent wavelengths, with very great precision. This is called GREAT which is an acronym for the German REceiver for Astronomy, at Terahertz frequencies, and this is perfectly suited for looking for the helium hydride ion in this nearby planetary nebula. Dr. David Neufeld 11:10 [Slide 11] We could go to the next slide please. This will be my last slide. So, we carried out these observations and reported the results this spring in an article in Nature, and what we found is that the helium hydride ions showed up as a spectral line of exactly the expected wavelengths.