Hi, I'm Dr. Johnson-Haas and welcome to Earth Parts. What you see here is NGC 1672. It's a barred spiral galaxy, very similar, we think, to what the Milky Way looks like from the outside. The problem is that we can't see the Milky Way from the outside. We're inside it and there's too much gas and dust in the way for us to see the other side of it.
This one's only 60 million light years away, so it's fairly close as galaxies go. Now, if you look at a galaxy like this, throughout those spiral arms, there aren't just stars. You're looking at stars, but you're also looking at a lot of diffuse hydrogen and helium gas mixed in with rarefied tiny amounts of dust. But there's a lot of material there that is not already made up into stars and planets. There's a lot of raw material for star formation.
And our galaxy is a galaxy where there's active star formation. our own Sun would have started off forming in a region within our Milky Way that was rich with gas and dust. The nice thing is that we can see this directly.
Because of the Hubble Space Telescope and the Spitzer Space Telescope and other technologies that are ground-based on Earth, telescopes, we can look out in space and see directly the process of formation at every stage. We can see star forming nebular clouds, we can see parts of them collapsing to form star systems, and we can see the star systems grow, as I'll show you in this presentation. Now these hydrogen and helium clouds, these molecular clouds or ionized clouds of hydrogen, are constantly moving, they're in constant motion like clouds in the sky.
They appear frozen in time because they move over much more majestic scales than we directly perceive. But they are clouds in constant motion, and clouds can stretch out and thin, and they can bunch up and roll into a tighter mass. And the total mass of all of that material cause it to fall in on itself. It has its own mass and gravity. So what happens is, occasionally in these clouds, if a passing disturbance, the wake of a passing star, or the shock wave of a supernova passes by, in that front, you can pile up...
gas and dust to a higher density and maybe in many cases cross over a threshold where the cloud becomes dense enough that it begins to collapse under its own mass. Parts of it do. And here's a nice example. This is the Carina Nebula, a star-forming region. It's a diffuse molecular gas cloud, meaning it's primarily made up of molecular hydrogen and helium with a sprinkling of trace elements in there too.
And our Sun would have begun in a region very much like this. Inside this structure, you can see thicker areas where the gas and the dust are denser and light doesn't pass through them. What happens in these situations where you have some fairly high density regions of a cloud, these are temporary structures, but while they're piled up like that, if they pass a certain threshold density, their own mass their own mutual gravitational attraction will begin to pull regions of the cloud inward on themselves. They begin to fall inwards toward what becomes a center of gravity locally. And this can happen dozens of times all throughout a cloud at the same time, stars at different stages of formation.
Here's a Hubble image from the Hubble Space Telescope of the Orion Nebula. It's a nearby region of active star formation. And looking into this cloud with infrared wavelengths to peer through some of the obscuring gas and dust that's opaque to visible light, astronomers have located around 700 young stars that are in the process of formation. This region contains a lot of stars forming at the same time, at different stages of development, but more or less at the same time in an astronomical timescale. And when the sun formed from a cloud like this, it would have not formed alone.
It would have formed with... with dozens or maybe hundreds of others. We'll never know now. They would have been, those stars are mixed with the galaxy.
We'll never find them. There's no way to identify that, as far as we know. But in addition to that, we also have, astronomers have seen about 150 protoplanetary disks where the gas cloud has collapsed in on itself. That region has enough to where it's spinning, it's flattening into a disk, it's organizing into what will be a star system. This is the Eagle Nebula.
a nearby star forming region where a lot of activity is going on. We're going to take a look at it because this image has become quite famous. This is... taken by the Hubble Space Telescope. Credit goes to a European Southern Observatory.
And the central features are perhaps the most famous. But if you look at this, this is a vast region where stars are forming, where planets around those stars are forming. And if you zoom in to the central feature, you can pull out a lot of very detailed information about what's going on. In this case, you're looking at what's called the Pillars of Creation.
This is that area that you just saw. but in much greater detail in this image. In this image you can see little structures, areas that appear to be little blobs or knots of material, and the pillars themselves appear to be very distinct against the background space.
There's a high density of material in there. There's lots of protostars and protoplanetary disks in the process of formation. Now if you zoom in, let's take a look at some of these structures. at a little bit closer range. Because what you see down in there are these little knots of material, these little bulbs of material, and the gas and dust is sort of streaming back away from behind them and they define little finger-like projections coming out of the cloud.
So what you're seeing right here, there are a number of these little blobs. You can see them poking around all over the place. And these little structures, these little blobs that you can see sticking out of the cloud, they're not really sticking out. The cloud's actually being pushed or pushed behind them, pushed away.
And in fact, it's the combined solar wind of the nearby surrounding stars that are pushing at the cloud material, causing it to gather up where the convergence of the solar wind sends it from, you know, from time to time. But not those little things. They're not sticking out, they're left behind. That's a high density region of gas and dust that has already begun to collapse. Every one of those little fingers at the tip of the finger inside there is where that star is forming, and the material is densest.
And inside there, where the planets around the star will form as well. We're looking at what our own solar system would have looked like in a very early stage of its initial accretion from a diffuse cloud to a protostar. And we have a name for these things, they're called propylids. These little clumps of compressed gas and dust are actively collapsing.
At the center of each one is the protostar that will light up eventually with nuclear fusion reactions. It'll be a fully functioning main sequence star at that point with planets around it. At this point it's essentially a diffuse but contracting ball of material.
And you see the bow shock and the bow shock around it where the closest solar wind influence is pushing the material out around it and leaving it there. This particular one is in the Orion Nebula. And this isn't the only one.
Thanks to Hubble and other telescopes, ground-based and otherwise, we have seen lots of these things. There are dozens of them out there in the Orion Nebula. There's hundreds of them, thousands out within our viewing range.
zoom in so we can see some of these in detail. What you notice immediately is that they all have a striking similarity to each other in that they have this knot of material in the middle. It's bright because it's hot.
Dense dust cloud around it that has a fairly distinct outer edge and sometimes they trail behind the material that's sort of streaming out behind it. It will not be part of the system. It'll actually just be lost in the nebula.
And some of them, though, you can actually see what appears to be a kind of a ring structure. You see those on the bottom there, especially, and one in the middle. It appears that there's a bright, intense source of light in the center, and then it's obscured by a dark ring of dust, and that's exactly what it is.
Here's an example of one. This propylate is in the Orion Nebula, and it's a very nice example. You can look at the brightness in the... this is an infrared image...
You can see the brightness in the core. It's where that Sun is growing. It's getting hotter and denser.
When its core temperature reaches several million kelvins, it will be hot enough then to trigger nuclear fusion and it'll become a normal star. In this NASA animation, we're looking at essentially a propylid in the process of collapsing to form a star system. This collapsing protoplanetary disk, it's called, surrounds the protostar and as it condenses, it forms a flatter and flatter ring where the gas and the dust inside there are being compressed together close enough that they begin to condense out into particles, into where you started off with atoms or molecules, now you have clusters of molecules forming, solids, growing, condensing into larger bits of dust, and eventually these things accrete into planets.
This animation shows a little further along in the process. What happens is that the earliest large objects to accumulate mass simply become the biggest local attractor. and begin sucking up everything around them, they begin accreting material.
And as they do so, they actually evacuate a ring of material. They use up the material that is in that region, in that orbital distance from their star, to make themselves. And so from a viewing perspective, you would see these rings begin to clear into a more orderly, organized shape as the planets form.
Here's a nice example of another accreting star system. This one is real. This is Formalhaut.
It is a young star, very recently formed. Its solar system is not fully formed yet and it's surrounded by this really amazing debris ring. And yes, I know what it looks like, but it's actually not that. It's a star system that is at its first baby steps.
The ring you see around there that density ring is real. Those spokes radiating out from the center are an artifact of the data rendering process. They're not real, but the overall density of material is.
So you see this ring of material that's flattened because it's at an angle to us. The star in the middle is blocked out. You put a coronagraphic mask over the star in the middle so its light won't completely drown out all the surrounding light from the ring itself. And this will only work in the infrared. This is an infrared image.
In visible light, the star would be too bright. Now, the nice thing about... the interesting thing about this system, Formalhaut, is that astronomers have found a planet already, an exoplanet. The edge of that ring orbits a gas giant. It's big and hot, which makes it easy to see in infrared.
And it's actually been called Dagon informally, although its official name is Formalhaut b. This is a beautiful example. of a young star with organized debris rings around it.
This is HL Tauri. And what you're looking at here is a star system where planets have begun to grow enough that they're using up the material in their orbital track. This looks like grooves on an old style phonograph record.
Those grooves are real and they're because there's a planet growing in there somewhere. We have numerous examples of these. When we're lucky, we can actually look right down the pole of one and see it as a perfect circle.
This is TW Hydrate, another protoplanetary disk around the star. In this case, we're lucky to be looking right down the pole rotational axis of the star, and it gives us a full circle view. So you see those empty gaps in there, those empty grooves where the material is not as bright. It's because there's less material there.
It's being used up. by planets that are growing there. As young planets begin to accrete and grow larger, they clear their surroundings of debris.
They accrete themselves by assimilating all the dust and gas and once you build up big enough objects, boulders, mountains, asteroid-sized objects, as you grow your planet you use up all the material in your orbital neighborhood. And we can see that looking at these young star systems. We can see them in all these stages. growth and it allows us to develop a much better picture of the history of our own star system and our planet.