We are made of star stuff.

The atoms and elements that form everything around us and in us were once forged inside stars.

But it's not quite that simple.

We're not just a blob of atoms, but rather, complex molecules, including rings of carbon, hormones and DNA and RNA and vitamins and steroids and more all contain rings and rings of carbon.

And for a long time, we thought that many complex ring structures could only be formed down here on Earth, but now, we're finding them in some of the coldest parts of space, molecular clouds.

Big, dusty molecular clouds.

Big, dusty molecular clou-.

Ring structures are incredibly important to life, and we have a variety of ways of making them.

For example, photosynthesis takes carbon dioxide and water and turns it into glucose, a ring that can later be broken to provide a cell with energy, or those rings can be linked together to make cellulose, holding plants up.

Plants, animals, and fungi all also turn oily squalene into hormones that send signals throughout our bodies.

The rings found in DNA bases help stabilize the molecule through pie stacking of their bonding orbitals.

And for many of these organic or carbon-containing ring structures, their synthesis fundamentally relies on enzymes.

We find lots of ring structures, including polycyclic aromatic hydrocarbons, or PAHs, in fossil fuels and as products of combustion too.

These PAHs are defined by multiple rings that contain lots of carbon and hydrogen, PAH.

They're usually flat and uncharged.

But remember, oil and gas and coal are ancient plants and animals and dinosaurs, so there too, those big rings were likely made by biology, not just chemistry, so there.

But for the past 30 years, scientists have theorized that these big ring structures might be the seeds of interstellar dust that, through a giant space snowball process, could go on to create asteroids and planets.

For a really long time, scientists assumed that forming these kinds of molecules could really only happen down here on Earth and not in space because space is an extreme environment in every sense of the word.

It is incredibly cold and a lot of chemical reactions take heat to form bonds.

There's stellar and UV radiation everywhere ready to degrade any molecules that do form.

And despite carbon being the fourth most abundant element in the universe, there's also just a lot of space in between all the stuff out there.

There are about 100 molecules per cubic centimeter out in space, which honestly sounds like a lot until you realize that the air that we breathe has about 10 to the 19th molecules per cubic centimeter.

This makes interactions between atoms and molecules a really low probability out in space.

And stars, which are chock full of elements, are also hot and full of energy and radiation, which is likely way too extreme in the other direction for organic molecules to survive.

But what if we did find these kinds of molecules out in space?

What if they could be formed not just in and around biology, but also in the cold, dark corners of our universe?

Scientists have wondered if they might have been early seeds for life on earth or even a stockpile of molecular building blocks deposited onto our planet and potentially others.

Now we started to find some molecules out in space about a century ago, but they were pretty simple, like H2 and N2.

In the 1930s and 1940s, we found CH and CN by looking at the optical or visible spectra of stars.

This is how we look for lots of simple molecules in elements out in space.

If you excite a molecule's electrons with energy, it gives off light of a certain signature of wavelengths.

So if you find light of that signature in the range of wavelengths emitted by a star, you can infer that the molecule or element is there too.

For example, this is a tiny handheld spectroscope.

If I point it at an LED bulb, you can see that the specific fingerprint of wavelengths that the light is split into is different from this fluorescent bulb, and it's different as well from pointing it at this flame.

Each emits its own signature of wavelengths.

Now this is all a step towards finding cool molecules out in space, but two atoms stuck together does not a complex molecule make.

In the late 1960s though, scientists pointing radio telescopes deep into space found water and formaldehyde.

Now this was much more exciting, both because formaldehyde is an important building block to make larger organic molecules, and because water is absolutely essential for life as we know it, and lots of chemistry, but also because we found that they were pretty ubiquitous in big, dusty molecular clouds.

To our own eyes, molecular clouds look like big blobs of nothing.

They're just some gas and dust.

But they are incredibly important to the formation of stars and galaxies.

They are full of the building blocks of stars, that same gas and dust that, when the pull of gravity is too much, can collapse in on itself to create a star.

All of that dust and debris blocks most of the visible light that they give off.

But in fact, they're still shining with the light that can escape through the interstellar medium.

That light is just all the way over here in the radio wave section of the electromagnetic spectrum, which you're gonna animate right here for me.

And we can use those radio waves to figure out if there are bigger molecules out there if we have telescopes sensitive enough to pick them up.

Now my little backyard telescope isn't gonna do the job.

It uses mirrors to reflect optical light into the eyepiece, and that's not what we're looking for.

I am talking about big radio telescopes.

If you've seen one, it often looks like a big dish.

That's a dish.

You know what I'm talking about.

Radio waves come in and the dish focuses those radio waves on the tip at the center, which then reflects them back into the receiver.

That receiver then amplifies the weak radio waves so that we can study them.

I really could have used a lot more of the whiteboard for this.

And when we use those telescopes to look for molecules, rather than the optical spectra that we talked about before, we are instead using rotational spectroscopy.

So when energy from the electromagnetic spectrum hits big molecules, or when those molecules collide with each other, they begin to spin.

But based on their configurations, they can only spin at certain speeds.

This speed-specific spinning gives off certain spectra of radio waves like a spritz of energy.

So on Earth, scientists and labs can run experiments exciting molecules and making them spin and then categorizing what their distinctive rotational spectra radio waves are.

So when we pick up those different spritzes from outer space, we can connect them back to the observations we've made in the lab, and that way, we can figure out what molecules are out there.

So when we started using rotational spectroscopy to look at molecular clouds, we started finding bigger and more complex molecules.

Now often, they are highly unsaturated carbon chains.

I know this looks like a really weird molecule, but they're big chains of carbons without many hydrogens.

Now since then, people have found aldehydes and alcohols and lots of stuff that you would need for all of our life-friendly organic molecules, but for a while, people weren't finding lots of five and six membered carbon rings.

This left scientists wondering how you go from chains to rings, and if you can really even do that out in the rough space environment.

That was until we started looking at molecular clouds, specifically TMC-1.

TMC-1, or the Taurus Molecular Cloud 1, is found in, you can guess it, the Taurus constellation.

It is the nearest big star-forming region to us and it is pretty early in its space cloud life cycle with a pretty simple homogeneous composition.

But when scientists turned their telescopes there in the 2010s, they found cyanobenzene, a building block that could be used to build bigger ring structures, including things like the polycyclic aromatic hydrocarbons we find in fossil fuels.

And at almost the same time, the publication dates were literally two days apart, scientists found signatures of these PAHs in TMC-1 as well by looking at light emitted in the infrared spectrum.

This indicates that aromatic rings, which on Earth are formed at high, high temperatures, or in biological systems, can be formed and found in these types of clouds despite them being cold and dark and low density.

Scientists keep proving themselves wrong, and I love it.

That's science.

And once they knew what to look for, scientists found these kinds of molecules in a handful of other molecular clouds too, meaning that it is likely not an anomaly.

This opens up a whole new environment where this kind of chemistry can happen and people are tracking it down.

For example, a group in Colorado published a paper in 2023 looking at ortho-benzyne.

So right before publishing this video, I learned that it's pronounced ortho-benzyne, not ortho-benzene, which makes sense because they're spelled differently.

So when I say that again in another minute in the video, just pretend I'm saying ortho-benzyne, or maybe Elaine will be really nice and dub it in for me if I just say ortho-benzyne, a six carbon ring that is missing two hydrogen atoms and its reactions with the methyl radical.

They found that this reaction makes a number of five carbon ring molecules.

And because ortho-benzyne loves to interact with other molecules really easily, it's a likely candidate to create bigger and bigger multi-ring or complex structures.

Now, there's still missing pieces like how these rings pick up nitrogens to form things like DNA and RNA, but we are starting to cobble together the molecules that we need, not just for life, but for the formation of stars and planets as well.

But we still don't know how these PAHs form.

In one scenario, small molecules might come together to form chains that could then form rings.

This is a bottom up scenario.

But they could also form top down, being created first as large molecules in soot from star death.

Now, this seems a little counterintuitive, but on Earth, we mentioned that these PAHs are often combustion products, which is a part of soot, so it actually does make sense that they could be soot from stars too.

And as these cyclical molecules get larger and larger and start to interact with other interstellar molecules, they could begin to create the dust grains and particles that then snowball into asteroids and planets.

That's cool on its own.

But even before they reach something that large, those dust grains could be really important chemical incubators.

Tiny interstellar dust grains covered in ice could be places where carbon comes together with oxygen and nitrogen, and then over time, hydrogen, to form important organic molecules.

And those could be the tiny seeds that wound up in a prebiotic soup to give us bigger molecules that could then catalyze reactions to create even bigger molecules like ring structures.

Space.