Hey, it's Diana, and you're watching "Physics Girl."

I am very excited to be back making videos, because I just got back from a trip to New York City.

I got to go to the Creator Summit, the YouTube Creator Summit, and hang out with a bunch of your favorite creators and my favorite creators and schmooze and pretend like I belonged there.

It was awesome, but that's not what this video is about.

While I was there, the last night, I stayed with my friend Daniella, who's an astrophysicist.

And I cornered her and made her tell me everything about her research.

She told me this little nugget about a conference that revolutionized the field of astronomy.

revolutionized the field of astronomy.

She may not have used those words.

She may not have used those words.

But anyways, back in 1995, astronomers held a conference called "Cool Stars 9"-- held a conference called "Cool Stars 9"-- great name-- in Florence, Italy, where great name-- in Florence, Italy, where a huge announcement was made.

The first gas giant exoplanet, that is, the first planet like Jupiter outside of our solar system, had been discovered.

That was crazy exciting news, to think of planets outside That was crazy exciting news, to think of planets outside of the eight that we're so familiar with.

of the eight that we're so familiar with.

But unfortunately, it probably overshadowed another announcement about a much more mysterious type of object, the moon.

Just kidding.

No, astronomers had found the first incontrovertible brown dwarf.

Those two things happened at the same time, so that was a crazy conference.

DIANA: Yeah, that was like the conference to end all conferences.

Yeah, seriously.

I don't know why we do conferences anymore.

So brown dwarfs, are they stars like red dwarfs?

No, they are really confusing objects.

Brown dwarfs are celestial bodies that are in-between stars like the sun and giant planets like Jupiter.

So it's way harder to characterize them.

Which makes them more fun.

They're like the liger of celestial objects, like the BMW X6 is halfway between a sedan and an SUV, as everyone knows.

Did I get off topic?

They're intermediate in terms of their properties, of how their atmospheres look, most importantly, in terms of their mass.

But we can generalize and say that all brown dwarfs are about the size of Jupiter.

However, they have about 8% of the mass of the sun.

So they're way, way denser.

Despite being so much more dense than planets, brown dwarfs are still not dense enough to have the key trait that defines a star.

They can't fuse hydrogen in their core.

And that's important.

In fact, brown dwarfs were originally theorized as just that-- as these objects that couldn't fuse hydrogen in their core.

They were originally called black dwarfs, but even back then they were referred to as stars.

The difficulty is in understanding exactly where the difference between a star and a brown dwarf.

You're gonna discover that it's really hard to draw the line between a planet and a brown dwarf and a star, which is weird, because that's, like, the number one thing that humans like to do-- categorize things.

How can you not know whether something is a planet or a star?

Although this confusion is the whole reason for the debacle where Pluto got demoted.

Anyways, the one definite characteristic is that thing about fusing hydrogen.

Stars can fuse hydrogen throughout their lives.

And that fusion creates helium and also releases light.

The photons travel outwards while the upper layers of the star are trying to push inwards, and those two forces, you can imagine as literally like two arrows going against each other.

They stabilize the star.

Brown dwarfs, of the other hand, we think that they're born in a similar way as stars, but they don't do enough nuclear reactions in their core.

but they don't do enough nuclear reactions in their core.

They don't do it at a fast enough rate They don't do it at a fast enough rate to actually hold them together, you know, to actually prevent gravity from compressing them.

So because brown dwarfs don't do a lot of fusion and they don't do any hydrogen fusion, they don't shine like stars.

they don't shine like stars.

They're faint.

They're faint.

Plus, they're small and cold.

So we couldn't find them.

So back in the '60s, there was an important technology that we needed to develop in order to be able to find brown dwarfs.

I'm gonna pause this story real quick and show you a photo that I took when I was visiting my friend William Osmond.

The device that I used to get this photo of William Osmond is pretty spectacular.

It takes photos of you glowing, like, actually.

William is emitting light, not reflecting, not like light shining on you, reflecting.

He's glowing, but it's invisible to our eyes.

It's so far beyond the red part of the spectrum that it's infrared.

And so we took that photo with a little infrared camera.

If you could see infrared light, you would be able to see William in the pitch dark.

Awkward.

Now, brown dwarfs are pretty much the same.

They're mostly admitting infrared light.

So we needed to develop infrared cameras, strong ones, specifically infrared telescopes, in order to be able to find them.

It took almost like 35 years until they were finally discovered, because in the '60s we didn't have any infrared telescopes.

Therefore, it was hard to spot one.

But once we did have a few candidates, it was still hard to tell whether they were actually brown dwarfs until 1995.

In '95, it was announced that a brown dwarf showing methane in their atmosphere was discovered, and that was definitely a brown dwarf.

Since 1995, some of the other original candidates have been confirmed, and so have many more new candidates, but we still sometimes observe objects and scratch our heads and say, "is it a brown dwarf?

We're not sure.

How do we even define brown dwarfs?

We're still working on that.

There's so many open questions.

It's really interesting.

So I think, personally, the thing that I find most exciting is that we don't actually know how they form.

We have all these mechanism scenarios, like, that we think how they could form, but we don't really know.

And for me, the most interesting thing is trying to find observational signatures as to what are brown dwarf formation pathways and what are planet formation pathways.

Daniella and I talked for, like, Daniella and I talked for, like, an hour about brown dwarfs, because they an hour about brown dwarfs, because they are so fascinating.

We didn't get to talk much about it, but one of Daniella's deepest parts of research-- by the way, she has studied brown dwarfs for like 10 years.

This woman is an expert.

I just spit a lot.

And what she studies most-- I was talking about that-- is brown dwarf binaries, which is where a brown dwarf is orbiting something else.

Might be another brown dwarf.

Cool stuff.

Thank you so much to Daniella for spending so much time with me answering my questions.

One of coolest parts of my job is that I-- the scientists do all the work, and then I just get to ask them as many questions as I want and learn from them.

I love it.

I wanna make one last announcement.

As you know, I'm part of the PBS Digital Studios network, and there's another channel on PBS Digital Studios called "above the noise."

What they are all about is that they try to talk about controversial and trending topics, like trolling, and get the facts about them.

So in that trolling video, I was actually in there reading some of your comments.

So thank you guys for providing the material.

Anyways, that's all I've got for brown dwarfs.

Thank you for watching, and happy physicsing.