When I was a kid, I was afraid of the dark. The darkness is where the monsters are. And I had this little night light outside of my bedroom so that it would never get too dark. But over time, my fear of the dark turned to curiosity. What is out there in the "dark-dark?" And it turns out that trying to understand the darkness is something that's fascinated humans for thousands of years, maybe forever. And we know this because we find their ancient relics of their attempts to map the sky.
This tusk is over 30,000 years old. Some people think that it's a carving of Orion or maybe a calendar. We don't know. The Fuxi star map is over 6,000 years old, and it's from a neolithic tomb in ancient China. And that little pile of clamshells underneath the dead guy's foot in the middle — that's supposed to be the Big Dipper. Maybe. The Nebra disk is uncontroversial. You don't have to be an astronomer to know that you're looking at the Moon phases or the Sun in eclipse. And that little group of seven stars, that's the Pleiades, the Seven Sisters.
But in any case, the point is clear: astronomers have been mapping the sky for a long time. Why? It's our calling card as a species in the galaxy to figure things out. We know our planet, we cure our diseases, we cook our food, we leave our planet. But it's not easy. Understanding the universe is battle. It is unrelenting, it is time-varying, and it is one we are all in together. It is a battle in the darkness against the darkness. Which is why Orion has weapons. In any case, if you're going to engage in this battle, you need to know the battlefield.
So at its core, mapping the sky involves three essential elements. You've got objects that are giving off light, you've got telescopes that are collecting that light, and you've got instruments that are helping you understand what that light is. Many of you have mapped the Moon phases over time with your eyes, your eyes being your more basic telescope. And you've understood what that means with your brains, your brains being one of your more basic instruments. Now, if you and a buddy get together, you would spend over 30 years, you would map 1,000 stars extremely precisely. You would move the front line to the battle. And that's what Tycho Brahe and his buddy, or his assistant, really, Johannes Kepler did back in the 1600s. And they moved the line, figured out how planets worked, how they moved around the Sun.
But it wasn't until about 100 years ago that we realized it's a big universe. It seems like the universe is just infinite, which it is, but the observable universe is finite. Which means we can win the battle. But if you're going to map the universe, you're not going to do it with one or two of your besties. Mapping the universe takes an army, an army of curious, creative, craftspeople who, working together, can accomplish the extraordinary. I lead this army of creatives, in the fifth generation of the Sloan Digital Sky Survey, SDSS. And this is how astronomers have managed to shepherd individual curiosity through its industrial age, preserving the individual ability to make discoveries but putting into place mega machinery to truly advance the frontier.
In SDSS, we divide the sky into three mappers: one for the stars, one for the black holes and one for the galaxies. My survey has two hemispheres, five telescopes, or 11, depending on how you count, 10 spectrographs and millions of objects. It's a monster. So let's go through the mappers.
The Milky Way galaxy has 250 billion plus or minus a few hundred billion stars. That is not a number that you hold in your head. That is a number that doesn't make practical sense to pretty much anybody. You never get 250 billion jelly beans in your hand. You know? We're nowhere near mapping all of those stars yet. So we have to choose the most interesting ones. In SDSS-V, we're mapping six million stars where we think we can measure their age. Because if you can measure the age of a star, that's like having six million clocks spread all throughout the Milky Way. And with that information, we can unravel the history and fossil record of our galaxy and learn how it formed.
I'm just going to cut right to the chase here. Black holes are among the most perplexing objects in the universe. Why? Because they are literally just math incarnate, in a physical form, that we barely understand. It's like the number zero being animated and walking around the corridors here. That would be super weird. These are weirder. And it's not just like a basketball that you smoosh down into a little point and it's super dense and that's weird. No, smooshed basketballs have a surface. These things don't have surfaces, and we know that now. Because we've seen it. Or the lack of it. What's really interesting about black holes is that we can learn a lot about them by studying the material just as it passes through that point of no information return. Because at that point, it's emitting lots of X-rays and optical and UV and radio waves. We can actually learn how these objects grow. And in SDSS, we're looking at over half a million supermassive black holes, to try to understand how they formed.
Like I said, we live in the Milky Way, you guys are all familiar with that. The Milky Way is a completely average galaxy. Nothing funny going on. But it's ours, which is great. We think that the Milky Way, and all the Milky Ways, have this really disturbing past of literally blowing themselves apart. It's like every average guy you know has a history as a punk rock teenager. That's very bizarre. Stars are blowing up in these systems, black holes are growing at their centers and emitting a tremendous amount of energy. How does that happen, how does this transformation happen? And at SDSS, we're going to the bellies of the beast and zooming way in, to look at these processes where they are occurring in order to understand how Sid Vicious grows up into Ward Cleaver.
My arsenal. These are my two big telescopes. The Apache Point Observatory hosts the Sloan telescope in New Mexico, and the Las Campanas Observatory in Chile hosts the two-and-a-half-meter telescope, the du Pont. Two and a half meters is the size of our mirror, which was huge for Tycho and Kepler. But it's actually not so big today. There are way bigger telescopes out there. But in SDSS we use new instruments on these old telescopes to make them interesting. We capture light from all of those objects into our aperture, and that light is then focused at the focal plane, where our instruments sit and process that light.
What's new in SDSS-V is that we're making the focal plane entirely robotic. That's right: robots.
So I'm going to show them to you, but they're fierce and terrifying, and I want you all to just take a breath. (Exhales) Trigger warning. And with no apologies to all the Blade Runners among you, here they are.
I have 1,000 of these, 500 in the focal plane of each telescope in each hemisphere. And this is how they move on the sky. So these are our objects and a star field, so you've got stars, galaxies, black holes. And our robots move to those objects as we pass over them in order to capture the light from those stars and galaxies and black holes, and yes, it is weird to capture black hole light, but we've already gone over that black holes are weird.
One more thing. Stars are exploding all the time, like this one did back in 1987 in our cosmic backyard. Black holes are growing all the time. There is a new sky every night. Which means we can't just map the sky one time. We have to map the sky multiple times. So in SDSS-V, we're going back to each part of the sky multiple times in order to see how these objects change over time. Because those changes in time encode the physics, and they encode how these objects are growing and changing. Mow the sky.
OK, let me just recap. Global survey, two hemispheres, five telescopes, 10 spectrographs, millions of objects, mow the sky, creative army, robots, yeah. So you're thinking, "Wow. She must have this industrial machine going, no room for the individual, curious, lone wolf genius," right? And you'd be 100 percent wrong.
Meet Hanny's Voorwerp. Hanny van Arkel was a Dutch schoolteacher who was analyzing the public versions of the SDSS data, when she found this incredibly rare type of object, which is now a subject of major study. She was able to do this because SDSS, since its beginning and by mandate from the Sloan Foundation, has made its data both publicly available and usable to a broad range of audiences. She's a citizen — yeah, clap for that. Clap for that.
Hanny is a citizen scientist, or as I like to call them, "citizen warriors." And she shows that you don't have to be a fancy astrophysicist to participate. You just have to be curious.
A few years ago, my four-year-old asked, "Can moons have moons?" And I set about to answer this question because even though many four-year-olds over all of time have probably asked this question, many experts, including myself, didn't know the answer. These are the moons in our solar system that can host hypothetical submoons. And that just goes to show you that there are so many basic questions left to be understood.
And this brings me to the most important point about SDSS. Because, yeah, the stars, the galaxies, the black holes, the robots — that's all super cool. But the coolest thing of all is that eensy-weensy creatures on a rubble pile around a totally average star in a totally average galaxy can win the battle to understand their world. Every dot in this video is a galaxy. Every dot.
I'm showing here the number of galaxies that astronomers have mapped in large surveys since about 1980. You can see SDSS kick in around Y2K. If we stay on this line, we will map every large galaxy in the observable universe by 2060. Think about that. Think about it: we've gone from arranging clamshells to general relativity to SDSS in a few thousand years — and if we hang on 40 more, we can map all the galaxies. But we have to stay on the line. Will that be our choice?
There are dark forces in this world that will rob our entire species of our right to understand our universe. Don't be afraid of the dark. Fight back. Join us.