200 most important Astronomy topics - Sykalo Eugen 2023

The Dark Energy Camera (DECam)

What do you see when you stare into darkness? Most of us blink, look away, or fill the void with imagined shapes. But what if the darkness is lying? What if it holds not absence—but an overwhelming presence, silent and invisible?

I’ve stood under Chilean skies at night. The kind of dark that feels like velvet soaked in ink. The kind of dark where the Milky Way splits the heavens like a river of crushed diamonds. But not even that beauty touches what lies beyond: the emptiness that isn’t empty. Enter the Dark Energy Camera (DECam)—one of the most powerful digital imagers ever built, not to capture stars, but to measure their trembling shadows.

This is not about light. This is about the unknown that bends it.

A Telescope in the Wilderness: Where DECam Lives

High atop Cerro Tololo in the Chilean Andes, where air is thin and silence is thicker than stone, the Victor M. Blanco Telescope peers across 570 megapixels of cosmic canvas. That’s where DECam lives. Not a camera in the Instagram sense—this beast weighs over four tons. It sits like a steel cyclops, staring into nothing, begging it to speak.

Installed in 2012, DECam was designed to do something gloriously unreasonable: to map the distribution of dark energy, the mysterious force responsible for the accelerating expansion of the Universe. Yes, that sentence should boggle you. The Universe isn’t just expanding—it’s speeding up, as if something is pushing it apart. And we don’t know what that something is. We call it dark energy, mostly because we’re out of better words.

How do you study something you can’t see, touch, or taste? DECam does it with shadows, redshifts, and the bending of light. The way galaxies clump. The way ancient light slouches through spacetime. Like a detective reconstructing a murder from blood spatter, DECam reads the residue of dark energy’s fingerprints.

What Exactly Is Dark Energy? (I Don’t Know Either—but Here’s What We Think)

Imagine dropping a ball and watching it fall up. That’s what dark energy did to cosmologists in the 1990s. When two independent teams studied Type Ia supernovae—standard candles used to measure distance—they found those explosions were dimmer than expected. Translation? The Universe had stretched more than it should have. Something was pushing it outward.

We expected cosmic gravity to slow the Universe’s growth over time. Instead, it's speeding up. Hence, dark energy. But what is it?

There are three leading suspects:

Cosmological Constant (): Einstein’s old fudge factor. A constant energy density woven into spacetime itself. Kind of boring, but consistent.
Quintessence: A hypothetical dynamic field that evolves over time. More poetic. More volatile.
Modified Gravity Theories: Maybe gravity itself doesn’t work the way we think on large scales. Heretical—but science loves a good heretic.

The truth? We don’t know. And DECam isn’t here to tell us—it’s here to trap dark energy in a statistical net so tight that whatever slips through might whisper its true name.

The Dark Energy Survey: Stitching the Cosmic Quilt

From 2013 to 2019, DECam led the Dark Energy Survey (DES), a six-year astronomical marathon covering over 5,000 square degrees of sky—about one-eighth of the celestial sphere. The results? A map of over 300 million galaxies, along with thousands of supernovae, galaxy clusters, and the faint gravitational fingerprints of dark matter.

Have you ever tried to piece together a shattered mirror, only to realize the fragments reflect different worlds? That’s what DES data feels like. It gave us a better estimate of (the fraction of the Universe’s matter content) and the dark energy equation-of-state parameter (w), which tells us how 'springy' this unknown energy is.

The early results: w is close to -1, supporting the idea of a cosmological constant. But we’re not done. Because if w changes over time—just a little—it could upend everything.

Oh, and a surprise: DES data hinted at a slight tension between the observed clustering of matter and the predictions from the Planck satellite’s measurements of the early Universe. Not a scandal yet—but enough to make theorists twitch.

Looking Sideways: DECam’s Unexpected Discoveries

Here’s the thing about building a giant eye and pointing it at the Universe: it sees more than you asked for. Like an archaeologist digging for bones and unearthing a buried temple, DECam has discovered:

New dwarf galaxies orbiting the Milky Way, some of them faint enough to be called “ghost galaxies.” These are relics of cosmic childhood.
Kilonovae: The optical afterglow of colliding neutron stars—one of which helped confirm that such mergers produce gravitational waves.
Interstellar interlopers: Like ’Oumuamua, the first known object from another star system. While DECam didn’t discover it, its deep-sky scans help refine our understanding of such wanderers.

Every side glance DECam takes fills in a blank spot on the Universe’s family tree.

The Philosophy of Not Knowing: A Necessary Ignorance

Sometimes, I wonder—if we ever do understand dark energy, will it make the Universe feel smaller? Less poetic? Or will it deepen the mystery?

There’s something almost mythological about our current predicament. A force we can’t name, pushing spacetime itself apart, leaving no trail but bent light and statistical oddities. It’s not a villain—it’s not even a character. It’s the stage, shifting under our feet.

I understand how this sounds. A camera, a telescope, a mountain. Not exactly poetry. But then you realize: DECam is an eye staring at the Universe as it runs from itself.

This is science at its most vulnerable. Acknowledge the unknown. Build a machine to chase it. Spend decades interpreting flickers of ancient photons and hope—hope—that clarity arrives.

The Road Ahead: DECam’s Legacy and Beyond

Though the Dark Energy Survey officially ended in 2019, DECam continues to be used for new projects—from hunting near-Earth asteroids to imaging gravitational wave counterparts. And its data? Still being mined, still revealing secrets.

Meanwhile, other eyes are opening. The Vera C. Rubin Observatory, with its Legacy Survey of Space and Time (LSST), will take this cosmic cartography to a whole new level. DECam’s legacy will be the baseline, the training ground, the first draft of a map that may one day include dark energy’s true face.

I think that’s beautiful. Science is always a chain of torch-passing. DECam is not the end. It’s the whisper that leads to a question that becomes a roar.

We Are the Shadows That Measure the Dark

So here we are. Creatures of carbon and curiosity, staring into a void that accelerates. We built a four-ton eye to track a whisper. We chart galaxies not to escape our world, but to better understand why it won’t hold still.

You and I? We’re part of this drama. Every time we wonder what’s out there, every time we feel small under the stars, we echo DECam’s mission: to find meaning in the unseeable.

What pushes the Universe apart?

Maybe the better question is: what pulls us to ask at all?