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Universe Expansion
At the upper limits of what's energetically possible, cosmic rays still persist. What happens if a human gets hit by the most energetic one?
Our great hope is that today's indirect, astrophysical evidence will someday lead to successful direct detection. What if that's impossible?
Our view of the world, the Universe, and ourselves can change with just one glimpse of what's out there. It's happened many times before.
Outer space begins just over 100 kilometers up, but what we can see extends for billions of light-years. Here's what all of it looks like.
Even in an expanding Universe, we expect both redshifted and blueshifted galaxies. But nearly every one we see is redshifted. Here's why.
With unprecedented resolution, wavelength sensitivity, and light-gathering power, JWST reveals our cosmos like no other observatory ever.
Gravitational lenses arise when foreground masses and background light sources properly align. Einstein rings are rare, but crosses abound.
It's not about particle-antiparticle pairs falling into or escaping from a black hole. A deeper explanation alters our view of reality.
The VENUS survey isn't about planets at all, but about finding multiply-lensed supernovae. The ambition? To save the expanding Universe.
Back in 1604, Johannes Kepler discovered the Milky Way's last naked-eye supernova. Here's how NASA's Chandra sees it over the 21st century.
The seeds of cosmic structure that were planted back during the Big Bang grew into the cosmic web we see today. What is it telling us?
When objects are gravitationally bound, they cannot escape from one another's influence. How does that work within the expanding Universe?
Even the youngest galaxies are often dust-rich, even with very low levels of heavy elements. Nearby dwarf galaxy Sextans A explains why.
Astronomers have found starless gas clouds before, but Cloud 9 might be the most pristine one of all, with big lessons for cosmic history.
In a galaxy less than 300 million years after the Big Bang, oxygen's presence abounds. That's expected; its absence would truly be profound.
In general relativity, matter and energy curve spacetime, which we experience as gravity. Why can't there be an "antigravity" force?
The very word "quantum" makes people's imaginations run wild. But chances are you've fallen for at least one of these myths.
There will always be "wolf-criers" whose claims wither under scrutiny. But aliens are certainly out there, if science dares to find them.
If you can identify a foreground star, the spike patterns are a dead giveaway as to whether it's a JWST image or any other observatory.
Perhaps the most remarkable fact about the Universe is simply that it, and everything in it, exists. But what's the reason why?
The highest-energy particles could be a sign of new, unexpected physics. But the simplest, most mundane explanation is particularly iron-ic.
While humanity has been skywatching since ancient times, much of our cosmic understanding has come about only recently. Very recently.
Our Universe doesn't just expand and cool, but the expansion itself is accelerating. Can stars form under such structure-erasing conditions?
Earth orbits the Sun while spinning on its tilted axis, with two annual occasions marking that maximal tilt. That's where solstices arise.
Our Standard Model of the Universe, for both particle physics and cosmology, remains intact for now. When will its foundations crack?
With the observation of SN 2025wny, a lensed superluminous supernova, astronomy's future comes into sharp, exciting focus.
It takes a wide variety of processes in the Universe to make all the elements that populate space today. We're still discovering new ones!
Science isn't absolute. Its truths and discoveries enable us to approximate reality, but we must always remain open-minded to revisions.
The method you use to measure the expanding Universe determines which of two answers you'll get. Lensed supernovae can't resolve that issue.
Scientific truths remain true regardless of belief. These 10, despite contrary claims, remain vitally important as 2025 draws to a close.