dark energy measurement

380 thousand years after the Big Bang, the universe cooled enough for light to decouple from plasma. That cosmic microwave background still pervades space, like the first chord of a symphony, the echo of a fiery beginning.

A drama is brewing in cosmology: two principal musical instruments, the orchestra of the early Universe and the chamber ensemble of the modern cosmos, play the same symphony of expansion at different tempos.

Cosmology is the music of the spheres, and the Hubble constant once seemed like a reliable metronome.

Cosmologists staged a showdown between two kinds of cosmic explosions. Type Ia supernovae are stars that flare up with nearly identical brightness, making them reliable beacons for measuring distances across the universe.

Imagine inflating a balloon. It expands quickly at first, then slows down, and then suddenly speeds up again, as if someone gave the pump another squeeze. That's what seems to be happening to our universe.

When a massive star explodes as a supernova, its outer layers are blasted into space at thousands of kilometers per second. A shock wave forms — a giant invisible bulldozer that sweeps up interstellar gas and dust. In this maelstrom, particles can be accelerated to energies comparable to that of a flying tennis ball compressed into a single proton.

Imagine inflating a balloon. At first, it expands slowly; then someone gives a sharp blast of air, and it swells faster. But as the airflow weakens, the balloon's growth slows again. According to a new study, the Universe has behaved much the same way: after the Big Bang, it expanded, then suddenly accelerated, and now that acceleration is fading.

If space is a canvas, then brushstrokes cannot be infinitely thin. There's a tiniest segment, shorter than which there's no point in measuring. This quantum 'graininess' alters the geometry itself: the motion of galaxies and the growth of large-scale structures bear its mark.

Until now, dark energy has been studied like a car engine — only by the acceleration the Universe's expansion gains.

Two methods of measuring the Universe's expansion rate yield conflicting results. Measurements from supernova explosions, carried out by Adam Riess's team, show faster expansion than data from the cosmic microwave background — the light left over from the Big Bang.

The universe is expanding, and the pace of that expansion is set by dark energy, the mysterious force accelerating the recession of galaxies. In the standard cosmological model, its density is constant: a cosmological constant, an unwavering metronome since the birth of the cosmos.

Quasar W2246–0526 is a beacon lit when the universe was just 1.3 billion years old. Its light has traveled 12.8 billion years to reach us, yet even at such a distance, astronomers have spotted what had eluded them for decades: the gravitational shadow of a black hole.