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Decoding the Dark: The Accelerating Universe and the Pursuit for Dark Energy

Dark energy’s role in driving the universe’s accelerated expansion presents a critical challenge in astrophysics, inspiring ongoing research and space missions dedicated to uncovering the nature of this enigmatic force.

Around 13.8 billion years ago, the universe started with a rapid expansion we call the Big Bang. After this preliminary expansion, which lasted a fraction of a second, gravity began to slow the universe down. But the universe wouldn’t stay this way. Nine billion years after the cosmos began, its expansion started to accelerate, driven by a mysterious unknown force that scientists have named dark energy.

But what is dark energy by the way?

We don’t know is the short answer. Still we do know that it exists, it’s behind the continued expansion at an accelerating rate of our cosmos, and roughly 68.3 to 70% of the cosmos is dark energy.

Discovery of the phenomenon of expanding universe

The detection of galactic redshift, the period-luminosity relation of Cepheid variables, and a brand-new ability to gauge a star or galaxy’s distance ultimately played a role in astronomers observing that galaxies were getting farther and farther away from us with passage of time, which showed how the universe was expanding. In the subsequent years, several scientists around the world began to put the pieces of an expanding universe together.

Discovery of the phenomenon that expansion is accelerating

Scientists earlier thought that the universe’s expansion had slowed down because of gravity over time, a prospect backed by Einstein’s theory of general relativity. But in 1998, everything changed when two separate teams of astronomers observing far-off supernovae observed that at a certain redshift the stellar explosions were dimmer than anticipated. These groups were commanded by astronomers Saul Perlmutter, Adam Riess, and Brian Schmidt. This trio earned the 2011 Nobel Prize in Physics for this work.

While dim supernovae may not seem like a major find, these astronomers were observing a Type 1a supernovae, which are known to have a certain level of luminosity. So they were aware that there must be a different factor making these objects appear dimmer. Scientists can determine distance (and speed) utilizing an objects’ brightness, and dimmer objects are characteristically farther away.

This led the scientists to infer that these supernovae were much farther away than they anticipated by looking at their redshifts. Using the objects’ brightness, the researchers calculated the distance of these supernovae. And using the spectrum, they were able to figure out the objects’ redshift and, so, how fast they were moving away from us. They discovered that the supernovae were not as close as anticipated, meaning they had traveled away from us faster than foreseen. These observations led researchers to ultimately conclude that the cosmos itself must be expanding faster over time.

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