Which is evidence for the existence of dark energy?
A. Black holes that are expanding at a constant rate.
B. Pulsars that seem to be moving closer at an accelerating rate.
C Supernovae that are moving away at an accelerating rate.
D. Galaxies that are rotating at a constant rate
C. Supernovae that are moving away at an accelerating rate.
The correct evidence for the existence of dark energy is C. Supernovae that are moving away at an accelerating rate.
The correct answer is C. Supernovae that are moving away at an accelerating rate.
To understand why this is evidence for the existence of dark energy, we need to consider the context of the expanding Universe. In the early 20th century, astronomer Edwin Hubble discovered that distant galaxies are moving away from us, and the further they are, the faster they appear to be receding. This led to the concept of the expanding Universe, suggesting that space itself is stretching, causing galaxies to move apart.
However, in the 1990s, observations of distant supernovae (exploding stars) revealed something unexpected. Instead of finding that the expansion of the Universe was slowing down over time due to the gravitational pull of matter, it was discovered that the expansion is actually accelerating. This observation raised the question: What is causing this accelerated expansion?
The answer to this question is believed to be dark energy. Dark energy is a theoretical form of energy that is thought to pervade all of space and possess a strong negative pressure, causing the expansion of the Universe to accelerate. Despite the "dark" in its name, it does not refer to a physical substance but rather an unknown property of the Universe.
Observations of supernovae that are moving away at an accelerating rate provide strong evidence for the existence of dark energy. If the expansion of the Universe was solely driven by the gravitational pull of matter, we would expect the expansion to slow down over time. However, the observed accelerated expansion suggests that an additional form of energy, like dark energy, is counteracting the gravitational pull and driving the Universe to expand faster.
Therefore, option C, supernovae that are moving away at an accelerating rate, is the evidence for the existence of dark energy.