Astronomy Deep Dive Quiz

Dark matter is an invisible form of matter that makes up about 27% of the universe's total mass-energy content. It does not interact with light but exerts gravitational effects — its existence was inferred from galaxy rotation curves that couldn't be explained by visible matter alone. Dark energy is even more mysterious, making up roughly 68% of the universe and driving its accelerating expansion. It was discovered in 1998 when astronomers found that distant supernovae were dimmer than expected, implying the universe's expansion was speeding up rather than slowing down.

Astronomers use several techniques to detect planets orbiting other stars. The transit method detects tiny dips in a star's brightness as a planet passes in front of it — this is how the Kepler Space Telescope found thousands of exoplanets. The radial velocity (Doppler) method measures the slight wobble a planet induces in its host star. Direct imaging captures the light of a planet directly, while gravitational microlensing detects planets via the bending of light from a background star. The first confirmed exoplanet around a Sun-like star, 51 Pegasi b, was found in 1995 using radial velocity.

In about 5 billion years, the Sun will exhaust its hydrogen fuel and expand into a red giant, swelling to perhaps 200 times its current size and engulfing Mercury and Venus (and possibly Earth). The outer layers will then shed as a planetary nebula, and the remaining core will become a white dwarf — a dense, slowly cooling remnant about the size of Earth. Because the Sun's mass is well below the 1.4 solar mass Chandrasekhar limit, it will never undergo a supernova explosion.