20 Stars & Galaxies Facts
1. The observable universe contains an estimated two trillion galaxies, each hosting billions to trillions of stars.
2. Light from the Sun takes about 8 minutes and 20 seconds to reach Earth — so we always see the Sun as it was slightly in the past.
3. Neutron stars are so dense that a teaspoon of their material would weigh about 10 million tonnes on Earth.
4. The Milky Way galaxy is estimated to contain between 100 and 400 billion stars and is about 100,000 light-years across.
5. Black holes don't actually "suck" — objects only fall in if they cross the event horizon, the point of no return where escape velocity exceeds the speed of light.
6. The largest known star, UY Scuti, is so massive that if placed at the center of our Solar System, it would extend beyond the orbit of Jupiter.
7. Supernovae — the explosive deaths of massive stars — are responsible for creating and spreading most of the heavy elements in the universe, including iron and gold.
8. The Andromeda Galaxy is on a collision course with the Milky Way, expected to merge in about 4.5 billion years.
9. Dark matter makes up about 27% of the universe's total mass-energy, yet it has never been directly detected — we only infer it from gravity's effects.
10. Pulsars are rapidly rotating neutron stars that emit beams of electromagnetic radiation — some spin hundreds of times per second.
11. The cosmic microwave background is faint radiation left over from the Big Bang, detectable in every direction we look in the universe.
12. Stars are born inside giant clouds of gas and dust called nebulae, which collapse under gravity until nuclear fusion ignites at their cores.
13. White dwarfs are the remnants of stars like our Sun — after billions of years they slowly cool into cold, dark objects called black dwarfs.
14. The Hubble Space Telescope, launched in 1990, has captured images of galaxies over 13 billion light-years away, near the edge of the observable universe.
15. Gravitational waves, ripples in spacetime predicted by Einstein in 1915, were first directly detected in 2015 from the collision of two black holes.
16. The Sun converts about 600 million tonnes of hydrogen into helium every second through nuclear fusion — and has enough fuel for another 5 billion years.
17. Quasars are among the most luminous objects in the universe — powered by supermassive black holes consuming vast amounts of matter.
18. Every atom of carbon, oxygen, and iron in your body was forged inside a star that exploded long before our Solar System was born.
19. The James Webb Space Telescope, launched in 2021, can observe the universe in infrared light, revealing galaxies that formed just a few hundred million years after the Big Bang.
20. Exoplanets — planets orbiting other stars — number in the thousands of confirmed discoveries, with some located in the "habitable zone" where liquid water might exist.