Astrophysics Vocabulary in English

A black hole is a region of space where gravity is so strong that nothing, not even light, can escape once it crosses the event horizon. Black holes form when massive stars collapse at the end of their lives, or through the merging of neutron stars. Supermassive black holes containing millions or billions of solar masses are found at the centres of most galaxies. Their existence was confirmed directly when the Event Horizon Telescope captured the first image of a black hole in 2019.

Redshift is the phenomenon in which light from an object moving away from the observer is stretched to longer wavelengths, shifting toward the red end of the electromagnetic spectrum. It is analogous to the Doppler effect for sound. Cosmological redshift provided Edwin Hubble with evidence that distant galaxies are receding from us, supporting the Big Bang theory. The greater the redshift of a galaxy, the faster it is moving away and the further it is from Earth.

The Big Bang theory is the prevailing cosmological model describing the origin and evolution of the universe. It proposes that approximately 13.8 billion years ago, all matter and energy was concentrated at an extremely hot, dense singularity that rapidly expanded. As the universe cooled, subatomic particles formed, then atoms, then stars and galaxies. Evidence supporting the Big Bang includes the cosmic microwave background radiation, the abundance of light elements, and the observed expansion of the universe.

Dark matter is a hypothetical form of matter that does not emit, absorb, or reflect light but exerts gravitational effects on visible matter. Its existence is inferred from the observed rotation of galaxies, gravitational lensing effects, and large-scale structure of the universe. Dark matter is estimated to make up approximately 27% of the total mass-energy content of the universe, compared to only 5% for ordinary visible matter.

A neutron star is the collapsed remnant of a massive star after a supernova explosion. With a mass roughly 1.4 times that of the Sun compressed into a sphere only about 20 kilometres across, neutron stars are among the densest objects in the universe. Some neutron stars rotate rapidly and emit beams of electromagnetic radiation — these are called pulsars. Neutron stars can also merge with one another, producing gravitational waves detectable on Earth.

A parsec is a unit of distance used in astronomy, equivalent to approximately 3.26 light-years or about 30.9 trillion kilometres. It is defined as the distance at which one astronomical unit subtends an angle of one arcsecond. The parsec is more convenient than the light-year for professional astronomers when describing distances between stars and galaxies. The nearest star system to the Sun, Alpha Centauri, is about 1.34 parsecs away.

A galaxy is a gravitationally bound system containing billions of stars, stellar remnants, interstellar gas, dust, and dark matter. A nebula is a cloud of gas and dust in space — some are regions where new stars are forming (stellar nurseries), while others are remnants of dead stars. Historically, before telescopes were powerful enough, distant galaxies were often mistakenly called nebulae by astronomers.

Gravitational lensing is the bending of light from a distant object as it passes near a massive body such as a galaxy cluster. Predicted by Einstein's general theory of relativity, it causes the distant object to appear distorted, magnified, or multiplied. Strong lensing produces visible arcs or multiple images; weak lensing causes subtle statistical distortions. Gravitational lensing is used to study dark matter, detect exoplanets, and observe the earliest galaxies in the universe.

The cosmic microwave background (CMB) is the thermal radiation left over from the early universe approximately 380,000 years after the Big Bang, when the universe first became transparent to light. It pervades the entire observable universe at a temperature of about 2.7 Kelvin. Tiny fluctuations in the CMB correspond to density variations in the early universe that eventually gave rise to galaxies. The CMB was first detected accidentally by Arno Penzias and Robert Wilson in 1965.

Start with frequently used terms: galaxy, star, black hole, redshift, supernova, and nebula. Then build to more technical vocabulary: parsec, event horizon, gravitational lensing, and spectroscopy. Watching NASA and ESA video releases with English captions and reading the astronomy section of Scientific American exposes you to these words in natural contexts. Creating mind maps that link related terms — for example, the stellar life cycle from nebula to supernova to neutron star or black hole — helps you remember them in meaningful clusters.