Astronomers caught a supermassive black hole turning on for the first time

black hole: A region of space having a gravitational field so intense that no matter or radiation (including light) can escape.

colleague: Someone who works with another; a co-worker or team member.

cosmic: An adjective that refers to the cosmos — the universe and everything within it.

galaxy: A group of stars — and usually invisible, mysterious dark matter — all held together by gravity. Giant galaxies, such as the Milky Way, often have more than 100 billion stars. The dimmest galaxies may have just a few thousand. Some galaxies also have gas and dust from which they make new stars.

insight: The ability to gain an accurate and deep understanding of a situation just by thinking about it, instead of working out a solution through experimentation.

light-year: The distance light travels in one year, about 9.46 trillion kilometers (almost 6 trillion miles). To get some idea of this length, imagine a rope long enough to wrap around the Earth. It would be a little over 40,000 kilometers (24,900 miles) long. Lay it out straight. Now lay another 236 million more that are the same length, end-to-end, right after the first. The total distance they now span would equal one light-year.

low-Earth orbit: An orbit fairly close to Earth’s surface — usually no more than 1,000 kilometers (620 miles), and perhaps no more than 160 km (99 mi) up. Commercial airlines, in contrast, tend to fly no higher than 14 km, or less than a tenth of the minimum low-Earth orbit.

matter: Something that occupies space and has mass. Anything on Earth with matter will have a property described as “weight.”

observatory: (in astronomy) The building or structure (such as a satellite) that houses one or more telescopes. Or it can be a system of structures that make up a telescope complex.

star: (adj. stellar) The basic building block from which galaxies are made. Stars develop when gravity compacts clouds of gas. When they become hot enough, stars will emit light and sometimes other forms of electromagnetic radiation. The sun is our closest star.

telescope: Usually a light-collecting instrument that makes distant objects appear nearer through the use of lenses or a combination of curved mirrors and lenses. Some, however, collect radio emissions (energy from a different portion of the electromagnetic spectrum) through a network of antennas.

transient: Lasting or taking place for a relatively short period of time.

transition: The boundary where one thing (paragraphs, ecosystems, life stage, state of matter) changes or converts into another. Some transitions are sharp or abrupt. Others slowly or gradually morph from one condition or environment to another.

universe: The entire cosmos: All things that exist throughout space and time. It has been expanding since its formation during an event known as the Big Bang, some 13.8 billion years ago (give or take a few hundred million years).

X-ray: A type of radiation analogous to gamma rays, but having somewhat lower energy.