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ASTROPHYSICS
How do black holes grow in mass?
Once born, black holes can grow by gobbling up gas, other stars or even other black holes. Black holes, particularly supermassive black holes sitting at the centres of galaxies, are often surrounded by gas. They can feed on this gas through an accretion disc – a pancake-like structure of gas that gradually spirals into the black hole. Some massive black holes take their time during this meal, but others go into a feeding frenzy. The rapid, messy eaters in active galactic nuclei try to double their mass over a timescale of around 100 million years, burping out excess energy in powerful jets that are observed as quasars.
Black holes can also pull material from stars that get too close. The black hole’s gravity raises tides on a nearby star – like the tides in Earth’s oceans, but potentially much stronger. If the tides become too strong, gas
