Red Giants: The Swollen Old Stars

Red giants are aging stars that have exhausted the hydrogen fuel in their cores.
As their cores contract, their outer layers expand up to hundreds of times the Sun’s size.
Despite their massive size, red giants have cooler surfaces, giving them a reddish glow.
Our Sun will become a red giant in about 5 billion years, engulfing nearby planets.
Red giants fuse helium into carbon and oxygen in their hot, dense cores.
Many well-known bright stars, like Betelgeuse and Aldebaran, are red giants.
These stars lose mass through strong stellar winds, enriching space with heavy elements.
Some red giants pulsate in brightness as their outer layers expand and contract.
The red giant phase lasts only a few million years—short compared to a star’s full life.
Eventually, most red giants shed their outer layers, leaving behind a white dwarf surrounded by a planetary nebula.