Many stars do not live alone. A binary star is a pair of stars bound by gravity, orbiting a common center of mass. Roughly half of Sun-like stars have at least one companion, and the share is higher for massive stars. Types by how we detect them Visual binaries: both stars can be seen separately … Read more
Galaxies did not exist at the very beginning. The early universe was a nearly smooth hot gas. Tiny differences in density, visible today in the cosmic microwave background, grew over hundreds of millions of years into the galaxies we see. Dark matter first According to the standard model of cosmology, dark matter clumped first, because … Read more
A neutron star is what remains when a massive star’s core collapses in a supernova. It packs more mass than the Sun into a sphere only about 20 kilometers (12 miles) across, roughly the size of a city. How extreme are they? The core is thought to be made mostly of neutrons, though what happens … Read more
The Milky Way is our home galaxy: a barred spiral of hundreds of billions of stars, including the Sun. It is an ordinary galaxy among hundreds of billions in the observable universe, but it is the only one we can study from the inside. Size and structure Where are we? The Sun sits about 26,000 … Read more
A white dwarf is the exposed core left behind when a star like the Sun runs out of fuel and sheds its outer layers. Roughly 97 percent of stars in the Milky Way, including the Sun, are expected to end as white dwarfs. Small, dense and hot A typical white dwarf has about half to … Read more
The three words are often used interchangeably, and the boundaries really are blurry. Still, each has a distinct emphasis. Astronomy: observing the sky Astronomy is the oldest of the natural sciences. It studies everything beyond Earth’s atmosphere: planets, stars, galaxies and more. Historically, it focused on measuring and observing: positions, motions, brightness and distances. Ancient … Read more
A quasar is the extremely bright core of a distant galaxy, powered by a supermassive black hole swallowing gas. A single quasar can outshine all the stars of its host galaxy combined, which makes quasars visible across billions of light-years. How quasars were found In the 1950s, radio astronomers found sources that looked like stars … Read more
The universe is about 13.8 billion years old. That figure comes mainly from measurements of the cosmic microwave background, and it is supported by independent checks on the oldest objects we can see. Method 1: the cosmic microwave background The cosmic microwave background is light released about 380,000 years after the Big Bang. The size … Read more
Stars are usually born in groups. A star cluster is a family of stars that formed from the same cloud at about the same time, so they share a similar age and chemical makeup. This makes clusters ideal laboratories for studying how stars evolve. Open clusters Famous examples: the Pleiades (the Seven Sisters), visible to … Read more
Despite the name, cosmic rays are not rays of light. They are high-energy particles, mostly atomic nuclei, that travel through space at nearly the speed of light and constantly hit Earth’s atmosphere. How cosmic rays were discovered In 1912, Austrian physicist Victor Hess carried instruments up in a balloon and found that radiation increased with … Read more
