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 Sun is an ordinary star but the center of everything in our solar system. Its gravity holds the planets in orbit, its light and heat make life on Earth possible, and its activity affects space all the way to the edge of the heliosphere. Gravity: the anchor The Sun contains about 99.8 percent of … Read more
No one has drilled into Jupiter or breathed the air of a planet around another star. Yet astronomers know a surprising amount about what planets and their atmospheres are made of, by combining several methods. Density: rock, ice or gas? If you know a planet’s mass (from the orbits of its moons, or how it … Read more
Since Sputnik in 1957, space exploration has achieved astonishing things: humans on the Moon, rovers on Mars, probes beyond the heliosphere. But every mission still faces hard problems, and sending people farther than the Moon multiplies them. Radiation Beyond Earth’s protective magnetic field, astronauts are exposed to galactic cosmic rays and solar particle events, which … Read more
An exoplanet is a planet orbiting a star other than the Sun. The first ones were confirmed in the 1990s, and the NASA Exoplanet Archive now lists more than 6,000. Most are never seen directly: they are detected through their effects on their star. The transit method When a planet passes in front of its … Read more
A supernova is the explosion of a star, briefly bright enough to outshine an entire galaxy. These explosions forge and scatter many of the elements in our bodies and planets, and leave behind neutron stars and black holes. Two main kinds Core-collapse supernovae (Types II, Ib and Ic) happen when a massive star, more than … Read more
Every star is born in a cloud of gas and dust and spends its life in a balance between gravity, which pulls inward, and the pressure of nuclear fusion pushing outward. Its mass at birth decides how long it lives and how it dies. Birth in molecular clouds Stars form in cold, dense clouds of … Read more
How the universe will end depends mainly on dark energy, the mysterious component that is making the expansion of space speed up. Nobody knows for sure, but current observations point toward a long, cold fade. The discovery that changed everything In 1998, two teams studying distant Type Ia supernovae found that they were dimmer than … Read more
Astronomers have not yet found a true “Earth twin”, a rocky planet of Earth’s size orbiting a Sun-like star at the right distance and with signs of life. But they have found many planets that share some of Earth’s key features, and statistics suggest that such worlds are common. What “Earth-like” means Scientists usually look … Read more
Stars look like identical points of light, but they differ enormously in temperature, size, brightness and lifespan. Astronomers sort them with two simple tools: a letter for temperature and a Roman numeral for size. Spectral classes: sorting by temperature The Harvard system, developed in the early 1900s by Annie Jump Cannon and colleagues, groups stars … Read more
