Composition. The Universe is composed almost completely of dark energy, dark matter, and ordinary matter. Other contents are electromagnetic radiation (estimated to constitute from 0.005% to close to 0.01% of the total mass-energy of the Universe) and antimatter.Read more
Our Milky Way Galaxy is teeming with exoplanets—statistically speaking at least one for each of the hundreds of billions of stars in the galaxy. Thousands of planets have been discovered, with thousands of more planet candidates identified. Several different planet-finding techniques have matured and contribute to our present knowledge of exoplanets. Each technique has different sensitivities that favor a planet-star separation and planet mass or size range limits. Because of the selection effect, none of the current exoplanet-finding techniques can find solar system copies. Astronomers have nonetheless found a completely unexpected diversity of exoplanets, a veritable “zoo” containing many astonishing planet types.Read more
We live in the Milky Way Galaxy, which is a collection of stars, gas, dust, and a supermassive black hole at it’s very center. Our Galaxy is a spiral galaxy, which are rotating structures that are flat (disk-like) like a DVD when looked upon edge-on. There is also a bulge in the middle that consists of mostly old stars. When you look at a spiral galaxy face-on, you can see beautiful spiral arms where stars are being born. Our solar system is in the Orion arm, and we are about 25,000 light years (2.5 X 10^17 miles) from the very center of the Galaxy.Read more
The very first stars likely formed when the Universe was about 100 million years old, prior to the formation of the first galaxies. … This started the cosmic chemical enrichment that led to the formation of the stars that we see in the Milky Way today, to rocky planets and eventually humans.Read more
Our Milky Way Galaxy was once thought to comprise the entire known universe. Today our universe encompasses many billions of galaxies, and its history can be recounted back to its earliest moments.
Our universe began with an explosion of space itself – the Big Bang. Starting from extremely high density and temperature, space expanded, the universe cooled, and the simplest elements formed. Gravity gradually drew matter together to form the first stars and the first galaxies. Galaxies collected into groups, clusters, and superclusters. Some stars died in supernova explosions, whose chemical remnants seeded new generations of stars and enabled the formation of rocky planets. On at least one such planet, life evolved to consciousness. And it wonders, “Where did I come from?”Read more
In 2014, a tiny planetesimal called 2014 MU69 and nicknamed Ultima Thule was discovered. The New Horizons spacecraft explored it on January 1, 2019, in a quick flyby. In 2016, another possible new world was found “out there” beyond the orbit of Neptune, and there could be many more waiting to be discovered.Read more
In the beginning – before the 1920s, these words had no place in our scientific understanding of the universe. Astronomers believed the cosmos to be eternal and unchanging. We knew of only one galaxy and a few million visible stars, and this was the scope of our observable universe.
Then astronomer Edwin Hubble observed, courtesy of redshift, distant galaxies speeding away from each other and formulated Hubble’s Law to explain the universe’s uniform expansion. Redshift just refers to a distant celestial body’s shift toward longer, or redder, wavelengths, compliments of the Doppler effect.Read more
Welcome to the Mysteries of the Sun. This unique NASA resource on the web, in print, and with companion videos introduces Heliophysics: the study of the Sun’s influence throughout the solar system and, in particular, its connection to the Earth and the Earth’s extended space environment. Learn about topics such as Space Weather, Solar Variability, the Heliosphere, Earth’s Magnetosphere, and the Earth’s Upper Atmosphere. Come and explore our Sun!Read more
Space-time is a mathematical model that joins space and time into a single idea called a continuum. This four-dimensional continuum is known as Minkowski space. Combining these two ideas helped cosmology to understand how the universe works on the big level (e.g. galaxies) and small level (e.g. atoms).Read more
A black hole cosmology is a cosmological model in which the observable universe is the interior of a black hole. Such models were originally proposed by theoretical physicist Raj Pathria, and concurrently by mathematician I. J. Good.
Any such model requires that the Hubble radius of the observable universe be equal to its Schwarzschild radius, that is, the product of its mass and the Schwarzschild proportionality constant. This is indeed known to be nearly the case; however, most cosmologists consider this close match a coincidence.
In the version as originally proposed by Pathria and Good, and studied more recently by, among others, Nikodem Popławski, the observable universe is the interior of a black hole existing as one of possibly many inside a larger parent universe, or multiverse.Read more