Long ago, people thought that the Earth was at the center of the Universe.

Milky Way Galaxy, large spiral system consisting of several hundred billion stars, one of which is the Sun. It takes its name from the Milky Way, the irregular luminous band of stars and gas clouds that stretches across the sky as seen from Earth. Although Earth lies well within the Milky Way Galaxy (sometimes simply called the Galaxy), astronomers do not have as complete an understanding of its nature as they do of some external star systems. A thick layer of interstellar dust obscures much of the Galaxy from scrutiny by optical telescopes, and astronomers can determine its large-scale structure only with the aid of radio and infrared telescopes, which can detect the forms of radiation that penetrate the obscuring matter. 

Earth and the Sun – our whole Solar System – are located in a spiral arm in the Milky Way galaxy, but it's only relatively recently that this has become a widely-accepted fact.

It’s hard to say much about the Milky Way’s structure with any certainty because we’re a part of it.

Unlike other galaxies that we can see through telescopes, we can’t look at the Milky Way face-on.

The Milky Way contains hundreds of billions of stars like our sun. (And like our sun, most of these stars have at least one planet orbiting them.) Earth is located about halfway between the center of the Milky Way and its outer edge.

Light bouncing off of Earth's surface takes about 25,000 light-years to travel to the galaxy's center. (A light-year is the distance light travels in one year.) So that means if you could somehow stand at the center of the Milky Way, you’d be observing light that possibly left Earth before humans first settled in North America.

At the center of the Milky Way is one of the strangest and deadliest things in the universe: a black hole. Black holes are born when a giant star runs out of energy. The star implodes, causing an explosion called a supernova. The star’s heart collapses under its own weight. It’s squashed into a tiny dot you can’t see.

Scientists suspect a black hole lurks at the center of most galaxies. The Milky Way’s black hole is called Sagittarius A*. (A* is scientist-code for “A-star.”) Its gravity, or attractive force, is so strong that it pulls in anything that gets too close, including stars. So we’re lucky that Earth is located far away from the center!

At the heart of our home galaxy lurks a gigantic black hole that’s more than a trillion times heavier than Earth, with all that mass stuffed into a region that is about 2,000 times wider than our planet. Now scientists have discovered the behemoth is throwing off a hot breeze.

The findings, detailed today in the Astrophysical Journal Letters, suggest not only that all black holes emit such a wind but also that these beasts are not total loners that are isolated from their environments.

“We have never seen a breeze from a black hole,” says study co-author Elena Murchikova of Northwestern University. “We usually see the consequences of outbursts or other violent activities. Seeing the black hole sitting there, being quiet but still dumping energy all over the region without doing anything violent, is terribly cute,” adds Murchikova, an assistant professor in Northwestern’s department of physics and astronomy.

Supermassive black holes are suspected to lurk at the centers of all galaxies. Despite plenty of investigations of our home galaxy’s monstrous resident, called Sagittarius A*, or Sgr A* for short, scientists have yet to detect gassy winds blowing from it—which they’ve long theorized to exist.

“To observe our own black hole, we have to look through the plane of our galaxy,” Murchikova said in a statement. “That means we have to peer through gas, dust and ionized structures, and you can’t really see through all of that easily.”

The cosmos (/ˈkɒzmɒs/, US also /-moʊs, -məs/;[1] Ancient Greek: κόσμος, romanized: kósmos) is an alternative name for the universe or its nature or order. Usage of the word cosmos implies viewing the universe as a complex and orderly system or entity.[2]

The cosmos is studied in cosmology – a broad discipline covering scientific, religious or philosophical aspects of the cosmos and its nature. Religious and philosophical approaches may include the cosmos among spiritual entities or other matters deemed to exist outside the physical universe.

The Universe’s History

The origin, evolution, and nature of the universe have fascinated and confounded humankind for centuries. New ideas and major discoveries made during the 20th century transformed cosmology – the term for the way we conceptualize and study the universe – although much remains unknown. Here is the history of the universe according to cosmologists’ current theories.

Cosmic Inflation

Around 13.8 billion years ago, the universe expanded faster than the speed of light for a fraction of a second, a period called cosmic inflation. Scientists aren’t sure what came before inflation or what powered it. It’s possible that energy during this period was just part of the fabric of space-time. Cosmologists think inflation explains many aspects of the universe we observe today, like its flatness, or lack of curvature, on the largest scales. Inflation may have also magnified density differences that naturally occur on space’s smallest, quantum-level scales, which eventually helped form the universe’s large-scale structures.

Big Bang and Nucleosynthesis

When cosmic inflation stopped, the energy driving it transferred to matter and light – the big bang. One second after the big bang, the universe consisted of an extremely hot (18 billion degrees Fahrenheit or 10 billion degrees Celsius) primordial soup of light and particles. In the following minutes, an era called nucleosynthesis, protons and neutrons collided and produced the earliest elements – hydrogen, helium, and traces of lithium and beryllium. After five minutes, most of today’s helium had formed, and the universe had expanded and cooled enough that further element formation stopped. At this point, though, the universe was still too hot for the atomic nuclei of these elements to catch electrons and form complete atoms. The cosmos was opaque because a vast number of electrons created a sort of fog that scattered light.

Recombination

Around 380,000 years after the big bang, the universe had cooled enough that atomic nuclei could capture electrons, a period astronomers call the epoch of recombination. This had two major effects on the cosmos. First, with most electrons now bound into atoms, there were no longer enough free ones to completely scatter light, and the cosmic fog cleared. The universe became transparent, and for the first time, light could freely travel over great distances. Second, the formation of these first atoms produced its own light. This glow, still detectable today, is called the cosmic microwave background. It is the oldest light we can observe in the universe.