Our Home in the Cosmos

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.”