Light from the Void by unknow

Author:unknow
Language: eng
Format: azw3
Publisher: Smithsonian
Published: 2019-10-21T16:00:00+00:00

3

KINGDOMS

OF THE VOID

Galactic Center, this page

Galaxy Center, this page

GALAXIES

GALAXIES ARE SYSTEMS of stars, gas, dust, and dark matter held together by gravity. There are billions of galaxies throughout the Universe, and they come in different shapes and sizes. There are irregular small dwarf galaxies, majestic spiral galaxies, and elliptical galaxies ranging in size from dwarfs to supergiants ten times larger than our Milky Way galaxy.

Within these galaxies are black holes, neutron stars, and bubbles of hot gas that reveal themselves in X-ray light. Astronomers use the Chandra X-ray Observatory to study how galaxies behave and what happens inside of them.

The X-ray images captured by Chandra are essential to our understanding of these island kingdoms in space. For example, Chandra’s view of elliptical galaxies reveals that they are filled with multimillion-degree gas, heated presumably by supernova explosions. Most of the gas in spiral galaxies is in the form of cool, dusty clouds. In both elliptical and spiral galaxies, X-ray images give us portraits of the end phases of stellar evolution—regions where supernovas have heated gas to millions of degrees, and objects where gravity has tightened its grip to form neutron stars and black holes.

The most extreme examples of gravity’s force are found deep in the centers of most galaxies, where supermassive black holes lurk. These gravitational monsters can contain masses ranging from a few million to a few billion Suns. In many galaxies, the supermassive black hole mainly makes its presence known through its gravitational force on the motions of stars, and by X-rays produced when gas is heated as it falls toward the black hole. But when large supplies of dust and gas surround supermassive black holes, the acceleration and heating of this gas as it is pulled into the black hole can produce stupendous amounts of energy at X-ray and other wavelengths and transform the appearance of the entire galaxy. Such galaxies are called active galaxies or quasars.

One of the most important galaxies that Chandra has studied is our own, the Milky Way. Chandra has provided an unparalleled view of the center of our Galaxy, some 26,000 light-years away, where a supermassive black hole called Sagittarius A* resides (see this page). Chandra provides us with views of galactic doppelgangers to the Milky Way, as well as visions of galaxies completely different from our own.

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