Chandra :: The X-ray Astronomy Field Guide

The X-ray Astronomy Field Guide

An overview to X-ray Astronomy and X-ray sources: from black holes to galaxy clusters.

Learn About

Field Guide Highlight

Telescopes & Light
Astronomers have built telescopes and detectors that can see far beyond the type of radiation we can detect with the human eye.

Podcast Highlight

Tour: Black Hole Destroys Star and Goes After Another
A massive black hole has torn apart one star and is...

X-ray Astronomy

A brief review of the history of X-ray astronomy, what X-rays are, how they are produced in the cosmos, why X-ray telescopes must be in space, and why X-ray astronomy is such a "hot" field.
Click one of the categories to jump down to that section.

History
X-ray Universe
X-rays & Light

X-ray Absorption
X-ray Images 101
Galactic Navigation

Dark Matter
Dark Energy
Chemistry & Cosmos

History of X-ray Astronomy
A brief overview of the history behind X-ray Astronomy: from the differences between optical and X-ray telescopes to descriptions of the major X-ray Astronomy missions.

• Major Milestones in X-ray Astronomy

Discovering the X-Ray Universe
What the "X-ray universe" refers to, how this is studied and why it is important to scientific research.

• Origin, Evolution & Destiny of the Universe

X-rays & Light
Discovered in 1895, X-rays are another form of light. Look at the electromagnetic spectrum, learn how X-rays are produced, and compare medical X-rays and X-ray Astronomy.

• X-Ray Astronomy vs. Medical X-Rays

X-ray Absorption
What happens when an X-ray is absorbed in the atmosphere? How do X-ray telescopes in orbit above the Earth's atmosphere collect X-rays?

X-ray Images 101
How are Chandra images made? What do the colors mean? Find out the answers to these questions and more in X-ray Images 101.

Galactic Navigation
Do you ever question, "Where are all those stars in the sky really located? How far are they from me?" Well then, take a tour of the Galactic Coordinate System.

Dark Matter Mystery
Is it possible that most galaxies are surrounded by some "dark" form of matter that cannot be observed by radio, infrared, optical, ultraviolet, X-ray, or gamma-ray telescopes?

• The Wonderful (And Fearful) Dark Side

Dark Energy
Dark energy is a hypothetical form of energy that permeates all space and exerts a negative pressure that causes the universe to expand at an ever-increasing rate.

Chemistry and the Universe
The familiar periodic table of elements -found in virtually every chemistry class- has been adapted to show how astronomers see the chemical Universe.

X-ray Sources

An explanation of different types of cosmic X-ray sources, and detailed descriptions of some of the individual sources observed by the Chandra X-ray Observatory by category.
Click one of the categories to jump down to that section.

Solar System
Stars
White Dwarfs
Supernovas

Neutron Stars
Black Holes
Galaxies
Quasars & AGN

Galaxy Clusters
X-ray Background
Brown Dwarfs
Gamma Ray Bursts

Solar System
Solar System: The Sun's hot outer atmosphere produces X-rays, but because it is so close (a mere 93 million miles!), it is too bright for Chandra's sensitive eyes. Chandra can observe other objects in our solar system such as comets and Jupiter.

Stars
The hot outer atmospheres, or coronas, of normal stars such as our sun produce X-rays. X-ray observations are useful for understanding how the flaring activity of stars can change as stars evolve, and how the evolution of stars is changed if they are in a close binary system.

Young Stars and Star Clusters Young stars are much brighter in X-rays than middle-aged stars such as the sun. Stars do not form in isolation, but in clusters which can have thousands of members, so most young stars are found in clusters.

Normal Stars Normal, middle-aged stars such as our sun have hot, X-ray- emitting outer atmospheres, or coronas. X-ray observations have proven to be a useful tracer for studying how the turbulent heating near the surface of stars depends on the age, rotation and type of the star, and how the flaring activity of stars changes as stars evolve.

Binary and Multiple Star Systems The evolution of stars can be changed dramatically if they are in a close binary system. These changes depend on how close the stars are to one another, and how massive the stars are. Some of the strongest X-ray sources in our galaxy are close binary systems containing neutron stars and black holes.

Stellar Evolution Stars shine as a result of nuclear reactions deep in their interior. As a star's nuclear energy supplies are used up, it evolves toward an end state that depends on its mass.

White Dwarf Stars
White dwarf stars are dense, burnt-out remnants of stars like the sun. They are formed when the star contracts after using up its nuclear fuel. When matter from a nearby star falls onto a white dwarf star, X-rays are produced.

Supernovas & Supernova Remnants
When a star blows apart in a supernova, the explosion creates a remnant of multi-million degree gas that shines brightly in X-rays for thousands of years. X-ray observations can reveal the dynamics of the explosion and heavy elements present in the remnant.
• Chandra's Celestial Fireworks Extravaganza (305 Kb requires flash)

Neutron Stars
When a massive star goes supernova, it can leave behind an extremely dense remnant star called a neutron star. Young neutron stars spew out high energy particles that produce X-rays for several thousand years. An old neutron star can produce X-rays when matter from a nearby star falls onto its surface.

Black Holes
When a collapsed star has more mass than three suns, it forms a black hole in space. These bizarre objects are found in rare double star systems or in the centers of galaxies where supermassive black holes have formed. X-ray telescopes provide an unequaled view of super- heated matter that is swirling toward the event horizon of a black hole.

Stellar Black holes with a mass of about 5 - 100 Suns formed at the end of very massive star's evolutionary cycle.

Mid-mass A newly discovered type of black hole that has a mass of 500 - 1,000's of Suns.

Supermassive Black holes with a mass of a million or more Suns located in the centers of galaxies.

Galaxies
X-ray observations of normal galaxies reveal the hot, energetic side of a galaxy's character by locating neutron stars, the remnants of supernovas, and black holes, and imaging hot superbubbles and galaxy-sized clouds of hot gas produced by bursts of star formation.

Normal Galaxies Large gravitationally bound systems consisting of hundreds of billions of stars, enough gas and dust to make billions more stars, and dark matter.

The Milky Way The Milky Way is our home galaxy - a vast rotating spiral of gas, dust, and hundreds of billions of stars. The Sun and its planetary system formed in the outer reaches of the Milky Way about 4.5 billion years ago.

Starburst Galaxies Galaxies in which a violent event, such as near-collision, has caused a sudden, intense burst of star formation in the recent past. X-ray observations provide the best means for studying the formation and expansion of starburst winds.

Quasars & Active Galaxies
Active galaxies show especially violent activity, usually near the centers of the galaxies. This activity is due to a supermassive black hole in the center of the galaxy, or a near collision with another galaxy, or both. Quasars are extreme examples of active galaxies.

Groups & Clusters of Galaxies
Among the most energetic events in the universe is the merger of groups of galaxies to form giant clusters containing thousands of galaxies. Vast, hot, X-ray emitting gas clouds in the clusters show this process in action.

Cosmology/Deep Fields/X-ray Background
The sky as observed in X-rays is not dark, but gives off a glow thought to be from many distant sources. Deep surveys with the Chandra X-ray Observatory should reveal the cause of this glow.

Brown Dwarfs
Clouds of collapsing gas and dust that did not contain enough mass to initiate core nuclear fusion. Such objects are then frozen somewhere along their pre- main sequence contraction phase, continuously cooling into compact dark objects. Because of their small size and low temperature, they are extremely difficult to detect observationally.

Gamma Ray Bursts
An outburst that radiates tremendous amounts of energy in a few minutes equal to or greater than a supernova, in the form of gamma rays. Such objects were discovered by accident in the late 1960's by satellites designed to detect gamma rays produced by atomic bomb tests on Earth.

Chandra X-ray Center, Operated for NASA by
the Smithsonian Astrophysical Observatory
This site was developed with funding from NASA under contract NAS8-03060.

Contact us: cxcpub@cfa.harvard.edu
Harvard-Smithsonian Center for Astrophysics
60 Garden Street, Cambridge, MA 02138 USA
Phone: 617.496.7941 Fax: 617.495.7356