Theme: Galaxy Structure

 

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Text, Viewspace. The show will continue in 15 seconds. Coming up: Explore galaxies, bright cities of stars. 

 

The timer at top right counts down from 15 seconds. 

 

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The text appears on a background of stars which move slowly towards and past us. 

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A multitude of galaxies in space.

 

Text, The universe is filled with snowflakes.

 

Not the frozen-water-falling-from-the-sky kind, but the kind made of stars, gas, and dust -- galaxies.

 

Like snowflakes on Earth, no two galaxies in space are exactly alike.

 

A sliding square puzzle with a galaxy on each square.

 

Text, We can classify galaxies into type -- spirals, ellipticals, irregulars -- based on their characteristics. SPIRAL GALAXIES. ELLIPTICAL GALAXIES. IRREGULAR GALAXIES.

 

Spiral galaxies have winding arms of gas and dust, similar to the blades of pinwheels.

 

Elliptical galaxies, the most common type of galaxy in our universe, range from circular to elongated, contain older stars, and smaller portions of gas and dust.

 

Irregular galaxies, which are abundant in the early universe, lack any defined shapes.

 

Interestingly, according to how these galaxies form, two galaxies of the same type may have different features that give each galaxy their own identity.

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A yellow, orange, pink, and white spiral galaxy.

 

Text, GALAXY N.G.C. 6217. This spiral galaxy is packed full of stars. Bright blue stars and clusters of stars swirl around the center of the galaxy along a coiled set of scaffolding known as spiral arms.

 

A swarm of yellow stars crowds into the center of the galaxy, forming a dense, bright core.

 

But this galaxy contains a lot more than just stars.

 

Broad veins of brown dust stretch along the starry spiral arms.

 

Pinkish clouds of gas, called nebulae, also pepper the arms.

 

At the hub of the whole thing, lurking within the galaxy's intense core, lies a massive beast that cannot be seen -- a supermassive black hole.

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Top left, a black and white picture of a minotaur. Top right, a color picture of space.

 

Text, MYTH versus REALITY

 

Myth side. Text, Galaxies are made only of stars.

 

Reality side. Text, Galaxies contain not just stars, but also planets, moons, and other rocky and icy bodies. Many galaxies also contain dust, great clouds of gas, and dark matter – matter that does not produce light.

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Text, Types of Galaxies

 

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A swirl of stars. Text, This is a classic example of a spiral galaxy.

 

Bright, curling arms of stars, laced with lanes of dust and clumps of gas, wrap around a bright central core.

 

These arms of stars, gas, and dust lie in a remarkably flat disk that stretches across tens of thousands of light-years.

 

Brown and gold galaxy, oriented diagonally. Text, If we could tilt the galaxy and look at it from the side, we would see something like this.

 

From this angle, it's not the bright stars that define the galaxies disk, but the thick, dark dust, made of different carbon and silicate compounds, within it.

 

Escaping the bounds of the disk, though, is a flock of stars around the galaxy's center.

 

These stars swell out of the disk, forming a central bulge.

 

Another fringe group of stars strays even farther from the disk.

 

Although you can't see it here, surrounding this galaxy is a large, spherical region called the halo.

 

The halo contains enormous and ancient clusters of stars, called globular clusters for their globe-light shape.

 

Galaxy halos do not contain as many stars as in the disk, so they are usually hard to see.

 

This halo, however, is different, due to the many globular clusters it contains - nearly 2,000, compared to only about 150 for our own Milky Way Galaxy.

 

The clusters appear as small white dots sprinkled above and below the galaxy's disk.

 

A halo of stars, a bright core or bulge, and arms that lie in a disk are the classic characteristics of a spiral galaxy.

 

But some galaxies have more or less than others.

 

Many spiral galaxies have an additional key feature; a bar of stars, gas, and dust streaming across the center of the galaxy.

 

This is a barred spiral galaxy.

 

In a barred spiral, the arms curl away from the ends of the bar instead of from the galaxy's core.

 

Curiously, some barred spiral galaxies also have a tight ring of stars encircling their heart.

 

There are some galaxies that look like spirals at first glance, but something about them isn't quite right.

 

They have a flat disk, a bright core, and a halo, just as a spiral does.

 

But they have no starry spiral arms.

 

Astronomers call them lenticular (or lens-shaped) galaxies.

 

Other galaxies have a long, flat disk, a bright core, and a halo, but they seem to lack a central bulge.

 

Meanwhile, some galaxies are nothing but bulge.

 

These, which are round or egg-shaped, and contain a bright core, are called elliptical galaxies.

 

But they do not have disks.

 

And then there are galaxies that have neither a disk nor a bulge.

 

They have no arms and no bright core.

 

In fact, they have no regular shape at all.

 

Naturally, they're called irregular galaxies.

 

Many irregular galaxies might have once been spiral or elliptical galaxies that were torn apart by the gravitational might of another, larger galaxy.

 

Our telescopes reveal many disruptive dances taking place between galaxies.

 

Close encounters between galaxies can demolish their structures and distort them into something quite bizarre.

 

Even classic spiral galaxies are not immune.

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A galaxy viewed edge on. A gray line of dust and stars.

 

Text, GALAXY N.G.C. 5866. This edge-on galaxy stretches across 60,000 light-years of space.

 

Murky dust lanes cut through the galaxy's huge halo.

 

Brown tendrils of dust reach out of the disk as if trying to touch the stars in the halo.

 

A reddish-yellow core bulges ever so slightly from the center of the disk.

 

The view tilts. A stream of blue extends from the left end of the galaxy.

 

Text, Bright blue stars extend the galaxy's disk even farther than the dust can reach.

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at-a-GLANCE. The Makeup of Galaxies.

 

A spiral galaxy on the left, distant star with hazy light surrounding it in the middle, random spread of stars and dust on the right

 

All galaxies contain stars, gas, and dust.

 

But the ways these contents are arranged, and the amounts of each, are different for each kind of galaxy.

 

spiral galaxy with bright core in the middle

 

Spiral galaxies are defined by their large, swirling disks of gas, dust, and stars.

 

The disk blazes with young stars but contains older stars as well.

 

The compact core of a spiral galaxy smolders with the golden glow of much older stars.

 

A spiral galaxy's halo contains a smaller population of ancient stars and star clusters that are often as old as the galaxy itself.

 

bright spot of light surrounded by hazy glow

 

Elliptical galaxies are round or elongated objects packed with ancient stars.

 

Small elliptical galaxies contain just a few million stars, but giant ellipticals can contain over a trillion.

 

Ellipticals usually have very little dust, but some have more than others.

 

Young stars are rare in elliptical galaxies. They can, however, be found in ellipticals that gained new gas and dust during a galactic merger to form young stars.

 

random configuration of stars floats in bright pink dust and gas

 

Irregular galaxies are messy blobs of gas, dust, and stars.

 

These galaxies tend to be especially dusty and gassy.

 

Dust and gas are the construction materials for new stars.

 

Patches of young stars and star-forming regions often give irregular galaxies a speckled appearance.

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 Bright teal lines separate the screen in half. Title. Myth versus Reality. Above the Myth side is a constellation map with a horned bull. On the Reality side is a dark sky with a bright white light. 

Text. Myth. Galaxies never change. 

Reality. Galaxies are continuously changing and evolving. Some changes, like those caused by galaxy collisions, happen slowly over a long timescale, and affect the entire galaxy. Others, like star explosions, occur very quickly, and affect small areas. 

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Two white, pink, and orange galaxies swirl around each other in a collision.

 

Text, Antennae GALAXIES. Two galaxies are engaged in a fiery collision that will ultimately lead to them merging into one enormous galaxy.

 

Remnants of the two galaxies' spiral arms and dust lanes are tossed about the accident site.

 

For now, the yellow cores of the two galaxies remain on opposite sides of this crash scene, but someday they will come together.

 

Gas and dust from the merging galaxies are smashing into each other, giving life to bright blue stars amidst brilliant pink nurseries.

 

Billions of new stars will be born before the merger is complete.