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Galaxies

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Goals

Learn the definition of “galaxy.”
Distinguish between shapes of the major galaxy types.
Discover where we lie within our galaxy.
Understand why the Milky Way galaxy appears the way that it does.
Discover how we can use photography to better image our galaxy.
Understand how different wavelengths of light allow us to see different parts of our galaxy.
Learn how we have recently imaged the center of our galaxy.
Describe how our galaxy is clustered together with other galaxies.

Worksheet: Click here to download the worksheet! Then open it in Google Docs.

A Hubble Space Telescope image of the Sombrero galaxy, M104 (credit: NASA)

A Hubble Space Telescope image of the Sombrero galaxy, M104 (credit: NASA)

Galaxies are huge collections of stars, dust and gas.

Contain millions, up to a trillion stars

Size: From a few thousand to several hundred thousand light-years across.

Types of galaxies

Galaxies come in many different sizes, shapes

May be by themselves, in pairs, or in larger groups (clusters)

Here are the basic types

Where is our solar system?

When we look up at night, what part of our galaxy do we see?
Let’s start by finding our solar system in this diagram.

Now let’s consider the same galaxy, looking at it from the side.
Again, first locate our solar system.

What would we see if we looked up, or down, perpendicular to the plane of the galaxy?

What would we see if we looked inwards, towards the galactic center?

Our solar system is basically in the flat plane of the galaxy.

“We can actually see the dense plane of the Milky Way stretch across the sky in dark places that do not have a lot of surrounding light pollution. The diffuse light is the combined light from millions of stars. Some of the light from these stars are obscured by large clouds of dust, which is why there are dark patches. Dust and gas are necessary to form stars, and most stars are formed within the spiral arms. Note that we can’t really see the center of the galaxy with our eyes – because there is dust in the way.”

– http://www.astro.ucla.edu/~ghezgroup/gc/journey/journey_intro.html

How can we better see the center of our galaxy?

Use photography techniques

dark-sky-galaxy-viewed-without-light-pollution

That’s good, but how can we see more? Regular photography only uses visible wavelengths of light.

So how about now looking at the galaxy with other wavelengths of light to look at our own galaxy.

Milky Way Galaxy in Multiple Wavelengths Pearson Prentice

What would we see if we used different wavelengths of light to look at other galaxies?

Multiwavelength whirlpool galaxy astronomy

Imaging the center of our galaxy

You’re looking at the center of our galactic home, the Milky Way, as imaged by 64 radio telescopes in the South African wilderness.

South African MeerKAT radio telescope

The black hole itself is invisible, but as material is pulled inside, some of that material emits light that escapes.

Also, not all material near a black hole actually enters it. Some is pulled around it, compressed and heated, and then flung out – all the time radiating various forms of radiation.

black hole center of the Milky Way By SARAO

The black hole at the center of the Milky Way and filaments. From SARAO, South African Radio Astronomy Observatory.

This image shows filaments of particles, structures that seem to exist in alignment with the galaxy’s central black hole. It’s unclear what causes these filaments. Maybe they are particles ejected by the spinning black hole; maybe they are hypothesized “cosmic strings;” and maybe they’re not unique, and there are other, similar structures waiting to be found, according to a 2017 release from Harvard-Smithsonian Center for Astrophysics. “This image from MeerKAT is awesome to me because the fine filaments seen in the radio image are excellent tracers of the galactic magnetic field, something we don’t get to see in most optical and infrared data,” Erin Ryan, research space scientist at the NASA Goddard Space Flight Center.

Interstellar travel

Could we ever travel to other solar systems in our galaxy? See The physics of interstellar travel

Superclusters

Large groups of galaxy clusters.

Our Milky Way galaxy is part of the Local Group galaxy group, which contains more than 54 galaxies, spanning over 10 million light-years.

This in turn is part of the Laniakea Supercluster, which spans over 500 million light-years

The number of superclusters in the observable universe is estimated to be 10 million.

_ from Supercluster, Wikipedia, 1/19

virgo-supercluster-galaxies

The various galaxies of the Virgo Supercluster, grouped and clustered together. On the largest scales, the Universe is uniform, but as you look to galaxy or cluster scales, overdense and underdense regions dominate. Image credit: Andrew Z. Colvin, via Wikimedia Commons.

Galaxies moving through the universe

There are hundreds of billions of galaxies in the Universe.

Gravitational repulsion and the Dipole Repeller

Learning Standards

Massachusetts Curriculum Frameworks Science and Technology/Engineering (2016) 

6.MS-ESS1-5(MA). Use graphical displays to illustrate that Earth and its solar system are one of many in the Milky Way galaxy, which is one of billions of galaxies in the universe.

A Framework for K-12 Science Education: Practices, Crosscutting Concepts, and Core Ideas (2012)

By the end of grade 8. Patterns of the apparent motion of the sun, the moon, and stars in the sky can be observed, described, predicted, and explained with models. The universe began with a period of extreme and rapid expansion known as the Big Bang. Earth and its solar system are part of the Milky Way galaxy, which is one of many galaxies in the universe.

By the end of grade 12. The star called the sun is changing and will burn out over a life span of approximately 10 billion years. The sun is just one of more than 200 billion stars in the Milky Way galaxy, and the Milky Way is just one of hundreds of billions of galaxies in the universe.

Benchmarks: American Association for the Advancement of Science

The sun is a medium-sized star located near the edge of a disc-shaped galaxy of stars, part of which can be seen as a glowing band of light that spans the sky on a very clear night. 4A/M1a

The universe contains many billions of galaxies, and each galaxy contains many billions of stars. To the naked eye, even the closest of these galaxies is no more than a dim, fuzzy spot. 4A/M1bc

Some distant galaxies are so far away that their light takes several billion years to reach the earth. People on earth, therefore, see them as they were that long ago in the past. 4A/M2de

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