Cosmology

Focus Questions: What are galaxies? Where do scientists think the universe came from?

Galaxies and the Universe The universe is everything that exists. The observable universe is everything we can observe.

Galaxies and the Universe Astronomers are not sure how old the universe is, but current estimates range from 10-20 billion years.

What are Galaxies? Galaxies are systems that contain millions or even billions of stars. Most estimates place the number of galaxies in the observable universe at 50-100 billion.

What are Galaxies? Space is so vast that most galaxies are light years apart.

What are Galaxies? We are part of the Milky Way galaxy. Our star is only one among hundreds of billions. The Milky Way galaxy is a spiral galaxy that is shaped like a thin disk with a central bulge.

What are Galaxies? The diameter of the Milky Way is about 100,000 light-years. Its greatest thickness is about 10,000 light-years. The sun is about 26,000 light-years from the Milky Way’s center.

What are Galaxies? The “milky” haze in the night sky is the large number of stars that are in this region of the sky.

What are Galaxies? Milky Way

What are Galaxies? The Milky Way belongs to a group of more than 30 galaxies called the Local Group. The Milky Way’s nearest neighbors in the Local Group are the two Magellanic Clouds, which can be seen without a telescope in the Southern Hemisphere.

What are Galaxies? The Andromeda Galaxy is faintly visible in the Northern Hemisphere with the unaided eye.

Types of Galaxies No two galaxies are exactly alike. Most galaxies can be classified by shape.

Tuning Fork Diagram Developed by Edwin Hubble

Types of Galaxies Spiral galaxies (like the Milky Way) come in a range of types – from ones with large, bright nuclei of stars and tightly wound spiral arms, to ones with very small, dim nuclei and open sprawling arms. The Andromeda Galaxy is also a spiral galaxy.

Types of Galaxies Some spiral galaxies have a bar across the central disc and arms that come off of the bar, not the nucleus. These are barred spirals.

Types of Galaxies Elliptical galaxies range from nearly spherical to lens-shaped. The galaxy called M87 is an elliptical galaxy.

Types of Galaxies Their stars are concentrated in their centers, and they have no arms. Elliptical galaxies contain far less interstellar gas and dust (than spiral galaxies), and contain few, if any, young stars.

Types of Galaxies Irregular galaxies have irregular shapes and are much smaller and fainter than both spiral and elliptical galaxies.

Types of Galaxies Stars in irregular galaxies are spread out unevenly. The two Magellanic Clouds are irregular galaxies.

Origin of the Universe Scientists cannot say where or how the universe originated. However, through observations and experiments they have put together a model about how the universe has developed.

Origin of the Universe This model is called the Big Bang model. The big bang model explains the history of the universe from a tiny fraction of a second after it came into being up to the present time.

A Model of the Beginning According to the big bang model, 10-20 billion years ago all matter existed in an incredibly hot and dense state. Matter expanded and cooled, slowly condensing into stars and galaxies.

A Model of the Beginning The first stars consisted mostly of hydrogen with a small amount of helium. No planets orbited yet, heavier elements did not yet exist.

A Model of the Beginning More and more stars formed, matured, and died, making more and more heavier elements. Supernovas and dying red giants released the heavier elements into space.

A Model of the Beginning Eventually our sun and its 8+ planets were formed from interstellar gas and dust.

Evidence for the Big Bang Model The distance between galaxies and groups of galaxies seems to have increased with time (Edwin Hubble found redshifts in galaxies he studied).

Evidence for the Big Bang Model Cosmic background radiation has been discovered (radiation left over from the universe’s beginning).

Evidence for the Big Bang Quasars- old objects at the edge of the universe. If the Big Bang happened, this supports it.

Doppler Effect Is the apparent change in wavelength of light or sound when an object is moving towards or away from you. How the Doppler Effect Works: If a train comes towards you, its sound waves get compressed and get shorter. (You hear a higher pitch.) If it moves away from you, the wavelength gets longer and you hear a lower pitch.

Doppler Effect The Doppler Effect also applies to light: If an object in space is moving toward us, its wavelength shortens, and the light shifts towards the blue end of the color spectrum. If an object is moving away fom us, its wavelength gets longer, and the light shifts towards the red end of the color spectrum.

Illustration by Flavio Robles Fate of the Universe What shape is the universe? "Closed," "open," and "flat" actually refer to the shape, or curvature, of space-time itself.

Fate of the Universe Open – universe will expand forever Flat – consume all energy from big bang, coast to a halt far in the future Closed – expand until it reaches maximum, then collapsing back on itself. HowStuffWorks

Fate of the Universe ­A closed universe will lead to a big CRUNCH

Hubble Telescope Hubble telescope a telescope that orbits the earth outside our atmosphere. It provides us with many of the images we have of space. It is an especially useful telescope because it does not have to view things through our atmosphere

The Milky Way Our Sun is just a small star in its main sequence among millions of other stars in our galaxy!!!

The Sombrero Galaxy - 28 million light years from Earth - was voted best picture taken by the Hubble telescope. It has 800 billion suns and is 50,000 light years across

The Ant Nebula, a cloud of dust and gas who resembles an ant when observed using ground-based telescopes. The nebula lies within our galaxy between 3,000 and 6,000 light years from Earth

This picture is called Eskimo because it looks like a face surrounded by a furry hood. The hood is, in fact, a ring of comet-shaped objects flying away from a dying star.

Cat's Eye Nebula

The Hourglass Nebula, 8,000 light years away, has a pinched-in-the-middle look because the winds that shape it are weaker at the center

Cone Nebula The part pictured here is 2 Cone Nebula The part pictured here is 2.5 light years in length (the equivalent of 23 million return trips to the Moon)

The Perfect Storm, a small region in the Swan Nebula, 5,500 light years away, described as 'a bubbly ocean of hydrogen and small amounts of oxygen, sulphur and other elements'

Starry Night, so named because it reminded astronomers of the Van Gogh painting. It is a halo of light around a star in the Milky Way

The glowering eyes from 114 million light years away are the swirling cores of two merging galaxies called NGC 2207 and IC 2163 in the distant Canis Major constellation

The Trifid Nebula. A 'stellar nursery', 9,000 light years from here, it is where new stars are being born

Wrap-Up What are galaxies? Where do scientists think the universe came from?