Ch 15-18 ISP 205

Astronomy Visions of the Universe

For distant objects, how do astronomers measure speeds?

They use spectra of those objects to measure the wavelengths of emission lines

Which of the universe expansion models on the graphic implies the oldest universe?

The accelerating universe

Which of the models best represents the supernova data?

The accelerating model

Which universe has the highest matter density?

Recollapsing universe

Which universe has little to matter density?

Coasting Universe

Which universe(s) has significant amounts of matter?

Critical and recollapsing Universe

Which Universe is the Youngest?

Recollapsing

Which Universe is the Oldest?

Accelerating universe

Which universe is expanding faster "now"?

all of these universes are expanding at the same rate today

what force prevents you from falling through your chair, the ground in a plunge to the center of the Earth

electromagnetic force

What keeps the Moon circling the Earth

force of gravity

What force affects neutrinos (in addition to gravity)

Weak nuclear force

What holds an atomic nucleus together

Strong nuclear force

What major event of the universe happened first?

Three fundamental forces became the four fundamental forces we have today – early universe, fractions of a second after the Big Bang.

What major event of the universe happened last?

Stars formed

What major event of the universe happened before stars formed?

Stable NEUTRAL hydrogen atoms form and persist for the first time, allowing the cosmic background radiation to stream freely through the universe.

What observation supports the Big Bang Theory?

High helium/hydrogen abundance of primordial gas and a relic radiation background that is the same in any direction we look.

Which black hole has the bigger mass M?

The one with the faster stars, but the same orbital radius (R).

Measuring the peak brightness of white dwarf supernovae light curves as standard candles

Used for distant galaxies.

Radar-bouncing light off solid surfaces

Used for planets and nearby objects

Measuring brightness and periods of Cepheid variables

Used for nearby galaxies and star clusters

Annual parallax angle measurement

Used for nearby stars

Lots of cold gas and dust

Spiral/disk galaxies

All of its stars are orbiting in random orientations and random directions; very little organization

Elliptical/spheroidal galaxies

Significant recent star formation

Spiral/disk galaxies

Most like the Milky Way galaxy

Spiral/disk galaxies

Most of the galaxies in the center of a cluster of galaxies

Elliptical/spheroidal galaxies

Which hypothetical universe is older, all other things about the universes being the same?

the one expanding slower

Youngest hypothetical universe

Hubble constant = 24 km/sec/million light years

Oldest hypothetical universe

Hubble constant = 20 km/sec/million light years

To create protogalactic clouds most likely to form disky spiral galaxies, what features would you give your protogalactic clouds?

low gas density, so they form stars gradually, far from other protogalaxy clouds with lots of rotation

If the Hubble Constant is 40 km/sec/million light years, what is the distance in light years of a galaxy that is moving away at 40,000 km/sec?

1000 million light years

Examples of observed evidence of a supermassive black hole in the center of the Milky Way.

The Event Horizon Telescope observed a dark circle surrounded by radio light, indicating a black hole in the Milky Way center.

Stars are orbiting a position in the center of the Milky Way at a rapid rate, but there is no star or other visible-light object at that position.

If the age of the universe is 13 billion years and the light travel distance from a distant galaxy to Earth is 9 billion light years, then what is the maximum possible age for that galaxy as we can observe it?

4 billion years

What was an observationally-based clue that the solar system was not in the center of the Milky Way Galaxy?

There are more globular clusters in the direction of the actual center of the Milky Way than in the opposite direction.

Stars are observed with:

Visible-light telescope

Hot, 10 million K halo gas is observed with:

X-ray telescope

Very cold, dense molecular gas (carbon monoxide) is observed with:

Radio Telescope

Cold, dusty gas is found in the Milky Way:

Disk

Ionized gas surrounding very blue main-sequence stars is found in the Milky Way:

Disk

Spiral arms are found in the Milk ways:

Disk

Only old stars with little to no recent star formation are found in the Milky Way:

Halo

Recently formed stars are found in the Milky Way:

Disk

Why can't we use UV telescopes to study the center of the Milky Way?

Dusty gas scatters blue light more than red light

Orbits are confined to a relatively thin, flat plane in space passing through the center of the galaxy. Spiral density waves form in the stellar orbits in this structure. Orbits circle the center of the Milky Way, and are all generally in the same general direction

Disk

Stellar orbits are so sparse in that this structure, the largest structure of the three choices, can barely be seen in a spiral galaxy outside of the Local Group. Orbits in random directions, circling the center of the Milky Way, with orbital radii as large as 50 thousand light years.

Halo

Orbits in random directions, circling the center of the Milky Way, but confined to a few thousand light years of the center of the Milky Way.

Bulge

Spiral arms

Prominent, curved structures of gas, dust, and young stars that extend outward from the center of a spiral galaxy

Elliptical galaxies

Galaxy with a smooth, ellipsoidal or spherical shape that are primarily composed of old, red stars with very little gas, dust, or star formation

Spiral galaxies

disk-shaped galaxy with bright, swirling arms of young stars, gas, and dust rotating around a central bulge of older stars

Irregular Galaxy

Galaxy with no distinct spiral arms or central bulge, giving it a chaotic and amorphous appearance

Where are the oldest stars located in the Milky Way?

Halo

Where are the youngest stars located in the Milky Way

The spiral arms and the galactic disk

Doppler shift

The change in frequency of a wave due to the relative motion between its source and an observer