astro Midterm 2 Flashcards

Question

What is the composition of interstellar gas

Answer 1

About 70% hydrogen, 28% helium, and a little bit of other heavy elements. We can figure this out by looking at absorption lines and star spectra

Answer 2

Molecular clouds like H2 or CO. Have a temperature of 10 to 30 K.

Answer 3

Gravity compacts the interstellar gas. Gravity must overcome thermal pressure in the cloud. Typical molecular clock must have a few hundred solar masses For gravity to overcome pressure.

Answer 4

Gravity become stronger as gas condenses. Gravity overcomes pressure in small pieces cousin to break. Multiple fragments going to form star. So large cloud can form whole cluster.

Answer 5

Must've been more massive For gravity to overcome pressure. No CO molecules to provide cooling

Answer 6

The center of the cloud fragment.

Answer 7

Gravitational Contraction produces thermal energy. When core becomes hot enough Fusion begins. Contraction stops one energy released by core balances gravitational contraction. *Is now a main sequence star.

Answer 8

Luminosity and temperature girl is matter clacks into protostar. Surface temp remains near 3000 k while convection Contraction occurs. Luminosity remains nearly constant during late stages of contraction. Core temperature continues to rise until fusion begins.

Answer 9

30 million years

Answer 10

Bigger than 150 to 300 m sun blow apart ( Because of radiation pressure). Less massive than 0.0 8 M sun Cant sustain fusion.

Answer 11

Start becomes larger and redder and more luminous. As the core contracts hydrogen begins fusing into helium in a shell around the core. Their core thermostat is broken so The increased fusion rate does not stop the core from contracting. So luminosity increases. After some time, helium fusion begins. This requires higher temperatures then hydrogen fusion. 3 he Molecules turns into 1 carbon molecule ( Plus a lot of energy)

Answer 12

Core temperature rises rapidly when helium fusion begins. Huene fusion rate skyrockets until thermal pressure takes over and expands the core again.

Answer 13

The red giant shrinks and becomes less luminous

Answer 14

When both the hydrogen shell and the helium shell Are burning around the carbon core. This stage never reaches equilibrium and so there are a series of thermal pulses. Each pulse pushes carbon up from the core and transports it to the surface.

Answer 15

When double show burning ends hydrogen and helium are pushed into space Because of a pulse. The court is left behind and becomes a white dwarf

Answer 16

Because no two electrons can fill the same space, they cannot collapse. the result is degeneracy pressure. This is why white dwarfs don't collapse under the pressure of gravity, Even though fusion is not occurring.

Answer 17

In about 12 billion years the suns luminosity will rise 1000 times what it is now. Also the suns radius will grow to nearly what the Earth's orbit is now. Earth will not Support life.

Answer 18

They act as catalysts when these stars fuse hydrogen to helium at a higher rate. Greater core temperature enables hydrogen to overcome greater repulsion

Answer 19

Helium(25%) and hydrogen (75%)came from the Big Bang. All the other elements came from stars. Helium fusion can make carbon and stars. CNO cycle can change carbon into nitrogen and oxygen in really big stars. High temperatures allows Huniand confuse with other heavier elements Making neon, magnesium, Silicon sulfur calcium iron.

Answer 20

Yes it produces a series of nested shells. But the end comes with iron. Nuclear reactions involving iron do not release energy. Iron builds up in the core until the degeneracy pressure can no longer support gravity ( Electrons combine with protons making neutrons) The core then collapses causing a supernova. Energy and neutrons emitted in the supernova allow elements heavier than iron to form.

Answer 21

The white dwarf with the same mass of the sun is about the size of the earth. A white dwarf with more mass is smaller. A white dwarf cannot be more massive than 1.4 M sun ( Called the white dwarf limit, or the Chandrasekhar limit)

Answer 22

The start with less mass can gain mass from its companion. Eventually the mass losing star can become a white dwarf. When mass gets large enough fusion can begin and then there is either a novae or a supernova.

Answer 23

Massive star supernova( The one that I already discussed) White dwarf supernova. ( Carbon fusion Suddenly begins when a white dwarf is in a close binary system reaches the white dwarf limit causing an explosión)

Answer 24

One way to tell supernova types apart by showing how luminosity changes with time.

Answer 25

A ball of neutrons left behind by a massive star supernova. Degeneracy pressure supports and neutron star against gravity. Usually has a radius of about 10 km. Discovered by Joslyn bell. She noticed regular pulses of radio intentions.

Answer 26

The spinning neutron star

Answer 27

1000 cps or 60,000 km/s. 20% of the speed of light. Anything else would get torn into pieces. So a pulsar must be a neutron star.

Answer 28

It's can obtain matter by forming a Accretion disk Just like a white dwarf. When it gets enough matter they can Begin helium fusion. This produces a burst of x-rays.

Answer 29

An object who's gravitational force is so strong that not even light can escape it. The surface of a blackhole is the radius at which the escape velocity equals the speed of light, this is known as the event horizon.

Answer 30

Schwartzchild radius.

Answer 31

It's just like a electron degeneracy pressure. Neutron degeneracy pressure cannot support a neutron star if the mass is greater than 3 M sun. Some massive star Supernovae can make a black hole if enough mass falls onto core

Answer 32

We see our galaxy on edge. Our view is obscured because of dusty gas clouds that absorb light. It's features are the bulge, disc, Halo, globular clusters.

Answer 33

Stars in the disk rotate All in the same directions with little up-and-down motion. Orbit of stars in the bulge and halo have random orientations.

Answer 34

Buy a looking at the sun's orbital motion( Radius velocity) We learned that the galaxies mass is 1×10 to the 11th M sun.

Answer 35

High mass and Low stars have stellar winds that blow bubbles of hot gas. Stars make new elements by fusion. Dying stars expel gas and new elements producing hot bubbles. Hot gas cools allowing atomic hydrogen clouds to form. Further cooling permits molecules to for making molecular clouds. Gravity forms new stars and planets from molecular clouds.

Answer 36

This forms as hot gas cools allowing electrons to join with protons

Answer 37

These form after atomic hydrogen gas as gas cools enough to allow Atoms to combine into molecules

Answer 38

Places where active star formation is taking place. They are found around short-lived high mass stars

Answer 39

Where light from stars is scattered. They look bluer than nearby stars because blue photons are scattered more efficiently than red photons

Answer 40

In the disk where there is ionizing nebulae and blue stars. Especially in the spiral arms. There is no star formation in the Halo because there is no ionization nebulae and no blue stars.

Answer 41

It started as a cloud of intergalactic gas. Halo stars formed first in clumps as gravity caused the gas to contract. The remaining gas turned into a spinning disc. Stars continue to form in the disc. We know this because most of the heavy elements are in the disk stars so there are stars of all ages there. Only old Starrs exist in the halo so halo stars first formed then stopped.

Answer 42

It's hard to see because there are radio infrared and x-rays unobscured our view toward the Galactic center. It appears there is swirling gas near the center and orbiting stars near the center. They are orbiting something that is massive but invisible. It must be a black hole because it's mass is about 4 million M sun.

Answer 43

1- spiral galaxy. Has a spheroid component ( halo and bulge yellowish, mostly old stars few gas clouds) and a disc component ( disk. Bluish in color, stars of all ages, lots of gas clouds) 2.5- sometimes barred galaxies and lenticular galaxies are considered intermediate between spiral and elliptical galaxies. 2- elliptical galaxy- is kinda football shaped. Has virtually all spheroidal component and no disc component. Redish yellow, so that means that it has mostly old stars. 3- irregular. They are irregular in shape. They are bluish white which indicates that they are areas of new star formation.

Answer 44

Usually spiral galaxies group together in several dozen. Called a group. And usually elliptical galaxies group together several nursed to several thousand. This is called a cluster.

Answer 45

When the universe was young and they have aged along with the universe.

Answer 46

Ppl didn't know if other galaxies were separate from ours or part of our milky way galaxy. He used cepheid variables as standard candles to measure the distance to andromeda. He found that virtually all galaxies are red shifted which means that they are moving away from us, and the further they are from us the faster they are receding from us. So there is a relation between amt of redshift or speed, and distance. It's a linear relationship.

Answer 47

The universe looks the same, no matter where you are in it. This is because matter is distributed evenly over a huge amount of space, there are no borders or center.. Hasn't been proven over say, but it is supported by all observations up to this point.

Answer 48

Distances between galaxies changes while the light is traveling to us, so really we are looking at "look back time" more so than a distance.

Answer 49

So as the photon is traveling to us it's wavelength is increased so it is red shifting too because the universe is expanding. Its getting stretched out. So the redshift of a photon is directly related to look back time.

astro Midterm 2 Flashcards

(74 cards)