Astro Exam 4

The first direct detection of gravitational waves by LIGO: waves came from?

Merger of two black holes

Where is the most likely place in the Milky Way for a super massive black hole?

The center of the galaxy, where matter is more crowded

If a radio wave is sent out from the event horizon, what will its fate be?

It will never emerge

One member of a binary system is a black hole, and flickering x-rays are detected from the system. Where do the x-rays come from?

A disk of material around the black hole (material pulled from companion star, falling towards black hole)

If you were freely falling in an elevator, your weight would be?

Equal to zero- weightless

According to the general theory of relativity, the presence of mass?

Causes curvature (or warping) of spacetime

The first time astronomers observed both gravitational and electromagnetic waves from the same event was when they were observing..?

Spiraling together of two neutron stars

What main sequence star is most likely to become a black hole?

Type O

To predict if a star will become a black hole, what property of the star should we look at?

Mass

How did scientists in 1919 show Einstein’s theory of relativity wasn’t just a hypothesis?

By observing starlight coming close to the Sun during an eclipse

Stars of different masses leave different types of..?

Stellar corpses

Low mass stars leave?

White dwarfs

High mass stars die in?

Massive explosions (super novae), leaving behind neutron stars or black holes

White dwarfs shine brightly in?

High energy UV and X-ray

White Dwarf composition

Resembles products of star’s final nuclear burning stage

More massive white dwarfs are?

Smaller and denser than less massive white dwarfs

No white dwarf can have a mass greater than..?

~1.4x the mass of the sun

If mass becomes greater than Chandrasekar Limit?

Supernova

Can distinguish from supernova and white dwarf supernova by..?

WD supernova has no hydrogen lines, and different light curve

Collapse of a high-mass star’s iron core creates?

Ball of neutrons

Neutron stars are like?

Giant atomic nuclei made almost entirely of neutrons and held together by gravity

How do neutron stars resist the crush of gravity?

Neutron Degeneracy Pressure

Basic idea for a black hole originated in?

18th century

Earth Escape Velocity

11km/s

If we could make Earth denser, but keep the mass the same- what would happen to the escape velocity?

It would raise

Electron degeneracy pressure can’t resist gravity above?

1.4MSun. Causes supernova above that.

Neutron degeneracy pressure can’t resist gravity above?

2-3MSun.

Evidence for black holes formed from supernovae comes from?

Study of x-ray binaries

What causes x-ray binaries?

Accretion disks around neutron stars in a close binary systems.

What two things in the universe are absolute?

Laws of nature are the same for everyone, speed of light is the same for everyone

Can a physical object move faster than light?

No.

Objects orbiting around the center of the Milky Way obey Kepler’s 3rd law. Therefore:

A cloud of gas or star that is further from the center will generally take more time to orbit

What objects did Harlow Shapely use as ‘signposts’ to figure out the extent of the Milky Way, and the location of its center?

Globular clusters

Astronomers now know that surrounding the main body of our Galaxy, and our fainter halo of stars there is:

an invisible halo made of ‘dark matter’

Where would you look for the youngest stars in the Milky Way?

In the disk

Is a visible light image by Hubble of an accretion disk at the center of the galaxy actual evidence of there being a black hole?

No

Why is the Sagittarius Dwarf Galaxy noteworthy?

It is on a collision course with the Milky Way, and will eventually be swallowed by it

What is evidence that when forming, our galaxy collided with smaller galaxies?

Observation of long moving streams of stars that still orbit through our galaxy’s halo

The milky way is what kind of galaxy?

Spiral

What can we use to find the distance to a globular cluster in a nearby galaxy?

Find a variable star (cepheid or RR Lyrae) in the cluster

Why did William Herschel not realize our true position in the milky way?

There’s so much dust in the disk, that Herschel could only see the small part of the Milky Way surrounding us

What type of galaxy contains mostly older stars

Elliptical

Type Ia supernovae are useful to astronomers for determining distances to other galaxies is because..?

They are very bright, and generally reach the same peak luminosity

Edwin Hubble was able to show that the farther a galaxy from us, the?

Faster it is moving away from us

What observation is important for measuring the mass of a spiral galaxy?

Obtain the speed at which stars or gas near the outer regions of the galaxy are moving around

What can change a galaxy’s shape?

Collisions and mergers between galaxies

What method do astronomers use with Hubble to find distances of galaxies millions of light years away?

Finding Cepheid variables and measuring their periods

What makes the small and large Magellanic cloud useful for astronomers?

They are (for galaxies) very close to us, so they are easy to study

The instrument that made it possible for Edwin Hubble to demonstrate the existence of other galaxies in the early 1920’s was:

The 100-inch reflector on Mount Wilson

What method would astronomers use to find the distance of a galaxy so far away the stars are impossible to resolve?

Find redshift with Hubble’s law

How did Herschel make a cross section of the Galaxy?

Counting stars in various directions

Who mapped globular clusters?

Harlow Shapley

What do the spiral arms do near the disk? How many stars does it contain?

Blend into the thin disk. 100 billion stars

Center of disk has a?

Bright central bulge

What can spiral galaxies have in the middle?

A bar

Measurements of the disk

100,000 LY in diameter, 1000 LY thick

What is surrounding the galaxy?

A halo of stars

How far is the sun from the galactic center?

~28,000 light years

What do spiral arms appear to be?

Enormous waves of star formation propagating through disks

What is responsible for spiral arms?

Spiral density waves

Where do stars and gas clouds get closely packed? Whats the effect of these things coming close?

Spiral arms. Pushing stars together has little effect, but the gas clouds collide and trigger heavier gravity

Gas clouds orbit faster than expected from the center, suggesting the presence of..?

Dark matter

Radio images reveal?

Presence of dark mattr

Disk population has?

Young and old stars, with heavy element proportions of ~2%, like our Sun

Spheroidal population has?

Stars in halo and bulge- stars are always old, and low in mass

What does a lack of heavy elements in halo stars imply?

They formed early in the galaxy’s history

Halo has lacked the gas for star formation for..?

A very long time

What do studies of heavy-element proportions suggest?

Our galaxy formed from several different gas clouds

Where are young stars and open clusters found?

The disk, not the halo

What did Shapley believe about distant nebulae?

They were relatively small and lay within the outskirts of the Milky Way

What did Curtis believe about distant nebulae?

They were independent galaxies- large and distant

What are Cephied variables a key tool for?

Exploring our location relative to other galaxies

Elliptical galaxies

Redder, rounder, longer in one direction than another. Very little cool gas and dust, lots of hot ionized gas

Spiral galaxies

Flat white disks, yellowish bulges at centers. Disks are full of cool gas and dust, interspersed with hotter ionized gas- has spiral arms.

Irregular galaxies

Neither disk like or round

How are elliptical galaxies labeled?

How stretched out they are (bigger number = more stretch)

How are spiral galaxies labeled?

Without bar: Sa
With bar: SB

Compared to elliptical galaxies, spirals are?

Flatter with bluer star populations

Why are ellipticals redder?

They contain older stars

Galaxies often?

Collide with each other