Astrophysics: Stellar Evolution, Galaxies, and Cosmology Concepts

What ultimately causes the end of a high mass super giant's life?

Its inert core becomes degenerate gas and finally exceeds the 1.4 Msun limit and collapses, causing rapid fusion and the explosion of the star.

How do stars appear brighter in the sky?

It depends on how far away each star is.

Why do neutron stars have such low luminosities?

They have very small surface areas.

Why was the first pulsar believed to possibly be an artifact of alien intelligence?

Because its regular radio pulse was unprecedented in nature.

What does the surface gravity of an object depend on?

The object's mass and radius.

Why don't black holes suck?

Because their gravity is normal gravity.

Why do black holes created in a Type II supernova explosion have extremely strong surface gravity?

They have extremely high mass compared to regular stars.

What does the escape velocity of a black hole depend on?

It depends on its mass.

How have black holes been proven to exist?

By observing their gravitational effects on matter near the black hole.

Which science fiction sounding thing could really be done with a black hole?

We could travel into the future.

What does the Milky Way Galaxy appear as on a clear night?

a faint band of light that encircles the sky.

What are the three main structural components of the Milky Way Galaxy?

the disk, the bulge, and the halo.

Which part of the Milky Way Galaxy is the largest?

The halo

Which part of the Milky Way Galaxy has a pronounced rotation?

The disk

What can be determined by measuring the velocity of stars orbiting the center of the Galaxy?

The mass of the Galaxy

What is expected to happen to the rotational velocities of disk stars as the radius increases?

The rotational velocities of disk stars were expected to decrease

When the rotational velocities of stars with orbital radii larger than the Sun's were finally measured, they were found to _____

remain constant with increasing radii.

Why can dark matter not be cold hydrogen gas?

It emits radio light, which is not detected in large enough abundance to account for dark matter.

Why can brown dwarfs not be considered dark matter?

We do not observe enough brown dwarfs to account for the total mass of dark matter.

What is dark matter?

a form of matter that does not emit light or energy, and its exact nature is still unknown.

What type of galaxy is also known as a disk galaxy?

A spiral galaxy, because it has a large, flat, rotating disk of stars.

Which type of galaxy is composed only of old stars?

An elliptical galaxy.

Which type of galaxy has no regular, overall structure?

An irregular galaxy.

Which type of galaxy can be the most massive?

An elliptical galaxy.

Which types of galaxy have ongoing star formation?

Spiral and irregular galaxies.

Just like stars collect together in galaxies, galaxies collect together in what?

Groups, clusters, and super clusters.

Our galaxy, the Milky Way, is a member of what?

The Local Group, a collection of about 30 galaxies.

Which of the following is NOT a name for a collection of galaxies?

Super group.

What is the primary cause of galaxies collecting together?

Gravity.

The largest objects in the Universe are what?

Galaxy super clusters.

What is the Cosmic Distance Ladder?

a series of methods by which astronomers determine the distances to celestial objects, where each technique depends on the previous one to measure further distances in the Universe.

What is a fundamental limitation of radar astronomy?

the signal bounced back must be strong enough to measure.

Why do Cepheid and RR Lyrae variable stars make good distance indicators?

their luminosities are directly related to their periods of brightness variation, and they are intrinsically very luminous.

Why is a type I supernova considered a 'standard candle'?

it has a known amount of energy (luminosity) when it explodes, allowing for distance measurements.

What did Edwin Hubble discover about galaxies?

the redshift of a galaxy is directly related to its distance.

Using Hubble's Law, how far away is a galaxy with a redshift of 750 km/sec?

10 Mpc away.

What happens to the temperature of the Universe as it expands?

it cools

What was the temperature of the Universe when it was 1/10th its current size?

its temperature was 27.26 K

What is the 'surface of last scattering'?

the state of the Universe just as it cooled below 3000 K and became transparent to photons, occurring when the Universe was about 400,000 years old.

What is the Big Bang Theory?

A well tested idea about how the Universe formed and conditions in the early Universe.

What does the Big Bang Theory predict?

It predicts when neutral atoms and chemical elements first formed in the early Universe.

What could efficient detection of neutrinos help us understand?

It could help discover when antimatter was created and observe what the Universe was like when it was 1 second old.

How far back can we understand the Universe according to the Big Bang Theory?

10^-43 seconds old.

What was observed in the mid-1990s regarding the Hubble constant?

by studying distant type I supernovae.

What did observations of distant supernovae reveal about the Universe's expansion?

They discovered that the expansion of the Universe is accelerating.

What is dark energy?

Energy that does not emit light and is a property of space-time that causes it to expand faster.

What is the potential end scenario for an open Universe without dark energy?

The Universe could face Heat Death.

Which end scenario of the Universe is ruled out by current cosmological knowledge?

The Big Rip is ruled out.

What can be said about the future end of the Universe?

distant future, with potentially 10s to 1000s of billions of years left until the end.