Stars and Galaxies

Why do some neutron stars give off pulses of x-rays?

(mass transfer from a normal companion star) Pulsating X-ray sources are also neutron stars in close binary systems. Some of these binary systems emit x-ray pulses.

The discoveries of Hubble consists of

1)Galaxies are not nebulae and not in our galaxy 2)Use of Cepheid variables for distance measurements. 3)The farther away a galaxy is the faster they are moving away from us = REDSHIFT.

In what way is a black hole blacker than black ink or a black piece of paper?

A black hole is blacker than any object that can be seen because absolutely no light at all can come from a black hole.

Starquake

A localized fracture of the surface of a highly magnetized neutron star, or magnetar. A starquake on the surface of a magnetar releases magnetic energy in the form of an intense blast of X rays and gamma rays.

Nova

A star that experiences a sudden outburst of radiant energy, temporarily increasing its luminosity roughly a thousandfold.

Supernova

A stellar outburst during which a star suddenly increases its brightness roughly a millionfold.

Why did astronomers rule out the idea that pulsars are rapidly rotating white dwarfs?

A white dwarf is too large to pulsate in and out in less than a second.

What do the stars in the Galaxy appear to form a bright band that extends around the sky?

As we look at the Milky Way in the sky, we are looking into the plane of the galaxy where the density of stars is greater.

Why do we think Cygnus X1 is a black hole.

Astronomers became intrigued with an X-ray source designated Cygnus X-1. The X-ray emissions from Cygnus X-1 are highly variable and irregular, they flicker on time scales an short as one-hundredth of a second. It occasionally radiates bursts of radio emission, radio astronomers used these bursts to show that the source was at the same location in the sky as the star HDE 226868. Because the unseen companion does not emil visible light it cannot be an ordinary star. Furthermore, because 7 solar masses is too large for either a white dwarf or a neutron star Cygnus X-1 is likely to be a black hole.

Explain why astronomers cannot use any of the standard candles described to determine the distances to quasars

Astronomers cannot use any of the standard candles to determine the distances to quasars because none of the standard candles can be seen at those distances.

Why are blackholes black?

Blackholes absorb light. They do not emit any light on own, because of gravity. If velocity equal to the speed of light no light can escape = blackhole. You cannot see a black hole (space around warped light bent) would see other things behind it.

What is a blazar ? What is unique about its spectrum ? How is it related to other active galaxies?

Blazars are the ultraluminous centers of distant galaxies whose spectra show no absorption or emission lines but the light is polarized. Blazars may be end-on views of double radio sources.

What are Blazars?

Bright star like objects that can vary rapidly in their luminosity. They're probably radio galaxies or quasars seen end-on with a jet relativistic particles aimed toward earth. Variable stars. Change luminosity. Has red shift (cannot be a star) Spins and comes toward you and pulses. Points at us. Synchritonradiation (realistic radiation) Particles and mass traveling at speed of light. Elliptical Galaxy. Strong strength of emission. 10^38 to 10^42 - putting out alot of energy. Matter being sucked in.

Why is Einstein's general theory of relativity a better description of gravity than Newton's universal law of gravitation? Under what circumstances is Newton's description of gravity adequate

Einstein's general theory of relativity is a better description of gravity than Newton's universal law of gravitation because relativity predicts the observed bending of light by gravity and Newton's law does not. Newton's descriptions work for such things as sending space probes to the planets, and determining at what angle to hit a golf ball.

How do we know that the universe is expanding at an accelerated rate?

Hubble Telescope. Things are moving faster and faster

Astronomer's cannot actually see the black hole candidates in close binary systems.How then, do they know that these candidates are not white dwarfs or neutron stars ?

If blackhole candidates were actually white dwarfs or neutron stars then they would not be able to affect the motion of the companions by as much as we actually observe.

How were black holes believed to be made?

If stellar corpse has a mass greater than about 2 to 3 M, gravitational compression will overwhelm any and all form of internal pressure. The stellar corpse will collapse to such a high density that its escape speed exceeds the speed of light.

Why do giant elliptical galaxies dominate rich clusters but not clusters

In rich clusters there is more opportunity for mergers of galaxies leading to giant ellipticals compared to poor clusters.

Length Contraction

In the special theory of relativity the shrinking of an objects length along its direction of motion. One prediction is that the length you measure an object to have depends on how that object is moving; the faster it moves the shorter its length along its direction of motion. Only when you approach the speed of light is this possible.

Our galaxy is a member of a poor irregular cluster called the

Local Group

What is a Neutron Star made of?

Mainly neutrons and a few stray protons and electrons. It consists of a superfluid, superconducting core surrounded by a superfluid mantle and a thin, brittle crust.

Why did many nineteenth-century astronomers think that the spiral nebulae are part of the milky way?

Many astronomers of the nineteenth century disagreed with the idea of the island universe. It seemed reasonable that "spiral nebulae," even though they are very different in shape from other sorts of nebulae in the Milky Way, could also be components of our galaxy.

3 Physical properties of a black hole

Mass, electric charge, and angular momentum

What are the neutron stars? What led scientists to propose their existence?

Neutron stars are the remains of cores of massive stars that have become supernovae. During the explosion, the cores were compressed into mostly degenerate neutrons. Scientists proposed their existence as an explanation of what happens to cores that exceed the Chandrasekhar limit.

Do all supernova remnants contain pulsars? Are all pulsars found within supernova remnants?

Not all supernova remnants contain pulsars. Some pulsars have a velocity higher than the expansion rate of the remnant and have left it. Not all pulsars are found within supernova remnants for the reason just mentioned and because remnants disperse into space and become no longer observable.

What are the six methods of the Distance Ladder?

Parallax, Spectroscopic, Population II, Population I, Tully-Fisher, fundamental plane, Type Ia supernovae

Standard Candle Scheme and what are some examples?

Standard Candle Scheme is old style word. Old optics term - something that puts out a standard amount of light. Example of one is: Type I Supernova.

What is the Hubble classification scheme? Which category includes the largest galaxies? Which includes the smallest? Which category of galaxy is the most common?

The Hubble classification scheme is a method of classifying galaxies according to their appearance. The elliptical category includes the largest, smallest, and most common galaxies.

Some galaxies in the Local Group exhibit blueshifted spectral lines. Why aren't these blueshifts violations of the Hubble law?

The Hubble law applies only to galaxies that are not gravitationally bound to the Milky Way. Therefore some of the local group galaxies show small blueshifts.

What is the Hubble law? How can it be used to determine distances?

The Hubble law is the linear relationship between the recessional velocity and the distance of galaxies. By measuring the redshift, the Hubble law gives the distances.

What is the Hubble classification scheme?

The Hubble sequence is a morphological classification scheme for galaxies invented by Edwin Hubble in 1926. It is often known colloquially as the Hubble tuning-fork diagram because of the shape in which it is traditionally represented. Tuning-fork style diagram of the Hubble sequence Hubble's scheme divides regular galaxies into 3 broad classes - ellipticals, lenticulars and spirals - based on their visual appearance (originally on photographic plates). A fourth class contains galaxies with an irregular appearance. To this day, the Hubble sequence is the most commonly used system for classifying galaxies

Why is it difficult to see the center of the galaxy and how we have overcome that problem?

The center of the universe has so much crap in the way of dust and particles. Sagittarius in the center of the galaxy which is very bright. Infrared measurements are very good for detecting dust and penetrating dust regions due to its long wavelengths.

The galactic halo is dominated by the population II stars whereas the galactic disk contains predominately Population I stars. In which of these parts of the Galaxy has star formation taken place recently?

The disk is where star formation has taken place recently. It has taken many generations of stars contributing heavy elements into the interstellar medium to reach the concentration that we find in population I stars today. Therefore, these stars formed recently.

What decides the radius of a black hole?

The distance from the center of a nonrotating black hole to its event horizon is called the Schwartzchild radium after the German physicist Karl Schwartzchild. How to calculate the Schwartzchild radius, which depends only on the black holes mass. The more massive the black hole the larger its horizon.

Properties of a Black Hole

The entire mass of black hole is concentrated in an infinitely dense singularity. The singularity is surrounded by a surface called the event horizon, where the escape speed equals the speed of light. Nothing, can escape from inside the event horizon. Black holes can evaporate but in most cases at an extremely slow rate. Therefore, there are NO properties of a blackhole. You cannot determine anything but radius and mass.

The distance from our sun to our galactic center and the direction it is in

The exact distance from the Sun to the Galactic center is about 8000 parsecs. Its center lies in the direction of the constellation Sagittarius, but very close to the border of both neighbor constellations Scorpius and Ophiuchus. The distance of 28,000 light years has recently been confirmed by the data of ESA's astrometric satellite Hipparcos.

Most interstellar hydrogen atoms emit only radio waves at a wavelength of 21 cm, but some hydrogen clouds emit profuse amounts of visible light.

The hydrogen that emits visible light is found in H II regions. The energy comes from nearby hot, bright stars and ionizes the hydrogen atoms.

How many spiral arms does the Milky Way have

The milky way is a barred spiral galaxy with 4 total arms

In what way are the orbits of stars in the galactic disk different from the orbits of planets in our solar system? What does this difference imply about the way that matter is distributed in the Galaxy?

The orbits of stars are different from the orbits of planets in that the stars are moving under the influence of the gravity of widely distributed mass rather than that of a single object. Although the nucleus of the galaxy has a concentration of mass, mass is distributed throughout the galaxy.

What is the evidence that there is a supermassive black hole at the center of our Galaxy? how is it possible to determine the mass of this black hole?

The rapid movement of stars surrounding Sagittarius A* suggests that it is a supermassive black hole whose mass is about 3 million times solar.

Cassiopeia A

The remnant of a supernova that occurred about 3000 pc (10,000 ly) from Earth. In the roughly 300 years since the supernova explosion a shock wave has expanded about 3 pc (10 ly) outward in all directions from the explosion site. The shock wave has warmed interstellar dust to a temperature of about 300 K and has heated instellar gases to temperatures that range from 10^4 K to 10^7 K

Time dilation

The slowing of time due to relativistic motion. When the airliner landed, they found that the on-board clock had actually ticked off slightly less time than an identical stationary clock on the ground. For the passengers on board the airliner during this experiment, however time flowed at a normal rate. The on-board clock ticked aoff the seconds as usual, their hearts beat at the normal rate and so on. You only measure a clock or beating heart to be running slow if it is moving relative to you.

How does the spectrum of a quasar differ from that of an ordinary galaxy? how do spectral lines help astronomers determine the distances to quasars?

The spectrum of a quasar shows emission lines that are enormously redshifted. Astronomers determine the distances to quasars using these redshifts and the Hubble law.

A friend summarizes the special theory of relativity by saying "Everthing is relative" Explain this statement

The two basic principles explain this: 1. your description of physical reality is the same regardless of the constant velocity at which you move 2. regardless of your speed or direction of motion, you always measure the speed of light to be the same.

Why did Issac Newton conclude that the universe was static? Was he correct?

The universe is not static. A man by the name of Hubble discovered that the universe is expanding and that, the farther something is from Earth, the faster it is moving away from Earth. Later on, scientists discovered that, not only is the universe expanding, the expansion is accelerating! So, I think based on our current understanding, the universe is certainly not static in the way that Newton concluded.

WHAT DOES IT MEAN WHEN ASTRONOMERS SAY THAT WE LIVE IN AN EXPANDING UNIVERSE?

The universe was "created" by the big bang, it caused everything to move out, and it's still going on today. That's why they say that we live in an expanding universe.

What is the relationship of quasars, Seyfert galaxies, and radio-galaxies. How were they discovered?

They are radio galaxies. They were discovered via radio telescopes. Spot in the sky putting out strong radio signals

Which type of Supernovas do we use?

Type A1

Why are Type la supernovae useful for finding the distances to very remote galaxies? Can they be used to find the distance to any galaxy you might choose?

Type Ia supernovae, are far more luminous than Cepheids, can be seen much farther away, and thus are used to determine the distances to very remote galaxies.

Does a neutron star contain only neutrons? If not, what else does it contain?

While neutron star is made up predominantly of neutrons, some protons and electrons must be scattered throughout the star's interior. A pulsar's magnetic field must be anchored to the neutron star by charged particles. Neutrons are electrically neutral, so without the protons and electrons in its interior a neutron star would rapidly lose its magnetic field.

Crab Nebula

Wrecked of an exploded star. When a dying star exploded in a supernova it left behind this elegant funnel shroud of glowing gases blasted violently into space. A thousand years after the explosion these gases are still moving outward at about 1800 kilometers per second (roughly 4 million miles per hour) It is 6500 light-years from Earth and 13 light-years across.

Suppose you saw an object on the sky that you suspected might be a quasar. What sort of observations might you perform to test your suspicion

You would look for a large redshift in the spectrum, emission lines in the spectrum, and emission in other parts of the electromagnetic spectrum.

The dimensions of the Milky Way galaxy is

about 17kpc or 55,000 ly

General relativity

adds effect due to gravity and other types of acceleration

Major components of Galaxies Mass

dark matter, and supermassive black holes

Magnetars or Magnetstars

is a pulsar with an extraordinary strong magnetic field. This field is produced by convection inside the pulsar when it first forms. The solid crust of a magnetar is under tremendous magnetic stress. When the surface rearranges in a starquake the released magnetic energy produces a powerful burst of X-rays and gamma rays.

Special relativity

is for objects moving in a straight line and constant speed

Galaxies can be grouped into four major categories

spirals, barred spirals, ellipticals and irregulars

What is a cosmological constant? Why did Einstein introduce it into cosmology?

was proposed by Albert Einstein as a modification of his original theory of general relativity to achieve a stationary universe. Einstein abandoned the concept after the observation of the Hubble redshift indicated that the universe might not be stationary, as he had based his theory on the idea that the universe is unchanging.However, the discovery of cosmic acceleration in 1998 has renewed interest in a cosmological constant.

Would it be correct to say that, due to the expansion of the universe, Earth is larger today than it was 4.56 billion years ago?

we don't even know if the universe is expanding, the movements in the universe have been going on for billions of years, we have had reasonable data for maybe 60 years, we have no idea what it is doing no amount of theory will change that, it could be pulsing, contracting rotating or anything 60 years is not long enough to make any reliable conclusions