Astronomy 101 SDSU- Leonard (Final)

Newton's view of Gravity

Gravitation = universal force of attraction between bodies with mass. Mass acts as the source that generates the force of gravitation (use on Earth, not in space)

F = G M^1 M^2

------------------

R^2

Einstein's view of Gravity

no such thing as the "force of gravitation" Gravitation arises when space has CURVATURE (replaced newton's theory) (use for black hole calculation)

General Relativity

Einstein's theory of gravity

Principle of Equivalence: no way to tell the difference between gravity and acceleration

Basic Effects:

1) Space Curvature: space is "curved" or "warped" near massive objects

2) Gravitational Time Dilation: Stronger gravity= slower pace of time

3) Gravitational Red shift: light traveling AWAY from a source of gravitation is red shifted

**the stronger the gravity the greater the effect of general relativity**

light is bent

Space Curvature

space is "curved" or "warped" near massive objects (General Relativity)

Gravitational Time Dilation

Stronger gravity= slower pace of time

Gravitational Red Shift

light traveling AWAY from a source of gravitation is red shifted (Opposite: light traveling TOWARDS a source of gravitation is blue shifted.)

How did Albert Einstein contribute to Astronomy knowledge

General Relativity Theory

-First "test" of general relativity: "Anomolous" Advance of Mercury's Periphelion (advances around the sun not by much-elliptical slightly changes) found this before he proposed general relativity

E = mc^2 (E- energy, M- mass, c- speed of light)

MASS= ENERGY

Spacetime

-a system of one time and three spatial coordinates with respect to which the time and place of an event can be specified.

-all measurements are relative to where and when you make them

-gravity alters both space and time thus spacetime

Photon Sphere

The sphere around a black hole 1.5 times the size of the event horizon, within which light can orbit

Only area where light can orbit in black hole

Black Hole

-space is extremely curved near event horizon

-light can orbit a black hole, but cannot escape

-Photons are stretched

-Tidal forces would tear a person apart; cannot survive falling into black hole "spaghettified"

Gravitationally collapsed object; matter nor light can escape

Tidal Force

A differential gravitational force acting on two sides of an object that tends to deform object (Black hole)

Nebula

"fuzzy" (actually thousands of individual faint stars) astronomical object- not sharp point of light (in our sky)

Who is Henrietta Leavitt (1868- 1921)?

She studied photographs of the Magellanic Clouds and found 1700 variable stars, including 20 cepheids.

She discovered a relationship between luminosity and the period of Cepheid variable stars that led to a new and much better way of estimating cosmic distances.

Cepheid stars could be used as standard candles.

Who is Edwin Hubble (1889-1953)?

Leavitt's discovery helped him figure out what andromeda actually was (a galaxy...use to be thought a nebula).

He figured out what Andromeda was by figuring out WHERE it was (how far it was).

Contributed to helping understand the size of the universe.

Determined other "Galaxies"

Galaxies behave like a bomb (Big Bang) based off of Einstein's General Relativity

Where/ Who is our closest stellar neighbor?

The Alpha Centauri System (Binary Star)

4.4 LY (~1.3pc) away

Parallax

The apparent displacement of an object caused by a change in the position from which it is viewed.

The greater the parallax, the closer the object.

1 parsec (pc)= 3.26 LY

A parallax of 1 ARCSEC indicates distance of 3.26 LY

D= 1/p

D=distace (in parsec) p= parallax (in arcsec)

Hubble Deep Field

is a very deep and detailed image of a small patch of sky taken by the Hubble Space Telescope.

Cepheid Star

a type of super giant star (up to 10,000 times more luminous than Sun)

Henrietta Leavitt determined they could be used as standard candles.

grow brighter and dimmer over periods of days (oscillate).

Very luminous and easy to spot in our night sky.

Polaris is a cepheid star.

Galaxy

-A large assemblage of stars; a typical galaxy contains millions-billions of stars

-remote stellar systems

closest galaxy to us?

Andromeda Galaxy (still over 2 million lightyears away)

What are the three types of galaxies?

Spiral, Elliptical, and Irregular

Spiral Galaxy

Old and young stars

Lots of gas and dust

New stars forming

Contains: Nuclear bulge, spiral arms, and interstellar dust

Material rotates around center

2 Types: Regular and Barred

Elliptical Galaxy

ONLY old stars

No dust and little gas

No new stars forming

How many light years away is the Sun?

8 lightMINUTES!!!!!

trick question!

When and who invented the telescope as it relates to astronomy?

1608- Galileo

How do we measure distances to the stars and the nebulae (2 best methods)?

1) Parallax (most accurate and least controversial technique- up to ~300LY away)

2) Cepheid Stars

Planetary Nebula

-result of dying star passing out its opaque gaseous envelope into outer space (we knew what these were before other nebula because they were brighter and smaller in our sky)

How far is the moon from Earth (light-)

~1 light second

Standard Candle

object of known luminosity

Apparent Brightness

how bright an object appears in the sky. A measure of the observed light received from a star or other object at the Earth.

Luminosity (or power)

The total amount of light emitted by an object each second (unit: watts)

Rotation Curve

A graph of the speed of rotation vs. distance from the center of a rotating object, like a galaxy

showed astronomers abundance of dark matter

Dark Matter

non-luminous matter, whose presence is inferred only because of it's gravitational influence on luminous matter.

Composition= Unknown

first found in spiral galaxies by Vera Rubin in orbit periods of stars that were shorter than expected because objects moving too fast...more mass inside orbit/galaxies than expected

In all galaxies

Supermassive Black Hole

A black hole of millions or billions of times the Sun's mass, inferred to be present at the centers of most, if not all galaxies.

Cosmology

The study of the universe as a whole: it's contents, structure, origin, evolution, and ultimate fate

Milton Humason

started out as janitor at observatory Hubble was working at in Los Angeles; eventually became Hubble's assistant and helped with Hubble's Velocity-Distance Relation and Hubble Diagram

Vesto Slipher

(1912) Studied great nebulae before they were known to be a galaxy

Found spectra of "nebulae" and figured that galaxies were moving very quickly and away from us "curious result"

Hubble Law

v=Hod

The linear relation between the speed and recession of a distant object and its current distance from us

Big Bang

-Galaxies behave like a bomb

-based off of Einstein's General Relativity

-expansion of universe began with a primeval explosion

Hubble's Constant

constant of proportionality between the velocities of remote galaxies and their distances

Units: (km/s) / Mpc

The Cosmological Principle

Assumes we are not in the center of the universe

All places in universe are alike, isotropic, and homogeneous

Starting point for modern cosmology

"cosmological conundrum"

How? Galaxies are separating from each other due to the expansion of the space between them.

Cosmological redshift

A redshift produced by the expansion of space itself

3 ways to redshift a photon

1) object traveling AWAY from observer from space (doppler effect)

2) strong gravity field (gravitational redshift)

3) by an object sufficiently far away that the universe expands significantly while the photon is in flight (cosmological redshift)

critical density

Pcrit

The density of matter that would allow the universe to expand forever, but at a rate that would decrease to 0 at infinite time

Type 1a Supernova

a stellar explosion that is up to 10 billion times more luminous than the Sun.

Determined as Standard Candle in 90s

White dwarf in binary system that is completely destroyed

Thermonuclear Supernova

Accelerating Universe

The model for the universe that the expansion of the universe is speeding up over time, rather than slowing down. Implies an eternally expanding universe that grows colder and darker over time.

Cosmological Constant

A term in the equations of general relativity that has the effect of producing a repulsive quality to space itself. Einstein abandoned it after Hubble discovered expansion.

To maintain a "static" universe

" ^ "

proved correct in 1998

Dark Energy

A hypothetical form of energy that permeates all of space and acts to push space apart at an accelerating rate

cosmological discovery that universe is accelerating and

expansion is speeding up. Energy works against gravity and pushes space apart at accelerating rate.

Unknown cause

Singularity

theoretical point of zero volume and infinite density to which any object that becomes a black hole must collapse

Event Horizon

The sphere around a singularity from within which nothing can escape; at this location the "escape velocity" is equal to the speed of light

Schwarschild Radius

The radius of the event horizon

depends on the mass enclosed within the event horizon

Type II Supernova

Core Collapse Supernova

Massive Star

Binary Stars

two stars that orbit each other and bound together by gravity

Accretion Disk

A disk of matter spiraling in toward the compact object

Final Evolution of Low Mass stars (<8Msun)

Not massive enough to fuse elements heavier than C and O

mass loss=leaves behind a very compact object

end state= white dwarf

closely packed electrons

Evolution of Binary Stars: Evolved star= White Dwarf

More massive star becomes white dwarf

companion star becomes red giant

mass transfer of hydrogen on white dwarf (accretion disk)

Results can either be Type 1a Supernova (white dwarf destroyed) / faster mass transfer "violent" OR a series of nova explosions (white dwarf left intact) /slower mass transfer "mild"

Evolution of Binary Stars: Evolved star= Neutron Star

more massive star becomes neutron star

companion becomes a red giant

mass transfer of hydrogen on white dwarf (accretion disk)

High energy X-ray bursts

Results in a nova: a sudden increase in brightness of a star

Neutron star survives short lived explosion

Escape velocity

The velocity a body needs to escape the gravity of another body and never return to it

Pulsar

a rotating neutron star emitting pulses of radio waves

example: The "Crab" Pulsar

Neutron Star

1.6 Msun

Extremely dense (billion times more than white dwarf)

Born spinning very rapidly and slows down over time

Emits beams of radio (sometimes visible) waves from magnetic poles (we can see pulsar if beams intercept Earth)

Many traveling through space at very high speeds

non-spherical explosion mechanism may be at work in core-collapse supernovae

Jocelyn Bell

discovered first radio pulsars from neutron stars

High Mass stars

born with 8 times greater mass than Sun

fusion ends after production of iron

becomes core collapse supernova and leaves behind neutron star or black hole

Chandrasekhar Limit

theoretical upper limit to the mass that a white dwarf can have

Stellar Evolution

The changes in a star's properties as it ages

Fusion

The building up of heavier atomic nuclei from lighter ones

Fission

The breakup of heavier atomic nuclei into two or more lighter ones (Atomic bomb)

Perigee

Lowest point in the satellite orbit around earth

Apogee

highest point in the satellite orbit around Earth

Perihelion

lowest point in the satellite orbit around the sun

Aphelion

highest point in the satellite orbit around the sun

Aristotle

Discovered Earth was spherical

Believed Geocentric but rejected idea because inability to detect stellar parallax

Eratosthenus

measured size of earth

Hipparchus

star catalog, defining system of star magnitudes, discovering precession in the apparent shift of the north celestial pole

Ptolemy

Almagest (book) → explained planetary motions

Retrograde motion

Used geocentric

Epicycles

Tetrabiblos: another book → astrology. Natal astrology is based on the assumption that the positions of the planets at the time of our birth, horoscope, describes our future.

Nicholaus Copernicus

Introduced heliocentric theory

Book: De Revolutionibus

Galileo Galilei

Father of both modern experimental physics and telescopic astronomy

First to use telescope for sky

Studied acceleration of moving objects

Discovered milky way, phases of venus, 4 satellites of jupiter, large-scale features of the moon

Went off Copernican theory

Tycho Brahe

pre-telescope era

But accurately described planetary positions that provided data used by Kepler

Johannes Kepler

Three fundamental laws of planetary motion:

1) Planetary orbits are ellipses (described by its semi-major axis and eccentricity) with the sun at its focus

2) In equal intervals, a planet sweeps out equal areas

3) Times expressed in years, and distance in astronomical units, the relationship between period (p) and semi-major axis (D) of an orbit is given by D^3 = P^2

Gas Pressure

The pressure resulting from the thermal motions of gas particles (dominates our Sun)

Radiation Pressure

The pressure resulting from the impact of photons on a surface or gas.

Hydrostatic Equilibrium

state of equilibrium in which the inward pull of gravity in a star is just balanced by the outward forces of gas and radiation pressure.

Nucleosynthesis

The building up of heavier elements from lighter ones by nuclear fusion

Interstellar gas

consists primarily of hydrogen

presence inferred by light it emits (emission-line spectrum)

Interstellar DUST

consists of tiny solid grains

presence inferred by light it ABSORBS. Dust blocks light coming from behind it

Interstellar Matter

The space between the stars (gas and dust)

Strong Force`

a very short-range but powerful force that binds nucleons (protons and neutrons) together

Thermonuclear Reaction

A nuclear reaction that results from encounter between particles that are given high velocities by heating them.

Photosphere

The visible surface of a star. The region in a star's atmosphere from which visible light escapes into space

Sunspot

region on sun's surface that is cooler and thus darker than surrounding areas

_______ interact with light by absorbing and emitting photons

Atoms

Ion

an atom that has lost or gained one or more electron

Ionization Energy

the minimum amount of energy required to remove an electron from an atom in its ground state.

Quantum Mechanics

The branch of physics that deals with the structure of atoms and their interactions with light

proper motion

Motion of a celestial object across the sky

Doppler Technique for Exoplanets

detection of exoplanets through the periodic motion of a star toward and away from an observer caused by the gravitational pull on the star by the planet (1995)

Transit Technique for Exoplanets

periodic dimming of a star due to the passage of a planet in front of it (transits) (1999)

Direct Imaging Technique for Exoplanets

taking their picture (2008)

Hα line

most prominent spectral feature due to hydrogen at visible wavelength (6563 Angstroms)

Neutrino

-rarely interact with other matter

-very little mass (very light)

-3 varieties

-"ghost particle"

-electrically neutral

-experience "neutrino oscillations"

-travel at nearly the speed of light

-pass through sun

-Created in abundance during nuclear fusion in center of sun

What temperature is the Sun's solar photosphere

5800 Kelvin