Life in the Universe

N

# of civilizations in the Milky Way where communication is possible

R_* term meaning

average rate at which stars are formed in the Milky Way

f_p

fraction of stars with planets

n_e

average number of planets per planet-hosting star that could support life

f_l

what fractionof planets that could support life do go on to develop life

f_i

what fraction of planets that develop life go on to develop intelligent life

f_c

what fraction of planets with intelligent life develop techno-communications

L in the context of the Drake

amount of time in which an intelligent civilization remains communicable

Scope of scientific endeavors of a professional astronomer

Taxonomy and physical characterization, both observationally and theoretically, of all extraterrestrial phenomena and objects

What does “taxonomy of extraterrestrial phenomena” mean

how do we classify the objects in the night and sometimes day sky

Planets

Large, gravitationally bound, sphericla bodies, that cannot support thermonuclear fusion

Types of planets

terrestrial and giant

Terrestrial planets

planets with a solid surface that are comprised mostly of metals and heavy elements

Giant Planets

Planets with a large mas, relative to Earth, have no solid surface, and are comprised of low BP materials

Types of Giant planets

Gas Giants and Ice Giants

Gas Giants

Planets comprised mostly of hydrogen and helium gas

Ice Giants

PLanets comprised mostly of low BP compounds and a Hydrogen and Helium atmosphere

“Normal” Stars

Stars that are normally fusion hydrogen and helium into heavy elements

Giant Stars

Stars undergoing a period of instability as they use up their fuel for nuclear fusion

Stellar Remanants

Objects like white dwards and neutron stars that represent the end-stage of stellar evolution (end product of nova and supernova)

Extended Objects

Celestial objects which appear large and extendedon the sky but originate from a common origin

Nebula

Large luminious regions of gas and dust that are often being illuminated by the birth of young stars

Star Clusters

Large collections of stars that are gravitationally bound that formed at generally the same time

Stellar Explosions

Large expanding regions causeed by the late-stage evolution of a dying star

Galaxies

Gravitationally bound collections of stars, gas, dust, black holes, and dark matter

What governs the dynamics of planetary motion

Gravitational interactions between the planets and the sun are the source

What properties of stars contribute to how bright they appear in the night sky?

For identiical stars, distant stars will be fainter than closer ones, but how bright they appear depends on their temp and radius

What governs how sprial galaxies spin?

Gravity is the governing force but it alone does not account for the motion. Outskirts of galaxies must contain large amounts of non-luminous matter aka dark matter

Why is it that as galaxies get farther away from us, they are also moving faster away from us? Who first observed it?

Hubble first observed it and it can be explained by an expanded universe using Einstein’s Equations

Why should general astronomy research be pursued and why should it be funded by national gov’ts

The pursuit of fundamental knowledge is always useful and curiosity about the workings of the universe is, he feels, an integral part of the human condition

Correlation between Einstein and GPS Satellites

Without his general relativity, GPS satellites would not be terribly useful for day to day navigation

Why were ancient civs interested in understanding astrnomy

Bc there was a religious/spiritual connection between lived experiences on Earth and the movements of the celestial bodies; also, the sky moves with regularity and could be used as a timekeeper or calendar

Who developed sexagesimal numbering system + what is it?

base 60 and Babylonians

Difference in speed (in a vacuum) of microwaves and gamma rays

No difference. All electromagnetic radiation propagates through empty space at a fixed speed

Light can be treated as

discrete packets of energy (quanta) named the photon

Wave-Particle Duality

Light is both a particle and a wave

Can a single source of light emit at multiple frequencies? Give a reason you know this?

Yes, the sun emits light at all wavelengths

Why does the sun emit light at all wavelengths?

It is an example of a non-ideal blackbody radiator

Blackbody radiation

Electromagnetic radiation that occurs at every frequency and the peak emission is set by the tempof the source

Wien’s Law

relates peak wavelength of blackbody radiation with temp of radiation source

What is different across the types of light in the electromagnetic spectrum

The wavelength

Why does the Milky Way look different at different wavelengths?

Diff components of the Milky @Wway shine brighter at different wavelengths

Lyman-Alpha Emission

When hydrogen atom goes from excited to ground state and releases a photon

Star

massive sphere of plasma that produces light and heat through thermonuclear fusion in its core which releases energy that balances the inward pull of gravity

A stars color can tell us about

temperature

A stars absolute magnitude can tell us about

luminosity

Stars fit into three categories

main sequence, giant stars, and compact objects

Main Sequence

Longest phase where star is normal fusing hydrogen into helium (90% of a stars life)

What percent of stars in the sky are observed to be in the main sequence?

90

Are all stars in the main sequence stars with the same properties

no they may have differing properties

Giant Stars are responsible for the

production of a lot fo the heavier elements responsible for life

What percent of observed stellar populations are giant stars

Less than 1%

TF: Giant Stars can only belong to a few spectral classificatinos

F

Giant Stars are characterized by

larger luminosity due to larger radius and cycles of instability and changes in size and luminosity

Compact Objects are called

Final stage of stellar evolution and often called stellar remnants

Compact objects are characterized as

very high density objects including, in word of increasing density, white dwarfs, neutron stars, and black holes

COmpact Obects make up

~10% of all stars

White dwarfs

stars with masses less than 10* Solar mass that become giant stars, go nova have the central regions collapse into a white dwarfs

Do white dwarfs undergo nuclear fusion?

No

What supports white dwarfs?

electron degeneracy pressure

Neutron Stars

Stars with masses between 10x and 25x solar mass that become giant stars, go suprnova and have the central regions collapse into a neutron star

What supports neutron stars

neutron degeneracy pressure

Do neutron stars undergo nuclear fusion?

no

What is special about neutron stars?

When imbedded in a magnetic field, they can product readily seen radio pulsars

Black Holes

When stars with masses greater than 25x solar mass become giant stars, go nova and the central regions collapse into a black hole

All mass of a black hole is concentrated in

a single singularity

Black holes warp space and time so significantly that

there are some distance from the center of the black hole where nothing can escape

Stefan Boltzman Law

relates size and temp of a blackbody emitter to total received luminosity

Molecular clouds

often referred to as stellar nursuries and properties of the clouds are correlated with the types of stars they form

What can cause the formation of stars in molecular clouds

once the clouds become dense enoughm the pressure of the gas can nno longer support the cloud and it collapses in on itself. This can happen naturally or by any manner of collisions

Can multiple stars form at the same time in a molecular cloud

Yes, if the cloud is large enough

What can regulate the collapse of the molecular clouds?

energetic processes from supermassive black holes to magnetic fields

Jeans radius

maximum radius a molecular cloud can have before it collapses dfue to gravity

Explain what happens after the gas in a molecular cloud collapses

the physical conditions become appropriate, mitigating material disperses, fusion can begin and a star is born

The dispersion of mitigating material leads to the formation of

a protoplanetary disk forms which has the protostar at the center

What are the gaps in the disks an indication of

active formation of planets

Young stars emit ____ which can be used to

UV light; estimate recent star formation

How can infrared light be used to extrapolate back to initial star formation?

Intense hot radiation is emitted by young OB stars. this light is absorbed and reemitted by intervening dust, which can be in turn measured again to extrapolate back to star formation

How can radiowaves be used to extrapolate back to initial star formation?

The large mass OB stars recently formed will eventually go supernova and release massive amounts of energetic electrons that inteact with the magnetic firelds of the galaxy and produce radiowaves. Measuring this radio emission can allow you to extrapolate back to initial star formation

Qualifications for a planet to be considered one in the solar system

Must be in orbit around the sun, must be massive enough to be rounded by its own gravity, must have cleared the neighborhood around its orbit

Which planets are the giants in our solar system

Jupiter, Saturn, Uranus, and Neptune

Describe Giant Planets

Radial profile is a seamless transition from gas to liquid to sometimes a solid core; often intense storms and bands of diff atmospheric composition; intense magnetic fields that can create brilliant aurorae

Which are the gas giants?

Jupiter and Saturn

Describe Gas Giants

Abt 90% of mass is H and He even though these exist in diff phases throughout and abt 10% can exist as heavier elements

Which are Ice Giants

Uranus and Neptune

Describe Ice Giants

abt 80% of mass from heavier elements and other 20 is atmospheric envelope of H and He

Why are they called ice giants

an old naming convention abt compounds that exist on them; not actually spheres of ice

Describe Terrestrial planets (surface and composition)

generally smaller than gas giants and contain mostly heavier eleements and metals with rocky hard surfaces

Inside to outside, what is the structure of a terrestrial planet

hot metallic core of mostly iron surrounded by silicate based mantle and crust with atmosphere of heavy gases

Surface attributes of terrestrial planets

volcanoes, canyons, mountains and valleys (stuff from earth). Surface of planets evolve through tectonism which only appears to exist on earth in this solar system

Atmospheric attributes of terrestrial planets

Lost original atmosphere of hydrogen and helium bc they were too. small to hang onto them. They then form atmosphres of heavier elements that evolve as the planet ages

Hot Jupiters

Gas giants found near host stars. Easiest to detect

Super Earths

Terrestrial type planets that have up to 10x the mass of Earth (almost up to size of ice giant) and can exist in many orbital parameters and can have wildly interesting climates

Newton’s FIrst Law

Body at rest will stay at rest unless acted upon by a force

Newton’s second law

net force is equal to body’s acceleeration multiplied by its mass or the rate at which the body’s momentum changes with time

Newton’s third law

if two bodies exert forces on each other, these forces have the same magnitude but opposite directions

Equation given by Newton’s Second Law

F=ma

Gravity is the ______ of space-time

curvature

Kepler’s THree Laws

Planet Orbit is an ellipse with the sun at one of two Foci, Line segment joining a planet and the sun sweeps out equal areas during equal intervals of time, Square of a planet’s orbital priod is proportional to the cube of the lenth of the semi-major axis of its orbit

Ellipse

Plane curve surrounding two focal points such that for all points on the curve, the sum of the two distances to the focal points is constant.