ISB 200 Exam 1
Fermi's Question
Fermi reasoned that: -the sun is a typical star, and there are billions of stars in the galaxy that are billions of years older -with high probability, some of these stars will have earth-like planets -if the earth is typical, other earth-like planets might develop intelligent life -Milky Way Galaxy could be crossed in about million years with currently-envisioned technology
Atmosphere
-an atmosphere is necessary to prevent damage (blocks dangerous solar radiation, provides a greenhouse effect, helps distribute water and other chemicals) -it is possible to imagine life without an atmosphere, but it only in the subsurface
Temperature of the Universe
-as the universe expands, it cools -modern universe is very old on average: just 2.7 degrees above absolute zero
AU
-astronomical unit -average distance between Earth and Sun -1 AU = 1.496x10 ^8 -scale of planetary systems
Hubble Space Telescope
-best tool for looking at distant galaxies -can detect faint signals without distortion from the atmosphere -in orbit since 1990
Dark Ages
-between 150 million and 800 million years after the Big Bang (Jan. 4-22 on the Cosmic Calendar) -the universe was opaque, free protons and electrons absorbed all light -no light remains for us to measure, era of dark ages
How to tell if an Exoplanet can support life
-chemical composition -the absorption of light that passes through it
Types of Galaxies
-color can also be used to categorize galaxies -3 main groups: red sequence of older, dead galaxies, blue cloud of young galaxies -green valley in between, rarest type, but contains milky way
Types of Galaxies - Spiral
-dead/mature galaxies -spiral arms which eventually stop making new stars, rotation causes this -two or more arms -may have a central line, called a barred spiral galaxy -our galaxy, the milky way is a spiral galaxy -accounts for the old ages of Halo Stars
Galaxy Evolution
-early on, star formation (blue) occurs in a disk -this disk gains a central bulge: the galactic core -as the galaxy ages, the core becomes "dead" (red); no longer forming new stars, old stars start to burn out -when the central stars burn out, a hollow sphere of old stars remain
Big Bang Theory
-first proposed in the late 1920s -states that there was an infinitely small, infinitely dense point that contained everything that is the universe -this singularity was incredibly dense and hot
The Modern Universe
-galaxies and stars are continually formed, the universe now is a mix of young and old -the universe now is incredibly large and cold, it has been growing and coming since the Big Bang, when it was infinitely small and hot
Globular Clusters
-groups of densely-packed stars, all of which are approximately the same age -can estimate the lifespan of a star based on its brightness -the oldest known globular clusters have stars the ages between 11 and 18 billion years old -creates a limit to the age of the universe; it must be at least 11 billion years old
The Arecibo Message
-humanity hasn't just leaked signals, but also intentionally broadcast information to space -was broadcast in 1974 from a large radio telescope in Puerto Rico -contains important information about humanity
Olber's Paradox
-if space goes on forever with sats scattered randomly throughout, then in any line of sight in any direction, you will eventually run into a star -using this logic, the sky should be the average brightness of all of these stars; the sky should be as bright as the sun, even at night
Isaac Newton
-in 1687, published the "Principa" -describes the motion of large bodies based on gravity -applies his theories to describe the motion of the observable stars and planets
Edwin Hubble
-in 1929, he studied light given off by distant galaxies -noticed that light from most galaxies was shifted to the red end of the electromagnetic spectrum -proposed Hubble's Law after studying these galaxies
Evidence of the Universe's age
Red shift - evidence of ongoing expansion Globular clusters - ancient stars Cosmic Microwave Background Radiation: leftovers from the Big Bang
Defining Life
-life exhibits complex behavior and often unpredictable interactions, grows and reproduces, metabolizes (a process involves breaking down compounds or changing their form to generate energy and obtain raw materials) -HOWEVER the problem with these characteristics individually is that many non-biological entities exhibit these behaviors
Water
-life on earth is carbon-based and requires liquid water -our first choice is to look for other planets like Earth -subsurface water may support life, but is not able to be measured with current methods because it does not modify the atmosphere enough
Pillars of Creation
-most famous stellar nursery due to its shape
What is an exoplanet?
-most of the objects we see are stars -exoplanets are things that orbit stars -the minimum stellar mass is out .075*Ms, otherwise there is no fusion at the core -planets don't emit light -low mass and no light are both used to identify planets
Simple vs Complex Life
-need a much longer time frame for complex life -simple life can exist in more extreme circumstances
Dark Matter
-not in the form of stars and planets -not in the form of dark clouds of matter -not antimatter -possibly made of exotic particles like axions (hypothetical elementary particle) or WIMPS (weakly interacting massive particles)
Science
-not just a body of knowledge, but a way of investigating the world -is skeptical and always seeks to disprove current theory with new evidence -scientific claims must be; testable, falsifiable, repeatable, natural
Direct Imaging
-not very practical because planets don't emit their own light -very weak signals are hard to measure, strongest signals are from super-jupiter -least often used of the 3 methods
Energy
-organisms depend on light or chemical energy to fuel their metabolism -heat may also be a factor; from the local star, radioactive decay inside the plant, tidal friction, these heat sources may mean the temperature is OK despite being outside the star's habitable zone
Cosmic Microwave Background Radiation
-predicted in the 1940s by the scientists Gamow, Dicke, Alpher and Herman -no evidence until 1964 -discovered accidentally by Arno Penzias and Robert Wilson at Bell Labs
Proof of Concept
-recently, astronomers used the Very Large Telescope to detect carbon monoxide in the atmosphere of a "Super Jupiter" that orbits Tau Bootis (a visible star) -gas giants have lots of atmosphere, so this is an "easy" measurement -much more challenging with an Earth-sized exoplanet
Drake Equation
-seeks to quantify the number of times civilization has arisen in the universe -there is no universally agreed-upon answer
Nebulae
-some portions of the ISM have more gas and dust, called nebulae -the sites of star formation -often called "stellar nurseries"
Types of Galaxies - Lenticular
-star formation has ceased -shaped like a lentil -central bulge becomes thick and organization of central stars begins -considered a transitional form of galaxy -possible merger of two older spiral galaxies
Nucleogenesis
-stars are engines of nuclear fusion, meaning they combine the nuclei of small atoms, forming larger atoms (called nucleogenesis) -first nucleogenesis occurred shortly after BB producing light elements
How big is the universe?
-takes light ~8 minutes to arrive at the Earth from the Sun -use Astronomical Units (AU)
Fermi Numbers
-the answer to a Fermi problem is often given as just the nearest power of ten. This is called a Fermi number - 100 piano tuners = 10 ^2 piano tuners = fermi number is 2
Light-year
-the distance that light travels in one year -1 ly = 9.46 x 10^12 km
Spectroscopy of exoplanets
-the focus has now shifted towards doing spectroscopy of exoplanet atmospheres -by breaking light (or infrared radiation) down into its component wavelengths, one can look for signatures of different molecules
The Steady State Theory
-the prevailing wisdom prior to the Big Bang Theory -Fred Hoyle was a major proponent, he named the Big Bang Theory, choosing the name to ridicule the theory -stated that although the universe was expanding, it had no beginning or end -this requires the constant creation of new matter -measuring the Cosmic Microwave Background disproved this theory
Solar System's Habitable Zone
-the ranges of distances from a star from which an orbiting planet can have liquid water on its surface -these distances may vary depending on the star's size, mass, and brightness -the intersection of two regions that must both be favorable to life: one within a planetary system, the other within a galaxy -planets in these regions are the likeliest candidates to be habitable and thus capable of bearing life similar to our own -concept general does not include moons, which may receive heat input from the planets they orbit
Hubble's Law
-the rate at which a galaxy is moving is directly proportional to its distance from us -in other words, the farther away a galaxy is from us, the faster it travels away from us -the universe is expanding
The Expanding Universe
-the space between galaxies between expands, not the galaxies themselves -ex. raisins in a loaf of bread
Kepler Planet Candidates
-the telescope may detect planets that are not there, the technology may not be good enough to tell the difference between a planet and some other phenomenon -scientists need to check the accuracy of the telescope's predictions of a planet. If the telescope shows a planet and the scientists confirm that it is a planet, then the scientists can spend more time trying to learn about the planet
The Doppler Effect
-this phenomenon is more familiar with sound -source moving toward you: pitch is higher and wavelength is shorter -source moving away from you: pitch is lower and wavelength longer
Einstein's Cosmological Constant
-to agree with the accepted theory of the time (Newton's), Einstein added a cosmological constant to get a static universe -we know the universe is expanding, so the cosmological constant is no longer used -without this idea of a cosmological constant, Einstein could've been the first to predict that the universe is not static
The Speed of Light
-travel time of light is able to be used as a yardstick because the speed of light in a vacuum is constant -c = 3 x 10^8 m/s
Newton's Static Universe
-universe is static and composed of an infinite number of stars that are scattered randomly throughout an infinite space -universe if infinitely old and will exist forever without any major changes -time and space are steady and independent of one another
Dark Energy
-used to explain the acceleration of the expansion of the Universe
Kepler Space Observatory
-utilizes transit method -uses statistical analysis to recognize planets
Hubble Ultra Deep Field
-very faint signal means a long exposure time is needed to see anything -Hubble was pointed at an area of dark sky for four months in 2003-2004
Biosignatures
-water, oxygen, and ozone are indicators of life as we know it -reactive compounds which will not remain without life to create them -such indicators are known as biosignatures -we can try to measure biosignatures in absorption spectra from exoplanets
Relation to expansion of the Universe
-wavelength corresponds to color in visible light, with loner wavelengths toward the red end of the spectrum -the longer (red-shifted) wavelengths of light observed from distant galaxies is evidence that they are moving away from us
Can we estimate the terms of the Drake Equation?
-we have discovered exactly one planet with intelligent, signal-releasing life -using Earth as a model can fell us a bit about the terms of the Drake Equation -we also have astronomical observations to help estimate these terms
Absorption spectra
-when a planet passes in front of a star, some of the wavelengths emitted by the star are absorbed by the planet's atmosphere
Planetary transits
-when a planet passes in front of a star, the star appears dimmer, the fraction depends on the ratio of the areas (radius of sun, radius of jupiter, radius of earth) -venus and mercury transit the sun from our perspective
Formation of Stars
-within a molecular cloud, gravity causes some areas to have increased density -the dense areas are pulled together more and more by their own gravity -eventually cloud collapses -dense fragments of the cloud break apart -these fragments form into protostars, and eventually stars
Types of Galaxies - Elliptical
-young galaxies with a lot of star formation -ellipsoid in shape -disorganized -less frequent in the early universe -likely formed from collisions later in the life of a galaxy
How old is the universe?
~13.8 billion years (short answer)
Factors of Habitability: Nutrients
Reason: without chemicals to make proteins and carbohydrates, organisms cannot grow
Cosmic Calendar
-Treating the entire history of the universe as a one-year calendar -each cosmic day is equal to 37.8 million years -438 years per Cosmic second
Goldilocks Planet
-a planet that falls within a Star's habitable zone, and the name is often specifically used for plants close to the size of Earth
Occam's Razor
-also called the Principle of Parsimony -among competing hypotheses, the one with the fewest assumptions should be selected -"the simple answer is best" -all hypotheses and conclusions should be checked with Occam's Razor
What are we looking for?: Life
That which distinguishes animals and plants from inorganic matter, including the capacity for growth, reproduction, functional activity, and continual change preceding death
Scientific Law
A statement of fact that describes an observation about nature and can sometimes be expressed as a mathematical equation -Law of Gravity, Newton's Law of Motion, Laws of Thermodynamics, Law of Conservation of Matter and Energy
Galaxy
A system of millions or billions of stars, together with gas and dust, held together by gravitational attraction
NASA Kepler mission
"a search for habitable planets" -uses an 85 megapixel camera to monitor more than 100,000 stars for transiting planets -launched in 2009, it is in solar (not earth) orbit
Characterizing Stars
-Stars are generally characterized based on visible signals (brightness and color) -from these signals, we can infer characteristics of the stars themselves (temperature, size, age, chemical makeup)
Several conditions make a planet habitable
-Temperature, water, atmosphere, energy, nutrients
Pseudoscience
-A theory or practice which is not supported by experimental evidence, but is explained using scientific sounding jargon. Ex) water dowsing, astrology, numerology, polygraphy, handwriting analysis
Georges Lemaitre
-Belgian astronomer and Jesuit priest -first suggested that the universe formed from a singularity, but had no evidence -"Father of the Big Bang"
Nutrients
-Chemicals to fuel metabolism and build structures -the most important for life are: Carbon, Hydrogen, Oxygen, Nitrogen, Phosphorus, Sulfur
Looking out = Looking back in time
-Distance is measured in light years -Light becomes fainter the further it travels, so distant/old signals are very weak
Albert Einstein
-Einstein overturned part of Newton's theory with his theories of special and general relativity, time and space were indeed related -based on general relativity, the structure of universe is either always expanding or always contracting
Habitability: summary
-Habitability is the ability of a planet (or moon) to support life 1. depends on 5 factors: temperature, water, atmosphere, energy and nutrients 2. easiest to assess is temp., so we look for planets in the habitable zone -exoplanets are detected by 3 methods: direct imaging, radial velocity (wobble), and transit (dimming) -biosignatures are chemicals that can be detected remotely which show that life is likely present
Fermi Problems
-How many piano tuners are there in Chicago? -take a difficult question in terms of simpler parts -Enrico Fermi required exercises for all of his students to learn skills of approximation
The Fermi Paradox
-How many times has civilization evolved in the universe? -we know it has happened at least once
Enrico Fermi
-Italian physicist who created the first nuclear reactor -"where is everyone?" -based mathematical model on the Drake Equation
The search continues...
-James Webb Space Telescope (2018) launch -Kepler (ongoing) -SETI prospects (radio signals) -Planetary spectroscopy (already in use for stars)
Formation of structure in the early universe
-Jan 22 on cosmic calendar, ~800 million years after BB -slight differences in the density of matter lead to gravitational collapse -first stars
Size of Exoplanets
-Kepler excels at detecting small planets, near Earth-size -previous methods could only detect very massive planets
Kepler: the Big Picture
-Kepler's 1,000 exoplanet discoveries (and counting) have demonstrated that planets are everywhere, and that small planets are more common than large ones -prior to Kepler, the vast majority of known exoplanets were Neptune-size or larger. This was a selection bias due to the difficulty of detecting smaller exoplanets -Kepler can detect, and is detecting, smaller planets not possible by other methods, and is increasing the odds of finding planets that resemble Earth
Approximation
-Many scientific discussions involve numbers that are very large or very small -these numbers are difficult to comprehend, making even simple ideas sound complicated -we can't ignore the numbers, but we can make them easier to comprehend (choose practical units, powers of ten, Fermi numbers)
Big Bang Theory Timeline
-Since the hot, dense singularity, the universe has been expanding and cooling -First 10 ^-32 seconds: Inflation (universe grew inconceivably quickly immediately following the Big Bang) -3 minutes: formation of nuclear, only Hydrogen, Helium, Lithium were formed -380,000 years: Cosmic Microwave Background, first time visible light existed
Scientific Method
1. A question 2. Observe 3. Hypothesis 4. Test the hypothesis 5. draw conclusion
What is the universe made of?
4% atoms 22% cold dark matter 74% dark energy
Early Universe in order
The Big bang > Inflation > Creation of matter > microwave background > dark ages > star formation > galaxy formation
World
A planet or moon; most often referring to Earth
Scientific Theory
A well-tested and widely accepted explanation of a natural event -Big Bang Theory, Theory of Evolution, Quantum Theory of Light, Theory of Plate Tectonics
Universe
All existing matter and space considered as a whole; the cosmos
Expanding of Space
As the universe is expanding,g space itself yes larger, but objects within it do not
Factors of Habitability: Energy
Reason: A lack of sunlight or too few of necessary chemicals that provide energy to cells, will cause organisms to die
Factors of Habitability: Water
Reason: chemicals a cell needs would be unable to dissolve or transport to the cell
Factors of Habitability: Atmosphere
Reason: insufficient gravity would be unable to hold an atmosphere, leaving the planet or moon without
Interstellar Medium
Made up of gas (atoms and molecules), and dust (small particles
Factors of Habitability: Temperature
Reason: low temperatures cause chemicals to react slowly, interfering with necessary reactions ideally in the range for liquid water
Red Shift
Spectrum of light from distant galaxies is shifted toward the red compared to light from the sun
Scientific Skepticism
The practice of questioning whether claims are supported by empirical research -skepticism deals with how to think, not what to think -not the same as philosophical skepticism -theories judged on many criteria: falsifiability, Occam's Razor, explanatory power, perceptions matching experimental results
Radial Velocity
The wobble method -when objects are orbiting each other, neither is stationary. The enter of mass remains fixed, and each object moves around it -this makes the star look like it "wobbles" from a distant perspective -the ratio of speeds equals the ratio of masses -the ratio of speeds equals the ratio of masses -we can measure the mass of the planet by measuring the speed of the star -speeds can be measure using the Doppler effect
How do we find exoplanets
Transit, Radial velocity (wobble), direct imaging
Finding Exoplanets
Two primary methods 1. The star wobbles as the planet orbits it (radial velocity) 2. The star becomes slightly dimmer if the planet passes in front of it (transit) -we'd like to observe planets both ways
Hertzsprung-Russell Diagram
Types of stars
What is radiation?
Visible light, microwave, radio, etc. are all forms of electromagnetic radiation with different wavelengths
