Welcome to Starry Monday at Otterbein Astronomy Lecture
Welcome to Starry Monday at Otterbein Astronomy Lecture Series -every first Monday of the monthMarch 3, 2008 Dr. Uwe Trittmann Todays Topics Recent Advances in Astronomy Part III
The Night Sky in March Recent Advances in Astronomy: Data Exoplanets discovered
Kuiper belt objects discovered Age of the universe Temperature of the cosmic microwave background Shape/Curvature of the universe Acceleration of cosmic expansion Nature of unknown content of universe How do we find Exoplanets? Direct Observation (works only for double
stars, planets are too dim) Observe gravitational wiggles (Doppler effect) Observe exoplanet transits (Brightness curve) Or: Look them up on the internet http://exoplanets.org/ Direct Observation Members of system are well separated, distinguishable Works only for double stars, not planets
Doppler Shift Shift in optical frequency, analogy to shift in acoustic frequency shift (emergency vehicle passing)
Doppler Detection Example: Jupiter's gravitational pull causes the Sun to wobble around in a circle with a velocity of 12 meters per second.
Doppler Shift Indirect observation by measuring the backand-forth Doppler shifts of the spectral lines Example: Exoplanet around HD 11964 Doppler shift: Red Blue
Doppler Detection: The Automated Planet Finder Telescope The Automated Planet Finder Telescope is optimized specifically for the Doppler detection of planets having masses 5 to 20 times that of Earth. Such planets would likely be rocky with atmospheres, and able to retain water. The 2.4meter, robotic, telescope will be
dedicated every night to this planet search. http://exoplanets.org/telescope.html Eclipsing (Transiting) Exoplanets Orbital plane of the planet need to be almost edge-on to our line of sight We observe periodic changes in the starlight as the (dark) planet passes in front of the star
Example: Amateur discovers Exoplanet Brightness/ time Kepler Satellite Mission Detect Earthsize exoplanets by observing transits
Exoplanet SWEEPS-10 orbits its parent star from a distance of only 740,000 miles, so close that one year on the planet happens every 10 hours. The exoplanet belongs to a new class of zippy exoplanets called ultra-short-period planets (USPPs), which have orbits of less than a day. [Space.com]
Exoplanet Upsilon Andromeda b is tidally locked to its sun like the Moon is to Earth, so one side of the planet is always facing its star. This setup creates one of the largest temperature differences astronomers have ever seen on an exoplanet. One side of the planet is always hot as lava, while the other is chilled possibly below freezing.
Exoplanet The oldest known planet is a primeval world 12.7 billion years old that formed more than 8 billion years before Earth and only 2 billion years after the Big Bang. The discovery suggested planets are very common in the universe and raised the prospect that life began far sooner than most scientists ever imagined.
Exoplanet A year on HD209458b is only 3.5 Earth-days long. The planet orbits so close to its star that its atmosphere is being blown away by gales of stellar wind. Scientists estimate the planet is losing at least 10,000 tons of material every second. Eventually, only a dead core of the shrinking planet will remain.
Exoplanet HD 189733b was among the first planets to have its air sniffed. By analyzing light from the starplanet system, astronomers determined the planets atmosphere contains thick clouds of silicates similar to grains of sand. Curiously, no water vapor was detected, but scientists suspect it is hidden beneath the clouds. Exoplanet
Gliese 581 C marked a milestone in the search for worlds beyond our solar system. It is the smallest exoplanet ever detected, and the first to lie within the habitable zone of its parent star, thus raising the possibility that its surface could sustain liquid water, or even life. It is 50 percent bigger and 5 times more massive than Earth. What kind of exoplanets are we
finding? So far mostly big Jupiters, as expected Two types of orbits: Either highly eccentric and close to star Or circular orbits and typical spacing Distances from Host Star Mercury Earth Jupiter
Resonances It seems that our solar system is very stable with respect to gravitational effects The heavy planets are far out The lighter planets are closer together (Force of gravity grow with mass, decreases with distance) This is no accident! If it werent like this, the big
planets would gravitationally bully the others around: Force them into eccentric orbits Throw them out of the solar system A refined Picture New picture emerges from lessons learned from exoplanets Formation of a solar system is not necessarily the final word on appearance of a planetary
system Dramatic changes can happen in the millions of years Collisions Clean up migration Heritage and History How a planetary system looks like today is determined by how it formed AND what
happened in its history Our solar system seems to be protected from drama by its hierarchy and associated stabilizing resonances Still: Jupiter probably migrated inward by throwing out lots of small bodies (gravitational slingshot) The Golden Age of Cosmology is Now !
Cosmology is one of the most exciting subfields of physics these days The is an intimate connection between cosmology and particle physics lots of data available and being measured Todays era is that of precision cosmology There is lots we dont know interesting for young scientists! Cosmology
Cosmology tries to understand how the cosmos itself changes The universe is seen not as a canvas or stage on which things happen, but as a dynamical object, a player itself The underlying theory is Einsteins description of gravity, or General Relativity! Its easy!
R -1/2 g R = 8G/c4 T OK, fine, but what does that mean? (Actually, it took Prof. Einstein 10 years to come up with that!) The Idea behind General Relativity In modern physics, we view space and time as a
whole, we call it four-dimensional space-time. Space-time is warped by the presence of masses like the sun, so Mass tells space how to bend Objects (like planets) travel in straight lines
through this curved space (we see this as orbits), so Space tells matter how to move Compare to Electrodynamics In electrodynamics the two players are charges and electromagnetic fields. Charges produce electromagnetic fields, so
Charges tell fields where and how to form Electromagnetic fields exert forces on charges, so Fields tell charges how to move Here is a picture Sun Planets orbit
Effects of General Relativity Bending of starlight by the Sun's gravitational field (and other gravitational lensing effects) What General Relativity tells us The more mass there is in the universe, the more braking of expansion there is So the game is: Mass vs. Expansion
And we can even calculate who wins! The Fate of the Universe determined by a single number! Critical density is the density required to just barely stop the expansion Well use 0 = actual density/critical density: 0 = 1 means its a tie 0 > 1 means the universe will recollapse (Big Crunch)
Mass wins! 0 < 1 means gravity not strong enough to halt the expansion Expansion wins! And the number is: 0 = 1 The Shape of the Universe
In the basic scenario there is a simple relation between the density and the shape of space-time: Density Curvature 2-D example Universe Time & Space 0>1
positive sphere closed, bound finite 0=1
zero (flat) plane open, marginal infinite 0<1
negative saddle open, unbound infinite The size of the Universe depends on time!
Expansion wins! Its a tie! Mass wins! Time So, how much mass is in the Universe? Can count all stars, galaxies etc.
this gives the mass of all bright objects But: there is also DARK MATTER Bright Matter All normal or bright matter can be seen in some way Stars emit light, or other forms of electromagnetic radiation All macroscopic matter emits EM radiation
characteristic for its temperature Microscopic matter (particles) interact via the Standard Model forces and can be detected this way First evidence for dark matter: The missing mass problem Showed up when measuring rotation curves of galaxies
Is Dark Matter real? It is real in the sense that it has specific properties The universe as a whole and its parts behave differently when different amounts of the dark stuff is in it Good news: it still behaves like mass, so Einsteins cosmology still works! Properties of Dark Matter
Dark Matter is dark at all wavelengths, not just visible light We cant see it (cant detect it) Only effect is has: it acts gravitationally like an additional mass Found in galaxies, galaxies clusters, large scale structure of the universe Necessary to explain structure formation in the universe at large scales
What is Dark Matter? More precise: What does Dark matter consist of? Brown dwarfs? Black dwarfs?
Black holes? Neutrinos? Other exotic subatomic particles? The Night Sky in March Long nights, getting shorter! Spring constellations come up: Leo, Cancer, Virgo, Big Dipper lots of galaxies! Saturn & Mars are visible most of the night
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