Starry Monday at Otterbein

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Starry Monday at Otterbein



Astronomy Lecture Series

-
every first Monday of the month
-


March 3, 2008


Dr. Uwe Trittmann

Welcome to

Today’s 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 back
-
and
-
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 2.4
-
meter, 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 Earth
-
size
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 star
-
planet system, astronomers determined the
planet’s 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 weren’t 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


Today’s era is that of “precision cosmology”


There is lot’s we don’t 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 Einstein’s
description of gravity, or …

General Relativity! It’s easy!

(Actually, it took Prof. Einstein
10

years to come up with that!)



R
μν

-
1/2 g
μν

R = 8
π
G/c
4
T
μν

OK, fine, but what does
that mean?

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


Planet’s 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


We’ll use

0

= actual density/critical density:



0
= 1
means
it’s 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!

It’s 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
Einstein’s cosmology still works!

Properties of Dark Matter


Dark Matter

is dark at all wavelengths, not
just visible light


We can’t see it (can’t 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

Moon Phases


Today
(Waning Crescent)



3 / 7 (New Moon)



3 / 14 (First Quarter Moon)



3 / 21 (Full Moon)



3 / 29 (Last Quarter Moon)

Today
at
Noon


Sun

at
meridian,
i.e.
exactly

south




10 PM


Typical
observing
hour,
early
February




Saturn

Mars

Star
Maps



Celestial
North Pole



everything
turns around
this point


Zenith


the
point right
above you &
the middle of
the map

40
º

90
º

Due
North


Big Dipper
points

to the
north pole

West

Perseus,

Auriga &
Taurus


with
Plejades

and the
Double
Cluster

South
-
West


Orion


Canis
Major &
Minor


Beautiful
open star
clusters


Orion
Nebula
M42

South


Gemini


Cancer


M44
Beehive
(open star
cluster)


Mars

South
-
East


Spring
constellations:


Leo


Hydra


M44 Beehive
(open star
cluster)


Saturn

East


Virgo &
Coma

High up
in the
East


Big
Dipper


Bootes

Mark your Calendars!



Next
Starry Monday
: April

7, 2008, 8 pm






(this is a Monday )



Observing at

Prairie Oaks Metro Park:


Friday, February 15, 6:30 pm



Web pages:


http://www.otterbein.edu/dept/PHYS/weitkamp.asp

(Obs.)


http://www.otterbein.edu/dept/PHYS/

(Physics Dept.)



Mark your Calendars II



Physics Coffee is every Monday
, 3:00 pm


Open to the public, everyone welcome!


Location: across the hall,
Science 244


Free coffee, cookies, etc.