Transcript Milky Way II

A105
Stars and Galaxies
Today’s APOD
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Milky Way Homework (#11) due today
Projects Due Nov. 30
For next week: Units 74, 75, 76, 78, 79
“rooftop” tonight, 8 PM, Swain West Roof
Four
Galaxies
similar
to the
MW
Barred
spirals
(seen
face-on)
Origin of the Milky Way
A huge, million-lightyear-sized blob of gas
contracts under gravity. The first stars and star
clusters form.
The rotating cloud of gas contracts toward its
equatorial plane.
The disk becomes very thin, and a “bulge” forms
in the center
Tidal Streams from CMa Wrap
around the Milky Way
A River of Stars
• Stars stripped from the
globular cluster NGC
5466
• NGC 5466 and its star
stream sit about 76,000
light-years from Earth
• Rises upwards from the
bright star Arcturus in the
constellation Bootes.
• The stream arcs over the
Milky Way galaxy
The Milky Way –
Review Vital Stats
• Consists of 100 billion stars.
• Stars are distributed in a central bulge, a
huge disk, and a galactic halo surrounding
both.
• The diameter of the disk is 30kpc (100,000
light years).
• The thickness of the disk is only 300pc
(1000 light years) on average.
• The total detectable mass is 200 billion
solar masses.
Galaxies evolve
and change
Rotation and spiral structure
Galaxy interactions
Galactic recycling
Galactic Recycling – the StarGas-Star Cycle
• The Galaxy
recycles
gas from
old stars
into new
star
systems
High-mass
stars have
strong stellar
winds that
blow bubbles
of hot gas
Lower mass stars
return gas to
interstellar space
through stellar winds
and planetary nebulae
Multiple
supernovae
create huge
hot bubbles
that can blow
out of disk
Gas clouds
cooling in the
halo can rain
back down on
disk
Atomic hydrogen gas forms
as hot gas cools, allowing
electrons to join with protons
Molecular clouds form next,
after gas cools enough to allow
to atoms to combine into
molecules
Gravity
forms stars
out of the
gas in
molecular
clouds,
completing
the stargas-star
cycle
Gas Cools
Summary of Galactic Recycling
• Stars make new elements by fusion
• Dying stars expel gas and new elements,
producing hot bubbles (~106 K)
• Hot gas cools, allowing atomic hydrogen
clouds to form (~100-10,000 K)
• Further cooling permits molecules to form,
making molecular clouds (~30 K)
• Gravity forms new stars (and planets) in
molecular clouds
How will the Milky Way change over the
next trillion years?
Where will the gas be in 1 trillion years?
A. Blown out of galaxy
B. Still recycling just like now
C. Locked into white dwarfs and lowmass stars
What kinds of stars will be found in the
Milky Way?
The Galactic Center!
At visual wavelengths,
this region is totally hidden
from us by gas and dust
that dim the light by a factor
of 10 billion!
The Galactic Center in the Near
Infrared
We can see through
the gas and dust, to
observe many of the
stars near the
Galactic center. But
the Galactic center
itself remains
undetected in the
infrared.
The Galactic Center Further in the
Infrared
Here we see not
only stars, but the
warm gas that
glows in the
infrared.
Galactic Center at Radio
Wavelengths – It’s a MESS!
•Sgr A is bright!
•Supernova remnants
•Arcs and threads
The Galaxy hosts a
super-massive black
hole at its center!
“A supermassive black hole at the
center of our galaxy is adequate to
explain the observations that have
been seen.”
Orbit of star S2 (followed for
ten years) around the central
mass is consistent with a 2.63.3 million solar mass object
within 10 light days of Sgr A*
Galactic Center Research at MPE
The Galactic Center in X-rays
This false-color image of the
central region of our Milky
Way Galaxy was made with
the Chandra X-ray telescope.
The bright, point-like source
at the center of the image
was produced by a huge X-ray
flare in the vicinity of the
supermassive black hole.
Galactic Center Detected in
Infrared Light!
• Seen with ESO Very
Large Telescope (8m) and Keck 10-m
Telescope
• Flares in infrared
light
• Within 10
Schwarzschild radii
of the black hole
• Cause still unknown
Key Ideas – The Galactic Center
• Powerful radio source
• Stars very densely packed
• Surrounded by ring of molecular gasempty in the center
• Central object is small – less than 4 AU
• Stars near center moving rapidly
• Black Hole! – 2 million times the mass of
the Sun
Black Holes
in the
Centers of
MOST
Galaxies
Left: Image of galaxy NGC4261, 45 million light
years from Earth. The orange part is radio
signals represented in false color.
Right: Hubble's space telescope image of the
same galaxy. It is suspected that there is a
black hole at the center of this image.
 Units 74, 75, 76, 78, 79
 News Quiz on Tuesday
 Project Due Nov 30