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Our Milky Way
in Space and Time
Caty Pilachowski
Mini-University 2013
Our Journey…
Where in the Galaxy Are We?
The Local Neighborhood
Top Milky Way Destinations!
The Dark Heart of the Galaxy
Formation of the Milky Way
Our Galaxy in the Cosmos
Where Are We???
100,000 Light Years
A Thin Disk of Stars
100,000 Light Years
What Is a Light Year?
The distance light travels in one year
(about 6 trillion miles)
Light travels at 186,000 miles per second
The Moon is 1
The Sun is 8
light-second
The Earth
nearest star,
light-minutes
from
Proxima
Centauri, is
from Earth
four light years from
the Sun
Our Home
The Sun
Dust
Lanes
Spiral
Arms
Disk
Hot Young Stars
Halo
Bulge
Galactic Center
Light takes 100,000 years to cross the Milky Way
Meet the
Neighbors
 Proxima Centauri
 Alpha/Beta Centauri
 Most nearby stars
are small, dim and cool
100 Light Years
Polaris
500 Light Years
Orion Nebula
Distance: ~1300 light years
X
Orion Nebula
Distance: ~1300 light years
X
Pillars of Creation
X
Eagle Nebula
with Hubble
Lower density
gas has been
eroded away,
leaving pillars
of higher
density gas
where stars
are forming
Crab Nebula
ESO
X
The remnant
of an exploded
star
The explosion
was recorded
in 1054 CE
Ring Nebula
WIYN
X
The remnant of
a dying star
The ring will
fade, and the
central star will
become a white
dwarf
Globular Cluster
X
Messier 3
Age – 13 billion
years
500,000 stars
WIYN
Cygnus X-1
X
A binary star
containing a
black hole
Mass from the
star is pulled
into the black
hole
The
Galactic
Center!
In visual light, this
region is hidden
from us by gas and
dust that dim the
light by a factor of
10 billion!
The Galactic
Center in
Infrared
Light
The dust is
transparent to
infrared light, and
we can see through
the gas and dust to
observe the
Galactic Center
The Galaxy hosts a supermassive black hole at its heart!
Orbits of stars
around the
central mass is
consistent with a
4 million solar
mass object at
the Galactic
Center
Massive Black Hole!
Detected in
infrared, radio,
and x-ray light
Mass 4 million
times the Sun’s
mass
Growing slowly
through accretion
All big galaxies
host central black
holes
A Gas Cloud
Approaches
the Black
Hole!
 The cloud will pass
within 36 light hours
next month (July)
~3 Earth masses
~2000 miles per sec
Animation!
The Universe
Contains Many
Spiral Galaxies
We learn about
our Milky Way
from other
galaxies
Forming the Milky Way
Galaxies like the Milky Way form from the
consolidation of many primordial gas clouds
Collisions of
gas clouds
create bursts
of star
formation to
shape the
Galaxy
The Milky Way Is Still Growing
Nearby dwarf galaxy discovered in 1994 in
the direction of Sagittarius
Distance about 88,000 light years
Merging with the Milky Way
Galaxy’s
“New”
Tidal
Stream
Sagittarius orbits the Milky Way
The orbital period is about a billion years
“Tidal stream” of stars from Sagittarius
circles the Milky Way
The
Local
Group
The Milky Way is
part of a small
group of galaxies
known as the local
group
2.5 million
light years
Andromdea Galaxy
Milky Way Galaxy
Triangulum Galaxy
Many small ones
Galaxy Collision!
The Local Group Is Part of
an EVEN BIGGER Group
The Local Group is part of the Virgo
Super Cluster of Galaxy Groups
Newly Discovered Galaxy!
The Leo P galaxy
was just discovered
here at IU using
the WIYN
Telescope
Five million light
years from the
Milky Way
Undisturbed, in an
empty part of
nearby space
Our Home in the Cosmos