Transcript The Hidden Lives of Galaxies NSTA 2001

GALAXIES
From: Jim Lochner, USRA & NASA/GSFC
What is a Galaxy ?
Solar System
Distance from Earth to Sun
= 93,000,000 miles
= 8 light-minutes
Size of Solar System
= 5.5 light-hours
What is a Galaxy?
Stellar Region
Sun
(solar system
too small to be
seen on this scale)
30
light-years
What is a Galaxy?
A
galaxy
Is a
massive
collection of
stars, gas, and
dust kept together
by gravity
Our galaxy is the
“Milky Way”
Sun’s Stellar
Region
200,000 light-years
What is a Galaxy?
If our solar system
was the size of a
cell in the human
body, then our
galaxy would still
measure
over one mile
across.
What is a Galaxy?
•The largest galaxies contain
more than a trillion stars.
•Smaller
ones have
only a few
million.
•Astronomers don’t count the stars, but
estimate how many stars a galaxy might have.
Types of Galaxies
Spiral
disk-like appearance
with arms
of stars and
Barred
Spiral
dust
forming
a spiral
similar
to spirals
but
pattern
with a bright bar of
Elliptical
stars and gas through
elliptically-shaped,
the
center
with less gas and dust
Irregular
than
spirals;
no disk
neither
elliptical
noror
“arms”in shape; gas and
spiral
Peculiar
dust
as in spirals
noof the above types, often due to
distorted
form ofbut
one
defined
collision“arms”
with another galaxy or similar catastrophic event
Types of Galaxies Quiz
?
A
B
D
C
E
Galaxy Formation
According to the Big
Bang theory, galaxies
began when large
clouds of gas and dust
collapse as a result of
their gravity.
As the cloud shrinks
and the debris is
compacted, stars and
planets form.
Contents of Galaxies
Gas Clouds
The Latin word for
“cloud” is nebula. In
space nebulas (or
nebulae) are giant
clouds of gas and
dust.
Contents of Galaxies
Open Cluster
Small group of new
stars that formed at the
same time from a cloud
of gas and dust.
Contents of Galaxies
Globular Clusters
A spherical bundle of
older stars that orbit a
galaxy as a satellite.
They are very tightly
gravitationally bound,
which gives them their
spherical shape and
dense inner core of
stars.
•.
Spirals vs. Ellipticals
Finally the type of galaxy depends on initial
rate of star formation:
- If stars form quickly, then galaxy becomes
elliptical. Stars form within initial distribution
of gas,and follow their initial orbits.
- If stars form later, the gas has time to
collapse into a disk. Most stars from within
the disk. The galaxy becomes a spiral.
Formation via Galaxy Mergers
In clusters, galaxies can pass close to one
another.
• Galaxies can become distorted, and often
merge.
• Mergers often lead to giant elliptical
galaxies at the heart of large clusters.
Spirals in Grazing Encounter
Antennae Galaxies