Galaxies

advertisement
Galaxies
1 of 20
17
© Boardworks Ltd 2004
What are Galaxies?
A galaxy is a massive, gravitationally bound system
consisting of hundreds of billions of stars, stellar remnants,
of gas and dust, and dark matter, an important but poorly
understood component.
From the Hubble Extreme
Deep field it is estimated
there are at least 176 billion
galaxies in the observable
Universe and possibly
trillions in the total Universe.
1
2 of 20
29
© Boardworks Ltd 2004
What are Galaxies?
At the turn of the 20th Century, a great debate was raging
in astronomy. The debate concerned faint, fuzzy objects
called "nebulae." Some astronomers believed nebulae
were small clusters of stars in our own galaxy. Others saw
some of them as vast, distant collections of stars, some
larger than the Milky Way itself.
1
3 of 20
29
© Boardworks Ltd 2004
What are Galaxies?
Finally, in 1924, American astronomer Edwin Hubble
measured the distance to what was then called the
Andromeda Nebula. He found it to lie over 2 million light
years from Earth. It was the first object to be recognized as
another galaxy.
Hubble's discovery totally changed
our view of the Universe. The already
vast distances between stars were
dwarfed by the incomprehensible
distances between galaxies. The
universe was suddenly a much
larger place than anyone imagined.
1
4 of 20
29
© Boardworks Ltd 2004
Classifying Galaxies – Part 1
Pretend that you are an astronomer
working shortly after Edwin Hubble
made his startling discovery. Now
that you know the "nebulae" are
actually other galaxies like our
own, you must come up with a way
to classify the galaxies.
Exercise 1: Look at the galaxy pictures. Divide them into
groups based on features they have in common. There is
no set number of groups.
1
5 of 20
29
© Boardworks Ltd 2004
Classifying Galaxies – Galaxy 1
1
6 of 20
29
© Boardworks Ltd 2004
Classifying Galaxies - Galaxy 2
1
7 of 20
29
© Boardworks Ltd 2004
Classifying Galaxies - Galaxy 3
1
8 of 20
29
© Boardworks Ltd 2004
Classifying Galaxies - Galaxy 4
1
9 of 20
29
© Boardworks Ltd 2004
Classifying Galaxies - Galaxy 5
1
10ofof20
29
© Boardworks Ltd 2004
Classifying Galaxies - Galaxy 6
1
11ofof20
29
© Boardworks Ltd 2004
Classifying Galaxies - Galaxy 7
1
12ofof20
29
© Boardworks Ltd 2004
Classifying Galaxies - Galaxy 8
1
13ofof20
29
© Boardworks Ltd 2004
Classifying Galaxies - Galaxy 9
1
14ofof20
29
© Boardworks Ltd 2004
Classifying Galaxies - Galaxy 10
1
15ofof20
29
© Boardworks Ltd 2004
Classifying Galaxies - Galaxy 11
1
16ofof20
29
© Boardworks Ltd 2004
Classifying Galaxies - Galaxy 12
1
17ofof20
29
© Boardworks Ltd 2004
Classifying Galaxies
How many galaxy classes do you have?
What distinctions did you use to create each class?
1
18ofof20
29
© Boardworks Ltd 2004
The Hubble Tuning Fork
After he discovered
what galaxies really
were, Edwin Hubble
became the first person
to classify galaxies.
Astronomers use his
system, called the
"Hubble Tuning Fork,"
even today.
First, Hubble divided
the galaxies into two
general categories:
elliptical and spiral
galaxies.
1
19ofof20
29
© Boardworks Ltd 2004
Elliptical Galaxies “E”
Elliptical galaxies are made of a central bulge
characterized by a smooth, ball shaped appearance.
They contain contain old stars and
possess little gas or dust. They are classified by the shape
of the ball, which can range from oval (E7) to round (E0)
(baseball-shaped to football-shaped). The stars in elliptical
galaxies do not revolve around the center in an organized
way. The stars move in randomly oriented orbits within the
galaxy, like a swarm of bees.
1
20ofof20
29
© Boardworks Ltd 2004
Elliptical Galaxies
Elliptical galaxies, such as M87, have very little gas and
dust. Because gas and dust are found in the clouds that are
the birthplaces of stars, we should expect to see very few
young stars in elliptical galaxies. In fact, elliptical galaxies
contain primarily old, red stars.
Elliptical galaxies also vary widely in size. Both the largest
and the smallest known galaxies are elliptical. Very large
elliptical galaxies can reach 300 million light years in
diameter. Dwarf ellipticals, which are very common, may
contain only 1/100,000th as many stars as the Milky Way!
1
21ofof20
29
© Boardworks Ltd 2004
Spiral Galaxies “S” or “SB”
Spiral galaxies consist of a flattened disk containing spiral
(pinwheel-shaped) arms, a central bulge, and a halo.
Spiral galaxies have a variety of forms, and they are
classified according to the size of the central bulge and
the tightness and appearance of the arms.
Type a galaxies have their arms
wound very tightly and have large
central bulges. Type c galaxies have
very their arms would loosely and
have small central bulges.
A barred spiral galaxy is a spiral that
has a bar-shaped collection of stars
running across its center. The arms of
a barred spiral are attached to the bar.
1
22ofof20
29
© Boardworks Ltd 2004
Spiral Galaxies “S” or “SB”
The spiral arms, which wrap around the bulge, contain many
young hot, blue stars and lots of gas and dust.
Stars in the central bulge where there is not a lot of gas and
dust tend to be older and redder.
Yellow stars like our Sun are
found throughout the disk of a
spiral galaxy where there are
young and middle aged stars
and lots of gas and dust.
This is the main region of
star formation.
Spiral galaxies rotate somewhat
like a hurricane or a whirlpool.
1
23ofof20
29
© Boardworks Ltd 2004
Lenticular Galaxies “SO” and “SBO”
Some galaxies are a transition type between
the elliptical and spiral galaxies, labeled S0 on
the tuning fork. These are called "lenticular galaxies."
They have a central bulge and a disk but no spiral arms.
Lenticular galaxies like M85 have a central
bulges and disks, but no spiral arms. If the
disk is faint, it is easy to mistake a lenticular
galaxy for an EO galaxy.
There is a second type of lenticular
galaxy called a barred lenticular
galaxy. Barred lenticular galaxies
have bars, much like the barred
spirals, and so they are denoted SB0.
1
24ofof20
29
© Boardworks Ltd 2004
Irregular Galaxies “Irr”
Galaxies that do not fit into either the spiral or elliptical classes
are called irregular galaxies. Irregular galaxies, such as M82,
have a wide variety of shapes and characteristics. They are
frequently the result of collisions between galaxies or
gravitational interactions between galaxies.
M82 has also been called "The Exploding Galaxy." It is
believed to have recently passed close to another galaxy
called M81. M81's gravity warped M82, and the warping
caused a burst of new stars to form. Today, M81 and M82
make a beautiful sight through binoculars.
1
25ofof20
29
© Boardworks Ltd 2004
Evolution of Galaxies
Hubble believed that galaxies started at the left end of the
diagram and evolved to the right. He called the elliptical
galaxies "early galaxies" and the spirals "late galaxies."
We now know that he was wrong: galaxies do not move
down the forks of the diagram as they evolve because spiral
galaxies rotate quickly while elliptical galaxies do not. There
is no way that an elliptical
galaxy could spontaneously
begin rotating, so there is no
way an elliptical galaxy could
turn into a spiral galaxy.
Instead, galaxies evolve from
spiral to elliptical.
1
26ofof20
29
© Boardworks Ltd 2004
Classifying Galaxies – Part 2
Exercise 2: Look at the galaxy cards and classify them to
create the Hubble Tuning Fork.
Irregular
E0
1
27ofof20
29
© Boardworks Ltd 2004
Glossary
 Galaxy- a massive, gravitationally bound system consisting
of hundreds of billions of stars, stellar remnants, of gas and
dust, and dark matter.
 Hubble Tuning Fork- Hubble’s classification system for
stars.
 Elliptical Galaxy- shaped like ellipses, and vary in shape
from circular to oval..
 Spiral Galaxy- shaped like spirals, with arms winding
in to a bright center.
 Lenticular Galaxy- transition galaxy between elliptical and
spiral galaxies
 Irregular Galaxy- no definite shape; do not fit in any other
class.
1
28ofof20
29
© Boardworks Ltd 2004
Download
Related flashcards

Halo (series)

17 cards

Dwarf galaxies

19 cards

Interacting galaxies

16 cards

Create Flashcards