Download Galaxy Powerpoint Notes

Galaxy Powerpoint Notes
What is a Galaxy? A galaxy is a relatively massive system composed of dark matter, gas,
dust, and is home to over billions of stars (can range from 100 000 to as large as 3000
billion), comets, and planets. The word ‘galaxy’ comes from the Greek word galaxias,
meaning “milky” (used to describe our own galaxy). There are many different types of
galaxies and altogether they make up the observable universe. It is believed that the
universe consists of hundreds of billions of galaxies, and still expanding. Astronomers
have been able to identify galaxies with the Hubble Space Telescope (HST), a space
telescope that was launched in April of 1990.
Discovery and Creation :
Discovery and Creation The discovery of galaxies was first announced on January 1st,
1925 by Edwin Hubble, who was the first astronomer to prove that there were other
galaxies outside of our own Milky Way. Prior to his announcement, in 1922-1923, Edwin
Hubble was searching for Cepheid variables (a type of star) and had found them in the
Great Nebula in Andromeda (M31, pictured left). He later found out that the distance
between the nebulae was so far apart, that is could not be apart of the Milky Way galaxy.
This led to the discovery of galaxies beyond our own.
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The creation of galaxies is a very mysterious topic as it is uncertain of how the universe
was created. The most common theory however, is the theory of the Big Bang, which
states that the universe expanded from a very dense state and continues to expand today.
Another common prediction of how galaxies were created is that due to the uneven
distribution of hydrogen and helium (The Big Bang theory states otherwise), large
amounts of gas began to compress after a pull of gravity. This small density gas-cloud
began to develop in areas of higher density and then formed planets, stars, and galaxies.
This is called the monolithic collapse, and the speed of rotation depended on whether or
not what type of galaxy it would become. Typically, a faster spinning gas-cloud became
spiral galaxies. Another way of galaxies forming is the hierarchical formation, when
larger galaxies were made up of several small ones.
Types of galaxies :
Types of galaxies There are many different types of galaxies in our universe. The main
types, however, are the spiral galaxies, elliptical galaxies, and irregular galaxies. A fourth
type, dwarf, can also be found, though they are relatively small compared to the other
types.
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I. Elliptical Galaxy :
I. Elliptical Galaxy Elliptical galaxies are galaxies that feature a ellipsoidal shape and
contain more middle aged stars and very little gas and dust. They can also have different
shapes that range from round, flattened, and elongated (which is the most common by
60%). These galaxies are believed to be created by a collision between two comparable
galaxies. It is also believed that at the centre of these galaxies lies a super massive black
hole. They make up about 10-15% of the total number of galaxies in the Local Group and
are often found in the center of galaxy clusters.
II. Spiral Galaxy :
II. Spiral Galaxy The appearance of spiral galaxies are very easy to distinguish. They
feature a shape that looks like a disk that usually has a bulge in the center and with arms
that spiral outwards as the galaxy rotates. The most common spiral galaxies in our
universe are the Milky Way Galaxy (the one we are in), and the Andromeda Galaxy (our
nearest neighbor). Combined with Irregular galaxies, they make up 60% of the total
amount of galaxies in the Local Group. However, unlike elliptical galaxies, they are
usually not found in the centre of galaxy clusters. They do, however, also consist of a
super massive black hole in its bulge. In a spiral galaxy, the younger stars are found in its
arms. Spiral galaxies can easily be confused with barred spiral galaxies, which look
similar but has a double ‘barred’ bulge. In 2005, it was considered that our Milky Way
Galaxy falls under this sub category.
III. Irregular and dwarf galaxies :
III. Irregular and dwarf galaxies Irregular galaxies do not have a regular shape, hence the
name ‘irregular’. They are very uncommon within our universe though they are believed
to once be spiral or elliptical galaxies that were altered by a gravitational pull. Irregular
galaxies contain an abundant amount of gas and dust. Examples of irregular galaxies
include Whirlpool Galaxy, Hoag’s Galaxy, Cartwheel Galaxy and Tadpole Galaxy.
Dwarf galaxies, on the other hand, contain a very few amount of stars compared to our
galaxy. They can have up to billions of stars. They are though to be formed by gases
lacking metals (as opposed to regular galaxies contain metal gases) There are many dwarf
galaxies in the Local Group, and they are known to orbit larger galaxies such as the
Andromeda galaxy and the Milky Way (14 are known to orbit it). An example of a dwarf
galaxy is Large Magellanic Cloud, which holds about 30 billion stars.
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The Milky Way Galaxy :
The milky way galaxy The Milky Way galaxy is where our planet, Earth, the solar
system, the Sun, and about 200-400 billion other stars are located. The diameter of the
Milky Way is 100,000 ly (light years) and the thickness is about 1000 ly. In case you
didn’t know, one light year is equivalent to about 10 trillion kilometers.
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The oldest star that has been found in the Milky Way is about 13.2 billion years old,
which is believed to be about the age of the universe. That being said, astronomers
consider that the Milky Way was one of the first galaxies to be formed after the Big
Bang. It is also considered to be a double barred spiral galaxy (as mentioned before).
After watching the brief video, you can see that there are many stars in our galaxy that
are quite large, and to put things in perspective and to compare, if we were to shrink our
solar system (all the planets and our Sun), and reduced it to the size of a quarter, the
galaxy would be the size of the width of the U.S.A. Also, the weight of our sun is
believed to hold 99.8% of the total mass of our solar system. Travelling at the speed of
light, which is about 300, 000 km/s, it would take many years for the human species to
travel the Milky Way.
Andromeda galaxy – m31 :
Andromeda galaxy – m31
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The Andromeda Galaxy (M31) is named after the Greek mythology of Princess
Andromeda. It is the Milky Way’s nearest neighbor in space, meaning it is the closest
galaxy to ours, though it is about 2,500,000 light years away. The galaxy is about 1.5
times bigger than ours and was first seen by the naked eye in 964 A.D by a Persian
astronomer named Abd Al-Rahman Al Sufi. It was then later discovered by a telescope in
1612 by Simon Marius. Because of its larger size, Andromeda is believed to consist of
more dark matter and also has two black holes in the center (as opposed to one in many
other galaxies). Andromeda is a very special galaxy to us as it travels at the speed of a
bullet, and eventually, in the next 4.5 billion years or so, it will collide with our own
galaxy, the Milky Way, and will likely create a gigantic elliptical galaxy.
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Galaxy collisions :
Galaxy collisions The Big Band Theory states that the Universe began a long time ago,
with galaxies and early stars forming just after. It also states that the Universe is still
expanding today, meaning that the galaxies that we see today are travelling at high
speeds. Eventually, sooner or later, these galaxies will collide, and since galaxies are
mostly made up of dark matter, the stars spread out are actually so far away that when a
collision occurs, most will be unaffected. However, the Andromeda galaxy and the Milky
Way galaxy will soon meet this fate, and as said before, they will create a gigantic
elliptical galaxy. When one galaxy meets another, the gas becomes so compressed that a
large amount of new stars will be born. There is also another fate, and that is when a very
large galaxy collides with another. This collision would make the larger galaxy add new
stars and become larger.
Inside of galaxies :
Inside of galaxies Ever wondered what was inside a galaxy? Well look no farther,
because you’re in one! Unfortunately, galaxies are massive, and we can’t see as much as
we wish, and that is why with the assistance of telescopes, astronomers have been able to
identify certain things in space. Our galaxy (the Milky Way, in case you didn’t know), is
made up of stars, gas, dust, a super massive black hole (that not even light can escape its
gravity), a Quasar (in other galaxies), and a large amount of dark matter. And by large,
we mean, large. Stars, as big as they are here, contribute to only 10% of what our galaxy
is made up of. The rest, you ask? Everything else. And most of that is dark matter, an
unknown substance that makes up most of a galaxy’s mass.
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The stars in a galaxy are often sorted into two classifications, which are population 1 and
population 2. Population 1 stars are younger stars that are rich in elements and are usually
located along the arms of galaxies. Meanwhile, population 2 stars can be as old as the
universe and have a very small amount of elements in them. Interstellar Medium (ISM) is
the amount of space between the stars and the galaxies. Since galaxies are also made up
of gas and dust, they fall under ISM, in which 99% of it is gas (90% of hydrogen) and
only 1% of dust. This gas and dust can range in temperatures and can be as cold as -410F.
Nebulae, is then created by clouds of gas. Stars, gas, and dust in the galaxies
Quasars :
Quasars Galaxies that have nuclei that produce a spectral line emission are formed from
highly ionized gases. This is called a quasar, and can fall under the class of “Seyfert
galaxies”. They are found in active galaxies (most often spiral), and emit high-energy
radiation in the form of x-rays. The appearance of quasars is truly unique, as they have an
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extremely bright nuclei, and spectra which have very bright emission lines of hydrogen,
helium, oxygen and nitrogen. Quasars are about a trillion times brighter than the sun and
are believed that they obtain their energy from black holes. The size of a quasar is very
large as well, and can be large in our entire solar system! Finally, the energy from a
quasar can take billion years to reach us.
The Local group :
The Local group We’ve already talked about the Andromeda Galaxy and how far it is.
Now, zooming out a little more, we come to something known as the Local Group. It is a
collection of over 36 galaxies that consist of all the different types. The galaxies all cover
about a 10 million light year radius. Its two largest members are the Milky Way and the
Andromeda Galaxies (pictured left). Of all the galaxies, only 3 are spiral, 13 are dwarf
elliptical, and the rest are irregular galaxies.
Star clusters :
star clusters Star Clusters are groups hundreds of thousands of stars in the universe. There
are 2 types of star clusters in the universe, Globular Clusters and Open Clusters. Globular
Clusters are groups of hundreds of thousands stars that are very old. Open Clusters have
fewer stars than Globular Clusters and the stars are much younger than the stars in
Globular Clusters.
Globular clusters :
Globular clusters Globular Star Clusters are roughly formed spherical and consist of older
yellow and red stars which are 12-30 billion years old. Globular Clusters are packed
together very tight rather than Open clusters where the stars are just scattered and loose.
Our galaxy the Milky Way has about 150 Globular Clusters. Some Globular Clusters can
be seen with the naked eye like Omega Centauri.
Open clusters :
Open clusters Open Clusters are somewhat different from Globular Clusters. Open
Clusters are confined to be a galactic plane and they are always found with spiral arms.
Open Clusters contain a few hundred members and are dominated by young blue stars.
These stars only live up to ten million years. Open Clusters have much less stars than
Globular Clusters.
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