TRIVIA DAY PRESENTATION
GALAXIES
SJCSF ASTRO CLUB
FRIDAY 27TH OCTOBER, 2023.
THE BUILDING BLOCKS OF THE UNIVERSE
Galaxies are vast cosmic islands of stars, gas, dust,
and dark matter held together by gravity.
Hubble’s keen eye has revealed intricate details of
the shapes, structures, and histories of galaxies —
whether alone, as part of small groups, or within
immense clusters. From supermassive black holes
at galactic centers to giant bursts of star
formation to titanic collisions between galaxies,
these discoveries allow astronomers to probe the
current properties of galaxies as well as examine
how they formed and developed over time.
WHAT IS A GALAXY?
Galaxies are concentrations of stars, gas, dust, and dark matter.
They come in a variety of shapes and sizes. Some are fated to
collide, like the Milky Way and Andromeda
WHAT KIND OF GALAXIES ARE THERE?
Astronomers classify galaxies
into three major categories:
elliptical, spiral and irregular.
These galaxies span a wide
range of sizes, from dwarf
galaxies containing as few as
100 million stars to giant
galaxies with more than a
trillion stars. Ellipticals, which
account for about one-third of
galaxies observed, vary from
nearly circular to very
elongated.
They possess comparatively little gas and dust,
contain older stars and are not actively forming
stars anymore. The largest and rarest of these,
called giant ellipticals, are about 300,000 light-
years across. Astronomers theorize that these
are formed by the mergers of smaller galaxies.
Much more common are dwarf ellipticals, which
are only a few thousand light-years wide. Spiral
galaxies appear as flat, blue-white disks of stars,
gas and dust with yellowish bulges in their
centers. These galaxies are divided into two
groups: normal spirals and barred spirals. In
barred spirals, the bar of stars runs through the
central bulge.
WHAT KIND OF GALAXIES ARE THERE?
The arms of barred spirals usually start at the end of the
bar instead of from the bulge. Spirals are actively forming
stars and comprise a large fraction of all the galaxies in the
local universe.
Irregular galaxies, which have very little dust, are neither
disk-like nor elliptical. Astronomers often see irregular
galaxies as they peer deeply into the universe, which is
equivalent to looking back in time. These galaxies are
abundant in the early universe, before spirals and ellipticals
developed. Aside from these three classic categories,
astronomers have also identified many unusually shaped
galaxies that seem to be in a transitory phase of galactic
development. These include those in the process of colliding
or interacting, and those with active nuclei ejecting jets of
gas.
WHAT IS DARK MATTER?
In the late 1970s, astronomer Vera Rubin made the
surprising discovery of dark matter. She was
studying how galaxies spin when she realized the
vast spiral Andromeda Galaxy seemed to be rotating
strangely. In an apparent violation of Newton and
Kepler’s Laws, the material at the galaxy’s edges
was moving just as fast as the material near the
center, even though most of the mass she could see
was concentrated at the center. Some extra non-
visible mass, dubbed dark matter, appeared to be
holding the galaxy together. She soon discovered
that a huge halo of dark matter was present in
galaxy after galaxy that she examined.
WHAT IS DARK MATTER?
Nearly half a century later, scientists still don’t know what
dark matter is. They do know, however, that dark matter
comprises some 84 percent of the universe’s material. Its
invisible and ubiquitous presence affects how stars move
within galaxies, how galaxies tug on each other and how
matter clumped together in the early universe. Some of the
best evidence for the existence of dark matter comes from
galaxy cluster 1E 0657-556, also known as the Bullet Cluster.
This cluster was formed after the collision of two large
clusters of galaxies, one of the most energetic events known
in the universe since the big bang. Because the major
components of the cluster pair — stars, gas and the apparent
dark matter — behave differently during collision, scientists
were able to study them separately.
The galaxies’ stars, which the Hubble and Magellan
telescopes observed in visible light, were mostly
unaffected by the collision, and passed right through.
The hot gas from the two colliding clusters, seen in X-
ray wavelengths by the Chandra X-ray Observatory,
contains most of the cluster pair’s normal matter.
Because the gases interact electromagnetically, the
gases of both clusters slowed down much more than
the stars. The third element in this collision, the dark
matter, was detected indirectly by the gravitational
lensing of background objects.
The dark matter by definition does not emit, reflect,
or refract any type of light — it’s dark! So during the
collision, the dark matter clumps from the two
clusters move ahead of the hot gas (most of the
normal matter), producing a separation of dark
matter and normal matter. Gravitational lensing
distorts light more significantly around objects with
larger masses. If hot gas were the most massive
component in the clusters, such an effect would not
be seen. Instead, these observations show that dark
matter — something that we can’t see but that must
have mass to have such a strong gravitational effect
— must exist.
CAN GALAXIES COLLIDE?
While the distances between galaxies seem large,
so too are galaxies’ diameters. Compared to stars,
galaxies are relatively close to one another. They
interact and even collide. When galaxies collide,
they pass through each other; their stars don’t
crash into each other because of the immense
distances between them. However, gravitational
interactions between colliding galaxies could
create new waves of star formation, supernovas
and even black holes. Collisions do distort a
galaxy’s shape and computer models show that
collisions between spiral galaxies can eventually
make ellipticals.
CAN GALAXIES COLLIDE?
SEVERAL BILLION YEARS FROM NOW, OUR
OWN MILKY WAY GALAXY IS DESTINED FOR
A COLLISION WITH THE NEIGHBORING
SPIRAL ANDROMEDA GALAXY. THE SUN WILL
LIKELY BE FLUNG INTO A NEW REGION OF
OUR GALAXY, BUT OUR EARTH AND SOLAR
SYSTEM ARE IN NO DANGER OF BEING
DESTROYED. ANDROMEDA, ALSO KNOWN AS
M31, IS NOW 2.5 MILLION LIGHT-YEARS
AWAY, BUT IT IS INEXORABLY FALLING
TOWARD THE MILKY WAY UNDER THE
MUTUAL PULL OF GRAVITY BETWEEN THE
TWO GALAXIES AND THE INVISIBLE DARK
MATTER THAT SURROUNDS THEM BOTH.
HOW DO GALAXIES FORM?
Computer simulations derived from Hubble data show
that it will take an additional two billion years or more
after the encounter for the interacting galaxies to
completely merge under the tug of gravity. They will
reshape into a single elliptical galaxy similar to the
kind commonly seen in the local universe. Simulations
show that our solar system will probably be tossed
much farther from the galactic core than it is today. To
make matters more complicated, the third largest
galaxy in the Local Group, the Triangulum galaxy or
M33, will join in the collision and perhaps later merge
with the Andromeda/Milky Way pair. There is a small
chance that M33 will hit the Milky Way first.
THIS ILLUSTRATION DEPICTS THE NIGHT SKY IN 3.75 BILLION
YEARS AS THE ANDROMEDA GALAXY APPROACHES. AT THIS
POINT, ANDROMEDA FILLS THE FIELD OF VIEW AND THE MILKY
WAY BEGINS TO SHOW DISTORTION DUE TO THE PULL OF
ANDROMEDA.
HOW DO GALAXIES FORM?
The appearance and make-up of galaxies are
shaped over billions of years by interactions
with groups of stars and other galaxies. While
we don't know for certain how galaxies formed
and took the many shapes that we presently
see, we have some ideas about their origins and
evolution. Using supercomputers, scientists can
look back in time and simulate how a galaxy
may have formed in the early universe and
grown into what we see today.
Astronomer Edwin Hubble’s observations led to the idea that
the universe is expanding. Scientists estimate the age of the
universe at 13.8 billion years based on the rate of expansion.
Because the deeper you look into space, the further you see
back in time, we can conclude that galaxies several billions of
light-years away formed fairly soon after the big bang. While
most galaxies formed early, data indicates that some galaxies
have formed within the past few billion years — relatively
recently in cosmic terms.The early universe was filled mainly
with hydrogen, helium, and dark matter, with some areas
slightly denser than others. These dense areas eventually
collapsed, allowing the hydrogen and helium to accumulate in
clumps of dark matter swirling through space and the first
stars and galaxies to form. While Hubble is unable to see the
very first galaxies, it can track the development of galaxies
over much of cosmic time.
TRIVIA DAY PRESENTATION
ARE YOU READY
FOR A
GALAXY
TRIVIA
There are about how many
stars in a galaxy?
A. Hundreds
B. Thousands
C. Millions
D. Billions
Correct Answer
D. Billions
Explanation
A galaxy is a vast system of stars, gas,
and dust held together by gravity. It is
estimated that there are billions of
stars in a galaxy. The exact number
can vary depending on the size and
type of the galaxy, but generally,
galaxies contain billions of stars.
There are about how many
galaxies in the universe?
A. Hundreds
B. Thousands
C. Millions
D. Billions
Correct Answer
D. Billions
Explanation
The answer to the question is billions because the
universe is vast and contains an incredibly large
number of galaxies. Galaxies are massive systems
of stars, planets, and other celestial objects, and
they come in various sizes and shapes. Scientists
estimate that there are billions of galaxies in the
observable universe based on observations and
mathematical models. This vast number of
galaxies indicates the immense scale and diversity
of the universe.
What is the correct order of the
objects from smallest to
largest?
A. Solar system, universe,
galaxy
B. Galaxy, universe, solar system
C. Solar system. galaxy,
universe
Correct Answer
C. Solar system, galaxy, universe
Explanation
The correct order of the objects from smallest to
largest is solar system, galaxy, universe. The solar
system is a small system consisting of a star (the
Sun) and all the objects that orbit around it,
including planets, moons, asteroids, and comets. A
galaxy is a much larger structure, consisting of
billions or even trillions of stars, along with gas, dust,
and other celestial objects. The universe is the
largest known structure, encompassing all galaxies,
including our own Milky Way galaxy, and everything
else that exists.
We live in the _________________________ galaxy.
A. Milky Spiral
B. Milky Way
C. Snickers
D. Solar Swirl
Correct Answer
B. Milky Way
Explanation
The correct answer is Milky Way because it
is the name of our own galaxy. The Milky
Way is a spiral galaxy that contains our
solar system and billions of stars. It is called
the Milky Way because it appears as a hazy
band of light in the night sky, resembling
spilled milk.
Our galaxy is a _________________ galaxy.
A. Irregular
B. Elliptical
C. Twirl
D. Spiral
Correct Answer
D. Spiral
Explanation
Spiral galaxies are characterized by their
spiral arms that extend outwards from a
central bulge. These arms are made up of
young stars, gas, and dust, giving them a
distinct appearance. Our galaxy, the Milky
Way, is a spiral galaxy, as it also has a central
bulge and spiral arms. Therefore, the correct
answer is spiral.
If you look outside at night to see a
galaxy it is
A. Very easy because of their shape
B. Very hard because they look like
stars
C. Very hard because they are invisible.
D. Very easy because of their color
Correct Answer
B. Very hard because they look like stars
Explanation
It is very hard to see a galaxy at night
because they look like stars. Galaxies are
vast collections of stars, gas, and dust, and
from a distance, they appear as tiny points of
light similar to individual stars. This
similarity in appearance makes it difficult to
distinguish galaxies from stars without the
aid of telescopes or other astronomical tools.
SJCSF ASTRO CLUB
GALAXIES
•END•
