Assignment 6
pdf
keyboard_arrow_up
School
University of Ottawa *
*We aren’t endorsed by this school
Course
2390
Subject
Astronomy
Date
Dec 6, 2023
Type
Pages
5
Uploaded by PresidentDuckMaster968
Chapter 9:
5:
How did our galaxy form and evolve?
A:
There are two major theories about how the first galaxies formed. The truth could be a
combination of both ideas. The monolithic model states that a galaxy is built from a single,
spherical cloud of turbulent gas which is slowly squashed into a disk which incorporates a
combination of other galaxies and gas supplied to the disk. Galaxies are formed when vast clouds
of dust and gas collapse due to their gravitational pull, thus creating stars. Astronomers inferred
that Halo was formed before the disk. The other theory, which has gained traction recently,
contends that the early universe contained many small "lumps" of matter that clumped together
to form galaxies. The Hubble Space Telescope has captured many images of such lumps, which
may be the forerunners of modern galaxies. The majority of the early large galaxies, according to
this theory, spiralled. However, many spirals merged over time to form ellipticals. The formation
of galaxies has not ceased. Our universe is constantly changing. More giant galaxies frequently
devour small galaxies. The Milky Way may contain the remnants of several smaller galaxies that
it has swallowed throughout its long existence. Even now, the Milky Way is digesting at least
two small galaxies and may swallow up more in the coming billions of years.
7:
Why didn't astronomers before Shapley realize how large the galaxy is?
A:
The distribution of visible stars in the night sky determined the size of the galaxy before
Shapley. Sir William Herschel and his sister, Caroline Herschel, believed they could see the
Milky Way's outskirts in all directions. They reasoned that they could calculate the relative
distance to the star system's edge by counting the number of visible stars in a given order. For
example, if they noticed a large number of stars in one direction, they reasoned that the edge of
the Milky Way in that direction is far away. In contrast, if they only saw a few stars in one order,
they assumed that the edge must be closer in that direction. The problem with this theory is that
interstellar dust and gas in between the stars can obscure, dim and redden the view of stars in a
specific direction. Furthermore, this interstellar dust is not distributed evenly. As a result, a
particularly dense interstellar cloud can completely obscure the view of the stars beyond it. All of
these factors can add up to an incorrect estimate of the galaxy's size.
8:
What is the evidence that our galaxy contains a large amount of dark matter?
A:
Gravitational lensing and X-ray radiation from massive galaxy clusters confirm the presence
of dark matter. Observations of gravitational lensing effects on distant objects have been used to
look in the outer region of our Galaxy for any dark matter in the form of compact, dim stars or
star remnants. Its existence can be inferred from the gravitational pull that is exerted on the
luminous material by the dark matter. The rising rotation curve indicates that the halo contains
much more mass. Orbital speeds in the Milky Way remain high even very far from the center,
indicating that a large amount of dark matter lies beyond our galaxy's visible regions. We have
also detected a small amount of radiation coming from this enormous amount of mass. The
evidence is clear that our extra mass lies in an extended halo. It may extend up to 10 times
farther than the edge of the visible disk and could contain 10 times more dark matter than visible
matter in our galaxy. On Earth, the dark matter is accounted for the unexplained mass in the
cluster. The hot gas in the cluster is held primarily by the gravity of the dark matter. By precisely
measuring the distribution of X-rays in the hot gases, the existence of dark matter could be
determined near the center of a galaxy cluster. These are all deeply studied factors indicating that
our galaxy contains a large amount of dark matter.
19:
Why must astronomers use infrared telescopes to observe the motions of stars around
SgrA*?
A:
The need for infrared telescopes to observe the motions of stars around SgrA* (the
supermassive black hole at the center of our Milky Way galaxy) is related to the nature of
infrared radiation and the conditions near the galactic center. The region at the center of the
galaxy contains dust and debris. X-rays and radio waves cannot penetrate. Infrared radiation can
penetrate dust and gas more effectively than visible light. The region around SgrA* is known to
have a significant amount of interstellar dust and gas. Infrared photons are emitted by warm
interstellar dust. Radiation coming from SgrA* at those wavelengths is intense. Infrared
observations allow astronomers to see through these obscuring materials, providing clearer views
of the central region. The Milky Way's disk, which includes the galactic center, is densely
populated with stars, gas, and dust. Infrared observations help astronomers see through the plane
of the Milky Way, where visible light would be absorbed and scattered. Cooler stars and other
objects near the galactic center emit a significant amount of their radiation in the infrared part of
the spectrum. Infrared telescopes are sensitive to this radiation, allowing astronomers to study
the motions of stars that might be cooler and less luminous than those observable in visible light.
Learning To Look 2:
A:
The blue colour of the spiral arms in a galaxy is often associated with the presence of young,
hot, and massive stars. These stars emit a significant amount of blue light due to their high
temperatures. The spiral arms are regions where new stars are actively forming from the
interstellar gas and dust. The abundance of these young, hot stars contributes to the overall blue
appearance of the spiral arms. If the Halo were bright enough to be seen, the colour would
depend on the types of stars present in that region. The halo typically contains older stars that are
cooler than the young stars found in the spiral arms. Cooler stars emit more red and orange light.
Therefore, if the halo were bright enough to be visible, it might appear more reddish or orange
compared to the blue colour of the spiral arms. The apparent colours in galaxies can also be
influenced by other factors such as dust, the composition of the interstellar medium, and the
observational techniques used to capture the images.
Chapter 10:
2:
How do astronomers measure the distances to galaxies, and how does that allow the sizes,
luminosities, and masses of galaxies to be determined?
A:
Parallax occurs when adjacent objects appear to shift relative to distant objects as an observer
travels. Parallax is the first "inch" since it serves as the standard by which astronomers measure
distances to things even further away. They employ Cepheid variables, which pulse in the
manner of hearts. The pulse length of a Cepheid is proportional to its real brightness.
Astronomers can determine the distance to a Cepheid by calculating its apparent brightness. This
method can then be used to determine the true brightness of a Cepheid. Cepheid stars are seen in
galaxies tens of millions of light-years away. The study of distant galaxies makes use of
supernovae or exploding stars. As with Cepheids, the rate at which a supernova brightens and
fades indicates its true brightness, which is used to determine the distance to the object. Accurate
calibration with parallax and Cepheids is also essential here. The mass of galaxies is determined
by their stars' orbital motions. Stars in a more massive galaxy will orbit quicker than those in a
less massive galaxy due to the huge galaxy's stronger gravitational force causing the stars to
accelerate more rapidly. You can determine the amount of gravity in a galaxy by measuring the
star speeds. The rotational curve is used to determine the masses of spiral galaxies, similar to
how the Milky Way's mass is determined. This illustrates how the orbital speed of an object in a
galaxy varies with its distance from the galaxy's centre. The orbital velocity is determined by the
Doppler changes of the atomic hydrogen gas's 21-cm line radiation. While the angular distance
of the disk piece from the centre is determined, the linear distance of the disc piece from the
centre must be determined to employ the enclosed mass formula.
5:
What is the energy source for active galaxies, what can trigger the activity, and what does that
reveal about the history of galaxies?
A:
The active galaxy is a type of galaxy whose central core is smaller and brighter as compared
to typical galaxies. This central core of an active galaxy is made up of the accumulation of small
particles, which makes the central portion much denser, known as the Accretion Disk.
The main energy source of an active galaxy is the constant accumulation of particles inside a
Highly Massive Black Hole while emitting X-ray radiation, this process is known as Accretion.
This is triggered by the gravitational force and the size of particles. If the particle is small →
grav. force is high and vice-versa. This better explains the activity in the nucleus of an active
Your preview ends here
Eager to read complete document? Join bartleby learn and gain access to the full version
- Access to all documents
- Unlimited textbook solutions
- 24/7 expert homework help
galaxy, where the black hole would be present. Galaxies with such forces (Black holes or a
higher gravitational force at their center) are more powerful than normal galaxies. Able to emit
1000 times more radiation than normal galaxies. This further explains how galaxies are made of
stars and dust.
7:
What is the difference between an Sa and an Sb galaxy? Between an S0 and an Sa galaxy?
Between an Sb and an SBb galaxy? Between an E7 and an S0 galaxy?
A:
Galaxies with a spiral shape are classed as spiral galaxies. Some spiral galaxies have a large
central bulge, and tightly wound arms, so it is difficult to make out the spirals. These types of
spirals are classed as Sa Galaxies, ranging to Sc Galaxies with a small central bulge and loosely
wound arms which are easy to make out. Sa galaxies have a large nucleus in the center and it is
surrounded by very tight wound spirals. The Sb galaxies are between moderate wound spirals
around a nucleus of average size. The nucleus of Sc galaxy is small and it has very loose wound
arms. S0 galaxies have a prominent central bulge, similar to elliptical galaxies. This bulge is
typically larger and more pronounced than that of spiral galaxies. S0 galaxies lack well-defined
spiral arms. Instead, they may have a faint disk and a central bar, but the structure is not as
organized or prominent as in spiral galaxies. Barred spiral galaxies (SB) have a bar of stars
through the centre, with spirals attached to the ends of the bar. If the spirals are difficult to make
out, it’s because they are tightly wound SBa, ranging to SBc with loose, easy to see spirals. Both
spiral galaxies (S) and barred spiral (SB) galaxies are referred to as disk galaxies because they
both have an obvious flat disk. Elliptical galaxies look like an ellipse (an ellipse is a squashed
circle). We think they are shaped like a squashed ball (or ellipsoid). Elliptical galaxies do not
have spirals or bars but range in shape from a perfect sphere (ball) to a very flat ellipse. The
galaxies shaped most like a sphere are called E0 galaxies, and the ones shaped like a flat disk are
classed as E7 galaxies.
8:
Explain how the rotation curve method of finding a galaxy's mass is similar to the method
used to find the masses of binary stars.
A:
The rotation curve method is used to find the mass of the galaxy and it is the most accurate
method to determine the mass of the nearby galaxies. Both use Kepler's third law; for binary
stars distance is the separation of two stars and for stars mass it's the distance to the galactic
center. In addition, each equation uses the object's orbital period and sum of masses. The total
mass of the binary star system can be calculated by knowing the size of the orbits, the orbital
period and the time taken by the stars to complete one orbit. Similarly, to determine the mass of
the Galaxy by the Rotation curve method, the velocity of the orbit, and the size of the orbit must
be known. From the values of velocity of the orbit, and size of the orbit, the orbital velocity can
be known through which the mass of the galaxy can be determined. Thus, there is a similarity in
determining the mass of the galaxy by the rotational curve method to the method used to
determine the mass of the binary stars.
17:
What evidence can you cite that galactic cannibalism really happens?
A:
Our galaxy, The Milky Way, is currently in a cannibalism state while it is merging with
Magellanic Clouds. Streams of gravitationally-attracted hydrogen are arcing from these dwarf
galaxies to the Milky Way. Its tides are also pulling in the Sagittarius and Canis Major dwarf
galaxies producing great streamers of stars wrapped around the Milky Way. The Hubble Space
Telescope shows evidence of this. The process of formation of galaxies by absorbing smaller
galaxies is known as galactic cannibalism. Evidence for galactic cannibalism is abundant. For
example, shells of stars that exist around the centers of some galaxies are thought to be the result
of a large galaxy eating another smaller galaxy. Also, giant elliptical galaxies at the center of rich
galaxy clusters have multiple nuclei. These are thought to be the densest parts of the smaller
galaxies that have been absorbed by the larger galaxy, but not yet fully digested. This is the
evidence that galactic cannibalism happens.