ASTR:1070 Spr20 Final
Lecture 27: The size and shape of the Milky Way
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Lecture 28: More about the size and shape of the Milky Way
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Lecture 29: The Sun's long path through the Milky Way
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Lecture 30: What is the mass of the Milky Way
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Lecture 31: The center of the Milky Way
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Lecture 32: Galaxies beyond the Milky Way
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Lecture 33: The Black Hole ( a big one) at the center of M87
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Lecture 34: A universe of galaxies
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Lecture 35: Further out in the extragalactic universe
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Lecture 36: Radio Galaxies and the distant universe
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Summing up: look at slide 16 for main points of what we know about the Milky Way Galaxy
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With modern telescopes, we can see galaxies "under" a bright starlike source in 1._____. The images are dominated by the brilliant 2.______.
1.) quasars 2.) point source
Quasars
An important development in extragalactic astronomy was the discovery of ______ (the early 1960s). Originally discovered as some strong radio sources that did not have galaxies (visible at that time) at the location of the radio source. Only a starlike image of it. See slide 11.
Messier 31 (M31)
Closest major galaxy to us is ______, the great nebula in the constellation of Andromeda.
1. greater 2. outside 3. Dark Matter
Conclusion of the rotation curve for the Milky Way is that the total mass of the Milky Way is much 1.___ than the mass in stars and that most of the mass lies 2.____ the luminous, star-filled part of the Galaxy. This leads to the conclusion that most of the mass in the Milky Way is in the form of 3.____
"flat" or independent of r for r > 10 kpc.
Describe the rotation curve of the Milky Way. Look at slide 15 of Lecture 30.
Keplerian
For an orbit that is outside most of the mass, M is the same as r gets bigger, so√V (r) = √r . This form of a rotation curve is referred to as _____
We are able to use their Cepheid Variables.
How are we able to determine the distances to globular star clusters?
By measuring the shift of the Galactic Center radio source against a system of distant extragalactic radio sources.
How do we measure the Galactic Year?
its distance is 780 kpc away
How far away is Messier 31 from our galaxy?
expansion of
Hubble's Law is evidence for _______ the universe. That is what the distances to galaxies through the application of Hubble's Law is telling us.
Read explanation
If the speed at which an object is moving is small compared with the speed of light (say 10 - 20 % or less), then the simple formula is w−W/W = ± v/c . * The + sign holds if the object is moving away from us (observed wavelength longer, or redder than the rest wavelength) * The - sign corresponds to motion towards us (observed wavelength smaller than rest wavelength).
the Galactic center
If we can determine the centroid of a distribution of globular star clusters, we should know the distance to ___
the size of the Milky Way
If we know the distance to the Galactic Center, we can determine ___
V(r) = 2πr/T
If we measure the Galactic Year T, we then have the orbital speed of the Sun in its orbit as ____
1. fainter 2. long
In early 1950s, found the optical object that corresponded to Cygnus A, elliptical galaxy with z=0.056. This was large for time. Indicated that 1.______ radio galaxies could be at very great distances in the universe, so that had very 2._____ "look-back times".
Due to the gravitational force of all the other stars, gas, and other matter
Look at map of Milky Way in our reading assignment 'mapping the mw'. The Sun is moving on an orbit in the Milky Way due to ________
Note*
Look at sky map of Abell Clusters in slide 7 and think about what it is showing
1.) 20 cm 2.) radio
Look at the "radio sky" (slide 18) which shows what the sky looks like at radio wavelengths of ____ cm. Most of these point sources are powerful natural _____ transmitters associated with distant galaxies.
M87
Major scientific result of the past year: direct imaging of a supermassive Black Hole in the center of ______. Remember ______ is one of the largest galaxies in the Virgo Cluster.
No, nothing surpasses the speed of light See slide 14.
Many quasars have z > 1. Does this mean that they are receding at faster than light speed?
Sloan Digital Sky Survey
Modern astronomical surveys detect and reveal in considerable detail galaxies out to great distances. The ___________ has information on a total of 1.3 million galaxies
spiral, elliptical, irregular
Name the 3 major classes of galaxies
infrared
Observations at ______ wavelengths show the presence of a compact star cluster right at the Galactic Center.
straight at us
Powerful quasars that emit strongly over all wavelengths (radio to visual to x-ray and gamma-ray) have supermassive Black Holes with masses of several billion solar masses. In many cases, the jet of matter and radiation that is coming out of the accretion disk is pointed _________ (in relation to our position in the universe)
30 years
Star S2 has been observed to pass periapsis twice within the last ____ years and has a very good orbit determined.
120 AU
Star S2 passes within _____ AU of the Galactic Center
The masses of the Black Holes in other galaxies usually range from about 10 million (10^7) solar masses to a billion or more (10^9) solar masses. See Table, slide 14
Supermassive black holes have been found in large numbers in other galaxies. What is the typical range of masses for these black holes?
False, every few Mpc spacing
T or F: Beyond the Local Group there are galaxies spaced every 5,000 Mpc
False, more common 5-10 billion years ago(or more) that they are now! This indicated that the universe has changed in its properties during that time.
T or F: For decades it has been known that powerful radio sources were more common now than there were in the distant past (5 - 10 billion years ago or more)
True, this indicates they were more common billions of years ago than they are now- Indicates evolution of the universe as a whole.
T or F: From early studies, we found that there are more fainter radio galaxies than brighter ones.
True!
T or F: The Black Hole at the center of the Milky Way is on the small end of the distribution of black holes
True
T or F: The Keplerian rotation curve was once thought to be true for the Milky Way (about 50 years ago), but now it is known to not be the case for any of the large galaxies
False, it is not alone; the Abell catalog, published in 1958, listed 2718 clusters similar in properties to the Virgo Cluster
T or F: The Virgo Cluster is a unique type of galaxy in that only a few other galaxies possess similar qualities
False! The nature of Dark Matter is not known. Most physicists think that it must contain some type of elementary particle like an electron or a proton, but at present, there is no proof, or even very good evidence, that this is the case.
T or F: The makeup of Dark Matter was discovered by Phil Cannon - it's made of mostly hydrogen
true
T or F: The rotation curve of the Milky Way, or any other galaxy, is the orbital speed as a function of distance from the center of the galaxy, V (r).
True!
T or F: There is a supermassive Black Hole in the center of our galaxy
True
T or F: This is the first time we have directly imaged a Black Hole
False, sometimes more than one black hole in the center of a galaxy :0
T or F: it looks like every large galaxy has a supermassive Black Hole at its center, but never more than one
False, we have seen other similar objects far out in space that are also spiral galaxies
T or F: our deduction about the nature of the Milky Way, particularly properties of spiral arms, is helped by the fact that it is the only spiral galaxy we have discovered so far
the speed at which an object is moving towards us or away from us
The Doppler shift depends on what?
That the universe has fundamentally changed over the many billions of years that it took the light from these galaxies to reach us
The HUDF galaxies seem to be very different in appearance from the present day galaxies that we see within a few tens of millions of light years of the Milky Way. This indicates what?
inverse time
The Hubble Constant has dimensions of ______ . So 1/H0 is a time.
very distant galaxies
The Hubble Ultra Deep Field (HUDF) is a very long exposure with the Hubble Space Telescope of a tiny piece of the sky. It was able to detect extremely faint objects. Most objects in the HUDF are ______
The Milky Way is one, M31 is another, and M33 is the third
The Local Group is dominated by three large spiral galaxies. Name them
the Local Group
The Milky Way is a member of a group of galaxies called
galaxies
The Milky Way is an example of a new class of astronomical objects called
the Orion-Cygnus arm
The Sun is in which arm of the Milky Way?
Cygnus A
The brightest radio galaxy in the sky is ______.
220 km/sec
The corresponding value of the orbital speed is ____
Sagittarius
The direction of the Galactic Center is towards the constellation _____
1.) 8.2 kiloparsecs 2.) 26,700 light-years
The distance to the Galactic center is 1.______(kpc) or 2._______ light-years
that we live in a disk-shaped system of stars
The existence of the Milky Way as a narrow band of light across the sky shows us what?
we are not at the center of the galaxy
The fact that the brightness of the Milky Way changes across the sky tells us...
Schwarzschild Radius
The image of M87 was made at millimeter wavelengths (short-wavelength radio) and shows very strong gravitational lensing close to the _________ ______ of the Black Hole
Hubble's Law (v = H0d)
The main way of determining distance to very distant galaxies involves
4.3×106 solar masses (4.3 million solar masses)
The mass of our central object(Galactic Center) is _____ solar masses.
1.) the Virgo Cluster 2.) 16.5 Mpc
The nearest "city of galaxies", i.e. a very large group, is 1._________, a group of about 1000 galaxies. It is about 2._____ Mpc away
Perseus Arm
The next spiral arm past the Orion-Cygnus arm is the _____.
Radio Astronomy
The original indication that very distant galaxies were out in the universe, and that they were energetically active, came from _______ astronomy
1. )6.4 milliarcseconds 2.) 220 million years
The shift of the Galactic Center radio source is measured to be 1._____ milliarcseconds per year, corresponding to a Galactic Year of 2.____ million years
6.5 × 10^19 solar masses
The size of lensed "bright ring" shows the mass of the Black Hole in M87 is ______ solar masses
1. orbit 2. a few years 3. mass
The stars in these compact star clusters are observed to 1.____ the Galactic Center. They move significantly over a period of 2.____ years. We can use these motions to determine the 3.____ of the object at Galactic Center. Look at Lect. 31 slide 11
the center of the Galaxy
The system of globular star clusters appears to be centered on ___
300 - 400 parsecs
The thickness of the Galactic plane is about ___ to ____ parsecs
13.5 billion years
The value of H0/ 1 is _____ years. This tells you something about the age of the universe.
luminosity or absolute magnitude Leavitt's Law after Henrietta Leavitt.
There is a relation between the period of variation of a Cepheid and its 1._____ or _____. This relation is referred to as 2._____.
What are the size, shape, and nature of the Milky Way as a stellar system?
This "Giant 'City of Stars'" is a disk of stars (pancake like shape). It's shape: it is a stellar disk approximately 300 - 400 parsecs thick, quite thin compared to its diameter
Doppler Effect
To measure the rotation curve of the Milky Way, we use the _____, which is applied to objects elsewhere in our Galaxy (look at slide 9, Lecture 30).
see slide 15
To see a representation of the galactic neighborhood
Black Hole
We interpret quasars as galaxies (often strong radio galaxies) in which the light is dominated by emission associated with its ____.
the planets in the solar system, and leads to Kepler's Laws of Planetary Motion
What do we mean the "Keplerian" rotation curve
Megaparsec (Mpc)
When discussing distances to other galaxies, it is helpful to have a new "yardstick" known as the ______, which is 1 million parsecs
1. ) "radio galaxies" 2.) centers
When observed with high angular resolution (such as provided by the Very Large Array radio telescope) these 1._______ appear as 2 "clouds" of radio emission flanking the 2._______ of elliptical galaxies - They usually have a compact point source there that is associated with the massive Black Hole that is there
redshifted
When sky positions of some quasars were measured with sufficient precision by radio telescopes, unambiguous identifications found. Spectra were seen to be highly _______, indicating (Hubble's Law) great distances.
The answer is synchrotron radiation, a process in which electrons spiraling in a magnetic field radiate electromagnetic waves
Why do radio galaxies shine at radio wavelengths? What is the radiation mechanism, or process by which matter generates electromagnetic waves?
Because it gives how much mass is in a galaxy, and how it is distributed, via the equation M = V 2r
Why is the rotation curve important?
radio and infrared
You can't see the center of the Milky Way at visual wavelengths because of interstellar dust. We can, however, see clearly at _____wavelengths, and also at ____ wavelengths.
elliptical galaxies (like M87)
are HUGE balls of stars
irregulars
are usually smaller than spirals and large ellipticals and have a range of properties
Quasars
galaxies, with brilliant emission associated with supermassive black holes at their centers.
Meaning of Galactic Year
how long it takes for the Sun to complete one circuit
Jean's Length
is a size scale such that gravity causes clouds to contract The sizes of molecular clouds and contracting clumps within molecular clouds seem related to it.
Interstellar dust
limits our view within the plane of the Milky Way
Lect. 26: Star formation:
link between molecular clouds and "protostars" . The nature of the Milky Way
spiral arms
spiral-shaped enhancements in gas, the number of young stars, and stars in general- Milky Way is this type of galaxy
Cepheid Variables
stars whose brightness changes in a periodic fashion
Jean's Length
this is the critical size for clumps of gas in the interstellar medium, such that they contract under their own gravity
Hubble's Law description
v = H0d where v is the speed of recession of a galaxy (in km/sec, measured from the spectrum of the galaxy and applying the Doppler Effect), d is the distance to the galaxy (in Mpc), and H0 is the Hubble Constant (units km/sec/Mpc)
Doppler Effect Formula
w−W/W where W is the "rest wavelength" of a spectral line, and w is the wavelength that we measure for in the spectrum of an object that is moving.
