T2: Lec 17-18 Flashcards
(24 cards)
What did early astonomers believe about the sun’s position in the milky way?
that it was in the or close to the center of the galaxy
What was the progression people that contributed to determing the position of the sun in the MW galaxy. Explain what each did:
Herschel - Made map of stars assuming sun was close to the center of the Milky way (dust from Milky way blocks out fainter stars
Jacobus Katpeyn (1852-1922) Measured size of galaxy using:
*Parallax - distance of nearby stars
*Proper motion - stars appear to move relative to other stars
*Closer stars appear to move quicker
*Estimate of distance from spectral type
Harlow Shapley: mapped Globular nebula initially thinking they were cepheids, found we that we are not in the center of the milky way, the milky way is much bigger, and thus sun is off to the side through the distribution of these globular clusters.
Also found the milky way is more 100,000 light years in diameter with lots of fail stars
What si a cepheid variable star?
a pulsating star that regularly increases and decreases in brightness over a set period which is linked to the star’s intrinsic brightness and luminosity making these variable stars useful standard candles
What is a variable star?
stars whose light output varies with time (unlike our sun which is stable)
Many different types of variables (reflecting different physical mechanisms)
What is a light curve?
pattern of variation/time of the star as it changes colors and brightness (graph)
Light curve of cepheid stars goes from white blue → red/orange → white blue
Variable star light curves link to their absolute brightness (we can get this absolute brightness from their relative brightness)
What is the Magellanic clouds?
two irregular dwarf galaxies that orbit the Milky Way galaxy that are fainly visible in the souther hemisphere.
Helped to develop the method of measuring distance of other galaxies using Cepheid variable stars.
Why are cepheids important to the cosmic ladder?
Cepheids could be used as standard candles due to cepheids with similar periods of light curve having similar intrinsic brightnesses. Depending on how long the period is, this can tell us the intrinsic brightness of the star, and the faintness of the star in the sky can then tell us how far away that cepheid is from us.
Helps us to map the universe to understand the distances of these cepheids from us
This helped the Great Debate to finally be settled.
What is a whtie nebula?
White nebula - the outdated term referring to nebula that appear white in color when viewed through a powerful telescope that actually were layered determined to be galaxies.
What is the Great Debate?
Great Debate - in April 26, 1920. Harlow Shapley argued that white (or spiral) nebulas are “local”, relatively small, part of our galaxy, and that the universe was a single, large galactic system
Herber Curtis argued that nebulas are vast, independent galaxies similar to our own galaxy but much larger and further away, implying a much larger and more complex universe. however Curtis still placed our sun closer to the center of our relatively small galaxy.
Herber Curtis was
What are the two reasons against white nebulas?
Spiral nebulae were unable to see where the Milky Way was located due to the dust in the galaxy blocking other nebular galaxies from being seen - called zone of avoidance.
Adriaan van Maanen (1916) - claimed to have observed proper motion of the M101 galaxy (this is total bullshit) but claimed these nebula are much closer and rotate much faster than they could if they were as large as galaxies. - his images were just incorrectly aligned.
How was the Great Debate settled due to M31 Cepheid variables?
Edwin hubble discovered cepheids in M31 using distance law to see how far away the cepheid was using 100 inch Hooker Telescope at Mt. Willson.
Used Blink comparison to show a change between images - showed the light curve of the cepheid star
This cepheid’s faint light showed that it was both much farther away outside of our galaxy by tens of thousands of light years, and that M31 (Andromeda) was much larger than our own Milky Way, proving that it was a separate galaxy and not part of our own.
Was hubble’s method of finding cepheids direct or indirect?
indirect
What makes cepheid variable stars expand and cool?
The core of the Cepheid star produces heat which causes the outer layers to heat up and expand. As the layers expand, they then cool down and contract down.
This causes the pulsating effect.
What is Lookback time?
the light coming from far away objects that is just now reaching Earth. The further away an object is in space, the larger the lookback time, meaning the further we are looking back in time.
Who discovered redshift? What did this phenomenon indicate?
After Hubble discovered M31 Andromeda in 1923 and that it as a distant galaxy, we found more cepheids in other galaxies and looked at star brightness as a distance indicator.
Looking at star spectra and spectral lines, the vast majority were redshifted. AND the amount of redshift increased as the galaxy distance increased.
How does redshift relate to the galaxy’s speed?
The percentage of galaxy speed was relational to the redshift percentage (e.g. 7% speed of light = 7% red shift)
When was Hubble’s Law made and what does it indicate?
In 1929, Hubble made Hubble’s Law - shows the velocity to distance of galaxies moving.
A galaxy moving 2x faster, shifts 2x more, and looks 2x further away)
Redshift can be used to measure galaxy speeds, and then to find its distance as further galaxies look “redder”
Who discovered the universe expanding? And how?
Hubble’s observation of redshift of galaxies was evidence that the universe was expanding. This matched new theoretical ideas from general relativity - thus linking to Hubble’s Constant.
How can supernova nad cepheids be used in the cosmic distance ladder? How does this relate to Hubble?
Type 1a supernovae are roughly similar - each made from a white dwarf sucking in energy from its neighbouring star until it reaches a critical mass of 1.4 solar masses before collapsing in on itself and exploding.
The distinct light curve from this explosion (peaking in Blue then quickly dying down) tells us its Type 1a SN. Each of these events has a relatively similar intrinsic brightness. This allows us to determine the distance of these events due to how faint they are in the night sky.
This helped create Hubble’s Diagram for Type 1a SN in addition to his work with Cepheids to show the relationship between distance and velocity.
What is a megaparsec?
1 million parsecs (1 parsec being 1 arcsec)
Īf Hubbles Constant is 75 km/sec/mpc, of a galaxy 200 mpc away. What is the speed of the galaxy?
15,000 km/sec
It takes 40 years to travel 1 light year. What is the distance (in years) of a galaxy 200 Mpc away?
26.08 billion years away
What is Hubble Deep Field?
an image taken from a couple telescopes that reveals some of the first galaxies having formed right after the big bang. redshift of 13 - very far.
Made from combining 800 images over 400 rotations from Hubble space Telescope and James Webb
Some images show distortion of galaxies due to dips from gravitation of galaxies.
What are distant galaxies? What does this indicate about bigger galaxies?
galaxies so far away that their redshift goes into the infrared spectrum so they end up visibly being invisible. They end up being smaller, consisting of more dwarf galaxies and each about 13.2 billion years old
Shows that small galaxies formed first with bigger galaxies merged from smaller galaxies.
