Cuesta College, San Luis Obispo, CA
Students have a weekly online reading assignment (hosted by SurveyMonkey.com), where they answer questions based on reading their textbook, material covered in previous lectures, opinion questions, and/or asking (anonymous) questions or making (anonymous) comments. Full credit is given for completing the online reading assignment before next week's lecture, regardless if whether their answers are correct/incorrect. Selected results/questions/comments are addressed by the instructor at the start of the following lecture.
The following questions were asked on reading textbook chapters and previewing presentations on the evolution of medium-mass stars, massive stars, neutron stars and black holes.
Selected/edited responses are given below.
Describe something you found interesting from the assigned textbook reading or presentation preview, and explain why this was personally interesting for you.
"I found it interesting how we can't see black holes but can feel them giving us a concept of what they could possibly look like."
"I found it interesting that you didn't tie in the food/starvation analogy into the binary star sys. explosion section. When a person who is starving to the point of their body consuming itself, if they were to suddenly eat something, they would likely vomit like the nova (so to speak)."
"The comparison to cars and the lifetimes of stars. I must say that I did almost assume that the stars could not be compared to these two vehicles because it is already known that smaller red dwarfs have a much longer lifespan than medium mass stars so it just mixes the two with the comparison to the cars in the fact that a red dwarf is like a SmartCar with the gas capacity of a Hummer. I like this analogy."
"The drastic difference between a star dying alone verses dying with another star. It makes sense that if a star that has no hydrogen it would take from another, but it's cool seeing that it explodes because it can't take more than it could already handle."
"The car/star model--if the two cars had the same size gas tanks, the SmartCar would go longer, so the less mass star lives longer."
"I thought the analogy of the refrigerator food chain worked really well to explain the reason stars use certain energy sources before others."
"The section on black holes. I've always wanted to learn about them, and I found it interesting that there is a certain area where you cannot just escape from it once you get there."
"The binary stars that feed off each other are interesting because that's seems really strange."
"The drastic difference between a star dying alone versus dying with another star interesting. It makes sense that if a star is loosing hydrogen from itself it would take from another, but it's cool seeing that it explodes because it can't take more than it could already handle."
"How a massive star could become either a black hole or neutron star...I wonder what occurs in the 'death' in order to make these two very different yet specific results."
"The fate of the sun, but it's scary at the same time. It's sad that this beautiful world will eventually end, because our sun is just like any other star and won't burn forever. The sun will take out Mercury, Venus and Earth. Wish leads me to think of the other planets, will it disrupt their course in our solar system? Will it affect them in anyway? Will they still be around even when tbe sun no longer exist or will they find another star to rotate around."
"That you can't see black holes."
"Radio waves from pulsars."
Describe something you found confusing from the assigned textbook reading or presentation preview, and explain why this was personally confusing for you.
"Honestly, I found the blog presentations pretty confusing this week. Maybe I just wasn't focusing very efficiently, but the concepts seemed to be harder to grasp. I specifically didn't follow along on black holes."
"I'm trying to grasp spacetime curvature. So, since this is everywhere in space, are we earthlings bearing the pressure of the space-time curvature that is pressing against this planet? How does that work exactly?"
"How exactly a star burns out. I understand it burn out its hydrogen then lets out helium and then becomes a white dwarf, super giant etc. But does it ever really stop giving out energy/heat/luminosity? If so, what happens then does it become another somar debris, does it explode like supernovae."
"I found how the medium-mass stars die to be confusing, because there were so many steps to it."
"The different medium-mass stages."
"I found the Ia supernova scheme a bit confusing and also the whole black hole thing was a bit confusing as well. I don't really understand the difference between the Ia supernova as well as the type II supernova and also the neutron star thing."
"Nothing was very confusing, but it's interesting to know how crazy stuff like binary stars stealing gas from each other is."
"Some of the star death stages are easy to confuse. Why do some stars become neutron stars and others black holes? What is the deciding factor?"
"I find black holes kind of confusing. It's just a hole that eats everything and goes to nowhere."
"I found the section regarding what happens when you enter a black hole to be confusing. The explanation just didn't stick with me and don't understand how that phenomenon would play out."
"Black holes are confusing as heck."
"I found the relation of black holes to time-space around them kind of confusing. I understand the concept of the 'event horizon' (or point of no return) but am confused about how space stuff gets close enough to it that that would be an issue and the black hole would start reeling it in."
"Nothing was very confusing, but it's interesting to know how crazy stuff like binary stars stealing gas from each other is."
"I thought I understood everything until I saw the first rule of astronomy question..."
"A Hummer H2 has a bigger gas tank but can only go a few miles per gallon. On the other hand, a SmartCar has a significantly smaller tank but can go a lot more miles per gallon."
"The Hummer H2 has a significantly larger tank size such that its low mpg is made up in the end in proportion to the SmartCar."
"Hummer has a larger tank but gets less mileage. SmartCar has smaller tank but gets more mileage to the tank."
"The Hummer has an insanely large gas tank but chugs it faster, whereas a SmartCar may have a smaller gas tank but it sips the gas."
Match the end-of-life stage with the corresponding main-sequence star.
(Only correct responses shown.)
Black hole: massive main sequence star [96%]
Neutron star: massive main sequence star [44%]
White dwarf: medium-mass main-sequence star [56%]
(No stellar remnant observed yet: low-mass main-sequence star [72%]
Match the type of explosion (if possible) with the corresponding main-sequence star.
(Only correct responses shown.)
Type II supernova: massive main sequence star: [96%]
Type Ia supernova: medium-mass main-sequence star [84%]
Nova: medium-mass main-sequence star [56%]
Low-mass main-sequence star: (no explosion possible) [84%]
If you were to leap into a black hole, your friends would typically watch you falling in for __________ before you entered the event horizon.
seconds. ******* [7] hours. [0] days. [0] a year. [0] many years. *** [3] forever. ********* [9] (Unsure/guessing/lost/help!) ****** [6]
The first rule of astronomy class is...
"Show up to class and participate."
"Do the reading."
"Always put on your safety goggles before playing with AstroBlasters."
"Don't jump into a black hole.? Go build a radio telescope?"
"To choose the unsure/guessing answer if you don't know the answer and it's not a test?"
"To ask questions? To sit down with your group? Be curious?"
"Not sure--is this a trick question?"
"I apologize but I'm not sure what you are asking. I checked your syllabus, all of the presentations for this week, my notes and even searched Google, where it popped up your first blog for this class. I'd love to learn this rule though."
"...you do not talk about astronomy. The second rule of astronomy is: you DO NOT talk about astronomy."
Ask the instructor an anonymous question, or make a comment. Selected questions/comments may be discussed in class.
"I didn't understand how to answer the black hole question. If you jumped directly into the black hole wouldn't you be past reaching the event horizon and therefore already be swallowed up by it? It sounds like jumping into the center of a whirlpool."
"This class seems to be getting a lot more confusing as we go, but it's still not overly confusing, which is good."
"Would a star rather become a black hole, a neutron star or explode in a blaze of glory? I might have just answered my own question." (Can't it do more than one of those choices?)
"How close to dying are the oldest red dwarfs?" (56 billion years – 14 billion years = 42 billion years left, or you can think of them as lived only 25% of its lifetime so far.)
Could two black holes connect with each other to create a bigger black hole and if so, how strong could it be?" (It would the combined mass and strength of two black holes.)
"I did not quite understand why the white dwarf would have not begun to quite literally 'siphon gas' during its earlier stages." (Usually stars are born too far apart to transfer hydrogen between them (if they were super close to begin with, they would have probably merged into a single star early on. Then the only way two far-apart stars would be able to transfer hydrogen is when the other star expands into its giant phase, so its hydrogen "spills" over to the other star.)
"How do you know the difference between a nova or a type Ia supernova?" (A nova will repeat; a type Ia supernova completely destroys the white dwarf. A nova is just the fusion of a thin layer of hydrogen surrounding the white dwarf; a type Ia supernova is the fusion of the entire carbon white dwarf.)
"What is the first rule of astronomy class?"
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