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AstroKatie's profile
Katie Mack
Katie Mack
Katie Mack
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@AstroKatie

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Katie MackVerified account

@AstroKatie

Cosmologist, pilot, connoisseur of cosmic catastrophes. @TEDFellow. Author: "The End of Everything (Astrophysically Speaking)". Personal account. She/her. Dr.

Raleigh, NC
astrokatie.com/book
Joined April 2009

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    1. Katie Mack‏Verified account @AstroKatie 5 Apr 2020

      Nuclei, by the way, are the protons and neutrons (nucleons) stuck together in the centers of atoms. The number of protons a nucleus has tells you what kind of element it is (the atomic number); the number of protons + neutrons tells you the atomic mass.

      2 replies 6 retweets 136 likes
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    2. Katie Mack‏Verified account @AstroKatie 5 Apr 2020

      Some nuclei are more tightly bound than others, meaning it’s easier or harder to break them apart. Here’s a chart of binding energy per nucleon, for a range of elements. For the ones lighter than iron, binding energy goes up as you add nuclei; for heavy ones, it goes down.pic.twitter.com/uoo5VdfYjP

      A plot of binding energy per nucleon vs atomic mass. A red line goes up steeply from the lower left corner (with some variations), then flattens out and curves slowly downward toward the right. Labeled at the start of the line is hydrogen, then helium right after (above and to the right) of it. Iron is at the peak. Then uranium is labeled on the far right.
      4 replies 6 retweets 152 likes
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    3. Katie Mack‏Verified account @AstroKatie 5 Apr 2020

      What the Sun and other stars do is stick light elements (hydrogen etc) together, thus going from less clingy to more clingy nuclei. That means that the fusion reactions *produce energy* — that’s what makes stars shine and keeps them from collapsing under their own gravity.pic.twitter.com/JRHxF9W58p

      A diagram showing fusion. Two circles labeled “H” coming together to make a circle labeled “He” and a starburst of radiation.
      1 reply 6 retweets 140 likes
      Show this thread
    4. Katie Mack‏Verified account @AstroKatie 5 Apr 2020

      The Sun is fusing hydrogen into helium in its core, producing energy. Eventually, the Sun will run out of hydrogen to fuse, and it’ll do a little bit of fusion of helium, but it isn’t massive enough to do much more, and it will eventually end up a dead “white dwarf” star.pic.twitter.com/KdstyVLlk6

      Two concentric circles. The larger one is labeled “hydrogen” and the smaller one “helium.”
      2 replies 5 retweets 141 likes
      Show this thread
    5. Katie Mack‏Verified account @AstroKatie 5 Apr 2020

      More massive stars can fuse heavier elements, all the way up to iron, in concentric shells in their interiors. But something bad happens when they produce iron. Iron is the most tightly bound nucleus. Fusing it doesn’t produce energy anymore, so the star can’t hold itself up.pic.twitter.com/PsHCpRDwjD

      Concentric circles with elements labeled in each circle. From the outermost to innermost, they are labeled: hydrogen, helium, carbon, neon, oxygen, silicon, iron. The iron circle is labeled in red; the others in blue.
      1 reply 5 retweets 154 likes
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    6. Katie Mack‏Verified account @AstroKatie 5 Apr 2020

      When a star gets a core of iron, it collapses on itself, producing a spectacular explosion called a core-collapse supernova. The most recent nearby one happened in 1987, and we can still see the debris glowing and expanding. (Gif credit: Larsson et al. 2011 + Mark McDonald)pic.twitter.com/9vuUK1u5fC

      3 replies 19 retweets 198 likes
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    7. Katie Mack‏Verified account @AstroKatie 5 Apr 2020

      What does this have to do with bombs? Atomic bombs make use of the clinginess of nuclei in the other direction. Since very heavy elements are LESS tightly bound than slightly less heavy ones, you get energy by breaking the nuclei apart, in a process called fission.pic.twitter.com/GgG3KwTUl3

      A plot of binding energy per nucleon vs atomic mass (see previous plot descriptions for details). On the left-hand side, before iron, is a line pointing up and to the right labeled “fusion.” On the right, a line up and to the left labeled “fission.”
      A diagram showing fission. A circle labeled “U” breaking up to a circle labeled “Kr” and a circle labeled “Ba” and a starburst of radiation.
      2 replies 5 retweets 139 likes
      Show this thread
    8. Katie Mack‏Verified account @AstroKatie 5 Apr 2020

      There are also hydrogen (“thermonuclear”) bombs, that use both fission and fusion. They set off a FISSION reaction using heavy elements like uranium to kick start the FUSION of hydrogen (specifically, a version of hydrogen with extra neutrons). Both these reactions release energypic.twitter.com/4gz4ar6Ecv

      A diagram showing fission and fusion. The fission part shows a circle labeled “U” breaking up to a circle labeled “Kr” and a circle labeled “Ba” and a starburst of radiation. The fusion part shows two circles labeled “H” coming together to make a circle labeled “He” and a starburst of radiation.
      3 replies 3 retweets 126 likes
      Show this thread
    9. Katie Mack‏Verified account @AstroKatie 5 Apr 2020

      I like to think of the elements lighter than iron as “extroverts” because they release energy by joining together, while the ones heavier than iron are “introverts” because it REQUIRES energy to make them stick together.pic.twitter.com/IwFKgF0MML

      A plot of binding energy per nucleon vs atomic mass. See descriptions of previous plots for full info on this one; it’s just a more annotated version of all the earlier ones. Elements to the left of iron are labeled “extroverts,” to the right, “introverts.”
      6 replies 38 retweets 282 likes
      Show this thread
    10. Katie Mack‏Verified account @AstroKatie 5 Apr 2020

      Stars CAN stick heavier-than-iron elements together, and they do, but they need to ADD energy to do it. Where do they get that energy? Supernovae! When they explode, they produce heavy elements, because the energy from the explosion can do fusion way up the periodic table.

      4 replies 3 retweets 171 likes
      Show this thread
      Katie Mack‏Verified account @AstroKatie 5 Apr 2020

      So: massive stars produce energy through fusion until they get a core full of iron, then they explode spectacularly, giving them enough extra energy to fuse elements heavier than iron in the exploded debris. All because iron is the element with the clingiest nuclei.

      11:59 AM - 5 Apr 2020
      • 9 Retweets
      • 221 Likes
      • ✊🏿🖖🏽✌🏻😷💉 chasg76 Dave Gallagher Just Will Emily Topham owo Diane llewelly Moises Jafet
      15 replies 9 retweets 221 likes
        1. Katie Mack‏Verified account @AstroKatie 5 Apr 2020

          One more thing: nuclear power plants are doing fission. Because it involves breaking up big nuclei, it creates smaller (but still heavy) nuclei that are themselves not so stable: nuclear waste. Hopefully we’ll one day produce fusion power plants which make less dangerous waste.

          13 replies 5 retweets 233 likes
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        1. Name cannot be blank  🐊  🐝‏ @comentarjsta 5 Apr 2020
          Replying to @AstroKatie

          following you after listening to your Ologies interview was the best thing i did last month just for this thread, ty

          0 replies 0 retweets 2 likes
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        1. RobertTheAddled‏ @RobertTheAddled 5 Apr 2020
          Replying to @AstroKatie

          Nuke school flashback to 30 year old nuclear physics class memory. Forgot I knew that until you brought up iron as a peak in the energy curve.

          0 replies 0 retweets 2 likes
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        2. jon rosenberg 🌮‏Verified account @jonrosenberg 5 Apr 2020
          Replying to @AstroKatie

          What is special about iron that makes it the turning point?

          1 reply 0 retweets 5 likes
        3. Katie Mack‏Verified account @AstroKatie 5 Apr 2020
          Replying to @jonrosenberg

          It has something to do with a balance between the strong nuclear force holding the nucleons together and the electromagnetic repulsion between the protons but that’s about the extent to which I’ve looked into it.

          1 reply 0 retweets 22 likes
        4. Show replies
        1. 1Iodin‏ @1Iodin 5 Apr 2020
          Replying to @AstroKatie

          How do gravitational waves escape from the collision of t2o black holes since the waves travel at the speed of light and black holes are black?

          0 replies 0 retweets 0 likes
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        1. Roger  😷 Freedman has been jabbed 3X‏ @RogerFreedman 5 Apr 2020
          Replying to @AstroKatie

          As a recovering nuclear theorist, I approve the idea of changing the name of the “curve of binding energy” to the “curve of clinginess.”

          0 replies 0 retweets 10 likes
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        1. Manjit Karve‏ @laaltoofan 5 Apr 2020
          Replying to @AstroKatie

          And that's why you can't *step* with iron... 😁

          0 replies 0 retweets 0 likes
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        2. Dr. Sanjana Curtis!  🦦‏ @sanjanacurtis 5 Apr 2020
          Replying to @AstroKatie

          Ahhh this is my research so i can't resist! I'd made a general schematic showing what happens to different layers of the star during the explosion, just sharing it here. Left to right goes from the center of the star towards the surface.pic.twitter.com/qMHyxSu0ZZ

          12 replies 16 retweets 115 likes
        3. Katie Mack‏Verified account @AstroKatie 5 Apr 2020
          Replying to @sanjanacurtis

          This is great, thanks!

          0 replies 0 retweets 9 likes
        4. End of conversation

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