The Birth of Stars and Planets

Unit 6: The Birth of Stars and Planets This material was developed by the Friends of the Dominion Astrophysical Observatory with the assistance of a Natural Science and Engineering Research Council PromoScience grant and the NRC. It is a part of a larger project to present grade-appropriate material that matches 2020 curriculum requirements to help students understand planets, with a focus on exoplanets. This material is aimed at BC Grade 6 students. French versions are available. Instructions for teachers ● For questions and to give feedback contact: Calvin Schmidt [email protected], ● All units build towards the Big Idea in the curriculum showing our solar system in the context of the Milky Way and the Universe, and provide background for understanding exoplanets. ● Look for Ideas for extending this section, Resources, and Review and discussion questions at the end of each topic in this Unit. These should give more background on each subject and spark further classroom ideas. We would be happy to help you expand on each topic and develop your own ideas for your students. Contact us at the [email protected]. Instructions for students ● If there are parts of this unit that you find confusing, please contact us at [email protected] for help. ● We recommend you do a few sections at a time. We have provided links to learn more about each topic. ● You don’t have to do the sections in order, but we recommend that. Do sections you find interesting first and come back and do more at another time. ● It is helpful to try the activities rather than just read them. ● Explore the “Ideas for extending this section” and “Resources” sections at the end of each topic in this Unit - they aren’t just for teachers! Learning Objectives ● The BC curriculum requires students to learn about the “How has the solar system changed over time (birth, formation of planets).” This unit covers that information. ● Math objectives:use ratios. Friends of the DAO - ExoExplorations - https://centreoftheuniverse.org/exoexplorations 1 Learning Outcomes ● Students will learn about the formation of solar systems: what they form out of, how long it takes, the theory about it, and see images of solar systems at different stages. ● What our own solar system formed out of and how it has evolved over time. Materials and tools needed for the activities ● Activities 1 and 2 : Stellarium installed Time Required ● Lesson time - 90 minutes ● Activity time ○ Activities 1 and 2 : 5 minutes each Contents The activities are marked in yellow. ● Stars and Planets have a beginning ● Early ideas about the formation of solar systems ● Clouds where stars and planets form ○ Activity 1: Find star forming regions on Stellarium ● Protostars and Proplyds ● Making planets ● Why do different types of objects form? ● The nebula becomes a star cluster, and star systems wander away ○ Activity 2: Observe the differences between open and globular star clusters in Stellarium ● How a star system changes over time (Summary) S tars and Planets have a beginning In this unit you are going to learn about the formation of solar systems, and, more generally, about stars and planets. By solar system we mean something like our own solar system with at least one star and planets going around the star (or stars). At the time of writing (August 2nd, 2020), astronomers know of 3,176 solar systems other than our own, and new ones are being found all the time. Were they always there? Where did they come from? We’ll show you what we know so far. Friends of the DAO - ExoExplorations - https://centreoftheuniverse.org/exoexplorations 2 In our own solar system we have one star, the Sun, and eight major planets and five smaller dwarf planets like Pluto. But in some solar systems, the planets orbit dead stars, two stars, or one star in a binary star system. There are even “rogue planets” that do not orbit stars at all and move by themselves through the Galaxy. We’ll talk about some of those combinations in upcoming units. When we talk about solar systems we’ll be referring to at least one star and a planet. E arly ideas about the formation of solar systems In the previous unit (Unit 5 - Galaxies and the Universe), we talked about how the 18th-century mathematician and astronomer, Pierre-Simon Laplace, had proposed how solar systems were formed. He was trying to understand why there are planets orbiting our Sun and how they got to be there. Astronomers saw mysterious swirly objects in telescopes and realized they looked something like what Laplace had proposed, objects they called the Spiral Nebulae. Hubble showed in 1925, however, that the spiral nebulae were galaxies similar in size and composition to the Milky Way. Astronomers still hadn’t seen evidence of how a solar system forms. Laplace’s ideas were based on his understanding of Sir Isaac Newton’s theories of gravity that were published 110 years earlier in 1687. One of his most important realizations was that gravity existed between all types of matter. Gravity’s pull also occurs between matter that is not in a solid state, meaning things in a gaseous or liquid state. The Sun, for example, is in a gaseous state and it certainly has a strong gravitational pull. Laplace was correct that even clouds create and experience a gravitational pull because they are composed of matter, just as Newton explained. Each atom or molecule in a cloud has its own gravitational pull, and pulls on all the others in the cloud. If a cloud is big enough, he reasoned, that should start pulling all the pieces together. Friends of the DAO - ExoExplorations - https://centreoftheuniverse.org/exoexplorations 3 Figure 1: Gravity would pull all pieces of the cloud to the centre if the cloud wasn’t turning (credit: FDAO) Laplace also understood that the pieces of the cloud were likely moving around, and that it could be turning slightly. As one collapsed down it would start to spin faster. If you’ve ever seen a figure skater pull his or her arms in as they start spinning you know what happens: they start spinning faster. If you’ve ever spun around in a chair, you’ve probably noticed that you start spinning faster if you pull your arms in (try it yourself but be careful). Similarly, as the materials of the solar nebula were being pulled towards its center, the nebula started spinning faster. Most of the material would fall to the centre and become a star, this is why almost all the mass of our own solar system is in the Sun. But because the cloud is spinning slowly some parts don’t fall there and instead spread out into a flat disk. Why would some matter go into orbit? One of the things Newton imagined was shooting a cannonball horizontally. You can see his drawing in Figure 2.This is Newton’s famous “Thought Experiment”. He didn’t actually do the experiment, he just predicted what would happen. If the cannonball wasn’t fired with much speed it would quickly fall to the ground. But if it was fired faster it would go farther before it hit the ground. Eventually it would be fired so far it would land out of view over the curve of the Earth. And if you fired it hard enough from a mountaintop, it would go around the Earth and never come down (assuming air resistance wasn’t there and no mountains were in the way). It would then be in orbit. Every time it is fired it is still pulled by the Earth’s gravity, but eventually it is fired so hard that it never lands on the Earth, even though it is still falling. Friends of the DAO - ExoExplorations - https://centreoftheuniverse.org/exoexplorations 4 That’s the same thing that happens to astronauts when they are “weightless” in orbit of the Earth. They are falling in the Earth’s gravity but are going so fast sideways that they always “miss” the Earth. That’s what being in orbit means. Figure 2: Newton’s cannonball thought experiment If the matter in the cloud didn’t fall directly into the star that was forming it would have some horizontal speed (at a 90 degree angle to the pull of gravity), and if it has enough speed would go into orbit around the new star, just like Newton’s imaginary cannonball went into orbit around the Earth. This motion at a right angle to the gravitational pull is also the same thing that keeps the Moon in orbit around the Earth, and the Earth in orbit around the Sun. Another way to think of it is a spinning ball. The points located near the equator of that ball will move much faster than those near the poles. If you have an Earth globe at home, try spinning it and look at different countries. Greenland will spin much slower than India for example. In a similar fashion, the matter near the poles of the solar nebula moved much slower than the equator. Just as with a slower moving cannon ball, matter near the poles of a spinning cloud has more trouble escaping the gravitational pull and falls into the middle. Thus, the nebula flattens into a disk, with most of the material in the centre. Friends of the DAO - ExoExplorations - https://centreoftheuniverse.org/exoexplorations 5 Ideas for extending this section: ● Learn about Sir Isaac Newton. What else did he accomplish? Resources and references: ● Sir Isaac Newton ● How objects spin faster when ‘collapsed’ (watch from 1:35 to 3:18) Review and discussion questions: ● Newton’s idea of shooting cannonballs was something people could relate to in the 1600s.

Load more