Lecture 17 - The Orion Nebula and the Formation of Stars

Lecture 17 - The Orion Nebula and the Formation of Stars -...

Info iconThis preview shows pages 1–6. Sign up to view the full content.

View Full Document Right Arrow Icon

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full Document Right Arrow Icon

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full Document Right Arrow Icon

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full Document Right Arrow Icon
This is the end of the preview. Sign up to access the rest of the document.

Unformatted text preview: The Orion Nebula and the Formation of Stars ASTRONOMY 3 Lesson 17 1 The Orion Nebula as observed with the Advanced Camera for Surveys of the Hubble Space Telescope. The different colors originate in the recombination emission lines of different elements, which got ionized by ultraviolet photons from the most massive and hot star in the center of the nebula. NATURE of the Universe Astronomy - Star Formation Review of Lesson 16 Review of Lesson 16 The absolute luminosity of a star scales with the 2nd power of its diameter and the 4th power of its surface temperature. The apparent brightness of a star is proportional to its absolute luminosity and inversely proportional to the square of its distance. Massive stars use up their hydrogen very fast. The life-span O-type stars is as short a 1 million years. Low-mass stars can produce energy by hydrogen fusion for up to 10 trillion years. The H-R diagram shows the luminosity versus the surface temperature of a star. The most prominent feature in the H-R diagram is the main sequence. The main-sequence is the location of stars which produce energy by hydrogen fusion in their core. 2 NATURE of the Universe Astronomy - Star Formation Questions from Lesson 16 Think about (questions from Lesson 16): How was the Sun born? Where do stars form? 3 NATURE of the Universe Astronomy - Star Formation Today's Topics Interstellar Medium (Ch. 11.1) Formation Stages (Ch. 11.3, 11.4) Stars with other Mass (Ch. 11.5) The Orion Nebula (Ch. 11.2, 11.6) Summary & Announcements 4 NATURE of the Universe Astronomy - Star Formation Interstellar Medium Time scales for stars and the universe The most massive O-type stars live 1 million years Our Sun (a G-type star) lives 10 billion years The lowest mass L-type stars live 10 trillion years The age of the universe (time since the Big Bang) 14 billion years. is If all O- and G-type stars formed at the time of the Big Bang, none would be left today. Stars are still forming today 5 NATURE of the Universe Astronomy - Star Formation Interstellar Medium Where and out of what do stars form? The solar wind has blown a "bubble" into the interstellar medium. Voyager 1 measures that the solar wind is slowing down as it starts to encounter the interstellar medium at a distance of more than 100 Astronomical Units from the Sun. The interstellar medium consists of gas and dust. The average density is very low with about 1 particle per cm3 . At some places, the interstellar medium gets compressed to much higher density and starts to form dark clouds made of dust and molecules. 6 NATURE of the Universe Astronomy - Star Formation Distances Southern Cross Coalsack Alpha Centauri The "coalsack" is a dense clouds of molecular gas and dust, which blocks the light from stars located behind it. There are millions of dark clouds in the Milky Way. 7 Image of a region of the southern Milky Way by Humayun Qureshi NATURE of the Universe Astronomy - Star Formation Interstellar Medium Dust blocks light strongly in the visual (at short wavelength). In the red and infrared (at longer wavelength) we can look through the cloud. This explains why stars at the edge of dark clouds appear reddish. To study star formation in dark clouds, observations in the infrared are often required. 8 See http://www.eso.org/outreach/gallery/vlt/images/Top20/Top20/press-rel/ pr-01-01_pf.html NATURE of the Universe Astronomy - Star Formation Formation Stages The interstellar medium gets compress into dark molecular clouds. Hubble Space Telescope observations of the spiral galaxy M51 reveal giant dark clouds. The largest of these clouds are called giant molecular clouds, and can be more than 100 light years across. They have masses up to 1 million times the mass of the Sun. 9 NATURE of the Universe Astronomy - Star Formation Formation Stages The giant molecular clouds split into smaller fragments. Some of the fragments get so dense that the gravitational force becomes larger than the gas pressure in these clouds. This is called gravitational collapse. One or more protostars form in the cores of the dense fragments. 10 NATURE of the Universe Astronomy - Star Formation Formation Stages As the clouds start with some angular momentum, the cloud around a protostar gets flatter and spins up as it collapses. disk A protostar ovserved in the infrared with the Hubble Space Telescope. The star itself is hidden by the disk seen from the side. This leads to the formation of a disk of gas and dust around the protostar. 11 See http://hubblesite.org/newscenter/archive/releases/1999/05/ for more infrared images of protostars with disks NATURE of the Universe Astronomy - Star Formation Formation Stages As the protostar contracts further, it heats up and gets so hot that it can be observed in the near-infrared and sometimes even in the visible. In the disk around the protostar, planets start to form. This stage is called the pre-main sequence phase, as density and temperature in the core of the protostar increase. 12 NATURE of the Universe Astronomy - Star Formation Formation Stages Finally, density and temperature in the core of the young star get high enough to start the fusion of hydrogen into helium. The star settles in a hydrostatic equilibrium and is now a main sequence star. 13 NATURE of the Universe Astronomy - Star Formation Formation Stages Star formation stages Interstellar Medium (low density), gets compressed into... Dark clouds, fragments starts to become gravitationally unstable, collapse to form a ... Protostar, surrounded by a disk of gas and dust, out which planets might evolve, heats up as it contracts to become a ... Pre-main sequence star, surrounded by protoplanets, once temperature and pressure in its core get high enough, hydrogen fusion starts, and it becomes a ... Main sequence star, new hydrostatic equilibrium, fuses hydrogen into helium (while supplies last) 14 NATURE of the Universe Astronomy - Star Formation Stars of other Masses Main sequence stars have a mass in the range 0.075 to 100 times the mass of the Sun. Stars with a higher mass form faster (i.e. the collapse of the gas clouds happens fast) than stars with a lower mass. Protostars have a luminosity as high or even higher than the resulting mainsequence stars. They start with larger diameters and lower temperatures. 15 NATURE of the Universe Astronomy - Star Formation Stars of other Masses What happens if a cloud with a mass of less than 0.075 the mass of the Sun collapses? The formation stages are the same as for stars, by the resulting objects does not have enough mass to start hydrogen fusion in its core. These "failed stars" are called brown dwarfs. stars on main sequence brown dwarfs planetary mass objects As brown dwarfs never reach the main sequence, they continue to cool down forever. 16 NATURE of the Universe Astronomy - Star Formation Are there any brown dwarfs nearby? Stars of other Masses SCR 1845-6537 The companion to SCR 1845-6537 has a temperature of 1,000 K and 20 times the mass of Jupiter. Indi B E Indi A has a binary brown dwarf as a companion. The two brown dwarfs have a temperatures of 1,500 and 1,100 K and masses of 50 and 28 times the mass of Jupiter, respectively. 17 NATURE of the Universe Astronomy - Star Formation The Orion Nebula Orion observed by the InfraRed Astronomical Satellite (IRAS) Orion houses a giant molecular cloud, which glows in the infrared. Its distance is 1,500 light years. 18 NATURE of the Universe Astronomy - Star Formation The Orion Nebula Reflection Nebula Emission Nebula At several places in the molecular cloud, star formation is taking place. 19 See http://www.seds.org/MESSIER/more/m-kc.html and http://www.celestialimage.com/ page8.html NATURE of the Universe Astronomy - Star Formation The Orion Nebula The Hubble Space Telescope reveals a young star still partially embedded in the clouds. The horsehead nebula is a small, cold, dark cloud of dust, illuminated from behind by an nebula, which emits light in the red hydrogen line. 20 See http://www.celestialimage.com/page8.html NATURE of the Universe Astronomy - Star Formation The Orion Nebula The Orion Nebula is a more extreme star forming site than the horsehead nebula. 10 light years 21 See http://members.aon.at/astrofotografie/galerie/deepsky/he_m42.htm NATURE of the Universe Astronomy - Star Formation The Orion Nebula How do emission and reflection nebula work? Hot stars produce ultraviolet photon, which ionize hydrogen gas. Eventually, electrons and protons recombine to form hydrogen atoms. As the electrons jump to lower orbits, photons corresponding to the hydrogen emission lines are emitted. Reflection nebula are dark clouds, which simply reflect light from nearby stars. 22 NATURE of the Universe Astronomy - Star Formation The Orion Nebula Where do the ultraviolet photons in the Orion Nebula come from? B0 B0.5 O6 B0.5 The Orion Nebula houses a cluster of young stars. In its center are four hot stars of spectral type O and B. The most massive star has a surface temperature of 41,000 K, and emits ultraviolet photons, which ionize atoms in the nebula. 23 NATURE of the Universe Astronomy - Star Formation How many stars are in the Orion Nebula Cluster? The Orion Nebula Near infrared observations reveal more than 1,000 stars with masses up 45 times the mass of the Sun, and at least 50 brown dwarfs with masses down to 0.05 times the mass of the Sun. 24 See http://www.eso.org/outreach/press-rel/pr-2001/phot-03-01.html NATURE of the Universe Astronomy - Star Formation The Orion Nebula Let's zoom in on some of the solar-type stars in the Orion Nebula Cluster... Dark silhouettes indicate the presence of disks around stars. These are the places where planets might form. Some disks, however, get ionized by the ultraviolet photons from the O-type star, and might not survive long enough to form planets. 25 NATURE of the Universe Astronomy - Star Formation How do stellar clusters form? The Orion Nebula Theoretical models and simulations indicate that protostars interact with each other and compete for the available reservoir of gas and dust. 26 See http://star-www.st-and.ac.uk/~iab1/anims.html NATURE of the Universe Astronomy - Star Formation Summary Summary: The Orion Nebula and the Formation of Stars The interstellar medium consists of gas and dust. When it gets compressed, it forms dark (molecular) clouds. Star formation begins when a part of a molecular cloud collapses. A disk of gas and dust forms around a contracting protostar. As the protostars heats up due to contracting, it becomes hot enough to be observable in the infrared. This is the beginning of the pre-main sequence phase. As density and temperature in the core get high enough, hydrogen fusion starts, and the star settles on the main sequence. 27 NATURE of the Universe Astronomy - Star Formation Summary Summary: The Orion Nebula and the Formation of Stars O-type stars can ionize the gas around them. This creates an emission nebula. Reflection nebula are dark clouds illuminated by a star. Stars quite often do not form in isolation, but in multiple systems or stellar clusters. 28 NATURE of the Universe Astronomy - Star Formation Homework Homework Reading assignment: Chapter 4.4 Homework 5 is online. Due date is Mo, Nov 13 at 12:00 pm (noon) Think about: How do we know about planets around other stars? Could (intelligent) life exist on extra-solar planets? 29 NATURE of the Universe Astronomy - The Solar System Homework Review Review of Homework 4: dose of statistics Distribution of scores 100 75 50 25 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 Question Percentage of correct answers Median: 13 correct answers Mean: 12 correct answers Questions #3, #5, and #7: less than 75% correct answers 30 Answer key to homework 4 is available at http://web.physics.ucla.edu/class/06F/ 3_BRANDNER/homework/index.html - select "Homework 4" and then "key". NATURE of the Universe Astronomy - The Solar System Homework Review Review of Homework 4 3. The southern part of the San Andreas fault is overdue for a movement, as it has not produced any major earthquake for over 300 years 5. Due to tidal resonance, Mercury presents the same side to the Sun every second orbit Mercury is in a 3 to 2 resonance, i.e. in the time Mercury orbits the Sun 2 times, it rotates 3 times around its axis. 31 NATURE of the Universe Astronomy - The Solar System Homework Review Review of Homework 4 7. Which planet or moon has the densest atmosphere? Venus Venus' atmospheric pressure is 90 times higher than Earth's. Titan's atmospheric pressure at the ground is 1.6 times the pressure at sea level on Earth's. Hubble Space Telescope observations of Venus 32 NATURE of the Universe Astronomy - Earth: Atmosphere Homework Mid-term 2: Wed, Nov 15 at 12:00 pm (noon), in class 45 multiple choice questions (only 4 possible answers!) Topics cover Lessons 12 to 18 (including some repeats, like, e.g, Stefan's law or the Doppler effect) Use copies of the lecture slides and the notes you took in class as a basis for your studies. Use the textbook to read up difficult points. Don't try to memorize all the numbers! You should, however, know a few "key numbers" or ratios like, e.g., the length of the sunspot cycle, or the mass of the Sun compared to Jupiter. You should also be familiar with the H-R diagram, and the location of the main sequence etc. 33 NATURE of the Universe Astronomy - Earth: Atmosphere Homework Mid-term 2: Wed, Nov 15 at 12:00 pm (noon), in class Some questions will involve simple math. No calculator is required! 6 to 7 are repeated homework questions See discussion board on class web page for additional details: http://web.physics.ucla.edu/class/06F/3_BRANDNER/wwwboard/index.shtml 34 NATURE of the Universe Astronomy - Star Formation Announcements This afternoon: 2:30 - 4:00 pm, in Math Sciences Building Planetarium (8th floor) and Telescopes (9th floor) (this is also an opportunity for you to earn your "telescope viewing" extra credits) Pick up telescope viewing forms here! 35 ...
View Full Document

{[ snackBarMessage ]}

Page1 / 35

Lecture 17 - The Orion Nebula and the Formation of Stars -...

This preview shows document pages 1 - 6. Sign up to view the full document.

View Full Document Right Arrow Icon
Ask a homework question - tutors are online