DOCSLIB.ORG

Your Guide to Planets, Stars, and Galaxies by Richard Talcott

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
Your Guide to Planets, Stars, and Galaxies by Richard Talcott FACTS500 INSIDE! Your guide to planets, stars, and galaxies by Richard Talcott A supplement to Astronomy magazine © 2012 Kalmbach Publishing Co. This material may not be reproduced in any form 618129 without permission from the publisher. www.Astronomy.com Saturn Saturn’s rings consist of icy particles ranging in size from tiny motes to house-sized icebergs. NASA/THE HUBBLE Planets HERItaGE TEam (STSCI/AURA) of the solar system arth may seem extraordinary to those who call it home, but it’s not a land of superlatives. Earth is neither too hot nor too cold, too big nor too small. It’s just right in so many ways — the perfect “Goldilocks” planet. Of course, as the only known abode of life in the universe, Earth doesE have one major claim to being special. The other planets in the solar system leave their marks in different ways. The planets divide into two broad categories: terrestrial and jovian. The small, rocky terrestrial planets include Mercury, Venus, Earth, and Mars. Mercury, the closest to the Sun, bakes Mars at temperatures up to 800° Fahrenheit at noon. But Mercury’s razor-thin atmosphere can’t hold heat; at night, the temperature plummets far below freezing. Venus most resembles Earth in mass and diameter, but a thick atmosphere of carbon dioxide has led to a runaway greenhouse effect. Venus’ surface remains a scorching 865° F year-round. Earth and Mars are the water worlds of the solar system. Our home planet is the only one with liquid water at the surface now, but spacecraft observations during the past 15 years leave no doubt that Mars once had loads of surface water. Even now, Mars has permafrost and permanent polar caps of water ice. Winds up to 70 mph blow around the ubiquitous martian dust, creating shifting seasonal patterns. FUN The jovian planets — Jupiter, Saturn, Uranus, and Neptune Mars boasts the largest vol- — are all gaseous behemoths. They consist mostly of hydrogen canoes in the solar system, and helium, the most abundant elements in the universe. Jupiter although they’re all extinct. The biggest — Olympus dwarfs the others: It contains more than twice as much matter Mons — spans nearly 400 as all the other planets combined. All the jovian planets pos- miles and rises 13 miles sess ring systems, but only Saturn’s appears bright. Its icy rings above the surrounding plains. span 170,000 miles and measure just 100 feet thick. Uranus FACT and Neptune are the true twin planets of the solar system, with nearly equal diameters, masses, compositions, and rotations. Most scientists no longer consider small, distant Pluto to be a major planet. A mixture of ice and rock, this world more closely resembles the thousands of so-called Kuiper Belt objects that lurk beyond Neptune. In 2006, astronomers demoted Pluto to a Mars’ ruddy appearance arises “dwarf planet,” a category that also includes the asteroid Ceres. because the sand on the planet’s surface consists largely of iron 2 Your guide to planets, stars, and galaxies oxides — rust. NASA/JPL/MSSS Jupiter Jupiter is so big that it would take 11 Earths wedged side by side to cross the giant’s girth and more than 1,000 Earths to fill its volume. NASA/JPL/UNIVERSITY OF ARIZONA Thick clouds blanket Venus, so astronomers use radar to see Venus its surface. The atmospheric pressure there is nearly 100 times that at Earth’s surface. NASA/JPL FUN Saturn has the lowest density of any planet. In fact, if you filled a solar-system-sized basin with water, the ringed world would float. FACT Mercury Earth Pluto & Charon FUN Sunlight takes just eight min- utes to reach Earth but more than four hours to cross the void to Neptune and Pluto. FACT Mercury's high density means Nearly three-quarters of more than half of it must be made Earth’s surface is covered with of the heavy elements iron and water. It’s what makes our home The orbit of dwarf planet Pluto (left; along with its moon, Charon) brings it closer nickel. NASA/JPL/USGS world conducive to life. NASA to the Sun than Neptune for 20 years out of its nearly 250-year-long circuit. ESA/NASA Uranus Neptune Solar system planets Planet Distance from Sun Orbital period Diameter Mass Density (Earth=1) (Earth=1) (Earth=1) (water=1) Mercury 0.39 87.97 days 0.383 0.055 5.43 Venus 0.72 224.70 days 0.949 0.815 5.24 Earth 1.00 365.26 days 1.000 1.000 5.52 Mars 1.52 686.98 days 0.532 0.107 3.93 Ceres 2.77 4.60 years 0.075 0.0002 1.93 Jupiter 5.20 11.86 years 11.209 317.832 1.33 Saturn 9.58 29.46 years 9.449 95.159 0.69 Uranus’ bland cloud tops mask Storms rage in Neptune’s atmos- Uranus 19.20 84.01 years 4.007 14.536 1.27 the fact that its rotation axis lies in phere, as they do in the massive Neptune 30.05 164.79 years 3.883 17.147 1.64 its orbital plane, so night and day at atmospheres of most of the jovian Pluto 39.48 247.68 years 0.187 0.002 1.75 the poles last 40 years each. NASA/JPL planets. NASA/JPL Note: Ceres and Pluto are officially considered to be dwarf planets. Titan Titan’s hazy atmosphere glows as it scatters incom- ing sunlight. The atmosphere of Saturn’s moon is thicker than Earth’s and, like ours, contains mainly nitrogen. NASA/JPL/SSI Small bodies Europa of the solar Ridges crack the surface of Jupiter’s moon Europa. Such ridges could be sites where slushy water erupted through the icy surface system and then froze. NASA/JPL fter the Sun and planets, there’s not much else in the Io solar system — certainly not in terms of mass. But More than 100 active volcanoes dot the surface in sheer number (and in a few notable instances, of Jupiter’s moon Io. The plumes can reach 100 prominence), the small objects hold their own. The miles high and spread debris over thou- biggest of the small bodies actually outrank the small- sands of miles. NASA/JPL est planet.A Both Ganymede, a Jupiter moon, and Titan, a Saturn moon, have diameters larger than Mercury. More than 170 moons have been discovered orbiting the eight planets, although the vast majority are little more than flying boulders. The smaller planets tend to have fewer moons. Earth has just one, which formed when an object the size of Mars struck the proto-Earth, ejecting debris that eventually coalesced. Mercury and Venus have no moons, and Mars possesses just two small ones. Oddly enough, Pluto’s large moon, Charon, is half the diam- eter of the dwarf planet — the largest ratio in the solar system. The hefty moons of the gas giants garner most of the atten- tion. Jupiter’s four big moons — Io, Europa, Ganymede, and Callisto — form a miniature solar system. Io ranks as the most volcanically active object in the solar system. Europa hides an ocean of liquid water — perhaps larger than all of Earth’s oceans — beneath its frigid ice crust. Giant Ganymede also may harbor an ocean and has a surface covered with intriguing grooved ter- rain. And Callisto sports more craters than any other object in the solar system. At the top of Saturn’s family of moons is Titan, which possesses a significant atmosphere and methane lakes. More than half a million asteroids also inhabit the solar system. The biggest, Ceres, has a diameter of 600 miles. Yet most are far smaller: If you add them all up, asteroids don’t equal the weight of Earth’s Moon. Most asteroids circle the Sun between the orbits of Mars and Jupiter, although a few wander into Earth’s vicinity. Perhaps the most spectacular small bodies are comets. Billions of these “dirty snowballs” lurk in the outer solar sys- tem. If their long, looping orbits bring them close to the Sun’s warmth, they shed gas and dust. The Sun then blows this mate- rial back to create a long tail. Although a comet’s nucleus may be only a mile or two across, its tail can stretch millions of miles. 4 Your guideguide to to planets, planets, stars, stars, and and galaxies galaxies Triton Callisto Geyser-like plumes deposited the dark streaks seen on Nep- tune’s moon Triton. At a FUN temperature of –390° F, Triton Saturn’s enigmatic outer has the coldest surface known in moon, Iapetus, has a split the solar system. NASA/JPL personality: Half of its surface appears as dark as freshly laid asphalt while the opposite Enceladus hemisphere reflects as much light as newly fallen snow. FACT Saturn’s icy moon Enceladus reflects more than 90 percent of the sunlight Multi-ringed impact basins, some stretching more than that reaches it, the highest percentage 1,000 miles, formed on Jupiter’s Callisto when massive of any object in the solar system. NASA/JPL impacts left concentric fractures and faults. NASA/JPL Io Hale-Bopp Eros One of the brightest comets of the past 40 years, Hale-Bopp wowed observers in 1997. It had a nucleus 25 miles wide and a tail that stretched more than 100 million miles. BILL AND SALLY FLETCHER Potato-shaped asteroid Eros, some 20 miles long, looks like a lot of other modest-sized asteroids, but this object might one day wander dangerously close to Earth.
Load more

Recommended publications
  • A Search for Ionized Gas in the Draco and Ursa Minor Dwarf Spheroidal Galaxies
    View metadata, citation and similar papers at core.ac.uk brought to you by CORE provided by CERN Document Server A Search for Ionized Gas in the Draco and Ursa Minor Dwarf Spheroidal Galaxies J.S. Gallagher, G. J. Madsen, R. J. Reynolds Department of Astronomy, University of Wisconsin–Madison, 475 North Charter Street, Madison, WI 53706-1582; [email protected], [email protected], [email protected] E. K. Grebel Max-Planck Institute for Astronomy, K¨onigstuhl 17, D-69117 Heidelberg, Germany; [email protected] T. A. Smecker-Hane Department of Physics & Astronomy, 4129 Frederick Reines Hall, University of California, Irvine, CA 92697-4575; [email protected] ABSTRACT The Wisconsin Hα Mapper has been used to set the first deep upper limits on the intensity of diffuse Hα emission from warm ionized gas in the Draco and Ursa Minor dwarf spheroidal 1 galaxies. Assuming a velocity dispersion of 15 km s− for the ionized gas, we set limits of IHα 0:024R and IHα 0:021R for the Draco and Ursa Minor dSphs, respectively, averaged ≤ ≤ over our 1◦ circular beam. Adopting a simple model for the ionized interstellar medium, these limits translate to upper bounds on the mass of ionized gas of .10% of the stellar mass, or 10 times the upper limits for the mass of neutral hydrogen. Note that the Draco and Ursa Minor∼ dSphs could contain substantial amounts of interstellar gas, equivalent to all of the gas injected by dying stars since the end of their main star forming episodes &8 Gyr in the past, without violating these limits on the mass of ionized gas.
    [Show full text]
  • Enrichment in R-Process Elements from Multiple Distinct Events in the Early Draco Dwarf Spheroidal Galaxy*
    The Astrophysical Journal Letters, 850:L12 (6pp), 2017 November 20 https://doi.org/10.3847/2041-8213/aa9886 © 2017. The American Astronomical Society. Enrichment in r-process Elements from Multiple Distinct Events in the Early Draco Dwarf Spheroidal Galaxy* Takuji Tsujimoto1,2 , Tadafumi Matsuno1,2 , Wako Aoki1,2, Miho N. Ishigaki3 , and Toshikazu Shigeyama4 1 National Astronomical Observatory of Japan, Mitaka, Tokyo 181-8588, Japan; [email protected] 2 Department of Astronomical Science, School of Physical Sciences, SOKENDAI (The Graduate University for Advanced Studies), Mitaka, Tokyo 181-8588, Japan 3 Kavli Institute for the Physics and Mathematics of the Universe (WPI), University of Tokyo, Kashiwa, Chiba 277-8583, Japan 4 Research Center for the Early Universe, Graduate School of Science, University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033, Japan Received 2017 October 11; revised 2017 October 26; accepted 2017 November 1; published 2017 November 16 Abstract The stellar record of elemental abundances in satellite galaxies is important to identify the origin of r-process because such a small stellar system could have hosted a single r-process event, which would distinguish member stars that are formed before and after the event through the evidence of a considerable difference in the abundances of r-process elements, as found in the ultra-faint dwarf galaxy Reticulum II (Ret II). However, the limited mass of these systems prevents us from collecting information from a sufficient number of stars in individual satellites. Hence, it remains unclear whether the discovery of a remarkable r-process enrichment event in Ret II explains the nature of r-process abundances or is an exception.
    [Show full text]
  • Eclipse Newsletter
    ECLIPSE NEWSLETTER The Eclipse Newsletter is dedicated to increasing the knowledge of Astronomy, Astrophysics, Cosmology and related subjects. VOLUMN 2 NUMBER 1 JANUARY – FEBRUARY 2018 PLEASE SEND ALL PHOTOS, QUESTIONS AND REQUST FOR ARTICLES TO [email protected] 1 MCAO PUBLIC NIGHTS AND FAMILY NIGHTS. The general public and MCAO members are invited to visit the Observatory on select Monday evenings at 8PM for Public Night programs. These programs include discussions and illustrated talks on astronomy, planetarium programs and offer the opportunity to view the planets, moon and other objects through the telescope, weather permitting. Due to limited parking and seating at the observatory, admission is by reservation only. Public Night attendance is limited to adults and students 5th grade and above. If you are interested in making reservations for a public night, you can contact us by calling 302-654- 6407 between the hours of 9 am and 1 pm Monday through Friday. Or you can email us any time at [email protected] or [email protected]. The public nights will be presented even if the weather does not permit observation through the telescope. The admission fees are $3 for adults and $2 for children. There is no admission cost for MCAO members, but reservations are still required. If you are interested in becoming a MCAO member, please see the link for membership. We also offer family memberships. Family Nights are scheduled from late spring to early fall on Friday nights at 8:30PM. These programs are opportunities for families with younger children to see and learn about astronomy by looking at and enjoying the sky and its wonders.
    [Show full text]
  • Arxiv:1907.03763V1 [Astro-Ph.GA] 8 Jul 2019 Keywords: Galaxy: Disk — Galaxy: Kinematics and Dynamics — Galaxy: Solar Neighborhood — Galaxy: Structure
    Draft version July 10, 2019 Typeset using LATEX twocolumn style in AASTeX62 Stellar Overdensity in the Local Arm in Gaia DR2 Yusuke Miyachi,1 Nobuyuki Sakai,2, 3 Daisuke Kawata,4 Junichi Baba,5 Mareki Honma,2, 6, 7 Noriyuki Matsunaga,8 and Kenta Fujisawa1 1Department of Physics, Faculty of Science, Yamaguchi University, Yoshida 1677-1, Yamaguchi-city, Yamaguchi 753-8512, Japan 2Mizusawa VLBI observatory, National Astronomical Observatory of Japan, 2-21-1 Osawa, Mitaka, Tokyo 181-8588, Japan 3Korea Astronomy & Space Science Institute, 776, Daedeokdae-ro, Yuseong-gu, Daejeon 34055, Korea 4Mullard Space Science Laboratory, University College London, Holmbury St. Mary, Dorking, Surrey RH5 6NT, UK 5National Astronomical Observatory of Japan, 2-21-1 Osawa, Mitaka, Tokyo 181-8588, Japan 6Mizusawa VLBI observatory, National Astronomical Observatory of Japan, 2-12 Hoshi-ga-oka-cho, Mizusawa-ku, Oshu, Iwate 023-0861, Japan 7The Graduate University for Advanced Studies (Sokendai), Mitaka, Tokyo 181-8588, Japan 8Department of Astronomy, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033, Japan (Received March 31, 2019; Revised June 17, 2019; Accepted July 2, 2019) Submitted to ApJ ABSTRACT Using the cross-matched data of Gaia DR2 and 2MASS Point Source Catalog, we investigated the surface density distribution of stars aged 1 Gyr in the thin disk in the range of 90◦ l 270◦. We ∼ ≤ ≤ selected 4,654 stars above the turnoff corresponding to the age 1 Gyr, that fall within a small box ∼ region in the color{magnitude diagram, (J K ) versus M(K ), for which the distance and reddening − s 0 s are corrected.
    [Show full text]
  • Search for Ultra-Faint Satellite Galaxies in the Milky Way Halo
    Search for Ultra-faint Satellite Galaxies in the Milky Way Halo filtering techniques and first results Helmut Jerjen SkyMapper Workshop April 2014 Cold Dark Matter Simulations of the Milky Way (Millennium II or Aquarius project) 0.5 Mpc Cold Dark Matter Simulations of the Milky Way (Millennium II or Aquarius project) predict ~1000 dark matter subhalos in the MW potential (e.g. Diemand et al. 2006, 2008) distributed spherically symmetric ⇒optical manifestation: satellite dwarf galaxies Milky Way Satellite Census (2004) The Disk of Satellites • Only 11 dwarf satellite galaxies known within the gravitational influence of the MW • 10 satellites are distributed in a common plane (Lynden-Bell 1976; Kroupa et al. 2005; Metz, Kroupa & Jerjen 2007, 2009) -> result of a major merger? Known Satellite Galaxies in Milky Way Halo (2014) SDSS Footprint 2004-10: 14 new Milky Way Satellites discovered out to 250 kpc (-7.9<Mv<-2.7), many consistent with DoS and 9 out the 11 brightest share the same dynamical orbital properties (Metz et al. 2008; Palowski & Kroupa 2013). More Results and Open Questions Strigari et al. 2008 •How many MW satellites are in the southern hemisphere? •What is their distribution and are there satellite galaxies that do not follow the DoS? •How much dark matter is in these MW satellite galaxies? (some may not be virialised) •Are there possibly two different types of satellites (tidal and cosmological origin)? •Do all MW satellites have the same total mass? •What is the evolutionary link between satellites and MW? The Stromlo Milky Way Satellite Survey SkyMapper key project SkyMapper Search for satellite galaxies to similar depth as SDSS over 20,000 sqr degrees.
    [Show full text]
  • Elements of Astronomy and Cosmology Outline 1
    ELEMENTS OF ASTRONOMY AND COSMOLOGY OUTLINE 1. The Solar System The Four Inner Planets The Asteroid Belt The Giant Planets The Kuiper Belt 2. The Milky Way Galaxy Neighborhood of the Solar System Exoplanets Star Terminology 3. The Early Universe Twentieth Century Progress Recent Progress 4. Observation Telescopes Ground-Based Telescopes Space-Based Telescopes Exploration of Space 1 – The Solar System The Solar System - 4.6 billion years old - Planet formation lasted 100s millions years - Four rocky planets (Mercury Venus, Earth and Mars) - Four gas giants (Jupiter, Saturn, Uranus and Neptune) Figure 2-2: Schematics of the Solar System The Solar System - Asteroid belt (meteorites) - Kuiper belt (comets) Figure 2-3: Circular orbits of the planets in the solar system The Sun - Contains mostly hydrogen and helium plasma - Sustained nuclear fusion - Temperatures ~ 15 million K - Elements up to Fe form - Is some 5 billion years old - Will last another 5 billion years Figure 2-4: Photo of the sun showing highly textured plasma, dark sunspots, bright active regions, coronal mass ejections at the surface and the sun’s atmosphere. The Sun - Dynamo effect - Magnetic storms - 11-year cycle - Solar wind (energetic protons) Figure 2-5: Close up of dark spots on the sun surface Probe Sent to Observe the Sun - Distance Sun-Earth = 1 AU - 1 AU = 150 million km - Light from the Sun takes 8 minutes to reach Earth - The solar wind takes 4 days to reach Earth Figure 5-11: Space probe used to monitor the sun Venus - Brightest planet at night - 0.7 AU from the
    [Show full text]
  • The Milky Way
    Astronomy Cast Episode 99: The Milky Way Fraser Cain: Ninety-nine episodes Pamela! Dr. Pamela Gay: I know [Laughter] it’s amazing how far and how long we’ve been doing this. Fraser: The Milky Way is our home galaxy but we’ve only understood its true nature for about a century. We share this beautiful barred spiral galaxy with at least 200 billion other stars. Let’s trace back the history, see how we learned about the Milky Way and then compare it to other galaxies out there. What does the future hold for the Milky Way? Pamela: The future holds death, because that’s kinda what happens in the Universe. [Laughter] Fraser: Shhh….we’re supposed to keep that as a surprise! It all ends in tears. But, let’s go back to the beginning. [Laughter] I find that kinda interesting. My dad had an antique book about Astronomy. It had all the constellations and stuff. It was back from like the 1920s or earlier. It had nebula for the Andromeda nebula and other stuff. Let’s go back like as far as we can and talk a bit about the history of the Milky Way. You could see the Milky Way in the night sky so people knew that there was something there. What did they think was going on? Pamela: Well the term Milky Way is actually derived from a Latin term. We’ve had that name for it for a long time. It basically comes from the fact that there is this band of light that to the naked eye is perceived as this light patch, this illuminated patch that spreads in an arc across the sky.
    [Show full text]
  • Afterschool Universe Session 9 Slide Notes: Galaxies
    This presentation supports the “Background” material in Session 9 of the Afterschool Universe program. This session is about galaxies. The picture shows the Whirlpool galaxy, a large, iconic, spiral galaxy. 1 Let us summarize the main concepts in this Session. We will discuss these in the rest of this presentation. 2 A galaxy is a huge collection of stars, gas and dust. A typical galaxy has about 100 billion stars (that’s 100,000,000,000 stars!), and light takes about 100,000 years to cross a galaxy (in other words, they are typically 100,000 light years ago). But some galaxies are much bigger and some are much smaller. 3 If you look at the sky from a DARK location, you can see a band of light stretching across the sky which is known as the Milky Way. This is our view of our Galaxy - more precisely, this is our view of the disk of our galaxy as seen from the INSIDE. 4 This picture shows another view of our galaxy taken in the infra-red part of the spectrum. The advantage of the infra-red is that it can penetrate the dust that pervades our galaxy’s disk and let us view the central parts of our galaxy. This picture also shows the full sky. The flat disk and central bulge of our galaxy can be seen in this picture. 5 We live in the suburbs of our galaxy. The Sun and its planetary system are about 25,000 light years from the center of the galaxy. This is about half way out to the edge of the disk.
    [Show full text]
  • Nd AAS Meeting Abstracts
    nd AAS Meeting Abstracts 101 – Kavli Foundation Lectureship: The Outreach Kepler Mission: Exoplanets and Astrophysics Search for Habitable Worlds 200 – SPD Harvey Prize Lecture: Modeling 301 – Bridging Laboratory and Astrophysics: 102 – Bridging Laboratory and Astrophysics: Solar Eruptions: Where Do We Stand? Planetary Atoms 201 – Astronomy Education & Public 302 – Extrasolar Planets & Tools 103 – Cosmology and Associated Topics Outreach 303 – Outer Limits of the Milky Way III: 104 – University of Arizona Astronomy Club 202 – Bridging Laboratory and Astrophysics: Mapping Galactic Structure in Stars and Dust 105 – WIYN Observatory - Building on the Dust and Ices 304 – Stars, Cool Dwarfs, and Brown Dwarfs Past, Looking to the Future: Groundbreaking 203 – Outer Limits of the Milky Way I: 305 – Recent Advances in Our Understanding Science and Education Overview and Theories of Galactic Structure of Star Formation 106 – SPD Hale Prize Lecture: Twisting and 204 – WIYN Observatory - Building on the 308 – Bridging Laboratory and Astrophysics: Writhing with George Ellery Hale Past, Looking to the Future: Partnerships Nuclear 108 – Astronomy Education: Where Are We 205 – The Atacama Large 309 – Galaxies and AGN II Now and Where Are We Going? Millimeter/submillimeter Array: A New 310 – Young Stellar Objects, Star Formation 109 – Bridging Laboratory and Astrophysics: Window on the Universe and Star Clusters Molecules 208 – Galaxies and AGN I 311 – Curiosity on Mars: The Latest Results 110 – Interstellar Medium, Dust, Etc. 209 – Supernovae and Neutron
    [Show full text]
  • Dark Matter Searches Targeting Dwarf Spheroidal Galaxies with the Fermi Large Area Telescope
    Doctoral Thesis in Physics Dark Matter searches targeting Dwarf Spheroidal Galaxies with the Fermi Large Area Telescope Maja Garde Lindholm Oskar Klein Centre for Cosmoparticle Physics and Cosmology, Particle Astrophysics and String Theory Department of Physics Stockholm University SE-106 91 Stockholm Stockholm, Sweden 2015 Cover image: Top left: Optical image of the Carina dwarf galaxy. Credit: ESO/G. Bono & CTIO. Top center: Optical image of the Fornax dwarf galaxy. Credit: ESO/Digitized Sky Survey 2. Top right: Optical image of the Sculptor dwarf galaxy. Credit:ESO/Digitized Sky Survey 2. Bottom images are corresponding count maps from the Fermi Large Area Tele- scope. Figures 1.1a, 1.2, 1.3, and 4.2 used with permission. ISBN 978-91-7649-224-6 (pp. i{xxii, 1{120) pp. i{xxii, 1{120 c Maja Garde Lindholm, 2015 Printed by Publit, Stockholm, Sweden, 2015. Typeset in pdfLATEX Abstract In this thesis I present our recent work on gamma-ray searches for dark matter with the Fermi Large Area Telescope (Fermi-LAT). We have tar- geted dwarf spheroidal galaxies since they are very dark matter dominated systems, and we have developed a novel joint likelihood method to com- bine the observations of a set of targets. In the first iteration of the joint likelihood analysis, 10 dwarf spheroidal galaxies are targeted and 2 years of Fermi-LAT data is analyzed. The re- sulting upper limits on the dark matter annihilation cross-section range 26 3 1 from about 10− cm s− for dark matter masses of 5 GeV to about 5 10 23 cm3 s 1 for dark matter masses of 1 TeV, depending on the × − − annihilation channel.
    [Show full text]
  • Our 'Island Universe' Transcript
    Our 'Island Universe' Transcript Date: Thursday, 30 October 2008 - 12:00AM OUR 'ISLAND UNIVERSE' Professor Ian Morison The Milky Way On a dark night with transparent skies, we can see a band of light across the sky that we call the Milky Way. (This comes from the Latin - Via Lactea.) The light comes from the myriads of stars packed so closely together that our eyes fail to resolve them into individual points of light. This is our view of our own galaxy, called the Milky Way Galaxy or often "the Galaxy" for short. It shows considerable structure due to obscuration by intervening dust clouds. The band of light is not uniform; the brightness and extent is greatest towards the constellation Sagittarius suggesting that in that direction we are looking towards the Galactic Centre. However, due to the dust, we are only able to see about one tenth of the way towards it. In the opposite direction in the sky the Milky Way is less apparent implying that we live out towards one side. Finally, the fact that we see a band of light tells us that the stars, gas and dust that make up the galaxy are in the form of a flat disc. Figure 1 An all-sky view of the Milky Way. The major visible constituent of the Galaxy, about 96%, is made up of stars, with the remaining 4% split between gas ~ 3% and dust ~ 1%. Here "visible" means that we can detect them by electromagnetic radiation; visible, infrared or radio. As we will discuss in detail in the next lecture, "The Invisible Universe", we suspect that there is a further component of the Galaxy that we cannot directly detect called "dark matter".
    [Show full text]
  • Structure of the Draco Dwarf Spheroidal Galaxy
    CORE Metadata, citation and similar papers at core.ac.uk Provided by CERN Document Server Structure of the Draco Dwarf Spheroidal Galaxy Slawomir Piatek Dept. of Physics, New Jersey Institute of Technology, Newark, NJ 07102 E-mail address: [email protected] Carlton Pryor1 Dept. of Physics and Astronomy, Rutgers, the State University of New Jersey, 136 Frelinghuysen Rd., Piscataway, NJ 08854–8019 E-mail address: [email protected] Taft E. Armandroff National Optical Astronomy Observatory, P.O. Box 26732, Tucson, AZ 85726 E-mail address: tarmandroff@noao.edu and Edward W. Olszewski1 Steward Observatory, University of Arizona, Tucson, AZ 85721 Email address: [email protected] ABSTRACT This article studies the structure of the Draco dwarf spheroidal galaxy with an emphasis on the question of whether the spatial distribution of its stars has been affected by the tidal interaction with the Milky Way, using R- and V-band CCD photometry for eleven fields. The article reports coordinates for the center, a position angle of the major axis, and the ellipticity. It also reports the results of searches for asymmetries in the structure of Draco. These results, and searches for a “break” in the radial profile and for the presence of principal sequences of Draco in a color-magnitude diagram for regions more than 50 arcmin from the center, yield no evidence that tidal forces from the Milky Way have affected the structure of Draco. Subject headings: galaxies: dwarf — galaxies: individual (Draco) — galaxies: stellar content — galaxies: structure — galaxies: Local Group 1Visiting Astronomer, Kitt Peak National Observatory, National Optical Astronomy Observatory, which is operated by the Association of Universities for Research in Astronomy, Inc.
    [Show full text]