1.3 Accretion Power in Astrophysics Accretion Power in Astrophysics the Strong Gravitational Force of the Compact Object Attracts Matter from the Companion
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Exploring Exoplanet Populations with NASA's Kepler Mission
SPECIAL FEATURE: PERSPECTIVE PERSPECTIVE SPECIAL FEATURE: Exploring exoplanet populations with NASA’s Kepler Mission Natalie M. Batalha1 National Aeronautics and Space Administration Ames Research Center, Moffett Field, 94035 CA Edited by Adam S. Burrows, Princeton University, Princeton, NJ, and accepted by the Editorial Board June 3, 2014 (received for review January 15, 2014) The Kepler Mission is exploring the diversity of planets and planetary systems. Its legacy will be a catalog of discoveries sufficient for computing planet occurrence rates as a function of size, orbital period, star type, and insolation flux.The mission has made significant progress toward achieving that goal. Over 3,500 transiting exoplanets have been identified from the analysis of the first 3 y of data, 100 planets of which are in the habitable zone. The catalog has a high reliability rate (85–90% averaged over the period/radius plane), which is improving as follow-up observations continue. Dynamical (e.g., velocimetry and transit timing) and statistical methods have confirmed and characterized hundreds of planets over a large range of sizes and compositions for both single- and multiple-star systems. Population studies suggest that planets abound in our galaxy and that small planets are particularly frequent. Here, I report on the progress Kepler has made measuring the prevalence of exoplanets orbiting within one astronomical unit of their host stars in support of the National Aeronautics and Space Admin- istration’s long-term goal of finding habitable environments beyond the solar system. planet detection | transit photometry Searching for evidence of life beyond Earth is the Sun would produce an 84-ppm signal Translating Kepler’s discovery catalog into one of the primary goals of science agencies lasting ∼13 h. -
Formation of TRAPPIST-1
EPSC Abstracts Vol. 11, EPSC2017-265, 2017 European Planetary Science Congress 2017 EEuropeaPn PlanetarSy Science CCongress c Author(s) 2017 Formation of TRAPPIST-1 C.W Ormel, B. Liu and D. Schoonenberg University of Amsterdam, The Netherlands ([email protected]) Abstract start to drift by aerodynamical drag. However, this growth+drift occurs in an inside-out fashion, which We present a model for the formation of the recently- does not result in strong particle pileups needed to discovered TRAPPIST-1 planetary system. In our sce- trigger planetesimal formation by, e.g., the streaming nario planets form in the interior regions, by accre- instability [3]. (a) We propose that the H2O iceline (r 0.1 au for TRAPPIST-1) is the place where tion of mm to cm-size particles (pebbles) that drifted ice ≈ the local solids-to-gas ratio can reach 1, either by from the outer disk. This scenario has several ad- ∼ vantages: it connects to the observation that disks are condensation of the vapor [9] or by pileup of ice-free made up of pebbles, it is efficient, it explains why the (silicate) grains [2, 8]. Under these conditions plan- TRAPPIST-1 planets are Earth mass, and it provides etary embryos can form. (b) Due to type I migration, ∼ a rationale for the system’s architecture. embryos cross the iceline and enter the ice-free region. (c) There, silicate pebbles are smaller because of col- lisional fragmentation. Nevertheless, pebble accretion 1. Introduction remains efficient and growth is fast [6]. (d) At approx- TRAPPIST-1 is an M8 main-sequence star located at a imately Earth masses embryos reach their pebble iso- distance of 12 pc. -
Water, Habitability, and Detectability Steve Desch
Water, Habitability, and Detectability Steve Desch PI, “Exoplanetary Ecosystems” NExSS team School of Earth and Space Exploration, Arizona State University with Ariel Anbar, Tessa Fisher, Steven Glaser, Hilairy Hartnett, Stephen Kane, Susanne Neuer, Cayman Unterborn, Sara Walker, Misha Zolotov Astrobiology Science Strategy NAS Committee, Beckmann Center, Irvine, CA (remotely), January 17, 2018 How to look for life on (Earth-like) exoplanets: find oxygen in their atmospheres How Earth-like must an exoplanet be for this to work? Seager et al. (2013) How to look for life on (Earth-like) exoplanets: find oxygen in their atmospheres Oxygen on Earth overwhelmingly produced by photosynthesizing life, which taps Sun’s energy and yields large disequilibrium signature. Caveats: Earth had life for billions of years without O2 in its atmosphere. First photosynthesis to evolve on Earth was anoxygenic. Many ‘false positives’ recognized because O2 has abiotic sources, esp. photolysis (Luger & Barnes 2014; Harman et al. 2015; Meadows 2017). These caveats seem like exceptions to the ‘rule’ that ‘oxygen = life’. How non-Earth-like can an exoplanet be (especially with respect to water content) before oxygen is no longer a biosignature? Part 1: How much water can terrestrial planets form with? Part 2: Are Aqua Planets or Water Worlds habitable? Can we detect life on them? Part 3: How should we look for life on exoplanets? Part 1: How much water can terrestrial planets form with? Theory says: up to hundreds of oceans’ worth of water Trappist-1 system suggests hundreds of oceans, especially around M stars Many (most?) planets may be Aqua Planets or Water Worlds How much water can terrestrial planets form with? Earth- “snow line” Standard Sun distance models of distance accretion suggest abundant water. -
Formation of the Solar System (Chapter 8)
Formation of the Solar System (Chapter 8) Based on Chapter 8 • This material will be useful for understanding Chapters 9, 10, 11, 12, 13, and 14 on “Formation of the solar system”, “Planetary geology”, “Planetary atmospheres”, “Jovian planet systems”, “Remnants of ice and rock”, “Extrasolar planets” and “The Sun: Our Star” • Chapters 2, 3, 4, and 7 on “The orbits of the planets”, “Why does Earth go around the Sun?”, “Momentum, energy, and matter”, and “Our planetary system” will be useful for understanding this chapter Goals for Learning • Where did the solar system come from? • How did planetesimals form? • How did planets form? Patterns in the Solar System • Patterns of motion (orbits and rotations) • Two types of planets: Small, rocky inner planets and large, gas outer planets • Many small asteroids and comets whose orbits and compositions are similar • Exceptions to these patterns, such as Earth’s large moon and Uranus’s sideways tilt Help from Other Stars • Use observations of the formation of other stars to improve our theory for the formation of our solar system • Use this theory to make predictions about the formation of other planetary systems Nebular Theory of Solar System Formation • A cloud of gas, the “solar nebula”, collapses inwards under its own weight • Cloud heats up, spins faster, gets flatter (disk) as a central star forms • Gas cools and some materials condense as solid particles that collide, stick together, and grow larger Where does a cloud of gas come from? • Big Bang -> Hydrogen and Helium • First stars use this -
University of Groningen Evaluating Galactic Habitability Using High
University of Groningen Evaluating galactic habitability using high-resolution cosmological simulations of galaxy formation Forgan, Duncan; Dayal, Pratika; Cockell, Charles; Libeskind, Noam Published in: International Journal of Astrobiology DOI: 10.1017/S1473550415000518 IMPORTANT NOTE: You are advised to consult the publisher's version (publisher's PDF) if you wish to cite from it. Please check the document version below. Document Version Final author's version (accepted by publisher, after peer review) Publication date: 2017 Link to publication in University of Groningen/UMCG research database Citation for published version (APA): Forgan, D., Dayal, P., Cockell, C., & Libeskind, N. (2017). Evaluating galactic habitability using high- resolution cosmological simulations of galaxy formation. International Journal of Astrobiology, 16(1), 60–73. https://doi.org/10.1017/S1473550415000518 Copyright Other than for strictly personal use, it is not permitted to download or to forward/distribute the text or part of it without the consent of the author(s) and/or copyright holder(s), unless the work is under an open content license (like Creative Commons). The publication may also be distributed here under the terms of Article 25fa of the Dutch Copyright Act, indicated by the “Taverne” license. More information can be found on the University of Groningen website: https://www.rug.nl/library/open-access/self-archiving-pure/taverne- amendment. Take-down policy If you believe that this document breaches copyright please contact us providing details, and we will remove access to the work immediately and investigate your claim. Downloaded from the University of Groningen/UMCG research database (Pure): http://www.rug.nl/research/portal. -
Pulsar Physics Without Magnetars
Chin. J. Astron. Astrophys. Vol.8 (2008), Supplement, 213–218 Chinese Journal of (http://www.chjaa.org) Astronomy and Astrophysics Pulsar Physics without Magnetars Wolfgang Kundt Argelander-Institut f¨ur Astronomie der Universit¨at, Auf dem H¨ugel 71, D-53121 Bonn, Germany Abstract Magnetars, as defined some 15 yr ago, are inconsistent both with fundamental physics, and with the (by now) two observed upward jumps of the period derivatives (of two of them). Instead, the class of peculiar X-ray sources commonly interpreted as magnetars can be understood as the class of throttled pulsars, i.e. of pulsars strongly interacting with their CSM. This class is even expected to harbour the sources of the Cosmic Rays, and of all the (extraterrestrial) Gamma-Ray Bursts. Key words: magnetars — throttled pulsars — dying pulsars — cavity — low-mass disk 1 DEFINITION AND PROPERTIES OF THE MAGNETARS Magnetars have been defined by Duncan and Thompson some 15 years ago, as spinning, compact X-ray sources - probably neutron stars - which are powered by the slow decay of their strong magnetic field, of strength 1015 G near the surface, cf. (Duncan & Thompson 1992; Thompson & Duncan 1996). They are now thought to comprise the anomalous X-ray pulsars (AXPs), soft gamma-ray repeaters (SGRs), recurrent radio transients (RRATs), or ‘stammerers’, or ‘burpers’, and the ‘dim isolated neutron stars’ (DINSs), i.e. a large, fairly well defined subclass of all neutron stars, which has the following properties (Mereghetti et al. 2002): 1) They are isolated neutron stars, with spin periods P between 5 s and 12 s, and similar glitch behaviour to other neutron-star sources, which correlates with their X-ray bursting. -
Why Should We Care About TRAPPIST-1?
PUBLISHED: 27 MARCH 2017 | VOLUME: 1 | ARTICLE NUMBER: 0104 news & views EXOPLANETS Why should we care about TRAPPIST-1? The discovery of a system of six (possibly system we’ve found with terrestrial planets seven) terrestrial planets around the tightly packed together and in resonance. TRAPPIST-1 star, announced in a paper Their orbits are also all co-planar, as the by Michaël Gillon and collaborators image shows, and luckily for us this orbital (Nature 542, 456–460; 2017) attracted a plane passes through the line of sight great deal of attention from researchers between us and TRAPPIST-1: all these as well as the general public. Reactions planets are ‘transiting’. This is much more ranged from the enthusiastic — already than a simple technical detail, as it allows us hypothesizing a string of inhabited to characterize all their atmospheres — an planets — to those who felt that it essential step to understand their climate didn’t add anything substantial to our and propensity for habitability. current knowledge of exoplanets and Finally and maybe most importantly, was ultimately not worth the hype. The these planets are distributed over all of cover of the Nature issue hosting the the three zones related to different phases paper (pictured), made by Robert Hurt, (IPAC) HURT NASA/JPL-CALTECH/ROBERT of water, as cleverly represented by the a visualization scientist at Caltech, is a illustration. However, this information, fine piece of artwork, but it also helps us They can thus be called ‘terrestrial’ without linked to the concept of habitable or in assessing the actual relevance of the any qualms about terminology. -
Progenitors of Magnetars and Hyperaccreting Magnetized Disks
Feeding Compact Objects: Accretion on All Scales Proceedings IAU Symposium No. 290, 2012 c International Astronomical Union 2013 C. M. Zhang, T. Belloni, M. M´endez & S. N. Zhang, eds. doi:10.1017/S1743921312020340 Progenitors of Magnetars and Hyperaccreting Magnetized Disks Y. Xie1 andS.N.Zhang1,2 1 National Astronomical Observatories, Chinese Academy Of Sciences, Beijing, 100012, P. R.China email: [email protected] 2 Key Laboratory of Particle Astrophysics, Institute of High Energy Physics, Chinese Academy of Sciences, Beijing, 100012, P. R. China email: [email protected] Abstract. We propose that a magnetar could be formed during the core collapse of massive stars or coalescence of two normal neutron stars, through collecting and inheriting the magnetic fields magnified by hyperaccreting disk. After the magnetar is born, its dipole magnetic fields in turn have a major influence on the following accretion. The decay of its toroidal field can fuel the persistent X-ray luminosity of either an SGR or AXP; however the decay of only the poloidal field is insufficient to do so. Keywords. Magnetar, accretion disk, gamma ray bursts, magnetic fields 1. Introduction Neutron stars (NSs) with magnetic field B stronger than the quantum critical value, 2 3 13 Bcr = m c /e ≈ 4.4 × 10 G, are called magnetars. Observationally, a magnetar may appear as a soft gamma-ray repeater (SGR) or an anomalous X-ray pulsar (AXP). It is believed that its persistent X-ray luminosity is powered by the consumption of their B- decay energy (e.g. Duncan & Thompson 1992; Paczynski 1992). However, the formation of strong B of a magnetar remains unresolved, and the possible explanations are divided into three classes: (i) B is generated by a convective dynamo (Duncan & Thompson 1992); (ii) B is essentially of fossil origin (e.g. -
Testing Quantum Gravity with LIGO and VIRGO
Testing Quantum Gravity with LIGO and VIRGO Marek A. Abramowicz1;2;3, Tomasz Bulik4, George F. R. Ellis5 & Maciek Wielgus1 1Nicolaus Copernicus Astronomical Center, ul. Bartycka 18, 00-716, Warszawa, Poland 2Physics Department, Gothenburg University, 412-96 Goteborg, Sweden 3Institute of Physics, Silesian Univ. in Opava, Bezrucovo nam. 13, 746-01 Opava, Czech Republic 4Astronomical Observatory Warsaw University, 00-478 Warszawa, Poland 5Mathematics Department, University of Cape Town, Rondebosch, Cape Town 7701, South Africa We argue that if particularly powerful electromagnetic afterglows of the gravitational waves bursts detected by LIGO-VIRGO will be observed in the future, this could be used as a strong observational support for some suggested quantum alternatives for black holes (e.g., firewalls and gravastars). A universal absence of such powerful afterglows should be taken as a sug- gestive argument against such hypothetical quantum-gravity objects. If there is no matter around, an inspiral-type coalescence (merger) of two uncharged black holes with masses M1, M2 into a single black hole with the mass M3 results in emission of grav- itational waves, but no electromagnetic radiation. The maximal amount of the gravitational wave 2 energy E=c = (M1 + M2) − M3 that may be radiated from a merger was estimated by Hawking [1] from the condition that the total area of all black hole horizons cannot decrease. Because the 2 2 2 horizon area is proportional to the square of the black hole mass, one has M3 > M2 + M1 . In the 1 1 case of equal initial masses M1 = M2 = M, this yields [ ], E 1 1 h p i = [(M + M ) − M ] < 2M − 2M 2 ≈ 0:59: (1) Mc2 M 1 2 3 M From advanced numerical simulations (see, e.g., [2–4]) one gets, in the case of comparable initial masses, a much more stringent energy estimate, ! EGRAV 52 M 2 ≈ 0:03; meaning that EGRAV ≈ 1:8 × 10 [erg]: (2) Mc M The estimate assumes validity of Einstein’s general relativity. -
The Planetary Luminosity Problem:" Missing Planets" and The
Draft version March 27, 2020 Typeset using LATEX twocolumn style in AASTeX62 The Planetary Luminosity Problem: \Missing Planets" and the Observational Consequences of Episodic Accretion Sean D. Brittain,1, ∗ Joan R. Najita,2 Ruobing Dong,3 and Zhaohuan Zhu4 1Clemson University 118 Kinard Laboratory Clemson, SC 29634, USA 2National Optical Astronomical Observatory 950 North Cherry Avenue Tucson, AZ 85719, USA 3Department of Physics & Astronomy University of Victoria Victoria BC V8P 1A1, Canada 4Department of Physics and Astronomy University of Nevada, Las Vegas 4505 S. Maryland Pkwy. Las Vegas, NV 89154, USA (Received March 27, 2020; Revised TBD; Accepted TBD) Submitted to ApJ ABSTRACT The high occurrence rates of spiral arms and large central clearings in protoplanetary disks, if interpreted as signposts of giant planets, indicate that gas giants form commonly as companions to young stars (< few Myr) at orbital separations of 10{300 au. However, attempts to directly image this giant planet population as companions to more mature stars (> 10 Myr) have yielded few successes. This discrepancy could be explained if most giant planets form \cold start," i.e., by radiating away much of their formation energy as they assemble their mass, rendering them faint enough to elude detection at later times. In that case, giant planets should be bright at early times, during their accretion phase, and yet forming planets are detected only rarely through direct imaging techniques. Here we explore the possibility that the low detection rate of accreting planets is the result of episodic accretion through a circumplanetary disk. We also explore the possibility that the companion orbiting the Herbig Ae star HD 142527 may be a giant planet undergoing such an accretion outburst. -
Strong Accretion on a Deuterium-Burning Brown Dwarf? F
Astronomy & Astrophysics manuscript no. GY11* c ESO 2010 June 27, 2010 Strong accretion on a deuterium-burning brown dwarf? F. Comeron´ 1, L. Testi1, and A. Natta2 1 ESO, Karl-Schwarzschild-Strasse 2, D-85748 Garching bei Munchen,¨ Germany e-mail: [email protected] 2 Osservatorio Astrofisico di Arcetri, INAF, Largo E. Fermi 5, I-50125 Firenze, Italy Received ; accepted ABSTRACT Context. The accretion processes that accompany the earliest stages of star formation have been shown in recent years to extend to masses well below the substellar limit, and even to masses close to the deuterium-burning limit, suggesting that the features characteristic of the T Tauri phase are also common to brown dwarfs. Aims. We discuss new observations of GY 11, a young brown dwarf in the ρ Ophiuchi embedded cluster. Methods. We have obtained for the first time low resolution long-slit spectroscopy of GY 11 in the red visible region, using the FORS1 instrument at the VLT. The spectral region includes accretion diagnostic lines such as Hα and the CaII infrared triplet. Results. The visible spectrum allows us to confirm that GY 11 lies well below the hydrogen-burning limit, in agreement with earlier findings based on the near-infrared spectral energy distribution. We obtain an improved derivation of its physical parameters, which −3 suggest that GY 11 is on or near the deuterium-burning phase. We estimate a mass of 30 MJup, a luminosity of 6 × 10 M , and a temperature of 2700 K. We detect strong Hα and CaII triplet emission, and we estimate from the latter an accretion rate M˙ acc = −10 −1 9:5 × 10 M yr , which places GY 11 among the objects with the largest M˙ acc=M∗ ratios measured thus far in their mass range. -
Lecture 32 Planetary Accretion –
Lecture 32 Planetary Accretion – Growth and Differentiation of Planet Earth Reading this week: White Ch 11 (sections 11.1 -11.4) Today – Guest Lecturer, Greg Ravizza 1. Earth Accretion 2. Core Formation – to be continued in Friday’s lecture Next time The core continued, plus, the origin of the moon GG325 L32, F2013 Growth and Differentiation of Planet Earth Last lecture we looked at Boundary Conditions for earth's early history as a prelude to deducing a likely sequence of events for planetary accretion. Today we consider three scenarios for actual accretion: homogeneous condensation/accretion, followed by differentiation – Earth accretes from materials of the same composition AFTER condensation, followed by differentiation heterogeneous condensation/accretion (partial fractionation of materials from each other) before and during planetary buildup – Earth accretes DURING condensation, forming a differentiated planet as it grows. something intermediate between these two end-members GG325 L32, F2013 1 Growth and Differentiation of Planet Earth Both homogeneous and heterogeneous accretion models require that the core segregates from the primitive solid Earth at some point by melting of accreted Fe. The molten Fe sinks to the Earth’s center because it is denser than the surrounding silicate rock and can flow through it in the form of droplets. However, the original distribution of the Fe and the size and character of the iron segregation event differ between these two models. GG325 L32, F2013 Heterogeneous accretion Earth builds up first from cooling materials (initially hot and then cool). This requires a very rapid build up of earth, perhaps within 10,000 yrs of the initiation of condensation.