Richard E. Hughes Dark Matter & GLAST; p.1 GLAST is a satellite designed to measure the direction, energy & arrival time of celestial gamma rays Launch is in 2007 Purpose Study AGN’s Study GRB’s Search for Dark Matter Dark Matter?? What the heck is that?! Why are gamma rays helpful? What are gamma rays anyway? Gamma-ray Large Area Space Telescope

Richard E. Hughes Dark Matter & GLAST; p.2 Dark Matters….. This is luminous matterThis is dark matter It is tempting to look at the universe, seeing stars and galaxies, clusters of galaxies and come to the conclusion that what you SEE is the matter, and what you don’t see is empty space. But, you would be wrong! There is general agreement that, in fact, MOST of the matter in the universe is in a form that we can’t SEE. This matter is imaginatively referred to as “Dark Matter”.

Richard E. Hughes Dark Matter & GLAST; p.3 Rotation Velocities in Our Solar System The curve below is exactly what one expects if most of the mass is inside the orbits of the planets. In our case, most of the mass in the solar system is due to the sun. Another way of viewing things is to say that if you know the orbital speed of ANY planet, you can determine how much massive “stuff” must be INSIDE that orbit.

Richard E. Hughes Dark Matter & GLAST; p.4 The Milky Way Galaxy Our sun is in the Milky way galaxy, about 28,000 light-years from its center. The speed of the solar system relative to the galactic center is approximately 220 km/s. At this speed, it takes about 200 million years to make one complete revolution. A galaxy is composed of stars and other material which are held together by gravity. The name ‘Milky Way’ comes from the band of light that can be seen during dark nights in the summer. This band is actually an edge-on view of the galaxy, and it is believed that when viewed “head on” it is a spiral glaxy. The Celestial River

Richard E. Hughes Dark Matter & GLAST; p.5 The Milky Way Galaxy  The COBE satellite was designed to investigate a phenomenon called the Cosmic Microwave Background.  COBE is sensitive to infra-red (IR) wavelengths of light.  The Milky Way viewed in the visible, is obscured by dust.  However, viewed in the IR, the Milky Way shows a clear central bulge overlaying a thin disk, as expected of an edge-on view of a spiral galaxy:

Richard E. Hughes Dark Matter & GLAST; p.6 The Milky Way Galaxy The image shown is a rendition of what we believe the Milky Way galaxy looks like if it were viewed head on:  The radius is about 50,000 light-years  The sun is about 28,000 light-years from the center  Near the Orion arm  Between the arms Perseus and Sagittarius

Richard E. Hughes Dark Matter & GLAST; p.7 The Rotation Curve For the Milky Way The same sort of rotation curve can be made for the Milky Way galaxy. Given that the Sun is on the outer edge of the galaxy (about 2/3 out), we expect that most of the mass is inside the galactic radius of the Sun. So we should see a decreasing rotation curve, like we do for the solar system. But instead, it is FLAT (if not increasing).

Richard E. Hughes Dark Matter & GLAST; p.8 How about other galaxies? NGC 6503: Galaxy in Constellation Draco

Richard E. Hughes Dark Matter & GLAST; p.9 Yet another galaxy…

Richard E. Hughes Dark Matter & GLAST; p.10 Why are the rotation curves flat?  Stars and gas in the galactic disks follow circular orbits whose velocity depends on the inner mass only:  A flat rotation curve means that the total M(<r) increases linearly with r, while the total luminosity approaches a finite asymptotic limit as r increases. Clearly a large amount of invisible gravitating mass (more than 90% of the total mass in the case of the Milky Way and other examples) is needed to explain these flat rotation curves.  This invisible mass is referred to as DARK MATTER  Is there any other supporting evidence?

Richard E. Hughes Dark Matter & GLAST; p.11 Gravitational Lensing

Richard E. Hughes Dark Matter & GLAST; p.12 Example of Gravitational Lensing Foreground cluster of galaxies CL (constellation Pisces) Blue galaxy behind the cluster “lensed” copy of blue galaxy

Richard E. Hughes Dark Matter & GLAST; p.13 What is causing the Lensing? The majority of the dark matter is distributed broadly and smoothly in the cluster, covering a region on the sky more than 1.6 million light-years across. The mass of the individual cluster galaxies appears as pinnacles on this mountain of dark matter mass. Overall, the dark matter in the cluster outweighs all the stars in the cluster's galaxies by 250 times! From

Richard E. Hughes Dark Matter & GLAST; p.14 What and where is the dark matter? The dark matter can’t be in the central disk of galaxies. Why? Interstellar clouds would be much thinner (due to gravitational forces of the dark matter. So the dark matter must be in “halos” of the galaxies. What the dark matter is NOT: 1) Stars: even faint one would radiate some light. 2) Dust: we would not be able to see our own galaxy or others, since dust absorbs and scatters light What the dark matter MIGHT be: 1) Black holes 2) Dim, old white dwarfs which are no longer bright 3) Proto-stars in which fusion did not start 4) Some new form of elementary matter

Richard E. Hughes Dark Matter & GLAST; p.15 Searching for Dark Matter  If we believe that Dark Matter really does exist, how do we look for it?  Well, we need a model. And one which is pretty handy is the Standard Model!  Well, actually not the Standard Model, but a close relative, which involves something called “SuperSymmetry”  A particle predicted by the SuperSymmetry theory is called the Neutralino  This particle is predicted for reasons having NOTHING to do with dark matter, but – in a happy coincidence – it COULD BE that the neutralino is the mysterious source of Dark Matter.  Once the neutralino is made, it can’t decay into something else  UNLESS: it meets its antiparticle.

Richard E. Hughes Dark Matter & GLAST; p.16 The Neutralino  Postulates:  The dark matter particle is the neutralino  There are enough dark matter particles in the halo of galaxies that the dark matter particles will collide from time to time  Since the dark matter particle is its OWN anti-particle, when the particles collide, they will ANNIHILATE

Richard E. Hughes Dark Matter & GLAST; p.17 Seeing the Annihilation of the Neutralino  Annihilation of the dark matter particles  This will result in other particles  Sometimes only 2 photons (gamma rays) of very distinct energy (equal to the mass x c 2 ) of the dark matter particle  Sometimes a number of photons of lower energy  We can see these photons  Using telescopes on earth (if the energies are large)  Using satellites designed to see lower energy photons  lines 50 GeV 300 GeV GLAST is such a satellite.

Richard E. Hughes Dark Matter & GLAST; p.18 GLAST Mission GLAST measures the direction, energy & arrival time of celestial gamma rays GLAST is two instruments: - Large Area Telescope(LAT) measures gamma-rays in the energy range ~20 MeV - >300 GeV - Gamma-ray Burst Monitor(GBM) provides correlative observations of transient events in the energy range ~20 keV – 20 MeV Launch: March 2007 Orbit: 550 km, 28.5 o inclination Lifetime: 5 years (minimum)

Richard E. Hughes Dark Matter & GLAST; p.19 Why study  -rays ? Gamma-rays carry a wealth of information  -rays offer a direct view into Nature’s largest accelerators  the Universe is mainly transparent to  -rays: can probe cosmological volumes.  -rays readily interact in detectors, with a clear signature.  -rays are neutral: no complications due to magnetic fields; point directly back to sources, etc.

Richard E. Hughes Dark Matter & GLAST; p.20 GLAST is an International Mission Germany FranceSwedenItaly USAJapan NASA - DoE Partnership on LAT LAT is being built by an international team Si Tracker: Stanford, UCSC, Japan, Italy CsI Calorimeter: NRL, France, Sweden Anticoincidence: GSFC Data Acquisition System: Stanford, NRL, Ohio State GBM is being built by US and Germany Detectors: MPE

Richard E. Hughes Dark Matter & GLAST; p.21 GLAST LAT Collaboration United States  California State University at Sonoma  University of California at Santa Cruz - Santa Cruz Institute of Particle Physics  Goddard Space Flight Center – Laboratory for High Energy Astrophysics  Naval Research Laboratory  The Ohio State University  Stanford University – Hanson Experimental Physics Laboratory  Stanford University - Stanford Linear Accelerator Center  Texas A&M University – Kingsville  University of Washington  Washington University, St. Louis France  Centre National de la Recherche Scientifique / Institut National de Physique Nucl é aire et de Physique des Particules  Commissariat à l'Energie Atomique / Direction des Sciences de la Mati è re/ D é partement d'Astrophysique, de physique des Particules, de physique Nucl é aire et de l'Instrumentation Associ é e Italy  Istituto Nazionale di Fisica Nucleare  Istituto di Fisica Cosmica, CNR (Milan) Japanese GLAST Collaboration  Hiroshima University  Institute for Space and Astronautical Science  RIKEN Swedish GLAST Collaboration  Royal Institute of Technology (KTH)  Stockholm University 124 Members (including 60 Affiliated Scientists) 16 Postdoctoral Students 26 Graduate Students

Richard E. Hughes Dark Matter & GLAST; p.22 Launch of Satellite Satellite Launch: Delta II Rocket 891 to 2,142 kg (1,965 to 4,723 lb) to geosynchronous transfer orbit (GTO) and 2.7 to 6.0 metric tons (5,934 to 13,281 lb) to low-Earth orbit (LEO). used for deep-space explorations such as NASA's missions to Mars, a comet or near-Earth asteroids.

Richard E. Hughes Dark Matter & GLAST; p.23 Gamma-ray Large Area Space Telescope GLAST Mission  high-energy gamma-ray observatory; 2 instruments - Large Area Telescope (LAT) - Gamma-ray Burst Monitor (GBM)  launch (March 2006): Delta 2 class  orbit: 550 km, 28.5 o inclination  mission operations  science - LAT Collaboration - GBM Collaboration - Guest Observers  lifetime: 5 years (minimum) GLAST Observatory spacecraft LAT GBM GRB Coordinates Network Burst and transient Alerts Alerts Large loads TOO commands Routine Data LAT Data Spacecraft, GBM data Schedules Spacecraft data for archiving Status Command Loads Status Command Loads LAT Inst. Ops. Center LAT data handling Instrument performance Level 1 data processing; selected higher level processing Support LAT Collaboration Science Investigation Science Support Center Science scheduling Archiving Guest Observer Support Standard product processing Mission Ops Center Observatory safety Spacecraft health Commanding Mission scheduling Level 0 processing GBM data handling GBM Inst. Ops. Center Instrument performance Standard product processing GBM Data

Richard E. Hughes Dark Matter & GLAST; p.24 GLAST LAT Overview: Design e+e+ e–e–  Si Tracker pitch = 228 µm channels 12 layers × 3% X layers × 18% X layers Data acquisition Grid (& Thermal Radiators) Flight Hardware & Spares 16 Tracker Flight Modules + 2 spares 16 Calorimeter Modules + 2 spares 1 Flight Anticoincidence Detector Data Acquisition Electronics + Flight Software 3000 kg, 650 W (allocation) 1.8 m  1.8 m  1.0 m 20 MeV – 300 GeV CsI Calorimeter Hodoscopic array 8.4 X 0 8 × 12 bars 2.0 × 2.7 × 33.6 cm  cosmic-ray rejection  shower leakage correction ACD Segmented scintillator tiles efficiency  minimize self-veto

Richard E. Hughes Dark Matter & GLAST; p.25 GLAST LAT Overview: Design e+e+ e–e–  Si Tracker pitch = 228 µm channels 12 layers × 3% X layers × 18% X layers Data acquisition Grid (& Thermal Radiators) Flight Hardware & Spares 16 Tracker Flight Modules + 2 spares 16 Calorimeter Modules + 2 spares 1 Flight Anticoincidence Detector Data Acquisition Electronics + Flight Software 3000 kg, 650 W (allocation) 1.8 m  1.8 m  1.0 m 20 MeV – 300 GeV CsI Calorimeter Hodoscopic array 8.4 X 0 8 × 12 bars 2.0 × 2.7 × 33.6 cm  cosmic-ray rejection  shower leakage correction ACD Segmented scintillator tiles efficiency  minimize self-veto

Richard E. Hughes Dark Matter & GLAST; p.26 GLAST Burst Monitor (GBM)  The secondary instrument onboard is the GLAST Burst Monitor, or GBM. The GBM is designed to observe gamma ray bursts, which are sudden, brief flashes of gamma rays that occur about once a day at random positions in the sky. These bursts are still a mystery to astronomers; no one knows what causes them, or what physical forces are at work. All that is known is that they are among the most powerful explosions in the Universe. The GBM has such a large field-of-view that it will be able to see bursts from over 2/3 of the sky at one time, providing locations for follow-up observations of these enigmatic explosions. The GBM is composed of two sets of detectors Ð 12 sodium iodide (NaI) scintillators and two cylindrical bismuth germanate (BGO) detectors. When gamma rays interact with these crystalline detectors, they produce flashes of visible light, which the detector can use to locate the gamma-ray burst on the sky

Richard E. Hughes Dark Matter & GLAST; p.27 The Large Area Telescope (LAT)  The LAT will detect gamma rays by using a technique known as pair-conversion. When a gamma ray slams into a layer of tungsten in the detector, it creates a pair of subatomic particles (an electron and its anti-matter counterpart, a positron). These particles in turn hit another, deeper layer of tungsten, each creating further particles and so on. The direction of the incoming gamma ray is determined by tracking the direction of these cascading particles back to their source using high-precision silicon detectors. Furthermore, a separate detector counts up the total energy of all the particles created. Since the total energy of the particles created depends on the energy of the original gamma ray, counting up the total energy determines the energy of that gamma ray. In this way, GLAST will be able to make gamma-ray images of astronomical objects, while also determining the energy for each detected gamma ray. e+e+ e–e– 

Richard E. Hughes Dark Matter & GLAST; p.28 Gamma Ray Bursts  Gamma Ray Bursts are intense flashes of gamma rays lasting from fractions of a second to hours, some with fading afterglows visible for months. What are they?  collisions between highly dense neutron stars or black holes?  signatures of the birth of a black hole?  Example: GRB Distance: 10 billion light-years Size: emitting region is light- seconds across Power: at maximum up to 1,000,000,000,000,000,000 (quintillion) times the Sun's power or roughly equal to the energy released by 100 billion Suns in a year's time  GLAST should observe more than a 200 bursts per year, measuring energy spectra of bursts from a few keV to hundreds of GeV in the short time after onset when the majority of the high-energy is released BATSE map of its 2704 detected GRBs Artists conception of a GRB

Richard E. Hughes Dark Matter & GLAST; p.29 Active Galactic Nuclei (AGN)  AGN are a special class of glaxies that are the source of tremendous energy, shining with power equivalent to trillions of suns. It is believed that at the center of these objects there lies a supermassive black hole, which ejects jets of matter in opposite directions at nearly the speed of light.  If one of the jets is directed toward us the AGN is referred to as a Blazar  GLAST will detect thousands of blazars and will try to answer questions like:  How are the jets formed?  How is the matter in the jets accelerated to such fantastic speeds?  Is a billion-solar-mass black hole really the central power source? Hubble HeritageHubble Heritage image of M87 Schematic diagram of an AGN