richard e. hughes dark matter & glast; p.1 glast is a satellite designed to measure the...

Dark Matter & GLAST; p.1Richard E. Hughes

GLAST is a satellite designed to measure the direction, energy & arrival time of celestial gamma rays

Launch is in 2007Purpose

Study AGN’sStudy GRB’sSearch 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


Dark Matters…..

This is luminous matter This 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”.


Rotation Velocities in Our Solar System

r

GMrv r2

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.


The Milky Way GalaxyOur 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


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:


The Milky Way GalaxyThe 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 centerNear the Orion armBetween the arms

Perseus and Sagittarius


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).


How about other galaxies?NGC 6503: Galaxy in Constellation Draco


Yet another galaxy…


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?


Gravitational Lensing


Example of Gravitational Lensing

Foreground cluster of galaxies CL0024+1654 (constellation Pisces)

Blue galaxy behind the cluster

“lensed” copy of blue galaxy


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 http://www.bell-labs.com/org/physicalsciences/projects/darkmatter/darkmatter1.html


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 forcesof 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 holes2) Dim, old white dwarfs which are no longer bright3) Proto-stars in which fusion did not start4) Some new form of elementary matter


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.


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


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 c2) 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

lines50 GeV

300 GeV

GLAST is such a satellite.


GLAST MissionGLAST 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, 28.5o inclination

Lifetime: 5 years (minimum)

LAT FoV

GBM FoV


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.


GLAST is an International Mission

Germany

FranceSweden Italy

USA Japan

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


GLAST LAT CollaborationUnited 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. LouisFrance Centre National de la Recherche Scientifique / Institut National de Physique Nucléaire et

de Physique des Particules Commissariat à l'Energie Atomique / Direction des Sciences de la Matière/ Département

d'Astrophysique, de physique des Particules, de physique Nucléaire et de l'Instrumentation Associée

Italy Istituto Nazionale di Fisica Nucleare Istituto di Fisica Cosmica, CNR (Milan)

Japanese GLAST Collaboration Hiroshima University Institute for Space and Astronautical Science RIKENSwedish GLAST Collaboration Royal Institute of Technology (KTH) Stockholm University

124 Members (including 60 Affiliated Scientists)

16 Postdoctoral Students

26 Graduate Students


Launch of SatelliteSatellite 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.


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, 28.5o inclination

mission operations

science

- LAT Collaboration

- GBM Collaboration

- Guest Observers

lifetime: 5 years (minimum)

GLAST Observatory• spacecraft• LAT• GBM

GRBCoordinates

Network

Burst and transient Alerts

AlertsLarge loadsTOO commands

Routine Data

LAT Data

Spacecraft, GBM data

Schedules

Spacecraft data for archiving

StatusCommand Loads

StatusCommand Loads

LAT Inst. Ops. CenterLAT data handling

Instrument performance

Level 1 data processing; selected higher level processing

Support LAT Collaboration Science Investigation

Science Support CenterScience schedulingArchivingGuest Observer Support Standard product processing

Mission Ops CenterObservatory safetySpacecraft healthCommandingMission schedulingLevel 0 processingGBM data handling

GBM Inst. Ops. CenterInstrument performanceStandard product processing

GBM Data


GLAST LAT Overview: Design

e+ e–

Si Trackerpitch = 228 µm8.8 105 channels12 layers × 3% X0

+ 4 layers × 18% X0

+ 2 layers

Data acquisition

Grid (& Thermal Radiators)

Flight Hardware & Spares16 Tracker Flight Modules + 2 spares16 Calorimeter Modules + 2 spares1 Flight Anticoincidence DetectorData Acquisition Electronics + Flight Software

3000 kg, 650 W (allocation)

1.8 m 1.8 m 1.0 m

20 MeV – 300 GeV

CsI CalorimeterHodoscopic array8.4 X0 8 × 12 bars

2.0 × 2.7 × 33.6 cm cosmic-ray rejection shower leakage correction

ACDSegmented scintillator tiles0.9997 efficiency

minimize self-veto


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


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–


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 990123

Distance: 10 billion light-yearsSize: emitting region is light-seconds acrossPower: 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


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 Heritage image of M87

Schematic diagram of an AGN

richard e. hughes dark matter & glast; p.1 glast is a satellite designed to measure the...

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