Discovery of rays from Star-Forming Galaxies

New class of nonthermal sources/gamma-ray galaxies(concept of temperature breaks down at high energies)

From cosmic-ray interactions, not black holes

How to accelerate energetic particles by natural processes?

Fermi particle acceleration mechanism

Fermilab, Batavia, ILEnrico Fermi (1901-1954)

Charles Dermer, Naval Research Laboratory2009 Fermi Conference Press conference, Feb. 2, 2009

Gamma Ray Galaxies: Black-Hole Powered

Two classes: 1. Active galaxies: Nearly 700 GeV,1 25 TeV; including 7 GeV and TeV

radio galaxies2. Star forming galaxies: Milky Way, LMC, others?

LAT 1 year sky image2

1talk, B. Lott2talk, J. Ormes

Gamma-ray luminosity of blazars: > trillion Solar luminosities

Gamma Ray Galaxies: Cosmic-ray/supernova powered

Two classes: 1. Active galaxies: Nearly 700 GeV,1 25 TeV; including 7 GeV and TeV

radio galaxies2. Star-forming galaxies: Milky Way, LMC, others?

LAT 1 year sky image2

1talk, B. Lott2talk, J. Ormes

Gamma-ray luminosity of Milky Way: ~100,000 Solar luminosities

Why is this important?

• Solve the problem of the origin of the cosmic radiation• Cosmic rays: energetic cosmic particles composed mainly of protons and ions • Cosmic rays: an important particle background in the space radiation environment

1. Cannot be trapped in the Solar cavity

2. Motions bent by magnetic field: do not point back to their sources

3. Cosmic rays make gamma rays by colliding with gas and dust

4. Cosmic rays are believed to be accelerated by supernova remnants

5. Identifying sites of cosmic ray acceleration in the Milky Way by gamma rays is hard because of “forest and trees” problem

6. Starburst galaxies should be more gamma-ray luminous than normal galaxies

Cosmic rays: the most energetic particles in the universeSources of

– Light elements Li, Be, B– Galactic radio emission – Galactic gamma-ray emission– Galactic pressure– Terrestrial 14C– Genetic mutations– Radiation effects on satellites

Discovery of cosmic rays by Victor Hess in 1912

The -ray/cosmic-ray connection

Nearby, low luminosity star-forming gamma-ray galaxies (millions x Solar luminosity) :

powered by supernovae explosions and collapse to neutron stars?

Distant, highly luminous active gamma-ray galaxies (trillions x Solar luminosity) :

powered by black holes?

Why so many detected black-hole powered gamma-ray galaxies (distant and therefore very luminous), and so few detected star-forming gamma-ray galaxies (nearby and therefore weak)?

Fermi mechanism predicts that highest energy particles made by sources with largest compactness = luminosity/size

Large compactness found in stellar core collapse to a neutron star forming supernovae and

supernova remnants

TeV ray/keV X-ray image of SNR RX J1713.7−3946

Sources of the highest energy radiations

Very highest energy radiations, including ultra-high energy cosmic rays, made by black holes1. stellar core collapse to a black hole (gamma ray burst)2. rotating supermassive black holes3. microquasars in galaxies

Huge compactness found near accreting black holes, especially if rotating

Ultra-high energy cosmic rays from Centaurus A?

Backup Slides

New Eyes in the Gamma-ray Sky paint a new picture of the universe

Fermi Gamma-ray Space Telescope: launched 11 June 2008

Very Energetic Radiation Imaging Telescope Array System (VERITAS)First light of 4-telescope array in 2007

Fermi LAT measures GeV (giga, or Billion electron Volts) photons

in scanning modeVERITAS (HESS, MAGIC) measures

TeV (trillion electron Volt) photonsin pointing mode

Fermi Large Area Telescope(LAT) and Gamma ray Burst Monitor (GBM)

Gamma Ray Galaxies: Large Magellanic Cloud

Previously detected with the EGRET Experiment on the Compton Observatory, establishing that GeV cosmic rays are not universal

Fermi mapping of the LMC shows distribution of sources of cosmic rays

First GeV map of star-forming galaxy other than Milky Way

Strong gamma-ray emission near 30 Doradus

Gamma Ray Galaxies: Large Magellanic Cloud

Previously detected with the EGRET Experiment on the Compton Observatory, establishing that GeV cosmic rays are not universal

Fermi mapping of the LMC shows distribution of sources of cosmic rays

First GeV map of star-forming galaxy other than Milky Way

Strong gamma-ray emission near 30 Doradus

Described by Jürgen Knödlseder

Discovery of Gamma-ray Emitting Starburst Galaxies

Starburst galaxies M82 and NGC 253 (about 10 Million lt-yrs)

(supernova rate 10 × Milky Way’sgas mass 2 × less than Milky Way)

Why not Andromeda (M31)?

Described by Keith BechtolDescribed by Niklas Karlsson