Dark Matter ASTR 2120 Sarazin Bullet Cluster of Galaxies - Dark Matter Lab
Mergers: Test of Dark Matter vs. Modified Gravity Gas behind DM Galaxies DM = location of gravity Gas = location of most baryons Whatever theory of gravity, not coming from where baryons are Require dark matter (not MOND or modified gravity)
What is Dark Matter? In principle, could be anything large
Detectability of Matter Visible matter is stars, gas, & dust Is that all there is? Problem is that these are easiest to detect 1. Gas: individual atoms, strong spectral lines (10 0 atoms) 2. Dust: a < λ, atoms act coherently (10 9 atoms) 3. Stars: fusion reactions, large luminosity (10 57 atoms) Cannot detect basketball, asteroids, avocados,... Dark Matter?
What is Dark Matter? In principle, could be anything large but not a star (avocados?) Astrophysically plausible: Stellar mass black holes? If made by death of stars, too many supernovae, too many heavy elements
What is Dark Matter? In principle, could be anything large but not a star (avocados?) Astrophysically plausible: Stellar mass black holes? Planets, brown dwarfs, etc. MACHOs = MAssive Compact Halo Objects
MACHO Project Detect MACHOs from Milky Way due to gravitational lensing of background stars
MACHO Project Detect MACHOs from Milky Way due to gravitational lensing of background stars background stars = Large Magellanic Cloud (LMC)
MACHO Project Detect MACHOs from Milky Way due to gravitational lensing of background stars background stars = Large Magellanic Cloud (LMC) Detect lensing brightening, same in all colors
MACHO Project Detect MACHOs from Milky Way due to gravitational lensing of background stars background stars = Large Magellanic Cloud (LMC) Detect lensing brightening, same in all colors Found expected number of brown dwarfs, planets, binary stars No MACHO dark matter
What is Dark Matter? In principle, could be anything large but not a star (avocados?) Astrophysically plausible: Stellar mass black holes? Planets, brown dwarfs, etc. MACHOs
General Problem with Baryonic Dark Matter Big Bang nucleosynthesis correctly gives composition of ordinary matter in Universe today Hydrogen, helium, trace amounts of 2 H, 3 He Gives very accurate measurement of amount of ordinary matter in Universe at t ~ 1 sec Too little to be dark matter (but agrees with amounts of matter in clusters of galaxies)
What is Dark Matter? In principle, could be anything large but not a star (avocados?) Astrophysically plausible: Stellar mass black holes? Planets, brown dwarfs (MACHOs) Weakly interacting, stable elementary particles made in Big Bang Gravity but no light or other interactions Neutrinos, axions, photinos, Is Dark Matter non-interacting particles? Dwarf galaxies suggest self-interacting DM?
Mergers: Test of Gravitational Physics Bullet Cluster 1E0657-56 Image = galaxies Red = X-rays = gas Blue = lensing mass = gravity Gas behind DM Galaxies Markevitch et al. 2004 Clowe et al. 2004
Mergers: Test of Collisional Dark Matter Gas behind DM Galaxies Gas collisional fluid Galaxies collisionless particles Limit on self-collision crosssection of DM σ/m (DM) 0.5 cm 2 /g < 5 cm 2 /g required for cores in dwarf galaxies
Made in Big Bang Particle Dark Matter Hot Dark Matter v ~ c when formed Example: neutrinos Problem: hard to get into cluster, form superclusters clusters galaxies stars But, galaxies old, structure appears to grow small to large Cold Dark Matter v << c when formed Example: axions Structure grows hierarchically, small to large But, what particle(s) makes up dark matter?
Hope for the Future LHC (Large Hadron Collider) Produce some of the (so far hypothetic) particle candidates, constrain properties
Hope for the Future LHC (Large Hadron Collider) Direct detection on Earth with cryogenic detectors Detect dark matter particles from Milky Way Halo Detect motion of Earth through Dark Matter Halo
Hope for the Future LHC (Large Hadron Collider) Direct detection on Earth with cryogenic detectors Detect decay or annihilation radiation from Dark Matter particles in nearby galaxies Particle 2 photons + X Particle + antiparticle 2 photons Gamma rays or X-rays XMM-Newton Fermi
Active Galactic Nuclei (AGNs) ASTR 2120 Sarazin Centaurus A - the Nearest AGN (Chandra image from UVa X-ray group)
Active Galaxies?
Non-stellar emission Active Galaxies Related to center of galaxy Here, I ll not include starburst galaxies = rapid star formation Most galaxies have some activity, but weak
Center of Milky Way
Carl Seyfert, 1940 s Spiral galaxies Bright star-like nuclei L AGN ~ L galaxy Seyfert Galaxies
Carl Seyfert, 1940 s Spiral galaxies Bright star-like nuclei Non-thermal continuum Seyfert Galaxies radio AGN log F ν star gamma-rays log ν
Carl Seyfert, 1940 s Spiral galaxies Bright star-like nuclei Non-thermal continuum f ν ν -α Seyfert Galaxies
Seyfert Galaxies Carl Seyfert, 1940 s Spiral galaxies Bright star-like nuclei Non-thermal continuum f ν ν -α Very broad spectrum, radio to gamma-rays
Seyfert Galaxies
Seyfert Galaxies Carl Seyfert, 1940 s Spiral galaxies Bright star-like nuclei Non-thermal continuum f ν ν -α Very broad spectrum, radio to gamma-rays Best way to detect all types of AGNs is in X-ray emission
Seyfert Galaxies Carl Seyfert, 1940 s Spiral galaxies Bright star-like nuclei L AGN ~ L galaxy Non-thermal continuum f ν ν -α Very broad spectrum, radio to gamma-rays Often highly polarized Synchrotron emission
Synchrotron Emission - Review Electrons spiral around magnetic field Accelerate -> make light Requires relativistic electrons (v ~ c) magnetic field Properties Polarized B Power-law spectrum, I ν -α, α ~ 0.7 B
Seyfert Galaxies Carl Seyfert, 1940 s Spiral galaxies Bright star-like nuclei L AGN ~ L galaxy Non-thermal continuum f ν ν -α Very broad spectrum, radio to gamma-rays Often highly polarized Synchrotron emission Requires electrons with E >> GeV
Carl Seyfert, 1940 s Spiral galaxies Bright star-like nuclei L AGN ~ L galaxy Non-thermal continuum Highly Variable Seyfert Galaxies
Seyfert Galaxies
Carl Seyfert, 1940 s Spiral galaxies Bright star-like nuclei L AGN ~ L galaxy Non-thermal continuum Highly Variable Time scale > hours Seyfert Galaxies
Size Limit - Review D D c dt 10 2 AU Similar in size to Solar System
Seyfert Galaxies - Cont. Emission lines H, He, C, O, etc. like H II regions Often very highly ionized, including X-ray lines Ionized by UV & X-rays from AGN Blazars (BL Lac) very weak emission lines
Seyfert Galaxies
Seyfert Galaxies
Seyfert Galaxies - Cont. Emission lines H, He, C, O, etc. like H II regions Often very highly ionized, including X-ray lines Ionized by UV & X-rays from AGN Blazars (BL Lac) very weak emission lines Narrow and Broad Lines
Seyfert Galaxies
Seyfert Galaxies - Cont. Emission lines H, He, C, O, etc. like H II regions Often very highly ionized, including X-ray lines Ionized by UV & X-rays from AGN Blazars (BL Lac) very weak emission lines Narrow and Broad Lines Narrow lines Include forbidden lines, low density n < 10 3 cm -3 Broad lines Width due to Doppler shifts, motions ~ 5000 km/s No broad forbidden lines, dense, n ~ 10 9 cm -3 Highly variable
Seyfert Galaxies
Type 1 vs. Type 2 AGN Type 1 Seyfert 1, Broad-Line Radio Galaxies, Quasars 1 Both Broad and Narrow Lines Type 2 Seyfert 2, Narrow-Line Radio Galaxies, Quasars 2 Only Narrow Lines
Radio Loud vs. Radio Quiet AGN Radio Quiet 90% of AGN Most Seyferts Radio Loud 10% of AGN Radio Galaxies radio IR visible UV X-ray
Radio Galaxies Karl Jansky: pioneers radio astronomy, pre-world War II 1931 - radio from the MW center Post WWII, rapid progress, due in part to radar research Detect Sun, Jupiter, Sgr A (MW center), Cas A (SN remnant) Also, some strange sources at high Galactic latitude
Radio Galaxies Cygnus A
Radio Galaxies Double radio lobes Nothing interesting in lobes at any other frequency Something completely new in Universe, unrelated to galaxies? Radio nucleus
Double radio lobes Radio nucleus Radio Galaxies Giant elliptical galaxy, often BCG, center = radio nucleus radio optical
Radio Galaxies Centaurus A - with merging elliptical galaxy
Double radio lobes Radio nucleus Radio Galaxies Giant elliptical galaxy, center = radio nucleus Very large, 100 s kpc to Mpc across radio lobe elliptical galaxy radio lobe ~ Mpc
Radio Galaxies Double Radio Lobes Radio nucleus Giant elliptical galaxy, center = radio nucleus Very large, 100 s kpc to Mpc across Luminous, L radio ~ 10 11 L ~ L (optical galaxy) Power-law radio spectra f ν ν -α Highly polarized in radio Synchrotron Emission requires lots of highly relativistic electrons
Radio Galaxy Energy Problem Requires lots of highly relativistic electrons High energy electrons lose energy rapidly, due to synchrotron emission t energy loss << D/c Radio lobes can t simply have come from galaxy Need energy source for lobes radio lobe elliptical galaxy radio lobe D
Radio Galaxy Energy Problem 1. Some thing in lobes (some kind of engine, e.g. black hole)? But, nothing ever found in lobes radio lobe elliptical galaxy radio lobe 2. Energy source is nucleus of galaxy Energy carried out to lobes as kinetic energy of fluid in jets
Radio Jets Very Large Array (VLA) - NRAO - near Socorro, NM
Radio Jets Cygnus A
Radio Jets Cygnus A
Radio Jets
Radio Jets
Radio Jets
Radio Jets
Nucleus makes jets Radio Jets Jets carry kinetic energy Jets stopped by intergalactic gas, inflate radio lobes Jets accelerate relativistic particles, including e s