galaxies and cosmology dr nicola loaring salt/saao [email protected]
TRANSCRIPT
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Introduction Less than 100 years ago the Sun was considered to be the centre of the Universe!
Shapley, 1918, studying variable stars in globular clusters deduced size and scale of the Milky Way as well as our position within it.
Hubble resolved the Andromeda nebula into individual stars a few years later, and studied variable stars in it, proving Andromeda to be a galaxy outside our own. [2.5 million light years away]
Sun takes 225 MY to orbit the Galaxy, we’re out in the suburbs!
Twice as much mass lies outside the luminous parts of our galaxy that inside! (6x1011 MSun)
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30 kpc ~ 96,000 LY across
Normal Galaxies
M33 spiral galaxy M83 – Spiral galaxyalaxy
1pc =3x1013 km = 3.2 light years = 206,000AU
• Each galaxy is made of a few 100 billions of stars together with gas and dust
• Stars gather together by mutual gravitational attraction
• 70% spiral, 30% elliptical
• Size ~9kpc (32,000 LYs!)
• There are a few 100 billion galaxies in the Universe!
Galaxy classification
• NGC 1316
• The radio lobes span over one million light years
• 3C219
• Radio lobes span several hundred thousand light years
Jets and Lobes
M87.
This jet extends at least 5000 light years from the nucleus of M87
The Hubble Ultra-Deep Field
This is the most distant optical image taken to date using the HST
The galaxies you see are nearly 13 billion light yrs away
We see them as they looked just after the Universe was formed ~13.7 billion yrs ago
These galaxies taken from 10 days of observing and are 4 billion times fainter than can be seen with the naked eye
The Hubble Ultra Deep Field
• Distant galaxies as they were nearly 13 million years ago• Still busy forming and interacting
Definition of an active galaxy
Over ten billion (10,000,000,000) galaxies are visible with modern telescopes.
Stars produce most of the light in these galaxies.
Galaxies with luminosities 1000x greater than normal galaxies are called active galaxies.
Extra light is confined to the central 1pc (~3.3 LY) (smaller distance than to our nearest star).
Properties of QuasarsMost luminous objects in the Universe! Luminosities up to 1013 Lsun
Typical power of 1040W (~10 solar masses consumed per year).
More than 300,000 known from all sky surveys.
Despite being discovered at radio wavelengths, only 10% are radio loud, infact X-rays are the most efficient way to search for them!
Standard model of Active Galactic Nuclei
NLR 10pc – 1kpc BLR ~1pc
Close in – the dusty torus
Black Holes Central engines of AGN
and Quasars.
Fed by infalling stellar material surrounding the black hole.
Material forms an accretion disk before being sucked into the black hole
The Universe is really old
The oldest globular clusters are between around 11-13 billion years old.
The Big Bang
•According to scientists the Universe began ~14 billion years ago in a Hot Big Bang.
•At creation the Universe was infinitely hot and infinitely small.
•Time started when the Universe began- there is no before the Big Bang!
10-34 seconds : Matter forms Scores of different building block particles - quarks, leptons, photons, and neutrinos flood the universe (the size of a melon).
10-6 seconds : Protons and Neutrons formQuarks combine to form protons and neutrons (hadrons). Each is made of 3 quarks. T~109 K, size of our solar system.
1s - 3 minutes : Nuclei formProtons and neutrons combine to form the atomic nuclei of the lightest elements deuterium,hydrogen, helium and lithium. T is 10,000 MK at start and 1000 MK at end.
~ 300,000 years : Atoms formThe temperature has fallen to ~3000K, electrons and protons can hold together to begin forming hydrogen atoms. CMB radiation emitted. Size is 1/1000th of present day size.
~300 million years: First StarsStars UV radiation ionises the neutral hydrogen.
~1 billion years: First Galaxies1/5th its present size.
The early Universe
Timeline of the Universe
Cool enough for the first atoms
Observational evidence for the Big Bang
Four pillars of the Big Bang Model:
-Cosmic microwave background (CMB) -Expansion of the Universe-Abundance of the light elements-Formation of galaxies and large scale structure
The Cosmic Microwave Background: Theory
Blackbody background radiation is a natural consequence of the whole universe having been in thermal equilibrium at one particular past time
Continuous creation of radiation does not lead to a blackbody background see photons from different distances, created at different times,
with different redshifts superposition of several blackbody spectra with different
temperatures is not a blackbody
Predicted (before it was discovered) in 1949!
• ~380,000 yrs after the HBB the Universe cooled sufficiently for electrons and protons to form atoms.
• The matter and radiation then stopped interacting and radiation was free to travel to us.
Initially T~3000K, now cooled to2.7K due to the expansion of space.
Light from the “surface of last scattering” has been travelling for >12 B yrs and covered a distance of ~ 1 M B B miles!
The cosmic microwave background
The cosmic microwave background radiation
• Discovered in 1964 by Penzias and Wilson.
• The Earth is bathed in CMB at a temperature of 2.73K (-270C).
• Very smooth in all directions, temperature variations of only 1 part in 105
• The temperature fluctuations are due to density fluctuations in the “soup” of particles.
WMAP probe currently measuring the CMB
1992
2004
http://map.gsfc.nasa.gov/
CMB Observations• COBE (~1990) T = 2.73 K smooth black body
• Evidence for tiny, small-scale fluctuations expected from gathering of matter to form superclusters
Big Bang – Evidence II• Abundance of light elements
– H, D, He and trace amounts of Li produced in first 3 mins of the Universe
– Predicted amount of D, He and Li depends on density of ordinary matter, can compare with the amount observed in stars and galaxies.
– He is relatively insensitive to the density, expect ~24% of ordinary matter to be He produced in the BB in agreement with observations
– The other light elements are more sensitive and the overall density of ordinary matter must be ~4% of the critical density
– Heavier elements not formed in the BB because temp dropped too rapidly before they could be formed
– Complicated by the fact that these elements could also be produced later during stellar nucleosynthesis
Big Bang Nucleosynthesis
• Predictions from BB nucleosynthesis models closely match the observed relative abundances of the light elements
Doppler shifts using light waves
Colour coded image of the doppler shift of the FeXIV 5308 Å line from the Sun’s corona. Supercluster of distant
galaxies (right), as compared to the Sun (left).
The Unverse is expanding!Hubble’s Law
• In 1929 Hubble found that the recession velocity of galaxies is proportional to their distance:
• v = HD, where H is the Hubble constant.
• Modern measurements place H0 at 74.2 +/- 3.6 km/s/Mpc. (1 Mpc = 3 MLY)DEMO
Redshift and time
z z Age(z) Lookback Time (yr) (yr) 0.0 1.3e+10 0.0e+00 0.5 7.9e+09 4.8e+09 1.0 5.4e+09 7.3e+09 2.0 3.0e+09 9.7e+09 5.0 1.1e+09 1.2e+10 9.0 5.0e+08 1.2e+10 10 4.3e+08 1.2e+10
Build up of structure via gravity - Galaxies
• 1 Light Year = 63,255 AU
= 9500 billion km!
• Have 100s of billions of stars.
• Size ~30,000 LY.
• Mass ~10 Billion x Sun
M33 spiral galaxy M83 – Spiral galaxy
M32 - Elliptical galaxy
Clusters:
Sizes 3.3-33 M LY.
Mass ~ 1014 -1015 SM.
Several 1000 galaxies.
Galaxy groups & clusters
•Groups:
•< 50 galaxies.
•Sizes 3 to 6 MLY.
•Mass ~ 1013 SM.
Structure we see today, could not have formed already unless substantial “dark matter” is present. The dark matter collapses before ordinary matter because it is not subject to radiation pressure, which resists gravitational collapse.
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Large Scale Structure – thanks to gravity
QuickTime™ and aYUV420 codec decompressor
are needed to see this picture.
http://cosmicweb.uchicago.edu/filaments.html
Evidence for Dark Matter
The cluster includes the galaxies and a hot gas (tens of millions of degrees) detected in X-rays.
By studying the distribution and temperature of the hot gas we can measure how much it is being squeezed by gravity from all the material in the cluster.
There is 5x more material in clusters of galaxies than we would expect from the galaxies and hot gas we can see. Most of the matter in clusters of galaxies is invisible.
Gravitational Lensing
Curved SpacetimeDEMO
Universal acceleration
Because all white dwarfs achieve the same mass before exploding, they all achieve the same luminosity and can be used by astronomers as "standard candles”. Observing their apparent brightness -> distance
Knowing the distance to a SN, we know how long ago it occurred.
Measuring the redshift of the supernova, astronomers can determine how much the Universe has expanded since the explosion.
By studying many supernovae at different distances, astronomers can piece together a history of the expansion of the Universe.
In the 1990's astronomers found the supernovae to be fainter than expected. Hence, the expansion of the universe was accelerating!
This expansion requires energy
SNe as probes of expansionThe Universal expansion is currently accelerating!
Composition of the Universe
The Fate of the Universe• Dark energy introduced by Einstein, anti-gravity energy to stop collapse• Appears to dominate the total mass-energy content of the Universe
Cosmology still has a lot to answer!
We only understand 5% of the constituents of our universe!
We do not know what the dark matter is
We do not know what the dark energy is
We do not know the fate of our Universe