Post on 23-Dec-2015
In this talk we'll see that :
We can only see about 1% of the Universe
The dark side
And ask:
What is the Universe made of?
The Milky Way --- our home galaxy
Dirbe infrared map of the Milky Way beautifully shows the Galactic disk and bulge...
The 'edge-on' Milky Way
The disk and bulge of the Galaxy are prominent at all wavelengths from gamma rays to radio...
... but that's only a tenth of the story.
Spiral galaxies rotate strangely
Emission lines from hot gaseous regions in the disk of a spiral galaxy allow its rotation to be measured.
Centre
This side of the galaxy is redshifted
This side is blueshifted
What we'd see with dark matter spectacles
Alternatives
Cold dark matter distribution as found in cosmological simulations of structure formation (Moore et al 2000)
I
Or maybe this ....
Alternatives
'Shroud' of dim white dwarfs in a thickened disk around the Galaxy (Gates and Gyuk 2001)
II
Or maybe this ....
Alternatives
Halo of supermassive black holes around the Galaxy (Ostriker and Lacey 1985)
III
Or maybe this ....
Alternatives
No dark matter --- our theory of gravity is wrong
IV
That's all folks, there isn't any more...
DARKSTAR : constraining the dark matter
Our home as we see it
If the dark matter is in the form of dim stars,we should see some near the Sun
If the dark matter is in the form of black holes, they could affect the Galactic disk
Studies done with the NASA/ESA Hubble Space Telescope and with ESA's Hipparcos satellite
Double check disk mass
Evidence: Clusters of galaxies
Clusters in galaxies move at higher speed
The visible mass of the galaxies themselves seems insufficient to hold them
X-rays from clusters of galaxies
The same goes for the hot, X-ray emitting gas in galaxy clusters
Simulations of the whole universe
Movie : density_flythru.mpg
Simulations of the universe must be quite dense in order for the right numbers of galaxies and clusters to form (when compared to observations)
Simulations of clusters of galaxies
Movie : xy.movie.mpg
Andromeda is headed our way!
Movie : merger.mpg
It's showtime, folks!
Movie : antobs.mpg
Movie : antobs.mpg
Movie : mice.mpg
Through a glass darkly...
Lenses map matter...
The bullet cluster
Highly significant cluster pair, because dark and visible matter are temporarily in different places (so their relative contributions can really be assessed)
Dark matter in cosmology
Dark matter in cosmology
Spying on the neighbours...
Your friend and mine, the Large Magellanic Cloud...
The DARKSTAR search for dim, low mass stars
... dead stars ... the 'white dwarfs'
... barely alive stars... 'red dwarfs'
Results with HST
HST ... the Hubble Space Telescope
Flynn, Gould and Bahcall searched for faint red stars in the Hubble Deep Field.
Stars in the HDF marked in yellow
None were found.
Many were expected if they comprise the dark matter.
Searching for dim, red stars
Astrophysical candidates - dim stars
Fast moving white dwarf star from Ibata et al, Nature, 2000
Results with HST and ground telescopes Searching for dim, blue stars
Flynn, Holopainen and Holmberg searched for faint blue stars in stellar motion catalogs
Very were found.
Many were expected if they comprise the dark matter.
It's probably not ... red dwarfs or white dwarfs
... dead stars ... the 'white dwarfs'
... barely alive stars... 'red dwarfs'
It's probably not ... the white dwarf shroud
Holopainen and Flynn 2003
Used new stellar motion surveys to search for dim white dwarfs
Can rule out normal white dwarfs in a shroud
Supermassive black holes...
Black holes, if they are heavy enough, cause the disk of the Galaxy to become thicker with time --- a process called disk heating.
Very massive black holes
Initially thin stellar disk
Supermassive black holes...
Heavy black holes destroy the Milky Way
Light black holes have no effect
Need a fine tuned compromise...
Disk has thickened
'Disk heating' observed
The European Space Agency's Hipparcos satellite
The European Space Agency's Hipparcos satellite has measured distances and spatial motions of 125,000 nearby stars with a huge increase in precision compared to a century of work done with telescopes on the ground
'Disk heating' observed and simulated
Simulated dark halo and GMCs
Required heating
Time [Gyr]
Kinetic
energy
Can be fine tuned to fit the Hipparcos data
Work well enough near the Sun and elsewhere in the disk...
BUT require special pleading to work in other galaxies
?
Hänninen and Flynn 2001, 2003
It's probably not ... supermassive black holes
The disk mass is well understood
Prediction for no disk dark matter
Hipparcos Observations
Holmberg and Flynn 2002, 2003
Observations match predictions very well; there is no missing matter in the disk…
Summary
Baryonic Dark Matter
• Particle physics has cause for optimism! The evidence is building against baryons as the dark matter in galaxies...