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...