Dark matter and black holes over cosmic time

TOMMASO TREU

Our view of the Universe (2009)

Now… wear your dark matter goggles!!

Elliptical Galaxies. Simple?

MOVIE

A big dark surprise

• They contain supermassive black holes at their centers.

• The mass of the black hole is proportional to that of the stars in the galaxy and that of the dark matter around it! – MBH = 0.2% M* = 0.001% MDM

The local Universe

… are thought to form by mergers of spirals…

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are needed to see this picture.

Questions and puzzles

1. Do elliptical galaxies live in dark matter halos consistent with those predicted by the model?

2. Why is the mass of the black hole proportional to the mass of the stars and that of dark matter?

3. How do (stars) black holes and dark matter evolve over cosmic time?

Telescopes as time machines

Into the invisible

• How do we “see” dark matter?

– Gravitational lensing

• How do we “weigh” black holes?

– Reverberation mapping

What is Gravitational Lensing?Matter curves space…

What is Gravitational Lensing?…and can create multiple images

Image separation is a direct measurement of mass, luminous or dark!

Why is it called Lensing?

A DOUBLE EINSTEIN RING

A DOUBLE EINSTEIN RING:

GEOMETRY

OBSERVER

MAIN LENS(2 billion light yrs)

INNER RING(6 billion light yrs)

OUTER RING(11 billion light yrs)

How likely?

More unlikely than winning two consecutive bets

on a single number at roulette!

The most precise mass density profile measurement

Dark matter halo!

(Atoms)

Really? Is there dark matter?

Cosmic collisions and dark matter

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Black holes on a “scale”?

Reverberation Mapping

Ring of gas with radius r

Gas along line of sight to observer will appear to respond with no delay

Gas that is furthest from observer will appear to have response delayed by 2r/c

Mean lag time is r/c, I.e radius / speed of light

Example: Arp 151

SDSS

The local Universe

Summary• Our standard cosmological model is undergoing rigorous

testing– We need to understand how galaxies and black holes form

• Things that appear to work include:– Galaxies live in dark matter halos. – Dark matter appears to be real although it would be good to know

what particle it is made of

• Things that we do not understand include:– Why are galaxies “isothermal”?– How do black holes know of their host galaxy and viceversa?– The most massive galaxies and their black holes appear to have

completed their evolution before the lower mass systems. In the model we naively expect the opposite.

• Is the model fundamentally wrong or is this because we do not understand the “gastrophysics”?

The end