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TheThe darkdark sideside ofof mattermatter François Mernier

[email protected] - Wallon Super Two biggest challenges for astronomers…

• Distance

• Mass Two biggest challenges for astronomers…

• Distance

• Mass The Solar System (+ Pluto…)

v v 47 km/s 13 km/s

Mercury Jupiter 35 km/s 10 km/s

Venus Saturn 30 km/s 7 km/s

Earth Uranus 24 km/s 5 km/s Mars Neptune 4 km/s Pluto Mass can be derived from velocity!

• Newton’s law: • Centripetal force =

M m

Isaac Newton (1685) Mass can be derived from velocity!

• Newton’s gravity law: • Centripetal force =

M m

Isaac Newton (1685) Mass can be derived from velocity!

(km/s)

50

40

Orbital velocity 30

20

10

0 1000 2000 3000 4000 5000 6000

Distance from centre (1000 000 km) Mass can be derived from velocity!

(km/s)

50 M = 2 x1030 kg 40

Orbital velocity = 20000000000 30 00000000000 000000000 kg 20

10

0 1000 2000 3000 4000 5000 6000

Distance from centre (1000 000 km) How about galaxies? How about galaxies?

Expected “rotation curve” How about galaxies?

Expected “rotation curve” How about galaxies?

Vera Rubin (1978) Expected “rotation curve”

Why do external stars move “too fast”?

“Visible” matter

“Dark” matter

Spherical halo around galaxies Beyond galaxies…

How to derive mass? Beyond galaxies…

How to derive mass? • 1) via velocities Mreal Beyond galaxies…

How to derive mass? • 1) via velocities Mreal • 2) via luminosity M visible (→ “count” stars) Beyond galaxies…

How to derive mass? • 1) via velocities Mreal • 2) via luminosity M visible (→ “count” stars) Mreal > 400 x Mvisible

Fritz Zwicky (1933)

$1 Million

What is “dark” matter made of? • Planets?

• Would require MANY of them, also far away from stars! • Inconsistent with our models of planetary formation… • Brown dwarfs?

• Astronomers have counted them (they still emit some light in infrared)… • But not enough to explain ! • Black holes? stars?

• Both are remnants from massive stars and supernovae… • Not observed in distant (=past) galaxies! • Supermassive black holes

• Co-evolve with galaxies (and form in / sink to their centre)… • Should cross the galaxy disk and eat some stars/gas… but not observed • Planets?

• Brown dwarfs?

• Black holes / neutron stars?

• Supermassive black holes?

Massive Compact Halo Objects (MACHOs) • …But does dark matter really exist? • …But does dark matter really exist?

• A bit of history…

Wtf ?!

Isaac Newton (1685) Sun

Mercury ?

There must be a hidden planet! (Vulcan) Urbain Le Verrier (1859) • …But does dark matter really exist?

• A bit of history…

Wtf ?!

Isaac Newton (1685) Sun

Mercury ?

There’s no “Vulcan”. Newton’s laws of gravitation were just incomplete Albert Einstein (especially in strong gravity (1915) fields). • …But does dark matter really exist?

• A bit of history…

Wtf ?!

Isaac Newton (1685) Sun

Mercury ?

There’s no “Vulcan”. Newton’s laws of gravitation were just incomplete Albert Einstein (especially in strong gravity (1915) fields).

Expected Expected Observed What if Newton’s laws of gravitation were incomplete also at very weak gravity fields?

Mordehai Milgrom Isaac Newton (1986) (1685)

Expected Observed What if Newton’s laws of gravitation were incomplete also at very weak gravity fields?

Mordehai Milgrom (1986)

Gravitational acceleration

Distance (R) What if Newton’s laws of gravitation were incomplete also at very weak gravity fields?

Mordehai Milgrom (1986) Threshold (a0) R

Gravitational acceleration

Distance (R)

“Modified Newtonian Dynamics” (MOND) What if Newton’s laws of gravitation were incomplete also at very weak gravity fields?

Expected “rotation curve” (MOND)

Mordehai Milgrom (1986)

Expected “rotation curve” (Newton)

“Modified Newtonian Dynamics” (MOND) What if Newton’s laws of gravitation were incomplete also at very weak gravity fields?

Expected “rotation curve” (MOND)

Mordehai Milgrom (1986)

Expected “rotation curve” (Newton)

“Modified Newtonian Dynamics” (MOND) What if Newton’s laws of gravitation were incomplete also at very weak gravity fields?

• “Ad hoc” theory, why would gravity behave so?

• “Dark” matter should always follow “visible” matter…

‣ Some galaxies have almost no dark matter, some others are almost entirely made of dark matter! NGC 1052-DF2 (almost no dark matter)

• …if dark matter really exists?

• What if Newton’s laws of gravitation were incomplete at very weak gravity fields too?

• “Ad hoc” theory, why would gravity behave so? • Some galaxies have almost no dark matter, some others are almost entirely made of dark matter!

van Dokkum et al. (2018) Dragonfly 44 (98% dark matter!)

van Dokkum et al. (2016) What if Newton’s laws of gravitation were incomplete also at very weak gravity fields?

• “Ad hoc” theory, why would gravity behave so?

• “Dark” matter should always follow “visible” matter…

‣ Some galaxies have almost no dark matter, some others are almost entirely made of dark matter!

‣ How to explain the Bullet Cluster? The Bullet Cluster The Bullet Cluster The Bullet Cluster The Bullet Cluster

(80% of the “visible” matter) Gravitational lensing

We can “map” dark matter! The Bullet Cluster The Bullet Cluster The Bullet Cluster

The cosmic microwave background Slightly cooler

Slightly hotter Microwaves: (almost) uniform emission in the sky… The cosmic microwave background Slightly cooler

Large scale fluctuations

Small scale fluctuations

Slightly hotter Microwaves: (almost) uniform emission in the sky… The cosmic microwave background Slightly cooler

Large scale fluctuations Small scale fluctuations

Slightly hotter Microwaves: (almost) uniform emission in the sky… The cosmic microwave background Slightly cooler

Large scale fluctuations Small scale fluctuations

Slightly hotter Microwaves: (almost) uniform emission in the sky… The cosmic microwave background Slightly cooler

80% of matter is “non-baryonic”! }

Large scale fluctuations Small scale fluctuations

Slightly hotter Microwaves: (almost) uniform emission in the sky… Also needed in cosmological simulations!

ILLUSTRIS Should we search for new particles?

• Weakly Interactive Massive Particles (WIMPs) • Supersymmetric particles (e.g. ) • (Sterile) neutrinos • • Gravitationally interacting massive particles

(GIMPs) Quarks

Standard model Bosons “Non-baryonic” dark matter Leptons Should we search for new particles?

XENON1T Large Hadron Collider (CERN) “Non-baryonic” dark matter Should we search for new particles?

CDMS

XENON1T Large Hadron Collider (CERN) “Non-baryonic” dark matter Should we search for new particles?

CDMS

IceCube XENON1T Large Hadron Collider (CERN) “Non-baryonic” dark matter Should we search for new particles?

CDMS EDELWEISS

IceCube XENON1T Large Hadron Collider (CERN) “Non-baryonic” dark matter Should we search for new particles?

No “dark matter particle”CDMS has been detected EDELWEISSso far! quite worrisome, given the great capabilities of accelerators and detectors…

IceCube XENON1T Large Hadron Collider (CERN) “Non-baryonic” dark matter But is MOND really dead…?

In galaxies, radial What if gravity did not acceleration of stars and of really exist as such, but was dark matter are remarkably the result of an emergent correlated… process?

Stacy McGaugh Work in progress… Erik Verlinde (2016) (2017)

McGaugh, Lelli & Schombert (2016) Verlinde (2017) Dark matter is NOT !

2 E = mc “Dark” matter

(Matter can be converted “Visible” into energy…) matter Dark energy

Albert Einstein (1905)

Dark energy is a problem in cosmology, required to explain the acceleration of the expansion of the Universe… Summary 1) What is the “dark matter” problem?

Stars Galaxies CMB

Stars and galaxies move too fast… They require some additional, invisible matter. Confirmed by the first light of the universe (cosmic microwave background).

2) What is that “dark matter” made of?

MACHOs WIMPs, axions, MOND neutrinos,…

Threshold R

Gravit. acceleration

Distance

We don’t know! Probably unknown particles, unless our understanding of gravitation is incomplete…