James Bullock @jbprime Universe of Galaxies (~ 10 -8 of observable - - PowerPoint PPT Presentation

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James Bullock @jbprime Universe of Galaxies (~ 10 -8 of observable - - PowerPoint PPT Presentation

Nov 13, 2023 317 likes •1.1k views

Cosmology & The Milky Way James Bullock @jbprime Universe of Galaxies (~ 10 -8 of observable part) Milky Way & Local Group Each dot is a galaxy ~100 million light years Why does the Universe look this way? Milky Way & Local Group

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Cosmology & The Milky Way

James Bullock

@jbprime

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Universe of Galaxies (~ 10-8 of observable part)

Each dot is a galaxy Milky Way & Local Group

~100 million light years

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Each dot is a galaxy Milky Way & Local Group

~100 million light years

Why does the Universe look this way?

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Why do galaxies have these shapes?

Each dot is a galaxy Milky Way & Local Group

~100 million light years

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Our Laboratory: The Local Group

~5 million light years

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Wally Pacholka/Astropics.com

Andromeda Galaxy Milky Way Mauna Kea, Hawaii.

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Wally Pacholka/Astropics.com

Andromeda Galaxy Milky Way Mauna Kea, Hawaii.

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Andromeda (M31)

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Rotation speed Distance from center

Vera Rubin 1969

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Dark Matter

Rotation speed Distance from center

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Cold Dark Matter Normal Matter 5% 25% Dark Energy 70%

Composition of the Cosmos

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Cosmic Microwave Background

WMAP (2003)

  • Temperature map of universe 300,000 yrs after Big Bang
  • Universe smooth to 1/100,000
  • Need extra mass to get clumpy universe today.

1990-2000’s

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Look-back time (Gyr) 200 million lt yrs

Allgood et al. 06 Dark Matter allows galaxies to grow:

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Map of real universe Simulated universe Each point = 1 galaxy

2 billion light years 2 billion light years

Springel et al.

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Map of real universe Simulated universe Broad brush: we seem to understand things

2 billion light years 2 billion light years

What about the details?

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The Milky Way in 2micron light

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The Milky Way in 2micron light

Satellite galaxies of the Milky Way

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The Milky Way in 2micron light

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The Milky Way in 2micron light

Sagittarius dwarf

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Sloan Digital Sky Ssurvey III (Koposov et al.)

The Milky Way in Star Counts

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Purcell, JSB, Tollerud, Rocha, Charkrabarti, Nature, 2011

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Purcell, JSB, Tollerud, Rocha, Charkrabarti, Nature, Sept. 2011

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Without Sag.

Sun

Sagittarius Dwarf ⇒ Spiralilty, Rings, Bar Evolution in the Galaxy

With Sag.

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⊙

? ? ?

Intermediate-scale spiral structure, similar to MW

Sgr Sgr

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Belokurov et al. 2006

100 degrees of sky

Size of full moon

More streams around the Milky Way

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JSB & Johnston 2005

Predicted accretion history of typical galaxy

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Data (+ models engineered to match)

Law & Majewski 06 Bullock & Johnston 05

Random LCDM realization

Halo Streams & Substructure

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Andromeda Galaxy (M31)

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McConnachie et al. 2009 M33 M31

Andromeda galaxy also surrounded by streams

Also: Guhathakurta et SPLASH

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Towards more detailed tests

Simulation Observed Universe

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250 million lt yrs

Miguel Rocha

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250 million lt yrs

Miguel Rocha

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250 million lt yrs

Miguel Rocha

1million lt yrs

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100,000 light years Shea Garrison-Kimmel

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Does the Milky Way look like this?

100,000 light years Shea Garrison-Kimmel

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Theory: N>>1000 Observation: Nbright~10 dark matter clumps (predicted) dwarf galaxies (observed)

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Theory: N>>1000 Observation: Nbright~10

“Missing Satellites Problem”

Klypin et al. 1999

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Theory: N>>1000 Observation: Nbright~10

Klypin et al. 1999

Maybe... only the biggest clumps have stars?

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Theory: N>>1000 Observation: Nbright~10

Bullock et al. 2000

Maybe... only the biggest clumps have stars?

Theory: N>>1000

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Theory: N>>1000 Observation: Nbright~10

Bullock et al. 2000

Maybe... only the biggest clumps have stars?

Theory: N>>1000

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  • 2. Measure dark

matter mass in each dwarf galaxy

  • 1. Predict dark

matter mass in each clump

  • 3. Compare
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Typical dwarf galaxy: about 5 million stars

3000 lt yrs

Use the mighty Keck telescope to measure speeds of the stars -- how much mass?

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Motions of stars => ~500 times more dark matter than visible!

Packed with Dark Matter

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Theory Data

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Theory Data

Predicted clumps are too dense to host any satellite The theory is broken?

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Maybe Cold Dark Matter is not so simple?

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Radius

1,500

Radius (light years)

15,000

DM Density (10-22 g/cm3) standard dark matter density profile (predicted) (~1 Hydrogen atom/cm3)

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Radius

1,500

Radius (light years)

15,000

DM Density (10-22 g/cm3) standard dark matter density profile (predicted) data data from galaxy rotation curves

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Theory

Radius (1000 light years) 15 30 45 60 Rotation speed (km/s)

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Radius

2,000

Radius (light years)

20,000

Density (10-22 g/cm3) data data

standard dark matter theory

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Radius

2,000

Radius (light years)

20,000

Density (10-22 g/cm3) data data New dark matter physics? Galaxy formation?

Flores & Primack 94

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Cold Dark Matter Normal Matter 5% 25% Dark Energy 70%

Composition of the Cosmos

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Cold Dark Matter Normal Matter 5% 25% Dark Energy 70%

What do we really know?

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Normal Matter 5%

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Normal Matter 5%

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Dark Matter 25%

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Dark Matter 25%

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Dark Matter 25%

Matches all large-scale data:

  • Single particle.
  • Only gravity.
  • No other interaction.
  • Mass > 10% proton mass
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Dark Matter 25%

Matches all large-scale data:

  • Single (lightest) particle.
  • Only gravity.
  • No other interaction (weak).
  • Mass > 10% proton mass

(~100 mp).

Reasonably well motivated

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Dark Matter 25%

Matches all large-scale data:

  • Single particle.
  • Only gravity.
  • No other interaction.
  • Mass > 10% proton mass

Could it be more complicated?

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Toy model: Self-interacting Dark Matter

Elastic scattering with: ¡σ/m ¡~ ¡1 ¡cm2 ¡/g ¡ ¡ ¡~ ¡(neutron-­‑neutron ¡sca-ering)

Γ = ρdm ⇣ σ m ⌘ vrms

Scattering rate:

25%

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Simula/ng ¡Self-­‑interac/ng ¡Dark ¡Ma9er

¡σ/m ¡= ¡1 ¡cm2 ¡/g

Standard ¡CDM

Self-­‑Interac/ng ¡CDM

250 million lt yrs

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¡σ/m ¡= ¡1 ¡cm2 ¡/g

250 million lt yrs

Iden/cal ¡large-­‑scale ¡structure

Simula/ng ¡Self-­‑interac/ng ¡Dark ¡Ma9er

Standard ¡CDM

Self-­‑Interac/ng ¡CDM

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¡σ/m ¡= ¡1 ¡cm2 ¡/g

Standard ¡CDM

Self-­‑Interac/ng ¡CDM

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¡σ/m ¡= ¡1 ¡cm2 ¡/g

Lower ¡central ¡densi/es, ¡ in ¡line ¡with ¡observa/ons.

Standard ¡CDM

Self-­‑Interac/ng ¡CDM

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Standard ¡CDM

Self-­‑Interac/ng ¡CDM

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Radius

2,000

Radius (light years)

20,000

Density (10-22 g/cm3) data data Standard Dark Matter Self-interacting DM

Rocha et al. 12; Peter et al. 12

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Normal Matter 5%

This piece of the pie is very interesting...

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Normal Matter 5% Dark Matter 25%

Maybe this one is too...

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Thanks.

James Bullock

@jbprime

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Belokurov et al. 2006

Not just star streams: new galaxies! 100 degrees of sky

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Probably ~100’s more faint dwarfs to be discovered

Stadel et al. 2009