Announcements
This presentation is the property of its rightful owner.
Sponsored Links
1 / 27

Announcements PowerPoint PPT Presentation


  • 40 Views
  • Uploaded on
  • Presentation posted in: General

Announcements. Projects are graded 3rd Midterm: Wednesday April 25th review session: Monday April 23rd, 6pm final projects due: Monday April 30th. Lecture 39: Dark Matter III – structure formation in the Universe. Structure formation in the Big-Bang model. How does structure form ?.

Download Presentation

Announcements

An Image/Link below is provided (as is) to download presentation

Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author.While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server.


- - - - - - - - - - - - - - - - - - - - - - - - - - E N D - - - - - - - - - - - - - - - - - - - - - - - - - -

Presentation Transcript


Announcements

Announcements

  • Projects are graded

  • 3rd Midterm: Wednesday April 25th

  • review session: Monday April 23rd, 6pm

  • final projects due: Monday April 30th

Astronomy 201 Cosmology - Lecture 39


Lecture 39 dark matter iii structure formation in the universe

Lecture 39:Dark Matter III –structure formation in the Universe

Astronomy 201 Cosmology - Lecture 39


Announcements

Structure formation in the Big-Bang model

Astronomy 201 Cosmology - Lecture 39


How does structure form

How does structure form ?

  • Wrinkles in the CMB: regions of higher and lower temperature

  • Those regions correspond to density fluctuations, regions of slightly higher/lower density than average

  • Gravitational instability

    • higher density  more mass in a given volume

    • more mass  stronger gravitational attraction

    • stronger gravitational attraction  mass is pulled in  even higher density

Astronomy 201 Cosmology - Lecture 39


Announcements

Astronomy 201 Cosmology - Lecture 39


Q what is it

Q: What is it ?

A: MACHOs or WIMPs

Astronomy 201 Cosmology - Lecture 39


Machos

MACHOs ?

  • MAssive Compact Halo Objects

  • Brown dwarfs (stars not massive enough to shine)

  • Dim white dwarfs (relics of stars like the Sun)

  • Massive black holes (stars that massive that even light cannot escape)

  • but: if the DM is really in MACHOs, something with the nucleosynthesis constraint must be wrong

Astronomy 201 Cosmology - Lecture 39


How can we see machos

How can we see MACHOs ?

  • Solution: monitor 10 million stars simultaneously

Astronomy 201 Cosmology - Lecture 39


How can we see machos1

How can we see MACHOs ?

Magnification due to gravitational lensing

There are not enough brown dwarfs to account for the dark matter in the Milky Way.

Alcock et al. 1993

Astronomy 201 Cosmology - Lecture 39


Wimps

WIMPs ?

  • Weakly Interacting Massive Particles

  • Massive neutrino

    • at least we know that it exists

    • we don’t know whether it has mass or not

    • hot dark matter (hot: moving at speeds near the speed of light)

  • Another (yet undiscovered) particle predicted by some particle physicists

    • cold dark matter (cold: moving much slower than the speed of light)

Astronomy 201 Cosmology - Lecture 39


Wimp candidate i massive neutrinos

WIMP candidate I: massive neutrinos

  • At least we know that they exist: + n  p+ + e-

  • We don’t know whether they have mass

  • In particle physics, masses are expressed in terms of their energy equivalent mc2[eV: electron volt]

  • 1 eV  1.810-33 g

    • electron: 512 keV

    • protron: 938 MeV

Astronomy 201 Cosmology - Lecture 39


Wimp candidate i massive neutrinos1

WIMP candidate I: massive neutrinos

  • What mass do we need to account for all the dark matter ?

    • There are~100neutrinos per cm3

    • A mass of20eVresults in0=0.3

  • Can we measure their mass ?

    • tricky …

    • use energy conservation. Measure all masses and velocities in the  + n  p+ + e- reaction with high precision. Difference between left and right hand side  neutrino mass

Astronomy 201 Cosmology - Lecture 39


Wimp candidate i massive neutrinos2

WIMP candidate I: massive neutrinos

  • Result: now clear detection, but an upper limit. The mass of the (electron) neutrino is less than a few eV  electron neutrino is ruled out as a dark matter candidate.

  • BUT: There are two more neutrino families, mu neutrinos and tau neutrinos (the muon and tauon are particles similar to the electron, but more massive and unstable)

  • a massive mu or tau neutrinos still must be considered

Astronomy 201 Cosmology - Lecture 39


Wimp candidate ii the least massive supersymmetric particle

WIMP candidate II: the least massive supersymmetric particle

  • Main goal of particle physics: to develop a theory that unifies the four forces of nature

  • Those models predict a whole zoo of particles, some of them are already detected, but most of them still very speculative. Most of these particles are unstable.

  • Supersymmetry is a particularly promising unifying theory

  • The least massive supersymmetric particle (neutralino) should be stable

Astronomy 201 Cosmology - Lecture 39


Wimp candidate ii the least massive supersymmetric particle1

WIMP candidate II: the least massive supersymmetric particle

  • It’s mass should be > 150 GeV, otherwise

    • its contribution would be irrelevant

    • it should already have been detected

  • But how to prove its existence ?

Astronomy 201 Cosmology - Lecture 39


How can we find cold wimps

How can we find cold WIMPs ?

  • Cryogenic (ultra cold) detectors

  • search for annual modulation of the signal

Astronomy 201 Cosmology - Lecture 39


Do we have already detected wimps

Do we have already detected WIMPs ?

Results are still very controversial and inconclusive

DAMA

collabor-

ation

Astronomy 201 Cosmology - Lecture 39


Can astronomy help to discriminate between neutrinos and neutralinos

Can astronomy help to discriminate between neutrinos and neutralinos ?

  • Neutrinos:

    • mass in the tens of eV  very low mass

    • very low mass  high velocities  “hot”

    • can travel several tens of Mpc over the age of the universe

  • Neutralinos

    • mass in the hundredst of GeV  very high mass

    • very high mass  low velocities  “cold”

    • cannot travel significant distances over the age of the universe

  • Neutrinos: Hot Dark Matter (HDM)

    • mass in the tens of eV  very low mass

    • very low mass  high velocities  “hot”

    • can travel several tens of Mpc over the age of the universe

  • Neutralinos Cold Dark Matter (CDM)

    • mass in the hundredst of GeV  very high mass

    • very high mass  low velocities  “cold”

    • cannot travel significant distances over the age of the universe

Astronomy 201 Cosmology - Lecture 39


Announcements

The spatial distribution of galaxies

  • Galaxies are not randomly distributed but correlated

  • Quantitative measure: two-point correlation function (r): excess probability (compared to random) to find a galaxy at distance r to another galaxy

Courtesy: Huan Lin

Astronomy 201 Cosmology - Lecture 39


Can astronomy help to discriminate between hot and cold dark matter

Can astronomy help to discriminate between hot and cold dark matter ?

HDM

CDM

Astronomy 201 Cosmology - Lecture 39


Structure formation hdm vs cdm

Structure formation: HDM vs CDM

  • Hot dark matter:

    • initial small scale structure (anything smaller than a galaxy cluster) washed out due to the high velocities of neutrinos

    • clusters and supercluster form first

    • galaxies form due to fragmentation of collapsing clusters and superclusters

  • top-down structure formation

Astronomy 201 Cosmology - Lecture 39


Structure formation hdm vs cdm1

Structure formation: HDM vs CDM

  • Cold dark matter:

    • plenty of small scale structure

    • small galaxies form first, clusters last

    • larger structures form due to merging of smaller structures

  • bottom-up or hierarchical structure formation

Astronomy 201 Cosmology - Lecture 39


Hierarchical structure formation

Hierarchical structure formation

Astronomy 201 Cosmology - Lecture 39


Structure formation hdm vs cdm2

Structure formation: HDM vs CDM

  • CDM fits observations much better than HDM

    • high-z galaxies are smaller

    • irregular shape of galaxy clusters indicate that they formed recently

    • there are only a very few clusters at high redshift, but many galaxies

    • two-point correlation function is much better reproduced

Astronomy 201 Cosmology - Lecture 39


A voyage through a cdm universe

A voyage through a CDM universe

Astronomy 201 Cosmology - Lecture 39


A voyage through a cdm universe1

A voyage through a CDM universe

Astronomy 201 Cosmology - Lecture 39


Announcements1

Announcements

  • Projects are graded

  • 3rd Midterm: Wednesday April 25th

  • review session: Monday April 23rd, 6pm

  • final projects due: Monday April 30th

Astronomy 201 Cosmology - Lecture 39


  • Login