Dark Matter & Dark Energy

Home , Dark matter halo, Draco Supercluster, Galaxy rotation curve, Laniakea Supercluster

Northeastern Illinois University

Greg Anderson Department of Physics & Astronomy Northeastern Illinois University

Winter-Spring 2020

c 2012-2020 G. Anderson Introduction to Astronomy – slide 1 / 90 Northeastern Illinois Outline University

Overview Dark Matter What is Dark Matter? Structure Hubble’s Law Our Accelerating Universe Review

c 2012-2020 G. Anderson Introduction to Astronomy – slide 2 / 90 Northeastern Illinois University

Overview A Great Unknown Pie Chart Visible Matter in the Universe Coma Cluster

Dark Matter What is Dark Matter? Structure Overview Hubble’s Law Our Accelerating Universe

Review

c 2012-2020 G. Anderson Introduction to Astronomy – slide 3 / 90 Northeastern Illinois A Great Unknown University

Q What is the universe made of? A Mostly, we do not know!

The vast majority of the universe can not be “seen”, it is composed of dark matter and dark energy.

c 2012-2020 G. Anderson Introduction to Astronomy – slide 4 / 90 Northeastern Illinois What is the Universe made of? University

Dark Matter 24% Ordinary Matter 4.6%: ∼ Outside Stars: 3.8% Stars: 0.6%

Dark Energy 71.4% ∼

The mass of dark matter in galaxies, clusters of galaxies, and the universe is ﬁve to six times the mass of ordinary matter.

c 2012-2020 G. Anderson Introduction to Astronomy – slide 5 / 90 Northeastern Illinois Visible Matter in the Universe University

Visible matter: stars, gas, dust There is more mass in gas than in stars. On large scales, > 100 1000 Mpc, matter appears∼ − to be isotropic and homogeneous.

c 2012-2020 G. Anderson Introduction to Astronomy – slide 6 / 90 Northeastern Illinois The Coma Cluster University

Large cluster, over 1000 galaxies, 99 Mpc from Earth.

Visible Light X-ray Image M (6 to 7)M gas ≈ stars c 2012-2020 G. Anderson Introduction to Astronomy – slide 7 / 90 Northeastern Illinois University

Overview

Dark Matter Dark Matter & Dark Energy Q: “Dark” Matter? Early Dark Matter Discoveries Citations Zwicky (1933) Evidence for Dark Matter Dark Matter Merry-Go-Round Planet Speeds Rotation Curves Milky Way Dark Matter Halo Andromeda Rubin 16.07 The Andromeda Galaxy (M31) Expectations vs. Observations Q: Rotation Curves? Other Spirals Q: Rotation without DM? Milky Way Q: c Dark2012-2020 Matter G. Anderson Introduction to Astronomy – slide 8 / 90 Distribution? Northeastern Illinois Dark Matter & Dark Energy University

We know very little about 95% of the universe which is dark invisible.

Dark matter is the invisible mass which surrounds galaxies and galactic clusters. The presence of dark matter is inferred by its gravitational eﬀects on observable stars, gas, galaxies, ....

Dark energy is the energy which is causing the expansion of the universe to accelerate.

dark energy = cosmological constant = vacuum energy

c 2012-2020 G. Anderson Introduction to Astronomy – slide 9 / 90 Northeastern Illinois Q: “Dark” Matter? University

Why do we call dark matter ”dark”? A) It absorbes light B) It is dark in color. C) It emits little or no radiation of any wavelength.

D) It blocks out the light of stars in a galaxy.

c 2012-2020 G. Anderson Introduction to Astronomy – slide 10 / 90 Northeastern Illinois Q: “Dark” Matter? University

Why do we call dark matter ”dark”? A) It absorbes light B) It is dark in color. C) It emits little or no radiation of any wavelength. D) It blocks out the light of stars in a galaxy.

c 2012-2020 G. Anderson Introduction to Astronomy – slide 10 / 90 Northeastern Illinois Early Dark Matter Discoveries University

1933 Zwicky measures radial velocities of eight galaxies in the Coma cluster and concludes M M . dark ≫ luminous 1935 Smith confirms Zwickly’s results for the Virgo cluster 1939 Babcock (M31) & 1940 Oort (NGC 3115) find unexpectedly large amounts of “dark” matter in spiral galaxies. 1959 Kahn & Wolter concluded that most of the mass of the Local Group exists in some invisible form. 1970 Rubin and Ford measure rotation curve of M31 and find evidence for dark matter. 1975 Roberts & Whitehurst observed the 21 cm line in M31 extending the flat rotation curve to 30 kpc.

c 2012-2020 G. Anderson Introduction to Astronomy – slide 11 / 90 Northeastern Illinois Citations Zwicky (1933) University

Year No. Citations

1955-59 2 1960-64 6 1965-69 5 1970-74 2 1975-89 63 1990-99 71

c 2012-2020 G. Anderson Introduction to Astronomy – slide 12 / 90 Northeastern Illinois Evidence for Dark Matter University

From individual galaxies • – Rotation curves of spiral galaxies – Broadening of spectral lines in elliptical galaxies

Clusters of galaxies • – Velocities of galaxies – Temperature of hot gas – Gravitational lensing

Structure formation • Temperature ﬂuctuations in the CMB • Primordial nucleosynthesis •

c 2012-2020 G. Anderson Introduction to Astronomy – slide 13 / 90 Northeastern Illinois Merry-Go-Round University

Rotation Curve A plot of orbital speed versus orbital distance from the center of rotation.

v Cbc bc bc bc B A B C bc speed Abc

distance r

v = ω r ×

c 2012-2020 G. Anderson Introduction to Astronomy – slide 14 / 90 Northeastern Illinois Orbital Speeds of Planets University

12 vp =2πr v =2π r =2π r ⇒ p r3/2 10 bc Mercury

8 bc Venus bc 2π GM 6 v = = ⊙ bc √r q r Mars (AU/years)

v 4 Jupiterbc Saturn bc Uranus 2 bc Neptunebc

0 0 10r (AU) 20 30

c 2012-2020 G. Anderson Introduction to Astronomy – slide 15 / 90 Northeastern Illinois Rotation Curves University M(r) = mass inside radius r.

b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b GM(r) b b b b b b b b b b b b b vb (r)= b b b b b b r b q b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b bb b b b b b b b b b b b b b b b b b b b b b b b b b b bb b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b bb b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b bb b b b b b b b b b b b b b b b b b bb b b b b b b b b b b b b b b bb b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b bb b b b b b b b bb b b b b b bb b b b b b b b b b b b b b b b b b b b b b b b b b b b b b bb b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b r b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b bb b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b uniformb b densityb b b b b b b b b b b b b b b b b b b b bb b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b decreasingb density b b b b b b b 2 b b b b b b b rv b b b b b b b b b b M(r)= b G b b b b b b b b

c 2012-2020 G. Anderson Introduction to Astronomy – slide 16 / 90 Northeastern Illinois Milky Way Dark Matter Halo University

Dark Matter Halo

b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b bb b b b b b b b b b b b b b b b b b b b b b b b b b bb b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b Modern estimates: halo b b b b b b b b b b b b b b b b b b b b b b b bb b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b mass 10 times the disk b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b mass.

c 2012-2020 G. Anderson Introduction to Astronomy – slide 17 / 90 M31: The Andromeda Galaxy Northeastern Illinois Vera Rubin’s Observational Result University

In the 1970s Vera Rubin determined rotational speeds of galaxies by measuring the doppler shift H-alpha emission from HII regions. These clouds of ionized hydrogen move with the stars and other visible matter.

She found the orbital velocities remained the same with increasing distance instead of decreasing. This required a huge, invisible mass exerting the gravitational force necessary explain those ﬂat rotation curves.

c 2012-2020 G. Anderson Introduction to Astronomy – slide 19 / 90

Northeastern Illinois The Andromeda Galaxy (M31) University

Most of the visible mass in M31 lies within Rs 6 kpc. Rotation curve ﬂat out to r = 30 kpc. ≈

Rubin and Ford (1970, ApJ, 159, 379) Roberts and Whitehurst (1975, ApJ, 201, 327).

c 2012-2020 G. Anderson Introduction to Astronomy – slide 21 / 90 Northeastern Illinois Expectations vs. Observations University

GM(r) Orbital Speed: v(r)= q r

rv2 Mass inside radius r: M(r)= G

v(r) Predition with Dark Matter Halo Predition without Dark Matter

c 2012-2020 G. Anderson Introduction to Astronomy – slide 22 / 90 Northeastern Illinois Q: Rotation Curves? University

How are rotation curves of spiral galaxies determined for distances beyond where starlight can be detected? A) by extrapolation of the measured rotation curve B) by observations of the 21 cm line of atomic hydrogen C) by observations of spectral lines emitted by dark matter D) by watching the galaxies rotate over a period of decades E) by measuring the broadening of the galaxy’s

c 2012-2020absorption G. Anderson lines Introduction to Astronomy – slide 23 / 90 Northeastern Illinois Q: Rotation Curves? University

c 2012-2020E) by G. Anderson measuring the broadening of theIntroduction galaxy’s to Astronomy – slide 23 / 90 absorption lines Northeastern Illinois Other Spirals University

c 2012-2020 G. Anderson Introduction to Astronomy – slide 24 / 90 Northeastern Illinois Q: Rotation without DM? University

Spiral galaxy rotation curves are generally fairly ﬂat out to large distances. Suppose that spiral galaxies did not contain dark matter. How would their rotation curves be diﬀerent?

A) The rotation curve would look the same with or without the presence of dark matter.

B) The orbital speeds would fall oﬀ sharply with increasing distance from the galactic center.

C) The orbital speeds would rise upward with increasing distance from the galactic center, rather than remaining approximately constant.

D) The rotation curve would be a straight, upward sloping diagonal line, like the rotation curve of a merry-go-round.

c 2012-2020 G. Anderson Introduction to Astronomy – slide 25 / 90 Northeastern Illinois Q: Rotation without DM? University

Spiral galaxy rotation curves are generally fairly ﬂat out to large distances. Suppose that spiral galaxies did not contain dark matter. How would their rotation curves be diﬀerent?

A) The rotation curve would look the same with or without the presence of dark matter.

B) The orbital speeds would fall oﬀ sharply with increasing distance from the galactic center.

C) The orbital speeds would rise upward with increasing distance from the galactic center, rather than remaining approximately constant.

D) The rotation curve would be a straight, upward sloping diagonal line, like the rotation curve of a merry-go-round.

c 2012-2020 G. Anderson Introduction to Astronomy – slide 25 / 90 Dark Matter Halo

The distribution of the dark matter in a spiral galaxy is A) approximately spherical and about the same size as the visible galaxy halo. B) approximately spherical and about ten times the size of the visible galaxy halo. C) predominantly concentrated in the spiral arms.

c 2012-2020 G. Anderson Introduction to Astronomy – slide 27 / 90 Northeastern Illinois Q: Dark Matter Distribution? University

c 2012-2020 G. Anderson Introduction to Astronomy – slide 27 / 90 Northeastern Illinois Doppler Eﬀect University v

∆λ v λ ≈ c

Applet

c 2012-2020 G. Anderson Introduction to Astronomy – slide 28 / 90 Northeastern Illinois Spectral Line Broadening University

fast

faster

fastest Brightness

Wavelength

The Doppler broadening of spectral lines in elliptical galaxies tells us how fast the stars/gas are moving. These galaxies also have substantial amounts of dark matter.

c 2012-2020 G. Anderson Introduction to Astronomy – slide 29 / 90 Northeastern Illinois Q: Doppler Broadening? University

When we measure the broadening of absorption lines in the spectrum of an elliptical galaxy, we can infer A) the galaxy’s rotation curve. B) the amount of gas and dust in the galaxy. C) how fast the stars in the galaxy are moving relative to one another. D) how quickly the galaxy is forming new stars. E) the mass of the black hole at the galaxy’s center.

c 2012-2020 G. Anderson Introduction to Astronomy – slide 30 / 90 Northeastern Illinois Q: Doppler Broadening? University

c 2012-2020 G. Anderson Introduction to Astronomy – slide 30 / 90 Northeastern Illinois Evidence for Dark Matter University

From individual galaxies • – Rotation curves of spiral galaxies – Broadening of spectral lines in elliptical galaxies

Clusters of galaxies • – Velocities of galaxies – Temperature of hot gas – Gravitational lensing

Structure formation • Temperature ﬂuctuations in the CMB • Primordial nucleosynthesis •

c 2012-2020 G. Anderson Introduction to Astronomy – slide 31 / 90 Northeastern Illinois Galactic Clusters University Motion of galaxies in Coma cluster (Zwicky 1930’s) • M v2 r /G ∼h i h Gravity (Mass) required to contain hot gas •

Gravity Pressure Pressure

Gravitational Lensing • Galactic halos: M (10 40)M halo ≈ − stars

c 2012-2020 G. Anderson Introduction to Astronomy – slide 32 / 90 Northeastern Illinois First Evidence for Dark Matter University

1933 Fritz Zwicky at CalTech applied Virial The- orem to Coma cluster. From the motion of galaxies in Coma cluster:

M(r) v2 r/G ∼h i More Mass Larger Speeds ⇔

From motions of galaxies near the cluster’s edge:

M M dark ≫ vis

c 2012-2020 G. Anderson Introduction to Astronomy – slide 33 / 90 Galaxy Cluster MACS J0717

85% dark matter, 13% hot gas, 2% stars Image Credit: NASA, ESA & L. Calcada Lensing in galaxy cluster CL0024+17 Image Credit: ESA/Hubble & NASA: Horseshoe Einstein Ring Hubble space telescope: Gravitational lensing in Abell 2218. STScI Photo: The Einsten Cross, galaxy lenses a background quasar.

Northeastern Illinois What is the Universe made of? University

Dark Matter 24% Ordinary Matter 4.6%: ∼ Outside Stars: 3.8% Stars: 0.6%

Dark Energy 71.4% ∼

The mass of dark matter in galaxies, clusters of galaxies, and the universe is ﬁve to six times the mass of ordinary matter.

c 2012-2020 G. Anderson Introduction to Astronomy – slide 42 / 90 Northeastern Illinois Conclusion University

Either There is something wrong with our • understanding of gravity on very large scales. Or, there is 5-6 times more dark matter in the • universe than visible matter.

c 2012-2020 G. Anderson Introduction to Astronomy – slide 43 / 90 Northeastern Illinois University

Overview

Dark Matter What is Dark Matter? Dark Matter & Dark Energy Dark Matter Candidates OGLE MACHOS 16.10 WIMPS What is Dark Matter? CERN Q: What is Dark Matter?

Structure

Hubble’s Law Our Accelerating Universe

Review

c 2012-2020 G. Anderson Introduction to Astronomy – slide 44 / 90 Northeastern Illinois Dark Matter & Dark Energy University

We know very little about 95% of the universe which is dark invisible.

Dark matter is the invisible mass which surrounds galaxies and galactic clusters. The presence of dark matter is inferred by its gravitational eﬀects on observable stars, gas, galaxies, ....

Dark energy is the energy which is causing the expansion of the universe to accelerate.

dark energy = cosmological constant = vacuum energy

c 2012-2020 G. Anderson Introduction to Astronomy – slide 45 / 90 Northeastern Illinois Dark Matter Candidates University

MACHOS (Massive Compact Halo Objects): dead or failed stars - white dwarfs, neutron stars, black holes, brown dwarfs, Jupiters, ....

Neutrinos νe, νµ, ντ . Lighter neutrinos would be an example of hot dark matter v c. Light and fast ≈ enough to escape a galaxies gravity. WIMPS (Weakly Interacting Massive Particles) M 100mp. WIMPS are cold dark matter (v c). ≈ ≪ Examples WIMPS include the Lightest Super Partner (LSP), sterile neutrinos, ...

c 2012-2020 G. Anderson Introduction to Astronomy – slide 46 / 90 Northeastern Illinois OGLE MACHOS University

c 2012-2020 G. Anderson Introduction to Astronomy – slide 47 / 90 Gravitational microlensing ...not enough lensing events to explain all of the dark matter. Northeastern Illinois WIMPS University The case for WIMPS There is not enough ordinary matter • WIMPS could be left over from the Big Bang • Computer models with WIMPS reproduce the observed formation • of galaxies. Searching for WIMPS Accelerator searches: Lightest superpartner at the LHC? Direct detection: WIMPS from our galactic halo as they move past the Earth. Indirect detection: Detect neutrinos from the self annihilation of WIMPS captured in the core of the Earth or Sun over the course of billions of years.

c 2012-2020 G. Anderson Introduction to Astronomy – slide 49 / 90

Northeastern Illinois Q: What is Dark Matter? University

Which of the following best sums up current scientiﬁc thinking about the nature of dark matter? A) Most dark matter probably consists of weakly interacting particles of a type that we have not yet identiﬁed. B) About 90% of dark matter consists of ordinary matter in the halo of the galaxy, and of the other 10% of WIMPs. C) Dark matter probably does not really exist, and rather indicates a fundamental problem in our

c 2012-2020understanding G. Anderson of gravity. Introduction to Astronomy – slide 51 / 90 Northeastern Illinois Q: What is Dark Matter? University

c 2012-2020understanding G. Anderson of gravity. Introduction to Astronomy – slide 51 / 90 Northeastern Illinois University

Overview

Dark Matter What is Dark Matter?

Structure Cosmological Principle Hubble XDF Galaxy Groups, Clusters & Superclusters Structure Formation Draco Grp M31 and M33 Hickson 44 The Virgo Cluster Large Scale Structure Walls, Filaments and Voids SDSS Survey 2dF Galaxy Redshift Survey Simulation Q: 3D Maps? Cosmography I Cosmography II Cosmography III Cosmography IV Great c 2012-2020 Attractor G. Anderson Introduction to Astronomy – slide 52 / 90 Hubble’s Law Northeastern Illinois The Cosmological Principle University

On large scales the universe is homogeneous and isotropic.

b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b bb b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b bb b b b b b b b b b b b b b b bb b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b bb b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b bb b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b bb b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b bb b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b bb b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b bb b b b b b b b b b b b b b b b b b b b bb b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b bb b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b bb b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b bb b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b bb b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b bb b b b b b b b b b bb b b b b b b b b b bb b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b bb b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b bb b b b b b b b b b b b b b b b b b b b bb b b b b b b b b b b b b b bb b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b bb b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b bb b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b bb b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b bb b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b bb b bb b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b bb b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b bb b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b bb b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b bb b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b bb b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b bb b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b bb b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b bb b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b bb b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b bb b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b bb b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b bb b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b bb b b b b b b b b b b b

Isotropic but not Homogeneous Homogeneous but not Isotropic Almost Homogeneous and Isotropic

Matter in the universe is evenly distributed, with no center or edge, and no preferred direction.

c 2012-2020 G. Anderson Introduction to Astronomy – slide 53 / 90 Hubble XD in Fornax, 5,500 galaxies 2′ 2.3’, exp= 22.5 d, dt 13.2 Gya × ∼ Northeastern Illinois Galaxy Groups, Clusters & Superclusters University

Galaxy Groups (. 50 galaxies) e.g., Local Group: Milky Way, Andromeda, Triangulum, ...about 54 galaxies including dwarf galaxies. Diameter 3.1 Mpc (10 Mly) Clusters of galaxies up to 1000 gravitationally ≈ bound galaxies. Superclusters Groups, clusters and other isolated galaxies form superclusters. There are millions of superclusters in the observable universe. Local Supercluster (LSC) aka Virgo Laniakea Supercluster (size 33 Mpc or 110 Mly) contains: Local Group, Virgo Cluster and > 100 galaxy groups and clusters. 100,000 galaxies ∼

c 2012-2020 G. Anderson Introduction to Astronomy – slide 55 / 90 The Draco Group: NGC 5981, NGC 5982, and NGC 5985 Andromeda and Triangulum Hickson 44, d = 100 Mly in Leo The Virgo Cluster, 48 Mly The Virgo Cluster, 48 Mly Northeastern Illinois Large Scale Structure University

Large three dimensional maps of the universe show walls, ﬁlaments, and large empty voids.

The voids are tens of millions of light years across and contain few or no bright galaxies.

These voids are bounded and separated by walls and ﬁlaments of superclusters.

c 2012-2020 G. Anderson Introduction to Astronomy – slide 60 / 90 Northeastern Illinois Walls, Filaments and Voids University

Largest known structures in the universe: Voids Giant bubble like regions contain little or no galaxies. (d = 11 150 Mpc) Voids are separated by − ﬁlaments and sheets. Filaments aka supercluster complexes, great walls, hyperclusters, great attractors. e.g. The Great Wall a ﬁlament of galaxies 200 Mly away. This sheet of galaxies is 500 Mly 200 Mly 15 Mly × × End of Greatness no more structure above 100-1000 Mpc homogeneous and isotropic ⇒

c 2012-2020 G. Anderson Introduction to Astronomy – slide 61 / 90 SDSS Galaxy Survey Sloan Great Wall: Largest Second largest known structure Simulation: growth of cosmic structure, Volker Springel Northeastern Illinois Q: 3D Maps? University

How do astronomers create three-dimensional maps of our universe? A) Through the comparison of computer models of galaxy formation with observations B) By using a galaxy’s position on the sky and its redshift to determine its distance along the line of sight C) by interpreting the peculiar velocities of each galaxy D) by carefully measuring the parallax of each galaxy

c 2012-2020 G. Anderson Introduction to Astronomy – slide 65 / 90 Northeastern Illinois Q: 3D Maps? University

c 2012-2020 G. Anderson Introduction to Astronomy – slide 65 / 90

Northeastern Illinois University

Overview

Dark Matter What is Dark Matter?

Structure

Hubble’s Law Distance Ladder Hubble Diagram for Type Ia SN Hubble Hubble’s Law Expansion Expanding Space Our Accelerating Universe

Review

c 2012-2020 G. Anderson Introduction to Astronomy – slide 71 / 90 Northeastern Illinois Simpliﬁed Cosmic Distance Ladder University

b Virgo Cluster LMC 1ly klyb Mly Gly b Hyades −3 SMC ly b δ Cep b 10 b α Cen Cepheids Hubble’s Law stellar parallax b radar MS Fitting b SN-Ia solar nearby system Milky stars Way nearby galaxies Polaris b

b Sgr A* b Pleiades Andromeda

b Coma Cluster

c 2012-2020 G. Anderson Introduction to Astronomy – slide 72 / 90

Northeastern Illinois Hubble’s Expanding Universe University

In 1929, Using Cepheid distances to several galaxies and their recessional velocities, Edwin Hubble found:

v = Hd b v b slope = H

speed b

distance d

Modern value of the Hubble parameter:

H 70km/s/Mpc ≈ Distant galaxies are moving away from us at speeds proportional to their distance. c 2012-2020 G. Anderson Introduction to Astronomy – slide 74 / 90 Northeastern Illinois Expanding Space University

1D Stretching a Knotted Rubber Band

b b b b b b b b b b

2D Surface of an Inﬂating Balloon b b b b

3D Expanding Raisin Cake z

b b

b b b z b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b y x b b b b x b b y b b

c 2012-2020 G. Anderson Introduction to Astronomy – slide 75 / 90 Northeastern Illinois University

Overview

Dark Matter What is Dark Matter?

Structure

Hubble’s Law Our Accelerating Universe Our Accelerating FRW Cosmology Energy Density and Expansion Single Component Universe Universes Fig 16.15 Fig 16.16 Q: Evidence for Acceleration? Density Parameters Matter & Dark Energy Best Fit Pie Chart For further study

Review

c 2012-2020 G. Anderson Introduction to Astronomy – slide 76 / 90 Northeastern Illinois Friedmann-Robertson-Walker Cosmology University

Friedmann Equation:

8πG kc2 H2 = ρ 3 − a2

closed flat open

k = +1 k =0 k = 1 −

c 2012-2020 G. Anderson Introduction to Astronomy – slide 77 / 90 Northeastern Illinois Energy Density and Expansion University

radiation

2 H2 = 8πG ρ kc 3 − a2 ρ

Dark Energy

ρΛ = constant Energy Density − ρ a 2 curvature curvature ∝ ρ a−3 matter ∝ matter ρ a−4 radiation ∝

Size a

c 2012-2020 G. Anderson Introduction to Astronomy – slide 78 / 90 Northeastern Illinois Single Component Universes University

H0t a e Dark Energy ∝

a a t ∝ 2/3 Size a t ∝ curvature (empty) matter a t1/2 ∝ radiation

2 H2 = 8πG ρ kc 3 − a2

t0 Time t

c 2012-2020 G. Anderson Introduction to Astronomy – slide 79 / 90

Northeastern Illinois Q: Evidence for Acceleration? University

What is the primary form of evidence that has led astronomers to conclude that the expansion of the universe is accelerating?

A) Observations of white dwarf supernovae

B) Observations of the speeds of individual galaxies in clusters

C) Measurements of the rotation curve of spiral galaxies

D) Measurements of how galaxy speeds away from the Milky Way have increased during the past century

c 2012-2020 G. Anderson Introduction to Astronomy – slide 82 / 90 Northeastern Illinois Q: Evidence for Acceleration? University

What is the primary form of evidence that has led astronomers to conclude that the expansion of the universe is accelerating?

A) Observations of white dwarf supernovae

B) Observations of the speeds of individual galaxies in clusters

C) Measurements of the rotation curve of spiral galaxies

D) Measurements of how galaxy speeds away from the Milky Way have increased during the past century

c 2012-2020 G. Anderson Introduction to Astronomy – slide 82 / 90 Northeastern Illinois Density Parameters University

Friedmann Equation: 8πG k H2 = ρ 3 − a2 2 Critical density ρ 3H =, energy density of a ﬂat universe. c ≡ 8πG ρ kc2 Ωtot = ΩΛ +Ωm =1+ 2 2 ρc ≈ a H

In a ﬂat universe Ωm +ΩΛ = 1:

2 1 = Ω + Ω k c matter dark energy − H2a2 2 = Ω + Ω k c m Λ − H2a2 = 0.3 +0.7 +0

The critical density is approx 5 atoms of H per cubic meter compared to the measures 0.2 per atoms cubic meter c 2012-2020 G. Anderson Introduction to Astronomy – slide 83 / 90 Northeastern Illinois Matter & Dark Energy University

“Bounce”

2 Big Chill (expand forever) No Big-Bang

1 Accelerating

(vacuum energy) closed Decelerating

Λ ﬂat

Ω open k 0 = +1 k = − 1 Big Crunch (recollapse) Big Crunch (recollapse) -1 0 1 2 3 Ωm (matter)

c 2012-2020 G. Anderson Introduction to Astronomy – slide 84 / 90 Northeastern Illinois Matter & Dark Energy University

“Bounce”

2 Big Chill (expand forever) No Big-Bang

1 Accelerating We are here!

(vacuum energy) closed Decelerating

Λ ﬂat

Ω open k 0 = +1 k = − 1 Big Crunch (recollapse) Big Crunch (recollapse) -1 0 1 2 3 Ωm (matter)

c 2012-2020 G. Anderson Introduction to Astronomy – slide 84 / 90 Northeastern Illinois Best Fit University

c 2012-2020 G. Anderson Introduction to Astronomy – slide 85 / 90 Northeastern Illinois What is the Universe made of? University

Dark Matter 24% Ordinary Matter 4.6%: ∼ Outside Stars: 3.8% Stars: 0.6%

Dark Energy 71.4% ∼

The mass of dark matter in galaxies, clusters of galaxies, and the universe is ﬁve to six times the mass of ordinary matter.

c 2012-2020 G. Anderson Introduction to Astronomy – slide 86 / 90 Northeastern Illinois For further study University

A ﬂight through the universe • http://hubblesite.org/hubble discoveries/dark energy/ • http://imagine.gsfc.nasa.gov/docs/ask astro/dark matter.html • http://chandra.harvard.edu/xray astro/dark matter/ • Cosmography of the Local Universe • Laniakea Supercluster •

c 2012-2020 G. Anderson Introduction to Astronomy – slide 87 / 90 Northeastern Illinois University

Overview

Dark Matter What is Dark Matter?

Structure

Hubble’s Law Our Accelerating Universe Review Review Review I Review II

c 2012-2020 G. Anderson Introduction to Astronomy – slide 88 / 90 Northeastern Illinois Review I University

What fraction of the universe is dark matter? • What fraction of the universe is dark energy? • Why do we call them dark? • List some of the evidence for dark matter. • List some of the evidence for dark energy. • How is dark matter distributed in a spiral galaxy? • What is a rotation curve? How do they give us evidence for dark • matter. Who was the astronomer who measured the rotation curve of • M31?

c 2012-2020 G. Anderson Introduction to Astronomy – slide 89 / 90 Northeastern Illinois Review II University

What is a WIMP? What is a MACHO? • Can gravitational lensing tell us about the mass of galactic • clusters? If so, how? What might be causing the expansion of the universe to • accelerate? How does doppler broadening in the spectral lines from elliptical • galaxies tell us about dark matter? What are Voids and ﬁlaments •

c 2012-2020 G. Anderson Introduction to Astronomy – slide 90 / 90