How long since the Big Bang ?How long since the Big Bang ?

Jeremy MouldNational Optical Astronomy Observatory

Introduction Introduction

• Subject today is the Expanding Universe• The Expanding Universe model describes

the motions of galaxies• Just like the model of Copernicus describes

the motions of the planets

OutlineOutline

• Hubble’s evidence for an expanding Universe• How fast is the Universe expanding now ?

(the Hubble Constant) • Variation of the expansion rate over time• How long is it since the Big Bang ?

EdwinEdwinHubbleHubble

18891889--

19531953

Hubble’s evidenceHubble’s evidence

Overview on the Hubble ConstantOverview on the Hubble Constant

• what is redshift ?

• measuring distances geometrically

• we start with the Large Magellanic Cloud

• the Hubble Space Telescope Key Project

• Cepheids as standard candles

• Supernovae as standard candles

redshiftredshift

• 1 parsec is

3 x 1013 km

• if we can

measure

the angle,

we can get

the distance

Supernova 1987ASupernova 1987A

• a massive star exploded in the LMC

• February 1987

• the LMC is our nearest neighbor galaxy

• in fact, it’s a satellite

SN1987ASN1987A

• the ring lit up 250 days after the supernova

• radius known

• angle known

• => distance

SN1987ASN1987A

Schematic of SN1987A

The Hubble Constant Key ProjectThe Hubble Constant Key Project

Goal:

Measure how fast the Universe is expanding

to 10% accuracy

The HST Key ProjectThe HST Key ProjectJeremy MouldRobert Kennicutt, U.ArizWendy Freedman, CIWShaun Hughes, RGOBarry MadoreNancy SilbermannShoko SakaiRandy PhelpsRobert HillAbi Saha, NOAOPeter Stetson, DAOBrad Gibson

Laura Ferrarese

Holland Ford

Garth Illingworth

Dan Kelson

John Graham

John Hoessell

Ming Sheng Han

John Huchra

Anne Turner

Paul Harding

Fabio Bresolin

servicing missionservicing mission

The first The first servicing servicing mission mission

replaced the replaced the WFPC with WFPC with WFPC2 in WFPC2 in December December 1993, thus 1993, thus remedying remedying spherical spherical aberrationaberration

The power of the Hubble Space TelescopeThe power of the Hubble Space Telescope

• From the ground we can resolve galaxies up to 2 or 3 Mpc away

• HST was designed to have ten times the resolution of ground based telescopes

• The project to find Cepheids up to 20 Mpc away was designated a Key Project for HST

The Cepheid period luminosity relationThe Cepheid period luminosity relation

M100M100

M100M100

Cepheid light curves in NGC 1365Cepheid light curves in NGC 1365

N1365 PLN1365 PL

top: visual

The PL relation in NGC 1365

bottom: infrared

Beyond the CepheidsBeyond the Cepheids• Beyond 20 Mpc even HST has difficulty resolving

Cepheids

• We use four other standard candles to measure distances a further factor of ten

• The Tully Fisher relation for spiral galaxies

• Supernovae of type Ia

• Surface brightness fluctuations = resolvability

• The fundamental plane for elliptical galaxies

Tully Fisher relationTully Fisher relation

• big galaxies rotate faster

• a galaxy with a given rotation speed is a standard candle

The Hubble ConstantThe Hubble Constant

• All 4 standard candles agree

• H lies in the range 65 to 77 km/s/Mpc

How standard are standard How standard are standard candles ? candles ?

• most stars have a chemical composition like that of the sun

• but there are some variations....

• Cepheids with different chemistry pulsate differently

• accounting for this changes our distances a few percent

How the expansion slowsHow the expansion slows

Expansion rate in the past divided by current rate

Big Bang

Now

low density universe

What is the density of the Universe ?What is the density of the Universe ?

2dF map of the 3d density of the local few billion light years

Colless and team

Dark energyDark energy

2dF found that the density of the Universe was only 25% of the critical density

But Boomerang found that the curvature of the Universe was nonetheless zero.

Rediscovery of

See www.mso.anu.edu.au/~brian

Measuring the ageMeasuring the age

13.5

a

time in billions of years

Scale factor

Size now

SummarySummary• we start with the distance of the LMC

• a Cepheid of period P is a standard candle of luminosity L

• HST maps the Cepheids out to 20 Mpc

• Four other standard candles map the expansion out to 200 Mpc

• H0 = 72 +/- 7 km/sec/Mpc

• Universe is 13.5 +/- 1.5 Gyrs old

Global Global parameters: parameters: the Hubblethe HubbleConstantConstantIs H0 > 60

km/sec/Mpc ?

Jim Jim Peebles’ Peebles’ rulingruling

What SIM will What SIM will do for do for

cosmology ?cosmology ?

SIM is the Space Interferometry Mission

SIM is proceeding with Phase B development and

on track for a launch in 2009.

http://sim.jpl.nasa.gov

Oldest starsOldest stars• globular

star clusters

• parallaxes with SIM or GAIA

• measure ages to half a billion years

LSST, a digital LSST, a digital survey of the survey of the

sky each weeksky each week• Weak lensing mass map of

the Universe

• 100,000 supernovae per year z (1,2)

• Earth crossing asteroids

• 10,000 primordial trans-Neptunian objects

View of the LSST telescope structure in the Steward Observatory straw man design. The primary mirror is at the center, and the secondary and tertiary are almost equidistant from the primary. The detectors are just ahead of the central hole in the primary (see: http://dmtelescope.org/ design.html)

Where to get more informationWhere to get more information

• ‘Measuring the Universe’ by Stephen Webb

• www.stsci.edu (Hubble Space Telescope)http://oposite.stsci.edu/pubinfo/1999.html

• www.noao.edu/noao/staff/jrm

PHOTO NO.: STScI-PRC99-25 MAGNIFICENT DETAILS IN A DUSTY SPIRAL GALAXY In 1995, the majestic spiral galaxy NGC 4414 was imaged by the Hubble Space Telescope as part of the HST Key Project on the Extragalactic Distance Scale. An international team of astronomers, led by Dr. Wendy Freedman of the Observatories of the Carnegie Institution of Washington, observed this galaxy on 13 different occasions over the course of two months. Images were obtained with Hubble's Wide Field Planetary Camera 2 (WFPC2) through three different color filters. Based on their discovery and careful brightness measurements of variable stars in NGC 4414, the Key Project astronomers were able to make an accurate determination of the distance to the galaxy. The resulting distance to NGC 4414, 19.1 megaparsecs or about 60 million light-years, along with similarly determined distances to other nearby galaxies, contributes to astronomers' overall knowledge of the rate of expansion of the universe. The Hubble constant (H0) is the ratio of how fast galaxies are moving away from us to their distance from us. This astronomical value is used to determine distances, sizes, and the intrinsic luminosities for many objects in our universe, and the age of the universe itself. Due to the large size of the galaxy compared to the WFPC2 detectors, only half of the galaxy observed was visible in the datasets collected by the Key Project astronomers in 1995. In 1999, the Hubble Heritage Team revisited NGC 4414 and completed its portrait by observing the other half with the same filters as were used in 1995. The end result is a stunning full-color look at the entire dusty spiral galaxy. The new Hubble picture shows that the central regions of this galaxy, as is typical of most spirals, contain primarily older, yellow and red stars. The outer spiral arms are considerably bluer due to ongoing formation of young, blue stars, the brightest of which can be seen individually at the high resolution provided by the Hubble camera. The arms are also very rich in clouds of interstellar dust, seen as dark patches and streaks silhouetted against the starlight.

Image Credit: Hubble Heritage Team (AURA/STScI/NASA)