Astrophysics from Space

Astrophysics from Space Astrophysics from Space - Start

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Astrophysics from Space - Description

Lecture 4: The extragalactic distance scale. Prof.. . Dr.. M. Baes (. UGent. ). Prof.. . Dr.. C. . Waelkens. (KUL). Academic year 2015-2016. The expanding Universe. One of the most important cosmological discoveries: . ID: 233399 Download Presentation

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Astrophysics from Space




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Presentations text content in Astrophysics from Space

Slide1

Astrophysics from SpaceLecture 4: The extragalactic distance scale

Prof.

Dr. M. Baes (UGent)Prof. Dr. C. Waelkens (KUL)Academic year 2015-2016

Slide2

The expanding Universe

One of the most important cosmological discoveries: the Universe is expanding.

Vesto

Slipher

Georges

Lemaître

Edwin Hubble

Slide3

The expanding Universe

One of the most important cosmological discoveries: the Universe is expanding.

Slide4

Hubble’s law

Hubble’s first determination resulted in H

0

= 500 km/s/MpcResulting age of the Universe: about 2 GyrRadioactive dating of Earth rocks (> 3Gyr)

Slide5

Hubble’s constant

1960s – 1970s:

two groups advocating two distinct values (50 and 100 km/s/Mpc)

Slide6

Cosmic distance ladder

Each rung of the ladder provides information that can be used to determine distances at the next higher rung.

Slide7

Fundamental distance measurements

Methods in which distances are measured directly, with no physical assumptions about the nature of the object.Fundamental distance: scale of the Solar SystemAstronomical Unit (AU)Kepler’s third law: if we knowthe distance to one planet, all distances in the Solar System are known

Slide8

Planetary parallax measurements

Late 1800s: efforts concentrated on Venus at inferior conjunction (in particular during Venus transit)

http://www.vt-2004.org

Early 1900s: Mars and Eros

Slide9

Radar echo measurements

From 1960s: radar echo measurements on Venus and other nearby planets and asteroidsAU = 149 597 870 691 ± 30 m

Slide10

Stellar parallax measurements

High astrometric precision is necessary to measure large distancesHipparcos: precision of milli-arcsecaccurate distances out to several 100 pcalso accurate distances to next distance ladder objects (Cepheids)

Contribution of

Hipparcos

to the cosmic distance ladder has been crucial

Slide11

Standard candles: cepheids

Slide12

Standard candles: cepheids

1908: Henrietta Leavitt discovers period-luminosity relation in cepheids (studying the LMC and SMC)

1915

: Harlow Shapley uses cepheids to determine the size of the Milky Way

1924

: Edwin Hubble uses

cepheids

to determine distance to Andromeda

Slide13

Standard candles: type Ia SN

White dwarfs in a binary system, where

infalling

matter pushes it over the Chandrasekhar limit.

Consequence: thermonuclear explosion.

Slide14

Standard candles: type Ia SN

The width of the light curve correlates with the peak luminosity.Huge advantage: type Ia supernovae are extremely bright.

Type

Ia

supernovae are ideal standard candles for cosmological studies

Slide15

Standard candles: caution…

Calibration issues: what is the absolute magnitude(requires thorough definition of a class and enough members in that class)Confusion with similar objects (different SN types, novae versus supernovae…)Interstellar extinctionHow standard are standard candles ?For example: there are two classes of cepheids….

Walter Baade

Slide16

Secondary distance indicators

Indirect distance indicators, often based on statistical relations in galaxies. To be used when no primary indicators can be used.

Prime example: Tully-Fisher relation

Slide17

HST Key Project

HST Key Projectslarge observations projects with significant impactseparate time budget (no competition)guaranteed completion in the early years

HST Key Project on the Extragalactic Distance Scale

measure direct distances to 25-30 galaxies using

cepheid

variables

use these distances to calibrate secondary distance indicators (TF) to probe structure of the Universe

Slide18

HST Key Project

Spectacular results obtained as soon as the optics were refurbished (late 1993).

8 observations of each target galaxy to detect

cepheids

with periods of 10 – 50 days.

E.g. more than 80

cepheids

discovered in M100.

Slide19

HST Key Project

Final result based on cepheids and cepheid-calibrated secondary methods: H0 ≈ 72 ± 8 km/s/Mpc


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