Some examples of Type I supernova light curves Narrow range of absolute magnitude at maximum light...

Some examples of Type I supernova light curves

Narrow range of absolute magnitude at maximum light indicates a good Standard Candle

B b

and

a bso

lute

mag

nitu

de

No. of days since maximum light

Apparent brightness, or flux, falls off with the square of the distance, because the surface area of a sphere increases with the square of its radius

Luminosity and flux

FDL 24Luminosity, (watts) Flux, (watts / square metre)

Distance, (metres)

A Type I supernova has a luminosity times that of the Sun.

As seen from the Earth, the supernova appears fainter than the Sun.

How far away is the supernova?


Distance, (metres)

910

1710

Measuring the Hubble Constant – 3

Although the errors which caused Hubble to findwere gradually eliminated, even by the late 1980s, the value of theHubble constant was still controversial, because of disagreements over the different steps of the Distance Ladder.

Some astronomers argued that

Others that

The Hubble Space Telescope launched in 1990 was to come to the rescue!

H0 ~ 500 kms-1 Mpc-1

H0 ~ 100 kms-1 Mpc-1

H0 ~ 50 kms-1 Mpc-1

HST has ‘bypassed’ one stage of the Distance Ladder, by observing Cepheids beyond the Local Group of galaxies

HST Key Project, led by Wendy FreedmanMeasure Cepheid distances to ~30 nearby galaxies,

Link Cepheids to Secondary distance indicators

Virgo Cluster galaxyM100, 60 million light years distant…..

HST has ‘bypassed’ one stage of the Distance Ladder, by observing Cepheids beyond the Local Group of galaxies

This has dramatically improved measurements of H0

A Type I supernova has a luminosity times that of the Sun.

As seen from the Earth, the supernova appears fainter than the Sun.

How far away is the supernova?


Distance, (metres)

910

1710

Morphological Segregation

Analysis of galaxy redshift surveys reveals that ellipticalgalaxies are preferentially found in the cores of rich clusters, while spirals are generally not found there.

This morphological segregation is a consequence of how galaxies formed:

Spirals existed briefly in galaxy clusters, but their disks could not survive the strong tidal forces there.

Early population of cluster spirals torn apart. Many may have been ‘cannibalised’ by the giant elliptical galaxies in the centre of the clusters.

Active Galaxies

Galaxies whose luminosity is significantly greater than that solely due to the stars which they contain are known as active galaxies.

Their cores are known as active galactic nuclei (AGN).

All types of active galaxies are observed predominantly at high redshift, indicating they are very distant.

Light travels at a finite speed, so we see active galaxies as they were in the remote past.

This suggests that they represent a phase in the early history of galaxy formation, which is now over.

Active Galaxies

We will consider three types of Active Galaxy:

o Radio galaxies

o Seyfert galaxies

o Quasars

Properties of Radio Galaxies

Cygnus A: radio map

Properties of Radio Galaxies

Synchrotron radiation

Properties of Seyfert Galaxies

NGC7742

Suppose gas moves in a circular orbit.

From Kepler’s third law:

But so

Hence

322gal 4 RPMG

v

2 RP

2

222

v

4 RP

G

RM

2

gal

v

Increasing exposure time

Seyfert galaxy nuclei

Properties of Quasars

Hydrogen emission line

Hydrogen Spectral Line Series

n = 1

n = 2

n = 4

(ground state)

n = 3

Lyman

Balmer

Paschen

Brackett

Ene

rgy

diff

eren

ce (

eV)

5

10

15

m = 2,3,4,… n = 1

n = 2m = 3,4,5,…

m = 4,5,6,… n = 3

m = 5,6,7,… n = 4Ionised above 13.6 eV

Shown here are downward transitions, from higher to lower energy levels, which produce emission lines. The corresponding upward transition of the same difference in energy would produce an absorption line with the same wavelength.


Lec 2

z = 2.0

Light travel time =10.3 billion years

z = 2.1


z = 2.2


z = 2.3


z = 2.4


z = 2.5


z = 2.6


z = 2.7


z = 2.8


z = 2.9


z = 3.0


z = 3.1


z = 3.2


z = 3.3


z = 3.4


z = 3.6


z = 3.7


z = 3.8


z = 4.0


z = 4.1


z = 4.3


z = 4.4


z = 4.5


z = 4.6


z = 5.0


Exit

Re-run


Absorption lines produced byatoms in young galaxies between us and the quasar

Quasars: Galaxies in Infancy

o Conclusive evidence that quasars are at cosmological distances: HST observed ‘host’ galaxies at same redshift


o Conclusive evidence that quasars are at cosmological distances: HST observed ‘host’ galaxies at same redshift

o How can such a high luminosity be produced in such a small volume?

Quasar powered by a supermassive black hole at its center. Infalling material releases large amounts of energy as it is swallowed up by the black hole.

No other satisfactory model can provide such a luminous source of energy .

Amount of energy released is of order

2mcE

Suppose a quasar ‘consumes’ the equivalent of 1 solar mass per year, and it converts 20% of this mass into energy.

What is the luminosity of the quasar?


Standard Model:

o Quasar is the core of a very young galaxy. Black hole forms at center during chaotic early collapse of protogalactic cloud.

o Infalling matter forms an accretion disk around the black hole

o Energy released by infalling matter accelerates electrons in beams, moving close to speed of light, which stream out from the disk. The electrons in turn produce synchrotron radiation


Standard Model:

o Quasar is the core of a very young galaxy. Black hole forms at center during chaotic early collapse of protogalactic cloud.

o Infalling matter forms an accretion disk around the black hole

o Energy released by infalling matter accelerates electrons in beams, moving close to speed of light, which stream out from the disk. The electrons in turn produce synchrotron radiation

o Radio galaxies and Seyferts powered by same mechanism, but less energetic and/or viewed from different orientation.

The Milky Way was very likely once an active galaxy.

Sgr A: very strong radio source at the galactic center;

remnant of an AGN.

Some examples of Type I supernova light curves Narrow range of absolute magnitude at maximum light...

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