Chapter 5: Galaxies and Active Galactic Nuclei Flashcards

1
Q

How many galaxies where known in early 1900s

A

Thought the Milky Way was the only galaxy

-we now know of trillions

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2
Q

William Herschel

A

In 1800 counted stars to sketch the Milky Way

  • he put sun at centre Milky Way
  • not round
  • was not completely accurate though no (ISM) cause dust blocks our view
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3
Q

Stars in disk

A

Circular orbits

  • young
  • lots of gas/dust/ ISM
  • blue
  • metallicity relatively high
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4
Q

Stars in the bulge

A
  • random orbits
  • old
  • no gas/ dust
  • red
  • relatively high metallicity
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5
Q

Stars in the halo

A

-random orbits
-old
-no gas and dust
-red
Metal poor

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6
Q

Milky Way

A
  • a spiral galaxy
  • due to dust can only see 1kpc of Galaxy
  • this is due to interstellar extinction
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7
Q

Galaxtic extinction laws

A
  • photon is lost due to dust
  • infrared doesn’t interact with dust very much
  • Bump has is extra extinction due to carbon
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8
Q

Mapping spiral arms

A
  • has near hot stars (HII region)
  • strongest emission lines are in optical, so still suffer from steal extinction
  • study wavelengths in radio
  • HI 21 cm is immune to dust l
  • electrons have two different energy spins corresponds to 21 cm
  • can map arms in infrared but has to be from space
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9
Q

Henrietta Swan-Leavitt

A
  • Cepheid variable stars pulsate
  • period-luminosity relation discovered 1910. Distance measure beyond parallax
  • she plotted period of peak vs luminosity which made a linear relation l
  • by knowing period we can find true luminosity, then apparent brightness from which we can find distance
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10
Q

Harlow Shapley

A

Early 20th century found the extend of MW by using distances to globular stars, spherically distributed over many Kpc

  • sun was not at centre
  • they were RRLyra stars not Cepheid
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11
Q

Synchrotron radiation

A

A nonthermal process, associated with the presence of strong magnetic fields
-comes mainly from supernova remnants

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12
Q

Galactic Centre

A

X-ray images find Sagitarius A which is a central black hole

  • lots of radiation coming from such compact centre
  • have a massive black hole in the centre
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13
Q

Charles Messier

A

The first to catalog extra-galactic objects in mid 1700 , to fuzzy to be comets

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14
Q

Leviathon of Parsonstown

A

Observed spiral galaxies in end of 19th century

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15
Q

Shapely-Curtis debate

A

1920

  • Shapley argues spiral nebulae that we’re in our galaxy and putting them outside would regress Einstein’s theory
  • Curtis claimed that it was a mistake and that they were outside and that there were many other galaxies
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16
Q

Edwin Hubble

A

Settles the great debate in 1923

  • first to make distances to these galaxies
  • showed that it was far away and Curtis was correct
    1. Hubble’s galaxy classification scheme
    2. Hubble’s law
17
Q
  1. Hubble’s classification scheme
A

Elliptical galaxies: no spiral arms, no dust

  • spiral galaxies: spiral arms, lots dust, blue disk, red bulge
    1. Bared spirals
    2. Unbared spirals
  • Irregular galaxies: don’t fit in with other groups properties
  • Lenticular galaxies: no obvious spiral arms, disk and bulge, ISM, blue/red
18
Q
  1. Hubble law
A
  • distance vs velocity (linear)
  • where H is constant that describes the gradient of the slope called Hubble’s constant
  • most galaxies moving away from us
  • the farther away the faster it travels
  • universe is expanding
19
Q

Corollary

A

Recessional velocity can be used as a distance measure

20
Q

Hubble flow

A

Universe is expanding and carrying galaxies with it

21
Q

Central supermassive black holes

A
  • Sag A in centre MW
  • all massive galaxies have SMBH whose mass is proportional to the mass of stars in the bulge (scales with rest of galaxy)
  • low mass shouldn’t have one but some do
22
Q

Active galaxies

A

Galaxies in which the black hole and switched on and producing large amounts of energy, cores called active galactic nuclei
-AGN fuelling: accretion disks, processes in accretion disk/ jet make black holes viable

23
Q

Parts SMBH

A

Black hole, accretion disk, broad-band radiation, Torus (dusty donut), infrared radiation, radio jets

24
Q

AGN detection methods

A

Radio jets, most common in massive ellipticals but can still be found in spirals

  1. x-ray emission detected around accretion disk
  2. Spectroscopy of broad emission lines
    • broad line region: line very broad
    • narrow line region: line very narrow
    • gas shows up both narrow and broad
25
Q

Quasars

A

A clue to what switches black holes on

  • so luminous that they can outshine AGN
  • material funneled into black holes and merged together
26
Q

Local group

A

Group of galaxies that had two big spirals and the Magellanic Clouds and 50 other galaxies spanning 10 million lyrs

27
Q

Hierarchical growth

A

Build galaxies in a hierarchy starting with the small to the big

28
Q

Galaxy clusters

A

Can have many thousand galaxies, more then groups

  • lots of x-ray emission between galaxies due to elliptical galaxies and the intra-cluster medium
  • more clusters of ellip then spies
29
Q

Zwicky

A

1933 found evidence of dark matter which was ignored for 49 years

30
Q

Dark matter

A
  • actual rotating curves are flat or even rising
  • dark matter causes this
  • most likely and exotic particle 80-90% matter
31
Q

High velocity stars

A

In halo, increase in galaxies dark velocity coming close to disk