Weighing a Galaxy What is a galaxy made of? STARS GAS DUST DARK - - PowerPoint PPT Presentation

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Weighing a Galaxy What is a galaxy made of? STARS GAS DUST DARK - - PowerPoint PPT Presentation

Jan 22, 2024 41 likes •382 views

Weighing a Galaxy What is a galaxy made of? STARS GAS DUST DARK MATTER! Weighing a Galaxy 2 What is HI? Majority of gas is atomic hydrogen (HI) It is the fuel for stars Emits light with wavelength 21cm (1420 MHz)

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SLIDE 1

Weighing a Galaxy

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SLIDE 2

Weighing a Galaxy

What is a galaxy made of?

  • STARS
  • GAS
  • DUST
  • DARK MATTER!

2

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SLIDE 3

Weighing a Galaxy

What is HI?

★ Majority of gas is atomic hydrogen

(HI)

★ It is the fuel for stars ★ Emits light with wavelength 21cm

(1420 MHz)

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SLIDE 4

Gamma Rays X Rays

Ultraviolet Radiation

Infrared Radiation Microwaves Radio Waves 400 nm 700 nm Visible Light 10 nm

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10 nm

  • 5

10 nm

  • 4

10 nm

  • 3

10 nm

  • 2

10 nm

  • 1

1 nm 10 nm 100 nm 1 µm 10 µm 100 µm 1 mm 1 cm 10 cm 1 m 10 m 100 m 1 km 10 km 100 km

Electromagnetic Spectrum

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SLIDE 5

Weighing a Galaxy

What do galaxies look like?

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SLIDE 6

Weighing a Galaxy 6

NGC 7531

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SLIDE 7

Weighing a Galaxy

What is a spectrum?

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SLIDE 8

Weighing a Galaxy

What is a spectrum?

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Why isn’t the spectrum centred on 1420MHz?

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SLIDE 9

Weighing a Galaxy

What is a spectrum?

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Why isn’t the spectrum centred on 1420MHz?

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SLIDE 10

Weighing a Galaxy

Redshift

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SLIDE 11

Weighing a Galaxy

Spectrum in Velocity

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SLIDE 12

Weighing a Galaxy 10

The ‘Double-Horned’ Profile

  • 1. What is the velocity width of the spectrum?
  • 2. Why are there two peaks in the spectrum?
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SLIDE 13

Weighing a Galaxy 10

The ‘Double-Horned’ Profile

  • 1. What is the velocity width of the spectrum?
  • 2. Why are there two peaks in the spectrum?
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SLIDE 14

Weighing a Galaxy 10

The ‘Double-Horned’ Profile

  • 1. What is the velocity width of the spectrum?
  • 2. Why are there two peaks in the spectrum?

Velocity Width = 2 x rotation velocity.

  • > v = velocity width/2

TIP: Don’t forget to convert from km/s to m/s!

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SLIDE 15

Weighing a Galaxy 11

Rotation in a spiral galaxy

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SLIDE 16

Weighing a Galaxy 12

Optical image of NGC 7531

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SLIDE 17

Weighing a Galaxy 13

  • 1. Describe the image

Optical image of NGC 7531

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SLIDE 18

Weighing a Galaxy 13

  • 1. Describe the image
  • 2. Measure NGC7531’s radius (in degrees)

Optical image of NGC 7531

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SLIDE 19

Weighing a Galaxy 13

  • 1. Describe the image
  • 2. Measure NGC7531’s radius (in degrees)

There are 60 arc minutes in a degree, and each grid square is two arcminutes wide. How many squares wide is the radius of NGC7531? (TIP: make sure you work out the radius, not the diameter!)

Optical image of NGC 7531

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SLIDE 20

Weighing a Galaxy 13

  • 1. Describe the image
  • 2. Measure NGC7531’s radius (in degrees)

There are 60 arc minutes in a degree, and each grid square is two arcminutes wide. How many squares wide is the radius of NGC7531? (TIP: make sure you work out the radius, not the diameter!)

1.5 squares = 3” = 3/60 degree = 0.05 degrees

Optical image of NGC 7531

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SLIDE 21

Weighing a Galaxy 13

  • 1. Describe the image
  • 2. Measure NGC7531’s radius (in degrees)

There are 60 arc minutes in a degree, and each grid square is two arcminutes wide. How many squares wide is the radius of NGC7531? (TIP: make sure you work out the radius, not the diameter!)

1.5 squares = 3” = 3/60 degree = 0.05 degrees If 1 degree = 11.5 x 1022 metres

Optical image of NGC 7531

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SLIDE 22

Weighing a Galaxy 13

  • 1. Describe the image
  • 2. Measure NGC7531’s radius (in degrees)

There are 60 arc minutes in a degree, and each grid square is two arcminutes wide. How many squares wide is the radius of NGC7531? (TIP: make sure you work out the radius, not the diameter!)

1.5 squares = 3” = 3/60 degree = 0.05 degrees If 1 degree = 11.5 x 1022 metres r = 0.05 x 11.5 x 1022 metres

Optical image of NGC 7531

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SLIDE 23

Weighing a Galaxy 13

  • 1. Describe the image
  • 2. Measure NGC7531’s radius (in degrees)

There are 60 arc minutes in a degree, and each grid square is two arcminutes wide. How many squares wide is the radius of NGC7531? (TIP: make sure you work out the radius, not the diameter!)

1.5 squares = 3” = 3/60 degree = 0.05 degrees If 1 degree = 11.5 x 1022 metres r = 0.05 x 11.5 x 1022 metres r = 5.75 x 1020 m

Optical image of NGC 7531

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SLIDE 24

Weighing a Galaxy 14

Working out the distance

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SLIDE 25

Weighing a Galaxy 14

Working out the distance

  • 3. a. Calculate the mass of NGC 7531 in kg
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SLIDE 26

Weighing a Galaxy 14

Working out the distance

  • 3. a. Calculate the mass of NGC 7531 in kg

(hint: use the formula on page one and the radius - r - and velocity - v - that you worked out earlier and G = 6.673 x 10-11)

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SLIDE 27

Weighing a Galaxy 14

Working out the distance

  • 3. a. Calculate the mass of NGC 7531 in kg

(hint: use the formula on page one and the radius - r - and velocity - v - that you worked out earlier and G = 6.673 x 10-11) M = (r x v2)/G

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SLIDE 28

Weighing a Galaxy 14

Working out the distance

  • 3. a. Calculate the mass of NGC 7531 in kg

(hint: use the formula on page one and the radius - r - and velocity - v - that you worked out earlier and G = 6.673 x 10-11) M = (r x v2)/G M = (5.75x1020 x (150,0002))/(6.673x10-11)

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SLIDE 29

Weighing a Galaxy 14

Working out the distance

  • 3. a. Calculate the mass of NGC 7531 in kg

(hint: use the formula on page one and the radius - r - and velocity - v - that you worked out earlier and G = 6.673 x 10-11) M = (r x v2)/G M = (5.75x1020 x (150,0002))/(6.673x10-11) M = 1.9 x 1041kg

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SLIDE 30

Weighing a Galaxy 14

Working out the distance

  • 3. a. Calculate the mass of NGC 7531 in kg

(hint: use the formula on page one and the radius - r - and velocity - v - that you worked out earlier and G = 6.673 x 10-11) M = (r x v2)/G M = (5.75x1020 x (150,0002))/(6.673x10-11) M = 1.9 x 1041kg

  • b. Calculate the mass of NGC7531 in Solar

Masses (TIP: 1 solar mass is 2x1030 kg)

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SLIDE 31

Weighing a Galaxy 14

Working out the distance

  • 3. a. Calculate the mass of NGC 7531 in kg

(hint: use the formula on page one and the radius - r - and velocity - v - that you worked out earlier and G = 6.673 x 10-11) M = (r x v2)/G M = (5.75x1020 x (150,0002))/(6.673x10-11) M = 1.9 x 1041kg

  • b. Calculate the mass of NGC7531 in Solar

Masses (TIP: 1 solar mass is 2x1030 kg)

M = 1.9x1041/(2x1030)

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SLIDE 32

Weighing a Galaxy 14

Working out the distance

  • 3. a. Calculate the mass of NGC 7531 in kg

(hint: use the formula on page one and the radius - r - and velocity - v - that you worked out earlier and G = 6.673 x 10-11) M = (r x v2)/G M = (5.75x1020 x (150,0002))/(6.673x10-11) M = 1.9 x 1041kg

  • b. Calculate the mass of NGC7531 in Solar

Masses (TIP: 1 solar mass is 2x1030 kg)

M = 1.9x1041/(2x1030) M = 9.7 x 1010 Solar Masses

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SLIDE 33

Weighing a Galaxy 14

Working out the distance

  • 3. a. Calculate the mass of NGC 7531 in kg

(hint: use the formula on page one and the radius - r - and velocity - v - that you worked out earlier and G = 6.673 x 10-11) M = (r x v2)/G M = (5.75x1020 x (150,0002))/(6.673x10-11) M = 1.9 x 1041kg

  • b. Calculate the mass of NGC7531 in Solar

Masses (TIP: 1 solar mass is 2x1030 kg)

M = 1.9x1041/(2x1030) M = 9.7 x 1010 Solar Masses M = 100 Billion times heavier than the Sun!

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SLIDE 34

Congratulations, you’ve just weighed one

  • f the largest objects in the Universe!