Galaxy rota3on curves: A story of astronomical discovery

Transcription

1 The Swan Nebula

2 Galaxy rota3on curves: A story of astronomical discovery

3 How can you measure the velocity (speed) of a star? Write down a set of instruc3ons for a budding astronomer who wants to measure the velocity of a star.

4 I ll share my instruc3ons, if you share yours

5 ColeJe s recipe for measuring the velocity of a star 1. Point a telescope and spectrograph at the star 2. Measure a spectrum of the star 3. Find an emission line in the spectrum of the star 4. Measure the Doppler shis of the line 5. Use the Doppler shis to calculate the star s velocity

6 This is a spectrum of the atom Hydrogen

7 This is a spectrum of the atom Hydrogen Short wavelength (blue) Long wavelength (red) Bright lines represent wavelengths where Hydrogen prefers to emit (or absorb) light.

8 This is also a spectrum of the atom Hydrogen (a black and white version of what we saw in the last slide) Short wavelength (blue) Long wavelength (red)

9 Astronomers can choose the wavelength range of an observed spectrum Short wavelength (blue) Long wavelength (red)

10 Astronomers can choose the wavelength range of an observed spectrum Short wavelength (blue) Long wavelength (red)

11 Suppose this spectrum represents a star that is not moving rela3ve to the Earth. What would the spectrum look like if the star were moving away from us?

12 Suppose this spectrum represents a star that is not moving rela3ve to the Earth. What would the spectrum look like if the star were moving towards us?

13 Veloci3es of stars can be used to study the mo3ons inside galaxies

14 How would you expect the stars to move in the Andromeda galaxy (shown below)? c. 1970, the veloci3es of stars in galaxies had not yet been measured

15 We re now going to think about this in more detail. Lecture Tutorial: Rota3on curves

16 Actual spectra from work by Vera Rubin Spectra of galaxy. Bright line is Hydrogen (H- alpha), faint line is from Nitrogen Rubin et al Picture of galaxy Black bar is the slit of a spectrograph (just like on your hand- held spectrograph)

17 Actual spectra from work by Vera Rubin Spectra of galaxy. Bright line is Hydrogen (H- alpha), faint line is from Nitrogen Rubin et al Picture of galaxy Black bar is the slit of a spectrograph (just like on your hand- held spectrograph)

18 Nearly all galaxies have similar spectra Rubin et al. 1978

19 Spectra and corresponding rota3on curves

20 "The conclusion is inescapable that non- luminous majer exists beyond the op3cal galaxy. Rubin et al. 1980

21 Other evidence for dark majer: gravita3onal lenses

22 What might non- luminous (dark) majer be? (First: What are examples of luminous (bright) majer?)

23 What might non- luminous (dark) majer be? - Planets - Dust - Black holes - Neutron stars - None of the above

24 What might non- luminous (dark) majer be? - Planets - Dust - Black holes - Neutron stars - None of the above

25 We s3ll have no idea what dark majer is. We only know that it s NOT anything else we ve ever detected (NOT stars, not dust, not neutron stars, not black holes, not planets..), and that it doesn t interact with light.

26 What makes up the universe?

27 Vera Rubin (with Diedre Hunter) in the control room of the KiJ Peak 4 meter telescope (c. 1999)

28 Vera Rubin: Some interes3ng quotes On discrimina+on she faced: I met him in the hall, and probably said the first thing I had ever said to him outside of the class, and I told him I got the scholarship to Vassar and he said to me, "As long as you stay away from science, you should do okay." It takes an enormous self- esteem to listen to things like that and not be demolished. So rather than teaching lijle girls physics, you have to teach them that they can learn anything they want to. On studying galaxies: "I some3mes ask myself whether I would be studying galaxies if they were ugly. I really do, and I'm not sure. I mean I see ugly bugs. My garden is full of slugs. I some3mes think, well, maybe if I started studying them, they wouldn't appear [to be so ugly] On our understanding of the universe: I s3ll believe there may be many really fundamental things about the universe that we don't know. I think our ignorance is probably greater than our knowledge. I wouldn't put us at the point of knowing about the universe.