Presentation is loading. Please wait.

Presentation is loading. Please wait.

Interstellar Space Not as Empty as You Might Think Dr. Andrew Fox Space Telescope Science Institute/European Space Agency Hubble Science Briefing April.

Similar presentations


Presentation on theme: "Interstellar Space Not as Empty as You Might Think Dr. Andrew Fox Space Telescope Science Institute/European Space Agency Hubble Science Briefing April."— Presentation transcript:

1 Interstellar Space Not as Empty as You Might Think Dr. Andrew Fox Space Telescope Science Institute/European Space Agency Hubble Science Briefing April

2 What is a galaxy made of? 2 2 Stars Dark Matter Interstellar Gas & Dust

3 Presentation Outline INTERSTELLAR MATTER - how do we detect it? - what forms does it take, and what’s its composition? - how empty is interstellar space (density)? - effects on starlight passing through it (reddening) - importance to galaxies overall (role in galactic evolution) Andrew Fox, Hubble Science Briefing, April

4 A Historical Note… First recorded use of the word “interstellar”, by Francis Bacon: “The Interstellar Skie.. hath.. so much Affinity with the Starre, that there is a Rotation of that, as well as of the Starre.” 1674 Suggestion that interstellar space was not empty, by Robert Boyle: “The inter-stellar part of heaven, which several of the modern Epicureans would have to be empty.” Andrew Fox, Hubble Science Briefing, April

5 Part I: Interstellar clouds Andrew Fox, Hubble Science Briefing, April The easiest way to see interstellar matter is to observe the dark clouds along the Milky Way

6 Band of light: unresolved stars Dark clouds of interstellar gas & dust Part I: Interstellar clouds Andrew Fox, Hubble Science Briefing, April The easiest way to see interstellar matter is to observe the dark clouds along the Milky Way

7 Band of light: unresolved stars Dark clouds of interstellar gas & dust Part I: Interstellar clouds Interstellar clouds often called nebulae Many types of nebulae exist (emission, reflection, dark, planetary) Andrew Fox, Hubble Science Briefing, April The easiest way to see interstellar matter is to observe the dark clouds along the Milky Way

8 Dark Clouds Barnard 68 in Ophiuchus Why is it dark? An empty region of space? Or a dense interstellar cloud blocking the light from the background stars? (the latter) Andrew Fox, Hubble Science Briefing, April

9 Dark Clouds Coal Sack (next to the Southern Cross) “visible” with naked eye Really seeing its shadow (absence of light from background stars) Andrew Fox, Hubble Science Briefing, April

10 Emission Nebula Eagle Nebula (M 16) “Pillars of Creation” Clouds of gas and dust being heated and sculpted by radiation from nearby young star cluster Traces regions of star formation Andrew Fox, Hubble Science Briefing, April

11 Reflection Nebula IC 349 Shows reflected light from a nearby star, not light emitted by the nebula itself As if the star is shining a flashlight on its surroundings Andrew Fox, Hubble Science Briefing, April

12 Planetary Nebula Eskimo Nebula Final state of solar-mass star (after it runs out of fuel) Gas irradiated by hot white dwarf star in centre Thought to be the eventual fate of the Sun (in another 5 billion years) Andrew Fox, Hubble Science Briefing, April

13 Andrew Fox, Hubble Science Briefing, April

14 Supernova Remnant Name: N63A Final state of stars many times more massive than the Sun Leftover material from supernova explosion Andrew Fox, Hubble Science Briefing, April

15 Part II: Diffuse interstellar gas (not seen with naked eye) Andrew Fox, Hubble Science Briefing, April Nebulae make up a tiny fraction of the volume of interstellar space. Diffuse gas exists between the nebulae, but you need a spectrograph to see it…

16 Spectroscopy Andrew Fox, Hubble Science Briefing, April Modern telescopes use diffraction gratings instead of prisms to split up the light

17 Spectroscopy: The Science of Rainbows Pattern of lines in stellar spectrum indicates composition and velocity of the star and the interstellar gas between the star and us. Each element has its own set of spectral lines (“fingerprints”). If the star is moving relative to the Earth, those lines will move by the Doppler effect Andrew Fox, Hubble Science Briefing, April

18 Spectroscopic Binaries Andrew Fox, Hubble Science Briefing, April Spectroscopic binary has two sets of lines (one from each star) moving back and forth. Astronomers can measure the period and amplitude of the shift.

19 In 1904 German astronomer Johannes Hartmann took a spectrum of the spectroscopic binary star delta Orionis (Mintaka) He found three sets of lines, two moving and one staying still. “these sharp lines probably did not have their origin in the [star] itself, but in a nebulous mass lying in the line of sight” Andrew Fox, Hubble Science Briefing, April Telescope withDiffuse Interstellar Cloud Binary Star spectrographContaining Ionized Calcium Delta Orionis (spectral lines stay same color) (lines become redder and bluer)

20 Multiple interstellar clouds can exist along a line of sight through the Galaxy Andrew Fox, Hubble Science Briefing, April courtesy Bart Wakker, UW-Madison

21 In a hydrogen atom, the proton and electron normally spin in the same direction. Occasionally the electron flips to spin the other direction. Happens only about once every 100 million years for each atom. When the electron flips it emits a radio wave with a frequency of 1420 MHz and a wavelength of 21 cm (was predicted in 1944 by Dutch astronomer Hendrik van de Hulst) 21 cm emission from interstellar space first detected in 1951 Hydrogen atom Radio telescope Andrew Fox, Hubble Science Briefing, April

22 All-sky 21 cm map of neutral hydrogen (Galactic coordinates) Galactic disk of neutral hydrogen, thickness of several hundred parsecs → The Milky Way is full of diffuse interstellar gas radiating radio waves Andrew Fox, Hubble Science Briefing, April

23 Galactic disk of ionized hydrogen, thickness of ~1000 parsecs Andrew Fox, Hubble Science Briefing, April courtesy Matt Haffner All-sky 21 cm map of ionized hydrogen (Galactic coordinates)

24 How empty is the Diffuse Interstellar Medium? ObjectDensity (particles per cm 3 ) Water ~10 22 (H 2 O molecules) Earth’s atmosphere 5 x (mostly N 2 & O 2 molecules) Vacuum Cleaner ~10 19 Incandescent Light Bulb ~ Best vacuum ever produced on Earth ~ (cryopumped chamber) Giant Molecular Clouds ~ (mostly molecular hydrogen) Diffuse Interstellar Medium ~ 1 (mostly atomic and ionized hydrogen) Diffuse Intergalactic Medium ~10 -5 Andrew Fox, Hubble Science Briefing, April The diffuse interstellar medium is about 50 million trillion times less dense than the air we breathe

25 Part III: Interstellar dust Andrew Fox, Hubble Science Briefing, April “Dust” means small solid particles (silicates and carbonate chemicals), rather than gaseous atoms or molecules Dust makes up only about 1% of the mass of interstellar matter (the rest is gas) Dust causes interstellar extinction (scattering of starlight out of the beam) Dust changes the colour of starlight passing through it (interstellar reddening)

26 The Blue-Sky Effect Red light passes straight through Earth’s atmosphere Blue light is scattered toward us Not to Scale EARTH ATMOSPHERE Sun Here the scattering is caused by molecules in the Earth’s atmosphere Andrew Fox, Hubble Science Briefing, April

27 Red light passes straight through Blue light is scattered out of beam INTERSTELLAR CLOUD CONTAINING DUST Here the scattering is caused by interstellar dust grains The more interstellar gas along the sight line, the more reddening occurs Distant stars appear redder than nearby ones Astronomers have to correct (de-redden) a stellar spectrum to account for this and to derive the star’s true color. STAR OBSERVER Interstellar Extinction (Blue Sky Effect viewed from different angle) Andrew Fox, Hubble Science Briefing, April

28 Interstellar dust Andrew Fox, Hubble Science Briefing, April As well as scattering visible light, dust emits infra-red and microwave radiation Horsehead Nebula (Barnard 33) at different wavelengths Interstellar clouds are often opaque to optical (visible) light but transparent to infrared and radio light These wavelengths open new windows to studying interstellar gas

29 Planck is a microwave satellite designed to measure the leftover radiation from the Big Bang. To Planck, interstellar dust is a foreground source of contamination (noise). Andrew Fox, Hubble Science Briefing, April

30 Andrew Fox, Hubble Science Briefing, April

31 Andrew Fox, Hubble Science Briefing, April

32 NASA Press Release June 2011 Centaurus A (radio galaxy with active galactic nucleus) Imaged with Hubble’s Wide Field Camera 3 Numerous dust lanes Star formation in red (H-alpha emission) Andrew Fox, Hubble Science Briefing, April

33 Interstellar dust in Andromeda (M31) Andrew Fox, Hubble Science Briefing, April Infra-red (IR) emission maps are used to trace the interstellar dust in other galaxies

34 Part IV: Interstellar gas and importance to galaxy evolution Interstellar clouds are the start and end points of a star’s life. Dying stars release heavy elements back into interstellar space, which becomes richer and richer in heavy elements over time (its metallicity goes up) All the heavy elements in the Earth were made in stars, then spent time in interstellar space before the Solar System formed INTERSTELLAR GAS Andrew Fox, Hubble Science Briefing, April

35 - contains many different types of nebulae - contains diffuse gas and dust - can be studied with spectroscopy at many wavelengths wavelengths - changes color of starlight passing through it - plays a key part in the life cycle of galaxies Summary: Interstellar space ….. is not completely empty. It: Andrew Fox, Hubble Science Briefing, April

36 Questions? Andrew Fox, Hubble Science Briefing, April

37 ESA Video: Andromeda (M31) at multiple wavelengths: Andrew Fox, Hubble Science Briefing, April


Download ppt "Interstellar Space Not as Empty as You Might Think Dr. Andrew Fox Space Telescope Science Institute/European Space Agency Hubble Science Briefing April."

Similar presentations


Ads by Google