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The Galactic Centre: a hidden treasure

The Galactic Centre: a hidden treasure. How can we study the Galactic centre? What is do we find there? What does it tell us about our Galaxy, and galaxies in general?. Galactic Bulges. Classic view of spiral galaxies young stars in spiral arms old stars in halo and bulge

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The Galactic Centre: a hidden treasure

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  1. The Galactic Centre:a hidden treasure • How can we study the Galactic centre? • What is do we find there? • What does it tell us about our Galaxy, and galaxies in general?

  2. Galactic Bulges • Classic view of spiral galaxies • young stars in spiral arms • old stars in halo and bulge • therefore, expect Galactic centre to be a quiet collection of old stars (like a globular cluster)?

  3. Observing the Milky Way 75 cm 21 cm 11 cm 2.6 mm 60 μm 8 μm 2 μm optical X-ray γ-ray http://adc.gsfc.nasa.gov/mw/milkyway.html

  4. The Galactic Centre: Radio • central 4° square • numerous supernova remnants • so, not a quiet region of old stars! • filamentary structures suggesting complicated magnetic fields • bright central source, Sgr A

  5. Zooming In • The Very Large Array, New Mexico • 27 telescopes in Mercedes star • movable on rails • data processed to mimic one large telescope • resolution can be better than HST!

  6. Zooming In 20 cm 6 cm Sgr A* 1.2 cm 3.6 cm NRAO / AUI / NSF

  7. The Galactic Centre: X-rays X-ray images pick up hot gas and “astrophysical par-ticle accelerators” such as pulsars and X-ray binaries radio image for comparison images from Chandra website

  8. The Galactic Centre: X-rays radio image for comparison

  9. The Galactic Centre: infra-red MSX 4.5° mid-infrared view (4.2 – 26 microns) showing mostly warm dust

  10. The Galactic Centre: infra-red MPG/ESO near infrared (2 microns) shows stars

  11. Mysteries of the Galactic Centre • A region of intense star formation surrounding a point source of radio and X-ray emission • Where does the gas come from? • What is the central point source?

  12. Bringing in the Gas • Evidence from star counts and extinction studies shows Milky Way is a barred spiral with a ring structure, like M95 • This allows gas from the disc to be drawn in towards the centre Image by Jean-Charles Cuillandre and Giovanni Anselme, CFHT

  13. Sgr A* • Stars in infra-red images are seen to move around Sgr A* • plot orbits • determine mass of Sgr A* • result: approximately 4 million solar masses!

  14. The Milky Way’s dark heart • Is Sgr A* a supermassive black hole? • YES! • How do we know? • Basically, it’s too small to be anything else • orbit of star S2 • rapid flares in X-ray and near infra-red

  15. The black hole mystery • The Milky Way is not alone! • most large galaxies have central supermassive black holes • the black hole mass is closely correlated with the mass of the galaxy’s bulge • we don’t know why (yet) • note that we believe these central black holes are the power sources of active galactic nuclei

  16. Conclusions • The centre of the Milky Way galaxy is an exciting place (if not an ideal holiday spot!) • it is a site of active star formation with numerous young, massive stars and recent supernovae • at its heart is a 3-million-solar-mass black hole • further studies may give new insights on galaxy formation

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