Transcript The Galactic Centre: a hidden treasure

The Galactic Centre:
a hidden treasure
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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
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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)?
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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
The Galactic Centre: Radio
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central 4° square
numerous supernova
remnants
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so, not a quiet region of old
stars!
filamentary structures
suggesting complicated
magnetic fields
bright central source,
Sgr A
Zooming In
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The Very Large
Array, New
Mexico
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27 telescopes in
Mercedes star
movable on rails
data processed to
mimic one large
telescope
resolution can be
better than HST!
Zooming In
20 cm
6 cm
Sgr A*
NRAO / AUI / NSF
1.2 cm
3.6 cm
The Galactic Centre: X-rays
X-ray images pick
up hot gas and
“astrophysical particle accelerators”
such as pulsars
and X-ray binaries
images from
Chandra website
radio image for
comparison
The Galactic Centre: X-rays
radio image for comparison
The Galactic Centre: infra-red
MSX
4.5°
mid-infrared view (4.2 – 26 microns)
showing mostly warm dust
The Galactic Centre: infra-red
MPG/ESO
near infrared (2 microns) shows stars
Mysteries of the Galactic Centre
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A region of intense star
formation surrounding a
point source of radio and
X-ray emission
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Where does the gas come
from?
What is the central point
source?
Bringing in the Gas
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Image by Jean-Charles
Cuillandre and Giovanni
Anselme, CFHT
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
Sgr A*
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Stars in infra-red images
are seen to move
around Sgr A*
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plot orbits
determine mass of Sgr A*
result: approximately
4 million solar masses!
The Milky Way’s dark heart
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Is Sgr A* a supermassive
black hole?
YES!
How do we know?
Basically, it’s too small to
be anything else
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orbit of star S2
rapid flares in X-ray and
near infra-red
The black hole mystery
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The Milky Way is not alone!
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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
Conclusions
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The centre of the Milky Way galaxy is an
exciting place (if not an ideal holiday spot!)
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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