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Colour

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by

David Gilbank

on 10 May 2016

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Transcript of Colour

A Universe of Colour
Rigel
Infra-red (IR)
Thermal
camera
(as used by firemen to see through smoke, for example)
Betelgeuse -
Red giant:
Surface
Temperature

~3500 C
Galaxy clusters
nearby
distant
Irregular
Lenticular/S0
Blue
=> hot, young stars which don't live long
=> galaxy is actively “Star-forming”

Red
=> only cool, old stars
=> galaxy is
not forming

new stars
= "Dead”
The
farther
away an object is in the distant Universe, the
redder
its light appears
(redshift)
Eventually, the light from a distant object shifts
from
the
visible

to
the
infrared
, because of its
distance
Hubble Space Telescope
- mainly works at
visible
wavelengths
James Webb Space Telescope
(JWST)
- Will mainly work in the
infrared
, allowing it to study much more distant objects
Ultraviolet
Blocked by the Earth's atmosphere
Must be studied from space (with
satellites
such as
GALEX
)
Ultraviolet
image
from GALEX
Optical
image
Credit: McGraw-Hill Observatory, Kitt Peak, Arizona, provided by Greg Bothum, Univ. of Oregon.
The
ultraviolet light
traces the hottest (shortest-lived, newest) stars and shows that new
star-formation
is clearly concentrated
along the spiral arms
Galaxy M81
X-rays
Gamma Rays
Microwaves
The Cosmic Microwave Background (CMB)
from the WMAP satellite
The
heat left over from the Big Bang



The radiation from the initial fireball has now been redshifted (stretched) so that it appears only
3 degrees above absolute zero
(-270 C)

It appears as a glow over the whole sky at
microwave
frequencies.
The Square Kilometre Array (SKA)
Radio
Here, the
radio emission
is
not related to the temperature
of the object

(It is due to charged particles being accelerated in a magnetic field)

In this case, a
supermassive black hole
at the centre of the galaxy is
blowing out jets
of material!
Galaxy Centaurus A
Optical + radio image
The Southern African Large Telescope (SALT) in Sutherland
Not all UV is blocked
by the Earth's atmosphere.
The weakest (longest wavelength) UV still makes it through.

SALT
is an optical telescope, but it is optimised to observe in this
UV
window
See: http://ska.ac.za for more info
Chandra X-ray Observatory
The Swift
gamma ray burst telescope
Gamma ray bursts
are the most distant and powerful
cosmic explosions
ever recorded!
Gamma Ray Bursts
Optical afterglow
from GRB080319B
Another way to study gamma rays -- from the ground!
HESS
-- High Energy Stereoscopic System
The HESS 1 array in Namibia
Large (12m) but relatively poor quality optical telescopes study the
optical flashes
as
gamma rays interact with the Earth's atmosphere
(Cherenkov light)
A larger HESS 2 array is being developed at the moment and Namibia is one of the countries bidding to host it.
White hot
Red Hot
hotter
The Orion Nebula, M42
"Stellar Nursery"
Cloud of gas and dust in which new stars are being born
Summary
The (
colour
of) light from an object, in most cases, tells us about its
temperature

Optical/visible light is a tiny, tiny portion of the EM spectrum

Only by adopting a
multiwavelength
approach can we hope to put together a complete picture of astrophysics.

Many of the state-of-the-art facilities which will allow this will be based in
Southern Africa
Dr David Gilbank (SAAO)
Galaxies are "
cities of stars
"
Galaxy clusters contain a "dense" atmosphere of hot (~1 -10 million C) gas which emits strongly in X-rays
Our Sun
Surface temperature
~5 500K
Blue supergiant
Surface temperature
~12 000 C
White hot
Red Hot
hotter
hotter
Blue hot
Humans
(~30 C) radiate mostly in the IR
The Universe seen ~380 000 years after the Big Bang
3 distant galaxy clusters
2319 supercluster
Optical +
X-ray
The
colour
of a star gives its
temperature
Also: the
hotter
a star, the
faster it burns
its fuel, and so the shorter its lifetime
o
o
o
o
size of wavelength
roughly 1/1000 mm
The Electromagnetic Spectrum
o
Our Sun is ~6000 C
and emits most of its light here
human vision
blue limit
red limit
wavelength (millionths of a metre)
o
Full transcript