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The Hubble Space Telescope
- the first 10 years
• Our only optical telescope in space
– Why, when and how
• Observations
• The Next Generation Space Telescope
• An Orbital
• Launched
April 24th ‘90
• Serviced
mid-Dec ‘93
• Visible From
Earth by Eye
The Launch:
• April 24th 1990
• Space Shuttle
Mission ST-31
• 10x faster than a
rifle bullet !
• 2.4 metre
• Solar Panels
for energy
• 4 instrument
• Comms
• Shutter
• Gyros
The Benefits of Space
• No atmosphere = crystal sharp images
• No sky glow = very deep images
Hubble Trouble
• But,to our horror we discovered Hubble’s
mirror was the wrong shape !
• In 1993 a service mission (ST-62) was sent
up to replace
some of the
• Since then
its worked
• Here’s the
difference >
Hubble Trivia
• Named after Edwin Hubble who discovered
the expansion of the universe
• Project conceived in 1971
• Total cost around US $1 billion !
• Now Operational for 10 years
• Observed 14,000 objects
• Orbited the Earth 58,400 times
• Travelled 1.5 billion miles
• Can see back to when the Universe was
10% of its current age (13 billion years ago)
Where HST has been looking
• This shows the places on the sky where
HST has looked. Milky-way across centre.
Our Solar System
• In our Solar System are 9 planets: Mercury,
Venus, Earth, Mars, Jupiter, Saturn, Uranus,
Neptune and Pluto plus an asteroid belt,
Kuiper belt, moons and of course the sun.
• HST cannot look at Mercury because it is
too close to the sun and would damage the
• It has looked at everything else though >>>
Our Solar System with HST
• Comets are gigantic icy rocks which whiz
through the Solar System at v.high speeds.
• It is believed a comet killed the dinosaurs
and the impact created the gulf of Mexico
• Thankfully Comet impacts are very rare.
• However: In 1995 a comet hit Jupiter !
The Impact of Fragment G
• Provided
on the
rotation of
its thickness
and its
• Stars form from giant gas clouds floating in space
• The cloud first starts to collapse due to gravity
• When sub-clumps reach a sufficiently high density
Nuclear fusion occurs bathing the region in radiation
• This radiation blows away any remaining dust
• Finally we’re left with a star cluster
• Eventually each star explodes (Supernovae)
• All that remains is a black hole, neutron star or
white dwarf
• HST has looked at all stages of this process >>>
Stars: Gas Collapses
• The Trifid Nebula:
Stellar Nursery
• Gas is collapsing
due to gravity
and where it
becomes dense
enough stars are
formed and nuclear
fusion occurs
Stars: Stars Ignite
• The Eagle Nebula
• Radiation from the
newly formed stars
moulds the gas
remaining into
the spectacular
gaseous pillars we
see here
Stars: The First Stars
• An emerging star
cluster: NGC3603
• As the gas is blown
away the newly
formed star cluster
becomes visible
• At this stage the
light is dominated
by the very hot but
short-lived blue stars
Stars: A Cluster is formed
• A Star Cluster
• As the hot blue stars
burn out we are left
with a star cluster.
remaining gas is
blown far away
cluster will
this for
and this
stay like
many billions
Stars: Stellar Outflows
• Eta Carinae
• Many stars form as
binary systems, during
the course of their
active phases mass is
often transferred from
one star to the other. If
matter is accreted
fast it squirts out
the poles of the
Stars: Supernova
• Superova: NGC6543
• Stars end their life-cycle
by going Supernova or
Nova depending on their
initial mass
• The most massive go
supernova and blow
off their outer shell
whilst the core collapses
into a black hole
Stars: Planetary Nebulae
• The Spiral Nebula
• The shell of material
blow off settles down
and the remaining core
can often pulsate if it
is not massive enough
to form a black hole
• Galaxies consist of about 1billion stars
• Once called “Island Universes”(Kant)
• 3 main types:
– Ellipticals (Smooth, Old and Red)
– Spirals (Bulge plus spiral arms)
– Irregulars (Newly formed or interacting)
• HST allows us to look closely at the regions
where stars form and to see their structure
back to when the Universe was young
Galaxy Clusters
• Here we see a
typical example
of an elliptical galaxy
(centre) and a spiral
galaxy (right).
• Galaxies often form
in groups of clusters.
Here we see the nearby
core of the Coma
cluster of galaxies
Galaxies and star-formation
• The smaller panel shows NGC4314 as viewed
from the ground. The larger panel shows the core
as seen by HST. The purple and blue regions
indicate where star clusters are forming
Peculiar Galaxies and mergers
• Galaxies are believed start from small sub-clumps
which through merging build themselves up to
giant ellipticals and spirals. Here we see the
merger of two giant spirals which will one day
become a giant elliptical. The core of each galaxy
is seen in red and
most likely each
core contains a
giant black hole.
• Our galaxy is on
collision course
with Andromeda
and one day may
look like this.
The Hubble Deep Field
• The most famous single image is:
The Hubble Deep Field (150 orbits of data)
• It only covers 1millionth of the sky but:
– It’s the deepest image ever taken of the Universe
looking back to when the Universe was:
1 billion years old (I.e., 10% of its current age)
– In it we see that the most distant galaxies are very
irregular unlike the spirals and ellipticals we see
– With HST we finally see the main epoch of
GALAXY FORMATION ~8billion years ago
The Hubble Deep Field
• The Deepest image ever taken of our Universe
Galaxy Evolution
From the Hubble Deep Field we see that galaxies look
normal back until 30% of the age of the Universe at
which point the number of Peculiars and mergers
increases. This panel shows samples of galaxies at
different ages
starting from
today and
stretching back
until the Universe
was 10% of its
current age.
• There are 4 numbers that define our universe
1) The Expansion Rate (Hubble Constant)
2) The Density of Matter
3) The Density of Radiation
4) The Density of Space-time
• The Hubble Space Telescope is measuring (1)
the expansion rate of the universe today !
• The other parameters are being measured from
other satellites which are looking at the
Cosmic Microwave Background
An Analogy (Car=Universe)
• Think of a car heading down the street out
of control with the brake, hand brake and
accelerator all jammed on !
• We want to know whether it’s going to stop,
get faster or stay at a constant speed !
• Whether this happens is determined by its
current speed, and the battle between the
brakes and the accelerator !
The Car and the Universe
• The car is the Universe and we want to
know whether the Universe is going to stop
expanding and recollapse or continue to
expand for ever.
The Hubble constant is the cars speed right now
The density of matter is the footbrake
The density of radiation is the handbrake
The density of Spacetime is the accelerator
(also known as the Cosmological Constant)
• Measuring the Hubble Constant is a crucial
The HST Key Program
• Aim, to measure the expansion rate of the Universe
=> the age of the universe!
• To do this we need a very accurate distance
measurement, the velocity we already know
• But how do we measure distances ?
• Well some stars are known to pulsate at a rate
which depends on their brightness.
• We can use this to calculate the distances to nearby
• In the case M100 in the Virgo cluster
The Age of the Universe
All galaxies are moving away from us
The furthest galaxies move away faster
Hubble’s law => Universal Expansion
If we measure a galaxies speed and its
distance we can calculate how long it’s been
travelling for (I.e., time=distance/velocity).
• All galaxies gives us the same answer !
• This is an approximate* age of the
Universe, the point in space-time from
which all matter originated
(*as this ignores any braking and accelerating)
Calculating Distances
• If you move an object away it gets fainter
• Once its 10x further away it is 100x fainter
• Hence if we know how bright a star SHOULD
be and we measure how bright it ACTUALLY
is we can estimate the distance
• This relies on finding stars with KNOWN
brightness and luckily their exist a class of star
known as Cepheids which pulsate according
to their brightness
• We can use these to measure distances
The Galaxy M100
The galaxy M100
lies in the nearby
Virgo cluster, we
know how fast
Virgo is moving
so now all we need
is its distance to get
the age of the
Finding the Cephieds
To measure the distance we need to find Cepheids,
variable stars which pulsate according their brigthness.
To do this we need to
observe M100 many
times and look for
stars whose
brightness varies
periodically. Here’s a
Cepheid found on the
outskirts of the galaxy
Monitoring their Brightness
Once a Cepheid has been found we must measure its
brightness frequently to determine the period (which
tells us its INTRINSIC brightness) and by comparing
this to its
brightness we can
estimate the
distance to M100.
Even with HST
this is very hard
Distance to M100
• Here’s the equation that we use:
m=The APPARENT Brightness in logarithmic units
M=The INTRINSIC Brightness in logarithmic units
d =The distance in parsecs (1parsec=3.3 light years)
• The APPARENT brightness we measure from the
image, the INTRINSIC brightness we calculate from
the PERIOD of the Cephied
• Eventually we get the crucial distance to M100
The Hubble Constant
• HST provides a distance to M100 of:
16 Mpc = 50 million light years !
• From the ground we can measure the speed
with which this galaxy is moving away:
1250 km/s I.e., Every day M100 gets 108
million km further away !
• The ratio gives us the Expansion Rate of the
Universe =78 km/s/Mpc
• It also gives an approximate age of the
universe, remember t = d/v which gives
about: 10 billion years
The Universe Today
• Thanks to the Hubble Space Telescope we
have a picture in which our universe formed
10 billion years ago and 2 billion years into
this the galaxies formed through mergers of
smaller building blocks into the large and
well ordered galaxies we see around us
today - this new perspective into our
Universe has only been possible by looking
through the eye of the Hubble Space
• So what is the next big question ?
The Fate of the Universe
• Remember the Car hurtling our of control ?
– HST has measured its speed today
• We still have three more parameters to find
– The Density of Matter = the footbrake
– The Density of Radiation = the handbrake
– The Density of Space-Time = the accelerator
• To measure these requires a combination of
even more sophisticated telescopes and
The Next Generation Space Telescope
NASA is planning an 8-metre telescope, a collecting
area 11x large the the HST. To be launched in 2015.
This will see even further and over larger chunks of
sky. It will also see in other wavelengths and in
particular the Infrared.
This telescope will
be sent into deep
space and a solar
shield will keep it
protected from the
Finally: my favourite image
• Gravitational Lensing by a Galaxy Cluster
• Cosmology and Astronomy is an exciting
science entering a golden era of discovery. Soon
we will know either the fate of the Universe or
we’ll overturn the Big Bang model. Either way
its an exciting time and an exciting place to be.
• HST Websites: