Transcript Overview IR Astronomy Explore hidden universe , Cosmic dust, Cool

Overview IR Astronomy
Explore hidden universe , Cosmic dust, Cool
objects , Dying stars, Forming stars, Early
Universe
Why IR?
 between wavelengths of about 1 and 300 microns
 The human eye detects only 1% of light at 0.69 microns,
and 0.01% at 0.75 microns, and so effectively cannot see
wavelengths longer than about 0.75 microns unless the
light source is extremely bright.
 The Universe sends us a tremendous amount of
information in the form of electromagnetic radiation .
 Much of this information is in the infrared, which we
cannot see with our eyes or with visible light telescopes.
All Sky Map of IRAS Point
Sources
 IRAS (Infrared Astronomical Satellite), 1980 :The first IR
satellite
 detected about 350,000 infrared sources, increasing the
number of cataloged astronomical sources by about 70%.
 All Sky Map of IRAS Point Sources. The plane of our galaxy
runs horizontally across the image
A. Exploring the Hidden
Universe
 study objects hidden by gas and dust in the infrared,

Galactic Center
Cygnus region
 Red : seeing the light from billions of stars, particularly the
largest, brightest ones. The dark bands where vast clouds of
dust block our view
NIR : stars, but now it better
traces the smaller,
cooler ones. the lanes
of dust have become
partially transparent
 Far IR : stars hardly emit any

light at all, almost

everything we see is
 generated by the dust clouds themselves.
B. Cosmic dust
 collections of just a few molecules to
grains of 0.1 mm in size.
 Dust is important because we find lots
of it around young stars.
 it helps them to form, and it is also
the raw material from which planets
like the Earth are formed.

cosmic dust cycle.
 Dust is formed in stars and is then blown off in a slow wind
or a massive star explosion.
 The dust is then 'recycled' in the clouds of gas and some
of it is consumed when the next generation of stars begins
to form.
 The dust converts the absorbed starlight into light at longer
wavelengths.
 see the dust shining using special instruments sensitive to
the far-infrared and submillimeter.
 Herschel is designed to work at these wavelengths, and see
the dust shining at temperatures between 8 and 100 K.
Clouds of dust
 in the far-infrared, this dust is seen to
glow as it is heated by the young stars
within.
 Rosette Nebula in visible light, seen by
Herschel in the far-infrared.
The Infrared Glow
 The extragalactic background is
made up of radiation from distant
objects beyond our own Milky
Way.
 All the visible light from stars is
plotted in the graph as the blue
line. The infrared glow produced
by cosmic dust which has been
warmed by all the stars since the
beginning of time is shown in red.
This 'background glow' of the
Universe tells us the total amount
of energy released by stars.
 But this reveals a very surprising
result: the amount of energy
radiated by stars and dust is
almost the same.
C. Detecting Cool Objects
 cool stars, infrared galaxies, clouds of
particles around stars, nebulae, interstellar
molecules, brown dwarfs and planets.
 In the infrared, where planets have their
peak brightness, the brightness of the star is
reduced, making it possible to detect a
planet in the infrared.
 Recently, an infrared survey of the
Trapezium star cluster in the Orion Nebula
revealed over 100 low mass objects which
are brown dwarf candidates.
C-1Brown Dwarf candidates
 Recently, an infrared survey of the
Trapezium star cluster in the Orion Nebula
revealed over 100 low mass objects which
are brown dwarf candidates
 BD : stars with masses so low (about 8% of
the Sun's) that they can not sustain nuclear
hydrogen burning but be still massive
enough to burn deuterium for energy,
 the deuterium burning limit : about 1.3% of
the Sun's mass
C-2 "free-floating planets"
 "free-floating planets"
thirteen of the low mass objects show
evidence of lying below even the
deuterium burning limit,
as little as 8 times as massive as
Jupiter and likely formed along with the
cluster stars a million or so years ago.
 They are detectable in the infrared
BD & planets
 If the Trapezium is typical of young
star clusters , then the survey results
suggest that brown dwarfs and freefloating planets may be fairly common,
but there are not enough to solve the
mystery of dark matter in the Universe.
D. Dying Stars
Spitzer's view of the Cassiopiea A
supernova remnant
 In death, extremely massive stars explode in a
supernova, blasting their chemical creations into
space, and seeding the universe for a new
generation of stars to grow.
 medium mass stars like our Sun puff up to become
red giants before sloughing off their outer layers, like
snakes shedding their skin, sending newly-formed
elements and molecules floating slowly off into
space.
 IR study : solve the longstanding mystery of where
the dust in our very young universe came from.
pathways for massive stars and
lower mass stars
Low-mass stars
 Stars less than about eight times the mass of the Sun live for a
long time (100 million to 10 billion years). At the end of its
current middle-aged period, the Sun will become a Red Giant
star, expanding by a factor of a hundred with its outer layers
extending out to the orbit of Mars!
 Such stars puff away their outer layers, leaving behind the hot,
dense core of the star. before they die stars actually lose most
of their mass.
 This happens mostly in a period called the Asymptotic Giant
Branch (AGB) phase, in which material is ejected in cycles,
producing a series of shells around the star.
  These multiple shells are effectively a fossil record of the
star’s mass-loss history.
Shells
 the shells are too cold and faint to have been
detected by previous infrared telescopes.
 Herschel’s sensitive submillimetre camera, SPIRE, is
perfectly suited to seeing the cold dusty shells,
revealing exactly how much mass has been lost.
 These shells are also rich in atoms and molecules
which emit light at specific wavelengths that depend
on their chemical make-up, and which will be
examined by Herschel’s spectrometers.
Herschel obs of shells
 looking at water molecules : for life,
 interesting compounds seen around dying stars :
 PAHs (Polycyclic Aromatic Hydrocarbons), made from
hydrocarbon chains in a ring structure (see next inset),
 “bucky-ball” fullerene chain molecules, and amino acids,
the building block of proteins.
  will tell us about the mass, temperature, and density of
the gas, and what chemistry is going on.
  how stars evolve, how much mass they eject, how they
make dust, what chemicals exist in their environments, and
how this material influences the formation of new stars and
planets.
Polycyclic Aromatic
Hydrocarbons
 Left: Polycyclic Aromatic Hydrocarbons in the Horsehead
Nebula. Inset is an example of the structure of PAHs, this
example includes a nitrogen atom (red). Right: Fingerprints of
PAHs (spikes) seen in the spectrum of a star-forming region.
Image credit: NASA/Spitzer.
High-mass stars
 Stars more than eight times heavier than the Sun
also enrich galaxies with cosmic dust and heavy
elements.
 Near the end of their relatively short lives they go
through several phases in which they eject material
in intense winds, sometimes with speeds up to 6
million km/h, and with huge amounts of ejected
material.
 The star eta Carinae is thought to have lost over 80
times the mass of our Sun in the last 1,000 years in
the form of gas and dust.
supernova explosions
 how much mass they lose before they explode, are
largely unknown.
  find the colder ejected material to solve this
problem

Left: Cold dust bubble around an evolved massive star
(RCW120). The submillimetre light is from cold dust (green) and
visible light is shown for comparison (red and blue) (credit:
ESO). Right: The massive star Eta Carinae in X-rays, visible
light and submillimetre (credit: NASA/JCMT/H.Gomez et al.)
supernova dust
 wondered if the supernova itself may create cosmic dust.
 Observations of supernova remnants with NASA’s Spitzer
Space Telescope (below, left) and the ground-based
SCUBA camera (below, right) indicate amounts of dust
ranging from 10,000 Earth masses up to the mass of our
Sun in dust alone!

Left: Spitzer’s infrared image of the supernova remnant Cassiopeia A with
argon gas (green), 10,000 Earth’s worth of warm cosmic dust (red) and silicon
gas (blue) (credit: NASA/J.Rho et al.). Right: SCUBA submillimetre image of
very cold dust in Cassiopeia A (credit: SCUBA/L.Dunne et al.).
E. stellar embryos and infants
 Stars form like raindrops in
space, from condensing
clouds of gas and dust.
 The Fairy of Eagle Nebula Image Credit: The
Hubble Heritage Team, (STScI/AURA), ESA,
NASA
 The greater Eagle Nebula, M16, is actually a
giant evaporating shell of gas and dust inside of
which is a growing cavity filled with a
spectacular stellar nursery currently forming an
open cluster of stars.
G. Exploring the Early Universe
 As a result of the Big Bang, the
universe is expanding and most of the
galaxies within it are moving away
from each other. The light that
galaxies emit are " redshifted ".
 The image to the right is an infrared view of
some of the farthest galaxies ever seen.
Image credit: RI Thompson (U. Arizona),
NICMOS, HST, NASA)
Missing Galaxies
 missing the galaxies which are hidden by lots of dust.
 Work with previous infrared and submillimetre telescopes showed that
only a few billion years after the Big Bang there were lots of dusty
galaxies that are so hidden by dust that they can barely be seen by
optical telescopes. At the moment, it seems quite likely that these
galaxies are the ancestors of elliptical-shaped galaxies we see around
us today.
 The image on the right shows the SCUBA 'deep field'. This is the
submillimetre view of the Hubble Deep field, the dusty view of the
Universe. There are far fewer galaxies (seen as white blobs) in this
sub-mm image than in the optical one left but these few galaxies
alone are responsible for around a third of the total optical light in the
Hubble picture.
  The amount of stars being born in these dusty galaxies is between
100 - 1000 times more than what we see in optical galaxies.
H. Adding To Our Knowledge
Of Visible Objects
 To get a complete picture of any
object in the Universe we need to
study all of the radiation that it emits.
  add a great deal to our knowledge
about the Universe and the origins of
our Solar System.