All-sky radio image at 408 MHz radio, taken with Jodrell, Effelsberg, and Parkes.

1
All-sky radio image at 408 MHz radio, taken with
Jodrell, Effelsberg, and Parkes.
We begin here a tour of our home galaxy, the
Milky Way. Moving from low to high frequencies
(energies), the results are displayed using the
Aitoff-Hammer equal area projection centered
towards the direction to the Galactic center and
with an orientation along the lane of the galaxy.
1.69x10-6 eV, 73.5 cm
Diffuse radio emission is a tracer of
relativistic electrons in a field. Compact
sources can be compact synchrotron sources or
self-absorbed bremsstrahlung as in an HII region.
Most thermal sources (such as dust reprocessors
of starlight) are at higher energies. The ridge
of emission above the compact sources in the
thick disk is thought to be primarily cosmic ray
electron synchrotron emission. The prominent
North polar spur could be the projected shell of
a nearby recent supernova.
2
All-sky COBE DIRBE, 240 mm false-color
intensity maps
5.18x10-3 eV 1250 GHz
The fluffy dust and smoke of the galaxy show up
here in this portrait of the Milky Way. Micron-
and submicron-sized particles heat up and
reradiate. Infrared intensity is also a good
tracer of dense concentrations of matter such as
sites of star formation and core collapse
supernovae, and OB (hot) star associations. The
zodiacal light begins to make its appearance (see
Great Discovery Poster by Dwek (GDcobe).
3
All-sky COBE DIRBE intensity map at 3.5 mm
0.36 eV 8.6x1013 Hz
The zodiacal light in all its glory. This is the
Suns thermal emission reprocessed by the dust
remaining from the formation of the Solar system.
(Note that this map could be symetrically cast
as an Aitoff projection in Solar system
coordinates. The Milky Way shows up as a dusty
ridge of emission with a slight east/west
asymmetry and some enhancement in the anticenter
direction (see GDcobe).
4
All-sky, optical, Lund Obseratory.
2.5 eV 6.0x1014 Hz 5x10-5 cm
5000 A all-sky image. This is not mainly diffuse
optical, but rather the integrated starlight from
the disk of the Milky Way. The stellar disk has
typically a FWHM thickness of 160 pc, compared
with the 8.5 kpc distance to the center of our
Galaxy. Strong mottling of the stellar radiation
is due to clouds of absorbing dust, which redden
the direct emission from the stars. This is the
waveband to which many Earth-based phylum are
sensitive, probably due to the transparency of
water and air at these frequencies.
5
All-sky X-ray intensity map from the A2
experiment on HEAO-1.
2-10 keV 0.5-2.5x1018 Hz 6.2-1.2 A
2-10 keV X-ray all-sky image. Diffuse and point
sources of X-rays from all-sky map made from
roughly six months of scanning data. Note the
ridge and central bulge of sources, in addition
to some high latitude outliers. The implication
is that these are mainly galactic sources, and
indeed some prevalent source population in the
disk consist of accreting high-mass X-ray
binaries, low mass X-ray binaries and millisecond
pulsars, black-hole candidate systems (see GDbh
by Grove and Grindlay, GDns by Finger et al.).
Only the faintest sources give evidence for being
isotropically distributed and hence perhaps
extragalactic in fact, identifications of X-rays
from AGN are common (see GDagn by Weaver).
6
All-sky, 0.511 MeV, OSSE on CGRO overlaid on
optical.
Electron-positron annihilation radiation 511
keV 1.2x1020 Hz
511 keV line radiation showing activity at the
center of our galaxy. Reanalyses continue to
support this discovery image, overlaid on the
optical galaxy projection, of a bridge of
electron-positron annihilation emission projected
above the direction to the center of the Galaxy.
An epsiode of starburst activity driving a hot
wind into the Galaxys halo is one possibility
the asymmetry stems from a preferential venting.
Nuclear activity is also possible, not to mention
chance foreground effects. An X-ray nova, Rho
Ophiuchus 1977, is along the line-of-sight to the
high-latitude emission component. The integrated
0.511 MeV radiation from the entire Galaxy is 1
photon every hour or so per square centimeter.
7
All-sky COMPTEL image of 1.809 MeV from the
decay of 26Al
Compton Telescope (COMPTEL) on CGRO
Galactic longitude l (0o-360o) and latitude
b(-90o - 90o) Galactic center (l,b 0o,0o),
Galactic anticenter (l,b 0o, 180o)
1.809 MeV g rays are a good tracer of recent
stellar nucleosynthesis from 26Al (106
half-life) made in novae and SNe of massive
stars. Note the strong clumping toward the
galactic disk and the clumping associated with
the central regrion, the Cygnus (l 75o) and Vela
(l 270o) regions.
8
All-sky gt 100 MeV gamma rays from EGRET initial
(18 months) full-sky survey.
EGRET spark chamber experiment on CGRO (100
MeV-5 Gpc)
gt100 MeV g-ray all-sky image. Diffuse g rays are
largely due to secondary pion decay from cosmic
ray proton interactions with gas and dust, and
nonthermal CR electron free-free and Compton
emissions off diffuse galactic fields. Some high
latitude point sources associated with blazars
(3C 279 at top, right) and unidentified sources
are evident. Young isolated rotation-powered
pulsars (see GDpsr by Strickman and Harding) such
as Vela (l 270o), Crab and Geminga (l190o)
are powerful gamma-ray sources. The spiral
structure of our galaxy is traced out in diffuse
galactic gt100 MeV emission were viewing down
the Orion (l200o, b -25o) arm as can be seen.
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All-sky gt 100 MeV gamma rays from EGRET analysis
of 6 years of data
EGRET spark chamber experiment on CGRO (100
MeV-5 Gpc)
The importance of long observing and integration
times in gamma-ray astronomy is evident in this
figure, again showing gt100 MeV g-rays. Detailed
structure -- or is it statistics? -- is now
beginning to become visible away from the plane
of the galaxy. The gradient away from the
Galactic ridge is a convolution of relativistic
particle intensities, and the intensity and
directional properties of the magnetic and
radiation fields. Sorting out the right particle
and field intensities provide a global picture of
the particle and current flows that, with
gravity, regulate the workings of the Milky Way
and, by implication, other (spiral) galaxies.
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Multiwavelength mural. For more information,
visit the backdrop. Credit D. Leisawitz and J.
Friedlander.
11
X-ray emission from the SNR of SN 1006.
ASCA image 2-10 keV

• SNR 1006, at 1.7-3 kpc, was formed when a star
  with mass 10-20 Mo exploded. The bright remnant
  ridge emission, coupled with the oddly weak or
  absent X-ray line signature from bound-bound and
  bound-free processes, suggests that the emission
  is probably synchrotron from TeV electrons
  accelerated at a shock front. Asymmetry in the
  shock emission has to do with global magnetic
  field geometry and surrounding medium structure.
  Much theoretical work argues that supervova shock
  fronts are efficient sites of nonthermal
  electron acceleration through the mechanism of
  diffusive (Fermi type-1) shock acceleration.
  This does not prove the cosmic ray acceleration
  hypothesis because surrounding nonthermal
  electrons could be compressively heated and
  enhanced (see GDcr by Lingenfelter).

12
Vela and Puppis A SNRs in X-rays
ROSAT PSPC (1.7-3.1 keV)

• Vela and Puppis A SNRs. The larger roughly
  circular Vela, at 0.5 kpc, covers most of the
  field. Puppis A, at 2 kpc, is the bright
  enhancement at upper right. Vela is 104 years
  old and has a diameter of 75 pc. Many of X-ray
  SNRs have rich line structure in the 0.1 -
  several keV from collision electron excitation of
  the highly enriched (from the supernova)
• material. Though invoked for simplicity, the
  assumption of local thermodynamic equilibrium
  often proves to be wrong.

13
SNR Puppis A in X-rays with Rosat
ROSAT HRI (0.5-2 keV)

• This supernova remnant brings up the subject of
  pulsar/SNR associations. Though not shown here,
  Puppis A has a convincing pulsar association.
  Perhaps 10 of Sne do. Is the beaming factor 10,
  or do SNe collapse into other forms, such as
  quark stars, strange stars, or black holes.

14
Eagle Nebula (Detail)

• showing settling and gravitational sedimentation
  of gaseous matter in the gravitational field of
  our Galaxy. Gravitational collapse leading to
  star formation will result if photo-erosion does
  not disperse it first .

15
Eta Carina with HST WFPC2

• Eta Carinae at 2.6 kpc, shows dust lanes, tiny
  condensations, and strange radial streaks from an
  analysis of HST WFPC2 data using a combination of
  image processing techniques such as dithering,
  subsampling and deconvolution. Images taken
  through red and near-ultraviolet filters were
  subsequently combined to produce the color image
  shown. A sequence of eight exposures was
  necessary to cover the object's huge dynamic
  range the outer ejecta blobs are 100,000 times
  fainter than the brilliant central star. Eta
  Carinae was the site of a giant outburst about
  150 years ago, when it became one of the
  brightest stars in the southern sky. Though the
  star released as much visible light as a
  supernova explosion, it survived the outburst.
  Somehow, the explosion produced two polar lobes
  and a large thin equatorial disk. The new
  observation shows that excess violet light
  escapes along the equatorial plane between the
  bipolar lobes. Apparently there is relatively
  little dusty debris between the lobes down by the
  star most of the blue light is able to escape.
  The lobes, on the other hand, contain large
  amounts of dust which preferentially absorb blue
  light, causing the lobes to appear reddish.
  Estimated to be 100 times more massive than our
  Sun, Eta Carinae may be one of the most massive
  stars in our Galaxy. It radiates about five
  million times more power than our Sun. This
  star's outburst may provide unique clues to
  other, more modest stellar bipolar explosions and
  to hydrodynamic flows from stars in general.

16
Hourglass (MyCn18) Nebula
HST WFPC2

• Hourglass nebula, MyCn18, a young planetary
  nebula 2.6 kpc away. This picture has been
  composed from three separate images taken in the
  light of ionized nitrogen (represented by red),
  hydrogen (green), and doubly-ionized oxygen
  (blue). Ejection of stellar matter which
  accompanies the slow death of Sun-like stars is
  studied. According to one theory for the
  formation of planetary nebulae, the hourglass
  shape is produced by the expansion of a fast
  stellar wind within a slowly expanding cloud
  which is more dense near its equator than near
  its poles. What appears as a bright elliptical
  ring in the center, and at first sight might be
  mistaken for an equatorially dense region, is
  seen on closer inspection to be a potato shaped
  structure with a symmetry axis dramatically
  different from that of the larger hourglass. The
  hot star which has been thought to eject and
  illuminate the nebula, and therefore expected to
  lie at its center of symmetry, is clearly off
  center.

17
Southern Ring Nebula with HST

• This photo reveals elongated dark clumps of
  material embedded in the gas at the edge of the
  nebula the dying central star floating in a blue
  haze of hot gas. The nebula is about a light-year
  in diameter and is located some 2,000 light-years
  from Earth in the direction of the constellation
  Lyra. The colors are approximately true colors.
  The color image was assembled from three
  black-and-white photos taken through different
  color filters with the Hubble telescope's Wide
  Field Planetary Camera 2. Blue isolates emission
  from very hot helium, which is located primarily
  close to the hot central star. Green represents
  ionized oxygen, which is located farther from the
  star. Red shows ionized nitrogen, which is
  radiated from the coolest gas, located farthest
  from the star. The gradations of color illustrate
  how the gas glows because it is bathed in
  ultraviolet radiation from the remnant central
  star, whose surface temperature is a white-hot
  216,000 degrees Fahrenheit (120,000 degrees
  Celsius).

18
Lagoon Nebula

• The Lagoon Nebula (Messier 8) which lies 1.7 kpc
  away in the direction of the constellation
  Sagittarius. The central hot star, O Herschel 36
  (lower right), is the primary source of the
  ionizing radiation for the brightest region in
  the nebula, called the Hourglass. Other hot
  stars, also present in the nebula, are ionizing
  the extended optical nebulosity. The ionizing
  radiation induces photo-evaporation of the
  surfaces of the clouds and drives away violent
  stellar winds tearing into the cool clouds. The
  Lagoon Nebula and nebulae in other galaxies are
  sites where new stars are being born from dusty
  molecular clouds. HST WFPC2 images through three
  narrow-band filters (red light - ionized sulphur
  atoms, blue light - double ionized oxygen atoms,
  green light - ionized hydrogen).

19
Ring Nebula, HST

• M57. Note elongated dark clumps of material
  embedded in the gas at the edge of the nebula
  the dying central star floating in a blue haze of
  hot gas. The colors are approximately true
  colors. Blue isolates emission from very hot He,

which is located primarily close to the hot
central star. Green represents ionized O, which
is located farther from the star. Red shows
ionized N, which is radiated from the coolest
gas, located farthest from the star. The
gradations of color illustrate how the gas glows
because it is bathed in UV radiation from the
remnant central star, with surface temperature
1.2x105 K).
HST WFPC2 700 pc
20
Orion Nebula with HST

• At 1500 lt-years (500 parsecs), Orion is one of
  the closest sites recent star formation (300,000
  years ago). The nebula is a giant gas cloud
  illuminated by bright young stars. Many of the
  fainter young stars are surrounded by disks of
  dust and gas that are slightly more than twice
  the diameter of the Solar System.
• Red light depicts emission in Nitrogen green is
  Hydrogen and blue is Oxygen. elongated dark
  clumps of material embedded in the gas at the
  edge of the nebula the dying central star
  floating in a blue haze of hot gas. The colors
  are approximately true colors. Blue isolates
  emission from very hot He,

21
Orion Proplyds with HST

• These are possibly protoplanetary disks, or
  "proplyds," that might evolve on to agglomerate
  planets. The proplyds which are closest to the
  hottest stars of the parent star cluster are seen
  as bright objects, while the object farthest from
  the hottest stars is seen as a dark object. The
  field of view is only 0.14 light-years across.

22
Crab Nebula
_at_Anglo-Australian Observatory credit David Malin

• M1, the Crab nebula, is justly famous for
  historical supernova, plerionic (filled-center)
  supernova remnant, 33 ms young neutron star with
  inferred polar surface magnetic field of gt 1012
  Gauss, nonthermal optical, X-ray, soft to hard (gt
  100 MeV) pulsed and steady gamma rays, TeV
  emission, and the structure shown here, to name a
  few.

23
Polarization map of the Crab Nebula

• Polarization map, Keck image, demonstrating a
  nonthermal synchrotron origin of the emission.
  The burned-out pixels mark the Crab pulsar.

24
Vela SNR nebula

• About 120 centuries ago an inconspicuous star in
  the constellation of Vela brightened by about 100
  million times to rival the Moon as the brightest
  object in the night sky. This photograph shows a
  portion of the north-western quadrant of an
  expanding nebulous shell, which now surrounds the
  site of the explosion. Near the centre of the
  nebula (and not seen here) is the Vela pulsar, a
  rapidly-spinning neutron star only a few
  kilometres in diameter, the remnant of the star
  that exploded. This tiny object spins about 11
  times a second and is among the faintest stars
  ever studied at optical wavelengths, a far cry
  from its brief glory as one of the brightest
  stars ever seen.

_at_Anglo-Australian Observatory credit David Malin
25
47 Tuc

• Among the many spectacular objects in the
  southern skies are two magnificent naked-eye
  globular clusters, omega Centauri and 47 Tucanae.
  These ancient cities of stars are captives of the
  Milky Way but were formed long before our Galaxy
  assumed its present shape, indeed these clusters
  have some of the oldest known stars. 47 Tuc is
  about 15,000 light years distant and contains
  several million stars, as many as some minor
  galaxies. The crowded central region leads to
  occasional stellar encounters and it is in 47 Tuc
  that rapidly-spinning pulsars have recently been
  discovered by radio astronomers. Though the light
  of globular clusters is dominated by so-called
  'red' giant stars, their colour is no redder than
  a domestic tungsten lamp, so the true colour of
  47 Tuc is close to the pale yellow reproduced
  here.

_at_Anglo-Australian Observatory credit David Malin
26
Antares and Rho Ophiuchus molecular cloud
complexes

• The dusty region between Ophiuchus and Scorpius
  contains some of the most colourful and
  spectacular nebulae ever photographed. The upper
  part of the picture is filled with the bluish
  glow of reflected light from hot stars near a
  huge, cool cloud of dust and gas where stars are
  born. Dominating the lower half of the picture is
  the over-exposed image of the red supergiant star
  Antares, a star that it is steadily shedding
  material from its distended surface as it nears
  the end of its life. These solid particles
  reflect Antares' light and hide it in a nebula of
  its own making. Finally, partly surrounding Sigma
  Scorpii at the left of the picture is a red
  emission nebula, completing the most
  comprehensive collection of nebular types ever
  seen in one photograph.

_at_Anglo-Australian Observatory credit David Malin
27
Trifid Nebula

• Vast clouds of hydrogen mixed with tiny dust
  grains are distributed throughout the Milky Way.
  The hydrogen can only be seen at visible
  wavelengths when it is illuminated by very hot
  stars. The light from these stars is sufficiently
  rich in ultraviolet light to cause the gas to
  glow with its characteristic red colour. In most
  cases, such as here, the hot stars formed
  recently from the hydrogen cloud. The stars found
  at the heart of the Trifid Nebula are here seen
  associated with dust lanes which are silhouetted
  against the glowing background. This nebula is in
  the constellation of Sagittarius at a distance of
  about 3000 light years.

_at_Anglo-Australian Observatory credit David Malin
28
Around Eta Carina

• This wonderfully complex region at the heart of
  the NGC 3372 nebula was first described in detail
  by Sir John Herschel in 1838. He saw the bright
  circular shell visible in the upper part of the
  picture extending to the south to form a
  keyhole-shaped nebula. This luminous outline is
  no longer seen and the southern extension appears
  only as a dark dust cloud. It seems that the
  curious, explosively variable star Eta Carinae
  (in the tiny orange nebula to the left of the
  dust cloud) has enveloped itself in a cocoon of
  obscuring matter in the years since Herschel's
  observations and light from the star is no longer
  able to illuminate the rim of the dust cloud.

_at_Anglo-Australian Observatory credit David Malin
29
Milky Way (Detail)
This completes our brief tour of the Milky Way
in 3 frames you return to main menu.

• This wide-angle picture, covering over 50 degrees
  of the southern Milky Way, was made using color
  film in a conventional camera, which was pointed
  towards the centre of our Galaxy. The Galactic
  center itself is totally obscured at visible
  wavelengths by the band of dust which divides the
  Milky Way along much of its span. Against this
  dark lane can be seen many bright red emission
  nebulae. The brightest, near the center of the
  picture, is Messier 8, the Lagoon Nebula, which
  is visible to the unaided eye. At least 16 other
  prominent objects catalogued by Messier can be
  found on the photograph.

_at_Anglo-Australian Observatory credit David Malin
30
Hertzsprung-Russell Diagram
HR Diagram shows the dependence of stellar
surface temperature (abscissa) as a function of
luminosity (ordinate). Oftentimes the B-V colors
are substituted for temperature, and the
bolometric magnitude -- or luminosity -- has
large uncertainties due to reddening. An
accurate distance scale is essential to construct
an HR diagram, so that HR diagrams of localized
star clusters are most reliable. The
solutions to the equations of stellar structure
can explain, though not without assumptions about
convective mixing, the HR diagram .
_at_ Cambridge University Press
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Aitoff-Hammer equal area projections
as shown for the Earth note the freedom of
choosing projection center direction