Title: All-sky radio image at 408 MHz radio, taken with Jodrell, Effelsberg, and Parkes.
1All-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.
2All-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).
3All-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).
4All-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.
5All-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).
6All-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.
7All-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.
8All-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.
9All-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.
10Multiwavelength mural. For more information,
visit the backdrop. Credit D. Leisawitz and J.
Friedlander.
11X-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).
12Vela 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.
13SNR 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.
14Eagle 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 .
15Eta 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.
16Hourglass (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.
17Southern 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).
18Lagoon 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).
19Ring 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
20Orion 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,
21Orion 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.
22Crab 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.
23Polarization 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.
24Vela 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
2547 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
26Antares 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
27Trifid 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
28Around 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
29Milky 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
30Hertzsprung-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
31Aitoff-Hammer equal area projections
as shown for the Earth note the freedom of
choosing projection center direction