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RAADSELS
VAN
DE
STERRENKUNDE
Ronald Westra
Dep. Mathematics
Maastricht University
February 23, 2006
lectures :
http://www.math.unimaas.nl/personal/ronaldw/home1.htm
4.
De Melkweg
en andere
Sterrenstelsels
IInhoud College 4:
1. Soorten stelsels
2. Onze Melkweg
3. Spiraalstelsels en de Golftheorie
4. Sterrenstelsels en Superzware Zwarte Gaten
5. Botsende Sterrenstelsels
6. Actieve Stelsels
7. Rotatiecurven en Donkere Materie
4.1 Soorten Sterrenstelsels
De Melkweg als één sterrenstelsel onder vele
Tot de 20-er jaren van de 20e eeuw was het niet bekend
dat er zich buiten onze Melkweg nog andere
sterrenstelsels bevinden. Men ging er algemeen van uit
dat het Melkwegstelsel identiek was aan het heelal.
Weliswaar had de filosoof Immanuel Kant (1724-1804) al
een suggestie gedaan dat door de astronomen waargenomen
"nevels" in werkelijkheid andere "melkwegen" zouden
kunnen zijn, zoals het onze, maar aan deze suggestie was
niet veel aandacht geschonken. De astronoom Vesto Slipher
toonde in 1914 het bestaan aan van de roodverschuiving in
de spectra van bepaalde spiraalnevels en de daaraan
gekoppelde stralingssnelheid, die veel hoger was dan
mogelijk was voor objecten binnen de Melkweg. Hij legde
met deze observaties de basis voor de ontdekkingen van de
astronoom Edwin Hubble. Met behulp van de principes van
het dopplereffect (roodverschuiving) en zijn supersterke
telescoop stelde deze zijn theorie op van de uitbreiding
van het heelal, geformuleerd in de Wet van Hubble.
Hubble´s classification of galaxies
Hubble´s classification of galaxies
Hubble´s classification of galaxies
Hubble´s classification of galaxies
Elliptical galaxy
Spiral galaxy
Barred galaxy (balk stelsel)
Irregular galaxy
4.2 Onze Melkweg
Karakteristieken
Melkweg
Artistieke reconstructie
Diameter
80.000–100.000 lichtjaar
Massa
1011 sterren
Omlooptijd 225×106 jaar
Afstand zon-melkweg
27.000 ljr
Hubble-Type balk-stelsel Sbb
Snelheid tov
locale groep: 600 km/sec
Richting:
naar Hydra stelsel
Onze Melkweg (vanaf de zon gezien met Chandra)
Onze Melkweg:
waargenomen structuur van de spiraalarmen
Onze Melkweg:
waargenomen
En gextrapoleerde
structuur van de
spiraalarmen
Onze Melkweg
Sbb Balkstelsel
(artist’s impression)
Future of our Milky Way
Current measurements suggest the Andromeda Galaxy
is approaching us at 300 kilometres per second,
and that the Milky Way may collide with it in
several (3-4) billion years.
If they do collide, it is thought that our sun
and other stars will probably not collide with
other stars, but merge to form an ellipticalshaped galaxy over the course of about a billion
years.
4.3 Spiraalstelsels en de Golftheorie
Spiraalstelsels
Spiraalstelsels
Swirling Galaxy Parents Generations of Stars
in Its Center
The NASA/ESA Hubble Space Telescope has snapped a view of
several star generations in the central region of the Whirlpool Galaxy
(M51), a spiral region 23 million light-years from Earth in the
constellation Canes Venatici (the Hunting Dogs).
The galaxy's massive center, the bright ball of light in the center of the
photograph, is about 80 light-years across and has a brightness of
about 100 million suns. Astronomers estimate that it is about 400
million years old and has a mass 40 million times larger than our Sun.
The concentration of stars is about 5,000 times higher than in our solar
neighborhood, the Milky Way Galaxy. We would see a continuously
bright sky if we lived near the bright center.
GALACTIC SILHOUETTES
This new image from NASA's Hubble Space Telescope and its Wide
Field Planetary Camera 2 (WFPC2) shows the unique galaxy pair
called NGC 3314. Through an extraordinary chance alignment, a faceon spiral galaxy lies precisely in front of another larger spiral. This lineup provides us with the rare chance to visualize dark material within the
front galaxy, seen only because it is silhouetted against the object
behind it.
Dust lying in the spiral arms of the foreground galaxy stands out where
it absorbs light from the more distant galaxy. This silhouetting shows us
where the interstellar dust clouds are located, and how much light they
absorb. The outer spiral arms of the front galaxy appear to change from
bright to dark, as they are projected first against deep space, and then
against the bright background of the other galaxy.
Star-forming regions in Galaxy NGC 1512
Center of NGC 1512, with NASA HST at all wavelengths from
ultraviolet to infrared. NGC 1512 is a barred spiral galaxy in the
southern constellation of Horologium.
The colors map where newly born star clusters exist in both "dusty" and
"clean" regions of the galaxy.
The galaxy spans 70,000 light-years, nearly as much as our own Milky
Way galaxy.
The galaxy’s core is unique for its stunning 2,400 light-year-wide circle
of infant star clusters, called a "circumnuclear" starburst ring.
Starbursts are episodes of vigorous formation of new stars and are
found in a variety of galaxy environments.
Taking advantage of Hubble’s sharp vision, as well as its unique
wavelength coverage, a team of Israeli and American astronomers
performed one of the broadest and most detailed studies ever of such
star-forming regions.
Edge-on Galaxy ESO 510-G13
NASA's Hubble Space Telescope has captured this image of an
unusual edge-on galaxy, revealing remarkable details of its warped
dusty disk and showing how colliding galaxies spawn the formation of
new generations of stars.
The dust and spiral arms of normal spiral galaxies, like our own Milky
Way, appear flat when viewed edge-on. This Hubble Heritage image of
ESO 510-G13 shows a galaxy that, by contrast, has an unusual twisted
disk structure. ESO 510-G13 lies in the southern constellation Hydra,
roughly 150 million light-years from Earth.
Runaway Galaxy UGC 10214
Against a stunning backdrop of thousands of galaxies, this odd-looking
galaxy with the long streamer of stars appears to be racing through
space, like a runaway pinwheel firework.
This picture of the galaxy UGC 10214 was taken by the Advanced
Camera for Surveys (ACS), which was installed aboard NASA's Hubble
Space Telescope in March during Servicing Mission 3B. Dubbed the
"Tadpole," this spiral galaxy is unlike the textbook images of stately
galaxies. Its distorted shape was caused by a small interloper, a very
blue, compact galaxy visible in the upper left corner of the more
massive Tadpole.
The Tadpole resides about 420 million light-years away in the
constellation Draco.
4.4 Sterrenstelsels en Superzware
Zwarte Gaten
Centrum van onze
melkweg bij Sagitarius A*
(NASA/Chandra)
Centrum van onze
melkweg bij Sagitarius A*
(ESO)
The centre of our galaxy (near Sagitarius A*) has
been known for years to host a black hole, a 'supermassive' yet very quiet one.
New observations with Integral, ESA's gamma-ray observatory,
have now revealed that 350 years ago the black hole was much
more active, releasing a million times more energy than at
present. Scientists expect that it will become active again in the
future.
Most galaxies harbour
a super-massive black
hole in their centre,
weighing a million or
even a thousand million
times more than our Sun.
Centrum van onze melkweg bij Sagitarius A*
Filmpje van Centrum van ons Melkwegstelsel
met superzwaar zwart gat
Op de volgende slide ziet u een opname van ESO van Sagitarius A*,
het centrum van ons melkwegstelsel. Over enkele jaren ziet u sterren
rond het zwarte gat bewegen, hetgeen het mogelijk maakte om de
plaats en massa van het zwarte gat te bepalen.
!!! ALS HET FILMPJE NIET AUTOMATISCH OPSTART KUNT HET
BEKIJKEN OP DE MEEGELEVERDE MPEG-MOVIE:
vid-02-02.mpeg
De banen
van de
sterren
nabij
Sagitarius
A*
verraden
de exacte
positie en
massa van
het centrale
zwarte gat
Superzware zwarte
gaten
Tegenwoordig wordt
vermoed dat zich in de
centra van alle
sterrenstelsels
superzware zwarte
gaten (105-1010
zonmassa’s) bevinden
Top: artist's conception of a
supermassive black hole.
Bottom: images believed to
show a supermassive black
hole devouring a star in
galaxy RXJ 1242-11. Left: Xray image, Right: optical
image.
Chandra ziet superzwaar zwart gat in centrum van
het Perseus sterrenstelsel
A 53-hour Chandra observation of the central region of the Perseus galaxy
cluster (left) has revealed wavelike features (right) that appear to be sound
waves.
Chandra ziet superzwaar zwart gat in centrum van
het Perseus sterrenstelsel
The Chandra data show the
ripples in the hot gas that fills
the Perseus cluster.
The features were discovered
by using a special imageprocessing technique to bring
out subtle changes in brightness.
These ripples are sound waves
thought to have been
generated by cavities blown
out by jets from a supermassive
black hole (bright white spot)
at the center of the
Perseus cluster.
4.5 Botsende Spiraalstelsels
Sterrenstelsels
kunnen botsen.
Door de
zwaartekracht
kunnen ze elkaar
dan helemaal
uitelkaar rukken.
De verschillende
stadia van die
botsingen verklaren
vele van de
´onregelmatige
stelsels´.
Filmpje van computer-simulaties van botsende
Melkwegstelsels
Op de volgende twee slides ziet u computersimulaties van botsende
sterrenstelsels.
!!! ALS HET FILMPJE NIET AUTOMATISCH OPSTART KUNT HET
BEKIJKEN OP DE MEEGELEVERDE MPEG-MOVIES:
2002-11-a-low_mpeg.mpg
2001-22-d-low_mpeg.mpeg
Colliding galaxies Antennae (NGC4038/4039).
Colliding galaxies Antennae
(NGC4038/4039) 60 million
light years away in the
constellation Corvus.
Data from ESA's Infrared
Space Observatory (ISO)
First direct evidence that
shock waves genarated by
the collision excite the gas
and create the right
conditions for star formation.
The excited gas is observed
in the overlapping region
(enclosed within the white
dashed lines).
New stars will be born there
and in the course of the next
million year they will make
the Antennae galaxies twice
as bright in the infrared.
Astrophysicists Predict Rapid Merging
of Black Holes in Colliding Galaxies
Andres Escala, Paolo Coppi, Richard Larson, Yale University.
Voorbeeld van invloed superzwarte gaten op
botsende melkwegstelsels.
VLA image of the galaxy NGC 326, with HST image
of jets inset. CREDIT: NRAO/AUI, STScI (inset)
Too Fast, Too Furious: A Galaxy's Fatal Plunge
The following images offer a dramatic look at a spiral galaxy like our
Milky Way being ripped apart as it races at 4.5 million miles per hour
through the heart of a distant cluster of galaxies.
The images, taken over several wavelengths, provide evidence of the
"galactic assault and battery," namely, gas being stripped from the
doomed galaxy, called C153.
Seyferts Sextet: Hubble Watches Galaxies
Engage in Dance of Destruction
NASA's Hubble Space Telescope is witnessing a grouping of galaxies
engaging in a slow dance of destruction that will last for billions of
years. The galaxies are so tightly packed together that gravitational
forces are beginning to rip stars from them and distort their shapes.
Those same gravitational forces eventually could bring the galaxies
together to form one large galaxy. The name of this grouping, Seyfert's
Sextet, implies that six galaxies are participating in the action. But only
four galaxies are on the dance card. The small face-on spiral with the
prominent arms [center] of gas and stars is a background galaxy
almost five times farther away than the other four. Only a chance
alignment makes it appear as if it is part of the group. The sixth
member of the sextet isn't a galaxy at all but a long "tidal tail" of stars
[below, right] torn from one of the galaxies. The group resides 190
million light-years away in the constellation Serpens.
Seyferts Sextet: Computer simulation
Multiple Galaxy Collisions Surprise Hubble
Astronomers
Hubble astronomers conducting research on a class of galaxies called
ultra-luminous infrared galaxies (ULIRG) have discovered that over two
dozen of these are found within "nests" of galaxies, apparently
engaged in multiple collisions that lead to fiery pile-ups of three, four or
even five galaxies smashing together.
Intergalactic Pipeline in NGC 1409
This visible-light picture, taken by NASA's Hubble Space Telescope,
reveals an intergalactic "pipeline" of material flowing between two
battered galaxies that bumped into each other about 100 million years
ago. The pipeline [the dark string of matter] begins in NGC 1410 [the
galaxy at left], crosses over 20,000 light-years of intergalactic space,
and wraps around NGC 1409 [the companion galaxy at right] like a
ribbon around a package. Although astronomers have taken many
stunning pictures of galaxies slamming into each other, this image
represents the clearest view of how some interacting galaxies dump
material onto their companions.
Star Clusters Born in the Wreckage of Cosmic
Collisions
Close-up view of Stephan's Quintet, a group of five galaxies.
The clusters, each harboring up to millions of stars, were born from the
violent interactions between some members of the group. The rude
encounters also have distorted the galaxies' shapes, creating
elongated spiral arms and long, gaseous streamers.
The NASA Hubble Space Telescope photo showcases three regions of
star birth: the long, sweeping tail and spiral arms of NGC 7319 [near
center]; the gaseous debris of two galaxies, NGC 7318B and NGC
7318A [top right]; and the area north of those galaxies, dubbed the
northern starburst region [top left].
Galaxy collision in NGC 6745
When galaxies collide, the stars that normally comprise the major portion of
the luminous mass of each of the two galaxies will almost never collide with
each other but will pass rather freely between each other with little
damage. This occurs because the physical size of individual stars is tiny
compared to their typical separations, making the chance of physical
encounter relatively small. In our own Milky Way galaxy, the space
between our Sun and our nearest stellar neighbor, Proxima Centauri (part
of the Alpha Centauri triple system), is a vast 4.3 light-years.
However, the situation is quite different for the interstellar media in the
above two galaxies - material consisting largely of clouds of atomic and
molecular gases and of tiny particles of matter and dust, strongly coupled
to the gas. Wherever the interstellar clouds of the two galaxies collide, they
do not freely move past each other without interruption but, rather, suffer a
damaging collision. High relative velocities cause ram pressures at the
surface of contact between the interacting interstellar clouds. This
pressure, in turn, produces material densities sufficiently extreme as to
trigger star formation through gravitational collapse. The hot blue stars in
this image are evidence of this star formation.
Polar Ring Galaxy NGC4650
Located about 130 million light-years away, NGC 4650A is one of only
100 known polar-ring galaxies. Their unusual disk-ring structure is not
yet understood fully. One possibility is that polar rings are the
remnants of colossal collisions between two galaxies sometime in the
distant past, probably at least 1 billion years ago. During the collision
the gas from a smaller galaxy would have been stripped off and
captured by a larger galaxy, forming a new ring of dust, gas, and stars,
which orbit around the inner galaxy almost at right angles to the larger
galaxy's disk.
A GRAZING ENCOUNTER BETWEEN TWO
SPIRAL GALAXIES
NASA's Hubble Space Telescope snapped this image of two spiral
galaxies passing by each other. The near-collision has been caught in
images taken by NASA's Hubble Space Telescope and its Wide Field
Planetary Camera 2.
The larger and more massive galaxy is cataloged as NGC 2207 (on the
left in), and the smaller one on the right is IC 2163. Strong tidal forces
from NGC 2207 have distorted the shape of IC 2163, flinging out stars
and gas into long streamers stretching out a hundred thousand lightyears toward the right-hand edge of the image.
Computer simulations demonstrate the leisurely timescale over which
galactic collisions occur.
4.6 Actieve Stelsels
Seyfert galaxy
Centaurus A: Active X-Ray Galaxy (Chandra NASA)
Centaurus A: X-Rays
from an Active Galaxy
(Chandra NASA)
Giant elliptical galaxy
Centaurus A with 30,000
light-years long jet. Blasting
toward the upper left corner
of the picture, the jet seems
to arise from the galaxy's
bright central x-ray source -suspected of harboring a
black hole with a million or so
times the mass of the Sun.
Centaurus A is also seen to
be teeming with other
individual x-ray sources and
a pervasive, diffuse x-ray
glow. Most of these individual
sources are likely to be
neutron stars or solar mass
black holes accreting
Freewheeling Galaxies Collide in a Blaze of
Star Birth
A dusty spiral galaxy appears to be rotating on edge, like a pinwheel,
as it slides through the larger, bright galaxy NGC 1275, in this NASA
Hubble Space Telescope image.
These images, taken with Hubble's Wide Field Planetary Camera 2
(WFPC2), show traces of spiral structure accompanied by dramatic
dust lanes and bright blue regions that mark areas of active star
formation. Detailed observations of NGC 1275 indicate that the dusty
material belongs to a spiral system seen nearly edge-on in the
foreground. The second galaxy, lying beyond the first, is actually a
giant elliptical with peculiar faint spiral structure in its nucleus. These
galaxies are believed to be colliding at over 6 million miles per hour.
Giant Radio Jet Coming from Wrong Kind of
Galaxy
Composite images showing the galaxy 0313-192, the first spiral galaxy
known to be producing a giant radio-emitting jet. At left is a wide view
of 0313-192 and its surroundings, as seen with the Advanced Camera
for Surveys of the NASA Hubble Space Telescope (HST), in an image
made in July 2002. The radio-emitting jet, as seen with the Very Large
Array (VLA) at a wavelength of 20 centimeters, is overlaid, in red on the
color image. The galaxy is seen edge-on.
At right is a close-up of the HST image, with another red overlay from a
higher-resolution, 3-centimeter VLA image, showing the inner portion of
the jet.
The prominent spiral galaxy in the upper right of the large-scale image
is not related to 0313-192, nearly a billion light-years from Earth, but is
more than 200 million light-years closer.
VLBA Reveals Formation Region of Giant
Cosmic Jet Near a Black Hole
Space Telescope Science Institute astronomers and their coinvestigators have gained their first glimpse of the mysterious region
near a black hole at the heart of a distant galaxy, where a powerful
stream of subatomic particles spewing outward at nearly the speed of
light is formed into a beam, or jet, that then goes nearly straight for
thousands of light-years.
The astronomers used radio telescopes in Europe and the U.S.,
including the National Science Foundation's (NSF) Very Long Baseline
Array (VLBA) to make the most detailed images ever of the center of
the galaxy M87, some 50 million light-years away.
4.7 Rotatiecurven en Donkere Materie
Rotatiecurven van het Zonnestelsel
Binnen het zonnestelsel worden de omlooptijden van de
planeten bepaald door de
wetten van Kepler en feitelijk
Newton:
met v de omloopsnelheid
en r de afstand tot de zon,
M de massa van de zon
en G de gravitatieconstante.
De omloopssnelheid neemt
dus af met toenemende
afstand tot het centrum!
Deze grafiek heet een
rotatiecurve.
Rotatiecurven van het Zonnestelsel
Deze relatie stelt ons eenvoudig in staat om M(r), de
massa binnen een straal r van het centrum te bepalen:
meet omloopsnelheid v(r) voor een sterrenstelsel met
behulp van het Doppler effect, en los M op uit:
Oftewel:
Rotatiecurven van Sterrenstelsels
Laten we dit idee eens toepassen op de Andromedanevel M31
Rotatiecurve van Andromedastelsel M31
Hieronder de rotatiecurve van de Andromedanevel:
de omloopsnelheid neemt niet af met de afstand!!!
Rotatiecurve van Andromedastelsel M31
* Voor grote r is de rotatiecurve vlak, dus is v constant (nl: ~230
km/sec) – dit betekent dat de massa toeneemt met de afstand en
wel als:
* Als we de hele massa van het systeem willen bepalen is er een
probleem, want de rotatiecurve stopt als er geen sterren meer zijn
* Daartoe kunnen we kijken naar de EM-straling van waterstof, de
21 cm lijn, en die geeft de omloopsnelheid van stof- en gaswolken.
Rotatiecurven van Sterrenstelsels
Hieronder de kaart van de 21.1 cm radiostraling van het
stelsel NGC 3198
Rotatiecurven van Sterrenstelsels
Hieronder de rotatiecurve van NGC 3198, bepaald uit
Doppler-verschuiving van H-gaswolken.
Rotatiecurven van Sterrenstelsels
De sterren in NGC3198 reiken tot zo’n 10 kpc, maar de
rotatiecurve blijft vlak tot zo’n 30 kpc ?!
Er moet ‘iets’ anders zijn dat behalve de sterren de massa
van het stelsel bepaalt.
De curve "disk" geeft de
verwachte rotatiecurve
tgv de stermassa’s in het
stelsel
De curve "halo" geeft de
rotatiecurve tgv deze
ontbrekende materie in
de halo van het stelsel.
De ontbrekende materie wordt “donkere materie” genoemd.
Rotatiecurven van Sterrenstelsels
Hier een andere mogelijke fit voor NGC3198.
Ook hier domineert de donkere materie.
Rotatiecurven van Sterrenstelsels
Hier een samenvatting voor rotatiecurven van
sterrenstelsels:
A: verwacht,
B: waargenomen
Rotatiecurven van Sterrenstelsels
Ook voor onze melkweg:
Zo ziet de melkweg er dus echt uit: met DM
Zo ziet de melkweg er dus echt uit: met DM
Donkere Materie
komt in alle
stelsels voor.
Hier gravitational
lensing in
CL2244-02,
hetgeen onmogelijk
zou kunnen met de
waargenomen dus
zichtbare materie.
Donkere Materie komt
in alle stelsels voor.
Hier een opname van
de Rosat-sateliet van
het Coma-cluster in
Rontgen-straling, met
gas dat zo heet is dat
het alleen zou kunnen
met aanzienlijk meer
materie dan zichtbaar
is.
Donkere Materie
komt in Comacluster.
Hier een opname
van het Comacluster met
visueel+Rontgen,
over elkaar
‘Donkere Materie’ en ‘Donkere Energie’ vormen sinds 1998 de
grootste uitdaging voor de natuur- en sterrenkunde ...
The End