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: Soorten stelsels Onze Melkweg   Soorten stelsels Onze Melkweg Spiraalstelsels en de Golftheorie Sterrenstelsels en Superzware Zwarte Gaten Botsende Sterrenstelsels Actieve Stelsels 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

Artistieke reconstructie Karakteristieken 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 Melkweg Artistieke reconstructie

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 elliptical-shaped 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 face-on spiral galaxy lies precisely in front of another larger spiral. This line-up 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 The centre of our galaxy (near Sagitarius A*) has been known for years to host a black hole, a 'super-massive' 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 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: X-ray 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 image- processing 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 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 light-years 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 material from their less exotic binary companion stars. The diffuse high-energy glow represents gas throughout the galaxy heated to temperatures of millions of degrees C. At 11 million light-years distant in the constellation Centaurus, Centaurus A (NGC 5128) is the closest active galaxy.

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 co-investigators 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 gravitatie- constante. 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 Coma-cluster. Hier een opname van het Coma-cluster met visueel+Rontgen, over elkaar

‘Donkere Materie’ en ‘Donkere Energie’ vormen sinds 1998 de grootste uitdaging voor de natuur- en sterrenkunde ...

The End