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💫M101



This image of the spiral galaxy Messier 101 (M101) is a composite of data from NASA's Chandra X-ray Observatory, the Hubble Space Telescope, and the Spitzer Space Telescope. The colors correspond to the following wavelengths: The X-rays detected by Chandra are colored blue. Sources of X-rays include million-degree gas, the debris from exploded stars, and material zooming around black holes and neutron stars. The red color shows Spitzer's view in infrared light. It highlights the heat emitted by dust lanes in the galaxy where stars can form. Finally, the yellow coloring is visible light data from Hubble. Most of this light comes from stars, and they trace the same spiral structure as the dust lanes. M101 is a face-on spiral galaxy about 22 million light years away in the constellation Ursa Major. It is similar to the Milky Way galaxy in many ways, but is larger. The new "Great Observatories" composite image of M101 was distributed to over 100 planetariums, museums, nature centers, and schools across the country in conjunction with Galileo's birthday on February 15.

Credit:
X-ray: NASA / CXC / JHU / K.Kuntz; Optical: NASA / ESA / STScI / JHU / K. Kuntz; IR: NASA / JPL-Caltech / STScI / K. Gordon


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💫V838 Monocerotis light echo

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The unusual variable star V838 Monocerotis (V838 Mon) continues to puzzle astronomers. This previously inconspicuous star underwent an outburst early in 2002, during which it temporarily increased in brightness to become 600,000 times more luminous than our Sun. Light from this sudden eruption is illuminating the interstellar dust surrounding the star, producing the most spectacular "light echo" in the history of astronomy. As light from the eruption propagates outward into the dust, it is scattered by the dust and travels to the Earth. The scattered light has travelled an extra distance in comparison to light that reaches Earth directly from the stellar outburst. Such a light echo is the optical analogue of the sound echo produced when an Alpine yodel is reflected from the surrounding mountainsides. The NASA/ESA Hubble Space Telescope has been observing the V838 Mon light echo since 2002. Each new observation of the light echo reveals a new and unique "thin-section" through the interstellar dust around the star.




This release shows new images of the light echo from the Hubble Advanced Camera for Surveys taken in November 2005 (left) and again in September 2006 (right). The numerous whorls and eddies in the interstellar dust are particularly noticeable. Possibly they have been produced by the effects of magnetic fields in the space between the stars. The Hubble observations have been used to determine the distance to V838 Mon, using a technique based on the polarisation of the reflected light. Hubble has polarising filters that only pass light that vibrates at certain angles. This method yields a distance of 20,000 light-years for V838 Mon, suggesting that, during its outburst, V838 Mon was one of the brightest stars in the entire Milky Way. Although the reason for the eruption is still unclear, some astronomers have suggested it might have resulted from the collision of two stars.

Credit: NASA, ESA and H. Bond (STScI)


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💫Black Hole Outflows From Centaurus A



This image of Centaurus A shows a spectacular new view of a supermassive black hole's power. Jets and lobes powered by the central black hole in this nearby galaxy are shown by submillimeter data (colored orange) from the Atacama Pathfinder Experiment (APEX) telescope in Chile and X-ray data (colored blue) from the Chandra X-ray Observatory. Visible light data from the Wide Field Imager on the Max-Planck/ESO 2.2 m telescope, also located in Chile, shows the dust lane in the galaxy and background stars. The X-ray jet in the upper left extends for about 13,000 light years away from the black hole. The APEX data shows that material in the jet is travelling at about half the speed of light.

Credit:
X-ray: NASA / CXC / CfA / R.Kraft; Submillimeter: MPIfR / ESO / APEX / A.Weiss; Optical: ESO / WFI


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💫Stellar sorting in globular cluster 47 Tucanae

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A seven year study with the NASA/ESA Hubble Space Telescope has provided astronomers with the best observational evidence yet that globular clusters sort out stars according to their mass, governed by a gravitational billiard ball game between stars. Heavier stars slow down and sink to the cluster's core, while lighter stars pick up speed and move across the cluster to its periphery. This process, called "mass segregation", has long been suspected for globular star clusters, but has never before been directly seen in action. This image shows the core of 47 Tucanae. Multiple photos of this region allowed astronomers to track the "beehive swarm" motion of stars. Precise velocities were obtained for nearly 15,000 stars in this cluster. This image was taken with Hubble's Advanced Camera for Surveys. A typical globular cluster contains several hundred thousand stars. Although the density of stars is very small at the outskirts of such clusters, near the centre it can be more than 10,000 times higher than in the local vicinity of our Sun. If we lived in such a crowded region of space, the night sky would be ablaze with 10,000 stars, all closer to us than the nearest star to the Sun, Alpha Centauri, which is 4.3 light-years away (or approximately 215,000 times the distance between Earth and the Sun). Just as bumps and jostles are much more likely in a crowded commuter train, so are encounters between stars in a densely populated cluster more likely than here in our quiet stellar backwater.




These encounters can be as dramatic as collisions or even mergers. Theory predicts that the cumulative result of many such encounters is mass segregation, but the crowded conditions make it extremely difficult to identify individual stars accurately. Astronomers needed Hubble's pinpoint resolution to trace the motions of many thousands of stars in a single globular cluster. Highly accurate speeds have been measured for almost 15,000 stars at the very centre of the nearby globular cluster 47 Tucanae, one of the densest globular clusters in the southern hemisphere. 23 of these stars are of a very rare type known as "blue stragglers": unusually hot and bright stars thought to be the product of collisions between two normal stars. The slower measured velocities of the blue straggler stars agree with the predictions of mass segregation. In particular, a comparison between blue stragglers (that have twice the mass of the average star) and other stars shows that, as expected, they do move more slowly than the more typical, lighter stars. Georges Meylan of the ?cole Polytechnique Federale de Lausanne (EPFL) in Sauverny, Switzerland and collaborators took ten sets of multiple images of the central region (within about 6 light-years of the centre) of 47 Tucanae using Hubble's Wide Field and Planetary Camera 2 and the newer Advanced Camera for Surveys.




Images were taken at regular intervals over nearly seven years. Extremely small position changes could be measured over time by carefully measuring the positions of as many as 130,000 stars in every one of these "snapshots", revealing the motions of the stars across the sky. The velocities of 15,000 stars were measured precisely. This is the largest sample of velocities ever gathered for a globular cluster in the Milky Way by any technique with any instrument. The results were also used to look for the gravitational pull of a black hole to check whether one exists in the cluster's core. The measured stellar motions have ruled out the presence of a very massive black hole. The study would have been impossible without Hubble's sharp vision. From the ground, the smearing effect of the Earth's atmosphere blurs the individual images of the numerous stars in the crowded cluster core. The typical angular motion of even the normal stars in the centre of 47 Tucanae was found to be just over one ten millionth of a degree (equivalent to the angular size of a 10 cent coin seen from 7,000 kilometres away) per year.

Credit: NASA, ESA, and G. Meylan (École Polytechnique Fédérale de Lausanne)


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💫NGC 604




A new study unveils NGC 604, the largest region of star formation in the nearby galaxy M33, in its first deep, high-resolution view in X-rays. This composite image from Chandra X-ray Observatory data (colored blue), combined with optical light data from the Hubble Space Telescope (red and green), shows a divided neighborhood where some 200 hot, young, massive stars reside. Throughout the cosmic metropolis, giant bubbles in the cool dust and warm gas are filled with diffuse, multi-million degree gas that emits X-rays. Scientists think these bubbles are generated and heated to X-ray temperatures when powerful stellar winds from the young massive stars collide and push aside the surrounding gas and dust. So, the vacated areas are immediately repopulated with the hotter material seen by Chandra. However, there is a difference between the two sides of this bifurcated stellar city. On the western (right) side, the amount of hot gas found in the bubbles corresponds to about 4300 times the mass of the sun.

This value and the brightness of the gas in X-rays imply that the western part of NGC 604 is entirely powered by winds from the 200 hot massive stars. This result is interesting because previous modeling of other bubbles usually predicted them to be fainter than observed, so that additional heating from supernova remnants is required. The implication is that in this area of NGC 604, none or very few of the massive stars must have exploded as supernovas. The situation is different on the eastern (left) side of NGC 604. On this side, the X-ray gas contains 1750 times the mass of the sun and winds from young stars cannot explain the brightness of the X-ray emission. The bubbles on this side appear to be much older and were likely created and powered by young stars and supernovas in the past. A similar separation between east and west is seen in the optical results. This implies that a massive wall of gas shields the relatively quiet region in the east from the active star formation in the west.

Credit:
X-ray: NASA / CXC / CfA / R. Tuellmann; Optical: NASA / AURA / STScI


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💫The Spiderweb Galaxy and its surroundings

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This image shows the full ACS overview of the region around the Spiderweb Galaxy (just to the right of the center). The galaxy is sitting at the centre of an emergent galaxy cluster, surrounded by hundreds of other galaxies from the cluster. In nature spiders earn our respect by constructing fascinating, well-organised webs in all shapes and sizes. But the beauty masks a cruel, fatal trap. Analogously, the NASA/ESA Hubble Space Telescope has found a large galaxy 10.6 billion light-years away from Earth (at a redshift of 2.2) that is stuffing itself with smaller galaxies caught like flies in a web of gravity. The galaxy is so far away that astronomers are seeing it as it looked in the early formative years of the Universe, only 2 billion years after the Big Bang. The Hubble image shows the Spiderweb Galaxy sitting at the centre of an emergent galaxy cluster, surrounded by hundreds of other galaxies from the cluster. Team leader George Miley from Leiden Observatory in the Netherlands explains: "The new Hubble image is the best demonstration so far that large massive galaxies are built up by merging smaller ones. " The image reaches much deeper than previous ones and shows the merging process in unprecedented detail.




Galaxies can be seen as they are sucked into the Spiderweb at speeds of several hundred kilometres per second, from distances of more than a hundred thousand light-years around it. Radio telescopes have shown that jets of fast particles are being spewed out from the centre of the Spiderweb Galaxy with enormous energies. These jets are believed to be produced by a massive black hole buried deep in the nucleus of the system. The infalling galaxy "flies" are a source of food for this black hole "spider", allowing it to continue disgorging the jets. The new Hubble image provides a unique real-world example for testing theoretical models of massive galaxy formation. The complexity and clumpiness of the Spiderweb agrees qualitatively with the predictions of such models, but a surprising feature of the Spiderweb Galaxy is the presence of several faint small linear galaxies within the merging structure. The Spiderweb Galaxy is located in the southern constellation of Hydra (the water snake) and is one of the most massive galaxies known.

Credit: NASA, ESA, G. Miley and R. Overzier (Leiden Observatory), and the ACS Science Team


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