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💫Mars in opposition 2016

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During May 2016 the Earth and Mars get closer to each other than at any time in the last ten years. The NASA/ESA Hubble Space Telescope has exploited this special configuration to catch a new image of our red neighbour, showing some of its famous surface features. This image supplements previous Hubble observations of Mars and allows astronomers to study large-scale changes on its surface. On 22 May Mars will come into opposition, the point at which the planet is located directly opposite the Sun in the sky. This means that the Sun, Earth and Mars line up, with Earth sitting in between the Sun and the red planet. Opposition also marks the planet’s closest approach to Earth, so that Mars appears bigger and brighter in the sky than usual. This event allows astronomers using telescopes in space and on the ground to see more details on the Martian surface. For observers using ground-based instruments the opposing planet is visible throughout the night and is also fully illuminated, making it a great opportunity for detailed studies. On 12 May Hubble took advantage of this favourable alignment and turned its gaze towards Mars to take an image of our rusty-hued neighbour, adding it to the collection of previous images. From this distance the telescope could see Martian features as small as 30 kilometres across. Hubble observed Mars using its Wide Field Camera 3 (WFC3).



The final image shows a sharp, natural-colour view of Mars and reveals several prominent geological features, from smaller mountains and erosion channels to immense canyons and volcanoes. The large, dark region to the far right is Syrtis Major Planitia, one of the first features identified on the surface of the planet by seventeenth century observers. Syrtis Major is an ancient, inactive shield volcano. Late-afternoon clouds surround its summit in this view. The oval feature south of Syrtis Major is the bright Hellas Planitia basin, the largest crater on Mars. About 1,800 kilometres across and eight kilometres deep, it was formed about 3.5 billion years ago by an asteroid impact. The orange area in the centre of the image is Arabia Terra, a vast upland region. The landscape is densely cratered and heavily eroded, indicating that it could be among the oldest features on the planet. South of Arabia Terra, running east to west along the equator, are the long dark features known as Sinus Sabaeous (to the east) and Sinus Meridiani (to the west). These darker regions are covered by bedrock from ancient lava flows and other volcanic features. An extended blanket of clouds can be seen over the southern polar cap. The icy northern polar cap has receded to a comparatively small size because it is now late summer in the northern hemisphere.

Credit: NASA, ESA, the Hubble Heritage Team (STScI/AURA), J. Bell (ASU), and M. Wolff (Space Science Institute)


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💫Direct Proof of Dark Matter


This composite image shows the galaxy cluster 1E 0657-56, also known as the "bullet cluster." This cluster was formed after the collision of two large clusters of galaxies, the most energetic event known in the universe since the Big Bang. Hot gas detected by Chandra in X-rays is seen as two pink clumps in the image and contains most of the "normal," or baryonic, matter in the two clusters. The bullet-shaped clump on the right is the hot gas from one cluster, which passed through the hot gas from the other larger cluster during the collision. An optical image from Magellan and the Hubble Space Telescope shows the galaxies in orange and white. The blue areas in this image show where astronomers find most of the mass in the clusters. The concentration of mass is determined using the effect of so-called gravitational lensing, where light from the distant objects is distorted by intervening matter.

Most of the matter in the clusters (blue) is clearly separate from the normal matter (pink), giving direct evidence that nearly all of the matter in the clusters is dark. The hot gas in each cluster was slowed by a drag force, similar to air resistance, during the collision. In contrast, the dark matter was not slowed by the impact because it does not interact directly with itself or the gas except through gravity. Therefore, during the collision the dark matter clumps from the two clusters moved ahead of the hot gas, producing the separation of the dark and normal matter seen in the image. If hot gas was the most massive component in the clusters, as proposed by alternative theories of gravity, such an effect would not be seen. Instead, this result shows that dark matter is required.

Credit:
X-ray: NASA / CXC / CfA / M.Markevitch; Optical: NASA / STScI; Magellan / U.Arizona / D.Clowe; Lensing Map: NASA / STScI; ESO WFI; Magellan / U.Arizona / D.Clowe


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💫Andromeda Galaxy

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Peering deep inside the hub of the neighboring Andromeda galaxy, NASA's Hubble Space Telescope has uncovered a large, rare population of hot, bright stars. While Hubble has spied these ultra-blue stars before in Andromeda, the new observation covers a much broader area, revealing that these stellar misfits are scattered throughout the galaxy's bustling center.


Astronomers used Hubble's Wide Field Camera 3 to find roughly 8,000 of the ultra-blue stars in a stellar census made in ultraviolet light, which traces the glow of the hottest stars. The study is part of the multi-year Panchromatic Hubble Andromeda Treasury survey to map stellar populations across the Andromeda galaxy.

Credit: T. Rector and B. Wolpa (NOAO/AURA/NSF)


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💫Rough and Crowded Neighborhood at Galactic Center


The center of the Milky Way is a crowded neighborhood and not always a calm one, according to the latest image from NASA's Chandra X-ray Observatory. In addition to the supermassive black hole at the center, the area is filled with all sorts of different inhabitants that affect and influence one another. The new X-ray image shows three massive star clusters, the Arches (upper right), Quintuplet (upper center), and the GC star cluster (bottom center), which is near the enormous black hole known as Sagittarius A*. The massive stars in these clusters can themselves be very bright, point-like X-ray sources, when winds blowing off their surfaces collide with winds from an orbiting companion star. The stars in these clusters also release vast amounts of energy when they reach the ends of their lives and explode as supernovas, which, in turn, heat the material between the stars. The stars near the Galactic Center also can emit X-rays as stellar corpses -- either in the form of neutron stars or black holes in binary systems -- and are also seen as point-like sources in the Chandra image.

While the individual stars in these clusters are experiencing their own hectic lives, the clusters themselves are also busy interacting with other residents of the Galactic center neighborhood. For instance, the star clusters are slamming into cooler, dense clouds of molecular gas. These powerful collisions between the clusters and clouds may result in a higher proportion of more massive stars than low-mass ones in the Galactic center, compared to a quieter neighborhood. The collisions may also explain some of the diffuse X-ray emission seen in the Chandra image. Over the course of several years, over two million seconds of Chandra observing time has been devoted to studying the center of the Galaxy. This latest image from Chandra represents more than 1 million seconds of time and covers the area of 168 by 130 light years across. In this image, red, green, and blue correspond to lower, medium, and high-energy X-rays respectively.

Credit:
NASA / CXC / UMass Amherst / Q.D.Wang


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💫A long-dead star

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This Hubble Space Telescope image captures the remnants of a long-dead star. These rippling wisps of ionised gas, named DEM L316A, are located some 160 000 light-years away within one of the Milky Way’s closest galactic neighbours, the Large Magellanic Cloud (LMC). The explosion that formed DEM L316A was an example of an especially energetic and bright variety of supernova, known as a Type Ia. Such supernova events are thought to occur when a white dwarf star steals more material than it can handle from a nearby companion, and becomes unbalanced.


The result is a spectacular release of energy in the form of a bright, violent explosion, which ejects the star’s outer layers into the surrounding space at immense speeds. As this expelled gas travels through the interstellar material, it heats it up and ionise it, producing the faint glow that Hubble’s Wide Field Camera 3 has captured here. The LMC orbits the Milky Way as a satellite galaxy and is the fourth largest in our group of galaxies, the Local Group. DEM L316A is not alone in the LMC.

Credit: ESA / Hubble & NASA, Y. Chu


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💫The Heat Is On in Andromeda's Center


This color-coded Chandra image (red/low energy, green/medium energy, and blue/high energy X-rays) shows the central region of the Andromeda Galaxy, a.k.a. M31 where a diffuse, X-ray emitting cloud of hot gas was discovered in the midst of a collection of point-like sources. Analysis of the X-ray data shows that the point sources are associated with binary star systems that contain a neutron star or black hole that is pulling matter away from a normal star. As the matter falls toward the neutron star or black hole, it is heated by frictional forces to tens of millions of degrees, and produces X-rays. The diffuse X-ray cloud is due to gas that has accumulated in the central region and been heated to millions of degrees, probably by shock waves from supernova explosions.

The energy input from the supernovas could also be driving gas out of the central region. This process may affect both the shape and evolution of the galaxy by depleting the raw material for the formation of new stars and preventing more gas from accumulating there. Andromeda, a large spiral galaxy much like our Milky Way Galaxy, is relatively nearby and can be easily seen with binoculars in the autumn sky. The galaxy's central region is called the galactic bulge because the stars form a ball a few thousand light years in diameter that extends above and below the disk of the galaxy.

Credit:
NASA / UMass / Z.Li & Q.D.Wang


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