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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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💫Scattered stars in Sagittarius

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This colourful and star-studded view of the Milky Way galaxy was captured when the NASA/ESA Hubble Space Telescope pointed its cameras towards the constellation of Sagittarius (The Archer). Blue stars can be seen scattered across the frame, set against a distant backdrop of red-hued cosmic companions. This blue litter most likely formed at the same time from the same collapsing molecular cloud. The colour of a star can reveal many of its secrets. Shades of red indicate a star much cooler than the Sun, so either at the end of its life, or much less massive.


These lower-mass stars are called red dwarfs and are thought to be the most common type of star within the Milky Way. Similarly, brilliant blue hues indicate hot, young, or massive stars, many times the mass of the Sun. A star’s mass decides its fate; more massive stars burn brightly over a short lifespan, and die young after only tens of millions of years. Stars like the Sun typically have more sedentary lifestyles and live longer, burning for approximately ten billion years. Smaller stars, on the other hand, live life in the slow lane and are predicted to exist for trillions of years, well beyond the current age of the Universe.

Credit: ESA/Hubble & NASA


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💫Stunning View of Starburst Galaxy


Images from three of NASA's Great Observatories were combined to create this spectacular, multiwavelength view of the starburst galaxy M82. Optical light from stars (yellow-green/Hubble Space Telescope) shows the disk of a modest-sized, apparently normal galaxy. Another Hubble observation designed to image 10,000 degree Celsius hydrogen gas (orange) reveals a startlingly different picture of matter blasting out of the galaxy. The Spitzer Space Telescope infrared image (red) shows that cool gas and dust are also being ejected. Chandra's X-ray image (blue) reveals gas that has been heated to millions of degrees by the violent outflow. The eruption can be traced back to the central regions of the galaxy where stars are forming at a furious rate, some 10 times faster than in the Milky Way Galaxy.

Many of these newly formed stars are very massive and race through their evolution to explode as supernovas. Vigorous mass loss from these stars before they explode, and the heat generated by the supernovas drive the gas out of the galaxy at millions of miles per hour. It is thought that the expulsion of matter from a galaxy during bursts of star formation is one of the main ways of spreading elements like carbon and oxygen throughout the universe. The burst of star formation in M82 is thought to have been initiated by shock waves generated in a close encounter with a large nearby galaxy, M81, about 100 million years ago. These shock waves triggered the collapse of giant clouds of dust and gas in M82. In another 100 million years or so, most of the gas and dust will have been used to form stars, or blown out of the galaxy, so the starburst will subside.

Credit:
X-ray: NASA/CXC/JHU/D.Strickland; Optical: NASA/ESA/STScI/AURA/The Hubble Heritage Team; IR: NASA/JPL-Caltech/Univ. of AZ/C. Engelbracht


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💫Overview of the Hyades star cluster

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This image shows the Hyades star cluster, the nearest cluster to us. The Hyades cluster is very well studied due to its location, but previous searches for planets have produced only one. A new study led by Jay Farihi of the University of Cambridge, UK, has now found the atmospheres of two burnt-out stars in this cluster, known as white dwarfs, to be “polluted” by rocky debris circling the star.


Seeing evidence of asteroids points to the possibility of Earth-sized planets in the same system, as asteroids are the building blocks of major planets. Planet-forming processes are inefficient, and spawn many times more small bodies than large bodies, but once rocky embryos the size of asteroids are built, planets are sure to follow.

Credit: NASA, ESA, and STScI.


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💫Black Holes Determined to be Bound


This composite X-ray (blue)/radio (pink) image of the galaxy cluster Abell 400 shows radio jets immersed in a vast cloud of multimillion degree X-ray emitting gas that pervades the cluster. The jets emanate from the vicinity of two supermassive black holes (bright spots in the image). These black holes are in the dumbbell galaxy NGC 1128 (see optical image), which has produced the giant radio source, 3C 75. The peculiar dumbbell structure of this galaxy is thought to be due to two large galaxies that are in the process of merging. Such mergers are common in the relatively congested environment of galaxy clusters. An alternative hypothesis is that the apparent structure is the result of a coincidence in time when the two galaxies are passing one another, like ships in the cosmic sea. Careful analysis of the recent Chandra and radio data on 3C 75 indicates that the galaxies and their supermassive black holes are indeed bound together by their mutual gravity. By using the shape and direction of the radio jets, astronomers were able to determine the direction of the motion of the black holes.

The swept-back appearance of the radio jets is produced by the rapid motion of the galaxy through the hot gas of the cluster, in much the same way that a motorcyclist's scarf is swept back while speeding down the road. The binary black holes in 3C 75 are about 25,000 light years apart. They are likely at an earlier stage in their evolution than the pair found in NGC 6240, which are about 3,000 light years apart. Computer simulations indicate that binary supermassive black holes gradually spiral toward each other until they coalesce to form a single, more massive black hole, accompanied by an enormous burst of gravitational waves. These gravitational waves would spread through the Universe and produce ripples in the fabric of space, which would appear as minute changes in the distance between any two points. Sensitive gravitational wave detectors scheduled to be operational in the next decade could detect one of these events, which are estimated to occur several times each year in the observable Universe.

Credit:
X-ray: NASA/CXC/AIfA/D.Hudson & T.Reiprich et al.; Radio: NRAO/VLA/NRL


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💫Intense and short-lived

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This NASA/ESA Hubble Space Telescope picture shows a galaxy named SBS 1415+437 or SDSS CGB 12067.1, located about 45 million light-years from Earth. SBS 1415+437 is a Wolf–Rayet galaxy, a type of starbursting galaxy with an unusually high number of extremely hot and massive stars known as Wolf–Rayet stars. These stars can be around 20 times as massive as the Sun, but seem to be on a mission to shed surplus mass as quickly as possible, they blast substantial winds of particles out into space, causing them to dwindle at a rapid rate. A typical star of this type can lose a mass equal to that of our Sun in just 100 000 years!


These massive stars are also incredibly hot, with surface temperatures some 10 to 40 times that of the Sun, and very luminous, glowing at tens of thousands to several million times the brightness of the Sun. Many of the brightest and most massive stars in the Milky Way are Wolf–Rayet stars. Because these stars are so intense they do not last very long, burning up their fuel and blasting their bulk out into the cosmos on very short timescale ‒ only a few hundred thousand years. Because of this it is unusual to find more than a few of these stars per galaxy, except in Wolf–Rayet galaxies, like the one in this image.

Credit: ESA/Hubble & NASA


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