Wednesday, November 28, 2007

3 million miles per hour

Click on Image to Enlarge.

This graphic shows a wide-field view of the Puppis A supernova remnant along with a close-up image of the neutron star, known as RX J0822-4300. The larger field-of-view is a composite of X-ray data from the ROSAT satellite (pink) and optical data (purple), from the Cerro Tololo Inter-American Observatory 0.9-meter telescope, which highlights oxygen emission. Astronomers think Puppis A was created when a massive star ended its life in a supernova explosion about 3,700 years ago, forming an incredibly dense object called a neutron star and releasing debris into space.

The neutron star was ejected by the explosion. The inset box shows two observations of this neutron star obtained with the Chandra X-ray Observatory over the span of five years, between December 1999 and April 2005. By combining how far it has moved across the sky with its distance from Earth, astronomers determined the cosmic cannonball is moving at over 3 million miles per hour, one of the fastest moving stars ever observed. At this rate, RX J0822-4300 is destined to escape from the Milky Way after millions of years, even though it has only traveled about 20 light years so far.

The results from this study suggest the supernova explosion was lop-sided, kicking the neutron star in one direction and much of the debris from the explosion in the other. The estimated location of the explosion is shown in the above composite image. The direction of motion of the cannonball, shown by an arrow, is in the opposite direction to the overall motion of the oxygen debris, seen in the upper left. The arrows show the estimated motion over the next 1,000 years. The oxygen clumps are believed to be massive enough so that momentum is conserved in the aftermath of the explosion.

Credit: Chandra: NASA/CXC/Middlebury College/F.Winkler et al.; ROSAT: NASA/GSFC/S.Snowden et al.; Optical: NOAO/CTIO/Middlebury College/F.Winkler et al.
Star cluster's extreme speed puzzles astronomers from New Scientist
ESO's VLT takes the search for young galaxies to new limits from ESO

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Saturday, November 24, 2007

The Closest Galaxy

The Closest Galaxy: Canis Major Dwarf. - Illustration Credit & Copyright: R. Ibata (Strasbourg Observatory, ULP) et al., 2MASS, NASA

What is the closest galaxy to the Milky Way? The new answer to this old question is the Canis Major dwarf galaxy. For many years astronomers thought the Large Magellan Cloud (LMC) was closest, but its title was supplanted in 1994 by the Sagittarius dwarf galaxy.

Recent measurements indicate that the Canis Major dwarf is only 42,000 light years from the Galactic center, about three quarters of the distance to the Sagittarius dwarf and a quarter of the distance to the LMC. The discovery was made in data from the 2MASS-sky survey, where infrared light allows a better view through our optically opaque Galactic plane.

The labeled illustration above shows the location of the newly discovered Canis Major dwarf and its associated tidal stream of material in relation to our Milky Way Galaxy. The Canis Major dwarf and other satellite galaxies are slowly being gravitationally ripped apart as they travel around and through our Galaxy
Astronomers Discover Stars With Carbon Atmospheres from Space Daily
New Type of Dying Star Discovered by Charles Q Choi @ Space dot com
Astronomers Observe Acidic Milky Way Galaxies from Science Daily

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Wednesday, November 21, 2007

LIGO scanning the skies

Searching for one of Einstein's greatest predictions:

Gravitational waves are produced when massive objects in space move violently. The waves carry the imprint of the events that cause them. Scientists already have indirect evidence that gravitational waves exist, but have not directly detected them.

The Laser Interferometer Gravitational-wave Observatory, or LIGO, consists of detectors at two U.S. sites managed by the California Institute of Technology (Caltech) and Massachusetts Institute of Technology (MIT).

The LIGO observatories use lasers to accurately monitor the distance between a central station and mirrors suspended three miles away along perpendicular arms. When a gravitational wave, a traveling ripple in space-time, passes by, the mirror in one arm will move closer to the central station, while the other mirror will move away.

The change in distance caused by stretching and squeezing is what LIGO is designed to measure, says Alan Wiseman - associate professor @ UWM's Center for Cosmology and Gravitation.

Those changes will be inconceivably tiny. LIGO can record distortions at a scale so small, it is comparable in distance to a thousandth of the size of an atomic nucleus.

LIGO records a series of numbers - lots of them - and feeds them to several supercomputer clusters around the country, including UWM's Nemo cluster.

The computer's job is to sort out the numerical patterns representing gravitational waves buried in ambient noise produced by lots of other vibrations - from internal vibrations of the equipment itself, to magnetic fluctuations from lightning storms, to seismic vibrations from trains rolling along the tracks a few miles from the observatory, or from earthquakes on the other side of the world.

There are thousands or even millions of different signals that could be emitted from space. So you have to take each segment of data individually. Nemo performs many billions of calculations per second in its search for these signals.

The strings of numbers from LIGO are like tracks on a compact disk. Once detected, gravitational-wave signals can be converted into sound. Scientists have already simulated, based on mathematical predictions, what certain events in space will sound like.

When two black holes are merging, for example, you might expect to hear a "chirp" that represents the spiraling together of the black holes just before they collide. "The spiral can go on for thousands of years," says Brady, a UWM professor of physics. "The sound is the identifying signal of the last few seconds of the process!"

Gravitational waves may hold secrets to the nature of black holes, the unknown properties of nuclear material, and maybe even how the universe began.

"We've only been able to find out about the universe since it became cool. But with gravitational waves, we'll see the universe when it was much younger -- and hotter." "I think we're in for a surprise," says Siemens from UWM's Center for Cosmology and Gravitation. "We have all these ideas about what we think we will find, but it could be something completely different."
Can 3D movies like Beowulf save the World of Cinema
What Space Telescopes of Tomorrow Will See from LiveScience
Surrogate Memory - Back Up Your Brain from The Galactic Emporium

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Thursday, November 15, 2007

Bustling Hub of Star Formation

Credit: X-ray: NASA/CXC/CfA/S.Wolk et al;
Optical: NSF/AURA/WIYN/Univ. of Alaska/T.A.Rector

NGC 281 is a bustling hub of star formation about 10,000 light years away in the Constellation of Cassiopeia. This composite image of optical and X-ray emission includes regions where new stars are forming and older regions containing stars about 3 million years old.

The optical data (seen in red, orange, and yellow) show a small open cluster of stars, large lanes of obscuring gas and dust, and dense knots where stars may still be forming. The X-ray data (purple), based on a Chandra observation lasting more than a day, shows a different view. More than 300 individual X-ray sources are seen, most of them associated with IC 1590, the central cluster.

The edge-on aspect of NGC 281 allows scientists to study the effects of powerful X-rays on the gas in the region, the raw material for star formation.

A second group of X-ray sources is seen on either side of a dense molecular cloud, known as NGC 281 West, a cool cloud of dust grains and gas, much of which is in the form of molecules. The bulk of the sources around the molecular cloud are coincident with emission from polycyclic aromatic hydrocarbons, a family of organic molecules containing carbon and hydrogen.

There also appears to be cool diffuse gas associated with IC 1590 that extends toward NGC 281 West.

The X-ray spectrum of this region shows that the gas is a few million degrees and contains significant amounts of magnesium, sulfur and silicon. The presence of these elements suggests that supernova recently went off in that area.

More Images of NGC 281 from Chandra
Hubble's Island Universes: Watching Galaxies Grow Old Gracefully

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Monday, November 12, 2007

Highest-Energy Cosmic Rays

Active Galactic Nuclei (AGN) are found at the hearts of some galaxies and are thought to be powered by supermassive black holes that are devouring large amounts of matter.

They have long been considered sites where high-energy particle production might take place. They swallow gas, dust and other matter from their host galaxies and spew out particles and energy.

While most galaxies have black holes at their centre, only a fraction of all galaxies have an AGN. The exact mechanism of how AGNs can accelerate particles to energies 100 million times higher than the most powerful particle accelerator on Earth is still a mystery.
[+/-] Click here to expand

Cosmic rays are protons and atomic nuclei that travel across the universe at close to the speed of light. When these particles smash into the upper atmosphere of our planet, they create a cascade of secondary particles called an air shower that can spread across 40 or more square kilometres as they reach the Earth’s surface.

Professor Subir Sarkar of the Physics Department at Oxford University, a member of the Auger Collaboration, said: ‘The Auger data indicates that the sources of ultrahigh energy cosmic rays are associated with nearby 'active galaxies' which harbour supermassive black holes that are gobbling up stellar matter and ejecting huge jets of plasma. Our own galaxy too has such a black hole at its centre but, fortunately for us, it is not 'feeding' at the moment!’

The Pierre Auger Observatory records cosmic ray showers through an array of 1,600 particle detectors placed 1.5 kms apart in a grid spread across 3,000 square kms. Twenty-four specially designed telescopes record the emission of fluorescence light from the air shower. The combination of particle detectors and fluorescence telescopes provides an exceptionally powerful instrument for this research.

While the observatory has recorded almost a million cosmic-ray showers, only the rare, highest-energy cosmic rays can be linked to their sources with sufficient precision. Auger scientists so far have recorded 81 cosmic rays with energy above 4 x1019 electron volts, or 40 EeV. This is the largest number of cosmic rays with energy above 40 EeV recorded by any observatory.

At these ultra-high energies, the uncertainty in the direction from which the cosmic ray arrived is only a few degrees, allowing scientists to determine the location of the particle’s cosmic source.

The Auger collaboration discovered that the 27 highest-energy events, with energy above 57 EeV, do not come equally from all directions. Comparing the clustering of these events with the known locations of 381 Active Galactic Nuclei, the collaboration found that most of these events correlated well with the locations of AGNs in some nearby galaxies, such as Centaurus A.

Click Image to Enlarge: Centaurus A

Low-energy cosmic rays are abundant and come from all directions, mostly from within our own Milky Way galaxy. Until now the only source of cosmic ray particles known with certainty has been the sun. Cosmic rays from other likely sources such as exploding stars take meandering paths through space so that when they reach Earth it is impossible to determine their origins.

"But when you look at the highest-energy cosmic rays from the most violent sources, they point back to their sources. The challenge now is to record enough of these cosmic bullets to understand the processes that hurl them into space," said Paul Mantsch, project manager of the Pierre Auger Observatory.

Cosmic rays with energy higher than about 60 EeV lose energy in collisions with the cosmic microwave background, (radiation left over from the Big Bang that fills all of space). But cosmic rays from nearby sources are less likely to lose energy in collisions on their relatively short trip to Earth. Auger scientists found that most of the 27 events with energy above 57 EeV came from locations in the sky that include the nearest AGNs, within a few hundred million light years of Earth.

Scientists think that most galaxies have black holes at their centres, with masses ranging from a million to a few billion times the mass of our sun. The black hole at the centre of our Milky Way galaxy weighs about 3 million solar masses, but it is not an AGN. Galaxies that have an AGN seem to be those that suffered a collision with another galaxy or some other massive disruption in the last few hundred million years. The AGN swallows the mass coming its way while releasing prodigious amounts of radiation. The Auger result indicates that AGNs may also produce the universe's highest-energy particles.

Cosmic-ray astronomy is challenging, because low-energy cosmic rays provide no reliable information on the location of their sources: as they travel across the cosmos, they are deflected by galactic and intergalactic magnetic fields that lead to blurry images. In contrast, the most energetic particles come almost straight from their sources, as they are barely affected by the magnetic fields. Unfortunately, they hit Earth at a rate of only about one event per square kilometre per century, which demands a very large observatory.

Because of its size, the Auger Observatory can record about 30 ultra-high-energy events per year. The Auger collaboration is developing plans for a second, larger installation in Colorado to extend coverage to the entire sky while substantially increasing the number of high-energy events recorded.

"Our current results show the promising future of cosmic-ray astronomy," said Auger co-spokesperson Giorgio Matthiae, of the University of Rome. "So far we have installed 1400 of the 1600 particle detectors of the Auger Observatory in Argentina. A northern site would let us look at more galaxies and black holes, increasing the sensitivity of our observatory. There are even more nearby AGNs in the northern sky than in the southern sky."

Source: Auger Observatory closes in on long standing mystery, links highest-energy cosmic rays with violent black holes

Breakthrough in Cosmic Ray mystery from SciTech
AGN and Ultra High Energy Cosmic Rays from Space Daily
AUGER: millions of TeV cosmic rays from black holes from The Reference Frame
Ultra High Energy Cosmic Rays (UHECR) from Auger @ BackReaction

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Saturday, November 10, 2007

Stellar Bubble Blower

HH 46/47. NASA/JPL-Caltech/T. Velusamy (Jet Propulsion Laboratory)

A new image from NASA's Spitzer Space Telescope shows a baby star 1,140 light-years away from Earth blowing two massive "bubbles." This young Star, called HH 46/47, is using powerful jets of gas to make bubbles in outer space.

The infant star can be seen as a white spot toward the center of the Spitzer image. The two bubbles are shown as hollow elliptical shells of bluish-green material extending from the star. Wisps of green in the image reveal warm molecular hydrogen gas, while the bluish tints are from starlight scattered by surrounding dust.

These bubbles formed when powerful jets of gas, traveling at 200 to 300 kilometers per second, or about 120 to 190 miles per second, smashed into the cosmic cloud of gas and dust that surrounds HH 46/47. Red specks at the end of each bubble show the presence of hot sulfur and iron gas where the star's narrow jets are currently crashing head-on into the cosmic cloud's gas and dust material.

According to Dr. Thangasamy Velusamy of NASA's Jet Propulsion Laboratory in Pasadena, Calif., baby stars and their potential planet-forming disks grow by gravitationally pulling in and absorbing surrounding gas and dust. Scientists suspect that these disks stop growing when the central baby star develops powerful winds and jets that blow away surrounding material.

"Spitzer can image these jets and winds in infrared light and help us understand the details of these phenomena," says Velusamy.

Spitzer's supersensitive infrared instruments are excellent tools for studying young stars embedded within thick clouds of cosmic dust and gas, revealing information about their growth.

When you see a star through a telescope, its image is blurred in a known way. The smaller the telescope the larger is the blurring.

To clear up this blurring, astronomers at JPL developed an advanced image-processing technique for Spitzer data called Hi-Res deconvolution. This process reduces blurring and makes the image sharper and cleaner, enabling astronomers to see the emissions around forming stars in greater detail. When Velusamy and his team applied this technique to the Spitzer image of HH 46/47, they were able to see winds from the star and jets of gas that are carving the celestial bubbles.

According to Dr. William Langer, also of JPL, this image will help scientists determine which of many different mechanisms are responsible for producing the winds and jets of baby stars.

This infrared image is a three-colour composite, with data at 3.6 microns represented in blue, 4.5 and 5.8 microns shown in green, and 24 microns represented as red.

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Thursday, November 08, 2007

Light from Young Galaxies

The artist's illustration shows a typical massive galaxy as it would have appeared when the universe was only about a quarter of its current age. This young galaxy contains an active galactic nucleus (AGN), or quasar, in its center, a luminous object powered by the rapid growth of a supermassive black hole. Some of the light from the AGN is obscured by dense gas and dust near the center of the galaxy. The galaxy itself is undergoing a growth spurt, as shown by bright regions of star formation in the spiral arms.

Spitzer Space Telescope observations are extremely efficient at detecting distant AGN like this because dust and gas should absorb high-energy radiation from the AGN and re-emit it at longer wavelengths, generating copious amounts of infrared emission.

Large numbers of galaxies thought to contain such highly obscured AGN have been discovered in the Great Observatories Origins Deep Survey. The infrared emission for these galaxies exceeds the levels likely to be caused by star formation. However, X-ray observations were required to confirm the presence of obscured AGN, by looking for the high energy X-rays expected from such objects (less energetic X-rays are mostly absorbed).
[+/-] Click here to expand

The image on the left shows a "stacked" Chandra image of distant, massive galaxies detected with Spitzer. Image stacking is a procedure used to detect emission from objects that is too faint to be detected in single images. To enhance the signal, images of these faint objects are stacked on top of one another. In this image, low-energy X-rays are shown in orange and high-energy X-rays in blue, and the stacked object is in the center of the image (the other sources beyond the center of the image are individual AGN that were directly detected and are not part of the source stacking).

The blue stacked source confirms the hypothesis that large numbers of these young, massive galaxies contain heavily obscured AGN. Spitzer also detected infrared emission from young, massive galaxies that is consistent with expectations for star formation. These galaxies do not contain AGN, because their supermassive black holes are dormant.

A stacked Chandra image (right) of these "normal" massive galaxies shows mainly soft X-ray emission at the center, as expected.

This image, taken with Spitzer's infrared vision, shows a fraction of these black holes, which are located deep in the bellies of distant, massive galaxies. Spitzer originally scanned the field of galaxies shown in the picture as part of a multiwavelength program called the Great Observatories Origins Deep Survey, or Goods.

This picture shows a portion of the Goods field called Goods-South. When astronomers saw the Spitzer data, they were surprised to find that hundreds of the galaxies between 9 and 11 billion light years away were shining with an unexpected excess of infrared light.

They then followed up with X-ray data from Chandra of the same field, and applied a technique called stacking, which adds up the faint light of multiple galaxies. The results revealed that the infrared-bright galaxies are hiding many black holes that had been theorized about before but never seen. This excess infrared light is being produced by the growing black holes.

Credit: Illustration: NASA/JPL-Caltech/T.Pyle (SSC); X-ray: NASA/CXC/Durham/D.Alexander et al.; Infrared: NASA/JPL-Caltech/CEA/E.Daddi

Monster black holes power highest-energy cosmic rays from SNS
Cosmic 'Bullets' Traced to Galactic Black Holes from Live Science
'Violent' Black Holes Linked To High Energy Cosmic Rays from Scientic Blogging
Finding Antimatter & Collecting Natural Antimatter Centauri Dreams

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Tuesday, November 06, 2007

Powerful Cosmic Winds

Black Holes Launch Powerful Cosmic Winds
Black holes often are thought of as just endless pits in space and time that destroy everything they pull toward them. But new findings confirm the reverse is true, too: Black holes can drive extraordinarily powerful winds that push out and force star formation and shape the fate of a galaxy.

Supermassive black holes are suspected to lurk in the hearts of many - if not all - large galaxies. These holes drag gas inward, which accrues in rapidly spinning, glowing disks.

Astronomers have long thought that such "accretion disks" give off mighty winds that shape the host galaxies, profoundly influencing how they grow.

"In the early universe, galaxies formed from clumps of gas coagulating from mutual gravitational attraction. If unhindered, they would have formed rather bigger structures than what we see today," said astrophysicist Andrew Robinson at the Rochester Institute of Technology in New York. "But if we take into account these winds blowing away surrounding gas, that could help explain the galaxy sizes we see."

Until now, scientists had only theorized that accretion disks launched these winds. No one had actually seen this happen. These accretion disks are comparable in size to our solar system - big for us - but on the scale of galaxies they're really tiny, and far away to boot, making it virtually impossible to distinguish any details such as winds.

To attempt to observe the winds, Robinson and his colleagues investigated a galaxy roughly 3 billion light years from Earth using the William Herschel Telescope on the Canary Islands off the coast of Africa. At the core of that galaxy lies a quasar, an extremely powerful source of radiation as bright as up to 1 trillion suns that originates from the superheated gas of a black hole's accretion disk.

The researchers discovered that light from the quasar was scattered by electrons in super-fast gas. The specific way in which this light was scattered suggests the gas was rotating at speeds similar to the accretion disk's rate of spin. In other words, they confirmed the accretion disk was launching wind.

The researchers will next try to find out if these disk winds are launched only when the black hole is growing rapidly, or just by quasars, which have the most massive black holes, or by all active galactic nuclei.

Findings detailed in the Nov. 1 issue of the journal Nature.
By Charles Q. Choi @
Live Science
'Spitting' black holes may be key to cosmic mysteries from Space New Scientist
Supermassive Black Holes Produce Powerful Galaxy-shaping Winds - Science Daily

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Monday, November 05, 2007

Weighing the Universe's Mass

Spiral Galaxy NGC1232 Credit: ESO.

This image of the large spiral galaxy NGC 1232 was obtained with the Very Large Telescope (VLT). Its distance from Earth is about 100 million light-years. It is thought to contain more dark matter than visible matter.

The same University of Alabama (UAH) group that in 2002 found what was theorized to be a significant fraction of the "missing mass" that binds together the universe has discovered that some x-rays thought to come from intergalactic clouds of "warm" gas are instead probably caused by lightweight electrons.

If the source of so much x-ray energy is tiny electrons instead of hefty atoms, it is as if billions of lights thought to come from billions of aircraft carriers were found instead to come from billions of extremely bright fireflies.

"This means the mass of these x-ray emitting clouds is much less than we initially thought it was," said Dr. Max Bonamente, an assistant professor in UAH's Physics Department. "A significant portion of what we thought was missing mass turns out to be these 'relativistic' electrons."

Travelling at almost the speed of light (and therefore "relativistic"), these feather weight electrons collide with photons from the cosmic microwave background. Energy from the collisions converts the photons from low-energy microwaves to high-energy x-rays.

In 2002 the UAH team reported finding large amounts of extra "soft" (relatively low-energy) x-rays coming from the vast space in the middle of galaxy clusters. This was in addition to previously-discovered "hot" gas in that space, which emits higher energy "hard" x-rays.

Although the soft x-ray-emitting atoms were thought to be spread thinly through space (less than one atom per cubit meter), they would have filled billions of billions of cubic light years. Their cumulative mass was though to account for as much as ten percent of the mass and gravity needed to hold together galaxies, galaxy clusters and perhaps the universe itself.

When Bonamente and his associates looked at data gathered by several satellite instruments, including the Chandra X-ray Observatory, from a galaxy cluster in the southern sky, however, they found that energy from those additional soft x-rays doesn't look like it should.

"We have never been able to detect spectral emission lines associated with those detections," he explained. "If this 'bump' in the data were due to cooler gas, it would have emission lines."

The best, most logical explanation seems to be that a large fraction of the energy comes from electrons smashing into photons instead of from warm atoms and ions, which would have recognizable spectral emission lines. Finding these electrons, however, is like finding "the tip of the iceberg," said Bonamente, because they would not be limited to emitting only the soft x-ray signal. The signal from these electrons would also make up part of the previously observed harder X-rays, which would reduce the amount of mass thought to make up the hot gas at the center of galaxy clusters.

The energy from these electrons might also "puff up" the cluster. Previously, astrophysicists used the energy coming from inside these clusters to calculate how much mass is needed to reach the equilibrium seen there; too much mass and the cloud would collapse; too little and the hot gas cloud would expand. Since the energy coming from these hot clouds can be accurately measured, it was thought the mass could be calculated with reasonable confidence.

Instead, says Bonamente, if a significant portion of the total x-ray energy comes from fast electrons, "that could trick us into thinking there is more gas than is actually there." It means we need to revise how we calculate both the gas mass and the total mass. If part of the hard x-ray energy comes from electrons and photons, it might also shift what we think is the mix of elements in the universe.

Outside of the excess soft x-rays, the x-ray energy coming from galaxy clusters has emission lines which are especially prominent around iron and other metals. Non-thermal x-rays from electrons colliding with photons might mask those emission lines, like thick snow can mask the height of fence posts. "This is also telling us there is fractionally more iron and other metals than we previously thought," said Bonamente. "Less mass but more metals."
Missing Mass Theory Revised from Centauri Dreams
Big Chunk Of The Universe Is Missing - Again from Science Daily
Dark Matter & visible Matter in Galaxies from Life in the Universe

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Saturday, November 03, 2007

Dark 'Black Eye' Galaxy

Messier 64 (M64) has a spectacular dark band of absorbing dust in front of the galaxy's bright nucleus, giving rise to its nicknames of the "Black Eye" galaxy.

Fine details of the dark band are revealed in this image of the central portion of M64 obtained with the Hubble Space Telescope. First cataloged in the 18th century by the French astronomer Messier, M64 is located in the northern constellation Coma Berenices, and resides roughly 17 million light-years from Earth.

At first glance, M64 appears to be a fairly normal pinwheel-shaped spiral galaxy. As in the majority of galaxies, all of the stars in M64 are rotating in the same direction, clockwise as seen in the Hubble image. However, detailed studies in the 1990's led to the remarkable discovery that the interstellar gas in the outer regions of M64 rotates in the opposite direction from the gas and stars in the inner regions.

Active formation of new stars is occurring in the shear region where the oppositely rotating gases collide, are compressed, and contract. Particularly noticeable in the image are hot, blue young stars that have just formed, along with pink clouds of glowing hydrogen gas that fluoresce when exposed to ultraviolet light from newly formed stars.

Astronomers believe that the oppositely rotating gas arose when M64 absorbed a satellite galaxy that collided with it, perhaps more than one billion years ago. This small galaxy has now been almost completely destroyed, but signs of the collision persist in the backward motion of gas at the outer edge of M64.

This image of M64 was taken with Hubble's Wide Field Planetary Camera 2 (WFPC2). The colour image is a composite from pictures taken through four different colour filters. These filters isolate blue and near-infrared light, along with red light emitted by hydrogen atoms and green light from Strömgren y.
Modified Gravity in the absence of Dark Matter
Dark Matter's Rival Theory Challenges "Invisible Mass"
Supermassive Black Holes Shape Their Galaxies from Universe Today

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Thursday, November 01, 2007

Massive "Stellar" Black Hole

Credit: Aurore Simonnet/Sonoma State University/NASA

Astronomers have discovered a massive stellar black hole with an orbiting companion: a hot, highly evolved star. The new black hole, is the heftiest known black hole that orbits another star.

Formed in the death throes of massive stars, "stellar-mass" black holes are smaller than the monster black holes found in galactic cores. The previous record holder for largest stellar-mass black hole is a 16-solar-mass black hole in the galaxy M33, announced on October 17.

Located in the nearby dwarf galaxy IC 10, 1.8 million light-years from Earth in the constellation Cassiopeia. The star is ejecting gas in the form of a wind. Some of this material spirals toward the black hole, heats up, and gives off powerful X-rays before crossing the point of no return.

In November 2006, Andrea Prestwich of the Harvard-Smithsonian Center for Astrophysics in Cambridge, Mass., and her colleagues observed the dwarf galaxy with NASA’s Chandra X-ray Observatory.

The group discovered that the galaxy’s brightest X-ray source, IC 10 X-1, exhibits sharp changes in X-ray brightness. Such behavior suggests a star periodically passing in front of a companion black hole and blocking the X-rays, creating an eclipse. In late November, NASA’s Swift satellite confirmed the eclipses and revealed details about the star’s orbit.

The star in IC 10 X-1 appears to orbit in a plane that lies nearly edge-on to Earth’s line of sight, so a simple application of Kepler’s Laws show that the companion black hole has a mass of at least 24 Suns.

The black hole’s large mass is surprising because massive stars generate powerful winds that blow off many Suns worth of gas before the stars explode. Calculations suggest massive stars in our galaxy leave behind black holes no heavier than about 15 Suns.

The IC 10 X-1 black hole has gained mass since its birth by gobbling up gas from its companion star, but the rate is so slow that the black hole would have gained no more than 1 or 2 solar masses. "This black hole was born fat; it didn’t grow fat," says astrophysicist Richard Mushotzky of NASA Goddard Space Flight Center in Greenbelt, Md., who is not a member of the discovery team.

The progenitor star probably started its life with 60 or more solar masses. Like its host galaxy, it was probably deficient in elements heavier than hydrogen and helium. In massive, luminous stars with a high fraction of heavy elements, the extra electrons of elements such as carbon and oxygen “feel” the outward pressure of light and are more susceptible to being swept away in stellar winds.

But with its low fraction of heavy elements, the IC 10 X-1 progenitor shed comparatively little mass before it exploded, so it could leave behind a heavier black hole.

"Massive stars in our galaxy today are probably not producing very heavy stellar-mass black holes like this one," says coauthor Roy Kilgard of Wesleyan University in Middletown, Conn. "But there could be millions of heavy stellar-mass black holes lurking out there that were produced early in the Milky Way’s history, before it had a chance to build up heavy elements."

This release is being issued jointly with NASA
Massive Black Hole Smashes Record
New Spin on how Stars Are Born from Live Science
Black Holes may harbour their own universes from Space New Scientist
White Dwarf "Sibbling Rivalry" explodes into Supernova CfA Press Release

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