Spiral in Serpens

This new NASA/ESA Hubble Space Telescope image shows a beautiful spiral galaxy known as PGC 54493, located in the constellation of Serpens (The Serpent). This galaxy is part of a galaxy cluster that has been studied by astronomers exploring an intriguing phenomenon known as weak gravitational lensing.
This effect, caused by the uneven distribution of matter (including dark matter) throughout the Universe, has been explored via surveys such as the Hubble Medium Deep Survey. Dark matter is one of the great mysteries in cosmology. It behaves very differently from ordinary matter as it does not emit or absorb light or other forms of electromagnetic energy — hence the term “dark”.
Even though we cannot observe dark matter directly, we know it exists. One prominent piece of evidence for the existence of this mysterious matter is known as the “galaxy rotation problem”. Galaxies rotate at such speeds and in such a way that ordinary matter alone — the stuff we see — would not be able to hold them together. The amount of mass that is “missing” visibly is dark matter, which is thought to make up some 27% of the total contents of the Universe, with dark energy and normal matter making up the rest. PGC 55493 has been studied in connection with an effect known as cosmic shearing. This is a weak gravitational lensing effect that creates tiny distortions in images of distant galaxies.

Image credit: ESA/Hubble & NASA

Spiral in Serpens

This new NASA/ESA Hubble Space Telescope image shows a beautiful spiral galaxy known as PGC 54493, located in the constellation of Serpens (The Serpent). This galaxy is part of a galaxy cluster that has been studied by astronomers exploring an intriguing phenomenon known as weak gravitational lensing.

This effect, caused by the uneven distribution of matter (including dark matter) throughout the Universe, has been explored via surveys such as the Hubble Medium Deep Survey. Dark matter is one of the great mysteries in cosmology. It behaves very differently from ordinary matter as it does not emit or absorb light or other forms of electromagnetic energy — hence the term “dark”.

Even though we cannot observe dark matter directly, we know it exists. One prominent piece of evidence for the existence of this mysterious matter is known as the “galaxy rotation problem”. Galaxies rotate at such speeds and in such a way that ordinary matter alone — the stuff we see — would not be able to hold them together. The amount of mass that is “missing” visibly is dark matter, which is thought to make up some 27% of the total contents of the Universe, with dark energy and normal matter making up the rest. PGC 55493 has been studied in connection with an effect known as cosmic shearing. This is a weak gravitational lensing effect that creates tiny distortions in images of distant galaxies.

Image credit: ESA/Hubble & NASA

(Source: spacetelescope.org)

Caterpillar comet poses for pictures en route to Mars

Comet C/2013 A1 Siding Spring wriggles between the globular clusters NGC 362 (upper left) and 47 Tucanae (NGC 104) while skirting the edge of the Small Magellanic Cloud

Image credit: Rolando Ligustri

Caterpillar comet poses for pictures en route to Mars

Comet C/2013 A1 Siding Spring wriggles between the globular clusters NGC 362 (upper left) and 47 Tucanae (NGC 104) while skirting the edge of the Small Magellanic Cloud

Image credit: Rolando Ligustri

(Source: universetoday.com)

Airglow ripples over Tibet

Why would the sky look like a giant target? Airglow. Following a giant thunderstorm over Bangladesh in late April, giant circular ripples of glowing air appeared over Tibet, China, as pictured above. The unusual pattern is created by atmospheric gravity waves, waves of alternating air pressure that can grow with height as the air thins, in this case about 90 kilometers up. Unlike auroras powered by collisions with energetic charged particles and seen at high latitudes, airglow is due to chemiluminescence, the production of light in a chemical reaction. More typically seen near the horizon, airglow keeps the night sky from ever being completely dark.

Image credit & copyright: Jeff Dai

Airglow ripples over Tibet

Why would the sky look like a giant target? Airglow. Following a giant thunderstorm over Bangladesh in late April, giant circular ripples of glowing air appeared over Tibet, China, as pictured above. The unusual pattern is created by atmospheric gravity waves, waves of alternating air pressure that can grow with height as the air thins, in this case about 90 kilometers up. Unlike auroras powered by collisions with energetic charged particles and seen at high latitudes, airglow is due to chemiluminescence, the production of light in a chemical reaction. More typically seen near the horizon, airglow keeps the night sky from ever being completely dark.

Image credit & copyright: Jeff Dai

(Source: apod.nasa.gov)

The starry sky under Hollow Hill

Look up in New Zealand’s Hollow Hill Cave and you might think you see a familiar starry sky. And that’s exactly what Arachnocampa luminosa are counting on. Captured in this long exposure, the New Zealand glowworms scattered across the cave ceiling give it the inviting and open appearance of a clear, dark night sky filled with stars. Unsuspecting insects fooled into flying too far upwards get trapped in sticky snares the glowworms create and hang down to catch food. Of course professional astronomers wouldn’t be so easily fooled, although that does look a lot like the Coalsack Nebula and Southern Cross at the upper left.

Image credit & copyright: Phill Round

The starry sky under Hollow Hill

Look up in New Zealand’s Hollow Hill Cave and you might think you see a familiar starry sky. And that’s exactly what Arachnocampa luminosa are counting on. Captured in this long exposure, the New Zealand glowworms scattered across the cave ceiling give it the inviting and open appearance of a clear, dark night sky filled with stars. Unsuspecting insects fooled into flying too far upwards get trapped in sticky snares the glowworms create and hang down to catch food. Of course professional astronomers wouldn’t be so easily fooled, although that does look a lot like the Coalsack Nebula and Southern Cross at the upper left.

Image credit & copyright: Phill Round

(Source: apod.nasa.gov)


An optical image of the Pleiades
Image credit: NOAO / AURA / NSF

An optical image of the Pleiades

Image credit: NOAO / AURA / NSF

(Source: universetoday.com)

Astronomers spot pebble-size dust grains in the Orion Nebula


Stars and planets form out of vast clouds of dust and gas. Small pockets in these clouds collapse under the pull of gravity. But as the pocket shrinks, it spins rapidly, with the outer region flattening into a disk.
Eventually the central pocket collapses enough that its high temperature and density allows it to ignite nuclear fusion, while in the turbulent disk, microscopic bits of dust glob together to form planets. Theories predict that a typical dust grain is similar in size to fine soot or sand.
In recent years, however, millimeter-size dust grains — 100 to 1,000 times larger than the dust grains expected — have been spotted around a few select stars and brown dwarfs, suggesting that these particles may be more abundant than previous thought. Now, observations of the Orion nebula show a new object that may also be brimming with these pebble-size grains.
The team used the National Science Foundation’s Green Bank Telescope to observe the northern portion of the Orion Molecular Cloud Complex, a star-forming region that spans hundreds of light-years. It contains long, dust-rich filaments, which are dotted with many dense cores. Some of the cores are just starting to coalesce, while others have already begun to form protostars.
Based on previous observations from the IRAM 30-meter radio telescope in Spain, the team expected to find a particular brightness to the dust emission. Instead, they found that it was much brighter.
“This means that the material in this region has different properties than would be expected for normal interstellar dust,” said Scott Schnee, from the National Radio Astronomy Observatory, in a press release. “In particular, since the particles are more efficient than expected at emitting at millimeter wavelengths, the grains are very likely to be at least a millimeter, and possibly as large as a centimeter across, or roughly the size of a small Lego-style building block.”
Such massive dust grains are hard to explain in any environment.
Around a star or a brown dwarf, it’s expected that drag forces cause large particles to lose kinetic energy and spiral in toward the star. This process should be relatively fast, but since planets are fairly common, many astronomers have put forth theories to explain how dust hangs around long enough to form planets. One such theory is the so-called dust trap: a mechanism that herds together large grains, keeping them from spiraling inward.
But these dust particles occur in a rather different environment. So the researchers propose two new intriguing theories for their origin.
The first is that the filaments themselves helped the dust grow to such colossal proportions. These regions, compared to molecular clouds in general, have lower temperatures, high densities, and lower velocities — all of which encourage grain growth.
The second is that the rocky particles originally grew inside a previous generation of cores or even protoplanetary disks. The material then escaped back into the surrounding molecular cloud.
This finding further challenges theories of how rocky, Earth-like planets form, suggesting that millimeter-size dust grains may jump-start planet formation and cause rocky planets to be much more common than previously thought.

Image credit: S. Schnee, et al. / B. Saxton, B. Kent (NRAO/AUI/NSF)

Astronomers spot pebble-size dust grains in the Orion Nebula

Stars and planets form out of vast clouds of dust and gas. Small pockets in these clouds collapse under the pull of gravity. But as the pocket shrinks, it spins rapidly, with the outer region flattening into a disk.

Eventually the central pocket collapses enough that its high temperature and density allows it to ignite nuclear fusion, while in the turbulent disk, microscopic bits of dust glob together to form planets. Theories predict that a typical dust grain is similar in size to fine soot or sand.

In recent years, however, millimeter-size dust grains — 100 to 1,000 times larger than the dust grains expected — have been spotted around a few select stars and brown dwarfs, suggesting that these particles may be more abundant than previous thought. Now, observations of the Orion nebula show a new object that may also be brimming with these pebble-size grains.

The team used the National Science Foundation’s Green Bank Telescope to observe the northern portion of the Orion Molecular Cloud Complex, a star-forming region that spans hundreds of light-years. It contains long, dust-rich filaments, which are dotted with many dense cores. Some of the cores are just starting to coalesce, while others have already begun to form protostars.

Based on previous observations from the IRAM 30-meter radio telescope in Spain, the team expected to find a particular brightness to the dust emission. Instead, they found that it was much brighter.

“This means that the material in this region has different properties than would be expected for normal interstellar dust,” said Scott Schnee, from the National Radio Astronomy Observatory, in a press release. “In particular, since the particles are more efficient than expected at emitting at millimeter wavelengths, the grains are very likely to be at least a millimeter, and possibly as large as a centimeter across, or roughly the size of a small Lego-style building block.”

Such massive dust grains are hard to explain in any environment.

Around a star or a brown dwarf, it’s expected that drag forces cause large particles to lose kinetic energy and spiral in toward the star. This process should be relatively fast, but since planets are fairly common, many astronomers have put forth theories to explain how dust hangs around long enough to form planets. One such theory is the so-called dust trap: a mechanism that herds together large grains, keeping them from spiraling inward.

But these dust particles occur in a rather different environment. So the researchers propose two new intriguing theories for their origin.

The first is that the filaments themselves helped the dust grow to such colossal proportions. These regions, compared to molecular clouds in general, have lower temperatures, high densities, and lower velocities — all of which encourage grain growth.

The second is that the rocky particles originally grew inside a previous generation of cores or even protoplanetary disks. The material then escaped back into the surrounding molecular cloud.

This finding further challenges theories of how rocky, Earth-like planets form, suggesting that millimeter-size dust grains may jump-start planet formation and cause rocky planets to be much more common than previously thought.

Image credit: S. Schnee, et al. / B. Saxton, B. Kent (NRAO/AUI/NSF)

(Source: universetoday.com)

Take a step back to see the whole picture

Sometimes it requires a step back in order to see a pattern…#BlueDot
Image taken by ESA astronaut Alexander Gerst aboard the International Space Station, during his Blue Dot mission. August 2014

Image credits: ESA/NASA

Take a step back to see the whole picture

Sometimes it requires a step back in order to see a pattern…#BlueDot

Image taken by ESA astronaut Alexander Gerst aboard the International Space Station, during his Blue Dot mission. August 2014

Image credits: ESA/NASA

(Source: esa.int)


Hubble looks at light and dark in the universe







This new NASA/ESA Hubble Space Telescope image shows a variety of intriguing cosmic phenomena.
Surrounded by bright stars, towards the upper middle of the frame we see a small young stellar object (YSO) known as SSTC2D J033038.2+303212. Located in the constellation of Perseus, this star is in the early stages of its life and is still forming into a fully-grown star. In this view from Hubble’s Advanced Camera for Surveys(ACS) it appears to have a murky chimney of material emanating outwards and downwards, framed by bright bursts of gas flowing from the star itself. This fledgling star is actually surrounded by a bright disk of material swirling around it as it forms — a disc that we see edge-on from our perspective.
However, this small bright speck is dwarfed by its cosmic neighbor towards the bottom of the frame, a clump of bright, wispy gas swirling around as it appears to spew dark material out into space. The bright cloud is a reflection nebula known as [B77] 63, a cloud of interstellar gas that is reflecting light from the stars embedded within it. There are actually a number of bright stars within [B77] 63, most notably the emission-line star LkHA 326, and it nearby neighbor LZK 18.
These stars are lighting up the surrounding gas and sculpting it into the wispy shape seen in this image. However, the most dramatic part of the image seems to be a dark stream of smoke piling outwards from [B77] 63 and its stars — a dark nebula called Dobashi 4173. Dark nebulae are incredibly dense clouds of pitch-dark material that obscure the patches of sky behind them, seemingly creating great rips and eerily empty chunks of sky. The stars speckled on top of this extreme blackness actually lie between us and Dobashi 4173.

Image credit: ESA/NASA

Hubble looks at light and dark in the universe

This new NASA/ESA Hubble Space Telescope image shows a variety of intriguing cosmic phenomena.

Surrounded by bright stars, towards the upper middle of the frame we see a small young stellar object (YSO) known as SSTC2D J033038.2+303212. Located in the constellation of Perseus, this star is in the early stages of its life and is still forming into a fully-grown star. In this view from Hubble’s Advanced Camera for Surveys(ACS) it appears to have a murky chimney of material emanating outwards and downwards, framed by bright bursts of gas flowing from the star itself. This fledgling star is actually surrounded by a bright disk of material swirling around it as it forms — a disc that we see edge-on from our perspective.

However, this small bright speck is dwarfed by its cosmic neighbor towards the bottom of the frame, a clump of bright, wispy gas swirling around as it appears to spew dark material out into space. The bright cloud is a reflection nebula known as [B77] 63, a cloud of interstellar gas that is reflecting light from the stars embedded within it. There are actually a number of bright stars within [B77] 63, most notably the emission-line star LkHA 326, and it nearby neighbor LZK 18.

These stars are lighting up the surrounding gas and sculpting it into the wispy shape seen in this image. However, the most dramatic part of the image seems to be a dark stream of smoke piling outwards from [B77] 63 and its stars — a dark nebula called Dobashi 4173. Dark nebulae are incredibly dense clouds of pitch-dark material that obscure the patches of sky behind them, seemingly creating great rips and eerily empty chunks of sky. The stars speckled on top of this extreme blackness actually lie between us and Dobashi 4173.

Image credit: ESA/NASA

(Source: nasa.gov)

Clouds above, clouds below

A northern hemisphere summertime view of the Milky Way in Sagittarius.

Image credit and copyright: Greg Redfern

Clouds above, clouds below

A northern hemisphere summertime view of the Milky Way in Sagittarius.

Image credit and copyright: Greg Redfern

Rosetta’s comet looms in the dark in close-up spacecraft shot

The Rosetta navigation camera sent back this image of Comet 67P/Churyumov-Gerasimenko on Aug. 23, showing about a quarter of the four-kilometer (2.5-mile) comet. This image was acquired from a distance of 61 kilometers (38 miles).

Image credit: ESA/Rosetta/NAVCAM

Rosetta’s comet looms in the dark in close-up spacecraft shot

The Rosetta navigation camera sent back this image of Comet 67P/Churyumov-Gerasimenko on Aug. 23, showing about a quarter of the four-kilometer (2.5-mile) comet. This image was acquired from a distance of 61 kilometers (38 miles).

Image credit: ESA/Rosetta/NAVCAM

(Source: universetoday.com)

Messier 20 and 21

The beautiful Trifid Nebula, also known as Messier 20, is easy to find with a small telescope in the nebula rich constellation Sagittarius. About 5,000 light-years away, the colorful study in cosmic contrasts shares this well-composed, nearly 1 degree wide field with open star cluster Messier 21 (top right). Trisected by dust lanes the Trifid itself is about 40 light-years across and a mere 300,000 years old. That makes it one of the youngest star forming regions in our sky, with newborn and embryonic stars embedded in its natal dust and gas clouds. Estimates of the distance to open star cluster M21 are similar to M20’s, but though they share this gorgeous telescopic skyscape there is no apparent connection between the two. In fact, M21’s stars are much older, about 8 million years old.

Image credit & copyright: Lorand Fenyes

Messier 20 and 21

The beautiful Trifid Nebula, also known as Messier 20, is easy to find with a small telescope in the nebula rich constellation Sagittarius. About 5,000 light-years away, the colorful study in cosmic contrasts shares this well-composed, nearly 1 degree wide field with open star cluster Messier 21 (top right). Trisected by dust lanes the Trifid itself is about 40 light-years across and a mere 300,000 years old. That makes it one of the youngest star forming regions in our sky, with newborn and embryonic stars embedded in its natal dust and gas clouds. Estimates of the distance to open star cluster M21 are similar to M20’s, but though they share this gorgeous telescopic skyscape there is no apparent connection between the two. In fact, M21’s stars are much older, about 8 million years old.

Image credit & copyright: Lorand Fenyes

(Source: apod.nasa.gov)

Witnessing the early growth of a giant

Astronomers have uncovered for the first time the earliest stages of a massive galaxy forming in the young Universe. The discovery was made possible through combining observations from the NASA/ESA Hubble Space Telescope, NASA’s Spitzer Space Telescope, ESA’s Herschel Space Observatory, and the W.M. Keck Observatory in Hawaii. The growing galaxy core is blazing with the light of millions of newborn stars that are forming at a ferocious rate.
Elliptical galaxies are large, gas-poor gatherings of older stars and are one of the main types of galaxy along with their spiral and lenticular relatives. Galaxy formation theories suggest that giant elliptical galaxies form from the inside out, with a large core marking the very first stages of formation.




However, evidence of this early construction phase has eluded astronomers — until now.
Astronomers have now spotted a compact galactic core known as GOODS-N-774, and nicknamed Sparky. It is seen as it appeared eleven billion years ago, just three billion years after the Big Bang.
"This core formation process is a phenomenon unique to the early Universe,"explains Erica Nelson of Yale University, USA, lead author of the science paper announcing the results, "we do not see galaxies forming in this way any more. There’s something about the Universe at that time that could form galaxies in this way that it now can’t. We suspect that the Universe could produce denser objects because the Universe as a whole was denser shortly after the Big Bang. It is much less dense now, so it can’t do it anymore."
Although only a fraction of the size of the Milky Way, the infant galaxy is crammed with so many young stars that it already contains twice as much mass as our entire galaxy. It is thought that the fledgling galaxy will continue to grow, eventually becoming a giant elliptical galaxy. The astronomers think that this barely visible galaxy may be representative of a much larger population of similar objects that are too faint or obscured by dust to be spotted — just like the Sun can appear red and faint behind the smoke of a forest fire.
Alongside determining the galaxy’s size from the Hubble images, the team dug into archival far-infrared images from NASA’s Spitzer Space Telescope and the ESAHerschel Space Observatory to see how fast the compact galaxy is churning out stars. GOODS-N-774 is producing 300 stars per year. "By comparison, the Milky Way produces thirty times fewer than this — roughly ten stars per year," says Marijn Franx of Leiden University in the Netherlands, a co-author of the study. "This star-forming rate is really intense!"
This tiny powerhouse contains about twice as many stars as our galaxy, all crammed into a region only 6000 light-years across. The Milky Way is about 100 000 light-years across.
Astronomers believe that this frenzied star formation occurs because the galactic centre is forming deep inside a gravitational well of dark matter, an invisible form of matter that makes up the scaffolding upon which galaxies formed in the early Universe. A torrent of gas is flowing into the well and into the compact galaxy, sparking waves of star birth.
The sheer amount of gas and dust within an extreme star-forming region like this may explain why they have eluded astronomers until now. Bursts of star formation create dust, which builds up within the forming core and can block some starlight— GOODS-N-774 was only just visible, even using the resolution and infrared capabilities of Hubble’s Wide Field Camera 3.

Image credit: NASA, ESA, Z. Levay and G. Bacon (Space Telescope Science Institute)

Witnessing the early growth of a giant

Astronomers have uncovered for the first time the earliest stages of a massive galaxy forming in the young Universe. The discovery was made possible through combining observations from the NASA/ESA Hubble Space Telescope, NASA’s Spitzer Space Telescope, ESA’s Herschel Space Observatory, and the W.M. Keck Observatory in Hawaii. The growing galaxy core is blazing with the light of millions of newborn stars that are forming at a ferocious rate.

Elliptical galaxies are large, gas-poor gatherings of older stars and are one of the main types of galaxy along with their spiral and lenticular relatives. Galaxy formation theories suggest that giant elliptical galaxies form from the inside out, with a large core marking the very first stages of formation.

However, evidence of this early construction phase has eluded astronomers — until now.

Astronomers have now spotted a compact galactic core known as GOODS-N-774, and nicknamed Sparky. It is seen as it appeared eleven billion years ago, just three billion years after the Big Bang.

"This core formation process is a phenomenon unique to the early Universe,"explains Erica Nelson of Yale University, USA, lead author of the science paper announcing the results, "we do not see galaxies forming in this way any more. There’s something about the Universe at that time that could form galaxies in this way that it now can’t. We suspect that the Universe could produce denser objects because the Universe as a whole was denser shortly after the Big Bang. It is much less dense now, so it can’t do it anymore."

Although only a fraction of the size of the Milky Way, the infant galaxy is crammed with so many young stars that it already contains twice as much mass as our entire galaxy. It is thought that the fledgling galaxy will continue to grow, eventually becoming a giant elliptical galaxy. The astronomers think that this barely visible galaxy may be representative of a much larger population of similar objects that are too faint or obscured by dust to be spotted — just like the Sun can appear red and faint behind the smoke of a forest fire.

Alongside determining the galaxy’s size from the Hubble images, the team dug into archival far-infrared images from NASA’s Spitzer Space Telescope and the ESAHerschel Space Observatory to see how fast the compact galaxy is churning out stars. GOODS-N-774 is producing 300 stars per year. "By comparison, the Milky Way produces thirty times fewer than this — roughly ten stars per year," says Marijn Franx of Leiden University in the Netherlands, a co-author of the study. "This star-forming rate is really intense!"

This tiny powerhouse contains about twice as many stars as our galaxy, all crammed into a region only 6000 light-years across. The Milky Way is about 100 000 light-years across.

Astronomers believe that this frenzied star formation occurs because the galactic centre is forming deep inside a gravitational well of dark matter, an invisible form of matter that makes up the scaffolding upon which galaxies formed in the early Universe. A torrent of gas is flowing into the well and into the compact galaxy, sparking waves of star birth.

The sheer amount of gas and dust within an extreme star-forming region like this may explain why they have eluded astronomers until now. Bursts of star formation create dust, which builds up within the forming core and can block some starlight— GOODS-N-774 was only just visible, even using the resolution and infrared capabilities of Hubble’s Wide Field Camera 3.

Image credit: NASA, ESA, Z. Levay and G. Bacon (Space Telescope Science Institute)

(Source: spacetelescope.org)


Eta Carinae: our neighboring superstars







The Eta Carinae star system does not lack for superlatives. Not only does it contain one of the biggest and brightest stars in our galaxy, weighing at least 90 times the mass of the sun, it is also extremely volatile and is expected to have at least one supernova explosion in the future.
As one of the first objects observed by NASA’s Chandra X-ray Observatory after its launch some 15 years ago, this double star system continues to reveal new clues about its nature through the X-rays it generates.
Astronomers reported extremely volatile behavior from Eta Carinae in the 19th century, when it became very bright for two decades, outshining nearly every star in the entire sky. This event became known as the “Great Eruption.” Data from modern telescopes reveal that Eta Carinae threw off about ten times the sun’s mass during that time. Surprisingly, the star survived this tumultuous expulsion of material, adding “extremely hardy” to its list of attributes.
Today, astronomers are trying to learn more about the two stars in the Eta Carinae system and how they interact with each other. The heavier of the two stars is quickly losing mass through  wind streaming away from its surface at over a million miles per hour. While not the giant purge of the Great Eruption, this star is still losing mass at a very high rate that will add up to the sun’s mass in about a millennium. 
Though smaller than its partner, the companion star in Eta Carinae is also massive, weighing in at about 30 times the mass of the sun. It is losing matter at a rate that is about a hundred times lower than its partner, but still a prodigious weight loss compared to most other stars. The companion star beats the bigger star in wind speed, with its wind clocking in almost ten times faster.
When these two speedy and powerful winds collide, they form a bow shock – similar to the sonic boom from a supersonic airplane – that then heats the gas between the stars. The temperature of the gas reaches about ten million degrees, producing X-rays that Chandra detects.
The Chandra image of Eta Carinae shows low energy X-rays in red, medium energy X-rays in green, and high energy X-rays in blue. Most of the emission comes from low and high energy X-rays. The blue point source is generated by the colliding winds, and the diffuse blue emission is produced when the material that was purged during the Great Eruption reflects these X-rays. The low energy X-rays further out show where the winds from the two stars, or perhaps material from the Great Eruption, are striking surrounding material. This surrounding material might consist of gas that was ejected before the Great Eruption.     An interesting feature of the Eta Carinae system is that the two stars travel around each other along highly elliptical paths during their five-and-a-half-year long orbit. Depending on where each star is on its oval-shaped trajectory, the distance between the two stars changes by a factor of twenty. These oval-shaped trajectories give astronomers a chance to study what happens to the winds from these stars when they collide at different distances from one another.
Throughout most of the system’s orbit, the X-rays are stronger at the apex, the region where the winds collide head-on. However, when the two stars are at their closest during their orbit (a point that astronomers call “periastron”), the X-ray emission dips unexpectedly. To understand the cause of this dip, astronomers observed Eta Carinae with Chandra at periastron in early 2009. The results provided the first detailed picture of X-ray emission from the colliding winds in Eta Carinae. The study suggests that part of the reason for the dip at periastron is that X-rays from the apex are blocked by the dense wind from the more massive star in Eta Carinae, or perhaps by the surface of the star itself.  Another factor responsible for the X-ray dip is that the shock wave appears to be disrupted near periastron, possibly because of faster cooling of the gas due to increased density, and/or a decrease in the strength of the companion star’s wind because of extra ultraviolet radiation from the massive star reaching it. Researchers are hoping that Chandra observations of the latest periastron in August 2014 will help them determine the true explanation.

Image credit: NASA/CXC/GSFC/K.Hamaguchi, et al.

Eta Carinae: our neighboring superstars

The Eta Carinae star system does not lack for superlatives. Not only does it contain one of the biggest and brightest stars in our galaxy, weighing at least 90 times the mass of the sun, it is also extremely volatile and is expected to have at least one supernova explosion in the future.

As one of the first objects observed by NASA’s Chandra X-ray Observatory after its launch some 15 years ago, this double star system continues to reveal new clues about its nature through the X-rays it generates.

Astronomers reported extremely volatile behavior from Eta Carinae in the 19th century, when it became very bright for two decades, outshining nearly every star in the entire sky. This event became known as the “Great Eruption.” Data from modern telescopes reveal that Eta Carinae threw off about ten times the sun’s mass during that time. Surprisingly, the star survived this tumultuous expulsion of material, adding “extremely hardy” to its list of attributes.

Today, astronomers are trying to learn more about the two stars in the Eta Carinae system and how they interact with each other. The heavier of the two stars is quickly losing mass through  wind streaming away from its surface at over a million miles per hour. While not the giant purge of the Great Eruption, this star is still losing mass at a very high rate that will add up to the sun’s mass in about a millennium. 

Though smaller than its partner, the companion star in Eta Carinae is also massive, weighing in at about 30 times the mass of the sun. It is losing matter at a rate that is about a hundred times lower than its partner, but still a prodigious weight loss compared to most other stars. The companion star beats the bigger star in wind speed, with its wind clocking in almost ten times faster.

When these two speedy and powerful winds collide, they form a bow shock – similar to the sonic boom from a supersonic airplane – that then heats the gas between the stars. The temperature of the gas reaches about ten million degrees, producing X-rays that Chandra detects.

The Chandra image of Eta Carinae shows low energy X-rays in red, medium energy X-rays in green, and high energy X-rays in blue. Most of the emission comes from low and high energy X-rays. The blue point source is generated by the colliding winds, and the diffuse blue emission is produced when the material that was purged during the Great Eruption reflects these X-rays. The low energy X-rays further out show where the winds from the two stars, or perhaps material from the Great Eruption, are striking surrounding material. This surrounding material might consist of gas that was ejected before the Great Eruption.    
 
An interesting feature of the Eta Carinae system is that the two stars travel around each other along highly elliptical paths during their five-and-a-half-year long orbit. Depending on where each star is on its oval-shaped trajectory, the distance between the two stars changes by a factor of twenty. These oval-shaped trajectories give astronomers a chance to study what happens to the winds from these stars when they collide at different distances from one another.

Throughout most of the system’s orbit, the X-rays are stronger at the apex, the region where the winds collide head-on. However, when the two stars are at their closest during their orbit (a point that astronomers call “periastron”), the X-ray emission dips unexpectedly.
 
To understand the cause of this dip, astronomers observed Eta Carinae with Chandra at periastron in early 2009. The results provided the first detailed picture of X-ray emission from the colliding winds in Eta Carinae. The study suggests that part of the reason for the dip at periastron is that X-rays from the apex are blocked by the dense wind from the more massive star in Eta Carinae, or perhaps by the surface of the star itself. 
 
Another factor responsible for the X-ray dip is that the shock wave appears to be disrupted near periastron, possibly because of faster cooling of the gas due to increased density, and/or a decrease in the strength of the companion star’s wind because of extra ultraviolet radiation from the massive star reaching it. Researchers are hoping that Chandra observations of the latest periastron in August 2014 will help them determine the true explanation.

Image credit: NASA/CXC/GSFC/K.Hamaguchi, et al.

(Source: nasa.gov)

Milky Way over Yellowstone

The Milky Way was not created by an evaporating lake. The colorful pool of water, about 10 meters across, is known as Silex Spring and is located in Yellowstone National Park in Wyoming,USA. Illuminated artificially, the colors are caused by layers of bacteria that grow in the hot spring. Steam rises off the spring, heated by a magma chamber deep underneath known as the Yellowstone hotspot. Unrelated and far in the distance, the central band of our Milky Way Galaxy arches high overhead, a band lit by billions of stars. The above picture is a 16-image panorama taken late last month. If the Yellowstone hotspot causes another supervolcanic eruption as it did 640,000 years ago, a large part of North America would be affected.

Image credit & copyright: Dave Lane

Milky Way over Yellowstone

The Milky Way was not created by an evaporating lake. The colorful pool of water, about 10 meters across, is known as Silex Spring and is located in Yellowstone National Park in Wyoming,USA. Illuminated artificially, the colors are caused by layers of bacteria that grow in the hot spring. Steam rises off the spring, heated by a magma chamber deep underneath known as the Yellowstone hotspot. Unrelated and far in the distance, the central band of our Milky Way Galaxy arches high overhead, a band lit by billions of stars. The above picture is a 16-image panorama taken late last month. If the Yellowstone hotspot causes another supervolcanic eruption as it did 640,000 years ago, a large part of North America would be affected.

Image credit & copyright: Dave Lane

(Source: apod.nasa.gov)

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