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Gallery: Supernova remnant B0049-73.6

THE PRECISE DETAILS of how massive stars explode at the end of their lives – a process known as a supernova – remains one of the biggest questions in astrophysics.

Located in the neighbouring galaxy of the Small Magellanic Cloud, this false-colour image shows the aftermath of such a supernova – an enormous, expanding debris cloud called a supernova remnant.

SNR B0049-73.6

Chandra X-ray Observatory image of supernova remnant SNR B0049-73.6, the aftermath of a stellar explosion. Image credit: X-ray: NASA / CXC / Drew Univ. / S.Hendrick et al, Infrared: 2MASS / Umass / IPAC-Caltech / NASA / NSF

Known only by its catalogue number, SNR B0049-73.6, it provides astronomers with an excellent example with which to study the after effects of a supernova. Chandra observations of the motions and composition of the debris from the explosion support the view that the explosion was produced by the collapse of the core of a star.

In this image, X-rays from NASA’s Chandra X-ray Observatory satellite (purple) are combined with infrared data from the 2MASS survey (red, green, and blue).

More information and downloadable wallpapers images: nasa.gov/mission_pages/chandra/multimedia/small-magellanic-cloud-supernova-remnant.html

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Inside-out exploding star

Cassiopeia A: artist's impression of the precursor star and real X-ray image of the remnant

Before and after the explosion. Colour coded elements in artist's impression of the star's core match up with real observations of Cassiopeia A. Iron, shown in blue, has somehow gone from being in the middle of the star to the outskirts of the supernova remnant.

IN THE NORTHERN CONSTELLATION Cassiopeia lies a famous supernova remnant, a gas cloud that represents the shattered remains of a once-titanic star.

Known as Cassiopeia A, it is hard to see at normal visible light wavelengths but shines strongly at radio and X-ray wavelengths.

A supernova of this kind occurs when a massive star runs out of nuclear fuel and can no longer produce energy. Without an outflow of energy to keep the star “inflated”, it’s huge mass crushes inwards … producing an implosion followed by an explosion that tears the star apart.

In the millions of years leading up to the explosion, the star’s innards become layered with different elements as a result of different nuclear fusion processes. In the core there is a globe of iron. Surrounding that are layers of sulphur, silicon, magnesium, neon and oxygen.

It would seem to make sense that when the star explodes, the outer layers would end up on the outskirts of the resulting gas cloud, with the iron concentrated toward the middle.

But by compiling a staggering one million seconds worth of X-ray observations by satellite telescopes, astronomers have found that this is not the case for Cassiopeia A.

The observations show that the distribution of sulphur, silicon, magnesium and neon is about as expected. But the iron is spread around the outer part of the supernova remnant, and there’s none in the middle.

The astronomers think there must have been some sort of “instability” in the supernova explosion process, which turned the star inside out.

Story by Jonathan Nally. Images courtesy (illustration) NASA / CXC / M.Weiss; (X-ray) NASA / CXC / GSFC / U.Hwang & J.Laming.

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Ancient supernova seen in a new light

RCW 86

This is all that remains of a supernova explosion that was seen by Chinese astronomers in the year 185 CE. The remnant gas cloud is called RCW 86, and is approximately 8,000 light-years from Earth.

A TWISTED AND TANGLED GAS CLOUD is all that remains of the oldest documented example of a supernova, called RCW 86.

Chinese stargazers witnessed the event in 185 CE, documenting a mysterious ‘guest star’ that remained in the sky for eight months.

The image combines data from four different space telescopes to create a multi-wavelength view.

X-ray images from the European Space Agency’s XMM-Newton Observatory and NASA’s Chandra X-ray Observatory are combined to form the blue and green colours in the image. The X-rays show the interstellar gas that has been heated to millions of degrees by the passage of the shock wave from the supernova.

Infrared data from NASA’s Spitzer Space Telescope, as well as NASA’s Wide-Field Infrared Survey Explorer (WISE) are shown in yellow and red, and reveal dust radiating at a temperature of several hundred degrees below zero, warm by comparison to normal dust in our Milky Way galaxy.

By studying the X-ray and infrared data together, astronomers were able to determine that the cause of the explosion witnessed nearly 2,000 years ago was a Type Ia supernova, in which an otherwise-stable white dwarf, or dead star, was pushed beyond the brink of stability when a companion star dumped material onto it.

Furthermore, scientists used the data to solve another mystery surrounding the remnant—how it got to be so big in such a short amount of time.

By blowing out a ‘wind’ prior to exploding, the white dwarf was able to clear out a huge ‘cavity,’ a region of very low-density surrounding the system. The explosion was able to expand into this cavity much faster than it otherwise would have.

RCW 86 is approximately 8,000 light-years away.

Adapted from information issued by NASA / JPL-Caltech / B. Williams (NCSU).

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Aussie shares Nobel Prize for physics

Artist's impression of a black hole

In 1998, two research teams announced the discovery that the expansion of the universe was accelerating.

THE ROYAL SWEDISH ACADEMY OF SCIENCES has awarded the Nobel Prize in Physics for 2011 to the leaders of the teams that discovered the accelerating expansion of the universe.

One half of the prize has been awarded to Saul Perlmutter (The Supernova Cosmology Project, Lawrence Berkeley National Laboratory and University of California) and the other half jointly to Brian P. Schmidt (The High-z Supernova Search Team, Australian National University, Australia) and Adam G. Riess (The High-z Supernova Search Team, Johns Hopkins University and Space Telescope Science Institute, Baltimore, USA).

In 1998, cosmology was shaken at its foundations as the two teams presented their findings. Headed by Saul Perlmutter, one of the teams had set to work in 1988. Brian Schmidt headed another team, launched at the end of 1994, where Adam Riess was to play a crucial role.

The research teams raced to map the Universe by locating the most distant supernovae (exploding stars). More sophisticated telescopes on the ground and in space, as well as more powerful computers and new digital imaging sensors, opened the possibility in the 1990s to add more pieces to the cosmological puzzle.

The teams used a particular kind of supernova, called type Ia supernova. It is an explosion of an old compact starthat is as heavy as the Sun but as small as the Earth. A single such supernova can emit as much light as a whole galaxy.

Brian Schmidt, Saul Perlmutter, Adam Riess

Recipients of the 2011 Nobel Prize for Physics— Brian Schmidt, Saul Perlmutter and Adam Riess.

Greatest enigma in physics

All in all, the two research teams found over 50 distant supernovae whose light was weaker than expected—this was a sign that the expansion of the Universe was accelerating.

The potential pitfalls had been numerous, and the scientists found reassurance in the fact that both groups had reached the same astonishing conclusion.

For almost a century, the Universe has been known to be expanding as a consequence of the Big Bang about 14 billion years ago. However, the discovery that this expansion is accelerating is astounding. If the expansion will continue to speed up the Universe will end in ice.

The acceleration is thought to be driven by dark energy, but what that dark energy is remains an enigma—perhaps the greatest in physics today.

What is known is that dark energy constitutes about three quarters of the Universe.

Therefore the findings of the 2011 Nobel Laureates in Physics have helped to unveil a Universe that to a large extent is unknown to science. And everything is possible again.

More information: Check out this great video on dark energy and the expansion of the universe. It features one of the Nobel Prize winners, Saul Perlmutter.

Adapted from information issued by the Royal Swedish Academy of Sciences.

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Fried Egg nebula home to hypergiant

ASTRONOMERS HAVE TAKEN AN IMAGE of a colossal star that belongs to one of the most rare classes of stars in the Universe…the yellow hypergiants.

The new picture is the best ever taken of a star in this class and shows for the first time a huge dusty double shell surrounding the star.

The star and its shells resemble an egg white around a yolky centre, leading the astronomers to nickname the object the Fried Egg Nebula.

The monster star, known to astronomers as IRAS 17163-3907, has a diameter about a thousand times bigger than our Sun.

And at a distance of about 13,000 light-years from Earth, it is the closest yellow hypergiant found to date and new observations show it shines some 500,000 times more brightly than the Sun.

Unexpected discovery

Yellow hypergiants are in an extremely active phase of their evolution, undergoing a series of explosive events. This particular star has ejected four times the mass of the Sun in just a few hundred years.

The material flung out during these bursts has formed the extensive double shell of the nebula, which is made of dust rich in silicates and mixed with gas.

Fried Egg Nebula

This picture of the nebula around a rare yellow hypergiant star called IRAS 17163-3907 is the best ever taken of a star in this class and shows for the first time a huge dusty double shell surrounding the star. The star and its shells resemble an egg white around a yolky centre, leading astronomers to nickname the object the Fried Egg Nebula.

“This object was known to glow brightly in the infrared but, surprisingly, nobody had identified it as a yellow hypergiant before,” said Eric Lagadec (European Southern Observatory, ESO), who led the team that produced the new images using ESO’s Very Large Telescope (VLT).

The next supernova?

If the Fried Egg Nebula were placed in the centre of the Solar System the Earth would lie deep within the star itself and the planet Jupiter would be orbiting just above its surface.

The much larger surrounding nebula would engulf all the planets and dwarf planets and even some of the comets that orbit far beyond the orbit of Neptune.

The outer shell has a radius of 10,000 times the distance from the Earth to the Sun.

The star is likely to soon die an explosive death—it will be one of the next supernova explosions in our galaxy.

Supernovae provide much-needed chemicals to the surrounding interstellar environment and the resulting shock waves can kick start the formation of new stars.

Adapted from information issued by ESO / E. Lagadec.

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Galaxy caught blowing bubbles

Hubble Space Telescope image of Holmberg II

The Hubble Space Telescope captured this image of dwarf irregular galaxy Holmberg II. The main part of the galaxy is the spread of stars in the lower left half of the image. Huge bubbles of glowing gas produced by stellar explosions dominate the galaxy; they are now sites of ongoing star formation.

HUBBLE’S FAMOUS IMAGES OF GALAXIES typically show them to be elegant spirals or soft-edged elliptical shapes.

But these neat forms are only representative of large galaxies. Smaller galaxies like the dwarf irregular galaxy Holmberg II come in many shapes and types that are harder to classify.

Holmberg II’s indistinct shape is punctuated by huge glowing bubbles of gas, captured in this image from the Hubble Space Telescope.

The intricate glowing shells of gas were formed by the energetic life cycles of many generations of stars. High-mass stars form in dense regions of gas, and later in life expel strong stellar winds that blow away the surrounding material.

At the very end of their lives, they explode in as a supernova. Shock waves rip through these less dense regions blowing out and heating the gas, forming the delicate shells we see today.

Holmberg II is a patchwork of dense star-forming regionsand extensive barren areas with less material, which can stretch across thousands of light-years.

Keck Observatory view of Holmberg II

A wider view of Holmberg II. Courtesy B. Mendez / Keck Observatory.

As a dwarf galaxy, it has neither the spiral arms typical of galaxies like the Milky Way nor the dense nucleus of an elliptical galaxy.

This makes Holmberg II, gravitationally speaking, a gentle haven where fragile structures such as these bubbles can hold their shape.

A hidden black hole?

While the galaxy is unremarkable in size, Holmberg II does have some intriguing features. As well as its unusual appearance—which earned it a place in Halton Arp’s Atlas of Peculiar Galaxies, a treasure trove of weird and wonderful objects—the galaxy hosts an ultraluminous X-ray source in the middle of the three gas bubbles in the top right of the image.

There are competing ideas as to what causes this powerful radiation—one intriguing possibility is that an intermediate-mass black hole is pulling in material from its surroundings, with the material giving off energy as it nears the black hole.

The colourful image is a composite of visible and near-infrared exposures taken using the Wide Field Channel of Hubble’s Advanced Camera for Surveys. Hubble is a project of international cooperation between the European Space Agency and NASA.

Download the Hubble wallpapers:

Holmberg II (1024×768, 588.2 KB)

Holmberg II (1280×1024, 1.0 MB)

Holmberg II (1600×1200, 1.5 MB)

Holmberg II (1920×1200, 1.8 MB)

Adapted from information issued by HEIC / NASA / ESA.

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Take a tour of the Crab Nebula

THE CRAB NEBULA IS ONE OF THE BRIGHTEST sources of high-energy radiation in the sky. Little wonder—it’s the expanding remains of an exploded star, a supernova seen in 1054.

Scientists have used virtually every telescope at their disposal, including NASA’s Chandra X-ray Observatory, to study the Crab.

The supernova left behind a magnetised neutron star—a pulsar. It’s about the size of Washington DC, but it spins 30 times per second. Each rotation sweeps a lighthouse-like beam past us, creating a pulse of electromagnetic energy detectable across the spectrum.

The pulsar in the Crab Nebula is among the brightest sources of high-energy gamma rays. Recently, NASA’s Fermi Gamma Ray Observatory and Italy’s AGILE Satellite detected strong gamma-ray flares from the Crab, including a series of “superflares” in April 2011.

To help pinpoint the location of these flares, astronomers enlisted Chandra space telescope.

With its keen X-ray eyes, Chandra saw lots of activity, but none of it seems correlated with the superflare. This hints that whatever is causing the flares is happening with about a third of a light-year from the pulsar. And rapid changes in the rise and fall of gamma rays imply that the emission region is very small, comparable in size to our Solar System.

The Chandra observations will likely help scientists to home in on an explanation of the gamma-ray flares one day.

Even after a thousand years, the heart of this shattered star still offers scientists glimpses of staggering energies and cutting edge science.

Adapted from information issued by Harvard-Smithsonian Centre for Astrophysics. Still image courtesy (X-ray) NASA / CXC / SAO / F.Seward, (optical) NASA / ESA / ASU / J.Hester & A.Loll, (infrared) NASA / JPL-Caltech / Univ. Minn. / R.Gehrz.

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Supernovae make raw material for planets

SN 1987A

Observations with the Herschel Space Observatory show that supernova 1987A produced enough dust to make 200,000 new planets.

THE HERSCHEL SPACE OBSERVATORY has discovered that titanic stellar explosions can be excellent dust factories. In space, the dust mixes with gas to become the raw material for new stars, planets and, ultimately, life. This discovery may solve a mystery of the early Universe.

The discovery was made while Herschel was charting emission from cold dust in the Large Magellanic Cloud, a small galaxy near to the Milky Way. It is the perfect observatory for the job because cold dust radiates far-infrared light, the wavelengths Herschel is designed to detect.

Herschel saw a spot of light at the location of supernova 1987A, an exploding star first seen from Earth in February 1987, and the closest known supernova in the past 400 years.

Astronomers have been studying the remains of the explosion as its blast wave expands into its surroundings.

Planet factories

Herschel’s images are the first clear-cut far-infrared observations of SN1987A. They reveal cold dust grains at about -250 degrees C, which nevertheless emit more than 200 times the Sun’s energy.

“The supernova remnant was much brighter at infrared wavelengths than we were expecting,” says Mikako Matsuura, University College London, who is the lead author on the scientific paper detailing these results.

The remnant’s brightness was used to estimate the amount of dust. Surprisingly, there turned out to be about a thousand times more dust than astronomers had thought a supernova was capable of producing—enough to make 200,000 planets the size of Earth.

Artist's impression of the Herschel Space Observatory.

Artist's impression of the Herschel Space Observatory.

The origin of dust in the Universe is of great interest. The dust’s heavy atoms like carbon, silicon, oxygen and iron were not produced in the Big Bang and must have formed later.

Although they are only a minor part of the Universe and our Solar System, they are the main constituents of rocky planets like Earth and thus of life itself—many of the atoms we are made of were once part of the dust in the Universe.

Dust factories

However, it is not fully understood where this dust comes from, and especially where it came from in the young Universe. But scientists now have a clue.

The many old red giant stars in today’s Universe are thought to be the major dust producers, with the grains condensing like soot in a chimney as warm gases flow away from the star.

However, there were no such stars in the early Universe—yet we know there was already dust.

Now Herschel has shown that supernovae can produce enormous amounts of dust. The astronomers speculate that the dust condenses from the gaseous debris as it expands from the explosion and cools.

Since there were plenty of supernovae in the young Universe, this could help to explain the origin of dust seen at those times.

Adapted from information issued by ESA. Images courtesy ESA / C. Carreau / P. Challis (CfA).

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Happy birthday, Crab Nebula!

Crab Nebula

The Crab Nebula is a supernova remnant, the aftermath of a titanic stellar explosion that was seen on Earth in the year 1054 CE.

ALMOST A THOUSAND YEARS AGO, on July 4 in the year 1054 CE, astronomers in China and the Middle East noticed a bright new star in the night sky. It appeared in the constellation Taurus, and remained visible for roughly two years.

They couldn’t have known what it really was—a supernova, a titanic stellar explosion that occurred when a massive star reached the end of its life. The explosion was matched by an implosion, which crushed the star’s core and produced a neutron star—made of matter so dense that the atoms’ electrons were forced into their nuclei and combined with the protons to form more neutrons.

The density is so high, that a teaspoon of neutron star material has as much mass as 900 Great Pyramids.

And the neutron star is spinning, making it a pulsar…so called because the natural radiation it emits is sent out along beams, which sweep across our field of view like a lighthouse, seeming to pulse on and off.

So much for the implosion. The explosion hurled enormous quantities of gas into space, eventually forming the glowing cloud, or supernova remnant, we see today. On early photographs, which didn’t show much detail, the nebula looked very crab-like, hence its name.

The distance to the Crab Nebula is a bit uncertain, but it’s probably around 6,300 light-years away. And the cloud is expanding at a speed of 1,500 kilometres per second!

Download a 1280 x 1280 wallpaper image of the Crab Nebula here.

Story by Jonathan Nally. Image courtesy NASA, ESA and Allison Loll/Jeff Hester (Arizona State University). Image acknowledgement: Davide De Martin (ESA/Hubble).

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Meet the Meathook Galaxy

The Meathook Galaxy

This wide view of the Meathook Galaxy shows its bent spiral arms, and glowing pink regions of hydrogen gas where lots of stars have recently formed.

THE MEATHOOK GALAXY, or NGC 2442, has a dramatically lopsided shape. One spiral arm is tightly folded in on itself and played host to a recent supernova (exploding star), while the other, dotted with glowing regions of recent star formation, extends far out from the galaxy’s core or nucleus.

The galaxy’s distorted shape is thought to be the result of the gravitational pull of a passing galaxy at some point in the past, though astronomers so far have not been able to positively identify the culprit.

The broad view, taken by the Wide Field Imager on the MPG/ESO 2.2-metre telescope at La Silla, Chile, very clearly shows the double hook shape that gives the galaxy its nickname. It also captures several other galaxies close to NGC 2442 as well as many more remote galaxies in the background.

Hubble image of the Meathook Galaxy

A close-up Hubble view of the Meathook Galaxy shows its core as well as the more compact of its two spiral arms.

The close-up image from the NASA/ESA Hubble Space Telescope focuses on the galaxy’s nucleus and the more compact of its two spiral arms. In 1999, a massive star at the end of its life exploded in this arm…a phenomenon known as a supernova.

By comparing older ground-based observations, previous Hubble images made in 2001, and these shots taken in late 2006, astronomers have been able to study in detail what happened to the star in its dying moments. (By the time of this latest Hubble image, the supernova had faded and is not visible.)

Although the Wide Field Imager, being a ground-based instrument, cannot approach the sharpness of images from Hubble in space, it covers a much bigger section of sky in a single exposure. Combining ground- and space-based imagery often gives astronomers deeper insights.

The wide view also highlights the starting point of the life cycle of stars. Dotted across much of the galaxy, and particularly in the longer of the two spiral arms, are patches of pink and red. This colour comes from hydrogen gas in star-forming cloud regions—the powerful radiation of new-born stars ‘excites’ the gas in the clouds, making them glow a bright shade of red.

The near miss with the other galaxy is likely to have been the trigger for this recent burst of star formation. The same tidal forces that deformed the galaxy also disrupted the gas clouds and made them gravitationally collapse in on themselves, leading to the birth of new stars.

Download wallpapers of the Meathook Galaxy:

1024 x 768 (269.6kb)

1280 x 1024 (411.0kb)

1600 x 1200 (552.8kb)

Adapted from information issued by ESO. Images courtesy NASA/ESA and ESO.

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