Hubble Spotted a Supernova in NGC 5806

A new image from the NASA/ESA Hubble Space Telescope shows NGC 5806, a spiral galaxy in the constellation Virgo (the Virgin). It lies around 80 million light years from Earth. Also visible in this image is a supernova explosion called SN 2004dg.

The exposures that are combined into this image were carried out in early 2005 in order to help pinpoint the location of the supernova, which exploded in 2004. The afterglow from this outburst of light, caused by a giant star exploding at the end of its life, can be seen as a faint yellowish dot near the bottom of the galaxy.

NGC 5806 was chosen to be one of a number of galaxies in a study into supernovae because Hubble’s archive already contained high resolution imagery of the galaxy, collected before the star had exploded. Since supernovae are both relatively rare, and impossible to predict with any accuracy, the existence of such before-and-after images is precious for astronomers who study these violent events.

Aside from the supernova, NGC 5806 is a relatively unremarkable galaxy: it is neither particularly large or small, nor especially close or distant.

The galaxy’s bulge (the densest part in the center of the spiral arms) is a so-called disk-type bulge, in which the spiral structure extends right to the center of the galaxy, instead of there being a large elliptical bulge of stars present. It is also home to an active galaxy nucleus, a supermassive black hole which is pulling in large amounts of matter from its immediate surroundings. As the matter spirals around the black hole, it heats up and emits powerful radiation.

This image is produced from three exposures in visible and infrared light, observed by Hubble’s Advanced Camera for Surveys. The field of view is approximately 3.3 by 1.7 arcminutes.

A version of this image was entered into the Hubble’s Hidden Treasures Image Processing Competition by contestant Andre van der Hoeven (who won second prize in the competition for his image of Messier 77). Hidden Treasures is an initiative to invite astronomy enthusiasts to search the Hubble archive for stunning images that have never been seen by the general public. The competition has now closed.
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Cygnus Loop Nebula

Wispy tendrils of hot dust and gas glow brightly in this ultraviolet image of the Cygnus Loop nebula, taken by NASA’s Galaxy Evolution Explorer. The nebula lies about 1,500 light-years away, and is a supernova remnant, left over from a massive stellar explosion that occurred between 5,000 to 8,000 years ago. The Cygnus Loop extends over three times the size of the full moon in the night sky, and is tucked next to one of the “swan’s wings” in the constellation of Cygnus.

The filaments of gas and dust visible here in ultraviolet light were heated by the shockwave from the supernova, which is still spreading outward from the original explosion. The original supernova would have been bright enough to be seen clearly from Earth with the naked eye.
Image credit: NASA/JPL-Caltech
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The Enigmas of Supernova 1987A

Supernova 1987A exploded on February 23, 1987 in the Large Magellanic Cloud. Because of its relative proximity to us (a mere 168,000 light years) SN 1987A is by far the best-studied supernova of all time. Immediately after the discovery was announced, literally every telescope in the southern hemisphere started observing this exciting new object.
The origin and the nature of the beautiful circumstellar rings are still a mystery. They have been measured to expand rather slowly, “only” 70,000-100,000 miles per hour (this is considered slow because the supernova material in the center is expanding outward at speeds that are 100-2000 times higher!). Spectroscopic observations show that the rings are enriched in the element nitrogen.
Both the slow speeds and the unusual composition show that the rings were expelled from the progenitor star when it was a red supergiant, more than 20,000 years before that star exploded as a supernova. However, one would have expected such a star to eject material in a more regular fashion, steadily expelling material in all directions.

Another puzzle is that the observations of the star just prior to the explosion show that it was a blue supergiant. This was a puzzle in 1987, because up to that time theorists had believed that only red supergiants could explode as a supernova. Apparently the star was, until relatively recently, indeed a red supergiant, but over the millennia before the explosion, it shrank in size and its surface heated up gradually.

In addition to light, particle emission was detected from the supernova. “Kamiokande II” is a neutrino telescope whose heart is a huge cylindrical tub, 52 feet in diameter and 53 feet high, containing about 3000 metric tons of water; it is located in the Kamioka mine in Japan, 3,300 feet underground. On February 23, around 7:36 am Greenwich time, the Kamiokande II recorded the arrival of 9 neutrinos within an interval of 2 seconds, followed by 3 more neutrinos 9 to 13 seconds later.

Simultaneously, the same event was revealed by the IMB detector (located in the Morton-Thiokol salt mine near Faiport, Ohio), counted 8 neutrinos within about 6 seconds. A third neutrino telescope (the “Baksan” telescope, located in the North Caucasus Mountains of Russia, under Mount Andyrchi) also recorded the arrival of 5 neutrinos within 5 seconds from each other.

This made a total of 25 neutrinos detected on Earth, out of the 10 billions of billions of billions of billions of billions of billions of them produced in the explosion! Neutrinos are elusive particles of very small (possibly zero) mass and very high energy, which are produced in huge quantities in the supernova explosion of a massive star. They interact so infrequently with ordinary matter that almost all of them of them can travel through the entire diameter of the Earth without being stopped; so they are extremely difficult to detect.

Nevertheless, a little more than two dozen neutrinos was more than enough to understand what was going on. And, in fact, the detection of those neutrinos was a perfect confirmation of the theoretical expectations for the core collapse of a massive star. The core-collapse process is believed to be the cause of the explosions of massive stars at the end of their lives, and SN 1987A provided strong experimental confirmation of this idea.

Unfortunately, the Hubble Space Telescope was not yet in operation when the supernova exploded, since it was not launced until April 1990. The first images of SN 1987A, taken with the ESA Faint Object Camera on August 23-24, 1990, revealed the inner circumstellar ring.
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Preview of a Forthcoming Supernova

NASA’s Hubble Telescope captured an image of Eta Carinae. This image consists of ultraviolet and visible light images from the High Resolution Channel of Hubble’s Advanced Camera for Surveys. The field of view is approximately 30 arcseconds across.

The larger of the two stars in the Eta Carinae system is a huge and unstable star that is nearing the end of its life, and the event that the 19th century astronomers observed was a stellar near-death experience. Scientists call these outbursts supernova impostor events, because they appear similar to supernovae but stop just short of destroying their star.

Although 19th century astronomers did not have telescopes powerful enough to see the 1843 outburst in detail, its effects can be studied today. The huge clouds of matter thrown out a century and a half ago, known as the Homunculus Nebula, have been a regular target for Hubble since its launch in 1990. This image, taken with the Advanced Camera for Surveys High Resolution Channel, is the most detailed yet, and shows how the material from the star was not thrown out in a uniform manner, but forms a huge dumbbell shape.

Eta Carinae is one of the closest stars to Earth that is likely to explode in a supernova in the relatively near future (though in astronomical timescales the “near future” could still be a million years away). When it does, expect an impressive view from Earth, far brighter still than its last outburst: SN 2006gy, the brightest supernova ever observed, came from a star of the same type, though from a galaxy over 200 million light-years away.
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Twenty-five years after supernova 1987A

While primitive humans of the Middle Paleolithic hunted prey and sheltered in caves in Africa, a distant star eighteen times more massive than the Sun, located faraway in the Large Magellanic Cloud (LMC) endured a catastrophic collapse as it reached the end of its life. As the star caved in, its outer layers rebounded off its dense core and blasted outwards, ripping the star apart in a supernova. Some 160,000 years later the light of this supernova, travelling at 300 million kilometres per second, finally reached Earth to shine in Southern Hemisphere skies on 24 February 1987.

The supernova as it went off in the Tarantula Nebula. Image: ESO

Twenty-five years later supernova (SN) 1987A, as it has become known, is giving astronomers an unprecedented look at what happens to a massive star before and after it explodes. A careful perusal of star charts prior to the supernova allowed the exact star that exploded – Sanduleak (Sk) –69° 202 – to be identified. Sk –69° 202 had been a luminous blue supergiant located on the edge of the great Tarantula Nebula, a giant star-forming region in the LMC. Here stars are born fast and die hard, the glowing veils of the nebula littered with the whorls of ancient supernova remnants – SN 1987A was merely the latest addition to its collection….

Space Diamonds Reveal Supernova Origins

Collisions in space may be behind mysterious diamonds found in meteorites.
By Brian Jacobsmeyer, ISNS Contributor
Inside Science News Service

Space diamonds may now be an astrophysicist’s best friend.
For years, scientists have found DNA-sized diamonds in meteorites on Earth. New research suggests that these diamonds spring from violent cosmic collisions, which may help scientists unravel mysteries surrounding exploding stars — the birthplaces of ancient materials that predate our solar system.

Although diamonds are rare on Earth, scientists believe that minuscule “nanodiamonds” abound in space. Researchers have been trying to decipher the origin of these enigmatic minerals for decades.

On Earth, traditional diamonds are forged deep underground under intense heat and pressure over the course of billions of years. Space diamonds, however, can form in a millionth of a millionth of a second according to new research appearing in the journal Physical Review Letters.

“The transformation is quite astonishing,” said Nigel Marks, a materials scientist at Curtin University in Perth, Australia, and coauthor of the research paper. “I never would have imagined this was possible.”

Marks simulated space dust collisions on his computer and found that diamond formation didn’t require blistering temperatures or crushing pressures. Instead, in simulations, diamonds formed when carbon-containing dust grains smashed together at speeds exceeding 10,000 miles per hour.

Within the original grains, spherical fullerenes — soccer-ball-shaped carbon molecules — enclose one another like Russian nesting dolls. Together, these concentric molecules compose layered carbon “onions.”

When the carbon onions slammed into each other, the molecules flattened, squeezed and linked together. During this process, the onions rearranged themselves into hexagonal shapes indicative of diamond structure.

If they collided at high enough speeds, then the carbon onions were destroyed. And if the particles weren’t moving fast enough, then the carbon onions did not complete the transition to diamonds. The researchers found that the narrow speed range that facilitates nanodiamond formation is common in space.

“They found that there’s sort of a sweet spot,” said Andrew Davis, a geochemist at the University of Chicago, who was not affiliated with the research. “If you can do it just right, you can make nanodiamonds. That was interesting.”

With this new model for nanodiamond formation, scientists hope to unlock some of the secrets these diamonds contain. Until now, scientists have only extracted limited information from nanodiamonds partly because they didn’t have a suitable theory for their formation, said Marks.

“There’s a huge message embedded in the nanodiamond,” said Marks. “[Researchers] just couldn’t figure out what it was.”

Forms of elements such as gaseous xenon with different amounts of neutrons have been found inside meteorite nanodiamonds. Called isotopes, these variants of the same elements convey information about exploding stars from earlier in the universe’s history. Different ratios of isotopes are produced in different nuclear reactions, giving scientists clues as to what types of dying stars gave birth to these isotopes.

According to Marks and his team, xenon is likely incorporated into carbon onions before they collide and produce nanodiamonds. By better understanding where these embedded isotopes originate, scientists can glean new information about the death of stars and the origins of our solar system.

Several competing theories, however, suggest nanodiamonds were formed differently than Marks’ research indicates. For instance, some scientists think that shock waves from exploding stars may have created nanodiamonds. Intense pressure and heat from the shock wave could also have led to the implantation of noble gases like xenon.

But all theories put forth so far have been hampered by limited experimental evidence. Because nanodiamonds are so small, it’s been extremely difficult to look at them individually.

To help resolve this issue, Marks and his colleagues hope to translate their simulations into lab experiments in the coming months. By creating nanodiamonds on Earth, the research team could produce large enough samples to analyze.

The samples could also be used for biomedical and industrial applications.

Manufacturers already create similarly sized nanodiamonds to use as drug markers or dry lubricants. Current methods require extremely high temperatures, though, limiting the types of materials that can be coated. Using the method put forth by Marks and his team, manufacturers could create coatings for materials that melt relatively easily, such as steel.

High speeds on such a small scale can be tricky, however.

“I think it’s probably not trivial to accelerate these grains to 5 kilometers per second,” said Davis. “That’s a hard thing to do in a lab.”

Nonetheless, Marks hopes that his simulations will guide future experiments.

“Now that we know this possibility exists, we want to go on and figure out what you can do with it,” said Davis….

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The chemistry of exploding stars

Meteorite contains evidence of formation of sulfur molecules derived from the ejecta of a supernova explosion

Fundamental chemical processes in predecessors of our solar system are now a bit better understood: An international team led by Peter Hoppe, researcher at the Max Planck Institute for Chemistry in Mainz, has now examined dust inclusions of the 4.6 billion years old Murchison, meteorite, which had been already found in 1969, using a very sensitive method. The stardust grains originate from a supernova, and are older than our solar system. The scientists discovered chemical isotopes, which indicate that sulfur compounds such as silicon sulfide originate from the ejecta of exploding stars. Sulfur molecules are central to many processes and important for the emergence of life.

Star dust from a supernova. The electron microscopic image shows a silicon carbide grain from the meteorite Murchinson. The approximately one micrometre small grains originate from a supernova as an isotopic analysis has shown. Isotopes are forms of an element with different weights. Picture: Peter Hoppe, Max Planck Institute for Chemistry © Peter Hoppe, MPI for Chemistry

Models already predicted the formation of sulfur molecules in the ejecta of exploding stars – the supernovae. Scientists from Germany, Japan and the U.S. now provided evidence to substantiate the theory with the help of isotope analyses of stardust from meteorites.

The team around the Mainz Max Planck researcher Peter Hoppe initially isolated thousands of about 0.1 to 1 micrometre-sized silicon carbide stardust grains from the Murchison meteorite, which was already found on Earth in 1969. The stardust grains originate from a supernova, and are older than our solar system. The researchers then determined with a highly sensitive spectrometer, the so-called NanoSIMS, the isotopic distribution of the samples. With this technique an ion beam is shot onto the individual stardust grains and releases atoms from the surface. The spectrometer then separates them according to their mass and measures the isotopic abundances. Isotopes of a chemical element have the same number of protons but different numbers of neutrons.

In five silicon carbide samples the astrophysicists found an unusual isotopic distribution: They measured a high amount of heavy silicon and a low amount of heavy sulfur isotopes, a result that does not fit with current models of isotope abundances in stars. At the same time they were able to detect the decay products of radioactive titanium which can be produced only in the innermost zones of a supernova. This proves that the stardust grains indeed derive from a supernova.

A proof for the model of the chemistry of the ejecta of supernovae

“The stardust grains we found are extremely rare. They represent only about the 100 millionth part of the entire meteorite material. That we have found them is very much a coincidence – especially since we were actually looking for silicon carbide stardust with isotopically light silicon,” says Peter Hoppe. “The signature of isotopically heavy silicon and light sulfur can only be plausibly explained if silicon sulfide molecules were formed in the innermost zones in the ejecta of a supernova.” Afterwards, the sulfide molecules were enclosed in the condensing silicon carbide crystals. These crystals then reached the solar nebula around 4.6 billion years ago and were subsequently incorporated into the forming planetary bodies. They finally reach the Earth in meteorites which are fragments of asteroids.

Carbon monoxide and silicon monoxide were already detected in infrared spectra of the ejecta of supernova explosions. Although models predicted the formation of sulfur molecules, it has not yet been possible to prove this. The measurements on silicon carbide stardust now provide support to the predictions that silicon sulfide molecules arise a few months after the explosion at extreme temperatures of several thousand degrees Celsius in the inner zones of supernova ejecta.

The meteorite studied was named after the Australian city of Murchison, where it was found in 1969. For astronomers, it is an inexhaustible diary about the formation of our solar system, as it has remained almost unaltered since its formation. Besides the stardust inclusions from the ejecta of a supernova Murchison also transported dust to the Earth which has been formed in the winds of giant red stars. Through further analyses, the researchers hope to learn more about the origin of their parent stars.