Supernovae
Supernovae are massive giant exploding stars. When the explosion occurs, the resulting illumination can be as bright as an entire galaxy! Supernova occurs at the end of a star's lifetime, when its nuclear fuel is exhausted and it is no longer supported by the release of nuclear energy. If the star is particularly massive, then its core will collapse and in so doing will release a huge amount of energy. This will cause a blast wave that ejects the star's envelope into interstellar space. The result of the collapse may be, in some cases, a rapidly rotating neutron star that can be observed many years later as a radio pulsar.
As a result of gravitational forces acting against the nuclear structure of the core of a fuel depleted star, tremendous shock waves are generated which cause the outside layers of the star to be blown away from the core.
One type of Supernova involves two stars, one of them being a white dwarf whose gravitational attraction is so intense that it is capable of siphoning off material from its companion. Unfortunately for the star (but fortunately for us at a long distance!), the white dwarf exceeds its Chandrasekhar limit of stability causing it to go into thermonuclear instability and produces one of the largest explosions known in the Universe.
Another type of supernova involves a collapse of the core of a fuel depleted star, tremendous shock waves are generated which cause the outside layers of the star to be blown away from the core. Gravitational forces condensing hydrogen gas raises the temperature at the center of the star to the point where nuclear fusion is initiated. Hydrogen is fused into helium and energy is given off in the process. As more helium accumulates at the center, the temperature rises due to compression until another nuclear fusion is initiated. This time helium is converted to carbon and oxygen and additional energy is given off during the nuclear fusion.
A similar process continues with carbon and oxygen fusing to neon, magnesium, and oxygen. These elements then undergo another fusion process as the temperature and pressure increase to produce silicon and sulfur. The latter two elements then fuse into iron. During each nuclear fusion, energy is given off. This takes two orders of magnitude less time to happen than on the previous fusion. However, nuclear fusion stops at iron because energy is no longer produced by fusion. The iron core collapses very quickly (within hours or less).
Since the iron core can collapse only so far and can no longer undergo fusion, it becomes extremely hot and now begins to expand rapidly. This occurs while the star's outer shells are rushing in to fill the void left by the collapsed iron core. The expanding iron and the collapsing outer gases collide with each other producing tremendous shock waves which blow the outer layers away from the core, thus causing the supernova's gigantic explosion.
What happens after the explosion depends on the type and mass of the progenitor stars. Mostly they produce a gas cloud called a supernova remnant which initially expands at a rate of about 10,000 km/s. Gradually the expansion rate slows down while dissipating into the interstellar medium, seeding the neighborhood with heavy elements and providing the necessary shock waves for new stellar formation.
Brightest Known Supernova Detected National Geographic - October 15, 2007
Enigmatic supernova smashes brightness record New Scientist - October 12, 2007
Supernova blazed like 100 billion suns MSNBC - October 12, 2007
The Brightest Supernova Ever NASA - May 7, 2007
Astrophysicists Explain Differences In Brightness Of Supernova Explosions Science Daily - February 23, 2007
Brightest supernova discovery hints at stellar collision New Scientist - January 4, 2007
Supernova captured in 'real time' BBC - August 30, 2006
Mystery object found in supernova's heart Space.com - July 7, 2006
... energetic X-ray emissions of the blue point-like object cycles every 6.7 hours
tens of thousands of times longer than expected for a freshly created neutron star
Native Americans may have recorded supernova explosion in 1006 AD Space.com - June 6, 2006
Supernova shock wave creates halo effect New Scientist - August 19, 2005
The shock wave from a bright supernova that exploded in 1987 has now reached the edge of a cavity around the dead star, reveal new observations with the Hubble Space Telescope and the Chandra X-ray Observatory.As intense heat from the shock wave continues to spread, it will illuminate the dense gas blown off by the detonating star, which was originally about 20 times more massive than our Sun.Called 1987A, the supernova was the brightest recorded in 400 years and exploded in a nearby galaxy called the Large Magellanic Cloud. Astronomers believe that about a million years before the supernova, the star lost most of its outer layers through a slow-moving wind of particles.
The Last Supernova - 1604: 400-Year-Old Explosion Imaged - Space.com - October 2004
Hubble Reveals Dramatic New Phase of a Supernova Explosion Space.com - February 2004
A shock wave from an exploding star known as Supernova 1987A lights up spots in a surrounding ring of dust and gas, in the latest snapshot from the Hubble Space Telescope. It's the most dramatic stellar explosion witnessed in centuries - New images from the Hubble Space Telescope show the dying star's "ring of fire" entering a new phase of brightness
Star Survivor: Companion Endures Explosion Space.com - January 2004
Astronomers have found a bright blue companion star to an exploded supernova,
a stellar survivor to one of the most violent eruptions in the universe.
Where do supernovae come from? Physics Web - August 2003
Hubble looks at dark Universe BBC - April 2003
Astronomers using the Hubble Space Telescope have found two
distant supernovae - exploding stars - that provide new clues
about the accelerating Universe and its mysterious "dark energy".
Hubble looks at dark Universe BBC - April 2003
Thanks to a burster that was remarkably close in cosmic terms,
their true nature may have been revealed. The bursts seem
to come from exploding stars called supernovae.
Astronomers predict stellar explosion for the first time BBC - April 2003
Hubble looks at dark Universe BBC - April 2003
Astronomers using the Hubble Space Telescope have found two
distant supernovae - exploding stars - that provide new clues
about the accelerating Universe and its mysterious "dark energy".
Astronomers Discover "Bulls-Eye" Pulsar In Supernova Remnant June 2002 - Science Daily
This will help scientists better understand how neutron
stars channel enormous amounts of energy into particles
moving near the speed of light.
April 2, 2001 - AP
The Hubble Space Telescope peering 10 billion years back in time to when the universe was in its adolescence, has spotted the most distant exploding star ever observed.
Researchers said the discovery bolsters the controversial theory that mysterious ``dark energy'' is accelerating the expansion of the cosmos.
Invisible and poorly understood, dark energy might account for as much as two-thirds of space. Proposed a century ago by Einstein, it may counteract more familiar forces such as gravity.
The supernova, barely discernible with the most powerful instruments, provides clues to dark energy. While dim, the dying star gleams brighter and moves differently than it would if the universe had expanded at a steady rate since the beginning of time.
The Hubble finding is prompting researchers to rethink how the universe works.
''(Dark energy) is every bit as amazing as black holes,'' said University of Chicago cosmologist Michael Turner in a briefing at NASA news web sites in Washington headquarters. ``It controls the density of nature. It's the key to understanding how all of nature's particles and forces fit together.
``The discovery that the universe is speeding up will be viewed as one of the most important discoveries in all of science in the past 25 years,'' Turner said.
A supernova is an exploding star, a cosmic flashbulb. One occurs each second somewhere in space, and that single star beams brighter than the billions of stars in its galaxy combined.
But astronomers have to search mightily for supernovae, making the discovery of a supernova a dramatic event.
Supernova 1997ff exploded more than 10 billion light years from Earth, or 1.5 times farther than any previously recorded exploding star, when the universe was a quarter of its current age.
Only recently did the flash reach Hubble. In that way, telescopes act as time machines allowing astronomers to observe events in the early history of the universe as they are happening.
Ten billion years ago, the universe was only about 4 billion years old. Supernova 1997ff probably was a white dwarf star about the size of the sun, but extremely dense.
It sucked matter from a companion star until it reached critical mass and temperature. The carbon ignited in a runaway thermonuclear explosion of ``astonishing brightness,'' said co-discoverer Peter Nugent of Lawrence Berkeley National Laboratory.
In 1995 and 1997, Hubble examined a tiny part of the northern Hemisphere sky. One object was visible only in the later images - meaning it was so distant its light didn't reach Earth until then. That was supernova 1997ff.
Later images by infrared instruments allowed researchers to track the supernova's motion and other characteristics. They reached firm conclusions about the supernova several months ago.
Cosmologists believe the universe probably was born in an explosion known as the Big Bang 12 billion to 15 billion years ago.
Gravity put the brakes on the immediate expansion. Then, they suspect, the universe started expanding more rapidly again 4 billion to 8 billion years ago. The reason is unclear; possibly dark energy gained the upper hand.
If astronomers were to look deep into time and space, theorists have predicted objects would appear brighter than expected because gravity was restraining galaxies from flying apart.
Sure enough, the relative brightness and motion of 1997ff might be the first tantalizing clues the theorists were right.
``This supernova shows us the universe is behaving like a driver who slows down approaching a red stoplight, then accelerates when the light turns green,'' said Adam Reiss of the Space Telescope Science Institute in Baltimore.
Alternative theories suggest that dust in the universe was not as dense 10 billion years ago, making the dying star appear brighter than expected. Scientists agreed more observations are needed.
This Chandra image clearly locates a pulsar exactly at the geometric center of the supernova remnant known as G11.2-0.3.
January 11, 2001 - NASA News
New evidence from NASA's Chandra X-ray Observatory suggests that a known pulsar is the present-day counterpart to a supernova that exploded in 386 AD, a stellar explosion witnessed by ancient Chinese astronomers. If confirmed, this will be only the second known pulsar to be clearly associated with an historic event.
In roughly the past 2,000 years, less than 10 reports of probable supernovae have been archived, mostly by Asian astronomers. Until now, the Crab Nebula has been the only pulsar whose birth is associated with an historic event, the supernova of 1054 AD, making it the only neutron star with a firm age.
Determining the true ages of astronomical objects is notoriously difficult," said Victoria Kaspi of McGill University in Montreal, Canada, "and for this reason, historical records of supernova are of great importance."
Kaspi and colleagues, who presented their results yesterday at the American Astronomical Society meeting in San Diego, CA, used Chandra to locate the pulsar exactly at the geometric center of the supernova remnant known as G11.2-0.3. This location provides very strong evidence that the pulsar, a neutron star spinning 14 times per second, was formed in the supernova of 386 AD, making it 1,615 years old.
Because pulsars, once they are formed, race away from the site of the supernova explosion, Chandra's ability to pinpoint the pulsar at the remnant's center implies the system must be very young.
"We believe that the pulsar and the supernova remnant G11.2-0.3 are both likely to be left over from the explosion seen by the Chinese observers over 1,600 years ago," said Mallory Roberts of McGill University. "While this is exciting by itself, it also raises new questions about what we know about pulsars, especially during their infancies."
These questions arose when the research team of the Japanese Advanced Satellite for Cosmology and Astrophysics (ASCA) applied the present spin rate to current models to determine the pulsar's estimated lifetime and compared it to the age of G11.2-0.3. The result was an age of roughly 24,000 years -- far predating the birth year of 386 AD.
This Chandra image reveals a young pulsar inside the Crab Nebula, the remnant of a supernova that Chinese astronomers saw in 1054 AD.
Between mid-April and mid-May in the year 386 AD, the sudden appearance of a new star, presumably a supernova, was recorded by Chinese observers in the direction of the sky now known as the constellation of Sagittarius. In the 1970s, radio astronomers discovered an expanding nebula of gas and high-energy particles, called G11.2-0.3, believed to be the remnant of that explosion. In 1997, a team of X-ray astronomers used ASCA to discover a pulsar in the same area of the sky.
Chandra observed G11.2-0.3 with the Advanced CCD Imaging Spectrometer at two points in time: Aug. 6, 2000, and Oct. 15, 2000, for approximately 20,000 and 15,000 seconds respectively.
March 1, 2000 - Uni- Sci
A college senior has identified nine new supernovae -- including the most distant one found to date -- as part of a National Science Foundation (NSF) program that provides undergraduates with hands-on research experience.
"It's thrilling to shout across the room, 'I've got one!' when you spot the first supernova during an observing run," said Soderberg, a Bates College senior from Mashpee, Mass. Soderberg is a math-physics major who was on leave from Bates to participate in the NSF's Research Experience for Undergraduates program.
As part of a team of astrophysicists working in Hawaii and at the Cerro Tololo Inter-American Observatory in Chile in early November 1999, Soderberg used the Canada-France Hawaii (CFH) Telescope and the Keck Observatory, both on Mauna Kea, Hawaii, to make the discovery.
Identifying supernovae is a process of elimination. The CFH Telescope takes two digital pictures of the sky three weeks apart. Soderberg compared the two pictures to identify "residuals" -- light objects that changed brightness.
Based on her knowledge of luminous astronomical objects, she then distinguished the residuals likely to be supernovae from variable stars, asteroids and active galactic nuclei. She and her team then confirmed her supernovae identifications with the low-resolution spectrograph on the Keck Telescope.
Since research time at large observatories is strictly scheduled, Soderberg's recommendations on what to look for with the Keck Telescope were key to the discovery. "With research time at the Keck Observatory so limited, you want to make sure that you don't waste four hours looking for dust," she said.
The team launched its search for supernovae -- bright, dying stars located billions of light years from Earth -- in the hope that measuring the light from these stars can help determine whether the expansion of the universe is accelerating or decelerating. Preliminary results imply that the universe is accelerating, not slowing down.
Considering all that could have gone wrong, Soderberg says she felt "tremendous relief" at the discovery of so many supernovae. Bad weather and software glitches routinely upset the best-laid research plans. Working on the project via the Internet with colleagues collecting data across time zones meant "stress, little sleep and lots of junk food," Soderberg said.
"Discovering supernovae requires one to remain organized and focused for several 20-hour work days in a row, something Alicia can do as well as any of the team's scientists," said Brian Schmidt, astronomer at Australia's Mount Stromlo and Siding Spring observatories and lead investigator of the supernova discovery team. "Very few students are given opportunities like this. Alicia has made the most of them by proving herself a hard worker, finding her own funding and asking the right questions of the right people."
With encouragement from Eric Wollman, professor of physics at Bates, Soderberg applied for and received her first NSF Research Experience for Undergraduates grant to study at the Harvard-Smithsonian Center for Astrophysics after her sophomore year at Bates in summer 1997.
Soderberg stayed at Harvard during the first semester of her junior year, studying astrophysics and becoming a resident expert on the computer software used to help identify supernovae. She spent the second semester of her junior year at the Cerro Tololo Inter-American Observatory in Chile, developing a short list of possible supernovae to find with the low-resolution spectrograph at the Keck Observatory.
Soderberg's research will culminate in a Bates honors thesis, but she doesn't get starry-eyed about supernovae alone. She has also studied binary stars in globular clusters from Arizona's Kitt Peak National Observatory and looked for the existence of water in central-belt asteroids from Cornell University's Arecibo Observatory in Puerto Rico.
Before returning to Bates for the second semester of her senior year, she received another grant -- this one from the U.S. Department of Energy -- to study gamma ray bursts at Los Alamos National Laboratory in New Mexico.
August 24, 1999
A tempestuous relationship between an unlikely pair of stars may have created an oddly shaped, gaseous nebula that resembles an hourglass nestled within an hourglass.
Images taken with Earth-based telescopes have shown the larger, hourglass-shaped nebula. But this picture, taken with NASA's Hubble Space Telescope, reveals a small, bright nebula embedded in the center of the larger one (close-up of nebula in inset). Astronomers have dubbed the entire nebula the "Southern Crab Nebula" (He2-104), because, from ground-based telescopes, it looks like the body and legs of a crab. The nebula is several light-years long.
The possible creators of these shapes cannot be seen at all in this Wide Field and Planetary Camera 2 image. It's a pair of aging stars buried in the glow of the tiny, central nebula. One of them is a red giant, a bloated star that is exhausting its nuclear fuel and is shedding its outer layers in a powerful stellar wind. Its companion is a hot, white dwarf, a stellar zombie of a burned-out star. This odd duo of a red giant and a white dwarf is called a symbiotic system. The red giant is also a Mira Variable, a pulsating red giant, that is far away from its partner. It could take as much as 100 years for the two to orbit around each other.
Astronomers speculate that the interaction between these two stars may have sparked episodic outbursts of material, creating the gaseous bubbles that form the nebula. They interact by playing a celestial game of "catch": as the red giant throws off its bulk in a powerful stellar wind, the white dwarf catches some of it. As a result, an accretion disk of material forms around the white dwarf and spirals onto its hot surface. Gas continues to build up on the surface until it sparks an eruption, blowing material into space. This explosive event may have happened twice in the "Southern Crab." Astronomers speculate that the hourglass-shaped nebulae represent two separate outbursts that occurred several thousand years apart. The jets of material in the lower left and upper right corners may have been accelerated by the white dwarf's accretion disk and probably are part of the older eruption.
The nebula, located in the Southern Hemisphere constellation of Centaurus, is a few thousand light-years from Earth.
This image, taken in May 1999, captures the glow of nitrogen gas energized by the white dwarf's intense radiation.
These results were presented at the "Asymmetrical Planetary Nebulae II: From Origins to Microstructures" conference, which took place at the Massachusetts Institute of Technology, August 3-6, 1999.
Supernovae are used to measure the age of the Universe
July 7, 1999 - BBC News Online
Atoms that have travelled to Earth from a distant, exploded star have been discovered for the first time, scientists claim.
The radioactive iron-60 atoms were recovered from ocean sediment on a seafloor site in the South Pacific. German astronomers believe they came to Earth from a supernova, one of nature's grandest spectacles.
When a single star explodes, it can outshine an entire galaxy of suns for several days. It becomes brighter than a hundred thousand million stars and light from the explosion can still be detected on Earth even if the explosion is right on the edge of the known Universe.
Scientists are seeing supernovae all the time - they have become useful tools for measuring the size of the Universe. On one occasion, rare and ghostly particles called neutrinos have even been detected from a supernova.
However, finding atoms that have been ejected in the explosion is a little controversial. In a sense, all the atoms on Earth, with the exception of hydrogen and helium, have been processed through, or created in, supernovae many millions - even billions - of years ago. Without supernovae there would be no heavier elements in the Universe.
But the German team, from Technische Universität München and the Max-Plank Institute, say the iron-60 atoms were deposited on Earth relatively recently - only a few million years ago.
Several sediment layers in the South Pacific were dated, and the samples looked at with a device called an accelerator mass spectroscope that can detect faint traces of iron isotopes.
Because Iron-60 decays by half every 1.5 million years, the levels detected in the sample, and the lack of terrestrial sources of the isotope point to a relatively nearby and recent supernova as its source, the researchers say.
They think the supernova may have been just 90-180 light years from the Earth.
If this is true, our hominid ancestors must have seen it as the brightest thing in the sky after the Sun. If the supernova had been any closer, it might even have affected the Earth's climate, possibly causing the extinction of species and damage to the land and upper layers of the oceans.
Reuters - Washington - April 13, 1999
Astronomers said they had found evidence of a stellar explosion that would have lit up the night sky 700 years ago -- yet no medieval star-gazer recorded it.
Readings from space show that a star 15 times as massive as the sun and just 500 light-years away -- right in our neighborhood by galactic standards -- must have collapsed and exploded in a huge supernova. Wan Chen and Neil Gehrels of NASA's Goddard Space Flight Center in Greenbelt, Maryland, said the supernova would have been as bright as the moon in the night sky.
"It's a real mystery," Chen said in a statement. "This supernova was very bright. People had to have seen it, but we haven't found any written records yet."
The pair found out about the explosion in an unusual way. Using X-ray scans, they detected both radioactive titanium and aluminum coming from the same source.
Previously, astronomers assumed they could only see one element or the other in the remnant of an explosion.
They named the newly discovered supernova remnant GRO/RX J0852, they reported in the Astronomical Journal.
Glittering stars and wisps of gas create a breathtaking backdrop for the self-destruction of a massive star, called supernova 1987A, in the Large Magellanic Cloud, a nearby galaxy. Astronomers in the Southern hemisphere witnessed the brilliant explosion of this star on Feb. 23, 1987.
Shown in this NASA Hubble Space Telescope image, the supernova remnant, surrounded by inner and outer rings of material, is set in a forest of ethereal, diffuse clouds of gas. This three-color image is composed of several pictures of the supernova and its neighboring region taken with the Wide Field and Planetary Camera 2 in Sept. 1994, Feb. 1996 and July 1997.
The many bright blue stars nearby the supernova are massive stars, each more than six times heftier than our Sun. They are members of the same generation of stars as the star that went supernova about 12 million years ago. The presence of bright gas clouds is another sign of the youth of this region, which still appears to be a fertile breeding ground for new stars.
In a few years the supernova's fast moving material will sweep the inner ring with full force, heating and exciting its gas, and will produce a new series of cosmic fireworks that will offer a striking view for more than a decade.
November 11, 1998 - Reuters - London
There is no record of it ever happening, yet astrophysicists have found a remnant from what would have been the biggest, brightest explosion in the galaxy about 700 years ago. The discovery of the debris from the closest supernova, or explosion of a dying star, to Earth is reported in two studies in the science journal Nature on Wednesday.
It is perplexing because someone, somewhere should have seen it. But Bernd Aschenbach, of the Max Planck Institute for Extraterrestrial Physics in Garching, Germany, said there was no historical mention of it. "This is an entirely new remnant from an unknown supernova. It had not been observed by anyone 700 years ago. This is the mystery. Supernovas are supposed to be very bright. It should have outshone everything in the sky, every star and every planet except the moon."
The discovery is the closest remnant of a supernova found in our galaxy in the last 2,000 years. Aschenbach located it by its X-ray emission. In a separate study, Anatoli Iyudin and other astrophysicists at the institute described how they used gamma ray emissions to spot and date the remnant. They estimate its age to be about 700 years old, so it puts it between 1200-1300 AD. There are only two or three remnants known to be younger than that in our galaxy. Although there are about 100 billion stars in the Milky Way galaxy, no one has witnessed a supernova for about 400 years. Only about 200 supernova remnants have been found and only six are less than 1,000 years old.
A supernova is the end of the life of a star which can live, depending on its mass, to a billion years old. The star lives from the nuclear fusion processes that produce the energy that counteracts its own gravity. At some time they will have no nuclei left to fuse and the gravity of the star overcomes the internal pressure and the star collapses. It is initially a big implosion, because the star collapses, and then by some repelling forces it explodes.
Some fraction of the enormous energy is generated as light which is seen as the explosion. Finding a remnant of a supernova provides scientists with valuable information about the whole process. The astrophysicists have searched through records dating back to when the supernova should have been seen. Chinese royal astronomers had been observing the sky long before and after that time but they did not mention it in any records.
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