This Chandra image clearly locates a pulsar exactly at the geometric center of the supernova remnant known as G11.2-0.3.
Nova Makes Quick Recovery Astronomy.com - October 2002
A star goes back to normal less than three years after going nova
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.
Computer Simulation Gives 3-D View of Supernova June 2002 - Reuters
Supernova poised to go off near Earth May 2002 - New Scientist
A star in our galactic backyard on the brink of exploding in a supernova
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.
NASA News - September 21, 1999
Images released yesterday from NASA's Chandra X-ray Observatory reveal previously unobserved features in the remnants of three different supernova explosions. Two of the objects, G21.5-0.9 and PSR 0540-69, show details of the prodigious production of energetic particles by a rapidly rotating, highly magnetized neutron star, as well as the enormous shell structures produced by the explosions. The image of the third remnant, E0102-72, reveals puzzling spoke-like structures in its interior.
G21.5-0.9, in the constellation of Scutum, is about 16,000 light years from Earth. One light year equals six trillion miles. Chandra's image shows a bright nebula surrounded by a much larger diffuse cloud.
Inside the inner nebula is a bright central source that is thought to be a rapidly rotating, highly magnetized neutron star. A rotating neutron star acts like a powerful generator, creating intense electric voltages that accelerate electrons to speeds close to the velocity of light. The total output of this generator is greater than a thousand suns. The fluffy appearance of the central nebula is thought to be due to magnetic field lines which constrain the motions of the high energy electrons.
"It's a remarkable image," said Dr. Patrick Slane of the Harvard-Smithsonian Center for Astrophysics in Cambridge, Mass. "Neither the inner core nor the outer shell has ever been seen before."
"It is as though we have a set of Russian dolls, with structures embedded within structures," said Professor Gordon Garmire of Pennsylvania State University in University Park, Pa., and principal investigator of Chandra's Charge-Coupled Device X-ray camera, used to make the image.
NASA's project scientist, Dr. Martin Weisskopf of the Marshall Space Flight Center in Huntsville, Ala., said, "Chandra's capability to provide surprises and insights continues!"
The existence of a rotating neutron star, or pulsar, in the center of G21.5-0.9 is inferred from the appearance of the nebula and the energy distribution of X-rays and radio waves from the nebula. This distribution, called non-thermal radiation, is characteristic of radiation produced by high energy electrons in a magnetic field.
A previously known pulsar is observed directly in the Chandra image of PSR 0540-69. This pulsar, located in a 180,000 light-year-distant satellite galaxy to our Milky Way, emits pulses of radio, optical and X -ray energy at a rate of 50 per second. These pulses, which come from a neutron star rotating at this incredible rate, comprise only a few percent of the total energy output of the neutron star powerhouse.
"The Chandra image gives us a much better idea of how this energy source works," said Dr. Stephen Murray, principal investigator for the High Resolution Camera, the X-ray camera used to make this image. "You can see X-ray jets blasting out from the pulsar in both directions."
The third Chandra image is of E0102-72, in the Small Magellanic Cloud, another satellite galaxy of the Milky Way. This galaxy is 190,000 light years from Earth. This object, like G21.5-0.9 and PSR 0540-69, is believed to have resulted from the explosion of a massive star several thousand years ago. Stretching across 40 light years of space, the multi-million-degree source resembles a flaming cosmic wheel.
"Chandra's gallery of supernova remnants is giving us a lot to think about," said Dr. Fred Seward of Harvard-Smithsonian, who, with his colleagues, discovered E0102-72 and PSR 0540-69 by using a Chandra predecessor, NASA's Einstein Observatory, over a decade ago. "We're seeing many things we thought should be there, and many others that we never expected. It's great!"
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