Astronomers See Historical Supernova From a New Angle

Chandra X-ray Observatory image of the supernova remnant Cassiopeia A (Cas A). The red, green, and blue regions in this X-ray image of Cas A show where the intensity of low, medium, and high-energy X-rays, respectively, is greatest. While this photo shows the remains of the exploded star, light echoes show us reflected light from the explosion itself.

Credit: NASA/CXC/MIT/UMass Amherst/M.D.Stage et al.

Since Galileo first pointed a telescope at the sky 400 years ago, a myriad of technological advances have allowed astronomers to look at very faint objects, very distant objects, and even light that's invisible to the human eye. Yet, one aspect usually remains out of reach - the benefit of a 3-D perspective.

Our telescopes show the Milky Way galaxy only as it appears from one vantage point: our solar system. Now, using a simple but powerful technique, a group of astronomers led by Armin Rest of Harvard University has seen an exploding star or supernova from several angles.

"The same event looks different from different places in the Milky Way," said Rest. "For the first time, we can see a supernova from an alien perspective."

The supernova left behind the gaseous remnant Cassiopeia A. The supernova's light washed over the Earth about 330 years ago. But light that took a longer path, reflecting off clouds of interstellar dust, is just now reaching us. This faint, reflected light is what the astronomers have detected.

The technique is based on the familiar concept of an echo, but applied to light instead of sound. If you yell, "Echo!" in a cave, sound waves bounce off the walls and reflect back to your ears, creating echoes. Similarly, light from the supernova reflects off interstellar dust to the Earth. The dust cloud acts like a mirror, creating light echoes that come from different directions depending on where the clouds are located.

"Just like mirrors in a changing room show you a clothing outfit from all sides, interstellar dust clouds act like mirrors to show us different sides of the supernova," explained Rest.

Moreover, an audible echo is delayed since it takes time for the sound waves to bounce around the cave and back. Light echoes also are delayed by the time it takes for light to travel to the dust and reflect back. As a result, light echoing from the supernova can reach us hundreds of years after the supernova itself has faded away.

Not only do light echoes give astronomers a chance to directly study historical supernovae, they also provide a 3-D perspective since each echo comes from a spot with a different view of the explosion.

Most people think a supernova is like a powerful fireworks blast, expanding outward in a round shell that looks the same from every angle. But by studying the light echoes, the team discovered that one direction in particular looked significantly different than the others.

They found signs of gas from the stellar explosion streaming toward one point at a speed almost 9 million miles per hour (2,500 miles per second) faster than any other observed direction.

"This supernova was two-faced!" said Smithsonian co-author and Clay Fellow Ryan Foley. "In one direction the exploding star was blasted to a much higher speed."

Previous studies support the team's finding. For example, the neutron star created when the star's core collapsed is zooming through space at nearly 800,000 miles per hour in a direction opposite the unique light echo. The explosion may have kicked gas one way and the neutron star out the other side (a consequence of Newton's third law of motion, which states that every action has an equal and opposite reaction).

By combining the new light-echo measurements and the movement of the neutron star with X-ray data on the supernova remnant, astronomers have assembled a 3-D perspective, giving them new insight into the Cas A supernova.

"Now we can connect the dots from the explosion itself, to the supernova's light, to the supernova remnant," said Foley.

Cassiopeia A is located about 16,000 light-years from Earth and contains matter at temperatures of around 50 million degrees F, causing it to glow in X-rays. A 3-D computer model of the remnant is online.

The Mayall 4-meter telescope at Kitt Peak National Observatory was used to locate the light echoes. Follow-up spectra were obtained with the 10-meter Keck I Telescope.

The journal paper describing this discovery is available online.

Headquartered in Cambridge, Mass., the Harvard-Smithsonian Center for Astrophysics (CfA) is a joint collaboration between the Smithsonian Astrophysical Observatory and the Harvard College Observatory. CfA scientists, organized into six research divisions, study the origin, evolution and ultimate fate of the universe.

Ashes To Ashes Dust To Dust Chandra And Spitzer Have The Gos

A composite image from NASA's Chandra (blue) and Spitzer (green and red-yellow) space telescopes shows the dusty remains of a collapsed star, a supernova remnant called G54.1+0.3. The white source at the center is a dead star called a pulsar, generating a wind of high-energy particles seen by Chandra in blue. The wind expands into the surrounding environment. The infrared shell that surrounds the pulsar wind, seen in red, is made up of gas and dust that condensed out of debris from the supernova explosion. A nearby cluster of stars is being engulfed by the dust. The nature and quantity of dust produced in supernova explosions is a long-standing mystery, and G54.1+0.3 supplies an important piece to the puzzle. Image credit: NASA/CXC/JPL-Caltech/Harvard-Smithsonian CfA

A new image from NASA's Chandra and Spitzer space telescopes shows the dusty remains of a collapsed star. The dust is flying past and engulfing a nearby family of stars.

"Scientists think the stars in the image are part of a stellar cluster in which a supernova exploded," said Tea Temin of the Harvard-Smithsonian Center for Astrophysics, Cambridge, Mass., who led the study. "The material ejected in the explosion is now blowing past these stars at high velocities."

The composite image of G54.1+0.3 shows the Chandra X-ray Observatory data in blue, and data from the Spitzer Space Telescope in green (shorter wavelength) and red-yellow (longer).

The white source near the center of the image is a dense, rapidly rotating neutron star, or pulsar, left behind after a core-collapse supernova explosion. The pulsar generates a wind of high-energy particles - seen in the Chandra data - that expands into the surrounding environment, illuminating the material ejected in the supernova explosion.

The infrared shell that surrounds the pulsar wind is made up of gas and dust that condensed out of debris from the supernova. As the cold dust expands into the surroundings, it is heated and lit up by the stars in the cluster so that it is observable in infrared.

The dust closest to the stars is the hottest and is seen glowing in yellow in the image. Some of the dust is also being heated by the expanding pulsar wind as it overtakes the material in the shell.

The unique environment into which this supernova exploded makes it possible for astronomers to observe the condensed dust from the supernova that is usually too cold to emit in infrared. Without the presence of the stellar cluster, it would not be possible to observe this dust until it becomes energized and heated by a shock wave from the supernova.

However, the very action of such shock heating would destroy many of the smaller dust particles. In G54.1+0.3, astronomers are observing pristine dust before any such destruction.

G54.1+0.3 provides an exciting opportunity for astronomers to study the freshly formed supernova dust before it becomes altered and destroyed by shocks. The nature and quantity of dust produced in supernova explosions is a long-standing mystery, and G54.1+0.3 supplies an important piece to the puzzle.

NASA's Marshall Space Flight Center in Huntsville, Ala., manages the Chandra program for NASA's Science Mission Directorate in Washington. The Smithsonian Astrophysical Observatory controls Chandra's science and flight operations from Cambridge, Mass.

The Spitzer observations were made before the telescope ran out of its coolant in May 2009 and began its "warm" mission. NASA's Jet Propulsion Laboratory in Pasadena, Calif., manages Spitzer for NASA's Science Mission Directorate, Washington. Science operations are conducted at the Spitzer Science Center at the California Institute of Technology in Pasadena. Caltech manages JPL for NASA.

Super Supernova: White Dwarf Star System Exceeds Mass Limit

Cosmologists use Type Ia supernovae, like the one visible in the lower left corner of this galaxy, to explore the past and future expansion of the universe and the nature of dark energy. (Credit: High-Z Supernova Search Team, HST, NASA)

An international team led by Yale University has, for the first time, measured the mass of a type of supernova thought to belong to a unique subclass and confirmed that it surpasses what was believed to be an upper mass limit. Their findings, which appear online and will be published in an upcoming issue of the Astrophysical Journal, could affect the way cosmologists measure the expansion of the universe.

Cosmologists use Type Ia supernovae -- the violent explosions of dead cores of stars called white dwarfs -- as a kind of cosmic ruler to measure distances to the supernovae's host galaxies and, as such, to understand the past and future expansion of the universe and explore the nature of dark energy. Until recently, it was thought that white dwarfs could not exceed what is known as the Chandrasekhar limit, a critical mass equaling about 1.4 times that of the Sun, before exploding in a supernova. This uniform limit is a key tool in measuring distances to supernovae.

Since 2003, four supernovae have been discovered that were so bright, cosmologists wondered whether their white dwarfs had surpassed the Chandrasekhar limit. These supernovae have been dubbed the "super-Chandrasekhar" supernovae.

Now Richard Scalzo of Yale, as part of a collaboration of American and French physicists called the Nearby Supernova Factory, has measured the mass of the white dwarf star that resulted in one of these rare supernovae, called SN 2007if, and confirmed that it exceeded the Chandrasekhar limit. They also discovered that the unusually bright supernova had not only a central mass, but a shell of material that was ejected during the explosion as well as a surrounding envelope of pre-existing material. The team hopes this discovery will provide a structural model with which to understand the other supermassive supernovae.

Using observations from telescopes in Chile, Hawaii and California, the team was able to measure the mass of the central star, the shell and the envelope individually, providing the first conclusive evidence that the star system itself did indeed surpass the Chandrasekhar limit. They found that the star itself appears to have had a mass of 2.1 times the mass of the Sun (plus or minus 10 percent), putting it well above the limit.

Being able to measure masses for all parts of the star system tells the physicists about how the system may have evolved -- a process that is currently poorly understood. "We don't really know much about the stars that lead to these supernovae," Scalzo said. "We want to know more about what kind of stars they were, and how they formed and evolved over time."

Scalzo believes there's a good chance that SN 2007if resulted from the merging of two white dwarfs, rather than the explosion of a single white dwarf and hopes to study the other super-Chandrasekhar supernovae to determine whether they, too, could have involved a merger of two white dwarfs.

Theorists continue to explore how stars with masses above the Chandrasekhar limit, which is based on a simplified star model, could exist without collapsing under their own weight. Either way, a subclass of supernovae governed by different physics could have a dramatic effect on the way cosmologists use them to measure the expansion of the universe.

"Supernovae are being used to make statements about the fate of the universe and our theory of gravity," Scalzo said. "If our understanding of supernovae changes, it could significantly impact of our theories and predictions."

Other Yale authors of the paper include Charles Baltay and David Rabinowitz.

Story Source:

Adapted from materials provided by Yale University.

Journal Reference:

1. Authors: R. A. Scalzo, G. Aldering, P. Antilogus, C. Aragon, S. Bailey, C. Bongard, C. Buton, M. Childress, N. Chotard, Y. Copin, H. K. Fakhouri, A. Gal-Yam, E. Gangler, S. Hoyer, M. Kasliwal, S. Loken, P. E. Nugent, R. Pain, E. Pecontal, R. Pereira, S. Perlmutter, D. Rabinowitz, A. Rau, G. Rigaudier, K. Runge, G. Smadja, C. Tao, R. C. Thomas, B. Weaver, C. Wu. Title: Nearby Supernova Factory Observations of SN 2007if: First Total Mass Measurement of a Super-Chandrasekhar-Mass Progenitor. Astrophysical Journal, 2010; (forthcoming) DOI: http://arxiv.org/abs/1003.2217

Super Supernova: SN 2007if Exceeds Chandrasekhar Limit

Until recently, it was thought that white dwarfs could not exceed what is known as the Chandrasekhar limit, a critical mass equaling about 1.4 times that of the Sun, before exploding in a supernova.

Since 2003, four supernovae have been discovered that were so bright, cosmologists wondered whether their white dwarfs had surpassed the Chandrasekhar limit, dubbed the "super-Chandrasekhar" supernovae.

Now, a team of astronomers has measured the mass of the white dwarf star that resulted in one of these rare supernovae, called SN 2007if, and confirmed that it has exceeded the Chandrasekhar limit. They also discovered that the unusually bright supernova had not only a central mass, but a shell of material that was ejected during the explosion as well as a surrounding envelope of pre-existing material. The team hopes this discovery will provide a structural model with which to understand the other supermassive supernovae.

Using observations from telescopes in Chile, Hawaii and California, astronomers were able to measure the mass of the central star, the shell and the envelope individually, providing the first conclusive evidence that the star system itself did indeed surpass the Chandrasekhar limit. They found that the star itself appears to have had a mass of 2.1 times the mass of the Sun (plus or minus 10 percent), putting it well above the limit.

Being able to measure masses for all parts of the star system tells the physicists about how the system may have evolved—a process that is currently poorly understood. "We don't really know much about the stars that lead to these supernovae," said Richard Scalzo, an astronomer at Yale. "We want to know more about what kind of stars they were, and how they formed and evolved over time."

There's a good chance, the team says, that SN 2007if resulted from the merging of two white dwarfs, rather than the explosion of a single white dwarf.

Theorists continue to explore how stars with masses above the Chandrasekhar limit, which is based on a simplified star model, could exist without collapsing under their own weight. Either way, a subclass of supernovae governed by different physics could have a dramatic effect on the way cosmologists use them to measure the expansion of the universe.

"Supernovae are being used to make statements about the fate of the universe and our theory of gravity," Scalzo said. "If our understanding of supernovae changes, it could significantly impact of our theories and predictions."

Citation: Scalzo et al., 'Nearby Supernova Factory Observations of SN 2007if: First Total Mass Measurement of a Super-Chandrasekhar-Mass Progenitor', Astrophysical Journal, 2010; doi: http://arxiv.org/abs/1003.2217

Explaining a Supernova That Shouldn't Have Existed

Regularly, when Earth-based telescopes surveying the skies take notice of a supernova explosion somewhere in the Universe, they record a tiny flash of light, which then shortly disappears, as the remnants of the star spread away from its core. The Nearby Supernova Factory survey, at the Palomar Observatory in California, detected in April 2007 such an explosion, but that followed a different pattern. Rather than fading back into obscurity, the light from this supernova event got more intense, until it became visible even to the human eye.

As this happened, astronomers started wondering how come this explosion could produce such massive amounts of energy. Approximately 77 days later, the incoming light reached its peak intensity, but the supernova continued to burn brightly even 200 days later. The spot on the sky where the explosion occurred finally became black after 555 days, in October 2008. This even lasted several tens of times longer than any previously recorded supernova flash, and researchers were puzzled as to why this happened. To further amplify the mystery, they also learned that the event shouldn't have happened in the first place.

In order for such a massive explosion to occur, the star that generated it should have been “impossibly massive.” The only explanation that astrophysicists could think of was that it belonged to the old Universe, a relic of a times long gone that was forgotten. A breakthrough was achieved when researchers started peering through 40-year-old journal entries, and discovered the concept of a “pair-instability” supernova. The more scientists at the Weizmann Institute of Science in Rehovot, Israel, compared the theory with observations of SN 2007bi, the weird event, the more they saw the resemblance.

The reason why nobody figured this out before was that pair-instability supernovae were only a theoretical supposition, with no actual observations on record. In massive stars, photons generated by the nuclear fusion of hydrogen push against the weight that heavy elements exert towards the core, preventing the star from collapsing on itself. When this balance is broken, the star implodes, creating a type II supernova. In the case of pair-instability supernovae, the massive stars need to be up to 200 times the mass of the Sun. Inside, the temperatures generated by nuclear fusion become so large, that photons begin to convert on their own in pairs of electrons, and their antimatter equivalent, positrons.

As this happens, the amount of photons counteracting the weight of the star decreases, until the balance is broken, and the core collapses, triggering an unbelievably massive explosion, such as the one produced by SN 2007bi, NewScientist reports.

Cosmic Protons Gone Wild

Supernova remnants act as giant, superefficient particle accelerators.

Credit: ESO/Eveline Helder et al./NASA/Chandra CXC

Shock waves launched into space by a supernova--the explosive death of a giant star--produce cosmic-ray particles carrying tremendous amounts of energy, astronomers have confirmed. The findings, reported today in Science, will give astronomers and physicists a better understanding of some of the universe's more bizarre phenomena.

Astronomers have suspected for more than a decade that supernova shock waves can act like giant particle accelerators. The basic idea is this: As the remnant of a dead star hurtles through space at up to 30 million kilometers per hour, it creates a shock wave as it interacts with the so-called interstellar medium (ISM). Protons in the shock wave get trapped by the magnetic field of the ISM, which bounces the protons back toward the remnant. But the remnant has its own magnetic field, which repels the protons.

Each bounce adds more energy, and eventually the magnetic tennis match accelerates the protons to nearly the speed of light. Knocked free of the remnant and out into deep space, some of the protons finally hit Earth's atmosphere. The particles are so energetic that astronauts have reported seeing flashes of light--caused by single protons striking their retinas--even when their eyes are closed.

Now an international team of astronomers has finally observed the acceleration of protons within a shock wave. Using the Very Large Telescope in Paranal, Chile, and NASA's Chandra spacecraft, they measured the visible light and x-ray emissions of the remnant of a supernova about 8200 light-years away in the direction of the constellation Circinus. These measurements, taken over several years, allowed them to calculate the energies of the protons behind and in front of the shock wave.

The results suggest that the remnant's energy accelerates protons as much as researchers had thought, says physicist and lead author Eveline Helder of Utrecht University in The Netherlands. "We did not expect such a high shock velocity," she says, referring to the speed of the protons in the shock wave. Based on that velocity, the team concludes that more than 50% of the energy of the shock wave must be going to accelerating the protons instead of generating heat.

It's an important paper, says physicist Donald Ellison of North Carolina State University in Raleigh. "It confirms predictions that shocks can be extremely efficient proton accelerators," he says, and it's going to improve understanding "of the physics of the universe's more exotic phenomenon," such as gamma-ray bursts and quasars, which also produce strong shock waves, as well as supernovae.

Read the whole article on Science NOW

Supernova Remnant Is An Unusual Suspect

The main graphic shows the area around SNR 0104 in infrared light from Spitzer (red and green) and X-rays from Chandra (purple). The inset shows a close-up of SNR 0104. (Credit: X-ray: NASA/CXC/PSU/S. Park and J. Lee; IR: NASA/JPL-Caltech)

ScienceDaily (June 14, 2009) — A new image from NASA's Chandra X-ray Observatory shows a supernova remnant with a different look. This object, known as SNR 0104-72.3 (SNR 0104 for short), is in the Small Magellanic Cloud, a small neighboring galaxy to the Milky Way. Astronomers think that SNR 0104 is the remains of a so-called Type Ia supernova caused by the thermonuclear explosion of a white dwarf.

In this composite made of X-rays from Chandra shown in purple and infrared data from Spitzer shown in green and red, SNR 0104 looks unlike other likely Type Ia remnants found in our own Galaxy. While objects such as the Kepler and Tycho supernova remnants appear circular, the shape of SNR 0104 in X-rays is not. Instead, the image is dominated by two bright lobes of emission (seen to the upper right and lower left). The large amount of iron in these lobes indicates that SNR 0104 was likely formed by a Type Ia supernova.

One possible explanation for this structure is that the explosion of the white dwarf itself was strongly asymmetrical and produced two jets of iron. Another possibility is that the complicated environment seen in the image is responsible. The green shells on the left and right side of SNR 0104 correspond to surrounding material that has been swept up by the explosion. So, the unusual shape of the remnant might be caused by a lack of material to the north and south of the star to interrupt the outward path of the stellar debris. This explanation, however, is still in question and scientists hope more data from Chandra and other telescopes will help settle the debate.

The presence of a nearby massive star and the shells of gas and dust seen in the wide-field view from Spitzer shows that SNR 0104 might be located within a star-forming region. This suggests that SNR 0104 may belong to a little-studied class of so-called "prompt" Type Ia supernovas caused by the demise of younger, more massive stars than average. Again, more data will be needed to test this theory.

This research was led by Sangwook Park and Jae-Joon Lee of Penn State University and was presented at the 214th meeting of the American Astronomical Society in Pasadena, California. NASA's Marshall Space Flight Center in Huntsville, Ala., manages the Chandra program for NASA's Science Mission Directorate in Washington. The Smithsonian Astrophysical Observatory controls Chandra's science and flight operations from Cambridge, Mass.

Source: http://www.sciencedaily.com/releases/2009/06/090609130800.htm

Junior-Sized Supernova Discovered by New York Teen

In November 2008, Caroline Moore, a 14-year-old student from upstate New York, discovered a supernova in a nearby galaxy, making her the youngest person ever to do so. Additional observations determined that the object, called SN 2008ha, is a new type of stellar explosion, 1000 times more powerful than a nova but 1000 times less powerful than a supernova. Astronomers say that it may be the weakest supernova ever seen.

Even though this explosion was a weakling compared to most supernovae, for a short time SN 2008ha was 25 million times brighter than the sun. However, since it is 70 million light years away, it appeared very faint viewed from Earth.

The peculiar object effectively bridged the gap between a nova (a nuclear explosion on the surface of an old, compact star called a white dwarf) and a type Ia supernova (the destructive death of a white dwarf caused by a runaway nuclear reaction starting deep in the star). SN 2008ha likely was a failed supernova where the explosion was unable to destroy the entire star.

“If a normal supernova is a nuclear bomb, then SN 2008ha is a bunker buster,” said team leader Ryan Foley, Clay fellow at the Harvard-Smithsonian Center for Astrophysics and first author on the paper reporting the findings. “From one perspective, this supernova was an underachiever, however you still wouldn’t want be anywhere near the star when it exploded.”

Caroline was able to discover the object using a relatively small telescope, but some of the most advanced telescopes in the world were needed to determine the nature of the explosion. Data came from the Magellan telescopes in Chile, the MMT telescope in Arizona, the Gemini and Keck telescopes in Hawaii, and NASA’s Swift satellite.

In typical supernova explosions, light from different chemical elements (such as calcium or iron) is smeared out across the electromagnetic spectrum by the Doppler effect (the same principle that makes a police siren change pitch as it passes). Because the ejected bits of the star were “only” moving at 4.5 million miles per hour (compared to 22 million miles per hour for a typical supernova), the light wasn’t as smeared out, allowing the team to analyze the composition of the explosion to a new precision.

“You can imagine many ways for a star to explode that might resemble SN 2008ha,” said Robert Kirshner of the Harvard-Smithsonian Center for Astrophysics. “It could have been a massive star suddenly collapsing to form a black hole, with very little energy leaking out. But it looks a lot like its brighter cousins, which we think are nuclear explosion of white dwarfs. Maybe this one was an explosion of that general type, just much, much weaker.”

One reason astronomers haven’t seen this type of explosion before might be because they are so faint. “SN 2008ha was a really wimpy explosion,” said Alex Filippenko, leader of the University of California, Berkeley supernova group, which monitors thousands of relatively nearby galaxies with a robotic telescope at Lick Observatory in California. But a new generation of telescopes and instruments is beginning to search greater distances than ever before, effectively monitoring millions of galaxies. Foley’s team concludes that hundreds of this type of event may be spotted in the next few years.

“Coincidentally, the youngest person to ever discover a supernova found one of the most peculiar and interesting supernovae ever,” remarked Filippenko. “This shows that no matter what your age, anyone can make a significant contribution to our understanding of the Universe.”

The paper has been accepted for publication in the Astronomical Journal and is available online at http://arxiv.org/abs/0902.2794.

Other coauthors of the paper are Ryan Chornock, Mohan Ganeshalingam, Weidong Li, Bradley Cenko, Maryam Modjaz, and Jeffrey Silverman of UC Berkeley, Peter Challis and Andrew Friedman of the Harvard-Smithsonian Center for Astrophysics, and Michael Wood-Vasey of the University of Pittsburgh. The research was supported in part by the National Science Foundation, the Sylvia and Jim Katzman Foundation, and the TABASGO Foundation.

Headquartered in Cambridge, Mass., the Harvard-Smithsonian Center for Astrophysics (CfA) is a joint collaboration between the Smithsonian Astrophysical Observatory and the Harvard College Observatory. CfA scientists, organized into six research divisions, study the origin, evolution and ultimate fate of the universe.