ALMA and ATCA Astronomers dissect the remnants of a supernova

Simulated still showing components of Supernova Remnant 1987A. 

Credit: The International Centre for Radio Astronomy Research (ICRAR)

In research published today in the Astrophysical Journal, an Australian led team of astronomers has used radio telescopes in Australia and Chile to see inside the remains of a supernova.

The supernova, known as SN1987A, was first seen by observers in the Southern Hemisphere in 1987 when a giant star suddenly exploded at the edge of a nearby dwarf galaxy called the Large Magellanic Cloud.

In the two and a half decades since then the remnant of Supernova 1987A has continued to be a focus for researchers the world over, providing a wealth of information about one of the Universe's most extreme events.

PhD Candidate Giovanna Zanardo at The University of Western Australia node of the International Centre for Radio Astronomy Research (ICRAR) led the team that used the Atacama Large Millimetre/submillimeter Array (ALMA) in Chile's Atacama Desert and the Australia Telescope Compact Array (ATCA) in New South Wales to observe the remnant at wavelengths spanning the radio to the far infrared.

"By combining observations from the two telescopes we've been able to distinguish radiation being emitted by the supernova's expanding shock wave from the radiation caused by dust forming in the inner regions of the remnant," said Zanardo.

A panel of images showing different views of Supernova 1987A. 

Left Panel: SNR1987A as seen by the Hubble Space Telescope in 2010. 

Middle Panel: SNR1987A as seen by the ATCA in New South Wales and the ALMA in Chile. 

Right Panel: A computer generated visualisation of the remnant showing the possible location of a Pulsar. 

Credit: ATCA & ALMA Observations & data - G. Zanardo et al. / HST Image: NASA, ESA, K. France (University of Colorado, Boulder), P. Challis and R. Kirshner (Harvard-Smithsonian Center for Astrophysics)

"This is important because it means we're able to separate out the different types of emission we're seeing and look for signs of a new object which may have formed when the star's core collapsed. It's like doing a forensic investigation into the death of a star."

"Our observations with the ATCA and ALMA radio telescopes have shown signs of something never seen before, located at the centre or the remnant. It could be a pulsar wind nebula, driven by the spinning neutron star, or pulsar, which astronomers have been searching for since 1987."

"It's amazing that only now, with large telescopes like ALMA and the upgraded ATCA, we can peek through the bulk of debris ejected when the star exploded and see what's hiding underneath."

More research published recently in the Astrophysical Journal also attempts to shine a light on another long-standing mystery surrounding the supernova remnant.

Since 1992 the radio emission from one side of the remnant has appeared 'brighter' than the other.

More information: 'Spectral and Morphological Analysis of the Remnant of Supernova 1987a with ALMA & ATCA' G. Zanardo, L. Staveley-Smith, R. Indebetouw et al. Astrophysical Journal November 10th, 2014: arxiv.org/abs/1409.7811 and iopscience.iop.org/0004-637X/796/2/82

'Multi-dimensional simulations of the expanding supernova remnant SN 1987a' T.M Potter, L Staveley-Smith, B. Reville et al. Astrophysical Journal October 20th, 20144: arxiv.org/abs/1409.4068 and iopscience.iop.org/0004-637X/794/2/174

Supernova iPTF13bvn: First evidence of a hydrogen-deficient supernova progenitor

An artist’s conception of a binary progenitor system of the supernova iPTF13bvn. 

Larger diameter but smaller mass (4 times mass of the Sun) helium star shown on the left is to explode. 

The companion star shown on the right is a hydrogen rich star and 30 times mass of the Sun. 

Credit: Kavli Institute for the Physics and Mathematics of the Universe

A group of researchers led by Melina Bersten of Kavli IPMU recently presented a model that provides the first characterization of the progenitor for a hydrogen-deficient supernova.

Their model predicts that a bright hot star, which is the binary companion to an exploding object, remains after the explosion.

To verify their theory, the group secured observation time with the Hubble Space Telescope (HST) to search for such a remaining star.

Their findings, which are reported in the October 2014 issue of The Astronomical Journal, have important implications for the evolution of massive stars.

For years astronomers have searched for the elusive progenitors of hydrogen-deficient stellar explosions without success.

However, this changed in June 2013 with the appearance of supernova iPTF13bvn and the subsequent detection of an object at the same location in archival images obtained before the explosion using the HST.

The interpretation of the observed object is controversial. The team led by Bersten presented a self-consistent picture using models of supernova brightness and progenitor evolution.

In their picture, the more massive star in a binary system explodes after transferring mass to its companion.

One of the challenges in astrophysics is identifying which star produces which supernova. This is particularly problematic for supernovae without hydrogen, which are called Types Ib or Ic, because the progenitors have yet to be detected directly.

However, the ultimate question is: "How do progenitor stars remove their hydrogen-rich envelopes during their evolution?"

Two competing mechanisms have been proposed. One hypothesizes that a strong wind produced by a very massive star blows the outer hydrogen layers, while the other suggests that a gravitationally bound binary companion star removes the outer layers.

The latter case does not require a very massive star. Because these two scenarios predict vastly different progenitor stars, direct detection of the progenitor for this type of supernova can provide definitive clues about the preferred evolutionary path.

When young Type Ib supernova iPTF13bvn was discovered in nearby spiral galaxy NGC 5806, astronomers hoped to find its progenitor.

Inspecting the available HST images did indeed reveal an object, providing optimism that the first hydrogen-free supernova progenitor would at last be identified.

Due to the object's blue hue, it was initially suggested that the object was a very hot, very massive, evolved star with a compact structure, called a "Wolf-Rayet" star.

NB: Using models of such stars, a group based in Geneva was able to reproduce the brightness and color of the pre-explosion object with a Wolf-Rayet star that was born with over 30 times the mass of the Sun and died with 11 times the solar mass.

Supernova iPTF13bvn discovered in nearby spiral galaxy NGC 5806. 

Credit: Jean Marie Llapasset

"Based on such suggestions, we decided to check if such a massive star is consistent with the supernova brightness evolution," says Melina Bersten.

However, the results are inconsistent with a Wolf-Rayet star; the exploding star must have been merely four times the mass of the Sun, which is much smaller than a Wolf-Rayet star.

"If the mass was this low and the supernova lacked hydrogen, our immediate conclusion is that the progenitor was part of a binary system," adds Bersten.

More information: The Astronomical Journal, 148:68 (6pp), 2014 October. DOI: 10.1088/0004-6256/148/4/68

Chandra & XMM-Newton Image: Detailed X-ray view of Puppis A supernova

The destructive results of a powerful supernova explosion reveal themselves in a delicate tapestry of X-ray light, as seen in this image from NASA’s Chandra X-Ray Observatory and the European Space Agency's XMM-Newton.

Image credit: NASA /CXC /IAFE /G.Dubner et al & ESA /XMM-Newton

The image shows the remains of a supernova that would have been witnessed on Earth about 3,700 years ago.

The remnant is called Puppis A, and is around 7,000 light years away and about 10 light years across.

This image provides the most complete and detailed X-ray view of Puppis A ever obtained, made by combining a mosaic of different Chandra and XMM-Newton observations.

Low-energy X-rays are shown in red, medium-energy X-rays are in green and high energy X-rays are coloured blue.

These observations act as a probe of the gas surrounding Puppis A, known as the interstellar medium.

The complex appearance of the remnant shows that Puppis A is expanding into an interstellar medium that probably has a knotty structure.

ESA XMM-Newton

Supernova explosions forge the heavy elements that can provide the raw material from which future generations of stars and planets will form.

Studying how supernova remnants expand into the galaxy and interact with other material provides critical clues into our own origins.

A paper describing these results was published in the July 2013 issue of Astronomy and Astrophysics and is available online.

The first author is Gloria Dubner from the Instituto de Astronomía y Física del Espacio in Buenos Aires in Argentina.

Hubble finds supernova companion star after two decades

This is an artist’s impression of supernova 1993J, which exploded in the galaxy M81. 

Using the Hubble Space Telescope, astronomers have identified the blue helium-burning companion star, seen at the center of the expanding nebula of debris from the supernova. 

Credit: NASA, ESA, G. Bacon (STScI)

Using NASA's Hubble Space Telescope, astronomers have discovered a companion star to a rare type of supernova.

The discovery confirms a long-held theory that the supernova, dubbed supernova 1993J, occurred inside what is called a binary system, where two interacting stars caused a cosmic explosion.

"This is like a crime scene, and we finally identified the robber," said Alex Filippenko, professor of astronomy at University of California (UC) at Berkeley.

"The companion star stole a bunch of hydrogen before the primary star exploded."

SN 1993J is an example of a Type IIb supernova, unusual stellar explosions that contains much less hydrogen than found in a typical supernova.

Astronomers believe the companion star took most of the hydrogen surrounding the exploding main star and continued to burn as a super-hot helium star.

"A binary system is likely required to lose the majority of the primary star's hydrogen envelope prior to the explosion."

"The problem is that, to date, direct observations of the predicted binary companion star have been difficult to obtain since it is so faint relative to the supernova itself," said lead researcher Ori Fox of UC Berkeley.

SN 1993J resides in the Messier M81 galaxy, about 11 million light-years away in the direction of Ursa Major, the Great Bear constellation.

Since its discovery 21 years ago, scientists have been looking for the companion star.

Observations at the W. M. Keck Observatory on Mauna Kea, Hawaii, suggested that the missing companion star radiated large amounts of ultraviolet (UV) light, but the area of the supernova was so crowded that scientists could not be sure they were measuring the right star.

The team combined optical light data and Hubble's UV light images to construct a spectrum that matched the predicted glow of a companion star, also known as the continuum emission. Scientists were only recently able to directly detect this light.

"We were able to get that UV spectrum with Hubble. This conclusively shows that you have an excess of continuum emission in the UV, even after the light from other stars has been subtracted," said Azalee Bostroem of the Space Telescope Science Institute (STScI) in Baltimore, Maryland.

Astronomers estimate a supernova occurs once every second somewhere in the universe, yet they don't fully understand how stars explode.

Further research will help astronomers better understand the properties of this companion star and the different types of supernovae.

The results of this study were published in the July 20 issue of the Astrophysical Journal.

More Information: "UNCOVERING THE PUTATIVE B-STAR BINARY COMPANION OF THE SN 1993J PROGENITOR" Authors: Ori D. Fox, K. Azalee Bostroem et al. - 2014 ApJ 790 17 doi:10.1088/0004-637X/790/1/17

Spectacular Type la supernova's mysteries revealed

Galaxy M82 in which the supernova exploded. 

Credit: NASA, ESA, & Hubble Heritage

New research by a team of UK and European-based astronomers is helping to solve the mystery of what caused a spectacular supernova in a galaxy 11 million light years away, seen earlier this year.

The supernova, a giant explosion of a star and the closest one to the Earth in decades, was discovered earlier this year by chance at the University of London Observatory.

These phenomena are extremely important to study because they provide key information about our universe, including how it is expanding and how galaxies evolve.

The new research into its cause, published in the latest issue of the Astrophysical Journal, used vast networks of radio telescopes in the UK and across Europe including the seven telescopes of e-MERLIN operated from The University of Manchester's Jodrell Bank Observatory.

These enabled them to obtain extremely deep images revealing a lack of radio emission from the supernova.

Known as 2014J, this was a Type la supernova caused by the explosion of a white dwarf star, the inner core of star once it has run out of nuclear fuel and ejected its outer layers.

A white dwarf star can explode if its mass increases to about 1.4x times that of the Sun. At this point its core temperature reaches the point where carbon starts to undergo nuclear fusion.

This spreads rapidly through the star resulting in a catastrophic thermonuclear explosion which rips the star apart, causing it to appear like a brilliant 'new star' shining billions of times brighter than the Sun.

For decades there has been a dispute about how this happens but these new results rule out the vast majority of models and show the merger of two white dwarf stars is by far the most likely cause.

The research was led by Miguel Pérez-Torres, researcher of the Spanish National Research Council who explained: "Supernovae play a fundamental role in the chemistry of galaxies and their evolution, as they are responsible for ejecting most of the heavy elements we see around us, including elements that cannot be formed in the interior of normal stars."

"A Nobel Prize was awarded in 2011 for the use of Type Ia supernovae to discover that the expansion of the Universe is accelerating. Yet, the basic question of what causes a Type Ia supernova was still a mystery".

Rob Beswick, a co-author of the research paper from the University of Manchester's Jodrell Bank Centre for Astrophysics added: "The explosion of a Type Ia supernova is a rare event in the nearby Universe."

"Supernova 2014J is the closest Type Ia supernova to Earth since 1986, and it's likely that more than a hundred years will pass until we see another such supernova so close to us."

"This was an amazing opportunity to learn more about these extremely important astrophysical phenomena and their underlying cause."

More information: "Constraints on the progenitor system and the environs of SN 2014J from deep radio observations" By M. A. Perez-Torres, P. Lundqvist, R. J. Beswick, C. I. Bjornsson, T. W. B. Muxlow, Z. Paragi, S. Ryder, A. Alberdi, C. Fransson, J. M. Marcaide, I. Marti-Vidal, E. Ros, M. K. Argo, J. C. Guirado are published in The Astrophysical Journal. iopscience.iop.org/0004-637X/792/1

NASA Chandra: Supernova SN 2014J Explosion

Image Credit: NASA/CXC/SAO/R.Margutti et al

New data from NASA’s Chandra X-ray Observatory has provided stringent constraints on the environment around one of the closest supernovas discovered in decades.

The Chandra results provide insight into possible cause of the explosion, as described in our press release.

On January 21, 2014, astronomers witnessed a supernova soon after it exploded in the Messier 82, or M82, galaxy.

Telescopes across the globe and in space turned their attention to study this newly exploded star, including Chandra.

Astronomers determined that this supernova, dubbed SN 2014J, belongs to a class of explosions called “Type Ia” supernovas.

These supernovas are used as cosmic distance-markers and played a key role in the discovery of the Universe’s accelerated expansion, which has been attributed to the effects of dark energy.

Scientists think that all Type Ia supernovas involve the detonation of a white dwarf.

One important question is whether the fuse on the explosion is lit when the white dwarf pulls too much material from a companion star like the Sun, or when two white dwarf stars merge.

This image contains Chandra data, where low, medium, and high-energy X-rays are red, green, and blue respectively.

Raffaella Margutti

The boxes in the bottom of the image show close-up views of the region around the supernova in data taken prior to the explosion (left), as well as data gathered on February 3, 2014, after the supernova went off (right).

The lack of the detection of X-rays detected by Chandra is an important clue for astronomers looking for the exact mechanism of how this star exploded.

The non-detection of X-rays reveals that the region around the site of the supernova explosion is relatively devoid of material.

This finding is a critical clue to the origin of the explosion. Astronomers expect that if a white dwarf exploded because it had been steadily collecting matter from a companion star prior to exploding, the mass transfer process would not be 100% efficient, and the white dwarf would be immersed in a cloud of gas.

If a significant amount of material were surrounding the doomed star, the blast wave generated by the supernova would have struck it by the time of the Chandra observation, producing a bright X-ray source.

Since they do not detect any X-rays, the researchers determined that the region around SN 2014J is exceptionally clean.

A viable candidate for the cause of SN 2014J must explain the relatively gas-free environment around the star prior to the explosion.

One possibility is the merger of two white dwarf stars, in which case there might have been little mass transfer and pollution of the environment before the explosion.

Another is that several smaller eruptions on the surface of the white dwarf cleared the region prior to the supernova.

Further observations a few hundred days after the explosion could shed light on the amount of gas in a larger volume, and help decide between these and other scenarios.

A paper describing these results was published in the July 20 issue of The Astrophysical Journal and is available online.

More Information: "No X-rays from the very nearby Type Ia SN2014J: constraints on its environment" The first author is Raffaella Margutti from the Harvard-Smithsonian Center for Astrophysics (CfA) in Cambridge, MA, and the co-authors are Jerod Parrent (CfA), Atish Kamble (CfA), Alicia Soderberg (CfA), Ryan Foley (University of Illinois at Urbana-Champaign), Dan Milisavljevic (CfA), Maria Drout (CfA), and Robert Kirshner (CfA). 

The source of the sky's X-ray glow

In findings that help astrophysicists understand our corner of the galaxy, an international research team has shown that the soft X-ray glow blanketing the sky comes from both inside and outside the solar system.

The source of this "diffuse X-ray background" has been debated for the past 50 years.

Does it originate from the solar wind colliding with interplanetary gases within our solar system?

Or is it born further away, in the "local hot bubble" of gas that a supernova is believed to have left in our galactic neighborhood about 10 million years ago?

The scientists found evidence that both mechanisms contribute, but the bulk of the X-rays come from the bubble.

The solar wind, a stream of charged particles continuously emitted by the sun, appears to be responsible for at most 40 percent of the radiation, according to new findings published in the journal Nature.

"The overarching science goal of our work is to try to answer questions like: What does the local astrophysical environment look like? And what is the environment in which the sun was born?" said Susan Lepri, an associate professor of atmospheric, oceanic and space sciences in the University of Michigan College of Engineering.

"It's part of trying to understand our place in the universe."

Lepri, who studies the physics of the sun, provided key measurements of the solar wind and its charge states.

"This is a significant discovery," said Massimiliano Galeazzi, associate chair in the Department of Physics in the College of Arts and Sciences at the University of Miami and principal investigator of the study.

"Specifically, the existence or nonexistence of the local bubble affects our understanding of the galaxy in the proximity to the sun and can be used as foundation for future models of the galaxy structure."

The findings confirm the existence of a local hot bubble, which had been previously debated.

The research team launched a research rocket into the upper atmosphere in 2012 to analyze the diffuse X-ray background. They focused on low-energy X-rays.

"At that low energy, the light gets absorbed by the neutral gas in our galaxy, so the fact that we observe it means that the source must be 'local,' possibly within a few hundred light-years from Earth," Galeazzi said.

"Until now it was unclear whether it comes from within the solar system (within few astronomical units from Earth), or a very hot bubble of gas in the solar neighbourhood (hundreds of light-years from Earth)."

That's like trying to decide if a bright light in the sky is from an airplane or a star, Lepri said.

The next phase of the mission is scheduled to launch in December 2015. The research team also included scientists from NASA, the University of Wisconsin, the University of Kansas, Johns Hopkins University and CNES in France.

More information: The origin of the local 1/4-keV X-ray flux in both charge exchange and a hot bubble. Nature. DOI: 10.1038/nature13525

ESA's XMM-Newton: Pulsar encased in a supernova bubble

Credit: ESA /XMM-Newton /L. Oskinova /M. Guerrero; CTIO /R. Gruendl / Y.H. Chu

Massive stars end their lives with a bang: exploding as spectacular supernovas, they release huge amounts of mass and energy into space.

These explosions sweep up any surrounding material, creating bubble remnants that expand into interstellar space.

At the heart of bubbles like these are small, dense neutron stars or black holes, the remains of what once shone brightly as a star.

Since supernova-carved bubbles shine for only a few tens of thousands of years before dissolving, it is rare to come across neutron stars or black holes that are still enclosed within their expanding shell.

Pulsar SXP 1062

This image captures such an unusual scene, featuring both a strongly magnetised, rotating neutron star – known as a pulsar – and its cosmic cloak, the remains of the explosion that generated it.

Small Magellanic Cloud

This pulsar, named SXP 1062, lies in the outskirts of the Small Magellanic Cloud, one of the satellite galaxies of our Milky Way galaxy.

It is an object known as an X-ray pulsar: it hungrily gobbles up material from a nearby companion star and burps off X-rays as it does so.

In the future, this scene may become even more dramatic, as SXP 1062 has a massive companion star that has not yet exploded as a supernova.

Most pulsars whirl around incredibly quickly, spinning many times per second.

However, by exploring the expanding bubble around this pulsar and estimating its age, astronomers have noticed something intriguing: SXP 1062 seems to be rotating far too slowly for its age. It is actually one of the slowest pulsars known.

While the cause of this weird sluggishness is still a mystery, one explanation may be that the pulsar has an unusually strong magnetic field, which would slow the rotation.

The diffuse blue glow at the centre of the bubble in this image represents X-ray emission from both the pulsar and the hot gas that fills the expanding bubble.

The other fuzzy blue objects visible in the background are extragalactic X-ray sources.

This image combines X-ray data from ESA's XMM-Newton (shown in blue) with optical observations from the Cerro Tololo Inter-American Observatory in Chile.

The optical data were obtained using two special filters that reveal the glow of oxygen (shown in green) and hydrogen (shown in red).

The size of the image is equivalent to a distance of 457 light-years on a side.

This image was first published in 2011.

More information: "Discovery of a Be/X-ray pulsar binary and associated supernova remnant in the Wing of the Small Magellanic Cloud." V. Hénault-Brunet, L. M. Oskinova, M. A. Guerrero, et al. Monthly Notices of the Royal Astronomical Society: Letters 420 (1) L13 (2012) DOI: 10.1111/j.1745-3933.2011.01183.x

Table-top supernova: Amplification of cosmic magnetic fields replicated

Astrophysicists have established that cosmic turbulence could have amplified magnetic fields to the strengths observed in interstellar space. 

"Magnetic fields are ubiquitous in the universe," said Don Lamb, the Robert A. Millikan Distinguished Service Professor in Astronomy & Astrophysics at the University of Chicago.

"We're pretty sure that the fields didn't exist at the beginning, at the Big Bang. So there's this fundamental question: how did magnetic fields arise?"

Helping to answer that question, which is of fundamental importance to understanding the universe, were millions of hours of supercomputer simulations at Argonne National Laboratory.

Lamb and his collaborators, led by scientists at the University of Oxford, report their findings in an article published in the June 1 issue of Nature Physics.

The paper describes experiments at the Vulcan laser facility of the United Kingdom's Rutherford Appleton Laboratory that recreates a supernova (exploding star) with beams 60,000 billion times more powerful than a laser pointer.

The research was inspired by the detection of magnetic fields in Cassiopeia A, a supernova remnant, which are approximately 100 times stronger than those in adjacent interstellar space.

Physics at multiple scales
"It may sound surprising that a tabletop laboratory experiment that fits inside an average room can be used to study astrophysical objects that are light years across," said Gianluca Gregori, professor of physics at Oxford.

"In reality, the laws of physics are the same everywhere, and physical processes can be scaled from one to the other in the same way that waves in a bucket are comparable to waves in the ocean. So our experiments can complement observations of events such as the Cassiopeia A supernova."

Making the advance possible was the extraordinarily close cooperation between Lamb's team at University of Chicago's Flash Center for Computational Science and Gregori's team of experimentalists.

"Because of the complexity of what's going on here, the simulations were absolutely vital to inferring exactly what's going on and therefore confirming that these mechanisms are happening and that they are behaving in the way that theory predicts," said Jena Meinecke, graduate student in physics at Oxford and lead author of the Nature Physics paper.

Magnetic fields range from quadrillionths of a gauss in the cosmic voids of the universe, to several microgauss in galaxies and galaxy clusters (ordinary refrigerator magnets have magnetic fields of approximately 50 gauss). Stars like the sun measure thousands of gauss.

Neutron stars, which are the extremely compact, burned out cores of dead stars, exhibit the largest magnetic fields of all, ones exceeding quadrillions of gauss.

In 2012, Gregori's team successfully created small magnetic fields, called "seed fields," in the laboratory via an often-invoked effect called the Biermann battery mechanism but how could seed fields grow to gigantic sizes in interstellar space?

Building on their earlier findings, Gregori and his collaborators at 11 institutions worldwide now have demonstrated the amplification of magnetic fields by turbulence.

In their experiment, the scientists focused laser beams onto a small carbon rod sitting in a chamber filled with a low-density gas.

The lasers, generating temperatures of a few million degrees, caused the rod to explode, creating a blast that expanded throughout the gas.

"The experiment demonstrated that as the blast of the explosion passes through the grid it becomes irregular and turbulent, just like the images from Cassiopeia," Gregori said.

More information: "Turbulent amplification of magnetic fields in laboratory laser-produced shock waves," by J. Meinecke and 26 others, Nature Physics, June 1, 2014. DOI: 10.1038/nphys2978

A 3-D model of stellar core collapse

A massive stellar core not quite managing to transition to a supernova explosion because of a small "kink" instability in its rotational axis. 

Credit: Philipp Mösta and Sherwood Richers

What happens when massive stars collapse? One potential result is a core-collapse supernova.

Astronomers can make observations of such events that tell us what is happening on the surface of a star when it explodes in a supernova, but it is considerably more difficult to know what is driving the process inside the star at its hot, dense core.

Philipp Mösta

Astrophysicists attempt to simulate these events based on the properties of different kinds of stars and knowledge of the fundamental interactions of mass and energy, hopefully providing astronomers with ready predictions that can be tested with observational data.

Christian Ott

In a recent publication, Caltech postdoctoral scholar Philipp Mösta and Christian Ott, professor of theoretical astrophysics, present a three-dimensional model of a rapidly rotating star with a strong magnetic field undergoing the process of collapse and explosion . . . or at least trying to.

Stars with a very rapid spin and a strong magnetic field are comparatively rare: no more than one in a hundred massive stars (those at least 10 times the mass of our sun) have these features.

According to Mösta and Ott's research, when these bodies undergo core collapse, small perturbations around its axis of rotation may inhibit the process that would ordinarily lead to a supernova explosion.

Previous models of the collapse of rapidly rotating magnetized stellar cores assumed perfect symmetry around the axis of rotation. In effect, these models were two-dimensional.

The models yielded the expectation that as these cores collapsed, the strong magnetic field combined with the rapid spin would squeeze the stellar material out into two narrow "jets" along the axis of symmetry, as shown at left.

Assuming perfect symmetry around the axis of rotation can be excused in part as a matter of simplifying the scenario so that it could be simulated on an ordinary computer rather than the kind of supercomputer that Mösta and Ott's three-dimensional simulations require: 20,000 processors to output 500 terabytes—over 500 trillion bytes—of data that represent only some 200 milliseconds in time.

But, says Ott, "Even working with paper and pencil, writing down equations and discussing them with other theoretical astrophysicists, we should have known that small perturbations can trigger an instability in the stellar core."

"Nothing in nature is perfect. As we learn from this model, even small asymmetries can have a dramatic effect on the process of stellar collapse and the subsequent supernova explosion."

More information: The paper, "Magnetorotational Core-collapse Supernovae in Three Dimensions," is available online: authors.library.caltech.edu/45202/1/2041-8205_785_2_L29.pdf

NASA Chandra Image: Companion star survives supernova blast

Credit X-ray: NASA /CXC /SAO /F.Seward et al; Optical: NOAO /CTIO /MCELS, DSS

When a massive star runs out fuel, it collapses and explodes as a supernova.

Although these explosions are extremely powerful, it is possible for a companion star to endure the blast.

A team of astronomers using NASA's Chandra X-ray Observatory and other telescopes has found evidence for one of these survivors.

This hardy star is in a stellar explosion's debris field, also called its supernova remnant, located in an HII region called DEM L241.

An HII region is created when the radiation from hot, young stars strips away the electrons from neutral hydrogen atoms (HI) to form clouds of ionized hydrogen (HII).

This HII region is located in the Large Magellanic Cloud, a small companion galaxy to the Milky Way.

A new composite image of DEM L241 contains Chandra data (purple) that outlines the supernova remnant.

The remnant remains hot and therefore X-ray bright for thousands of years after the original explosion occurred.

Also included in this image are optical data from the Magellanic Cloud Emission Line Survey (MCELS) taken from ground-based telescopes in Chile (yellow and cyan), which trace the HII emission produced by DEM L241.

Additional optical data from the Digitized Sky Survey (white) are also included, showing stars in the field.

R. Davies, K. Elliott, and J. Meaburn, whose last initials were combined to give the object the first half of its name, first mapped DEM L241 in 1976.

The recent data from Chandra revealed the presence of a point-like X-ray source at the same location as a young massive star within DEM L241's supernova remnant.

Astronomers can look at the details of the Chandra data to glean important clues about the nature of X-ray sources.

For example, how bright the X-rays are, how they change over time, and how they are distributed across the range of energy that Chandra observes.

In this case, the data suggest that the point-like source is one component of a binary star system.

In such a celestial pair, either a neutron star or black hole (formed when the star went supernova) is in orbit with a star much larger than our Sun.

As they orbit one another, the dense neutron star or black hole pulls material away its companion star through the wind of particles that flows away from its surface.

If this result is confirmed, DEM L241 would be only the third binary containing both a massive star and a neutron star or black hole ever found in the aftermath of a supernova.

More information: A paper describing these results is available online and was published in the November 10, 2012, issue of The Astrophysical Journal: dx.doi.org/10.1088/0004-637X/759/2/123

New improved view of supernova explosion and death throes

Three-dimensional turbulent mixing in a stratified burning oxygen shell which is four pressure scale heights deep. 

The yellow ashes of sulphur are being dredged up from the underlying orange core. 

The multi-scale structure of the turbulence is prominent. 

Entrained material is not particularly well mixed, but has features which trace the large scale advective flows in the convection zone. 

Also visible are smaller scale features, which are generated as the larger features become unstable, breaking apart to become part of the turbulent cascade. 

The white lines indicate the boundary of the computational domain. 

Credit: Arnett, Meakin and Viallet/AIP Advances

A powerful, new three-dimensional model provides fresh insight into the turbulent death throes of supernovas, whose final explosions outshine entire galaxies and populate the universe with elements that make life on Earth possible.

W. David Arnett

The model is the first to represent the start of a supernova collapse in three dimensions, said its developer, W. David Arnett, Regents Professor of Astrophysics at the University of Arizona, who developed the model with Casey Meakin and Nathan Smith at Arizona and Maxime Viallet of the Max-Planck Institut fur Astrophysik.

Described in the journal AIP Advances, it shows how the turbulent mixing of elements inside stars causes them to expand, contract, and spit out matter before they finally detonate.

Arnett, a pioneer in building models of physical processes inside stars, traces his fascination with turbulence to 1987A, the first supernova of 1987.

Located in a nearby galaxy, it was bright enough to see with the naked eye.

The star puzzled astronomers, Arnett recalled, because the material ejected by its explosion appeared to mix with material previously ejected from the star.

Existing models could not explain that. "Instead of going gently into that dark night, it is fighting. It is sputtering and spitting off material. This can take a year or two. There are small precursor events, several peaks, and then the big explosion.

"Perhaps what we need is a more sophisticated notion of what an explosion is, to explain what we are seeing," Arnett concludes.

More information: The article, "Chaos and turbulent nucleosynthesis prior to a supernova explosion" by David Arnett, Casey Meakin and Maxime Viallet appears in the journal AIP Advances (DOI: 10.1063/1.4867384). 

The article will be published online on March 18, 2014. dx.doi.org/10.1063/1.4867384

Critical mass not needed for Type Ia supernovae explosions

A global collaboration of astronomers searching for clues about dark energy, the mysterious force that is speeding up the expansion of the Universe, have uncovered new evidence about the nature of supernovae, finding many are lighter than scientists had expected.

The findings, from an international team from the Nearby Supernova Factory project, overturn previous understanding of white dwarf stars and raise new questions about how these stars explode.

"White dwarfs are dead stars, the corpses of stars that were once like our Sun.'

Richard Scalzo

'They won't explode on their own - they need another star to help blow them up," said ANU astronomer Dr Richard Scalzo, who led the latest research.

"We now know it's much easier to blow them up than we used to think."

A supernova is a star that explodes and shines much more brilliantly as it reaches the end of its life.

By studying "nearby" Type Ia (1a) supernovae - within a billion light years from earth - astronomers can then compare them with older and fainter supernovae even further out in space, allowing them to measure distances in the Universe.

Dr Scalzo said most of the supernovae his team studied had blown up well before dinosaurs walked on Earth.

He said astronomers had previously believed white dwarfs needed to be around 1.4 times the mass of the Sun before they could explode.

Using the University of Hawaii's 2.2-metre telescope, his team studied 19 Type Ia supernovae.

By carefully watching how quickly the supernovae faded away after their brightest point, and comparing to calculations made by computer, the team could then "weigh" each explosion to figure out the white dwarf's mass.

They were surprised to find that as many as half were well below the previously-assumed tipping point for an explosion.

That meant the life the dying stars led, and the cause of their violent deaths, also had to be totally different from what scientists once thought.

Brian Schmidt

Dr. Scalzo said the ultimate aim of the research was to better understand dark energy, for which the 2011 Nobel Prize in Physics was awarded to ANU professor Brian Schmidt, Adam Riess (Johns Hopkins University), and Saul Perlmutter (Lawrence Berkeley National Laboratory - LBNL).

"Brian Schmidt used type Ia supernovae to discover that dark energy exists," he said.

"We're now trying to understand what it is. This new information about how white dwarfs explode is a huge step forward towards that goal."

Cosmologist Greg Aldering, who leads the international Nearby Supernova Factory project in Berkeley, said: "This is a significant advance in furthering Type Ia supernovae as cosmological probes for the study of dark energy."

Dr Scalzo was previously based in the Nearby Supernova Factory headquarters at Lawrence Berkeley National Laboratory in California, and is a member of the ARC Centre of Excellence for All-sky Astrophysics (CAASTRO).

More Information: 'Type Ia supernova bolometric light curves and ejected mass estimates from the Nearby Supernova Factory' arXiv:1402.6842 [astro-ph.CO]

NuSTAR telescope takes observes core of supernova

Cassiopeia A is among the best-studied supernova remnants. 

This image blends data from NASA's Spitzer (red), Hubble (yellow), and Chandra (green and blue) observatories. 

Credit: NASA /JPL-Caltech /STScI /CXC /SAO

Astronomers have peered for the first time into the heart of an exploding star in the final minutes of its existence.

The feat by the high-energy X-ray satellite NuSTAR provides details of the physics of the core explosion inaccessible until now, says team member Steven Boggs of UC Berkeley.

NuSTAR mapped radioactive titanium in the Cassiopeia A supernova remnant, which has expanded outward and become visible from Earth since the central star exploded in 1671.

Astronomers for the first time have peered into the heart of an exploding star in the final minutes of its existence.

The feat is one of the primary goals of NASA's NuSTAR mission, launched in June 2012 to measure high-energy X-ray emissions from exploding stars, or supernovae, and black holes, including the massive black hole at the center of our Milky Way Galaxy.

The NuSTAR team reported in this week's issue of the journal Nature the first map of titanium thrown out from the core of a star that exploded in 1671.

That explosion produced the beautiful supernova remnant known as Cassiopeia A (Cas A).

The well-known supernova remnant has been photographed by many optical, infrared and X-ray telescopes in the past, but these revealed only how the star's debris collided in a shock wave with the surrounding gas and dust and heated it up.

NuSTAR has produced the first map of high-energy X-ray emissions from material created in the actual core of the exploding star: the radioactive isotope titanium-44, which was produced in the star's core as it collapsed to a neutron star or black hole.

The energy released in the core collapse supernova blew off the star's outer layers, and the debris from this explosion has been expanding outward ever since at 5,000 kilometers per second.

Steven Boggs

"This has been a holy grail observation for high energy astrophysics for decades," said coauthor and NuSTAR investigator Steven Boggs, UC Berkeley professor and chair of physics.

"For the first time we are able to image the radioactive emission in a supernova remnant, which lets us probe the fundamental physics of the nuclear explosion at the heart of the supernova like we have never been able to do before."

"Supernovae produce and eject into the cosmos most of the elements are important to life as we know it," said UC Berkeley professor of astronomy Alex Filippenko, who was not part of the NuSTAR team.

Alex Filippenko

"These results are exciting because for the first time we are getting information about the innards of these explosions, where the elements are actually produced."

Boggs says that the information will help astronomers build three-dimensional computer models of exploding stars, and eventually understand some of the mysterious characteristics of supernovae, such as jets of material ejected by some.

Previous observations of Cas A by the Chandra X-ray telescope, for example, showed jets of silicon emerging from the star.

Fiona Harrison

"Stars are spherical balls of gas, and so you might think that when they end their lives and explode, that explosion would look like a uniform ball expanding out with great power," said Fiona Harrison, the principal investigator of NuSTAR at the California Institute of Technology.

"Our new results show how the explosion's heart, or engine, is distorted, possibly because the inner regions literally slosh around before detonating."

More information: Study paper: dx.doi.org/10.1038/nature12997

Nearest supernova in 27 years explodes in M82 galaxy

Credit: UCL/University of London Observatory/Steve Fossey/Ben Cooke/Guy Pollack/Matthew Wilde/Thomas Wright

A supernova has been spotted in the constellation Ursa Major (between the Big and Little Dipper in the night sky) in the M82 galaxy (affectionately known as the cigar galaxy) by a team of students at University College London.

The discovery was posted on the (CBAT) Central Bureau's Transient Object Confirmation Page which led to follow-up observations by other teams around the world.

It's real, and not only is it bright enough for amateur astronomer's to view, but it's the closet known supernova explosion since 1987.

Initial study has revealed the supernova to be classified as 1a, the type described by astronomers as "standard candles" because their brightness is uniform enough to allow for using them to measure distances across the universe.

Sometimes they start out as a white dwarf, pulling in material from around them until they reach a critical mass and explode. Other times they are the result of two such stars (binaries) colliding.

What's perhaps most exciting about this newest observation is that it's so close (just 11.4 million light years from us) that it's likely that images of the star that exploded have been previously recorded by different telescopes around the globe which means scientists might be able to watch the process that led to the supernova occurring, something that has never been seen before.

If that turns out to be the case, other space researchers note, the stage could be set for allowing for reducing uncertainties in measuring dark energy—standard candle observations are the means by which such theories first came to exist after all.

Also, while the explosion has undoubtedly unleashed a torrent of neutrinos, its unlikely monitors here on Earth will notice much of an uptic in activity due to distance and them getting lost in other sources.

Because of the timing of the discovery, it appears that there is more to come—it's going to get brighter over the next few days before growing dimmer and dimmer, eventually fading to black.

That means that anyone wishing to observe a supernova as its happening can do so—likely a once in a lifetime opportunity. Binoculars should be enough, though a telescope would be much better.

Universe Today has published a map to help those looking find it.

More information: www.astronomerstelegram.org/ remanzacco.blogspot.nl/2014/