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

NASA Chandra X-Ray Image: The remarkable remnants of a recent supernova

Credit: X-ray (NASA/CXC/NCSU/K.Borkowski et al.); Optical (DSS)

Astronomers estimate that a star explodes as a supernova in our Galaxy, on average, about twice per century.

In 2008, a team of scientists announced they discovered the remains of a supernova that is the most recent, in Earth's time frame, known to have occurred in the Milky Way.

The explosion would have been visible from Earth a little more than a hundred years ago if it had not been heavily obscured by dust and gas.

Its likely location is about 28,000 light years from Earth near the center of the Milky Way.

A long observation equivalent to more than 11 days of observations of its debris field, now known as the supernova remnant G1.9+0.3, with NASA's Chandra X-ray Observatory is providing new details about this important event.

The source of G1.9+0.3 was most likely a white dwarf star that underwent a thermonuclear detonation and was destroyed after merging with another white dwarf, or pulling material from an orbiting companion star.

This is a particular class of supernova explosions (known as Type Ia) that are used as distance indicators in cosmology because they are so consistent in brightness and incredibly luminous.

The explosion ejected stellar debris at high velocities, creating the supernova remnant that is seen today by Chandra and other telescopes.

This new image is a composite from Chandra where low-energy X-rays are red, intermediate energies are green and higher-energy ones are blue.

Also shown are optical data from the Digitized Sky Survey, with appearing stars in white.

The new Chandra data, obtained in 2011, reveal that G1.9+0.3 has several remarkable properties.

The Chandra data show that most of the X-ray emission is "synchrotron radiation," produced by extremely energetic electrons accelerated in the rapidly expanding blast wave of the supernova.

This emission gives information about the origin of cosmic rays - energetic particles that constantly strike the Earth's atmosphere - but not much information about Type Ia supernovas.

In addition, some of the X-ray emission comes from elements produced in the supernova, providing clues to the nature of the explosion. The long Chandra observation was required to dig out those clues.

Most Type Ia supernova remnants are symmetrical in shape, with debris evenly distributed in all directions.

However, G1.9+0.3 exhibits an extremely asymmetric pattern. The strongest X-ray emission from elements like silicon, sulphur, and iron is found in the northern part of the remnant, giving an extremely asymmetric pattern.

More information: dx.doi.org/10.1088/2041-8205/771/1/L9

Remnants of Ancient Supernova Explosion found in Magnetotactic Bacteria

Back in 2004, German scientists discovered traces of supernova ejecta that had been deposited in the deep-sea ferromanganese crust of the pacific ocean. 

They dated the supernova event to 2.8 million years ago (Mya), using estimates from the decay of iron-60 radioisotope.

They were also able to estimate the distance of the supernova event to 10 parsecs (pc) from our sun, based on the amount of iron-60 deposited.

Prof Shawn Bishop

At the April 14th meeting of the American Physical Society (APS), another German scientist, Shawn Bishop, reported finding traces of iron-60 of supernova origin in the fossilized remains of a common bacteria.

By accurately dating the sediment cores in which the samples were found, Bishop appears to have discovered the first biological signature of an ancient supernova event, and may even be able to link it to a specific exploding star.

Bishop analyzed sample cores from strata roughly 100,000 years apart within deposits from 1.7 to 3.3 Mya. Iron-60 is not a product of any processes occurring here on earth, so any supply of it can be assumed to from a non-terrestrial source.

Bishop was able to extract out all the iron-60 of biological origin, and quantify it with a mass spectrometer.

The amounts found were small, but they were enough to reliably date the sample to a period around 2.2 Mya.

Other researchers, peripheral to the project, were then able to suggest a possible candidate star that dates to this period may lie in the Scorpius-Centaurus stellar association, roughly 130 pcs (424 light-years) from the sun.

More information: Abstract: X8.00002 : Search for Supernova 60Fe in the Earth's Fossil Record, Bulletin of the American Physical Society, meetings.aps.org/Meeting/APR13/Event/192798

Kepler Supernova: Crucial Cosmic Distance Markers

This is the remnant of Kepler's supernova, the famous explosion that was discovered by Johannes Kepler in 1604. 

The red, green and blue colors show low, intermediate and high energy X-rays observed with NASA's Chandra X-ray Observatory, and the star field is from the Digitized Sky Survey. 

Credit: X-ray: NASA/CXC/NCSU/M.Burkey et al; Optical: DSS

A new study using data from NASA's Chandra X-ray Observatory points to the origin of a famous supernova.

This supernova, discovered in 1604 by Johannes Kepler, belongs to an important class of objects that are used to measure the rate of expansion of the Universe.

Astronomers have used a very long Chandra observation of the remnant of Kepler’s supernova to deduce that the supernova was triggered by an interaction between a white dwarf and a red giant star.

This is significant because another study has already shown that a so-called Type Ia supernova caused the Kepler supernova remnant.

The thermonuclear explosion of a white dwarf star produces such supernovas. Because they explode with nearly uniform brightness, astronomers have used them as cosmic distance markers to track the accelerated expansion of the Universe.

However, there is an ongoing controversy about Type Ia supernovas. Are they caused by a white dwarf pulling so much material from a companion star that it becomes unstable and explodes? Or do they result from the merger of two white dwarfs?

Mary Burkey

"While we can't speak to all Type Ia supernovas, our evidence points to Kepler being caused by a white dwarf pulling material from a companion star, and not the merger of two white dwarfs," said the first author of the new Chandra study, Mary Burkey of North Carolina State University (NCSU).

"To continue improving distance measurements with these supernovas, it is crucial to understand how they are triggered."

The Kepler supernova remnant is one of only a few Type Ia supernovas known to have exploded in the Milky Way galaxy. Its proximity and its identifiable explosion date make it an excellent object to study.

Stephen Reynolds

“Johannes Kepler made such good naked-eye observations in 1604 that we can identify the supernova as Type Ia,” said co-author Stephen Reynolds, also of NCSU. “He would be thrilled that we can use today’s terrific instruments to reveal the hidden secrets of his supernova.”

The new Chandra images reveal a disk-shaped structure near the center of the remnant. The researchers interpret this X-ray emission to be caused by the collision between supernova debris and disk-shaped material that the giant star expelled before the explosion. Another possibility is that the structure is just debris from the explosion.

The evidence that this disk-shaped structure was left behind by the giant star is two-fold: first, a substantial amount of magnesium – an element not produced in great amounts in Type Ia supernovas – was found in the Kepler remnant. This suggests the magnesium came from the giant companion star.

Secondly, the disk structure seen by Chandra in X-rays bears a remarkable resemblance in both shape and location to one observed by the Spitzer Space Telescope.

These infrared-emitting disks are thought to be dusty bands expelled by stars in a wind, rather than material ejected in a supernova.

The researchers found a remarkably large and puzzling concentration of iron on one side of the center of the remnant but not the other.

Kazimierz Borkowski

The authors speculate that the cause of this asymmetry might be the "shadow" in iron that was cast by the companion star, which blocked the ejection of material.

Previously, theoretical work has suggested this shadowing is possible for Type Ia supernova remnants.

“One remaining challenge is to find the damaged and fast-moving leftovers of the giant star that was pummeled by the explosion at close quarters,” said co-author Kazimierz Borkowski, also of NCSU.

The above story is reprinted from materials provided by Chandra X-ray Observatory.

Remnants of Ancient Streambed Discovered on Mars

NASA's Curiosity rover found evidence for an ancient, flowing stream on Mars at a few sites, including the rock outcrop pictured here, which the science team has named "Hottah" after Hottah Lake in Canada's Northwest Territories.

It may look like a broken sidewalk, but this geological feature on Mars is actually exposed bedrock made up of smaller fragments cemented together, or what geologists call a sedimentary conglomerate.

Scientists theorize that the bedrock was disrupted in the past, giving it the titled angle, most likely via impacts from meteorites.

The key evidence for the ancient stream comes from the size and rounded shape of the gravel in and around the bedrock.

Hottah has pieces of gravel embedded in it, called clasts, up to a couple inches (few centimeters) in size and located within a matrix of sand-sized material.

Some of the clasts are round in shape, leading the science team to conclude they were transported by a vigorous flow of water. The grains are too large to have been moved by wind.

A close-up view of Hottah reveals more details of the outcrop. Broken surfaces of the outcrop have rounded, gravel clasts, such as the one circled in white, which is about 1.2 inches (3 centimeters) across.

Erosion of the outcrop results in gravel clasts that protrude from the outcrop and ultimately fall onto the ground, creating the gravel pile at left.

This image mosaic was taken by Curiosity's 100-millimeter Mastcam telephoto lens on its 39th Martian day, or sol, of the mission (Sept. 14, 2012 PDT/Sept. 15 GMT).

Image credit: NASA/JPL-Caltech/MSSS