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Tag: Cassiopeia A supernova remnant
From RIKEN [理研](JP): “Smoking-gun evidence for neutrinos’ role in supernova explosions”
A model for supernova explosions first proposed in the 1980s has received strong support from the observation by RIKEN astrophysicists of titanium-rich plumes emanating from a remnant of such an explosion [1].
Some supernova explosions are the death throes of stars that are at least eight times more massive than our Sun. They are one of the most cataclysmic events in the Universe, unleashing as much energy in a few seconds as the Sun will generate in 10 billion years.
In contrast, neutrinos are among the most ethereal of members of the elementary-particle zoo—they are at least 5 million times lighter than an electron and about 10 quadrillion of them flit through your body every second without interacting with it.
It’s hard to conceive that there could be any connection between supernovas and neutrinos, but a model advanced in the 1980s proposed that supernovas would not occur if it were not for the heating provided by neutrinos.
This type of supernova starts when the core of a massive star collapses into a neutron star—an incredibly dense star that is roughly 20 kilometers in diameter. The remainder of the star collapses under gravity, hits the neutron star, and rebounds off it, creating a shockwave.
However, many supernova models predict that this shockwave will fade before it can escape the star’s gravity. Factoring in heating generated by neutrinos ejected from the neutron star could provide the energy needed to sustain shockwaves and hence the supernova explosion.
Now, Shigehiro Nagataki at the RIKEN Astrophysical Big Bang Laboratory, Toshiki Sato, who was at the RIKEN Nishina Center for Accelerator-Based Science at the time of the study, and co-workers have found strong evidence supporting this model by detecting titanium and chromium in iron-rich plumes of a supernova remnant.
The neutrino-driven supernova model predicts that trapped neutrinos will generate plumes of high-entropy material, leading to bubbles in supernova remnants rich in metals such as titanium and chromium. That is exactly what Nagataki and his team saw in their spectral analysis based on observational data from the Chandra X-ray Observatory on Cassiopeia A (Fig. 1), a supernova remnant from about 350 years ago. This observation is thus strong confirmation that neutrinos play a role in driving supernova explosions.
“The chemical compositions we measured strongly suggest that these materials were driven by neutrino-driven winds from the surface of the neutron star,” says Nagataki. “Thus, the bubbles we found had been conveyed from the heart of the supernova to the outer rim of the supernova remnant.”
Nagataki’s team now intends to perform numerical simulations using supercomputers to model the process in more detail. “Our finding provides a strong impetus for revisiting the theory of supernova explosions,” Nagataki adds.
RIKEN [理研](JP) is Japan’s largest comprehensive research institution renowned for high-quality research in a diverse range of scientific disciplines. Founded in 1917 as a private research foundation in Tokyo, RIKEN has grown rapidly in size and scope, today encompassing a network of world-class research centers and institutes across Japan.
Riken (Institute of Physical and Chemical Research) [理研], formally Rikagaku Kenkyūjo (理化学研究所)(JP) (full name in Japanese Kokuritsu Kenkyū Kaihatsu Hōjin Rikagaku Kenkyūsho (国立研究開発法人理化学研究所) is a large scientific research institute in Japan. Founded in 1917, it now has about 3,000 scientists on seven campuses across Japan, including the main site at Wakō, Saitama Prefecture, just outside Tokyo. Riken is a Designated National Research and Development Institute, and was formerly an Independent Administrative Institution.
Riken conducts research in many areas of science including physics; chemistry; biology; genomics; medical science; engineering; high-performance computing and computational science and ranging from basic research to practical applications with 485 partners worldwide. It is almost entirely funded by the Japanese government, and its annual budget is about ¥88 billion (US$790 million).
Organizational structure:
The main divisions of Riken are listed here. Purely administrative divisions are omitted.
Headquarters (mostly in Wako)
Wako Branch
Center for Emergent Matter Science (research on new materials for reduced power consumption)
Center for Sustainable Resource Science (research toward a sustainable society)
Nishina Center for Accelerator-Based Science (site of the Radioactive Isotope Beam Factory, a heavy-ion accelerator complex)
Center for Brain Science
Center for Advanced Photonics (research on photonics including terahertz radiation)
Research Cluster for Innovation
Cluster for Pioneering Research (chief scientists)
Interdisciplinary Theoretical and Mathematical Sciences Program
Tokyo Branch
Center for Advanced Intelligence Project (research on artificial intelligence)
Tsukuba Branch
BioResource Research Center
Harima Institute
Riken SPring-8 Center (site of the SPring-8 synchrotron and the SACLA x-ray free electron laser)
Yokohama Branch (site of the Yokohama Nuclear magnetic resonance facility)
Center for Sustainable Resource Science
Center for Integrative Medical Sciences (research toward personalized medicine)
Center for Biosystems Dynamics Research (also based in Kobe and Osaka) [6]
Program for Drug Discovery and Medical Technology Platform
Structural Biology Laboratory
Sugiyama Laboratory
Kobe Branch
Center for Biosystems Dynamics Research (developmental biology and nuclear medicine medical imaging techniques)
Center for Computational Science (R-CCS, home of the K computer and The post-K (Fugaku) computer development plan)
Scientists have found fragments of titanium blasting out of a famous supernova. This discovery, made with NASA’s Chandra X-ray Observatory, could be a major step in pinpointing exactly how some giant stars explode.
This work is based on Chandra observations of the remains of a supernova called Cassiopeia A (Cas A), located in our galaxy about 11,000 light-years from Earth. This is one of the youngest known supernova remnants, with an age of about 350 years.
For years, scientists have struggled to understand how massive stars — those with masses over about 10 times that of the Sun — explode when they run out of fuel. This result provides an invaluable new clue.
“Scientists think most of the titanium that is used in our daily lives — such as in electronics or jewelry — is produced in a massive star’s explosion,” said Toshiki Sato of Rikkyo University [立教大学](JP), who led the study that appears in the journal Nature. “However, until now scientists have never been able to capture the moment just after stable titanium is made.”
When the nuclear power source of a massive star runs out, the center collapses under gravity and forms either a dense stellar core called a neutron star or, less often, a black hole. When a neutron star is created, the inside of the collapsing massive star bounces off the surface of the stellar core, reversing the implosion.
The heat from this cataclysmic event produces a shock wave — similar to a sonic boom from a supersonic jet — that races outwards through the rest of the doomed star, producing new elements by nuclear reactions as it goes. However, in many computer models of this process, energy is quickly lost and the shock wave’s journey outwards stalls, preventing the supernova explosion.
Recent three-dimensional computer simulations suggest that neutrinos — very low-mass subatomic particles — made in the creation of the neutron star play a crucial role in driving bubbles that speed away from the neutron star. These bubbles continue driving the shock wave forward to trigger the supernova explosion.
With the new study of Cas A, the team discovered powerful evidence for such a neutrino-driven explosion. In the Chandra data they found that finger-shaped structures pointing away from the explosion site contain titanium and chromium, coinciding with iron debris previously detected with Chandra. The conditions required for the creation of these elements in nuclear reactions, such as the temperature and density, match those of bubbles in simulations that drive the explosions.
The titanium that was found by Chandra in Cas A and that is predicted by these simulations is a stable isotope of the element, meaning that the number of neutrons its atoms contain implies that it does not change by radioactivity into a different, lighter element. Previously astronomers had used NASA’s NuSTAR telescope to discover an unstable isotope of titanium in different locations in Cas A. Every 60 years about half of this titanium isotope transforms into scandium and then calcium.
“We have never seen this signature of titanium bubbles in a supernova remnant before, a result that was only possible with Chandra’s incredibly sharp images,” said co-author Keiichi Maeda of Kyoto University [京都大学](JP). “Our result is an important step in solving the problem of how these stars explode as supernovae.”
“When the supernova happened, titanium fragments were produced deep inside the massive star. The fragments penetrated the surface of the massive star, forming the rim of the supernova remnant, Cas A,” said co-author Shigehiro Nagataki of the RIKEN Cluster for Pioneering Research [開拓研究本部 ](JP).
These results strongly support the idea of a neutrino-driven explosion to explain at least some supernovae.
“Our research could be the most important observational result probing the role of neutrinos in exploding massive stars since the detection of neutrinos from Supernova 1987A,” said co-author Takashi Yoshida of Kyoto University[京都大学](JP).
Astronomers used over a million and half seconds, or over 18 days, of Chandra observing time from the supernova Cassiopeia A (Cas A) taken between 2000 and 2018. The amount of stable titanium produced in Cas A exceeds the total mass of the Earth.
In 1976 the Chandra X-ray Observatory (called AXAF at the time) was proposed to National Aeronautics and Space Administration(US) by Riccardo Giacconi and Harvey Tananbaum. Preliminary work began the following year at NASA’s Marshall Space Flight Center(US) and the Harvard Smithsonian Center for Astrophysics(US) . In the meantime, in 1978, NASA launched the first imaging X-ray telescope, Einstein (HEAO-2), into orbit. Work continued on the AXAF project throughout the 1980s and 1990s. In 1992, to reduce costs, the spacecraft was redesigned. Four of the twelve planned mirrors were eliminated, as were two of the six scientific instruments. AXAF’s planned orbit was changed to an elliptical one, reaching one third of the way to the Moon’s at its farthest point. This eliminated the possibility of improvement or repair by the space shuttle but put the observatory above the Earth’s radiation belts for most of its orbit. AXAF was assembled and tested by TRW (now Northrop Grumman Aerospace Systems) in Redondo Beach, California.
AXAF was renamed Chandra as part of a contest held by NASA in 1998, which drew more than 6,000 submissions worldwide. The contest winners, Jatila van der Veen and Tyrel Johnson (then a high school teacher and high school student, respectively), suggested the name in honor of Nobel Prize–winning Indian-American astrophysicist Subrahmanyan Chandrasekhar. He is known for his work in determining the maximum mass of white dwarf stars, leading to greater understanding of high energy astronomical phenomena such as neutron stars and black holes. Fittingly, the name Chandra means “moon” in Sanskrit.
Originally scheduled to be launched in December 1998, the spacecraft was delayed several months, eventually being launched on July 23, 1999, at 04:31 UTC by Space Shuttle Columbia during STS-93. Chandra was deployed from Columbia at 11:47 UTC. The Inertial Upper Stage’s first stage motor ignited at 12:48 UTC, and after burning for 125 seconds and separating, the second stage ignited at 12:51 UTC and burned for 117 seconds. At 22,753 kilograms (50,162 lb), it was the heaviest payload ever launched by the shuttle, a consequence of the two-stage Inertial Upper Stage booster rocket system needed to transport the spacecraft to its high orbit.
Chandra has been returning data since the month after it launched. It is operated by the SAO at the Chandra X-ray Center in Cambridge, Massachusetts, with assistance from Massachusetts Institute of Technology(US) and Northrop Grumman Space Technology. The ACIS CCDs suffered particle damage during early radiation belt passages. To prevent further damage, the instrument is now removed from the telescope’s focal plane during passages.
Although Chandra was initially given an expected lifetime of 5 years, on September 4, 2001, NASA extended its lifetime to 10 years “based on the observatory’s outstanding results.” Physically Chandra could last much longer. A 2004 study performed at the Chandra X-ray Center indicated that the observatory could last at least 15 years.
On October 10, 2018, Chandra entered safe mode operations, due to a gyroscope glitch. NASA reported that all science instruments were safe. Within days, the 3-second error in data from one gyro was understood, and plans were made to return Chandra to full service. The gyroscope that experienced the glitch was placed in reserve and is otherwise healthy.
An optical image of the Horsehead Nebula [Barnard 33] in Orion, whose dust obscures the glowing gas behind it. Interstellar dust grains have long been thought to be produced in supernovae ejecta but grains can also be destroyed by supernovae. Astronomers have completed detailed new calculations of dust production and destruction using data on the Cassiopeia A supernova remnant. They conclude that under the right conditions supernovae can indeed be significant sources of interstellar dust.
NASA/ESA Hubble [below], and Nigel A. Sharp, National Optical Astronomy Observatory(US)/Association of Universities for Research in Astronomy(US)/National Science Foundation(US)
Dust grains in the interstellar medium are responsible for the dramatic shapes darkening the faces of bright nebulae, the Horsehead Nebula for example. The grains absorb ultraviolet and optical light, and when gathered in molecular clouds or other high density regions they block the background light from our view. About one percent of the mass of the interstellar medium is in the form of dust with the rest being gas, mostly hydrogen. Dust also plays important roles in the lifecycle of stars and galaxies. Dust and molecules cool the gas, facilitating the star-formation process. The grains assist in the formation of molecules as atoms in the gas become attached to their cold surfaces and then interact with one another; in the presence of ionizing radiation, the grains also shield the molecules from destruction. Not least, the dust radiates away thermal energy at infrared wavelengths, and luminous galaxies are often dominated by the infrared emitted by their radiation-heated dust.
Dust grains are made of elements produced in stars, especially silicon and carbon; moreover, their surfaces can be coated with layers of water ice or other kinds of frozen molecules. Dust is therefore a repository of elements in a galaxy and helps regulate their abundances and transport. In the first few billion years of the universe, and especially in the epoch when star formation was most active, all of these effects make the role of dust particularly important. Where does the dust come from? The cores of dust grains are known to form in the dense ejecta of supernovae and in the slow, dense winds from evolved giant stars. But grains can also be destroyed by radiation or hot gas, in particular by shocks and by grain–grain collisions, both also typically produced by supernovae. As a result, there has been a persistent uncertainty in the theory about an apparent imbalance between grain destruction and creation rates. One suggested solution proposed that accretion of gas onto pre-existing grain cores helps maintain the dust abundance, but the idea nonetheless requires that grain cores be injected at high enough rates.
CfA astronomer Jonathan Slavin led a group of astronomers investigating how much dust produced by supernovae can escape into the interstellar medium. They completed new hydrodynamic calculations of the evolution of dust grains based on observations of the Cassiopeia A supernova, located about eleven thousand light-years away.
They trace the grain evolution from the formation in dense ejecta through their experience of shocks and other destructive processes. They find that larger grains can survive (those with radii slightly smaller than a wavelength of light for silicate-composed grains, and half that for carbon-based grains) while even smaller ones are destroyed. Once these larger grains are ejected into the interstellar medium, their high velocities make them vulnerable to collisional destruction, but the scientists find that about 10%-20% of silicate grains survive (30-50% for carbon-based grains). They conclude that supernovae can indeed be significant contributors to the dust, with the supernova of a nineteen solar-mass star producing about one-tenth of a solar-mass of dust.
Founded in 1973 and headquartered in Cambridge, Massachusetts, the CfA leads a broad program of research in astronomy, astrophysics, Earth and space sciences, as well as science education. The CfA either leads or participates in the development and operations of more than fifteen ground- and space-based astronomical research observatories across the electromagnetic spectrum, including the forthcoming Giant Magellan Telescope(CL) and the Chandra X-ray Observatory(US), one of NASA’s Great Observatories.
Hosting more than 850 scientists, engineers, and support staff, the CfA is among the largest astronomical research institutes in the world. Its projects have included Nobel Prize-winning advances in cosmology and high energy astrophysics, the discovery of many exoplanets, and the first image of a black hole. The CfA also serves a major role in the global astrophysics research community: the CfA’s Astrophysics Data System(ADS)(US), for example, has been universally adopted as the world’s online database of astronomy and physics papers. Known for most of its history as the “Harvard-Smithsonian Center for Astrophysics”, the CfA rebranded in 2018 to its current name in an effort to reflect its unique status as a joint collaboration between Harvard University and the Smithsonian Institution. The CfA’s current Director (since 2004) is Charles R. Alcock, who succeeds Irwin I. Shapiro (Director from 1982 to 2004) and George B. Field (Director from 1973 to 1982).
The Center for Astrophysics | Harvard & Smithsonian is not formally an independent legal organization, but rather an institutional entity operated under a Memorandum of Understanding between Harvard University and the Smithsonian Institution. This collaboration was formalized on July 1, 1973, with the goal of coordinating the related research activities of the Harvard College Observatory (HCO) and the Smithsonian Astrophysical Observatory (SAO) under the leadership of a single Director, and housed within the same complex of buildings on the Harvard campus in Cambridge, Massachusetts. The CfA’s history is therefore also that of the two fully independent organizations that comprise it. With a combined lifetime of more than 300 years, HCO and SAO have been host to major milestones in astronomical history that predate the CfA’s founding.
History of the Smithsonian Astrophysical Observatory (SAO)
Samuel Pierpont Langley, the third Secretary of the Smithsonian, founded the Smithsonian Astrophysical Observatory on the south yard of the Smithsonian Castle (on the U.S. National Mall) on March 1,1890. The Astrophysical Observatory’s initial, primary purpose was to “record the amount and character of the Sun’s heat”. Charles Greeley Abbot was named SAO’s first director, and the observatory operated solar telescopes to take daily measurements of the Sun’s intensity in different regions of the optical electromagnetic spectrum. In doing so, the observatory enabled Abbot to make critical refinements to the Solar constant, as well as to serendipitously discover Solar variability. It is likely that SAO’s early history as a solar observatory was part of the inspiration behind the Smithsonian’s “sunburst” logo, designed in 1965 by Crimilda Pontes.
In 1955, the scientific headquarters of SAO moved from Washington, D.C. to Cambridge, Massachusetts to affiliate with the Harvard College Observatory (HCO). Fred Lawrence Whipple, then the chairman of the Harvard Astronomy Department, was named the new director of SAO. The collaborative relationship between SAO and HCO therefore predates the official creation of the CfA by 18 years. SAO’s move to Harvard’s campus also resulted in a rapid expansion of its research program. Following the launch of Sputnik (the world’s first human-made satellite) in 1957, SAO accepted a national challenge to create a worldwide satellite-tracking network, collaborating with the United States Air Force on Project Space Track.
With the creation of National Aeronautics and Space Administration(US) the following year and throughout the space race, SAO led major efforts in the development of orbiting observatories and large ground-based telescopes, laboratory and theoretical astrophysics, as well as the application of computers to astrophysical problems.
History of Harvard College Observatory (HCO)
Partly in response to renewed public interest in astronomy following the 1835 return of Halley’s Comet, the Harvard College Observatory was founded in 1839, when the Harvard Corporation appointed William Cranch Bond as an “Astronomical Observer to the University”. For its first four years of operation, the observatory was situated at the Dana-Palmer House (where Bond also resided) near Harvard Yard, and consisted of little more than three small telescopes and an astronomical clock. In his 1840 book recounting the history of the college, then Harvard President Josiah Quincy III noted that “…there is wanted a reflecting telescope equatorially mounted…”. This telescope, the 15-inch “Great Refractor”, opened seven years later (in 1847) at the top of Observatory Hill in Cambridge (where it still exists today, housed in the oldest of the CfA’s complex of buildings). The telescope was the largest in the United States from 1847 until 1867. William Bond and pioneer photographer John Adams Whipple used the Great Refractor to produce the first clear Daguerrotypes of the Moon (winning them an award at the 1851 Great Exhibition in London). Bond and his son, George Phillips Bond (the second Director of HCO), used it to discover Saturn’s 8th moon, Hyperion (which was also independently discovered by William Lassell).
Under the directorship of Edward Charles Pickering from 1877 to 1919, the observatory became the world’s major producer of stellar spectra and magnitudes, established an observing station in Peru, and applied mass-production methods to the analysis of data. It was during this time that HCO became host to a series of major discoveries in astronomical history, powered by the Observatory’s so-called “Computers” (women hired by Pickering as skilled workers to process astronomical data). These “Computers” included Williamina Fleming; Annie Jump Cannon; Henrietta Swan Leavitt; Florence Cushman; and Antonia Maury, all widely recognized today as major figures in scientific history. Henrietta Swan Leavitt, for example, discovered the so-called period-luminosity relation for Classical Cepheid variable stars, establishing the first major “standard candle” with which to measure the distance to galaxies. Now called “Leavitt’s Law”, the discovery is regarded as one of the most foundational and important in the history of astronomy; astronomers like Edwin Hubble, for example, would later use Leavitt’s Law to establish that the Universe is expanding, the primary piece of evidence for the Big Bang model.
Upon Pickering’s retirement in 1921, the Directorship of HCO fell to Harlow Shapley (a major participant in the so-called “Great Debate” of 1920). This era of the observatory was made famous by the work of Cecelia Payne-Gaposchkin, who became the first woman to earn a Ph.D. in astronomy from Radcliffe College (a short walk from the Observatory). Payne-Gapochkin’s 1925 thesis proposed that stars were composed primarily of hydrogen and helium, an idea thought ridiculous at the time. Between Shapley’s tenure and the formation of the CfA, the observatory was directed by Donald H. Menzel and then Leo Goldberg, both of whom maintained widely recognized programs in solar and stellar astrophysics. Menzel played a major role in encouraging the Smithsonian Astrophysical Observatory to move to Cambridge and collaborate more closely with HCO.
Joint history as the Center for Astrophysics (CfA)
The collaborative foundation for what would ultimately give rise to the Center for Astrophysics began with SAO’s move to Cambridge in 1955. Fred Whipple, who was already chair of the Harvard Astronomy Department (housed within HCO since 1931), was named SAO’s new director at the start of this new era; an early test of the model for a unified Directorship across HCO and SAO. The following 18 years would see the two independent entities merge ever closer together, operating effectively (but informally) as one large research center.
This joint relationship was formalized as the new Harvard–Smithsonian Center for Astrophysics on July 1, 1973. George B. Field, then affiliated with UC Berkeley(US), was appointed as its first Director. That same year, a new astronomical journal, the CfA Preprint Series was created, and a CfA/SAO instrument flying aboard Skylab discovered coronal holes on the Sun. The founding of the CfA also coincided with the birth of X-ray astronomy as a new, major field that was largely dominated by CfA scientists in its early years. Riccardo Giacconi, regarded as the “father of X-ray astronomy”, founded the High Energy Astrophysics Division within the new CfA by moving most of his research group (then at American Sciences and Engineering) to SAO in 1973. That group would later go on to launch the Einstein Observatory (the first imaging X-ray telescope) in 1976, and ultimately lead the proposals and development of what would become the Chandra X-ray Observatory. Chandra, the second of NASA’s Great Observatories and still the most powerful X-ray telescope in history, continues operations today as part of the CfA’s Chandra X-ray Center. Giacconi would later win the 2002 Nobel Prize in Physics for his foundational work in X-ray astronomy.
Shortly after the launch of the Einstein Observatory, the CfA’s Steven Weinberg won the 1979 Nobel Prize in Physics for his work on electroweak unification. The following decade saw the start of the landmark CfA Redshift Survey (the first attempt to map the large scale structure of the Universe), as well as the release of the Field Report, a highly influential Astronomy & Astrophysics Decadal Survey chaired by the outgoing CfA Director George Field. He would be replaced in 1982 by Irwin Shapiro, who during his tenure as Director (1982 to 2004) oversaw the expansion of the CfA’s observing facilities around the world, including the newly named Fred Lawrence Whipple Observatory(US), the Infrared Telescope (IRT) aboard the Space Shuttle, the 6.5-meter Multiple Mirror Telescope(US), the NASA SOHO satellite(US), and the launch of Chandra [above] in 1999.
CfA-led discoveries throughout this period include canonical work on Supernova 1987A, the “CfA2 Great Wall” (then the largest known coherent structure in the Universe), the best-yet evidence for supermassive black holes, and the first convincing evidence for an extrasolar planet.
The 1990s also saw the CfA unwittingly play a major role in the history of computer science and the internet: in 1990, SAO developed SAOImage, one of the world’s first X11-based applications made publicly available (its successor, DS9, remains the most widely used astronomical FITS image viewer worldwide). During this time, scientists at the CfA also began work on what would become the Astrophysics Data System (ADS), one of the world’s first online databases of research papers. By 1993, the ADS was running the first routine transatlantic queries between databases, a foundational aspect of the internet today.
The CfA Today
Research at the CfA
Charles Alcock, known for a number of major works related to massive compact halo objects, was named the third director of the CfA in 2004. Today Alcock overseas one of the largest and most productive astronomical institutes in the world, with more than 850 staff and an annual budget in excess of $100M. The Harvard Department of Astronomy, housed within the CfA, maintains a continual complement of approximately 60 Ph.D. students, more than 100 postdoctoral researchers, and roughly 25 undergraduate majors in astronomy and astrophysics from Harvard College. SAO, meanwhile, hosts a long-running and highly rated REU Summer Intern program as well as many visiting graduate students. The CfA estimates that roughly 10% of the professional astrophysics community in the United States spent at least a portion of their career or education there.
The CfA is either a lead or major partner in the operations of the Fred Lawrence Whipple Observatory, the Submillimeter Array, MMT Observatory, the South Pole Telescope, VERITAS, and a number of other smaller ground-based telescopes. The CfA’s 2019-2024 Strategic Plan includes the construction of the Giant Magellan Telescope as a driving priority for the Center.
CfA Submillimeter Array, Mauna Kea, Hawaii, USA, Altitude 4,080 m (13,390 ft).
Along with the Chandra X-ray Observatory, the CfA plays a central role in a number of space-based observing facilities, including the recently launched Parker Solar Probe, Kepler Space Telescope, the Solar Dynamics Observatory (SDO), and HINODE. The CfA, via the Smithsonian Astrophysical Observatory, recently played a major role in the Lynx X-ray Observatory, a NASA-Funded Large Mission Concept Study commissioned as part of the 2020 Decadal Survey on Astronomy and Astrophysics (“Astro2020”). If launched, Lynx would be the most powerful X-ray observatory constructed to date, enabling order-of-magnitude advances in capability over Chandra.
NASA Parker Solar Probe Plus named to honor Pioneering Physicist Eugene Parker.NASA/Kepler Telescope, and K2 March 7, 2009 until November 15, 2018.NASA/Solar Dynamics Observatory.JAXA/NASA HINODE spacecraft.
SAO is one of the 13 stakeholder institutes for the Event Horizon Telescope Board, and the CfA hosts its Array Operations Center. In 2019, the project revealed the first direct image of a black hole.
Messier 87*, The first image of the event horizon of a black hole. This is the supermassive black hole at the center of the galaxy Messier 87. Image via JPL/ Event Horizon Telescope Collaboration released on 10 April 2019.
The result is widely regarded as a triumph not only of observational radio astronomy, but of its intersection with theoretical astrophysics. Union of the observational and theoretical subfields of astrophysics has been a major focus of the CfA since its founding.
In 2018, the CfA rebranded, changing its official name to the “Center for Astrophysics | Harvard & Smithsonian” in an effort to reflect its unique status as a joint collaboration between Harvard University and the Smithsonian Institution. Today, the CfA receives roughly 70% of its funding from NASA, 22% from Smithsonian federal funds, and 4% from the National Science Foundation. The remaining 4% comes from contributors including the United States Department of Energy, the Annenberg Foundation, as well as other gifts and endowments.
Cassiopeia A is a supernova remnant in the constellation Cassiopeia. Credit: NASA/CXC/SAO.
Michigan State University researchers have discovered that one of the most important reactions in the universe can get a huge and unexpected boost inside exploding stars known as supernovae.
In the triple-alpha process, stars fuse three helium nuclei, also called alpha particles together (left) to create a single carbon atom with a surplus of energy, known as a Hoyle state. That Hoyle state can split back into three alpha particles or relax to the ground state of stable carbon by releasing a couple gamma rays (center). Inside supernovae, however, the creation of stable carbon can be enhanced with the help of extra protons (right). Credit: Facility for Rare Isotope Beams.
This finding also challenges ideas behind how some of the Earth’s heavy elements are made. In particular, it upends a theory explaining the planet’s unusually high amounts of some forms, or isotopes, of the elements ruthenium and molybdenum.
“It’s surprising,” said Luke Roberts, an assistant professor at the Facility for Rare Isotope Beams and the Department of Physics and Astronomy, at MSU. Roberts implemented the computer code that the team used to model the environment inside a supernova. “We certainly spent a lot of time making sure the results were correct.”
The results, published online on Dec. 2 in the journal Nature, show that the innermost regions of supernovae can forge carbon atoms over 10 times faster than previously thought. This carbon creation happens through a reaction known as the triple-alpha process.
“The triple-alpha reaction is, in many ways, the most important reaction. It defines our existence,” said Hendrik Schatz, one of Roberts’s collaborators. Schatz is a University Distinguished Professor in the Department of Physics and Astronomy and at the Facility for Rare Isotope Beams and the director of the Joint Institute for Nuclear Astrophysics – Center for the Evolution of the Elements, or JINA-CEE.
Nearly all of the atoms that make up the Earth and everything on it, people included, were forged in the stars. Fans of the late author and scientist Carl Sagan may remember his famous quote, “We’re all made of star stuff.” Perhaps no star stuff is more important to life on Earth than the carbon made in the cosmos by the triple-alpha process.
The process starts with alpha particles, which are the cores of helium atoms, or nuclei. Each alpha particle is made up of two protons and two neutrons.
In the triple-alpha process, stars fuse together three alpha particles, creating a new particle with six protons and six neutrons. This is the universe’s most common form of carbon. There are other isotopes made by other nuclear processes, but those make up just over 1% of Earth’s carbon atoms.
Still, fusing three alpha particles together is usually an inefficient process, Roberts said, unless there’s something helping it along. The Spartan team revealed that the innermost regions of supernovae can have such helpers floating around: excess protons. Thus, a supernova rich in protons can speed up the triple-alpha reaction.
But accelerating the triple-alpha reaction also puts the brakes on the supernova’s ability to make heavier elements on the periodic table, Roberts said. This is important because scientists have long believed that proton-rich supernovae created Earth’s surprising abundance of certain ruthenium and molybdenum isotopes, which contain closer to 100 protons and neutrons.
“You don’t make those isotopes in other places,” Roberts said.
But based on the new study, you probably don’t make them in proton-rich supernovae, either.
“What I find fascinating is that you now have to come up with another way to explain their existence. They should not be here with this abundance,” Schatz said of the isotopes. “It’s not easy to come up with alternatives.”
“It’s kind of a bummer in a way,” said the project’s originator, Sam Austin, an MSU Distinguished Professor Emeritus and former director of the National Superconducting Cyclotron Laboratory, FRIB’s predecessor. “We thought we knew it, but we don’t know it well enough.”
There are other ideas out there, the researchers added, but none that nuclear scientists find completely satisfying. Also, no existing theory includes this new discovery yet.
“Whatever comes up next, you have to consider the effects of an accelerated triple-alpha reaction. It’s an interesting puzzle,” Schatz said.
Although the team has no immediate solutions to that puzzle, the researchers said it will impact upcoming experiments at FRIB, which was recently designated as a U.S. Department of Energy Office of Science user facility.
Furthermore, MSU provides fertile ground for new theories to germinate. It’s home to the nation’s top-ranked graduate program for training the next generation of nuclear physicists. It’s also a core institution of JINA that’s promoting collaborations across nuclear physics and astrophysics like this one, which also included Shilun Jin. Jin worked on the project as an MSU postdoc and has since gone on to join the Chinese Academy of Sciences.
So, although Austin expressed a little disappointment that this result contradicts longstanding notions of element creation, he also knows it will fuel new science and a better understanding of the universe.
“Progress comes when there’s a contradiction,” he said.
“We love progress,” Schatz said. “Even when it’s destroying our favorite theory.”
This work was supported by the National Science Foundation and JINA-CEE, which is an NSF Physics Frontiers Center, and DOE’s Advanced Computing program. Additionally, Jin was supported by a postdoctoral fellowship furnished by MSU and the China Scholarship Council.
Michigan State University (MSU) is a public research university located in East Lansing, Michigan, United States. MSU was founded in 1855 and became the nation’s first land-grant institution under the Morrill Act of 1862, serving as a model for future land-grant universities.
MSU pioneered the studies of packaging, hospitality business, plant biology, supply chain management, and telecommunication. U.S. News & World Report ranks several MSU graduate programs in the nation’s top 10, including industrial and organizational psychology, osteopathic medicine, and veterinary medicine, and identifies its graduate programs in elementary education, secondary education, and nuclear physics as the best in the country. MSU has been labeled one of the “Public Ivies,” a publicly funded university considered as providing a quality of education comparable to those of the Ivy League.
Following the introduction of the Morrill Act, the college became coeducational and expanded its curriculum beyond agriculture. Today, MSU is the seventh-largest university in the United States (in terms of enrollment), with over 49,000 students and 2,950 faculty members. There are approximately 532,000 living MSU alumni worldwide.
Credit: X-ray: NASA/CXC/RIKEN/T. Sato et al.; Optical: NASA/STScI
Located about 11,000 light-years from Earth, Cas A (as it’s nicknamed) is the glowing debris field left behind after a massive star exploded. When the star ran out of fuel, it collapsed onto itself and blew up as a supernova, possibly briefly becoming one of the brightest objects in the sky. (Although astronomers think that this happened around the year 1680, there are no verifiable historical records to confirm this.)
The shock waves generated by this blast supercharged the stellar wreckage and its environment, making the debris glow brightly in many types of light, particularly X-rays. Shortly after Chandra was launched aboard the Space Shuttle Columbia on July 23, 1999, astronomers directed the observatory to point toward Cas A. It was featured in Chandra’s official “First Light” image, released Aug. 26, 1999, and marked a seminal moment not just for the observatory, but for the field of X-ray astronomy. Near the center of the intricate pattern of the expanding debris from the shattered star, the image revealed, for the first time, a dense object called a neutron star that the supernova left behind.
Since then, Chandra has repeatedly returned to Cas A to learn more about this important object. A new video shows the evolution of Cas A over time, enabling viewers to watch as incredibly hot gas — about 20 million degrees Fahrenheit — in the remnant expands outward. These X-ray data have been combined with data from another of NASA’s “Great Observatories,” the Hubble Space Telescope, showing delicate filamentary structures of cooler gases with temperatures of about 20,000 degrees Fahrenheit. Hubble data from a single time period are shown to emphasize the changes in the Chandra data.
The video shows Chandra observations of Cas A from 2000 to 2013. In that time, a child could enter kindergarten and graduate from high school. While the transformation might not be as apparent as that of a student over the same period, it is remarkable to watch a cosmic object change on human time scales.
The blue, outer region of Cas A shows the expanding blast wave of the explosion. The blast wave is composed of shock waves, similar to the sonic booms generated by a supersonic aircraft. These expanding shock waves produce X-ray emission and are sites where particles are being accelerated to energies that reach about two times higher than the most powerful accelerator on Earth, the Large Hadron Collider. As the blast wave travels outwards at speeds of about 11 million miles per hour, it encounters surrounding material and slows down, generating a second shock wave – called a “reverse shock” – that travels backwards, similar to how a traffic jam travels backwards from the scene of an accident on a highway.
These reverse shocks are usually observed to be faint and much slower moving than the blast wave. However, a team of astronomers led by Toshiki Sato from RIKEN in Saitama, Japan, and NASA’s Goddard Space Flight Center, have reported reverse shocks in Cas A that appear bright and fast moving, with speeds between about 5 and 9 million miles per hour. These unusual reverse shocks are likely caused by the blast wave encountering clumps of material surrounding the remnant, as Sato and team discuss in their 2018 study. This causes the blast wave to slow down more quickly, which re-energizes the reverse shock, making it brighter and faster. Particles are also accelerated to colossal energies by these inward moving shocks, reaching about 30 times the energies of the LHC.
Cassiopeia A in X-ray and optical light.
This recent study of Cas A adds to a long collection of Chandra discoveries over the course of the telescope’s 20 years. In addition to finding the central neutron star, Chandra data have revealed the distribution of elements essential for life ejected by the explosion (shown above), have constructed a remarkable three dimensional model of the supernova remnant, and much more.
Scientists also created a historical record in optical light of Cas A using photographic plates from the Palomar Observatory in California from 1951 and 1989 that had been digitized by the Digitized Access to a Sky Century @ Harvard (DASCH) program, located at the Center for Astrophysics | Harvard & Smithsonian (CfA). These were combined with images taken by the Hubble Space Telescope between 2000 and 2011. This long-term look at Cas A allowed astronomers Dan Patnaude of CfA and Robert Fesen of Dartmouth College to learn more about the physics of the explosion and the resulting remnant from both the X-ray and optical data.
Team uses detailed data to create a virtual-reality display of what’s left after explosion.
Cassiopeia A, the youngest known supernova remnant in the Milky Way, is the remains of a star that exploded almost 400 years ago. The star was approximately 15 to 20 times the mass of our sun and sat in the Cassiopeia constellation, almost 11,000 light-years from earth.
Though stunningly distant, it’s now possible to step inside a virtual-reality (VR) depiction of what followed that explosion.
Wearing VR goggles Kim Arcand views a 3-D representation of the Cassiopeia A supernova remnant, pictured above, at the YURT VR Cave at Brown.
A team led by Kimberly Kowal Arcand from the Harvard-Smithsonian Center for Astrophysics (CfA) and the Center for Computation and Visualization at Brown University has made it possible for astronomers, astrophysicists, space enthusiasts, and the simply curious to experience what it’s like inside a dead star. Their efforts are described in a recent paper in Communicating Astronomy with the Public.
The VR project — believed to be the first of its kind, using X-ray data from NASA’s Chandra X-ray Observatory mission (which is headquartered at CfA), infrared data from the Spitzer Space Telescope, and optical data from other telescopes — adds new layers of understanding to one of the most famous and widely studied objects in the sky.
“Our universe is dynamic and 3-D, but we don’t get that when we are constantly looking at things” in two dimensions, said Arcand, the visualization lead at CfA.
The project builds on previous research done on Cas A, as it’s commonly known, that first rendered the dead star into a 3-D model using the X-ray and optical data from multiple telescopes.
Cassiopeia A
Arcand and her team used that data to convert the model into a VR experience by using MinVR and VTK, two data visualization platforms. The coding work was primarily handled by Brown computer science senior Elaine Jiang, a co-author on the paper.
The VR experience lets users walk inside a colorful digital rendering of the stellar explosion and engage with parts of it while reading short captions identifying the materials they see.
“Astronomers have long studied supernova remnants to better understand exactly how stars produce and disseminate many of the elements observed on Earth and in the cosmos at large,” Arcand said.
When stars explode, they expel all of their elements into the universe. In essence, they help create the elements of life, from the iron in our blood to the calcium in our bones. All of that, researchers believe, comes from previous generations of exploded stars.
In the 3-D model of Cas A, and now in the VR model, elements such as iron, silicon, and sulfur are represented by different colors. Seeing it in 3-D throws Cas A into fresh perspective, even for longtime researchers and astronomers who build models of supernova explosions.
“The first time I ever walked inside the same data set that I have been staring at for 20 years, I just immediately was fascinated by things I had never noticed, like how various bits of the iron were in different locations,” Arcand said. “The ability to look at something in three dimensions and being immersed in it just kind of opened up my eyes to think about it in different ways.”
The VR platforms also opens understanding of the supernova remnant, which is the strongest radio source beyond our solar system, to new audiences. VR versions of Cas A are available by request for a VR cave (a specially made room in which the floors and walls are projection screens), as well as on Oculus Rift, a VR computer platform. As part of this project, the team also created a version that works with Google Cardboard or similar smartphone platforms. In a separate but related project, Arcand and a team from CfA worked with the Smithsonian Learning Lab to create a browser-based, interactive, 3-D application and 360-degree video of Cas A that works with Google Cardboard and similar platforms.
“My whole career has been looking at data and how we take data and make it accessible or visualize it in a way that adds meaning to it that’s still scientific,” Arcand said.
VR is an almost perfect avenue for this approach, since it has been surging in popularity as both entertainment and an educational tool. It has been used to help medical staff prepare for surgeries, for example, and video game companies have used it to add excitement and immersion to popular games.
Arcand hopes to make Cas A accessible to even more people, such as the visually impaired, by adding sound elements to the colors in the model.
Reaction to the VR experience has been overwhelmingly positive, Arcand said. Experts and non-experts alike are hit by what Arcand calls “awe moments” of being inside and learning about something so massive and far away.
“Who doesn’t want to walk inside a dead star?” Arcand said.
Harvard University is the oldest institution of higher education in the United States, established in 1636 by vote of the Great and General Court of the Massachusetts Bay Colony. It was named after the College’s first benefactor, the young minister John Harvard of Charlestown, who upon his death in 1638 left his library and half his estate to the institution. A statue of John Harvard stands today in front of University Hall in Harvard Yard, and is perhaps the University’s best known landmark.
Harvard University has 12 degree-granting Schools in addition to the Radcliffe Institute for Advanced Study. The University has grown from nine students with a single master to an enrollment of more than 20,000 degree candidates including undergraduate, graduate, and professional students. There are more than 360,000 living alumni in the U.S. and over 190 other countries.
Where do most of the elements essential for life on Earth come from? The answer: inside the furnaces of stars and the explosions that mark the end of some stars’ lives.
Astronomers have long studied exploded stars and their remains — known as “supernova remnants” — to better understand exactly how stars produce and then disseminate many of the elements observed on Earth, and in the cosmos at large.
Due to its unique evolutionary status, Cassiopeia A (Cas A) is one of the most intensely studied of these supernova remnants. A new image from NASA’s Chandra X-ray Observatory shows the location of different elements in the remains of the explosion: silicon (red), sulfur (yellow), calcium (green) and iron (purple). Each of these elements produces X-rays within narrow energy ranges, allowing maps of their location to be created. The blast wave from the explosion is seen as the blue outer ring.
X-ray telescopes such as Chandra are important to study supernova remnants and the elements they produce because these events generate extremely high temperatures — millions of degrees — even thousands of years after the explosion. This means that many supernova remnants, including Cas A, glow most strongly at X-ray wavelengths that are undetectable with other types of telescopes.
Chandra’s sharp X-ray vision allows astronomers to gather detailed information about the elements that objects like Cas A produce. For example, they are not only able to identify many of the elements that are present, but how much of each are being expelled into interstellar space.
The Chandra data indicate that the supernova that produced Cas A has churned out prodigious amounts of key cosmic ingredients. Cas A has dispersed about 10,000 Earth masses worth of sulfur alone, and about 20,000 Earth masses of silicon. The iron in Cas A has the mass of about 70,000 times that of the Earth, and astronomers detect a whopping one million Earth masses worth of oxygen being ejected into space from Cas A, equivalent to about three times the mass of the Sun. (Even though oxygen is the most abundant element in Cas A, its X-ray emission is spread across a wide range of energies and cannot be isolated in this image, unlike with the other elements that are shown.)
Astronomers have found other elements in Cas A in addition to the ones shown in this new Chandra image. Carbon, nitrogen, phosphorus and hydrogen have also been detected using various telescopes that observe different parts of the electromagnetic spectrum. Combined with the detection of oxygen, this means all of the elements needed to make DNA, the molecule that carries genetic information, are found in Cas A.
Periodic Table of Elements. Credit: NASA/CXC/K. Divona
Oxygen is the most abundant element in the human body (about 65% by mass), calcium helps form and maintain healthy bones and teeth, and iron is a vital part of red blood cells that carry oxygen through the body. All of the oxygen in the Solar System comes from exploding massive stars. About half of the calcium and about 40% of the iron also come from these explosions, with the balance of these elements being supplied by explosions of smaller mass, white dwarf stars.
While the exact date is not confirmed , many experts think that the stellar explosion that created Cas A occurred around the year 1680 in Earth’s timeframe. Astronomers estimate that the doomed star was about five times the mass of the Sun just before it exploded. The star is estimated to have started its life with a mass about 16 times that of the Sun, and lost roughly two-thirds of this mass in a vigorous wind blowing off the star several hundred thousand years before the explosion.
Earlier in its lifetime, the star began fusing hydrogen and helium in its core into heavier elements through the process known as “nucleosynthesis.” The energy made by the fusion of heavier and heavier elements balanced the star against the force of gravity. These reactions continued until they formed iron in the core of the star. At this point, further nucleosynthesis would consume rather than produce energy, so gravity then caused the star to implode and form a dense stellar core known as a neutron star.
Pre-Supernova Star: As it nears the end of its evolution, heavy elements produced by nuclear fusion inside the star are concentrated toward the center of the star. Illustration Credit: NASA/CXC/S. Lee
The exact means by which a massive explosion is produced after the implosion is complicated, and a subject of intense study, but eventually the infalling material outside the neutron star was transformed by further nuclear reactions as it was expelled outward by the supernova explosion.
Chandra has repeatedly observed Cas A since the telescope was launched into space in 1999. The different datasets have revealed new information about the neutron star in Cas A, the details of the explosion, and specifics of how the debris is ejected into space.
June 26, 2017
Dr. Hans-Thomas Janka
Max Planck Institute for Astrophysics, Garching
Phone:+49 89 30000-2228
Fax:+49 89 30000-2235
thj@mpa-garching.mpg.de
Dr. Hannelore Hämmerle
Max Planck Institute for Astrophysics, Garching
Phone:+49 89 30000-3980
hhaemmerle@mpa-garching.mpg.de
Radioactive elements in gaseous supernova remnant Cassiopeia A provide glimpses into the explosion of massive stars.
Cassiopeia A. NASA/CXC/SAO
NASA/Chandra Telescope
Stars exploding as supernovae are the main sources of heavy chemical elements in the Universe. In these star explosions, radioactive atomic nuclei are synthesized in the hot, innermost regions during the explosion and can thus provide insights into the unobservable physical processes that initiate the blast. Using elaborate computer simulations, a team of researchers from the Max Planck Institute for Astrophysics (MPA) and the research institute RIKEN in Japan were able to explain the recently measured spatial distributions of radioactive titanium and nickel in Cassiopeia A, a roughly 340 year old gaseous remnant of a nearby supernova.
RIKEN campus
The computer models yield strong support for the theoretical idea that such stellar death events can be initiated and powered by neutrinos escaping from the neutron star left behind at the origin of the explosion.
Massive stars end their lives in gigantic explosions, so-called supernovae. Within millions of years of stable evolution, these stars have built up a central core composed of mostly iron. When the core reaches about 1.5 times the mass of the Sun, it collapses under the influence of its own gravity and forms a neutron star. Enormous amounts of energy are released in this catastrophic event, mostly by the emission of neutrinos. These nearly massless elementary particles are abundantly produced in the interior of the new-born neutron star, where the density is higher than in atomic nuclei and the temperature can reach 500 billion degrees Kelvin.
The physical processes that trigger and drive the explosion have been an unsolved puzzle for more than 50 years. One of the theoretical mechanisms proposed invokes the neutrinos, because they carry away more than hundred times the energy needed for a typical supernova. Leaking out from the hot interior of the neutron star, a small fraction of the neutrinos are absorbed in the surrounding gas. This heating causes violent motions of the gas, similar to those in a pot of boiling water on a stove. When the bubbling of the gas becomes sufficiently powerful, the supernova explosion sets in as if the lid of the pot were blown off. The outer layers of the dying star are expelled into circumstellar space, and with them all the chemical elements that the star has assembled by nuclear burning during its life. But also new elements are created in the hot ejecta of the explosion, among them radioactive species such as 44Ti (titanium with 22 protons and 22 neutrons in its atomic nuclei) and 56Ni (28/28 neutrons/protons), which decay to stable calcium and iron, respectively. The thus released radioactive energy makes a supernova shine bright for years.
Because of the wild boiling of the neutrino-heated gas, the blast wave starts out non-spherically and imprints a large-scale asymmetry on the ejected stellar matter and the supernova as a whole, in agreement with the observation of clumpiness and asymmetries in many supernovae and their gaseous remnants. The initial asymmetry of the explosion has two immediate consequences. On the one hand, the neutron star receives a recoil momentum opposite to the direction of the stronger explosion, where the supernova gas is expelled with more violence. This effect is similar to the kick a rowing boat receives when a passenger jumps off. On the other hand, the production of heavy elements from silicon to iron, in particular also of 44Ti and 56Ni, is more efficient in directions where the explosion is stronger and where more matter is heated to high temperatures. “We have predicted both effects some years ago by our three-dimensional (3D) simulations of neutrino-driven supernova explosions”, says Annop Wongwathanarat, researcher at RIKEN and lead author of the corresponding publication of 2013, at which time he worked at MPA in collaboration with his co-authors H.-Thomas Janka and Ewald Müller. “The asymmetry of the radioactive ejecta is more pronounced the larger the neutron star kick is”, he adds. Since the radioactive atomic nuclei are synthesized in the innermost regions of the supernova, in the very close vicinity of the neutron star, their spatial distribution reflects explosion asymmetries most directly.
New observations of Cassiopeia A (Cas A), the gaseous remnant of a supernova whose light reached the Earth around the year 1680, could meanwhile confirm this theoretical prediction. Because of its young age and relative proximity at a distance of just 11,000 light years, Cas A offers two great advantages for the measurements. First, the radioactive decay of 44Ti is still an efficient energy source, and the presence of this atomic nucleus can therefore be mapped in 3D with high precision in the whole remnant by detecting the high-energy X-ray radiation from the radioactive decays. Second, also the velocity of the neutron star is known with its magnitude and its direction on the plane of the sky.
Since the neutron star propagates with an estimated speed of at least 350 kilometres per second, the asymmetry in the spatial distribution of the radioactive elements is expected to be very pronounced. Exactly this is seen in the observations . While the compact remnant speeds toward the lower hemisphere, the biggest and brightest clumps with most of the 44Ti are found in the upper half of the gas remnant. The computer simulation, viewed from a suitably chosen direction, exhibits a striking similarity to the observational image. But not only the spatial distributions of titanium and iron resemble those in Cas A (for a 3D visualization, see Fig. 3 in comparison with the 3D imaging of Cas A available at the weblink http://3d.si.edu/explorer?modelid=45). Also the total amounts of these elements, their expansion velocities, and the velocity of the neutron star are in amazing agreement with those of Cas A. “This ability to reproduce basic properties of the observations impressively confirms that Cas A may be the remnant of a neutrino-driven supernova with its violent gas motions around the nascent neutron star”, concludes H.-Thomas Janka.
But more work is needed to finally prove that the explosions of massive stars are powered by energy input from neutrinos. “Cas A is an object of so much interest and importance that we must also understand the spatial distributions of other chemical species such as silicon, argon, neon, and oxygen”, remarks Ewald Müller, pointing to the beautiful multi-component morphology of Cas A revealed by 3D imaging (see http://3d.si.edu/explorer?modelid=45). One example is also not enough for making a fully convincing case. Therefore the team has joined a bigger collaboration to test the theoretical predictions for neutrino-driven explosions by a close analysis of a larger sample of young supernova remnants. Step by step the researchers thus hope to collect evidence that is able to settle the long-standing problem of the supernova mechanism.
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