Superluminous Supernova 20 Times Brighter Than 100 Billion Stars Wows Astronomers

Records are made to be broken, as the expression goes, but rarely are records left so thoroughly in the dust. Stunned astronomers have witnessed a cosmic explosion about 200 times more powerful than a typical supernova--events which already rank amongst the mightiest outbursts in the universe--and more than twice as luminous as the previous record-holding supernova. At its peak intensity, the explosion--called ASASSN-15lh--shone with 570 billion times the brightness of the Sun. If that statistic does not impress, consider that this luminosity level is approximately 20 times the entire output of the 100 billion stars comprising our Milky Way galaxy. The record-breaking blast is thought to be an outstanding example of a "superluminous supernova," a recently discovered, supremely rare variety of explosion unleashed by certain stars when they die. Scientists are frankly at a loss, though, regarding what sorts of stars and stellar scenarios might be responsible for these extreme supernovae. These are pseudo-color images showing the host galaxy before the explosion of ASASSN-15lh taken by the Dark Energy Camera (DECam) [Left], and the supernova by the Las Cumbres Observatory Global Telescope Network (LCOGT) 1-meter telescope network [Right]. As described in a new study published today in Science, ASASSN-15lh

Credit: The Dark Energy Survey, B. Shappee and the ASAS-SN team

is amongst the closest superluminous supernovae ever beheld, at around 3.8 billion light years away. Given its uncanny brightness and closeness, ASASSN-15lh might offer key clues in unlocking the secrets of this baffling class of celestial detonations. "ASASSN-15lh is the most powerful supernova discovered in human history," said study lead author Subo Dong, an astronomer and a Youth Qianren Research Professor at the Kavli Institute for Astronomy and Astrophysics (KIAA) at Peking University. "The explosion's mechanism and power source remain shrouded in mystery because all known theories meet serious challenges in explaining the immense amount of energy ASASSN-15lh has radiated." ASASSN-15lh was first glimpsed in June 2015 by twin telescopes with 14-centimeter diameter lenses in Cerro Tololo, Chile conducting the All Sky Automated Survey for SuperNovae (ASAS-SN), an international collaboration headquartered at The Ohio State University. (Hence ASASSN-15lh's somewhat menacing moniker.) These two tiny telescopes sweep the skies to detect suddenly appearing objects like ASASSN-15lh that are intrinsically very bright, but are too far away for human observers to notice. "ASAS-SN is the first astronomical project in history to frequently scan the entire optical sky for optical transients," said Krzysztof Stanek, professor of astronomy at the Ohio State University and the co-Principal Investigator of ASAS-SN. "Every time in science we open up a new discovery space, exciting findings should follow. The trick is not to miss them." Dong and colleagues immediately put out word about the sighting of ASASSN-15lh in order for as much data as possible to be gathered. Multiple, far larger ground-based telescopes across the globe, as well as NASA's Swift satellite, have since taken part in an intense observing campaign that continues to this day. In just the first four months after it went kablooie, so much energy beamed out of ASASSN-15lh that it would take our Sun in its current state more than 90 billion years to equal its emissions. By examining this bright, slowly fading afterglow, astronomers have gleaned a few basic clues about the origin of ASASSN-15lh. Using the 2.5-meter du Pont telescope in Chile, Dong's colleagues Ben Shappee and Nidia Morrell at the Carnegie Observatories in the United States took the first spectrum of ASASSN-15lh to identify the signatures of chemical elements scattered by the explosion. This spectrum puzzled the ASAS-SN team members, for it did not resemble any of spectra from the 200 or so supernovae the project had discovered to date. These are two of the 14-centimeter diameter lens telescopes in use for the All Sky Automated Survey for SuperNovae (ASAS-SN) that discovered ASASSN-15lh. Since this photo was taken, two more

Credit: Wayne Rosing

telescopes have been added to the ASAS-SN station in Cerro Tololo, Chile. Inspired by suggestions from Jose Prieto at Universidad Diego Portales and Millennium Institute of Astrophysics in Chile and Stanek, Dong realized that ASASSN-15lh might in fact be a superluminous supernova. Dong found a close spectral match for ASASSN-15lh in a 2010 superluminous supernova, and if they were indeed of a kind, then ASASSN-15lh's distance would be confirmable with additional observations. Nearly 10 days passed as three other telescopes, stymied by bad weather and instrument mishaps, attempted to gather these necessary spectra. Finally, the 10-meter South African Large Telescope (SALT) secured the observations of elemental signatures verifying ASASSN-15lh's distance and extreme potency. "Upon seeing the spectral signatures from SALT and realizing that we had discovered the most powerful supernova yet, I was too excited to sleep the rest of the night," said Dong, who had received word of the SALT results at 2 AM in Beijing on July 1, 2015. The ongoing observations have further revealed that ASASSN-15lh bears certain features consistent with "hydrogen-poor" (Type I) superluminous supernovae, which are one of the two main types of these epic explosions so named for lacking signatures of the chemical element hydrogen in their spectra. ASASSN-15lh has likewise shown a rate of temperature decrease and radius expansion similar to some previously discovered Type I superluminous supernova. Yet in other ways, besides its brute power, ASASSN-15lh stands apart. It is way hotter, and not just brighter, than its apparently nearest of supernova kin. The galaxy it calls home is also without precedent. Type I superluminous supernova seen to date have all burst forth in dim galaxies both smaller in size and that churn out stars much faster than the Milky Way. Noticing the pattern, astronomers hoped this specific sort of galactic environment had something to do with superluminous supernovae, either in the creation of the exotic stars that spawn them or in setting these stars off. Exceptionally, however, ASASSN-15lh's galaxy appears even bigger and brighter than the Milky Way. On the other hand, ASASSN-15lh might in fact reside in an as-yet-unseen, small, faint neighboring galaxy of its presumed, large galactic home. To clear up where exactly ASASSN-15lh is located, as well as numerous other mysteries regarding it and its hyper-kinetic ilk, the research team has been granted valuable time this year on the Hubble Space Telescope. With Hubble, Dong and colleagues will obtain the most detailed views yet of the aftermath of ASASSN-15lh's stunning explosion. Important insights into the true wellspring of its power should then come to light. One of the best hypotheses is that superluminous supernovae's stupendous energy comes from highly magnetized, rapidly spinning neutron stars called magnetars, which are the leftover, hyper-compressed cores of massive, exploded stars. But ASASSN-15lh is so potent that this compelling magnetar scenario just falls short of the required energies. Instead, ASASSN-15lh-esque supernovae might be triggered by the demise of incredibly massive stars that go beyond the top tier of masses most astronomers would speculate are even attainable. "The honest answer is at this point that we do not know what could be the power source for ASASSN-15lh," said Dong. "ASASSN-15lh may lead to new thinking and new observations of the whole class of superluminous supernova, and we look forward to plenty more of both in the years ahead." 

Contacts and sources:  Jim Cohen: The Kavli Institute for Astronomy and Astrophysics (KIAA) 

More information:

• 1] The Kavli Institute for Astronomy and Astrophysics (KIAA) is jointly supported by Peking University and the Kavli Foundation. Website: http://kiaa.pku.edu.cn
• 2] ASAS-SN Survey. Website: http://www.astronomy.ohio-state.edu/~assassin/index.shtml
• 3] The preprint of the paper can be accessed at: http://arxiv.org/abs/1507.03010
• 4] A review article on superluminous supernova by Prof. Avishay Gal-Yam published in Sciencein 2012 can be found at: http://arxiv.org/abs/1208.3217

Source: http://www.ineffableisland.com/

Read More........→January 15, 2016

Earth Collects 5 to 300 Tons of Cosmic Dust a Day

Image credit: ESO/Y. Beletsky

Currently, estimates of the Earth's intake of space dust vary from around five tons to as much as 300 tons every day. A €2.5 million international project, led by Professor John Plane from the University's School of Chemistry, will seek to address this discrepancy. Scientists at the University of Leeds are looking to discover how dust particles in the solar system interact with the Earth's atmosphere. Currently, estimates of the Earth's intake of space dust vary from around five tons to as much as 300 tons every day. A € 2.5 million international project, led by ERC Advanced grantee John Plane from the University's School of Chemistry, will seek to address this discrepancy. The Cosmic Dust in the Terrestrial Atmosphere (CODITA) project will investigate what happens to the dust from its origin in the outer solar system all the way to the earth's surface. The work, funded by the European Research Council, will also explore whether cosmic dust has a role in the Earth's climate and how it interacts with the ozone layer in the stratosphere. "People tend to think space is completely empty, but if all the dust between the Sun and Jupiter was compressed it would create a moon 16 miles across. It's surprising that we aren't more certain how much of this comes to Earth" said Professor Plane. "If the dust input is around 300 tons per day, then the particles are being transported down through the atmosphere considerably faster than generally believed; if the 5-ton figure is correct, we will need to revise substantially our understanding of how dust evolves in the Solar System and is transported from the edge of space around 50 miles high to the surface," added Professor Plane. Over the next five years, the scientists at Leeds, and visiting

Zodiacal Light Seen from Paranal, Credit: ©ESO/Y.Beletsky

colleagues from Germany and the United States, will replicate in the laboratory the chemical processes that dust particles undergo as they enter and filter through the atmosphere."Our work in the lab will look at the nature of cosmic dust evaporation and the formation of meteoric smoke particles, which play a role in ice nucleation and the freezing of polar stratospheric clouds," said Professor Plane. In the atmosphere, the dust particles undergo very rapid heating through collisions with air molecules, reaching temperatures well in excess of 1600 degrees Celsius. At this point they melt and evaporate. The larger particles can be seen as "shooting stars", whilst the electrons produced from ionizing collisions with air enable smaller dust particles to be detected using specialist high-powered radar equipment. By replicating this heating in the lab, it is hoped that radar measurements of meteors can be better understood and used to make accurate measurements of the dust input. The metallic vapours recondense in the atmosphere to form nanometre-sized particles known as meteor smoke. In 2014, the team will be involved in a Norwegian rocket experiment to measure meteor smoke in ice particles in the upper atmosphere. "Cosmic dust and meteor smoke are both believed to interact with the clouds which play a key role in causing stratospheric ozone depletion - most notably the formation of the Antarctic Ozone Hole," said Professor Martyn Chipperfield, from the University's School of Earth and Environment. "We will use the lab data in a detailed chemistry-climate model of the whole atmosphere. This will make it possible, for the first time, to model the effects of cosmic dust consistently from the outer reaches of the Solar System all the way down to the Earth's surface," said Professor Chipperfield. "It has been suggested that to combat global warming sulphate aerosol could be released into the atmosphere to reflect some of the Sun's heat. Understanding the quantity of cosmic dust and the potential chemical reactions which may occur is crucial to moving this idea forward," said Professor Chipperfield. CODITA is funded by the European Research Council (ERC). The climate model which will be used in the project is supported at Leeds by the Natural Environment Research Council (NERC), and is a flagship model produced by the US National Center for Atmospheric Research (NCAR). Contacts and sources: University of Leeds, Cosmic Dust in the Terrestrial Atmosphere. Source: Article

Read More........→August 20, 2015

Brighter Than 100 Billion Stars

Three-dimensional simulation of a Type Ia supernova explosion, Image: F. K. Röpke MPI for Astrophysics, Garching

Modern astronomy began with a supernova. In November 1572, Danish astronomer Tycho Brahe discovered a new star – and destroyed the idea of a sky of fixed stars. Today, we know that Brahe was observing the death of a star, which ended in a massive explosion. Friedrich Röpke aims to find out how these supernova explosions proceed. The astrophysicist is now leader of the new research group "Physics of Stellar Objects" (PSO) at Heidelberg Institute for Theoretical Studies (HITS). As of March 1, 2015, he has been appointed professor for Theoretical Astrophysics at Heidelberg University. His workplace is HITS. This joint appointment is a perfect proof for the close cooperation between the two institutes. With Friedrich Röpke and Volker Springel, there now are two HITS astrophysicists who are also professors at Heidelberg University. “The new group is another important component of our concept, “ says Klaus Tschira who founded the HITS in 2010 as a non-profit research institute. “Research on stellar astrophysics, like Friedrich Röpke does, is a perfect complement of the work of Volker Springel’s group on large-scale processes like galaxy formation.“ Friedrich Röpke (40) studied Physics at the University of Jena and the University of Virginia, Charlottesville/USA, and received his PhD in 2003 from the Technische Universität München. In the following years, he worked as a postdoc at the Max-Planck-Institute for Astrophysics (MPA) in Garching and at the University of California, Santa Cruz/USA. In 2008, Friedrich Röpke habilitated at the TU München and also became leader of an Emmy Noether research group at MPA. Three years later, he got appointed professor for Astrophysics at the University of Würzburg. In 2010, the researcher was awarded the "ARCHES Award" by the German Federal Ministry for Education and Research together with Prof. Avishay Gal-Yam from the Weizmann Institute, Rehovot/Israel. The award honors young scientists whose work shows great potential to have noticeable impact on their respective fields of research. Friedrich Röpke studies Type Ia supernovae. Observation of these cosmic explosions allows astronomers to determine distances in space. In 2011, the Nobel Prize in Physics was awarded to researchers who proved the accelerated expansion of the Universe with supernovae. The PSO group collaborates closely with one of the laureates from 2011, Brian Schmidt (Australian National University, Canberra) in a program supported by the German Academic Exchange Service DAAD. Friedrich Röpke’s research aims to understand exactly what happens when stars die. Remnant of SN 1572 as seen in X-ray light from the Chandra X-ray Observatory. The supernova of 1572 is often called "Tycho's supernova", because of Tycho Brahe's extensive work De nova et nullius aevi memoria prius visa stella ("Concerning the Star, new and never before seen in the life or memory of anyone", published in 1573 with reprints overseen by Johannes Kepler in 1602, and 1610), a work containing both Tycho Brahe's own observations and the analysis of sightings from many other

Credit: Chandra X-ray Observatory.

observers. Together with other scientists, he used computer simulations to show that some highly-luminous supernovae are the result of two compact stars, so-called “white dwarfs", merging together. He also investigates alternatives by modeling the explosion of a white dwarf when it reaches its maximum stable mass (the so-called Chandrasekhar limit), using highly complex simulations on supercomputers. White dwarfs are only about the size of the Earth and are extremely dense. When they explode as supernova, they shine brighter than the whole galaxy. "Our detailed simulations helped us to predict data that closely reproduce actual telescope observations of Type Ia supernovae, " explains the astrophysicist. “Modelling of supernova explosions is, however, just one part of our research at HITS,” says Friedrich Röpke. “We also strive for a better understanding of how stars evolve and how the elements that make up our world are formed within them.” Classical astrophysics follows stellar evolution based on very simplifying assumptions. "To improve the predictive power of the models, we have to describe the physical processes taking place within stars in a dynamic way," says the astrophysicist. He and his group have developed a new computer code that – combined with the rapidly increasing capacities of supercomputers – opens new perspectives for the modelling of stars. In contrast to what we are used to from our solar system, most stars in the Universe exist as part of multiple star systems. The interaction between those stars greatly affects their evolution but the involved physical processes are poorly understood until today. The two astrophysics groups at HITS are cooperating on new computer simulations to bring some light into the darkness. Contacts and sources: Heidelberg Institute for Theoretical Studies, Source: inffableislamd.com

Read More........→March 12, 2015

Two Stars Merging Into A Supermassive Star Seen By Astronomers

Credit: Javier Lorenzo (Universidad de Alicante)

A study of "MY Camelopardalis" binary system, published in the journal Astronomy & Astrophysics, shows that the most massive stars are made up by merging with other smaller stars, as predicted by theoretical models. Most of the stars in our galaxy have been formed in binary or multiple systems, some of which are "eclipsing", this is consists of two or more stars which, observed from Earth, undergo eclipses and mutual transits because of their orbital plane facing our planet. One such system is the eclipsing binary MY Camelopardalis (MY Cam). Artistic rendering of MY Cam system. The proportions between the components reflect the analysis results. The stars are deformed by its very fast rotation and the gravitational pull of the companion. The journal Astronomy & Astrophysics has published an article on MY Cam, one of the most massive star known, with the results of observations from the Calar Alto Observatory (Almería) signed by astronomers at the University of Alicante, the Astrobiology Centre of the Spanish National Research Council (CAB-CSIC) and the Canaries’ Astrophysics Institute (IAC), along with amateur astronomers. This article concludes that MY Cam is the most massive binary star observed and its components, two stars of spectral type O (blue, very hot and bright), 38 and 32 times the Sun's mass, are still on the main sequence and are very close to each other, with an orbital period of less than 1.2 days, in other words, the shortest orbital period in this type of stars. This indicates that the binary was virtually formed as it is now: the stars were almost in contact at the time they were formed. The expected development is the merger of both components into a single object over 60 solar masses before any of them have time to evolve significantly. Hence, these results demonstrate the viability of some theoretical models suggesting that most massive stars are formed by merging less massive stars. Massive binary systems: Stars which, like the Sun, move alone in the Galaxy by trailing only their planetary system are a minority. Most stars spend their lives tied by gravity to a companion star (forming what is called a binary system) or several (what was known as multiple system). As explained by Javier Lorenzo, from the University of Alicante and first author of article, in these systems all stars describe their orbits around a common centre of mass. In particular, the stars much more massive than the Sun contain an equivalent mass to many suns and tend to always appear in company. Recent studies suggest that these high-mass stars, that are much larger and hotter than the Sun, form part of systems with at least one other companion of comparable mass. A particularly striking example is the binary system known as MY Camelopardalis (MY Cam), in the constellation of the Giraffe. This object is the brightest star in the open cluster "Alicante 1", which was recently identified as a small stellar nursery by researchers at the University of Alicante. Although it has been known for over fifty years that MY Cam is a high-mass star, it was only ten years ago that it was recognised as an eclipsing binary, a system in which one star passes in front of the other every time they complete their orbit, leading to changes in the brightness of the system that we perceive from Earth. This property of eclipsing binaries allows us to know many of the characteristics of the component stars through a careful study of the light that comes from them and the simple application of Newton’s law of universal gravitation. For the study of MY Cam, professional astrophysicists obtained a large number of spectra of the system with FOCES spectrograph, which operated for many years in the 2.2 m telescope of Calar Alto Observatory. Using the Doppler Effect, these spectra allow us to measure the velocities with which the stars move in their orbits. Also, astrophysicists can determine the fundamental properties of stars, as their surface temperature and its size through a comprehensive analysis of the characteristics of the spectra. To complete the work, they had the help of amateur astronomers who measured the changes in the amount of light coming from the system along the orbit, what astrophysicists call the light curve of the system. Analysis of these data has shown that MY Cam is a truly exceptional system. The light curve- as explained by Sergio Simon, IAC researcher and one of the authors of the article - shows that the orbital period of the system is only 1.2 days. Given the large size of the stars, they have to be extremely close to be able to do a full turn so quickly. The stars are moving at a speed of over one million km/h, but being so close, the tidal forces between them make them rotate about themselves with the same period, ie, each star turns on itself in just over a day, while the Sun, which is much smaller, turns on itself once every 26 days. Stars are like giant spinning tops and every point of the surface moves with a speed of over one million km/h. Each has a radius around 700 times bigger than the Earth’s, but turns on itself at about the same time. But also, the stars are extremely massive. Their masses are 38 and 32 times the Sun's mass. Such huge stars do not fit so easily into such a small orbit and the conclusion of the study is that they are actually in touch and the material of their outer layers is mixing, giving place to a common envelope (what is known as a contact binary). MY Cam is one of the most massive contact binaries known and by far the most massive whose components are so young they have not yet begun to evolve. As stated by Ignacio Negueruela, another author from the University of Alicante, this is the most interesting aspect of MY Cam since its foreseeable future confirms some of the current theories of formation of extremely massive stars. The properties of the two components of MY Cam suggest that they are extremely young stars formed in the past two million years. This extreme youth allows us to suspect that the system was formed essentially as it is now, although perhaps the two stars were not touching initially. As they get older, their natural evolution is to become larger. Given that they have no clearance between them, this process will lead to the merger of the two stars in a single object, a real star mastodon. The details of the merger process are not known, because it has never been seen before. Some theoretical models suggest that the merger process is extremely fast, releasing a huge amount of energy in a kind of explosion. Other studies favor a less violent process, but in any event spectacular. Anyway, many astrophysicists believe that the merger of the components of a close binary is probably the most effective way to generate extremely massive stars. MY Cam is the first example of a system that can lead to one of these objects. Contacts and sources: Asociación RUVID, Citation: J. Lorenzo, I. Negueruela, A.K.F. Val Baker (Universidad de Alicante), M. García (CAB-CSIC), S. Simón-Díaz (IAC), P. Pastor, M. Méndez Majuelos (amateurs). “MY Camelopardalis, a very massive merger progenitor”. Astronomy & Astrophysics. 2014. http://arxiv.org/abs/1410.5575, Source: ineffableisland.com

Read More........→January 14, 2015

Astronomers Create First Realistic Virtual Universe

Credit: Dr Debora Sijacki, Cambridge University

Tracking 13 billion years of cosmic evolution, astronomers have created the first realistic virtual simulation of the Universe. A newly-developed computer simulation has created the first realistic version of the Universe, enabling researchers to understand how galaxies, black holes and other cosmic phenomena developed from shortly after the Big Bang to the present day. The simulation, known as Illustris, follows the complex development of both normal and dark matter over 13 billion years, matching many of the features observed in the real Universe for the first time. Developed by an international team of researchers, Illustris tracks the development of the Universe from 12 million years after the Big Bang up to the present, and identified more than 41,000 galaxies in a cube of simulated space 350 million light years on each side. The results are reported in the May 8th issue of the journal Nature.  Over the past two decades, researchers have been attempting to build accurate computer simulations of the development of the Universe, using computer programs which are capable of encapsulating all the relevant laws of physics governing the formation of galaxies. Previous attempts to simulate the universe were hampered by lack of computing power and the complexities of the underlying physics.As a result those programseither were limited in resolution, or forced to focus on a small portion of the universe. Earlier simulations also had trouble modelling complex feedback from star formation, supernova explosions, and supermassive black holes. Illustris employs a sophisticated computer program to recreate the evolution of the universe in high fidelity. It includes both normal matter and dark matter using 12 billion 3D “pixels,” or resolution elements. Illustris yields a realistic mix of spiral galaxies like the Milky Way and giant elliptical galaxies. It also recreated large-scale structures like galaxy clusters and the bubbles and voids of the cosmic web. The team dedicated five years to developing the Illustris project. The actual calculations took three months of run time, using a total of 8,000 CPUs running in parallel. In comparison, the same calculations would have taken an average desktop computer more than 2,000 years to complete. “Until now, no single simulation was able to reproduce the Universe on both large and small scales simultaneously,” says lead author Dr Mark Vogelsberger of the Massachusetts Institute of Technology and Harvard University, who conducted the work in collaboration with researchers at the University of Cambridge, the Harvard-Smithsonian Center for Astrophysics and the Heidelberg Institute for Theoretical Studies. “The Illustris simulation is a remarkable technical achievement,” said Dr Debora Sijacki of Cambridge’s Institute of Astronomy, one of the paper’s co-authors. “It shows us for the first time how the bewildering variety of galaxies and the supermassive black holes at their centres have formed.” Since light travels at a fixed speed, the farther away astronomers look, the farther back in time they can see. A galaxy one billion light-years away is seen as it was a billion years ago. Telescopes like Hubble can give us views of the early Universe by looking to greater distances. However, astronomers can’t use Hubble to follow the evolution of a single galaxy over time. “Illustris is like a time machine. We can go forward and backward in time. We can pause the simulation and zoom into a single galaxy or galaxy cluster to see what’s really going on,” said co-author Dr Shy Genel of Harvard University. A selection of videos and imagery from the project are available online at www.illustris-project.org, Source: Ineffableisia.com 

• Contacts and sources: Dr Debora Sijacki, Institute of Astronomy, Cambridge University

Read More........→May 28, 2014