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  • richardmitnick 4:33 pm on February 14, 2019 Permalink | Reply
    Tags: , , , , , , High-z Supernova Search Team, Supernova Cosmology Project at Lawrence Berkeley National Laboratory, Type Ia supernovae   

    From ESOblog: “A Nobel Achievement (part II)” Bruno Leibundgut 

    ESO 50 Large

    From ESOblog


    Bruno Leibundgut

    8 February 2019

    In 2011, the High-z Supernova Search Team won the Nobel Prize in Physics for the discovery that the expansion of the Universe is accelerating. Bruno Leibundgut, ESO’s Very Large Telescope Programme Scientist, was one of two ESO scientists who contributed to this extraordinary discovery, with the other being Jason Spyromilio. Bruno tells us the story of this game-changing piece of astronomical research in the second post in a two-part series about this prize-winning discovery.

    Also see: A Nobel Achievement (part I) https://sciencesprings.wordpress.com/2019/02/01/from-esoblog-a-nobel-achievement-part-i-bruno-leibundgut/

    At the beginning of the 1990s, the biggest question in astronomy was probably: what is the future of the Universe? Is it going to collapse? Or will it expand forever? Nobody knew.

    At the time many astronomers were looking at type Ia supernovae, which are the extremely bright explosions that occur when two stars in a binary system merge. This type of supernova always produces a similar amount of light, so we know how far away they are by how bright they look from Earth. And because they are so bright, we can often see supernovae even when they are really distant. This all means that we can use type Ia supernovae to find out about the past and future of the Universe; by comparing the apparent distance predicted by their brightness to their actual distance, it is possible to determine whether the expansion of the Universe has decelerated since the explosion occurred.

    Artist´s impression of a binary system before and after merging to create a supernova. Credit: ESO

    I was working as part of a team that was trying to do just that. In 1995 and 1996, team member Adam Riess collected our observations on the brightness of ten distant supernovae, and the and team leader Brian Schmidt compared their distances and their brightnesses.

    They came up with the result that the expansion of the Universe was not decelerating. This was very surprising as we had expected that all the matter in the Universe is pulled together by gravity, leading to a decelerating expansion. But then in December 1997, Adam said to us: “Those distant supernovae are too far away. It’s like something has pushed them away from us. Could it be that the expansion of the Universe is actually accelerating?”

    This sparked a heated discussion — via email as the team was distributed all over the world! Brian was in Australia, Adam was on the west coast of the US, we had people on the east coast, we had people in Hawaii. And I was in Germany working with the data from the ESO telescopes. We would send an email in the evening and get up in the morning to find out about a number of other issues. But in the end, Adam and Brian could prove that there was no obvious mistake in the analysis. [Saul Perlmutter heads the Supernova Cosmology Project at Lawrence Berkeley National Laboratory at the same time with the same goal. He shared the Nobel prize with Adam Riess and Brian Schmidt.]

    In this much sped-up artist´s impression showing a collection of distant galaxies, the occasional supernova can be seen. Each of these exploding stars briefly rivals the brightness of its host galaxy. Credit: ESO/L. Calçada

    So, we decided we would have to submit a paper presenting our results, and we were sure that someone else would tell us what was wrong. But this didn’t happen. There were some people who didn’t believe us, but they were in the minority, and they couldn’t prove we were wrong.

    I’m not sure we were fully aware at the time what a big deal this discovery was. The fact that the expansion of the Universe is accelerating means that there must be some invisible “thing” in the Universe driving the expansion, causing the objects in it to flow apart faster than we would expect even for a universe without matter. The calculations tell us that this “thing” must be about three quarters of the energy content of the Universe. In a way, this was like discovering three quarters of the Universe that people had no idea existed.

    We were helped by another discovery made around the same time, related to the Cosmic Microwave Background (CMB).

    CMB per ESA/Planck

    ESA/Planck 2009 to 2013

    People were using the CMB to study the geometry of the Universe. The tiny temperature fluctuations in the CMB indicated that the geometry of spacetime is flat, which requires a specific amount of matter and energy. Einstein’s famous equation E=mc2 tells us that mass (matter) and energy are equivalent. But determinations of the amount of matter and energy known to exist in the Universe made up just 25% of the amount required by a flat Universe. In other words, 75% of the matter and energy was missing.

    This value matched perfectly with our discovery of the extra energy component that makes up three quarters of the matter/energy content of the Universe. It was the combination of the two discoveries at almost the same time that convinced most people.

    This new component is now called dark energy. But more than twenty years later, we still have no idea what dark energy actually is! There is no physical explanation for it, but astronomers all over the world are working to find one.

    This discovery certainly affected my career. All of a sudden, I became one of the best-known observational cosmologists in Europe, which came with its pros and cons.

    As one of only two Europeans on the High-z Supernova Search Team, I got invited to many, many conferences here in Europe to present the result, and was asked to write major review papers on it. This took a lot of time out of my research.

    And then in 2011, Adam Riess and Brian Schmidt won the Nobel Prize in Physics for this research — they each won a quarter, and Saul Perlmutter of the Supernova Cosmology Project won the other half. We all went along for the Nobel Prize celebrations, which was an amazing experience.

    The High-z Supernova Search Team just after the Nobel Prize award ceremony. Bruno stands on the right and Jason Spyromilio on the left of the back row.
    Credit: Nicolas Suntzeff

    But in the long run, I decided that I didn’t want to be part of large collaborations any more. The High-z Supernova Search Team wasn’t that big — around 25 people — but there were still so many teleconferences and meetings. I just felt tired of all that. I wanted to do things that I could be recognised for directly, rather than being a member of a team. I wanted to create something that people could recognise as coming from me.

    I’m still doing cosmology, though not the same type any more. That kind of research now requires large teams of hundreds of people. I’ve started to pick smaller problems again — things that I can do with students, to solve some of the smaller questions that we have about supernovae. It’s interesting to come from a big stage, from a place where the whole world pays attention to you, to go back to smaller problems that are not necessarily seen by everybody, and maybe not even seen as interesting by a lot of people. But that’s OK.

    See the full article here .


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    ESO is the foremost intergovernmental astronomy organisation in Europe and the world’s most productive ground-based astronomical observatory by far. It is supported by 16 countries: Austria, Belgium, Brazil, the Czech Republic, Denmark, France, Finland, Germany, Italy, the Netherlands, Poland, Portugal, Spain, Sweden, Switzerland and the United Kingdom, along with the host state of Chile. ESO carries out an ambitious programme focused on the design, construction and operation of powerful ground-based observing facilities enabling astronomers to make important scientific discoveries. ESO also plays a leading role in promoting and organising cooperation in astronomical research. ESO operates three unique world-class observing sites in Chile: La Silla, Paranal and Chajnantor. At Paranal, ESO operates the Very Large Telescope, the world’s most advanced visible-light astronomical observatory and two survey telescopes. VISTA works in the infrared and is the world’s largest survey telescope and the VLT Survey Telescope is the largest telescope designed to exclusively survey the skies in visible light. ESO is a major partner in ALMA, the largest astronomical project in existence. And on Cerro Armazones, close to Paranal, ESO is building the 39-metre European Extremely Large Telescope, the E-ELT, which will become “the world’s biggest eye on the sky”.

    ESO VLT at Cerro Paranal in the Atacama Desert, •ANTU (UT1; The Sun ),
    •KUEYEN (UT2; The Moon ),
    •MELIPAL (UT3; The Southern Cross ), and
    •YEPUN (UT4; Venus – as evening star).
    elevation 2,635 m (8,645 ft) from above Credit J.L. Dauvergne & G. Hüdepohl atacama photo,

    ESO LaSilla
    ESO/Cerro LaSilla 600 km north of Santiago de Chile at an altitude of 2400 metres.

    ESO VLT 4 lasers on Yepun

    ESO Vista Telescope
    ESO/Vista Telescope at Cerro Paranal, with an elevation of 2,635 metres (8,645 ft) above sea level.

    ESO/NTT at Cerro LaSilla 600 km north of Santiago de Chile at an altitude of 2400 metres.

    ESO VLT Survey telescope
    VLT Survey Telescope at Cerro Paranal with an elevation of 2,635 metres (8,645 ft) above sea level.

    ALMA Array
    ALMA on the Chajnantor plateau at 5,000 metres.

    ESO/E-ELT,to be on top of Cerro Armazones in the Atacama Desert of northern Chile. located at the summit of the mountain at an altitude of 3,060 metres (10,040 ft).

    APEX Atacama Pathfinder 5,100 meters above sea level, at the Llano de Chajnantor Observatory in the Atacama desert.

    Leiden MASCARA instrument, La Silla, located in the southern Atacama Desert 600 kilometres (370 mi) north of Santiago de Chile at an altitude of 2,400 metres (7,900 ft)

    Leiden MASCARA cabinet at ESO Cerro la Silla located in the southern Atacama Desert 600 kilometres (370 mi) north of Santiago de Chile at an altitude of 2,400 metres (7,900 ft)

    ESO Next Generation Transit Survey at Cerro Paranel, 2,635 metres (8,645 ft) above sea level

    SPECULOOS four 1m-diameter robotic telescopes 2016 in the ESO Paranal Observatory, 2,635 metres (8,645 ft) above sea level

    ESO TAROT telescope at Paranal, 2,635 metres (8,645 ft) above sea level

    ESO ExTrA telescopes at Cerro LaSilla at an altitude of 2400 metres

  • richardmitnick 10:44 am on January 14, 2019 Permalink | Reply
    Tags: A giant interstellar bubble being grown in the Andromeda Galaxy, , , ‘M31N 2008–12a’ a recurrent nova located in our neighbouring Andromeda Galaxy, , , , , Type Ia supernovae   

    From Instituto de Astrofísica de Canarias – IAC via Manu Garcia: “A giant interstellar bubble being grown in the Andromeda Galaxy” 

    From Manu Garcia, a friend from IAC.

    The universe around us.
    Astronomy, everything you wanted to know about our local universe and never dared to ask.


    From Instituto de Astrofísica de Canarias – IAC

    Jan. 9, 2019
    Pablo Rodríguez-Gil

    An international team of astrophysicists that includes researchers at the Instituto de Astrofísica de Canarias (IAC) and the University of La Laguna (ULL) has uncovered an enormous bubble current being ‘blown’ by the regular eruptions from a binary star system within the Andromeda Galaxy. The results have been published today in Nature.


    Observations with the Liverpool Telescope and Hubble Space Telescope, supported by spectroscopy from the Gran Telescopio Canarias (GTC) and the Hobby–Eberly Telescope (some of the largest astronomy facilities on Earth), discovered this enormous shell-like nebula surrounding ‘M31N 2008–12a’, a recurrent nova located in our neighbouring Andromeda Galaxy.

    2-metre Liverpool Telescope at La Palma in the Canary Islands,

    Liverpool Telescope at the Observatorio del Roque de los Muchachos, altitude 2,363 m (7,753 ft)

    NASA/ESA Hubble Telescope

    At almost 400 light years across ––and still growing, this shell is far bigger than a typical nova remnant (usually around a light year in size) and even larger than most supernova remnants.

    Lead author Dr Matt Darnley, Reader in Time Domain Astrophysics at Liverpool John Moores University’s (LJMU) Astrophysics Research Institute explains: “Each year ‘12a’ (as we lovingly refer to it) undergoes a thermonuclear eruption on the surface of its white dwarf. These are essentially hydrogen bombs, which eject material equivalent to about the mass of the Moon in all directions at a few 1000 kilometres per second. These ejecta act like a snow plough, piling the surrounding interstellar medium up to form the shell we observe ––the outer ‘skin’ of the bubble, or the ‘super-remnant’ as we have named it.”

    These new observations coupled with state-of-the-art hydrodynamic simulations (carried out at LJMU and the University of Manchester) have revealed that this vast shell is in fact the remains of not just one nova eruption but possibly millions ––all from the same system.

    Despite its uniqueness and staggering scale, the discovery of this super-remnant may have further significance. Dr Matt Darnley continued: “Studying 12a and its super-remnant could help us to understand how some white dwarfs grow to their critical upper mass and how they actually explode once they get there as a ‘type Ia supernova’. Type Ia supernovae are critical tools used to work out how the universe expands and grows.”

    Dr Rebekah Hounsell, second author of this study and a post-doctoral researcher at the University of Pennsylvania, was at the Space Telescope Science Institute when she took part in the research. She explains: “Type Ia supernovae are some of the largest explosions in the Universe and our most mature cosmological probes. The recurrent novae M31N 2008–12a is the most likely type Ia supernova progenitor to date and provides us with the unique opportunity to study such a system before its final demise. Lying within our nearest galactic spiral neighbour, Andromeda, the explosion of 12a would be one of the closest supernovae observed by telescopes. The last observed supernova within our own galaxy occurred in 1604.”

    “In a previous work we predicted that 12a will ultimately explode as a type Ia supernova in less than 20,000 years ––a very short time in cosmological terms. But, in the meantime, we will continue to monitor the next nova eruptions of this system”, explains Dr Pablo Rodríguez-Gil, co-author of the paper, researcher at the IAC, and associate professor at the ULL. “A missing piece of the puzzle is the nature of the companion star that provides the material to the white dwarf. It is extremely faint, but its detection is within the reach of the largest telescopes, such as GTC. This is a crucial next step toward our understanding and ultimate fate of this recurrent nova”.

    See the full article here.

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    The Instituto de Astrofísica de Canarias(IAC) is an international research centre in Spain which comprises:

    The Instituto de Astrofísica, the headquarters, which is in La Laguna (Tenerife).
    The Centro de Astrofísica en La Palma (CALP)
    The Observatorio del Teide (OT), in Izaña (Tenerife).

    These centres, with all the facilities they bring together, make up the European Northern Observatory(ENO).

    The IAC is constituted administratively as a Public Consortium, created by statute in 1982, with involvement from the Spanish Government, the Government of the Canary Islands, the University of La Laguna and Spain’s Science Research Council (CSIC).

    The International Scientific Committee (CCI) manages participation in the observatories by institutions from other countries. A Time Allocation Committee (CAT) allocates the observing time reserved for Spain at the telescopes in the IAC’s observatories.

    The exceptional quality of the sky over the Canaries for astronomical observations is protected by law. The IAC’s Sky Quality Protection Office (OTPC) regulates the application of the law and its Sky Quality Group continuously monitors the parameters that define observing quality at the IAC Observatories.

    The IAC’s research programme includes astrophysical research and technological development projects.

    The IAC is also involved in researcher training, university teaching and outreachactivities.

    The IAC has devoted much energy to developing technology for the design and construction of a large 10.4 metre diameter telescope, the ( Gran Telescopio CANARIAS, GTC), which is sited at the Observatorio del Roque de los Muchachos.

    Gran Telescopio Canarias at the Roque de los Muchachos Observatory on the island of La Palma, in the Canaries, SpainGran Telescopio CANARIAS, GTC

  • richardmitnick 3:06 pm on October 24, 2018 Permalink | Reply
    Tags: A double-degenerate model in which a one white dwarf explodes in a binary pair flinging the other one out into space, , , , , , Dynamically driven double-degenerate double-detonation” model — or D6 for short, Speeding White Dwarfs May Point to Past Explosions, , Type Ia supernovae   

    From AAS NOVA: “Speeding White Dwarfs May Point to Past Explosions” 


    From AAS NOVA

    24 October 2018
    Susanna Kohler

    A new study suggests that binary white dwarfs be the key to understanding Type Ia supernovae like the explosion featured in this artist’s impression. [ESO/M. Kornmesser]

    A recent study has discovered three of the fastest stars known in the Milky Way. But these stars may be more than just speeders — they might also be evidence of how Type Ia supernovae occur.

    Two competing theoretical models for the progenitors of Type Ia supernova explosions: the single-degenerate model (top) and the double-degenerate model (bottom). Today’s study focuses on a double-degenerate model in which a one white dwarf explodes in a binary pair, flinging the other one out into space. [NASA/CXC/SAO and GSFC/D. Berry]

    Seeking a Source

    Given the extent to which we rely on Type Ia supernovae as standard candles used to measure vast distances, you might think that we’ve got them fairly well figured out. But these stellar explosions are complicated, and it turns out that we don’t know some of the most fundamental things about them! Scientists are still working hard to find answers about what systems Type Ia supernovae originate from, and how the explosions are caused.

    Led by astronomer Ken Shen (University of California, Berkeley), a team of astronomers has explored one particular model for Type Ia supernovae further: the “dynamically driven double-degenerate double-detonation” model — or D6, for short. In this scenario, a pair of white dwarfs orbit each other in a binary system. Two back-to-back detonations then cause one of the white dwarfs to explode as a supernova while the other white dwarf survives and is flung free of the explosion site.

    Shen and collaborators note that if the D6 model proves to be the primary means of producing Type Ia supernovae, then there’s an observable outcome: there should be white dwarfs speeding throughout our galaxy that were suddenly liberated by the supernova explosions of their companions.

    Posterior probability distributions for the total galactocentric velocities for estimated for the three hypervelocity white dwarf candidates: D6-1, D6-2, and D6-3. [Shen et al. 2018]

    Hunt for Speeders

    Based on the estimated supernova rate in our galaxy and the properties of binary white dwarfs, Shen and collaborators predict that there should be ~30 hypervelocity white dwarfs within ~3,000 light-years of us. But how to spot these compact stars speeding across the sky? With one of the best tools in the business: Gaia.

    Shen and collaborators combed through the numbers from the Gaia mission’s second data release, which presents the astrometric parameters of more than a billion stars across the sky. In this treasure trove of information, they discovered seven candidates that they then followed up with ground-based observations. After ruling out four as ordinary stars, the authors were left with three candidate hypervelocity white dwarfs.

    Associated Remnant?


    The three candidates have total galactocentric velocities between 1,000 and 3,000 km/s (that’s 2.2 to 6.7 million miles per hour!), making them some of the fastest known stars in the Milky Way. That alone is enough to qualify them as potential progenitors of Type Ia supernovae via the D6 model — but Shen and collaborators look for one more clue: whether they can be tracked back to a supernova remnant.

    Two of the candidates show no sign of having traveled from a nearby remnant — not necessarily surprising, as the remnants could be very faint, or even have already dissipated completely. But the third candidate can be tracked back to a location within the faint, old supernova remnant G70.0–21.5.

    While not yet a smoking gun, these hypervelocity white dwarfs represent important support for the D6 model. And continued follow-up of additional candidates — as well as new candidates discovered in future Gaia releases — may further confirm this model for how Type Ia supernovae occur.


    “Three Hypervelocity White Dwarfs in Gaia DR2: Evidence for Dynamically Driven Double-Degenerate Double-Detonation Type Ia Supernovae,” Ken J. Shen et al 2018 ApJ 865 15.

    See the full article here .


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    AAS Mission and Vision Statement

    The mission of the American Astronomical Society is to enhance and share humanity’s scientific understanding of the Universe.

    The Society, through its publications, disseminates and archives the results of astronomical research. The Society also communicates and explains our understanding of the universe to the public.
    The Society facilitates and strengthens the interactions among members through professional meetings and other means. The Society supports member divisions representing specialized research and astronomical interests.
    The Society represents the goals of its community of members to the nation and the world. The Society also works with other scientific and educational societies to promote the advancement of science.
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  • richardmitnick 8:38 am on October 11, 2017 Permalink | Reply
    Tags: A Helium-Powered Supernova, A supernova called MUSSES1604D, , , , , , , Type Ia supernovae   

    From Astrobites: “A Helium-Powered Supernova” 

    Astrobites bloc


    Oct 11, 2017
    Matthew Green

    Title: A hybrid type Ia supernova with an early flash triggered by helium-shell detonation
    Authors: Ji-an Jiang, Mamoru Doi, Keiichi Maeda, et al.
    First Author’s Institution: Institute of Astronomy, The University of Tokyo, Japan
    Status: Accepted by Nature, open access

    Today we’re going to be talking about an unusual supernova, MUSSES1604D, which appears to be the first strong evidence for one of the proposed models of Type Ia Supernovae. First, we should talk about what the model is.


    Type Ia Supernovae, and Where They Come From

    Figure 1: Artist’s impression of the ignition of an accreting white dwarf. Credit: David A. Hardy, STFC.

    Everyone loves a good explosion, and supernovae are among the biggest. They’re also complicated, and there exists a whole menagerie of different classes. Today we’re going to be talking about one particular subclass, ‘Type Ia Supernovae‘ (SNe Ia). These supernovae get a lot of press. As well as being interesting for their own sake, they are useful objects for astronomy as a whole, because they allow us to measure the distances of far-off galaxies. This comes from the fact that the brightness of an SN Ia is easy to calculate from other properties of the supernova. If we know how bright a supernova is, and we can measure how much of its light we receive, it’s relatively straightforward to work out how far away that supernova is. A lot of interesting science regarding the most distant galaxies is based on distance measurements that required SNe Ia.

    Despite this, there is a nagging problem with SNe Ia: we still don’t fully understand how exactly SNe Ia happen. We do know that SNe Ia result from exploding white dwarfs. A white dwarf has a maximum mass (named the Chandrasekhar mass after the theoretician who first proposed it) beyond which it cannot support itself against its own gravity. If a white dwarf grows to be heavier than the Chandrasekhar mass, it will collapse in upon itself. Collapsing causes the matter that makes up the white dwarf to become incredibly hot and dense. Past a certain point, atoms of carbon and oxygen can undergo nuclear fusion in a runaway nuclear reaction, causing an explosion which rips the white dwarf apart. This is the standard picture of what causes SNe Ia.

    This basic idea still has a number of unsolved problems surrounding it, however. For today, the most important problem is this: there just don’t seem to be enough high-mass white dwarfs to match the rate of supernovae that we see. As a result, an alternative model has been developed over the past few years, which would allow white dwarfs to explode without needing to reach the Chandrasekhar limit: the so-called ‘double detonation’ model. This model needs a white dwarf composed mostly of carbon and oxygen, surrounded by a thin atmosphere of helium. If the helium is hot and dense enough to trigger nuclear burning, this can ignite an explosion that sweeps through the entire helium atmosphere. Then, a resulting shockwave through the body of the white dwarf can trigger a second explosion in the core, ripping the white dwarf apart and creating a supernova even if the white dwarf is below the Chandrasekhar mass limit.

    MUSSES1604D: The First Helium-Triggered Supernova?

    Figure 2: Brightness of the supernova over time, as observed through blue (left) and green (right) filters. The measured brightness of the supernova is shown by the coloured squares, while various model fits are shown by different lines. It isn’t clear from the data that the team collected whether the supernova dips in brightness as the models predict, or whether it just plateaus for a few days. Either way there are clearly two separate periods in which the source is brightening. This is Figure 3 in today’s paper.

    Today’s paper is about a supernova called MUSSES1604D, which was first detected in April 2016. It was discovered by a survey using the impressively named Hyper Suprime-Cam instrument (a camera which is larger than a person and heavier than the average car).

    NAOJ Subaru Hyper Suprime-Cam

    NAOJ/Subaru Telescope at Mauna Kea Hawaii, USA,4,207 m (13,802 ft) above sea level

    This survey is optimised towards finding supernovae in the first few days after they start, while their brightness is still shooting up. While the team were watching MUSSES1604D it did several interesting things. Firstly it showed signs of what they call an ‘early flash’: an initial period in which the supernova was growing brighter, after which it seemed to either stall or fade in brightness for several days before continuing to brighten. Secondly, during this early flash the supernova turned very red, before becoming blue again during the main explosion.

    Figure 3: Spectra of MUSSES1604D, compared with models from various helium shell ignition models. Heavy metals in the supernova produce the features at the left hand side of the spectrum, while the dips on the right hand side (beyond around 6000 angstroms) are produced by silicon. Note that the models do not quite fit with the data, implying some further development of the models might be necessary. This is Figure 4 in today’s paper.

    A spectrum taken of the supernova showed that its composition was also odd. The elements that you see in an SN Ia are generally dependent on the temperature of the explosion. Most of the features in the spectrum MUSSES1604D are from silicon and indicate a fairly average temperature — which agrees with the brightness that they measure. However, the spectrum also shows the presence of heavy metals, such as iron and titanium. These would generally be found in cooler SNe Ia. The presence of these heavy metals is probably linked to the red colour of the explosion’s early flash, as these elements tend to absorb a lot of blue light.

    These unusual characteristics — the early flash, its red colour, and the odd mix of elements — are difficult to explain with any of the classical models of SNe Ia. However, these traits do fit rather well with the double detonation model. In this model, the early flash would come from the ignition of the white dwarf’s helium atmosphere, before the main peak in brightness which comes from the explosion of the white dwarf core. The first explosion would, through nuclear fusion, produce a burst of heavy elements that cause it to appear red. These heavy elements would then hang around during the main explosion, causing the unusual mix of elements seen in MUSSES1604D.

    This is the first strong evidence we have of an SN Ia with an early helium explosion. It’s a promising sign that the double detonation model can explain at least some supernovae, and gives theorists a known example to constrain their models. This is an exciting result for the field, and brings us closer to solving the decades-long question about how SNe Ia occur.

    See the full article here .

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    Astrobites is a daily astrophysical literature journal written by graduate students in astronomy. Our goal is to present one interesting paper per day in a brief format that is accessible to undergraduate students in the physical sciences who are interested in active research.
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    Reading a technical paper from an unfamiliar subfield is intimidating. It may not be obvious how the techniques used by the researchers really work or what role the new research plays in answering the bigger questions motivating that field, not to mention the obscure jargon! For most people, it takes years for scientific papers to become meaningful.
    Our goal is to solve this problem, one paper at a time. In 5 minutes a day reading Astrobites, you should not only learn about one interesting piece of current work, but also get a peek at the broader picture of research in a new area of astronomy.

  • richardmitnick 3:26 pm on October 5, 2017 Permalink | Reply
    Tags: , , , , NAOJ Cray XC30 ATERUI, , , Type Ia supernovae,   

    From NOAJ Subaru: “Surface Helium Detonation Spells End for White Dwarf” 



    October 4, 2017
    No writer credit

    An international team of researchers has found evidence that the brightest stellar explosions in our Universe could be triggered by helium nuclear detonation near the surface of a white dwarf star. Using Hyper Suprime-Cam mounted on the Subaru Telescope, the team detected a type Ia supernova within a day after the explosion, and explained its behavior through a model calculated using the supercomputer ATERUI.

    NAOJ Cray XC30 ATERUI, installed in the NAOJ Mizusawa campus

    Figure 1: A type Ia supernova detected within a day after exploding. Taken with Hyper Suprime-Cam mounted on the Subaru Telescope. Figure without the labels is linked here. (Credit: University of Tokyo/NAOJ)

    NAOJ Subaru Hyper Suprime-Cam

    Some stars end their lives with a huge explosion called a supernova. The most famous supernovae are the result of a massive star exploding, but a white dwarf, the remnant of an intermediate mass star like our Sun, can also explode. This can occur if the white dwarf is part of a binary star system. The white dwarf accretes material from the companion star, then at some point, it might explode as a type Ia supernova.

    Because of the uniform and extremely high brightness (about 5 billion times brighter than the Sun) of type Ia supernovae, they are often used for distance measurements in astronomy. However, astronomers are still puzzled by how these explosions are ignited. Moreover, these explosions only occur about once every 100 years in any given galaxy, making them difficult to catch.

    An international team of researchers led by Ji-an Jiang, a graduate student of the University of Tokyo, and including researchers from the University of Tokyo, the Kavli Institute for the Physics and Mathematics of the Universe (IPMU), Kyoto University, and the National Astronomical Observatory of Japan (NAOJ), tried to solve this problem. To maximize the chances of finding a type Ia supernova in the very early stages, the team used Hyper Suprime-Cam (HSC) mounted on the Subaru Telescope, a combination which can capture an ultra-wide area of the sky at once. Also they developed a system to detect supernovae automatically in the heavy flood of data during the survey, which enabled real-time discoveries and timely follow-up observations.

    They discovered over 100 supernova candidates in one night with Subaru/Hyper Suprime-Cam, including several supernovae that had only exploded a few days earlier. In particular, they captured a peculiar type Ia supernova within a day of it exploding. Its brightness and color variation over time are different from any previously-discovered type Ia supernova. They hypothesized this object could be the result of a white dwarf with a helium layer on its surface. Igniting the helium layer would lead to a violent chain reaction and cause the entire star to explode. This peculiar behavior can be totally explained with numerical simulations calculated using the supercomputer ATERUI. “This is the first evidence that robustly supports a theoretically predicted stellar explosion mechanism!” said Jiang.

    This result is a step towards understand the beginning of type Ia supernovae. The team will continue to test their theory against other supernovae, by detecting more and more supernovae just after the explosion. The details of their study are to be published in Nature on October 5, 2017 (Jiang et al. 2017, A hybrid type la supernova with an early flash triggered by helium-shell detonation, Nature).

    See the full article here .

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    The National Astronomical Observatory of Japan (NAOJ) is an astronomical research organisation comprising several facilities in Japan, as well as an observatory in Hawaii. It was established in 1988 as an amalgamation of three existing research organizations – the Tokyo Astronomical Observatory of the University of Tokyo, International Latitude Observatory of Mizusawa, and a part of Research Institute of Atmospherics of Nagoya University.

    In the 2004 reform of national research organizations, NAOJ became a division of the National Institutes of Natural Sciences.

    NAOJ Subaru Telescope

    NAOJ Subaru Telescope interior

    ESO/NRAO/NAOJ ALMA Array in Chile in the Atacama at Chajnantor plateau, at 5,000 metres

    Solar Flare Telescope

    Nobeyama Radio Telescope - Copy
    Nobeyama Radio Observatory

    Nobeyama Solar Radio Telescope Array
    Nobeyama Radio Observatory: Solar

    Misuzawa Station Japan
    Mizusawa VERA Observatory

    NAOJ Okayama Astrophysical Observatory Telescope
    Okayama Astrophysical Observatory

    The National Astronomical Observatory of Japan (NAOJ) is an astronomical research organisation comprising several facilities in Japan, as well as an observatory in Hawaii. It was established in 1988 as an amalgamation of three existing research organizations – the Tokyo Astronomical Observatory of the University of Tokyo, International Latitude Observatory of Mizusawa, and a part of Research Institute of Atmospherics of Nagoya University.

    In the 2004 reform of national research organizations, NAOJ became a division of the National Institutes of Natural Sciences.

  • richardmitnick 6:58 am on May 19, 2016 Permalink | Reply
    Tags: , , , Type Ia supernovae   

    From ANU: “Supernova reserve fuel tank clue to big parents” 

    ANU Australian National University Bloc

    Australian National University

    19 May 2016
    Dr Phil Dooley
    +61 2 6125 7979

    No image capton. No image credit.

    Some supernovae have a reserve tank of radioactive fuel that cuts in and powers their explosions for three times longer than astronomers had previously thought.

    A team of astronomers jointly led by Dr Ivo Seitenzahl from ANU Research School of Astronomy and Astrophysics detected the faint afterglow of a supernova, and found it was powered by radioactive cobalt-57.

    The discovery gives important new clues about the causes of Type Ia supernovae, which astronomers use to measure vast distances across the Universe.

    Dr Seitenzahl said the discovery of cobalt-57 fingerprints in a Type Ia supernova gave insights into the star that exploded and suggested it was at the top of its weight range.

    “This explosion suggested that it was a star stealing matter from an orbiting partner until it got so massive that its core of carbon ignited and set off the explosion,” said Dr Seitenzahl.

    “It’s exciting to work this out because there are conflicting theories about what causes Type Ia supernovae.

    “It’s curious to me that we still don’t know exactly what these things are, even though they are so important for cosmology.”

    Type Ia supernovae are explosions that can be seen even in far-away galaxies and help astronomers study the large-scale structure of the Universe. For a period of weeks after they explode they can outshine the billions of other stars in their galaxy, and do so in a predictable fashion that makes them a reliable cosmic beacon [“standard candle”].

    Astronomers believe that Type Ia supernovae occur when matter falls into an old white-dwarf star and pushes its mass over a threshold at which the carbon core ignites and triggers the star to explode.

    However, it was unclear whether the star sucked in matter slowly from a companion star, or a collision between two smaller stars pushed the system over the edge.

    In the case of a collision, theories suggest a white dwarf can be as small as 1.1 times the mass of the Sun when it explodes, but this finding pointed towards a heavier star, around 1.4 solar masses, supporting the slow suck model.

    The team, from Australia and the US, calculated the star’s mass from the abundance of the cobalt isotopes created by nuclear fusion in the supernova.

    When the core ignites, carbon and oxygen fuse to form lots of radioactive cobalt-56, whose radioactive decay into iron-56 with a half-life of 77 days powers the peak brightness of a supernova.

    However, Dr Seitenzahl had believed traces of cobalt-57 must be created too, and the exact amount would distinguish between a 1.1 and 1.4 solar mass explosion.

    “It doesn’t seem like a big difference, but it amounts to 100 times higher density in the core of the star, which means a lot more cobalt-57 is created.”

    Even so, the amount of cobalt-57 is tiny, so the team needed patience to see it against the glare of the cobalt-56. Cobalt-57’s longer half life, 270 days, means it keeps glowing after the cobalt-56 has died out after a couple of years.

    The international team watched the supernova for 1,055 days after the explosion with the Hubble Space Telescope, and found a persistent glow after the cobalt-56 had faded that matched Dr Seitenzahl’s predictions, from 2009.

    NASA/ESA Hubble Telescope
    NASA/ESA Hubble Telescope

    “I was skeptical whether clues for the presence of cobalt-57 in Type Ia supernovae would be observed in my lifetime,” Seitenzahl said.

    “I am absolutely thrilled that now, only seven years after our predictions, the Hubble Space Telescope has enabled us to make these incredibly faint observations and proved the theory right,” he said.

    See the full article here .

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    ANU Campus

    ANU is a world-leading university in Australia’s capital city, Canberra. Our location points to our unique history, ties to the Australian Government and special standing as a resource for the Australian people.

    Our focus on research as an asset, and an approach to education, ensures our graduates are in demand the world-over for their abilities to understand, and apply vision and creativity to addressing complex contemporary challenges.

  • richardmitnick 10:34 am on May 14, 2016 Permalink | Reply
    Tags: , , , Type Ia supernovae   

    From Ethan Siegel: “Could A New Type Of Supernova Eliminate Dark Energy?” 

    Starts with a Bang

    May 13, 2016
    Ethan Siegel

    Supernova in Messier 101
    A game-changing supernova in the galaxy Messier 101, observed in 2011. Image credit: NASA / Swift.

    NASA/SWIFT Telescope
    NASA/SWIFT Telescope

    Every once in a while, some Earth-shattering discoveries come along that forever change our view of the Universe. Back in the late 1990s, observations of distant supernovae made it clear that the Universe wasn’t only expanding, but that distant galaxies were actually speeding up as they moved away from us, a Nobel Prize-worthy discovery that told us the fate of our Universe. By measuring their optical properties and comparing them to supernovae seen nearby, we were able to determine their distances, finding that they were fainter (and hence, more distant) compared to what we’d expect. The interpretation was that this was because the Universe was accelerating due to some form of dark energy, but a 2015 study* showed another possibility: that these supernovae appeared fainter because they were inherently different from the supernovae we saw nearby. Could this alternative explanation eliminate the need for dark energy?

    Triangulum Galaxy, European Southern Observatory (ESO).
    Triangulum Galaxy, VLT, European Southern Observatory (ESO)

    This is potentially a very, very big deal for our understanding of all there is, and how our Universe will end. Let’s go back nearly 100 years to a lesson we should have learned, and then come forward to today to see why. Back in 1923, Edwin Hubble was looking at a particular class of objects — the obscure, faint “spiral nebulae” in the sky — studying novae occurring in them and trying to add to our knowledge of just what these objects were. Some people contended that they were proto-stars within the Milky Way, while others believed them to be island Universes, millions of light years beyond our own galaxy, consisting of billions of stars apiece.

    While observing the great nebula in Andromeda on October 6th of that year, he saw a nova go off, then a second, and then a third. And then something unprecedented happened: a fourth nova went off in the same location as the first.

    Andromeda Galaxy NASA/ESA Hubble
    Andromeda Galaxy NASA/ESA Hubble

    The star in the great Andromeda Nebula that changed our view of the Universe forever, as imaged first by Edwin Hubble in 1923 and then by the Hubble Space Telescope nearly 90 years later. Image credit: NASA, ESA and Z. Levay (STScI) (for the illustration); NASA, ESA and the Hubble Heritage Team (STScI/AURA) (for the image).

    NASA/ESA Hubble Telescope
    NASA/ESA Hubble Telescope

    Novae do sometimes repeat, but it usually takes hundreds or thousands of years for them to do so, as they occur only when enough fuel builds up on the surface of a collapsed star to ignite. Of all the novae we’ve ever discovered, even the most rapidly replenishing takes many years to go off again. The idea that one would repeat in only a few hours? Absurd.

    But there was something we knew about that could go from very bright to dim to bright again in just a few hours: a variable star! (Hence, his crossing out of “N” for nova and excitedly writing “VAR!”)

    The Variable Star RS Puppis, with its light echoes shining through the interstellar clouds. Image credit: NASA, ESA, and the Hubble Heritage Team.

    The incredible work of Henrietta Leavitt taught us that some stars in the Universe — Cepheid variable stars — get brighter-and-dimmer with a certain period, and that period is related to their intrinsic brightness. This is important, because it means that if you measure the period (something easy to do), then you know the intrinsic brightness of the thing you’re measuring. And since you can easily measure the apparent brightness, then you can immediately know how far away that object is, because the brightness/distance relationship is something we’ve known for hundreds of years!

    The brightness/distance relationship dates back to at least Christiaan Huygens in the 17th century. Image credit: E. Siegel, from his book Beyond The Galaxy.

    Now, Hubble used this knowledge of variable stars and the fact that we could find them in these spiral nebulae (now known to be galaxies) to measure their distances from us. He then combined their known redshift with these distances to derive Hubble’s Law and figure out the rate of expansion of the Universe.

    Remarkable, right? But unfortunately, we often gloss over something about this discovery: Hubble’s conclusions for what that expansion rate actually was were totally wrong!

    The original graph from Hubble’s findings, and the first demonstration of Hubble’s Law. Image credit: E. Hubble, 1929.

    The problem, you see, was that the Cepheid variable stars that Hubble measured in these galaxies were intrinsically different than the Cepheids that Henrietta Leavitt measured. As it turned out, Cepheids come in two different classes, something Hubble didn’t know at the time. While Hubble’s Law still held, his initial estimates for distances were far too low, and so his estimates for the expansion rate of the Universe were far too high. In time, we got it right, and while the overall conclusions — that the Universe was expanding and that these spiral nebulae were galaxies far beyond our own — didn’t change, the details of how the Universe was expanding definitely did!

    An extragalactic supernova, along with the galaxy that hosts it, from 1994. Image credit: NASA/ESA, The Hubble Key Project Team and The High-Z Supernova Search Team.

    And that brings us to the present day, and a very similar problem, this time with supernovae. Far brighter than Cepheids, supernovae can often shine nearly as brightly — albeit for a very short time — as the entire galaxy that hosts it! Instead of millions of light years away, they can be seen, under the right circumstances, more than ten billion light years distant, allowing us to probe farther and farther into the Universe. In addition, a special type of supernova, type Ia supernovae, arises from a runaway fusion reaction taking place inside a white dwarf.

    When these reactions occur, the entire star is destroyed, but more importantly, the light curve of the supernova, or how it brightens and then dims over time, is well-known, and has some universal properties.

    Universal light-curve properties for Type Ia supernovae. Image credit: S. Blondin and Max Stritzinger.

    By the late 1990s, enough supernova data had been collected at large enough distances that two independent teams — the High-z Supernova Search Team and the Supernova Cosmology Project — both announced that based on this data, the Universe’s expansion was accelerating, and that there was some form of dark energy dominating the Universe.

    It’s important to be appropriately skeptical of a revolutionary discovery like this. If it turned out that there was something amiss with the interpretation of this supernova data, the entire set of conclusions reached — that the Universe was accelerating — would have disappeared entirely. There were some possibilities for why this data might not be trustworthy:

    For one, there were two different methods by which supernovae could occur: from accretion of matter from a companion star (L), and from a merger with another white dwarf (R). Would both of these result in the same type of supernova?

    Two different ways to make a Type Ia supernova: the accretion scenario (L) and the merger scenario (R). These may be fundamentally different from one another. Images credit: NASA / CXC / M. Weiss.

    For another, these supernovae at great distances may have been occurring in very different environments from the ones we see close by today. Are we positive that the light curves we see today reflect the light curves at great distances?

    And for still another, it’s possible that something happened to this light during their incredible travels from great distances to our eyes. Are we sure there isn’t some new type of dust or some other light-dimming property (like photon-axion oscillations) at work here?

    As it turns out, these issues were all able to be resolved and ruled out; these things aren’t issues. But recently — and this is what the 2015 study concluded — we’ve discovered that these so-called “standard candles” may not be so standard after all. Just like the Cepheids come in different varieties, these type Ia supernovae come in different varieties too.

    A Type Ia supernova in the nearby galaxy M82. This one is fundamentally different from the one atop this page, observed in 2011 in M101. Image credit: NASA/Swift/P. Brown, TAMU

    Imagine you had a box of candles that you thought were all identical to one another: you could light them up, put them all at different distances, and immediately, just from measuring the brightness you saw, know how far away they are. That’s the idea behind a standard candle in astronomy, and why type Ia supernovae are so powerful.

    But now, imagine that these candle flames aren’t all the same brightness! Suddenly, some are a little brighter and some are a little dimmer; you have two classes of candles, and while you might have more of the brighter ones close by, you might have more of the dimmer ones far away.

    That’s what we think we’ve just discovered with supernovae: there are actually two separate classes of them, where one’s a little brighter in the blue/UV, and one’s a little brighter in the red/IR, and the light curves they follow are slightly different. This might mean that, at high redshifts (large distances), the supernovae themselves are actually intrinsically fainter, and not that they’re farther away.

    In other words, the inference we drew — that the Universe is accelerating — might be based on a misinterpretation of the data!

    Image credit: Ned Wright, based on the latest data from Betoule et al. (2014), via http://www.astro.ucla.edu/~wright/sne_cosmology.html.

    If we’ve got the distances wrong for these supernovae, maybe we’ve got dark energy wrong, too! At least, that would be the big worry. The smaller worry would be that dark energy is still real, but there might be less of it than we previously thought.

    So which of these worries are valid? As it turns out, only the small one, and not the big one! You see, in 1998, we only had supernova data pointing towards dark energy. But as time went on, we gained two other pieces of evidence that provided evidence that was just as strong.

    The best map of the CMB and the best constraints on dark energy from it. Images credit: ESA & the Planck Collaboration (top); P. A. R. Ade et al., 2014, A&A (bottom).

    1.) The Cosmic Microwave Background. The fluctuations in the leftover glow from the Big Bang — as measured by WMAP and later, to higher precision, Planck — strongly indicated that the Universe was about 5% normal matter, 27% dark matter, and about 68% dark energy. While the microwave background doesn’t do a great job by itself of telling you what the properties of this dark energy are, it does tell you that you have about 2/3 of the Universe’s energy in a form that isn’t clumpy and massive.

    For a while, this was actually an even bigger problem, as supernovae alone indicated that about 3/4 of the Universe’s energy was dark energy. It’s possible that these new revelations about supernovae, that there are two types of Type Ia supernovae with different intrinsic light curves, could help the data line up better.

    An illustration of clustering patterns due to Baryon Acoustic Oscillations. Image credit: Zosia Rostomian, Lawrence Berkeley National Laboratory.

    2.) The way galaxies cluster. In the early Universe, dark matter and normal matter — and how they do-and-do-not interact with radiation — govern how galaxies wind up clustered together in the Universe today. If you see a galaxy anywhere in the Universe, there’s this odd property that you’re more likely to have another galaxy about 500 million light years away from it than you are to have one either 400 or 600 million light years away. This is due to a phenomenon known as Baryon Acoustic Oscillations (BAO), and it’s because normal matter gets pushed out by radiation, while dark matter doesn’t.

    The thing is, the Universe is expanding due to everything in it at all times, including dark energy. So as the Universe expands, that preferred scale of 500 million light years changes. Instead of a “standard candle,” BAO allows us to have a “standard ruler,” which we can also use to measure dark energy.

    While this wasn’t the case in the late 1990s, as surveys like the 2dF GRS weren’t complete and the SDSS hadn’t even started, today’s measurements from BAO are just as good at present as the measurements from supernovae.

    SDSS Telescope at Apache Point, NM, USA
    SDSS Telescope at Apache Point, NM, USA

    What’s even more compelling is the fact that they seem to give the same results: a Universe that’s about 70% dark energy, and consistent with a cosmological constant and not domain walls, cosmic strings, or many other exotic types.

    In fact, if we combine all three data sets, we find that they all point roughly towards the same picture.

    Constraints on dark energy from three independent sources: supernovae, the CMB and BAO. Note that even without supernovae, we’d need dark energy. Image credit: Supernova Cosmology Project, Amanullah, et al., Ap.J. (2010).

    What we’ve learned from this is that the amount of dark energy and the type of dark energy we infer from supernovae may change slightly and in a subtle manner, and this may actually be good for bringing the three methods — supernovae, the CMB and BAO — into better alignment. This is one of those great moments in science where one incorrect assumption doesn’t cause us to throw all our results and conclusions out, but rather where it helps us more accurately understand a phenomenon that’s puzzled us since we first discovered it. Dark energy is real, and thanks to this new discovery, we just might come to understand it — and its effects on the Universe — better than ever before.

    *Science paper:

    See the full article here .

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    “Starts With A Bang! is a blog/video blog about cosmology, physics, astronomy, and anything else I find interesting enough to write about. I am a firm believer that the highest good in life is learning, and the greatest evil is willful ignorance. The goal of everything on this site is to help inform you about our world, how we came to be here, and to understand how it all works. As I write these pages for you, I hope to not only explain to you what we know, think, and believe, but how we know it, and why we draw the conclusions we do. It is my hope that you find this interesting, informative, and accessible,” says Ethan

  • richardmitnick 2:52 pm on March 22, 2016 Permalink | Reply
    Tags: , , , Type Ia supernovae   

    From CfA: “First Discovery of a Binary Companion for a Type Ia Supernova” 

    Harvard Smithsonian Center for Astrophysics

    Center For Astrophysics

    March 22, 2016
    Rebecca Johnson
    The University of Texas at Austin
    +1 512-475-6763

    Christine Pulliam
    Media Relations Manager
    Harvard-Smithsonian Center for Astrophysics

    The blue-white dot at the center of this image is supernova 2012cg, seen by the 1.2-meter telescope at Fred Lawrence Whipple Observatory. At 50 million light-years away, this supernova is so distant that its host galaxy, the edge-on spiral NGC 4424, appears here as only an extended smear of purple light. Peter Challis/Harvard-Smithsonian CfA

    Whipple 1.2 meter telescope interior Harvard, located in Amado, Arizona on Mount Hopkins
    Whipple 1.2 meter telescope interior Harvard, located in Amado, Arizona on Mount Hopkins

    A team of astronomers including Harvard’s Robert Kirshner and Peter Challis has detected a flash of light from the companion to an exploding star. This is the first time astronomers have witnessed the impact of an exploding star on its neighbor. It provides the best evidence on the type of binary star system that leads to Type Ia supernovae. This study reveals the circumstances for the violent death of some white dwarf stars and provides deeper understanding for their use as tools to trace the history of the expansion of the universe. These types of stellar explosions enabled the discovery of dark energy, the universe’s accelerating expansion that is one of the top problems in science today.

    The subject of how Type Ia supernovae arise has long been a topic of debate among astronomers.

    “We think that Type Ia supernovae come from exploding white dwarfs with a binary companion,” said Howie Marion of The University of Texas at Austin (UT Austin), the study’s lead author. “The theory goes back 50 years or so, but there hasn’t been any concrete evidence for a companion star before now.”

    Astronomers have battled over competing ideas, debating whether the companion was a normal star or another white dwarf.

    “This is the first time a normal Type Ia has been associated with a binary companion star,” said team member and professor of astronomy J. Craig Wheeler (UT Austin). “This is a big deal.”

    The binary star progenitor theory for Type Ia supernovae starts with a burnt-out star called a white dwarf. Mass must be added to that white dwarf to trigger its explosion – mass that the dwarf pulls off of a companion star. When the influx of mass reaches the point that the dwarf is hot enough and dense enough to ignite the carbon and oxygen in its interior, a thermonuclear reaction starts that causes the dwarf to explode as a Type Ia supernova.

    For a long time, the leading theory was that the companion was an old red giant star that swelled up and lost matter to the dwarf, but recent observations have virtually ruled out that notion. No red giant is seen. The new work presents evidence that the star providing the mass is still burning hydrogen at its center, that is, that this companion star is still in the prime of life.

    According to team member Robert P. Kirshner of the Harvard-Smithsonian Center for Astrophysics, “If a white dwarf explodes next to an ordinary star, you ought to see a pulse of blue light that results from heating that companion. That’s what theorists predicted and that’s what we saw.

    “Supernova 2012cg is the smoking — actually glowing — gun: some Type Ia supernovae come from white dwarfs doing a do-si-do with ordinary stars.”

    Located 50 million light-years away in the constellation Virgo, Supernova 2012cg was discovered on May 17, 2012 by the Lick Observatory Supernova Search. Marion’s team began studying it the next day with the telescopes of the Harvard-Smithsonian Center for Astrophysics.

    “It’s important to get very early observations,” Marion said, “because the interaction with the companion occurs very soon after the explosion.”

    The team continued to observe the supernova’s brightening for several weeks using many different telescopes, including the 1.2-meter telescope at Fred Lawrence Whipple Observatory and its KeplerCam instrument, the Swift gamma-ray space telescope, the Hobby-Eberly Telescope at McDonald Observatory, and about half a dozen others.

    NASA/SWIFT Telescope
    NASA/SWIFT Telescope

    U Texas McDonald Observatory Hobby-Eberle 9.1 meter Telescope
    U Texas McDonald Observatory Hobby-Eberle 9.1 meter Telescope

    “This is a global enterprise,” Wheeler said. Team members hail from about a dozen U.S. universities, as well as institutions in Chile, Hungary, Denmark, and Japan.

    What the team found was evidence in the characteristics of the light from the supernova that indicated it could be caused by a binary companion. Specifically, they found an excess of blue light coming from the explosion. This excess matches with the widely accepted models created by U.C. Berkeley astronomer Dan Kasen for what astronomers expect to see when a star explodes in a binary system.

    “The supernova is blowing up next to a companion star, and the explosion impacts the companion star,” Wheeler explained. “The side of that companion star that’s hit gets hot and bright. The excess blue light is coming from the side of the companion star that gets heated up.”

    Combined with the models, the observations indicate that the binary companion star has a minimum mass of six suns.

    “This is an interpretation that is consistent with the data,” said team member Jeffrey Silverman, stressing that it is not concrete proof of the exact size of the companion, like would come from a photograph of the binary star system. Silverman is a postdoctoral researcher at UT Austin.

    Only a few other Type Ia supernovae have been observed as early as this one, Marion said, but they have not shown an excess of blue light. More examples are needed.

    “We need to study a hundred events like this and then we’ll be able to know what the statistics are,” Wheeler said.

    The work is published today in The Astrophysical Journal.

    This press release is being issued jointly with The University of Texas at Austin.

    Other scientific institutions involved in this study:

    University of Texas at Austin, 1 University Station C1400,
    Austin, TX, 78712-0259, USA
    2 Harvard-Smithsonian Center for Astrophysics, 60 Garden
    St., Cambridge, MA 02138, USA; ghmarion@gmail.com
    3 George P. and Cynthia Woods Mitchell Institute for Fun-
    damental Physics & Astronomy, Texas A. & M. University,
    Department of Physics and Astronomy, 4242 TAMU, College
    Station, TX 77843, USA
    4 Department of Optics and Quantum Electronics, University
    of Szeged, Domter 9, 6720, Szeged, Hungary
    5 NSF Astronomy and Astrophysics Postdoctoral Fellow
    6 Physics Department, Texas Tech University, Lubbock, TX ,
    79409, USA
    7 Department of Physics and Astronomy, Rutgers the State
    University of New Jersey, 136 Frelinghuysen Road, Piscataway,
    NJ 08854 USA
    8 Department of Physics, Lehigh University, 16 Memorial
    Drive East, Bethlehem, Pennsylvania 18015, USA
    9 Department of Physics, Southern Methodist University,
    Dallas, TX 75275, USA
    10 Astronomy Department, University of Illinois at Urbana-
    Champaign,1002 W. Green Street, Urbana, IL 61801 USA
    11 Department of Physics, University of Illinois Urbana-
    Champaign, 1110 W. Green Street, Urbana, IL 61801 USA
    12 Center for Theoretical Physics and Department of Physics,
    Massachusetts Institute of Technology, Cambridge, MA 02139
    13 Department of Astronomy, University of California, Berke-
    ley, CA 94720-3411, USA
    14 Las Cumbres Observatory Global Telescope Network, 6740
    Cortona Dr., Suite 102, Goleta, CA 93117, USA
    15 Department of Physics, University of California, Santa
    Barbara, Broida Hall, Mail Code 9530, Santa Barbara,CA
    93106, USA
    16 Carnegie Observatories, Las Campanas Observatory,
    Colina El Pino, Casilla 601, Chile
    17 Department of Physics and Astronomy, Aarhus University,
    Ny Munkegade 120, DK-8000 Aarhus C, Denmark
    18 Department of Astronomy, Kyoto University,
    Kitashirakawa-Oiwake-cho, Sakyo-ku, Kyoto 606-8502, Japan
    19 Kavli Institute for the Physics and Mathematics of the
    Universe (WPI), University of Tokyo, 5-1-5 Kashiwanoha,
    Kashiwa, Chiba 277-8583, Japan
    20 Department of Astrophysical Sciences, Peyton Hall, Prince-
    ton University, Princeton, NJ 08544, USA
    21 Department of Physics & Astronomy, Western Washington
    University, 516 High Street, Bellingham, WA 98225

    The science team (numbers refer to above institutions):

    G. H. Marion1,2, Peter J. Brown3, Jozsef Vink´o1,4, Jeffrey M. Silverman1,5, David J. Sand6, Peter Challis2,
    Robert P. Kirshner2, J. Craig Wheeler1, Perry Berlind2, Warren R. Brown2, Michael L. Calkins2,
    Yssavo Camacho7,8, Govinda Dhungana9, Ryan J. Foley10,11, Andrew S. Friedman12,2, Melissa L. Graham13,
    D. Andrew Howell14,15, Eric Y. Hsiao16,17, Jonathan M. Irwin2, Saurabh W. Jha7, Robert Kehoe9,
    Lucas M. Macri3, Keiichi Maeda18,19, Kaisey Mandel2, Curtis McCully14, Viraj Pandya7,20, Kenneth J. Rines21,
    Steven Wilhelmy21 and Weikang Zheng13

    Other observatories included:
    Las Cumbres Observatory Global Telescope Network
    LCOGT Las Cumbres Observatory Global Telescope Network

    Piszk´estet˝o Mountain Station of the Konkoly Observatory

    Magellan Observatory
    Magellan 6.5 meter telescopes
    Baade and Clay telescopes

    Caltech Palomar 1.5 meter 60 inch telescope interior

    CfA Whipple 1.5 meter Tillinghast telescope
    CfA Whipple 1.5 meter Tillinghast telescope

    South African Large Telescope
    SALT South African Large Telescope

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

    See the full article here .

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    The Center for Astrophysics combines the resources and research facilities of the Harvard College Observatory and the Smithsonian Astrophysical Observatory under a single director to pursue studies of those basic physical processes that determine the nature and evolution of the universe. The Smithsonian Astrophysical Observatory (SAO) is a bureau of the Smithsonian Institution, founded in 1890. The Harvard College Observatory (HCO), founded in 1839, is a research institution of the Faculty of Arts and Sciences, Harvard University, and provides facilities and substantial other support for teaching activities of the Department of Astronomy.

  • richardmitnick 3:30 pm on December 29, 2015 Permalink | Reply
    Tags: , , , , Type Ia supernovae   

    From AAS NOVA: “Two Kinds of Type Ia Supernovae” 


    American Astronomical Society

    29 December 2015
    Susanna Kohler

    The Changing Fractions of Type Ia Supernova NUV–Optical Subclasses with Redshift
    Published April 2015
    [I missed this the first time around. Glad it was reposted in AAS NOVA’s 2015 review.]

    Swift ultraviolet image of M101; the yellow bars point out the location of a type Ia supernova. A study published this year identified two different color classes of these supernovae. [NASA/Swift]

    Main takeaway:

    A team of scientists led by Peter Milne (University of Arizona) used ultraviolet observations from the Swift spacecraft to determine that type Ia supernovae, stellar explosions previously thought to all belong in the same class, actually fall into two subgroups: those that are slightly redder in NUV wavelengths and those that are slightly bluer.

    NASA SWIFT Telescope

    Plot of the percentage of supernovae that are NUV-blue (rather than NUV-red), as a function of redshift. NUV-blue supernovae dominate at higher redshifts. [Milne et al. 2015]

    Why it’s interesting:

    It turns out that the fraction of supernovae in each of these two groups is redshift-dependent. At low redshifts (i.e., nearby), the population of type Ia supernovae is dominated by NUV-red supernovae. At high redshifts (i.e., far away), the population is dominated by NUV-blue supernovae. Since cosmological distances are measured using Type Ia supernovae as standard candles, the fact that we’ve been modeling these supernovae all the same way (rather than treating them as two separate subclasses) means we may have been systematically misinterpreting distances.

    What this means for the universe’s expansion:

    This seemingly simple discovery carries hefty repercussions — in fact, our estimates of the expansion rate of the universe may be incorrect! The authors believe that if we correct for this error, we’ll find that the universe is not expanding as quickly as we thought.

    Peter A. Milne et al 2015 ApJ 803 20. doi:10.1088/0004-637X/803/1/20

    See the full article here .

    Please help promote STEM in your local schools.

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  • richardmitnick 2:32 pm on July 22, 2015 Permalink | Reply
    Tags: , , Type Ia supernovae,   

    From Weizmann: “Seeing a Supernova in a New Light” 

    Weizmann Institute of Science logo

    Weizmann Institute of Science

    29 Jun 2015

    No Writer Credit

    Supernova 3C58, first observed in the year 1181 AD by Chinese and Japanese astronomers, imaged by the Chandra telescope in X-ray emissions. NASA/CXC/SAO

    X-Ray image of 3C58 by Chandra X-Ray Observatory.
    The pullout box shows the inner toroidal-shaped nebula

    Type Ia supernovae are the “standard candles” astrophysicists use to chart distance in the Universe. But are these dazzling exploding stars truly all the same? To answer this, scientists must first understand what causes stars to explode and become supernovae. Recently, a unique collaborative project between the California Institute of Technology (Caltech) and the Weizmann Institute of Science provided a rare glimpse of the process. Their findings were published in Nature.

    The project, called the Palomar Transient Factory, is a robotic telescope system based in Southern California that scans the night sky for changes.

    Caltech Palomar Intermediate Palomar Transient Factory telescope
    Caltech Palomar Transit Factory interior
    Palomar Transient Factory

    In May, halfway around the world at the Weizmann Institute, Dr. Ilan Sagiv realized that one of the bright new lights the Palomar telescope had pinpointed was, indeed, a supernova – just four days into the explosion – and he sounded the alert sending the Swift Space Telescope on NASA’s Swift Satellite to observe the blast. But the Swift Telescope also observed in an unusual way – in the invisible, ultraviolet range.

    NASA SWIFT Telescope

    “Ultraviolet is crucial,” says the Weizmann Institute’s Prof. Avishay Gal-Yam of the Particle Physics and Astrophysics Department, “because initially, supernova blasts are so energetic that the most important information can only be gathered in short wavelengths. And it can only be seen from a space telescope, because the ultraviolet wavelengths are filtered out in the Earth’s atmosphere.”

    The researchers collected observations ranging from the energetic X-ray and UV all the way to the radio wavelengths, the latter effort led by the Institute’s Dr. Assaf Horesh. Caltech graduate student Yi Cao, who was the lead author on the paper, and his advisor Prof. S. Kulkarni, compared the figures from the observations to various models to see which fit. Astrophysicists mostly agree that the exploding stars that become type Ia supernova are extremely dense, old stars called white dwarves. But a number of models have been proposed to explain what makes them suddenly blow up.

    Ultraviolet observation enabled the researchers to see something they had never seen before: a unique, brief spike in the high-energy radiation very early on. This spike, says Gal-Yam, fits a model in which a dwarf star has a giant companion. “The white dwarf is the mass of the Sun packed into a sphere the size of the Earth, while its companion is around 50-100 times bigger around than the Sun.” Material flows from the diffuse star to the dense one until, at some point the pressure from the added mass causes the smaller star to detonate. The radiation spike is caused by the initial material thrown off in the blast slamming into the companion.

    Gal-Yam says that the group’s findings show, among other things, the importance of ultraviolet-range observations. He is hopeful that the ULTRASAT mini-satellite planned by the Weizmann Institute’s Prof. Eli Waxman, together with other researchers, the Israeli Space Agency and NASA, which will observe in the ultraviolet range, will help researchers discover whether this explosive process is common to type Ia supernovae.

    Prof. Avishay Gal-Yam’s research is supported by the Helen and Martin Kimmel Award for Innovative Investigation’ the Helen Kimmel Center for Planetary Science; the Nella and Leon Benoziyo Center for Astrophysics; and the Benoziyo Endowment Fund for the Advancement of Science.

    Prof. Eli Waxman’s research is supported by the Nella and Leon Benoziyo Center for Astrophysics, which he heads. Prof. Waxman is the incumbent of the Max Planck Professorial Chair of Quantum Physics.

    See the full article here.

    Please help promote STEM in your local schools.

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    Weizmann Institute Campus

    The Weizmann Institute of Science is one of the world’s leading multidisciplinary research institutions. Hundreds of scientists, laboratory technicians and research students working on its lushly landscaped campus embark daily on fascinating journeys into the unknown, seeking to improve our understanding of nature and our place within it.

    Guiding these scientists is the spirit of inquiry so characteristic of the human race. It is this spirit that propelled humans upward along the evolutionary ladder, helping them reach their utmost heights. It prompted humankind to pursue agriculture, learn to build lodgings, invent writing, harness electricity to power emerging technologies, observe distant galaxies, design drugs to combat various diseases, develop new materials and decipher the genetic code embedded in all the plants and animals on Earth.

    The quest to maintain this increasing momentum compels Weizmann Institute scientists to seek out places that have not yet been reached by the human mind. What awaits us in these places? No one has the answer to this question. But one thing is certain – the journey fired by curiosity will lead onward to a better future.

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