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  • richardmitnick 10:17 am on July 1, 2019 Permalink | Reply
    Tags: , , , , Eta Carinae,   

    From NASA/ESA Hubble Telescope: “Hubble Captures the Galaxy’s Biggest Ongoing Stellar Fireworks Show” 

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    NASA/ESA Hubble Telescope


    From NASA/ESA Hubble Telescope

    July 01, 2019

    Donna Weaver
    Space Telescope Science Institute, Baltimore, Maryland
    410-338-4493
    dweaver@stsci.edu

    Ray Villard
    Space Telescope Science Institute, Baltimore, Maryland
    410-338-4514
    villard@stsci.edu

    Nathan Smith
    University of Arizona, Tucson, Arizona
    520-621-4513
    nathans@as.arizona.edu

    Jon Morse
    BoldlyGo Institute, New York, New York
    646-380-1813
    jamorse@boldlygo.org

    1

    2
    Compass Image for Eta Carinae
    These images are a composite of separate exposures acquired by the WFC3/UVIS instrument on the Hubble Space Telescope. Several filters were used to sample narrow and wide wavelength ranges. The color results from assigning different hues (colors) to each monochromatic (grayscale) image associated with an individual filter. In this case, the assigned colors are: Blue: F280N Green: F336W Red: F658N

    Eta Carinae (Observations in UV Light Uncover Magnesium Embedded in Warm Gas)

    Imagine slow-motion fireworks that started exploding 170 years ago and are still continuing. This type of firework is not launched into Earth’s atmosphere, but rather into space by a doomed super-massive star, called Eta Carinae, the largest member of a double-star system. A new view from NASA’s Hubble Space Telescope, which includes ultraviolet light, shows the star’s hot, expanding gases glowing in red, white, and blue. Eta Carinae resides 7,500 light-years away.

    The celestial outburst takes the shape of a pair of ballooning lobes of dust and gas and other filaments that were blown out from the petulant star. The star may have initially weighed more than 150 Suns. For decades, astronomers have speculated about whether it is on the brink of total destruction.

    The fireworks started in the 1840s when Eta Carinae went through a titanic outburst, called the Great Eruption, making it the second-brightest star visible in the sky for over a decade. Eta Carinae, in fact, was so bright that for a time it became an important navigational star for mariners in the southern seas.

    The star has faded since that eruption and is now barely visible to the unaided eye. But the fireworks aren’t over yet because Eta Carinae still survives. Astronomers have used almost every instrument on Hubble over the past 25 years to study the rambunctious star.

    Using Hubble’s Wide Field Camera 3 to map the ultraviolet-light glow of magnesium embedded in warm gas (shown in blue), astronomers were surprised to discover the gas in places they had not seen it before.

    NASA/ESA Hubble WFC3

    Scientists have long known that the outer material thrown off in the 1840s eruption has been heated by shock waves after crashing into the doomed star’s previously ejected material. In the new images, the team had expected to find light from magnesium coming from the same complicated array of filaments as seen in the glowing nitrogen (shown in red). Instead, a completely new luminous magnesium structure was found in the space between the dusty bipolar bubbles and the outer shock-heated nitrogen-rich filaments.

    “We’ve discovered a large amount of warm gas that was ejected in the Great Eruption but hasn’t yet collided with the other material surrounding Eta Carinae,” explained Nathan Smith of Steward Observatory at the University of Arizona in Tucson, Arizona, lead investigator of the Hubble program. “Most of the emission is located where we expected to find an empty cavity. This extra material is fast, and it ‘ups the ante’ in terms of the total energy for an already powerful stellar blast.”

    The newly revealed gas is important for understanding how the eruption began, because it represents the fast and energetic ejection of material that may have been expelled by the star shortly before the expulsion of the bipolar lobes. Astronomers need more observations to measure exactly how fast the material is moving and when it was ejected.

    The streaks visible in the blue region outside the lower-left lobe are a striking feature in the image. These streaks are created when the star’s light rays poke through the dust clumps scattered along the bubble’s surface. Wherever the ultraviolet light strikes the dense dust, it leaves a long, thin shadow that extends beyond the lobe into the surrounding gas. “The pattern of light and shadow is reminiscent of sunbeams that we see in our atmosphere when sunlight streams past the edge of a cloud, though the physical mechanism creating Eta Carinae’s light is different,” noted team member Jon Morse of BoldlyGo Institute in New York.

    This technique of searching in ultraviolet light for warm gas could be used to study other stars and gaseous nebulas, the researchers say.

    “We had used Hubble for decades to study Eta Carinae in visible and infrared light, and we thought we had a pretty full accounting of its ejected debris. But this new ultraviolet-light image looks astonishingly different, revealing gas we did not see in other visible-light or infrared images,” Smith said. “We’re excited by the prospect that this type of ultraviolet magnesium emission may also expose previously hidden gas in other types of objects that eject material, such as protostars or other dying stars. Only Hubble can take these kinds of pictures.”

    Eta Carinae has had a violent history, prone to chaotic eruptions that blast parts of itself into space like an interstellar geyser. One explanation for the monster star’s antics is that the convulsions were caused by a complex interplay of as many as three stars, all gravitationally bound in one system. In this scenario, the most massive member would have swallowed one of the stars, igniting the massive Great Eruption of the mid-1800s. Evidence for that event lies in the huge, expanding bipolar lobes of hot gas surrounding the system.

    A fortuitous trick of nature also allowed astronomers in a previous Hubble study to analyze the Great Eruption in detail. Some of the light from the eruption took an indirect path to Earth and is just arriving now. The wayward light was heading away from our planet when it bounced off dust clouds lingering far from the turbulent stars and was rerouted to Earth, an effect called a “light echo.”

    The stellar behemoth will eventually reach its fireworks show finale when it explodes as a supernova. This may have already happened, although the geyser of light from such a brilliant blast hasn’t yet reached Earth.

    See the full article here .


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    The Hubble Space Telescope is a project of international cooperation between NASA and the European Space Agency. NASA’s Goddard Space Flight Center manages the telescope. The Space Telescope Science Institute (STScI), is a free-standing science center, located on the campus of The Johns Hopkins University and operated by the Association of Universities for Research in Astronomy (AURA) for NASA, conducts Hubble science operations.

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  • richardmitnick 7:17 am on August 29, 2018 Permalink | Reply
    Tags: , , , , , Eta Carinae, Stars v. Dust in the Carina Nebula   

    From European Southern Observatory: “Stars v. Dust in the Carina Nebula” 

    ESO 50 Large

    From European Southern Observatory

    29 August 2018
    Jim Emerson
    School of Physics & Astronomy, Queen Mary University of London
    London, UK
    Email: j.p.emerson@qmul.ac.uk

    Calum Turner
    Public Information Officer
    Garching bei München, Germany
    Tel: +49 89 3200 6670
    Email: pio@eso.org

    VISTA gazes into one of the largest nebulae in the Milky Way in infrared

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    The Carina Nebula, one of the largest and brightest nebulae in the night sky, has been beautifully imaged by ESO’s VISTA telescope at the Paranal Observatory in Chile. By observing in infrared light, VISTA has peered through the hot gas and dark dust enshrouding the nebula to show us myriad stars, both newborn and in their death throes.

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    This image is a colour composite made from exposures from the Digitized Sky Survey 2 (DSS2). The field of view is approximately 4.7 x 4.9 degrees. Credit: ESO/Digitized Sky Survey 2. Acknowledgement: Davide De Martin.


    ESOcast 175 Light: Stars and Dust in the Carina Nebula (4K UHD)
    The VISTA telescope has allowed us to peer through the hot gas and dark dust shrouding the spectacular Carina nebula to show us myriad stars, both newborn and in their death throes.

    The video is available in 4K UHD.

    The ESOcast Light is a series of short videos bringing you the wonders of the Universe in bite-sized pieces. The ESOcast Light episodes will not be replacing the standard, longer ESOcasts, but complement them with current astronomy news and images in ESO press releases. Credit: ESO.
    Directed by: Nico Bartmann.
    Editing: Nico Bartmann.
    Web and technical support: Mathias André and Raquel Yumi Shida.
    Written by: Ivana Kurecic and Calum Turner.
    Music: tonelabs.
    Footage and photos: ESO, G. Hüdepohl (atacamaphoto.com), DSS, N. Risinger (skysurvey.org), M. Kornmesser.
    Executive producer: Lars Lindberg Christensen


    The VISTA telescope has allowed us to peer through the hot gas and dark dust shrouding the spectacular Carina nebula to show us myriad stars, both newborn and in their death throes. This visualisation shows a 3D conversion of images of the Carina Nebula. Credit: ESO, M. Kornmesser

    About 7500 light-years away, in the constellation of Carina, lies a nebula within which stars form and perish side-by-side. Shaped by these dramatic events, the Carina Nebula is a dynamic, evolving cloud of thinly spread interstellar gas and dust.

    The massive stars in the interior of this cosmic bubble emit intense radiation that causes the surrounding gas to glow. By contrast, other regions of the nebula contain dark pillars of dust cloaking newborn stars. There’s a battle raging between stars and dust in the Carina Nebula, and the newly formed stars are winning — they produce high-energy radiation and stellar winds which evaporate and disperse the dusty stellar nurseries in which they formed.

    Spanning over 300 light-years, the Carina Nebula is one of the Milky Way’s largest star-forming regions and is easily visible to the unaided eye under dark skies. Unfortunately for those of us living in the north, it lies 60 degrees below the celestial equator, so is visible only from the Southern Hemisphere.

    Within this intriguing nebula, Eta Carinae takes pride of place as the most peculiar star system.

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    The Carina Nebula (catalogued as NGC 3372; also known as the Grand Nebula, Great Nebula in Carina, or Eta Carinae Nebula) is a large, complex area of bright and dark nebulosity in the constellation Carina, and is located in the Carina–Sagittarius Arm. The nebula lies at an estimated distance between 6,500 and 10,000 light-years (2,000 and 3,100 pc) from Earth.

    This stellar behemoth — a curious form of stellar binary— is the most energetic star system in this region and was one of the brightest objects in the sky in the 1830s. It has since faded dramatically and is reaching the end of its life, but remains one of the most massive and luminous star systems in the Milky Way.

    Eta Carinae can be seen in this image as part of the bright patch of light just above the point of the “V” shape made by the dust clouds. Directly to the right of Eta Carinae is the relatively small Keyhole Nebula — a small, dense cloud of cold molecules and gas within the Carina Nebula — which hosts several massive stars, and whose appearance has also changed drastically over recent centuries.

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    Colour-composite image of the Keyhole, a dark nebula within the Carina Nebula.
    Date 12 February 2009 (released)
    Source http://www.eso.org/public/images/eso0905a/
    Author ESO

    The Carina Nebula was discovered from the Cape of Good Hope by Nicolas Louis de Lacaille in the 1750s and a huge number of images have been taken of it since then. But VISTA — the Visible and Infrared Survey Telescope for Astronomy — adds an unprecedentedly detailed view over a large area; its infrared vision is perfect for revealing the agglomerations of young stars hidden within the dusty material snaking through the Carina Nebula. In 2014, VISTA was used to pinpoint nearly five million individual sources [Astronomy and Astrophysics] of infrared light within this nebula, revealing the vast extent of this stellar breeding ground. VISTA is the world’s largest infrared telescope dedicated to surveys and its large mirror, wide field of view and exquisitely sensitive detectors enable astronomers [1] to unveil a completely new view of the southern sky.

    Notes

    [1] The Principal Investigator of the observing proposal which led to this spectacular image was Jim Emerson (School of Physics & Astronomy, Queen Mary University of London, UK). His collaborators were Simon Hodgkin and Mike Irwin (Cambridge Astronomical Survey Unit, Cambridge University, UK). The data reduction was performed by Mike Irwin and Jim Lewis (Cambridge Astronomical Survey Unit, Cambridge University, UK).

    Links

    More information about VISTA
    Photos of VISTA
    More ESO images of the Carina Nebula

    See the full article here .


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    Please help promote STEM in your local schools.


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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 EEuropean Extremely Large Telescope, the E-ELT, which will become “the world’s biggest eye on the sky”.

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    ESO 3.6m telescope & HARPS at Cerro LaSilla, Chile, 600 km north of Santiago de Chile at an altitude of 2400 metres.

    ESO 2.2 meter telescope at La Silla, 600 km north of Santiago de Chile at an altitude of 2400 metres.

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

    ESO VLT Platform at Cerro Paranal elevation 2,635 m (8,645 ft)

    Glistening against the awesome backdrop of the night sky above ESO_s Paranal Observatory, four laser beams project out into the darkness from Unit Telescope 4 UT4 of the VLT.

    ESO/NTT at Cerro La Silla, Chile, at an altitude of 2400 metres

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

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

    ESO/E-ELT,to be on top of Cerro Armazones in the Atacama Desert of northern Chile, at an altitude 3,046 m (9,993 ft)

    ESO/APEX high on the Chajnantor plateau in Chile’s Atacama region, at an altitude of over 4,800 m (15,700 ft)

    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 1:36 pm on August 2, 2018 Permalink | Reply
    Tags: Eta Carinae, , , The Star that Wouldn’t Die   

    From NASA/ESA Hubble Telescope and Gemini Observatory: “Astronomers Uncover New Clues to the Star that Wouldn’t Die”(Hubble) and “Astronomers Blown Away by Historic Stellar Blast” (Gemini) 

    NASA Hubble Banner

    NASA/ESA Hubble Telescope

    From NASA/ESA Hubble Telescope

    Aug 2, 2018

    Donna Weaver
    Space Telescope Science Institute, Baltimore, Maryland
    410-338-4493
    dweaver@stsci.edu

    Ray Villard
    Space Telescope Science Institute, Baltimore, Maryland
    410-338-4514
    villard@stsci.edu

    Nathan Smith
    University of Arizona, Tucson
    520-621-4513
    nathans@as.arizona.edu

    Armin Rest
    Space Telescope Science Institute, Baltimore, Maryland
    410-338-4358
    arest@stsci.edu

    1
    Brawl Among Three Rowdy Stellar Siblings May Have Triggered Eruption

    It takes more than a massive outburst to destroy the mammoth star Eta Carinae, one of the brightest known stars in the Milky Way galaxy. About 170 years ago, Eta Carinae erupted, unleashing almost as much energy as a standard supernova explosion.

    Yet that powerful blast wasn’t enough to obliterate the star, and astronomers have been searching for clues to explain the outburst ever since. Although they cannot travel back to the mid-1800s to witness the actual eruption, they can watch a rebroadcast of part of the event — courtesy of some wayward light from the explosion. Rather than heading straight toward Earth, some of the light from the outburst rebounded or “echoed” off of interstellar dust, and is just now arriving at Earth. This effect is called a light echo.

    The surprise is that new measurements of the 19th-century eruption, made by ground-based telescopes, reveal material expanding with record-breaking speeds of up to 20 times faster than astronomers expected. The observed velocities are more like the fastest material ejected by the blast wave in a supernova explosion, rather than the relatively slow and gentle winds expected from massive stars before they die.

    Based on the new data, researchers suggest that the 1840s eruption may have been triggered by a prolonged stellar brawl among three rowdy sibling stars, which destroyed one star and left the other two in a binary system. This tussle may have culminated with a violent explosion when Eta Carinae devoured one of its two companions, rocketing more than 10 times the mass of our Sun into space. The ejected mass created gigantic bipolar lobes resembling the dumbbell shape seen in present-day images.

    The Full Story

    What happens when a star behaves like it exploded, but it’s still there?

    About 170 years ago, astronomers witnessed a major outburst by Eta Carinae, one of the brightest known stars in the Milky Way galaxy. The blast unleashed almost as much energy as a standard supernova explosion.

    Yet Eta Carinae survived.

    Eta Carinae Image Credit: N. Smith, J. A. Morse (U. Colorado) et al., NASA

    An explanation for the eruption has eluded astrophysicists. They can’t take a time machine back to the mid-1800s to observe the outburst with modern technology.

    However, astronomers can use nature’s own “time machine,” courtesy of the fact that light travels at a finite speed through space. Rather than heading straight toward Earth, some of the light from the outburst rebounded or “echoed” off of interstellar dust, and is just now arriving at Earth. This effect is called a light echo. The light is behaving like a postcard that got lost in the mail and is only arriving 170 years later.

    By performing modern astronomical forensics of the delayed light with ground-based telescopes, astronomers uncovered a surprise. The new measurements of the 1840s eruption reveal material expanding with record-breaking speeds up to 20 times faster than astronomers expected. The observed velocities are more like the fastest material ejected by the blast wave in a supernova explosion, rather than the relatively slow and gentle winds expected from massive stars before they die.

    Based on this data, researchers suggest that the eruption may have been triggered by a prolonged stellar brawl among three rowdy sibling stars, which destroyed one star and left the other two in a binary system. This tussle may have culminated with a violent explosion when Eta Carinae devoured one of its two companions, rocketing more than 10 times the mass of our Sun into space. The ejected mass created gigantic bipolar lobes resembling the dumbbell shape seen in present-day images.

    The results are reported in a pair of papers by a team led by Nathan Smith of the University of Arizona in Tucson, Arizona, and Armin Rest of the Space Telescope Science Institute in Baltimore, Maryland.

    The light echoes were detected in visible-light images obtained since 2003 with moderate-sized telescopes at the Cerro Tololo Inter-American Observatory in Chile. Using larger telescopes at the Magellan Observatory and the Gemini South Observatory, both also located in Chile, the team then used spectroscopy to dissect the light, allowing them to measure theejecta’s expansion speeds. They clocked material zipping along at more than 20 million miles per hour (fast enough to travel from Earth to Pluto in a few days).

    The observations offer new clues to the mystery surrounding the titanic convulsion that, at the time, made Eta Carinae the second-brightest nighttime star seen in the sky from Earth between 1837 and 1858. The data hint at how it may have come to be the most luminous and massive star in the Milky Way galaxy.

    “We see these really high velocities in a star that seems to have had a powerful explosion, but somehow the star survived,” Smith explained. “The easiest way to do this is with a shock wave that exits the star and accelerates material to very high speeds.”

    Massive stars normally meet their final demise in shock-driven events when their cores collapse to make a neutron star or black hole. Astronomers see this phenomenon in supernova explosions where the star is obliterated. So how do you have a star explode with a shock-driven event, but it isn’t enough to completely blow itself apart? Some violent event must have dumped just the right amount of energy onto the star, causing it to eject its outer layers. But the energy wasn’t enough to completely annihilate the star.

    One possibility for just such an event is a merger between two stars, but it has been hard to find a scenario that could work and match all the data on Eta Carinae.

    The researchers suggest that the most straightforward way to explain a wide range of observed facts surrounding the eruption is with an interaction of three stars, where the objects exchange mass.

    If that’s the case, then the present-day remnant binary system must have started out as a triple system. “The reason why we suggest that members of a crazy triple system interact with each other is because this is the best explanation for how the present-day companion quickly lost its outer layers before its more massive sibling,” Smith said.

    In the team’s proposed scenario, two hefty stars are orbiting closely and a third companion is orbiting farther away. When the most massive of the close binary stars nears the end of its life, it begins to expand and dumps most of its material onto its slightly smaller sibling.

    The sibling has now bulked up to about 100 times the mass of our Sun and is extremely bright. The donor star, now only about 30 solar masses, has been stripped of its hydrogen layers, exposing its hot helium core.

    Hot helium core stars are known to represent an advanced stage of evolution in the lives of massive stars. “From stellar evolution, there’s a pretty firm understanding that more massive stars live their lives more quickly and less massive stars have longer lifetimes,” Rest explained. “So the hot companion star seems to be further along in its evolution, even though it is now a much less massive star than the one it is orbiting. That doesn’t make sense without a transfer of mass.”

    The mass transfer alters the gravitational balance of the system, and the helium-core star moves farther away from its monster sibling. The star travels so far away that it gravitationally interacts with the outermost third star, kicking it inward. After making a few close passes, the star merges with its heavyweight partner, producing an outflow of material.

    In the merger’s initial stages, the ejecta is dense and expanding relatively slowly as the two stars spiral closer and closer. Later, an explosive event occurs when the two inner stars finally join together, blasting off material moving 100 times faster. This material eventually catches up with the slow ejecta and rams into it like a snowplow, heating the material and making it glow. This glowing material is the light source of the main historical eruption seen by astronomers a century and a half ago.

    Meanwhile, the smaller helium-core star settles into an elliptical orbit, passing through the giant star’s outer layers every 5.5 years. This interaction generates X-ray emitting shock waves.

    A better understanding of the physics of Eta Carinae’s eruption may help to shed light on the complicated interactions of binary and multiple stars, which are critical for understanding the evolution and death of massive stars.

    The Eta Carinae system resides 7,500 light-years away inside the Carina nebula, a vast star-forming region seen in the southern sky.

    The team published its findings in two papers, which appear online Aug. 2 in The Monthly Notices of the Royal Astronomical Society.

    The Hubble Space Telescope is a project of international cooperation between NASA and ESA (European Space Agency). NASA’s Goddard Space Flight Center in Greenbelt, Maryland, manages the telescope. The Space Telescope Science Institute (STScI) in Baltimore, Maryland, conducts Hubble science operations. STScI is operated for NASA by the Association of Universities for Research in Astronomy in Washington, D.C.

    The science paper by N. Smith et al. MNRAS

    The science paper by N. Smith et al. MNRAS

    Gemini Observatory’s Release

    August 2nd, 2018
    Gemini Observatory Press Release
    Astronomers Blown Away by Historic Stellar Blast

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    This sequence of images show’s an artist’s conception of the expanding blast wave from Eta Carinae’s 1843 eruption. The first image shows the star as it may have appeared before the eruption, as a hot blue supergiant star surrounded by an older shell of gas that was ejected in a previous outburst about 1,000 years ago. Then in 1843, Eta Carinae suffered its explosive giant outburst, which created the well-known two-lobed “Homunculus” nebula, plus a fast shock wave porpagating ahead of the Homunculus. New evidence for this fast material is reported here. As time procedes, both the faster shock wave and the denser Homunculus nebula expand and fill the interior of the old shell. Eventually, we see that the faster blast wave begins to catch-up with and overtake parts of the older shell, producing a bright fireworks display that heats the older shell. See: https://www.gemini.edu/node/11120 for more images.

    Media Contact:

    Peter Michaud
    Public Information and Outreach manager
    Gemini Observatory
    Email: pmichaud”at”gemini.edu
    Phone: 808-974-2510
    Cell: 808-936-6643

    Science Contacts

    Nathan Smith
    Associate Professor
    Department of Astronomy and Steward Observatory
    University of Arizona
    E-mail: nathans”at”as.arizona.edu
    Desk: 520-621-4513

    Armin Rest
    Associate Astronomer
    Space Telescope Science Institute
    E-mail: arest”at”stsci.edu
    Desk: 410-338-4358
    Cell: 443-794-4838

    Observations from the Gemini South and other telescopes in Chile played a critical role in understanding light echoes from a stellar eruption which occurred almost 200 years ago. Gemini spectroscopy shows that ejected material from the blast is the fastest ever seen from a star that remained intact.


    Gemini South telescope, Cerro Tololo Inter-American Observatory (CTIO) campus near La Serena, Chile, at an altitude of 7200 feet

    Imagine traveling to the Moon in just 20 seconds! That’s how fast material from a 170 year old stellar eruption sped away from the unstable, eruptive, and extremely massive star Eta Carinae.

    Astronomers conclude that this is the fastest jettisoned gas ever measured from a stellar outburst that didn’t result in the complete annihilation of the star.

    The blast, from the most luminous star known in our galaxy, released almost as much energy as a typical supernova explosion that would have left behind a stellar corpse. However, in this case a double-star system remained and played a critical role in the circumstances that led to the colossal blast.

    Over the past seven years a team of astronomers led by Nathan Smith, of the University of Arizona, and Armin Rest, of the Space Telescope Science Institute, determined the extent of this extreme stellar blast by observing light echoes from Eta Carinae and its surroundings.

    Light echos occur when the light from bright, short-lived events are reflected off of clouds of dust, which act like distant mirrors redirecting light in our direction. Like an audio echo, the arriving signal of the reflected light has a time delay after the original event due to the finite speed of light. In the case of Eta Carinae, the bright event was a major eruption of the star that expelled a huge amount of mass back in the mid-1800s during what is known as the “Great Eruption.” The delayed signal of these light echoes allowed astronomers to decode the light from the eruption with modern astronomical telescopes and instruments, even though the original eruption was seen from Earth back in the mid-19th century. That was a time before modern tools like the astronomical spectrograph were invented.

    “A light echo is the next best thing to time travel,” Smith said. “That’s why light echoes are so beautiful. They give us a chance to unravel the mysteries of a rare stellar eruption that was witnessed 170 years ago, but using our modern telescopes and cameras. We can also compare that information about the event itself with the 170-year old remnant nebula that was ejected. This was a behemoth stellar explosion from a very rare monster star, the likes of which has not happened since in our Milky Way Galaxy.”

    The Great Eruption temporarily promoted Eta Carinae to the second brightest star visible in our nighttime sky, vasty outshining the energy output every other star in the Milky Way, after which the star faded from naked eye visibility. The outburst expelled material (about 10 times more than the mass of our Sun) that also formed the bright glowing gas cloud known as the Homunculus. This dumbbell-shaped remnant is visible surrounding the star from within a vast star-forming region. The eruptive remnant can even be seen in small amateur telescopes from the Earth’s Southern Hemisphere and equatorial regions, but is best seen in images obtained with the Hubble Space Telescope.

    The team used instruments on the 8-meter Gemini South telescope, Cerro Tololo Inter-American Observatory 4-meter Blanco telescope, and the Magellan Telescope at Las Campanas Observatory to decode the light from these light echoes and to understand the expansion speeds in the historical explosion.


    NOAO/CTIO Victor M Blanco 4m Telescope which houses the DECam at Cerro Tololo, Chile, housing DECam at an altitude of 7200 feet

    Carnegie 6.5 meter Magellan Baade and Clay Telescopes located at Carnegie’s Las Campanas Observatory, Chile. over 2,500 m (8,200 ft) high

    “Gemini spectroscopy helped pin down the unprecedented velocities we observed in this gas, which clocked in at between about 10,000 to 20,000 kilometers per second,” according to Rest. The research team, Gemini Observatory, and Blanco telescope are all supported by the U.S. National Science Foundation (NSF).

    “We see these really high velocities all the time in supernova explosions where the star is obliterated.” Smith notes. However, in this case the star survived, and explaining that led the researchers into new territory. “Something must have dumped a lot of energy into the star in a short amount of time,” said Smith. The material expelled by Eta Carinae is travelling up to 20 times faster than expected for typical winds from a massive star so, according to Smith and his collaborators, enlisting the help of two partner stars might explain the extreme outflow.

    The researchers suggest that the most straightforward way to simultaneously explain a wide range of observed facts surrounding the eruption and the remnant star system seen today is with an interaction of three stars, including a dramatic event where two of the three stars merged into one monster star. If that’s the case, then the present-day binary system must have started out as triple system, with one of those two stars being the one that swallowed its sibling.

    “Understanding the dynamics and environment around the largest stars in our galaxy is one of the most difficult areas of astronomy,” said Richard Green, Director of the Division of Astronomical Sciences at NSF, the major funding agency for Gemini. “Very massive stars live short lives compared to stars like our Sun, but nevertheless catching one in the act of a major evolutionary step is statistically unlikely. That’s why a case like Eta Carinae is so critical, and why NSF supports this kind of research.”

    Chris Smith, Head of Mission at the AURA Observatory in Chile and also part of the research team adds a historical perspective. “I’m thrilled that we can see light echoes coming from an event that John Herschel observed in the middle of the 19th century from South Africa,” he said. “Now, over 150 years later we can look back in time, thanks to these light echoes, and unveil the secrets of this supernova wannabe using the modern instrumentation on Gemini to analyze the light in ways Hershel couldn’t have even imagined!”

    Eta Carinae is an unstable type of star known as a Luminous Blue Variable (LBV), located about 7,500 light years from Earth in a young star forming nebula found in the southern constellation of Carinae. The star is one of the intrinsically brightest in our galaxy and shines some five million times brighter than our Sun with a mass about one hundred times greater. Stars like Eta Carinae have the greatest mass-loss rates prior to undergoing supernova explosions, but the amount of mass expelled in Eta Carinae’s 19th century Great Eruption exceeds any others known.

    Eta Carinae will probably undergo a true supernova explosion sometime within the next half-million years at most, but possibly much sooner. Some types of supernovae have been seen to experience eruptive blasts like that of Eta Carinae in only the few years or decades before their final explosion, so some astronomers speculate that Eta Carinae might blow sooner rather than later.

    The Gemini Observations utilized the Gemini Multi-Object Spectrograph on the Gemini South telescope in Chile and used a powerful technique called Nod and Shuffle that enables greatly improved spectroscopic measurements of extremely faint sources by reducing the contaminating effects of the night sky.

    Gemini Observatory GMOS on Gemini South

    The new results are presented in two papers accepted for publication in the Monthly Notices of the Royal Astronomical Society.

    See the full Hubble article here .
    See the full Gemini article here .


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    The Hubble Space Telescope is a project of international cooperation between NASA and the European Space Agency. NASA’s Goddard Space Flight Center manages the telescope. The Space Telescope Science Institute (STScI), is a free-standing science center, located on the campus of The Johns Hopkins University and operated by the Association of Universities for Research in Astronomy (AURA) for NASA, conducts Hubble science operations.

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  • richardmitnick 8:10 pm on July 3, 2018 Permalink | Reply
    Tags: , , , , Eta Carinae, , , NASA's NuSTAR Mission Proves Superstar Eta Carinae Shoots Cosmic Rays   

    From NASA Goddard Space Flight Center: “NASA’s NuSTAR Mission Proves Superstar Eta Carinae Shoots Cosmic Rays” 

    NASA Goddard Banner
    From NASA Goddard Space Flight Center

    July 3, 2018
    Francis Reddy
    francis.j.reddy@nasa.gov
    NASA’s Goddard Space Flight Center, Greenbelt, Md.

    A new study using data from NASA’s NuSTAR space telescope suggests that Eta Carinae, the most luminous and massive stellar system within 10,000 light-years, is accelerating particles to high energies — some of which may reach Earth as cosmic rays.

    NASA NuSTAR X-ray telescope

    Eta Carinae Image Credit: N. Smith, J. A. Morse (U. Colorado) et al., NASA

    “We know the blast waves of exploded stars can accelerate cosmic ray particles to speeds comparable to that of light, an incredible energy boost,” said Kenji Hamaguchi, an astrophysicist at NASA’s Goddard Space Flight Center in Greenbelt, Maryland, and the lead author of the study. “Similar processes must occur in other extreme environments. Our analysis indicates Eta Carinae is one of them.”

    Astronomers know that cosmic rays with energies greater than 1 billion electron volts (eV) come to us from beyond our solar system. But because these particles — electrons, protons and atomic nuclei — all carry an electrical charge, they veer off course whenever they encounter magnetic fields. This scrambles their paths and masks their origins.


    Zoom into Eta Carinae, where the outflows of two massive stars collide and shoot accelerated particles — cosmic rays — into space.
    Credits: NASA’s Goddard Space Flight Center

    Eta Carinae, located about 7,500 light-years away in the southern constellation of Carina, is famous for a 19th century outburst that briefly made it the second-brightest star in the sky. This event also ejected a massive hourglass-shaped nebula, but the cause of the eruption remains poorly understood.

    The system contains a pair of massive stars whose eccentric orbits bring them unusually close every 5.5 years. The stars contain 90 and 30 times the mass of our Sun and pass 140 million miles (225 million kilometers) apart at their closest approach — about the average distance separating Mars and the Sun.

    “Both of Eta Carinae’s stars drive powerful outflows called stellar winds,” said team member Michael Corcoran, also at Goddard. “Where these winds clash changes during the orbital cycle, which produces a periodic signal in low-energy X-rays we’ve been tracking for more than two decades.”

    NASA’s Fermi Gamma-ray Space Telescope also observes a change in gamma rays — light packing far more energy than X-rays — from a source in the direction of Eta Carinae. But Fermi’s vision isn’t as sharp as X-ray telescopes, so astronomers couldn’t confirm the connection.

    1
    Eta Carinae shines in X-rays in this image from NASA’s Chandra X-ray Observatory.

    NASA/Chandra X-ray Telescope

    The colors indicate different energies. Red spans 300 to 1,000 electron volts (eV), green ranges from 1,000 to 3,000 eV and blue covers 3,000 to 10,000 eV. For comparison, the energy of visible light is about 2 to 3 eV. NuSTAR observations (green contours) reveal a source of X-rays with energies some three times higher than Chandra detects. X-rays seen from the central point source arise from the binary’s stellar wind collision. The NuSTAR detection shows that shock waves in the wind collision zone accelerate charged particles like electrons and protons to near the speed of light. Some of these may reach Earth, where they will be detected as cosmic ray particles. X-rays scattered by debris ejected in Eta Carinae’s famous 1840 eruption may produce the broader red emission. Credits: NASA/CXC and NASA/JPL-Caltech

    To bridge the gap between low-energy X-ray monitoring and Fermi observations, Hamaguchi and his colleagues turned to NuSTAR. Launched in 2012, NuSTAR can focus X-rays of much greater energy than any previous telescope. Using both newly taken and archival data, the team examined NuSTAR observations acquired between March 2014 and June 2016, along with lower-energy X-ray observations from the European Space Agency’s XMM-Newton satellite over the same period.

    ESA/XMM Newton

    Eta Carinae’s low-energy, or soft, X-rays come from gas at the interface of the colliding stellar winds, where temperatures exceed 70 million degrees Fahrenheit (40 million degrees Celsius). But NuSTAR detects a source emitting X-rays above 30,000 eV, some three times higher than can be explained by shock waves in the colliding winds. For comparison, the energy of visible light ranges from about 2 to 3 eV.

    The team’s analysis, presented in a paper published on Monday, July 2, in Nature Astronomy, shows that these “hard” X-rays vary with the binary orbital period and show a similar pattern of energy output as the gamma rays observed by Fermi.

    The researchers say that the best explanation for both the hard X-ray and the gamma-ray emission is electrons accelerated in violent shock waves along the boundary of the colliding stellar winds. The X-rays detected by NuSTAR and the gamma rays detected by Fermi arise from starlight given a huge energy boost by interactions with these electrons.

    Some of the superfast electrons, as well as other accelerated particles, must escape the system and perhaps some eventually wander to Earth, where they may be detected as cosmic rays.

    “We’ve known for some time that the region around Eta Carinae is the source of energetic emission in high-energy X-rays and gamma rays”, said Fiona Harrison, the principal investigator of NuSTAR and a professor of astronomy at Caltech in Pasadena, California. “But until NuSTAR was able to pinpoint the radiation, show it comes from the binary and study its properties in detail, the origin was mysterious.”

    NuSTAR is a Small Explorer mission led by Caltech and managed by JPL for NASA’s Science Mission Directorate in Washington. NuSTAR was developed in partnership with the Danish Technical University and the Italian Space Agency (ASI). The spacecraft was built by Orbital Sciences Corp., Dulles, Virginia. NuSTAR’s mission operations center is at UC Berkeley, and the official data archive is at NASA’s High Energy Astrophysics Science Archive Research Center. ASI provides the mission’s ground station and a mirror archive. Caltech manages JPL for NASA.

    For more information on NuSTAR, visit:

    https://www.nasa.gov/nustar

    http://www.nustar.caltech.edu

    See the full article here.


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    NASA’s Goddard Space Flight Center is home to the nation’s largest organization of combined scientists, engineers and technologists that build spacecraft, instruments and new technology to study the Earth, the sun, our solar system, and the universe.

    Named for American rocketry pioneer Dr. Robert H. Goddard, the center was established in 1959 as NASA’s first space flight complex. Goddard and its several facilities are critical in carrying out NASA’s missions of space exploration and scientific discovery.


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  • richardmitnick 8:14 am on March 26, 2018 Permalink | Reply
    Tags: , , , , , , Eta Carinae   

    From ESA: “Chaotic web of filaments in a Milky Way stellar nursery” 

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    European Space Agency

    26/03/2018

    1
    Chaotic web of filaments in a Milky Way stellar nursery. ESA/Herschel/PACS, SPIRE/Hi-GAL Project. Acknowledgement: UNIMAP / L. Piazzo, La Sapienza – Università di Roma; E. Schisano / G. Li Causi, IAPS/INAF, Italy

    ESA/Herschel spacecraft

    The plane of the Milky Way is rich in star-forming regions, such as the one pictured in this stunning scene by ESA’s Herschel space observatory. To the far-infrared eye of Herschel, this region reveals an intricate network of gas filaments and dark bubbles interspersed by bright hotspots where new stars come to life.

    The cooler regions, which emit light at longer wavelengths, are displayed in a red-brownish colour. Hotter areas, where star formation is more intense, shine in blue and white tones. Some areas are particularly bright, suggesting a number of luminous, massive stars are forming there.

    Particularly striking is the chaotic web of gas filaments we see in this scene. Astronomers think there is a link between star formation and the filamentary structures in the interstellar medium. In the densest strands, the gas that makes up the filaments becomes unstable and forms clumps of material bound together by gravity. If dense enough, these collapsed blobs of gas eventually go on to become newborn stars.

    Observations by Herschel showed the filamentary complexity to be ubiquitous in the plane of our Galaxy, from a few to hundreds of light-years. In nearby star-forming clouds, within 1500 light-years of the Sun, these filaments seem to be roughly all the same width – about a third of a light-year. This suggests a common physical mechanism in their origin, possibly linked to the turbulent nature of interstellar gas clouds.

    The star-formation region in this image, centred around –70º longitude in galactic coordinates, is located in the Carina neighbourhood, home to the glorious Carina Nebula. Located some 7500 light-years away, Carina is one of the largest clouds of gas and dust in the plane of the Milky Way. It hosts the famous Eta Carinae, one of the most luminous and massive stellar systems in our galaxy.

    Nebula in the constellation Carina, contains the central cluster of huge, hot stars, called NGC 3603. NASA/ESA Hubble

    Eta Carinae Image Credit: N. Smith, J. A. Morse (U. Colorado) et al., NASA

    Herschel, which operated from 2009 until 2013, was a large space telescope observing in the far-infrared and submillimetre parts of the spectrum. This spectral range is ideal to observe the glow from cool dust in the regions where stars form. As part of Hi-GAL, the Herschel infrared Galactic Plane Survey, the observatory surveyed the plane of our Galaxy, exploring the Milky Way’s star-formation regions in unprecedented detail. This image, a product of Hi-GAL, combines observations at three different wavelengths: 70 microns (blue), 160 microns (green) and 250 microns (red).

    See the full article here .

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    The European Space Agency (ESA), established in 1975, is an intergovernmental organization dedicated to the exploration of space, currently with 19 member states. Headquartered in Paris, ESA has a staff of more than 2,000. ESA’s space flight program includes human spaceflight, mainly through the participation in the International Space Station program, the launch and operations of unmanned exploration missions to other planets and the Moon, Earth observation, science, telecommunication as well as maintaining a major spaceport, the Guiana Space Centre at Kourou, French Guiana, and designing launch vehicles. ESA science missions are based at ESTEC in Noordwijk, Netherlands, Earth Observation missions at ESRIN in Frascati, Italy, ESA Mission Control (ESOC) is in Darmstadt, Germany, the European Astronaut Centre (EAC) that trains astronauts for future missions is situated in Cologne, Germany, and the European Space Astronomy Centre is located in Villanueva de la Cañada, Spain.

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  • richardmitnick 8:03 pm on May 26, 2017 Permalink | Reply
    Tags: , , , , , Eta Carinae, The Carina Nebula   

    From AAS NOVA: ” Observations of a Windy Star” 

    AASNOVA

    American Astronomical Society

    26 May 2017
    Susanna Kohler

    1
    The Carina Nebula, as seen by the 1.5-m Danish telescope at ESO’s La Silla Observatory. Eta Carinae is the brightest star in the image. [ESO/IDA/Danish 1.5 m/R.Gendler, J-E. Ovaldsen, C. Thöne, and C. Feron]

    3
    2
    ESO LaSilla 1.5 meter Danish telescope

    4
    Eta Carinae. N. Smith / J.A. Morse (U. Colorado) et al. / NASA

    The incredibly luminous massive star Eta Carinae has long posed a challenge for astronomers to model. New observations are now in … so were our models correct?

    Dramatic Target

    The massive evolved star Eta Carinae, located ~7,500 light-years away in the constellation Carina, is the most luminous star in the Milky Way. Eta Carinae has a quite a reputation for drama: it has been very unstable in the past, exhibiting repeated eruptions that have created the spectacular Homunculus Nebula surrounding it. Its present-day wind has the highest mass-loss rate of any hot star we’ve observed.

    Picture of Stellar Wind

    5
    Top panel: February 2017 observations of Eta Carinae in continuum (left) and H-alpha. Middle panel: the normalized radial profile for H-alpha and continuum emission. Bottom panel: the full width at half maximum for H-alpha and continuum emission of Eta Carinae. The H-alpha is about 2.5 to 3 milliarcseconds wider than the continuum. [Adapted from Wu et al. 2017]

    In our goal to understand the late evolutionary phases of very massive stars, we’ve developed radiative-transfer models to explain the behavior of Eta Carinae. One of the most well-known models, developed by John Hillier and collaborators in 2001, describes Eta Carinae’s mass loss via stellar winds. With the right observations, this model is testable, since it predicts observable locations for different types of emission. In particular, one prediction of the Hillier et al. model is that the dense, ionized winds surrounding the star should emit in H-alpha at distances between 6 and 60 AU, with a peak around 20 AU.

    This nicely testable hypothesis is rendered less convenient by the fact that it’s hard to get resolved images of Eta Carinae’s H-alpha emission. Its distance from us — and the fact that it’s shrouded in the complex nebula it created — have thus far prevented us from resolving the H-alpha emission from this star. Now, however, a team of scientists from Steward Observatory, University of Arizona have changed this.

    Confirming the Model

    Led by Ya-Lin Wu, the team obtained diffraction-limited images of Eta Carinae using the Magellan adaptive optics system. The observations, made in both H-alpha and continuum, show that the H-alpha emitting region is significantly wider than the continuum emitting region, as predicted by the model. In fact, the measured emission implies that the H-alpha line-forming region may have a characteristic emitting radius of ~25–30 AU — in very good agreement with the Hillier et al. stellar-wind model.

    This confirmation is strong support of the physical wind parameters estimated for Eta Carinae in the model, like the mass-loss rate of 10^-3 solar masses per year. These parameters are enormously helpful as we attempt to understand the physics of strong stellar-wind mass loss and the late evolutionary phases of very massive stars.
    Citation

    Ya-Lin Wu et al 2017 ApJL 841 L7. doi:10.3847/2041-8213/aa70ed

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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.
    The Society, through its members, trains, mentors and supports the next generation of astronomers. The Society supports and promotes increased participation of historically underrepresented groups in astronomy.
    The Society assists its members to develop their skills in the fields of education and public outreach at all levels. The Society promotes broad interest in astronomy, which enhances science literacy and leads many to careers in science and engineering.

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  • richardmitnick 2:25 pm on May 26, 2017 Permalink | Reply
    Tags: , , , , Eta Carinae,   

    From Manu: “Eta Carinae, the prelude to a supernova” 


    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.

    1

    In the early nineteenth century, the binary star system Eta Carinae was weak and undistinguished. In the first decades it became increasingly brighter until April 1843 was the second brightest star in the sky, just behind Sirius (nearly a thousand times closer to Earth). In the years that followed, gradually he eased again in the twentieth century and was completely invisible to the naked eye. Star varying in brightness has continued since then and while once again visible to the naked eye on a dark night has never come close to its peak of 1843.

    The star system Eta Carinae is a binary system is composed of two stars, the larger of the two stars is a huge and unstable star nearing the end of his life and the events observed by the astronomers of the nineteenth century was a stellar experience near death. Scientists call these outbursts supernova impostor events that appear similar to supernovae but stop just in time to destroy the star.

    Although nineteenth – century astronomers did not have telescopes powerful enough to see the outbreak of 1843 in detail, its effects can be studied today. Huge clouds of matter thrown a century and a half ago, known as the Nebula Homúncula have been a regular target for Hubble since its launch in 1990. This image, taken with the Advanced Camera for Surveys High Resolution Channel is the most detailed , however, it shows us how the star material was not ejected in a uniform manner but held as a huge dumbbell.

    Eta Carinae is not only interesting for its past, but also for its future. It is one of the closest stars to Earth is likely to explode in a supernova in the relatively near future (though in astronomical timescales the “near future” could still be a million years). When you do, wait a breathtaking view from Earth, visible only from the southern hemisphere, much brighter even than the latest outbreak observed SN 2006gy , the brightest supernova ever observed coming from a star of the same type.

    This image consists of visible and ultraviolet images of high resolution channel of Hubble’s Advanced Camera for Surveys light. The field of view is about 30 arcseconds. Eta Carinae is located at a distance of 7,500 light-years away in the constellation Carina.

    Credit:
    ESA / Hubble and NASA

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  • richardmitnick 3:57 pm on September 3, 2016 Permalink | Reply
    Tags: , Eta Carinae, The Supernova That Wasn't: A Tale of 3 Cosmic Eruptions,   

    From U Arizona- “The Supernova That Wasn’t: A Tale of 3 Cosmic Eruptions” 

    U Arizona bloc

    University of Arizona

    Sept. 1, 2016
    Daniel Stolte

    1
    Huge, billowing gas and dust clouds are captured in this stunning NASA Hubble Space Telescope image of the supermassive star Eta Carinae. (Image: Nathan Smith/UA and NASA)

    Combining images taken with Hubble Space Telescope over more than 20 years, a team of UA researchers has discovered that Eta Carinae, a very massive star system that has puzzled astronomers since it erupted in a supernova-like event in the mid-19th century, has a past that’s much more violent than they thought. The findings help rewrite the story of how this iconic and mysterious star system came to be and present a critical piece of the puzzle of how very massive stars die.

    In the mid-1800s, astronomers surveying the night sky in the Southern Hemisphere noticed something strange: Over the course of a few years, a previously inconspicuous star named Eta Carinae grew brighter and brighter, eventually outshining all other stars except Sirius, before fading again over the next decade, becoming too dim to be seen with the naked eye.

    What had happened to cause this outburst? Did 19th-century astronomers witness some strange type of supernova, a star ending its life in a cataclysmic explosion?

    2
    This animated view of Hubble Space Telescope images taken between 1993 and 2014 reveals how much the mass ejections from Eta Carinae have moved outward into space, some at a speed of 2 million miles per hour. The outermost ejecta visible in this image stem from previously unknown eruptions predating the Great Eruption of the 1840s. (Image: Kiminki et al./NASA)

    “Not quite,” says Megan Kiminki, a doctoral student in the University of Arizona’s Department of Astronomy and Steward Observatory. “Eta Carinae is what we call a supernova impostor. The star became very bright as it blew off a lot of material, but it was still there.”

    Indeed, in the mid-20th century Eta Carinae began to brighten again.

    The aftermath of the “Great Eruption” of the mid-1800s, which is now readily visible through a small telescope if you happen to be in the Southern Hemisphere, made Eta Carinae a celebrity among objects in the universe known for their bizarre beauty. An hourglass-shaped, billowing cloud of glowing gas and dust enshrouds the star and its companion. Known as the Homunculus nebula, the cloud consists of stellar material hurled into space during the Great Eruption, drifting away at 2 million miles per hour.

    3
    Zooming in on the “N bow,” a massive protrusion of gas and dust jutting out from the central portion of the Homunculus nebula. The feature is long enough to accommodate about 250 solar systems, lined up side by side and arbitrarily defined by Pluto’s orbit. In this image, the light is inverted, rendering bright areas dark and vice versa. (Image: Megan Kiminki et al.)

    By carefully analyzing images of Eta Carinae taken with NASA’s Hubble Space Telescope, Kiminki and her team were surprised to discover that the Great Eruption was only the latest in a series of massive outbursts launched by the star system since the 13th century. Published in the journal Monthly Notices of the Royal Astronomical Society, the paper was co-authored by Nathan Smith, associate professor in the UA’s Department of Astronomy, and Megan Reiter, who obtained her Ph.D. from the same department last year and is now a postdoctoral fellow at the University of Michigan.

    The expansion rate of gas that was far outside the Homunculus indicated that it was moving slowly and must have been ejected centuries before the observed 19th-century brightening. In fact, the motions of the outer material point to two separate eruptions in the mid-13th and mid-16th centuries.

    For scientists trying to piece together what makes star systems such as Eta Carinae tick, the findings are like the stereotypical smoking gun in a detective story.

    “From the first reports of its 19th-century outburst up to the most recent data obtained with advanced capabilities on modern telescopes, Eta Carinae continues to baffle us,” Smith says. “The most important unsolved problem has always been the underlying cause of its eruption, and now we find that there were multiple previous eruptions. This is a bit like reconstructing the eruption history of a volcano by discovering ancient lava flows.”

    Although the glowing gases of the Homunculus nebula prevent astronomers from getting a clear look at what’s inside, they have figured out that Eta Carinae is a binary system of two very massive stars that orbit each other every 5.5 years. Both are much bigger than our sun and at least one of them is nearing the end of its life.

    4
    Here, color-coded arrows trace the observed proper motions of 792 features in the ejecta of Eta Carinae. Until now, only one eruption was known (red arrows). Blue and green arrows mark previous eruptions (mid-13th and mid-16th centuries, respectively). (Image: Kiminki et al./NASA)

    “These are very large stars that appear very volatile, even when they’re not blowing off nebulae,” Kiminki says. “They have a dense core and very fluffy envelopes. If you replaced our sun by the larger of the two, which has about 90-100 solar masses, it could very well extend into the orbit of Mars.”

    Because the Homunculus nebula is such an iconic and visually stunning object, it has been a popular target of astronomical observations. A total of eight images, taken over the course of two decades with Hubble, turned out to be a treasure trove for Kiminki and her co-authors.

    The original goal of the team’s observing program was to measure proper motions of stars and protostellar jets — fast streams of matter ejected by young stars during formation — in the Carina Nebula, but the same data also provided a powerful way to measure the motion of debris ejected by Eta Carinae itself.

    “As I was aligning the images, I noticed that the one that Eta Carinae in it was more difficult to align,” Kiminki says. “We can only use objects as alignment points that aren’t moving, and I thought, ‘Wow, a lot of this stuff is really moving.’ And then we decided to take a closer look.”

    By aligning the multi-epoch images of the nebula, the team was able to track the movement of more than 800 blobs of gas Eta Carinae had ejected over time and derived a likely ejection date for each. The analyses showed that the Homunculus nebula and the observed 19th-century brightening tell only part of the story. Measuring the speed with which wisps of ejected material expand outward into space revealed that they must have resulted from two separate eruptions that occurred about 600 and 300 years before the Great Eruption of the 19th century.

    In addition to having a separate origin in time, the older material also showed a very different geometry from the Homunculus, where material was ejected out from the star’s poles and appears symmetric about its rotation axis.

    “We found one of the prior eruptions was similarly symmetric, but at a totally different angle from the axis of the Great Eruption,” Kiminki explains. “Even more surprising was that the oldest eruption was very one-sided, suggesting two stars were involved, because it would be very unlikely for one star to blow material out toward just one side.”

    Though perplexing, the findings are a big step forward for astronomers trying to understand what causes the frequent outbursts.

    “We don’t really know what’s going on with Eta Carinae,” Kiminki says. “But knowing that Eta Carinae erupted at least three times tells us that whatever causes those eruptions must be a recurring process, because it wouldn’t be very likely that each eruption is caused by a different mechanism.”

    “Even though we still have not figured out the underlying physical mechanism that caused the 19th-century eruption, we now know that it isn’t a one-time event,” Smith says. “That makes it harder to understand, but it is also a critical piece of the puzzle of how very massive stars die. Stars like Eta Carinae apparently refuse to go quietly into the night.”

    Eta Carinae’s eruptions provide unique insights into the last unstable phases of a very massive star’s life. Researchers who study supernovae have identified a subclass of supernova explosions that appear to suffer violent eruptions shortly before they finally explode. Smith notes that Eta Carinae might be our nearest example of this.

    Because it takes light 7,000 years to travel from Eta Carinae to Earth, much could have happened in the meantime, Kiminki says. “Eta Carinae may have gone supernova by now, and we wouldn’t know until 7,000 years from now.”

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    U Arizona campus

    The University of Arizona (UA) is a place without limits-where teaching, research, service and innovation merge to improve lives in Arizona and beyond. We aren’t afraid to ask big questions, and find even better answers.

    In 1885, establishing Arizona’s first university in the middle of the Sonoran Desert was a bold move. But our founders were fearless, and we have never lost that spirit. To this day, we’re revolutionizing the fields of space sciences, optics, biosciences, medicine, arts and humanities, business, technology transfer and many others. Since it was founded, the UA has grown to cover more than 380 acres in central Tucson, a rich breeding ground for discovery.

    Where else in the world can you find an astronomical observatory mirror lab under a football stadium? An entire ecosystem under a glass dome? Visit our campus, just once, and you’ll quickly understand why the UA is a university unlike any other.

     
  • richardmitnick 9:00 am on November 28, 2015 Permalink | Reply
    Tags: , , Eta Carinae,   

    From New Scientist: “A threesome may explain behaviour of galaxy’s most bizarre star” 

    NewScientist

    New Scientist

    27 November 2015
    Colin Stuart

    1
    Image credit: ESA/NASA

    One of the biggest and most bizarre star systems in our galaxy has puzzled astronomers since the 1800s, but now an explanation of its origins might finally be in sight.

    The system, known as Eta Carinae, is made up of a pair of stars each considerably more massive than our own sun, but that’s only half the story. The stars are also surrounded by huge clouds of chaotic gas, part of which forms the Homunculus nebula.

    “It is flowing outwards in bubbles, knots and skirts – it’s a mess,” says Simon Portegies Zwart from the Leiden Observatory in the Netherlands.

    Records from the 19th century deepen the mystery, detailing how the star rocketed in brightness in 1838 and again in 1843 when it dazzled as the second brightest star in the night sky before fading away. This strange behaviour earned Eta Carinae the label of supernova imposter, because it mimicked the sudden burst of light from exploding, dying stars but did not destroy itself in the process.

    Three’s a party

    None of these properties match any of our models of stellar evolution. “It is different to anything we’ve ever seen before,” says Portegies Zwart, but now he and Edward van den Heuvel from the University of Amsterdam believe they have a solution: the system started out with three stars, not two.

    According to their model, the gravitational influence of an outer star caused two inner stars to merge. This not only caused the atmosphere of the newly merged star to bloat, it also pulled the outer star into a much tighter orbit, giving us the close pair we see today. “The 1838 event was caused by the merger and the 1843 event when the outer star grazed the bloated layers of the inner star,” says Portegies Zwart.

    As the merging stars squeezed together, the model shows them emitting a strong stellar wind which formed the Homunculus nebula, while the grazing event created distinctive skirt features like those observed today.

    “It’s an intriguing idea that certainly fires the imagination,” says Ian Bonnell from the University of St Andrews, UK. But the puzzle might not be entirely solved just yet, because the explanation relies on an unlikely series of events. “What they describe is quite a complicated process requiring many steps,” he says. “Individually all the steps are reasonable, but take any one of them away and it no longer works to explain this object.”

    Reference: arxiv arxiv.org/abs/1511.06889

    See the full article here .

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