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  • richardmitnick 8:30 am on July 21, 2021 Permalink | Reply
    Tags: "Stellar explosion could be a failed supernova giving birth to a black hole", , , AT2018cow, , , ,   

    From Science Magazine: “Stellar explosion could be a failed supernova giving birth to a black hole” 

    From Science Magazine

    Jul. 20, 2021
    Jonathan O’Callaghan

    1
    The strange “Cow” explosion, the right hand of two bright spots below and to the right of the galactic center, may be an odd variety of supernova.
    R. MARGUTTI/W. M. Keck Observatory, MaunaKea, Hawai’i (US)/Wikimedia Commons (CC-BY)

    When a massive star reaches the end of its life, it can explode as a supernova, leaving behind a dense remnant in the form of a neutron star or black hole. We typically can’t see these objects because supernovae tend to occur in distant galaxies, making their remnants hard to spot. But astronomers now say they’ve seen one inside a rare failed stellar explosion.

    The result hasn’t yet been peer reviewed. If the finding is correct, it would be “one of the very first times we’ve seen direct evidence for a star collapsing and forming one of these compact objects,” says Anna Ho, an astrophysicist at the University of California-Berkeley (US), who was not involved in the work.

    In 2018, astronomers spotted a new type of stellar explosion inside a comparatively close galaxy, 200 million light-years away. Dubbed AT2018cow, but informally known as “the Cow,” the event was both much brighter and faster—reaching its peak brightness in just days before dimming 3 weeks later—than a regular supernova, defying explanation. Scientists’ best guess for the cause of the bright blip, known as a fast blue optical transient (FBOT), was that the interior of a star collapsed to become a neutron star or black hole before a true supernova could form. The result was a “central engine”—a rapidly spinning object inside the outer layers of the star. Scientists think powerful jets of matter coming from the neutron star or black hole burst through the outer shells of material, making the object appear extremely bright.

    Now, in a preprint on the server Research Square, scientists report spotting such an object inside the Cow. Using a telescope on the International Space Station called the Neutron Star Interior Composition Explorer [NICER], the scientists observed x-ray light emitted by the Cow for 60 days following the explosion.

    After precisely timing the arrival of the photons, they calculated that the object producing the light was spinning once every 4.4 milliseconds.

    “This rapid periodicity is hinting that the x-ray source is compact and small,” says Brian Metzger, an astrophysicist at Columbia University (US) and a co-author on the study. Because the rotation stayed constant at 4.4 milliseconds, even after billions of observed spins, a black hole explanation is more likely than a neutron star, he adds, because a neutron star’s rotation speed would be expected to decrease over time.

    Daniel Perley, an astrophysicist at Liverpool John Moores University (UK), calls the finding “very exciting.” If correct, it would rule out other possible explanations for the Cow, including the idea that its light comes from a larger, intermediate-mass black hole devouring a star. “Whatever is producing these x-rays must be extremely compact, on the scale of kilometers, which essentially rules out a large black hole and points strongly in favor of the central engine models,” he says.

    Three events similar to the Cow have been spotted since 2018, most recently “the Camel” in 2020, but none is as close or bright as the Cow, making comparison difficult. Metzger calls the Cow a “Rosetta Stone event” that could be useful in interpreting more of these failed supernovae. “It’s a nearby event that we can hope to understand,” he says. “And if this is telling us this is a black hole, then every time we see an FBOT in the distant universe, we will know that was a black hole that formed.”

    See the full article here .


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  • richardmitnick 8:04 am on March 29, 2019 Permalink | Reply
    Tags: "Mysterious burst confounds astrophysicists", An unlucky compact object was destroyed when coming too close to a black hole – a phenomenon called a tidal disruption event, , , AT2018cow, , , , , The opposing theory is that the Cow was a special type of supernova in which either a black hole or a quickly rotating highly magnetic neutron star- a magnetar is produced, Variable X-ray emission is produced by radiating gas falling into the compact objectariable X-ray emission is produced by radiating gas falling into the compact object   

    From CERN Courier: “Mysterious burst confounds astrophysicists” 


    From CERN Courier

    8 March 2019

    1
    Holy cow!

    On 16 June 2018, a bright burst of light was observed by the Asteroid Terrestrial-impact Last Alert System (ATLAS) telescope in Hawaii, which automatically searches for optical transient events.

    ATLAS is an asteroid impact early warning system of two telescopes being developed by the University of Hawaii and funded by NASA


    ATLAS telescope, First Asteroid Terrestrial-impact Last Alert system (ATLAS) fully operational 8/15/15 Haleakala , Hawaii, USA, Altitude 4,205 m (13,796 ft)

    The event, which received the automated catalogue name “AT2018cow”, immediately received a lot of attention and acquired a shorter name: “the Cow”. While transient objects are observed on the sky every day – caused, for example, by nearby asteroids or supernovae – two factors make the Cow intriguing. First, the very short time it took for the event to reach its extreme brightness and fade away again indicates that this event is nothing like anything observed before. Second, it took place relatively close to Earth, 200 million light years away in a star-forming arm of a galaxy in the Hercules constellation, making it possible to study the event in a wide range of wavelengths.

    Soon after the ATLAS detection, the object was observed by more than 20 different telescopes around the world, revealing it to be 10–100 times brighter than a typical supernova. In addition to optical measurements, the object was observed for several days by space-based X- and gamma-ray telescopes such as NuSTAR, XMM-Newton, INTEGRAL and Swift, which also observed it in the UV energy range, as well as by radio telescopes on Earth.

    NASA/DTU/ASI NuSTAR X-ray telescope

    ESA/XMM Newton

    ESA/Integral

    NASA Neil Gehrels Swift Observatory

    The IceCube observatory in Antarctica also identified two possible neutrinos coming from the Cow, although the detection is still compatible with a background fluctuation.

    U Wisconsin ICECUBE neutrino detector at the South Pole

    The combination of all the data – demonstrating the power of multi-messenger astronomy – confirmed that this was not an ordinary supernova, but potentially something completely different.

    Right spark

    While standard supernovae take several days to reach maximum brightness, the Cow did so in just 1.5 days, after which the brightness also started to decrease much faster than a typical supernova. Another notable feature was the lack of heavy-element decays. Normally, elements such as 56Ni produced during the explosion are the main source of supernovae brightness, but the Cow only revealed signs of lighter elements such as hydrogen and helium. Furthering the event’s mystique is the variability of the X-ray emission several days after its discovery, which is a clear sign of an energy source at its centre. Half a year after its discovery, two opposing theories aim to explain these features.

    The first theory states that an unlucky compact object was destroyed when coming too close to a black hole – a phenomenon called a tidal disruption event. The fast increase in brightness excludes normal stars. On the other hand, a smaller object (such as a neutron star, a very dense star consisting of neutron matter) cannot explain the hydrogen and helium observed in the remnant, since it contains no proper elements. The remaining possibility is a white dwarf, a dense star remaining after a normal star has ceased fusion but kept from gravitational collapse into a neutron star or black hole by the electron-degeneracy pressure in its core. The observed emission from the Cow could be explained if a white dwarf was torn apart by tidal forces in the vicinity of a massive black hole. One problem with this theory, however, is the event’s location, since black holes with the sizes required for such an event are normally not found in the spiral arms of galaxies.

    The opposing theory is that the Cow was a special type of supernova in which either a black hole or a quickly rotating highly magnetic neutron star, a magnetar, is produced. While the bright emission in the optical and UV bands are produced by the supernova-like event, the variable X-ray emission is produced by radiating gas falling into the compact object. Normally the debris of a supernova blocks most of the light from reaching us, but the progenitor of the Cow was likely a relatively low-mass star that caused little debris. A hint of its low mass was also found in the X-ray data. If so, the observations would constitute the first observation of the birth of a compact object, making these data very valuable for further theoretical development. Such magnetar sources could also be responsible for ultra-high-energy cosmic rays as well as high-energy neutrinos, two of which might have been observed already. The debate on the nature of the Cow continues, but the wealth of information gathered so far indicates the growing importance of multi-messenger astronomy.

    Further reading

    R Margutti et al. 2018 arXiv:1810.10720.

    K Fang et al. 2018 arXiv:1812.11673.

    N Paul and M Kuin 2018 arXiv:1808.08492.

    See the full article here .


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    THE FOUR MAJOR PROJECT COLLABORATIONS

    ATLAS

    CERN/ATLAS detector

    ALICE

    CERN/ALICE Detector


    CMS
    CERN CMS New

    LHCb
    CERN LHCb New II

    LHC

    CERN map

    CERN LHC Grand Tunnel

    CERN LHC particles

     
  • richardmitnick 10:30 am on September 28, 2018 Permalink | Reply
    Tags: , , , AT2017gfo the first confirmed kilonova, AT2018cow, , , Spatially coincident with the galaxy CGCG 137-068 in the constellation Hercules   

    From AAS NOVA: “Unexpected Discovery of a Bright Cow” 

    AASNOVA

    From AAS NOVA

    28 September 2018
    Susanna Kohler

    1
    Image from the Sloan Digital Sky Survey with cross hairs pinpointing the location of AT2018cow. It is spatially coincident with the galaxy CGCG 137-068 in the constellation Hercules. [Sloan Digital Sky Survey]

    SDSS Telescope at Apache Point Observatory, near Sunspot NM, USA, Altitude 2,788 meters (9,147 ft)

    The recent discovery of an unusual transient event, nicknamed “the Cow”, has set the community of transient astronomers abuzz (amoo?). What do we know about this odd event so far?

    2
    The location of AT2018cow: a post-discovery image (top left), a pre-discovery reference image (top right), a subtracted difference image (bottom left), and a Pan-STARRS multi-color image (bottom right). [Prentice et al. 2018]

    Pann-STARSR1 Telescope, U Hawaii, Mauna Kea, Hawaii, USA, Altitude 3,052 m (10,013 ft)

    Thinking Outside the Box

    Once upon a time, supernovae seemed somewhat well characterized. But with the advent of today’s large, wide-field transient surveys that scan the visible sky every few nights, it seems like we’re now constantly discovering new supernova-like events that don’t quite fit into previous, neatly defined categories.

    Among the large variety of new classes of transients uncovered by these surveys are supernova-like events whose lightcurves rise and fall much faster than standard supernovae. One example is AT2017gfo, the first confirmed kilonova, which was paired with the neutron-star merger first detected in gravitational waves in August 2017. Additional examples of these rapidly evolving transients span a wide range of peak absolute magnitudes (from –15 to –22 magnitude) and rise times (~1–10 days), making them difficult to explain through a single scenario.

    3
    ATLAS, LT, GROND, and SWIFT light curves of AT2018cow. [Adapted from Prentice et al. 2018]

    Now astronomers have found one more unusual, luminous, and fast-evolving transient: AT2018cow. In a new study, a team of astronomers led by Simon Prentice (Queen’s University Belfast, UK) has presented the discovery and initial analysis of the first 18 days of this event.

    An Unusual Transient

    The Cow was first discovered with ATLAS, a twin 0.5-m telescope system located in Hawaii, on the night of 16 June 2018. Post-discovery monitoring of the Cow with various telescopes spanning optical, near-infrared, and ultraviolet wavelengths reveals a variety of odd properties.

    ATLAS is an asteroid impact early warning system of two telescopes being developed by the University of Hawaii and funded by NASA

    ATLAS telescope, First Asteroid Terrestrial-impact Last Alert system (ATLAS) fully operational 8/15/15 Haleakala , Hawaii, USA, Altitude 4,205 m (13,796 ft)

    2-metre Liverpool Telescope at La Palma in the Canary Islands, Altitude 2,363 m (7,753 ft)

    Liverpool Telescope at the Observatorio del Roque de los Muchachos

    The Cow’s peak luminosity was remarkably high: ~1.77 x 10^44 erg/s, or about 10–100 times brighter than a typical supernova. It reached the peak very quickly, brightening by more than 5 mag in just 3.3 days, while typical supernovae have rise times of perhaps 10–20 days. In addition, the Cow had a high peak blackbody temperature (~27,000 K), low estimated ejecta mass (just 0.1–0.4 solar masses), and relatively featureless and non-evolving spectra.

    ESO GROND imager on 2.2 meter MPG/ESO telescope at LaSilla


    ESO GROND imager on 2.2 meter MPG/ESO telescope at LaSilla


    ESO 2.2 meter telescope 600 km north of Santiago de Chile at Cerro LaSilla, at an altitude of 2400 metres

    NASA Neil Gehrels Swift Observatory

    Magnetar from a Collision?

    The combination of the Cow’s odd properties eliminates a number of more common progenitor explanations, such as supernova shock breakout. The authors do explore one scenario that could produce properties similar to the Cow’s, however: the formation of a magnetar — a strongly magnetized neutron star — from the merger of a binary neutron star system. Such a model, Prentice and collaborators say, would predict a transient with a peak luminosity, decline rate, and effective temperature that are all consistent with those of the Cow.

    How can we confirm this picture? The next step will be to compare additional observations of AT2018cow in radio and X-ray wavelengths — which were made simultaneously with those reported here in near-infared through ultraviolet — to the magnetar models to see if the models also match those observations. If so, we may have an explanation for this unusual transient.

    Citation

    “The Cow: Discovery of a Luminous, Hot, and Rapidly Evolving Transient,” S. J. Prentice et al 2018 ApJL 865 L3. http://iopscience.iop.org/article/10.3847/2041-8213/aadd90/meta

    See the full article here .


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    1

    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.

    Adopted June 7, 2009

     
  • richardmitnick 11:35 am on July 1, 2018 Permalink | Reply
    Tags: , , AT2018cow, ATLAS telescopes operated by the University of Hawaii's Institute for Astronomy, ,   

    From Keck and U Hawaii via EarthSky: “Astronomers see mystery explosion 200 million light-years away” 

    Keck Observatory, Maunakea, Hawaii, USA.4,207 m (13,802 ft) above sea level, with Subaru and IRTF (NASA Infrared Telescope Facility). Vadim Kurland


    From Keck Observatory

    and

    U Hawaii Institute for Astronomy

    July 1, 2018
    Paul Scott Anderson

    Supernovae, or exploding stars, are relatively common. But now astronomers have observed a baffling new type of cosmic explosion, believed to be some 10 to 100 times brighter than an ordinary supernova.

    Space might seem unchanging as you stand on Earth looking up at the inky blackness, but it isn’t, always. Indeed, the stillness can be punctuated at times by immense explosions, such as when stars go supernova in brilliant bursts of light. Supernovae are common, relatively speaking. But now scientists have observed a new type of explosion in space, and so far they don’t have an explanation for it. A science team reported the explosion on June 17, 2018, in The Astronomer’s Telegram, which is an internet-based publication service for disseminating new astronomical information quickly. The discovery team then discussed the explosion in a June 22 article in the popular weekly science magazine New Scientist. They said they saw the immense flash coming to us from another galaxy, 200 million light-years away. And, they said, this flash must have been 10 to 100 times brighter than a typical supernova.

    The mysterious flash has been nicknamed The Cow by astronomers since it was listed as AT2018cow in a database, thanks to the randomized three-letter naming system.

    The asteroid-tracking ATLAS telescopes at Keck Observatory in Hawaii were the first to see the mystery explosion.

    ATLAS is an asteroid impact early warning system of two telescopes being developed by the University of Hawaii and funded by NASA

    At first, astronomers thought it originated in our own galaxy. They thought it might be what’s called a cataclysmic variable star, typically two stars orbiting one another and interacting in a way that increases the whole system’s brightness irregularly. But subsequent spectroscopic observations showed the explosion came from another galaxy – labeled CGCG 137-068 – located some 200 million light-years away in the direction of the constellation Hercules.

    As astronomer Kate Maguire of Queen’s University Belfast noted simply to New Scientist:

    “It really just appeared out of nowhere.”

    1
    The ATLAS telescopes acquired these images of AT2018cow, before the explosion (middle) and after it (left) in the galaxy CGCG 137-068. The far-right image shows the difference between the two and reveals the sudden brightening. Image via Stephen Smartt/ATLAS.

    Indeed, and it certainly took astronomers by surprise. But apart from the brightness, the most unusual aspect of the explosion was its speed, reaching peak brightness in just two days; most supernovae take weeks to do that. As Maguire also noted:

    “There are other objects that have been discovered that are as fast, but the fastness and the brightness, that’s quite unusual. There hasn’t really been another object like this.”

    Stephen Smartt, an astrophysicist at Queen’s University Belfast and a lead scientist for the ATLAS survey, commented to the Washington Post on June 25 that:

    “I’ve never seen anything like this before in the local universe.”

    As to what caused this intense blast, scientists don’t know yet, but they say that it is composed of a 16,000 degree Fahrenheit (9,000 degree Celsius) cloud of high-energy particles, expanding outward at 12,000 miles (20,000 kilometers) per second. It is also very bright in all parts of the electromagnetic spectrum, and its spectrum is also “surprisingly smooth,” unlike most supernovae which have distinct absorption lines. According to Smartt:

    “No one has successfully matched them yet to the known features we normally see in supernova.”

    3
    Artist’s concept shows dust forming in an environment around a supernova explosion. Could The Cow be an object like this? If so, why is it so much brighter than an ordinary supernova? Image via ESO/M. Kornmesser.

    After the flash was reported to The Astronomer’s Telegram, astronomy teams used at least 18 telescopes from around the world to study the occurrence. According to Robert Rutledge, editor-in-chief of The Astronomer’s Telegram and an astrophysicist at McGill University in Canada:

    I think it’s the most notices for any individual object in such a short period of time. It has produced a lot of interest.

    But if the flash isn’t a typical supernova, then what is it? As Maguire noted:

    “We’re not sure yet what it is, but the normal powering mechanism for a supernova is radioactive decay of nickel, and this event is too bright and too fast for that.”

    It could be a type 1c supernova, where the core has collapsed in a massive star that has already lost its outer veil of hydrogen and helium, but only further observations will help to determine that, or rule it out as an explanation. Astronomers will continue to study this fascinating mystery, even though the blast has already started to fade now.

    4
    Location of AT2018cow in the distant galaxy CGCG 137-068, located in our sky in the direction of the constellation Hercules. Image via Wikimedia Commons.

    Bottom line: Astronomers have another fascinating mystery on their hands, as they try to figure out the nature of a huge, unusual explosion – labeled AT2018cow, nicknamed The Cow by astronomers – in a distant galaxy. Is it a type of supernova, or something more exotic?

    See the full article here .


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    Mission
    To advance the frontiers of astronomy and share our discoveries with the world.

    The W. M. Keck Observatory operates the largest, most scientifically productive telescopes on Earth. The two, 10-meter optical/infrared telescopes on the summit of Mauna Kea on the Island of Hawaii feature a suite of advanced instruments including imagers, multi-object spectrographs, high-resolution spectrographs, integral-field spectrometer and world-leading laser guide star adaptive optics systems. Keck Observatory is a private 501(c) 3 non-profit organization and a scientific partnership of the California Institute of Technology, the University of California and NASA.

    Today Keck Observatory is supported by both public funding sources and private philanthropy. As a 501(c)3, the organization is managed by the California Association for Research in Astronomy (CARA), whose Board of Directors includes representatives from the California Institute of Technology and the University of California, with liaisons to the board from NASA and the Keck Foundation.


    Keck UCal

     
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