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  • richardmitnick 10:58 am on May 30, 2018 Permalink | Reply
    Tags: , , , , Dark Matter: Checkmate?, , , Stellar-mass black holes   

    From MEDIUM: “Dark Matter: Checkmate?” 

    From Medium

    Jan 10, 2018
    Robert Oldershaw

    1
    No image caption or credit

    For a couple of years I have been arguing that if Fast Radio Bursts are associated with stellar-mass black holes, then the identity of the enigmatic dark matter will have been revealed. Today the premier scientific journal Nature has published a paper [An extreme magneto-ionic environment associated with the fast radio burst source FRB 121102]presenting strong evidence that FRBs are associated with stellar-mass ultracompacts, with black holes being a prime suspect, although neutron stars are the more conservative choice. Both, however, are stellar-mass ultracompact objects.

    Stellar-mass primordial black holes, of the Kerr-Newman class, could constitute the sources of the estimated 6,000/day Fast Radio Bursts that have been discovered/inferred in the last few years by several astrophysical research groups (Science News, Aug. 9, 2014 issue; and many papers subsequently posted to the arxiv preprint repository).
    PBHs would also constitute a viable candidate population for the 100,000,000,000 MACHOs that have been discovered through microlensing research, and for the galactic dark matter that has remained unidentified for over 35 years.

    So let’s summarize the evidence:

    Microlensing research implies a very large population of BHs.
    Gamma-Ray Burst research implies large populations of BHs.
    LIGO/VIRGO gravitational wave events imply unexpectedly large populations of BHs.
    Fast Radio Burst research now hints at extremely large populations of ultracompact objects: BHs or NSs.
    Correlations between the X-ray and IR backgrounds suggest the dark matter is composed of stellar-mass BHs.

    Maybe we are not quite ready to shut down the heroic WIMP searches yet, but they and other searches for exotic particles have come up empty for 40 years. I think we are rapidly approaching a convincing answer to a question that has plagued us for decades: the dark matter is probably composed of stellar-mass black holes, and they are as fundamental as any object in nature.

    See the full article here .


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  • richardmitnick 7:28 am on January 17, 2018 Permalink | Reply
    Tags: , , , , , , , Stellar-mass black holes   

    From ESO: “Odd Behaviour of Star Reveals Lonely Black Hole Hiding in Giant Star Cluster” 

    ESO 50 Large

    European Southern Observatory

    17 January 2018

    Benjamin Giesers
    Georg-August-Universität Göttingen
    Göttigen, Germany
    Email: giesers@astro.physik.uni-goettingen.de

    Stefan Dreizler
    Georg-August-Universität Göttingen
    Göttigen, Germany
    Email: dreizler@astro.physik.uni-goettingen.de

    Richard Hook
    ESO Public Information Officer
    Garching bei München, Germany
    Tel: +49 89 3200 6655
    Cell: +49 151 1537 3591
    Email: rhook@eso.org

    1
    Astronomers using ESO’s MUSE instrument on the Very Large Telescope in Chile have discovered a star in the cluster NGC 3201 that is behaving very strangely. It appears to be orbiting an invisible black hole with about four times the mass of the Sun — the first such inactive stellar-mass black hole found in a globular cluster and the first found by directly detecting its gravitational pull. This important discovery impacts on our understanding of the formation of these star clusters, black holes, and the origins of gravitational wave events.


    This important discovery impacts on our understanding of the formation of these star clusters, black holes, and the origins of gravitational wave events.
    This short ESOcast takes a look at this discovery and its significance.
    Credit: ESO.
    Directed by: Nico Bartmann.
    Editing: Nico Bartmann.
    Web and technical support: Mathias André and Raquel Yumi Shida.
    Written by: Rosa Jesse, Nicole Shearer and Richard Hook.
    Music: Music written and performed by: John Stanford (johnstanfordmusic.com).
    Footage and photos: ESO, Luís Calçada, spaceengine (spaceengine.org).


    This video takes us towards the southern constellation of Vela (The Sails), where we find the bright globular star cluster NGC 3201. This huge and ancient ball of stars has been found to harbour an invisible black hole with four times the mass of the Sun. The final sharp view of the centre of the cluster comes from the NASA/ESA Hubble Space Telescope.

    Credit: ESO/ESA/NASA/Digitized Sky Survey 2/N. Risinger (skysurvey.org). Music: Astral Electronic

    2
    This image from the NASA/ESA Hubble Space Telescope shows the central region of the rich globular star cluster NGC 3201 in the southern constellation of Vela (The Sails).
    A star that has been found to be orbiting a black hole with four times the mass of the Sun is indicated with blue circle. Credit: NASA/ESA Hubble

    NASA/ESA Hubble Telescope

    One particular cluster, called NGC 3201 and situated in the southern constellation of Vela (The Sails), has now been studied using the MUSE instrument on ESO’s Very Large Telescope in Chile. An international team of astronomers has found that one of the stars [1] in NGC 3201 is behaving very oddly — it is being flung backwards and forwards at speeds of several hundred thousand kilometres per hour, with the pattern repeating every 167 days [2].

    ESO MUSE on the VLT

    Lead author Benjamin Giesers (Georg-August-Universität Göttingen, Germany) was intrigued by the star’s behaviour: “It was orbiting something that was completely invisible, which had a mass more than four times the Sun — this could only be a black hole! The first one found in a globular cluster by directly observing its gravitational pull.”

    The relationship between black holes and globular clusters is an important but mysterious one. Because of their large masses and great ages, these clusters are thought to have produced a large number of stellar-mass black holes — created as massive stars within them exploded and collapsed over the long lifetime of the cluster [3][4].

    ESO’s MUSE instrument provides astronomers with a unique ability to measure the motions of thousands of far away stars at the same time. With this new finding, the team have for the first time been able to detect an inactive black hole at the heart of a globular cluster — one that is not currently swallowing matter and is not surrounded by a glowing disc of gas. They could estimate the black hole’s mass through the movements of a star caught up in its enormous gravitational pull [5].

    From its observed properties the star was determined to be about 0.8 times the mass of our Sun, and the mass of its mysterious counterpart was calculated at around 4.36 times the Sun’s mass — almost certainly a black hole [6].

    Recent detections of radio and X-ray sources in globular clusters, as well as the 2016 detection of gravitational-wave signals produced by the merging of two stellar-mass black holes, suggest that these relatively small black holes may be more common in globular clusters than previously thought.

    Giesers concludes: “Until recently, it was assumed that almost all black holes would disappear from globular clusters after a short time and that systems like this should not even exist! But clearly this is not the case — our discovery is the first direct detection of the gravitational effects of a stellar-mass black hole in a globular cluster. This finding helps in understanding the formation of globular clusters and the evolution of black holes and binary systems — vital in the context of understanding gravitational wave sources.”

    Notes

    [1] The star found is a main sequence turn-off star, meaning it is at the end of the main sequence phase of its life. Having exhausted its primary hydrogen fuel supply it is now on the way to becoming a red giant.

    [2] A large survey of 25 globular clusters around the Milky Way is currently being conducted using ESO’s MUSE instrument with the support of the MUSE consortium. It will provide astronomers with the spectra of 600 to 27 000 stars in each cluster. The study includes analysis of the “radial velocity” of individual stars — the speed at which they move away from and toward the Earth, along the line of sight of the observer. With radial velocity measurements the orbits of stars can be determined, as well as the properties of any massive object they may be orbiting.

    [3] In the absence of continuous star formation, as is the case for globular clusters, stellar-mass black holes soon become the most massive objects present. Generally, stellar-mass black holes in globular clusters are about four times as massive as the surrounding low-mass stars. Recent theories have concluded that black holes form a dense nucleus within the cluster, which then becomes detached from the rest of the globular material. Movements at the centre of the cluster are then thought to eject the majority of black holes, meaning only a few would survive after a billion years.

    [4] Stellar-mass black holes — or collapsars — are formed when massive stars die, collapsing under their own gravity and exploding as powerful hypernovae. Left behind is a black hole with most of the mass of the former star, which can range from a few times the mass of our Sun to several tens of times as massive.

    [5] As no light is able to escape black holes because of their tremendous gravity, the primary method of detecting them is through observations of radio or X-ray emissions coming from hot material around them. But when a black hole is not interacting with hot matter and so not accumulating mass or emitting radiation, as in this case, the black hole is “inactive” and invisible, so another method of detection is required.

    [6] Because the non-luminous object in this binary system cannot be directly observed there are alternative, although much less persuasive, explanations for what it could be. It is perhaps a triple star system made up of two tightly bound neutron stars, with the observed star orbiting around them. This scenario would require each tightly bound star to be at least twice the mass of our Sun, a binary system that has never been observed before.
    More information

    This research was presented in a paper entitled A detached stellar-mass black hole candidate in the globular cluster NGC 3201, by B. Giesers et al., to appear in the journal Monthly Notices of the Royal Astronomical Society.

    The team is composed of Benjamin Giesers (Georg-August-Universität Göttingen, Germany), Stefan Dreizler (Georg-August-Universität Göttingen, Germany), Tim-Oliver Husser (Georg-August-Universität Göttingen, Germany), Sebastian Kamann (Georg-August-Universität Göttingen, Germany; Liverpool John Moores University, Liverpool, United Kingdom), Guillem Anglada Escudé (Queen Mary University of London, United Kingdom), Jarle Brinchmann (Leiden Observatory, Leiden University, Leiden, The Netherlands; Universidade do Porto, CAUP, Porto, Portugal), C. Marcella Carollo (Swiss Federal Institute of Technology, ETH, Zurich, Switzerland) Martin M. Roth (Leibniz-Institut für Astrophysik Potsdam, Potsdam, Germany), Peter M. Weilbacher (Leibniz-Institut für Astrophysik Potsdam, Potsdam, Germany) and Lutz Wisotzki (Leibniz-Institut für Astrophysik Potsdam, Potsdam, Germany).

    See the full article here .

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

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

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

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

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

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

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

    ESO E-ELT
    ESO/E-ELT to be built at Cerro Armazones at 3,060 m.

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

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

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

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

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

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

     
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