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  • richardmitnick 9:45 pm on June 18, 2021 Permalink | Reply
    Tags: "Capricious Cosmos", , , , Black Holes, , , , , Merging neutron stars   

    From ESOblog (EU): Women in STEM-Cyrielle Opitom “Capricious Cosmos” 

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    From ESOblog (EU)

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    European Southern Observatory [Observatoire européen austral][Europäische Südsternwarte] (EU) (CL)

    18 June 2021
    Science@ESO

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    Juan Carlos Muñoz Mateos.
    Juan Carlos Muñoz Mateos is Media Officer at ESO in Garching and editor of the ESO blog. He completed his PhD in astrophysics at Complutense University of Madrid[Universidad Complutense Madrid](ES) . Previously he worked for several years at ESO in Chile, combining his research on galaxy evolution with duties at Paranal Observatory.

    Astronomical observations are usually planned months in advance, which is not a problem as most celestial objects remain unchanged for millions if not billions of years. But certain astronomical phenomena can occur unexpectedly on timescales of just days –– sometimes even minutes. To learn how we can deal with these sudden events we have talked to three astronomers who study some of the most unpredictable phenomena in the Universe.

    “Comets are like cats: they have tails and they do precisely what they want.” This quote by David H. Levy, an amateur astronomer who co-discovered a comet that impacted on Jupiter in 1994, perfectly describes the capricious personality of comets –– large blocks of ice and rock that traverse the solar system.

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    A NASA Hubble Space Telescope (HST) image of comet Shoemaker-Levy 9, taken on May 17, 1994, with the Wide Field Planetary Camera 2 (WFPC2) in wide field mode.

    But these aren’t the only unpredictable objects out there. Violent supernova explosions, black holes gobbling material from closeby stars, or neutron stars smashing against each other are just a few examples of astronomical phenomena known for not caring about the daily routine of the astronomers who study them. How can we observe these events without even knowing when or where they will happen? Let’s find out.

    Celestial wanderers

    Cyrielle Opitom, a former ESO Fellow and now a Royal Astronomical Society (UK) Norman Lockyer Research Fellow at the University of Edinburgh (SCT), is very familiar with the changeable nature of comets –– fossils that allow us to study how our own solar system formed and evolved. “Comets are very unpredictable,” she says. “Some suddenly split into different fragments, crash into a planet, or become ten times brighter from one day to the next. And we are still trying to understand why those things are happening. That also makes comets very fun to study. You never know what to expect and it never gets boring.”

    When a comet gets close to the Sun, its ices become gaseous. This ejects dust particles as well, creating a huge envelope of dust and gas around the nucleus of the comet, called ‘coma’. Cyrielle uses spectroscopy, a technique that splits light into its constituent colours or wavelengths, “to detect molecules in the coma, and to know what cometary ices are made of.”

    But it’s hard to know in advance when a comet may undergo a sudden burst of activity. To address this, ESO and other observatories offer a type of observing programme called “Target of Opportunity”. “This allows us to decide in advance that we want to observe an outburst of activity, have the observations ready to be executed, and when an event is detected we can ask for the observations to be done within just a few days,” says Cyrielle.

    A Target of Opportunity still requires astronomers to submit an observing proposal months in advance describing their scientific idea, even if they don’t know when they will trigger the observations. “But there are events that we can’t predict, or new interesting comets that are discovered after the deadline for observing time proposals has passed.” For situations like these, observatories offer the opportunity to obtain observing slots using “Director’s Discretionary Time (DDT)”, which allows astronomers to submit an observing proposal on-the-fly for urgent scientific reasons. For instance, these DDT slots came in handy to observe 2I/Borisov, the first interstellar comet, immediately after its discovery, allowing astronomers to study this alien visitor while it was still close to the Earth.

    Comets can still surprise you even when you are already pointing a telescope at them, as Cyrielle knows all too well. In December 2018 she was observing comet 46P/Wirtanen with the ESPRESSO spectrograph at the UT3 telescope [1], part of ESO’s Very Large Telescope.

    “The comet was bright and very close to the Earth,” she says, “so it was quite big in the sky. However, when we tried to point the instrument at the comet, we could not find it.”

    As it turns out, the comet was too far from its predicted position. Luckily, she was observing it simultaneously with the UVES spectrograph on the UT2 telescope. “We managed to find it with UVES, which has a larger field of view.

    We computed the offset from the predicted position and finally found the comet with ESPRESSO as well. But our problems were not over: the comet was not moving the way we expected, so we had to constantly adjust the position of the telescope during the observations. Thanks to the great skills of our support astronomer we got amazing data in the end.”

    When black holes take a midnight snack

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    Combining observations done with ESO’s Very Large Telescope and NASA’s Chandra X-ray telescope, astronomers have uncovered the most powerful pair of jets ever seen from a stellar black hole.

    The black hole blows a huge bubble of hot gas, 1000 light-years across or twice as large and tens of times more powerful than the other such microquasars. The stellar black hole belongs to a binary system as pictured in this artist’s impression. Credit:L. Calçada/M.Kornmesser/ESO.

    Black holes may not be as evasive as comets, but they are still tricky to observe. Teo Muñoz-Darias, a Ramón y Cajal Fellow at the Institute of Astrophysics of the Canaries[Instituto de Astrofísica de Canarias] (ES), is trying to understand what makes black holes hungry. “I study systems called X-ray binaries,” he says, “where a normal star orbits a black hole at such close distance that the black hole steals material from the star.” But since both are rotating around each other, the material doesn’t fall directly into the black hole; instead, it forms an accretion disc around it. “Gas in the accretion disc gets really hot, up to ten million degrees, thus emitting highly energetic radiation like X-rays.”

    This doesn’t happen all the time though. “Most black holes are sleeping and they wake up every now and then,” Teo explains.“If there is little gas in the disc, it will just stay there orbiting the black hole. But when enough gas accumulates, it becomes hotter and friction increases; the gas then loses energy and spirals towards the black hole.” Not all the gas suffers that demise, though; sometimes it can leave the system via powerful winds and jets.

    When one of these systems becomes active, dedicated space telescopes will pick up the sudden burst of X-rays. Astronomers worldwide are notified about this and start collecting additional data from ground-based telescopes, quickly sharing their findings via The Astronomer’s Telegram. Teo constantly keeps an eye on this, as interesting targets can show up anytime. “Black holes don’t care about Saturdays, Sundays, or holidays,” he jokes. “In fact they tend to pick holidays!”

    Upon finding a suitable target, Teo triggers Target of Opportunity observations with various instruments, like the X-shooter spectrograph at ESO’s VLT.

    “X-shooter is probably the best instrument worldwide for this kind of science,” he says. “With it you are able to get a spectrum all the way from the ultraviolet to the near infrared in one go, and this is fantastic. It’s not only that you get a lot of data, but you get it simultaneously.” This is key with rapidly changing objects, as it allows astronomers to follow how they evolve at different colours without having to coordinate observations with separate instruments.

    Thanks to observations like these, Teo and his team could study in great detail the complex balance between gas accretion onto the black hole and gas being expelled outwards due to winds. They found that winds are present even when the system is asleep, and that when they are awake their activity can end prematurely when a lot of gas is removed.

    The most energetic explosions in the Universe

    When it comes to unpredictability, nothing beats gamma-ray bursts (GRBs) –– sudden flashes of high-energy gamma radiation. “GRBs are the brightest things known to science,” says Nial Tanvir, a professor at the University of Leicester (UK).

    “Some are produced when a massive star implodes at the end of its lifetime, leaving behind a neutron star or a black hole. Other GRBs are caused by the merger of two neutron stars. GRBs give us access to the most extreme physics that we know of in the Universe.”

    As opposed to comets and black holes feasting off closeby stars, which require astronomers to react within days, GRBs sometimes need to be observed minutes after they occur. “GRBs start out bright and decline in luminosity quickly,” Nial says. “So if you can get there early, there’s just so much more information that you can get with a shorter amount of telescope time. If you can get observations within minutes and then continue to monitor over a few hours, in some cases you see variability, which can tell you important things about the GRB and its environment.”

    To allow astronomers to react so quickly, ESO offers them a unique observing mechanism called “Rapid Response Mode”. When this mode is triggered, an alarm instantly goes off in the Paranal control room: the ongoing observations will be aborted –– if it’s safe to do so –– and the telescope will automatically slew towards the sky coordinates of the GRB. Unfortunately, this requires knowing the exact location of the GRB from the get go, which isn’t always the case.

    One of the most exciting events that Nial has studied was the first-ever detection of light from two merging neutron stars. On 17 August 2017 the LIGO and Virgo interferometers registered gravitational waves –– ripples in space-time –– passing through Earth. Two seconds later, the Fermi and INTEGRAL space telescopes detected a GRB coming from the same area of the sky.


    Both were the smoking-gun evidence of a kilonova: two neutron stars smashing against each other.

    As night fell in Chile, dozens of telescopes started to chase this unique event. “Neither the gravitational waves nor the gamma rays gave us a tremendously accurate localisation,” says Nial. So this was like looking for a needle in a haystack, scanning a large patch of the sky looking for a small dot that wasn’t there before. The Swope telescope at Las Campanas Observatory was the first one to locate the host galaxy: NGC4993, an elliptical galaxy about 140 million lightyears away.

    Five other teams found it independently during those hectic first couple of hours, including Nial’s group using ESO’s VISTA telescope [below].

    “You just did have that strong sense that you were sort of living through history, perhaps more so than anything else I’ve been involved with.” During the next few weeks, astronomers worldwide monitored the evolution of this object with pretty much every telescope they could, including 14 instruments from 7 ESO-related telescopes. “As the days went by this thing started to become redder and redder, just as predicted. The collision pulled very radioactive material out of the neutron stars, which then decayed to form a whole lot of elements heavier than iron like gold, platinum and uranium, whose origin had previously been quite mysterious.”

    It’s all about teamwork

    Observing these unpredictable events is only possible thanks to team spirit. In the case of the kilonova, for instance, astronomers barely had a couple of hours after sunset to observe it before it sank under the horizon. As Nial says, “The success of all of these campaigns really came down to the staff at the telescopes, who were doing their very best to squeeze in those observations in difficult circumstances.”

    But this is only part of the story, as good planning is also key. “ESO is not just Paranal or La Silla observatories,” explains Cyrielle. “It also has an amazing team at the User Support Department to help us prepare and adjust our observations, so that we make the best possible use of the instruments. When I was preparing observations of the interstellar comet 2I/Borisov, they helped me design unusual observations that spanned several months. Without them we could never have obtained such high-quality data to study an interstellar comet.”
    Note

    [1] Unlike other instruments, ESPRESSO isn’t physically attached to a Unit Telescope. The light from any UT, even all four of them, can be fed into the instrument.

    See the full article here .


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    European Southern Observatory [Observatoire européen austral][Europäische Südsternwarte] (EU) 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”.

    European Southern Observatory [Observatoire européen austral][Europäische Südsternwarte] (EU) 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,

    European Southern Observatory(EU) , Very Large Telescope at Cerro Paranal in the Atacama Desert •ANTU (UT1; The Sun ) •KUEYEN (UT2; The Moon ) •MELIPAL (UT3; The Southern Cross ), and •YEPUN (UT4; Venus – as evening star). Elevation 2,635 m (8,645 ft) from above Credit J.L. Dauvergne & G. Hüdepohl atacama photo. [/caption]

    ESO Very Large Telescope 4 lasers on Yepun (CL)

    European Southern Observatory(EU)/MPG Institute for Radio Astronomy [MPG Institut für Radioastronomie](DE) ESO’s Atacama Pathfinder Experiment(CL) high on the Chajnantor plateau in Chile’s Atacama region, at an altitude of over 4,800 m (15,700 ft).

    European Southern Observatory(EU) ExTrA telescopes at erro LaSilla at an altitude of 2400 metres.

     
  • richardmitnick 1:02 pm on May 26, 2021 Permalink | Reply
    Tags: "Binary Black Hole Simulations Provide Blueprint for Future Observations", , , Black Holes, , Scientists did not capture the first radio image of a black hole until 2019.   

    From NASA Goddard Space Flight Center: “Binary Black Hole Simulations Provide Blueprint for Future Observations” 

    NASA Goddard Banner

    From NASA Goddard Space Flight Center

    May 26, 2021
    Emma Edmund
    NASA’s Goddard Space Flight Center, Greenbelt, Md.

    Astronomers continue to develop computer simulations to help future observatories better home in on black holes, the most elusive inhabitants of the universe.

    Though black holes likely exist abundantly in the universe, they are notoriously hard to see. Scientists did not capture the first radio image of a black hole until 2019.

    Only about four dozen black hole mergers have been detected through their signature gravitational ripples since the first detection in 2015.

    That is not a lot of data to work with. So scientists look to black hole simulations to gain crucial insight that will help find more mergers with future missions. Some of these simulations, created by scientists like astrophysicist Scott Noble, track supermassive black hole binary systems. That is where two monster black holes like those found in the centers of galaxies orbit closely around each other until they eventually merge.


    Simulation Reveals Spiraling Supermassive Black Holes.
    Gas glows brightly in this computer simulation of supermassive black holes only 40 orbits from merging. Models like this may eventually help scientists pinpoint real examples of these powerful binary systems. Credit: NASA’s Goddard Space Flight Center.

    The simulations, created by computers working through sets of equations too complicated to solve by hand, illustrate how matter interacts in merger environments. Scientists can use what they learn about black hole mergers to identify some telltale characteristics that let them distinguish black hole mergers from stellar events. Astronomers can then look for these telltale signs and spot real-life black hole mergers.

    Noble, who works at NASA’s Goddard Space Flight Center in Greenbelt, Maryland, said these binary systems emit gravitational waves and influence surrounding gases, leading to unique light shows detectable with conventional telescopes. This allows scientists to learn about different aspects of the same system. Multimessenger observations that combine different forms of light or gravitational waves could allow scientists to refine their models of black hole binary systems.

    “We’ve been relying on light to see everything out there,” Noble said. “But not everything emits light, so the only way to directly ‘see’ two black holes is through the gravitational waves they generate. Gravitational waves and the light from surrounding gas are independent ways of learning about the system, and the hope is that they will meet up at the same point.”

    Binary black hole simulations can also help the Laser Interferometer Space Antenna (LISA) mission.

    This space-based gravitational wave observatory, led by the European Space Agency [Agence spatiale européenne][Europäische Weltraumorganisation](EU) with significant contributions from NASA, is expected to launch in 2034. If simulations determine what electromagnetic characteristics distinguish a binary black hole system from other events, scientists could detect these systems before LISA flies, Noble said. These observations could then be confirmed through additional detections once LISA launches.

    That would allow scientists to verify that LISA is working, observe systems for a longer period before they merge, predict what is going to happen, and test those predictions.

    “We’ve never been able to do that before,” Noble said. “That’s really exciting.”

    The simulations rely on code which describes how the density and pressure of plasma changes in strong-gravity regions near a single black hole or neutron star, Noble said. He modified the code to allow for two black holes to evolve.

    Noble is working with Goddard and university partners, including Bernard Kelly at the University of Maryland, Manuela Campanelli leading a team of researchers at the Rochester Institute of Technology, and Julian Krolik leading a Johns Hopkins University research team.

    Kelly creates simulations using a special approach called a moving puncture simulation.

    These simulations allow scientists to avoid representing a singularity inside the event horizon — the part of the black hole from which nothing can escape, Kelly said. Everything outside of that event horizon evolves, while the objects inside remain frozen from earlier in the simulation. This allows scientists to overlook the fact that they do not know what happens within an event horizon.

    To mimic real-life situations, where black holes accumulate accretion disks of gas, dust, and diffuse matter, scientists have to incorporate additional code to track how the ionized material interacts with magnetic fields.

    “We’re trying to seamlessly and correctly glue together different codes and simulation methods to produce one coherent picture,” Kelly said.

    In 2018, the team published an analysis of a new simulation in The Astrophysical Journal that fully incorporated the physical effects of Einstein’s general theory of relativity to show a merger’s effects on the environment around it. The simulation established that the gas in binary black hole systems will glow predominantly in ultraviolet and X-ray light.

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    This visualization of supercomputer data shows the X-ray glow of the inner accretion disc of a black hole.
    Credit: Jeremy Schnittman/Scott Noble /NASA Goddard.

    Simulations also showed that accretion disks in these systems are not completely smooth. A dense clump forms orbiting the binary, and every time a black hole sweeps close, it pulls off matter from the clump. That collision heats up the matter, producing a bright signal and creating an observable fluctuation of light.

    In addition to improving their confidence in the accuracy of the simulations, Goddard astrophysicist Jeremy Schnittman said they also need to be able to apply the same simulation code to a single black hole or a binary and show the similarities and also the differences between the two systems.

    “The simulation are going to tell us what the systems should look like,” Schnittman said. “LISA works more like a radio antenna as opposed to an optical telescope. We’re going to hear something in the universe and get its basic direction, but nothing very precise. What we have to do is take other telescopes and look in that part of the sky, and the simulations are going to tell us what to look for to find a merging black hole.”

    Kelly said LISA will be more sensitive to lower gravitational wave frequencies than the current ground-based gravitational wave observer, the Laser Interferometer Gravitational-Wave Observatory (LIGO). That means LISA will be able to sense smaller-mass binary systems much earlier and will likely detect merging systems in time to alert electromagnetic telescopes.

    For Schnittman, these simulations are key to understanding the real-life data LISA and other spacecraft collect. The case for models may be even stronger for binary black holes, Schnittman said, because the scientific community has little data.

    “We probably will never find a binary black hole with a telescope until we simulate them to the point we know exactly what we’re looking for, because they’re so far away, they’re so tiny, you’re going to see just one speck of light,” Schnittman said. “We need to be able to look for that smoking gun.”

    See the full article here.


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    NASA/Goddard Campus

    NASA’s Goddard Space Flight Center, Greenbelt, MD (US) 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.

    GSFC also operates two spaceflight tracking and data acquisition networks (the NASA Deep Space Network(US) and the Near Earth Network); develops and maintains advanced space and Earth science data information systems, and develops satellite systems for the National Oceanic and Atmospheric Administration(US) .

    GSFC manages operations for many NASA and international missions including the NASA/ESA Hubble Space Telescope; the Explorers Program; the Discovery Program; the Earth Observing System; INTEGRAL; MAVEN; OSIRIS-REx; the Solar and Heliospheric Observatory ; the Solar Dynamics Observatory; Tracking and Data Relay Satellite System ; Fermi; and Swift. Past missions managed by GSFC include the Rossi X-ray Timing Explorer (RXTE), Compton Gamma Ray Observatory, SMM, COBE, IUE, and ROSAT. Typically, unmanned Earth observation missions and observatories in Earth orbit are managed by GSFC, while unmanned planetary missions are managed by the Jet Propulsion Laboratory (JPL) in Pasadena, California(US).

    Goddard is one of four centers built by NASA since its founding on July 29, 1958. It is NASA’s first, and oldest, space center. Its original charter was to perform five major functions on behalf of NASA: technology development and fabrication; planning; scientific research; technical operations; and project management. The center is organized into several directorates, each charged with one of these key functions.

    Until May 1, 1959, NASA’s presence in Greenbelt, MD was known as the Beltsville Space Center. It was then renamed the Goddard Space Flight Center (GSFC), after Robert H. Goddard. Its first 157 employees transferred from the United States Navy’s Project Vanguard missile program, but continued their work at the Naval Research Laboratory in Washington, D.C., while the center was under construction.

    Goddard Space Flight Center contributed to Project Mercury, America’s first manned space flight program. The Center assumed a lead role for the project in its early days and managed the first 250 employees involved in the effort, who were stationed at Langley Research Center in Hampton, Virginia. However, the size and scope of Project Mercury soon prompted NASA to build a new Manned Spacecraft Center, now the Johnson Space Center, in Houston, Texas. Project Mercury’s personnel and activities were transferred there in 1961.

    The Goddard network tracked many early manned and unmanned spacecraft.

    Goddard Space Flight Center remained involved in the manned space flight program, providing computer support and radar tracking of flights through a worldwide network of ground stations called the Spacecraft Tracking and Data Acquisition Network (STDN). However, the Center focused primarily on designing unmanned satellites and spacecraft for scientific research missions. Goddard pioneered several fields of spacecraft development, including modular spacecraft design, which reduced costs and made it possible to repair satellites in orbit. Goddard’s Solar Max satellite, launched in 1980, was repaired by astronauts on the Space Shuttle Challenger in 1984. The Hubble Space Telescope, launched in 1990, remains in service and continues to grow in capability thanks to its modular design and multiple servicing missions by the Space Shuttle.

    Today, the center remains involved in each of NASA’s key programs. Goddard has developed more instruments for planetary exploration than any other organization, among them scientific instruments sent to every planet in the Solar System. The center’s contribution to the Earth Science Enterprise includes several spacecraft in the Earth Observing System fleet as well as EOSDIS, a science data collection, processing, and distribution system. For the manned space flight program, Goddard develops tools for use by astronauts during extra-vehicular activity, and operates the Lunar Reconnaissance Orbiter, a spacecraft designed to study the Moon in preparation for future manned exploration.

     
  • richardmitnick 9:52 am on May 1, 2021 Permalink | Reply
    Tags: "eROSITA witnesses the awakening of massive black holes", , , , Black Holes, ,   

    From MPG Institute for Extraterrestrial Physics [MPG Institut für extraterrestrische Physik] (DE): “eROSITA witnesses the awakening of massive black holes” 

    From MPG Institute for Extraterrestrial Physics [MPG Institut für extraterrestrische Physik] (DE)

    April 29, 2021

    Arcodia, Riccardo, phd student
    Tel +49 (0)89 30000-3643
    arcodia@mpe.mpg.de

    Dr. Andrea Merloni, Senior Scientist +49
    Tel(0)89 30000-3893 +49
    Fax(0)89 30000-3569
    am@mpe.mpg.de

    Dr. Hannelore Hämmerle, press officer
    Tel +49 (0)89 30000-3980
    Fax +49 (0)89 30000-3569
    hanneh@mpe.mpg.de

    April 29, 2021

    Using the SRG/eROSITA all-sky survey data, scientists at the Max Planck Institute for Extraterrestrial Physics have found two previously quiescent galaxies that now show quasi-periodic eruptions.

    The nuclei of these galaxies light up in X-rays every few hours, reaching peak luminosities comparable to that of an entire galaxy. The origin of this pulsating behaviour is unclear. A possible cause is a stellar object orbiting the central black hole. As these galaxies are relatively close and small, this discovery could help scientists to better understand how black holes are activated in low-mass galaxies.

    1
    Optical image of the first galaxy found with quasi-periodic eruptions in the eROSITA all-sky data, the NICER X-ray light-curve is overlayed in green. The galaxy was identified as 2MASS 02314715-1020112 at a redshift of z~0.05. About 18.5 hours pass between the peaks of the X-ray outbursts. Credit: MPE; optical image: LBNL DESI (US) Legacy Imaging Surveys/D. Lang (Perimeter Institute (CA))

    2
    Optical image of the second galaxy found with quasi-periodic eruptions in the eROSITA all-sky data, the XMM-Newton X-ray light-curve is overlayed in magenta. The galaxy was identified as 2MASX J02344872-4419325 at a redshift of z~0.02. This source shows much narrower and more frequent eruptions, approximately every 2.4 hours.

    Quasars or “active galactic nuclei” (AGN) are often called the lighthouses of the distant universe. The luminosity of their central region, where a very massive black hole accretes large amounts of material, can be thousands of times higher than that of a galaxy like our Milky Way. However, unlike a lighthouse, AGN shine continuously.

    “In the eROSITA all-sky survey, we have now found two previously quiescent galaxies with huge, almost periodic sharp pulses in their X-ray emission,” says Riccardo Arcodia, PhD student at the Max Planck Institute for Extraterrestrial Physics (MPE), who is the first author of the study now published in Nature. These kinds of objects are fairly new: only two such sources were known before, found either serendipitously or in archival data in the past couple of years. “As this new type of erupting sources seems to be peculiar in X-rays, we decided to use eROSITA as a blind survey and immediately found two more,” he adds.

    The eROSITA telescope currently scans the entire sky in X-rays and the continuous data stream is well suited to find transient events such as these eruptions. Both new sources discovered by eROSITA showed high-amplitude X-ray variability within just a few hours, which was confirmed by follow-up observations with the XMM-Newton and NICER X-ray telescopes. Contrary to the two known similar objects, the new sources found by eROSITA were not previously active galactic nuclei.

    “These were normal, average low-mass galaxies with inactive black holes,” explains Andrea Merloni at MPE, principal investigator of eROSITA. “Without these sudden, repeating X-ray eruptions we would have ignored them.” The scientists now have the chance to explore the vicinity of the smallest super-massive black holes. These have 100 000 to 10 million times the mass of our Sun.

    Quasi-periodic emission such as the one discovered by eROSITA is typically associated with binary systems. If these eruptions are indeed triggered by the presence of an orbiting object, its mass has to be much smaller than the black hole’s – of the order of a star or even a white dwarf, which might be partially disrupted by the huge tidal forces close to the black hole at each passage.

    “We still do not know what causes these X-ray eruptions,” admits Arcodia. “But we know that the black hole’s neighbourhood was quiet until recently, so a pre-existing accretion disk as the one present in active galaxies is not required to trigger these phenomena.” Future X-ray observations will help to constrain or rule out the “orbiting object scenario” and to monitor possible changes in the orbital period. These kinds of objects could also be observable with gravitational waves signals, opening up new possibilities in multi-messenger astrophysics.

    Science paper:
    Nature

    See the full article here .

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    For their astrophysical research, the MPG Institute for Extraterrestrial Physics [MPG Institut für extraterrestrische Physik] ( DE) scientists measure the radiation of far away objects in different wavelenths areas: from millimetere/sub-millimetre and infared all the way to X-ray and gamma-ray wavelengths. These methods span more than twelve decades of the electromagnetic spectrum.

    The research topics pursued at MPE range from the physics of cosmic plasmas and of stars to the physics and chemistry of interstellar matter, from star formation and nucleosynthesis to extragalactic astrophysics and cosmology. The interaction with observers and experimentalists in the institute not only leads to better consolidated efforts but also helps to identify new, promising research areas early on.

    The structural development of the institute mainly has been directed by the desire to work on cutting-edge experimental, astrophysical topics using instruments developed in-house. This includes individual detectors, spectrometers and cameras but also telescopes and integrated, complete payloads. Therefore the engineering and workshop areas are especially important for the close interlink between scientific and technical aspects.

    The scientific work is done in four major research areas that are supervised by one of the directors:

    Center for Astrochemical Studies (CAS)
    Director: P. Caselli

    High-Energy Astrophysics
    Director: P. Nandra

    Infrared/Submillimeter Astronomy
    Director: R. Genzel

    Optical & Interpretative Astronomy
    Director: R. Bender

    Within these areas scientists lead individual experiments and research projects organised in about 25 project teams.

    The Max Planck Society is Germany’s most successful research organization. Since its establishment in 1948, no fewer than 18 Nobel laureates have emerged from the ranks of its scientists, putting it on a par with the best and most prestigious research institutions worldwide. The more than 15,000 publications each year in internationally renowned scientific journals are proof of the outstanding research work conducted at Max Planck Institutes – and many of those articles are among the most-cited publications in the relevant field.

    What is the basis of this success? The scientific attractiveness of the Max Planck Society is based on its understanding of research: Max Planck Institutes are built up solely around the world’s leading researchers. They themselves define their research subjects and are given the best working conditions, as well as free reign in selecting their staff. This is the core of the Harnack principle, which dates back to Adolph von Harnack, the first president of the Kaiser Wilhelm Society, which was established in 1911. This principle has been successfully applied for nearly one hundred years. The Max Planck Society continues the tradition of its predecessor institution with this structural principle of the person-centered research organization.

    The currently 83 Max Planck Institutes and facilities conduct basic research in the service of the general public in the natural sciences, life sciences, social sciences, and the humanities. Max Planck Institutes focus on research fields that are particularly innovative, or that are especially demanding in terms of funding or time requirements. And their research spectrum is continually evolving: new institutes are established to find answers to seminal, forward-looking scientific questions, while others are closed when, for example, their research field has been widely established at universities. This continuous renewal preserves the scope the Max Planck Society needs to react quickly to pioneering scientific developments.

    eRosita DLR MPG, on Russian German space telescope The Russian-German space probe Spektrum-Roentgen-Gamma (SRG).

     
  • richardmitnick 1:52 pm on April 21, 2021 Permalink | Reply
    Tags: "Black hole is closest to Earth among the smallest ever discovered", , , , Black Holes,   

    From Ohio State University via phys.org : “Black hole is closest to Earth among the smallest ever discovered” 

    From Ohio State University

    via

    phys.org

    April 21, 2021

    1
    Credit: Lauren Fanfer.

    Scientists have discovered one of the smallest black holes on record—and the closest one to Earth found to date.

    Researchers have dubbed it ‘The Unicorn,’ in part because it is, so far, one of a kind, and in part because it was found in the constellation Monoceros—’The Unicorn.’ The findings are publishing today, April 21, in the journal MNRAS [no link available].

    “When we looked at the data, this black hole—the Unicorn—just popped out,” said lead author Tharindu Jayasinghe, a doctoral student in astronomy at The Ohio State University and an Ohio State presidential fellow.

    The Unicorn is about three times the mass of our sun—tiny for a black hole. Very few black holes of this mass have been found in the universe. This black hole is 1,500 light years away from Earth, still inside the Milky Way galaxy. And, until Jayasinghe started analyzing it, it was essentially hiding in plain sight.

    The black hole appears to be a companion to a red giant star, meaning that the two are connected by gravity. Scientists can’t see the black hole—they are, by definition, dark, not only visually, but to the tools astronomers use to measure light and other wavelengths.

    But in this case, they can see the black hole’s companion star. That star had been well-documented by telescope systems including KELT, run out of Ohio State; All Sky Automated Survey-ASAS (USA), the precursor to Ohio State ASAS-SN, which is now run out of Ohio State, and TESS, a NASA satellite that searches for planets outside our solar system. Data about it had been widely available but hadn’t yet been analyzed in this way.

    When Jayasinghe and the other researchers analyzed that data, they noticed something they couldn’t see appeared to be orbiting the red giant, causing the light from that star to change in intensity and appearance at various points around the orbit.

    Something, they realized, was tugging at the red giant and changing its shape. That pulling effect, called a tidal distortion, offers astronomers a signal that something is affecting the star. One option was a black hole, but it would have to be small—less than five times the mass of our sun, falling into a size window that astronomers call the “mass gap.” Only recently have astronomers considered it a possibility that black holes of that mass could exist.

    “When you look in a different way, which is what we’re doing, you find different things,” said Kris Stanek, study co-author, astronomy professor at Ohio State and university distinguished scholar. “Tharindu looked at this thing that so many other people had looked at and instead of dismissing the possibility that it could be a black hole, he said, ‘Well, what if it could be a black hole?'”

    That tidal disruption is produced by the tidal force of an unseen companion—a black hole.

    “Just as the moon’s gravity distorts the Earth’s oceans, causing the seas to bulge toward and away from the moon, producing high tides, so does the black hole distort the star into a football-like shape with one axis longer than the other,” said Todd Thompson, co-author of the study, chair of Ohio State’s astronomy department and university distinguished scholar. “The simplest explanation is that it’s a black hole—and in this case, the simplest explanation is the most likely one.”

    The velocity of the red giant, the period of the orbit and the way in which the tidal force distorted the red giant told them the black hole’s mass, leading them to conclude that this black hole was about three solar masses, or three times that of the sun.

    For about the last decade, astronomers and astrophysicists wondered whether they weren’t finding these black holes because the systems and approaches they used were not sophisticated enough to find them. Or, they wondered, did they simply not exist?

    Then, about 18 months ago, many of the members of this Ohio State research team, led by Thompson, published a scientific article in the journal Science, offering strong evidence that these types of black holes existed. That discovery motivated Jayasinghe and others, both at Ohio State and around the world, to search in earnest for smaller black holes. And that evaluation led them to the Unicorn.

    Finding and studying black holes and neutron stars in our galaxy is crucial for scientists studying space, because it tells them about the way stars form and die.

    But finding and studying black holes is, almost by definition, difficult: Individual black holes don’t emit the same kind of rays that other objects emit in space. They are, to scientific equipment, electromagnetically silent and dark. Most known black holes were discovered because they interacted with a companion star, which created a lot of X-rays—and those X-rays are visible to astronomers.

    In recent years, more large-scale experiments to try and locate smaller black holes have launched, and Thompson said he expects to see more “mass gap” black holes discovered in the future.

    “I think the field is pushing toward this, to really map out how many low-mass, how many intermediate-mass and how many high-mass black holes there are, because every time you find one it gives you a clue about which stars collapse, which explode and which are in between,” he said.

    See the full article here .

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    Please help promote STEM in your local schools.

    Stem Education Coalition

    The Ohio State University ( is a public research university in Columbus, Ohio. Founded in 1870 as a land-grant university and the ninth university in Ohio with the Morrill Act of 1862, the university was originally known as the Ohio Agricultural and Mechanical College. The college originally focused on various agricultural and mechanical disciplines but it developed into a comprehensive university under the direction of then-Governor (later, U.S. President) Rutherford B. Hayes, and in 1878 the Ohio General Assembly passed a law changing the name to “The Ohio State University”. The main campus in Columbus, Ohio, has since grown into the third-largest university campus in the United States. The university also operates regional campuses in Lima, Mansfield, Marion, Newark, and Wooster.

    The university has an extensive student life program, with over 1,000 student organizations; intercollegiate, club and recreational sports programs; student media organizations and publications, fraternities and sororities; and three student governments. Ohio State athletic teams compete in Division I of the NCAA and are known as the Ohio State Buckeyes. As of the 2016 Summer Olympics, athletes from Ohio State have won 104 Olympic medals (46 gold, 35 silver, and 23 bronze). The university is a member of the Big Ten Conference for the majority of sports.

     
  • richardmitnick 5:18 pm on January 23, 2021 Permalink | Reply
    Tags: "Neutrons' 'evil twins' may be crushing stars into black holes", , Black Holes, ,   

    From Live Science: “Neutrons’ ‘evil twins’ may be crushing stars into black holes” 

    From Live Science

    1.22.21
    Paul Sutter

    1
    Neutron stars are essentially city-size atomic nuclei composed of individual neutrons crammed together just about as tightly as possible. Shown here, an illustration of a neutron star whose gravity is distorting its neighbor, a white dwarf star. © Mark Garlick/Getty Images.

    The universe may be filled with “mirror” particles — and these otherwise-undetectable particles could be shrinking the densest stars in the universe, turning them into black holes, a new study suggests.

    These hypothetical evil twins of ordinary particles would experience a flipped version of the laws of physics, as if the rules that govern known particles were reflected in a looking glass. According to a new study, published in December 2020 in the preprint database [Neutron – mirror neutron mixing and neutron stars] but not yet peer-reviewed, if these particles exist, they would be shrinking the densest stars in the universe into black holes.

    Through the looking glass

    Several fundamental symmetries in nature give rise to the laws of physics. For example, the ability to move an experiment or interaction in space and have the same outcome leads to conservation of momentum.

    But one of these symmetries, the symmetry of reflection, isn’t always obeyed.The symmetry of reflection is when you look at the mirror image of a physical reaction. In almost all cases, you get the exact same result. For example, if you toss a ball up in the air and catch it, it looks exactly the same in the mirror — the gravity respects reflection symmetry.

    But not all forces play along. The violator of reflection symmetry (also known as mirror symmetry, P-symmetry or parity) is the weak nuclear force. Whenever the weak force is involved in some particle interaction, the mirror image of that interaction will look different. The classic experiment that first detected this effect found that when a radioactive version of cobalt decays, the electron it emits prefers to go in one direction (in particular, opposite the direction of the spin of the cobalt), rather than any random direction. If the weak nuclear force obeyed reflection symmetry, then those electrons shouldn’t have “known” which direction is which, and popped out anywhere they please.

    Physicists have no idea why the mirror symmetry is broken in our universe, so some have proposed a radical explanation: Maybe it’s not broken at all, and we’re just looking at the universe the wrong way.

    You can rescue mirror symmetry if you allow for the existence of some extra particles. And by “some,” I mean “a lot” — a mirror-image copy of every single particle. There would be mirror electrons, mirror neutrons, mirror photons, mirror Z bosons. You name it, it’s got a mirror. (This is different from antimatter, which is like normal matter but with opposite electric charge.)

    Other names for mirror matter include “shadow matter” and “Alice matter” (as in, Through the Looking-Glass). By introducing mirror matter, reflection is preserved in the universe: Ordinary matter performs left-handed interactions, and mirror matter performs right-handed interactions. Everything syncs up at the mathematical level.

    The heart of the star

    But how can scientists test this radical idea? Because the only force that violates mirror symmetry is the weak nuclear force, that’s the only force that can provide a “channel” for regular matter to communicate with its mirror counterparts. And the weak force is really, really weak, so even if the universe were flooded with mirror particles, they’d be barely detectable.

    Many experiments have focused on neutral particles, like neutrons, because they don’t have electromagnetic interactions, thereby making the experiments easier. Searches for mirror neutrons haven’t turned up anything yet, but all hope is not lost. That’s because those experiments have taken place on Earth, which doesn’t have a superstrong gravitational field. But theoretical physicists predict a very strong gravitational field can enhance the connection between neutrons and mirror neutrons. Thankfully, nature has already crafted a far superior experimental device to hunt for mirror matter: neutron stars.

    Neutron stars are the leftover cores of giant stars. They are extraordinarily dense — a single teaspoon of neutron star material would outweigh the Great Pyramids — and extremely small. Imagine cramming 10 suns’ worth of material into a volume no bigger than Manhattan.

    Neutron stars are essentially city-size atomic nuclei composed of individual neutrons crammed together just about as tightly as possible.

    Neutrons’ evil twins

    With that incredible neutron abundance, coupled with the extreme gravitational field (the tallest “mountains” on neutron stars are barely a half inch high), weird things are bound to happen. One of those things, the new study proposes, is neutrons occasionally turning into their mirror neutron counterparts.

    When a neutron turns into a mirror neutron, a few things happen. The mirror neutron still hangs out inside the star; it’s gravitationally bound and thus can’t go anywhere. And the mirror neutron has a (tiny) gravitational influence of its own, so the star doesn’t evaporate. But mirror neutrons don’t participate in the interactions that scientists detect in neutron stars, so that changes the internal chemistry. They do take part in a “mirror neutron star” life, with its own set of interesting atomic interactions, but that life is hidden from us, like a ghost inhabiting the body of a regular neutron star.

    It’s like going to a crowded football game and slowly replacing the fans with cardboard cutouts: The stadium is still filled, but the energy is gone.

    As neutrons slowly convert to mirror neutrons, the star shrinks. At a 1:1 ratio of regular neutrons to mirror neutrons, the neutron star finds itself about 30% smaller.

    Neutron stars can hold themselves up from the crushing weight of their own gravity by a quantum mechanical process called degeneracy pressure. But that pressure has a limit, and with fewer regular neutrons, that limit shrinks. If a star had a 1:1 ratio of ordinary neutrons to mirror neutrons, the maximum mass of neutron stars in the universe would be about 30% less massive than what we would normally expect. More massive than this, and neutron stars would collapse into black holes.

    Scientists have observed neutron stars bigger than this, which at first glance might mean that mirror matter is a dead-end idea (and we have to find some other explanation for mirror symmetry violation). But the case isn’t closed: The universe is only so old (13.8 billion years), and we have no idea how long this changeover process can take. It’s possible there just hasn’t been enough time for the neutron stars to make the switch.

    The cool thing about neutron stars is that scientists are looking at them all the time. By finding and observing more neutron stars, they might just find a sign in any of those signals that there’s a hidden, mirror — and dare I say “evil”? — sector of the universe.

    See the full article here .

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  • richardmitnick 4:45 pm on January 13, 2021 Permalink | Reply
    Tags: "Quantum projects launched to solve universe’s mysteries", , Black Holes, , Determination of Absolute Neutrino Mass using Quantum Technologies will be led by UCL., , Quantum Simulators for Fundamental Physics project led by the University of Nottingham., Researchers from the University of Cambridge have been awarded funding on four of the seven projects., STFC Quantum Technologies for Fundamental Physics programme, The programme is part of the National Quantum Technologies Programme., The Quantum Sensors for the Hidden Sector (QSHS) project led by the University of Sheffield has been awarded £4.8 million in funding., UK Research and Innovation (UKRI) is supporting seven projects with a £31 million investment to demonstrate how quantum technologies could solve some of the greatest mysteries in fundamental physics.   

    From Kavli Institute for Cosmology Cambridge (UK): “Quantum projects launched to solve universe’s mysteries” 

    KavliFoundation

    The Kavli Foundation

    From Kavli Institute for Cosmology, Cambridge (UK)

    Jan 13, 2021
    Sarah Collins
    sarah.collins@admin.cam.ac.uk
    Communications team

    Researchers will use cutting-edge quantum technologies to transform our understanding of the universe and answer key questions such as the nature of dark matter and black holes.

    1
    New Simulation Sheds Light on Spiraling Supermassive Black Holes. Credit: NASA Goddard Space Flight Center.

    UK Research and Innovation (UKRI) is supporting seven projects with a £31 million investment to demonstrate how quantum technologies could solve some of the greatest mysteries in fundamental physics. Researchers from the University of Cambridge have been awarded funding on four of the seven projects.

    Just as quantum computing promises to revolutionise traditional computing, technologies such as quantum sensors have the potential to radically change our approach to understanding our universe.

    The projects are supported through the Quantum Technologies for Fundamental Physics programme, delivered by the Science and Technology Facilities Council (STFC) and the Engineering and Physical Sciences Research Council (EPSRC) as part of UKRI’s Strategic Priorities Fund. The programme is part of the National Quantum Technologies Programme.

    AION: A UK Atom Interferometer Observatory and Network has been awarded £7.2 million in funding and will be led by Imperial College London. The project will develop and use technology based on quantum interference between atoms to detect ultra-light dark matter and sources of gravitational waves, such as collisions between massive black holes far away in the universe and violent processes in the very early universe. The team will design a 10m atom interferometer, preparing the construction of the instrument in Oxford and paving the way for larger-scale future experiments to be located in the UK. Members of the AION consortium will also contribute to MAGIS, a partner experiment in the US.

    The Cambridge team on AION is led by Professor Valerie Gibson and Dr Ulrich Schneider from the Cavendish Laboratory, alongside researchers from the Kavli Institute for Cosmology, the Institute of Astronomy and the Department of Applied Mathematics and Theoretical Physics. Dr Tiffany Harte will co-lead the development of the cold atom transport and final cooling sequences for AION, and Dr Jeremy Mitchell will co-lead the data readout and network capabilities for AION and MAGIS, and undertake data analysis and theoretical interpretation.

    “This announcement from STFC to fund the AION project, which alongside some seed funding from the Kavli Foundation, will allow us to target key open questions in fundamental physics and bring new interdisciplinary research to the University for the foreseeable future,” said Gibson.

    “Every physical effect, known or unknown, leaves its fingerprint on the phase evolution of a coherent quantum system such as cold atoms; it only requires sufficiently sensitive detectors,” said Schneider. “We are excited to contribute our cold-atom technology to this interdisciplinary endeavour and to develop atom interferometry into a powerful detector for fundamental physics.”

    The Quantum Sensors for the Hidden Sector (QSHS) project, led by the University of Sheffield, has been awarded £4.8 million in funding. The project aims to contribute to the search for axions, low-mass ‘hidden’ particles that are candidates to solve the mystery of dark matter. They will develop new quantum measurement technology for inclusion in the US ADMX experiment, which can then be used to search for axions in parts of our galaxy’s dark matter halo that have never been explored before.

    “The team will develop new electronic technology to a high level of sophistication and deploy it to search for the lowest-mass particles detected to date,” said Professor Stafford Withington from the Cavendish Laboratory, Co-Investigator and Senior Project Scientist on QSHS. “These particles are predicted to exist theoretically, but have not yet been discovered experimentally. Our ability to probe the particulate nature of the physical world with sensitivities that push at the limits imposed by quantum uncertainty will open up a new frontier in physics.

    “This new window will allow physicists to explore the nature of physical reality at the most fundamental level, and it is extremely exciting that the UK will be playing a major international role in this new generation of science.”

    Professor Withington is also involved in the Determination of Absolute Neutrino Mass using Quantum Technologies, which will be led by UCL. The project aims to harness recent breakthroughs in quantum technologies to solve one of the most important outstanding challenges in particle physics – determining the absolute mass of neutrinos. One of the universe’s most abundant particles neutrinos are a by-product of nuclear fusion within stars, therefore being key to our understanding of the processes within stars and the makeup of the universe. Moreover, knowing the value of the neutrino mass is critical to our understanding of the origin of matter and evolution of the universe. They are poorly understood however, and the researchers aim to develop pioneering new spectroscopy technology capable to precisely measure the mass of this elusive but important particle.

    Professor Zoran Hadzibabic has received funding as part of the Quantum Simulators for Fundamental Physics project, led by the University of Nottingham. The project aims to develop quantum simulators capable of providing insights into the physics of the very early universe and black holes. The goals include simulating aspects of quantum black holes and testing theories of the quantum vacuum that underpin ideas on the origin of the universe.

    See the full article here .


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    Please help promote STEM in your local schools.

    Stem Education Coalition

    Kavli Institute for Cosmology, Cambridge (UK)

    For centuries, the University of Cambridge (UK) has been pushing back the frontiers of knowledge about the Universe. Joining this rich tradition of inquiry is the Kavli Institute for Cosmology, founded in 2006 as the first member of the Kavli network in the UK.

    Cambridge’s long history as a center for astronomy and cosmology includes Isaac Newton’s discovery of the law of gravitation and, in modern times, the discovery of pulsars and crucial contributions to the development of the Big Bang model of the Universe. The Kavli Institute is helping to continue this work by creating a single site at which the University’s cosmologists and astrophysicists from different academic departments can share knowledge and work together on major projects. In particular, KICC brings together scientists from the University’s Institute of Astronomy, the Cavendish Laboratory (the Department of Physics) and the Department of Applied Mathematics and Theoretical Physics.

    The Institute started operations in 2008, thanks to an endowment from the Kavli Foundation, and now has about 50 researchers working on the following themes:

    Cosmic Microwave Background and the Early Universe
    Large Scale Structures and Precision Cosmology
    Epoch of Cosmic Reionization
    Formation and Evolution of Galaxies and Supermassive Black Holes
    Evolution of the Intergalactic Medium
    Gravitational Waves
    The institute offers these scientists the benefit of close interaction as well as advanced technologies, including access to giant telescopes and space satellites. Meanwhile, the Institute’s fellowships program host promising scholars from around the globe for stays of up to five years. They are free to pursue their own independent research as well as taking part in the world-class flagship projects led by distinguished Cambridge scientists.

    The Kavli Foundation, based in Oxnard, California, is dedicated to the goals of advancing science for the benefit of humanity and promoting increased public understanding and support for scientists and their work.

    The Foundation’s mission is implemented through an international program of research institutes, professorships, and symposia in the fields of astrophysics, nanoscience, neuroscience, and theoretical physics as well as prizes in the fields of astrophysics, nanoscience, and neuroscience.

     
  • richardmitnick 2:56 pm on January 3, 2021 Permalink | Reply
    Tags: "How a silence solved the weird maths inside black holes", “The singularity problem”, , Black Holes, By the 1950s Albert Einstein’s theory of General Relativity was wildly successful but many of its predictions were still regarded as improbable and untestable., Katie Bouman and Messier 87*, , Roger Penrose-Nobel Prize winner   

    From BBC (UK): “How a silence solved the weird maths inside black holes” 

    From BBC (UK)

    8th October 2020 [From Year End Wrap Up]
    Patchen Barss

    Theoretical physicist Roger Penrose had a moment’s inspiration that upended our view of the Universe, writes his biographer Patchen Barss.

    3
    Roger Penrose has been awarded the Nobel Prize in Physics for his work on singularities. Credit: Alamy.

    On a crisp September day in 1964, Roger Penrose had a visit from an old friend. The British cosmologist Ivor Robinson was back in England from Dallas, Texas, where he lived and worked. Whenever the two met up, they never lacked for conversation, and their talk on this occasion was non-stop and wide ranging.

    As the pair walked near Penrose’s office at Birkbeck College in London, they paused briefly on the curb, waiting for a break in the traffic. The momentary halt in their stroll coincided with a lull in conversation and they fell into silence as they crossed the road.

    In that moment, Penrose’s mind drifted. It travelled 2.5 billion light years through the vacuum of outer space to the seething mass of a whirling quasar. He imagined how gravitational collapse was taking over, pulling an entire galaxy in deeper and closer to the centre. Like a twirling figure skater pulling their arms in close to their body, the mass would spin more and more quickly as it contracted.

    This brief mental flicker led to a revelation – one that 56 years later would win him the Nobel Prize in Physics. ­

    Like many relativists — theoretical physicists working to test, explore and extend Albert Einstein’s General Theory of Relativity — Penrose had spent the early 1960s studying a strange, but particularly knotty contradiction known as “the singularity problem”.

    Einstein published his General Theory in 1915, revolutionising scientists’ understanding of space, time, gravity, matter and energy. By the 1950s, Einstein’s theory was wildly successful, but many of its predictions were still regarded as improbable and untestable. His equations showed, for instance, that it was theoretically possible for gravitational collapse to force enough matter into a sufficiently small region that it would become infinitely dense, forming a “singularity” from which not even light could escape. These became known as black holes.

    But within such a singularity, the known laws of physics — including Einstein’s own theory of relativity that predicted it — would no longer apply.

    Singularities were fascinating to mathematical relativists for this very reason. Most physicists, however, agreed our Universe was too orderly to actually contain such regions. And even if singularities did exist, there would be no way to observe them.

    “There was huge scepticism for a long time,” says Penrose. “People expected there to be a bounce: that an object would collapse and swirl around in some complicated way, and come swishing back out again.”

    In the late 1950s, observations from the emerging field of radio astronomy threw these ideas into turmoil. Radio astronomers detected new cosmic objects that appeared to be very bright, very distant and very small. First known as “quasi-stellar objects” – later shortened to “quasars” – these objects appeared to exhibit too much energy in too small a space. While it seemed impossible, every new observation pointed toward the idea that quasars were ancient galaxies in the process of collapsing into singularities.

    Scientists were forced to ask themselves whether singularities were not as unlikely as everyone thought? Was this prediction of relativity more than just a mathematical flight of fancy?

    In Austin, Princeton, and Moscow, at Cambridge and Oxford, in South Africa, New Zealand, India, and elsewhere, cosmologists, astronomers, and mathematicians scrambled to find a definitive theory that could explain the nature of quasars.

    Most scientists approached the challenge by trying to identify highly specialised circumstances under which a singularity might form.

    Penrose, then a reader at Birkbeck College in London, took a different approach. His natural instinct had always been to search for general solutions, underlying principles and essential mathematical structures. He spent long hours at Birkbeck, working at a large chalkboard covered in curves and twists of diagrams of his own design.

    In 1963, a team of Russian theorists led by Isaac Khalatnikov published an acclaimed paper that confirmed what most scientists still believed – singularities were not a part of our physical Universe. In the Universe, they said, collapsing dust clouds or stars would indeed expand back out again long before they reached the point of singularity. There had to be some other explanation for quasars.

    Penrose was sceptical.

    5
    The singularity at the heart of a black hole produces heat so intense that extremely bright radiation is blasted out in every direction. Credit: NASA.

    “I had the strong feeling that with the methods they were using, it was unlikely they could have come to a firm conclusion about it,” he says. “It seemed to me the problem needed to be looked at in a more general way than they were doing, which was a somewhat limited focus.”

    Still, while he rejected their arguments, he still could not develop a general solution for the singularity problem. That was until the visit by Robinson. Although Robinson too was researching the singularity problem, the pair didn’t discuss it during their conversation on that autumn day of 1964 in London.

    During the brief quiet of that fateful street crossing, however, Penrose realised that the Russians were wrong.

    All of that energy, movement and mass shrinking together would create a heat so intense that radiation would blast out on every wavelength in every direction. The smaller and faster it got, the brighter it would glow.

    He mentally mapped his chalkboard drawings and journal sketches onto that distant object, searching his mind for the point the Russians’ predicted, where this cloud would explode back out again.

    No such point existed. In his mind’s eye, Penrose at last saw how the collapse would continue unimpeded. Outside the densifying centre, the object would shine with more light than all the stars in our galaxy. And deep within, light would bend at dramatic angles, spacetime warping until every direction converged on every other.

    There would come a point of no return. Light, space and time would all come to a full stop. A black hole.

    At that moment, Penrose knew a singularity didn’t require any special circumstances. In our Universe, singularities weren’t impossible. They were inevitable.

    6
    Stephen Hawking and Roger Penrose worked together to create theories on singularities during the 1970s. Credit: John Cairns/University of Oxford.

    Back on the other side of the street, he picked up his conversation with Robinson, and immediately forgot what he had been thinking about. They bid farewell, and Penrose returned to the chalk clouds and stacks of paper in his office.

    The rest of the afternoon went as normal, except Penrose found himself in an inordinately good mood. He could not figure out why. He began reviewing his day, investigating what might be powering his euphoria.

    His mind returned to that moment of silence crossing the street. And it all came flooding back. He had solved the singularity problem.

    He began writing down equations, testing, editing, rearranging. The argument was still rough, but it all worked. A gravitational collapse required only some very general, easy-to-meet energy conditions, to collapse into infinite density. Penrose knew at that moment there had to be billions of singularities littering the cosmos.

    It was an idea that would upend our understanding of the Universe and shape what we now know about it today.

    Within two months, Penrose had begun giving talks on the theorem. In mid-December, he submitted a paper to the academic journal Physical Review Letters, which was published on 18 January 1965 – just four months after he crossed the street with Ivor Robinson.

    The response was not quite what he hoped. The Penrose Singularity Theorem was debated. Refuted. Contradicted.

    The debate came to a head at the International Congress on General Relativity and Gravity in London later that year.

    “It was not very friendly. The Russians were pretty annoyed, and people were reluctant to admit they were mistaken,” says Penrose. The conference ended with the debate unresolved.

    But not long after, it came out that the Russian paper had errors in its calculations – the mathematics was fatally flawed, their thesis no longer tenable.

    “There was an error in the way they were doing it,” says Penrose.

    By late 1965, the Penrose Singularity Theorem was gaining traction all over the world. His singular flash of insight became a driving force in cosmology. He had done more than explain what a quasar was – he had revealed a major truth about the underlying reality of our Universe. Whatever models of the Universe people came up with from then on had to include singularities, which meant including science that goes beyond relativity.

    Singularities also began to seep into the public consciousness, thanks partly to their becoming known evocatively as “black holes”, a term first used publicly by American science journalist Ann Ewing.

    Stephen Hawking famously built on Penrose’s theorem to upend theories about the origin of the Universe after the pair worked together on singularities [Proceeding of The Royal Society A]. Singularities became central to every theory about the nature, history and future of the Universe. Experimentalists identified other singularities – including the one at the heart of the hypermassive black hole at the centre of our own galaxy discovered by Reinhard Genzel and Andrea Ghez, who shared the Nobel Prize in Physics with Penrose this year.

    Penrose himself went on to develop an alternative to the Big Bang Theory known as Conformal Cyclic Cosmology, the evidence for which could come from the remnant signals from ancient black holes.

    In 2013, engineer and computer scientist Katie Bouman* led a team of researchers which developed an algorithm that they hoped would allow black holes to be photographed.

    Now iconic image of Katie Bouman-Harvard Smithsonian Astrophysical Observatory after the image of Messier 87 was achieved. Headed from Harvard to Caltech as an Assistant Professor. Katie is on the committee for the next iteration of the EHT .

    In April 2019, the Event Horizons telescope used an algorithm to capture the first images of a black hole, providing dramatic visual confirmation of both Einstein’s and Penrose’s once controversial theories.

    EHT map.

    Messier 87*, The first image of the event horizon of a black hole. This is the supermassive black hole at the center of the galaxy Messier 87. Image via JPL/ Event Horizon Telescope Collaboration released on 10 April 2019.

    While Penrose, now 89 years old, is pleased to have been awarded the highest honour in physics, the Nobel Prize, but there is something else pressing on his mind.

    “It feels weird. I’ve just been trying to adjust myself. It’s very flattering and a huge honour and much appreciated,” he tells me a few hours after receiving the news. “But on the other hand, I am trying to write three different (scientific) articles at the same time, and this makes it harder than it was before.” The phone, he explains, hasn’t stopped ringing with people congratulating him and journalists asking for interviews. And all that clamour is distracting him from focusing on his latest theories.

    Penrose knows better than anyone the power of silence and the flash of insight it can deliver.

    *It is not correct to say that Katie Bouman’s team’s algorithm was the one which enabled the capture of the image of the event horizon of Messier 87*. Nor is it correct to say that she “led a team of researchers”. She was in fact a very important person in this work and led one of four teams developing the hoped for successful algorithm. Alas, her team’s algorithm was not the winner of this friendly competition. It is correct to say she is “On the committee for the next iteration of the EHT”

    See the full article here .

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  • richardmitnick 2:48 pm on November 8, 2020 Permalink | Reply
    Tags: "The Most Famous Paradox in Physics Nears Its End", , , Black Holes, ,   

    From WIRED: “The Most Famous Paradox in Physics Nears Its End” 


    From WIRED

    11.08.2020
    George Musser

    In a landmark series of calculations, physicists have proved that black holes can shed information, which seems impossible by definition.

    1
    Illustration: Ashley Mackenzie for Quanta Magazine

    In a series of breakthrough papers, theoretical physicists have come tantalizingly close to resolving the black hole information paradox that has entranced and bedeviled them for nearly 50 years. Information, they now say with confidence, does escape a black hole. If you jump into one, you will not be gone for good. Particle by particle, the information needed to reconstitute your body will reemerge. Most physicists have long assumed it would; that was the upshot of string theory, their leading candidate for a unified theory of nature. But the new calculations, though inspired by string theory, stand on their own, with nary a string in sight. Information gets out through the workings of gravity itself—just ordinary gravity with a single layer of quantum effects.

    This is a peculiar role reversal for gravity. According to Einstein’s general theory of relativity, the gravity of a black hole is so intense that nothing can escape it. The more sophisticated understanding of black holes developed by Stephen Hawking and his colleagues in the 1970s did not question this principle. Hawking and others sought to describe matter in and around black holes using quantum theory, but they continued to describe gravity using Einstein’s classical theory—a hybrid approach that physicists call “semiclassical.” Although the approach predicted new effects at the perimeter of the hole, the interior remained strictly sealed off. Physicists figured that Hawking had nailed the semiclassical calculation. Any further progress would have to treat gravity, too, as quantum.

    That is what the authors of the new studies dispute. They have found additional semiclassical effects—new gravitational configurations that Einstein’s theory permits, but that Hawking did not include. Muted at first, these effects come to dominate when the black hole gets to be extremely old. The hole transforms from a hermit kingdom to a vigorously open system. Not only does information spill out, anything new that falls in is regurgitated almost immediately. The revised semiclassical theory has yet to explain how exactly the information gets out, but such has been the pace of discovery in the past two years that theorists already have hints of the escape mechanism.

    “That is the most exciting thing that has happened in this subject, I think, since Hawking,” said one of the coauthors, Donald Marolf of UC Santa Barbara.

    “It’s a landmark calculation,” said Eva Silverstein of Stanford University, a leading theoretical physicist who was not directly involved.

    You might expect the authors to celebrate, but they say they also feel let down. Had the calculation involved deep features of quantum gravity rather than a light dusting, it might have been even harder to pull off, but once that was accomplished, it would have illuminated those depths. So they worry they may have solved this one problem without achieving the broader closure they sought. “The hope was, if we could answer this question—if we could see the information coming out—in order to do that we would have had to learn about the microscopic theory,” said Geoff Penington of UC Berkeley, alluding to a fully quantum theory of gravity.

    What it all means is being intensely debated in Zoom calls and webinars. The work is highly mathematical and has a Rube Goldberg quality to it, stringing together one calculational trick after another in a way that is hard to interpret. Wormholes, the holographic principle, emergent space-time, quantum entanglement, quantum computers: Nearly every concept in fundamental physics these days makes an appearance, making the subject both captivating and confounding.

    And not everyone is convinced. Some still think that Hawking got it right and that string theory or other novel physics has to come into play if information is to escape. “I’m very resistant to people who come in and say, ‘I’ve got a solution in just quantum mechanics and gravity,’” said Nick Warner of the University of Southern California. “Because it’s taken us around in circles before.”

    But almost everyone appears to agree on one thing. In some way or other, space-time itself seems to fall apart at a black hole, implying that space-time is not the root level of reality but an emergent structure from something deeper. Although Einstein conceived of gravity as the geometry of space-time, his theory also entails the dissolution of space-time, which is ultimately why information can escape its gravitational prison.

    The Curve Becomes the Key

    In 1992, Don Page and his family spent their Christmas vacation house-sitting in Pasadena, enjoying the swimming pool and watching the Rose Parade. Page, a physicist at the University of Alberta in Canada, also used the break to think about how paradoxical black holes really are. His first studies of black holes, when he was a graduate student in the 1970s, were key [Hawking Radiation and Black Hole Thermodynamics] to his adviser Stephen Hawking’s realization that black holes emit radiation—the result of random quantum processes at the edge of the hole. Put simply, a black hole rots from the outside in.

    7
    Don Page at the University of Alberta in 2017.Credit: John Ulan/University of Alberta.

    The particles it sheds appear to carry no information about the interior contents. If a 100-kilogram astronaut falls in, the hole grows in mass by 100 kilograms. Yet when the hole emits the equivalent of 100 kilograms in radiation, that radiation is completely unstructured. Nothing about the radiation reveals whether it came from an astronaut or a lump of lead.

    That’s a problem, because at some point the black hole emits its last ounce and ceases to be. All that’s left is a big amorphous cloud of particles zipping here and there at random. It would be impossible to recover whatever fell in. That makes black hole formation and evaporation an irreversible process, which appears to defy the laws of quantum mechanics.

    Hawking and most other theorists at the time accepted that conclusion—if irreversibility flouted the laws of physics as they were then understood, so much the worse for those laws. But Page was perturbed, because irreversibility would violate the fundamental symmetry of time. In 1980 he broke with his former adviser and argued that black holes must release or at least preserve information. That caused a schism among physicists. “Most general relativists I talked to agreed with Hawking,” said Page. “But particle physicists tended to agree with me.”

    On his Pasadena vacation, Page realized that both groups had missed an important point. The puzzle wasn’t just what happens at the end of the black hole’s life, but also what leads up to it.

    He considered an aspect of the process that had been relatively neglected: quantum entanglement. The emitted radiation maintains a quantum mechanical link to its place of origin. If you measure either the radiation or the black hole on its own, it looks random, but if you consider them jointly, they exhibit a pattern. It’s like encrypting your data with a password. The data without the password is gibberish. The password, if you have chosen a good one, is meaningless too. But together they unlock the information. Maybe, thought Page, information can come out of the black hole in a similarly encrypted form.

    Page calculated what that would mean for the total amount of entanglement between the black hole and the radiation, a quantity known as the entanglement entropy. At the start of the whole process, the entanglement entropy is zero, since the black hole has not yet emitted any radiation to be entangled with. At the end of the process, if information is preserved, the entanglement entropy should be zero again, since there is no longer a black hole. “I got curious how the radiation entropy would change in between,” Page said.

    Initially, as radiation trickles out, the entanglement entropy grows. Page reasoned that this trend has to reverse. The entropy has to stop rising and start dropping if it is to hit zero by the endpoint. Over time, the entanglement entropy should follow a curve shaped like an inverted V.

    2
    Credit: Samuel Velasco/Quanta Magazine.

    Page calculated that this reversal would have to occur roughly halfway through the process, at a moment now known as the Page time. This is much earlier than physicists assumed. The black hole is still enormous at that point—certainly nowhere near the subatomic size at which any putative exotic effects would show up. The known laws of physics should still apply. And there is nothing in those laws to bend the curve down.

    With that, the problem got much more acute. Physicists had always figured that a quantum theory of gravity came into play only in situations so extreme that they sound silly, such as a star collapsing to the radius of a proton. Now Page was telling them that quantum gravity mattered under conditions that, in some cases, are comparable to those in your kitchen.

    Page’s analysis [Physical Review Letters] justified calling the black hole information problem a paradox as opposed to merely a puzzle. It exposed a conflict within the semiclassical approximation. “The Page-time paradox seems to point to a breakdown of low-energy physics in a place where it has no business breaking down, because the energies are still low,” said David Wallace, a philosopher of physics at the University of Pittsburgh.

    On the bright side, Page’s clarification of the problem paved the way to a solution. He established that if entanglement entropy follows the Page curve, then information gets out of the black hole. In doing so, he transformed a debate into a calculation. “Physicists are not always so good at words,” said Andrew Strominger of Harvard University. “We do best with sharp equations.”

    Now physicists just had to calculate the entanglement entropy. If they could pull it off, they’d get a straight answer. Does the entanglement entropy follow an inverted V or not? If it does, the black hole preserves information, which means particle physicists were right. If it doesn’t, the black hole destroys or bottles up information, and general relativists can help themselves to the first doughnut at faculty meetings.

    Yet even though Page spelled out what physicists had to do, it took theorists nearly three decades to figure out how.

    The Inside-Out Black Hole

    Over the past two years, physicists have shown that the entanglement entropy of black holes really does follow the Page curve, indicating that information gets out. They did the analysis in stages. First, they showed how it would work using insights from string theory. Then, in papers published last fall, researchers cut the tether to string theory altogether.

    The work began in earnest in October 2018, when Ahmed Almheiri of the Institute for Advanced Study laid out a procedure for studying how black holes evaporate [Holographic Quantum Error Correction and the Projected Black Hole Interior]. Almheiri, joined soon by several colleagues, applied a concept first developed by Juan Maldacena, now at IAS, in 1997 [The entropy of bulk quantum fields and the entanglement wedge of an evaporating black hole]. (Penington was working in parallel [Entanglement Wedge Reconstruction and the Information Paradox].)

    8
    Ahmed Almheiri gives a lecture on black holes and quantum information at the Institute for Advanced Study in 2018. Credit: Andrea Kane/Institute for Advanced Study.

    Consider a universe encased in a boundary like a snow globe. Apart from having a big wall around it, the interior is basically like our universe: It has gravity, matter, and so forth. The boundary, too, is a kind of universe. It does not have gravity and, being just a surface, lacks depth. But it makes up for that with vibrant quantum physics, and all in all it’s exactly as complex as the interior. Different though these two universes may look, they are perfectly matched. Everything in the interior, or “bulk,” has a counterpart on the boundary. And even though the geometry of the bulk is unlike the geometry of our own universe, this “AdS/CFT” duality has been string theorists’ favorite playground ever since Maldacena introduced it.

    By the logic of this duality, if you have a black hole in the bulk, it has a simulacrum on the boundary. Because the boundary is governed by quantum physics without the complications of gravity, it unequivocally preserves information. So must the black hole.

    When researchers set out to analyze how black holes evaporate in AdS/CFT, they first had to overcome a slight problem: In AdS/CFT, black holes do not, in fact, evaporate. Radiation fills the confined volume like steam in a pressure cooker, and whatever the hole emits it eventually reabsorbs. “The system will reach a steady state,” said Jorge Varelas da Rocha, a theoretical physicist at the University Institute of Lisbon.


    Albert Einstein, Holograms and Quantum Gravity

    To deal with that, Almheiri and his colleagues adopted a suggestion of Rocha’s [Evaporation of large black holes in AdS: coupling to the evaporon] to put the equivalent of a steam valve on the boundary to bleed off the radiation and prevent it from falling back in. “It sucks the radiation out,” said Netta Engelhardt of the Massachusetts Institute of Technology, one of Almheiri’s coauthors. The researchers plopped a black hole at the center of the bulk space, began bleeding off radiation, and watched what happened.

    To track the entanglement entropy of the black hole, they drew on the more granular understanding of AdS/CFT that Engelhardt and others, including Aron Wall at the University of Cambridge, have developed in the past decade [Quantum Extremal Surfaces: Holographic Entanglement Entropy beyond the Classical Regime]. Physicists are now able to pinpoint which part of the bulk corresponds to which part of the boundary, and which properties of the bulk correspond to which properties of the boundary.

    The key to relating the two sides of the duality is what physicists call a quantum extremal surface. (These surfaces are general features—you don’t need a black hole to have one.) Basically you imagine blowing a soap bubble in the bulk. The bubble naturally assumes a shape that minimizes its surface area. The shape need not be round, like the bubbles at a child’s birthday party, because the rules of geometry can differ from the ones we are familiar with; thus the bubble is a probe of that geometry. Quantum effects can distend it, too.

    By calculating where the quantum extremal surface lies, researchers obtain two important pieces of information. First, the surface carves the bulk into two pieces and matches each to a portion of the boundary. Second, the area of the surface is proportional to part of the entanglement entropy between those two portions of the boundary. Thus the quantum extremal surface relates a geometric concept (area) to a quantum one (entanglement), providing a glimpse into how gravity and quantum theory might become one.

    9
    Netta Engelhardt, a professor at the Massachusetts Institute of Technology, has developed ways to measure the entropy inside black hole interiors.Credit: Darren Pellegrino.

    But when researchers used these quantum extremal surfaces to study an evaporating black hole, a strange thing happened. Early in the evaporation process, they found, as expected, that the entanglement entropy of the boundary rose. Because the hole was the only thing inside space, the authors deduced that its entanglement entropy was rising. In terms of Hawking’s original calculations, so far so good.

    Suddenly that changed. A quantum extremal surface abruptly materialized just inside the horizon of the black hole. Initially this surface had no effect on the rest of the system. But eventually it became the deciding factor for entropy, leading to a drop. The researchers compare it to a transition like boiling or freezing. “We think of this as a change in phase analogous to thermodynamic phases—between gas and liquid,” Engelhardt said.

    It meant three things. First, the sudden shift signaled the onset of new physics not covered by Hawking’s calculation. Second, the extremal surface split the universe in two. One part was equivalent to the boundary. The other was a here-be-dragons realm about which the boundary had no information, indicating that bleeding radiation from the system was having an effect on its information content.

    Third, the position of the quantum extremal surface was highly significant. It was located just inside the horizon of the black hole. As the hole shrank, so did the quantum extremal surface and, with it, the entanglement entropy. That would produce the downward slope that Page predicted—the first time any calculation had done that.

    4
    Credit: Samuel Velasco/Quanta Magazine.

    By showing that the entanglement entropy tracked the Page curve, the team was able to confirm that black holes release information. It dribbles out in a highly encrypted form made possible by quantum entanglement. In fact, it is so encrypted that it doesn’t look as if the black hole has given up anything. But eventually the black hole passes a tipping point where the information can be decrypted. The research, posted in May 2019, showed all this using new theoretical tools that quantify entanglement in a geometric way.

    Even with these tools, the calculation had to be stripped to its essence to be doable. The bulk in this AdS/CFT universe had just a single dimension of space, for example. The black hole was not a big black ball but a short line segment. Still, the researchers argued, gravity is gravity, and what goes for this impoverished Lineland should hold for the real universe. (In April 2020, Koji Hashimoto, Norihiro Iizuka and Yoshinori Matsuo of Osaka University analyzed black holes in a more realistic flat geometry and confirmed that the findings still hold [Islands in Schwarzschild black holes].)

    In August 2019 Almheiri and another set of colleagues took the next step [The Page curve of Hawking radiation from semiclassical geometry]and turned their attention to the radiation. They found that the black hole and its emitted radiation both follow the same Page curve, so that information must be transferred from one to the other. The calculation does not say how it is transferred, only that it is.

    As part of the work, they discovered that the universe undergoes a baffling rearrangement. At the outset, the black hole is at the center of space and the radiation is flying out. But after enough time has passed, the equations say, particles deep inside the black hole are no longer part of the hole anymore, but part of the radiation. They have not flown outward, they’ve simply been reassigned.

    This is significant because these interior particles would ordinarily contribute to the entanglement entropy between the black hole and the radiation. If they are not part of the black hole anymore, they no longer contribute to the entropy, explaining why it begins to decrease.

    The authors dubbed the inner core of radiation the “island” and called its existence “surprising.” What does it mean for particles to be in the black hole, but not of the black hole? In confirming that information is retained, the physicists eliminated one puzzle only to create an even bigger one. Whenever I asked Almheiri and others what it meant, they looked off into the distance, momentarily lost for words.

    Enter the Wormholes

    So far the calculations presumed the AdS/CFT duality—the snow globe world—which is an important test case but ultimately somewhat contrived. The next step was to consider black holes more generally.

    The researchers drew on a concept that Richard Feynman had developed in the 1940s [Reviews of Modern Physics]. Known as the path integral, it is the mathematical expression of a core quantum mechanical principle: Anything that can happen does happen. In quantum physics, a particle going from point A to point B takes all possible paths, which are combined in a weighted sum. The highest-weighted path is generally the one you’d expect from ordinary classical physics, but not always. If the weights change, the particle can abruptly lurch from one path to another, undergoing a transition that would be impossible in old-fashioned physics.

    The path integral works so well for particle motion that theorists in the ’50s proposed it as a quantum theory of gravity. That meant replacing a single space-time geometry with a mélange of possible shapes. To us, space-time appears to have a single well-defined shape—near Earth, it is curved just enough that objects tend to orbit the center of our planet, for example. But in quantum gravity, other shapes, including much curvier ones, are latent, and they can make an appearance under the right circumstances. Feynman himself took up this idea in the ’60s, and Hawking championed it [Physical Review D] in the ’70s and ’80s. But even their considerable genius struggled with how to execute the gravitational path integral, and physicists set it aside in favor of other approaches to quantum gravity. “We never really knew how to define exactly what it is—and guess what, we still don’t,” said John Preskill of the California Institute of Technology.


    What Happens if You Fall Into a Black Hole?
    David Kaplan explores one of the biggest mysteries in physics: the apparent contradiction between general relativity and quantum mechanics. Video: Petr Stepanek; MK12; Steven Gutheinz.

    For starters, what are “all” possible shapes? For Hawking, that meant all topologies. Space-time might knot itself into doughnut- or pretzel-like shapes. The extra connectivity creates tunnels, or “wormholes,” between otherwise far-flung places and moments. These come in different types.

    Spatial wormholes are like the portals beloved of science-fiction writers, linking one star system to another. So-called space-time wormholes are little universes that bud off our own and reunite with it sometime later. Astronomers have never seen either type, but general relativity permits these structures, and the theory has a good track record of making seemingly bizarre predictions, such as black holes and gravitational waves, that are later vindicated. Not everyone agreed with Hawking that these exotic shapes belong in the mix, but the researchers doing the new analyses of black holes adopted the idea provisionally.

    They couldn’t realistically consider all possible topologies, which are literally uncountable, so they looked only at those that were most important to an evaporating black hole. These are known, for mathematical reasons, as saddle points, and they look like fairly placid geometries. In the end, the teams didn’t actually perform the full summation of shapes, which was beyond them. They used the path integral mostly as a vehicle to identify the saddle points.

    The next step, after applying the path integral to the black hole and its radiation, was to calculate the entanglement entropy. This quantity is defined as the logarithm of a matrix—an array of numbers. The calculation is difficult in the best of times, but in this case the physicists didn’t actually have the matrix, which would have required evaluating the path integral. So they had to perform an operation they couldn’t do on a quantity they didn’t know. For that, they busted out another mathematical trick.

    They noticed that entropy doesn’t require knowledge of the full matrix. They could instead imagine performing a repeated series of measurements on the black hole and then combining those measurements in a way that retained the knowledge they needed. This so-called replica trick goes back to the study of magnets in the ’70s and was first applied to gravity in 2013 [Generalized gravitational entropy].

    One of the authors of the new work, Tom Hartman of Cornell University, compared the replica trick to checking whether a coin is fair.

    5
    Tom Hartman (right) discusses replica wormholes with his co-author Amirhossein Tajdini, who is now at U.C. Santa Barbara. Credit:Dave Burbank.

    Normally you’d toss it many times and see whether it lands on each side with 50–50 probability. But suppose for some reason you can’t do that. So instead you toss two identical coins—the “replicas”—and note how often they land on the same side. If this happens half the time, the coins are fair. Even though you still don’t know the individual probabilities, you can make a basic judgment about randomness. This is analogous to not knowing the full matrix for the black hole, yet still evaluating its entropy.

    Trick though it is, it has real physics in it. The gravitational path integral doesn’t distinguish replicas from a real black hole. It takes them literally. This activates some of the latent topologies that the gravitational path integral includes. The result is a new saddle point containing multiple black holes linked by space-time wormholes. It competes for influence with the regular geometry of a single black hole surrounded by a mist of Hawking radiation.

    The wormholes and the single black hole are inversely weighted by, basically, how much entanglement entropy they have. Wormholes have a lot, so they receive a low weighting and are thus unimportant at first. But their entropy decreases, whereas that of the Hawking radiation keeps climbing. Eventually the wormholes become the dominant of the two, and they take over the dynamics of the black hole. The shift from one geometry to the other is impossible in classical general relativity—it is an inherently quantum process. The extra geometric configuration and the transition process that accesses it are the two main discoveries of the analysis.

    In November 2019, two teams of physicists—known as the West Coast [Replica wormholes and the black hole interior] and East Coast [Replica Wormholes and the Entropy of Hawking Radiation] groups for their geographical affiliations—posted their work showing that this trick allows them to reproduce the Page curve. In this way, they confirmed that the radiation spirits away the informational content of whatever falls into the black hole. String theory needn’t be true; even a staunch critic of string theory can get on board with the gravitational path integral. Still, as sophisticated as the analysis is, it doesn’t yet say how the information makes its getaway.

    The Construction of Space-Time

    By these calculations, the radiation is rich in information. Somehow, by measuring it, you should be able to learn what fell into the black hole. But how?

    Theorists in the West Coast group imagined sending the radiation into a quantum computer. After all, a computer simulation is itself a physical system; a quantum simulation, in particular, is not altogether different from what it is simulating. So the physicists imagined collecting all the radiation, feeding it into a massive quantum computer, and running a full simulation of the black hole.

    And that led to a remarkable twist in the story. Because the radiation is highly entangled with the black hole it came from, the quantum computer, too, becomes highly entangled with the hole. Within the simulation, the entanglement translates into a geometric link between the simulated black hole and the original. Put simply, the two are connected by a wormhole. “There’s the physical black hole and then there’s the simulated one in the quantum computer, and there can be a replica wormhole connecting those,” said Douglas Stanford, a theoretical physicist at Stanford and a member of the West Coast team. This idea is an example of a proposal by Maldacena and Leonard Susskind of Stanford in 2013 that quantum entanglement can be thought of as a wormhole [Cool horizons for entangled black holes]. The wormhole, in turn, provides a secret tunnel through which information can escape the interior.

    6
    Juan Maldacena has spent over two decades at the center of efforts to understand information in and around black holes.Credit: Sasha Maslov/Quanta Magazine.

    Theorists have been intensely debating how literally to take all these wormholes. The wormholes are so deeply buried in the equations that their connection to reality seems tenuous, yet they do have tangible consequences. “It’s hard to answer what’s physical and what’s unphysical,” said Raghu Mahajan, a physicist at Stanford, “because there’s something clearly right about these wormholes.”

    But rather than think of the wormholes as actual portals sitting out there in the universe, Mahajan and others speculate that they are a sign of new, nonlocal physics. By connecting two distant locations, wormholes allow occurrences at one place to affect a distant place directly, without a particle, force or other influence having to cross the intervening distance—making this an instance of what physicists call nonlocality. “They seem to suggest that you have nonlocal effects that come in,” Almheiri said. In the black hole calculations, the island and radiation are one system seen in two places, which amounts to a failure of the concept of “place.” “We’ve always known that some kind of nonlocal effects have to be involved in gravity, and this is one of them,” Mahajan said. “Things you thought were independent are not really independent.”

    At first glance, this is very surprising. Einstein constructed general relativity with the express purpose of eliminating nonlocality from physics. Gravity does not reach out across space instantly. It has to propagate from one place to another at finite speed, like any other interaction in nature. But over the decades it has dawned on physicists that the symmetries on which relativity is based create a new breed of nonlocal effects.

    This past February, Marolf and Henry Maxfield, also at Santa Barbara, studied the nonlocality [Transcending the ensemble: baby universes, spacetime wormholes, and the order and disorder of black hole information] implied by the new black hole calculations. They found that the symmetries of relativity have even more extensive effects than commonly supposed, which may give space-time the hall-of-mirrors quality seen in the black hole analyses.

    All this reinforces many physicists’ hunch that space-time is not the root level of nature, but instead emerges from some underlying mechanism that is not spatial or temporal. To many, that was the main lesson of the AdS/CFT duality. The new calculations say much the same thing, but without committing to the duality or to string theory. Wormholes crop up because they are the only language the path integral can use to convey that space is breaking down. They are geometry’s way of saying the universe is ultimately nongeometric.

    The End of the Beginning

    Physicists not involved in the work, or even in string theory, say they are impressed, if duly skeptical. “Hats off to them, since those calculations are highly nontrivial,” said Daniele Oriti of the Ludwig Maximilian University of Munich.

    But some feel uneasy about the tottering pile of idealizations used in the analysis, such as the restriction of the universe to less than three spatial dimensions. The previous wave of excitement over the path integral in the ’80s, driven by Hawking’s work, fizzled out in part because theorists were unnerved by the accumulation of approximations. Are today’s physicists falling into the same trap? “I see people make the same hand-waving arguments that were made 30 years ago,” said Renate Loll of Radboud University in the Netherlands, an expert on the gravitational path integral. She has argued that wormholes need to be expressly forbidden if the integral is to give sensible results.

    Skeptics also worry that the authors have overinterpreted the replica trick. In supposing that replicas can be connected gravitationally, the authors go beyond past invocations of the maneuver. “They are postulating that all geometries connecting different replicas are allowed, but it’s not clear how that fits into the framework of quantum rules,” said Steve Giddings of Santa Barbara.

    Given the uncertainties of the calculation, some are unconvinced that a solution is available within semiclassical theory. “There’s no good choice if you restrict to quantum mechanics and gravity,” Warner said. He has championed models in which stringy effects prevent black holes from forming in the first place. But the upshot is broadly similar: Space-time undergoes a phase transition to a very different structure.

    Skepticism is warranted if for no other reason than because the recent work is complicated and raw. It will take time for physicists to digest it and either find a fatal flaw in the arguments or become convinced that they work. After all, even the physicists behind the efforts didn’t expect to resolve the information paradox without a full quantum theory of gravity. Indeed, they thought the paradox was their fulcrum for prying out that more detailed theory. “If you had asked me two years ago, I would have said: ‘The Page curve—that’s a long way away,’” Engelhardt said. “We’re going to need some kind of [deeper] understanding of quantum gravity.’”

    But assuming that the new calculations stand up to scrutiny, do they in fact close the door on the black hole information paradox? The recent work shows exactly how to calculate the Page curve, which in turn reveals that information gets out of the black hole. So it would seem as though the information paradox has been overcome. The theory of black holes no longer contains a logical contradiction that makes it paradoxical.

    But in terms of making sense of black holes, this is at most the end of the beginning. Theorists still haven’t mapped the step-by-step process whereby information gets out. “We now can compute the Page curve, and I don’t know why,” said Raphael Bousso at Berkeley. To astronauts who ask whether they can get out of a black hole, physicists can answer, “Sure!” But if the astronauts ask how to do it, the disquieting reply will be: “No clue.”

    See the full article here .

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  • richardmitnick 11:24 am on October 29, 2020 Permalink | Reply
    Tags: "Designing new mirror materials for better gravitational-wave detection", , , , Black Holes, , , , ,   

    From MIT News: “Designing new mirror materials for better gravitational-wave detection” 

    MIT News

    From MIT News

    October 28, 2020
    Kelso Harper | MIT Kavli Institute

    MIT Kavli Institute for Astrophysics and Space Research.

    Nicholas Demos, a first-generation college graduate and MathWorks Fellow in MIT’s Kavli Institute, is improving our ability to listen to the cosmos.

    1
    Nicholas Demos (left) shows a mirror-testing apparatus to Satoshi Tanioka, a visiting student from Sokendai University (JP).
    Credits: Photo courtesy of the researchers.

    Nicholas Demos, a physics graduate student, didn’t travel a conventional path to MIT. A first-generation college student, Demos didn’t have a clear trajectory in mind when he first attended California State University at Fullerton after high school. “It was kind of the path of least resistance,” Demos says.

    When his father passed away in the middle of his undergraduate studies, Demos left school to run the family business, Novatech Lighting Systems, which makes handheld spotlights. He ran the company for five years, but business didn’t suit him, he says: “The pursuit of money wasn’t motivating at all to me.”

    As soon as his brother graduated and could take over the business, Demos was ready to go back to school — this time with a clearer purpose. He chose to study physics, since he’d always excelled in math and science. Demos was the only student in his high school class to pass the AP calculus exam and even had what he calls a “side hustle” of building and selling computers out of his garage.

    His renewed determination for academics paid off. After his first year back at CSU Fullerton, Demos’ physics professor, Geoffrey Lovelace, asked him to join his lab. The following summer, Demos began researching gravitational waves, just as a more sensitive version of the Laser-Interferometer Gravitational Wave Observatory (LIGO) became operational.

    “The detector was reaching a sensitivity where everyone thought it should work,” says Demos, “Being on the cusp of a big discovery was exciting.”

    On Sept. 14, 2015, a little more than a year after Demos began his research, LIGO detected a gravitational wave for the very first time. It thrilled everyone in the small but growing field, including Demos. The ability to observe gravitational waves provides “a totally different way to look at the universe,” says Demos. “It’s a big step forward for astrophysics; there’s potential for things we haven’t even thought of appearing. A lot of unknown unknowns.”

    When Demos completed his undergraduate degree in 2017, he applied to MIT, hoping to continue working on LIGO. Matthew Evans, the MIT MathWorks Professor of Physics and Demos’ current advisor, says he was immediately impressed with Demos’ work. And according to Evans, Demos’ old advisor told him, “Nick was the best undergraduate he’d ever had.”

    Demos measures mirrors

    Whereas telescopes look for cosmic phenomena, LIGO listens.

    MIT /Caltech Advanced aLigo .

    Caltech/MIT Advanced aLigo detector installation Livingston, LA, USA.

    Caltech/MIT Advanced aLigo detector installation Hanford, WA, USA.

    VIRGO Gravitational Wave interferometer, near Pisa, Italy.

    VIRGO Gravitational Wave interferometer, near Pisa, Italy.

    “LIGO is listening for the densest objects in the universe — neutron stars and black holes,” Demos says.

    Localizations of gravitational-wave signals detected by LIGO in 2015 (GW150914, LVT151012, GW151226, GW170104), more recently, by the LIGO-Virgo network (GW170814, GW170817). After Virgo (IT) came online in August 2018.

    When these massive bodies near each other, they fall into a collapsing orbit, spinning faster and faster, closer and closer, until they collide.

    “What LIGO detects is this chirp — this faster and faster, louder and louder signal — that is like the sound of spacetime vibrating,” Demos says.

    These vibrations, or gravitational waves, travel vast distances through the universe, warping everything — stars, planets, people — in their path. What LIGO does is measure this stretching and squeezing of spacetime. “It’s basically a big, four-kilometer ruler,” Demos says.

    To measure gravitational waves, a LIGO detector has dual four-kilometer vacuum chambers laid in an enormous “L” shape [above]. Scientists split a beam of light and send it to the end of each chamber, where it bounces off of highly reflective mirrors and returns to the corner of the “L.”

    When a gravitational wave ripples through the Earth, it will stretch one arm of LIGO while squashing the other. The light, which has a fixed speed and won’t warp with the rest of the world, then takes a different length of time to travel down each arm. The scientists can measure this difference to detect the wave.

    The challenge is that the ripples caused by gravitational waves are minuscule since, despite appearances, gravity is a very weak force. In terms of the squashing and stretching, “we’re talking about these tiny, fractional changes,” says Demos, “roughly one-thousandth the size of a proton.”

    This means that everything in the LIGO experiment must be extremely precise and very still. Otherwise, the gravitational wave signals will be lost in a sea of noise. Unfortunately, some sources of noise are harder to eliminate than others.

    “The surface of the mirror is made up of atoms, and these atoms are jiggling about,” Demos says. “If you’re trying to measure something that’s smaller than a proton, that’s a problem, because your ruler is jiggling about on both ends.”

    The noise from the movement of atoms, also called thermal noise, is nearly unavoidable — the motion only stops at the unreachable temperature of absolute zero. However, some materials have less of this thermal noise than others.

    Demos’ job is to design and test new mirror materials to find those with the lowest thermal noise. In fact, he is one of the few people in the world able to test these samples. Matthew Evans and Research Scientist Slawomir Gras have developed the only apparatus able to quickly test full mirror samples, as opposed to just a single layer or a few layers of the materials used to coat the mirrors.

    “Any coating that LIGO wants to use will first be characterized by our experiment,” Demos says.

    The Evans lab is in the process of upgrading their setup to measure thermal noise across the surface of a sample, as opposed to only at a single point.

    “This is a job which is really at the heart of progress in gravitational wave detection,” Evans adds. “Nick’s persistent determination to get things done has really made a big difference for us.”

    Demos makes math work with MATLAB

    In September, Demos was one of a select group of students in the School of Science to receive a $70,000 fellowship from MathWorks, a software company that produces mathematical computing programs like MATLAB and Simulink.

    “The MathWorks Fellowship is a big honor,” says Demos, “It’s a huge relief financially because I don’t have to worry, my lab doesn’t have to worry, and I’ll be able to really pursue this.”

    It’s particularly appropriate for Demos to win this fellowship, as he frequently uses MATLAB in his research. “He’s gone through all of our analysis software in MATLAB and really refactored that code from the ground up,” says Evans. He adds that Demos is very deserving of this award, but he’s not worried about the recognition going to Demos’ head.

    “There’s a certain humility in his approach to things, which is not something you always find.”
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  • richardmitnick 9:35 am on October 6, 2020 Permalink | Reply
    Tags: A trio of scientists were awarded the Nobel Physics Prize on Tuesday for their research into black holes., Andrea Ghez- UCLA Galactic Center Group., , , , Black Holes, , , , Reinhard Genzel- Max Planck Institute for Extraterrestrial Physics and University of California Berkeley., Roger Penrose- Emeritus Rouse Ball Professor of Mathematics at the University of Oxford.,   

    From phys.org: “Black holes: devourers of stars reveal their secrets” 


    From phys.org

    October 6, 2020

    1
    Messier 87 imaged by the Event Horizon Telescope.

    EHT map.

    A trio of scientists were awarded the Nobel Physics Prize on Tuesday for their research into black holes, some of the most mysterious objects in the universe that gobble stars like specks of dust.

    1
    Roger Penrose, Emeritus Rouse Ball Professor of Mathematics at the University of Oxford.
    Andrea Ghez, UCLA Galactic Center Group.
    Reinhard Genzel, Max Planck Institute for Extraterrestrial Physics, University of California, Berkeley.

    So powerful they bend the laws of nature, not even Albert Einstein, the father of general relativity, was convinced they could exist.

    Two varieties

    A black hole is a celestial object that compresses a huge mass into an extremely small space. Their gravitational pull is so strong nothing can escape their maw, not even light.

    This has made these exotic entities difficult to spot. But scientists now know a lot about black holes from the impact they have on their surroundings.

    There are two kinds.

    The first are garden-variety black holes that form when the centre of a very big star collapses in on itself, creating a supernova.

    These can be up to 20 times more massive than the Sun, but are tiny in space.

    Trying to see the one closest to Earth would be like looking for a human cell on the surface of the moon.

    In contrast, so-called supermassive black holes—such as the one sitting at the centre of the Milky Way for which two of Tuesday’s laureates were awarded prizes—are at least a million times bigger than the Sun.

    Last month, teams of scientists from the US and Europe detected for the first time a so-called “intermediate mass” black hole with 142 times the mass of the Sun. It was formed, they determined, from the merger of two smaller black holes.

    Time stoppers

    When he released it in November 1915, Einstein’s general theory of relativity upended all previously held concepts of space and time.

    It described how everything, from the tiniest atom to the largest supernova, is held in the grip of gravity.

    Since gravity is proportionate to mass, an extremely heavy entity has such a strong gravitational pull that it can bend space and slow time.

    According to Einstein’s theory, an extremely heavy mass, such as a black hole, could stop time altogether.

    Yet Einstein himself was not convinced that black holes existed.

    It took British physicist Roger Penrose, Emeritus Rouse Ball Professor of Mathematics at the University of Oxford—honoured with the Nobel on Tuesday—to show that general relativity could result in these enormous, all-devouring objects.

    Supermassive black hole

    Perhaps the most famous black hole of all sits at the centre of our galaxy. At more than four million times the mass of our Sun, Sagittarius A* is a monster object responsible for the characteristic swirl of the stars in the Milky Way.

    SGR A* , the supermassive black hole at the center of the Milky Way. NASA’s Chandra X-Ray Observatory.

    SGR A and SGR A* from Penn State and NASA/Chandra.

    But, since black holes devour light and are therefore invisible, for decades it was impossible to spot.

    In the early 1990s, physicists Reinhard Genzel and Andrea Ghez each led a team of researchers using the latest technology to gaze at the heart of our galaxy.

    But even with the world’s largest telescopes the teams were limited in what they could see by distortion caused by Earth’s atmosphere.

    Keck Observatory, operated by Caltech and the University of California, Maunakea, Hawaii, USA.4,207 m (13,802 ft), above sea level.

    The same effect that makes stars twinkle in the night sky was ruining the clarity of images taken of the Milky Way.

    Genzel and Ghez helped develop new technology, including more sensitive digital light sensors and better smart optics, improving image resolution more than one thousandfold.

    They used their new methods to track 30 of the brightest stars near the centre of the Milky Way.

    One star, S2, was found to complete its orbit of the galaxy in less than 16 years. Our own Sun, by contrast, takes more than 200 million years to complete its lap.

    Star S0-2 Andrea Ghez Keck/UCLA Galactic Center Group at SGR A*, the supermassive black hole at the center of the Milky Way.

    The speed at which the stars were moving allowed both teams to conclude that it was a supermassive black hole driving the galactic swirl.

    See the full article here .

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