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  • richardmitnick 3:11 pm on November 14, 2017 Permalink | Reply
    Tags: , , Caltech/MIT aLIGO, ,   

    From Symmetry: “Q&A with Nobel laureate Barry Barish” 

    Symmetry Mag
    Symmetry

    11/14/17
    Leah Hesla

    1
    Illustration by Ana Kova

    These days the LIGO experiment seems almost unstoppable.


    VIRGO Gravitational Wave interferometer, near Pisa, Italy

    Caltech/MIT Advanced aLigo Hanford, WA, USA installation


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

    Cornell SXS, the Simulating eXtreme Spacetimes (SXS) project

    Gravitational waves. Credit: MPI for Gravitational Physics/W.Benger-Zib

    ESA/eLISA the future of gravitational wave research

    1
    Skymap showing how adding Virgo to LIGO helps in reducing the size of the source-likely region in the sky. (Credit: Giuseppe Greco (Virgo Urbino group)

    In September 2015, LIGO detected gravitational waves directly for the first time in history. Afterward, they spotted them three times more, definitively blowing open the doors on the new field of gravitational-wave astronomy.

    On October 3, the Nobel Committee awarded their 2017 prize in physics to some of the main engines behind the experiment. Just two weeks after that, LIGO scientists revealed that they’d seen, for the first time, gravitational waves from the collision of neutron stars, an event confirmed by optical telescopes—yet another first.

    These recent achievements weren’t inevitable. It took LIGO scientists decades to get to this point.

    LIGO leader Barry Barish, one of the three recipients of the 2017 Nobel, recently sat down with Symmetry writer Leah Hesla to give a behind-the-scenes look at his 22 years on the experiment.

    2
    Barry Barish, who obtained his B.S. and Ph.D from UC Berkeley in 1957 and 1962, respectively, shared the 2017 Nobel Prize in Physics for the discovery of gravitational waves. Barish is the Ronald and Maxine Linde Professor of Physics, Emeritus, at Caltech. (Caltech photo)

    What has been your role at LIGO?

    I started in 1994 and came on board at a time when we didn’t have the money. I had to get the money and have a strategy that [the National Science Foundation] would buy into, and I had to have a plan that they would keep supporting for 22 years. My main mission was to build this instrument—which we didn’t know how to make—well enough to do what it did.

    So we had to build enough trust and success without discovering gravitational waves so that NSF would keep supporting us. And we had to have the flexibility to evolve LIGO’s design, without costing an arm and a leg, to make the improvements that would eventually make it sensitive enough to succeed.

    We started running in about 2000 and took data and improved the experiment over 10 years. But we just weren’t sensitive enough. We managed to get a major improvement program to what’s called Advanced LIGO from the National Science Foundation. After a year and a half or so of making it work, we turned on the device in September of 2015 and, within days, we’d made the detection.

    What steps did LIGO take to be as sensitive as possible?

    We were limited very much by the shaking of the Earth—at the low frequencies, the Earth just shakes too much. We also couldn’t get rid of the background noise at high frequencies—we can’t sample fast enough.

    In the initial LIGO, we reduced the shaking by something like 100 million. We had the fanciest set of shock absorbers possible. The shock absorbers in your car take a bump that you go over, which is high-frequency, and transfer it softly to low-frequency. You get just a little up and down; you don’t feel very much when you go over a bump. You can’t get rid of the bump—that’s energy—but you can transfer it out of the frequencies where it bothers you.

    So we do the same thing. We have a set of springs that are fancier but are basically like shock absorbers in your car. That gave us a factor of 100 million reduction in the shaking of the Earth.

    But that wasn’t good enough [for initial LIGO].

    What did you do to increase sensitivity for Advanced LIGO?

    After 15 years of not being able to detect gravitational waves, we implemented what we call active seismic isolation, in addition to passive springs. It’s very much equivalent to what happens when you get on an airplane and you put those [noise cancellation] earphones on. All of a sudden the airplane is less noisy. That works by detecting the ambient noise—not the noise by the attendant dropping a glass or something. That’s a sharp noise, and you’d still hear that, or somebody talking to you, which is a loud independent noise. But the ambient noise of the motors and the shaking of the airplane itself are more or less the same now as they were a second ago, so if you measure the frequency of the ambient noise, you can cancel it.

    In Advanced LIGO, we do the same thing. We measure the shaking of the Earth, and then we cancel it with active sensors. The only difference is that our problem is much harder. We have to do this directionally. The Earth shakes in a particular direction—it might be up and down, it might be sideways or at an angle. It took us years to develop this active seismic isolation.

    The idea was there 15 years ago, but we had to do a lot of work to develop very, very sensitive active seismic isolation. The technology didn’t exist—we developed all that technology. It reduced the shaking of the Earth by another factor of 100 [over LIGO’s initial 100 million], so we reduced it by a factor of 10 billion.

    So we could see a factor of 100 further out in the universe than we could have otherwise. And each factor of 10 gets cubed because we’re looking at stars and galaxies [in three dimensions]. So when we improved [initial LIGO’s sensitivity] by a factor of 100 beyond this already phenomenal number of 100 million, it improved our sensitivity immediately, and our rate of seeing these kinds of events, by a factor of a hundred cubed—by a million.

    That’s why, after a few days of running, we saw something. We couldn’t have seen this in all the years that we ran at lower sensitivity.

    What key steps did you take when you came on board in 1994?

    First we had to build a kind of technical group that had the experience and abilities to take on a $100 million project. So I hired a lot of people. It was a good time to do that because it was soon after the closure of the Superconducting Super Collider in Texas. I knew some of the most talented people who were involved in that, so I brought them into LIGO, including the person who would be the project manager.

    Second, I made sure the infrastructure was scaled to a stage where we were doing it not the cheapest we could, but rather the most flexible.

    The third thing was to convince NSF that doing this construction project wasn’t the end of what we had to do in terms of development. So we put together a vigorous R&D program, which NSF supported, to develop the technology that would follow similar ones that we used.

    And then there were some technical changes—to become as forward-looking as possible in terms of what we might need later.

    What were the technical changes?

    The first was to change from what was the most popularly used laser in the 1990s, which was a gas laser, to a solid-state laser, which was new at that time. The solid-state laser had the difficulty that the light was no longer in the visible range. It was in the infrared, and people weren’t used to interferometers like that. They like to have light bouncing around that they can see, but you can’t see the solid-state laser light with your naked eye. That’s like particle physics. You can’t see the particles in the accelerator either. We use sensors to do that. So we made that kind of change, going from analog controls to digital controls, which are computer-based.

    We also inherited the kind of control programs that had been developed for accelerators and used at the Superconducting Super Collider, and we brought the SSC controls people into LIGO. These changes didn’t pay off immediately, but paved the road toward making a device that could be modern and not outdated as we moved through the 20 years. It wasn’t so much fixing things as making LIGO much more forward-looking—to make it more and more sensitive, which is the key thing for us.

    Did you draw on past experience?

    I think my history in particle physics was crucial in many ways, for example, in technical ways—things like digital controls, how we monitored beam. We don’t use the same technology, but the idea that you don’t have to see it physically to monitor it—those kinds of things carried over.

    The organization, how we have scientific collaborations, was again something that I created here at LIGO, which was modeled after high-energy physics collaborations. Some of it has to be modified for this different kind of project—this is not an accelerator—but it has a lot of similarities because of the way you approach a large scientific project.

    Were you concerned the experiment wouldn’t happen? If not, what did concern you?

    As long as we kept making technical progress, I didn’t have that concern. My only real concern was nature. Would we be fortunate enough to see gravitational waves at the sensitivities we could get to? It wasn’t predicted totally. There were optimistic predictions—that we could have detected things earlier — but there are also predictions we haven’t gotten to. So my main concern was nature.

    When did you hear about the first detection of gravitational waves?

    If you see gravitational waves from some spectacular thing, you’d also like to be able to see something in telescopes and electromagnetic astronomy that’s correlated. So because of that, LIGO has an early alarm system that alerts you that there might be a gravitational wave event. We more or less have the ability to see spectacular things early. But if you want people to turn their telescopes or other devices to point at something in the sky, you have to tell them something in time scales of minutes or hours, not weeks or months.

    The day we saw this, which we saw early in its running, it happened at 4:50 in the morning in Louisiana, 2:50 in the morning in California, so I found out about it at breakfast time for me, which was about four hours later. When we alert the astronomers, we alert key people from LIGO as well. We get things like that all the time, but this looked a little more serious than others. After a few more hours that day, it became clear that this was nothing like anything we’d seen before, and in fact looked a lot like what we were looking for, and so I would say some people became convinced within hours.

    I wasn’t, but that’s my own conservatism: What’s either fooling us or how are we fooling ourselves? There were two main issues. One is the possibility that maybe somebody was inserting a rogue event in our data, some malicious way to try to fool us. We had to make sure we could trace the history of the events from the apparatus itself and make sure there was no possibility that somebody could do this. That took about a month of work. The second was that LIGO was a brand new, upgraded version, so I wasn’t sure that there weren’t new ways to generate things that would fool us. Although we had a lot of experience over a lot of years, it wasn’t really with this version of LIGO. This version was only a few days old. So it took us another month or so to convince us that it was real. It was obvious that there was going to be a classic discovery if it held up.

    What does it feel like to win the Nobel Prize?

    It happened at 3 in the morning here [in California]. [The night before], I had a nice dinner with my wife, and we went to bed early. I set the alarm for 2:40. They were supposed to announce the result at 2:45. I don’t know why I set it for 2:40, but I did. I moved the house phone into our bedroom.

    The alarm did go off at 2:40. There was no call, obviously—I hadn’t been awakened, so I assumed, kind of in my groggy state, that we must have been passed over. I started going to my laptop to see who was going to get it. Then my cell phone started ringing. My wife heard it. My cell phone number is not given out, generally. There are tens of people who have it, but how [the Nobel Foundation] got it, I’m not sure. Some colleague, I suppose. It was a surprise to me that it came on the cell phone.

    The president of the Nobel Foundation told me who he was, said he had good news and told me I won. And then we chatted for a few minutes, and he asked me how I felt. And I spontaneously said that I felt “thrilled and humbled at the same time.” There’s no word for that, exactly, but that mixture of feeling is what I had and still have.

    Do you have advice for others organizing big science projects?

    We have an opportunity. As I grew into this and as science grew big, we always had to push and push and push on technology, and we’ve certainly done that on LIGO. We do that in particle physics, we do that in accelerators.

    I think the table has turned somewhat and that the technology has grown so fast in the recent decades that there’s incredible opportunities to do new science. The development of new technologies gives us so much ability to ask difficult scientific questions. We’re in an era that I think is going to propagate fantastically into the future.

    Just in the new millennium, maybe the three most important discoveries in physics have all been done with, I would say, high-tech, modern, large-scale devices: the neutrino experiments at SNO and Kamiokande doing the neutrino oscillations, which won a Nobel Prize in 2013; the Higgs boson—no device is more complicated or bigger or more technically advanced than the CERN LHC experiments; and then ours, which is not quite the scale of the LHC, but it’s the same scale as these experiments—the billion dollar scale—and it’s very high-tech.

    Einstein thought that gravitational waves could never be detected, but he didn’t know about lasers, digital controls and active seismic isolation and all things that we developed, all the high-tech things that are coming from industry and our pushing them a little bit harder.

    The fact is, technology is changing so fast. Most of us can’t live without GPS, and 10 or 15 years ago, we didn’t have GPS. GPS exists because of general relativity, which is what I do. The inner silicon microstrip detectors in the CERN experiment were developed originally for particle physics. They developed rapidly. But now, they’re way behind what’s being done in industry in the same area. Our challenge is to learn how to grab what is being developed, because technology is becoming great.

    I think we need to become really aware and understand the developments of technology and how to apply those to the most basic physics questions that we have and do it in a forward-looking way.

    What are your hopes for the future of LIGO?

    It’s fantastic. For LIGO itself, we’re not limited by anything in nature. We’re limited by ourselves in terms of improving it over the next 15 years, just like we improved in going from initial LIGO to Advanced LIGO. We’re not at the limit.

    So we can look forward to certainly a factor of 2 to 3 improvement, which we’ve already been funded for and are ready for, and that will happen over the next few years. And that factor of 2 or 3 gets cubed in our case.

    This represents a completely new way to look at the universe. Everything we look at was with electromagnetic radiation, and a little bit with neutrinos, until we came along. We know that only a few percent of what’s out there is luminous, and so we are opening a new age of astronomy, really. At the same time, we’re able to test Einstein’s theories of general relativity in its most important way, which is by looking where the fields are the strongest, around black holes.

    That’s the opportunity that exists over a long time scale with gravitational waves. The fact that they’re a totally different way of looking at the sky means that in the long term it will develop into an important part of how we understand our universe and where we came from. Gravitational waves are the best way possible, in theory—we can’t do it now—of going back to the very beginning, the Big Bang, because they weren’t absorbed. What we know now comes from photons, but they can go back to only 300,000 years from the Big Bang because they’re absorbed.

    We can go back to the beginning. We don’t know how to do it yet, but that is the potential.

    See the full article here .

    Please help promote STEM in your local schools.

    STEM Icon

    Stem Education Coalition

    Symmetry is a joint Fermilab/SLAC publication.


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  • richardmitnick 3:28 pm on October 16, 2017 Permalink | Reply
    Tags: , , Caltech/MIT aLIGO, , , ,   

    From Symmetry: “Scientists observe first verified neutron-star collision” 


    Symmetry

    10/16/17
    Sarah Charley

    1
    Fermilab

    Today scientists announced the first verified observation of a neutron star collision. LIGO detected gravitational waves radiating from two neutron stars as they circled and merged, triggering 50 additional observational groups to jump into action and find the glimmer of this ancient explosion.


    VIRGO Gravitational Wave interferometer, near Pisa, Italy

    Caltech/MIT Advanced aLigo Hanford, WA, USA installation


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

    Cornell SXS, the Simulating eXtreme Spacetimes (SXS) project

    Gravitational waves. Credit: MPI for Gravitational Physics/W.Benger-Zib

    ESA/eLISA the future of gravitational wave research

    1
    Skymap showing how adding Virgo to LIGO helps in reducing the size of the source-likely region in the sky. (Credit: Giuseppe Greco (Virgo Urbino group)

    This observation represents the first time experiments have seen both light and gravitational waves from a single celestial crash, unlocking a new era of multi-messenger astronomy.

    On August 17 at 7:41 a.m. Eastern Time, NASA astronomer Julie McEnery had just returned from an early morning row on the Anacostia River when her experiment, the Fermi Gamma Ray Space Telescope, sent out an automatic alert that it had just recorded a burst of gamma rays coming from the southern constellation Hydra.

    NASA/Fermi Telescope


    NASA/Fermi LAT

    By itself, this wasn’t novel; the Gamma-ray Burst Monitor instrument on Fermi has seen approximately 2 gamma-ray outbursts per day since its launch in 2008.

    “Forty minutes later, I got an email from a colleague at LIGO saying that our trigger has a friend and that we should buckle up,” McEnery says.

    Most astronomy experiments, including the Fermi Gamma Ray Space Telescope, watch for light or other particles emanating from distant stars and galaxies. The LIGO experiment, on the other hand, listens for gravitational waves. Gravitational waves are the equivalent of cosmic tremors, but instead of rippling through layers of rock and dirt, they stretch and compress space-time itself.

    Exactly 1.7 seconds before Fermi noticed the gamma ray burst, a set of extremely loud gravitational waves had shaken LIGO’s dual detectors.

    “The sky positions overlapped, strongly suggesting the two signals were coming from the same astronomical event,” says Daniel Holz, a professor at the University of Chicago and member of LIGO collaboration and the Dark Energy Survey Gravitational Wave group.

    Dark Energy Survey


    Dark Energy Camera [DECam], built at FNAL


    NOAO/CTIO Victor M Blanco 4m Telescope which houses the DECam at Cerro Tololo, Chile, housing DECam

    LIGO reconstructed the location and distance of the event and sent an alert to their allied astronomers. About 12 hours later, right after sunset, multiple astronomical surveys found a glowing blue dot just above the horizon in the area LIGO predicted.

    “It lasted for two weeks, and we observed it for about an hour every night,” says Jim Annis, a researcher at the US Department of Energy’s Fermi National Accelerator Laboratory, the lead institution on the Dark Energy Survey. “We used telescopes that could see everything from low-energy radio waves all the way to high-energy X-rays, giving us a detailed image of what happened immediately after the initial collision.”

    Neutron stars are roughly the size of the island of Nantucket but have more mass than the sun. They have such a strong gravitational pull that all their matter has been squeezed and transformed into a single, giant atomic nucleus consisting entirely of neutrons.

    “Right before two neutron stars collide, they circle each other about 100 times a second,” Annis says. “As they collide, huge electromagnetic tornados erupt at the poles and material is sprayed out in all directions at close to the speed of light.”

    As they merge, neutron stars release a quick burst of gamma radiation and then a spray of decompressing neutron star matter. Exotic heavy elements form and decay, dumping enough energy that the surface reaches temperatures of 20,000 degrees Kelvin. That’s almost four times hotter than the surface of the sun and much brighter. Scientists theorize that a good portion of the heavy elements in our universe, such as gold, originated in neutron star collisions and other massively energetic events.

    Since coming online in September 2015, the US-based LIGO collaboration and their Italy-based partners, the Virgo collaboration, have reported detecting five bursts of gravitational waves. Up until now, each of these observations has come from a collision of black holes.

    “When two black holes collide, they emit gravitational waves but no light,” Holz says. “But this event released an enormous amount of light and numerous astronomical surveys saw it. Hearing and seeing the event provides a goldmine of information, and we will be mining the data for years to come.”

    This is a Rosetta Stone-type discovery, Holz says. “We’ve learned about the processes that neutron stars are undergoing as they fling out matter and how this matter synthesizes into some of the elements we find on Earth, such as gold and platinum,” he says. “In addition to teaching us about mysterious gamma-ray bursts, we can use this event to calculate the expansion rate of the universe. We will be able to estimate the age and composition of the universe in an entirely new way.”

    For McEnery, the discovery ushers in a new age of cooperation between gravitational-wave experiments and experiments like her own.

    “The light and gravitational waves from this collision raced each other across the cosmos for 130 million years and hit earth 1.7 seconds apart,” she says. “This shows that both are moving at the speed of light, as predicted by Einstein. This is what we’ve been hoping to see.”

    Editor’s note: See LIGO scientific publications here.

    See the full article here .

    Please help promote STEM in your local schools.

    STEM Icon

    Stem Education Coalition

    Symmetry is a joint Fermilab/SLAC publication.


     
  • richardmitnick 12:04 pm on October 16, 2017 Permalink | Reply
    Tags: , , , Caltech/MIT aLIGO, , , ,   

    From ESO: “ESO Telescopes Observe First Light from Gravitational Wave Source” 

    ESO 50 Large

    European Southern Observatory

    16 October 2017
    Stephen Smartt
    Queen’s University Belfast
    Belfast, United Kingdom
    Tel: +44 7876 014103
    Email: s.smartt@qub.ac.uk

    Elena Pian
    Istituto Nazionale di Astrofisica (INAF)
    Bologna, Italy
    Tel: +39 051 6398701
    Email: elena.pian@inaf.it

    Andrew Levan
    University of Warwick
    Coventry, United Kingdom
    Tel: +44 7714 250373
    Email: A.J.Levan@warwick.ac.uk

    Nial Tanvir
    University of Leicester
    Leicester, United Kingdom
    Tel: +44 7980 136499
    nrt3@leicester.ac.uk

    Stefano Covino
    Istituto Nazionale di Astrofisica (INAF)
    Merate, Italy
    Tel: +39 02 72320475
    Cell: +39 331 6748534
    stefano.covino@brera.inaf.it

    Marina Rejkuba
    ESO Head of User Support Department
    Garching bei München, Germany
    Tel: +49 89 3200 6453
    mrejkuba@eso.org

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

    1
    ESO’s fleet of telescopes in Chile have detected the first visible counterpart to a gravitational wave source. These historic observations suggest that this unique object is the result of the merger of two neutron stars. The cataclysmic aftermaths of this kind of merger — long-predicted events called kilonovae — disperse heavy elements such as gold and platinum throughout the Universe. This discovery, published in several papers in journals [listed below], also provides the strongest evidence yet that short-duration gamma-ray bursts are caused by mergers of neutron stars.

    For the first time ever, astronomers have observed both gravitational waves and light (electromagnetic radiation) from the same event, thanks to a global collaborative effort and the quick reactions of both ESO’s facilities and others around the world.

    On 17 August 2017 the NSF’s Laser Interferometer Gravitational-Wave Observatory (LIGO) in the United States, working with the Virgo Interferometer in Italy, detected gravitational waves passing the Earth.


    VIRGO Gravitational Wave interferometer, near Pisa, Italy

    Caltech/MIT Advanced aLigo Hanford, WA, USA installation


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

    Cornell SXS, the Simulating eXtreme Spacetimes (SXS) project

    Gravitational waves. Credit: MPI for Gravitational Physics/W.Benger-Zib

    ESA/eLISA the future of gravitational wave research

    1
    Skymap showing how adding Virgo to LIGO helps in reducing the size of the source-likely region in the sky. (Credit: Giuseppe Greco (Virgo Urbino group)

    This event, the fifth ever detected, was named GW170817. About two seconds later, two space observatories, NASA’s Fermi Gamma-ray Space Telescope and ESA’s INTErnational Gamma Ray Astrophysics Laboratory (INTEGRAL), detected a short gamma-ray burst from the same area of the sky.

    NASA/Fermi Telescope


    NASA/Fermi LAT

    ESA/Integral

    The LIGO–Virgo observatory network positioned the source within a large region of the southern sky, the size of several hundred full Moons and containing millions of stars [1]. As night fell in Chile many telescopes peered at this patch of sky, searching for new sources. These included ESO’s Visible and Infrared Survey Telescope for Astronomy (VISTA) and VLT Survey Telescope (VST) at the Paranal Observatory, the Italian Rapid Eye Mount (REM) telescope at ESO’s La Silla Observatory, the LCO 0.4-meter telescope at Las Cumbres Observatory,

    LCOGT Las Cumbres Observatory Global Telescope Network, Haleakala Hawaii, USA

    and the American DECam at Cerro Tololo Inter-American Observatory.

    Dark Energy Survey


    Dark Energy Camera [DECam], built at FNAL


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

    The Swope 1-metre telescope was the first to announce a new point of light. It appeared very close to NGC 4993, a lenticular galaxy in the constellation of Hydra, and VISTA observations pinpointed this source at infrared wavelengths almost at the same time. As night marched west across the globe, the Hawaiian island telescopes Pan-STARRS and Subaru also picked it up and watched it evolve rapidly.

    Carnegie Institution Swope telescope at Las Campanas, Chile

    Pan-STARRS1 located on Haleakala, Maui, HI, USA


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

    “There are rare occasions when a scientist has the chance to witness a new era at its beginning,” said Elena Pian, astronomer with INAF, Italy, and lead author of one of the Nature papers. “This is one such time!”

    ESO launched one of the biggest ever “target of opportunity” observing campaigns and many ESO and ESO-partnered telescopes observed the object over the weeks following the detection [2]. ESO’s Very Large Telescope (VLT), New Technology Telescope (NTT), VST, the MPG/ESO 2.2-metre telescope, and the Atacama Large Millimeter/submillimeter Array (ALMA) [3] all observed the event and its after-effects over a wide range of wavelengths. About 70 observatories around the world also observed the event, including the NASA/ESA Hubble Space Telescope.

    Distance estimates from both the gravitational wave data and other observations agree that GW170817 was at the same distance as NGC 4993, about 130 million light-years from Earth. This makes the source both the closest gravitational wave event detected so far and also one of the closest gamma-ray burst sources ever seen [4].

    The ripples in spacetime known as gravitational waves are created by moving masses, but only the most intense, created by rapid changes in the speed of very massive objects, can currently be detected. One such event is the merging of neutron stars, the extremely dense, collapsed cores of high-mass stars left behind after supernovae [5]. These mergers have so far been the leading hypothesis to explain short gamma-ray bursts. An explosive event 1000 times brighter than a typical nova — known as a kilonova — is expected to follow this type of event.

    The almost simultaneous detections of both gravitational waves and gamma rays from GW170817 raised hopes that this object was indeed a long-sought kilonova and observations with ESO facilities have revealed properties remarkably close to theoretical predictions. Kilonovae were suggested more than 30 years ago but this marks the first confirmed observation.

    Following the merger of the two neutron stars, a burst of rapidly expanding radioactive heavy chemical elements left the kilonova, moving as fast as one-fifth of the speed of light. The colour of the kilonova shifted from very blue to very red over the next few days, a faster change than that seen in any other observed stellar explosion.

    “When the spectrum appeared on our screens I realised that this was the most unusual transient event I’d ever seen,” remarked Stephen Smartt, who led observations with ESO’s NTT as part of the extended Public ESO Spectroscopic Survey of Transient Objects (ePESSTO) observing programme. “I had never seen anything like it. Our data, along with data from other groups, proved to everyone that this was not a supernova or a foreground variable star, but was something quite remarkable.”

    Spectra from ePESSTO and the VLT’s X-shooter instrument suggest the presence of caesium and tellurium ejected from the merging neutron stars. These and other heavy elements, produced during the neutron star merger, would be blown into space by the subsequent kilonova. These observations pin down the formation of elements heavier than iron through nuclear reactions within high-density stellar objects, known as r-process nucleosynthesis, something which was only theorised before.

    “The data we have so far are an amazingly close match to theory. It is a triumph for the theorists, a confirmation that the LIGO–VIRGO events are absolutely real, and an achievement for ESO to have gathered such an astonishing data set on the kilonova,” adds Stefano Covino, lead author of one of the Nature Astronomy papers.

    “ESO’s great strength is that it has a wide range of telescopes and instruments to tackle big and complex astronomical projects, and at short notice. We have entered a new era of multi-messenger astronomy!” concludes Andrew Levan, lead author of one of the papers.
    Notes

    [1] The LIGO–Virgo detection localised the source to an area on the sky of about 35 square degrees.

    [2 The galaxy was only observable in the evening in August and then was too close to the Sun in the sky to be observed by September.

    [3] On the VLT, observations were taken with: the X-shooter spectrograph located on Unit Telescope 2 (UT2); the FOcal Reducer and low dispersion Spectrograph 2 (FORS2) and Nasmyth Adaptive Optics System (NAOS) – Near-Infrared Imager and Spectrograph (CONICA) (NACO) on Unit Telescope 1 (UT1); VIsible Multi-Object Spectrograph (VIMOS) and VLT Imager and Spectrometer for mid-Infrared (VISIR) located on Unit Telescope 3 (UT3); and the Multi Unit Spectroscopic Explorer (MUSE) and High Acuity Wide-field K-band Imager (HAWK-I) on Unit Telescope 4 (UT4). The VST observed using the OmegaCAM and VISTA observed with the VISTA InfraRed CAMera (VIRCAM). Through the ePESSTO programme, the NTT collected visible spectra with the ESO Faint Object Spectrograph and Camera 2 (EFOSC2) spectrograph and infrared spectra with the Son of ISAAC (SOFI) spectrograph. The MPG/ESO 2.2-metre telescope observed using the Gamma-Ray burst Optical/Near-infrared Detector (GROND) instrument.

    [4] The comparatively small distance between Earth and the neutron star merger, 130 million light-years, made the observations possible, since merging neutron stars create weaker gravitational waves than merging black holes, which were the likely case of the first four gravitational wave detections.

    [5] When neutron stars orbit one another in a binary system, they lose energy by emitting gravitational waves. They get closer together until, when they finally meet, some of the mass of the stellar remnants is converted into energy in a violent burst of gravitational waves, as described by Einstein’s famous equation E=mc2.
    More information

    This research was presented in a series of papers to appear in Nature, Nature Astronomy and The Astrophysical Journal Letters.

    [see https://sciencesprings.wordpress.com/2017/10/16/from-hubble-nasa-missions-catch-first-light-from-a-gravitational-wave-event/ for science papers.]

    The extensive list of team members is available in this PDF file

    See the full article here .

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

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

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

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

     
  • richardmitnick 10:13 am on October 16, 2017 Permalink | Reply
    Tags: , , , , Caltech/MIT aLIGO, , Neutron-Star Merger Detected By Many Eyes and Ears, , What We Saw (and Didn’t See)   

    From AAS NOVA: “Neutron-Star Merger Detected By Many Eyes and Ears” 

    AASNOVA

    AAS NOVA

    16 October 2017
    Susanna Kohler

    1
    LIGO has officially detected gravitational waves from what appears to be a merger of two neutron stars — and electromagnetic counterparts have been found! [NSF/LIGO/Sonoma State University/A. Simonnet]

    Where were you on Thursday, 17 August 2017? I was in Idaho, getting ready for Monday morning’s solar eclipse. What I didn’t know was that, at the time, around 70 teams around the world were mobilizing to point their ground- and space-based telescopes at a single patch of sky suspected to host the first gravitational-wave-detected merger of two neutron stars.

    Sudden Leaps for Science

    2
    The masses for black holes detected through electromagnetic observations (purple), black holes measured by gravitational-wave observations (blue), neutron stars measured with electromagnetic observations (yellow), and the neutron stars that merged in GW170817 (orange). [LIGO-Virgo/Frank Elavsky/Northwestern University]

    The process of science is long and arduous, generally occurring at a slow plod as theorists make predictions, and observations are then used to chip away at these theories, gradually confirming or disproving them. It is rare that science progresses forward in a giant leap, with years upon years of theories confirmed in one fell swoop.

    14 September 2015 marked the day of one such leap, as the Laser Interferometer Gravitational-Wave Observatory (LIGO) detected gravitational waves for the first time — simultaneously verifying that black holes exist, that black-hole binaries exist, and that they can merge on observable timescales, emitting signals that directly confirm the predictions of general relativity.

    As it turns out, 17 August 2017 was another such day. On this day, LIGO observed a gravitational-wave signal unlike its previous black-hole detections. Instead, this was a signal consistent with the merger of two neutron stars.

    4
    Artist’s illustrations of the stellar-merger model for short gamma-ray bursts. In the model, 1) two neutron stars inspiral, 2) they merge and produce a gamma-ray burst, 3) a small fraction of their mass is flung out and radiates as a kilonova, 4) a massive neutron star or black hole with a disk remains after the event. [NASA, ESA, and A. Feild (STScI)]

    What We Predicted

    Theoretical models describing the merger of two compact objects predict a chirping gravitational-wave signal as the objects spiral closer and closer. Unlike in a black-hole merger, however, the end of the chirp from merging neutron stars should coincide with a phenomenon known as a short gamma-ray burst: a powerful storm of energetic gamma rays produced as the objects finally collide.

    According to the models, these gravitational waves and gamma rays will be followed by a kilonova — a transient source visible in infrared, optical, and ultraviolet — which arises from radioactive decay of heavy elements formed in the collision. This source should gradually decay over a timescale of weeks.

    Lastly, the merger could create a powerful jet of high-energy particles, which could be visible to us in X-ray and radio wavelengths as it is emitted and interacts with its surrounding environment. We could also detect neutrinos from this outflow.

    What We Saw (and Didn’t See)

    3
    The localization of the gravitational-wave, gamma-ray, and optical signals of the neutron-star merger detected on 17 August, 2017. [Abbott et al. 2017]

    So what did we see on 17 August, 2017 and thereafter? Here’s what was found by the army of collaborations searching in gravitational waves, electromagnetic signals across the spectrum, and neutrinos:

    Gravitational Waves
    The gravitational-wave signature of a binary neutron-star merger was observed with all three gravitational-wave detectors currently operating as a part of the LIGO-Virgo collaboration. GW170817’s signal was in the sensitivity band of these detectors for ~100 seconds, arriving first at the Virgo detector in Italy, next at LIGO-Livingston in Louisiana 22 milliseconds later, and finally at LIGO-Hanford in Washington 3 milliseconds after that. These detections localized the source to a region of 31 square degrees at a relatively nearby distance of ~130 million light-years, and they identified the binary components to be neutron stars.

    Gamma-Ray Burst
    The Fermi Gamma-Ray Burst Monitor detected a short (~2-second) gamma-ray burst, GRB170817A, which appears to have occurred 1.7 seconds after the merger indicated by the gravitational-wave signal. This source was later identified by the International Gamma-Ray Astrophysics Laboratory (INTEGRAL) spacecraft as well.

    5
    Locations of the many observatories that observed the neutron-star merger first detected on 17 August, 2017. [Abbott et al. 2017]

    Electromagnetic Counterpart and Host Galaxy
    Though they were initially foiled by the signal’s location (the localized region of GW170817 only became visible in Chile 10 hours after its detection), the One-Meter, Two-Hemisphere team used the Swope telescope at Las Campanas Observatory in Chile to discover an optical counterpart to the LIGO and Fermi detection, located in the early-type galaxy NGC 4993. Within an hour, five other teams had independently detected the optical source in NGC 4993, with more following after.

    In the subsequent hours, days, and weeks, observatories across the electromagnetic spectrum monitored the transient. The source soon faded from view in the ultraviolet and gradually reddened in the optical and infrared bands. Delayed X-ray emission was discovered ~9 days after the LIGO signal, and a radio counterpart was discovered a week after that.

    No Neutrinos
    Though several neutrino observatories searched for high-energy neutrinos in the direction of NGC 4993 in the two-week period following the merger, none were detected.

    6
    Summary and timeline of the observations of the neutron-star merger detected on 17 August, 2017 relative to the time tc of the gravitational-wave event. Click for a closer look. [Abbott et al. 2017]

    A Spectacular Confirmation

    So what do these observations tell us? Our model for neutron-star mergers appears to be remarkably successful! The associated detections of gravitational waves and electromagnetic counterparts have confirmed that merging neutron stars produce the expected gravitational-wave signal, that they are the source of gamma-ray bursts, that some of the heaviest elements in the universe are produced during the collision of these stars, and that jets of high-energy particles are created that subsequently interact with their environment.

    As with any interesting scientific discovery, new points of exploration have arisen — we can now wonder why the gamma-ray burst was unusually weak given its close distance, for instance, or why we didn’t detect any neutrinos from the outflow.

    In spite of our new questions, the combination of these recent discoveries provide a resounding verification of our understanding of how compact objects merge. The various signals that began on 17 August, 2017 have simultaneously confirmed a stack of carefully constructed theories that were crafted over decades to explain how seemingly unrelated electromagnetic signals might all tie together. It’s a beautiful thing when science works out this well!

    For more information, check out the ApJL Focus Issue on this result here:
    Focus on The Electromagnetic Counterpart of the Neutron Star Binary Merger GW170817

    Citation

    Abbott, B.P. et al 2017 ApJL 848 L12. doi:10.3847/2041-8213/aa91c9

    See the full article here .

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    1

    AAS Mission and Vision Statement

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

    The Society, through its publications, disseminates and archives the results of astronomical research. The Society also communicates and explains our understanding of the universe to the public.
    The Society facilitates and strengthens the interactions among members through professional meetings and other means. The Society supports member divisions representing specialized research and astronomical interests.
    The Society represents the goals of its community of members to the nation and the world. The Society also works with other scientific and educational societies to promote the advancement of science.
    The Society, through its members, trains, mentors and supports the next generation of astronomers. The Society supports and promotes increased participation of historically underrepresented groups in astronomy.
    The Society assists its members to develop their skills in the fields of education and public outreach at all levels. The Society promotes broad interest in astronomy, which enhances science literacy and leads many to careers in science and engineering.

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  • richardmitnick 1:05 pm on October 9, 2017 Permalink | Reply
    Tags: , , , Caltech/MIT aLIGO, , , Unsung heroes of LIGO and Virgo   

    From Nature: “LIGO’s unsung heroes” 

    Nature Mag
    Nature

    09 October 2017
    Davide Castelvecchi

    1
    LIGO hunts gravitational waves with the help of two laser interferometers — and hundreds of people. Joe McNally/Getty

    Every October, the announcements of the Nobel Prizes bring with them some controversy. This year’s physics prize — in recognition of the Laser Interferometer Gravitational-Wave Observatory (LIGO) in the United States — was less debated than most. The three winners — Kip Thorne and Barry Barish, both at the California Institute of Technology (Caltech) in Pasadena, and Rainer Weiss at the Massachusetts Institute of Technology (MIT) in Cambridge — had attracted near-universal praise for their roles in the project’s success.

    But the award has still put into stark relief the difficulty of singling out just a few individuals from the large collaborations of today’s ‘Big Science’. The LIGO collaboration uses two giant laser interferometers to listen for deformations in space-time caused by some of the Universe’s most cataclysmic events. Physicists detected their first gravitational waves — interpreted as being produced by the collision of two black holes more than a billion years ago — in September 2015. The resulting paper, published in February 20161, has a mind-boggling 1,004 authors.

    Some of those are members of the LIGO Laboratory, the Caltech–MIT consortium that manages LIGO’s two interferometers in Louisiana and Washington State. But the list also includes the larger LIGO Scientific Collaboration: researchers from 18 countries, some of which — such as Germany and the United Kingdom — have made crucial contributions to the detectors.

    Yet more authors are from LIGO’s sister Virgo Collaboration, led by France and Italy, which built the Virgo interferometer near Pisa, Italy. The two experiments pool their data and analyse them together. Countless other people not named on the paper have also been involved in LIGO’s design, development, construction and operation since Weiss first detailed how to build a laser interferometer in 1972.

    To honour the many unsung heroes of gravitational waves, Nature collected testimonials about just a few of them. Like the Nobel Prize, this list is inevitably very incomplete.

    1. The pioneer: Joseph Weber

    Researchers using two detectors in the United States shook the world when they announced their discovery of gravitational waves. The year was 1969, and the detectors were not LIGO but tonne-sized cylinders of aluminium built by Joseph Weber, a physicist at the University of Maryland in College Park. His claim was later found to be invalid, but many physicists still credit Weber for having founded the field. “Joe Weber indeed started thinking about how to detect gravitational waves in about 1957,” Virginia Trimble, an astrophysicist and Weber’s widow, told Nature in an e-mail. At that time, many researchers were not even sure that gravitational waves existed. In the 1960s, Weber was also one of the first researchers to consider the possibility of using interferometers to detect them.

    2. The German connection: Heinz Billing

    The founder of Germany’s side of LIGO, Heinz Billing, a physicist at the Max Planck Institute for Astrophysics near Munich, first heard of Weiss’s pioneering interferometer designs in 1975, when he was asked to review Weiss’s request to the National Science Foundation to fund a prototype at MIT. Billing and his team liked it so much that they started building one themselves. “The Munich group quickly invented some of the most important ingredients that made the detectors possible,” says Karsten Danzmann, a director at the Max Planck Institute for Gravitational Physics in Hanover, Germany. Billing, in particular, came up with an idea to stabilize the laser that was later used in the UK–German GEO600 interferometer based near Hanover — and in LIGO itself. GEO600 is still a crucial testing and development centre for technologies introduced in the successive rounds of LIGO upgrades. “There is an awful lot of GEO in LIGO,” says Danzmann. Billing, who died on 4 January at the age of 102, was also a pioneer in magnetic data storage.

    3. The laser expert: Alain Brillet

    The 1980s were years of intense research and development for gravitational-wave detectors. Alain Brillet, an optical physicist with extensive experience in interferometers, then at the University of Paris-Sud in Orsay, France, saw an opportunity to contribute. “I decided to start with the optical part, the lasers and optics, because that was my specialty,” he says. Brillet went on to co-found Virgo. But many of his ideas — in particular, the type of laser that would give the most stable signal — were implemented in LIGO and other interferometers as well, says MIT physicist David Shoemaker, who studied with Brillet in Orsay and is now LIGO’s spokesperson.

    4. The facilitator: Richard Isaacson

    Gravitational theorist Richard Isaacson went to Washington DC to work at the National Science Foundation (NSF) in 1973 for what he thought would be a brief stint as one of the programme directors. During the handover, his predecessor advised him to pay attention to an “interesting guy” called Rainer Weiss. Isaacson secured Weiss a small grant for his 1975 prototype, and later became LIGO’s chief advocate inside government. He was instrumental in the project’s winning hundreds of millions of dollars in funding, despite the uncertain prospect of success. It was the first time that the NSF had managed a large project: US facilities such as particle accelerators were traditionally the remit of the Department of Energy, which had field offices staffed with dozens of experts. Isaacson did it by himself for more than ten years, and by the early 1990s he had paid a high personal cost. “Eventually, my health broke and my marriage went bad,” says Isaacson. By the time he retired in 2001, the construction of LIGO had been completed.

    5. The first director: Rochus ‘Robbie’ Vogt

    Before Barry Barish took the reins of LIGO, another director had left his mark on the collaboration: Rochus Vogt. The Caltech physicist, a veteran of the NASA Voyager mission, was put in charge in 1987. Until then, the project had been led by the ‘troika’ of visionary founders — Thorne, Weiss, and the physicist Ronald Drever, who started UK research on gravitational waves at the University of Glasgow before moving to Caltech — but managing large organizations was not their strength. “Thank God that was done,” Weiss recalled in a talk at NSF headquarters last year. “You don’t manage it with three guys who are sort of a little bit flaky.” Vogt, who was once described as a taller and leaner Henry Kissinger, had a booming voice and forceful style that did not please everyone. But he was able to put together the first major request for NSF funding and, Thorne recalled in a 5 October press conference, “laid the foundations for moving LIGO forward to our construction”.

    6. The theorist: Alessandra Buonanno

    As Thorne realized early on, in the future field of gravitational-wave astronomy, it would not be enough to collect data; researchers would also need to know what signals to look for. But it is notoriously difficult to extract quantitative predictions from the equations of Einstein’s general relativity. Theoretical physicist Alessandra Buonanno had devised formulae for calculating the approximate orbits of spiralling objects and the gravitational waves they would generate in work she had done, in part with her PhD adviser Thibault Damour, at the Institute of Advanced Scientific Studies near Paris. The LIGO and Virgo collaborations use a database of hundreds of thousands of these waveforms for spotting gravitational waves in their data in real time. Buonanno is now a director at the Max Planck Institute for Gravitational Physics in Potsdam and a senior member of the LIGO Scientific Collaboration.


    VIRGO Gravitational Wave interferometer, near Pisa, Italy

    Caltech/MIT Advanced aLigo Hanford, WA, USA installation


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

    Cornell SXS, the Simulating eXtreme Spacetimes (SXS) project

    Gravitational waves. Credit: MPI for Gravitational Physics/W.Benger-Zib

    ESA/eLISA the future of gravitational wave research

    1
    Skymap showing how adding Virgo to LIGO helps in reducing the size of the source-likely region in the sky. (Credit: Giuseppe Greco (Virgo Urbino group)

    See the full article here .

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    Nature is a weekly international journal publishing the finest peer-reviewed research in all fields of science and technology on the basis of its originality, importance, interdisciplinary interest, timeliness, accessibility, elegance and surprising conclusions. Nature also provides rapid, authoritative, insightful and arresting news and interpretation of topical and coming trends affecting science, scientists and the wider public.

     
  • richardmitnick 8:13 am on September 3, 2017 Permalink | Reply
    Tags: , , , Caltech/MIT aLIGO, , , Neutron star mergers are the largest hadron colliders ever conceived, , What the Rumored Neutron Star Merger Might Teach Us   

    From Nautilus: “What the Rumored Neutron Star Merger Might Teach Us” 

    Nautilus

    Nautilus

    Aug 29, 2017
    Dan Garisto

    1
    In a sense, neutron star mergers are the largest hadron colliders ever conceived. Image by NASA Goddard Space Flight Center / Flickr

    This month, before LIGO, the Laser Interferometer Gravitational Wave Observatory, and its European counterpart Virgo, were going to close down for a year to undergo upgrades, they jointly surveyed the skies.


    Caltech/MIT Advanced aLigo Hanford, WA, USA installation


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

    Cornell SXS, the Simulating eXtreme Spacetimes (SXS) project


    Gravitational waves. Credit: MPI for Gravitational Physics/W.Benger-Zib

    ESA/eLISA the future of gravitational wave research

    VIRGO Gravitational Wave interferometer, near Pisa, Italy

    It was a small observational window—the 1st to the 25th—but that may have been enough: A rumor that LIGO has detected another gravitational wave—the fourth in two years—is making the rounds. But this time, there’s a twist: The signal might have been caused by the merger of two neutron stars instead of black holes.

    If the rumor holds true, it would be an astonishingly lucky detection. To get a sense of the moment, Nautilus spoke to David Radice, a postdoctoral researcher at Princeton who simulates neutron star mergers, “one of LIGO’s main targets,” he says.

    This potential binary neutron star merger sighting reminds me of when biologists think they’ve discovered a new species. How would you describe it?

    I do agree that this is the first time something like this has been seen.

    For me, a nice analogy is one of particle colliders. In a sense, neutron star mergers are the largest hadron colliders ever conceived. Instead of smashing a few nucleons, it’s like smashing 1060 of them. So by looking at the aftermath, we can learn a lot about fundamental physics. There is a lot that can happen when these stars collide and I don’t think we have a full knowledge of all the possibilities. I think we’ll learn a lot and see new things.

    What it would it mean if they were detecting a neutron star binary merger?

    I expected this neutron star merger to be detected further in the future—the possibility that this merger has been detected earlier suggests that that rate of these events is higher than we thought. There is maybe also a counterpart—an electromagnetic wave. There are many things that you can only really do with an electromagnetic counterpart. For example, even when we have, in the far future, five detectors worldwide, we will not be able to pinpoint the exact location to the source with the precision to say: “OK, this is the host galaxy.”

    Well, if you have an electromagnetic counterpart, especially in the optical region, you can really pinpoint a galaxy and say, “This merger happened in this galaxy that has these properties.”

    What makes a neutron star binary merger different from a black hole binary merger?

    One of the main things is that in a black hole binary merger, you’re just looking at the space-time effects. In this case we are looking at this extremely dense matter. There are a lot of things that you can hope to learn about neutron star mergers. We’re looking at them for a source of gamma ray bursts, or as the origin of heavy elements, or as a way to learn about physics of very high density matter.

    One idea that has been around now for a few years is that many of the heavy elements—elements, for example, like platinum or gold—may actually be produced in neutron star mergers. Material is ejected, and because of nuclear processes, it will produce these heavy elements that are otherwise difficult to produce in normal stars.

    You’ve created visual simulations of neutron star mergers, like the one below. How much power is required to run them?

    It’s publicly available—anyone can download the code and do simulations similar to those…but you need to run them on a supercomputer. It typically takes weeks on thousands of processors, but it can tell you a lot about these mergers. Now the two detectors both LIGO and Virgo are expected to shut down and go through a series of upgrades. When they come back online, their sensitivity will be significantly boosted so we can see much farther out and learn more about each event.

    See the full article here .

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    Welcome to Nautilus. We are delighted you joined us. We are here to tell you about science and its endless connections to our lives. Each month we choose a single topic. And each Thursday we publish a new chapter on that topic online. Each issue combines the sciences, culture and philosophy into a single story told by the world’s leading thinkers and writers. We follow the story wherever it leads us. Read our essays, investigative reports, and blogs. Fiction, too. Take in our games, videos, and graphic stories. Stop in for a minute, or an hour. Nautilus lets science spill over its usual borders. We are science, connected.

     
  • richardmitnick 1:11 pm on August 31, 2017 Permalink | Reply
    Tags: , , , , Caltech/MIT aLIGO, , Could Dark Matter be Black Holes?   

    From astrobites: “Could Dark Matter be Black Holes?” 

    Astrobites bloc

    Astrobites

    Aug 31, 2017
    Nora Shipp

    Title: Did LIGO Detect Dark Matter?
    Authors: Simeon Bird, Ilias Cholis, Julian B. Muñoz, Yacine Ali-Haïmoud, Marc Kamionkowski, Ely D. Kovetz, Alvise Raccanelli, Adam G. Riess
    First Author’s Institution: Department of Physics and Astronomy, Johns Hopkins University

    Status: Published in Physical Review Letters, Open Access

    The mystery of the nature of dark matter is deepening. Dark matter particles have evaded our detection again and again, bringing into question the most popular theories (like WIMPS), and thereby opening the door to more exotic and unexpected dark matter models. In the midst of this growing uncertainty, a new possibility has arisen. LIGO has detected gravitational waves resulting from the merging of two black holes. This may seem irrelevant to dark matter, but black holes are really not unreasonable dark matter candidates. They don’t emit light, and they definitely do interact via gravity, and those are basically the only two things we know about dark matter.

    The LIGO black holes have revived the idea of larger-than-particle dark matter, called MACHOs (Massive Astrophysical Compact Halo Objects). MACHOs are large, dark objects that are not made up of smaller fundamental dark matter particles, but actually act as the dark matter “particles” themselves. (Read more about them in this astrobite.) In the past, this kind of dark matter was a popular alternative to particle dark matter, but many years of work revealed that most sizes of these larger dark matter objects would disrupt the Universe in some way, leaving it different than the true Universe that we observe.

    For example, black holes with masses around that of an individual star would have given themselves away in searches for the bending of starlight in their gravitational field (an effect called microlensing – read more about it in this astrobite).

    Gravitational microlensing, S. Liebes, Physical Review B, 133 (1964): 835

    More massive black holes would have left an imprint on the early Universe that would show up in the Cosmic Microwave Background.

    CMB per ESA/Planck

    ESA/Planck

    These are only two examples of the many ways in which astrophysical observations tell us which masses are not possible for MACHOs (Figure 1). One mass that could be possible, is about 30 times the mass of the sun. It just so happens that LIGO has detected black holes of this mass!

    2
    Figure 1. The ruled out black hole MACHO masses from astrophysical observations. The x-axis is the mass of the black hole (in units of solar masses), and the y-axis is the fraction of dark matter that is made up of black holes. Each colored line surrounds a range of masses that has been ruled out (with more masses ruled out when black holes make up a larger fraction of dark matter). The black dashed line labeled PBH (Primordial Black Hole) is the allowed region in which the LIGO black holes fall. Source: Clesse et al, 2015.

    The question then, is whether black hole dark matter is really consistent with the black hole mergers observed by LIGO. The first step – confirming that LIGO has detected black holes with the correct mass – is all set. The next step is not so simple. LIGO must detect black hole collisions that correspond to the known properties of dark matter.

    We know that dark matter was an important part of the evolution of the early Universe, meaning that dark matter black holes must have existed at this time, and therefore cannot be typical stellar black holes that form in the death of massive stars. They must be a type of black hole that forms much earlier, referred to as “primordial black holes.”

    So how do we tell whether LIGO is detecting stellar black holes or primordial black holes? The primary difference between them (apart from their origin) is their location. Stellar black holes should exist in regions with lots of stars, while primordial black holes should exist in regions with lots of dark matter. There is overlap between these regions, but they are not identical.

    Primordial black holes, if they really are dark matter, have an additional constraint. They do not only need to exist in the known locations of dark matter, they must also exist in known quantities. We know quite a bit about the mass of dark matter halos around galaxies and galaxy clusters (Figure 2), so if we want primordial black holes to explain all of that dark matter, we have a pretty good idea of how many primordial black holes there must be.

    Currently, it’s pretty difficult to tell exactly where a gravitational wave is coming from, so it’s not possible to say whether the black hole collisions happen in regions with lots of stars or lots of dark matter. The way to tell whether LIGO black holes could possibly be primordial black hole dark matter is to see whether the rate of LIGO observations matches up with the expected rate of primordial black hole collisions.

    This is exactly the topic of today’s paper. The authors predict the rate of primordial black hole collisions and compare it to the LIGO observations. The predicted collision rate depends on the quantity of primordial black holes and their spatial distribution (regions of higher density have higher collision rates). Since this requires a precise knowledge of the spatial distribution of invisible matter, the prediction is quite approximate, but the authors do their best to use observations and simulations to make realistic assumptions about the shape and mass of dark matter halos. They find that the expected rate of primordial black hole mergers (Figure 3) is in fact consistent with the rate inferred from LIGO observations.

    4
    Figure 3. The rate of primordial black hole mergers per dark matter halo, as a function of halo mass (in units of solar masses). The two lines use different theories of dark matter halo structure. Source: Figure 2 in the paper.

    Although this result is very approximate and certainly doesn’t rule out stellar black holes, it means that primordial black hole dark matter is a possibility!

    As LIGO continues to detect more and more gravitational wave signals, we will be able to learn more about the rate of black hole collisions and the possibility of dark matter black holes.


    Caltech/MIT Advanced aLigo Hanford, WA, USA installation


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

    Cornell SXS, the Simulating eXtreme Spacetimes (SXS) project


    Gravitational waves. Credit: MPI for Gravitational Physics/W.Benger-Zib

    ESA/eLISA the future of gravitational wave research

    Additionally, as more gravitational wave detectors start collecting data, we will have more precise information on the location of each black hole merger. This will allow for a comparison between the spatial distribution of black holes and the relative spatial distributions of dark matter and stars. Even though all this sounds extremely complicated, and maybe a bit unlikely, it’s awesome that the seemingly unrelated detection of gravitational waves has opened the door to discussions of new theories of dark matter.

    See the full article here .

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    What do we do?

    Astrobites is a daily astrophysical literature journal written by graduate students in astronomy. Our goal is to present one interesting paper per day in a brief format that is accessible to undergraduate students in the physical sciences who are interested in active research.
    Why read Astrobites?

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

     
  • richardmitnick 6:42 am on August 29, 2017 Permalink | Reply
    Tags: , , , , Caltech/MIT aLIGO, , , Rumors swirl that LIGO snagged gravitational waves from a neutron star collision,   

    From Science News: “Rumors swirl that LIGO snagged gravitational waves from a neutron star collision” 

    ScienceNews bloc

    ScienceNews

    August 25, 2017
    Emily Conover

    1
    CRASH AND FLASH Rumors suggest that LIGO may have detected gravitational waves from a new source: colliding neutron stars (illustrated). Such cataclysms are expected to generate a high-energy flash of light, called a gamma-ray burst (yellow jets). Several telescopes made observations seemingly in search of light from such events.

    Speculation is running rampant about potential new discoveries of gravitational waves, just as the latest search wound down August 25.

    Publicly available logs from astronomical observatories indicate that several telescopes have been zeroing in on one particular region of the sky, potentially in response to a detection of ripples in spacetime by the Advanced Laser Interferometer Gravitational-Wave Observatory, LIGO.


    Caltech/MIT Advanced aLigo Hanford, WA, USA installation


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

    Cornell SXS, the Simulating eXtreme Spacetimes (SXS) project


    Gravitational waves. Credit: MPI for Gravitational Physics/W.Benger-Zib

    ESA/eLISA the future of gravitational wave research

    These records have raised hopes that, for the first time, scientists may have glimpsed electromagnetic radiation — light — produced in tandem with gravitational waves. That light would allow scientists to glean more information about the waves’ source. Several tweets from astronomers reporting rumors of a new LIGO detection have fanned the flames of anticipation and amplified hopes that the source may be a cosmic convulsion unlike any LIGO has seen before.

    “There is a lot of excitement,” says astrophysicist Rosalba Perna of Stony Brook University in New York, who is not involved with the LIGO collaboration. “We are all very anxious to actually see the announcement.”

    An Aug. 25 post on the LIGO collaboration’s website announced the end of the current round of data taking, which began November 30, 2016. Virgo, a gravitational wave detector in Italy, had joined forces with LIGO’s two on August 1 (SN Online: 8/1/17).


    VIRGO Gravitational Wave interferometer, near Pisa, Italy

    The three detectors will now undergo upgrades to improve their sensitivity. The update noted that “some promising gravitational-wave candidates have been identified in data from both LIGO and Virgo during our preliminary analysis, and we have shared what we currently know with astronomical observing partners.”

    When LIGO detects gravitational waves, the collaboration alerts astronomers to the approximate location the waves seemed to originate from. The hope is that a telescope could pick up light from the aftermath of the cosmic catastrophe that created the gravitational waves — although no light has been found in previous detections.


    SPIRAL IN Two neutron stars orbit one another and spiral inward until they merge in this animation. The collision emits gravitational waves and a burst of light.

    Since mid-August, seemingly in response to a LIGO alert, several telescopes have observed a section of sky around the galaxy NGC 4993, located 134 million light-years away in the constellation Hydra. The Hubble Space Telescope has made at least three sets of observations in that vicinity, including one on August 22 seeking “observations of the first electromagnetic counterparts to gravitational wave sources.”

    NASA/ESA Hubble Telescope

    Likewise, the Chandra X-ray Observatory targeted the same region of sky on August 19.

    NASA/Chandra Telescope

    And records from the Gemini Observatory’s telescope in Chile indicate several potentially related observations, including one referencing “an exceptional LIGO/Virgo event.”


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

    “I think it’s very, very likely that LIGO has seen something,” says astrophysicist David Radice of Princeton University, who is not affiliated with LIGO. But, he says, he doesn’t know whether its source has been confirmed as merging neutron stars.

    LIGO scientists haven’t commented directly on the veracity of the rumor. “We have some substantial work to do before we will be able to share with confidence any quantitative results. We are working as fast as we can,” LIGO spokesperson David Shoemaker of MIT wrote in an e-mail.

    See the full article here .

    Science News is edited for an educated readership of professionals, scientists and other science enthusiasts. Written by a staff of experienced science journalists, it treats science as news, reporting accurately and placing findings in perspective. Science News and its writers have won many awards for their work; here’s a list of many of them.

    Published since 1922, the biweekly print publication reaches about 90,000 dedicated subscribers and is available via the Science News app on Android, Apple and Kindle Fire devices. Updated continuously online, the Science News website attracted over 12 million unique online viewers in 2016.

    Science News is published by the Society for Science & the Public, a nonprofit 501(c) (3) organization dedicated to the public engagement in scientific research and education.

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  • richardmitnick 1:26 pm on August 26, 2017 Permalink | Reply
    Tags: , , , Caltech/MIT aLIGO, , , , Neutron star mergers, Rumours swell over new kind of gravitational-wave sighting,   

    From Nature: “Rumours swell over new kind of gravitational-wave sighting” 

    Nature Mag
    Nature

    24 August 2017
    Davide Castelvecchi

    Gossip over potential detection of colliding neutron stars has astronomers in a tizzy.

    1
    The galaxy NGC 4993 (fuzzy bright spot) in the constellation Hydra, where detectors are rumoured to have spotted gravitational waves from a neutron star merger. Digitized Sky Survey

    Astrophysicists may have detected gravitational waves last week from the collision of two neutron stars in a distant galaxy — and telescopes trained on the same region might also have spotted the event.

    Rumours to that effect are spreading fast online, much to researchers’ excitement. Such a detection could mark a new era of astronomy: one in which phenomena are both seen by conventional telescopes and ‘heard’ as vibrations in the fabric of space-time. “It would be an incredible advance in our understanding,” says Stuart Shapiro, an astrophysicist at the University of Illinois at Urbana–Champaign.

    Scientists who work with gravitational-wave detectors won’t comment on the gossip because the data is still under analysis. Public records show that telescopes around the world have been looking at the same galaxy since last week, but astronomers caution that they could have been picking up signals from an unrelated source.

    As researchers hunt for signals in their data, Nature explains what is known so far, and the possible implications of any discovery.

    What is the gossip?

    The Laser Interferometer Gravitational-Wave Observatory (LIGO) in Louisiana and Washington state has three times detected gravitational waves — ripples in the fabric of space-time — emerging from colliding black holes.


    Caltech/MIT Advanced aLigo Hanford, WA, USA installation


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

    Cornell SXS, the Simulating eXtreme Spacetimes (SXS) project


    Gravitational waves. Credit: MPI for Gravitational Physics/W.Benger-Zib

    ESA/eLISA the future of gravitational wave research

    But scientists have been hoping to detect ripples from another cosmic cataclysm, such as the merger of neutron stars, remnants of large stars that exploded but were not massive enough to collapse into a black hole. Such an event should also emit radiation across the electromagnetic spectrum — from radio waves to γ-rays — which telescopes might be able to pick up.

    On 18 August, astronomer J. Craig Wheeler of the University of Texas at Austin began the public rumour mill when he tweeted, “New LIGO. Source with optical counterpart. Blow your sox off!” An hour later, astronomer Peter Yoachim of the University of Washington in Seattle tweeted that LIGO had seen a signal with an optical counterpart (that is, something that telescopes could see) from a galaxy called NGC 4993, which is around 40 million parsecs (130 million light years) away in the southern constellation Hydra. “Merging neutron-neutron star is the initial call”, he followed up. Some astronomers who do not want to be identified say that rumours had been privately circulating before Wheeler’s and Yoachim’s tweets.

    If gravitational-wave researchers saw a signal, it is plausible that they could know very quickly whether it emerged from colliding black holes or neutron stars, because each type of event has its own signature, even though data must be studied carefully to be more precise about an event’s origin.

    It’s also possible that LIGO’s sister observatory Virgo in Pisa, Italy, which has been helping LIGO to hunt for gravitational waves since August, after taking a break for an upgrade, might have spotted the event.

    VIRGO Gravitational Wave interferometer, near Pisa, Italy

    That would give researchers more confidence about its source. (Virgo has an average sensitivity for neutron-star mergers of only 25 million to 27 million parsecs, but in some regions of the sky, it can see farther, up to 60 million parsecs away, says physicist Giovanni Losurdo, who led the detector’s upgrade work.)

    Both Wheeler and Yoachim declined to comment, and Wheeler later apologized on Twitter. “Right or wrong, I should not have sent that tweet. LIGO deserves to announce when they deem appropriate. Mea culpa,” he wrote.

    What about the telescope observations?

    Public records show that NASA’s Fermi Gamma-ray Space Telescope has spotted γ-rays emerging from the same region of sky as the potential gravitational-wave source.

    NASA/Fermi Telescope

    A senior Fermi member declined to comment on the observation, but it would be consistent with expectations that neutron-star collisions may be behind the enigmatic phenomena known as short γ-ray bursts (GRBs), which typically last a couple of seconds and are usually followed by an afterglow of visible light and sometimes, radio waves and x-rays, lasting up to a few days.

    But although the Fermi telescope has seen a GRB, it may not be able to pinpoint its origin with high precision, astronomers caution.

    2
    A simulation of the merger of a binary neutron star: magnetic field lines are in white. Simulations by M. Ruiz, R. N. Lang, V. Paschalidis and S. L.Shapiro at the University of Illinois at Urbana-Champaign, with visualization assistance from the Illinois Relativity REU team.

    Other telescopes were also turned to look at NGC 4993 after an alert about a potential gravitational wave sighting. On 22 August, a Twitter feed called Space Telescope Live, which provides live updates of what the Hubble Space Telescope is looking at, suggested that a team of astronomers was looking at a binary neutron-star merger using the probe’s on-board spectrograph, which is what astronomers would normally use to look at the afterglow of a short GRB. The Hubble tweet has since been deleted. Public records also confirm that multiple teams have used the Hubble Space Telescope over the last week to examine NGC 4993, and state as their reason that they are trying to follow up on a candidate observation of gravitational waves.

    On 23 August, a commenter on the blog of astrophysicist Peter Coles, of Cardiff University in the UK, noted that NASA’s Chandra X-ray observatory had jumped into the action, too.

    The Chandra website contains a public record of an observation made on 19 August.

    NASA/Chandra Telescope

    The telescope pointed at celestial coordinates in the galaxy NGC 4993 and observed an event called SGRB170817A — indicating ‘short GRB of 2017-August-17’. The most revealing part of the report is the “trigger criteria” section, which explains the reason for over-riding any previously scheduled observation to turn the telescope in that direction. It says: “Gravitational wave source detected by aLIGO, VIRGO, or both.”

    Publicly available records from other major astronomy facilities — including the European Southern Observatory’s Very Large Telescope and the world’s premiere radio observatory, the Atacama Large Millimeter/submillimeter Array (ALMA), both in Chile — show that those also targeted NGC 4993 on 18 and 19 August.

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

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

    What could we learn from a neutron-star merger?

    Gravitational-wave signals from black-hole mergers are brief, typically lasting a second or less. But a neutron-star merger could yield a signal that lasts up to a minute: neutron stars are less massive than black holes and emit less-powerful gravitational waves, so it takes longer for their orbits to decay and for the stars to spiral into each other. Longer events enable much more precise tests of Albert Einstein’s general theory of relativity, which predicts gravitational waves — perhaps giving more clues to the origins of neutron stars.

    The short GRB that telescopes might have observed would be significant, too — not least because if it is associated with gravitational waves, it would validate decades of astrophysical theorizing that GRBs are associated with neutron-star collisions. “Only gravitational waves could give us the smoking gun,” says Eleonora Troja, an astrophysicist at NASA’s Goddard Space Flight Center in Greenbelt, Maryland.

    Still, a short GRB would be an important discovery on its own. Most such events are seen in the distant Universe, billions of parsecs away. NGC 4993, at 40 million parsecs away, would probably be the closest short GRB ever detected, says astrophysicist Derek Fox of Pennsylvania State University in University Park.

    Details of the gravitational waves at the time of the collision and in the following instances could also reveal information about the structure of neutron stars — which is largely unknown — and whether their merger resulted again in a neutron star or in the formation of a new black hole.

    When will we know?

    On 25 August, LIGO and Virgo will end their current data-collecting run. After that, researchers will post only a “top-level update”, meaning a brief note indicating whether the observatories have picked up potential ‘candidate events’ that need further analysis, says David Shoemaker, a physicist at the Massachusetts Institute of Technology who is LIGO’s spokesperson.

    “It will take time to do justice to the data, and ensure that we publish things in which we have very high confidence,” he says.

    Update 25 August: The LIGO–Virgo collaboration posted its top-level update, saying: “Some promising gravitational-wave candidates have been identified in data from both LIGO and Virgo during our preliminary analysis, and we have shared what we currently know with astronomical observing partners. We are working hard to assure that the candidates are valid gravitational-wave events, and it will require time to establish the level of confidence needed to bring any results to the scientific community and the greater public. We will let you know as soon we have information ready to share.”

    See the full article here .

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    Nature is a weekly international journal publishing the finest peer-reviewed research in all fields of science and technology on the basis of its originality, importance, interdisciplinary interest, timeliness, accessibility, elegance and surprising conclusions. Nature also provides rapid, authoritative, insightful and arresting news and interpretation of topical and coming trends affecting science, scientists and the wider public.

     
    • Jose 5:40 am on October 29, 2017 Permalink | Reply

      The detection of the gravitational waves produced by the merger of two neutron stars –GW170817– has allowed scientists to fix at 70 km/s per megaparsec * the value of the increase in speed of the expansion of the universe in the 130 million light years that separate us from the origin of said merger.
      As these calculations approach the speed of light throughout the age of the universe, we can do the inverse calculation to determine the average increase in the velocity of expansion so that the observable universe is of the age stated by the Big Bang Theory.
      The result is 300.000 km/s /(13.799/3,26) Mpc =70,820 km/s Mpc. https://molwick.com/en/gravitation/072-gravitational-waves.html#big-bang

      Like

    • richardmitnick 7:09 am on October 29, 2017 Permalink | Reply

      Thanks for visiting sciencesprings. I went to your site. Beautiful and instructive.

      Like

    • Jose 12:34 pm on October 29, 2017 Permalink | Reply

      Thank you too. My pleasure!

      Like

  • richardmitnick 8:10 pm on August 24, 2017 Permalink | Reply
    Tags: , , , Caltech/MIT aLIGO, , Gravitational wave research may tell us how black holes are formed, , , U Birmingham   

    STFC: “Gravitational wave research may tell us how black holes are formed” 


    STFC

    24 August 2017

    1

    The new field of gravitational wave astronomy, which started with the first gravitational wave detection two years ago, is already offering possible explanations of how black holes form.

    A team of physicists from the UK and the United States has studied the landmark observations of gravitational waves by the LIGO gravitational wave detector in 2015 and again in 2017.

    1

    The UK’s Science and Technology Facilities Council provides grant funding to enable UK researchers, including those at the University of Birmingham, to be involved in the LIGO scientific collaboration.


    Caltech/MIT Advanced aLigo Hanford, WA, USA installation


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

    In the paper published in Nature today, the team says the evidence gathered from these detections limit the possible explanations for the formation of black holes outside of our galaxy; either they are spinning more slowly than black holes in our own galaxy or they spin rapidly but are ‘tumbled around’ with spins randomly oriented to their orbit.

    By ruling out other explanations and narrowing it down to two, researchers will now be able to carry out more specific research and get closer to a definite answer.

    Professor Ilya Mandel, also from the University of Birmingham, said: “We will know which explanation is right within the next few years. This is something that has only been made possible by the recent LIGO detections of gravitational waves.

    “This field is in its infancy; I’m confident that in the near future we will look back on these first few detections and rudimentary models with nostalgia and a much better understanding of how these exotic binary systems form.”

    More information is available on the University of Birmingham website.

    See the full article here .

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    STFC Hartree Centre

    Helping build a globally competitive, knowledge-based UK economy

    We are a world-leading multi-disciplinary science organisation, and our goal is to deliver economic, societal, scientific and international benefits to the UK and its people – and more broadly to the world. Our strength comes from our distinct but interrelated functions:

    Universities: we support university-based research, innovation and skills development in astronomy, particle physics, nuclear physics, and space science
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    We support an academic community of around 1,700 in particle physics, nuclear physics, and astronomy including space science, who work at more than 50 universities and research institutes in the UK, Europe, Japan and the United States, including a rolling cohort of more than 900 PhD students.

    STFC-funded universities produce physics postgraduates with outstanding high-end scientific, analytic and technical skills who on graduation enjoy almost full employment. Roughly half of our PhD students continue in research, sustaining national capability and creating the bedrock of the UK’s scientific excellence. The remainder – much valued for their numerical, problem solving and project management skills – choose equally important industrial, commercial or government careers.

    Our large-scale scientific facilities in the UK and Europe are used by more than 3,500 users each year, carrying out more than 2,000 experiments and generating around 900 publications. The facilities provide a range of research techniques using neutrons, muons, lasers and x-rays, and high performance computing and complex analysis of large data sets.

    They are used by scientists across a huge variety of science disciplines ranging from the physical and heritage sciences to medicine, biosciences, the environment, energy, and more. These facilities provide a massive productivity boost for UK science, as well as unique capabilities for UK industry.

    Our two Campuses are based around our Rutherford Appleton Laboratory at Harwell in Oxfordshire, and our Daresbury Laboratory in Cheshire – each of which offers a different cluster of technological expertise that underpins and ties together diverse research fields.

    The combination of access to world-class research facilities and scientists, office and laboratory space, business support, and an environment which encourages innovation has proven a compelling combination, attracting start-ups, SMEs and large blue chips such as IBM and Unilever.

    We think our science is awesome – and we know students, teachers and parents think so too. That’s why we run an extensive Public Engagement and science communication programme, ranging from loans to schools of Moon Rocks, funding support for academics to inspire more young people, embedding public engagement in our funded grant programme, and running a series of lectures, travelling exhibitions and visits to our sites across the year.

    Ninety per cent of physics undergraduates say that they were attracted to the course by our sciences, and applications for physics courses are up – despite an overall decline in university enrolment.

     
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