#GRAVITATIONAL_WAVE#

GRAVITATIONAL_WAVE

Gravitational waves are ripples in the curvature of space time that are generated in certain gravitational interactions and propagate as waves outward from their source at the speed of light. The possibility of gravitational waves was discussed in 1893 by Oliver Heaviside using the analogy between the inverse- square law in gravitation and electricity. In 1905 Henri Poincare first proposed gravitational waves (ondes gravifiques) emanating from a body and propagating at the speed of light as being required by the Lorentz transformations. Predicted in 1916 by Albert Einstein on the basis of his theory of general relativity, gravitational waves transport energy as gravitational radiation, a form of radiant energy similar to electromagnetic radiation. Gravitational waves cannot exist under Newton's law of universal gravitation since that law is predicated on the assumption that physical interactions propagate at infinite speed. Gravitational-wave astronomy is a branch of observational astronomy which uses gravitational waves to collect observational data about sources of detectable gravitational waves such as binary star systems composed of white dwarfs, neutron stars, and black holes; and events such as supernovae, and the formation of the early universe shortly after the Big Bang.

On February 11, 2016, the LIGO and Virgo Scientific Collaboration announced that they had made the first observation of gravitational waves. The observation itself was made on 14 September 2015, using the Advanced LIGO detectors. The gravity waves originated from a pair of merging black holes After the initial announcement the LIGO instruments detected two more confirmed, and one potential, gravitational wave events. In August 2017, the two LIGO instruments, and the Virgo instrument, observed a fourth gravitational wave from merging black holes. Several other gravitational- wave detectors are planned or under construction.

In 2017, the Nobel Prize in Physics was awarded to Rainer Weiss, Kip Thorne and Barry Barish for their role in the detection of gravitational waves.

Neutrino Detection

Neutrino Detection

We can only detect the presence of a neutrino in our experiment if it interacts. Neutrinos interact in two ways charged-current interactions, where the neutrino converts into the equivalent charged lepton (e.g. inverse beta decay, ν+ p → n + e ) – the experiment detects the charged lepton; neutral-current interactions,

where the neutrino remains a neutrino, but transfers energy and momentum to whatever it interacted with we detect this energy transfer, either because the target recoils (e.g. neutrino-electron scattering, ν + e → ν + e) or because it breaks up (e.g. H + ν → p + n + ν). Charged-current interactions occur through the exchange of a W particle, neutral- current through the exchange of a Z .

In principle, charged-current interactions are easier to work with, because electrons and moons have characteristic signatures in particle detectors and are thus fairly easy to identify. They also have the advantage that they “flavor-tag” the neutrino if an electron is produced, it came from an electron-neutrino. However, there must be enough available energy to allow the mass of the lepton to be created from E = mc – this means that for very low- energy neutrinos (e.g. solar and reactor neutrinos) charged-current interactions are only possible for electron- neutrinos. Various different detector technologies have been used in neutrino experiments over the years, depending on the requirements of the particular study. Desirable features of a neutrino experiment will typically include several of the following:

low energy threshold, so that low-energy neutrinos can be detected and studied (especially for solar neutrinos); good angular resolution, so that the direction of the detected particle can be accurately reconstructed (especially for astrophysical  neutrinos) good particle identification, so that electrons and moons can be well separated (essential for oscillation experiments); good energy measurement, so that the energy of the neutrino can be reconstructed (useful for oscillation measurements and astrophysics); good time resolution, so that the time evolution of transient signals can be studied (essential for supernova neutrinos, and important for other astrophysical sources); charge identification, so that leptons and ant leptons can be separated (will be essential for neutrino factory experiments).

It is not possible to have all of these things in one experiment – for example, experiments with very low energy threshold tend not to have good angular or energy resolution. Neutrino physicists will select the most appropriate technology for the aims of their particular experiment.

#Physics_Alert

Hubble Just Confirmed The Largest Ocean World in Our Solar System And Its Not On Earth

The Ganymede ocean is believed to contain more water than Europa's,” says Olivier Witasse, a project scientist working on ESA’s future Jupiter Icy Moon Explorer (JUICE). “Six times more water in Ganymede’s ocean than in Earth's ocean, and three times more than Europa.”

In March of 2016, NASA's Hubble Space Telescope revealed the best evidence yet for an underground saltwater ocean on Ganymede, Jupiter's largest moon --larger than Mercury and not much smaller than Mars. Identifying liquid water is crucial in the search for habitable worlds beyond Earth and for the search for life, as we know it.

"This discovery marks a significant milestone, highlighting what only Hubble can accomplish," said John Grunsfeld, now retired assistant administrator of NASA's Science Mission Directorate at NASA Headquarters. "In its 25 years in orbit, Hubble has made many scientific discoveries in our own solar system. A deep ocean under the icy crust of Ganymede opens up further exciting possibilities for life beyond Earth."

Ganymede is the largest moon in our solar system and the only moon with its own magnetic field. The magnetic field causes aurorae, which are ribbons of glowing, hot electrified gas, in regions circling the north and south poles of the moon. Because Ganymede is close to Jupiter, it is also embedded in Jupiter's magnetic field. When Jupiter's magnetic field changes, the aurorae on Ganymede also change, "rocking" back and forth.

Just as Saturn's moon, Dione is perennially overshadowed by Enceladus and Titan, Ganymede's fame is eclipsed by its sister ocean world, Europa, slated for flybys by NASA’s Europa Clipper mission in the 2020s.

Ganymede's cycles of auroral activity on the surface, detected by the Hubble Space Telescope, reveal oscillations in the moon’s magnetic field best explained by the internal heat-generating tidal sloshing of a huge ocean hundreds of kilometers below the surface.

JUICE will fly by the moons at distances between 1000 and 200 kilometers, orbiting Ganymede for nine months, with the latter four months at an altitude of about 500 km. While the oceans of Jupiter's moons are likely buried at significant depth below their icy crusts, radar will be able to help piece together clues as to their complex evolution.

For example, it will explore Europa's potentially active regions and be able to distinguish where the composition changes, such as if there are local, shallow reservoirs of water sandwiched between icy layers. It will be able to find 'deflected' subsurface layers, which will help to determine the tectonic history of Ganymede in particular.

The distinction between ice and non-ice materials will also be possible, perhaps enabling the detection of buried cyrovolcanic reservoirs. On Callisto, radar profiling will help to understand the evolution of large impact crater structures that are apparent on the surface, which typically display multiple rims and a central dome. Their nature provides clues to the nature of the surface and subsurface at the time of the impact.

"Seeing into the subsurface of these moons with radar will be like looking back in time, helping us to determine the geological evolution of these enigmatic worlds," says Witasse.

On the way, reports NASA the space craft will make several flybys of another potentially ocean-bearing Jovian moon, Callisto. “We think that Callisto also harbors a subsurface ocean, but the available data is unclear,” Witasse says. “What we hope to do is to check whether there is an ocean or not and if yes, at which depth.”

An easy to build Desktop Muon Detector

On airplanes I am often asked about the blinking metallic device connected to my laptop’s USB port. To assuage any suspicions, I explain that I’m a third-year physics graduate student at MIT and that the little device is actually a cosmic-ray-muon detector.

Over the past few years that detector has evolved from an instrument for a multimillion-dollar experiment to a device that high school and college physics students can construct themselves. The goal of a new program called CosmicWatch is to encourage students to build the detectors, which weigh in at less than 100 g and cost less than $100, and explore the effects of the particles that are constantly raining down on Earth’s surface.

My foray into muon-detector construction began when my supervisor, Janet Conrad, and I were tasked with assisting in an upgrade of the IceCube Neutrino Observatory, a cubic-kilometer particle detector built deep in the Antarctic glacier near the South Pole. IceCube has the ability to detect the occasional astrophysical neutrino from phenomena such as gamma-ray bursts, supernovae, and black holes (see Physics Today, June 2014, page 30). On a far more regular basis, the observatory sees a drizzle of cosmic-ray muons. The charged particles are a decay product of the particles that form when high-energy cosmic rays collide with molecules in Earth’s atmosphere. Muons are extremely penetrating, which enables a small fraction of them to travel the more than 1.5 km through the Antarctic ice to the IceCube detector.

As part of IceCube’s low-energy upgrade, called PINGU, Conrad and I planned to build optically isolated scintillator targets and place them throughout the detector. If a charged particle passed through the plastic scintillator, it would emit light that we could collect using a silicon photomultiplier. Whenever the photomultiplier registered enough light at the same time as a triggered event in IceCube, we would know that the particle that triggered IceCube also passed through our target; we could use that information to help determine the particle’s location and trajectory. Conrad and I called the targets muon-tagging optical modules.

The first detector prototype was very simple. I filled a small PVC pipe with liquid scintillator and inserted some circuitry and a silicon photomultiplier. Two wires penetrated the PVC cap: one for biasing the photomultiplier and one for outputting data to an oscilloscope. It was not a great design. The scintillator leaked around the cap threads, and the device looked more like a homemade bomb from a cheap movie than a particle detector. But hey, it worked. We could immediately see the signals produced from cosmic-ray muons passing through the scintillator.

The next iteration of the detector did away with the liquid scintillator and PVC piping. We found some centimeter-thick plastic scintillator panels from an old cosmic-ray experiment and built a proper light-tight enclosure from some scrap aluminum found in the machine shop. I also came across an Arduino and high-speed operational amplifiers in the MIT electronics recycling pile. Those parts, along with some pulse-shaping circuitry, resulted in a simple data acquisition system. We were able to record data directly to a computer as well as on the oscilloscope. The cost of the whole device was less than $100, with the photomultiplier accounting for the bulk of the expense.

In a June 2016 paper, we described exactly how we built the detector and provided a website link that contained all the information about our circuit boards, computer-aided design drawings, and Arduino software. Within a few days after submission to the arXiv, emails began pouring in. I was stunned to see that many of them came not from particle astrophysicists but from high school students with their own ideas for measurements or improvements. An MIT student, Mgcini Keith Phuthi, read the paper and modified our design so that his detector would communicate with his laptop through Bluetooth.

Phuthi and several other undergraduate students joined our little group to set up a small production facility. Once we started working with the new students, it was obvious that building the detector touched on several important skills. The students learned about shop practices, working with printed circuit boards, and programming microcontrollers.

We set out to see if our device would be suitable for MIT’s Junior Lab course, a class on physics lab work for undergrads. In the process, we stumbled on another use for the detector. We approached a cabinet in the corner of one lab, and as soon as we were within a meter of it, the count rate exploded; there was obviously something radioactive in there. We had a pretty good idea that it must be coming from some active gamma-ray source. One by one we took each radioactive isotope out of the cabinet and brought it close to the detector. We each had our own guess (I was thinking it would be a new cobalt-60 source), but it turned out the culprit was a large jar partially filled with dark gray powder: uranium salts. Not something I thought you could store in an undergraduate lab.

We also found something interesting in Conrad’s office. On the wall, next to negatives from a bubble chamber and a lead-glass calorimeter, was a bright orange ceramic plate. It turns out that decades ago, Fiesta dinnerware was glazed with a depleted uranium–based coating. Uranium has a very long half-life, and many of the decay daughters emit radiation in the form of gamma rays. I was surprised to see so much radiation coming from dinnerware!

Over the next few weeks, we received many emails from students who wanted to build detectors for high-altitude balloon missions. The appeal of our detector stemmed from the fact that it was small and could be battery (or USB) powered, with data stored locally in a Raspberry Pi. To help with such projects, we decided to redesign the detector one more time to make it lighter and easier to build.

Our latest detector weighs 68 g (the model in our 2016 paper was about 10 times as heavy), draws less than a watt of power, and has an improved low-signal response. The design is so simple that it should take students just a few hours to build a full detector from scratch.

The detector is starting to gain international interest. Recently I started working with Katarzyna Frankiewicz, a PhD student from the National Center for Nuclear Research (NCBJ) in Poland. She and a colleague, Paweł Przewłocki, are working on improving the software side of the detector; they created a website for project information and data acquisition. And in collaboration with NCBJ’s education and training division, Frankiewicz and Przewłocki are about to start a new educational program for high school students using 20 detectors that NCBJ and MIT built together.

Now that we have a unique detector, an international group of enthusiastic scientists, and lots of experience helping students build desktop muon detectors, we are ready to launch the CosmicWatch program. This summer our goal is to produce the first set of 100 kits, which we will use to teach a class on particle detection and astrophysics for incoming students at the Wisconsin IceCube Particle Astrophysics Center and NCBJ. Some of those detectors will be sent to local high schools for teachers to use in demonstrations. Instructors could measure the angular dependence of the cosmic-ray-muon flux, demonstrate relativistic effects with a high-altitude measurement, and conduct muon tomography. Over the winter we will move to the next generation of detectors, which will have single-photon detection and hardware-coincidence capabilities, an SD card reader, and environmental sensors.

We are not alone in the community of cosmic-ray-muon programs. Upon developing the detector, we discovered that several other groups are working toward a similar goal. We are hoping to collaborate with them to expand on what we’ve designed. As the project grows, we hope to be able to use the detectors for useful physics measurements. One idea is to install the detectors on planes and ships to map out cosmic-ray fluxes throughout the world. Of course, that would require further R&D and therefore more funding.

The airplane conversations regarding my strange little USB device typically end here. But I’m able to capture my questioners’ attention at least one last time when I show them the measurement of the cosmic-ray-muon rate, shown in the graph below. The beauty of a good muon detector—even a small, cheap one—is that it transforms a fundamental but invisible aspect of nature into something we can see.

The design of a simple, inexpensive cosmic-ray-muon detector has led to an international outreach program.

ESO Observations Show First Interstellar Asteroid is Like Nothing Seen Before VLT reveals dark, reddish and highly-elongated object

For the first time ever astronomers have studied an asteroid that has entered the Solar System from interstellar space. Observations from ESO’s Very Large Telescope in Chile and other observatories around the world show that this unique object was traveling through space for millions of years before its chance encounter with our star system. It appears to be a dark, reddish, highly-elongated rocky or high-metal-content object. The new results appear in the journal Nature on 20 November 2017.
On 19 October 2017, the Pan-STARRS 1 telescope in Hawai`i picked up a faint point of light moving across the sky. It initially looked like a typical fast-moving small asteroid, but additional observations over the next couple of days allowed its orbit to be computed fairly accurately. The orbit calculations revealed beyond any doubt that this body did not originate from inside the Solar System, like all other asteroids or comets ever observed, but instead had come from interstellar space. Although originally classified as a comet, observations from ESO and elsewhere revealed no signs of cometary activity after it passed closest to the Sun in September 2017. The object was reclassified as an interstellar asteroid and named 1I/2017 U1.
“We had to act quickly,” explains team member Olivier Hainaut from ESO in Garching, Germany. “`Oumuamua had already passed its closest point to the Sun and was heading back into interstellar space.”
ESO’s Very Large Telescope was immediately called into action to measure the object’s orbit, brightness and colour more accurately than smaller telescopes could achieve. Speed was vital as `Oumuamua was rapidly fading as it headed away from the Sun and past the Earth’s orbit, on its way out of the Solar System. There were more surprises to come.
Combining the images from the FORS instrument on the VLT using four different filters with those of other large telescopes, the team of astronomers led by Karen Meech (Institute for Astronomy, Hawai`i, USA) found that `Oumuamua varies dramatically in brightness by a factor of ten as it spins on its axis every 7.3 hours.
Karen Meech explains the significance: “This unusually large variation in brightness means that the object is highly elongated: about ten times as long as it is wide, with a complex, convoluted shape. We also found that it has a dark red colour, similar to objects in the outer Solar System, and confirmed that it is completely inert, without the faintest hint of dust around it.”
These properties suggest that `Oumuamua is dense, possibly rocky or with high metal content, lacks significant amounts of water or ice, and that its surface is now dark and reddened due to the effects of irradiation from cosmic rays over millions of years. It is estimated to be at least 400 metres long.
Preliminary orbital calculations suggested that the object had come from the approximate direction of the bright star Vega, in the northern constellation of Lyra. However, even travelling at a breakneck speed of about 95 000 kilometres/hour, it took so long for the interstellar object to make the journey to our Solar System that Vega was not near that position when the asteroid was there about 300 000 years ago. `Oumuamua may well have been wandering through the Milky Way, unattached to any star system, for hundreds of millions of years before its chance encounter with the Solar System.
Astronomers estimate that an interstellar asteroid similar to `Oumuamua passes through the inner Solar System about once per year, but they are faint and hard to spot so have been missed until now. It is only recently that survey telescopes, such as Pan-STARRS, are powerful enough to have a chance to discover them.
“We are continuing to observe this unique object,” concludes Olivier Hainaut, “and we hope to more accurately pin down where it came from and where it is going next on its tour of the galaxy. And now that we have found the first interstellar rock, we are getting ready for the next ones!”
[1] The Pan-STARRS team’s proposal to name the interstellar objet was accepted by the International Astronomical Union, which is responsible for granting official names to bodies in the Solar System and beyond. The name is Hawaiian and more details are given here. The IAU also created a new class of objects for interstellar asteroids, with this object being the first to receive this designation. The correct forms for referring to this object are now: 1I, 1I/2017 U1, 1I/`Oumuamua and 1I/2017 U1 (`Oumuamua). Note that the character before the O is an okina. So, the name should sound like H O u mu a mu a. Before the introduction of the new scheme, the object was referred to as A/2017 U1.
This research was presented in a paper entitled “A brief visit from a red and extremely elongated interstellar asteroid”, by K. Meech et al., to appear in the journal Nature on 20 November 2017.
The team is composed of Karen J. Meech (Institute for Astronomy, Honolulu, Hawai`i, USA [IfA]) Robert Weryk (IfA), Marco Micheli (ESA SSA-NEO Coordination Centre, Frascati, Italy; INAF–Osservatorio Astronomico di Roma, Monte Porzio Catone, Italy), Jan T. Kleyna (IfA) Olivier Hainaut (ESO, Garching, Germany), Robert Jedicke (IfA) Richard J. Wainscoat (IfA) Kenneth C. Chambers (IfA) Jacqueline V. Keane (IfA), Andreea Petric (IfA), Larry Denneau (IfA), Eugene Magnier (IfA), Mark E. Huber (IfA), Heather Flewelling (IfA), Chris Waters (IfA), Eva Schunova-Lilly (IfA) and Serge Chastel (IfA).
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 and by Australia as a strategic partner. 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 and its world-leading Very Large Telescope Interferometer as well as two survey telescopes, VISTA working in the infrared and the visible-light VLT Survey Telescope. ESO is also a major partner in two facilities on Chajnantor, APEX and ALMA, the largest astronomical project in existence. And on Cerro Armazones, close to Paranal, ESO is building the 39-metre Extremely Large Telescope, the ELT, which will become “the world’s biggest eye on the sky”.

Night Being "Lost" to Artificial Light

A study of pictures of Earth by night has revealed that artificial light is growing brighter and
more extensive every year.

Between 2012 and 2016, the planet's artificially lit outdoor area grew by more than 2% per
year. Scientists say a "loss of night" in many countries is having negative consequences for
"flora, fauna, and human well-being".
A team published the findings in the journal Science Advances.
Their study used data from a Nasa satellite radiometer - a device designed specifically to
measure the brightness of night time light.It showed that changes in brightness over time
varied greatly by country. Some of the world's "brightest nations", such as the US and Spain, remained the same. Most nations in South America, Africa and Asia grew brighter.

Only a few countries showed a decrease in brightness, such as Yemen and Syria -
both experiencing warfare. The nocturnal satellite images - of glowing coastlines and
spider-like city networks - look quite beautiful but artificial lighting has unintended
consequences for human health and the environment.

Let the Sun go down

• In 2016, the American Medical Association officially recognised the "detrimental 
• effects of poorly designed, high-intensity LED lighting", saying it encouraged 
• communities to "minimise and control blue-rich environmental lighting by using 
• the lowest emission of blue light possible to reduce glare.
• The sleep-inducing hormone melatonin is particularly sensitive to blue light.
• A recent study published in the journal Nature revealed that artificial light was a threat 
• To crop pollination - reducing the pollinating activity of nocturnal insects.
• Research in the UK revealed that trees in more brightly lit areas burst their buds 
• up to a week earlier than those in areas without artificial lighting.
• A study published earlier this year found that urban light installations 
• "dramatically altered" the behaviour of nocturnally migrating birds.

Lead researcher Christopher Kyba from the German Research Centre for Geoscience 

in Potsdam said that the introduction of artificial light was "one of the most dramatic 

physical changes human beings have made to our environment".He and his colleagues
had expected to see a decrease in brightness in wealthy cities
and industrial areas as they switched from the orange glow of sodium lights to more
energy-efficient LEDs the light sensor on the satellite is not able to measure the bluer
part of the spectrum of light that LEDs emit."I expected that in wealthy countries -
like the US, UK, and Germany - we'd see overall decreases in light, especially in
brightly lit areas," he told BBC News. "Instead we see countries like the US staying
the same and the UK and Germany becoming increasingly bright."
Since the satellite sensor does not "see" the bluer light that humans can see, the
increases in brightness that we experience will be even greater than what the
researchers were able to measure.
Prof Kevin Gaston from the University of Exeter told BBC News that humans were
 "imposing abnormal light regimes on ourselves".

'Less light, better vision'

"You now struggle to find anywhere in Europe with a natural night sky - without that
skyglow we're all familiar with."
Prof Gaston added that he found the continuing increase in light pollution curious.
"Usually," he explained, "when we think of how humanity messes with environment,
 it's a costly thing to fix or reverse. "For light, it's just a case of directing it where
we need it and not wasting it where we don't."
Dr Kyba said that we could make our urban areas much dimmer and not actually cause
 any problems for visibility. "Human vision relies on contrast, not the amount of light,"
 he explained. "So by reducing contrast outdoors - avoiding glaring lamps -
it is actually possible to have improved vision with
"That could mean big energy savings - but our data show that on a national and
global scale, this is not the direction we are heading."

h less light.