Gravitational wave detector LIGO is back online after 3 years of upgrades – how the world’s most sensitive yardstick reveals secrets of the universe

 After a three-year hiatus, scientists in the U.S. have just turned on detectors capable of measuring gravitational waves - tiny ripples in space itself that travel through the universe.

Unlike light waves, gravitational waves are nearly unimpeded by the galaxies, stars, gas and dust that fill the universe. This means that by measuring gravitational waves, astrophysicists like me can peek directly into the heart of some of these most spectacular phenomena in the universe.

Since 2020, the Laser Interferometric Gravitational-Wave Observatory - commonly known as LIGO – has been sitting dormant while it underwent some exciting upgrades. These improvements will significantly boost the sensitivity of LIGO and should allow the facility to observe more-distant objects that produce smaller ripples in spacetime.

By detecting more events that create gravitational waves, there will be more opportunities for astronomers to also observe the light produced by those same events. Seeing an event through multiple channels of information, an approach called multi-messenger astronomy, provides astronomers rare and coveted opportunities to learn about physics far beyond the realm of any laboratory testing.

Ripples in spacetime

According to Einstein’s theory of general relativity, mass and energy warp the shape of space and time. The bending of spacetime determines how objects move in relation to one another – what people experience as gravity.

Gravitational waves are created when massive objects like black holes or neutron stars merge with one another, producing sudden, large changes in space. The process of space warping and flexing sends ripples across the universe like a wave across a still pond. These waves travel out in all directions from a disturbance, minutely bending space as they do so and ever so slightly changing the distance between objects in their way.

Even though the astronomical events that produce gravitational waves involve some of the most massive objects in the universe, the stretching and contracting of space is infinitesimally small. A strong gravitational wave passing through the Milky Way may only change the diameter of the entire galaxy by three feet (one meter).

The first gravitational wave observations

Though first predicted by Einstein in 1916, scientists of that era had little hope of measuring the tiny changes in distance postulated by the theory of gravitational waves.

Around the year 2000, scientists at Caltech, the Massachusetts Institute of Technology and other universities around the world finished constructing what is essentially the most precise ruler ever built – the LIGO observatory.

LIGO is comprised of two separate observatories, with one located in Hanford, Washington, and the other in Livingston, Louisiana. Each observatory is shaped like a giant L with two, 2.5-mile-long (four-kilometer-long) arms extending out from the center of the facility at 90 degrees to each other.

To measure gravitational waves, researchers shine a laser from the center of the facility to the base of the L. There, the laser is split so that a beam travels down each arm, reflects off a mirror and returns to the base. If a gravitational wave passes through the arms while the laser is shining, the two beams will return to the center at ever so slightly different times. By measuring this difference, physicists can discern that a gravitational wave passed through the facility.

LIGO began operating in the early 2000s, but it was not sensitive enough to detect gravitational waves. So, in 2010, the LIGO team temporarily shut down the facility to perform upgrades to boost sensitivity. The upgraded version of LIGO started collecting data in 2015 and almost immediately detected gravitational waves produced from the merger of two black holes.

Since 2015, LIGO has completed three observation runs. The first, run O1, lasted about four months; the second, O2, about nine months; and the third, O3, ran for 11 months before the COVID-19 pandemic forced the facilities to close. Starting with run O2, LIGO has been jointly observing with an Italian observatory called Virgo.

Between each run, scientists improved the physical components of the detectors and data analysis methods. By the end of run O3 in March 2020, researchers in the LIGO and Virgo collaboration had detected about 90 gravitational waves from the merging of black holes and neutron stars.

The observatories have still not yet achieved their maximum design sensitivity. So, in 2020, both observatories shut down for upgrades yet again.

International Conference on Gravitational Waves

visit:gravity.sfconferences.com

Nomination link: https://x-i.me/granom

#gravitational#LIGO#stars#detector#observatories

Gravity can transform into light, mind-bending physics paper suggests

 Gravity can turn itself into light, but only if space-time behaves in just the right way, a research team has found.

Under normal circumstances, you cannot get something from nothing. Specifically, the Standard Model of particle physics, the reigning theory that explains the subatomic zoo of particles, usually forbids the transformation of massless particles into massive ones. While particles in the Standard Model constantly change into each other through various reactions and processes, the photon — the massless carrier of light — cannot normally change into other particles. But if the conditions are just right, it is possible — for example, when a photon interacts with a heavy atom, it can spontaneously split off to become an electron and a positron, both of which are massive particles.

With this well-known example in hand, a team of theoretical physicists, writing in a paper posted March 28 to the preprint database arXiv(opens in new tab), asked if gravity itself could transform into other particles. We normally think of gravity through the lens of general relativity, where bends and warps in space-time influence the motion of particles. In that picture, it would be very difficult to imagine how gravity could create particles. But we can also view gravity through a quantum lens, picturing the gravitational force as carried by countless invisible particles called gravitons. While our picture of quantum gravity is far from complete, we do know that these gravitons would behave like any other fundamental particle, including potentially transforming.

To test this idea, the researchers studied the conditions of the extremely early universe. When our cosmos was very young, it was also small, hot and dense. In that youthful cosmos, all forms of matter and energy were ramped up to unimaginable scales, far greater than even our most powerful particle colliders are capable of achieving. 

The researchers found that in this setup, gravitational waves — ripples in the fabric of space-time generated by collisions between the most massive cosmic objects — play an important role. Normally, gravitational waves are exceedingly weak, capable of nudging an atom through a distance less than the width of its own nucleus. But in the early universe, the waves could have been much stronger, and that  could have seriously influenced everything else.

Those early waves would have sloshed back and forth, amplifying themselves. Anything else in the universe would have gotten caught up in the push and pull of the waves, leading to a resonance effect. Like a kid pumping their legs at just the right time to send a swing higher and higher, the gravitational waves would have acted as a pump, driving matter into tight clumps over and over again.

The researchers found that in general, this process is rather inefficient. The early universe was also expanding, so the standard patterns of gravitational waves would not have lasted long. However, the team found that if the early universe contained enough matter that the speed of light was reduced (the same way light travels more slowly through a medium such as air or water), the waves could have stuck around long enough to really get things going, generating floods of extra photons.

Physicists do not yet fully understand the complicated, tangled physics of the early universe, which was capable of achieving feats never observed since. This new research adds one more strand to the rich tapestry: the capability for gravity to create light. That radiation would presumably then go on to influence the formation of matter and the evolution of the universe, so working out the full implications of this surprising process could lead to new revolutions in our understanding of the earliest moments of the cosmos.

International Conferences on Gravitational Waves

visit:https://gravitational-waves.sfconferences.com

Nomination link:https://x-i.me/granom

Registration link: https://x-i.me/grareg2

#gravitationalradiation#gravitytolight#gravitywaveconversion#lightfromgravity#quantumgravity 

To Measure Earth’s Water, NASA Satellite Relies on a Ka-band Radar Interferometer

 

Using radar technology onboard a satellite, NASA’s latest launch is mapping the planet’s water supply and helping combat climate change.

NASA has successfully launched the Surface Water and Ocean Topography (SWOT) mission, a low-earth orbit satellite built to measure the interactions of the Earth’s oceans, rivers, and lakes. NASA says this feat represents a “quantum leap” in progressing knowledge of the Earth’s water supply. Working among the subsystems and instruments onboard the payload is the Ka-band Radar Interferometer (KaRIn): a new instrument capable of measuring the water level with up to a centimeter of accuracy, all from space.

The SWOT mission is not the first time NASA has shown interest in characterizing the Earth in an effort to combat climate change. Earlier this year, the EMIT mission was launched to determine the mineral content of dust clouds. The SWOT mission does, however, represent a major advancement in effective ranging from space and developing a planetary-level climate model. In this article, we'll discuss the technology behind the SWOT mission and KaRIn and how it gives climate scientists a new tool for understanding the planet.

New Data Every 21 Days

When it comes to developing a model for climate change, scientists need accurate data on a planetary scale. Several key indicators such as global tide levels are required, and oftentimes the lack of information can lead to an inaccurate model. This becomes especially true for systems involving freshwater, where fewer traditional resources are allocated to measurements.

To increase data availability, NASA launched a joint effort with the French space agency CNES to survey the planet with a considerably broader view. Following a successful launch, the spacecraft is currently in a six-month calibration and validation phase, after which it will begin sending over one terabyte of data per day. In addition to the massive amount of data, the SWOT mission’s 21-day repeat orbit ensures that new data can constantly be gathered.

Using Radio Waves to Measure Sea Levels

One of the greatest engineering feats onboard the SWOT spacecraft, the KaRIn uses Ka-band (26.5 GHz–40 GHz) radio waves to detect the distance from the craft to the surface with up to 1 cm of resolution. The instrument closely resembles synthetic aperture radar (SAR), which uses the motion of the transceiver to simulate a large antenna with a narrow beamwidth.

This narrow beamwidth, combined with the stereoscopic vision provided by two antennas, allows the instrument to accurately determine the distance to the surface, which in turn is used to determine the water level at one point. By repeating this measurement over time and using existing methods to determine the satellite’s orbiting altitude, an accurate model of the water’s motion may be drawn to identify currents, eddies, or changes in water level.

 

Learning More About the Blue Planet

As the SWOT mission continues and the spacecraft begins collecting and transmitting data, it will be interesting to see if any issues arise with the craft or the KaRIn instrument. The signal processing, for example, is quite cumbersome for SAR and could introduce points of error over time or prove to be a source of inefficiency. In addition, the high level of integration may introduce numerous points of failure if one subsystem begins to fail.

Despite the fact that it may be too early to call the entire mission a perfect success, the advances made by NASA and CNES are a remarkable feat of engineering, and the data produced by SWOT is expected to be invaluable for the future of climate science.

International Conferences on Gravitational Waves

visit:https://gravitational-waves.sfconferences.com/

Nomination link:https://x-i.me/granom

Registration link:https://x-i.me/grareg2

New type of black hole merger may have just been observed

 More than seven years have passed since the first detection of gravitational waves emitted by the merger of two black holes, and during this time, researchers have recorded several dozen other such events. Analysis of the radiation allowed scientists to deduce the masses of the merging black holes and the trajectories of their movement prior to these collisions.

Until recently, physicists believed that in all such events, pairs of black holes originated from binary stars whose gravitational collapse was the last stage of their evolution. However, in a recent study published in Nature Astronomy, researchers from Friedrich-Schiller-Universität Jena in Germany and INFN sezione di Torino, Italy have performed a more detailed analysis of the gravitational wave signal dubbed, GW190521, and found that in this particular case, the more likely scenario was the collision of two black holes that had formed independently, and which were not gravitationally bound to each other before the collision.

The loudest collision

The GW190521 signal is especially interesting because it corresponds to the merger of the most massive pair of black holes ever recorded. A previous analysis of the radiation caught by the gravitational wave observatories LIGO and Virgo showed that in this event, the waves were emitted when black holes with masses around 85 and 66 solar masses merged, resulting in a black hole 142 times heavier than our Sun, and the remaining nine solar masses were radiated out as the gravitational wave energy.

Another reason this signal is interesting is that the deduced black holes’ masses do not agree the existing theory of stellar evolution, which claims that a sufficiently heavy star should end its life in a supernova explosion without leaving a black hole behind, meaning the existence of binary black hole with masses greater than 50 solar masses is not expected.

The new analysis of GW190521 has led to similar estimates of the black hole’s masses though with different movement trajectories, close to the free motion of the two before the collision occurred, indicating that the pair may not have formed from a binary star.

“People speculate that they can be second generation black holes, the ones that are already the outcome of mergers of black holes that had formed by gravitational collapse in binary systems,” said Alessandro Nagar, a researcher at INFN and one of the study’s authors, in an e-mail. “But this is at the moment uncertain.”

The comparison of the new analysis with the previous one implies odds of approximately 24,300 to 1 in favor of their interpretation against the binary star scenario.

To confirm their conclusions, the physicists say they are going to improve the analysis further by exploring the impact of black hole rotation on the gravitational waves spectrum and systematically comparing their analytical results with numerical simulations. And, of course, future observations of black hole mergers will help scientists better understand all the possible mechanisms and scenarios for this incredible physical process.

“If more [similar mergers] will be detected in the future, it is likely that we will be able to improve our current knowledge about formation channels of black hole binaries,” concluded Nagar. “Our study is simply suggesting that a proposed merging scenario is compatible with data, actually more compatible that standard interpretations. Future will tell whether this is just a coincidence, or it is the indication of a deeper truth that waits to be discovered in full.”

International Conference on Gravitational Waves

visit:https://gravitational-waves.sfconferences.com/

Nomination link:https://x-i.me/granom

Registration link:https://x-i.me/grareg2

Weak Gravitational Lensing Tests the Cosmological Model

An international team of cosmologists and astrophysicists, led by Princeton University and the astronomical communities of Japan and Taiwan, and including researchers from Carnegie Mellon University, used precision measurements of the cosmological model of the universe to find that the universe is slightly less “clumpy” than it should be based on the cosmological standard model. Their findings, which could lead to a better understanding of dark matter, use data from the Hyper Suprime-Cam’s year 3 results and are contained in a series of five papers, available on arXiv.

Dark energy and dark matter make up 95% of the universe. Since dark matter can’t be seen, it can’t be measured directly. Instead, researchers must derive information by measuring its effects on other visible objects like galaxies and stars.

One way this is done is by measuring a phenomenon called weak gravitational lensing. As the universe has expanded since the Big Bang, dark matter and galaxies have been drawn together by gravity, resulting in a clumpy distribution of matter throughout the universe. These clumps of matter exert a gravitational pull that bends light as it travels from distant galaxies toward Earth. As a result, when galaxies are observed by telescopes, the resulting images are slightly distorted. By measuring these distortions, researchers can learn more about the distribution of matter in the universe and the nature of dark matter and dark energy.

The new papers use data from the Hyper Suprime-Cam (HSC) sky survey, a wide-field imaging survey carried out by Japan’s 8.2-meter Subaru Telescope on the summit of Maunakea in Hawaii. The data set includes the measurements for 25 million galaxies as they appeared billions of years ago. With measurements from so many galaxies, researchers were able to create a very precise analysis of weak gravitational lensing using a combination of sophisticated computer simulations and observations from the HSC.

They found that the value for the clumpiness of the universe’s dark matter, a number referred to as S8, to be 0.78. While this number aligns with what other recent gravitational lensing surveys have found, it does not align with the S8 value of 0.83 derived from the radiation emitted in the earliest days of the universe called the cosmic microwave background (CMB).

The results suggest that the differences between these two numbers may not be coincidental. It could indicate that there is an unrecognized error in one of the two measurements or that the standard cosmological model, called the Lambda Cold Dark Matter Model, might be incomplete.

“The HSC weak lensing group has done a meticulous job of ensuring that our weak lensing results are robust, and there is about a 5% chance that the results disagree with the CMB only by chance,” said Rachel Mandelbaum(opens in new window), professor of physics and member of the McWilliams Center for Cosmology(opens in new window) at Carnegie Mellon, and a member of the HSC collaboration. “It will be important to confirm this result with future data sets that can make the measurement even more precisely and to continue to refine our understanding of potential systematic biases. But this result is a tantalizing hint of potential physics beyond the Lambda Cold Dark Matter cosmological paradigm.”

Three different analysis techniques were used on the HSC weak gravitational lensing data. The development and validation of the data catalog was led by Xiangchong Li while he was a doctoral student at the University of Tokyo. The analyses were blinded, so the researchers couldn’t compare results with each other or even view their results until they had finished all their sanity checks on the analysis. After revealing the results, they were ecstatic to see that all methods yielded the same conclusions about S8. 

Li, who is now a Carnegie Mellon postdoctoral fellow working with Mandelbaum, led the real space analysis. This analysis established how the images of galaxies have been lensed by matter, including dark matter, by measuring the correlations of galaxy shapes from different time points. 

Other papers used Fourier space analysis, which maps galaxy shapes and measures the power spectrum of the dark matter density field in Fourier space, and 3x2pt analysis, which constrains the cosmological constant by combining the galaxy shape data collected by HSC with the BOSS density distribution of foreground galaxies. 

“Real space and Fourier space analyses are sensitive to the information of the matter distribution at different scales, and they have different responses to systematic errors. Doing two independent blinded analyses is an important test to validate the robustness of the cosmology constraint,” said Li. “3x2pt analysis includes observables from BOSS galaxy density distribution, which provides independent information to the measurement.”

Much of the analysis of the HSC data relied on methods developed by Tianqing Zhang, a physics graduate student at Carnegie Mellon. One was a statistically principled method(opens in new window) to propagate the uncertainty in redshift (or distance) measurements of the HSC galaxies. The second method(opens in new window) establishes the impact of the point spread function, which describes the combined effect of atmospheric turbulence and telescope optics and detector on weak lensing observations. 

“Our work is the ‘last line of defense’ to shield the cosmological results from the impact of the variables included in point spread function,” said Zhang. “Although the HSC enjoys one of the best atmospheric conditions on planet Earth and is equipped with a state-of-the-art optical and detector system, this problem is still a big challenge.” 

Information about all five papers and the HSC public data release is available online

International Conference on Gravitational Waves

visit:https://gravitational-waves.sfconferences.com/

Nomination link :https://x-i.me/granom

Registration link :https://x-i.me/grareg2

Hidden tide in Earth's magnetospheric 'plasma ocean' revealed in new study

The moon exerts a previously unknown tidal force on the "plasma ocean" surrounding Earth's upper atmosphere, creating fluctuations that are similar to the tides in the oceans, a new study suggests.

In the study, published Jan. 26 in the journal Nature Physics(opens in new tab), scientists used more than 40 years of data collected by satellites to track the minute changes in the shape of the plasmasphere, the inner region of Earth's magnetosphere, which shields our planet from solar storms and other types of high-energy particles. 

The plasmasphere is a roughly doughnut-shaped blob of cool plasma that sits on top of Earth's magnetic field lines, just above the ionosphere, the electrically charged part of the upper atmosphere. The plasma, or ionized gas, in the plasmasphere is denser than the plasma in the outer regions of the magnetosphere, which causes it to sink to the bottom of the magnetosphere. The boundary between this dense sunken plasma and the rest of the magnetosphere is known as the plasmapause. 

"Given its cold, dense plasma properties, the plasmasphere can be regarded as a 'plasma ocean,' and the plasmapause represents the 'surface' of this ocean," the researchers wrote in the paper. The moon's gravitational pull can distort this "ocean," causing its surface to rise and fall like the ocean tides.

The moon is already known to exert tidal forces on Earth's oceans, crust, near-ground geomagnetic field and the gas within the lower atmosphere. However, until now, nobody had tested to see if there was a tidal effect on the plasmasphere. 

To investigate this question, the researchers analyzed data from more than 50,000 crossings of the plasmasphere by satellites belonging to 10 scientific missions, including NASA's Time History of Events and Macroscale Interactions during Substorms (THEMIS) mission. The satellites' sensors are capable of detecting minute changes in the concentrations of plasma, which allowed the team to map out the exact boundary of the plasmapause in greater detail than ever before.   

The satellite crossings occurred between 1977 and 2015, and during this period, there were four complete solar cycles. This information allowed the team to factor in the role of solar activity on Earth's magnetosphere. Once the sun's influence was accounted for, it started to become clear that fluctuations in the shape of the plasmapause followed daily and monthly patterns that were very similar to the ocean's tides, indicating that the moon was the most likely cause of the plasma tides. 

The researchers are unsure exactly how the moon causes the plasma tides, but their current best guess is that the moon's gravity causes perturbations in Earth's electromagnetic field. But further research is needed to tell for sure.

The team thinks this previously unknown interaction between Earth and the moon could help researchers understand other parts of the magnetosphere in greater detail, such as the Van Allen radiation belts, which capture highly energetic particles from solar wind and trap them in the outer magnetosphere.

"We suspect that the observed plasma tide may subtly affect the distribution of energetic radiation belt particles, which are a well-known hazard to space-based infrastructure and human activities in space," the researchers wrote. Better understanding the tides could therefore help to improve work in these areas, they added.

International Conferences on Gravitational Waves

visit:https://gravitational-waves.sfconferences.com/

Nomination link : https://x-i.me/granom Registration link : https://x-i.me/grareg2

LIGO India, a major breakthrough initiative to probe Gravitational Wave

 On the path of establishing India’s efforts towards becoming a developed nation, the central government has given a nod to set up Laser Interferometer Gravitational-Wave Observatory (LIGO), the country’s biggest facility to probe the universe through the detection of gravitational waves. Science and Technology is a key aspect of the progress and development of any nation and LIGO is one such initiative in realising a major scientific breakthrough in India.

Gravitational waves are ripples in space-time created by some of the Universe’s most destructive and energetic processes or produced by cataclysmic events such as colliding black holes, massive stars exploding and colliding neutron stars. In his general theory of relativity, Albert Einstein predicted the existence of gravitational waves, which encapsulates the understanding of how gravitation works.

LIGO- World’s most powerful observatory

LIGO is the world’s most powerful observatory and a large-scale Physics experiment carried out to detect Gravitational waves. It is a planned Gravitational-Wave Observatory that will operate as part of a worldwide network to capture and measure gravitational waves coming straight from space. Gravitational waves were first discovered in 2015 by two LIGOs based in the US and two years later, in 2017, this experiment of the century-old theory received the Nobel Prize in Physics.

With the central government’s final go-ahead and approved budget of Rs 2,600 crore, LIGO-India will be built in the Hingoli district of Maharashtra, which is about 450 km east of Mumbai. Hingoli was selected as the suitable location as it is not prone to tectonic activities and where lasers can be captured without any disruptions to find out if there is any gravitational wave or not. It was competing with two other sites, in Rajasthan and Madhya Pradesh. LIGO-India gained in-principle permission from the Indian government in February 2016. Since then, the project has passed various milestones, including the selection and acquisition of a site and the construction of the observatory. The observatory will be built in an L-shape and is scheduled to begin its scientific runs from 2030.

A grand collaborative effort

LIGO-India is part of the plan to expand the network of this experiment and is envisioned as a collaborative initiative between an Indian consortium of research institutions and the LIGO Laboratory in the United States, as well as its international partners like Germany, Australia, and the United Kingdom. The project promises breakthrough research outcomes, the development of cutting-edge technology, and opportunities for students and researchers.

The project will be built by the Government of India’s Departments of Atomic Energy (DAE) and Science and Technology (DST), with a Memorandum of Understanding (MoU) with the National Science Foundation (NSF) in the United States, as well as several national and international research and academic institutions. The Raja Ramanna Centre for Advanced Technology (RRCAT) in Indore, the Institute for Plasma Research (IPR) in Ahmedabad, and the Inter-University Centre for Astronomy and Astrophysics (IUCAA) in Pune are the three Indian institutions that collaborate under the name LIGO-India. At least 10 events producing gravitational waves have been detected. LIGO-India is said to be the fifth and final node of the planned network.

International Conferences on Gravitational Waves

visit:https://gravitational-waves.sfconferences.com/

Nomination link : https://x-i.me/granom Registration link : https://x-i.me/grareg2