NASA's Orion Craft Buzzes Past Moon, Feels Lunar Gravity In Historic Flyby

The Orion spacecraft is to take astronauts to the Moon in the coming years

Nasa's Orion spacecraft today flew past the moon, five days after it was launched off the Florida coast in the US. Orion is on a 25-day mission to orbit the moon before it returns safely to earth.

The spacecraft is to take astronauts to the Moon in the coming years - the first to set foot on its surface since the last Apollo mission in 1972.

This mission, called Artemis 1 aims to ensure that the vehicle is safe for human travel.

The outbound powered flyby burn that Orion performed today is the first of a pair of maneuvers required to enter a distant retrograde orbit around the Moon, Nasa said.

Orion came within 100 kilometers of the lunar surface, using the moon's gravity to enter an elongated orbit. Orion needs to demonstrate that it can get in and out of lunar orbit before returning home, surviving reentry in Earth's atmosphere, and splashing down in the Pacific Ocean on December 11.

"At the time of the burn, Orion was 328 miles above the Moon, travelling at 5,023 mph. Shortly after the burn, Orion passed 81 miles above the Moon, travelling at 5,102 mph," Nasa said in a blog post.

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Artemis-1: Orion spacecraft feels lunar gravity, set to buzz Moon today

 

The spacecraft has entered the lunar sphere of influence making the Moon, instead of Earth, the main gravitational force acting on the spacecraft.

By India Today Web Desk: Days after it was launched from the shores of Florida in Cape Canaveral, the Orion spacecraft is set to reach its target destination - the Moon. The spacecraft, which will soon return humans to the lunar world, will buzz the Moon on the sixth day of its 25.5-day-long mission.

The Orion spacecraft completed its third trajectory correction burn, firing the auxiliary thruster engines for a duration of 6 seconds at a rate of 3.39 feet per second to accelerate Orion and adjust the spacecraft’s path while en route to the Moon. The burn led to a speed change and determined which of Orion’s service module engines – reaction control, auxiliary, or orbital maneuvering system – to use for a particular maneuver.

Nasa said that with the Orion feeling the lunar gravity flight controllers will conduct the outbound powered flyby burn by firing the orbital maneuvering system engine for 2 minutes and 30 seconds to accelerate the spacecraft, harness the force from the Moon’s gravity, and direct it toward a distant retrograde orbit beyond the Moon.

“The outbound powered flyby burn is the first of a pair of maneuvers required to enter a distant retrograde orbit around the Moon,” Nasa said.

The burn will begin later in the day, with Orion’s closest approach to the Moon targeted following that, when it will pass about 80 miles above the lunar surface. A communication loss with the spacecraft is expected as is passes behind the Moon for approximately 34 minutes.

Nasa said that the spacecraft has captured additional imagery of the Moon using the optical navigation camera. Gathering imagery of the Earth and the Moon at different phases and distances will provide an enhanced body of data to certify its effectiveness as a location determination aid for future missions under changing lighting conditions.

The $4.1 billion test flight is set to last 25 days, roughly the same as when crews will be aboard. The space agency intends to push the spacecraft to its limits and uncover any problems before astronauts strap in. The test dummies — Nasa calls them moonikins — are fitted with sensors to measure such things as vibration, acceleration and cosmic radiation.

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Astronomers observe gravitational waves giving high-speed kick to black hole

 Astronomers have observed a cosmic event where two black holes merged into one and the subsequent gravitation waves gave the newly formed black hole a high-speed kick at close to 5 million kilometres per hour, according to ScienceNews.  The scientists documented the observation in a research article titled, “Evidence of large recoil velocity from a black hole merger signal,” accepted by the journal Physical Review Letters.

Vijay Varma, the lead author of the research article told ScienceNews that the study of these ‘kicks’ could potentially help scientists understand how heavy stellar-mass black holes form.

The newly-formed black hole was launched at that high speed by gravitational waves, which are ripples in space-time caused by massive objects moving with high accelerations. In this case, the gravitational waves were emitted when the two black holes merging, spiralling inwards and coalescing.

When these gravitational waves shot off in one direction, it caused the black hole to ‘kick’ (launch) in another direction, similar to how a gun recoils when it is used to shoot a bullet.

These waves were detected by the Laser Interferometer Gravitational-Wave Observatory (LIGO) and Virgo interferometer in the United States when they reached earth on January 29, 2020. Observation of the waves revealed how the black holes merged.

As both black holes began orbiting each other due to their extremely strong gravitational forces, it caused the plane in which they orbited to rotate. This can be compared to the wobbling of a top as it spins.

The researchers compared the observed data from the event with simulated data from predicted versions of black hole mergers to estimate the kick velocity of the black hole. The researchers found that it was launched at such a high speed that it was probably ejected from its ‘globular cluster’.

Globular clusters are dense groups of stars and black holes where black holes are expected to come together and merge. The research group estimates that there is only a 0.5 per cent chance that this particular black hole stayed in its globular cluster after it got launched due to the velocity.

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Astronomers poised to hunt new kind of gravitational wave

 Astronomers are getting closer to finding sources of continuous gravitational waves, thanks to observations of Scorpius X-2, a neutron star accreting matter from a low-mass binary companion.

So far, astronomers have only detected gravitational waves in the form of brief bursts from the mergers of black holes and neutron stars. However, non-merging compact objects can in theory produce a nonstop torrent of gravitational waves, albeit weaker than those emitted by mergers. In particular, low-mass X-ray binary systems, in which a dense neutron star sweeps up matter torn from a close companion star, are likely suspects for emitting continuous gravitational waves.

Scorpius X-2 is a classic example. It's a binary system 9,000 light-years away, featuring a 1.4-solar-mass neutron star accreting material from a companion star with half the mass of our sun. As the stolen gas flows onto the surface of the neutron star, it grows hot and radiates brightly in X-rays. The accretion of the material results in the neutron star becoming asymmetrically deformed as the gas piles up, and this deformation results in a torque (a rotational force) being imparted on the neutron star's spin, speeding it up.

So astronomers turned to observations from the Laser Interferometer Gravitational-Wave Observatory (LIGO) in the U.S. and its European and Japanese counterparts Virgo and KAGRA. Analyzing data from the system's third observing run, which ran from April 2019 to the onset of the COVID-19 pandemic in early 2020, scientists were unable to detect continuous gravitational wave emission from Scorpius X-2. 

However, they were able to place much tighter constraints on the strength and frequency of any continuous gravitational waves — constraints that suggest such signals could be detectable during the collaboration's next observing run, which is scheduled to begin in May and will be much more sensitive than previous observing runs, detecting fainter gravitational-wave signals.

Calculations suggest that the rate of flow of material onto a neutron star (indicated by the strength of the X-rays) is correlated with the frequency of a neutron star's spin and the frequency of gravitational waves it emits, since the higher accretion rate results in a stronger torque. In order for the system to remain in equilibrium so that the neutron star doesn't fly apart, the stronger rotational torque causes an equally strong torque exerted by the emission of the gravitational waves that acts in the opposite direction so that the system is in balance.

"For the first time, this search is now sensitive to models of the possible torque balance scenario of the system, which states that the torques of the gravitational waves and accretion of matter onto the neutron star are in balance," Jared Wofford, a Ph.D. candidate at the Rochester Institute of Technology in New York who worked on the study, said in a statement. "In the coming years, we expect better sensitivities from more data taken by Advanced LIGO observing runs probing deeper into the torque balance scenario in hopes to make the first continuous wave detection."

The results set upper limits for the strength of the gravitational waves across a range of frequencies spanning 25 Hz to 1,600 Hz, corresponding to spin frequencies of 12.5 Hz to 800 Hz (i.e. a neutron star rotating between 12.5 and 800 times per second). Discovering the continuous emission of gravitational waves from such a system would allow scientists to gain greater insights into the process of accretion in low-mass X-ray binaries, as well as the properties of neutron stars in those systems.

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New Tool Uses Gravitational Waves to Peer Inside Neutron Stars

 Imagine taking a star with twice the mass of the Sun and crushing it down to the size of Manhattan. The result would be a neutron star—one of the densest objects found anywhere in the Universe. In fact, they exceed the density of any material found naturally on Earth by a factor of tens of trillions. Although neutron stars are remarkable astrophysical objects in their own right, their extreme densities may also allow them to function as laboratories for studying fundamental questions of nuclear physics, under conditions that could never be reproduced on Earth.

Because of these exotic conditions, scientists still do not understand what exactly neutron stars themselves are made from, their so-called “equation of state” (EoS). Determining this is a major goal of modern astrophysics research. A new piece of the puzzle, constraining the range of possibilities, has been discovered by a pair of scholars at the Institute for Advanced Study (IAS): Carolyn Raithel, John N. Bahcall Fellow in the School of Natural Sciences; and Elias Most, Member in the School and John A. Wheeler Fellow at Princeton University. Their paper was published recently in The Astrophysical Journal Letters.

Ideally, astrophysicists would like to look inside these exotic objects, but they are too small and distant to be imaged with standard telescopes. Researchers instead rely on indirect properties that they can measure—such as the mass and radius of a neutron star—to calculate the EoS. This is much like how one might use the length of two sides of a right-angled triangle to work out its hypotenuse. However, one issue here is that the radius of a neutron star is very difficult to measure precisely. A promising alternative for future observations is to instead use a quantity called the “peak spectral frequency” (or f₂) in its place.

But how is f₂ measured? Collisions between neutron stars, which are governed by the laws of Einstein’s Theory of Relativity, lead to strong bursts of gravitational wave emission. In 2017, scientists directly measured such emissions for the first time. “At least in principle, the peak spectral frequency can be calculated from the gravitational wave signal emitted by the wobbling remnant of two merged neutron stars,” says Most.

This new finding will allow researchers working with the next generation of gravitational wave observatories (the successors of the currently operating LIGO) to better utilize the data obtained following neutron star mergers. According to Raithel, this data could reveal the fundamental constituents of neutron star matter. “Some theoretical predictions suggest that within neutron star cores, phase transitions could be dissolving the neutrons into sub-atomic particles called quarks,” stated Raithel. “This would mean that the stars contain a sea of free quark matter in their interiors. Our work may help tomorrow’s researchers determine whether such phase transitions actually occur.”

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LIGO will be back in 2023, able to detect even ‘fainter’ gravitational waves

 The Laser Interferometer Gravitational-wave Observatory (LIGO) is scheduled to begin its fourth run of operations in March 2023 after over two years of maintenance work and upgrades. During its latest operational run, LIGO and its two detectors will work in tandem with the Virgo Interferometer in Italy and the KAGRA observatory in Japan.

But this time, after two years of major upgrades to LIGO’s more sensitive detectors will be able to sense even “fainter” gravitational waves than before. Gravitational waves are space-time ripples caused by the most explosive and energetic processes in the universe. Their existence was initially predicted by Albert Einstein in 1916 in his general theory of relativity.

The theory posits that massive accelerating objects like neutron stars would disrupt the space-time continuum and send “waves” in all directions.  These gravitational waves would travel at the speed of light and they would also carry information about what caused them, along with information that could help scientists understand the nature of gravity itself.

LIGO is the world’s largest gravitational wave observatory and comprises of two massive laser interferometers that are located about 3,000 kilometres apart. It is used to detect and understand the origins of gravitational waves. Interferometers can calculate very small measurements that cannot be done using conventional equipment.

For example, LIGO’s interferometers can measure a distance that is 1/10,000 smaller than the width of a proton. This is why scientists were able to confirm the existence of gravitational waves for the first time in 2016 with the help of LIGO and Virgo.

With its latest upgrades, LIGO is calibrated to be sensitive enough to detect gravitational waves from two neutron stars colliding over 619 million light-years.

LIGO and Virgo recently observed a black hole merger with a final mass of 142 times that of the sun, making it the largest of its kind observed in gravitational waves to date. (Illustration credit: LIGO/Caltech/MIT/R. Hurt (IPAC)) 

 

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Physicists Create New Model of Ringing Black Holes

 When two black holes collide into each other to form a new bigger black hole, they violently roil spacetime around them, sending ripples called gravitational waves outward in all directions. Previous studies of black hole collisions modeled the behavior of the gravitational waves using what is known as linear math, which means that the gravitational waves rippling outward did not influence, or interact, with each other. Now, a new analysis has modeled the same collisions in more detail and revealed so-called nonlinear effects.

"Nonlinear effects are what happens when waves on the beach crest and crash" says Keefe Mitman, a Caltech graduate student who works with Saul Teukolsky (PhD '74), the Robinson Professor of Theoretical Astrophysics at Caltech with a joint appointment at Cornell University. "The waves interact and influence each other rather than ride along by themselves. With something as violent as a black hole merger, we expected these effects but had not seen them in our models until now. New methods for extracting the waveforms from our simulations have made it possible to see the nonlinearities."

The research, published in the journal Physical Review Letters, come from a team of researchers at Caltech, Columbia University, University of Mississippi, Cornell University, and the Max Planck Institute for Gravitational Physics.

In the future, the new model can be used to learn more about the actual black hole collisions that have been routinely observed by LIGO (Laser Interferometer Gravitational-wave Observatory) ever since it made history in 2015 with the first direct detection of gravitational waves from space. LIGO will turn back on later this year after getting a set of upgrades that will make the detectors even more sensitive to gravitational waves than before.

Mitman and his colleagues are part of a team called the Simulating eXtreme Spacetimes collaboration, or SXS. Founded by Teukolsky in collaboration with Nobel Laureate Kip Thorne (BS '62), Richard P. Feynman Professor of Theoretical Physics, Emeritus, at Caltech, the SXS project uses supercomputers to simulate black hole mergers. The supercomputers model how the black holes evolve as they spiral together and merge using the equations of Albert Einstein's general theory of relativity. In fact, Teukolsky was the first to understand how to use these relativity equations to model the "ringdown" phase of the black hole collision, which occurs right after the two massive bodies have merged.

"Supercomputers are needed to carry out an accurate calculation of the entire signal: the inspiral of the two orbiting black holes, their merger, and the settling down to a single quiescent remnant black hole," Teukolsky says. "The linear treatment of the settling down phase was the subject of my PhD thesis under Kip quite a while ago. The new nonlinear treatment of this phase will allow more accurate modeling of the waves and eventually new tests of whether general relativity is, in fact, the correct theory of gravity for black holes."

The SXS simulations have proved instrumental in identifying and characterizing the nearly 100 black hole mergers detected by LIGO so far. This new study represents the first time that the team has identified nonlinear effects in simulations of the ringdown phase.

"Imagine there are two people on a trampoline," Mitman says. "If they jump gently, they shouldn't influence the other person that much. That's what happens when we say a theory is linear. But if one person starts bouncing with more energy, then the trampoline will distort, and the other person will start to feel their influence. This is what we mean by nonlinear: the two people on the trampoline experience new oscillations because of the presence and influence of the other person."

In gravitational terms, this means that the simulations produce new types of waves. "If you dig deeper under the large waves, you will find an additional new wave with a unique frequency," Mitman says.

In the big picture, these new simulations will help researchers to better characterize future black hole collisions observed by LIGO and to better test Einstein's general theory of relativity.

Says co-author Macarena Lagos of Columbia University, "This is a big step in preparing us for the next phase of gravitational-wave detection, which will deepen our understanding of gravity in these incredible phenomena taking place in the far reaches of the cosmos."

The study titled "Nonlinearities in black hole ringdowns," was funded by the Sherman Fairchild Foundation, National Science Foundation, the Innovative Theoretical Cosmology Fellowship of Columbia University, the Department of Energy, and the Simons Foundation. Other Caltech-affiliated authors include Sizheng Ma, Yanbei Chen, Nils Deppe, François Hébert, Jordan Moxon, and Mark Scheel. Additional authors include Leo Stein (BS '06), Lam Hui, Lawrence Kidder, William Throwe, and Nils Vu.

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Black Hole Carnivals May Lead to Cosmic Crashes Seen by Gravitational-Wave Detectors

 Since 2015, the LIGO-Virgo-KAGRA Collaboration has detected about 85 pairs of black holes crashing into each other. We now know that Einstein was right: gravitational waves are generated by these systems as they inspiral around each other, distorting space-time with their colossal masses as they go. We also know that these cosmic crashes happen frequently: as detector sensitivity improves, we are expecting to sense these events on a near-daily basis in the next observing run, starting in 2023. What we do not know — yet — is what causes these collisions to happen.

Black holes form when massive stars die. Typically, this death is violent, an extreme burst of energy that would either destroy or push away nearby objects. It is therefore difficult to form two black holes that are close enough together to merge within the age of the Universe. One way to get them to merge is to push them together within densely populated environments, like the centers of star clusters.

In star clusters, black holes that start out very far apart can be pushed together via two mechanisms. Firstly, there’s mass segregation, which leads the most massive objects to sink toward the middle of the gravitational potential well. This means that any black holes dispersed throughout the cluster should wind up in the middle, forming an invisible “dark core.” Secondly, there are dynamical interactions. If two black holes pair up in the cluster, their interactions can be influenced by the gravitational influence of nearby objects. These influences can remove orbital energy from the binary and push it closer together.

The mass segregation and dynamical interactions that can take place in star clusters can leave their fingerprints on the properties of merging binaries. One key property is the shape of the binary’s orbit just before it merged. Since mergers in star clusters can happen very quickly, the orbital shapes can be quite elongated — less like the calm, sedate circle that the Earth traces around the Sun, and more like the squished ellipse that Halley’s Comet races along in its visits in and out of the Solar System. When two black holes are in such an elongated orbit, their gravitational wave signal has characteristic modulations, and can be studied for clues as to where the two objects met.

A team of OzGrav researchers and alumni are working together to study the orbital shapes of black hole binaries. The group, led by Dr. Isobel Romero-Shaw (formerly of Monash University, now based at the University of Cambridge) together with Professors Paul Lasky and Eric Thrane of Monash University, have found that some of the binaries observed by the LIGO-Virgo-KAGRA collaboration are indeed likely to have elongated orbits, indicating that they may have collided in a densely populated star cluster. Their findings indicate that a large chunk of the observed binary black hole collisions — at least 35% — could have been forged in star clusters.

“I like to think of black hole binaries like dance partners,” explains Dr. Romero-Shaw. “When a pair of black holes evolve together in isolation, they’re like a couple performing a slow waltz alone in the ballroom. It’s very controlled and careful; beautiful, but nothing unexpected. Contrasting to that is the carnival-style atmosphere inside a star cluster, where you might get lots of different dances happening simultaneously; big and small dance groups, freestyle, and lots of surprises!” While the results of the study cannot tell us — yet — exactly where the observed black hole binaries are merging, they do suggest that black hole carnivals in the centers of star clusters could be an important contribution.

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Astronomers hunt gravitational waves with ear to black hole symphony

 Indian astronomers have released their first set of data that will be vital for an international collaboration to detect extremely weak gravitational waves by listening to the “symphony of black holes in the universe.”

Once detected, such low-frequency gravitational waves would provide scientists with a novel look at the universe from a completely new window that was opened in 2015 with the discovery of the first gravitational wave. gravitational waves are extreme...

gravitational waves are extremely feeble ripples in spacetime caused by massive objects like black holes. But they are so elusive that it took scientists decades to capture them using an instrument built after spending nearly a billion dollars. Some ...

But that was one half of the story. All the gravitational wave signatures picked up so far are high-frequency waves as identifying the low-frequency ones is even more complicated. This is what an international collaboration spread over four continent...

“It is akin to watching a star in the X-ray spectrum, but not in the visible range. For a holistic view we need to see the star from both sides of the electromagnetic band,” lead researcher from India Bhal Chandra Joshi from TIFR’s National Centre of...

For more than a decade Joshi and his team members observed pulsars using the upgraded Giant Metrewave Radio Telescope (uGMRT) at Khodad near Pune.

The pulsars are rotating neutron stars that are known to emit beams of electromagnetic radiation from their poles with such precise intervals that they are considered better than atomic clocks. They are known as nature’s best timekeepers.

But there are fine delays in the arrival times of radio pulses from one particular group of pulsars (millisecond pulsar), which Indian scientists captured in the last three and half years. The data would help filter signals from background noise whil...

“The interplay of gravitational waves in the universe is similar to a symphony being played by nature. But the symphony has a hiss underneath making the lower notes inaudible. We must filter these distracting sounds to enjoy the true symphony,” the s...

The InPTA is a part of an Asian consortium involving Indian and Japanese scientists. There are three similar consortia working in Australia, North America and Europe. All four groups periodically share their results in the global hunt to look for the...

“With millisecond pulsars as our probes, we measure the noise so that together with the other scientific groups, we can listen to the symphony of black holes in the universe,” said Joshi. “It would complete the history of the universe.”

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