general relativity (10)

Heart of Darkness...

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The first direct image of the Milky Way's supermassive black hole shows an orange glowing ring — gas heated as it falls into the singularity — with the shadow of the black hole at the center. EHT Collaboration

Topics: Astrophysics, Black Holes, Cosmology, Einstein, General Relativity

In a triumph of observation and data processing, astronomers at the Event Horizon Telescope have captured the first-ever picture of the supermassive black hole at the center of the Milky Way Galaxy.

The black hole is named Sagittarius A* (pronounced “A-star”), and the reveal of its image received an international rollout this morning in simultaneous press conferences held by the National Science Foundation (NSF) at the National Press Club in Washington, D.C., and the European Southern Observatory headquarters in Garching, Germany.

The image represents 3.5 million gigabytes of data taken at millimeter wavelengths by eight radio telescopes around the world. “It took several years to refine our image and confirm what we had,” said Feryal Özel, an astronomer at the University of Arizona in Tucson, at the NSF press conference. “But we prevailed.”

Blackhole at the center of Milky Way imaged for the first time, Mark Zastrow, Astronomy

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Shadow of Infinity...

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Figure 1: A cartoon showing the “self-lensing” of light by a supermassive black hole binary system. Jordy Davelaar and Zoltán Haiman of Columbia University predict that this effect could be used to study black hole binaries that are too far from Earth to probe with other techniques

Topics: Black Holes, Cosmology, Einstein, General Relativity

When galaxies collide, the central supermassive black holes that they contain begin to orbit each other. This supermassive black hole binary attracts gas, which flows through the system to form two disk-shaped structures, one around each of the supermassive black holes. The gas in these “minidisks” heats as it falls toward the holes and begins to radiate light. Astronomers have detected around 150 galaxies with candidate supermassive black hole binaries. And, as observations become more detailed, they expect the light from the minidisks in those systems to bear recognizable, time-dependent signatures from black hole distortions [1]. Now, Jordy Davelaar and Zoltán Haiman of Columbia University have theoretically tested how one such distortion—the “shadow” of the black hole—affects this light signature, finding that it causes a dip in the signal that should be observable in about 1% of candidate systems [23]. The technique could allow astronomers to study black holes that are currently beyond the reach of conventional imaging methods (Fig. 1).

From gravitational-wave measurements of merging black holes to direct imaging of the plasma circling a black hole, the last decade has seen an explosion of observational evidence for black holes (see Viewpoint: The First Sounds of Merging Black Holes and News Feature: Black Hole Imaging Tests Einstein’s Limits) [46]. Yet despite these achievements, many questions remain about black holes, including a critical one: How do black holes grow to supermassive scales—millions to billions of times the mass of the Sun?

A black hole is a simple object, described by its mass, angular momentum, and electrical charge. Supermassive black holes are typically electrically neutral, so their mass and angular momentum parameters determine their gravitational fields. The gravitational field determines how the black holes bend light and thus how they appear to an observer on Earth. Light passing near the black hole is deflected by the gravitational field, producing a black hole shadow—a dark region that is often encircled by a bright light ring—whose size and shape come directly from the black hole’s mass and angular momentum.

Measuring a Black Hole Shadow, George N. Wong, APS Physics

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Rogue Singularity...

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A lone black hole gives off no light - but its gravity does distort the path of light traveling around it. Ute Kraus (background Milky Way panorama: Axel Mellinger), Institute of Physics, Universität Hildesheim

Topics: Astrophysics, Black Holes, Cosmology, Einstein, General Relativity

Each second, a brand new baby black hole is born somewhere in the cosmos as a massive star collapses under its own weight.

But black holes themselves are invisible. Historically, astronomers have only been able to detect these stellar-mass black holes when they are acting on a companion.

Now, a team of scientists has made the first-ever confirmed detection of a stellar-mass black hole that’s completely alone. The discovery opens up the possibility of finding even more — an exciting prospect, considering there should be around 100 million such “rogue” black holes drifting through our galaxy unseen.

Relying on the neighbors

Black holes are difficult to find because they don’t shine like stars. Anything with mass warps the fabric of space-time, and the greater the mass, the more extreme the warp. Black holes pack so much mass into such a tiny area that space folds back in on itself. That means that if anything, even light, gets too close, its path will always bend back toward the center of the black hole.

Astronomers have found a couple hundred of these ghostly goliaths indirectly, by seeing how they influence their surroundings. They’ve identified around 20 black holes of the small, stellar-mass variety in our galaxy by watching as stars are devoured by invisible companions. As the black hole pulls matter from its neighbor, the material forms a swirling, glowing accretion disk that signals the black hole’s presence.

Astronomers detect the first potential 'rogue' black hole, Ashley Balzer, Astronomy Magazine

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Aharonov-Bohm Effect

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A quantum probe for gravity: Physicists have detected a tiny phase shift in atomic wave packets due to gravity-induced relativistic time dilation – an example of the Aharonov-Bohm effect in action. (Courtesy: Shutterstock/Evgenia Fux)

Topics: General Relativity, Gravity, Modern Physics, Quantum Mechanics

The idea that particles can feel the influence of potentials even without being exposed to a force field may seem counterintuitive, but it has long been accepted in physics thanks to experimental demonstrations involving electromagnetic interactions. Now physicists in the US have shown that this so-called Aharonov-Bohm effect also holds true for a much weaker force: gravity. The physicists based their conclusion on the behavior of freefalling atomic wave packets, and they say the result suggests a new way of measuring Newton’s gravitational constant with far greater precision than was previously possible.

Yakir Aharonov and David Bohm proposed the effect that now bears their name in 1959, arguing that while classical potentials have no physical reality apart from the fields they represent, the same is not true in the quantum world. To make their case, the pair proposed a thought experiment in which an electron beam in a superposition of two wave packets is exposed to a time-varying electrical potential (but no field) when passing through a pair of metal tubes. They argued that the potential would introduce a phase difference between the wave packets and therefore lead to a measurable physical effect – a set of interference fringes – when the wave packets are recombined.

Seeking a gravitational counterpart

In the latest research, Mark Kasevich and colleagues at Stanford University show that the same effect also holds true for gravity. The platform for their experiment is an atom interferometer, which uses a series of laser pulses to split, guide and recombine atomic wave packets. The interference from these wave packets then reveals any change in the relative phase experienced along the two arms.

Physicists detect an Aharonov-Bohm effect for gravity, Edwin Cartlidge, Physics World

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Cosmic Existentialism...

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An illustration of a black hole and its event horizon. (Image credit: Nicholas Forder/Future Publishing)

Topics: Astronomy, Astrophysics, Black Holes, Cosmology, Einstein, General Relativity

"Small" black holes are estimated to make up 1% of the universe's matter.

Scientists have estimated the number of "small" black holes in the universe. And no surprise: It's a lot.

This number might seem impossible to calculate; after all, spotting black holes is not exactly the simplest task. Because there are as pitch-black as the space they lurk in, the light swallowing cosmic goliaths can be detected only under the most extraordinary circumstances — like when they're bending the light around them, snacking on the unfortunate gases and stars that stray too close, or spiraling toward enormous collisions that unleash gravitational waves.

But that hasn't stopped scientists from finding some ingenious ways to guess the number. Using a new method, outlined Jan. 12 in The Astrophysical Journal, a team of astrophysicists has produced a fresh estimate for the number of stellar-mass black holes — those with masses 5 to 10 times that of the sun — in the universe.

And it's astonishing: 40,000,000,000,000,000,000, or 40 quintillions, stellar-mass black holes populate the observable universe, making up approximately 1% of all normal matter, according to the new estimate.

So how did the scientists arrive at that number? By tracking the evolution of stars in our universe they estimated how often the stars — either on their own or paired into binary systems — would transform into black holes, said first author Alex Sicilia, an astrophysicist at the International School of Advanced Studies (SISSA) in Trieste, Italy.

40 quintillion stellar-mass black holes are lurking in the universe, a new study finds, Ben Turner, Space.com

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E=mc^2...

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Image source: link below

Topics: Applied Physics, Einstein, General Relativity, Special Relativity

According to Einstein’s theory of special relativity, first published in 1905, light can be converted into matter when two light particles collide with intense force. But, try as they might, scientists have never been able to do this. No one could create the conditions needed to transform light into matter — until now.

Physicists claim to have generated matter from pure light for the first time — a spectacular display of Einstein’s most famous equation.

This is a significant breakthrough, overcoming a theoretical barrier that seemed impossible only a few decades ago.

What does E=mc2 mean? The world’s most famous equation is both straightforward and beyond comprehension at the same time: “Energy equals mass times the speed of light squared.” 

At its most fundamental level, it means energy and mass are various forms of the same thing. Energy may transform into mass and vice versa under the right circumstances. 

However, imagine a light beam transforming into, say, a paper clip, and it seems like pure magic. That’s where the “speed of light squared” factors in. It determines how much energy a paper clip or any piece of matter contains. The speed of light is the factor needed to make mass and energy equal. If every atom in a paper clip could be converted to pure energy, it would generate 18 kilotons of TNT. That’s around the size of the Hiroshima bomb from 1945. 

(Still can’t picture it? Me neither.) 

You can go the other way, too: if you crash two highly energized light particles, or photons, into each other, then you can create energy and mass. It sounds simple enough, but no one has been able to make it happen.

Since they couldn’t accelerate light particles, the team opted for ions and used the Relativistic Heavy Ion Collider (RHIC) to accelerate them at extreme speeds. In two accelerator rings at RHIC, the accelerated gold ions to 99.995% of the speed of light. With 79 protons, a gold ion has a strong positive charge. When a charged heavy ion is accelerated to incredible speeds, a strong magnetic field swirls around it. 

That magnetic field produces “virtual photons.” So, in a roundabout way, they accelerated light particles by piggybacking them on an ion.

When the team sped the ions in the accelerator rings with significant energy, the ions nearly collided, allowing the photon clouds surrounding them to interact and form an electron-positron pair — essentially, matter. They published their work in the journal Physical Review Letters.

Scientists observed what Einstein predicted a century ago, Teresa Carey, Free Think

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Five Stages...

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Image source: Link below

Topics: Astrophysics, Cosmology, Einstein, General Relativity, Star Trek

Note: One of the things you find out about sophomore, or junior year in physics is faster-than-light travel violates causality: the arrow of time points forward, not in "loop-de-loop." Thus, we can suspend belief as every version of Trek did time travel episodes, because superluminal speeds would allow grandfather paradoxes, so why not?

As a lifelong Trekkie, it pains me to critique genuine attempts at warp field mechanics. Just note the five stages of grief I have traveled often as I read such articles: "denial, anger, bargaining, depression and acceptance" (Elisabeth Kubler-Ross, and David Kessler), but based on the post that will appear in the morning, a little diversion might be a good thing.

For Erik Lentz, it all started with Star Trek. Every few episodes of Star Trek: The Next Generation, Captain Jean-Luc Picard would raise his hand and order, “Warp one, engage!” Then stars became dashes, and light-years flashed by at impossible speed. And Lentz, still in elementary school, wondered whether warp drive might also work in real life.

“At some point, I realized that the technology didn’t exist,” Lentz says. He studied physics at the University of Washington, wrote his Ph.D. dissertation on dark matter, and generally became far too busy to be concerned with science fiction. But then, at the start of the coronavirus pandemic, Lentz found himself alone in Göttingen, Germany, where he was doing postdoctoral work. He suddenly had plenty of free time on his hands—and childhood fancies in his head.

Lentz read everything he could find on warp drives in the scientific literature, which was not very much. Then he began to think about it for himself. After a few weeks, something occurred to him that everyone else seemed to have overlooked. Lentz put his idea on paper and discussed it with more experienced colleagues. A year later it was published in a physics journal.

It quickly became clear that Lentz was not the only person dreaming about warp drives. Media outlets all over the world picked up the story, and a dozen journalists asked for interviews. A discussion on the online forum Reddit attracted 2,700 comments and 33,000 likes. One Internet user wrote, “Anyone else feels like they were born 300 years too soon?”

Star Trek’s Warp Drive Leads to New Physics, Robert Gast, Scientific American

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Black Hole Storm...

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Topics: Astrophysics, Black Holes, Cosmology, Einstein, General Relativity

Note: From comments on a previous post, maybe science writers need to work on their chosen list of metaphors?

In the far reaches of the Universe, a supermassive black hole is throwing a tantrum.

It's blowing a tremendous wind into intergalactic space, and we're seeing the storm light from 13.1 billion years ago when the Universe was less than 10 percent of its current age. It's the most distant such tempest we've ever identified, and its discovery is a clue that could help astronomers unravel the history of galaxy formation.

"The question is when did galactic winds come into existence in the Universe?" said astronomer Takuma Izumi of the National Astronomical Observatory of Japan (NAOJ).

"This is an important question because it is related to an important problem in astronomy: How did galaxies and supermassive black holes coevolve?"

A Colossal Black Hole Storm Has Been Detected Raging in The Early Universe, Michelle Starr, Science Alert

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Adversary, Friendly, or Neutral...

 

An unidentified flying object as seen in a declassified Department of Defense video, DoD

Topics: Aerodynamics, Applied Physics, Biology, Exoplanets, General Relativity, SETI

May 17, 2019- No, little green men aren't likely after the conquest of humanity. Boyd's piece for Phys.org highlights the reason why the Pentagon wants to identify UFOs: they're unidentified. If a warfighter on the ground or in the sky can't ID an object, that creates an issue since they don't know if it's friendly, adversarial, or neutral.

U.S. Navy pilots and sailors won't be considered crazy for reporting unidentified flying objects, under new rules meant to encourage them to keep track of what they see writes Iain Boyd for Phys.org.

Why is the Pentagon interested in UFOs? Intelligent Aerospace

The Pentagon refers to them as "transmedium vehicles," meaning vehicles moving through air, water, and space. Carolina Coastline breathlessly uses the term "defying the laws of physics." So I looked at what the paper might have meant. The objects apparently exceed the speed of sound without a sonic boom (signature of breaking the barrier). Even though this is reported by Popular Mechanics, they're quoting John Ratcliffe, whose name somehow sounds like a pejorative. Consider the source.

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U.S. Navy F/A-18 flying faster than the speed of sound. The white cloud is formed by decreased air pressure and temperature around the tail of the aircraft.
ENSIGN JOHN GAY, U.S. NAVY

The speed of sound is 343 meters per second (761.21 miles per hour, 1,100 feet per second). Mach 1 is the speed of sound, Mach 2 is 1522.41 mph, Mach 3 is 2283.62 mph. NASA's X-43A scramjet sets the record at Mach 9.6 (7,000 mph), so, it's easy to see where Star Trek: The Next Generation got its Warp Speed analog from. The top speed of the F/A-18 is 1,190 mph. Pilots and astronauts under acceleration experience G Forces, and have suits to keep them from blacking out in a high-speed turn.

A Science Magazine article in 1967 reported the dimensions and speeds for the object were undeterminable. History.com reported an object exceeding 70 knots, or 80.5546 mph underwater (twice the speed of a nuclear submarine, so I can see the US Navy's concern). I found some of the descriptions on the site interesting:

5 UFO traits:

1. Anti-gravity lift (no visible means of propulsion), 2. Sudden and instantaneous acceleration (fast), 3. Hypersonic velocities without signatures (no sonic boom), 4. Low observability, or cloaking (not putting this on Romulans, or Klingons), 5. Trans-medium travel (air, water, space).

When I look at these factors, I don't get "little green men." First caveat: there are a lot of planets between us, and them with resources aplenty. Second caveat: any interest an alien intelligence might have in us is as caretakers of an experiment, or cattle. That's disturbing: ever see a rancher have conversations with a chicken, sow, or steer before slaughter?

My hypothesis (Occam's razor) - these are projections, but of a special kind:

For the first time, a team including scientists from the National Institute of Standards and Technology (NIST - 2016) have used neutron beams to create holograms of large solid objects, revealing details about their interiors in ways that ordinary laser light-based visual holograms cannot.

Holograms -- flat images that change depending on the viewer's perspective, giving the sense that they are three-dimensional objects -- owe their striking capability to what's called an interference pattern. All matter, such as neutrons and photons of light, has the ability to act like rippling waves with peaks and valleys. Like a water wave hitting a gap between the two rocks, a wave can split up and then re-combine to create information-rich interference patterns.

Move over, lasers: Scientists can now create holograms from neutrons, too, Science Daily

This of course doesn't explain the decades of observations, since holograms came into being in a 1948 paper by the Hungarian inventor Denis Gabor: “The purpose of this work is a new method for forming optical images in two stages. In the first stage, the object is lit using a coherent monochrome wave, and the diffraction pattern resulting from the interference of the secondary coherent wave coming from the object with the coherent background is recorded on the photographic plate. If the properly processed photographic plate is placed after its original position and only the coherent background is lit, an image of the object will appear behind it, in the original position.” Gabor won the Nobel Prize in 1971 for "his invention and development of the holographic method." Also: History of Holography

This is purely speculative. I have no intelligence other than what I've shared. It does in my mind, explain the physics-defying five traits described above. It does not explain the previous supposition of sightings since humans started recording history, or trying to hypothesize their sightings in antiquity. Solid objects flying at hypersonic speeds make sonic booms; projections - ball lightning, 3D laser, or solid neutron holograms - likely won't.

If these are projections (adversary, friendly, neutral), who is doing them, and why?

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No Strings Attached...

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Image Source: Physicist finds loose thread of string theory puzzle, Cay Leytham-Powell, University of Colorado at Boulder, Phys.org

Topics: Einstein, General Relativity, Quantum Mechanics, String Theory

For decades, most physicists have agreed that string theory is the missing link between Einstein's theory of general relativity, describing the laws of nature at the largest scale, and quantum mechanics, describing them at the smallest scale. However, an international collaboration headed by Radboud physicists has now provided compelling evidence that string theory is not the only theory that could form the link. They demonstrated that it is possible to construct a theory of quantum gravity that obeys all fundamental laws of physics, without strings. They described their findings in Physical Review Letters last week.

When we observe gravity at work in our universe, such as the motion of planets or light passing close to a black hole, everything seems to follow the laws written down by Einstein in his theory of general relativity. On the other hand, quantum mechanics is a theory that describes the physical properties of nature at the smallest scale of atoms and subatomic particles. Though these two theories have allowed us to explain every fundamental physical phenomenon observed, they also contradict each other. As of today, physicists have severe difficulties to reconcile the two theories to explain gravity on both the largest and smallest scale.

Explaining gravity without string theory, Radboud University, Phys.org

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