BLOGS

Multiple images of a background image created by gravitational lensing can be seen in the system HS 0810+2554. Credit: Hubble Space Telescope / NASA / ESA

Topics: Astronomy, Astrophysics, Dark Matter, Einstein, General Relativity

Physicists believe most of the matter in the universe is made up of an invisible substance that we only know about by its indirect effects on the stars and galaxies we can see.

We're not crazy! Without this "dark matter," the universe as we see it would make no sense.

But the nature of dark matter is a longstanding puzzle. However, a new study by Alfred Amruth at the University of Hong Kong and colleagues, published in Nature Astronomy, uses light's gravitational bending to bring us a step closer to understanding.

Invisible but omnipresent

We think dark matter exists because we can see its gravity's effects on galaxies' behavior. Specifically, dark matter seems to make up about 85% of the universe's mass, and most of the distant galaxies we can see appear to be surrounded by a halo of the mystery substance.

But it's called dark matter because it doesn't give off light or absorb or reflect it, which makes it incredibly difficult to detect.

So what is this stuff? We think it must be some kind of unknown fundamental particle, but beyond that, we're not sure. All attempts to detect dark matter particles in laboratory experiments have failed, and physicists have debated its nature for decades.

Scientists have proposed two leading hypothetical candidates for dark matter: relatively heavy characters called weakly interacting massive particles (or WIMPs) and extremely lightweight particles called axions. Theoretically, WIMPs behave like discrete particles, while axions behave more like waves due to quantum interference.

It has been difficult to distinguish between these two possibilities—but now light bent around distant galaxies has offered a clue.

New look at 'Einstein rings' around distant galaxies just got us closer to solving the dark matter debate, Rossana Ruggeri, Phys.org.

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

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 [2, 3]. 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) [4–6]. 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

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

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

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

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

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

Topics: Chemistry, Einstein, Materials Science, Research

To date, researchers have created more than two dozen synthetic chemical elements that don’t exist naturally on Earth. Neptunium (atomic number Z = 93) and plutonium (Z = 94), the first two artificial elements after naturally occurring uranium, are produced in nuclear reactors by thousands of kilograms. But the accessibility of transuranic elements drops quickly with Z: Einsteinium (Z = 99) can be made only in microgram quantities in specialized laboratories, fermium (Z = 100) is produced by the picogram and has never been purified, and all elements after that are made just one atom at a time.

There are ways to probe the atomic properties of elements produced atom by atom (see, for example, Physics Today, June 2015, page 14). But when it comes to the traditional way of investigating how atoms behave—mixing them with other substances in solution to form chemical compounds—Es is effectively the end of the periodic table.

Now Rebecca Abergel (head of Lawrence Berkeley National Laboratory’s heavy element chemistry program) and her colleagues have performed the most complicated and informative Es chemistry experiment to date. They chose to react Es with a so-called octadentate ligand—a single organic molecule, held together by the backbone shown in blue, that wraps around a central metal atom and binds to it from all sides—to create the molecular structure shown in the figure. In their previous work, Abergel and colleagues used the same ligand to study transition metals, lanthanides, and lighter actinides. When they were fortunate enough to acquire a few hundred nanograms of Es from Oak Ridge National Laboratory, they used it on that as well.

Einsteinium chemistry captured, Johanna L. Miller, Physics Today

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

Snapshot from the central region of a numerical simulation of two merging neutron stars. It shows the stars stretched out by tidal forces just before their collision. Credit: CoRe/Jena FSU

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

Did Astronomers Just Discover Black Holes from the Big Bang? Nola Taylor Redd, Scientific American

(Just_Super/iStock)

Topics: Black Holes, Cosmology, Dark Energy, Einstein, General Relativity, Gravity

Black Holes May Hide Cores of Pure Dark Energy That Keep The Universe Expanding
Mike McCrae, Science Alert

Testing Einstein: conceptual image showing S0-2 (the blue and green object) as it made its closest approach to the supermassive black hole at the center of the Milky Way. The huge gravitational field of the black hole is illustrated by the distorted grid in space–time. (Courtesy: Nicolle R Fuller/National Science Foundation)

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

Einstein’s general theory of relativity tested by star orbiting a black hole
Sam Jarman, Physics World

Physicists take first-ever photo of quantum entanglement. Credit: University of Glasgow/CC by 4.0

Topics: Einstein, Entanglement, Laser, Quantum Mechanics

'Spooky' Quantum Entanglement Finally Captured in Stunning Photo
Yasemin Saplakoglu, Live Science

Credit: CC0 Public Domain

Topics: Black Holes, Einstein, General Relativity, Science Fiction, Wormholes

Travel through wormholes is possible, but slow, American Institute of Physics, Phys.org

Scientists have obtained the first-ever image of a black hole — at center of the galaxy M87. Credit: Event Horizon Telescope collaboration et al.

Topics: Astrophysics, Black Holes, Cosmology, Einstein

Image Source: HDQ Walls dot com

At Last, a Black Hole’s Image Revealed, Lee Billings, Scientific American

An artist’s rendition of a neutron star. Credit: Kevin Gill Flickr (CC by 2.0)

Topics: Astronomy, Astrophysics, Einstein, Gravitational Waves, Neutron Stars

Gravitational Observatories Hunt for Lumpy Neutron Stars
David Appell, Scientific American