Missing Link...

A cosmic homicide in action, with a wayward star being shredded by the intense gravitational pull of a black hole that contains tens of thousands of solar masses in an artist's impression obtained by Reuters April 2, 2020. NASA-ESA/D. Player/Handout via REUTERS.

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

Using data from the Hubble Space Telescope and two X-ray observatories, the researchers determined that this black hole is more than 50,000 times the mass of our sun and located 740 million light years from Earth in a dwarf galaxy, one containing far fewer stars than our Milky Way.

Black holes are extraordinarily dense objects possessing gravitational pulls so powerful that not even light can escape.

This is one of the few “intermediate-mass” black holes ever identified, being far smaller than the supermassive black holes that reside at the center of large galaxies but far larger than so-called stellar-mass black holes formed by the collapse of massive individual stars.

“We confirmed that an object that we discovered originally back in 2010 is indeed an intermediate-mass black hole that ripped apart and swallowed a passing star,” said University of Toulouse astrophysicist Natalie Webb, a co-author of the study published this week in Astrophysical Journal Letters.

Astronomers spot 'missing link' black hole - not too big and not too small
Will Dunham, Reuters Science

Primordial Black Holes...

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

In the nearly five years since their first direct detection, gravitational waves have become one of the hottest topics in astronomy. With facilities such as the Laser Interferometer Gravitational-Wave Observatory (LIGO), researchers have mostly used these ripples in spacetime to study the inner workings of merging black holes, but LIGO has also detected gravitational waves from other sorts of celestial crashes, such as the collisions of ultradense stellar remnants called neutron stars. Sometimes, however, LIGO serves up gravitational waves that leave astronomers scratching their heads—as was the case for GW190425, an event detected last April that was recently attributed to a neutron star merger.

The trouble is that LIGO’s data suggest this neutron star pair was substantially overweight—collectively, some 3.4 times the mass of the sun, which is half a solar mass heavier than the most massive neutron star binaries ever seen. “It is the heaviest known by a pretty wide margin,” says Chad Hanna, an astrophysicist at Pennsylvania State University who hunts gravitational waves.

The trouble is that LIGO’s data suggest this neutron star pair was substantially overweight—collectively, some 3.4 times the mass of the sun, which is half a solar mass heavier than the most massive neutron star binaries ever seen. “It is the heaviest known by a pretty wide margin,” says Chad Hanna, an astrophysicist at Pennsylvania State University who hunts gravitational waves.

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

Geodes...

(Just_Super/iStock)

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

A fifty-year-old hypothesis predicting the existence of bodies dubbed Generic Objects of Dark Energy (GEODEs) is getting a second look in light of a proposed correction to assumptions we use to model the way our Universe expands.

If this new version of a classic cosmological model is correct, some black holes could hide cores of pure dark energy, pushing our Universe apart at the seams.

University of Hawaii astrophysicist Kevin Croker and mathematician Joel Weiner teamed up to challenge the broadly accepted notion that when it comes to the Universe's growing waistline, its contents are largely irrelevant.

"For 80 years, we've generally operated under the assumption that the Universe, in broad strokes, was not affected by the particular details of any small region," said Croker.

"It is now clear that general relativity can observably connect collapsed stars – regions the size of Honolulu – to the behavior of the Universe as a whole, over a thousand billion billion times larger."

Not only could this alternative interpretation of fundamental physics change how we understand the Universe's expansion, but we might need to also consider how that growth might affect compact objects like the cores of collapsing stars.

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

Easy-Peasy...

(Image: © Shutterstock)

Topics: Black Holes, Cosmology, General Relativity, Wormholes

Everybody wants a wormhole. I mean, who wants to bother traveling the long-and-slow routes throughout the universe, taking tens of thousands of years just to reach yet another boring star? Not when you can pop into the nearest wormhole opening, take a short stroll, and end up in some exotic far-flung corner of the universe.

There's a small technical difficulty, though: Wormholes, which are bends in space-time so extreme that a shortcut tunnel forms, are catastrophically unstable. As in, as soon as you send a single photon down the hole, it collapses faster than the speed of light.

But a recent paper, published to the preprint journal arXiv on July 29, has found a way to build an almost-steady wormhole, one that does collapse but slowly enough to send messages — and potentially even things — down it before it tears itself apart. All you need are a couple of black holes and a few infinitely long cosmic strings.

Easy-peasy.

In principle, building a wormhole is pretty straightforward. According to Einstein's Theory of General Relativity, mass and energy warp the fabric of space-time. And a certain special configuration of matter and energy allows the formation of a tunnel, a shortcut between two otherwise distant portions of the universe.

Unfortunately, even on paper, those wormholes are fantastically unstable. Even a single photon passing through the wormhole triggers a catastrophic cascade that rips the wormhole apart. However, a healthy dose of negative mass — yes, that's matter but with an opposite weight — can counteract the destabilizing effects of regular matter trying to pass through the wormhole, making it traversable.

OK, matter with negative mass doesn't exist, so we need a new plan.

Physicists Just Released Step-by-Step Instructions for Building a Wormhole
Paul Sutter, Live Science

The Gravity of the Matter...

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

A key aspect of Einstein’s general theory of relativity has passed its most rigorous test so far. An international team led by Tuan Do and Andrea Ghez at the University of California, Los Angeles confirmed the Einstein equivalence principle (EEP) by analyzing the redshift of light from the star S0-2 at its closest approach to Sagittarius A* – the supermassive black hole at the center of the Milky Way. The study combined over 20 years of existing spectroscopic and astrometric measurements of S0-2 with the team’s own observations.

Since Einstein first proposed his general theory of relativity in 1915, the idea has stood up to intense experimental scrutiny by explaining the behaviors of gravitational fields in the solar system, the dynamics of binary pulsars, and gravitational waves emitted by mergers of black holes.

In 2018, the GRAVITY collaboration carried out a particularly rigorous test – observing S0-2 at its closest approach to Sagittarius A* in its 16-year orbit.

As expected, the GRAVITY astronomers observed a characteristic relativistic redshift in light from S0-2. This redshift is a lengthening of the wavelength of the light and arises from both the motion of the star (the Doppler effect) and the EEP. The latter is a consequence of general relativity and predicts a redshift in light from a source that is in a gravitational field such as that of a supermassive black hole.

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

Wormhole Slow-Mo...

Credit: CC0 Public Domain

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

“Sometimes people don't want to hear the truth because they don't want their illusions destroyed.” Friedrich Nietzsche, Good Reads

A Harvard physicist has shown that wormholes can exist: tunnels in curved space-time, connecting two distant places, through which travel is possible.

But don't pack your bags for a trip to other side of the galaxy yet; although it's theoretically possible, it's not useful for humans to travel through, said the author of the study, Daniel Jafferis, from Harvard University, written in collaboration with Ping Gao, also from Harvard and Aron Wall from Stanford University.

"It takes longer to get through these wormholes than to go directly, so they are not very useful for space travel," Jafferis said. He will present his findings at the 2019 American Physical Society April Meeting in Denver.

Despite his pessimism for pan-galactic travel, he said that finding a way to construct a wormhole through which light could travel was a boost in the quest to develop a theory of quantum gravity.

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

Multi Messenger Astronomy...

Figure 1: On 17 August 2017 LIGO detected gravitational waves from a neutron-star collision. Within 12 hours observatories had identified the source of the event GW170817 within the galaxy NGC 4993 – shown in this Hubble Space Telescope image – and located the associated radioactive emissions, or “kilonova”. Hubble observed that flare of light fade over the course of six days, as shown in these observations taken on 22, 26 and 28 August (insets). (Courtesy: NASA, ESA; A Levan (University of Warwick), N Tanvir (University of Leicester), A Fruchter and O Fox (STScI))

Topics: Astronomy, Astrophysics, General Relativity, Gravitational Waves, LIGO, Neutron Stars

04 Jan 2018

Congratulations to Imre Bartos, whose article "A new cosmic messenger" has been picked as one of Physics World's five favourite features of 2018. Taken from the January 2018 issue of Physics World. Members of the Institute of Physics can enjoy the full issue via the Physics World app.

The first observation of gravitational waves from two merging neutron stars that was recently made by the LIGO and Virgo detectors has – along with data from telescopes across the globe and in space – kicked off a new era in multimessenger astronomy. Imre Bartos describes this watershed moment, which crowned decades of research and will shape the future of observational astronomy.

It was almost over. There was only one week to go before the Advanced LIGO and Virgo detectors would complete their observational run, and be shutdown for a year. Indeed, many of my colleagues from the LIGO–Virgo team were already on vacation, while I was awaiting relatives who were visiting. Then my phone buzzed. An automated text message, which read “ALERT FROM GWHEN | New event: G298048 | Check your email!” prompted me to rush to my computer, to look at the signal in a LIGO database. When a flurry of agitated phone calls from collaborators followed, it became clear that a historic moment was unfolding. We observational astronomers needed to act quickly, and as our findings were still a secret, I couldn’t even tell my relatives, who had arrived in the middle of the excitement, why I would need to work.

On 17 August 2017 the LIGO detectors in Louisiana and Washington detected gravitational waves from the collision of two neutron stars – ultracompact dead stars that weigh as much as our Sun, but are barely 20 km in diameter, roughly the size of Manhattan. Such an event had been anticipated for decades, but had never been observed until now. Within two seconds of the arrival of gravitational waves at LIGO, NASA’s Fermi Gamma-ray Space Telescope detected a short gamma-ray burst. This made it even clearer: the gravitational-wave detection – dubbed GW170817 – was not a false alarm, and observatories across the globe quickly needed to turn towards the direction of the collision, or the data would be lost forever. More than 70 telescopes and observatories around the globe and in space were rapidly notified, and were able to execute a co-ordinated survey of the merger and its aftermath, across the full electromagnetic spectrum – gamma-rays, X-rays, light, radio waves – and neutrinos. A new era in multimessenger astronomy had begun (figure 1).

What did we learn?

Neutron-star mergers may be the main source of heavy elements in the universe.

The expansion of the universe can be measured by neutron-star mergers,

We have a new upper limit on the mass of neutron stars.

The neutron stars in GW170817 orbited each other for billions of years before colliding.

The colliding neutron stars created a gamma-ray burst.

There’s something strange about the energetic jet.

A New Cosmic Messenger, Imre Bartos, Physics World
Imre Bartos is an assistant professor at the University of Florida in the US, where he studies extreme cosmic explosions related to the formation and evolution of black holes. He is a member of the LIGO Scientific Collaboration and an associate member of the IceCube Collaboration

Graphene Black Hole Hologram...

An image to illustrate the concept of holographic duality between a graphene flake and a black hole. Physics World

Topics: Black Holes, Einstein, General Relativity, Graphene, Nanotechnology, Quantum Mechanics

Much research on black holes is theoretical since it is difficult to make actual measurements on real black holes. Such experiments also need to be undertaken over decades or longer. Physicists are therefore keen to create laboratory systems that are analogous to these cosmic entities. New theoretical calculations by a team in Canada, the US, UK and Israel have now revealed that a material as simple as a graphene flake with an irregular boundary subjected to an intense external magnetic field can be used to create a quantum hologram that faithfully reproduces some of the signature characteristics of a black hole. This is because the electrons in the carbon material behave according to the Sachdev-Ye-Kitaev model.

Some of the most important unresolved mysteries in modern physics come from the “incompatibility” between Einstein’s theory of general relativity and the theory of quantum mechanics. General relativity describes the physics of the very big (the force of gravity and all that it affects: spacetime, planets, galaxies and the expansion of the Universe). The theory of quantum mechanics is the physics of the very small – and the other three forces, electromagnetism and the two nuclear forces.

“In recent years, physicists have gleaned important new insights into these questions through the study of the SYK model,” explains Marcel Franz of the University of British Columbia in Canada, who led this research effort. “This model is an illustration of a type of ‘holographic duality’ in which a lower-dimensional system can be represented by a higher dimensional one. In our calculations, the former is N graphene electrons in (0+1) dimensions and the latter the dilation gravity of a black hole in (1+1) dimensional anti-de Sitter (AdS2) space.

Black hole hologram appears in a graphene flake, Belle Dumé, Physics World

Galactic Validation...

Scientists have tested Einstein’s theory of general relativity to new degrees of precision using the giant elliptical galaxy ESO 325-G004, the yellow ball of stars near the upper left side of this image. Credit: NASA, ESA, and The Hubble Heritage Team (STScI/AURA)

Topics: Astrophysics, Cosmology, Einstein, General Relativity

Astronomers have used a pair of galaxies far beyond the Milky Way to test general relativity with unprecedented precision

Three years ago astrophysicist Tom Collett set out to test a theory. Not just any theory, but one that sets scientists’ expectations for how the universe operates at large: Einstein’s general relativity. First published in 1915, the theory mathematically describes how gravity emerges from the fundamental geometry of space and time, or spacetime, as physicists call it. It postulates that dense objects, such as Earth and the sun, create valleylike dips in spacetime that manifest as gravity—the force that binds together a galaxy’s swirling stars, places planets around suns and, on Earth (or any other planet), keeps your feet on the ground.

Einstein’s equations underpin a host of real-world applications such as the global positioning satellites that make precise navigation and split-second financial transactions possible around the planet. They also elucidate several otherwise-inexplicable phenomena, including Mercury’s oddball orbit, as well as predict new ones, such as gravitational waves—ripples in spacetime that were only directly observed a century after general relativity’s debut. In test after test, whether here on Earth or in observations of the distant universe, the theory has emerged unscathed—a success so stunningly unshakeable it draws a certain breed of scientists like moths to a flame—each seeking to reveal cracks in Einstein’s edifice that could lead to the next breakthrough in physics.

Collett, a research fellow at the University of Portsmouth in England, is among them. “General relativity is so fundamental to the assumptions we make in our interpretation of cosmological and astrophysical data sets that we’d better be sure it’s right,” he says. With that mind-set, in 2015 Collett partnered with nine colleagues to perform the most sensitive experiment yet to test whether Einstein’s famed theory holds up at the scale of an entire galaxy. Their results, published June 21 in Science, reiterate Einstein’s theory still reigns supreme.

Einstein’s Greatest Theory Validated on a Galactic Scale, Maya Miller, Scientific American

The Pretenders...

Credit: NASA, ESA; D. Coe; J. Anderson; R. van der Marel (STScI)

Topics: Astrophysics, Black Holes, Cosmology, General Relativity, Quantum Gravity

New research reveals a possible mechanism allowing “black stars” and “gravastars” to exist

When giant stars die, they don’t just fade away. Instead they collapse in on themselves, leaving behind a compressed stellar remnant, usually a city-size, superdense ball of neutrons appropriately called a neutron star. In extreme cases, however, most theorists believe an expiring giant star will form a black hole—a pointlike “singularity” with effectively infinite density and a gravitational field so powerful that not even light, the fastest thing in the universe, can escape once falling in. Now a new study is reinvigorating an alternate idea, that objects with names such as “black stars,” or “gravastars,” might exist midway between neutron stars and black holes. If real, these exotic stellar corpses should appear nearly identical to black holes save in one key way—they could not irretrievably swallow light.

There are good reasons to seek such alternatives, because black holes raise a host of theoretical problems. For instance, their singularities are supposedly hidden by invisible boundaries known as event horizons. Throw something into a black hole, and once it passes the event horizon it should be gone—forever—with no hope whatsoever of return. But such profound annihilation clashes with other long-cherished laws of physics that suggest the destruction of information is impossible, including information encoded within anything falling into black holes.

Conceived and developed across the past two decades, in part to sidestep such conundrums, models of black stars and gravastars postulate these objects would lack singularities and event horizons. But questions have lingered as to whether such objects could actually form—and remain stable after they did. New research from theoretical physicist Raúl Carballo-Rubio at the International School for Advanced Studies in Italy provides a novel mechanism that might allow black stars and gravastars to exist.

Carballo-Rubio investigated a strange phenomenon known as quantum vacuum polarization. Quantum physics, the best description yet of how all known subatomic particles behave, suggests reality is fuzzy, limiting how precisely one can know the properties of the most basic units of matter—for instance, one can never absolutely know a particle's position and momentum at the same time. One strange consequence of this uncertainty is that a vacuum is never completely empty but instead foams with so-called “virtual particles” that continuously fluctuate into and out of existence.

Black Hole Pretenders Could Really Be Bizarre Quantum Stars, Charles Q. Choi, Scientific American

The First Black Holes...

Credit: Mark Ross

Topics: Astrophysics, Black Holes, Cosmology, General Relativity

How could the oldest black holes have grown so big so early in the universe?

Imagine the universe in its infancy. Most scientists think space and time originated with the big bang. From that hot and dense start the cosmos expanded and cooled, but it took a while for stars and galaxies to start dotting the sky. It was not until about 380,000 years after the big bang that atoms could hold together and fill the universe with mostly hydrogen gas. When the cosmos was a few hundred million years old, this gas coalesced into the earliest stars, which formed in clusters that clumped together into galaxies, the oldest of which appears 400 million years after the universe was born. To their surprise, scientists have found that another class of astronomical objects begins to appear at this point, too: quasars.

Quasars are extremely bright objects powered by gas falling onto supermassive black holes. They are some of the most luminous things in the universe, visible out to the farthest reaches of space. The most distant quasars are also the most ancient, and the oldest among them pose a mystery.

To be visible at such incredible distances, these quasars must be fueled by black holes containing about a billion times the mass of the sun. Yet conventional theories of black hole formation and growth suggest that a black hole big enough to power these quasars could not have formed in less than a billion years. In 2001, however, with the Sloan Digital Sky Survey, astronomers began finding quasars that dated back earlier. The oldest and most distant quasar known, which was reported last December, existed just 690 million years after the big bang. In other words, it does not seem that there had been enough time in the history of the universe for quasars like this one to form.

Many astronomers think that the first black holes—seed black holes—are the remnants of the first stars, corpses left behind after the stars exploded into supernovae. Yet these stellar remnants should contain no more than a few hundred solar masses. It is difficult to imagine a scenario in which the black holes powering the first quasars grew from seeds this small.

To solve this quandary, a decade ago some colleagues and I proposed a way that seed black holes massive enough to explain the first quasars could have formed without the birth and death of stars. Instead these black hole seeds would have formed directly from gas. We call them direct-collapse black holes (DCBHs). In the right environments, direct-collapse black holes could have been born at 10⁴ or 10⁵ solar masses within a few hundred million years after the big bang. With this head start, they could have easily grown to 10⁹ or 10¹⁰ solar masses, thereby producing the ancient quasars that have puzzled astronomers for nearly two decades.

The question is whether this scenario actually happened. Luckily, when the James Webb Space Telescope (JWST) launches in 2019, we should be able to find out.

The Puzzle of the First Black Holes, Priyamvada Natarajan, Scientific American

Proto Bang...

and before the beginning...Image Source: Link below

Topics: Astrophysics, Big Bang, Cosmology, General Relativity

Although for five decades, the Big Bang theory has been the best known and most accepted explanation for the beginning and evolution of the Universe, it is hardly a consensus among scientists.

Brazilian physicist Juliano Cesar Silva Neves part of a group of researchers who dare to imagine a different origin. In a study recently published in the journal General Relativity and Gravitation, Neves suggests the elimination of a key aspect of the standard cosmological model: the need for a spacetime singularity known as the Big Bang.

In raising this possibility, Neves challenges the idea that time had a beginning and reintroduces the possibility that the current expansion was preceded by contraction. "I believe the Big Bang never happened," the physician said, who Works as a researcher at the University of Campinas's Mathematics, Statistics and Scientific Computation Institute (IMECC-UNICAMP) in Sao Paulo State, Brazil.

For Neves, the fast spacetime expansion stage does not exclude the possibility of a prior contraction phase. Moreover, the switch from contraction to expansion may not have destroyed all traces of the preceding phase.

Physicist assumes the possibility of vestiges of an Universe previous to the Big Bang
Staff Writers, Space Daily

Milky Way and Einstein...

This artist’s rendition shows the orbits of stars circling the supermassive black hole (blue halo) at the Milky Way’s center. A close analysis suggests the stars’ orbits are showing subtle effects predicted by Einstein’s theory of general relativity. Credit: ESO/M. Parsa/L. Calçada

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

A giant star near the center of our galaxy hints, once again, that Albert Einstein was correct about gravity.

A group of astronomers in Germany and the Czech Republic observed three stars in a cluster near the supermassive black hole at the center of the Milky Way galaxy. Using data from the Very Large Telescope in Chile, among others, the researchers tracked how the stars moved as they went around the monster black hole.

One of the stars, called S2, showed slight deviations in its orbit that might indicate relativistic effects, scientists said. If the observations are confirmed, then it shows that Einstein's theory of general relativity holds even under extreme conditions — in gravity fields produced by objects like the galactic center's black hole, which contains the mass of 4 million suns. General relativity says that massive objects bend the space around them, causing other objects to deviate from straight lines they would follow absent any forces on them.

Closest Supermassive Black Hole Tests Einstein’s Relativity, Jesse Emspak, SPACE.com and Scientific American

Aiming at Einstein...

Images Source: Link below

Topics: Astrophysics, Black Holes, Einstein, General Relativity, Diversity in Science, Women in Science

If you cast an observational lasso into the center of the Milky Way galaxy and pull it closed, you will find a dense, dark lump: a mass totaling some four million suns, crammed into a space no wider than twice Pluto’s orbit in our solar system.

In recent years, astronomers have come to agree that inside this region is a supermassive black hole, and that similar black holes lurk at the cores of nearly all other galaxies as well. And for those revelations, they give a lot of credit to Andrea Ghez.

Since 1995, Ghez, an astrophysicist at the University of California, Los Angeles, has used the W.M. Keck telescope on Mauna Kea in Hawaii to see fine details at the center of the galaxy. The observations that Ghez has made of stars racing around the Milky Way’s core (alongside those of rival Reinhard Genzel, an astrophysicist at the Max Planck Institute for Astrophysics in Garching, Germany) have proven to most astronomers that the central object can be nothing but a black hole. But to be able to see these fine details, Ghez had to become a pioneering user of adaptive optics, a technology that measures distortions in the atmosphere and then adjusts the telescope in real time to cancel out those fluctuations. The technique produces images that look as if they were taken under the calmest possible skies.

In Ghez’s mind, new discoveries require that scientists take risks. “If you have a new idea, the thing you are going to encounter first and foremost is ‘no, you can’t do it,’” she said. “I can’t tell you how many times in the course of this project I have been told ‘this won’t work.’” Her first proposal to image the galactic center was turned down; two decades later, Ghez, now 52, has received a MacArthur Fellowship, among other awards, and was the first woman to receive a Crafoord Prize from the Royal Swedish Academy of Sciences.

Black-Hole Hunter Takes Aim at Einstein, Joshua Sokol, Quanta Magazine

Star Weight...

Image Source: Link below

Topics: Astronomy, Astrophysics, Einstein, General Relativity, Gravitational Lensing, White Dwarfs

The passage of a white dwarf almost in front of a distant background star created the conditions for gravitational lensing

Einstein’s general theory of relativity predicts that in the gravitational field of a massive body, light rays should bend by an angle that depends on the body’s mass. Researchers at the Space Telescope Science Institute have now exploited that effect, known as gravitational lensing, to determine the mass of a star. For two years, the team tracked white dwarf Stein 2051 B as it crossed in front of a distant background star. The Hubble image shows Stein 2051 B and the background star, labeled “Source,” on 1 October 2013. Overlain are the nearer star’s trajectory and dots indicating its location on seven subsequent imaging dates. (The trajectory appears curved due to parallax.) At their closest, the stars were separated by a mere 10th of an arcsecond—roughly the angle subtended in the sky by Pluto.

As the stars came into alignment, gravitational lensing by the white dwarf subtly distorted the apparent position of the background star. Specifically, the background star appeared to trace an ellipse a couple of milliarcseconds wide, even though its actual position in the sky all but remained fixed. From the ellipse’s dimensions the researchers could infer Stein 2051 B’s mass, roughly two-thirds that of the Sun.

Weighing a star with light, Ashley G. Smart, Physics Today

Confirmed Again...

FILE PHOTO: This NASA/ESA Hubble Space Telescope image shows the bright star-forming ring that surrounds the heart of the barred spiral galaxy NGC 1097, a Seyfert galaxy. NASA/ESA/Hubble/Handout via REUTERS/File Photo

Topics: Astrophysics, Einstein, General Relativity, Gravitational Lensing

The first observation of gravitational microlensing by a star other than the Sun has been reported by astronomers using the Hubble Space Telescope. Predicted by Albert Einstein as a consequence of his general theory of relativity, gravitational microlensing involves the gravitational field of a star bending light coming from a more distant star. It was first observed during a total eclipse in 1919 by looking for deflections in the positions of stars in parts of the sky next to the Sun. Now, Kailash Sahu of the Space Telescope Science Institute in the US and an international team have measured the gravitational lensing of a background star by a white dwarf star called Stein 2051 B. Because the background star is not lined-up perfectly with Earth and Stein 2051 B, a combination of gravitational lensing and Earth's motion around the Sun causes the background star to appear to trace out a loop around Stein 2051 B. Sahu and colleagues mapped its position at five different times in 2013-14 and used this information to calculate the mass of Stein 2051 B. It turns out that astronomers have puzzled over the mass of the white dwarf for over 100 years. It is part of a binary system and the motion of its distant companion suggests that Stein 2051 B has a smaller mass than most white dwarfs, implying that it might have an exotic composition. This recent work, however, suggests that the star has a mass expected for a white dwarf of its radius. The observations will be described in and upcoming paper in Science. [1]

* * * * * * * * * *

CAPE CANAVERAL, Fla. - Astronomers have found a new application for Albert Einstein's century-old theory of relativity - using it to directly measure the size of a star beyond the sun.

In research published on Wednesday, scientists said they used the Hubble Space Telescope to plot minute changes in the path of light coming from a distant background star as it passed by a relatively close target star, known as Stein 2051B.

Researchers applied Einstein's findings to measure how Stein 2051B's gravity warped the background star's light, a phenomenon the physicist predicted more than 100 years ago and a direct means to assess its mass. The technique could be applied to other stars.

"It was like measuring the motion of a little firefly in front of a light bulb from 1,500 miles away," astronomer Kailash Sahu of the Space Telescope Science Institute in Baltimore said at a news conference.

The research was presented at a meeting of the American Astronomical Society in Austin, Texas, on Wednesday and also published in this week's issue of the journal Science. [2]

1. Flash Physics: Bent light reveals stellar mass, amorphous topological insulators, Tibetan Plateau rose rapidly, Sarah Tesh, Physics World
2. Einstein's theory provides new technique to size up stars, Reporting by Irene Klotz; Editing by Letitia Stein and Bill Trott, Reuters Science

Pushing the Quantum Limit...

A zoom in on the Josephson junctions. Two layers of niobium are visible in the image, with the upper film colored blue and the lower film colored red. Josephson junctions are formed in the circular pits (they look a bit like an element of a muffin tin) where the two layers overlap (green). Credit: K. Lehnert/NIST/JILA

Topics: Black Holes, Dark Matter, General Relativity

Here’s a surprising fact: We don’t know what makes up 80 percent of the matter in the universe. I don’t mean that the matter is made of atoms, and we just don’t know which kind of atoms. What I mean is that four-fifths of the universe appears to be made of something that isn’t atoms at all, or more to the point, it’s not made from any of the fundamental particles that we know of.

Why do we think that this mystery matter exists? The short answer is that Albert Einstein’s theory of gravity, general relativity, has painted us into a corner. When we look through telescopes at stars and galaxies moving through the universe, something we can’t see is causing their motion to bend in a particular way. Einstein’s theory of gravity tells how much of this invisible mass—physicists call it “dark matter”—there must be to bend the trajectory of things we can see.

Faced with a situation like this, we make guesses (hypotheses) that we hope explain our strange observations. A good hypothesis should both be consistent with every known fact and have other detectable consequences. If we look for these other consequences and don’t find them, we discard or revise our hypothesis.

Somewhat to my surprise, I find myself working on an experiment designed to look for the consequences of a hypothetical dark matter particle known as the axion. This was surprising because physicists, like those in all professions, divide themselves up into distinct sub-fields. Predictably there are rivalries between, and stereotypes associated with, different cultures that build up around the subfields—the rough equivalent of engineering versus sales in the corporate world.

NIST: Pushing the Quantum Limit in the Search for Dark Matter, Konrad Lehnert

Fifth at the Center...

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

General relativity has stood the test of time. But researchers are still exploring alternatives to the theory, attempting to unify gravity with other forces or to explain observations attributed to dark matter and dark energy. Many of these theories involve an additional force beyond the four known fundamental forces. Now, Andrea Ghez and Aurélien Hees at the University of California, Los Angeles, and co-workers, have analyzed the orbits of stars around the Milky Way’s center to derive limits on such a fifth force. While similar constraints had been obtained in weak gravitational fields, this is the first time fifth-force scenarios have been tested in a strong field, such as that created by the supermassive black hole at the center of our Galaxy. [1]

* * * * * * * * * *

Our current understanding of the Universe states that it's governed by four fundamental forces: gravity, electromagnetic, and the strong and weak nuclear forces.

But there are hints of a fifth force of nature, and if it exists, we'd not only be able to fill the remaining holes in Einstein's general relativity - we'd have to rethink our understanding of how the Universe actually works. And now physicists have figured out how to put this mysterious force to the ultimate test.

Gravity and the electromagnetic force are on the larger end of the scale - electromagnetic force is needed to keep our molecules together, while gravity is responsible for ensuring that entire galaxies and planets aren't ripped apart.

It's all very neat and sensible, but there's a problem - in a lot of ways, gravity is the 'odd one out' in this very important group.

For one thing, gravity is the last of the four fundamental forces that humans haven't figured out how to produce and control.

It also doesn't appear to explain everything that it should - studies have shown that there's more gravity in our Universe than can be produced by all the visible matter out there. [2]

1. Synopsis: Restricting the Fifth Force, Matteo Rini
2. Physicists Are Probing The Centre of Our Galaxy to Find The Missing Fifth Force of Nature,
BEC CREW

#P4TC related link

Fifth Force...May 31, 2016

Given The Boot...

This Hubble Space Telescope image shows a quasar (bright object at center) and its host galaxy, 3C186 (the diffuse object behind it). Scientists think 3C186’s central black hole was ejected from the galaxy’s core by gravitational waves.
Credit: NASA, ESA, and M. Chiaberge (STScI/ESA)

Topics: Black Holes, Cosmology, General Relativity, Gravitational Waves

A supermassive black hole heftier than 1 billion suns has been ejected from the core of its galaxy by gravitational waves, a new study suggests.

The monster black hole has already zoomed 35,000 light-years away from its galaxy's center, farther than Earth and its sun are from the core of our own Milky Way. And the behemoth is currently traveling outward at 4.7 million mph (7.6 million km/h) — fast enough for the black hole to escape its galaxy completely in 20 million years, researchers said.

“We estimate that it took the equivalent energy of 100 million supernovae exploding simultaneously to jettison the black hole,” study co-author Stefano Bianchi, from Roma Tre University in Italy, said in a statement.

Space.com: Gravitational Waves Boot Gigantic Black Hole from Galaxy's Core
Mike Wall

Crib Notes...

Topics: Einstein, General Relativity, Special Relativity

Sometimes I get questions clear out of the blue that are a joy to answer, as curiosity should be rewarded with a sincere response.

A friend emailed me (I left their name out to protect their privacy) and said: "I'm interested in many different things - I love How The Universe Works and Secrets of the Universe type programs. Of course there are things I don't understand but I get the basics. Anyway, I am watching one entitled 'Was Einstein Wrong?' and they talk about his General Theory of Relativity AND his Special Theory of Relativity. My question is are they the same theory and are names the interchangeable? When I search online for General it refers to E=mc2. When I search for Special, E=mc2 is the only equation that's displayed."

My friend also asked about this:

The program periodically shows this...but doesn't say what it is and no, I have no idea what it means, but is this the Special theory?

I have to admit, it's a refreshing thing not being trolled and actually asked questions about science.

I purposely didn't go into the math (but I left reference links below for the stout-of-heart), this was my reply:

Dear (friend's name omitted),

1905: The Special Theory of Relativity – think speed. Prior to Einstein, everything was in a slower, Newtonian universe, and Newton’s 3 Laws of Motion applied to things like inertia, acceleration and recoil.

However, as we started discovering things like the speed of light (186,232 miles per second, 300,000,000 meters per second), measured in the Michelson-Morley Experiment. “C” is just shorthand. It’s kind of lazy, but everyone knows what you mean when they see it or say it.

Alpha particles, electrons and measuring their speeds at some fraction of c, the Newtonian rules didn’t apply anymore. Special Relativity deals with objects or observers (or, frames of reference) that are moving with uniform velocities relative to each other, hence “relativity.”

Albert Einstein determined that the laws of physics are the same for all non-accelerating observers, and that the speed of light in a vacuum was independent of the motion of all observers. This was the theory of special relativity. It introduced a new framework for all of physics and proposed new concepts of space and time, coining a new term for the public lexicon: space-time.

This was also called Einstein’s annus mirabilis, or “Miracle Year.” He published four papers: The Photoelectric Effect, Brownian Motion, Special Relativity and Mass-Energy Equivalence (E = mc-squared). A video: https://youtu.be/91XI7M9l3no

1915: Einstein then spent ten years trying to include acceleration in the theory and published his theory of general relativity in 1915. In it, he determined that massive objects cause a distortion in space-time, which is felt as gravity. Think of a bowling ball on a trampoline, in this case, space-time is the trampoline, the stars, planets, brown dwarfs, white dwarfs, black holes the bowling balls. One of the applications of General Relativity is Global Positioning Systems (GPS). This theory was confirmed in 1919 during a solar eclipse where Gravitational Lensing (bending of starlight) was observed.

Nerd Trivia: 3/14/2015 was Einstein’s birthday, and such was used as National Pi Day (3.14159 – get it?), and 100 years on November 25th of his paper on General Relativity, but you can’t get Pi out of 11/25/15, o_9.

On the symbolic equation above:

This is Tensor Calculus, or Differential Geometry. Einstein learned it from Grossmann (a mathematician) to describe space-time curvature in General Relativity. The Mu (μ) and Nu (ν) are Tensor coordinates; G in the numerator next to 8π is Newton's gravitational constant (“c” in the denominator you know). Believe it or not, Einstein struggled a little bit as Grossmann taught him; Einstein in turn taught him physics. His related quote:

“Do not worry about your difficulties in mathematics. I can assure you that mine are greater.”

One of my favorite quotes from Einstein. Albert Einstein was a contemporary of Paul Robeson, and due to the way Jews were treated (and exterminated) in Germany by the Nazis, he was a champion of Civil Rights:

From "Ideas and Opinions," by Albert Einstein:

"It seems to be a universal fact that minorities--especially when the individuals composing them can be recognized by physical characteristics--are treated by the majorities among whom they live as an inferior order of beings. The tragedy of such a fate lies not merely in the unfair treatment to which these minorities are automatically subjected in social and economic matters, but also in the fact that under the suggestive influence of the majority most of the victims themselves succumb to the same prejudice and regard their kind as inferior beings. This second and greater part of the evil can be overcome by closer association and by deliberate education of the minority, whose spiritual liberation can thus be accomplished.

"The resolute efforts of the American Negroes in this direction deserve approval and assistance."

Mein Weltbild (my conception of the world), Amsterdam: Querido Verlog, 1934, pp 117-118.

Einstein’s advice to a little girl that wanted to be a scientist: Dear Professor Einstein

As you can tell, I'm a BIG fan. :-)

Blessings,

Reggie

The long answer on “c”: http://math.ucr.edu/home/baez/physics/Relativity/SpeedOfLight/c.html

Helpful math reference links:

Wm. Robert Johnson: Some equations of special relativity

Wikipedia: Einstein Field Equations (EFE), not to be confused with "BFE," of course.

Wolfram Physics

Special Relativity
General Relativity

"Let us remember: One book, one pen, one child, and one teacher can change the world." Malala Yousafzai

"It is the supreme art of the teacher to awaken joy in creative expression and knowledge." Albert Einstein