Our Galaxy’s Supermassive Black Hole Has Emitted a Mysteriously Bright Flare



Our Galaxy’s Supermassive Black Hole Has Emitted a Mysteriously Bright Flare

12 AUG 2019

The supermassive black hole at the heart of the Milky Way, Sagittarius A*, is relatively quiet. It’s not an active nucleus, spewing light and heat into the space around it; most of the time, the black hole’s activity is low key, with minimal fluctuations in its brightness.

Most of the time. Recently, astronomers caught it going absolutely bananas, suddenly growing 75 times brighter before subsiding back to normal levels. That’s the brightest we’ve ever seen Sgr A* in near-infrared wavelengths.

“I was pretty surprised at first and then very excited,” astronomer Tuan Do of the University of California Los Angeles told ScienceAlert.

“The black hole was so bright I at first mistook it for the star S0-2, because I had never seen Sgr A* that bright. Over the next few frames, though, it was clear the source was variable and had to be the black hole. I knew almost right away there was probably something interesting going on with the black hole.”

But what? That’s what astronomers are on a mission to find out. Their findings so far are currently in press with The Astrophysical Journal Letters.

Do and his team took observations of the galactic center galaxy

using the WM Keck Observatory in Hawaii over four nights earlier this year. The strange brightening was observed on May 13, and the team managed to capture it in a time lapse, two hours condensed down to a few seconds.

Tuan Do@quantumpenguin

Here’s a timelapse of images over 2.5 hr from May from @keckobservatory of the supermassive black hole Sgr A*. The black hole is always variable, but this was the brightest we’ve seen in the infrared so far. It was probably even brighter before we started observing that night!

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That brightly glowing dot right at the beginning of the video is the dust and gas swirling around Sgr A*. Black holes themselves don’t emit any radiationthat can be detected by our current instruments, but the stuff nearby doeswhen the black hole’s gravitational forces generate immense friction, in turn producing radiation.

When we view that radiation with a telescope using the infrared range, it translates as brightness. Normally, the brightness of Sgr A* flickers a bit like a candle, varying from minutes to hours. But when the surroundings of a black hole flare that brightly, it’s a sign something may have gotten close enough to be grabbed by its gravity.

The first frame – taken right at the beginning of the observation – is the brightest, which means Sgr A* could have been even brighter before they started observing, Do said. But no one was aware that anything was drawing close enough to be swallowed by the black hole.

The team is busily gathering data to try and narrow it down, but there are two immediate possibilities. One is G2, an object thought to be a gas cloud that approached within 36 light-hours of Sgr A* in 2014. If it was a gas cloud, this proximity should have torn it to shreds, and parts of it devoured by the black hole – yet nothing happened.

The flyby was later called a “cosmic fizzle“, but the researchers believe the black hole’s May fireworks show may have been a delayed reaction.

sgr a s02(Do et al., arXiv, 2019)

But – have a look at the timelapse again. See that bright dot at around 11 o’clock from the black hole? That’s S0-2, a star on a long, looping, 16-year elliptical orbit around Sgr A*. Last year, it made its closest approach, coming within 17 light-hours of the black hole.

“One of the possibilities,” Do told ScienceAlert, “is that the star S0-2, when it passed close to the black hole last year, changed the way gas flows into the black hole, and so more gas is falling on it, leading it to become more variable.”

The only way to find out is having more data. They are currently being collected, across a larger range of wavelengths. More observations will take place over the coming weeks with the ground-based Keck Observatory before the galactic centre is no longer visible at night from Earth.

But many other telescopes – including Spitzer, Chandra, Swift and ALMA – were observing the galactic centre over the last few months, too. Their data could reveal different aspects of the physics of the change in brightness, and help us understand what Sgr A* is up to.

“I’m eagerly awaiting their results,” Do said.

The paper has been accepted into The Astrophysical Journal Letters, and is available on arXiv.

“Gargantua” –The Black Hole That Could Swallow Our Solar System



“Gargantua” –The Black Hole That Could Swallow Our Solar System


M87 Galaxy


This past April, with an event that was as epic as the Apollo 11 landing on the Moon, the world viewed its first image of what had once been purely theoretical, a black hole at the heart of galaxy M87 the size of our solar system, and bigger, with the mass of six and a half billion suns that was captured by a lens the size of planet Earth and 4,000 times more powerful than the Hubble Space Telescope.

Astronomers have theorized that the galaxy that harbors the black hole grew to its massive size by merging with several other black holes in elliptical galaxy M87, the largest, most massive galaxy in the nearby universe thought to have been formed by the merging of 100 or so smaller galaxies. The M87 black hole’s large size and relative proximity, led astronomers to think that it could be the first black hole that they could actually “see.”

The black hole that that we can now actually see is frozen in time it was 55 million years ago, because it’s so far away the light took that long to reach us. “Over those eons, we emerged on Earth along with our myths, differentiated cultures, ideologies, languages and varied beliefs,” says astrophysicist Janna Levin with Columbia University.

“The Gates of Hell, The End of Spacetime” –World’s Scientists Speak Out On EHT’s Black Hole Picture

The Event Horizon Telescope that imaged the black hole is actually 10 telescopes, linked across four continents in the United States, Mexico, Chile, Spain, and Antarctica, and designed to scan the cosmos in radio waves. For a few days in April 2017, the observatories studied the skies in tandem, creating a gargantuan telescope nearly the size of the planet.

“A medium-sized galaxy fell through the center of M87, and as a consequence of the enormous gravitational tidal forces, its stars are now scattered over a region that is 100 times larger than the original galaxy!” said Ortwin Gerhard, head of the dynamics group at the Max Planck Institute for Extraterrestrial Physics.  Observations July 2018 with ESO’s Very Large Telescope revealed that the giant elliptical galaxy swallowed the entire medium-sized galaxy over the last billion years.

“What Sparked the Big Bang?” –The Black Hole at the Beginning of the Universe

M87, imaged above by NASA’s Spitzer Space Telescope, is home to the supermassive black hole that spews two jets of material out into space at nearly the speed of light. The inset shows a close-up view of the shockwaves created by the two jets. This image from NASA’s Spitzer Space Telescope shows the entire M87 galaxy in infrared light.

Located about 55 million light-years from Earth, M87 has been a subject of astronomical study for more than 100 years and has been imaged by many NASA observatories, including the Hubble Space Telescope, the Chandra X-ray Observatory and NuSTAR.

“Worlds in Collision” –Dangers of Milky Way’s ‘Reawakened’ Supermassive Black Hole

In 1918, astronomer Heber Curtis first noticed “a curious straight ray” extending from the galaxy’s center. This bright jet of high-energy material, produced by a disk of material spinning rapidly around the black hole, is visible in multiple wavelengths of light, from radio waves through X-rays. When the particles in the jet impact the interstellar medium (the sparse material filling the space between stars in M87), they create a shockwave that radiates in infrared and radio wavelengths of light but not visible light. In the Spitzer image, the shockwave is more prominent than the jet itself.



This zoom video above starts with a view of the ALMA telescope array in Chile and zooms in on the heart of M87, showing successively more detailed observations and culminating in the first direct visual evidence of a supermassive black hole’s silhouette. (ESO/L. Calçada, Digitized Sky Survey 2, ESA/Hubble, RadioAstron, De Gasperin et al., Kim et al., EHT Collaboration).


M87 Black Hole


On the right is the first-ever image of the black hole at the heart of galaxy M87, taken by the Event Horizon Telescope. The NASA Chandra X-ray Observatory’s wide-field view of the M87 galaxy (left) reveals the jet of high-energy particles launched by the intense gravitational and magnetic fields around the black hole. Credit: X-ray (left): NASA/CXC/Villanova University/J. Neilsen; Radio (right): Event Horizon Telescope Collaboration.

Harvard history of science professor Peter L. Galison, a collaborator on Event Horizon Telescope (EHT), said that scientists proposed theoretical arguments for black holes as early as 1916. It was not until the 1970s, however, that researchers substantiated the theory by observing extremely dense areas of matter. Scientists announced in 2016 that, for the first time, they had detected gravitational waves — which many argued were produced by black holes merging, and therefore were evidence that black holes exist.

The image marked the culmination of years of work undertaken by a team of 200 scientists in 59 institutes across 18 countries. The project, to which other scientists at Harvard’s Black Hole Institute also contributed, drew on data collected by eight telescopes whose locations range from Hawaii to the South Pole.

“A Fractured Cosmos?” –Unknown Object Detected at Milky Way’s Black Hole

In contrast to M87’s monster, 1,500 times more massive than the Milky Way’s central black hole, Sag A* has four million times the mass of our sun, which means that it’s about 44 million kilometers across. That may sound like a big target, but for the telescope array on Earth some 26,000 light-years (or 245 trillion kilometers) away, it’s like trying to photograph a golf ball on the Moon.

“The Last Photon Orbit” –Milky Way’s Supermassive Black Hole ‘On Deck’ for the EHT

“More than 50 years ago, scientists saw that there was something very bright at the center of our galaxy,” Paul McNamara, an astrophysicist at the European Space Agency and an expert on black holes, AFP’s Marlowe Hood. It has a gravitational pull strong enough to make stars orbit around it very quickly—as fast as 20 years, compared to our Solar System’s journey, which takes about 230 million years to circle the center of the Milky Way.

“We are sitting in the plain of our galaxy—you have to look through all the stars and dust to get to the center,” said McNamara.

The Daily Galaxy via EHTThe GuardianThe AtlanticNew York Times

Astrophysicists announce discovery that could rewrite story of how galaxies die



Astrophysicists announce discovery that could rewrite story of how galaxies die

Astrophysicist announces her discovery that could rewrite story of how galaxies die
This artist conception depicts an energetic quasar which has cleared the center of the galaxy of gas and dust, and these winds are now propagating to the outskirts. Soon, there will be no gas and dust left, and only a luminous blue quasar will remain. Credit: Michelle Vigeant

At the annual meeting of the American Astronomical Society in St. Louis, Missouri, Allison Kirkpatrick, assistant professor of physics and astronomy at the University of Kansas, will announce her discovery of “cold quasars”—galaxies featuring an abundance of cold gas that still can produce new stars despite having a quasar at the center—a breakthrough finding that overturns assumptions about the maturation of galaxies and may represent a phase of every galaxy’s lifecycle that was unknown until now.

Her news briefing, entitled “A New Population of Cold Quasars,” takes place Wednesday, June 12, on the 2nd floor of the St. Louis Union Station Hotel.

A quasar, or “quasi-stellar radio source,” is essentially a  on steroids. Gas falling toward a quasar at the center of a galaxy forms an “accretion disk” which can cast off a mind-boggling amount of electromagnetic energy, often featuring luminosity hundreds of times greater than a typical galaxy. Typically, formation of a quasar is akin to galactic retirement, and it’s long been thought to signal an end to a galaxy’s ability to produce .

“All the gas that is accreting on the black hole is being heated and giving off X-rays,” Kirkpatrick said. “The wavelength of light that you give off directly corresponds to how hot you are. For example, you and I give off infrared light. But something that’s giving off X-rays is one of the hottest things in the universe. This gas starts accreting onto the black hole and starts moving at relativistic speeds; you also have a magnetic field around this gas, and it can get twisted up. In the same way that you get solar flares, you can have jets of material go up through these magnetic field lines and be shot away from the black hole. These jets essentially choke off the gas supply of the galaxy, so no more gas can fall on to the galaxy and form new stars. After a galaxy has stopped forming stars, we say it’s a passive dead galaxy.”

But in Kirkpatrick’s survey, about 10 percent of  hosting accreting supermassive  had a supply of cold gas remaining after entering this phase, and still made new .

Astrophysicist announces her discovery that could rewrite story of how galaxies die
An optical blue quasar at a lookback time of 7 billion years (this is not a nearby galaxy). Normally, something like this would not have infrared emission. Credit: Dark Energy Camera Legacy Survey DR7/NOAO

“That in itself is surprising,” she said. “This whole population is a whole bunch of different objects. Some of the galaxies have very obvious merger signatures; some of them look a lot like the Milky Way and have very obvious spiral arms. Some of them are very compact. From this diverse population, we then have a further 10 percent that is really unique and unexpected. These are very compact, blue, luminous sources. They look exactly like you would expect a supermassive black hole to look in the end stages after it has quenched all of the star formation in a galaxy. This is evolving into a passive elliptical galaxy, yet we have found a lot of cold gas in these as well. These are the population that I’m calling ‘cold quasars.'”

The KU astrophysicist suspected the “cold quasars” in her survey represented a brief period yet to be recognized in the end-phases of a galaxy’s lifespan—in terms of a human life, the fleeting “cold quasar” phase may something akin to a galaxy’s retirement party.

“These galaxies are rare because they’re in a transition phase—we’ve caught them right before star formation in the galaxy is quenched and this transition period should be very short,” she said.

Kirkpatrick first identified the objects of interest in an area of the Sloan Digital Sky Survey, the most detailed digital map of the universe available. In an area dubbed “Stripe 82,” Kirkpatrick and her colleagues were able to visually identify quasars.

“Then we went over this area with the XMM Newton telescope and surveyed it in the X-ray,” she said. “X-rays are the key signature of growing black holes. From there, we surveyed it with the Herschel Space Telescope, a far infrared telescope, which can detect dust and gas in the host galaxy. We selected the galaxies that we could find in both the X-ray and in the infrared.”

Astrophysicist announces her discovery that could rewrite story of how galaxies die
The dust emission of the same blue-quasar galaxy. It is surprisingly bright — in fact, it’s one of the brightest objects in the field, indicating a lot of dust. Due to the resolution of the telescope, we cannot see what that dust actually looks like. Credit: Herschel/ESA

The KU researcher said her findings give scientists new understanding and detail of how the quenching of star formation in galaxies proceeds, and overturns presumptions about quasars.

“We already knew quasars go through a dust-obscured phase,” Kirkpatrick said. “We knew they go through a heavily shrouded phase where dust is surrounding the supermassive black hole. We call that the red quasar phase. But now, we’ve found this unique transition regime that we didn’t know before. Before, if you told someone you had found a luminous quasar that had a blue optical color—but it still had a lot of dust and gas in it, and a lot of star formation—people would say, ‘No, that’s not the way these things should look.'”

Next, Kirkpatrick hopes to determine if the “cold quasar” phase happens to a specific class of galaxies or every galaxy.

“We thought the way these things proceed was you have a growing black hole, it’s enshrouded by dust and gas, it begins to blow that material out,” she said. “Then it becomes a luminous blue object. We assumed when it blew out its own gas, it would blow out its host gas as well. But it seems with these objects, that’s not the case. These have blown out their own dust—so we see it as a blue object—but they haven’t yet blown out all of the dust and gas in the host galaxies. This is a transition phase, let’s say of 10 million years. In universal timescales, that’s really short—and it’s hard to catch this thing. We’re doing what we call a blind survey to find objects we weren’t looking for. And by finding these objects, yes, it could imply that this happens to every galaxy.”

Black hole BOMBSHELL: NASA astronomer hints universe could be a HOLOGRAM



Black hole BOMBSHELL: NASA astronomer hints universe could be a HOLOGRAM

BLACK holes could hold all of the secrets of the universe and prove once and for all we live in a “giant hologram”, a NASA astronomer has spectacularly claimed.

NASA claim that WATER is present on the moon’s surface



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Black holes are incredible wells of gravity, where the force of attraction traps everything including light. Black holes are often found at the hearts of galaxies and up until April this year have been purely theoretical. In April, astronomers behind the Event Horizon Telescope (EHT) collaboration photographed the first ever shadow of a black hole millions of light-years from Earth. But little is still known about the exact nature of these terrifying objects and speculation is rampant.

This is why astronomer Michelle Thaller, who is the assistant director of Science Communications at , said dark holes challenge our understanding of physics.

The  experts appeared in a science video for Big Think, where she discussed the idea black holes are key to cracking the secrets of the universe.

And perhaps most shockingly, the astronomer suggested the universe in which we live is nothing more than a two-dimensional hologram.

Dr Thaller said: “Things are stopped in time as they fell into the black hole. And right at the boundary, there is almost kind of a sphere, a two-dimensional surface that somehow contains all the information about what’s inside the black hole.


Black hole shock: The universe is a hologram

Black hole SHOCK: Black holes and the universe could be a hologram in a shock twist (Image: GETTY)

“And this reminds people of something that humans invented, called a hologram.

“Now, a hologram is a two-dimensional object. You can make it out of glass or a piece of film. And you shine a light through it and all of a sudden, there seems to be three-dimensional projections.

“And the idea is that we are looking at some fundamental way the universe stores information. Around a black hole, where space and time have been crushed out of existence, could there be a shell of information, something like a hologram?”

But how does this cosmic revelation suggest the universe at large is a form of a hologram?


According to Dr Thaller, black holes could be a miniaturised representation of how the universe works on a big scale.

This all sounds incredibly strange

Dr Michelle Thaller, NASA

In this scenario, all of the information in the universe is spread out across a 2D surface and we could be part of it.

But the astronomer said this does not in any way imply intent or creative design behind the hologram.

She said: “We’re just talking about the universe may really be information contained in a two-dimensional structure, not the three dimensions that we’re aware of now. This all sounds incredibly strange.


Black hole in space: Universe is a hologram

Black holes are incredible wells of gravity peppered throughout the cosmos (Image: GETTY)

Black hole: Dr Michelle Thaller

Black hole: Dr Michelle Thaller said the universe could be two-dimensional information (Image: BIG THINK)

“I’m always a little bit afraid to talk about it. But I think that the thing to really kind of gain from this is that black holes are staring us right in the face. We’re now observing them.

“They’re right there. And we cannot really describe how the universe should work with one of these things. They don’t make sense.”

On April 10, 2019, the EHT collaboration published the world’s first ever photograph of a distant black hole at the heart of galaxy Messier 87.

The historic achievement confirmed the existence of black holes 100 years after they were theorised by Albert Einstein’s theory of relativity and by astronomer Karl Schwarzschild.

Did ‘Interstellar’ get it right about Black Holes?



Did ‘Interstellar’ get it right?



A supermassive black hole with millions to billions times the mass of our sun is seen in an undated NASA artist’s concept illustration.

The world will finally get to see how a black hole looks like.

The first-ever close-up of a black hole — the spaces at the center of every large galaxy — can be seen by the public at 9pm Beijing time today when six simultaneous press conferences are held in Shanghai, Taipei, Brussels, Chile’s Santiago, Tokyo and Washington.

The picture will have been captured by the Event Horizon Telescope, a network of eight radio telescopes scattered across the globe, thus creating a giant virtual telescope with a diameter equaling that of the Earth.

The EHT allows astronomers to clearly see an orange on the Moon.

The project’s researchers obtained the first data in April 2017 from the global network of telescopes.

The telescopes that collected that initial data are located in the US states of Arizona and Hawaii as well as Mexico, Chile, Spain and Antarctica. Since then, telescopes in France and Greenland have been added to the network.

The telescopes were trained on two supermassive black holes in very different corners of the universe to collect data. Sagittarius A*, in a mass of 4 million suns, is located at the center of the Milky Way, and another, unnamed, is located at the center of the neighboring Virgo A galaxy, weighing 1,500 times of Sagittarius A*.

The picture to be unveiled today is likely to zoom in on one or the other. The data collected by the far-flung telescope array still had to be collected and collated.

“The imaging algorithms we developed fill the gaps of data we are missing in order to reconstruct a picture of a black hole,” the team said on its website.

The EHT project involves more than 200 astronomers from across the world, including those from China.

The research will put to the test a scientific pillar — physicist Albert Einstein’s theory of general relativity, according to University of Arizona astrophysicist Dimitrios Psaltis, project scientist for the EHT. That theory, put forward in 1915, was intended to explain the laws of gravity and their relation to other natural forces.

Black holes live up to their name. Basically, it is a place in space that swallows almost everything.

A black hole’s event horizon, one of the most violent places in the universe, is the point of no return beyond which anything — stars, planets, gas, dust, all forms of electromagnetic radiation including light — gets sucked in irretrievably.

For us, black holes are “dark stars.” So how do astronomers find black holes?

When black holes tear up nearby stars and swallow things in the space, they will emit great energy, generating bright light and massive radiation, through collision and friction.

That lead astronomers to the locations of black holes.

How do black holes look like?

No one knows, at least not until we discover it today.


Over the years, they have been depicted in many ways in the movies, but it is widely regarded that its image in the hit Hollywood movie “Interstellar” is the closest to the real thing.

Similar to the shape of Saturn, a star with rings, the black hole as depicted in “Interstellar” is very massive and rapidly spinning black with a glowing ring of matter encircling it.

The image was created after consultations with physicist and Nobel Laureate Kip Thorne of the California Institute of Technology.

Einstein’s theory, if correct, should allow for an extremely accurate prediction of the size and shape of a black hole.

“The shape of the shadow will be almost a perfect circle in Einstein’s theory,” Psaltis said. “If we find it to be different than what the theory predicts, then we go back to square one and we say, ‘Clearly, something is not exactly right.’”

Breakthrough observations in 2015 that earned the scientists involved a Nobel Prize used gravitational wave detectors to track two black holes smashing together.

As they merged, ripples in the curvatures of time-space created a unique, and detectable, signature.

“Einstein’s theory of general relativity says that this is exactly what should happen,” said Paul McNamara, an astrophysicist at the European Space Agency and an expert on black holes.

But those were tiny black holes — only 60 times more massive than the Sun — compared with either of the ones under the gaze of the EHT.

“Maybe the ones that are millions of times more massive are different — we just don’t know yet,” said McNamara.

How big is a black hole?

The diameter of a black hole depends on its mass but it is always double what we call the Schwarzschild radius. If the sun were to shrink to a singularity point, the Schwarzschild radius would be 3 kilometers and the diameter would be 6. For Earth, the diameter would be 18 millimeters, or about three quarters of an inch. The event horizon of the black hole at the center of the Milky Way, Sagittarius A*, measures about 24 million kilometers across.

What will the image look like?

The Event Horizon Telescope is not looking at the black hole per se, but the material it has captured. It won’t be a big disk in high resolution like in the Hollywood movie “Interstellar.” But we might see a black core with a bright ring — the accretion disk — around it. The light from behind the black hole gets bent like a lens. No matter what the orientation of the disk, you will see it as a ring because of the black hole’s strong gravity. Visually, it will look very much like an eclipse.

How is the image generated?

Rather than having one telescope that is 100 meters across, they have lots of telescopes with an effective diameter of 12,000km — the diameter of Earth. The data is recorded with very high accuracy, put onto hard disks, and shipped to a central location where the image is reconstructed digitally. This is very, very long baseline interferometry — over the entire surface of the Earth.

Dark Matter And Black Holes



WHEN IT COMES to the nature of dark matter, astronomers are still largely, well, in the dark. The existence of this mysterious substance was hypothesized more than 40 years ago to explain discrepancies between the calculations of how galaxies ought to behave, based on their mass, and what was actually observed. In short, it seemed like mass was missing. So Vera Rubin, the astronomer who first discovered this discrepancy, conjured an invisible substance that is far more abundant than “normal” matter and acts as the scaffolding for the large-scale structure of the universe. Today we call it dark matter.

Yet decades of hunting for the elusive dark matter particle still have not yielded direct evidence of its existence. Most cosmologists still believe that dark matter must exist, but some have splintered off to propose other explanations that explain away dark matter by modifying our understanding of gravity.

But two findings are now casting doubt on the modified gravity explanation. In March, a team of astronomers led by Yale professor Pieter van Dokkum and his graduate student Shany Danieli published two papers, one confirming the existence of a galaxy that appears to have almost no dark matter and the other announcing the discovery of a second galaxy of this type. The irony, the researchers say, is that the seeming lack of dark matter in these galaxies is strong evidence that it exists.

The reason they believe these galaxies have no dark matter is that their dynamics can be predicted using our traditional theories of gravity. The discrepancy of the “missing mass” that’s seen in most galaxies isn’t present here, meaning there’s no need for dark matter to explain their behavior. And it means that the modified version of gravity proposed by some cosmologists doesn’t predict these galaxies’ movements as cleanly as good old Newtonian physics.

The discovery of these dark-matter-free galaxies traces back to 2014, when van Dokkum and his colleagues finished building Dragonfly, a new kind of telescope, made of off-the-shelf telephoto camera lenses, that specializes in observing extremely faint celestial objects. Only a year after its first light, Dragonfly discovered a new galaxy characterized by an extreme lack of stars relative to its size. Known as an ultra-diffuse galaxy, this ghostly celestial object had roughly the same mass as our Milky Way, but only one hundredth of one percent of that mass could be attributed to “normal” matter like stars. In other words, van Dokkum and his colleagues had discovered a galaxy made of 99.99 percent dark matter.

While this galaxy was unique, its existence isn’t entirely surprising. Most cosmologists think that dense collections of dark matter act as a sort of seed for the formation of large celestial objects like galaxies. The general idea, says Anže Slosar, an astrophysicist at Brookhaven National Laboratory, is that once a collection of dark matter reaches a critical density, it collapses under its own gravity and forms a so-called “dark matter halo.” This halo, in turn, gravitationally attracts hydrogen gas to its center, where it begins to form stars and, eventually, galaxies. The mass of a dark matter halo varies from galaxy to galaxy, but it seemed like every galaxy must have at least some dark matter to keep its form. Indeed, this assumption was precisely what made Dragonfly’s next discovery so surprising.

In 2016, van Dokkum and his colleagues at Yale discovered NGC 1052-DF2, an ultra-diffuse galaxy that appeared to contain little to no dark matter at all. Last year, when the Yale astronomers published their results in the journal Nature, their peers in the cosmological community were incredulous. This was the first galaxy ever discovered that appeared to lack any dark matter, and as Carl Sagan rightly observed, “extraordinary claims require extraordinary evidence”—which is what many cosmologists thought the Yale team was missing.

University of Pennsylvania astrophysicist Robyn Sanderson says the skepticism about DF2 sprang mostly from the limited amount of data used to draw the conclusion. In this case, the Yale team was using data from just 10 star clusters observed over a period of two nights. This meant it was possible they were overlooking key details of the star clusters’ motion, which would distort their estimations of the galaxy’s mass—and undermine their claim that it lacked dark matter.

The Yale researchers recognized this possible source of error themselves when they published their paper on DF2. The only way to resolve this conundrum was to make more detailed measurements or to find another galaxy with characteristics similar to DF2. In March, the Yale team published two papers that did exactly these things.

The first paper offered more refined measurements of stellar velocities within DF2. This time, rather than just measuring the velocities of 10 star clusters, van Dokkum and Danieli used the Keck telescope in Hawaii to observe the velocities of the stars within the star clusters. This approach produced far more data that reinforced the team’s earlier conclusion that the galaxy lacked dark matter.

The other paper announced the discovery of a second galaxy, DF4, which also appears to have little, if any, dark matter. Not only does this increase the odds that the DF2 observations are accurate, it also means such ultra-diffuse galaxies might not be so rare. The fact that two were found in quick succession, Danieli says, was “really reassuring.” Nevertheless, she says “it’s still too early to say whether they are super rare or quite common.” The team will begin observing other nearby ultra-diffuse galaxies next month in an effort to answer this question.

But that won’t resolve the mystery of how these strange galaxies came to exist in the first place. Theoretical cosmologists will have to run simulations to determine how a galaxy can lose its dark matter, she says. One leading theory involves tidal interactions, which is astronomer-speak for when the gravitational forces of two neighboring galaxies pull material from each galaxy and distort them. DF2 and DF4 are both near the galaxy NGC 1052, which makes it a strong candidate for the galaxy that stole their dark matter.

However they came to be, Danieli argues that the existence of these galaxies is a blow to the modified gravityexplanation for why most galaxies don’t behave as we’d expect.

Known as modified Newtonian dynamics, or MOND, this theory recasts gravity such that it has different effects at the galactic scale. Although MOND has successfully predicted the stellar dynamics of hundreds of galaxies, most of which are relatively isolated, it must be able to predict the dynamics of all galaxies to dethrone dark matter as the going cosmological theory.

As Slosar explains it, the discovery of DF2 and DF4 strengthens the case for the existence of a dark matter particle because it means that it can be separated from normal matter. Because these galaxies behave in line with standard gravitational theory, using the equations discovered by Newton and Kepler, they present a challenge to MOND.

“If you find galaxies, some of which have a lot of dark matter and some of which have a little dark matter, you can’t explain it with the loss of gravity unless you’re willing to say that one part of the universe has a different law of gravity than another part, which is just silly,” Slosar says. “The entire point of physics is to find unified laws that are always there. This is why it is an argument for the existence of dark matter.”

So does the existence of galaxies devoid of dark matter pose an existential threat for MOND? Stacy McGaugh, an astronomer at Case Western Reserve University, doesn’t think so. “When DF2 was first discovered, it was portrayed as a huge problem for MOND,” McGaugh says. “On more careful analysis, it turned out that the prediction of MOND was spot-on what was observed.”

The analysis by McGaugh and his colleagues of DF2’s implications for MOND hinges on the galaxy’s proximity to the massive elliptical galaxy NGC1052. Under a set of “reasonable” assumptions, paired with equations from MOND, McGaugh and his colleagues found that NGC1052’s gravitational effects on DF2 would return stellar velocities similar to what van Dokkum and Danieli actually observed. Although he hasn’t had the chance to repeat this analysis for DF4, McGaugh says it also “appears to be consistent with MOND, since it is likely affected by NGC 1052.”

The existence of these galaxies poses a number of vexing problems for the theory of galactic formation, which must account for how a galaxy can come to be violently stripped of its dark matter and still retain the relative order seen, for example, in the presence of star clusters in DF2 and DF4. Will further observations of ultra-diffuse galaxies resolve the dark matter debate? Probably not, but they will, at least, shed some light on the matter.

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Gargantuan ‘X-ray Chimneys’ in the Center of Our Galaxy



Astronomers Spot Gargantuan ‘X-ray Chimneys’ in the Center of Our Galaxy

The monster black hole that anchors our galaxy is safely 28,000 light years away from Earth. That’s a good thing, too. The region around that back hole is overflowing with dangerous radiation and fragmented stars. Astronomers observing the center of the Milky Way have spotted some unusual features that drive home just how violent the area is. The galaxy sports a pair of gargantuan “X-ray chimneys” that expel the matter and energy building up around the black hole.

UCLA professor of astronomy and astrophysics Mark Morris, who contributed to the research, likens the features to exhaust vents, bleeding off energy from the galaxy in the form of X-rays. The international team looked to the black hole, known as Sagittarius A* (pronounced “Sagittarius A Star”) in an effort to learn more about star formation in the Milky Way. All galaxies foster the development of stars, but the rate of new star formation can vary wildly. The fate of the matter and energy spiraling toward a galaxy’s central black hole can be a significant factor in star formation.

To track the material blasted out around Sagittarius A*, the researchers turned to the European Space Agency’s XMM-Newton satellite. This X-ray observatory launched almost 20 years ago, but it’s still going strong. The team used data from 2012, as well as 2016 to 2018 to see what the black hole was doing with all the stars getting smashed to bits in its general vicinity.

According to the researchers, Sagittarius A* produces “chimneys” of X-ray that extend north and south from the disk of the galaxy. The structures are more appropriately known as Fermi bubbles, massive cavities carved out of the gas cloud surrounding the galaxy. The north and south chimney both start within 160 light years of the black hole, extending outward about 25,000 light years. That’s almost the distance from Sagittarius A* to Earth.

The black hole in our galaxy is about 4 million times the size of the sun, but other galaxies have central black holes that are much larger. We can study the Milky Way close up, which could provide insights into how these more energetic galaxies work. Understanding how energy moves through the chimneys and into surrounding space could help explain why some regions become rich in star formation, and others are relatively barren.

Astronomers Have Detected 83 Black Holes in The Early Universe



Astronomers Have Detected 83 Black Holes in The Early Universe, Challenging Cosmology

19 MAR 2019

Astronomers have just found 83 quasars, powered by supermassive black holes and dating back to the infancy of the Universe, when it was less than 10 percent of its current age.

This discovery reveals that such objects were more common at the dawn of time than we thought, and challenges our entire cosmological model.

Quasars are among the brightest objects in the Universe, extremely luminous galactic cores powered by actively feeding supermassive black holes. As material swirls around the black hole, its friction generates such intense radiation that it can be seen, even from billions of light-years away.

There’s just one big problem. We think we know how black holes form – they are the collapsed cores of massive stars. And supermassive black holes can have up to billions of times the mass of the Sun.

This takes time, and requires copious amounts of matter. So how the heck did all these quasars pop up so early in the Universe’s history?

“It is remarkable that such massive dense objects were able to form so soon after the Big Bang,” said astrophysicist Michael Strauss of Princeton University.

“Understanding how black holes can form in the early Universe, and just how common they are, is a challenge for our cosmological models.”

old quasarA quasar 13.05 billion light-years away. (National Astronomical Observatory of Japan)

We’ve known there were quasars hanging out back then. The oldest one we’ve seen dates back to around 690 million years after the Big Bang, when the Universe was around five percent of its current age – and a few others have been spotted too.

But these – although still a puzzle – were thought to be relatively rare. So astronomers from Japan, Taiwan and the US broadened the search, using data from the Hyper Suprime-Cam mounted on the Subaru Telescope in Hawaii.

With this instrument, they could look for much fainter quasars than ones discovered previously. The oldest quasar they found was a massive 13.05 billion light-years away, tying for the second-most distant quasar ever found.

The Universe is thought to be about 13.8 billion years old, and the first stars – we think – didn’t appear until around 500 million years after the Big Bang, after the neutral hydrogen of the early-early Universe was reionised. That just leaves a couple of hundred million years for the quasars to form.

The team’s survey suggests that these objects were actually fairly abundant back then. They identified candidate quasars in the HSC data, then conducted a dedicated survey using multiple telescopes to obtain light signatures, or spectra, from these objects.

smbh quasars(National Astronomical Observatory of Japan)

These spectra turned up the 83 new quasars, over the last few years. Together with 17 previously known quasars in the survey region, the team calculated that there’s roughly one quasar for every cubic giga-light-year; that is, cube of space with a billion light-years per side.

While that’s more than previously thought, it’s not quite enough for another hypothesis.

Just after the Big Bang, the Universe was a sort of dark, hot “primordial soup” on a cosmic scale, rapidly expanding.

As it expanded, it cooled, causing protons and neutrons to start to combine into ionised hydrogen atoms; around 240,000-300,000 years after the Big Bang, these hydrogen atoms attracted electrons, coalescing into neutral hydrogen.

But it wasn’t until gravity started to pull together the first stars and galaxies in this murky, hydrogen-filled void that starlight appeared… and not long after that, according to current theories, the neutral hydrogen was excited by the ultraviolet light of these newborn stars, galaxies, as-yet undetected quasars, or a combination of all three.

This is called the Epoch of Reionisation, and we just don’t know how it happened. But now we know – based on this research – there weren’t enough quasars to be solely responsible for this process.

The new quasar population data will help us learn more about the formation of supermassive black holes in the early Universe – and the team is going to continue the search to see if they can find quasars that are even older. This could help researchers to figure out when the first black holes were born.

“The quasars we discovered will be an interesting subject for further follow-up observations with current and future facilities,” said astronomer Yoshiki Matsuoka of Ehime University in Japan.

“We will also learn about the formation and early evolution of supermassive black holes, by comparing the measured number density and luminosity distribution with predictions from theoretical models.”

The discoveries have been detailed in five papers, which can be found herehereherehere and here.

Magnetic fields may be the key to black hole activity



Magnetic fields may be the key to black hole activity

October 17, 2018, NASA
Magnetic fields may be the key to black hole activity
Artist’s conception of the core of Cygnus A, including the dusty donut-shaped surroundings, called a torus, and jets launching from its center. Magnetic fields are illustrated trapping the dust in the torus. These magnetic fields could be …more

Collimated jets provide astronomers with some of the most powerful evidence that a supermassive black hole lurks in the heart of most galaxies. Some of these black holes appear to be active, gobbling up material from their surroundings and launching jets at ultra-high speeds, while others are quiescent, even dormant. Why are some black holes feasting and others starving? Recent observations from the Stratospheric Observatory for Infrared Astronomy, or SOFIA, are shedding light on this question.

SOFIA data indicate that magnetic fields are trapping and confining dust near the center of the active galaxy, Cygnus A, and feeding material onto the supermassive black hole at its center.

The , which attempts to explain the different properties of active galaxies, states that the core is surrounded by a donut-shaped dust cloud, called a torus. How this obscuring structure is created and sustained has never been clear, but these new results from SOFIA indicate that magnetic fields may be responsible for keeping the dust close enough to be devoured by the hungry black hole. In fact, one of the fundamental differences between active galaxies like Cygnus A and their less active cousins, like our own Milky Way, may be the presence or absence of a  around the black hole.

Although celestial magnetic fields are notoriously difficult to observe, astronomers have used polarized light—optical light from scattering and radio light from accelerating electrons—to study magnetic fields in galaxies. But optical wavelengths are too short and the radio wavelengths are too long to observe the torus directly. The infrared wavelengths observed by SOFIA are just right, allowing scientists, for the first time, to target and isolate the dusty torus.

Magnetic fields may be the key to black hole activity
Two images of Cygnus A layered over each other to show the galaxy’s jets glowing with radio radiation (shown in red). Quiescent galaxies, like our own Milky Way, do not have jets like this, which may be related to magnetic fields. The …more

SOFIA’s new instrument, the High-resolution Airborne Wideband Camera-plus (HAWC+), is especially sensitive to the infrared emission from aligned dust grains. This has proven to be a powerful technique to study magnetic fields and test a fundamental prediction of the unified model: the role of the dusty torus in the active-galaxy phenomena.

“It’s always exciting to discover something completely new,” noted Enrique Lopez-Rodriguez, a scientist at the SOFIA Science Center, and the lead author on the report of this new discovery. “These observations from HAWC+ are unique. They show us how infrared polarization can contribute to the study of galaxies.”

Recent observations of the heart of Cygnus A made with HAWC+ show infrared radiation dominated by a well-aligned dusty structure. Combining these results with archival data from the Herschel Space Observatory, the Hubble Space Telescope and the Gran Telescopio Canarias, the research team found that this powerful active galaxy, with its iconic large-scale jets, is able to confine the obscuring torus that feeds the supermassive black hole using a strong .

The results of this study were published in the July 10th issue of The Astrophysical Journal Letters.

Cygnus A is in the perfect location to learn about the role magnetic fields play in confining the dusty torus and channeling material onto the supermassive black hole because it is the closest and most powerful active galaxy. More observations of different types of galaxies are necessary to get the full picture of how magnetic fields affect the evolution of the environment surrounding . If, for example, HAWC+ reveals highly polarized  from the centers of active galaxies but not from quiescent , it would support the idea that magnetic fields regulate black hole feeding and reinforce astronomers’ confidence in the unified model of .

 Explore further: Black holes play hide-and-seek in low-luminosity radio galaxies

More information: Enrique Lopez-Rodriguez et al. The Highly Polarized Dusty Emission Core of Cygnus A, The Astrophysical Journal (2018). DOI: 10.3847/2041-8213/aacff5

Read more at: https://phys.org/news/2018-10-magnetic-fields-key-black-hole.html#jCp

New Evidence That Supermassive Black Holes Eventually Suck the Life out of Big Galaxies



New Evidence That Supermassive Black Holes Eventually Suck the Life out of Big Galaxies

The Centaurus A galaxy, showing the characteristic jets of gas thrown off by a supermassive black hole. (Image: ESO/WFI (Optical); MPIfR/ESO/APEX/A.Weiss et al. (Submillimetre); NASA/CXC/CfA/R.Kraft et al. (X-ray))

At the core of each large galaxy lies a supermassive black hole with the mass of 1 million suns. New research shows that these celestial vacuum cleaners do more than just devour nearby objects—they also grow to a size that eventually suppresses a galaxy’s ability to churn out new stars, effectively rendering them sterile.

Young galaxies are absolutely bursting with bright, newly formed stars. As time passes, however, star formation eventually grinds to a halt. A new study published in Nature shows that supermassive black holes play a critical role in determining when large galaxies stop producing new stars, a process known as “quenching.”

Stars form out of cold gas, so when a galaxy runs out of cold gas it’s effectively quenched. One possible way this could happen—at least for galaxies with supermassive black holes—is that the gas that pours onto a supermassive black hole triggers the production of high-energy jets. The energy released by these jets can expel cold gas out of the galaxy, causing star formation to shut down.

At least that’s the theory. This idea has been around for quite some time, but no observational evidence existed to support the alleged correlation between supermassive black holes and star formation. The new study, led by Ignacio Martín-Navarro from the University of California Santa Cruz, now fills this gap in our knowledge.

Using data collected by the Hobby-Eberly Telescope Massive Galaxy Survey, Martín-Navarro’s team analyzed the spectra of light coming from distant galaxies. This allowed them to separate and measure the varying wavelengths of light coming from these distant objects. The scientists used this data to create a historical snapshot of a galaxy’s star formation history. They then compared this history with black holes of different masses, which resulted in some striking differences—differences that correlated with black hole mass, but not the shape, size, or other properties of black holes.

“The subsequent quenching of star formation takes place earlier and more efficiently in galaxies that host higher-mass central black holes,” wrote the researchers. “The observed relation between black-hole mass and star formation efficiency applies to all generations of stars formed throughout the life of a galaxy, revealing a continuous interplay between black-hole activity and… cooling.”

As Martín-Navarro clarified in an accompanying statement, for galaxies with the same mass of stars, but with a different black hole mass in the center, “those galaxies with bigger black holes were quenched earlier and faster than those with smaller black holes.” This means that star formation will last longer in galaxies with smaller central black holes. “[…Accretion onto more massive black holes leads to more energetic feedback from active galactic nuclei, which would quench star formation faster,” he said.

It’s an exciting result, but there’s still lots of work to do. While the researchers managed to produce observational evidence showing that black hole mass can be connected to the quenching of star formation, they’re still unclear about the exact mechanical processes involved. As study co-author Aaron Romanowsky explained, “There are different ways a black hole can put energy out into the galaxy, and theorists have all kinds of ideas about how quenching happens, but there’s more work to be done to fit these new observations into the models.”

Our galaxy, the Milky Way, features its own super massive black hole and is not immune to this process. It is currently transitioning from star-forming mode to a passive, sterile existence. Eventually, a few billion years from now, all the stars in the Milky Way will be extinguished, and the super massive black hole at center will evaporate into nothing. It’s a grim prospect, but such is the way of the indifferent cosmos.

John Eli

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