X-ray emissions from the supermassive black hole in the center of the Milky Way galazy, about 26,000 light years from Earth. Credit: NASA/CXC/APC/Université Paris Diderot/M.Clavel et al
How’s that for a beacon? NASA’s Chandra X-ray Observatory has tracked down evidence of at least a couple of past luminous outbursts near the Milky Way’s huge black hole. These flare-ups took place sometime in the past few hundred years, which is very recently in astronomical terms.
“The echoes from Sagittarius A were likely produced when large clumps of material, possibly from a disrupted star or planet, fell into the black hole,” the Chandra website stated.
“Some of the X-rays produced by these episodes then bounced off gas clouds about 30 to 100 light years away from the black hole, similar to how the sound from a person’s voice can bounce off canyon walls. Just as echoes of sound reverberate long after the original noise was created, so too do light echoes in space replay the original event.”
The astronomers saw evidence of “rapid variations” in how X-rays are emitted from gas clouds circling the hole, revealing clues that the area likely got a million times brighter at times.
A quasar resides in the hub of the nearby galaxy NGC 4438. Credit: NASA/ESA, Jeffrey Kenney (Yale University), Elizabeth Yale (Yale University)
50 million light-years away a quasar resides in the hub of galaxy NGC 4438, an incredibly bright source of light and radiation that’s the result of a supermassive black hole actively feeding on nearby gas and dust (and pretty much anything else that ventures too closely.) Shining with the energy of 1,000 Milky Ways, this quasar — and others like it — are the brightest objects in the visible Universe… so bright, in fact, that they are used as beacons for interplanetary navigation by various exploration spacecraft.
“I must go down to the seas again, to the lonely sea and the sky,
And all I ask is a tall ship and a star to steer her by.”
Deep-space missions require precise navigation, especially when approaching bodies such as Mars, Venus, or comets. It’s often necessary to pinpoint a spacecraft traveling 100 million km from Earth to within just 1 km. To achieve this level of accuracy, experts use quasars – the most luminous objects known in the Universe – as beacons in a technique known as Delta-Differential One-Way Ranging, or delta-DOR.
How delta-DOR works (ESA)
Delta-DOR uses two antennas in distant locations on Earth (such as Goldstone in California and Canberra in Australia) to simultaneously track a transmitting spacecraft in order to measure the time difference (delay) between signals arriving at the two stations.
Unfortunately the delay can be affected by several sources of error, such as the radio waves traveling through the troposphere, ionosphere, and solar plasma, as well as clock instabilities at the ground stations.
Delta-DOR corrects these errors by tracking a quasar that is located near the spacecraft for calibration — usually within ten degrees. The chosen quasar’s direction is already known extremely well through astronomical measurements, typically to closer than 50 billionths of a degree (one nanoradian, or 0.208533 milliarcsecond). The delay time of the quasar is subtracted from that of the spacecraft’s, providing the delta-DOR measurement and allowing for amazingly high-precision navigation across long distances.
“Quasar locations define a reference system. They enable engineers to improve the precision of the measurements taken by ground stations and improve the accuracy of the direction to the spacecraft to an order of a millionth of a degree.”
– Frank Budnik, ESA flight dynamics expert
So even though the quasar in NGC 4438 is located 50 million light-years from Earth, it can help engineers position a spacecraft located 100 million kilometers away to an accuracy of several hundred meters. Now that’s a star to steer her by!
Radio telescope image of the galaxy 4C12.50, nearly 1.5 billion light-years from Earth. Inset shows detail of location at end of superfast jet of particles, where a massive gas cloud (yellow-orange) is being pushed by the jet.
(Credit: Morganti et al., NRAO/AUI/NSF)
It’s long been a mystery for astronomers: why aren’t galaxies bigger? What regulates their rates of star formation and keeps them from just becoming even more chock-full-of-stars than they already are? Now, using a worldwide network of radio telescopes, researchers have observed one of the processes that was on the short list of suspects: one supermassive black hole’s jets are plowing huge amounts of potential star-stuff clear out of its galaxy.
Astronomers have theorized that many galaxies should be more massive and have more stars than is actually the case. Scientists proposed two major mechanisms that would slow or halt the process of mass growth and star formation — violent stellar winds from bursts of star formation and pushback from the jets powered by the galaxy’s central, supermassive black hole.
“With the finely-detailed images provided by an intercontinental combination of radio telescopes, we have been able to see massive clumps of cold gas being pushed away from the galaxy’s center by the black-hole-powered jets,” said Raffaella Morganti, of the Netherlands Institute for Radio Astronomy and the University of Groningen.
The scientists studied a galaxy called 4C12.50, nearly 1.5 billion light-years from Earth. They chose this galaxy because it is at a stage where the black-hole “engine” that produces the jets is just turning on. As the black hole, a concentration of mass so dense that not even light can escape, pulls material toward it, the material forms a swirling disk surrounding the black hole. Processes in the disk tap the tremendous gravitational energy of the black hole to propel material outward from the poles of the disk.
NGC 253, aka the Sculptor Galaxy, is also blowing out gas but as the result of star formation (Image: T.A. Rector/University of Alaska Anchorage, T. Abbott and NOAO/AURA/NSF)
At the ends of both jets, the researchers found clumps of hydrogen gas moving outward from the galaxy at 1,000 kilometers per second. One of the clouds has much as 16,000 times the mass of the Sun, while the other contains 140,000 times the mass of the Sun.
The larger cloud, the scientists said, is roughly 160 by 190 light-years in size.
“This is the most definitive evidence yet for an interaction between the swift-moving jet of such a galaxy and a dense interstellar gas cloud,” Morganti said. “We believe we are seeing in action the process by which an active, central engine can remove gas — the raw material for star formation — from a young galaxy,” she added.
The researchers published their findings in the September 6 issue of the journal Science.
X-ray and infrared image of Sgr A*, the supermassive black hole in the center of the Milky Way
Like most galaxies, our Milky Way has a dark monster in its middle: an enormous black hole with the mass of 4 million Suns inexorably dragging in anything that comes near. But even at this scale, a supermassive black hole like Sgr A* doesn’t actually consume everything that it gets its gravitational claws on — thanks to the Chandra X-ray Observatory, we now know that our SMB is a sloppy eater and most of the material it pulls in gets spit right back out into space.
(Perhaps it should be called the Cookie Monster in the middle.*)
New Chandra images of supermassive black hole Sagittarius A*, located about 26,000 light-years from Earth, indicate that less than 1% of the gas initially within its gravitational grasp ever reaches the event horizon. Instead, much of the gas is ejected before it gets near the event horizon and has a chance to brighten in x-ray emissions.
The new findings are the result of one of the longest campaigns ever performed with Chandra, with observations made over 5 weeks’ time in 2012.
“This new Chandra image is one of the coolest I’ve ever seen,” said study co-author Sera Markoff of the University of Amsterdam in the Netherlands. “We’re watching Sgr A* capture hot gas ejected by nearby stars, and funnel it in towards its event horizon.”
As it turns out, the wholesale ejection of gas is necessary for our resident supermassive black hole to capture any at all. It’s a physics trade-off.
“Most of the gas must be thrown out so that a small amount can reach the black hole”, said co-author Feng Yuan of Shanghai Astronomical Observatory in China. “Contrary to what some people think, black holes do not actually devour everything that’s pulled towards them. Sgr A* is apparently finding much of its food hard to swallow.”
X-ray image of Sgr A*
If it seems odd that such a massive black hole would have problems slurping up gas, there are a couple of reasons for this.
One is pure Newtonian physics: to plunge over the event horizon, material captured — and subsequently accelerated — by a black hole must first lose heat and momentum. The ejection of the majority of matter allows this to occur.
The other is the nature of the environment in the black hole’s vicinity. The gas available to Sgr A* is very diffuse and super-hot, so it is hard for the black hole to capture and swallow it. Other more x-ray-bright black holes that power quasars and produce huge amounts of radiation have much cooler and denser gas reservoirs.
Illustration of gas cloud G2 approaching Sgr A* (ESO/MPE/M.Schartmann/J.Major)
Located relatively nearby, Sgr A* offers scientists an unprecedented view of the feeding behaviors of such an exotic astronomical object. Currently a gas cloud several times the mass of Earth, first spotted in 2011, is moving closer and closer to Sgr A* and is expected to be ripped apart and partially consumed in the coming weeks. Astronomers are eagerly awaiting the results.
“Sgr A* is one of very few black holes close enough for us to actually witness this process,” said Q. Daniel Wang of the University of Massachusetts at Amherst, who led the study.
An artist’s impression showing a galaxy in the process of pulling in cool gas from its surroundings. (ESO/L. Calçada/ESA/AOES Medialab)
If you live in the U.S. you may be enjoying a sultry summer day off in honor of Independence Day, or at least have plans to get together with friends and family at some point to partake in some barbecued goodies and a favorite beverage (or three). And as you saunter around the picnic table scooping up platefuls of potato salad, cole slaw, and deviled eggs, you can also draw a correlation between your own steady accumulation of mayonnaise-marinated mass and a distant hungry galaxy located over 11 billion light-years away.
Astronomers have always suspected that galaxies grow by pulling in material from their surroundings, but this process has proved very difficult to observe directly. Now, ESO’s Very Large Telescope has been used to study a very rare alignment between a distant galaxy and an even more distant quasar — the extremely bright center of a galaxy powered by a supermassive black hole. The light from the quasar passes through the material around the foreground galaxy before reaching Earth, making it possible to explore in detail the properties of the in-falling gas and giving the best view so far of a galaxy in the act of feeding.
“This kind of alignment is very rare and it has allowed us to make unique observations,” said Nicolas Bouché of the Research Institute in Astrophysics and Planetology (IRAP) in Toulouse, France, lead author of the new paper. “We were able to use ESO’s Very Large Telescope to peer at both the galaxy itself and its surrounding gas. This meant we could attack an important problem in galaxy formation: how do galaxies grow and feed star formation?”
A beam from the Laser Star Guide on one of the VLT’s four Unit Telescopes helps to correct the blurring effect of Earth’s atmosphere before making observations (ESO/Y. Beletsky)
Galaxies quickly deplete their reservoirs of gas as they create new stars and so must somehow be continuously replenished with fresh gas to keep going. Astronomers suspected that the answer to this problem lay in the collection of cool gas from the surroundings by the gravitational pull of the galaxy. In this scenario, a galaxy drags gas inwards which then circles around it, rotating with it before falling in.
Although some evidence of such accretion had been observed in galaxies before, the motion of the gas and its other properties had not been fully explored up to now.
Astronomers have already found evidence of material around galaxies in the early Universe, but this is the first time that they have been able to show clearly that the material is moving inwards rather than outwards, and also to determine the composition of this fresh fuel for future generations of stars. And in this particular instance, without the quasar’s light to act as a probe the surrounding gas would be undetectable.
“In this case we were lucky that the quasar happened to be in just the right place for its light to pass through the infalling gas. The next generation of extremely large telescopes will enable studies with multiple sightlines per galaxy and provide a much more complete view,” concluded co-author Crystal Martin of the University of California Santa Barbara.
This research was presented in a paper entitled “Signatures of Cool Gas Fueling a Star-Forming Galaxy at Redshift 2.3”, to appear in the July 5, 2013 issue of the journal Science.
A new analysis of data from the Chandra space telescope revealed 26 black hole candidates in the Andromeda Galaxy. This is the largest collection of possible black holes found in another galaxy besides that of the Milky Way, Earth's home galaxy. Credit: X-ray (NASA/CXC/SAO/R.Barnard, Z.Lee et al.), Optical (NOAO/AURA/NSF/REU Prog./B.Schoening, V.Harvey; Descubre Fndn./CAHA/OAUV/DSA/V.Peris)
More than two DOZEN potential black holes have been found in the nearest galaxy to our own. As if that find wasn’t enough, another research group is teaching us why extremely high-energy X-rays are present in black holes.
The Andromeda Galaxy (M31) is home to 26 newly found black hole candidates that were produced from the collapse of stars that are five to 10 times as massive as the sun.
Using 13 years of observations from NASA’s Chandra X-Ray Observatory, a research team pinpointed the locations. They also corroborated the information with X-ray spectra (distribution of X-rays with energy) from the European Space Agency’s XMM-Newton X-ray observatory.
“When it comes to finding black holes in the central region of a galaxy, it is indeed the case where bigger is better,” stated co-author Stephen Murray, an astronomer at Johns Hopkins University and the Harvard-Smithsonian Center for Astrophysics.
A close-up of the candidate black holes in Andromeda, as seen by the Chandra X-Ray Observatory. Credit: X-ray (NASA/CXC/SAO/R.Barnard, Z.Lee et al.), Optical (NOAO/AURA/NSF/REU Prog./B.Schoening, V.Harvey; Descubre Fndn./CAHA/OAUV/DSA/V.Peris
“In the case of Andromeda, we have a bigger bulge and a bigger supermassive black hole than in the Milky Way, so we expect more smaller black holes are made there as well,” Murray added.
The total number of candidates in M31 now stands at 35, since the researchers previously identified nine black holes in the area. All told, it’s the largest number of black hole candidates identified outside of the Milky Way.
Meanwhile, a study led by the NASA Goddard Space Flight Center examined the high-radiation environment inside a black hole — by simulation, of course. The researchers performed a supercomputer modelling of gas moving into a black hole, and found that their work helps explain some mysterious X-ray observations of recent decades.
Researchers distinguish between “soft” and “hard” X-rays, or those X-rays that have low and high energy. Both types have been observed around black holes, but the hard ones puzzled astronomers a bit.
Here’s what happens inside a black hole, as best as we can figure:
– Gas falls towards the singularity, orbits the black hole, and gradually becomes a flattened disk;
– As gas piles up in the center of the disk, it compresses and heats up;
– At a temperature of about 20 million degrees Fahrenheit (12 million degrees Celsius), the gas emits “soft” X-rays.
So where did the hard X-rays — that with energy tens or even hundreds of times greater than soft X-rays — come from? The new study showed that magnetic fields are amplified in this environment that then “exerts additional influence” on the gas, NASA stated.
Artist’s conception of the Chandra X-Ray Observatory. Credit: NASA
“The result is a turbulent froth orbiting the black hole at speeds approaching the speed of light. The calculations simultaneously tracked the fluid, electrical and magnetic properties of the gas while also taking into account Einstein’s theory of relativity,” NASA stated.
One key limitation of the study was it modelled a non-rotating black hole. Future work aims to model one that is rotating, NASA added.
You can check out more information about these two studies below:
Artist's concept of a supermassive black hole at the center of a galaxy. Credit: NASA/JPL-Caltech
It’s a simple menu, but smoking hot. The black hole at the center of the Milky Way galaxy is sucking in ultra-hot molecular gas, as seen through the eyes of the Herschel space telescope.
“The biggest surprise was quite how hot the molecular gas in the innermost central region of the galaxy gets. At least some of it is around 1000ºC [1832º F], much hotter than typical interstellar clouds, which are usually only a few tens of degrees above the –273ºC [-460ºF] of absolute zero,” stated the European Space Agency.
Herschel, which is out of coolant and winding down its scientific operations, will continue producing results in the next few years as scientists crunch the results. The telescope has found a bunch of basic molecules in the Milky Way that include water vapour and carbon monoxide, and has been engaged in looking to learn more about the gas that surrounds the massive black hole at our galaxy’s center.
In a region called Sagittarius* (Sgr A*), this huge black hole — four million times the mass of the sun — is thankfully a safe distance from Earth. It’s 26,000 light years away from the solar system.
At left, ionized gas in the galaxy as seen in radio wavelengths; at right, the spectrum at the center seen by Herschel. Credit: Radio-wavelength image: National Radio Astronomy Observatory/Very Large Array (courtesy of C. Lang); spectrum: ESA/Herschel/PACS & SPIRE/J.R. Goicoechea et al. (2013).
Trouble is, there’s a heckuva lot of dust blocking our view to the center of the galaxy. Herschel got around that problem by taking pictures in the far-infrared, seeking heat signatures that can bely intense activity in and around the black hole.
“Herschel has resolved the far-infrared emission within just 1 light-year of the black hole, making it possible for the first time at these wavelengths to separate emission due to the central cavity from that of the surrounding dense molecular disc,” stated Javier Goicoechea of the Centro de Astrobiología, Spain, lead author of a paper reporting the results.
The science team supposes that there are strong shocks within the gas (which is magnetized) that help turn up the heat. The shocks could occur when gas clouds butt up against each other, or material shoots out Fast and Furious-style between stars and protostars (young stars.)
“The observations are also consistent with streamers of hot gas speeding towards Sgr A*, falling towards the very center of the galaxy,” stated Goicoechea. “Our galaxy’s black hole may be cooking its dinner right in front of Herschel’s eyes.”
Illustration of gas cloud G2 approaching Sgr A* . Our central supermassive black hole periodically snacks on clouds and other material like this. That gives off X-rays and other emissions. (ESO/MPE/M.Schartmann/J.Major)
The heart of our Milky Way galaxy is an exotic place. It’s swarming with gigantic stars, showered by lethal blasts of high-energy radiation and a veritable cul-de-sac for the most enigmatic stellar corpses known to science: black holes. And at the center of the whole mélange is the granddaddy of all the black holes in the galaxy — Sagittarius A*, a supermassive monster with 4 million times more mass than the Sun packed into an area smaller than the orbit of Mercury.
Sgr A* dominates the core of the Milky Way with its powerful gravity, trapping giant stars into breakneck orbits and actively feeding on anything that comes close enough. Recently astronomers have been watching the movement of a large cloud of gas that’s caught in the pull of Sgr A* — they’re eager to see what exactly will happen once the cloud (designated G2) enters the black hole’s dining room… it will, in essence, be the first time anyone watches a black hole eat.
But before the dinner bell rings — estimated to be sometime this September — the cloud still has to cover a lot of space. Some scientists are now suggesting that G2’s trip through the crowded galactic nucleus could highlight the locations of other smaller black holes in the area, revealing their hiding places as it passes.
In a new paper titled “G2 can Illuminate the Black Hole Population near the Galactic Center” researchers from Columbia University in New York City and the Harvard-Smithsonian Center for Astrophysics (CfA) in Cambridge, Massachusetts propose that G2, a cloud of cool ionized gas over three times more massive than Earth, will likely encounter both neutron stars and other black holes on its way around (and/or into) SMBH Sgr A*.
Estimated number of stellar-mass black holes to be encountered by G2 along its trajectory (Bartos et al.)
The team notes that there are estimated to be around 20,000 stellar-mass black holes and about as many neutron stars in the central parsec of the galaxy. (A parsec is equal to 3.26 light-years, or 30.9 trillion km. In astronomical scale it’s just over 3/4 the way to the nearest star from the Sun.) In addition there may also be an unknown number of intermediate-mass black holes lurking within the same area.
These ultra-dense stellar remains are drawn to the center region of the galaxy due to the effects of dynamical friction — drag, if you will — as they move through the interstellar material.
Of course, unless black holes are feeding and actively throwing out excess gobs of hot energy and matter due to their sloppy eating habits, they are very nearly impossible to find. But as G2 is observed moving along its elliptical path toward Sgr A*, it could very well encounter a small number of stellar- and intermediate-mass black holes and neutron stars. According to the research team, such interactions may be visible with X-ray spotting spacecraft like NASA’s Chandra and NuSTAR.
NuSTAR X-ray image of a flare emitted by Sgr A* in July 2012 (NASA/JPL-Caltech)
The chances of G2 encountering black holes and interacting with them in such a way as to produce bright enough x-ray flares that can be detected depends upon a lot of variables, like the angles of interaction, the relative velocities of the gas cloud and black holes, the resulting accretion rates of in-falling cloud matter, and the temperature of the accretion material. In addition, any observations must be made at the right time and for long enough a duration to capture an interaction (or possibly multiple interactions simultaneously) yet also be able to discern them from any background X-ray sources.
Still, according to the researchers such observations would be important as they could provide valuable information on galactic evolution, and shed further insight into the behavior of black holes.
Read the full report here, and watch an ESO news video about the anticipated behavior of the G2 gas cloud around the SMBH Sgr A* below:
This research was conducted by Imre Bartos, Zoltán Haiman, and Bence Kocsis of Columbia University and Szabolcs Márka of the Harvard-Smithsonian Center for Astrophysics.
Visible-light Hubble image of the jet emitted by the 3-billion-solar-mass black hole at the heart of galaxy M87 (Feb. 1998) Credit: NASA/ESA and John Biretta (STScI/JHU)
Even though black holes — by their definition and very nature — are the ultimate hoarders of the Universe, gathering and gobbling up matter and energy to the extent that not even light can escape their gravitational grip, they also often exhibit the odd behavior of flinging vast amounts of material away from them as well, in the form of jets that erupt hundreds of thousands — if not millions — of light-years out into space. These jets contain superheated plasma that didn’t make it past the black hole’s event horizon, but rather got “spun up” by its powerful gravity and intense rotation and ended up getting shot outwards as if from an enormous cosmic cannon.
The exact mechanisms of how this all works aren’t precisely known as black holes are notoriously tricky to observe, and one of the more perplexing aspects of the jetting behavior is why they always seem to be aligned with the rotational axis of the actively feeding black hole, as well as perpendicular to the accompanying accretion disk. Now, new research using advanced 3D computer models is supporting the idea that it’s the black holes’ ramped-up rotation rate combined with plasma’s magnetism that’s responsible for shaping the jets.
In a recent paper published in the journal Science, assistant professor at the University of Maryland Jonathan McKinney, Kavli Institute director Roger Blandford and Princeton University’s Alexander Tchekhovskoy report their findings made using computer simulations of the complex physics found in the vicinity of a feeding supermassive black hole. These GRMHD — which stands for General Relativistic Magnetohydrodynamic — computer sims follow the interactions of literally millions of particles under the influence of general relativity and the physics of relativistic magnetized plasmas… basically, the really super-hot stuff that’s found within a black hole’s accretion disk.
What McKinney et al. found in their simulations was that no matter how they initially oriented the black hole’s jets, they always eventually ended up aligned with the rotational axis of the black hole itself — exactly what’s been found in real-world observations. The team found that this is caused by the magnetic field lines generated by the plasma getting twisted by the intense rotation of the black hole, thus gathering the plasma into narrow, focused jets aiming away from its spin axes — often at both poles.
At farther distances the influence of the black hole’s spin weakens and thus the jets may then begin to break apart or deviate from their initial paths — again, what has been seen in many observations.
This “magneto-spin alignment” mechanism, as the team calls it, appears to be most prevalent with active supermassive black holes whose accretion disk is more thick than thin — the result of having either a very high or very low rate of in-falling matter. This is the case with the giant elliptical galaxy M87, seen above, which exhibits a brilliant jet created by a 3-billion-solar-mass black hole at its center, as well as the much less massive 4-million-solar-mass SMBH at the center of our own galaxy, Sgr A*.
Image of lenticular galaxy NGC 1277 taken with Hubble Space Telescope. (NASA/ESA/Andrew C. Fabian)
It’s thought that at the heart of most if not every spiral galaxy (as well as some dwarf galaxies) there’s a supermassive black hole, by definition containing enormous amounts of mass — hundreds of millions, even billions of times the mass of our Sun packed into an area that would fit inside the orbits of the planets. Even our own galaxy has a central SMBH — called Sgr A*, it has the equivalent of 4.1 million solar masses.
Now, astronomers using the Hobby-Eberly Telescope at The University of Texas at Austin’s McDonald Observatory have identified what appears to be the most massive SMBH ever found, a 17 billion solar mass behemoth residing at the heart of galaxy NGC 1277.
Located 220 million light-years away in the constellation Perseus, NGC 1277 is a lenticular galaxy only a tenth the size of the Milky Way. But somehow it contains the most massive black hole ever discovered, comprising a staggering 14% of the galaxy’s entire mass.
“This is a really oddball galaxy,” said Karl Gebhardt of The University of Texas at Austin, a team member on the research. “It’s almost all black hole. This could be the first object in a new class of galaxy-black hole systems.”
The study was led by Remco van den Bosch, who is now at the Max Planck Institute for Astronomy (MPIA).
It’s estimated that the size of this SMBH’s event horizon is eleven times the diameter of Neptune’s orbit — an incredible radius of over 300 AU.
How the diamater of the black hole compares with the orbit of Neptune (D. Benningfield/K. Gebhardt/StarDate)
Although previously imaged by the Hubble Space Telescope, NGC 1277’s monster black hole wasn’t identified until the Hobby-Eberly Telescope Massive Galaxy Survey (MGS) set its sights on it during its mission to study the relationship between galaxies and their central black holes. Using the HET data along with Hubble imaging, the survey team calculated the mass of this black hole at 17 billion solar masses.
“The mass of this black hole is much higher than expected,” said Gebhardt, “it leads us to think that very massive galaxies have a different physical process in how their black holes grow.”
To date, the HET team has observed 700 of their 800 target galaxies.
In the video below, Remco van den Bosch describes the discovery of this unusually super supermassive black hole:
