Posted on by Nancy Atkinson

Super-Size Me: Black Hole Bigger Than Previously Thought

The illustration shows the relationship between the mass of a galaxy’s central black hole and the mass of its central bulge. Credit: Tim Jones/UT-Austin after K. Cordes & S. Brown (STScI)

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Using a new computer model, astronomers have determined that the black hole in the center of the M87 galaxy is at least twice as big as previously thought. Weighing in at 6.4 billion times the Sun’s mass, it is the most massive black hole yet measured, and this new model suggest that the accepted black hole masses in other large nearby galaxies may be off by similar amounts. This has consequences for theories of how galaxies form and grow, and might even solve a long-standing astronomical paradox.

Astronomers Karl Gebhardt from the University of Texas at Austin and Jens Thomas from the Max Planck Institute for Extraterrestrial Physics detailed their findings Monday at the American Astronomical Society conference in Pasadena, California.

To try to understand how galaxies form and grow, astronomers start with basic information about the galaxies today, such as what they are made of, how big they are and how much they weigh. Astronomers measure this last category, galaxy mass, by clocking the speed of stars orbiting within the galaxy.

Studies of the total mass are important, Thomas said, but “the crucial point is to determine whether the mass is in the black hole, the stars, or the dark halo. You have to run a sophisticated model to be able to discover which is which. The more components you have, the more complicated the model is.”

To model M87, Gebhardt and Thomas used one of the world’s most powerful supercomputers, the Lonestar system at The University of Texas at Austin’s Texas Advanced Computing Center. Lonestar is a Dell Linux cluster with 5,840 processing cores and can perform 62 trillion floating-point operations per second. (Today’s top-of-the-line laptop computer has two cores and can perform up to 10 billion floating-point operations per second.)

Gebhardt and Jens’ model of M87 was more complicated than previous models of the galaxy, because in addition to modeling its stars and black hole, it takes into account the galaxy’s “dark halo,” a spherical region surrounding a galaxy that extends beyond its main visible structure, containing the galaxy’s mysterious “dark matter.”

“In the past, we have always considered the dark halo to be significant, but we did not have the computing resources to explore it as well,” Gebhardt said. “We were only able to use stars and black holes before. Toss in the dark halo, it becomes too computationally expensive, you have to go to supercomputers.”

The Lonestar result was a mass for M87’s black hole several times what previous models have found. “We did not expect it at all,” Gebhardt said. He and Jens simply wanted to test their model on “the most important galaxy out there,” he said.

Extremely massive and conveniently nearby (in astronomical terms), M87 was one of the first galaxies suggested to harbor a central black hole nearly three decades ago. It also has an active jet shooting light out the galaxy’s core as matter swirls closer to the black hole, allowing astronomers to study the process by which black holes attract matter. All of these factors make M87 the “the anchor for supermassive black hole studies,” Gebhardt said.

These new results for M87, together with hints from other recent studies and his own recent telescope observations (publications in preparation), lead him to suspect that all black hole masses for the most massive galaxies are underestimated.

That conclusion “is important for how black holes relate to galaxies,” Thomas said. “If you change the mass of the black hole, you change how the black hole relates to the galaxy.” There is a tight relation between the galaxy and its black hole which had allowed researchers to probe the physics of how galaxies grow over cosmic time. Increasing the black hole masses in the most massive galaxies will cause this relation to be re-evaluated.

Higher masses for black holes in nearby galaxies also could solve a paradox concerning the masses of quasars — active black holes at the centers of extremely distant galaxies, seen at a much earlier cosmic epoch. Quasars shine brightly as the material spiraling in, giving off copious radiation before crossing the event horizon (the region beyond which nothing — not even light — can escape).

“There is a long-standing problem in that quasar black hole masses were very large — 10 billion solar masses,” Gebhardt said. “But in local galaxies, we never saw black holes that massive, not nearly. The suspicion was before that the quasar masses were wrong,” he said. But “if we increase the mass of M87 two or three times, the problem almost goes away.”

Today’s conclusions are model-based, but Gebhardt also has made new telescope observations of M87 and other galaxies using new powerful instruments on the Gemini North Telescope and the European Southern Observatory’s Very Large Telescope. He said these data, which will be submitted for publication soon, support the current model-based conclusions about black hole mass.

For future telescope observations of galactic dark haloes, Gebhardt notes that a relatively new instrument at The University of Texas at Austin’s McDonald Observatory is perfect. “If you need to study the halo to get the black hole mass, there’s no better instrument than VIRUS-P,” he said. The instrument is a spectrograph. It separates the light from astronomical objects into its component wavelengths, creating a signature that can be read to find out an object’s distance, speed, motion, temperature, and more.

VIRUS-P is good for halo studies because it can take spectra over a very large area of sky, allowing astronomers to reach the very low light levels at large distances from the galaxy center where the dark halo is dominant. It is a prototype, built to test technology going into the larger VIRUS spectrograph for the forthcoming Hobby-Eberly Telescope Dark Energy Experiment (HETDEX).

Read the team’s paper.

Sources: AAS, McDonald Observatory

Posted on by Nancy Atkinson

No Nature VS. Nurture for Stars

The Arches Cluster, with young, massive stars, taken by the NACO on ESO’s Very Large Telescope.

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Stars don’t seem to mind where they grow up. Either in a nice quiet neighborhood or in the hellish environment near a supermassive black hole, astronomers were surprised to find the same proportions of low- and high-mass young stars in different types of star forming regions. Using the Very Large Telescope, astronomers snapped one of the sharpest views ever of the Arches Cluster — an extraordinary dense cluster of young stars near the supermassive black hole at the center of the Milky Way. “With the extreme conditions in the Arches Cluster, one might indeed imagine that stars won’t form in the same way as in our quiet solar neighbourhood,” says Pablo Espinoza, the lead author of the paper reporting the new results. “However, our new observations showed that the masses of stars in this cluster actually do follow the same universal law”.

The massive Arches Cluster is located 25 000 light-years away towards the constellation of Sagittarius. It contains about a thousand young, massive stars, less than 2.5 million years old. Astronomers say this region is an ideal laboratory to study how massive stars are born in extreme conditions, as the stars in the cluster experience huge opposing forces from all the activity going on near the supermassive black hole. The Arches Cluster is also ten times heavier than typical young star clusters scattered throughout our Milky Way and is enriched with chemical elements heavier than helium.

The Arches Cluster is located in the centre of the image, but its stars are hidden behind large amount of dust. The bright star at the top of the image is 3 Sagittarii, while the cluster of stars seen at the bottom left is NGC 6451. Credit: Digitized Sky Survey
The Arches Cluster is located in the centre of the image, but its stars are hidden behind large amount of dust. The bright star at the top of the image is 3 Sagittarii, while the cluster of stars seen at the bottom left is NGC 6451. Credit: Digitized Sky Survey

Using the NACO adaptive optics on the VLT, astronomers were able to take the clearest images yet of the Arches Cluster. Observing the Arches Cluster is very challenging because of the huge quantities of light-absorbing dust between Earth and the Galactic Centre, which visible light cannot penetrate. This is why NACO was used to observe the region in near-infrared light.

The new study confirms the Arches Cluster to be the densest cluster of massive young stars known. It is about three light-years across with more than a thousand stars packed into each cubic light-year — an extreme density a million times greater than in the Sun’s neighborhood.
Astronomers studying clusters of stars have found that higher mass stars are rarer than their less massive brethren, and their relative numbers are the same everywhere, following a universal law.

The astronomers were also able to study the brightest stars in the cluster. “The most massive star we found has a mass of about 120 times that of the Sun,” says co-author Fernando Selman. “We conclude from this that if stars more massive than 130 solar masses exist, they must live for less than 2.5 million years and end their lives without exploding as supernovae, as massive stars usually do.”

The total mass of the cluster seems to be about 30,000 times that of the Sun, much more than was previously thought. “That we can see so much more is due to the exquisite NACO images,” says co-author Jorge Melnick.

Read the team’s paper.

Source: ESO

Posted on by Nancy Atkinson

Could Ghost-Like Object Found by Chandra Be Another ‘Voorwerp’?

The ghost of HDF 130. Credit: X-ray (NASA/CXC/IoA/A.Fabian et al.); Optical (SDSS), Radio (STFC/JBO/MERLIN)

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The Chandra X-ray Observatory has found a cosmic “ghost” lurking around a distant supermassive black hole. Astronomers think this high-energy apparition is evidence of a huge eruption produced by the black hole. But this blue blob looks eerily similar to another cosmic blob of gas found by Galaxy Zoo member Hanny Van Arkel, the famous object called Hanny’s Voorwerp. Could the two objects be similar?

Astronomers say the “ghost” found by Chandra is the remains of a diffuse X-ray source, lingering after other radiation from the black hole’s outburst died away. The object, HDF 130 is over 10 billion light years away and existed at a time 3 billion years after the Big Bang, when galaxies and black holes were forming at a high rate.

Hanny's Voorwerp. Credit: Galaxy Zoo
Hanny's Voorwerp. Credit: Galaxy Zoo

Hanny’s Voorwerp has been a mystery ever since it was found in 2007 as part of the Galaxy Zoo project. Recent research on the object reveals that the Voorwerp is also likely to be a remnant from a black hole outburst. In the original Sloan Digital Sky Survey images of Hanny’s Voorwerp, the object showed up as blue, however further spectral analysis showed it is actually green. The Voorwerp was studied by the Swift gamma-ray satellite, which also can pick up ultraviolet and X-ray emissions, but the satellite didn’t come up with anything conclusive. However, the Westerbork Synthesis Radio Telescope (WSRT) took a look at Hanny’s Voorwerp and determined that indeed, black hole jets were allowing beams of intense optical and ultraviolet emissions from the black hole to heat and illuminate a small part of a large gas cloud that partially surrounds the nearby galaxy, IC 2497.

But Galaxy Zoo astronomers suspect X-rays might play a role in the Voorwerp, too. It was recently imaged by the Suzaku X-ray telescopes to see if is visible in that part of the spectrum, as well as to probe the current activity of the supermassive black hole. The results of that observation are still being analyzed. Yale astronomer Kevin Schawinski recently wrote in the Galaxy Zoo Blog that detecting hard X-ray photons would provide evidence of an active supermassive black hole in IC 2497, which would be illuminating the Voorwerp. “If on the other hand we don’t pick up anything, then we can be sure that the black hole has stopped feeding, i.e. it has genuinely shut down,” Schawinski wrote.

So are the two objects, the “ghost” of HDF 130 and Hanny’s Voorwerp similar? Yes – and no – said Chandra scientist Dr. Peter Edmonds.

“There are indeed some basic similarities between these two objects, in that both were generated by eruptions from a supermassive black hole, either in the form of bright radiation or jets, Edmonds told Universe Today.”Also, in both cases the eruption from the black hole seems to have died down.”

The details of the two objects, however, are very different, Edmonds said. “Hanny’s Voorwerp involves a light echo while the X-ray ghost was thought to form by an interaction between the comic background radiation and particles in a jet. They’re obviously seen at very different wavelengths. Also, the ghost is found in the early Universe at much greater distances than Hanny’s Voorwerp and is physically much larger.”

Additionally, the Chandra team suspects a very powerful and large eruption was responsible for the formation of the ghost, much more powerful than the one for Hanny’s Voorwerp.

Andy Fabian of the Cambridge University in the United Kingdom, lead author on the paper on the ghost of HDF 130, thinks the object’s X-ray glow is evidence of an outburst equivalent to about a billion supernovas, which blasted particles at almost the speed of light. When the eruption was ongoing, it produced prodigious amounts of radio and X-radiation, but after several million years, the radio signal faded from view as the electrons radiated away their energy.

This is the first X-ray ghost ever seen after the demise of radio-bright jets. Astronomers have observed extensive X-ray emission with a similar origin, but only from galaxies with radio emission on large scales, signifying continued eruptions. In HDF 130, only a point source is detected in radio images, coinciding with the massive elliptical galaxy seen in its optical image.

This radio source indicates that HDF 130’s supermassive black hole may be growing.

With Hanny’s Voorwerp, however, astronomers are still searching for any sign of activity from the black hole.

Another argument that the two objects are different is their shape. The linear shape of the HDF 130’s X-ray source is consistent with the shape of radio jets and not with that of a galaxy cluster, which is expected to be circular. The energy distribution of the X-rays is also consistent with the interpretation of an X-ray ghost.

WSRT observations of Hanny's Voorwerp. Credit: ASTRON
WSRT observations of Hanny's Voorwerp. Credit: ASTRON

Hanny’s Voorwerp has all the hallmarks of an interacting system. “The gas probably arises from a tidal interaction between IC 2497 and another galaxy, which occurred several hundred million years ago,” said Dr. Tom Oosterloo, part of the team that studied the Voorwerp with WSRT.

There are more differences between the two objects, primarily that ghosts like the one from HDF 130 may be prevalent in the universe, while the Voorwerp might just be a one-time occurance. “The stream of gas ends three hundred thousand light years westwards of IC2497, and all the evidence points towards a group of galaxies at the tip of the stream being responsible for this freak cosmic accident,” said Oosterloo.

Chandra astronomer Caitlin Casey, also of Cambridge said, “This result hints that the X-ray sky should be littered with such ghosts, especially if black hole eruptions are as common as we think they are in the early Universe.”

So now that astronomers know where and now to look for X-ray objects like the one by HDF 130, we’re likely to hear about more cosmic X-ray ghosts in the future. But Hanny’s Voorwerp appears to be unique.

Sources: Chandra, previous UT article, email exchange with Dr. Peter Edmonds, Galaxy Zoo

Posted on by Anne Minard

Distant black hole poses for a close-up

1H0707-495

 

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Astronomers have probed closer than ever to a supermassive black hole lying deep at the core of a distant active galaxy that was once thought to be shrouded in dust — which will greatly advance the look captured in this NASA file image from the mid-1990s. Using new data from ESA’s X-ray Multi-Mirror Mission (XMM)-Newton spaceborne observatory, researchers peered into the innermost depths of the object, which lies at the heart of the galaxy known as 1H0707-495.

“We can now start to map out the region immediately around the black hole,” says Andrew Fabian, at the University of Cambridge, who headed the observations and analysis.

Artist's conception of a black hole. Credit: ESA
Artist's conception of a black hole. Credit: ESA

The galaxy — known as 1H0707-495 — was observed during four 48-hr-long orbits of XMM-Newton around Earth, starting in January 2008. 

X-rays are produced as matter swirls into a supermassive black hole, illuminating and reflecting from the matter before eventually accreting into it. Iron atoms in the flow can be observed in the reflected light, affected by the speed of the orbiting iron atoms, the energy required for the X-rays to escape the black hole’s gravitational field, and the spin of the black hole. All these features indicate that the astronomers are tracking matter to within twice the radius of the black hole itself.  

XMM-Newton detected two bright features of iron emission in the reflected X-rays that had never been seen together in an active galaxy. These bright features are known as the iron L and K lines, and they can be so bright only if there is a high abundance of iron. Seeing both in this galaxy suggests that the core is much richer in iron than the rest of the galaxy. 

Statistical analysis of the data revealed a time lag of 30 seconds between changes in the X-ray light observed directly, and those seen in its reflection from the disc. This delay in the echo enabled the size of the reflecting region to be measured, which leads to an estimate of the mass of the black hole at about 3 to 5 million solar masses.

The observations of the iron lines also show that the black hole is spinning very rapidly and eating matter so quickly that it verges on the theoretical limit of its eating ability, swallowing the equivalent of two Earths per hour.

Source: ESA. The paper appears in Nature.

Posted on by Nancy Atkinson

Is Everything Made of Mini Black Holes?

In 1971 physicist Stephen Hawking suggested that there might be “mini” black holes all around us that were created by the Big Bang. The violence of the rapid expansion following the beginning of the Universe could have squeezed concentrations of matter to form miniscule black holes, so small they can’t even be seen in a regular microscope. But what if these mini black holes were everywhere, and in fact, what if they make up the fabric of the universe? A new paper from two researchers in California proposes this idea.

Black holes are regions of space where gravity is so strong that not even light can escape, and are usually thought of as large areas of space, such as the supermassive black holes at the center of galaxies. No observational evidence of mini-black holes exists but, in principle, they could be present throughout the Universe.

Since black holes have gravity, they also have mass. But with mini black holes, the gravity would be weak. However, many physicists have assumed that even on the tiniest scale, the Planck scale, gravity regains its strength.

Experiments at the Large Hadron Collider are aimed at detecting mini black holes, but suffer from not knowing exactly how a reduced-Planck-mass black hole would behave, say Donald Coyne from UC Santa Cruz (now deceased) and D. C. Cheng from the Almaden Research Center near San Jose.

String theory also proposes that gravity plays a stronger role in higher dimensional space, but it is only in our four dimensional space that gravity appears weak.

Since these dimensions become important only on the Planck scale, it’s at that level that gravity re-asserts itself. And if that’s the case, then mini-black holes become a possibility, say the two researchers.

They looked at what properties black holes might have at such a small scale, and determined they could be quite varied.

Black holes lose energy and shrink in size as they do so, eventually vanishing, or evaporating. But this is a very slow process and only the smallest back holes will have had time to significantly evaporate over the enter 14 billion year history of the universe.

The quantization of space on this level means that mini-black holes could turn up at all kinds of energy levels. They predict the existence of huge numbers of black hole particles at different energy levels. And these black holes might be so common that perhaps “All particles may be varying forms of stabilized black holes.”

“At first glance the scenario … seems bizarre, but it is not,” Coyne and Cheng write. “This is exactly what would be expected if an evaporating black hole leaves a remnant consistent with quantum mechanics… This would put a whole new light on the process of evaporation of large black holes, which might then appear no different in principle from the correlated decays of elementary particles.”

They say their research need more experimentation. This may come from the LHC, which could begin to probe the energies at which these kinds of black holes will be produced.

Original paper.

Source: Technology Review

Posted on by Nancy Atkinson

Rogue Black Holes May Wander the Galaxy

Artists concept of a rogue black hole floating near a globular cluster star near the outskirts of the Milky Way. Credit: David A. Aguilar, CfA

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Here’s another “rogue black hole” theory, which hopefully doesn’t set the doomsday crowd off on a new tangent. But new research suggests that hundreds of massive black holes, left over from the early galaxy-building days of the Universe, may wander the Milky Way. Astrophysicists Ryan O’Leary and Avi Loeb say that rogue black holes originally lurked at the centers of tiny, low-mass galaxies. Over billions of years, those dwarf galaxies smashed together to form full-sized galaxies like the Milky Way. But they also predict that Earth should be safe, as the closest rogue black hole should reside thousands of light-years away.

“These black holes are relics of the Milky Way’s past,” said Loeb, from the Harvard Smithsonian Center for Astrophysics. “You could say that we are archaeologists studying those relics to learn about our galaxy’s history and the formation history of black holes in the early universe.”

Astronomers say if these wandering black holes could be located, they could provides clues to the formation of the Milky Way.

The theory predicts that each time two proto-galaxies with central black holes collided, their black holes merged to form a single, “relic” black hole. During the merger, directional emission of gravitational radiation would cause the black hole to recoil. A typical kick would send the black hole speeding outward fast enough to escape its host dwarf galaxy, but not fast enough to leave the galactic neighborhood completely. As a result, such black holes would still be around today in the outer reaches of the Milky Way halo.

This sounds similar to another “rogue black hole” theory released in 2008 from Vanderbilt University, where a supercomputer simulation predicted colliding black holes created in globular clusters would be kicked out of their home and left to wander the galaxy. Astronomers have been looking for them for years, and even after all that searching, they’ve only come up with a couple of tentative candidates.
But Loeb and O’Leary say hundreds of rogue black holes should be traveling the Milky Way’s outskirts, each containing the mass of 1,000 to 100,000 suns. They would be difficult to spot on their own because a black hole is visible only when it is swallowing, or accreting, matter.

There could be on telltale sign, however. A surrounding cluster of stars could be yanked from the dwarf galaxy when the black hole escaped. Only the stars closest to the black hole would be tugged along, so the cluster would be very compact.

But still it would be hard to determine. Due to the cluster’s small size on the sky, appearing to be a single star, astronomers would have to look for more subtle clues to its existence and origin. For example, its spectrum would show that multiple stars were present, together producing broad spectral lines. The stars in the cluster would be moving rapidly, their paths influenced by the gravity of the black hole.
O’Leary and Loeb say now that they know what to look for, astronomers should begin scanning the skies for a population of highly compact star clusters in the Milky Way’s halo.

The number of rogue black holes in our galaxy will depend on how many of the proto-galactic building blocks contained black holes at their cores, and how those proto-galaxies merged to form the Milky Way. Finding and studying them will provide new clues about the history of our galaxy.

Loeb and O’Leary’s journal paper will be published in the Monthly Notices of the Royal Astronomical Society and is available online at arXiv.

Posted on by Nancy Atkinson

Dark Matter, Dark Energy; Now There’s “Dark Gulping”

The HST WFPC2 image of gravitational lensing in the galaxy cluster Abell 2218, indicating the presence of large amount of dark matter (credit Andrew Fruchter at STScI).

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For all you dark matter and dark energy fans out there, now there’s another new “dark” to add to the list. It’s called “dark gulping,” and it involves a process which may explain how supermassive black holes were able to form in the early universe. Astronomers from the University College of London (UCL) propose that dark gulping occurred when there were gravitational interactions between the invisible halo of dark matter in a cluster of galaxies and the gas embedded in the dark matter halo. This occurred when the Universe was less than a billion years old. They found that the interactions cause the dark matter to form a compact central mass, which can be gravitationally unstable, and collapse. The fast dynamical collapse is the dark gulping.

Dr. Curtis Saxton and Professor Kinwah Wu, both of UCL’s Mullard Space Science Laboratory, developed a model to study the process. They say that the dark gulping would have happened very rapidly, without a trace of electro-magnetic radiation being emitted.

There are several theories for how supermassive black holes form. One possibility is that a single large gas cloud collapses. Another is that a black hole formed by the collapse of a giant star swallows up enormous amounts of matter. Still another possibility is that a cluster of small black holes merge together. However, all these options take many millions of years and are at odds with recent observations that suggest that black holes were present when the Universe was less than a billion years old. Dark gulping may provide a solution to how the slowness of gas accretion was circumvented, enabling the rapid emergence of giant black holes. The affected dark mass in the compact core is compatible with the scale of supermassive black holes in galaxies today.

Dark matter appears to gravitationally dominate the dynamics of galaxies and galaxy clusters. However, there is still a great deal of conjecture about origin, properties and distribution of dark particles. While it appears that dark matter doesn’t interact with light, it does interacts with ordinary matter via gravity. “Previous studies have ignored the interaction between gas and the dark matter,” said Saxton, “but, by factoring it into our model, we’ve achieved a much more realistic picture that fits better with observations and may also have gained some insight into the presence of early supermassive black holes.”?

According to the model, the development of a compact mass at the core is inevitable. Cooling by the gas causes it to flow gently in towards the center. The gas can be up to 10 million degrees at the outskirts of the halos, which are few million light years in diameter, with a cooler zone towards the core, which surrounds a warmer interior a few thousand light years across. The gas doesn’t cool indefinitely, but reaches a minimum temperature, which fits well with X-ray observations of galaxy clusters.

The model also investigates how many dimensions the dark particles move in, as these determine the rate at which the dark halo expands and absorbs and emits heat, and ultimately affect the distribution of dark mass the system.

“In the context of our model, the observed core sizes of galaxy cluster halos and the observed range of giant black hole masses imply that dark matter particles have between seven and ten degrees of freedom,”?said Saxton. ?”With more than six, the inner region of the dark matter approaches the threshold of gravitational instability, opening up the possibility of dark gulping taking place.?

The findings have been published in the Monthly Notices of the Royal Astronomical Society.

Source: RAS

Posted on by Anne Minard

Black Hole Jets Pack One, Two Punch in Radio, Gamma Rays

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Compact, ultrabright jets at supermassive black holes in active galaxies were already known to pack an impressive punch in radio waves.  And now, an international team of scientists says they’re kicking out high-energy gamma rays too.

3c454-3-mojave

Distant galaxies host the super massive black holes, which are billions of times heavier than our Sun but are confined to a region no larger than our solar system. The rapidly rotating black holes attract stars, gas and dust, creating huge magnetic fields. The magnetic forces can trap some of the infalling gas and focus it into narrow jets that flow away from the core of the galaxy at velocities approaching the speed of light.

Theoreticians and observers alike have been puzzling for decades about the nature and composition of these energetic radio-emitting jets, and if they also radiate in other parts of the electromagnetic spectrum.

Some hints were provided by the EGRET instrument on the Compton Gamma Ray Observatory telescope in the late 1990s and more recent discoveries of X-ray emission made by the Chandra Observatory. 

Now, astronomers from Germany, the United States and Spain have paired observations of the bright gamma-ray sky by NASA’s orbiting Fermi Gamma-ray Space Telescope with those from the ground-based Very Long Baseline Array radio telescope in the United States to observe the material expelled with enormous speeds away from the black holes in the heart of very remote galaxies. These ejections take the form of narrow jets in radio telescope images, and appear to be producing the gamma-rays detected by Fermi.

“These objects are amazing: finally we know for sure that the fastest, most compact, and brightest jets that we see with radio telescopes are the ones which are able to kick the light up to the highest energies,” said Yuri Kovalev, Humboldt Fellow and scientist at the Max Planck Institute for Radio Astronomy.

The gamma-ray bright sources are now shown to be brighter, more compact and faster at light year scales than the gamma-ray quiet sources.

Fermi, formerly known as GLAST, has been operational since the summer of 2008. The telescope records an image of the whole sky every few hours to explore the most extreme environments in the universe, including pulsars and gamma-ray bursts, as well as black holes in galactic nuclei. Gamma-ray observations alone are not enough to discern the exact location of the radiation, however. The VLBA serves as a magnifying glass for zeroing in on the most energetic processes in the distant universe. Many objects found by Fermi to be extreme in gamma-rays are emitting strong bursts of radio emission at the same time.

The Very Long Baseline Array is a continent-wide system of ten radio telescope antennas, ranging from Hawaii in the west to the U.S. Virgin Islands in the east. Dedicated in 1993, the VLBA is operated by the U.S. National Radio Astronomy Observatory and is designed to monitor the brightest objects in the Universe at the highest available resolution in astronomy. 

The work for astronomers does not stop here: the team has concluded that the region of the jet closest to the black hole is undoubtedly the place where the gamma-ray and the radio bursts of light originate in about the same time. However, some parts of the puzzle have yet to be resolved, they say: some bright gamma-ray sources in the sky appear to have no radio or optical counterpart — their nature is still completely unknown. 

Source: Max-Planck Institute. The findings are being reported in two publications in the May 1, 2009 issue of Astrophysical Journal Letters (here and here).

Links:

Very Long Baseline Array
VLBA Monitoring of AGN Jets: The MOJAVE Project
Fermi Gamma-ray Space Telescope LAT Group

Posted on by Nancy Atkinson

Oldest and Most Distant Water in the Universe Detected

The image is made from HST data and shows the four lensed images of the dusty red quasar, connected by a gravitational arc of the quasar host galaxy. The lensing galaxy is seen in the centre, between the four lensed images. Credit: John McKean/HST Archive data

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Astronomers have found the most distant signs of water in the Universe to date. The water vapor is thought to be contained in a maser, a jet ejected from a supermassive black hole at the center of a galaxy, named MG J0414+0534. The radiation from the water maser was emitted when the Universe was only about 2.5 billion years old, a fifth of its current age. “The radiation that we detected has taken 11.1 billion years to reach the Earth, said Dr. John McKean of the Netherlands Institute for Radio Astronomy (ASTRON). “However, because the Universe has expanded like an inflating balloon in that time, stretching out the distances between points, the galaxy in which the water was detected is about 19.8 billion light years away.”

The water emission is seen as a maser, where molecules in the gas amplify and emit beams of microwave radiation in much the same way as a laser emits beams of light. The faint signal is only detectable by using a technique called gravitational lensing, where the gravity of a massive galaxy in the foreground acts as a cosmic telescope, bending and magnifying light from the distant galaxy to make a clover-leaf pattern of four images of MG J0414+0534. The water maser was only detectable in the brightest two of these images.

“We have been observing the water maser every month since the detection and seen a steady signal with no apparent change in the velocity of the water vapor in the data we’ve obtained so far, McKean said. “This backs up our prediction that the water is found in the jet from the supermassive black hole, rather than the rotating disc of gas that surrounds it.”

Detection of the earliest and most distant water. CREDIT: Milde Science Communication, STScI, CFHT, J.-C. Cuillandre, Coelum.
Detection of the earliest and most distant water. CREDIT: Milde Science Communication, STScI, CFHT, J.-C. Cuillandre, Coelum.

Although since the initial discovery the team has looked at five more systems that have not had water masers, they believe that it is likely that there are many more similar systems in the early Universe. Surveys of nearby galaxies have found that only about 5% have powerful water masers associated with active galactic nuclei. In addition, studies show that very powerful water masers are extremely rare compared to their less luminous counterparts. The water maser in MG J0414+0534 is about 10,000 times the luminosity of the Sun, which means that if water masers were equally rare in the early Universe, the chances of making this discovery would be improbably slight.

“We found a signal from a really powerful water maser in the first system that we looked at using the gravitational lensing technique. From what we know about the abundance of water masers locally, we could calculate the probability of finding a water maser as powerful as the one in MG J0414+0534 to be one in a million from a single observation. This means that the abundance of powerful water masers must be much higher in the distant Universe than found locally because I’m sure we are just not that lucky!” said Dr McKean.

The discovery of the water maser was made by a team led by Dr. Violette Impellizzeri using the 100-metre Effelsberg radio telescope in Germany during July to September 2007. The discovery was confirmed by observations with the Expanded Very Large Array in the USA in September and October 2007. The team included Alan Roy, Christian Henkel and Andreas Brunthaler, from the Max Planck Institute for Radio Astronomy, Paola Castangia from Cagliari Observatory and Olaf Wucknitz from the Argelander Institute for Astronomy at Bonn University. The findings were published in Nature in December 2008.

The team is now analyzing high-resolution data to find out how close the water maser lies to the supermassive black hole, which will give them new insights into the structure at the center of active galaxies in the early Universe.

“This detection of water in the early Universe may mean that there is a higher abundance of dust and gas around the super-massive black hole at these epochs, or it may be because the black holes are more active, leading to the emission of more powerful jets that can stimulate the emission of water masers. We certainly know that the water vapour must be very hot and dense for us to observe a maser, so right now we are trying to establish what mechanism caused the gas to be so dense,” said Dr McKean.

McKean presented the team’s findings at the European Week of Astronomy and Space Science in the UK this week.

Source: RAS

Posted on by Nancy Atkinson

What Would the View Be Like From Within a Black Hole?

The view from within a black hole? Credit: University of Colorado

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If you fell into a black hole, would you be engulfed in darkness? Could you see out beyond the event horizon? Are there wormholes inside black holes? Do black holes give birth to baby universes? Believe it or not, these questions may have been answered. Andrew Hamilton from the University of Colorado and Gavin Polhemus have created a video showing what falling into a Schwarzschild black hole might look like to the person falling in. The two researchers warn that based on our experience in the 3D world, we might imagine that falling through the horizon would be like falling through any other surface. However, they say, it’s not. And likely, a person falling into the black hole would be able to see outside of the event horizon.

“When an observer outside the horizon observes the horizon of a black hole,” the researchers say, “they are actually observing the outgoing horizon. When they subsequently fall through the horizon, they do not fall through the horizon they were looking at, the outgoing horizon; rather, they fall through the ingoing horizon, which was invisible to them until they actually passed through it. Once inside the horizon, the infaller sees both outgoing and ingoing horizons.”

As you might expect, this work has created a lot of interest, and the servers hosting the videos has already crashed once, but now has been put on a new server. Watch several different videos. along with written commentary here.

While this work is great fun to watch and delve into, it also has great scientific merit. Calculating what the universe looks like from inside a black hole is an important exercise because it forces physicists to examine how the laws of physics behave at a breaking point. For example, near the singularity, the observer’s view in the horizontal plane is highly blueshifted, but all directions other than horizontal appear highly redshifted.

Also, the principle of locality is severely tested inside a black hole. This is the idea that a point in space can only be influenced by its immediate surroundings. But when space is infinitely stretched, as physicists think it is at the heart of a black hole, the concept of “immediate surroundings” doesn’t make sense. So the concept of locality begins to lose its meaning too.

And that provides an interesting “thought laboratory” in which physicists can ask how ideas such as quantum mechanics and relativity might break down.

It also provides some other entertaining results. For example, space is so heavily curved inside a black hole that ordinary binocular vision would be no good for determining distances, says Hamilton. But trinoculars might work.

Read the paper here.

Sources: Technology Review Blog