Posted on by Nancy Atkinson

Data from Black Hole’s Edge Provides New Test of Relativity

From a NASA press release:

Last year, astronomers discovered a quiescent black hole in a distant galaxy that erupted after shredding and consuming a passing star. Now researchers have identified a distinctive X-ray signal observed in the days following the outburst that comes from matter on the verge of falling into the black hole.

This tell-tale signal, called a quasi-periodic oscillation or QPO, is a characteristic feature of the accretion disks that often surround the most compact objects in the universe — white dwarf stars, neutron stars and black holes. QPOs have been seen in many stellar-mass black holes, and there is tantalizing evidence for them in a few black holes that may have middleweight masses between 100 and 100,000 times the sun’s.

Until the new finding, QPOs had been detected around only one supermassive black hole — the type containing millions of solar masses and located at the centers of galaxies. That object is the Seyfert-type galaxy REJ 1034+396, which at a distance of 576 million light-years lies relatively nearby.

“This discovery extends our reach to the innermost edge of a black hole located billions of light-years away, which is really amazing. This gives us an opportunity to explore the nature of black holes and test Einstein’s relativity at a time when the universe was very different than it is today,” said Rubens Reis, an Einstein Postdoctoral Fellow at the University of Michigan in Ann Arbor. Reis led the team that uncovered the QPO signal using data from the orbiting Suzaku and XMM-Newton X-ray telescopes, a finding described in a paper published today in Science Express.

The X-ray source known as Swift J1644+57 — after its astronomical coordinates in the constellation Draco — was discovered on March 28, 2011, by NASA’s Swift satellite. It was originally assumed to be a more common type of outburst called a gamma-ray burst, but its gradual fade-out matched nothing that had been seen before. Astronomers soon converged on the idea that what they were seeing was the aftermath of a truly extraordinary event — the awakening of a distant galaxy’s dormant black hole as it shredded and gobbled up a passing star. The galaxy is so far away that light from the event had to travel 3.9 billion years before reaching Earth.

Video info: On March 28, 2011, NASA’s Swift detected intense X-ray flares thought to be caused by a black hole devouring a star. In one model, illustrated here, a sun-like star on an eccentric orbit plunges too close to its galaxy’s central black hole. About half of the star’s mass feeds an accretion disk around the black hole, which in turn powers a particle jet that beams radiation toward Earth. Credit: NASA’s Goddard Space Flight Center/Conceptual Image Lab

The star experienced intense tides as it reached its closest point to the black hole and was quickly torn apart. Some of its gas fell toward the black hole and formed a disk around it. The innermost part of this disk was rapidly heated to temperatures of millions of degrees, hot enough to emit X-rays. At the same time, through processes still not fully understood, oppositely directed jets perpendicular to the disk formed near the black hole. These jets blasted matter outward at velocities greater than 90 percent the speed of light along the black hole’s spin axis. One of these jets just happened to point straight at Earth.

Nine days after the outburst, Reis, Strohmayer and their colleagues observed Swift J1644+57 using Suzaku, an X-ray satellite operated by the Japan Aerospace Exploration Agency with NASA participation. About ten days later, they then began a longer monitoring campaign using the European Space Agency’s XMM-Newton observatory.

“Because matter in the jet was moving so fast and was angled nearly into our line of sight, the effects of relativity boosted its X-ray signal enough that we could catch the QPO, which otherwise would be difficult to detect at so great a distance,” said Tod Strohmayer, an astrophysicist and co-author of the study at NASA’s Goddard Space Flight Center in Greenbelt, Md.

As hot gas in the innermost disk spirals toward a black hole, it reaches a point astronomers refer to as the innermost stable circular orbit (ISCO). Any closer to the black hole and gas rapidly plunges into the event horizon, the point of no return. The inward spiraling gas tends to pile up around the ISCO, where it becomes tremendously heated and radiates a flood of X-rays. The brightness of these X-rays varies in a pattern that repeats at a nearly regular interval, creating the QPO signal.

The data show that Swift J1644+57’s QPO cycled every 3.5 minutes, which places its source region between 2.2 and 5.8 million miles (4 to 9.3 million km) from the center of the black hole, the exact distance depending on how fast the black hole is rotating. To put this in perspective, the maximum distance is only about 6 times the diameter of our sun. The distance from the QPO region to the event horizon also depends on rotation speed, but for a black hole spinning at the maximum rate theory allows, the horizon is just inside the ISCO.

“QPOs send us information from the very brim of the black hole, which is where the effects of relativity become most extreme,” Reis said. “The ability to gain insight into these processes over such a vast distance is a truly beautiful result and holds great promise.”

Read our previous article on Swift J1644+57

Lead image caption: This illustration highlights the principal features of Swift J1644+57 and summarizes what astronomers have discovered about it. Credit: NASA’s Goddard Space Flight Center

Posted on by Nancy Atkinson

First Light Image for NuSTAR

Here is the first image taken by the newest space mission, NuSTAR, or the Nuclear Spectroscopic Telescope Array, the first space telescope with the ability to see the highest energy X-rays in our universe and produce crisp images of them.

“Today, we obtained the first-ever focused images of the high-energy X-ray universe,” said Fiona Harrison, the mission’s principal investigator. “It’s like putting on a new pair of glasses and seeing aspects of the world around us clearly for the first time.”

With the successful “first light” images, the mission will begin its exploration of the most elusive and energetic black holes — as well as other areas of extreme physics in our cosmos — to help in our understanding of the structure of the universe.

The first images show Cygnus X-1, a black hole in our galaxy that is siphoning gas off a giant-star companion. This particular black hole was chosen as a first target because it is extremely bright in X-rays, allowing the NuSTAR team to easily see where the telescope’s focused X-rays are falling on the detectors.

NuSTAR launched on June 13 and its lengthy mast, which provides the telescope mirrors and detectors with the distance needed to focus X-rays, was deployed on June 21. The NuSTAR team spent the next week verifying the pointing and motion capabilities of the satellite, and fine-tuning the alignment of the mast.

The mission’s primary observing program is expected to start in about two weeks. But before it does, the team will continue tests and point the NuSTAR at two other bright calibration targets: G21.5-0.9, the remnant of a supernova explosion that occurred several thousand years ago in our own Milky Way galaxy; and 3C273, an actively feeding black hole, or quasar, located 2 billion light-years away at the center of another galaxy. These targets will be used to make a small adjustment to place the X-ray light at the optimum spot on the detector, and to further calibrate and understand the telescope in preparation for future science observations.

Other targets for the mission include the burnt-out remains of dead stars, such as those that exploded as supernovae; high-speed jets; the temperamental surface of our sun; and the structures where galaxies cluster together like mega-cities.

“This is a really exciting time for the team,” said Daniel Stern, the NuSTAR project scientist. “We can already see the power of NuSTAR to crack open the high-energy X-ray universe and reveal secrets that were impossible to get at before.”

Lead image caption: NASA’s Nuclear Spectroscopic Telescope Array, or NuSTAR, has taken its first snapshots of the highest-energy X-rays in the cosmos (lower right), producing images that are much crisper than previous high-energy telescopes (example in upper right). NuSTAR chose a black hole in the constellation Cygnus (shown in the skymap on the left) as its first target due to its brightness. Image credit: NASA/JPL-Caltech

Posted on by Nancy Atkinson

Gas Cloud Will Collide with our Galaxy’s Black Hole in 2013

Scientists have determined a giant gas cloud is on a collision course with the black hole in the center of our galaxy, and the two will be close enough by mid-2013 to provide a unique opportunity to observe how a super massive black hole sucks in material, in real time. This will give astronomers more information on how matter behaves near a black hole.

“The next few years will be really fantastic and exciting because we are probing new territory,” said Reinhard Genzel, leading a team from the ESO in observations with the Very Large Telescope. “Here this cloud comes in gets disrupted and now it will begin to interact with the hot gas right around the black hole. We have never seen this before.”

By June of 2013, the gas cloud is expected to be just 36 light-hours (equivalent to 40,000,000,000 km) away from our galaxy’s black hole, which is extremely close in astronomical terms.

Astronomers have determined the speed of the gas cloud has increased, doubling over the past seven years, and is now reaching more than 8 million km per hour. The cloud is estimated to be three times the mass of Earth and the density of the cloud is much higher than that of the hot gas surrounding black hole. But the black hole has a tremendous gravitational force, and so the gas cloud will fall into the direction of the black hole, be elongated and stretched and look like spaghetti, said Stefan Gillessen, astrophysicist at the Max Planck Institute for Extraterrestrial Physics in Munich, Germany, who has been observing our galaxy’s black hole, known as Sagittarius A* (or Sgr A*), for 20 years.

“So far there were only two stars that came that close to Sagittarius A*,” Gillessen said. “They passed unharmed, but this time will be different: the gas cloud will be completely ripped apart by the tidal forces of the black hole.”

Watch a video of observations of the cloud for the past 10 years:

No one really knows how the collision will unfold, but the cloud’s edges have already started to shred and it is expected to break up completely over the coming months. As the time of actual collision approaches, the cloud is expected to get much hotter and will probably start to emit X-rays as a result of the interaction with the black hole.

Although direct observations of black holes are impossible, as they do not emit light or matter, astronomers can identify a black hole indirectly due to the gravitational forces observed in their vicinity.

A black hole is what remains after a super massive star dies. When the “fuel” of a star runs low, it will first swell and then collapse to a dense core. If this remnant core has more than three times the mass of our Sun, it will transform to a black hole. So-called super massive black holes are the largest type of black holes, as their mass equals hundreds of thousands to a billion times the mass of our Sun.

Black holes are thought to be at the center of all galaxies, but their origin is not fully understood and astrophysicists can only speculate as to what happens inside them. And so this upcoming collision just 27,000 light years away will likely provide new insights on the behavior of black holes.

Lead image caption: Images taken over the last decade using the NACO instrument on ESO’s Very Large Telescope show the motion of a cloud of gas that is falling towards the supermassive black hole at the centre of the Milky Way. This is the first time ever that the approach of such a doomed cloud to a supermassive black hole has been observed and it is expected to break up completely during 2013. Credit: ESO/MPE

Read our previous article about this topic, from Dec. 2011.

Source: European Research Media Center

Posted on by John Williams

Early Black Holes were Grazers Rather than Glutonous Eaters

Faint quasars powered by black holes. Image credit NASA/ESA/Yale

Black holes powering distant quasars in the early Universe grazed on patches of gas or passing galaxies rather than glutting themselves in dramatic collisions according to new observations from NASA’s Spitzer and Hubble space telescopes.

A black hole doesn’t need much gas to satisfy its hunger and turn into a quasar, says study leader Kevin Schawinski of Yale “There’s more than enough gas within a few light-years from the center of our Milky Way to turn it into a quasar,” Schawinski explained. “It just doesn’t happen. But it could happen if one of those small clouds of gas ran into the black hole. Random motions and stirrings inside the galaxy would channel gas into the black hole. Ten billion years ago, those random motions were more common and there was more gas to go around. Small galaxies also were more abundant and were swallowed up by larger galaxies.”

Quasars are distant and brilliant galactic powerhouses. These far-off objects are powered by black holes that glut themselves on captured material; this in turn heats the matter to millions of degrees making it super luminous. The brightest quasars reside in galaxies pushed and pulled by mergers and interactions with other galaxies leaving a lot of material to be gobbled up by the super-massive black holes residing in the galactic cores.

Schawinski and his team studied 30 quasars with NASA’s orbiting telescopes Hubble and Spitzer. These quasars, glowing extremely bright in the infrared images (a telltale sign that resident black holes are actively scooping up gas and dust into their gravitational whirlpool) formed during a time of peak black-hole growth between eight and twelve billion years ago. They found 26 of the host galaxies, all about the size of our own Milky Way Galaxy, showed no signs of collisions, such as smashed arms, distorted shapes or long tidal tails. Only one galaxy in the study showed evidence of an interaction. This finding supports evidence that the creation of the most massive black holes in the early Universe was fueled not by dramatic bursts of major mergers but by smaller, long-term events.

“Quasars that are products of galaxy collisions are very bright,” Schawinski said. “The objects we looked at in this study are the more typical quasars. They’re a lot less luminous. The brilliant quasars born of galaxy mergers get all the attention because they are so bright and their host galaxies are so messed up. But the typical bread-and-butter quasars are actually where most of the black-hole growth is happening. They are the norm, and they don’t need the drama of a collision to shine.

“I think it’s a combination of processes, such as random stirring of gas, supernovae blasts, swallowing of small bodies, and streams of gas and stars feeding material into the nucleus,” Schawinski said.

Unfortunately, the process powering the quasars and their black holes lies below the detection of Hubble making them prime targets for the upcoming James Webb Space Telescope, a large infrared orbiting observatory scheduled for launch in 2018.

You can learn more about the images here.

Image caption: These galaxies have so much dust enshrouding them that the brilliant light from their quasars cannot be seen in these images from the NASA/ESA Hubble Space Telescope.

Posted on by Nancy Atkinson

Black Hole Hunter Drops from a Plane, Zooms to Orbit

NASA's NuSTAR and its rocket drop from the carrier "Stargazer" plane. Image Credit: Orbital Sciences Corporation.

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The newest mission to hunt for black holes soared to orbit today after first dropping from an aircraft. NASA’s Nuclear Spectroscopic Telescope Array (NuSTAR) launched 16:00 UTC (12 noon EDT, 9 a.m. PDT). NuSTAR was strapped to an Orbital Sciences Pegasus rocket, both of which strapped to an L-1011 “Stargazer” aircraft. The plane left Kwajalein Atoll in the central Pacific Ocean one hour before launch. Then at 9:00:35 a.m. PDT the rocket dropped, free-falling for five seconds before firing its first-stage motor.

“NuSTAR will help us find the most elusive and most energetic black holes, to help us understand the structure of the universe,” said Fiona Harrison, the mission’s principal investigator at the California Institute of Technology in Pasadena.

Watch the video of the launch below.

About 13 minutes after the rocket dropped, NuSTAR separated from the rocket, reaching its final low Earth orbit. The first signal from the spacecraft was received at 9:14 a.m. PDT via NASA’s Tracking and Data Relay Satellite System.

“NuSTAR spread its solar panels to charge the spacecraft battery and then reported back to Earth of its good health,” said Yunjin Kim, the mission’s project manager at NASA’s Jet Propulsion Laboratory in Pasadena, Calif. “We are checking out the spacecraft now and are excited to tune into the high-energy X-ray sky.”

The mission’s unique telescope design includes a 33-foot (10-meter) mast, which was folded up in a small canister during launch. In about seven days, engineers will command the mast to extend, enabling the telescope to focus properly. About 23 days later, science operations are scheduled to begin.
“With its unprecedented spatial and spectral resolution to the previously poorly explored hard X-ray region of the electromagnetic spectrum, NuSTAR will open a new window on the universe and will provide complementary data to NASA’s larger missions, including Fermi, Chandra, Hubble and Spitzer,” said Paul Hertz, NASA’s Astrophysics Division Director.

Combining all the data from the telescopes together will provide a more complete picture of the most energetic and exotic objects in space, such as black holes, dead stars and jets traveling near the speed of light.

NuSTAR will use a unique set of eyes to see the highest energy X-ray light from the cosmos. The observatory can see through gas and dust to reveal black holes lurking in our Milky Way galaxy, as well as those hidden in the hearts of faraway galaxies.

In addition to black holes and their powerful jets, NuSTAR will study a host of high-energy objects in our universe, including the remains of exploded stars; compact, dead stars; and clusters of galaxies. The mission’s observations, in coordination with other telescopes such as NASA’s Chandra X-ray Observatory, which detects lower-energy X-rays, will help solve fundamental cosmic mysteries. NuSTAR also will study our Sun’s fiery atmosphere, looking for clues as to how it is heated.

Learn more about NuStar at the mission website.

Posted on by Nancy Atkinson

Black Hole Growth Out of Whack in Some Galaxies

Galaxies NGC 4342 and NGC 4291. (X-ray: NASA/CXC/SAO/A.Bogdan et al; Infrared: 2MASS/UMass/IPAC-Caltech/ NASA/NSF)

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From a Chandra press release:

New evidence from NASA’s Chandra X-ray Observatory challenges prevailing ideas about how black holes grow in the centers of galaxies. Astronomers long have thought that a supermassive black hole and the bulge of stars at the center of its host galaxy grow at the same rate — the bigger the bulge, the bigger the black hole. However, a new study of Chandra data has revealed two nearby galaxies with supermassive black holes that are growing faster than the galaxies themselves.

The mass of a giant black hole at the center of a galaxy typically is a tiny fraction — about 0.2 percent — of the mass contained in the bulge, or region of densely packed stars, surrounding it. The targets of the latest Chandra study, galaxies NGC 4342 and NGC 4291, have black holes 10 times to 35 times more massive than they should be compared to their bulges. The new observations with Chandra show the halos, or massive envelopes of dark matter in which these galaxies reside, also are overweight.

This study suggests the two supermassive black holes and their evolution are tied to their dark matter halos and did not grow in tandem with the galactic bulges. In this view, the black holes and dark matter halos are not overweight, but the total mass in the galaxies is too low.

“This gives us more evidence of a link between two of the most mysterious and darkest phenomena in astrophysics — black holes and dark matter — in these galaxies,” said Akos Bogdan of the Harvard-Smithsonian Center for Astrophysics (CfA) in Cambridge, Mass., who led the new study.

NGC 4342 and NGC 4291 are close to Earth in cosmic terms, at distances of 75 million and 85 million light years. Astronomers had known from previous observations that these galaxies host black holes with relatively large masses, but are not certain what is responsible for the disparity. Based on the new Chandra observations, however, they are able to rule out a phenomenon known as tidal stripping.

Tidal stripping occurs when some of a galaxy’s stars are stripped away by gravity during a close encounter with another galaxy. If such tidal stripping had taken place, the halos mostly would have been missing. Because dark matter extends farther away from the galaxies, it is more loosely tied to them than the stars and more likely to be pulled away.

To rule out tidal stripping, astronomers used Chandra to look for evidence of hot, X-ray-emitting gas around the two galaxies. Because the pressure of hot gas — estimated from X-ray images — balances the gravitational pull of all the matter in the galaxy, the new Chandra data can provide information about the dark matter halos. The hot gas was found to be distributed widely around NGC 4342 and NGC 4291, implying that each galaxy has an unusually massive dark matter halo and that tidal stripping is unlikely.

“This is the clearest evidence we have, in the nearby universe, for black holes growing faster than their host galaxy,” said co-author Bill Forman, also of CfA. “It’s not that the galaxies have been compromised by close encounters, but instead they had some sort of arrested development.”

How can the mass of a black hole grow faster than the stellar mass of its host galaxy? The study’s authors suggest a large concentration of gas spinning slowly in the galactic center is what the black hole consumes very early in its history. It grows quickly, and as it grows, the amount of gas it can accrete, or swallow, increases along with the energy output from the accretion. After the black hole reaches a critical mass, outbursts powered by the continued consumption of gas prevent cooling and limit the production of new stars.

“It’s possible that the supermassive black hole reached a hefty size before there were many stars at all in the galaxy,” said Bogdan. “That is a significant change in our way of thinking about how galaxies and black holes evolve together.”

The results were presented June 11 at the 220th meeting of the American Astronomical Society in Anchorage, Alaska. The study also has been accepted for publication in The Astrophysical Journal.

Posted on by Nancy Atkinson

Spitzer Captures Ancient Fireworks of First Objects in the Universe

These two panels show the same slice of sky in the constellation Boötes, dubbed the "Extended Groth Strip." The area covered is about 1 by 0.12 degrees. Image credit: NASA/JPL-Caltech/GSFC

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The Spitzer Space Telescope has looked back in time to see what scientists called the “faint, lumpy glow” given off by the very first objects in the Universe, and these ancient objects obviously provided some early cosmic fireworks. While they are too faint and distant to figure out what the individual objects are – they may be massive stars or voracious black holes – Spitzer has captured what appears to be the collective pattern of their infrared light, revealing these first objects were numerous and furiously burned cosmic fuel.

“These objects would have been tremendously bright,” said Alexander “Sasha” Kashlinsky from the Goddard Space Flight Center, lead author of a new paper appearing in The Astrophysical Journal. “We can’t yet directly rule out mysterious sources for this light that could be coming from our nearby universe, but it is now becoming increasingly likely that we are catching a glimpse of an ancient epoch. Spitzer is laying down a roadmap for NASA’s upcoming James Webb Telescope, which will tell us exactly what and where these first objects were.”

This isn’t the first time astronomers have used Spitzer to search for the very first stars and black holes, and back in 2005 they saw hints of this remote pattern of light, known as the cosmic infrared background, and again with more precision in 2007. Now, Spitzer is in the extended phase of its mission, during which it performs more in-depth studies on specific patches of the sky. Kashlinsky and his colleagues used Spitzer to look at two patches of sky for more than 400 hours each.

The team then carefully subtracted all the known stars and galaxies in the images. Rather than being left with a black, empty patch of sky, they found faint patterns of light with several telltale characteristics of the cosmic infrared background. The lumps in the pattern observed are consistent with the way the very distant objects are thought to be clustered together.

Kashlinsky likens the observations to looking for Fourth of July fireworks in New York City from Los Angeles. First, you would have to remove all the foreground lights between the two cities, as well as the blazing lights of New York City itself. You ultimately would be left with a fuzzy map of how the fireworks are distributed, but they would still be too distant to make out individually.

“We can gather clues from the light of the Universe’s first fireworks,” said Kashlinsky. “This is teaching us that the sources, or the “sparks,” are intensely burning their nuclear fuel.”

The Universe formed roughly 13.7 billion years ago in a fiery, explosive Big Bang. With time, it cooled and, by around 500 million years later, the first stars, galaxies and black holes began to take shape. Astronomers say some of that “first light” might have traveled billions of years to reach the Spitzer Space Telescope. The light would have originated at visible or even ultraviolet wavelengths and then, because of the expansion of the universe, stretched out to the longer, infrared wavelengths observed by Spitzer.

The new study improves on previous observations by measuring this cosmic infrared background out to scales equivalent to two full moons — significantly larger than what was detected before. Imagine trying to find a pattern in the noise in an old-fashioned television set by looking at just a small piece of the screen. It would be hard to know for certain if a suspected pattern was real. By observing a larger section of the screen, you would be able to resolve both small- and large-scale patterns, further confirming your initial suspicion.

Likewise, astronomers using Spitzer have increased the amount of sky examined to obtain more definitive evidence of the cosmic infrared background. The researchers plan to explore more patches of sky in the future to gather more clues hidden in the light of this ancient era.

“This is one of the reasons we are building the James Webb Space Telescope,” said Glenn Wahlgren, Spitzer program scientist at NASA Headquarters in Washington. “Spitzer is giving us tantalizing clues, but James Webb will tell us what really lies at the era where stars first ignited.”

Read the team’s paper.
Source: NASA

Posted on by Nancy Atkinson

Are Rogue Black Holes Wandering the Universe?

A composite image of galaxy CID-4 shows evidence the black hole is being ejected. Credit: X-ray: NASA/CXC/SAO/F.Civano et al; Optical: NASA/STScI; Optical (wide field): CFHT, NASA/STScI

Talk about a tough neighborhood! Even black holes aren’t welcome in galaxy CID-42, located about 4 billion light-years away from Earth. Astronomers using the Chandra X-Ray Observatory have found strong evidence that a massive black hole is being ejected from this galaxy, moving out at a speed of several million kilometers per hour. This phenomenon, known as a recoiled black hole, happens due to a gravitational wave “kick” from the merger of two black holes.

While this event is likely to be rare, it could mean that there could be giant black holes roaming undetected out in the vast spaces between galaxies.
Continue reading “Are Rogue Black Holes Wandering the Universe?”

Posted on by Nancy Atkinson

Ghostly Jets Haunt the Milky Way’s Black Hole

This artist's conception shows an edge-on view of the Milky Way galaxy and newly discovered gamma-ray jets extending from the central black hole. Credit: David A. Aguilar (CfA)

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A ghost is haunting the Milky Way’s central black hole, revealing the galactic nucleus was likely much more active in the past than it is now. Scientists using the Fermi space telescope have found faint apparitions of what must have been powerful gamma-ray jets emanating from our galaxy’s center.

“These faint jets are a ghost or after-image of what existed a million years ago,” said Meng Su, an astronomer at the Harvard-Smithsonian Center for Astrophysics (CfA), and lead author of a new paper in the Astrophysical Journal. “They strengthen the case for an active galactic nucleus in the Milky Way’s relatively recent past.”

This is the first time this type of jet has been detected from the Milky Way’s black hole. Scientists know that other active galaxies have cores that glow brightly, powered by supermassive black holes swallowing material, and often spit twin jets in opposite directions.

The two beams, or jets found by Fermi observations extend from the galactic center to a distance of 27,000 light-years above and below the galactic plane.
The newfound jets may be related to mysterious gamma-ray bubbles that Fermi detected in 2010. Those bubbles also stretch 27,000 light-years from the center of the Milky Way. However, where the bubbles are perpendicular to the galactic plane, the gamma-ray jets are tilted at an angle of 15 degrees. This may reflect a tilt of the accretion disk surrounding the supermassive black hole.

“The central accretion disk can warp as it spirals in toward the black hole, under the influence of the black hole’s spin,” explained co-author Douglas Finkbeiner of the CfA. “The magnetic field embedded in the disk therefore accelerates the jet material along the spin axis of the black hole, which may not be aligned with the Milky Way.”

The two structures also formed differently. The jets were produced when plasma squirted out from the galactic center, following a corkscrew-like magnetic field that kept it tightly focused. The gamma-ray bubbles likely were created by a “wind” of hot matter blowing outward from the black hole’s accretion disk. As a result, they are much broader than the narrow jets.

Both the jets and bubbles are powered by inverse Compton scattering. In that process, electrons moving near the speed of light collide with low-energy light, such as radio or infrared photons. The collision increases the energy of the photons into the gamma-ray part of the electromagnetic spectrum.

The discovery leaves open the question of when the Milky Way was last active. A minimum age can be calculated by dividing the jet’s 27,000-light-year length by its approximate speed. However, it may have persisted for much longer.

“These jets probably flickered on and off as the supermassive black hole alternately gulped and sipped material,” said Finkbeiner.

It would take a tremendous influx of matter for the galactic core to fire up again. Finkbeiner estimates that a molecular cloud weighing about 10,000 times as much as the Sun would be required.

“Shoving 10,000 suns into the black hole at once would do the trick. Black holes are messy eaters, so some of that material would spew out and power the jets,” he said.

Source: CfA

Posted on by Jon Voisey

A Planetary System That Never Was Teaches About Those That May Be

While Kepler and similar missions are turning up planets by the fist full, there’s long been many places that astronomers haven’t expected to find planetary systems. The main places include regions where gravitational forces conspire to make the region around potential host stars too unstable to form into planets. And there’s no place in the galaxy with a larger gravitational force than the galactic center where a black hole four and a half million times more massive than the Sun, lurks. But a new study shows evidence that a disk, potentially far enough along to begin forming planets, is in the process of being disrupted.

The new study investigates an ionized cloud of gas discovered earlier this year, plummeting in towards the black hole. The cloud has been formed into an elliptical ring with a maximum distance of 0.04 parsecs (1 parsec 3.24 light years) which is coincident with a ring of young stars that orbit the black hole. At such distances from us, astronomers have been unable to learn much about the population of stars that may exist since only the brightest, most massive stars are visible.

However, such massive stars are able to determine an age limit for the group, which has been set somewhere between 4-8 million years. This age is crucial since most low-mass stars retain gas disks and are held to form planets at an age around 3 million years young. But by an age of 5 million years, the stars have begun clearing out that disk system halting planetary formation and only one fifth of stars less than 1 solar mass retain their disks.

This entire process is even more precarious because the gravitational perturbations from the nearby black hole would begin eating away at the edge of a potential disk. Astronomers predict that this should limit the size to 12 AU in radius. For even less massive stars, this could be as small as 8 AU. Still, theory predicts that these truncated disks could form in the vicinity of the Milky Way’s black hole. But such small disks would be impossible to observe directly with present technology.

The new research suggests that one of these stars was knocked from its stable orbit in the ring in much the same way that comets in the Oort cloud are occasionally jostled into falling towards the inner solar system. There, the tidal forces from the black hole as well as heavily ionizing UV radiation created by the black hole’s accretion disk would strip the gas and dust from the parent star, which is too faint to see directly, leaving it in an elliptical orbit.

If this theory is correct, it would provide the first indirect evidence of the presence of planet forming disks near the galactic center. This comes on top of evidence from earlier this year suggesting stars may be able to form in situ near the galactic center making this region a far more dynamic place than previously expected.

Yet, even if planets do form, living near a supermassive black hole is still not a hospitable place for life. The extreme amounts of UV radiation emitted as the black hole devours gas and dust is likely to sterilize the region.