Posted on by Steve Nerlich

Astronomy Without A Telescope – Galactic Gravity Lab

The center of the Milky Way containing Sagittarius A*. The black hole and several massive young stars in the chaotic region create a surrounding haze of superheated gas that shows up in X-ray light. Credit: chandra.harvard.edu and Kyoto University.

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Many an alternative theory of gravity has been dreamt up in the bath, while waiting for a bus – or maybe over a light beverage or two. These days it’s possible to debunk (or otherwise) your own pet theory by predicting on paper what should happen to an object that is closely orbiting a black hole – and then test those predictions against observations of S2 and perhaps other stars that are closely orbiting our galaxy’s central supermassive black hole – thought to be situated at the radio source Sagittarius A*.

S2, a bright B spectral class star, has been closely observed since 1995 during which time it has completed over one orbit of the black hole, given its orbital period is less than 16 years. S2’s orbital dynamics can be expected to differ from what would be predicted by Kepler’s 3rd law and Newton’s law of gravity, by an amount that is three orders of magnitude greater than the anomalous amount seen in the orbit of Mercury. In both Mercury’s and S2’s cases, these apparently anomalous effects are predicted by Einstein’s theory of general relativity, as a result of the curvature of spacetime caused by a nearby massive object – the Sun in Mercury’s case and the black hole in S2’s case.

S2 travels at an orbital speed of about 5,000 kilometers per second – which is nearly 2% of the speed of light. At the periapsis (closest-in point) of its orbit, it is thought to come within 5 billion kilometres of the Schwarzschild radius of the supermassive blackhole, being the boundary beyond which light can no longer escape – and a point we might loosely regard as the surface of the black hole. The supermassive black hole’s Schwarzschild radius is roughly the distance from the Sun to the orbit of Mercury – and at periapsis, S2 is roughly the same distance away from the black hole as Pluto is from the Sun.

The supermassive black hole is estimated to have a mass of roughly four million solar masses, meaning it may have dined upon several million stars since its formation in the early universe – and meaning that S2 only manages to cling on to existence by virtue of its stupendous orbital speed – which keeps it falling around, rather than falling into, the black hole. For comparison, Pluto stays in orbit around the Sun by maintaining a leisurely orbital speed of nearly 5 kilometers per second.

Some astrometrics of S2's orbit around the supermassive black hole Sagittarius A* at the center of the Milky Way. Credit: Schödel et al (2002), published in Nature.

The detailed data set of S2’s astrometric position (right ascension and declination) changes over time – and from there, its radial velocity calculated at different points along its orbit – provides an opportunity to test theoretical predictions against observations.

For example, with these data, it’s possible to track various non-Keplerian and non-Newtonian features of S2’s orbit including:

– the effects of general relativity (from a external frame of reference, clocks slow and lengths contract in stronger gravity fields). These are features expected from orbiting a classic Schwarzschild black hole;
– the quadrapole mass moment (a way of accounting for the fact that the gravitational field of a celestial body may not be quite spherical due to its rotation). These are additional features expected from orbiting a Kerr black hole – i.e. a black hole with spin; and
– dark matter (conventional physics suggests that the galaxy should fly apart given the speed it’s rotating at – leading to the conclusion that there is more mass present than meets the eye).

But hey, that’s just one way of interpreting the data. If you want to test out some alternative theories – like, say Oceanic String Space Theory – well, here’s your chance.

Further reading: Iorio, L. (2010) Long-term classical and general relativistic effects on the radial velocities of the stars orbiting Sgr A*.

Posted on by Nancy Atkinson

Colliding Galaxies Created the First Black Holes

The Antennae Galaxies in Collision Credit: NASA, ESA, and the Hubble Heritage Team (STScI/AURA)-ESA/Hubble Collaboration

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How were the Universe’s first supermassive black holes formed? A new model of the evolution of galaxies and black holes show collisions show that colliding galaxies likely spawned black holes that formed about 13 billion years ago. The discovery fills in a missing chapter of our universe’s early history, and could help write the next chapter — in which scientists better understand how gravity and dark matter formed the universe as we know it.

Following the recent discovery that galaxies formed much earlier in the Universe’s history than previously thought, Stelios Kazantzidis from The Ohio State University and his team created new computer simulations that show the first-ever super-massive black holes were likely born when those early galaxies collided and merged together. This likely happened during the first few billion years after the Big Bang.

“Our results add a new milestone to the important realization of how structure forms in the universe,” Kazantzidis said.

Previously, astronomers thought galaxies evolved hierarchically, where gravity drew small bits of matter together first, and those small bits gradually came together to form larger structures.

But the the new models turn that notion on its head.

“Together with these other discoveries, our result shows that big structures — both galaxies and massive black holes — build up quickly in the history of the universe,” he said. “Amazingly, this is contrary to hierarchical structure formation. The paradox is resolved once one realizes that dark matter grows hierarchically, but ordinary matter doesn’t. The normal matter that makes up visible galaxies and super-massive black holes collapses more efficiently, and this was true also when the universe was very young, giving rise to anti-hierarchical formation of galaxies and black holes.”

So, that means that big galaxies and super-massive black holes come together quickly, and smaller bits like our own Milky Way galaxy — and the comparatively small black hole at its center — form more slowly. The galaxies that formed those first super-massive black holes are still around, Kazantzidis said.
The new simulations done on supercomputers were able to resolve features that were 100 times smaller, and revealed details in the heart of the merged galaxies on a scale of less than a light year.

Because of this, the astronomers were able to see two things: First, gas and dust in the center of the galaxies condensed to form a tight nuclear disk. Then the disk became unstable, and the gas and dust contracted again, to form an even denser cloud that eventually spawned a super-massive black hole.

The implications for cosmology are far-reaching, Kazantzidis said.

“For example, the standard idea — that a galaxy’s properties and the mass of its central black hole are related because the two grow in parallel — will have to be revised. In our model, the black hole grows much faster than the galaxy. So it could be that the black hole is not regulated at all by the growth of the galaxy. It could be that the galaxy is regulated by the growth of the black hole.”

In the image, the panel illustrates the complexity of dynamical evolution in a typical collision between two equal-mass disk galaxies. The simulation follows dark matter, stars, gas, and supermassive black holes, but only the gas component is visualized. Brighter colors indicate regions of higher gas density and the time corresponding to each snapshot is given by the labels. The first 10 panel images measure 100 kpc on a side, roughly five times the diameter of the visible part of the Milky Way galaxy. The next five panels represent successive zooms on the central region. The final frame shows the inner 300 pc of the nuclear region at the end of the simulation. Credit: Ohio State University

This new model could also help astronomers who are searching the skies for direct evidence of Einstein’s theory of general relativity: gravitational waves.

According to general relativity, any ancient galaxy mergers would have created massive gravitational waves — ripples in the space-time continuum — the remnants of which should still be visible today.

New gravitational wave detectors, such as NASA’s Laser Interferometer Space Antenna, were designed to detect these waves directly, and open a new window into astrophysical and physical phenomena that cannot be studied in other ways.

Scientists will need to know how super-massive black holes formed in the early universe and how they are distributed in space today in order interpret the results of those experiments. The new computer simulations should provide a clue.

See this link for videos of the models of galaxy collisions.

Source: Ohio State University

Posted on by Steve Nerlich

Astronomy Without A Telescope – The Universe Is Not In A Black Hole

Does a spinning massive object wind up spacetime? Credit: J Bergeron / Sky and Telescope Magazine. An APOD for 7 November 1997.

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It has been reported that a recent scientific paper delivers the conclusion that our universe resides inside a black hole in another universe. In fact, this isn’t really what the paper concluded – although what the paper did conclude is still a little out of left field.

The Einstein-Cartan-Kibble-Sciama (ECKS) theory of gravity – claimed as an alternative to general relativity theory, although still based on Einstein field equations – seeks to take greater account of the effect of the spin of massive particles. Essentially, while general relativity has it that matter determines how spacetime curves, ECKS also tries to capture the torsion of spacetime, which is a more dynamic idea of curvature – where you have to think in terms of twisting and contortion, rather than just curvature.

Mind you, general relativity is also able to deal with dynamic curvature. ECKS proponents claim that where ECKS departs from general relativity is in situations with very high matter density – such as inside black holes. General relativity suggests that a singularity (with infinite density and zero volume) forms beyond a black hole’s event horizon. This is not a very satisfying result since the contents of black holes do seem to occupy volume – more massive ones have larger diameters than less massive ones – so general relativity may just not be up to the task of dealing with black hole physics.

ECKS theory attempts to step around the singularity problem by proposing that an extreme torsion of spacetime, resulting from the spin of massive particles compressed within a black hole, prevents a singularity from forming. Instead the intense compression increases the intrinsic angular momentum of the matter within (i.e. the spinning skater draws arms in analogy) until a point is reached where spacetime becomes as twisted, or as wound up, as it can get. From that point the tension must be released through an expansion (i.e. an unwinding) of spacetime in a whole new tangential direction – and voila you get a new baby universe.

But the new baby universe can’t be born and expand in the black hole. Remember this is general relativity. From any frame of reference outside the black hole, the events just described cannot sequentially happen. Clocks seem to slow to a standstill as they approach a black hole’s event horizon. It makes no sense for an external observer to imagine that a sequence of events is taking place over time inside a black hole.

Instead, it is proposed that the birth and expansion of new baby universe proceeds along a separate branch of spacetime with the black hole acting as an Einstein-Rosen bridge (i.e. a wormhole).

(Caption) The horizon problem in Big Bang cosmology. How is it that distant parts of the universe possess such similar physical properties? Well (putting your Occam brand razor aside), perhaps the whole contents of this universe was originally homogenized within a black hole from a parallel universe. Credit: Addison Wesley.

If correct, it’s a turtles on turtles solution and we are left to ponder the mystery of the first primeval universe which first formed the black holes from which all subsequent universes originate.

Something the ECKS hypothesis does manage to do is to provide an explanation for cosmic inflation. Matter and energy crunched within a black hole should achieve a state of isotropy and homogeneity (i.e. no wrinkles) – and when it expands into a new universe through a hypothetical wormhole, this is driven by the unwinding of the spacetime torsion that was built up within the black hole. So you have an explanation for why a universe expands – and why it is so isotropic and homogenous.

Despite there not being the slightest bit of evidence to support it, this does rank as an interesting idea.

Further reading: Poplawski, N.J. (2010) Cosmology with torsion – an alternative to cosmic inflation.

Posted on by Nicholos Wethington

First Quasar Gravitational Lens Discovered (w/video)

The quasi-stellar object SDSS J0013+1523 has been shown to warp the light of a background galaxy around it, producing a magnified double-image from our perspective on Earth. Image Credit: Courbin, Meylan, Djorgovski, et al., EPFL/Caltech/WMKO

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Gravitation lensing – a phenomenon that falls out of Einstein’s theory of general relativity – has been observed numerous times, making for some fantastic images of rings, arcs and crosses composed of massive galaxies light years away. As the light from a background object is bent by gravity around a foreground object, multiple, magnified images of the background object are produced from our vantage point.

For the first time, a quasar (quasi-stellar object) has been shown to gravitationally lens a galaxy behind it. About a hundred instances of gravitational lenses that consist of a foreground galaxy and a background quasar have been found, but this is the very first time where the opposite is the case; that is, a quasar bending the light from a background galaxy around it to create a multiple image of that galaxy.

Quasars are thought to be the result of a supermassive black hole at the center of a galaxy attempting to swallow up all of the matter that surrounds it. As the matter bunches up when it gets closer to the black hole, it heats up due to friction and begins to emit light across the electromagnetic spectrum. The light from a quasar can outshine an entire galaxy of stars, making it difficult to separate the light from a background galaxy from the overwhelming glare of the quasar itself.

To make this initial detection (there are surely many to follow), astronomers from the EPFL’s Laboratory of Astrophysics in cooperation with Caltech used data from the Sloan Digital Sky Survey (SDSS). They analyzed 22,298 quasars from the SDSS Data Release 7 catalog, and looked for images that had a strongly redshifted emission spectra. According to the paper announcing the results, “In these spectra, we look for emission lines redshifted beyond the redshift of the [quasar].”

In other words, a quasar that is lensing a galaxy in the background will exhibit a higher redshift than one that is not lensing a background galaxy, since the light from the galaxy and the quasar are combined in the SDSS data. So, quasars that had an expected redshift were thrown out, and a statistical analysis of quasars with emission lines that might mimic a gravitational lens eliminated many more of the objects. This left about 14 objects of the 22,298 analyzed as potential candidates. Of these 14, the team selected one to perform follow-up observations on, named SDSS J0013+1523.

SDSS J0013+1523 lies about 1.6 billion light years away, and is lensing a galaxy that is about 7.5 billion light years away from Earth. Using the Keck II telescope, they were able to confirm that SDSS J0013+1523 was indeed lensing the light from a galaxy located behind it. Hubble images of the discovery are in the works.

Here’s a video produced by the EPFL describing the results.

What is significant about this discovery – besides the novel aspect of a quasar acting as a lens – is that it will allow researchers to better refine their understanding of quasars. When light is bent around an object, it bends because of gravity, and gravity is a result of mass. So, something that is very massive will act as a stronger lens than something that is tiny, and the mass of the object doing all of the lensing work – in this case, the foreground quasar – can be determined.

Their results were published in a letter to Astronomy & Astrophysics on July 16th. The original paper is available for your perusal here.

Source: Eurekalert here and here, Arxiv paper here

Posted on by Nancy Atkinson

Powerhouse Black Hole Blows a Huge Bubble

Combining observations done with ESO's Very Large Telescope and NASA's Chandra X-ray telescope, astronomers have uncovered the most powerful pair of jets ever seen from a stellar black hole. The black hole blows a huge bubble of hot gas, 1,000 light-years across or twice as large and tens of times more powerful than the other such microquasars. The stellar black hole belongs to a binary system as pictured in this artist's impression. Credit: ESO/L. Calçada
Artist's impression of a Star feeding a black hole. Credit: ESO/L. Calçada

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A relatively small black hole is producing tremendously powerful jets while creating a huge bubble of hot gas. Both the jets and the bubble are the largest ever seen, meaning this mini black hole is a powerhouse. But the most unusual feature of this remarkable black hole is not its energy output, but how it is emitting energy.

“The energy output is impressive, but is comparable with the X-ray luminosity of so-called Ultraluminous X-ray sources,” said Manfred Pakull, the lead author of a new paper published today in Nature. “The notion that powerhouses exist that generate most of their energy in the form of jets (kinetic energy) and not as radiation (photons) is rather new.”

Black holes are known to release an incredible amount of energy when they swallow matter, and as Pakull told Universe Today, it was previously thought that most of the energy came out in the form of radiation, predominantly X-rays. But this new gas-blowing black hole, called S26, is showing that some black holes can release at least as much energy, and perhaps much more, in the form of collimated jets of fast moving particles.

“This black hole is just a few solar masses, but is a real miniature version of the most powerful quasars and radio galaxies,” said Pakull, “which contain black holes with masses of a few million times that of the Sun.”

This object is a microquasar, which are formed by two objects — either a white dwarf, neutron star or a black hole, along with a companion star. The X-rays are produced by matter falling from one component to the other, and can produce jets of high-speed particles. The fast jets slam into the surrounding interstellar gas, heating it and triggering an expanding bubble made of hot gas and ultra-fast particles colliding at different temperatures.

Of the dozen or so microquasars that have been found in the Milky Way Galaxy, most of the bubbles are fairly small, – less than 10 light-years across. But this one is 1,000 light-years wide. Plus this microquasar is tens of times more powerful than ones previously seen.

Using ESO’s Very Large Telescope and NASA’s Chandra X-ray telescope Pakull and his team were able to observe the areas where the jets smash into the interstellar gas around the black hole, and saw that the bubble of hot gas is inflating at a speed of almost one million kilometers per hour.

The jets are equally impressive, about 300 parsecs long, and although powerful jets have been seen from supermassive black holes, they were thought to be less frequent in the smaller microquasar variety. This new discovery may have astronomers looking more closely at other microquasars.

“The length of the jets in NGC 7793 is amazing, compared to the size of the black hole from which they are launched,” said co-author Robert Soria. “If the black hole were shrunk to the size of a soccer ball, each jet would extend from the Earth to beyond the orbit of Pluto.”

S26 is located 12 million light-years away, in the outskirts of the spiral galaxy NGC 7793. From the size and expansion velocity of the bubble the astronomers have found that the jet activity must have been ongoing for at least 200,000 years.

With all this incredible speed, size and activity, what do Pakull and his team project as the future of this microquasar?

“Yes, the expansion velocity (275 km/s) is quite impressive, but it will diminish with time,” Pakull told Universe Today. “If it was much lower at, say, 70 km/s the shocked gas would not emit so much optical light (for example the Balmer series of Hydrogen) and we would not have detected the bubble. The future of S26 depends on the evolution of the central microquasar which emits the jets. I expect that it could be active for another 100,000 to few million years.”

Pakull said it is interesting to imagine what would happen if the microqusar suddenly stopped emitting the jets. “Then the bubble would not suddenly disappear, but shine on like before for another few 100,000 years,” he said. “It would resemble a supernova remnant, albeit with a 100 times higher energy content.”

Pakull added that this new finding will help astronomers understand the similarity between small black holes formed from exploded stars and the supermassive black holes at the centers of galaxies, and he hopes this work will stimulate more theoretical work in how black holes produce energy.

Read the team’s paper (pdf file)

Sources: ESO, email exchange with Manfred Pakull.

Posted on by Nancy Atkinson

Radio Observations Provide New Explanation for Hanny’s Voorwerp

The green "blob" is Hanny's Voorwerp. Credit: Dan Herbert, Peter Smith, Matt Jarvis, Galaxy Zoo Team, Isaac Newton Telescope

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Is Hanny’s Voorwerp the result of a “light echo” of a violent event that happened long ago or perhaps is this mystifying blob of glowing gas being fueled by an ongoing, and current phenomenon? A just-released paper about the Voorwerp offers a new explanation for this perplexing, seemingly one-of-a-kind object in the constellation of Leo Minor. If you haven’t heard the remarkable story, the object was discovered in 2007 by Dutch school teacher Hanny Van Arkel while she was classifying galaxies for the Galaxy Zoo online citizen science project. Until now, the working hypothesis for the explanation of this unusual object was that we might be seeing the “light echo” of a quasar outburst event that occurred millions of years ago. But new radio observations reveal that instead, a black hole in that same nearby galaxy might be producing a radio jet, shooting a thin beam directly at this cloud of gas, causing it to light up.

Hanny’s Voorwerp (Dutch for object) consists of dust and gas – but no stars – so astronomers know it is not a galaxy, even though it is galaxy-sized. Previously, astronomers studying the object thought the gas and dust were illuminated by a quasar outburst within the nearby galaxy IC 2497. While the outburst would have faded within the last 100,000 years, the light only reached the dust and gas in time for our telescopes to see the effect. But this explanation was slightly unsatisfactory in that such an event, where an entire galaxy would flare up suddenly and briefly, is unexplained.

The naturally weighted 18 cm MERLIN radio map of IC 2497 (black contours), showing both C1 & C2, embedded within a region of smooth extended emission, overlaid over the same map with the point sources subtracted. Credit: Rampadarath, et al.

But radio observations with the European Very Long Baseline Interferometry (VLBI) Network at 18 cm, and the Multi-Element Radio Linked Interferometer Network (MERLIN) at 18 cm and 6 cm show evidence of black hole, or active galactic nuclei (AGN) activity and a nuclear starburst in the central regions of IC 2497.

This event is hard to see from our vantage point on Earth because another cloud of dust and gas sits between us on Earth and IC 2497, preventing us from directly seeing the black hole.

“The new data shows that the nucleus continues to produce a radio jet, in about the direction of Hanny’s Voorwerp,” said Bill Keel from the University of Alabama, one of the astronomers who has been studying the object intently ever since its discovery, and was part of the new observations. “The core is still too weak in the radio to be able to conclude that it puts off enough UV and X-rays to light up the gas, however. There may well be interaction between outflowing material connected with the jet and the gas outside the galaxy, helping to shape the Voorwerp, but the spectra in the discovery paper already made it clear that the gas is ionized not by shocks from such an interaction, but by radiation. ”

Keel said, though, there is still remaining uncertainty — and different astronomers have varying estimates of this likelihood – of whether the radiation from the quasar core remains strong or whether it shoots in fits and starts.

“Some active galaxies put out a lot of energy in jets and outflows compared to radiation, and we are considering the possibility that this one has switched to such a “radio mode” in the recent past,” he said. “If so, the Voorwerp would be an ionization echo, or light echo, since the re-radiation from ionized gas is not instantaneous, as scattering is.”

The Voorwerp has captured enough attention and curiosity that astronomers have trained numerous telescopes on the object in an effort to sort out the mystery. But Keel said this approach is essential in eventually figuring this out.

“Each wavelength range gives us a different, and usually complementary, piece of the story,” he said. “The earlier radio data tell us something about where all that gas came from, and we got another connection from recent data putting an apparent companion spiral galaxy at the same distance as IC 2497. Even the early X-ray data showed us that there was an interesting puzzle as to why we didn’t see the core AGN. The GALEX UV spectrum is informing our interpretation of the Hubble UV image.”

Yes, Hubble recently looked at the Voorwerp in a couple of different wavelengths, (read our article about the Hubble observations here) and while Keel couldn’t comment directly about data from the iconic telescope, (everything is still being analyzed) he did say it holds some interesting surprises.

“One of the first things we started checking with Hubble data was whether we have a clear view in at least the infrared to the nucleus, starting from the location of the radio source,” he said. “Also, these results give us particular reason to look at the structural details of the gas in Hanny’s Voorwerp, for signs that it may be affected by an outflow from the nucleus. I can mention that there are some interesting surprises from the HST data, which is what we always hope for!”

Keel said he also has been observing at Kitt Peak, looking at other candidate “voorwerpjes” – similar “ionized clouds on a somewhat smaller scale around AGN, where the same lifetime-versus-obscuration issues apply but we can usually see the AGN responsible,” he said.

And look for some upcoming public outreach projects on the Voorwerp based on the Hubble data, as well, including one in Bloomington, Minnesota on July 1-4 at the CONvergence, where writers and scienctists will be writing a graphic novel based on the discovery of Hanny’s Voorwerp. Check out this website for more information.

Read the team’s paper: Hanny’s Voorwerp: Evidence Of AGN Activity And A Nuclear Starburst In The Central Regions Of IC 2497.

Posted on by Nancy Atkinson

Retro Black Holes Are More Powerful

This artist's concept shows a galaxy with a supermassive black hole at its core. The black hole is shooting out jets of radio waves.Image credit: NASA/JPL-Caltech

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Black holes seem to defy our comprehension and be contrary to conventional understanding. So perhaps it is not entirely surprising to find that supermassive black holes which have a retrograde or backwards spin might be more powerful and produce more ferocious jets of gas. While this new finding goes against what astronomers had thought for decades, it also helps solve a mystery why some black holes have no jets at all.

Powerful jets stream out from the accretion disks that spin around many supermassive black holes. The black holes can spin either in the same direction as the disks, called prograde black holes, or against the flow – the retrograde black holes. For decades, astronomers thought that the faster the spin of the black hole, the more powerful the jet. But there were problems with this “spin paradigm” model. For example, some prograde black holes had been found with no jets.

Theoretical astrophysicist David Garofalo and his colleagues have been studying the motion of black holes for years, and in previous papers, they proposed that the backward, or retrograde, black holes spew the most powerful jets, while the prograde black holes have weaker or no jets.

Their new study links their theory with observations of galaxies across time, or at varying distances from Earth. They looked at both “radio-loud” galaxies with jets, and “radio-quiet” ones with weak or no jets. The term “radio” comes from the fact that these particular jets shoot out beams of light mostly in the form of radio waves.

The results showed that more distant radio-loud galaxies are powered by retrograde black holes, while relatively closer radio-quiet objects have prograde black holes. According to the team, the supermassive black holes evolve over time from a retrograde to a prograde state.

“This new model also solves a paradox in the old spin paradigm,” said David Meier, a theoretical astrophysicist at JPL not involved in the study. “Everything now fits nicely into place.”

The scientists say that the backward black holes shoot more powerful jets because there’s more space between the black hole and the inner edge of the orbiting disk. This gap provides more room for the build-up of magnetic fields, which fuel the jets, an idea known as the Reynold’s conjecture after the theoretical astrophysicist Chris Reynolds of the University of Maryland, College Park.

“If you picture yourself trying to get closer to a fan, you can imagine that moving in the same rotational direction as the fan would make things easier,” said Garofalo. “The same principle applies to these black holes. The material orbiting around them in a disk will get closer to the ones that are spinning in the same direction versus the ones spinning the opposite way.”

Jets and winds play key roles in shaping the fate of galaxies. Some research shows that jets can slow and even prevent the formation of stars not just in a host galaxy itself, but also in other nearby galaxies.

“Jets transport huge amounts of energy to the outskirts of galaxies, displace large volumes of the intergalactic gas, and act as feedback agents between the galaxy’s very center and the large-scale environment,” said team member Rita M. Sambruna, from Goddard Space Flight Center. “Understanding their origin is of paramount interest in modern astrophysics.”

The team’s paper was published in the May 27 Monthly Notices of the Royal Astronomical Society.

Source: JPL

Posted on by Nicholos Wethington

Andromeda’s Unstable Black Hole

The Andromeda galaxy as seen in optical light, and Chandra's X-ray vision of the changing supermassive black hole in Andromeda's heart. Image Credit: X-Ray NASA/CXC/SAO/Li et al.), Optical (DSS)

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The Andromeda galaxy, the closest spiral galaxy to our own Milky Way, has a supermassive blackhole at the center of it much like other galaxies. Because of its proximity to us, Andromeda – or M31 – is an excellent place to study just how the supermassive black holes in the centers of galaxies consume material to grow, and interact gravitationally with the surrounding material.

Over the course of the last ten years, NASA’s Chandra X-Ray observatory has monitored closely the supermassive black hole at Andromeda’s heart. This long-term data set gives astronomers a very nuanced picture of just how these monstrous black holes change over time. Zhiyuan Li of the Harvard-Smithsonian Center for Astrophysics (CfA) presented results of this decade-long observation of the black hole at the 216th American Astronomical Society meeting in Miami, Florida this week.

From 1999 to 2006, M31 was relatively quiet and dim. In January of 2006, though, the black hole in the center of Andromeda suddenly brightened by over 100 times, and has remained 10 times as bright since. This suggests that the black hole swallowed something massive, but the details of the outburst in 2006 remain unclear.

The black hole in M31, located in the Andromeda constellation, likely continues to feed off of the stellar winds of a nearby star or the material in a large gas cloud that is falling into the black hole. As material is consumed, it drives the productions of X-rays in a relativistic jet streaming out from the black hole, which are then picked up by Chandra’s X-ray eyes.

The black hole in M31 is 10 to 100,000 times dimmer than expected, given that it has a large reservoir of gas surrounding it.

“The black holes in both Andromeda and the Milky Way are incredibly feeble. These two ‘anti-quasars’ provide special laboratories for us to study some of the dimmest type of accretion even seen onto a supermassive black hole,” Li said.

Accretion of matter into supermassive black holes is important to study because the evolution of galaxies is influenced by this process, Li said. The gravitational interplay of the black hole with the surrounding material in a galaxy, as well as the energy released when such supermassive black holes consume material in their surrounding accretion disks, change the structure of the galaxy as it forms. A better understanding of just how these supermassive black holes act in the later stages of spiral galaxy life may give clues as to what astronomers can expect to see in other galaxies.

M31 is readily seen with the naked eye in the constellation Andromeda, and is breathtaking to see through a telescope or binoculars. You won’t be able to see the black hole at its center, however! For more information on observing Andromeda, see our Guide to Space article on M31.

Source: Eurekalert

Posted on by Nicholos Wethington

Black Hole in M87 Wanders using Jetpack

Hubble Space Telescope Images of M87. At right, a large scale image taken with the Wide-Field/Planetary Camera-2 from 1998. The zoom-in images on the left are of the central portion of M87. HST-1 is a knot in the jet from the SMBH. (NASA and the Hubble Heritage Team (STScI/AURA), J. A. Biretta, W. B. Sparks, F. D. Macchetto, E. S. Perlman)

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The elliptical galaxy M87 is known for a jet of radiation that is streaming from the supermassive black hole (SMBH) that the galaxy houses. This jet, which is visible through large-aperture telescopes, may have functioned as a black hole ‘jetpack’, moving the SMBH from the center of mass of the galaxy – where most SMBHs are thought to reside.

Observations taken with the Hubble Space Telescope by a collaboration of astronomy researchers at Rochester Institute of Technology, Florida Institute of Technology and University of Sussex in the United Kingdom show the SMBH in M87 to be displaced from the center of the galaxy by as much as 7 parsecs (22.82 light years). This contradicts the long-held theory that supermassive black holes reside at the center of the galaxies they inhabit, and may give astronomers one way to trace the history of galaxies that have grown through merging.

What caused M87’s SMBH to wander off so far from the center of the galaxy? The most likely cause is a merger between two smaller supermassive black holes sometime in the past. This merger could have created gravitational waves that gave the engorged black hole a swift kick. Elliptical galaxies like M87 are thought to become the size they are through the merger of smaller galaxies.

Another theory is that the jet of radiation that sprays out of the SMBH has pushed with enough energy to essentially propel the black hole away from the center of M87. Okay, so it’s not really a ‘black hole jetpack’, but you have to admit that the combination of black holes – which are cool – and jetpacks, also cool, is too good to pass up. The motion of the SMBH happens to be in the opposite direction of the jet that we can see streaming from the object. For this scenario to be true, however, the jet would have to have been much more energetic millions of years ago, the researchers concluded.

There also does exist evidence for another jet of material that is streaming out of the other side of the SMBH, which would cancel the pushing motion of the jet that we can see, making the merger scenario much more likely. If the two jets were asymmetric to a high degree, however, this scenario still may be the case. More information on the structure and history of the jets would better clarify the cause of the black hole’s displacement.

This study of M87 is part of a wider project aimed at constraining the placement of supermassive black holes, also known as Active Galactic Nuclei or quasars, in their home galaxies. David Axon, dean of mathematical and physical sciences at Sussex, said in a press release, “In current galaxy formation scenarios galaxies are thought to be assembled by a process of merging. We should therefore expect that binary black holes and post coalescence recoiling black holes, like that in M87, are very common in the cosmos.”

The displacement of such black holes would be apparent in archived Hubble Space Telescope images, and the researchers that discovered this phenomenon in M87 used the HST archives to pinpoint the location of the SMBH. Further analysis of these archives could yield many, many more ‘wandering’ black holes.

These findings were presented on May 25th at the American Astronomical Society meeting in Miami, Florida. The team of researchers that collaborated on the finding include Daniel Batcheldor and Eric Perlman of the Florida Institute of Technology, Andrew Robinson and David Merritt of the Rochester Institute of Technology and David Axon of the University of Sussex. Their results were accepted for publication in Astrophysical Journal Letters, and the original paper, A Displaced Supermassive Black Hole in M87, is available on Arxiv right here.

Source: Eurekalert, Arxiv, Eric Perlman’s website

Posted on by Nancy Atkinson

Galaxy Mergers Make Black Holes ‘Light Up’

The optical counterparts of many active galactic nuclei (circled) detected by the Swift BAT Hard X-ray Survey clearly show galaxies in the process of merging. Credit: NASA/Swift/NOAO/Michael Koss and Richard Mushotzky (Univ. of Maryland)

Only about 1% of supermassive black holes emit large amounts of energy, and astronomers have wondered for decades why so few exhibit this behavior. Data from Swift satellite, which normally studies gamma ray bursts, has allowed scientists to confirm that black holes “light up” when galaxies collide, and the data may offer insight into the future behavior of the black hole in our own Milky Way galaxy.

The intense emission from galaxy centers, or nuclei, arises near a supermassive black hole containing between a million and a billion times the sun’s mass. Giving off as much as 10 billion times the sun’s energy, some of these active galactic nuclei (AGN) are the most luminous objects in the universe. They include quasars and blazars.

“Theorists have shown that the violence in galaxy mergers can feed a galaxy’s central black hole,” said Michael Koss, the study’s lead author and a graduate student at the University of Maryland in College Park. “The study elegantly explains how the black holes switched on.”

Swift was launched in 2004, and while its Burst Alert Telescope (BAT) is waiting to detect the next gamma ray burst, it also has been mapping the sky using hard X-rays, said Neil Gehrels, Swift’s principal investigator. “In fact, it detected its 508th gamma ray burst about 30 minutes ago,” Gehrels said at the press conference the morning of May 26th at the 216th meeting of the American Astronomical Society. “But building up its exposure year after year, the Swift BAT Hard X-ray Survey is the largest, most sensitive and complete census of the sky at these energies.”

Until this hard X-ray survey, astronomers never could be sure they had counted the majority of the AGN. Thick clouds of dust and gas surround the black hole in an active galaxy, which can block ultraviolet, optical and low-energy, or soft X-ray, light. Infrared radiation from warm dust near the black hole can pass through the material, but it can be confused with emissions from the galaxy’s star-forming regions. Hard X-rays can help scientists directly detect the energetic black hole.

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The survey, which is sensitive to AGN as far as 650 million light-years away, uncovered dozens of previously unrecognized systems.

“The Swift BAT survey is giving us a very different picture of AGN,” Koss said. The team finds that about a quarter of the BAT galaxies are in mergers or close pairs. “Perhaps 60 percent of these galaxies will completely merge in the next billion years. We think we have the ‘smoking gun’ for merger-triggered AGN that theorists have predicted.”

“A big problem in astronomy is understanding how black holes grow and are fed,” said Joel Bregman from the University of Michigan. “We know growth in the early stages of a black hole’s life is a combination of mergers plus accretion of gas and dust from nearby stars, and we think that the accretion is the more important process. But this shows us that the feeding of the gas and dust has been channeled into the center at a fairly early stage, and the disturbance from the mergers allows gas to be funneled into the center and flow into the black hole.”

“We’ve never seen the onset of AGN activity so clearly,” said Bregman, who was not involved in the study. “The Swift team must be identifying an early stage of the process with the Hard X-ray Survey.”

Other members of the study team include Richard Mushotzky and Sylvain Veilleux at the University of Maryland and Lisa Winter at the Center for Astrophysics and Space Astronomy at the University of Colorado in Boulder.

The study will appear in the June 20 issue of The Astrophysical Journal Letters.

Source: NASA, NASA press conference