Posted on by John Williams

Dark Matter Filaments Bind Galaxies Together

A slim bridge of dark matter – just a hint of a larger cosmic skeleton – has been found binding a pair of distant galaxies together.

According to a press release from the journal Nature, scientists have traced a thread-like structure resembling a cosmic web for decades but this is the first time observations confirming that structure has been seen. Current theory suggests that stars and galaxies trace a cosmic web across the Universe which was originally laid out by dark matter – a mysterious, invisible substance thought to account for more than 80 percent of the matter in the Universe. Dark matter can only be sensed through its gravitational tug and only glimpsed when it warps the light of distant galaxies.

Astronomers led by Jörg Dietrich, a physics research fellow in the University of Michigan College of Literature, Science and the Arts, took advantage of this effect by studying the gravitational lensing of galactic clusters Abell 222 and 223. By studying the light of tens of thousands of galaxies beyond the supercluster; located about 2.2 billion light-years from Earth, the scientists were able to plot the distortion caused by the Abell cluster. The scientists admit it is extremely difficult to observe gravitational lensing by dark matter in the filaments because they contain little mass. Their workaround was to study a particularly massive filament that stretched across 18 megaparsecs (nearly 59 million light-years) of space. The alignment of the string enhanced the lensing effect.

The team’s results were published in the July 4, 2012 issue of Nature.

“It looks like there’s a bridge that shows that there is additional mass beyond what the clusters contain,” Dietrich said in a press release. “The clusters alone cannot explain this additional mass.”

By examining X-rays emanating from plasma in the filament, observed from the XMM-Newton satellite, the team calculated that no more than nine percent of the filament’s mass could be made up of the hot gas. Computer simulations further suggested that just 10 percent of the mass was due to visible stars and galaxies. Only dark matter, says Dietrich, could make up the remaining mass.

“What’s exciting,” says Mark Bautz, an astrophysicist at the Massachusetts Institute of Technology, “is that in this unusual system we can map both dark matter and visible matter together and try to figure out how they connect and evolve along the filament.”

Refining the technique could help physicists understand the structure of the Universe and pin down the identity of dark matter (whether it’s a cold slow-moving mass or a warm, fast-moving one. Different types would clump differently along the filament, say scientists.

Image caption: Dark-matter filaments, such as the one bridging the galaxy clusters Abell 222 and Abell 223, are predicted to contain more than half of all matter in the Universe. (credit: Jörg Dietrich, University of Michigan/University Observatory Munich)

Posted on by Jason Major

X-rays Reveal a Stellar-Mass Black Hole in Andromeda

This image shows the central region of the Andromeda galaxy in X-rays, where the newly discovered ULX outshines all other sources. Image: Landessternwarte Tautenburg, XMM-Newton, MPE

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An ultraluminous x-ray source (ULX) previously spotted in the neighboring Andromeda galaxy by NASA’s Chandra observatory has now been revealed to be a stellar-mass black hole, according to researchers at the Max Planck Institute for Extraterrestrial Physics.

The black hole was the first ULX seen in Andromeda, as well as the closest ever observed.

Ultraluminous x-ray sources are rare objects, observed in the near and distant Universe in the outer regions of galaxies. Typically only one or two ULXs are seen in any one particular galaxy — if there are any seen at all.

The large distances to ULXs makes detailed observations difficult, and so their exact causes have been hard to nail down.

This particular x-ray source was first identified in late 2009 by Chandra and was followed up with observations by Swift and Hubble. Classified by researchers at the Max Planck Institute as a low-luminosity source, it actually outshined the entire Andromeda galaxy in x-ray luminosity!

Continued observations with Chandra and ESA’s XMM-Newton showed behavior similar to known x-ray sources in our own Milky Way galaxy: actively feeding black holes.

“We were very lucky that we caught the ULX early enough to see most of its lightcurve, which showed a very similar behavior to other X-ray sources from our own galaxy,” said Wolfgang Pietsch from the Max Planck Institute for Extraterrestrial Physics. The emission decayed exponentially with a characteristic timescale of about one month, which is a common property of stellar mass X-ray binaries. “This means that the ULX in Andromeda likely contains a normal, stellar black hole swallowing material at very high rates.”

It’s estimated that the black hole is at least 13 times the mass of the Sun.

(Related: Stellar-Mass Black Hole Blows Record-Speed Winds)

Continued observations of the ULX/black hole will attempt to observe another outburst similar to the 2009 event, although if this black hole is anything like those observed in our galaxy it could be years before another such event occurs. Still, our relatively clear view of the Andromeda galaxy unobscured by intervening dust  and gas offers a chance to perhaps spot other potential x-ray sources residing there.

Read the report from the AlphaGalileo Foundation here, or on ScienceDaily here.

The first MPE team’s paper can be found here.

Posted on by Jason Major

Chandra Spots a Black Hole’s High-Speed Hurricane

Artist's impression of a binary system containing a stellar-mass black hole called IGR J17091-3624

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Astronomers using NASA’s Chandra X-ray Observatory have reported record-breaking wind speeds coming from a stellar-mass black hole.

The “wind”, a high-speed stream of material that’s being drawn off a star orbiting the black hole and ejected back out into space, has been clocked at a staggering 20 million miles per hour — 3% the speed of light! That’s ten times faster than any such wind ever measured from a black hole of its size!

The black hole, dubbed IGR J17091-3624 (IGR J17091 for short), is located about 28,000 light-years away in the constellation Scorpius. It is part of a binary system, with a Sun-like star in orbit around it.

“This is like the cosmic equivalent of winds from a category five hurricane,” said Ashley King from the University of Michigan, lead author of the study. “We weren’t expecting to see such powerful winds from a black hole like this.”

IGR J17091 exhibits wind speeds akin to black holes many times its mass… such winds have only ever been measured coming from black holes millions or even billions of times more massive.

“It’s a surprise this small black hole is able to muster the wind speeds we typically only see in the giant black holes,” said co-author Jon M. Miller, also from the University of Michigan.

Illustration of Cygnus X-1, another stellar-mass black hole located 6070 ly away. (NASA/CXC/M.Weiss)

Stellar-mass black holes are formed from the gravitational collapse of stars about 20 to 25 times the mass of our Sun.

“This black hole is performing well above its weight class,” Miller added.

IGR J17091 is also surprising in that it seems to be expelling much more material from its accretion disk than it is capturing. Up to 95% of the disk material is being blown out into space by the high-speed wind which, unlike polar jets associated with black holes, blows in many different directions.

While jets of material have been previously observed in IGR J17091, they have not been seen at the same time as the high-speed winds. This supports the idea that winds can suppress the formation of jets.

Chandra observations made two months ago did not show evidence of the winds, meaning they can apparently turn on and off. The winds are thought to be powered by constant variations in the powerful magnetic fields surrounding the black hole.

The study was published in the Feb. 20 issue of The Astrophysical Journal Letters.

Illustration credit: NASA/CXC/M.Weiss. Source: Chandra Press Room.

Posted on by Jason Major

X-rays Unwrap a Poky Little Pulsar

A pulsar within a supernova remnant in the Small Magellanic Cloud. X-rays are blue; optical data is red and green. (NASA/CXC/Univ.Potsdam/L.Oskinova et al.)

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For the first time astronomers have located a pulsar – the super-dense, spinning remains of a star – nestled within the remnants of a supernova in the Small Magellanic Cloud. The image above, a composite of x-ray  and optical light data acquired by NASA’s Chandra Observatory and ESA’s XMM-Newton, shows the pulsar shining brightly on the right surrounded by the ejected outer layers of its former stellar life.

The optically-bright area on the left is a large star-forming region of dust and gas nearby SXP 1062.

A pulsar is a neutron star that emits high-energy beams of radiation from its magnetic poles. These poles are not always aligned with its axis of rotation, and so the beams swing through space as the neutron star spins. If the Earth happens to be in direct line with the beams at some point along their path, we see them as rapidly flashing radiation sources… sort of like a cosmic lighthouse on overdrive.

What’s unusual about this pulsar – called SXP 1062 – is its slow rate of rotation. Its beams spin around at a rate of about once every 18 minutes, which is downright poky for a pulsar, most of which spin several times a second.

X-ray image of SXP 1062

This makes SXP 1062 one of the slowest known pulsars discovered within the Small Magellanic Cloud, a dwarf galaxy cruising alongside our own Milky Way about 200,000 light-years distant.

The supernova that presumably created the pulsar and its surrounding remnant wrapping is estimated to have taken place between 10,000 and 40,000 years ago – relatively recently, by cosmic standards. To see a young pulsar spinning so slowly is extra unusual since younger pulsars have typically been observed to have rapid rotation rates. Understanding the cause of its leisurely pace will be the next goal for SXP 1062 researchers.

Read more about SXP 1062on the Chandra photo album page.

 

Image credit: X-ray & Optical: NASA/CXC/Univ.Potsdam/L.Oskinova et al.

Posted on by Jason Major

A Four Cluster Pile-Up

Abell 2744, a.k.a. "Pandora's Cluster"

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Abell 2744, shown above in a composite of images from the Hubble Space Telescope, the ESO’s Very Large Telescope and NASA’s Chandra X-ray  Observatory, is one of the most complex and dramatic collisions ever seen between galaxy clusters.

X-ray image of Abell 2744

Dubbed “Pandora’s Cluster”, this is a region 5.9 million light-years across located 3.5 billion light-years away. Many different kinds of structures are found here, shown in the image as different colors. Data from Chandra are colored red, showing gas with temperatures in the millions of degrees. Dark matter is shown in blue based on data from Hubble, the European Southern Observatory’s VLT array and Japan’s Subaru telescope. Finally the optical images showing the individual galaxies have been added.

Even though there are many bright galaxies visible in the image, most of the mass in Pandora’s Cluster comes from the vast areas of dark matter and extremely hot gas. Researchers made the normally invisible dark matter “visible” by identifying its gravitational effects on light from distant galaxies. By carefully measuring the distortions in the light a map of the dark matter’s mass could be created.

Galaxy clusters are the largest known gravitationally-bound structures in the Universe, and Abell 2744 is where at least four clusters have collided together. The vast collision seems to have separated the gas from the dark matter and the galaxies themselves, creating strange effects which have never been seen together before. By studying the history of events like this astronomers hope to learn more about how dark matter behaves and how the different structures that make up the Universe interact with each other.

Check out this HD video tour of Pandora’s Cluster from the team at Chandra:

Read more on the Chandra web site or in the NASA news release.

Image credit: X-ray: NASA/CXC/ITA/INAF/J.Merten et al, Lensing: NASA/STScI; NAOJ/Subaru; ESO/VLT, Optical: NASA/STScI/R.Dupke.

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Jason Major is a graphic designer, photo enthusiast and space blogger. Visit his website Lights in the Dark and follow him on Twitter @JPMajor or on Facebook for the most up-to-date astronomy awesomeness!

 

Posted on by Ian O'Neill

Hinode Discovers the Sun’s Hidden Sparkle

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Blinking spots of intense light are being observed all over the lower atmosphere of the Sun. Not just in the active regions, but in polar regions, quiet regions, sunspots, coronal holes and loops. These small explosions fire elegant jets of hot solar matter into space, generating X-rays as they go. Although X-ray jets are known to have existed for many years, the Japanese Hinode observatory is seeing these small flares with unprecedented clarity, showing us that X-ray jets may yet hold the answers to some of the most puzzling questions about the Sun and its hot corona.

Although a comparatively small mission (weighing 875 kg and operating just three instruments), Hinode is showing the world some stunning high resolution pictures of our nearest star. In Earth orbit and kitted out with an optical telescope (the Solar Optical Telescope, SOT), Extreme ultraviolet Imaging Spectrometer (EIS) and an X-Ray Telescope (XRT), the light emitted from the Sun can be split into its component optical, ultraviolet and X-ray wavelengths. This in itself is not new, but never before has mankind been able to view the Sun in such detail.

It is widely believed that the violent, churning solar surface may be the root cause of accelerating the solar wind (blasting hot solar particles into space at a mind-blowing 1.6 million kilometers per hour) and heating the million plus degree solar atmosphere. But the small-scale processes close to the Sun driving the whole system are only just beginning to come into focus.

Up until now, small-scale turbulent processes have been impossible to observe. Generally, any feature below 1000 km in size has remained undetected. Much like trying to follow a golf ball in flight from 200 meters away, it is very difficult (try it!). Compare this with Hinode, the same golf ball can be resolved by the SOT instrument from nearly 2000 km away. That’s one powerful telescope!

The limit of observable solar features has now been lifted. The SOT can resolve the fine structure of the solar surface to 180 km, this is an obvious improvement. Also, the EIS and XRT can capture images very quickly, one per second. The SOT can produce hi-res pictures every 5 minutes. Therefore, fast, explosive events such as flares can be tracked easier.

Putting this new technology to the test, a team led by Jonathan Cirtain, a solar physicist at NASA’s Marshall Space Flight Center, Huntsville, Alabama, has unveiled new results from research with the XRT instrument. X-ray jets in the highly dynamic chromosphere and lower corona appear to occur with greater regularity than previously thought.

X-ray jets are very important to solar physicists. As magnetic field lines are forced together, snap, and form new configurations, vast quantities of heat and light are generated in the form of a “microflare”. Although these are small events on a solar scale, they still generate huge amounts of energy, heating solar plasma to over 2 million Kelvin, create spurts of X-ray emitting plasma jets and generate waves. This is all very interesting, but why are jets so important?

The solar atmosphere (or corona) is hot. In fact, very hot. Actually, it is too hot. What I’m trying to say is that measurements of coronal particles tell us the atmosphere of the Sun is actually hotter than the Suns surface. Traditional thinking would suggest that this is wrong; all sorts of physical laws would be violated. The air around a light bulb isn’t hotter than the bulb itself, the heat from an object will decrease the further away you measure the temperature (obvious really). If you’re cold, you don’t move away from the fire, you get closer to it!

The Sun is different. Through interactions near the surface of the Sun between plasma and magnetic flux (a field known as “magnetohydrodynamics” – magneto = magnetic, hydro = fluid, dynamics = motion: “magnetic-fluid-motion” in plain English, or “MHD” for short), MHD waves are able to propagate and heat up the plasma. The MHD waves under scrutiny are known as “Alfvén wavesâ€? (named after Hannes Alfvén, 1908-1995, the plasma physics supremo) which, theoretically, carry enough energy from the Sun to heat the solar corona hotter than the solar surface. The one thing that has dogged the solar community for the last half a century is: how are Alfvén waves produced? Solar flares have always been a candidate as a source, but observation suggested that there wasn’t enough flares to generate enough waves. But now, with advanced optics used by Hinode, many small-scale events appear to be common… bringing us back to our X-ray jets…

Previously, only the largest X-ray jets have been observed, putting this phenomenon at the bottom of the priority list. NASA’s Marshall Space Flight Center group has now turned this idea on its head by observing hundreds of jet events each and every day:

“We now see that jets happen all the time, as often as 240 times a day. They appear at all latitudes, within coronal holes, inside sunspot groups, out in the middle of nowhere–in short, wherever we look on the sun we find these jets. They are a major form of solar activity” – Jonathan Cirtain, Marshall Space Flight Center.

So, this little solar probe has very quickly changed our views on solar physics. Launched on September 23, 2006, by a consortium of countries including Japan, USA and Europe, Hinode has already revolutionized our thinking about how the Sun works. Not only looking deep into the chaotic processes in the solar chromosphere, it is also finding new sources where Alfvén waves may be generated. Jets are now confirmed as common events that occur all over the Sun. Could they provide the corona with enough Alfvén waves to heat the Sun’s corona more than the Sun itself? I don’t know. But what I do know is, the sight of solar jets flashing to life in these movies is awesome, especially as you see the jet launch into space from the original flash. This is also a very good time to be seeing this amazing phenomenon, as Jonathan Cirtain points out the site of solar jets reminds him of “the twinkle of Christmas lights, randomly oriented. It’s very pretty”. Even the Sun is getting festive.