Astronomers calculate Black hole's point of no return

At the center of most galaxies lie black holes, some of which are classed as supermassive black holes. These cosmic bodies can have a mass billions of times greater than that of the sun, crammed in just a fraction of the latter. Gravity goes completely haywire in such an environment where this humongous mass gets crushed in a very tight space. At the edge of black holes, gravity is so strong that any matter unfortunate enough to be in its proximity will get sucked in and never escape, not even light. This perfectly defined boundary is called the event horizon, once matter passes this line it’s lost forever. Now, a team of international researchers have for the first time measured the radius of a black hole, located at the center of a distant galaxy.

“Once objects fall through the event horizon, they’re lost forever,” Shep Doeleman, assistant director of the MIT Haystack Observatory and research associate at the Smithsonian Astrophysical Observatory, said in a statement Thursday (Sept. 27). “It’s an exit door from our universe. You walk through that door, you’re not coming back.”

In order to meet their goals of measuring an black hole radius -  the closest distance at which matter can approach before being irretrievably pulled into the black hole – the team of researchers, lead by scientists at MIT’s Haystack Observatory, arranged a telescope array dubbed the “Event Horizon Telescope” (EHT), comprised of Hawaii’s James Clerk Maxwell Telescope, the Submillimeter Telescope in Arizona, and two telescopes at CARMA in California. Using a technique called  Very Long Baseline Interferometry, or VLBI, the instruments of all these observatories located thousands of miles from one another could be linked, forming a sort of “virtual telescope”. The resolving power of a single telescope is as big as the space between the disparate dishes, thus allowing astronomers to peer through some of the distant galaxies.

Simulated event horizon-resolving images for the ultra-relativistic jet. It shows how the extreme gravity of the black hole in M87 distorts the appearance of the jet near the event horizon. Part of the radiation from the jet is bent by gravity into a ring that is known as the ‘shadow’ of the black hole.

And distant it was. The instruments of the combined Event HorizonTelescope were directed on M87, a galaxy some 50 million light years from the Milky Way. At the center of M87 lies a black hole with a mass 6 billion times that of the sun. At the edge of this black hole,astronomers observed glow of matter – they had just found the event horizon.
Now, the event horizon itself is impossible to measure, since it’s imaginary, but what scientists could measure was the closest stable orbit in which matter can circle the black hole, without being lost forever. Matter doesn’t get sucked all at once in the black hole, though, instead a sort of traffic jam ensues where matter, like gas and dust, build up into what’s called an accretion disk, which in familiar terms resembles a flat pancake.

Thus, the scientists found the accretion disk to be only 5.5 times the size of the black hole event horizon – that’s five times the size of the solar system, or 750 times the distance from Earth to the sun.Also, the same accretion disk was found to be the source of powerful jets of light often times seen radiating from the center of galaxies. These jets interact with the wind of particles coming from the accretion disk, which focuses them into narrow beams that move at nearly the speed of light  - in some cases, they’re so energetically charged that they’re able to propel particles for hundreds of thousands of light years, sending them entirely out of the galaxy, where the particles eventually slow down by interacting with the intergalactic medium. Until now, no telescope was powerful enough to verify the idea that these jets come from accretion disks around black holes.
“The basic nature of jets is still mysterious,” says Christopher Reynolds, a professor of astronomy at the University of Maryland. “Many astrophysicists suspect that jets are powered by black hole spin … but right now, these ideas are still entirely in the realm of theory. This measurement is the first step in putting these ideas on a firm observational basis.”

Halo around the Milky Way

Astronomers have used NASA's Chandra X-ray Observatory to find evidence our Milky Way Galaxy is embedded in an enormous halo of hot gas that extends for hundreds of thousands of light years. The estimated mass of the halo is comparable to the mass of all the stars in the galaxy.
If the size and mass of this gas halo is confirmed, it also could be an explanation for what is known as the "missing baryon" problem for the galaxy.

Baryons are particles, such as protons and neutrons, that make up more than 99.9 percent of the mass of atoms found in the cosmos.

Measurements of extremely distant gas halos and galaxies indicate the baryonic matter present when the universe was only a few billion years old represented about one-sixth the mass and density of the existing unobservable, or dark, matter. In the current epoch, about 10 billion years later, a census of the baryons present in stars and gas in our galaxy and nearby galaxies shows at least half the baryons are unaccounted for.
In a recent study, a team of five astronomers used data from Chandra, the European Space Agency's XMM-Newton space observatory and Japan's Suzaku satellite to set limits on the temperature, extent and mass of the hot gas halo.

Chandra observed eight bright X-ray sources located far beyond the galaxy at distances of hundreds of millions of light-years. The data revealed X-rays from these distant sources are absorbed selectively by oxygen ions in the vicinity of the galaxy. The scientists determined the temperature of the absorbing halo is between 1 million and 2.5 million kelvins, or a few hundred times hotter than the surface of the sun.
Other studies have shown that the Milky Way and other galaxies are embedded in warm gas with temperatures between 100,000 and 1 million kelvins. Studies have indicated the presence of a hotter gas with a temperature greater than 1 million kelvins. This new research provides evidence the hot gas halo enveloping the Milky Way is much more massive than the warm gas halo.

"We know the gas is around the galaxy, and we know how hot it is," said Anjali Gupta, lead author of The Astrophysical Journal paper describing the research. "The big question is, how large is the halo, and how massive is it?" To begin to answer this question, the authors supplemented Chandra data on the amount of absorption produced by the oxygen ions with XMM-Newton and Suzaku data on the X-rays emitted by the gas halo. They concluded that the mass of the gas is equivalent to the mass in more than 10 billion suns, perhaps as large as 60 billion suns.

"Our work shows that, for reasonable values of parameters and with reasonable assumptions, the Chandra observations imply a huge reservoir of hot gas around the Milky Way," said co-author Smita Mathur of Ohio State University in Columbus. "It may extend for a few hundred thousand light-years around the Milky Way or it may extend farther into the surrounding local group of galaxies. Either way, its mass appears to be very large." The estimated mass depends on factors such as the amount of oxygen relative to hydrogen, which is the dominant element in the gas.
Nevertheless, the estimation represents an important step in solving the case of the missing baryons, a mystery that has puzzled astronomers for more than a decade.

Although there are uncertainties, the work by Gupta and colleagues provides the best evidence yet that the galaxy's missing baryons have been hiding in a halo of million-kelvin gas that envelopes the galaxy.

The estimated density of this halo is so low that similar halos around other galaxies would have escaped detection.

The paper describing these results was published in the Sept. 1 issue of The Astrophysical Journal. Other co-authors were Yair Krongold of Universidad Nacional Autonoma de Mexico in Mexico City; Fabrizio Nicastro of Harvard-Smithsonian Center for Astrophysics in Cambridge, Mass.; and Massimiliano Galeazzi of University of Miami in Coral Gables, Fla.
NASA's Marshall Space Flight Center in Huntsville, Ala., manages the Chandra program for NASA's Science Mission Directorate in Washington.
The Smithsonian Astrophysical Observatory controls Chandra's science and flight operations from Cambridge.

The first galaxies formed very fast after the Big Bang – in cosmic time, that is. It’s estimated that the earliest ones appeared some 500 million years ago, a period about which researchers know very little.

How they observed it
Even though they are typically very bright, such galaxies are quite hard to observe because they are very far away and only a small fraction of their light can make its way towards Earth, a fraction so small it’s almost impossible to pick up. However, the Hubble telescope managed to detect light from a small galaxy emitted just 500 million years ago, a period when the Universe was still in its infancy.

The telescope was able to do this thanks to a phenomena calledgravitational lensing: basically, when you have an observer (Hubble), a distant source (the galaxy) and a certain distribution of matter (a galaxy cluster for example), the light emitted by the source can be bent and the observer can observe it easier; gravitational lensing is one of the predictions involved by Einstein‘s general theory of relativity. Basically, the massive gravity of the galaxy cluster acts just like a lens.

In this case, astronomer Wei Zheng and colleagues using the Hubble and Spitzer Space Telescopes reported light was magnified 15 times,making it just strong enough to be observed. Even so, the galaxy MACS 1149-JD appeared as a mere blob, and only after repeated measurements were they able to conclude that it is most likely a galaxy.

How they know its age

The Universe is expanding; galaxies produce light with specific spectral properties, based on the stars and gas they contain. Combine these two facts, and you can understand that light emitted by early galaxies was stretched shifting the entire spectrum into a different wavelength range, a phenomenon called cosmic redshift.All electromagnetic types of radiation (light included) have an electromagnetic spectrum – the range of all possible frequencies of electromagnetic radiation. Cosmic redshift means light seen coming from an object that is moving away is proportionally increased in wavelength, or shifted to the red end of the spectrum.

So, using multiple measurements from the Spitzer and Hubble telescope, they estimated that the light was emitted 490-505 million years after the Big Bang. But their conclusions are perhaps even more interesting. Instead of suggesting MACS 1149-JD is a special snowflake, astronomers believe there are many more such galaxies, formed in the same era, the ‘first’ era, just waiting to be discovered.

Nature at work or Martians?

In the past couple of months, all Mars-related attention has been almost unanimously shifted towars the Curiosity rover. Not to discredit any of its achievements thus far, which are just appetizers for marvelous fings to come off Curiosity, but the Opportunity rover has been trailing the Martian surface for the past eight years now, long before Curiosity had its first screw designed on the drawing board, and it’s not showing any hints of ending its scientific exploration mission any time too soon. Its most recent find, a group of spherical rocks of peculiar structure and composition, has baffled NASA scientists, reminding the media and common Mars and space enthusiasts alike that there’s another robot on wheels pitching in, and it’s doing a mighty fine job at it.

During its first run on the red planet, some eight and a half years ago, the Opportunity rover came by a group of spherules on the soil, which were dubbed by scientists as blueberries due to their uncanny resemblance, and which upon closer examination were found to beconcretions formed by action of mineral-laden water inside rocks, evidence of a wet environment on early Mars.

This most recent picture snapped by the same Opportunity rover is a 2.4 inch mosaic made out of four separate images which show small spherical objects approximately one-eighth inch in diameter. Opportunity snapped the images with its Microscopic Imager on the western rim of Endeavour Crater in an outcrop called Kirkwood in the Cape York segment.

“This is one of the most extraordinary pictures from the whole mission,” said Opportunity’s principal investigator, Steve Squyres of Cornell University in Ithaca, N.Y. “Kirkwood is chock full of a dense accumulation of these small spherical objects. Of course, we immediately thought of the blueberries, but this is something different. We never have seen such a dense accumulation of spherules in a rock outcrop on Mars.”

Although these may look similar to the Martian blueberries, scientists claim that they’re far from being the same rocks. The analysis is still preliminary, but it indicates that these spheres do not have the high iron content of Martian blueberries.

“They are different in concentration. They are different in structure. They are different in composition. They are different in distribution. So, we have a wonderful geological puzzle in front of us. We have multiple working hypotheses, and we have no favorite hypothesis at this time. It’s going to take a while to work this out, so the thing to do now is keep an open mind and let the rocks do the talking,” continued Squyres.

Apparently, the Kirkwood spherical rock formations are broken and eroded by the wind, presenting a concentric structure. Much more analysis is to be made before the NASA scientists can tell for sure what these peculiar rock formation represent. One thing’s for sure though - “they seem to be crunchy on the outside and softer in the middle,” according to Squyres. Yup, ancient martian sweets anyone?

Milky way's hungry blackhole.

A young star and its planet-forming cloud are being pulled towards the huge black hole at the centre of our galaxy, astronomers say.

Like other galaxies, the Milky Way hosts a black hole, known as Sagittarius A (SgrA),* at its centre.

SGrA* dislodged the star from its original orbit within a ring of young suns circling the black hole.

The disc of gas and dust will be devoured before it can evolve into a solar system.

The research by a team at the Harvard-Smithsonian Center for Astrophysics in Cambridge, US, is published in Nature Communications journal.

Earlier this year, researchers reported seeing a cloud of ionised gas and dust falling in towards SgrA*.

They suggested that it formed when gas streaming from two nearby stars collided, like wind-blown sand gathering into a dune.

Astronomers Ruth Murray-Clay and Abraham Loeb have come up with a different explanation: that the cloud is a proto-planetary disc surrounding a low-mass star.

Newborn stars retain a surrounding disc of gas and dust for millions of years. If one such star were to dive toward our galaxy's central black hole, radiation and gravitational tides would rip apart the surrounding matter in just a few years.

The star is now hurtling towards the black hole on an elliptical orbit.

While the star itself is too small to be directly observed, the proto-planetary dust cloud accompanying it is being disrupted on the way, and it is this debris that the researchers were able to detect.

"This unfortunate star got tossed toward the central black hole. Now it's on the ride of its life," said Dr Murray-Clay.

As the young sun continues to plummet towards the black hole over the next year, more of the disc's outer material will be torn away. The stripped gas will swirl into the yawning black hole. Friction will heat it to high enough temperatures that it will glow in X-rays.

But while the planetary cloud is heading for destruction, the star is likely to survive.

"The tidal forces from the black hole are strong enough to strip gas away from the star but not strong enough to pull the star itself apart," Dr Murray-Clay told BBC News.

"The same sort of forces that generate ocean tides are at work here. Ocean tides happen when the oceans are pulled away from the Earth a little bit by the Moon. In our case, the black hole is generating such strong tidal forces that they pull a large fraction of the disc entirely away from the star.

"The inner portion of the disc will survive - gas close to the young star is held more tightly since it is deeper in the star's gravitational well."

The results are interesting because the centre of the Milky Way should be a very inhospitable place to try to form a planet.

Stars crowd each other as they zip through space while exploding stars unleash shock waves and bathe the region in intense radiation.The powerful gravitational forces from a supermassive black hole twist and warp the fabric of space itself.

The research suggests, contrary to received wisdom, that planets can still form in this cosmic war zone.

Although this protoplanetary disc is being destroyed, the stars that remain in the ring can hold onto their planet-forming clouds. This means they could form planets despite the hostile surroundings.

"It's fascinating to think about planets forming so close to a black hole," said Abraham Loeb.

Lithium problem?

A team of astrophysicists from the Center for Astrophysics at the University of Notre Dame are exploring a discrepancy between the amount of lithium predicted by the standard models of elemental production during the Big Bang and the amount of lithium observed in the gas of the Small Magellanic Cloud.

The Small Magellanic Cloud is a dwarf galaxy with a diameter of about 7,000 light-years.  It contains several hundred million stars, and is one of the Milky Way’s nearest neighbors.

J. Christopher Howk, Nicolas Lehner and Grant Mathews published a paper this week in the journal Nature titled “Observation of interstellar lithium in the low-metallicity Small Magellanic Cloud.”

“The paper involves measuring the amount of lithium in the interstellar gas of a nearby galaxy, but it may have implications for fundamental physics, in that it could imply the presence of dark matter particles in the early universe that decay or annihilate one another,” Howk says. “This may be a probe of physics in the early universe that gives us a handle on new physics we don’t have another way to get a handle on right now.”

Using observations from the European Southern Observatory’s (ESO) Very Large Telescope (VLT), the team measured the amount of lithium in the interstellar gas of the Small Magellanic Cloud, which has far fewer star-produced heavy elements than the Milky Way.  Scientists believe that conditions immediately following the Big Bang led to the formation of some elements, including a small amount of lithium.  This is in addition to the production of elements by fusion in the core of stars.

ESO’s VLT is located Chile and is the flagship facility for European ground-based astronomy.  It consists of four Unit Telescopes with main mirrors of 8.2 meters in diameter and four movable 1.8-meter diameter Auxiliary Telescopes.  The telescopes can work together, or each can be used separately.  The VLT has such precision that it can reconstruct images with an angular resolution of milliarcseconds, equivalent to distinguishing the two headlights of a car at the distance of the Moon.

Big Bang predictions expect about four times more lithium on the surface of stars that is present in the Milky Way.  Some scientists argue that stellar activity might destroy lithium, or the element might sink from the surface through lighter hydrogen.  The ratio from star to star is remarkably consistent, however, challenging this view.

Observations of gas in the Small Magellanic Cloud revealed the amount of lithium that predictions say would have been produced at the Big Bang, but leave no room for subsequent production of the element.

One explanation could be a novel kind of physics operating at the Big Bang that left less lithium than the Standard Model predicts. To pursue this possibility, the team will conduct three nights of observations on the VLT in November. They will look for the lithium isotope 7Li in the Large Magellanic Cloud and 6Li in both the Large Magellanic Cloud and the Small Magellanic Cloud. The standard model predicts that no 6Li was created at the Big Bang.

Particle smasher in space?

This summer, particle astrophysicists from the Kavli Institute for Particle Astrophysics and Cosmology, along with colleagues from France and Japan, studied a supernova remnant located about 3000 light years away and discovered what is best described as a particle collider in space.
Supernova remnants, giant clouds of dust and gas thrown off by a self-destructing star, are known to accelerate particles. They’re one source of the cosmic rays – in reality not rays, but super-accelerated charged particles like protons – that bombard Earth. But when the team analyzed several different observations of the supernova remnant SNR S147, including gamma-ray observations from the LAT instrument on the Fermi Gamma-ray Space Telescope, they discovered something more than accelerating particles.
The researchers saw the accelerated particles smashing into a nearby obstacle, a molecular cloud of dense interstellar gas.
In their paper, the researchers report that the gamma rays from SNR S147 seem to come from the decay of neutral pions, which are produced by the high-energy collisions of two protons, just as sometimes happens at the Large Hadron Collider. In this case, accelerated protons from the supernova remnant collide with relatively slow hydrogen atoms (hydrogen consists of a single proton) in the molecular cloud. The gamma-ray emission is most intense where there are the most hydrogen atom targets.
Physicists cannot study these collisions up-close, as they do using several-story detectors built at collision points in the LHC. However, they can study their effects from afar. These results highlight how gamma-ray observations from the Fermi Gamma-ray Space Telescope are continuing to provide valuable data for understanding particle astrophysics and the fundamental high-energy physics of our universe.

Mars landing – a.k.a. the seven minutes of terror

The Mars landing isn’t an easy feat, even if you’re NASA; the car-sized Curiosity rover is on its way to fulfilling the two year $2.5 billion project it embarked on: finding out whether Mars has, or had at any time in its existence, life forms.

The rover has been traveling 8 months and a half, over 350 million miles, and it’s now just two days away from landing, or as NASA likes to call it: the seven minutes of terror. NASA likes to give suggestive nicknames to operations – and suggestive it is. Skimming the top of the Martian atmosphere at 13,000 mph, the Curiosity rover needs to brake to a stop — in no more than seven minutes. If this doesn’t work, then the whole mission is compromised.

All tests indicated the landing will go down smoothly, but NASA engineers are still terrified by the landing. If it survives the land, which will take place two days from now, at 1:17 a.m. EDT Monday, it will be able to use its 10 fancy pieces of equipment, which include a rock zapping laser, a high tech camera, a chemistry lab, and many more.

A short guide to NASA’s Curiosity equipment and lingo

With the Mars rover Curiosity due to land this weekend, it can be a real drag following NASA’s everyday lingo, which sometimes seems to resemble Martian more than English. Processes have nicknames, parts have nicknames or acronyms, and if you want to know if MSL will nail the EDL for example, you have to learn the talk.

Even NASA’s engineers and researchers admit the language is sometimes tiring and complicated, but necessary.

Let’s start with the basics: inside NASA’s Jet Propulsion Laboratory (JPL), it’s called MSL – which is short for Mars Science Laboratory. Spacecrafts typically have such names, only to be renamed following contests sponsored by NASA. The previous Mars Rovers, Spirit and Opportunity that landed in 2004 were known as as MER-A and MER-B for the longest time (MER is shorthand for Mars Exploration Rover). Interestingly enough, Curiosity didn’t get this nickname until 2009, when the name was proposed by a sixth-grader from Kansas.

Curiosity, which is about as big as a jeep, contains the most sophisticated instruments to study Mars’ environment – most of which have, of course, sophisticated names. For example, ‘Mastcam’ refers to the pair of 2-megapixel color cameras on the rover’s “head”. “SAM” – short for Sample Analysis at Mars, is the mobile chemistry lab designed mostly to sniff for carbon samples, which would hint at life on Mars. “ChemCam”, as you probably guessed, stands for ‘chemistry’ and ‘camera’, but what you probably didn’t know is that it could also act as a rock zapping laser. As for “Rad” – no surprises there, that’s the radiation detector.

Entry, descent and landing

But before Curiosity can put its sophisticated equipment to work, it must first survive EDL: entry, descent and landing, or how NASA has come to put it: the seven minutes of terror. NASA will receive signals from the shuttle through the DSN, or Deep Space Network, a worldwide network of antenna dishes that communicates with interplanetary spacecraft.

“It takes some time to pick it up,” said Ken Farley, a professor at the California Institute of Technology who is participating on his first space mission.

The dizzying terms take a while to get used to, but as JPL scientist Deborah Bass, who worked on that mission explained, it’s important to talk precisely and concise, but it’s also important not to alienate fans.

“We’re so jazzed about what we do,” Bass said. “We can forget that not everybody has the same fundamental background as we do.”
A field trip to Mars

“Until you’re actually staring at a rock outcrop and walking around it, you don’t have the intuition of what this rover’s going to do on Mars,” said Ashwin Vasavada, one of Grotzinger’s two deputies, recalling a 2008 field trip. “He would ask us, ‘If you were the rover, where would you drive? Where would you point your camera? How would we, as a team, explore this particular site, if this was what was in front of us on Mars?’ “

As I’ve already told you, only three days remain until the ‘seven minutes of terror’ – now you should know what this means.

How middleweight black holes are formed

A new model shows how an elusive type of black hole can be formed in the gas surrounding their supermassive counterparts. 

Scientists from the American Museum of Natural History, the City University of New York, the Jet Propulsion Laboratory of the California Institute of Technology, and the Harvard-Smithsonian Center for Astrophysics propose that intermediate-mass *black holes—light-swallowing celestial objects with masses ranging from hundreds to many thousands of times the mass of the Sun*—can grow in the gas disks around supermassive black holes in the centers of galaxies. 

The physical mechanism parallels the model astrophysicists use to describe the growth of giant planets in the gas disks surrounding stars. 

“We know about small black holes, which tend to be close to us and have masses a few to 10 times that of our Sun, and we know about supermassive black holes, which are found in the centers of galaxies and have a mass that’s millions to billions of times the mass of the sun,” said co-author Saavik Ford, who is a research associate in the Museum’s Department of Astrophysics as well as a professor at the Borough of Manhattan Community College, City University of New York (CUNY) and a faculty member at CUNY’s Graduate Center. 

“But we have no evidence for the middle stage. Intermediate-mass black holes are much harder to find,” Ford stated. 

The birth of an intermediate black hole starts with the death of a star that forms a stellar or low-mass black hole. In order for this “seed” to grow, it must collide with and consume other dead and living stars. But even though there are many billions of stars in large galaxies, there’s an even greater proportion of empty space, making collisions a very rare occurrence. 

The researchers’ new model suggests that previous searches for middleweight black holes might have been focused on the wrong birthing ground. 

“The recent focus had been on star clusters, but objects there move very quickly and there’s no gas, which makes the chances of a collision very slim,” said Barry McKernan, a research associate in the Museum’s Department of Astrophysics who is a professor at CUNY’s Borough of Manhattan Community College and a faculty member at CUNY’s Graduate Center. 

The new mechanism turns attention instead to active galactic nuclei, the piping hot and ultra-bright cores of galaxies that feed supermassive black holes. The gas in this system is key, causing the stars to slow down and conform to a circularized orbit. 

“You can think of the stars as cars travelling on a 10-lane highway. If there were no gas, the cars would be going at very different speeds and mostly staying in their lanes, making the odds of collision low. When you add gas, it slows the cars to matching speeds but also moves them into other lanes, making the odds of collision and consumption much higher,” McKernan said. 

The resulting collisions allow a stellar black hole to swallow stars and grow. The black hole’s size and gravitational pull increase as its mass expands, escalating its chance of further collisions. This phenomenon, called “runaway growth,” can lead to the creation of an intermediate-mass black hole. 

As they increase in size, the black holes start altering the gas disk that controls them. The researchers’ model shows that black holes of a certain mass can create a gap in the gas disk, a signature that might give scientists the first glimpse of intermediate black holes. 

*The research appeared in the Monthly Notices of the Royal Astronomical Society.* 

Dark Energy and Dark Matter

We believe that most of the matter in the universe is dark, i.e. cannot be detected from the light which it emits (or fails to emit). This is "stuff" which cannot be seen directly -- so what makes us think that it exists at all? Its presence is inferred indirectly from the motions of astronomical objects, specifically stellar, galactic, and galaxy cluster/supercluster observations. It is also required in order to enable gravity to amplify the small fluctuations in the Cosmic Microwave Background enough to form the large-scale structures that we see in the universe today.

Uranus: The seventh planet in our Solar system

Merging Galaxies

These Hubble snapshots capture merging galaxies at various stages in their collision. Astronomers estimate that only one out of one thousand galaxies in the nearby universe in the act of colliding. However, galaxy mergers were much more common long ago when they were closer together, because the expanding universe was smaller. 

For all their violence, galactic smash-ups take place at a glacial rate by human standards - timescales on the order of several hundred million years."

Astrophysics:Stars, stars and stars again...

Quick knowledge About History of 1752.

Here is an interesting historical fact. Just have a look at the calendar for the month of September 1752.
Go to Google type "September 1752 calendar" & see for yourself.
You will notice, 11 days are simply missing from the month.
Here's the explanation: This was the month during which England shifted from the Roman Julian Calendar to the Gregorian Calendar.
A Julian year was 11 days longer than a Gregorian year. So, the King of England ordered 11 days to be wiped off the face of that particular month.
So, the workers worked for 11 days less that month, but got paid for the whole month. That's how the concept of "paid leave" was born. Hail the King!!!
In the Roman Julian Calendar, April used to be the first month of the year; but the Gregorian Calendar observed January as the first month. Even after shifting to the Gregorian Calendar, many people refused to give up old traditions and continued celebrating 1st April as the New Year's Day. When simple orders didn't work, the King finally issued a royal dictum; which stated that those who celebrated 1st April as the new year's day would be labelled as fools.
From then on, 1st April became April Fool's Day. 

Amazing mother nature....

Phyllodes Imperialis-Imperial Fruit Sucking Moth

If touched or feels danger, then the caterpillar bends its head downwards beneath the raised front portion of its body, stretching the skin on its dorsum, revealing what appears to be a pair of large, blue-black 'eyes' and a double row of white teeth-like markings: a most remarkable effect which would be sufficient to startle any potential avian, reptilian or mammalian predator.