Tammy Plotner’s What’s Up articles and book have been so successful, I’ve decided to spin the column off as a separate blog, broken down into daily entries. This lets us have one entry for each day of the year, with a few photographs… every day. Tammy will also be posting additional entries for late breaking news, aurora sightings, sunspot activity. I’ll still be highlighting the articles, but I’ll be forwarding readers over to the blog from here on out. Each blog posting will also link to a special section of the Bad Astronomy/Universe Today forum, so you can chat with other astronomers about how your stargazing is going.
Two Stellar Futures
New images from the Gemini telescope show two paths stars can take as they near the end of their lives. One is NGC 6164-5, an emission nebula with an inverted S-shaped appearance. It’s 4,200 light-years away and contains a very massive star ejecting material – it should explode as a supernova in a few million years. The other, NGC 5189, contains a star much more similar to our own Sun. As it nears the end of the its life, the star blowing off its thin atmosphere into space, which collides with previously ejected clouds of gas.
Two new images from Gemini Observatory released today at the American Astronomical Society meeting in Calgary, Canada, show a pair of beautiful nebulae that were created by two very different types of stars at what may be similar points in their evolutionary timelines. One is a rare type of very massive spectral-type “O” star surrounded by material it ejected in an explosive event earlier in its life. It continues to lose mass in a steady “stellar wind.” The other is a star originally more similar to our Sun that has lost its outer envelope following a “red giant” phase. It continues to lose mass via a stellar wind as it dies, forming a planetary nebula. The images were made using the Gemini Multi-Object Spectrograph (GMOS) on Gemini
The first image shows the emission nebula NGC 6164-5, a rectangular, bipolar cloud with rounded corners and a diagonal bar producing an inverted S-shaped appearance. It lies about 1,300 parsecs (4,200 light-years) away in the constellation Norma. The nebula measures about 1.3 parsecs (4.2 light-years) across, and contains gases ejected by the star HD 148937 at its heart. This star is 40 times more massive than the Sun, and at about three to four million years of age, is past the middle of its life span. Stars this massive usually live to be only about six million years old, so HD 148397 is aging fast. It will likely end its life in a violent supernova explosion.
Like other O-type stars, HD148937 is heating up its surrounding clouds of gas with ultraviolet radiation. This causes them to glow in visible light, illuminating swirls and caverns in the cloud that have been sculpted by winds from the star. Some astronomers suggest that the cloud of material has been ejected from the star as it spins on its axis, in much the same way a rotating lawn sprinkler shoots out water as it spins. It’s also possible that magnetic fields surrounding the star may play a role in creating the complex shapes clearly seen in the new Gemini image.
Astronomers are also studying several “cometary knots” out on the boundaries of the cloud that are similar to those seen in planetary nebulae such as the Eskimo Nebula (NGC 2392) and the Helix Nebula (NGC 7293). These cometary knots (so called because they seem to resemble comets with their tails pointing away from the star) are inside what appears to be a low-density cavity in the cloud. The knots may be a result of the denser, slower shells being impacted by the faster stellar wind, as observed in planetary nebulae (formed during the deaths of much less massive stars like the Sun).
Massive stars like HD 148937 burn hydrogen to helium in a process called the CNO cycle. As a byproduct, carbon and oxygen are converted into nitrogen, so the appearance of enhanced nitrogen at the surface of the star or in the material it also blows off indicates an evolved star. According to astronomer Nolan Walborn of the Space Telescope Science Institute, who has been studying this star from the ground for several years now, it is a member of a very small class of O stars with certain peculiar spectral characteristics. “The ejected, nitrogen-rich nebulosities of HD 148937 suggest an evolved star, and a possible relationship to a class of star known as luminous blue variables,” he said.
Luminous blue variables are very massive, unstable stars advanced in their evolution. Many have nitrogen-rich nebulae that are arrayed symmetrically around the stars, similar to what we see in NGC 6164-5. One of the best-known examples is the star Eta Carinae, which ejected a nebula during an outburst in the 1840s.
Just as astronomers are still seeking to understand the process of mass loss from a star like HD 158937, they are also searching out the exact mechanisms at play when a star like the Sun begins to age and die. NGC 5189, a chaotic-looking planetary nebula that lies about 550 parsecs (1,800 light-years) away in the southern hemisphere constellation Musca, is a parallelogram-shaped cloud of glowing gas. The GMOS image of this nebula shows long streamers of gas, glowing dust clouds, and cometary knots pointing away from the central star. Its unruly appearance suggests some extraordinary action at the heart of this planetary nebula.
***image4:left***At the core of NGC 5189 is the hot, hydrogen-deficient star HD 117622. It appears to be blowing off its thin remnant atmosphere into interstellar space at a speed of about 2,700 kilometers (about 1,700 miles) per second. As the material leaves the star, it immediately begins to collide with previously ejected clouds of gas and dust surrounding the star. This collision of the fast-moving material with slower motion gas shapes the clouds, which are illuminated by the star. These so-called “low ionization structures” (or LIS) show up as the knots, tails, streamers, and jet-like structures we see in the Gemini image. The structures are small and not terribly bright, lending planetary nebulae their often-ghostly appearance.
“The likely mechanism for the formation of this planetary nebula is the existence of a binary companion to the dying star,” said Gemini scientist Kevin Volk. “Over time the orbits drift due to precession and this could result in the complex curves on the opposite sides of the star visible in this image.”
NGC 5189 was discovered by Scottish observer James Dunlop in 1826. when Sir John Herschel observed it in 1835 he described it as a “strange” object. It was not immediately identified as a planetary nebula, but its peculiar spectra, shows emission lines of ionized helium, hydrogen, sulfur and oxygen. These all indicate elements being burned inside the star as it ages and dies.As the material is blown out to space, it forms concentric shells of various gases from elements that were created in the star’s nuclear furnace.
The Gemini data used to produce these images is being released to the astronomical community for further research and follow-up analysis. Note to astronomers: Data can be found at the Gemini Science Archive by querying “NGC 6164” and “NGC 5189.”
Original Source: Gemini Observatory
Astrophoto: M13 by Cord Scholz
M13 by Cord Scholz
In 1938, television was still an experimental curiosity but three out of four homes owned a radio. This was a time when its power as a form of communication had yet to be fully recognized. That started to change on the evening of October 31 when a small cast of radio performers, lead by Orson Wells, convinced a lot of people that the United States was being invaded by creatures from somewhere other than our planet with his modern update of H.G. Well’s The War of the Worlds.
Almost seventy years ago, radio was exciting. People were still adjusting to its instantaneous connection with events from around the world as soon as they happened. Therefore, many listeners believed the dramatic presentation, presented as news during the radio play, was real. The broadcast has been followed by countless books, television shows and motion pictures which, combined, helped the notion of intelligent alien life to take firm roots in our culture. Science was also invaded by the possibility of extraterrestrial beings. In 1974, a carefully crafted message was transmitted from the world’s largest radio telescope and directed towards stars in M13, pictured here, in hopes someone or something would be listening.
M13 is one of the most prominent and best-known globular clusters in the night sky. It is the brightest that can be easily seen with a small telescope or pair of binoculars from most places in the northern hemisphere. Located in the constellation of Hercules, M13 is visible this time of year. It is twenty thousand lights years from Earth and its 100,000 stars form a ball so immense that it takes light 150 years to travel from one side to the other. The age of M13 is estimated at about 14 billion years.
The 1974 three minute message to M13 was beamed into space from the Arecibo Radio Telescope, in Puerto Rico, and was spearheaded by Dr. Frank Drake, a leading SETI proponent and colleague of the late Carl Sagan. A much longer three-hour message to other carefully selected stars was subsequently transmitted in 2001 from a radio telescope in the Ukraine. Of course, if anyone is around when our 1974 message arrives at a hypothetical planet orbiting a star in M13, their response will not return here until fifty thousand years have transpired.
This dazzling 1.2-hour exposure of M13 was produced by Cord Scholz from his imaging location in the northern German town of Hannover, which was also the birthplace of Wilhelm Herschel, the astronomer who discovered the planet Uranus. This image was taken with a 12.5 inch corrected newtonian telescope and an eleven mega-pixel camera. It also worth noting the number of far more distant galaxies that also fills this colorful picture.
Do you have photos you’d like to share? Post them to the Universe Today astrophotography forum or email them, and we might feature one in Universe Today.
Written by R. Jay GaBany
What’s Up This Week – June 5 – June 11, 2006
Jupiter. Image credit: Wes Higgins. Click to enlarge.
Greetings, fellow SkyWatchers! This week is all about Jupiter. While these sky guidelines were written before the appearance of the “Great Red Spot, Jr.” – that doesn’t mean the new storm can’t be spotted with an intermediate sized telescope. Be on the lookout for it to begin rotating inward about an hour after the GRS reaches meridian. Your best views will be achieved when Jr. also reaches meridian.
In the meantime, enjoy lunar features and meteor showers this week! It’s time to turn an eye towards the sky, because….
Here’s what’s up!
Monday, June 5 – Tonight let’s journey to the lunar surface and look at an area just south of crater Eratosthenes known as Sinus Aestuum. Its very smooth floor is curiously riddled to the north and east by dark stains. At one time Sinus Aestuum may have been completely submerged in lava. Later the molten rock sank to the Moon’s interior before it could do much more than melt away outer layers and older surface features.
Let’s continue to follow Jupiter. One thing you’ll notice is this gas giant doesn’t stand still. Even 10 minutes of observation reveals a definite drift of features across its globe. This wouldn’t be obvious if the entire planet was seen just as a series of light and dark bands running parallel to one another. There must be features on the planet that give observers reason to describe it as presenting “a wealth of detail.”
Although the Great Red Spot (GRS) has not been quite so red over the last few decades, it still remains “Great” in size. Almost three Earths could fit inside its length and two along its width! This vast anticyclone of upper atmospheric activity resides along the southern frontier of the South Equatorial Belt (SEB) but is largely embedded within it. Careful observation at higher magnifications shows that the GRS precedes a vast system of turbulence trailing it across the globe.
Since Jupiter’s day is two-fifths the length of our own, observers will be amazed to see the GRS come and go as the planet alternately presents its various faces. But, the GRS is not the only such spot in Jupiter’s turbulent cloud tops. Often great dark masses of far less longevity can be seen to come and go – particularly along, and embedded within, Jupiter’s NEB. Along with such dark “barge” formations, various semi-persistent white spots – or ovals – can also be detected. Many of these are seen south of the SEB and some can be detected in the planet’s polar region through large aperture scopes.
If you are out late, be sure to keep watch after the Moon sets for the Scorpiid meteor shower. Its radiant is near the constellation of Ophiuchus, and the average fall rate is about 20 per hour – with some fireballs!
Tuesday, June 6 – This evening on the lunar surface, look along the south shore of Mare Nubium. The thin, light ring you encounter will be crater Pitatus. Further south you will discover two mountain-walled plains whose exposed floors will show bright western and dark eastern walls. These twins are Wurzelbauer to the west and Gauricus to the east.
Wouldn’t it be nice if a telescope could actually “zoom” you towards anything as though you actually traveled that far? At 200x, Jupiter would hang suspended in space as though it were a little more than 4 million kilometers away. At this distance, the human eye could easily be overwhelmed with the many fine features visible in Jupiter’s dynamic cloud tops – especially when you consider that the planet would appear almost 5 times larger than the disk of the full moon!
Unfortunately, telescopes don’t quite work that way. The Earth’s atmosphere rules everything – even aperture – when it comes to what you can see in the night time sky. So observe every night possible and eventually you will get that “once in a lifetime” view of Jupiter!
Wednesday, June 7 – For late night or early morning SkyWatchers, be alert for the peak of the June Arietid meteor shower during the early morning hours. The radiant is in the constellation Aries and the fall rate is about 30 per hour. Most are slow moving with some fireballs.
Begin tonight by looking for bright Spica very close to the Moon. It will be so close that it will be occulted for some observers! Be sure to check with IOTA for more details.
Tonight’s lunar feature can be spotted in binoculars, but requires a telescope for detailed study. The Riphaeus Mountains can be found southwest of Copernicus. Highlighted by the bright ring of Euclides, the Montes Riphaeus show a variety of isolated hills and sharp peaks which may have been the original crater walls of Mare Cognitum before lava flow filled its floor. Northeast of the range is another smooth floored area on the border of Oceanus Procellarum. It is here that Surveyor 3 landed on April 19, 1967. After bouncing three times, the probe came to rest on a smooth slope in a sub-telescopic crater. As its on-board television monitors watched, Surveyor 3 deployed a “first of its kind” miniature shovel and dug to a depth of 18 inches. The view of sub-soil material and its clean-cut lines allowed scientists to conclude that the loose lunar soil could compact. Watching Surveyor 3 pound its shovel against the surface, the resulting tiny “dents” answered the crucial question. The surface of a mare would support the landing of a spacecraft and exploration by astronauts.
With Jupiter and the Moon so close tonight, why not try some comparison views? Observe Jupiter’s details through the telescope and compare what you see visually with the Moon. It gives you new respect for the wonders of lunar observation doesn’t it?
Thursday, June 8, 2006 – Born on this date in 1625 was the most notable observer after Galileo – Giovanni Cassini. Many of Cassini’s discoveries are easily reproduced by amateurs today. He was the first to see belts and spots on Jupiter – allowing him to accurately determine the planet’s rapid rotation. Cassini saw features on Mars clearly enough that he could determine its more Earth-like rotation as well. His observations of Saturn led to the discovery of its four brightest satellites. Cassini’s accurate records of Galilean transits across Jupiter allowed him to note discrepancies based on variations in the planet’s distance from Earth. In fact, Cassini came to think light might travel at a fixed speed! Astronomers particularly remember Cassini for his namesake division in Saturn’s ring system. Do you suppose we should name a spacecraft after him? And if so, where should we send it?
The three planets Cassini is most widely noted for observing are still visible in the evening sky. Look southwest for a rapidly setting Mars and Saturn, while Jupiter stands high the south at skydark.
Tonight’s lunar feature will be bright Aristarchus. Located on the terminator north of Kepler, this dazzling feature can sometimes be seen unaided and is easily noted in binoculars. For telescopic viewers, Aristarchus offers a splendid challenge – look for a thin, bright thread curling away from it. Named Schroter’s Valley, it is a sinuous rille and largest of its kind. It may have once been a lava tube, similar to our own terrestrial volcanic features.
Friday, June 9 – Today is the birthday of Johann Gottfried Galle. Born in Germany in 1812, Galle, along with d’Arrest, shared the distinction of discovering Neptune. This was based on calculations by Le Verrier predicting its expected position. Galle was Encke’s assistant at the Wilhelm Foerster Observatory in Berlin and became the first to see the faint “dusky ring” (Ring C) of Saturn. Galle was also one of the few astronomers ever to have seen Halley’s Comet twice. He died two months after the comet passed perihelion in 1910, at a ripe old age of 98.
Want to practice some astronomy during the day? Then grab an FM radio and enjoy the “static” as we enter a cometary debris trail and some of the strongest daytime radio meteor showers of the year. To listen to the action, all you need is an external antenna. Tune the receiver to the lowest frequency not producing a clear signal. Each time a meteor passes through our atmosphere, it leaves an ion trail that bounces back distant radio signals to you – even in a stationary car! Listen to the static for a quick rise in volume or a snatch of a distant station that lasts a second or two then fades back to static.
Tonight’s highlighted lunar feature can be seen in binoculars but is best viewed telescopically. Located in the southwest quadrant on the terminator just south of Shickard, crater Wargentin is most unique. Once upon a time, it was a very normal crater and remained that way for hundreds of millions of years – then it happened: either an interior fissure opened up, or the impact that originally formed it caused molten lava to seep slowly upward. Oddly enough, Wargentin’s walls lacked large enough breaks to allow the lava to escape and it eventually filled the crater to the rim. Often referred to as “the Cheese,” enjoy Wargentin tonight for its unusual appearance.
Saturday, June 10 – Begin your observations this evening by noting how close Antares is to the Moon. For some very lucky viewers, this means an occultation. Be sure to check IOTA for times and details in your area. You won’t want to miss this event…
Meanwhile on the surface, tonight’s lunar feature will be crater Galileo. It is a supreme challenge for binoculars to spot, but telescopes of any size at higher magnifications will easily reveal it perched on the terminator in the west-northwest section of the Moon. Set in the smooth sands of Oceanus Procellarum, Galileo is a very tiny, eye-shaped crater with a soft rille accompanying it. Of course, this crater was named for the man who first contemplated the Moon through a telescope. No matter what lunar resource you choose to follow, all agree that giving such an insignificant crater a great name like Galileo is like saying a Stradivarius is a stringed instrument! For those familiar with some of the outstanding lunar features, read any account of Galileo’s life and just look at how many spectacular craters were named for people he supported. We cannot change the names of lunar cartography, but we can remember Galileo’s many accomplishments each time we view this crater.
As the father of telescopic astronomy, Galileo blazed a trail across the night sky – one any amateur of the day can easily follow. Among his most well known discoveries were the four bright satellites of Jupiter – the Galilean moons. Of the four, Ganymede is now known to be the largest satellite in the solar system. At 5262 kilometers, Ganymede is significantly more than twice the diameter of Pluto and almost 10 percent larger than Mercury. Of all the satellites in our system other than the Earth’s moon, it is the only one capable of displaying a true disk in a moderate sized telescope. Tonight, at some 1.6 arc seconds in apparent size, Ganymede could reveal its disk to a mid-sized scope. Take the time to observe Galileo’s “solar system within a solar system.” Get a sense of the relative colors, brightness and size. If one of them is missing, Galileo didn’t miscount. Look for a transit shadow cast against the planet’s disk or watch for it to emerge from around behind.
Sunday, June 11– Tonight is the Full Moon. Often referred to as the Full Strawberry Moon, this name was a constant to every Algonquin tribe in North America. Our friends in Europe referred to it as the Rose Moon. The North American version came about because the comparatively short season for harvesting strawberries arrives each year during the month of June.
As its rises, we’ll voyage to something “strawberry” red – the brightest “carbon star” in the night skies. Aim scopes or binoculars about a fist width northeast of Beta Canes Venatici and behold “La Superba.”
Y Canes Venatici is a variable star which ranges between magnitudes 4.8 to 6.3 over a period of about half a year. When “Y” is at minimum it is around 4 times dimmer than at its peak. But, there is something very good about catching this star on a night when it is faint – its distinctive reddish hue. See if you agree with mid-18th century astronomer Father Angelo Secchi, in naming it “La Superba.”
May all your journeys be at light speed… ~Tammy Plotner with Jeff Barbour.
Huge Asteroid Crater in Antarctica
Image of Antarctica captured by Galileo. Image credit: NASA. Click to enlarge
The asteroid impact that killed the dinosaurs 65 million years ago was big, but geologists have found a new asteroid crater that’s even bigger: in Antarctica. This 482 km (300 mile) crater was discovered using NASA’s GRACE satellites, which can detect the gravity fluctuations beneath Antarctica’s ice sheets. This meteor was probably 48 km (30 miles) across and might have struck 250 million years ago – the time of the Permian-Triassic extinction, when almost all the animals on Earth died out.
Planetary scientists have found evidence of a meteor impact much larger and earlier than the one that killed the dinosaurs — an impact that they believe caused the biggest mass extinction in Earth’s history.
The 300-mile-wide crater lies hidden more than a mile beneath the East Antarctic Ice Sheet. And the gravity measurements that reveal its existence suggest that it could date back about 250 million years — the time of the Permian-Triassic extinction, when almost all animal life on Earth died out.
Its size and location — in the Wilkes Land region of East Antarctica, south of Australia — also suggest that it could have begun the breakup of the Gondwana supercontinent by creating the tectonic rift that pushed Australia northward.
Scientists believe that the Permian-Triassic extinction paved the way for the dinosaurs to rise to prominence. The Wilkes Land crater is more than twice the size of the Chicxulub crater in the Yucatan peninsula, which marks the impact that may have ultimately killed the dinosaurs 65 million years ago. The Chicxulub meteor is thought to have been 6 miles wide, while the Wilkes Land meteor could have been up to 30 miles wide — four or five times wider.
“This Wilkes Land impact is much bigger than the impact that killed the dinosaurs, and probably would have caused catastrophic damage at the time,” said Ralph von Frese, a professor of geological sciences at Ohio State University.
He and Laramie Potts, a postdoctoral researcher in geological sciences, led the team that discovered the crater. They collaborated with other Ohio State and NASA scientists, as well as international partners from Russia and Korea. They reported their preliminary results in a recent poster session at the American Geophysical Union Joint Assembly meeting in Baltimore.
The scientists used gravity fluctuations measured by NASA’s GRACE satellites to peer beneath Antarctica’s icy surface, and found a 200-mile-wide plug of mantle material — a mass concentration, or “mascon” in geological parlance — that had risen up into the Earth’s crust.
Mascons are the planetary equivalent of a bump on the head. They form where large objects slam into a planet’s surface. Upon impact, the denser mantle layer bounces up into the overlying crust, which holds it in place beneath the crater.
When the scientists overlaid their gravity image with airborne radar images of the ground beneath the ice, they found the mascon perfectly centered inside a circular ridge some 300 miles wide — a crater easily large enough to hold the state of Ohio.
Taken alone, the ridge structure wouldn’t prove anything. But to von Frese, the addition of the mascon means “impact.” Years of studying similar impacts on the moon have honed his ability to find them.
“If I saw this same mascon signal on the moon, I’d expect to see a crater around it,” he said. “And when we looked at the ice-probing airborne radar, there it was.”
“There are at least 20 impact craters this size or larger on the moon, so it is not surprising to find one here,” he continued. “The active geology of the Earth likely scrubbed its surface clean of many more.”
He and Potts admitted that such signals are open to interpretation. Even with radar and gravity measurements, scientists are only just beginning to understand what’s happening inside the planet. Still, von Frese said that the circumstances of the radar and mascon signals support their interpretation.
“We compared two completely different data sets taken under different conditions, and they matched up,” he said.
To estimate when the impact took place, the scientists took a clue from the fact that the mascon is still visible.
“On the moon, you can look at craters, and the mascons are still there,” von Frese said. “But on Earth, it’s unusual to find mascons, because the planet is geologically active. The interior eventually recovers and the mascon goes away.” He cited the very large and much older Vredefort crater in South Africa that must have once had a mascon, but no evidence of it can be seen now.
“Based on what we know about the geologic history of the region, this Wilkes Land mascon formed recently by geologic standards — probably about 250 million years ago,” he said. “In another half a billion years, the Wilkes Land mascon will probably disappear, too.”
Approximately 100 million years ago, Australia split from the ancient Gondwana supercontinent and began drifting north, pushed away by the expansion of a rift valley into the eastern Indian Ocean. The rift cuts directly through the crater, so the impact may have helped the rift to form, von Frese said.
But the more immediate effects of the impact would have devastated life on Earth.
“All the environmental changes that would have resulted from the impact would have created a highly caustic environment that was really hard to endure. So it makes sense that a lot of life went extinct at that time,” he said.
He and Potts would like to go to Antarctica to confirm the finding. The best evidence would come from the rocks within the crater. Since the cost of drilling through more than a mile of ice to reach these rocks directly is prohibitive, they want to hunt for them at the base of the ice along the coast where the ice streams are pushing scoured rock into the sea. Airborne gravity and magnetic surveys would also be very useful for testing their interpretation of the satellite data, they said.
NSF and NASA funded this work. Collaborators included Stuart Wells and Orlando Hernandez, graduate students in geological sciences at Ohio State; Luis Gaya-Piqu??bf? and Hyung Rae Kim, both of NASA’s Goddard Space Flight Center; Alexander Golynsky of the All-Russia Research Institute for Geology and Mineral Resources of the World Ocean; and Jeong Woo Kim and Jong Sun Hwang, both of Sejong University in Korea.
Original Source: Ohio State University
Colliding Galaxies Simulated
A supercomputer simulation gravitational interaction between colliding galaxies. Image credit: Stelios Kazantzidis. Click to enlarge
Just like many businesses, galaxies grow through mergers and acquisitions. As galaxies are made up of countless individual stars, simulating these mergers is tremendously challenging, even for the most powerful supercomputers. A international team of researchers have produced a new simulation that shows how colliding galaxies are connected by a bridge of material, and spew out enormous tails of dust and debris. New programming and hardware upgrades have made this kind of simulation possible to do.
A wispy collection of atoms and molecules fuels the vast cosmic maelstroms produced by colliding galaxies and merging supermassive black holes, according to some of the most advanced supercomputer simulations ever conducted on this topic.
“We found that gas is essential in driving the co-evolution of galaxies and supermassive black holes,” said Stelios Kazantzidis, a Fellow in the University of Chicago’s Kavli Institute for Cosmological Physics. He and his collaborators published their findings in February on astro-ph, an online repository of astronomical research papers. They also are preparing another study.
The collaboration includes Lucio Mayer from the Swiss Federal Institute of Technology, Zurich, Switzerland; Monica Colpi, University Milano-Bicocca, Italy; Piero Madau, University of California, Santa Cruz; Thomas Quinn, University of Washington; and James Wadsley, McMaster University, Canada. “This type of work became possible only recently thanks to the increased power of supercomputers,” Mayer said. Improvements in the development of computer code that describes the relevant physics also helped, he said.
“The combination of both code and hardware improvement makes it possible to simulate in a few months time what had required several years of computation time only four to five years ago.”
The findings are good news for NASA’s proposed LISA (Laser Interferometer Space Antenna) mission. Scheduled for launch in 2015, LISA’s primary objective is to search the early universe for gravitational waves. These waves, never directly detected, are predicted in Einstein’s theory of general relativity.
“At very early times in the universe there was a lot of gas in the galaxies, and as the Universe evolved the gas was converted into stars,” Kazantzidis said. And large amounts of gas mean more colliding galaxies and merging supermassive black holes. “This is important because LISA is detecting gravitational waves. And the strongest source of gravitational waves in the universe will be from colliding supermassive black holes,” he said.
Many galaxies, including the Milky Way galaxy that contains the sun, harbor supermassive black holes at their center. These black holes are so gravitationally powerful that nothing, including light, can escape their grasp.
Today the Milky Way moves quietly through space by itself, but one day it will collide with its nearest neighbor, the Andromeda galaxy. Nevertheless, the Milky Way served as a handy model for the galaxies in the merging supermassive black hole simulations. Kazantzidis’s team simulated the collisions of 25 galaxy pairs to identify the key factors leading to supermassive black hole mergers.
For these mergers to occur, the host galaxies must merge first. Two gas-poor galaxies may or may not merge, depending on the structure of the galaxies. But whenever gas-rich galaxies collide in the simulations, supermassive black-hole mergers typically followed.
“The more supermassive black holes that you predict will merge, the larger the number of sources that LISA will be able to detect,” Kazantzidis said. As two galaxies begin to collide, the gas they contain loses energy and funnels into their respective cores. This process increases the density and stability of the galactic cores. When these cores merge, the supermassive black holes they host also merge. When these cores become disrupted, their supermassive black holes fail to merge.
Each simulation conducted by Kazantzidis consumed approximately a month of supercomputing time at the University of Zurich, the Canadian Institute for Theoretical Astrophysics, or the Pittsburgh Supercomputing Center.
The simulations are the first to simultaneously track physical phenomena over vastly differing scales of time and space. “The computer can focus most of its power in the region of the system when many things are happening and are happening at a faster pace than somewhere else,” Mayer said.
When galaxies collide, the billions of stars contained in them fly past one another at great distances. But their surrounding gravity fields do interact, applying the cosmic brakes to the two galaxies’ respective journeys. The galaxies separate, but they come back together, again and again for a billion years. At each step in the process, the galaxies lose speed and energy.
“They come closer and closer and closer until the end, when they merge,” Kazantzidis said. The simulations have produced effects that astronomers have observed in telescopic observations of colliding galaxies. Most notable among these is the formation of tidal tails, a stream of stars and gas that is ejected during the collision by the strong tidal forces.
On a smaller scale, astronomers also observe that colliding galaxies display increased nuclear activity as indicated by brighter cores and increased star formation.
Despite the success of the simulations, Kazantzidis and his team still work to improve their results. “It’s a struggle every day to increase the accuracy of the computation,” he said.
Original Source: University of Chicago
Podcast: See the Universe with Gravity Eyes
Arial photograph of LIGO. Image credit: LIGO. Click to enlarge.
In the past, astronomers could only see the sky in visible light, using their eyes as receptors. New technologies extended their vision into different spectra: infrared, ultraviolet, radio waves, x-rays and gamma rays. But what if you had gravity eyes? Einstein predicted that the most extreme objects and events in the Universe should generate gravity waves, and distort space around them. A new experiment called Laser Interferometer Gravitational Wave Observatory (or LIGO) could make the first detection of these gravity waves.
Listen to the interview: Seeing with Gravity Eyes (7.9 MB)
Or subscribe to the Podcast: universetoday.com/audio.xml
What’s a Podcast?
Fraser Cain: All right, so what is a gravity wave?
Dr. Sam Waldman: So a gravity wave can be explained if you remember that mass distorts spacetime. So if you remember the analogy of a sheet pulled taut with a bowling ball tossed into the middle of the sheet, bending the sheet; where the bowling ball is a mass and the sheet represents spacetime. If you move that bowling ball back and forth very rapidly, you’ll make ripples in the sheet. The same thing is true for masses in our Universe. If you move a star back and forth very rapidly, you will make ripples in spacetime. And those ripples in spacetime are observable. We call them gravity waves.
Fraser: Now if I’m walking around the room, is that going to cause gravity waves?
Dr. Waldman: Well it will. As far as we know, gravity works at all scales and for all masses, but spacetime is very stiff. So something like my 200 pound self moving through my office won’t cause gravity waves. What are required are extremely massive objects moving very rapidly. So when we look to detect gravity waves, we’re looking for solar mass scale objects. In particular, we search for neutron stars, which are between 1.5 and 3 solar masses. We look for black holes, up to several hundred solar masses. And we look for these objects to be moving very rapidly. So when we talk about a neutron star, we’re talking about a neutron star moving at almost the speed of light. In fact, it has to be vibrating at the speed of light, it can’t just be moving, it has to be shaking back and forth very rapidly. So, they’re very unique, very massive cataclysmic systems that we’re searching for.
Fraser: Gravity waves are purely theoretical, right? They were predicted by Einstein, but they haven’t been seen yet?
Dr. Waldman: They’ve not been observed, they’ve been inferred. There is a pulsar system whose frequency is spinning down at a rate consistent with the emission of gravity waves. That’s PSR 1913+16. And that the orbit of this star is changing. That’s an inference, but of course, that’s not an observation directly of gravity waves. However, it’s pretty clear that they have to exist. If Einstein’s laws exist, if General Relativity works, and it works very well at very many length scales, then gravity waves exist too. They’re just very difficult to see.
Fraser: What’s it going to take to be able to detect them? It sounds like they’re very cataclysmic events. Great big black holes and neutron stars moving around, why are they so difficult to find?
Dr. Waldman: There’s two components to that. One thing is that black holes don’t collide all the time, and neutron stars don’t shake about in just any old place. So the number of events that can cause observable gravity waves is actually very small. Now we talk about, for example, the Milky Way galaxy with one event occuring every 30-50 years.
But the other part of that equation is that gravity waves themselves are very small. So they introduce what we call a strain; that’s a length change per unit length. For instance, if I have a yardstick one metre long, and a gravity wave will squish that yardstick as it comes through. But the level that it will squish the yardstick is extremely small. If I have a 1-metre yardstick, it will only induce a change of 10e-21 metres. So it’s a very very small change. Of course, observing 10e-21 metres is where the large challenge is in observing a gravity wave.
Fraser: If you were measuring the length of a yardstick with another yardstick, the length of that other yardstick would be changing. I can see that being difficult to do.
Dr. Waldman: Exactly, so you have a problem. The way we solve the yardstick problem is that we actually have 2 yardsticks, and we form them into an L. And the way we measure them is to use a laser. And the way that we have arranged our yardstick is actually in a 4-km long “L”. There’s 2 arms, each one’s 4 km long. And at the end of each arm there’s a 4-kg quartz test mass that we bounce lasers off of. And when a gravity wave comes through this “L” shaped detector, it stretches one leg while it shrinks the other leg. And it does this at say 100 hertz, within audio frequencies. So if you listen to the motion of these masses, you hear a buzzing at 100 hertz. And so what we measure with our lasers is the differential arm length of this large, “L” shaped interferometer. That’s why it’s LIGO. It’s the Laser Interferometer Gravitational-Wave Observatory.
Fraser: Let’s see if I understand this correctly. Billions of years ago a black hole collides with another and generates a bunch of gravity waves. These gravity waves cross the Universe and wash past the Earth. As they go past the Earth, they’re lengthening one of these arms and they’re shrinking the other one, and you can detect this change by that laser bouncing back and forth.
Dr. Waldman: That’s right. The challenge, of course, is that that length change is extremely small. In the case of our 4km interferometers, the length change that we measure right now is 10e-19 metres. And to put a scale on that, the diameter of an atomic nucleus is only 10e-15 metres. So our sensitivity is subatomic.
Fraser: And so what kinds of events should you be able to detect at this point?
Dr. Waldman: So that’s actually a fascinating area. The analogy we like to use is like it’s looking at the Universe with radio waves was to looking at the Universe with telescopes. The things you see are totally different. You’re sensitive to a totally different regime of the Universe. In particular, LIGO is sensitive to these cataclysmic events. We classify our events into 4 broad categories. The first one we call bursts, and that is something like a black hole forming. So a supernova explosion occurs, and so much matter moves so rapidly that it forms black holes, but you don’t know what the gravity waves look like. All you know is that there are gravity waves. So these are things that happen extremely rapidly. They last for 100 milliseconds at the most, and they come about from the formation of black holes.
Another event we look at is when two objects are in orbit with each other, say two neutron stars orbiting each other. Eventually the diameter of that orbit decays. The neutron stars will coalesce, they will fall into each other and form a black hole. And for the very last few orbits, those neutrons stars (keep in mind they’re objects that weigh 1.5 to 3 solar masses), are moving at large fractions of the speed of light; say 10%, 20% of the speed of light. And that motion is a very efficient generator of gravity waves. So that’s what we use as our standard candle. That’s what we think we know exists; we know they’re out there, but we aren’t sure how many of them are going off at any one time. We’re not sure what a neutron star in spiral looks like in radio waves, or x-rays, in optical radiation. So it’s a little bit difficult to calculate exactly how often you’ll see either an in-spiral or a supernova.
Fraser: Now will you be able to detect their direction?
Dr. Waldman: We have two interferometers. In fact we have two sites and three interferometers. One interferometer is in Livingston Louisiana, which is just north of New Orleans. And our other interferometer is in eastern Washington state. Because we have two interferometers, we can do triangulation in the sky. But there is some uncertainty left in where exactly the source is. There are other collaborations in the world that we work with quite closely in Germany, Italy, and Japan, and they also have detectors. So if multiple detectors in multiple sites see a gravity wave, then we can do a very good job in localizing. The hope is that we see a gravity wave and we know where it comes from. We then tell our radio astronomers colleagues and our x-ray astronomer colleagues, and our optical astronomer colleagues to go look at that portion of the sky.
Fraser: There are some new large telescopes on the horizon; overwhelmingly large and gigantically large, and Magellan… the big telescopes coming down the pipe with fairly large budgets to spend. Let’s say that you can reliably find gravity waves, it’s almost like it adds a new spectrum to our detection. If large budgets were put into some of these gravity wave detectors, what do you think they could be used for?
Dr. Waldman: Well, as I said before, it’s like the revolution in astronomy when radio telescopes first came online. We’re looking at a fundimentally different class of phenomena. I should say that the LIGO laboratory is a fairly large laboratory. We’re over 150 scientists working, so it’s a large collaboration. And we hope to collaborate with all of the optical and radio astronomers as we go forward. But it’s a little difficult to predict what path that science will take. I think if you speak to a lot of general relativists, the most exciting feature of gravity waves is that we’re doing something called Strong Field General Relativity. That is all the General Relativity you can measure looking at stars and galaxies is very weak. There’s not a lot of mass involved, it’s not moving very fast. It’s at very large distances. Whereas, when we’re talking about the collision of a black hole and a neutron star, that very last bit, when the neutron star falls into the black hole, is extremely violent and probes a realm of general relativity that just isn’t very accessible with normal telescopes, with radio, with x-ray. So the hope is that there are some fundamentally new and exciting physics there. I think that’s what primarily motivates us is, you could call it, fun with General Relativity.
Fraser: And when do you hope to have your first detection.
Dr. Waldman: So the LIGO interferometers – all three interferometers – that LIGO operates are all running at design sensitivities, and we are currently in the middle of our S5 run; our fifth science run, which is a year-long run. All we do for a year is try to look for gravity waves. As with a lot of things in astronomy, most of it is wait and see. If a supernova doesn’t explode, then we’re not going to see it, of course. And so we have to be online for as long as possible. The probibility of observing an event, like a supernova event, is thought to be in the region of – at our current sensitivity – it’s thought that we’re going to see one every 10-20 years. There’s a large range. In the literature, there are folks who claim that we will see multiple per year, and then there are folks who claim that we won’t see any ever at our sensitivity. And the conservative middle ground is once every 10 years. On the other hand, we’re upgrading our detectors as soon as this run is over. And we’re improving the sensitivity by a factor of 2, which would increase our detection rate by a factor of 2 cubed. Because sensitivity is a radius, and we’re probing a volume in space. With that factor of 8-10 in detection rate, we should be seeing an event once every year or so. And then after that, we’re upgrading to what’s called Advanced LIGO, which is a factor of 10 improvement in sensitivity. In which case we will almost definitely be seeing gravity waves once every day or so; every 2-3 days. That instrument is designed to be a very real tool. We want to do gravity astronomy; to be seeing events every few days. It’ll be like launching the Swift satellite. As soon as Swift went up, we started seeing gamma ray bursts all the time, and Advanced LIGO will be similar.
Neutron Star With a Tail Like a Comet
Supernova remnant IC 443. Image credit: Chandra X-ray. Click to enlarge
This beautiful image shows the supernova remnant IC 443. The area in the box contains what looks like a tiny comet with a tail, but it’s actually a neutron star, moving quickly through the nebula. Neutron stars have been seen moving away from supernova remnants before, but in this case, it’s moving perpendicular. One possibility is that the former star was moving quickly through the galaxy before it exploded. The gas and dust in the nebula have slowed down and drifted away from the neutron star.
The pullout, also a composite with a Chandra X-ray close-up, shows a neutron star that is spewing out a comet-like wake of high-energy particles as it races through space.
Based on an analysis of the swept-back shape of the wake, astronomers deduced that the neutron star known as CXOU J061705.3+222127, or J0617 for short, is moving through the multimillion degree Celsius gas in the remnant. However, this conclusion poses a mystery.
Although there are other examples where neutron stars have been located far away from the center of the supernova remnant, these neutron stars appear to be moving radially away from the center of the remnant. In contrast, the wake of J0617 seems to indicate it is moving almost perpendicularly to that direction.
One possible explanation is that the doomed progenitor star was moving at a high speed before it exploded, so that the explosion site was not at the observed center of the supernova remnant. Fast-moving gusts of gas inside the supernova remnant may have further pushed the pulsar’s wake out of alignment. An analogous situation is observed for comets, where a wind of particles from the Sun pushes the comet tail away from the Sun, out of alignment with the comet’s motion.
If this is what is happening, then observations of the neutron star with Chandra in the next 10 years should show a detectable motion away from the center of the supernova remnant.
Original Source: Chandra X-ray Observatory
Central Peaks of Zucchius Crater
Crater Zucchius captured by SMART-1. Image credit: ESA. Click to enlarge
This is a photograph of the central peaks of crater Zucchius, located on the Moon. ESA’s SMART-1 took the photo while it was about 753 kilometres (468 miles) above the surface of the Moon. The crater was formed in the Copernican era, a period that began 1.2 billion years ago. These central mountains are formed when a large object struck the Moon; the molten rocks splashed up and hardened into this shape.
This image, taken by the advanced Moon Imaging Experiment (AMIE) on board ESA’s SMART-1 spacecraft, shows the central peaks of crater Zucchius.
AMIE obtained this image on 14 January 2006 from a distance of about 753 kilometres from the surface, with a ground resolution of 68 metres per pixel.
The imaged area is centred at a latitude of 61.3 South and longitude 50.8 West. Zucchius is a prominent lunar impact crater located near the southwest limb. It has 66 kilometres diameter, but only its inside is visible in this image, as the AMIE field of view is 35 kilometres from this close-up distance.
Because of its location, the crater appears oblong-shaped due to foreshortening. It lies just to the south-southwest of Segner crater, and northeast of the much larger Bailly walled-plain. To the southeast is the Bettinus crater, a formation only slightly larger than Zucchius.
Zucchius formed in the Copernican era, a period in the lunar planetary history that goes from 1.2 thousand million years ago to present times. Another example of craters from this period are Copernicus (about 800 milion years old) and Tycho (100 million years old). Craters from the Copernican era show characteristic ejecta ray patterns – as craters age, ejecta rays darken due to weathering by the flowing solar wind.
The hills near the centre of the image are the so-called ‘central peaks’ of the crater, features that form in large craters on the Moon. The crater is formed by the impact of a small asteroid onto the lunar surface. The surface is molten and, similarly to when a drop of water falls into a full cup of coffee, the hit surface bounces back, it solidifies and then ‘freezes’ into the central peak.
The name of Zucchius crater is due to the Italian Mathematician and astronomer Niccolo Zucchi (1586-1670).
Original Source: ESA Portal
Podcast: See the Universe with Gravity Eyes
In the past, astronomers could only see the sky in visible light, using their eyes as receptors. New technologies extended their vision into different spectra: infrared, ultraviolet, radio waves, x-rays and gamma rays. But what if you had gravity eyes? Einstein predicted that the most extreme objects and events in the Universe should generate gravity waves, and distort space around them. A new experiment called Laser Interferometer Gravitational Wave Observatory (or LIGO) could make the first detection of these gravity waves.
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