Category: Astronomy

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

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

Reflection nebula IC4954. Image credit: ESA. Click to enlarge
Japan’s newly launched AKARI spacecraft took its first images on April 13, 2006, testing out its scientific instruments. AKARI (formally known as ASTRO-F) used its Far Infrared Surveyor and near-mid-infrared camera to make a survey of the entire sky in 6 infrared wavebands. It was then pointed towards the reflection nebula IC4954, and was able to distinguish newly born stars. The space observatory is now entering its first mission phase, which will last about 6 months.

AKARI, the new Japanese infrared sky surveyor mission in which ESA is participating, saw ‘first light’ on 13 April 2006 (UT) and delivered its first images of the cosmos. The images were taken towards the end of a successful checkout of the spacecraft in orbit.

The mission, formerly known as ASTRO-F, was launched on 21 February 2006 (UT) from the Uchinoura Space Centre in Japan. Two weeks after launch the satellite reached its final destination in space – a polar orbit around Earth located at an altitude of approximately 700 kilometres.

On 13 April, during the second month of the system checkout and verification of the overall satellite performance, the AKARI telescope’s aperture lid was opened and the on-board two instruments commenced their operation. These instruments – the Far Infrared Surveyor (FIS) and the near-mid-infrared camera (IRC) – make possible an all-sky survey in six infrared wavebands. The first beautiful images from the mission have confirmed the excellent performance of the scientific equipment beyond any doubt.

AKARI’s two instruments were pointed toward the reflection nebula IC4954, a region situated about 6000 light years away, and extending more than 10 light years across space. Reflection nebulae are clouds of dust which reflect the light of nearby stars. In these infrared images of IC4954 ? a region of intense star formation active for several million years – it is possible to pick out individual stars that have only recently been born. They are embedded in gas and dust and could not be seen in visible light. It is also possible to see the gas clouds from which these stars were actually created.

“These beautiful views already show how, thanks to the better sensitivity and improved spatial resolution of AKARI, we will be able to discover and study fainter sources and more distant objects which escaped detection by the previous infrared sky-surveyor, IRAS, twenty years ago,” says Pedro García-Lario, responsible for ‘pointing reconstruction’ – a vital part of the AKARI data processing – at ESA’s European Space Astronomy Centre (ESAC), Spain. “With the help of the new infrared maps of the whole sky provided by AKARI we will be able to resolve for the first time heavily obscured sources in crowded stellar fields like the centre of our Galaxy,” he continued.

With its near-mid-infrared camera, AKARI also imaged the galaxy M81 at six different wavelengths. M81 is a spiral galaxy located about 12 million light years away. The images taken at 3 and 4 microns show the distribution of stars in the inner part of the galaxy, without any obscuration from the intervening dust clouds. At 7 and 11 microns the images show the radiation from organic materials (carbon-bearing molecules) in the interstellar gas of the galaxy. The distribution of the dust heated by young hot stars is shown in the images at 15 and 24 microns, showing that the star forming regions sit along the spiral arms of the galaxy.

“It’s a feeling of tremendous accomplishment for all of us involved in the AKARI project to finally see the fruits of the long years of labour in these amazing new infrared images of our Universe,” said Chris Pearson, ESA astronomer located at ISAS and involved with AKARI since 1997, “We are now eagerly waiting for the next ‘infrared revelation’ about the origin and evolution of stars, galaxies and planetary systems.”

Having concluded all in-orbit checks, AKARI is now entering the first mission phase. This will last about six months and is aimed at performing a complete survey of the entire infrared sky. This part of the mission will then be followed by a phase during which thousands of selected astronomical targets will be observed in detail. During this second phase, as well as in the following third phase in which only the infrared camera will be at work, European astronomers will have access to ten percent of the overall pointed observation opportunity.

“The user support team at ESAC are enthusiastic about the first images. They show that we can expect a highly satisfactory return for the European observing programme,” said Alberto Salama, ESA Project Scientist for AKARI. “Furthermore, the new data will be of enormous value to plan follow-up observations of the most interesting celestial objects with ESA’s future infrared observatory, Herschel,” he concluded.

Original Source: ESA News Release

An illustartion of an early dwarf galaxy surrounded by red hydrogen gas. Image credit: David A. Aguilar/CfA. Click to enlarge
Shortly after the Big Bang, large clouds of hydrogen collapsed easily into the first galaxies and stars. These weren’t stars like our Sun; however, they were hot, massive and very short lived – blasting their environment with ultraviolet radiation. But after the first 100 million years of the Universe, it became very difficult for these dwarf galaxies to grow any larger as this radiation sabotaged further growth. Only the gravity of the largest galaxies could overcome this heat and pressure to grow into larger galaxies over time.

The first galaxies were small – about 10,000 times less massive than the Milky Way. Billions of years ago, those mini-furnaces forged a multitude of hot, massive stars. In the process, they sowed the seeds for their own destruction by bathing the universe in ultraviolet radiation. According to theory, that radiation shut off further dwarf galaxy formation by both ionizing and heating surrounding hydrogen gas. Now, astronomers Stuart Wyithe (University of Melbourne) and Avi Loeb (Harvard-Smithsonian Center for Astrophysics) are presenting direct evidence in support of this theory.

Wyithe and Loeb showed that fewer, larger galaxies, rather than more numerous, smaller galaxies, dominated the billion-year-old universe. Dwarf galaxy formation essentially shut off only a few hundred million years after the Big Bang.

“The first dwarf galaxies sabotaged their own growth and that of their siblings,” says Loeb. “This was theoretically expected, but we identified the first observational evidence for the self-destructive behavior of early galaxies.”

Their research is being reported in the May 18, 2006 issue of Nature.

Nearly 14 billion years ago, the Big Bang filled the universe with hot matter in the form of electrons and hydrogen and helium ions. As space expanded and cooled, electrons and ions combined to form neutral atoms. Those atoms efficiently absorbed light, yielding a pervasive dark fog throughout space. Astronomers have dubbed this era the “Dark Ages.”

The first generation of stars began clearing that fog by bathing the universe in ultraviolet radiation. UV radiation splits atoms into negatively charged electrons and positively charged ions in a process called ionization. Since the Big Bang created an ionized universe that later became neutral, this second phase of ionization by stars is known as the “epoch of reionization.” It took place in the first few hundred million years of existence.

“We want to study this time period because that’s when the primordial soup evolved into the rich zoo of objects we now see,” said Loeb.

During this key epoch in the history of the universe, gas was not only ionized, but also heated. While cool gas easily clumps together to form stars and galaxies, hot gas refuses to be constrained. The hotter the gas, the more massive a galactic “seed” must be to attract enough matter to become a galaxy.

Before the epoch of reionization, galaxies containing only 100 million solar masses of material could form easily. After the epoch of reionization, galaxies required more than 10 billion solar masses of material to be assembled.

To determine typical galaxy masses, Wyithe and Loeb looked at light from quasars – powerful light sources visible across vast distances. The light from the farthest known quasars left them nearly 13 billion years ago, when the universe was a fraction of its present age. Quasar light is absorbed by intervening clouds of hydrogen associated with early galaxies, leaving telltale bumps and wiggles in the quasar’s spectrum.

By comparing the spectra of different quasars along different lines of sight, Wyithe and Loeb determined typical galaxy sizes in the infant universe. The presence of fewer, larger galaxies leads to more variation in the absorption seen along various lines of sight. Statistically, large variation is exactly what Wyithe and Loeb found.

“As an analogy, suppose you are in a room where everybody is talking,” explains Wyithe. “If this room is sparsely populated, then the background noise is louder in some parts of the room than others. However if the room is crowded, then the background noise is the same everywhere. The fact that we see fluctuations in the light from quasars implies that the early universe was more like the sparse room than the crowded room.”

Astronomers hope to confirm the suppression of dwarf galaxy formation using the next generation of telescopes – both radio telescopes that can detect distant hydrogen and infrared telescopes that can directly image young galaxies. Within the next decade, researchers using these new instruments will illuminate the “Dark Ages” of the universe.

Headquartered in Cambridge, Mass., the Harvard-Smithsonian Center for Astrophysics (CfA) is a joint collaboration between the Smithsonian Astrophysical Observatory and the Harvard College Observatory. CfA scientists, organized into six research divisions, study the origin, evolution and ultimate fate of the universe.

Original Source: CfA News Release

Clusters of galaxies as seen by XMM-Newton. Image credit: ESA. Click to enlarge
Galaxy clusters are the largest objects in the Universe. Each cluster can contain hundreds or even thousands of galaxies held together by gravity. These clusters are filled with hot gas, emitting a tremendous amount of X-ray radiation. ESA’s XMM-Newton observatory recently watched two galaxy clusters enabling astronomers to learn that these clusters have higher quantities of Type 1a supernovae – exploding white dwarf stars – than our own galaxy.

Deep observations of two X-ray bright clusters of galaxies with ESA’s XMM-Newton satellite allowed a group of international astronomers to measure their chemical composition with an unprecedented accuracy. Knowing the chemical composition of galaxy clusters is of crucial importance to understanding the origin of chemical elements in the Universe.

Clusters, or conglomerates, of galaxies are the largest objects in the Universe. By looking at them through optical telescopes it is possible to see hundreds or even thousands of galaxies occupying a volume a few million light years across. However, such telescopes only reveal the tip of the iceberg. In fact most of the atoms in galaxy clusters are in the form of hot gas emitting X-ray radiation, with the mass of the hot gas five times larger than the mass in the cluster’s galaxies themselves.

Most of the chemical elements produced in the stars of galaxy clusters – expelled into the surrounding space by supernova explosions and by stellar winds – become part of the hot X-ray emitting gas. Astronomers divide supernovae into two basic types: ‘core collapse’ and ‘Type Ia’ supernovae. The ‘core collapse’ supernovae originate when a star at the end of its life collapses into a neutron star or a black hole. These supernovae produce lots of oxygen, neon and magnesium. The Type Ia supernovae explode when a white dwarf star consuming matter from a companion star becomes too massive and completely disintegrates. This type produces lots of iron and nickel.

Respectively in November 2002 and August 2003, and for one and a half day each time, XMM-Newton’s made deep observations of the two galaxy clusters called ‘Sersic 159-03’ and ‘2A 0335+096’. Thanks to these data the astronomers could determine the abundances of nine chemical elements in the clusters ‘plasma’ ??bf? a gas containing charged particles such as ions and electrons.

These elements include oxygen, iron, neon, magnesium, silicon, argon, calcium, nickel, and – detected for the first time ever in a galaxy cluster – chromium. “Comparing the abundances of the detected elements to the yields of supernovae calculated theoretically, we found that about 30 percent of the supernovae in these clusters were exploding white dwarfs (‘Type Ia’) and the rest were collapsing stars at the end of their lives (‘core collapse’),” said Norbert Werner, from the SRON Netherlands Institute for Space Research (Utrecht, Netherlands) and one of the lead authors of these results.

“This number is in between the value found for our own Galaxy (where Type Ia supernovae represent about 13 percent of the supernovae ‘population’) and the current frequency of supernovae events as determined by the Lick Observatory Supernova Search project (according to which about 42 percent of all observed supernovae are Type Ia),” he continued.

The astronomers also found that all supernova models predict much less calcium than what is observed in clusters and that the observed nickel abundance cannot be reproduced by these models. These discrepancies indicate that that the details of supernova enrichment is not yet clearly understood. Since clusters of galaxies are believed to be fair samples of the Universe, their X-ray spectroscopy can help to improve the supernova models.

The spatial distribution of elements across a cluster also holds information about the history of clusters themselves. The distribution of elements in 2A 0335+096 indicates an ongoing merger. The distribution of oxygen and iron across Sersic 159-03 indicates that while most of the enrichment by the core collapse supernovae happened long time ago, Type Ia supernovae still continue to enrich the hot gas by heavy elements especially in the core of the cluster.

Original Source: ESA Portal

Spiral galaxy NGC 3190. Image credit: ESO. Click to enlarge
Supernovae are rare enough, but astronomers discovered two going off in galaxy NGC 3190 at the same time. NGC 3190 is a large spiral galaxy that we see nearly edge on. Its shape has been warped through interactions between other nearby galaxies, and it has an active galactic nucleus. Astronomers uncovered one supernova in the southeastern part in March 2002, and then another team uncovered a second supernova on the other side two months later. This photograph of NGC 3190 was taken by ESO’s Very Large Telescope.

his beautiful edge-on spiral galaxy with tightly wound arms and a warped shape that makes it resemble a gigantic potato crisp lies in the constellation Leo (‘the Lion’) and is approximately 70 million light years away. It is the dominant member of a small group of galaxies known as Hickson 44, named after the Canadian astronomer, Paul Hickson. In addition to NGC 3190, Hickson 44 consists of one elliptical and two spiral galaxies. These are, however, slightly out of the field of view and therefore not visible here.

In 1982, Hickson published a catalogue of over 400 galaxies found in compact, physically-related groups of typically 4 to 5 galaxies per group (see the image of Robert’s Quartet in ESO PR Photo 34/05 as another example). Such compact groups allow astronomers to study how galaxies dynamically affect each other, and help them test current ideas on how galaxies form. One idea is that compact groups of galaxies, such as Hickson 44, merge to form a giant elliptical galaxy, such as NGC 1316 (see ESO PR 17/00).

Indeed, signs of tidal interactions are visible in the twisted dust lane of NGC 3190. This distortion initially misled astronomers into assigning a separate name for the southwestern side, NGC 3189, although NGC 3190 is the favoured designation.

NGC 3190 has an ‘Active Galactic Nucleus’, and as such, the bright, compact nucleus is thought to host a supermassive black hole.

In March 2002, a new supernova (SN 2002bo) was found in between the ‘V’ of the dust lanes in the southeastern part of NGC 3190. It was discovered independently by the Brazilian and Japanese amateur astronomers, Paulo Cacella and Yoji Hirose. SN 2002bo was caught almost two weeks before reaching its maximum brightness, allowing astronomers to study its evolution. It has been the subject of intense monitoring by a world-wide network of telescopes. The conclusion was that SN 2002bo is a rather unusual Type Ia supernova. The image presented here was taken in March 2003, i.e. about a year after the maximum of the supernova which is 50 times fainter on the image than a year before.

While observing SN 2002bo in May 2002, a group of Italian astronomers discovered another supernova, SN 2002cv, on the other side of NGC 3190. Two supernovae of this type appearing nearly simultaneously in the same galaxy is a rare event, as normally astronomers expect only one such event per century in a galaxy. SN 2002cv was best visible at infrared wavelengths as it was superimposed on the dust lane of NGC 3190, and therefore hidden by a large quantity of dust. In fact, this supernova holds the record for the most obscured Type Ia event.

The image was obtained with a total exposure time of 14 minutes only. Yet, with the amazing power of the Very Large Telescope, it reveals a large zoo of galaxies of varying morphologies. How many can you find?

Original Source: ESO News Release

NASA’s Swift captured this image of 73P/Schwassmann-Wachmann 3 as it bypassed the Ring Nebula. Image credit: NASA. Click to enlarge
Comet 73P/Schwassmann-Wachmann 3 is visible in the night sky with even a small backyard telescope, and it will make its closest approach to Earth next week (don’t worry, it’s still really far away). One of the features of this comet, however, is that it’s unusually bright in the X-ray spectrum. Three X-ray observatories will observe the comet in the coming weeks to determine what it’s made of, and maybe even the composition of the solar wind that causes its tail.

Scientists using NASA’s Swift satellite have detected X-rays from a comet that is now passing the Earth and rapidly disintegrating on what could be its final orbit around the sun.

Swift’s observations provide a rare opportunity to investigate several ongoing mysteries about comets and our solar system, and hundreds of scientists have tuned in to the event.

The comet, called 73P/Schwassmann-Wachmann 3, is visible with even a small, backyard telescope. Peak brightness is expected next week, when it comes within 7.3 million miles of Earth, or about 30 times the distance to the Moon. There is no threat to Earth, however.

This is the brightest comet ever detected in X-rays. The comet is so close that astronomers are hoping to determine not only the composition of the comet but also of the solar wind. Scientists think that atomic particles that comprise the solar wind interact with comet material to produce X-rays, a theory that Swift might prove true.

Three world-class X-ray observatories now in orbit—NASA’s Chandra X-ray Observatory, the European-led XMM-Newton, and the Japanese-led Suzaku—will observe the comet in the coming weeks. Like a scout, Swift has provided information to these larger facilities about what to look for. This type of observation can only take place in the X-ray waveband.

“The Schwassmann-Wachmann comet is a comet like no other,” said Scott Porter of NASA’s Goddard Space Flight Center in Greenbelt, Md., part of the Swift observation team. “During its 1996 passage it broke apart. Now we are tracking about three dozen fragments. The X-rays being produced provide information never before revealed.”

The situation is reminiscent of the Deep Impact probe, which penetrated comet Tempel 1 about a year ago. This time, nature itself has broken the comet. Because Schwassmann-Wachmann 3 is much closer to both the Earth and the sun than Tempel 1 was, it currently appears about 20 times brighter in X-rays. Schwassmann-Wachmann 3 passes Earth about every five years. Scientists could not anticipate how bright it would become in X-rays this time around.

“The Swift observations are amazing,” said Greg Brown of Lawrence Livermore National Laboratory in Livermore, Calif., who led the proposal for Swift observation time. “Because we are viewing the comet in X-rays, we can see many unique features. The combined results of data from several premier orbiting observatories will be spectacular.”

Swift is primarily a gamma-ray burst detector. The satellite also has X-ray and ultraviolet/optical telescopes. Because of its burst-hunting ability to turn rapidly, Swift has been able to track the progress of the fast-moving Schwassmann-Wachmann 3 comet. Swift is the first observatory to simultaneously observe the comet in both ultraviolet light and X-rays. This cross comparison is crucial for testing theories about comets.

Swift and the other three X-ray observatories plan to combine forces to observe Schwassmann-Wachmann 3 closely. Through a technique called spectroscopy, scientists hope to determine the chemical structure of the comet. Already Swift has detected oxygen and hints of carbon. These elements are from the solar wind, not the comet.

Scientists think that X-rays are produced through a process called charge exchange, in which highly (and positively) charged particles from the sun that lack electrons steal electrons from chemicals in the comet. Typical comet material includes water, methane and carbon dioxide. Charge exchange is analogous to the tiny spark seen in static electricity, only at a far greater energy.

By comparing the ratio of X-ray energies emitted, scientists can determine the content of the solar wind and infer the content of the comet material. Swift, Chandra, XMM-Newton and Suzaku each provide complementary capabilities to nail down this tricky measurement. The combination of these observations will provide a time evolution of the X-ray emission of the comet as it navigates through our solar system.

Porter and his colleagues at Goddard and Lawrence Livermore tested the charge exchange theory in an earthbound laboratory in 2003. That experiment, at Livermore’s EBIT-I electron beam ion trap, produced a complex spectrograph of intensity versus X-ray energy for a variety of expected elements in the solar wind and comet. “We are anxious to compare nature’s laboratory to the one we created,” Porter said.

The German-led ROSAT mission, now decommissioned, was the first to detect X-rays from a comet, from Hyakutake in 1996. This was a great surprise. It took about five years before scientists had a suitable explanation for X-ray emission. Now, ten years after Hyakutake, scientists could settle the mystery.

Original Source: NASA News Release

A schematic view of the new SDSS three-dimensional map. Image credit: Hogg/SDSS-II collaboration. Click to enlarge
Astronomers from UC Berkeley have created the most comprehensive three-dimensional map of the Universe ever published. Amazingly, this map is merely a slice containing 1/10th of the northern hemisphere. It contains 600,000 galaxies and extends out 5.6 billion light-years into space. This map allows astronomers to study evidence for dark energy – the mysterious force accelerating the expansion of the Universe.

A team of astronomers led by Nikhil Padmanabhan and David Schlegel has published the largest three-dimensional map of the universe ever constructed, a wedge-shaped slice of the cosmos that spans a tenth of the northern sky, encompasses 600,000 uniquely luminous red galaxies, and extends 5.6 billion light-years deep into space, equivalent to 40 percent of the way back in time to the Big Bang.

Schlegel is a Divisional Fellow in the Physics Division of Lawrence Berkeley National Laboratory, and Padmanabhan will join the Lab’s Physics Division as a Chamberlain Fellow and Hubble Fellow in September; presently he is at Princeton University. They and their coauthors are members of the Sloan Digital Sky Survey (SDSS), and have previously produced smaller 3-D maps by using the SDSS telescope in New Mexico to painstakingly collect the spectra of individual galaxies and calculate their distances by measuring their redshifts.

“What’s new about this map is that it’s the largest ever,” says Padmanabhan, “and it doesn’t depend on individual spectra.”

The principal motive for creating large-scale 3-D maps is to understand how matter is distributed in the universe, says Padmanabhan. “The brightest galaxies are like lighthouses – where the light is, is where the matter is.”

Schlegel says that “because this map covers much larger distances than previous maps, it allows us to measure structures as big as a billion light-years across.”

The variations in galactic distribution that constitute visible large-scale structures are directly descended from variations in the temperature of the cosmic microwave background, reflecting oscillations in the dense early universe that have been measured to great accuracy by balloon-borne experiments and the WMAP satellite.

The result is a natural “ruler” formed by the regular variations (sometimes called “baryon oscillations,” with baryons as shorthand for ordinary matter), which repeat at intervals of some 450 million light-years.

“Unfortunately it’s an inconveniently sized ruler,” says Schlegel. “We had to sample a huge volume of the universe just to fit the ruler inside.”

Says Padmanabhan, “Although the universe is 13.7 billion years old, that really isn’t a whole lot of time when you’re measuring with a ruler that’s marked only every 450 million light-years.”

The distribution of galaxies reveals many things, but one of the most important is a measure of the mysterious dark energy that accounts for some three-fourths of the universe’s density. (Dark matter accounts for roughly another 20 percent, while less than 5 percent is ordinary matter of the kind that makes visible galaxies.)

“Dark energy is just the term we use for our observation that the expansion of the universe is accelerating,” Padmanabhan remarks. “By looking at where density variations were at the time of the cosmic microwave background” – only about 300,000 years after the Big Bang – “and seeing how they evolve into a map that covers the last 5.6 billion years, we can see if our estimates of dark energy are correct.”

The new map shows that the large-scale structures are indeed distributed the way current ideas about the accelerating expansion of the universe would suggest. The map’s assumed distribution of dark matter, which although invisible is affected by gravity just like ordinary matter, also conforms to current understanding.

What made the big new 3-D map possible were the Sloan Digital Sky Survey’s wide-field telescope, which covers a three-degree field of view (the full moon is about half a degree), plus the choice of a particular kind of galactic “lighthouse,” or distance marker: luminous red galaxies.

“These are dead, red galaxies, some of the oldest in the universe – in which all the fast-burning stars have long ago burned out and only old red stars are left,” says Schlegel. “Not only are these the reddest galaxies, they’re also the brightest, visible at great distances.”

The Sloan Digital Sky Survey astronomers worked with colleagues on the Australian Two-Degree Field team to average the color and redshift of a sample of 10,000 red luminous galaxies, relating galaxy color to distance. They then applied these measurements to 600,000 such galaxies to plot their map.

Padmanabhan concedes that “there’s statistical uncertainty in applying a brightness-distance relation derived from 10,000 red luminous galaxies to all 600,000 without measuring them individually. The game we play is, we have so many that the averages still give us very useful information about their distribution. And without having to measure their spectra, we can look much deeper into space.”

Schlegel agrees that the researchers are far from achieving the precision they want. “But we have shown that such measurements are possible, and we have established the starting point for a standard ruler of the evolving universe.”

He says “the next step is to design a precision experiment, perhaps based on modifications to the SDSS telescope. We are working with engineers here at Berkeley Lab to redesign the telescope to do what we want to do.”

“The Clustering of Luminous Red Galaxies in the Sloan Digital Sky Survey Imaging Data,” by Nikhil Padmanabhan, David J. Schlegel, Uros Seljak, Alexey Makarov, Neta A. Bahcall, Michael R. Blanton, Jonathan Brinkmann, Daniel J. Eisenstein, Douglas P. Finkbeiner, James E. Gunn, David W. Hogg, ??bf?eljko Ivezić, Gillian R. Knapp, Jon Loveday, Robert H. Lupton, Robert C. Nichol, Donald P. Schneider, Michael A. Strauss, Max Tegmark, and Donald G. York, will appear in the Monthly Notices of the Royal Astronomical Society and is now available online at http://arxiv.org/archive/astro-ph.

SDSS is managed by the Astrophysical Research Consortium for the Participating Institutions, which are the American Museum of Natural History, Astrophysical Institute Potsdam, University of Basel, Cambridge University, Case Western Reserve University, University of Chicago, Drexel University, Fermilab, the Institute for Advanced Study, the Japan Participation Group, Johns Hopkins University, the Joint Institute for Nuclear Astrophysics, the Kavli Institute for Particle Astrophysics and Cosmology, the Korean Scientist Group, the Chinese Academy of Sciences (LAMOST), Los Alamos National Laboratory, the Max-Planck-Institute for Astronomy (MPIA), the Max-Planck-Institute for Astrophysics (MPA), New Mexico State University, Ohio State University, University of Pittsburgh, University of Portsmouth, Princeton University, the United States Naval Observatory, and the University of Washington.

SDSS funding is provided by the Alfred P. Sloan Foundation, the Participating Institutions, the National Science Foundation, the U.S. Department of Energy, the National Aeronautics and Space Administration, the Japanese Monbukagakusho, the Max Planck Society, and the Higher Education Funding Council for England. Visit the SDSS web site at http://www.sdss.org/.

Berkeley Lab is a U.S. Department of Energy national laboratory located in Berkeley, California. It conducts unclassified scientific research and is managed by the University of California. Visit our website at http://www.lbl.gov.

Original Source: Berkeley Lab

The Ant Nebula. Image credit: NASA/STScI. Click to enlarge
These photographs are composite images of various planetary nebulae created out of data from the Hubble Space Telescope and Chandra X-Ray Observatory. The Chandra data (in blue) shows the X-ray view while Hubble (red and green) reveals the optical view. As a massive star nears the end of its life, it expels material to surround itself in a dusty shroud. The intense ultraviolet radiation from the star heats up the material and forces it away at extremely high speeds. This creates the unusual shapes we see from Earth.

This panel of composite images shows part of the unfolding drama of the last stages of the evolution of sun-like stars. Dynamic elongated clouds envelop bubbles of multimillion degree gas produced by high-velocity winds from dying stars. In these images, Chandra’s X-ray data are shown in blue, while green and red are optical and infrared data from Hubble.

Planetary nebulas – so called because some of them resemble a planet when viewed through a small telescope – are produced in the late stages of a sun-like star’s life. After several billion years of stable existence (the sun is 4.5 billion years old and will not enter this phase for about 5 billion more years) a normal star will expand enormously to become a bloated red giant. Over a period of a few hundred thousand years, much of the star’s mass is expelled at a relatively slow speed of about 50,000 miles per hour.

This mass loss creates a more or less spherical cloud around the star and eventually uncovers the star’s blazing hot core. Intense ultraviolet radiation from the core heats the circumstellar gas to ten thousand degrees, and the velocity of the gas flowing away from the star jumps to about a million miles per hour.

This high speed wind appears to be concentrated into opposing supersonic funnels, and produces the elongated shapes in the early development of planetary nebulas (BD+30-3639 appears spherical, but other observations indicate that it is viewed along the pole.) Shock waves generated by the collision of the high-speed gas with the surrounding cloud create the hot bubbles observed by Chandra. The origin of the funnel-shaped winds is not understood. It may be related to strong, twisted magnetic fields near the hot stellar core.

Original Source: Chandra X-Ray Observatory