Category: Astronomy

Distant clusters of galaxies. Image credit: NASA/JPL-Caltech. Click to enlarge
NASA’s Spitzer Space Telescope has turned up 300 galaxy clusters at extreme distances; 8 – 10 billion light-years away. Galaxy clusters have been seen at extreme distances before, but never so many. This gives astronomers the ability to study their formation and evolution with many different examples. The discovery was made by combining images from Spitzer and optical light telescopes, to identify which galaxies are relatively nearby, and which are more distant.

A team of astronomers using NASA’s Spitzer Space Telescope has discovered a grand total of nearly 300 clusters of galaxies. Almost 100 of these are as far as 8 to 10 billion light-years away, which means they date back to a time when our universe was less than one-third its present age.

Galaxy clusters are the universe’s high-density environments, similar to cities on Earth. A single galaxy cluster can contain hundreds of galaxies like our own Milky Way.

“At this distance, we are literally looking at these galaxies as they were over 8 billion years ago,” said Dr. Mark Brodwin of NASA’s Jet Propulsion Laboratory in Pasadena, Calif., who co-led the discovery. “It’s like being able to take a picture of Rome during the peak of the Roman Empire.”

Brodwin presented the results today at the 208th meeting of the American Astronomical Society in Calgary, Canada.

Such observations should lead researchers to a better understanding of how massive galaxies form and evolve. “The oldest and most massive galaxies in the universe live in clusters,” said co-discoverer Dr. Anthony Gonzalez of the University of Florida, Gainesville. “This sample is exciting because, for the first time, we are able to look at these massive cluster galaxies while they are still forming and better understand when they formed their stars.”

While galaxy clusters have previously been found at similar distances, this is the first time that so many clusters have been detected so far away. In December of 2005 and March of 2006, the team reported finding two galaxy clusters located 9.1 and 8.2 billion light-years away, respectively. Today, they announced the discovery of 290 clusters of varying distances, some of which are referred to as galaxy “groups” because they contain fewer members. The nearly 100 distant clusters and groups belonging to this sample represent a six-fold increase over what was previously known.

According to the astronomers, the key to their success was a combination of infrared and optical imaging from Spitzer and Kitt Peak National Observatory in Arizona. The distant galaxies making up the clusters light up in the infrared images, but they cannot be distinguished from other galaxies lying between us and them. By combining the Spitzer images with those from Kitt Peak showing mainly the intervening galaxies, the scientists were able to isolate the distant ones. Finding the clusters of distant galaxies then becomes simply a matter of looking for dense clumps of distant objects.

“Distant galaxies show up best in infrared because during the billions of years it takes to reach us, their light expands along with the universe to longer, infrared wavelengths,” said team member Dr. Peter Eisenhardt of JPL, who led the Spitzer observations.

“With Spitzer, we were able to make deep infrared maps thousands of times faster than with the biggest ground-based telescopes, covering enough sky to find these relatively rare clusters. By adding the deep Kitt Peak optical maps, we could weed out all the galaxies cluttering up the view between us and these distant clusters.”

So far, the distances to seven of the farthest clusters identified have been confirmed using detailed data from the W.M. Keck Observatory in Mauna Kea, Hawaii.

The team will continue to study these ancient galactic cities using Spitzer and NASA’s Hubble Space Telescope. They hope to begin tackling two major questions: just how big are these cities, and how do they grow?

Brodwin is a native of Canada from Montreal. Other team members include: Dr. Adam Stanford of the University of California at Davis; Dr. Daniel Stern of JPL; Drs. Buell Jannuzi and Arjun Dey of the National Optical Astronomy Observatory, Tucson, Ariz.; and Dr. Michael J. I. Brown of Princeton University, Princeton, New Jersey.

JPL manages the Spitzer Space Telescope mission for NASA’s Science Mission Directorate, Washington. Science operations are conducted at the Spitzer Science Center at the California Institute of Technology in Pasadena. Spitzer’s infrared array camera, which observed the galaxy clusters, was built by NASA’s Goddard Space Flight Center, Greenbelt, Md. The instrument’s principal investigator is Dr. Giovanni Fazio of the Harvard-Smithsonian Center for Astrophysics.

Kitt Peak National Observatory, part of the National Optical Astronomy Observatory, is funded by the National Science Foundation and located on the land of the Tohono O’odham Nation.

Original Source: Spitzer Space Telescope

The massive cluster Abell 2218. Image credit: JHU/STScI. Click to enlarge
When regular telescopes aren’t powerful enough, astronomers turn to gravitational lenses; natural telescopes that can peer back to earliest times in the Universe. An international team of astronomers recently demonstrated this technique with Hubble. They can see how infant galaxies looked only a billion years after the Big Bang.

Using massive clusters of galaxies as “cosmic telescopes,” a research team led by a Johns Hopkins University astronomer has found what may be infant galaxies born in the first billion years after the beginning of the universe.

If these findings are confirmed, the extra magnification provided by these gargantuan natural telescopes will have given astronomers their best-ever view of galaxies as they formed in the early universe, more than 12 billion years ago, said Holland Ford, a professor in the Henry A. Rowland Department of Physics and Astronomy at the university’s Krieger School of Arts and Sciences. Ford is the head of the Hubble Space Telescope’s Advanced Camera for Surveys Science Team, which also includes researchers from the Space Telescope Science Institute, PUC in Chile, and other universities around the world.

Ford announced the team’s results this morning at the American Astronomical Society meeting in Calgary, Alberta, Canada. The team’s spectroscopic observations were made possible, he said, by gravitational lensing, the bending of light caused by gravity’s warping of space in the presence of such massive objects as clusters of galaxies.

“One of Einstein’s most startling predictions was that a gravitation field can be thought of as a distortion of space and time,” Ford said. “Gravitational lensing by massive clusters of galaxies that have about 1 million billion times more mass than the sun provide one of the most striking confirmations of Einstein’s prediction.”

Our view of distant galaxies behind a cluster can be magnified by amounts that vary from barely detectable to as many as 50 or 100 times normal size, depending on the location of the galaxy and the distribution of mass within the cluster, Ford said. The clusters are, in effect, giant cosmic telescopes that allow astronomers to find and study distant galaxies that otherwise would be too faint to study.

“Astronomers want to know when the first galaxies formed, how large and how bright galaxies are at birth, and how galaxies grow into large mature galaxies like our home Milky Way galaxy,” Ford said. “Our team is searching for infant galaxies that are less than a billion years old by comparing images of strongly lensing clusters taken by the Hubble Space Telescope with images of the same clusters taken by the Magellan, the Very Large Telescopes (VLT), and Gemini telescopes. The infant galaxies are so far away their light is almost or entirely redshifted to wavelengths that cannot be detected with Hubble’s Advanced Camera for Surveys, but can be detected with infrared detectors on the world’s largest telescopes.”

Using this technique, the ACS team has searched for infant galaxies behind 14 lensing clusters. If longer spectroscopic observations of the three brightest candidate galaxies confirm that they are indeed in the early universe, these galaxies will provide astronomers their clearest view yet of the youngest galaxies ever seen.

Today’s presentation is based on the AAS Abstract 66.03 “Bright Candidates of Galaxies at Redshift 7-8 in the ACS Cluster Fields” by Wei Zheng, H. Ford, L. Infante, V. Motta, M. Postman, and the ACS Science Team. (Johns Hopkins University, PUC, Chile, Space Telescope Science Institute.)

The ACS was developed under NASA contract NAS5-32865, and this research was supported by NASA grant NAG5-7697. These results are based on observations collected at the European Southern Observatory, Chile; the Las Campanas Magellan Telescopes in Chile; and Gemini North, a telescope operated by the Gemini Observatory/Association of Universities for Research in Astronomy.

Original Source: JHU News Release

An artist’s impression of a miniature solar system circling a planemos. Image credit: Jon Lomberg. Click to enlarge
Instead of forming around a star, planets and moons could collect around objects not much bigger than Jupiter; redefining the concept of a solar system. New research by an international team of astronomers suggests that these “planemos” could form out of gas and dust, and then freely float through space – without a parent star. Astronomers have turned up a few potential examples, including a planet with 8x the mass of Jupiter that has its own disk.

Forget our traditional ideas of where a planetary system forms – new research led by a University of Toronto astronomer reveals that planetary nurseries can exist not only around stars but also around objects that are themselves not much heftier than Jupiter. It suggests that miniature versions of the solar system may circle objects that are some 100 times less massive than our sun.

That’s the dramatic conclusion of two studies being presented today at the American Astronomical Society meeting in Calgary by Professor Ray Jayawardhana and his colleagues. The new findings show that objects only a few times more massive than Jupiter are born with disks of dust and gas, the raw material for planet making. Research done by Jayawardhana’s group and others in recent years had shown that disks are common around failed stars known as “brown dwarfs”. Now, they report, the same appears to be true for their even punier cousins, sometimes called planetary mass objects or “planemos.” These objects, discovered within the past five years, have masses similar to those of extra-solar planets, but they are not in orbit around stars – instead, they float freely through space.

“Now that we know of these planetary mass objects with their own little infant planetary systems, the definition of the word ‘planet’ has blurred even more,” says Jayawardhana, an associate professor of astronomy and astrophysics. “In a way, the new discoveries are not too surprising – after all, Jupiter must have been born with its own disk, out of which its bigger moons formed.”

Unlike Jupiter, however, these planemos are not circling stars. In the first study, Jayawardhana and Valentin Ivanov of the European Southern Observatory (ESO) in Chile used two of ESO’s telescopes – the 8.2-metre Very Large Telescope and the 3.5-metre New Technology Telescope – to obtain optical spectra of six candidates identified recently by researchers at the University of Texas at Austin. Two of the six turned out to have masses between five to 10 times that of Jupiter while two others are a tad heftier, at 10 to 15 times Jupiter’s mass. All four of these objects are just a few million years old and are located in star-forming regions about 450 light-years from Earth. The planemos show infrared emission from dusty disks that may evolve into miniature planetary systems over time.

In the other study, Subhanjoy Mohanty (Harvard-Smithsonian Center for Astrophysics, CfA), Jayawardhana (UofT), Nuria Huelamo (ESO) and Eric Mamajek (CfA) used the Very Large Telescope to obtain infrared images and spectra of a planetary mass companion discovered two years ago around a young brown dwarf that is itself about 25 times the mass of Jupiter. The brown dwarf, dubbed 2M1207 for short and located 170 light-years from Earth, was known to be surrounded by a disk. Now, this team has found evidence for a disk around the eight-Jupiter-mass companion as well. Researchers think the pair probably formed together, just like a binary star system, instead of the companion forming in a disk around the brown dwarf. Moreover, Jayawardhana says, it is quite likely that smaller planets or moons could now form in the disk around each one.

Both sets of discoveries point to objects not much more massive than Jupiter forming the same way as stars like the sun, and perhaps being accompanied by their own retinues of small planets. “The diversity of worlds out there is truly remarkable,” Jayawardhana adds. “Nature often seems more prolific than our imagination.”

Original Source: U of T News Release

The Andromeda galaxy. Image credit: NASA. Click to enlarge
NASA’s Spitzer space telescope has taken a new mosaic image of the familiar Andromeda galaxy. Under Spitzer’s infrared vision, the galaxy is a contrast of old stars and knots of gas and dust heated by younger stars. Although it looks like a single image, Spitzer took 3,000 individual frames, which were then stitched together on computer to produce this final mosaic. Andromeda is much larger than our own Milky Way galaxy, and contains roughly 1 trillion stars.

The Andromeda galaxy, named for the mythological princess who almost fell prey to a sea monster, appears tranquil in a new image from NASA’s Spitzer Space Telescope. The mesmerizing infrared mosaic shows red waves of dust over a blue sea of stars.

“What’s really interesting about this view is the contrast between the galaxy’s smooth, flat disk of old stars and its bumpy waves of dust heated by young stars,” said Dr. Pauline Barmby of the Harvard-Smithsonian Center for Astrophysics, Cambridge, Mass. Barmby and her colleagues recently observed Andromeda using Spitzer.

Barmby and her team used the Spitzer data to make drastically improved measurements of Andromeda’s infrared brightness. They found that the galaxy shines with the same amount of energy as about 4 billion suns. Based on these measurements, the astronomers confirmed that there are roughly 1 trillion stars in the galaxy. Our Milky Way galaxy is estimated to house a couple of hundred billion stars.

“This is the first time the stellar population of Andromeda has been determined using the galaxy’s infrared brightness,” said Barmby. “It’s reassuring to know our numbers are in agreement with previous estimates of the mass of the stars based on the stars’ motion.”

The new false-colored portrait also provides astronomers with the best look yet at the dust-drenched spiral arms that swirl out of the galaxy’s center, a region hidden by bright starlight in visible-light images. Dust and gas are the building materials of stars. They are clumped together throughout the spiral arms, where new stars are forming.

“The Spitzer data trace with startling clarity the star-forming material all the way into the inner part of the galaxy,” said Dr. George Helou, deputy director of NASA’s Spitzer Science Center at the California Institute of Technology in Pasadena. “The challenge is to understand what shapes the distribution of this gas and dust, and what modulates the star formation at different locations.”

Spitzer’s infrared array camera captured infrared light emanating from both older stars (blue) and dust made up of molecules called polycyclic aromatic hydrocarbons (red). These carbon-containing molecules are warmed by sunlight and glow at infrared wavelengths. They are often associated with dense clouds of new stars, and can be found on Earth in barbecue pits and car exhaust, among other places.

The Andromeda galaxy, also known by astronomers as Messier 31, is located 2.5 million light-years away in the constellation Andromeda. It is the closest major galaxy to the Milky Way, making it the ideal specimen for carefully examining the nature of galaxies. On a clear, dark night, the galaxy can be spotted with the naked eye as a fuzzy blob.

Andromeda spans about 260,000 light-years, which means that a light beam would take 260,000 years to travel from one end of the galaxy to the other. By comparison, the Milky Way is about 100,000 light-years across. When viewed from Earth, Andromeda occupies a portion of the sky equivalent to seven full moons.

Spitzer’s wide field of view allowed the telescope to capture a complete snapshot of the Andromeda galaxy, though the task wasn’t easy. The final mosaic consists of 3,000 or so individual picture frames stitched together seamlessly.

Barmby presented these observations today at the 208th meeting of the American Astronomical Society in Calgary, Canada. A previous image of Andromeda taken with Spitzer’s longer-wavelength infrared camera can be found at http://www.spitzer.caltech.edu/Media/releases/ssc2005-20/ssc2005-20a.shtml

For more information about Spitzer, visit www.spitzer.caltech.edu/spitzer

Other members of Barmby’s team include: Drs. Steven Willner, Matthew Ashby, John Huchra and Michael Pahre of the Harvard-Smithsonian Center for Astrophysics; Drs. Luciana Bianchi and David Thilker of The Johns Hopkins University, Baltimore, Md.; Drs. Charles Engelbracht, Karl Gordon, Joannah Hinz, Pablo Perez-Gonzalez and George Rieke of the University of Arizona, Tucson; and Drs. Robert Gehrz, Roberta Humphreys, Elisha Polomski and Charles Woodward of the University of Minnesota, Twin Cities.

NASA’s Jet Propulsion Laboratory, Pasadena, Calif., manages the Spitzer Space Telescope mission for NASA’s Science Mission Directorate, Washington. Science operations are conducted at the Spitzer Science Center. Spitzer’s infrared array camera was built by NASA’s Goddard Space Flight Center, Greenbelt, Md. The instrument’s principal investigator is Giovanni Fazio of the Harvard-Smithsonian Center for Astrophysics.

Original Source: NASA News Release

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.

Click here to visit.

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