Tuesday, May 31, 2011

Raging galactic storms sweep away gas

Artist's impression of a galaxy with an outflow from its centre. Click for high-res version. Image credit: ESA / AOES media lab.

Herschel has detected raging winds of molecular gas streaming away from galaxies. Suspected for years, these outflows may have the power to strip galaxies of gas and halt star formation in its tracks. The winds that Herschel has detected are extraordinary. The fastest is blowing at a speed of more than 1000 km/s, or about 10000 times faster than the wind in a hurricane on Earth.

This is the first time that such molecular gas outflows have been unequivocally observed in a sample of galaxies. This is an important discovery because stars form from molecular gas, and these outflows are robbing the galaxy of the raw material it needs to make new stars. If the outflows are powerful enough, they could even halt star formation altogether.

“With Herschel, we now have the chance to really study what these outflows mean for galactic evolution,” says Eckhard Sturm from the Max-Planck-Institut für extraterrestrische Physik in Germany, the lead author of this work.

Dr Sturm and colleagues used Herschel’s PACS instrument to study 50 galaxies, though this first result is based on just six of the sample. The galaxies are too far away to be seen as more than points of light, so the team looked at the spectrum of the light to glean more information. By looking in detail at the emission from the hydroxyl molecule (OH), the astronomers could work out the velocity of the gas relative to the galaxies themselves.

They infer that 1200 times the mass of our Sun is being lost each year from the galaxies with the most vigorous outflows. That is enough to strip them of their entire reserves of star-forming gas within one million to 100 million years. In other words, some galaxies could completely expel their star-forming gas in as little as a million years. This process of inhibiting star formation in a galaxy is known as negative feedback.

Herschel detects light from all of the gas at the same time, but analysis of the spectrum of light allows astronomers to work out the range of velocities of various types of gas. In some galaxies, gas was seen to be moving at over 1000 km/s. Click for more information. Image credit: ESA / AOES medialab. Hi-Res [jpg] 369.87 kb.

These winds could be generated by the intense emission of light and particles from young stars, or by shockwaves from the explosion of old stars. Alternatively, they may be triggered by the radiation given off as matter swirls around a black hole at the centre of the galaxy. The effect that such active black holes have on galaxies has been the subject of much debate for many years.

The fastest winds appear to be coming from the galaxies that contain the brightest ‘active galactic nuclei’, in which a giant black hole is feeding from its surroundings. Dr Sturm and colleagues are now testing this idea with the other galaxies in their sample. The results could be a step towards explaining how some elliptical galaxies are formed.

Elliptical galaxies are vast islands of stars that have now stopped producing appreciable numbers of new stars because they have exhausted their gas supplies.

As smaller galaxies interact and merge with each other, more food is supplied to the central black hole in the combined nucleus, making it larger and more active. This could result in a more powerful wind, which removes the molecular gas and prevents any further star formation taking place, thus leading to an elliptical galaxy.

“By catching molecular outflows in the act, Herschel has finally yielded long-sought-after evidence that powerful processes with negative feedback do take place in galaxies and dramatically affect their evolution,” adds Göran Pilbratt, ESA's Herschel Project Scientist.

Thursday, May 26, 2011

Spitzer Sees Crystal 'Rain' in Outer Clouds of Infant Star

NASA's Spitzer Space Telescope detected tiny green crystals, called olivine, thought to be raining down on a developing star. Image credit: NASA/JPL-Caltech/University of Toledo. Full image and caption

This image from NASA's Spitzer Space Telescope shows what lies near the sword of the constellation Orion -- an active stellar nursery containing thousands of young stars and developing protostars. Image credit: NASA/JPL-Caltech/University of Toledo. Full image and caption

Using NASA's Spitzer Space Telescope, astronomers have, for the first time, found signatures of silicate crystals around a newly forming protostar in the constellation of Orion. Image credit: NASA/JPL-Caltech/University of Toledo. Full image and caption

PASADENA, Calif. -- Tiny crystals of a green mineral called olivine are falling down like rain on a burgeoning star, according to observations from NASA's Spitzer Space Telescope.

This is the first time such crystals have been observed in the dusty clouds of gas that collapse around forming stars. Astronomers are still debating how the crystals got there, but the most likely culprits are jets of gas blasting away from the embryonic star.

"You need temperatures as hot as lava to make these crystals," said Tom Megeath of the University of Toledo in Ohio. He is the principal investigator of the research and the second author of a new study appearing in Astrophysical Journal Letters. "We propose that the crystals were cooked up near the surface of the forming star, then carried up into the surrounding cloud where temperatures are much colder, and ultimately fell down again like glitter."

Spitzer's infrared detectors spotted the crystal rain around a distant, sun-like embryonic star, or protostar, referred to as HOPS-68, in the constellation Orion.

The crystals are in the form of forsterite. They belong to the olivine family of silicate minerals and can be found everywhere from a periodot gemstone to the green sand beaches of Hawaii to remote galaxies. NASA's Stardust and Deep Impact missions both detected the crystals in their close-up studies of comets.

"If you could somehow transport yourself inside this protostar's collapsing gas cloud, it would be very dark," said Charles Poteet, lead author of the new study, also from the University of Toledo. "But the tiny crystals might catch whatever light is present, resulting in a green sparkle against a black, dusty backdrop."

Forsterite crystals were spotted before in the swirling, planet-forming disks that surround young stars. The discovery of the crystals in the outer collapsing cloud of a proto-star is surprising because of the cloud's colder temperatures, about minus 280 degrees Fahrenheit (minus 170 degrees Celsius). This led the team of astronomers to speculate the jets may in fact be transporting the cooked-up crystals to the chilly outer cloud.

The findings might also explain why comets, which form in the frigid outskirts of our solar system, contain the same type of crystals. Comets are born in regions where water is frozen, much colder than the searing temperatures needed to form the crystals, approximately 1,300 degrees Fahrenheit (700 degrees Celsius). The leading theory on how comets acquired the crystals is that materials in our young solar system mingled together in a planet-forming disk. In this scenario, materials that formed near the sun, such as the crystals, eventually migrated out to the outer, cooler regions of the solar system.

Poteet and his colleagues say this scenario could still be true but speculate that jets might have lifted crystals into the collapsing cloud of gas surrounding our early sun before raining onto the outer regions of our forming solar system. Eventually, the crystals would have been frozen into comets. The Herschel Space Observatory, a European Space Agency-led mission with important NASA contributions, also participated in the study by characterizing the forming star.

"Infrared telescopes such as Spitzer and now Herschel are providing an exciting picture of how all the ingredients of the cosmic stew that makes planetary systems are blended together," said Bill Danchi, senior astrophysicist and program scientist at NASA Headquarters in Washington.

The Spitzer observations were made before it used up its liquid coolant in May 2009 and began its warm mission.

NASA's Jet Propulsion Laboratory in Pasadena, Calif., manages the Spitzer Space Telescope mission for the agency's Science Mission Directorate in Washington. Science operations are conducted at the Spitzer Science Center at the California Institute of Technology in Pasadena. Caltech manages JPL for NASA.

For more information about Spitzer, visit http://www.nasa.gov/spitzer and http://spitzer.caltech.edu/ .

Whitney Clavin 818-354-4673
Jet Propulsion Laboratory, Pasadena, Calif.

Trent Perrotto 202-358-0321

Nature’s Best Magnifying Glass Views Eary Spiral Galaxy

The gravity of a gigantic cluster of galaxies has bent and magnified the light of the distant spiral galaxy Sp1149 making its spiral arms visible and available for study by astronomers. Normally gravitational lensing distorts the structures of distant galaxies beyond recognition. The inset labaled "galaxy" shows how Sp1149 would look without lensing. Credit: Karen Teramura, University of Hawai'i Institute for Astronomy. Press Image

Kamuela, HI – Astronomers in Hawaii have plucked unprecedented details from the life of an early galaxy using an unusually lucid gravitational lens coupled with the powerful 10-meter Keck II Telescope on Mauna Kea.

Gravitational lenses are Nature’s largest telescopes, created by colossally massive clusters of thousands of galaxies that bend and magnify the light of more distant objects behind them in a way similar to a glass lens. But gravitational lenses are far from perfect. Though they make very distant galaxies from the early universe visible to telescopes, they also put the images through a cosmic blender. As a result, the smeared and distorted images don’t offer much in the way of direct information about what the earliest galaxies looked like.

But that is not the case for an elegant little spiral galaxy called Sp1149, located 9.3 billion light-years away. The galaxy’s image has come through a gravitational lens magnified 22 times and fairly intact, as seen in a Hubble Space Telescope image. The image was first observed in detail by the University of Hawaii’s Tiantian Yuan and was initially taken by Harald Ebeling, also of Hawaii, and published by Graham P. Smith and colleagues in 2009. The giant cluster of galaxies that created the lens is located in the vast expanse of space between Sp1149 and Earth, and appears beside Sp1149 in the Hubble image.

The secret to Sp1149’s successful magnification is that it is in a special position behind the cluster which allows its light to be bent equally in all directions, explained astronomer Lisa Kewley of the University of Hawaii at Manoa.

“We’re lucky that it’s not being terribly distorted,” said Kewley. “Something so far away that’s not lensed would look like a blurred dot.”

The fact that you can distinguish the galactic core and spiral arms of Sp1149, plus the fact that we are seeing the galaxy as it was when the universe was only a third of its current age, makes it a great specimen for testing different models of how galaxies are born and then grow up to be places like our own Milky Way.

To that end, Yuan, Kewley and their colleagues aimed the Keck II Telescope at Sp1149. With the help of Laser Guide Star Adaptive Optics (which cancels out much of the optical distortions caused by Earth’s atmosphere) and the OSIRIS instrument (which filters out the noise created by hydroxyl molecules in Earth’s atmosphere) the researchers were able to get an unprecedented look at the distributions of elements in Sp1149. Oxygen, in particular, is very revealing because the element accumulates more in the older stellar neighborhoods – the parts of galaxies where stars have lived and died more. In the case of Sp1149, the oxygen distribution spoke volumes.

“The oxygen in the spiral galaxy was much more concentrated at the center,” said Kewley. “They had a lot of star formation at the center.”

This sharp oxygen gradient, from core to outer disk, suggests that stars in the cores of galaxies form first and create the oldest stellar neighborhoods in Sp1149, followed later by the disk and arms. That supports what’s called the inside-out model of galactic evolution, she said.

“This is an idea that has been out there,” explained Kewley. “Some models predict the opposite. “It’s been an open question for a long time.” What has been needed was something other than a local galaxy to study to see how the oxygen gradients looked much earlier in a galaxy’s history. Without that, astronomers would have nothing but middle aged galaxies to judge from. They would be like a biologist studying the lives of frogs without ever having seen a tadpole.

“This is the first time anyone has done such a detailed and precise oxygen gradient that wasn’t on a local galaxy,” said Kewley. Yuan, Kewley and their colleagues published their discovery in the journal May 1 issue of Astrophysical Journal Letters (available online at http://arxiv.org/abs/1103.3277)

Now that the team has found one galactic tadpole, they are hunting for more, said Kewley. They also are hoping to study some galaxies that are midway between the ages of our local galaxies and Sp1149. With these samples from different ages, Kewley and her colleagues hope to piece together a much clearer life history of galaxies like our own.

The W. M. Keck Observatory operates two 10-meter optical/infrared telescopes on the summit of Mauna Kea on the Big Island of Hawaii. The twin telescopes feature a suite of advanced instruments including imagers, multi-object spectrographs, high-resolution spectrographs, integral-field spectroscopy and a world-leading laser guide star adaptive optics system which cancels out much of the interference caused by Earth’s turbulent atmosphere. The Observatory is a private 501(c) 3 organization and a scientific partnership of the California Institute of Technology, the University of California and NASA.

Betting on the Most Distant Gamma Ray Burst Ever Seen

Figure 1. Gemini Observatory color composite image of the afterglow of GRB 090429B - a candidate for the most distant object in the universe. This "izH" image has been constructed from three images taken at the Gemini Observatory North telescope through different optical and infrared filters (the infrared images were obtained using the Gemini Near-Infrared Imager, NIRI, optical, non-detection data from the Gemini Multi-Object Spectrograph, GMOS). The red color results from the absence of all optical light, which has been absorbed by hydrogen gas in the distant universe. Without that absorption, the afterglow color would be bluer than any of the galaxies and stars seen in this field of view. The position of the afterglow is indicated. Credit: Gemini Observatory/AURA/Andrew Levan (University of Warwick, UK).
Download JPG 78 KB | TIFF 1.9 MB

Figure 2. Gemini Observatory images of GRB 090429B obtained using the Gemini Near-Infrared Imager (NIRI) using J, H, and K filters (labeled) and z filter (left, non detection) obtained with the Gemini Multi-Object Spectrograph, all images are from the Gemini North telescope on Mauna Kea, Hawai‘i. Credit: Gemini Observatory/AURA/Penn State/UC Berkeley/University of Warwick, UK

Betting on the Most Distant Gamma Ray Burst Ever Seen: Extreme distance determined with Gemini Observatory Images

In a game of cosmological one-upmanship, what is likely the most distant gamma ray burst (GRB) ever detected could be presenting humanity with a glimpse back to within about half a billion years of the Big Bang. "Like any finding of this sort there are uncertainties,” said the study's principal investigator Antonino Cucchiara. “However, if I were in Vegas, I would never bet against the odds that this is the most distant GRB ever seen and we estimate that there is even a 23% chance that it is the most distant object ever observed in the universe."

A unique set of images from the Gemini North telescope in Hawai‘i clearly reveals the infrared afterglow of this powerful burst. More importantly, the data allowed the researchers to estimate its distance with a relatively high degree of certainty, placing it near the edge of the observable universe.

The finding, announced today at the American Astronomical Society meeting in Boston Massachusetts, follows the evolution of a gamma ray burst (GRB 090429B) discovered by NASA's Swift satellite in April of 2009. GRBs like this one are a consequence of the deaths of massive stars, with an initial brief burst of high-energy emission gradually fading to an afterglow of light at other wavelengths. The subsequent afterglow was detected only at infrared wavelengths using the Gemini North telescope.

This result follows on the heels of other announcements by astronomers over the past few years that have extended the edge of the observable universe and pushed the depth of our vision deeper and deeper into the past by looking at both GRBs and galaxies.

Astronomers quantify large distances in terms of redshift, “z” where higher values of z indicate greater distance and greater lookback time into the early universe. The previous GRB record holder has an estimated redshift or z value of around 8.2, with GRB 090429B estimated at 9.4. Other galaxies at comparable or even larger redshifts may have already been detected, although some of their distance estimates are uncertain.

The research team, led by former Penn State University graduate student Antonino Cucchiara (now at the University of California at Berkeley), marshaled the extreme vision of Gemini and other large ground- and space-based telescopes to understand the object. According to Cucchiara, “Gemini was the right telescope, in the right place, at the right time. The data from Gemini was instrumental in allowing us to reach the conclusion that the object is likely the most distant GRB ever seen.” If the team is correct, this light embarked on its journey some 13.1 billion years ago or about 520 million years after the Big Bang – surprisingly close to the advent of the Big Bang 13.7 billion years ago. Additionally, this GRB appears to be normal, leading to the conclusion that it is not the consequence of the very first generation of stars formed in the universe. The implication is that the early, extremely young universe was already a busy star factory.

Reaching the conclusion that GRB 090429B is so distant was not easy and is one reason it has taken two years for this result to be announced. “Ideally we would have gathered a spectrum to measure the distance precisely, but we were foiled at the last minute when the weather took a turn for the worse on Mauna Kea. Since GRB afterglows fade so quickly, we never got a second chance,” said Derek Fox, Cucchiara’s advisor for his graduate research at Penn State University.

However, by using the existing data from Gemini and combining it in innovative ways with wider-field images from the United Kingdom Infrared Telescope (also on Hawaii’s Mauna Kea), the team was able to estimate the redshift of GRB 090429B with a high degree of confidence. “Also, the fact that we were never able to detect anything in the spot where we saw the afterglow in the Gemini data gave us the missing link in converging on this extremely high redshift estimate,” said Cucchiara. “We looked with Gemini, the Hubble Space Telescope and also with the Very Large Telescope in Chile and never saw anything once the afterglow faded. This means that this GRB's host galaxy is so distant that it couldn’t be seen with any existing telescopes. Because of this, and the information provided by the Swift satellite, our confidence is extremely high that this event happened very, very early in the history of our universe.”

The paper based on this work is accepted in The Astrophysical Journal Authors include: Antonino Cucchiara (Penn State University/UC Berkeley), Derek Fox (Penn State University), Andrew Levan (University of Warwick, UK) and Nial Tanvir (University of Leicester, UK) and 31 astronomers from around the world. A preprint of the paper can be found here later today.

For more information on this work, see the Penn State University press release here.

The Gemini Observatory is an international collaboration with two identical 8-meter telescopes. The Frederick C. Gillett Gemini Telescope is located at Mauna Kea, Hawai'i (Gemini North) and the other telescope at Cerro Pachón in northern Chile (Gemini South), and hence provide full coverage of both hemispheres of the sky. Both telescopes incorporate new technologies that allow large, relatively thin mirrors under active control to collect and focus both optical and infrared radiation from space.

The Gemini Observatory provides the astronomical communities in each partner country with state-of-the-art astronomical facilities that allocate observing time in proportion to each country's contribution. In addition to financial support, each country also contributes significant scientific and technical resources. The national research agencies that form the Gemini partnership include: the US National Science Foundation (NSF), the UK Science and Technology Facilities Council (STFC), the Canadian National Research Council (NRC), the Chilean Comisión Nacional de Investigación Cientifica y Tecnológica (CONICYT), the Australian Research Council (ARC), the Argentinean Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET) and the Brazilian Conselho Nacional de Desenvolvimento Científico e Tecnológico CNPq). The observatory is managed by the Association of Universities for Research in Astronomy, Inc. (AURA) under a cooperative agreement with the NSF. The NSF also serves as the executive agency for the international partnership.

Press Contacts:

Peter Michaud
Gemini Observatory, Hilo Hawai‘i
Cell: (808) 936-6643
Desk: (808) 974-2510

Barbara Kennedy
Director, Penn State University
Office of Media Relations and Public Information
Desk: (814) 863-4682

Science Contacts:

Antonino Cucchiara
University of California at Berkeley
Cell: (814) 777-3935

Derek Fox
Penn State University
Cell: (814) 404-2603
Desk:(814) 863-4989

Wednesday, May 25, 2011

NASA's Hubble Finds Rare Blue Straggler Stars in the Milky Way's Hub

Blue Straggler Stars in the Galactic Bulge
Image Type: Astronomical/Illustration
Credit: NASA, ESA, W. Clarkson (Indiana University and UCLA),
and K. Sahu (STScI)

Artist's View of a Blue Straggler Star
Artwork Credit: NASA, ESA, and G. Bacon (STScI)
Science Credit: NASA, ESA,
W. Clark (Indiana University and UCLA),
and K. Sahu (STScI)

This is an artist's concept of a close binary pair of stars that are merging to form a blue-straggler-class star. Blue stragglers are so named because they seem to be lagging behind in their rate of aging compared with the population from which they formed. The merger stirs up hydrogen fuel and causes the resulting more massive star to undergo nuclear fusion at a faster rate, causing it to burn hotter and bluer. Probing the star-filled, ancient hub of our Milky Way, the Hubble Space Telescope has found blue stragglers for the first time within our galaxy's bulge.

Probing the star-filled, ancient hub of our Milky Way, NASA's Hubble Space Telescope has found a rare class of oddball stars called blue stragglers, the first time such objects have been detected within our galaxy's bulge.

The size and nature of the blue straggler population detected in the bulge will allow astronomers to better understand if the bulge is exclusively old stars, or a mixture of both young and old stars. In addition, the discovery provides a new test case for formation models of the blue stragglers themselves.

Blue stragglers — so named because they seem to be lagging behind in their rate of aging compared with the population from which they formed — were first found inside ancient globular star clusters half a century ago. They have been detected in many globular and open clusters, as well as among the stars in the solar neighborhood. But they have never been seen inside the core of our galaxy until Hubble was trained on the region.

Hubble astronomers found blue straggler stars in an extensive set of Hubble exposures of the Milky Way's crowded hub. Blue stragglers are much hotter — and hence bluer — than they should be for the aging neighborhood in which they live. Now that blue stragglers have at last been found within the bulge, the size and characteristics of this population will allow astronomers to better understand the still-controversial processes of star formation within the bulge.

The results, to be published in The Astrophysical Journal, are being reported by lead author Will Clarkson of Indiana University and the University of California, Los Angeles, at the American Astronomical Society meeting in Boston, Mass.

These results support the idea that the Milky Way's central bulge stopped making stars billions of years ago. It is now home to aging Sun-like stars and cooler red dwarfs. Giant blue stars that once lived there exploded as supernovae billions of years ago. If our galaxy were the size of a dinner plate, the central bulge would be roughly the size of a grapefruit placed in the middle of the plate.

This discovery is a spin-off from a seven-day-long survey conducted in 2006 called the Sagittarius Window Eclipsing Extrasolar Planet Search (SWEEPS). Hubble peered at and obtained variability information for 180,000 stars in the crowded central bulge of our galaxy, 26,000 light-years away. The survey was intended to find hot Jupiter-class planets that orbit very close to their stars. But the SWEEPS team also uncovered 42 oddball blue stars among the bulge population with brightness and temperatures typical for stars much younger than ordinary bulge stars.

Blue stragglers have long been suspected to be living in the bulge. Until now, it has never been proven because younger stars in the disk of our galaxy lie along the line-of-sight to the core, confusing and contaminating the view.

But Hubble's view is so sharp that astronomers could distinguish the motion of the core population from foreground stars in the Milky Way. Bulge stars orbit the galactic nucleus at a different speed than foreground stars. Plotting their motion required returning to the SWEEPS target region with Hubble two years after the first-epoch observations were made.

Hence, the blue stragglers were identified as moving along with the other stars in the bulge. It's like looking into a deep, clear pond where the fish at the bottom of the pond are swimming at a faster rate than the fish closer to the surface.

"The size of the field of view on the sky is roughly that of the thickness of a human fingernail held at arm's length, and within this region, Hubble sees about a quarter million stars towards the bulge," Clarkson says. "Only the superb image quality and stability of Hubble allowed us to make this measurement in such a crowded field."

From the 42 candidate blue stragglers, the investigators estimate 18 to 37 of them are likely to be genuine blue stragglers, with the remainder consisting of a mixture of foreground objects and at most a small population of genuinely young bulge stars.

It's not clear how blue stragglers form, or if there is more than one mechanism at work. A common idea is that blue stragglers emerge from binary pairs. As the more massive star evolves and expands, the less massive star accretes material from the companion. This stirs up hydrogen fuel and causes the accreting star to undergo nuclear fusion at a faster rate. It burns hotter and bluer.

The seven-day observation allowed the fraction of blue straggler candidates presently in close binaries to be estimated by virtue of their changing light-curve. This is caused by the change of shape induced in one star due to the tidal gravitational pull of its companion. "The SWEEPS program was designed to detect transiting planets through small light variations. Therefore the program could easily detect the variability of binary pairs, which was crucial in confirming these are indeed blue stragglers," says Kailash Sahu of the Space Telescope Science Institute in Baltimore, Md., the principal investigator of the SWEEPS program.

The observations clearly indicate that if there is a young star population in the bulge, it is very small, and it was not detected in the SWEEPS program. "Although the Milky Way bulge is by far the closest galaxy bulge, several key aspects of its formation and subsequent evolution remain poorly understood," Clarkson says. "While the consensus is that the bulge largely stopped forming stars long ago, many details of its star-formation history remain controversial. The extent of the blue straggler population detected provides two new constraints for models of the star-formation history of the bulge."


Ray Villard
Space Telescope Science Institute, Baltimore, Md.

Will Clarkson
Indiana University, Bloomington, Ind., and
University of California, Los Angeles, Calif.

Kailash Sahu
Space Telescope Science Institute, Baltimore, Md.

NASA's WISE Mission Offers a Taste of Galaxies to Come

A new, colorful collection of galaxy specimens has been released by NASA's Wide-field Infrared Survey Explorer, or WISE, mission. It showcases galaxies of several types, from elegant grand design spirals to more patchy flocculent spirals. Some of the galaxies have roundish centers, while others have elongated central bars. The orientation of the galaxies varies as well, with some seeming to peer straight back at us in the face-on configuration while others point to the side, appearing edge-on. Image credit: NASA/JPL-Caltech . Full image with all nine galaxies

PASADENA, Calif. -- An assorted mix of colorful galaxies is being released today by NASA's Wide-field Infrared Survey Explorer mission, or WISE. The nine galaxies are a taste of what's to come. The mission plans to release similar images for the 1,000 largest galaxies that appear in our sky, and possibly more.

"Galaxies come in all sorts of delicious flavors," said Tom Jarrett, a WISE team member at the Infrared Processing and Analysis Center, California Institute of Technology, in Pasadena, who studies our Milky Way's neighboring galaxies. "Our first sample shows what WISE is capable of. We can produce spectacular high-resolution images of the largest galaxies."

The new collage showcases galaxies of varying types -- everything from "grand design spirals," with their elegant cinnamon bun-like swirling arms, to so-called "flocculent" galaxies, which have a more patchy appearance. They are close enough to us that WISE can see details of their structure, for example their sinuous arms and central bulges. Because WISE can study so many types of nearby galaxies, its observations will provide a better understanding of how these complex objects form and evolve.

WISE, which launched into space in Dec. 2009, scanned the whole sky one-and-a-half times in infrared light. It captured images of asteroids in our own solar system, distant galaxies billions of light-years away, and everything in between. The mission's first batch of data, which does not include all of the galaxies in the new collage, was released to the public in April of this year. The complete WISE catalog will follow a year later, in the spring of 2012.

"We can learn about a galaxy's stars -- where are they forming and how fast?" said Jarrett. "There's so much diversity in galaxies to explore."

The new collection of nine galaxies shows off this diversity, with members of different sizes, colors and shapes. Infrared light from the galaxies, which we can't see with our eyes, has been translated into visible-light colors that we can see. Blue colors show older populations of stars, while yellow indicates dusty areas where stars are forming.

Some of the galaxies are oriented toward us nearly face-on, such as Messier 83, and others are partly angled away from us, for example Messier 81. One galaxy, NGC 5907, is oriented completely edge-on, so that all we can see is its profile. The edge of its main galaxy disk appears pencil-thin, and its halo of surrounding stars is barely visible as a green glow above and below the disk.

The arms of the galaxies come in different shapes too. Messier 51 has arms that look like a spiral lollipop, while the arms of the flocculent galaxy NGC 2403 look choppy, perhaps more like layered frosting. Astronomers think that gravitational interactions with companion galaxies may lead to more well-defined spiral arms. One such companion can be seen near Messier 51 in blue. Some of the galaxies also have spokes, or spurs, that join the arms together, such as those in IC 342.

JPL manages and operates the Wide-field Infrared Survey Explorer for NASA's Science Mission Directorate, Washington. The principal investigator, Edward Wright, is at UCLA. The mission was competitively selected under NASA's Explorers Program managed by the Goddard Space Flight Center, Greenbelt, Md. The science instrument was built by the Space Dynamics Laboratory, Logan, Utah, and the spacecraft was built by Ball Aerospace & Technologies Corp., Boulder, Colo. Science operations and data processing take place at the Infrared Processing and Analysis Center at the California Institute of Technology in Pasadena. Caltech manages JPL for NASA.

Whitney Clavin 818-354-4673
Jet Propulsion Laboratory, Pasadena, Calif.

The Spitzer Photo Atlas of Galactic "Train Wrecks"

Three-color image of NGC 935 and its companion IC 1801 showing far-UV emission from young stars observed by GALEX in blue, heated dust mid-infrared emission observed by Spitzer in red, and stellar near-infrared emission observed by Spitzer in green. This pair of spiral galaxies is beginning to crash into each other. Credit: NASA / JPL-Caltech / L. Lanz (Harvard-Smithsonian CfA)

Three-color image of NGC 3448 (left) and its companion UGC 6016 (right) showing far-UV emission from young stars observed by GALEX in blue, heated dust mid-infrared emission observed by Spitzer in red, and stellar near-infrared emission observed by Spitzer in green. This pair of galaxies is only separated by 75,000 light-years, and its UV emission shows a bridge of material between the two galaxies. Credit: NASA / JPL-Caltech / L. Lanz (Harvard-Smithsonian CfA)

Three-color image of NGC 470 (top) and NGC 474 (bottom) showing far-UV emission from young stars observed by GALEX in blue, heated dust mid-infrared emission observed by Spitzer in red, and stellar near-infrared emission observed by Spitzer in green. These galaxies are likely to be on their first pass past each other and are therefore relatively undisturbed at a separation of 160,000 light-years. Credit: NASA / JPL-Caltech / L. Lanz (Harvard-Smithsonian CfA)

This montage shows three examples of colliding galaxies from a new photo atlas of galactic "train wrecks." The new images combine observations from NASA's Spitzer Space Telescope, which observes infrared light, and NASA's Galaxy Evolution Explorer (GALEX) spacecraft, which observes ultraviolet light. By analyzing information from different parts of the light spectrum, scientists can learn much more than from a single wavelength alone, because they observe different components of a galaxy. The panel at far left shows NGC 470 (top) and NGC 474 (bottom); at top right are NGC 3448 and UGC 6016; at bottom right are NGC 935 and IC 1801. In this representative-color image, far ultraviolet light from GALEX is blue, 3.6-micron light from Spitzer is cyan, 4.5-micron light from Spitzer is green, and red shows light at 5.8 and 8 microns from Spitzer. Credit: NASA / JPL-Caltech / L. Lanz (Harvard-Smithsonian CfA).

Cambridge, MA - Five billion years from now, our Milky Way galaxy will collide with the Andromeda galaxy. This will mark a moment of both destruction and creation. The galaxies will lose their separate identities as they merge into one. At the same time, cosmic clouds of gas and dust will smash together, triggering the birth of new stars.

To understand our past and imagine our future, we must understand what happens when galaxies collide. But since galaxy collisions take place over millions to billions of years, we can't watch a single collision from start to finish. Instead, we must study a variety of colliding galaxies at different stages. By combining recent data from two space telescopes, astronomers are gaining fresh insights into the collision process.

"We've assembled an atlas of galactic 'train wrecks' from start to finish. This atlas is the first step in reading the story of how galaxies form, grow, and evolve," said lead author Lauranne Lanz of the Harvard-Smithsonian Center for Astrophysics (CfA).

Lanz presented her findings today in a press conference at the 218th meeting of the American Astronomical Society.

The new images combine observations from NASA's Spitzer Space Telescope, which observes infrared light, and NASA's Galaxy Evolution Explorer (GALEX) spacecraft, which observes ultraviolet light. By analyzing information from different parts of the light spectrum, scientists can learn much more than from a single wavelength alone, because different components of a galaxy are highlighted.

GALEX's ultraviolet data captures the emission from hot young stars. Spitzer sees the infrared emission from warm dust heated by those stars, as well as from stellar surfaces. Therefore, GALEX's ultraviolet data and Spitzer's infrared data highlight areas where stars are forming most rapidly, and together permit a more complete census of the new stars.

In general, galaxy collisions spark star formation. However, some interacting galaxies produce fewer new stars than others. Lanz and her colleagues want to figure out what differences in physical processes cause these varying outcomes. Their findings will also help guide computer simulations of galaxy collisions.

"We're working with the theorists to give our understanding a reality check," said Lanz. "Our understanding will really be tested in five billion years, when the Milky Way experiences its own collision."

Lanz's co-authors are Nicola Brassington (Univ. of Hertfordshire, UK); Andreas Zezas (Univ. of Crete, Greece, and CfA); Howard Smith and Matt Ashby (CfA); Christopher Klein (UC Berkeley); and Patrik Jonsson, Lars Hernquist, and Giovanni Fazio (CfA).

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 at the California Institute of Technology, also in Pasadena. Caltech manages JPL for NASA. 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 CfA.

Caltech leads the Galaxy Evolution Explorer mission and is responsible for science operations and data analysis. NASA’s Jet Propulsion Laboratory, also in Pasadena, manages the mission and built the science instrument. The mission was developed under NASA’s Explorers Program managed by the Goddard Space Flight Center, Greenbelt, Md. Researchers sponsored by Yonsei University in South Korea and the Centre National d'Etudes Spatiales (CNES) in France collaborated on this mission.

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.

For more information, contact:

David A. Aguilar
Director of Public Affairs
Harvard-Smithsonian Center for Astrophysics

Christine Pulliam
Public Affairs Specialist
Harvard-Smithsonian Center for Astrophysics

Astronomers Unveil Most Complete 3-D Map of Local Universe

The 2MASS Redshift Survey (2MRS) has catalogued more than 43,000 galaxies within 380 million light-years from Earth (z<0.09). In this projection, the plane of the Milky Way runs horizontally across the center of the image. 2MRS is notable for extending closer to the Galactic plane than previous surveys - a region that's generally obscured by dust. Credit: T.H. Jarrett (IPAC/SSC) High Resolution Image (jpg) - Low Resolution Image (jpg)

Cambridge, MA - Today, astronomers unveiled the most complete 3-D map of the local universe (out to a distance of 380 million light-years) ever created. Taking more than 10 years to complete, the 2MASS Redshift Survey (2MRS) also is notable for extending closer to the Galactic plane than previous surveys - a region that's generally obscured by dust.

Karen Masters (University of Portsmouth, UK) presented the new map today in a press conference at the 218th meeting of the American Astronomical Society.

"The 2MASS Redshift Survey is a wonderfully complete new look at the local universe - particularly near the Galactic plane," Masters said. "We're also honoring the legacy of the late John Huchra, an astronomer at the Harvard-Smithsonian Center for Astrophysics, who was a guiding force behind this and earlier galaxy redshift surveys."

A galaxy's light is redshifted, or stretched to longer wavelengths, by the expansion of the universe. The farther the galaxy, the greater its redshift, so redshift measurements yield galaxy distances - the vital third dimension in a 3-D map.

2MRS chose galaxies to map from images made by the Two-Micron All-SkySurvey (2MASS). This survey scanned the entire sky in three near-infrared wavelength bands. Near-infrared light penetrates intervening dust better than visible light, allowing astronomers to see more of the sky. But without adding redshifts, 2MASS makes only a 2-D image. Some of the galaxies mapped had previously-measured redshifts, and Huchra started painstakingly measuring redshifts for the others in the late 1990s using mainly two telescopes: one at the Fred Lawrence Whipple Observatory on Mt. Hopkins, AZ, and one at the Cerro Tololo Inter-American Observatory in Chile. The last observations were completed by 2MRS observers on these telescopes shortly after Huchra's death in October 2010.

Robert Kirshner, Huchra's colleague at the Center for Astrophysics (CfA), said, "John loved doing redshift surveys and he loved the infrared. He had the insight to tell when infrared technology, formerly the province of the experts, was ripe for routine use in a big project."

"John was instrumental in setting up the 2MASS telescope at Mount Hopkins, seeing the infrared side of the project through, and making a much more complete survey of the local universe. It's a wonderful tribute to John that his colleagues have finished the infrared-selected galaxy redshift survey that John started," he added.

The 2MRS mapped in detail areas previously hidden behind our Milky Way to better understand the impact they have on our motion. The motion of the Milky Way with respect to the rest of the universe has been a puzzle ever since astronomers were first able to measure it and found it couldn't be explained by the gravitational attraction from any visible matter. Massive local structures, like the Hydra-Centaurus region (the "Great Attractor") were previously hidden almost behind the Milky Way but are now shown in great detail by 2MRS.

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.

For more information, contact:

David A. Aguilar
Director of Public Affairs
Harvard-Smithsonian Center for Astrophysics

Christine Pulliam
Public Affairs Specialist
Harvard-Smithsonian Center for Astrophysics

ESO's VLT Finds a Brilliant but Solitary Superstar

PR Image eso1117a
The brilliant star VFTS 682 in the Large Magellanic Cloud

PR Image eso1117b
The brilliant star VFTS 682 in the Large Magellanic Cloud (annotated)

PR Video eso1117a
Zooming in on the brilliant star VFTS 682 in the Large Magellanic Cloud

An extraordinarily bright isolated star has been found in a nearby galaxy — the star is three million times brighter than the Sun. All previous similar “superstars” were found in star clusters, but this brilliant beacon shines in solitary splendour. The origin of this star is mysterious: did it form in isolation or was it ejected from a cluster? Either option challenges astronomers’ understanding of star formation.

An international team of astronomers [1] has used ESO’s Very Large Telescope to carefully study the star VFTS 682 [2] in the Large Magellanic Cloud, a small neighbouring galaxy to the Milky Way. By analysing the star’s light, using the FLAMES instrument on the VLT, they have found that it is about 150 times the mass of the Sun. Stars like these have so far only been found in the crowded centres of star clusters, but VFTS 682 lies on its own.

“We were very surprised to find such a massive star on its own, and not in a rich star cluster,” notes Joachim Bestenlehner, the lead author of the new study and a student at Armagh Observatory in Northern Ireland. “Its origin is mysterious.”

This star was spotted earlier in a survey of the most brilliant stars in and around the Tarantula Nebula in the Large Magellanic Cloud. It lies in a stellar nursery: a huge region of gas, dust and young stars that is the most active star-forming region in the Local Group of galaxies [3]. At first glance VFTS 682 was thought to be hot, young and bright, but unremarkable. But the new study using the VLT has found that much of the star’s energy is being absorbed and scattered by dust clouds before it gets to Earth — it is actually more luminous than previously thought and among the brightest stars known.

Red and infrared light emitted by the star can get through the dust, but the shorter-wavelength blue and green light is scattered more and lost. As a result the star appears reddish, although if the view were unobstructed it would shine a brilliant blue-white.

As well as being very bright, VFTS 682 is also very hot, with a surface temperature of about 50 000 degrees Celsius [4]. Stars with these unusual properties may end their short lives not just as a supernova, as is normal for high-mass stars, but just possibly as an even more dramatic long-duration gamma-ray burst [5], the brightest explosions in the Universe.

Although VFTS 682 seems to now be alone it is not very far away from the very rich star cluster RMC 136 (often called just R 136), which contains several similar “superstars” (eso1030) [6].

“The new results show that VFTS 682 is a near identical twin of one of the brightest superstars at the heart of the R 136 star cluster,” adds Paco Najarro, another member of the team from CAB (INTA-CSIC, Spain).

Is it possible that VFTS 682 formed there and was ejected? Such “runaway stars” are known, but all are much smaller than VFTS 682 and it would be interesting to see how such a heavy star could be thrown from the cluster by gravitational interactions.

“It seems to be easier to form the biggest and brightest stars in rich star clusters,” adds Jorick Vink, another member of the team. “And although it may be possible, it is harder to understand how these brilliant beacons could form on their own. This makes VFTS 682 a really fascinating object.”

[1] The VFTS 682 analysis was led by Jorick Vink, Götz Gräfener and Joachim Bestenlehner from the Armagh Observatory,

[2] The name VFTS is short for VLT-FLAMES Tarantula Survey, an ESO Large Programme led by Christopher Evans of the UK Astronomy Technology Centre, Edinburgh, UK.

[3] The Local Group is a small group of galaxies that includes the Milky Way and Andromeda galaxies, as well as the Magellanic Clouds and many smaller galaxies.

[4] For comparison the surface temperature of the Sun is about 5500 degrees Celsius.

[5] Gamma-ray bursts are among the most energetic events in the Universe and the high energy radiation that they produce can be detected by orbiting space craft. Gamma-ray bursts lasting longer than two seconds are referred to as long bursts and those with a shorter duration are known as short bursts. Long bursts are associated with the supernova explosions of massive young stars in star-forming galaxies. Short bursts are not well understood, but are thought to originate from the merger of two compact objects such as neutron stars.

[6] If VFTS 682 is at the same distance from the Earth as R 136 then it lies about 90 light-years from the centre of the cluster. If the distances are significantly different then the separation could be much greater.
More information

This research was presented in a paper, “The VLT-FLAMES Tarantula Survey III: A very massive star in apparent isolation from the massive cluster R136”, to appear in Astronomy & Astrophysics.

The team is composed of Joachim M. Bestenlehner (Armagh Observatory, UK), Jorick S.Vink (Armagh), G. Gräfener (Armagh), F. Najarro (Centre of Astrobiology, Madrid, Spain), C. J. Evans (UK Astronomy Technology Centre, Edinburgh, UK), N. Bastian (Excellence Cluster Universe, Garching, Germany; University of Exeter, UK), A. Z. Bonanos (National Observatory of

Athens, Greece), E. Bressert (Exeter; ESO; Harvard Smithsonian Center for Astrophysics, Cambridge, USA), P. A. Crowther (University of Sheffield, UK), E. Doran (Sheffield), K. Friedrich (Argelander Institute, University of Bonn, Germany), V.Hénault-Brunet (University of Edinburgh, UK), A. Herrero (University of La Laguna, Tenerife, Spain; ESO), A. de Koter (University of Amsterdam; Utrecht University, Netherlands), N. Langer (Argelander Institute), D. J. Lennon (ESA; Space Telescope Science Institute, Baltimore, USA), J. Maíz Apellániz (Institute of Astrophysics of Andalucia, Granada, Spain), H. Sana (University of Amsterdam), I. Soszynski (Warsaw University, Poland), and W. D. Taylor (University of Edinburgh).

ESO, the European Southern Observatory, is the foremost intergovernmental astronomy organisation in Europe and the world’s most productive astronomical observatory. It is supported by 15 countries: Austria, Belgium, Brazil, the Czech Republic, Denmark, France, Finland, Germany, Italy, the Netherlands, Portugal, Spain, Sweden, Switzerland and the United Kingdom. ESO carries out an ambitious programme focused on the design, construction and operation of powerful ground-based observing facilities enabling astronomers to make important scientific discoveries. ESO also plays a leading role in promoting and organising cooperation in astronomical research. ESO operates three unique world-class observing sites in Chile: La Silla, Paranal and Chajnantor. At Paranal, ESO operates the Very Large Telescope, the world’s most advanced visible-light astronomical observatory and VISTA, the world’s largest survey telescope. ESO is the European partner of a revolutionary astronomical telescope ALMA, the largest astronomical project in existence. ESO is currently planning a 42-metre European Extremely Large optical/near-infrared Telescope, the E-ELT, which will become “the world’s biggest eye on the sky”.

Research paper
Photos of the VLT


Joachim M. Bestenlehner
PhD Student
Armagh Observatory, Northern Ireland, UK
Tel: +44 28 3751 2961
Cell: +44 75 9344 9888
Email: jbl@arm.ac.uk

Dr Jorick S. Vink
Senior Research Astronomer
Armagh Observatory, Northern Ireland, UK
Tel: +44 28 3751 2971
Cell: +44 79 7922 7817
Email: jsv@arm.ac.uk

Richard Hook
ESO, La Silla, Paranal, E-ELT and Survey Telescopes Public Information Officer
Garching bei München, Germany
Tel: +49 89 3200 6655
Cell: +49 151 15 37 3591
Email: rhook@eso.org

Tuesday, May 24, 2011

Carina Nebula: Nearby Supernova Factory Ramps Up

Carina Nebula
Credit NASA/CXC/PSU/L.Townsley et al.

This large Chandra image shows the Carina Nebula, a star-forming region in the Sagittarius-Carina arm of the Milky Way a mere 7,500 light years from Earth. Chandra's sharp X-ray vision has detected over 14,000 stars in this region, revealed a diffuse X-ray glow, and provided strong evidence that massive stars have already self-destructed in this nearby supernova factory.

The lower energy X-rays in this image are red, the medium energy X- rays are green, and the highest energy X-rays are blue. The Chandra survey has a large field of 1.4 square degrees, made of a mosaic of 22 individual Chandra pointings. In total, this image represents 1.2 million seconds -- or nearly two weeks -- of Chandra observing time. A great deal of multi-wavelength data has been used in combination with this new Chandra campaign, including infrared observations from the Spitzer Space Telescope and the Very Large Telescope (VLT).

Several pieces of evidence support the idea that supernova production has already begun in this star-forming region. Firstly, there is an observed deficit of bright X-ray sources in Trumpler 15, suggesting that some of the massive stars in this cluster were already destroyed in supernova explosions. Trumpler 15 is located in the northern part of the image, as shown in a labeled version (roll your mouse over the image above), and is one of ten star clusters in the Carina complex. Several other well known clusters are shown in the labeled image .

The detection of six possible neutron stars, the dense cores often left behind after stars explode in supernovas, provides additional evidence that supernova activity is ramping up in Carina. Previous observations had only detected one neutron star in Carina. These six neutron star candidates are too faint to be easily picked out in this large-scale image of Carina.

The diffuse emission observed by Chandra also supports the idea that supernovas have already erupted in Carina. Some of the diffuse X-ray emission almost certainly comes from the winds of massive stars, but some may also come from the remains of supernova explosions.

Finally, a new population of young massive stars has been detected in Carina, potentially doubling the number of known young, massive stars that are mostly destined to be destroyed later in supernova explosions. These stars are seen as bright X-ray sources scattered across the image. Also shown in the labeled image is the most famous member of the Carina Nebula, Eta Carinae, a massive, unstable star that may be on the verge of exploding as a supernova. These latest results suggest Eta Carinae is not alone in its volatility within the Carina Nebula.

Fast Facts for Carina Nebula:

Scale: Image is 1.13 deg across (about 148 light years)
Category: Normal Stars & Star Clusters
Coordinates: (J2000) RA 10h 45m 04s | Dec -59° 41' 03"
Constellation: Carina
Observation Date: 38 pointings between Sep 21, 2004 and Oct 15, 2008
Observation Time: 364 hours 39 min (15 days 4 hours 39 min)
Obs. ID: 4495, 6402, 6578, 9481-9499, 9508, 9816-9817, 9830-9831, 9849, 9856-9857, 9859-9861, 9889-9891, 9894, 10784
Color Code: X-ray 0.5-0.7 keV (Red), 0.7-0.86 (Green), 0.86-0.96 (Blue)
Instrument: ACIS
References: L.Townsley et al., 2011, ApJS, 194:1; M.Povich et al., 2011, ApJS, 194:6; J.Wang et al., 2011, ApJS, 194:11; L.Townsley et al., 2011, ApJS, 194:15
Distance Estimate: About 7,500 light years

Monday, May 23, 2011

Kepler-10 Stellar Family Portrait

Kepler-10 star ystem
Credit: NASA/Ames/JPL-Caltech/T. Pyle

This artist's conception depicts the Kepler-10 star system, located about 560 light-years away near the Cygnus and Lyra constellations. Kepler has discovered two planets around this star. Kepler-10b is, to date, the smallest known rocky exoplanet, or planet outside our solar system (dark spot against yellow sun). This planet, which has a radius of 1.4 times that of Earth's, whips around its star every .8 days. Its discovery was announced in Jan. 2011.

Now, in May 2011, the Kepler team is announcing another member of the Kepler-10 family, called Kepler-10c (larger foreground object). It's bigger than Kepler-10b with a radius of 2.2 times that of Earth's, and it orbits the star every 45 days. Both planets would be blistering hot worlds.

Kepler-10c was first identified by Kepler, and later validated using a combination of a computer simulation technique called "Blender," and NASA's Spitzer Space Telescope. Both of these methods are powerful ways to validate the Kepler planets that are too small and faraway for ground-based telescopes to confirm using the radial-velocity technique. The Kepler team says that a large fraction of their discoveries will be validated with both of these methods.

In the case of Kepler-10c, scientists can be 99.998 percent sure that the signal they detected is from an orbiting planet. Part of this confidence comes from the fact that Spitzer, an infrared observatory, saw a signal similar to what Kepler detected in visible light. If the signal were coming from something other than an orbiting planet -- for example an indistinguishable background pair of orbiting stars -- then scientists would expect to see different signals in visible and infrared light.

Hubble Views the Star that Changed the Universe

Cepheid Variable Star V1 in M31
NASA, ESA, and the Hubble Heritage Team (STScI/AURA)
View this image

Though the universe is filled with billions upon billions of stars, the discovery of a single variable star in 1923 altered the course of modern astronomy. And, at least one famous astronomer of the time lamented that the discovery had shattered his world view.

The star goes by the inauspicious name of Hubble variable number one, or V1, and resides in the outer regions of the neighboring Andromeda galaxy, or M31. But in the early 1900s, most astronomers considered the Milky Way a single "island universe" of stars, with nothing observable beyond its boundaries. Andromeda was cataloged as just one of many faint, fuzzy patches of light astronomers called "spiral nebulae."

Were these spiral nebulae part of the Milky Way or were they independent island universes lying outside our galaxy? Astronomers didn't know for sure, until Edwin Hubble found a star in Andromeda that brightened and faded in a predictable pattern, like a lighthouse beacon, and identified it as V1, a Cepheid variable. This special type of star had already been proven to be a reliable distance marker within our galaxy.

The star helped Hubble show that Andromeda was beyond our galaxy and settled the debate over the status of the spiral nebulae. The universe became a much bigger place after Hubble's discovery, much to the dismay of astronomer Harlow Shapley, who believed the fuzzy nebulae were part of our Milky Way.

Nearly 90 years later, V1 is in the spotlight again. Astronomers pointed Edwin Hubble's namesake, NASA's Hubble Space Telescope, at the star once again, in a symbolic tribute to the legendary astronomer's milestone observation.

Astronomers with the Space Telescope Science Institute's Hubble Heritage Project partnered with the American Association of Variable Star Observers (AAVSO) to study the star. AAVSO observers followed V1 for six months, producing a plot, or light curve, of the rhythmic rise and fall of the star's light. Based on this light curve, the Hubble Heritage team scheduled telescope time to capture images of the star.

"V1 is the most important star in the history of cosmology," says astronomer Dave Soderblom of the Space Telescope Science Institute (STScI) in Baltimore, Md., who proposed the V1 observations.

"It's a landmark discovery that proved the universe is bigger and chock full of galaxies. I thought it would be nice for the Hubble telescope to look at this special star discovered by Hubble, the man."

But Hubble Heritage team member Max Mutchler of the STScI says that this observation is more than just a ceremonial nod to a famous astronomer.

"This observation is a reminder that Cepheids are still relevant today," he explains. "Astronomers are using them to measure distances to galaxies much farther away than Andromeda. They are the first rung on the cosmic distance ladder."

The Hubble and AAVSO observations of V1 will be presented at a press conference May 23 at the American Astronomical Society meeting in Boston, Mass.

Ten amateur astronomers from around the world, along with AAVSO Director Arne Henden, made 214 observations of V1 between July 2010 and December 2010. They obtained four pulsation cycles, each of which lasts more than 31 days. The AAVSO study allowed the Hubble Heritage team to target Hubble observations that would capture the star at its brightest and dimmest phases.

The observations were still tricky, though. "The star's brightness has a gradual decline followed by a sharp spike upward, so if you're off by a day or two, you could miss it," Mutchler explains.

Using the Wide Field Camera 3, the team made four observations in December 2010 and January 2011.

"The Hubble telescope sees many more and much fainter stars in the field than Edwin Hubble saw, and many of them are some type of variable star," Mutchler says. "Their blinking makes the galaxy seem alive. The stars look like grains of sand, and many of them have never been seen before."

For Soderblom, the Hubble observations culminated more than 25 years of promoting the star. Shortly after Soderblom arrived at the Institute in 1984, he thought it would be fitting to place a memento of Edwin Hubble's aboard the space shuttle Discovery, which would carry the Hubble Space Telescope into space.

"At first, I thought the obvious artifact would be his pipe, but [cosmologist] Allan Sandage [Edwin Hubble's protégé] suggested another idea: the photographic glass plate of V1 that Hubble made in 1923," Soderblom recalls.

He made 15 film copies of the original 4-inch-by-5-inch glass plate. Ten of them flew onboard space shuttle Discovery in 1990 on the Hubble deployment mission. Fittingly, two of the remaining five film copies were part of space shuttle Atlantis's cargo in 2009 for NASA's fifth servicing mission to Hubble. One of those copies was carried aboard by astronaut and astronomer John Grunsfeld, now the STScI's deputy director.

Telltale Star Expands the Known Universe

Prior to the discovery of V1 many astronomers thought spiral nebulae, such as Andromeda, were part of our Milky Way galaxy. Others weren't so sure. In fact, astronomers Shapley and Heber Curtis held a public debate in 1920 over the nature of these nebulae. During the debate, Shapley championed his measurement of 300,000 light-years for the size of the Milky Way. Though Shapley overestimated its size, he was correct in asserting that the Milky Way was much larger than the commonly accepted dimensions. He also argued that spiral nebulae were much smaller than the giant Milky Way and therefore must be part of our galaxy. But Curtis disagreed. He thought the Milky Way was smaller than Shapley claimed, leaving room for other island universes beyond our galaxy.

To settle the debate, astronomers had to establish reliable distances to the spiral nebulae. So they searched for stars in the nebulae whose intrinsic brightness they thought they understood. Knowing a star's true brightness allowed astronomers to calculate how far away it was from Earth. But some of the stars they selected were not dependable milepost markers.

For example, Andromeda, the largest of the spiral nebulae, presented ambiguous clues to its distance. Astronomers had observed different types of exploding stars in the nebula. But they didn't fully understand the underlying stellar processes, so they had difficulty using those stars to calculate how far they were from Earth. Distance estimates to Andromeda, therefore, varied from nearby to far away. Which distance was correct? Edwin Hubble was determined to find out.

The astronomer spent several months in 1923 scanning Andromeda with the 100-inch Hooker telescope, the most powerful telescope of that era, at Mount Wilson Observatory in California. Even with the sharp-eyed telescope, Andromeda was a monstrous target, about 5 feet long at the telescope's focal plane. He therefore took many exposures covering dozens of photographic glass plates to capture the whole nebula.

He concentrated on three regions. One of them was deep inside a spiral arm. On the night of Oct. 5, 1923, Hubble began an observing run that lasted until the early hours of Oct. 6. Under poor viewing conditions, the astronomer made a 45-minute exposure that yielded three suspected novae, a class of exploding star. He wrote the letter "N," for nova, next to each of the three objects.

Later, however, Hubble made a startling discovery when he compared the Oct. 5-6 plate with previous exposures of the novae. One of the so-called novae dimmed and brightened over a much shorter time period than seen in a typical nova.

Hubble obtained enough observations of V1 to plot its light curve, determining a period of 31.4 days, indicating the object was a Cepheid variable. The period yielded the star's intrinsic brightness, which Hubble then used to calculate its distance. The star turned out to be 1 million light-years from Earth, more than three times Shapley's calculated diameter of the Milky Way.

Taking out his marking pen, Hubble crossed out the "N" next to the newfound Cepheid variable and wrote "VAR," for variable, followed by an exclamation point.

For several months the astronomer continued gazing at Andromeda, finding another Cepheid variable and several more novae. Then Hubble sent a letter along with a light curve of V1 to Shapley telling him of his discovery. After reading the letter, Shapley was convinced the evidence was genuine. He reportedly told a colleague, "Here is the letter that destroyed my universe."

By the end of 1924 Hubble had found 36 variable stars in Andromeda, 12 of which were Cepheids. Using all the Cepheids, he obtained a distance of 900,000 light-years. Improved measurements now place Andromeda at 2 million light-years away.

"Hubble eliminated any doubt that Andromeda was extragalactic," says Owen Gingerich, professor emeritus of Astronomy and of the History of Science at Harvard-Smithsonian Center for Astrophysics in Cambridge, Mass. "Basically, astronomers didn't know the distance to novae, so they had to make a rough estimate as to where they were and therefore what their absolute luminosity was. But that is on very treacherous ground. When you get a Cepheid that's been reasonably calculated, the period will tell you where it sits on the luminosity curve, and from that you can calculate a distance."

Shapley and astronomer Henry Norris Russell urged Hubble to write a paper for a joint meeting of the American Astronomical Society and American Association for the Advancement of Science at the end of December 1924. Hubble's paper, entitled "Extragalactic Nature of Spiral Nebulae," was delivered in absentia and shared the prize for the best paper. A short article about the award appeared in the Feb. 10, 1925, issue of The New York Times. Gingerich says Hubble's discovery was not big news at the meeting because the astronomer had informed the leading astronomers of his result months earlier.

Edwin Hubble's observations of V1 became the critical first step in uncovering a larger, grander universe. He went on to find many galaxies beyond the Milky Way. Those galaxies, in turn, allowed him to determine that the universe is expanding.

Could Hubble ever have imagined that nearly 100 years later, technological advances would allow amateur astronomers to perform similar observations of V1 with small telescopes in their backyards? Or, could Hubble ever have dreamed that a space-based telescope that bears his name would continue his quest to precisely measure the universe's expansion rate?


Donna Weaver / Ray Villard
Space Telescope Science Institute, Baltimore, Md.
410-338-4493 / 410-338-4514
dweaver@stsci.edu / villard@stsci.edu

Dave Soderblom / Max Mutchler
Space Telescope Science Institute, Baltimore, Md.
410-338-4543 / 410-338-1321

How to Learn a Star's True Age

Using the unique capabilities of NASA's Kepler space telescope, Soren Meibom (CfA) and his collaborators measured the rotation rates for stars in a 1-billion-year-old cluster called NGC 6811. They found rotation periods ranging from 1 to 11 days (with hotter, more massive stars spinning faster), compared to the 30-day spin rate of our Sun. More importantly, they found a strong relationship between stellar mass and rotation rate, with little scatter. This result confirms that gyrochronology is a promising new method to learn the ages of isolated stars. Credit: Anthony Ayiomamitis

Artist's conception of a hypothetical exoplanet. Gyrochronology is a promising new method to learn the ages of isolated stars, including all stars known to have planets. Credit: David A. Aguilar (CfA). High Resolution Image (jpg)

Cambridge, MA - For many movie stars, their age is a well-kept secret. In space, the same is true of the actual stars. Like our Sun, most stars look almost the same for most of their lives. So how can we tell if a star is one billion or 10 billion years old? Astronomers may have found a solution - measuring the star's spin.

"A star's rotation slows down steadily with time, like a top spinning on a table, and can be used as a clock to determine its age," says astronomer Soren Meibom of the Harvard-Smithsonian Center for Astrophysics.

Meibom presented his findings today in a press conference at the 218th meeting of the American Astronomical Society.

Knowing a star's age is important for many astronomical studies and in particular for planet hunters. With the bountiful harvest from NASA's Kepler spacecraft (launched in 2009) adding to previous discoveries, astronomers have found nearly 2,000 planets orbiting distant stars. Now, they want to use this new zoo of planets to understand how planetary systems form and evolve and why they are so different from each other.

"Ultimately, we need to know the ages of the stars and their planets to assess whether alien life might have evolved on these distant worlds," says Meibom. "The older the planet, the more time life has had to get started. Since stars and planets form together at the same time, if we know a star's age, we know the age of its planets too."

Learning a star's age is relatively easy when it's in a cluster of hundreds of stars that all formed at the same time. Astronomers have known for decades that if they plot the colors and brightnesses of the stars in a cluster, the pattern they see can be used to tell the cluster's age. But this technique only works on clusters. For stars not in clusters (including all stars known to have planets), determining the age is much more difficult.

Using the unique capabilities of the Kepler space telescope, Meibom and his collaborators measured the rotation rates for stars in a 1-billion-year-old cluster called NGC 6811. This new work nearly doubles the age covered by previous studies of younger clusters. It also significantly adds to our knowledge of how a star's spin rate and age are related.

If a relationship between stellar rotation and age can be established by studying stars in clusters, then measuring the rotation period of any star can be used to derive its age - a technique called gyrochronology (pronounced ji-ro-kron-o-lo-gee). For gyrochronology to work, astronomers first must calibrate their new "clock."

They begin with stars in clusters with known ages. By measuring the spins of cluster stars, they can learn what spin rate to expect for that age. Measuring the rotation of stars in clusters with different ages tells them exactly how spin and age are related. Then by extension, they can measure the spin of a single isolated star and calculate its age.

To measure a star's spin, astronomers look for changes in its brightness caused by dark spots on its surface - the stellar equivalent of sunspots. Any time a spot crosses the star's face, it dims slightly. Once the spot rotates out of view, the star's light brightens again. By watching how long it takes for a spot to rotate into view, across the star and out of view again, we learn how fast the star is spinning.

The changes in a star's brightness due to spots are very small, typically a few percent or less, and become smaller the older the star. Therefore, the rotation periods of stars older than about half a billion years can't be measured from the ground where Earth's atmosphere interferes. Fortunately, this is not a problem for the Kepler spacecraft. Kepler was designed specifically to measure stellar brightnesses very precisely in order to detect planets (which block a star's light ever so slightly if they cross the star's face from our point of view).

To extend the age-rotation relationship to NGC 6811, Meibom and his colleagues faced a herculean task. They spent four years painstakingly sorting out stars in the cluster from unrelated stars that just happened to be seen in the same direction. This preparatory work was done using a specially designed instrument (Hectochelle) mounted on the MMT telescope on Mt. Hopkins in southern Arizona. Hectochelle can observe 240 stars at the same time, allowing them to observe nearly 7000 stars over four years. Once they knew which stars were the real cluster stars, they used Kepler data to determine how fast those stars were spinning.

They found rotation periods ranging from 1 to 11 days (with hotter, more massive stars spinning faster), compared to the 30-day spin rate of our Sun. More importantly, they found a strong relationship between stellar mass and rotation rate, with little scatter. This result confirms that gyrochronology is a promising new method to learn the ages of isolated stars.

The team now plans to study other, older star clusters to continue calibrating their stellar "clocks." Those measurements will be more challenging because older stars spin slower and have fewer and smaller spots, meaning that the brightness changes will be even smaller and more drawn out. Nevertheless, they feel up to the challenge.

"This work is a leap in our understanding of how stars like our Sun work. It also may have an important impact on our understanding of planets found outside our solar system," said Meibom.

The paper reporting this research has been accepted for publication in The Astrophysical Journal Letters and is posted online.

NASA Ames Research Center is responsible for the ground system development, mission operations and science data analysis. NASA's Jet Propulsion Laboratory in Pasadena, Calif., managed the Kepler mission development. Ball Aerospace and Technologies Corp. in Boulder, Colo., developed the Kepler flight system, and supports mission operations with the Laboratory for Atmospheric and Space Physics at the University of Colorado, Boulder. The Space Telescope Science Institute in Baltimore archives, hosts and distributes the Kepler science data.

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.

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David A. Aguilar
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Harvard-Smithsonian Center for Astrophysics

Christine Pulliam
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Harvard-Smithsonian Center for Astrophysics