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The galaxy, Dragonfly 44, is located in the nearby Coma constellation and had been overlooked until last year because of its unusual composition: It is a diffuse "blob" about the size of the Milky Way, but with far fewer stars. "Very soon after its discovery, we realized this galaxy had to be more than meets the eye. It has so few stars that it would quickly be ripped apart unless something was holding it together," said Yale University astronomer Pieter van Dokkum, lead author of a paper in the Astrophysical Journal Letters. Van Dokkum's team was able to get a good look at Dragonfly 44 thanks to the W.M. Keck Observatory and the Gemini North telescope, both in Hawaii. Astronomers used observations from Keck, taken over six nights, to measure the velocities of stars in the galaxy. They used the 8-meter Gemini North telescope to reveal a halo of spherical clusters of stars around the galaxy's core, similar to the halo that surrounds our Milky Way galaxy. Star velocities are an indication of the galaxy's mass, the researchers noted. The faster the stars move, the more mass its galaxy will have. "Amazingly, the stars move at velocities that are far greater than expected for such a dim galaxy. It means that Dragonfly 44 has a huge amount of unseen mass," said co-author Roberto Abraham of the University of Toronto. Scientists initially spotted Dragonfly 44 with the Dragonfly Telephoto Array, a telescope invented and built by van Dokkum and Abraham. Dragonfly 44's mass is estimated to be 1 trillion times the mass of the Sun, or 2 tredecillion kilograms (a 2 followed by 42 zeros), which is similar to the mass of the Milky Way. However, only one-hundredth of 1% of that is in the form of stars and "normal" matter. The other 99.99% is in the form of dark matter—a hypothesized material that remains unseen but may make up more than 90% of the universe. The researchers note that finding a galaxy composed mainly of dark matter is not new; ultra-faint dwarf galaxies have similar compositions. But those galaxies were roughly 10,000 times less massive than Dragonfly 44. "We have no idea how galaxies like Dragonfly 44 could have formed," said Abraham. "The Gemini data show that a relatively large fraction of the stars is in the form of very compact clusters, and that is probably an important clue. But at the moment we're just guessing." Van Dokkum, the Sol Goldman Family Professor of Astronomy and Physics at Yale, added: "Ultimately what we really want to learn is what dark matter is. The race is on to find massive dark galaxies that are even closer to us than Dragonfly 44, so we can look for feeble signals that may reveal a dark matter particle." Additional co-authors are Shany Danieli, Allison Merritt, and Lamiya Mowla of Yale, Jean Brodie of the University of California Observatories, Charlie Conroy of Harvard, Aaron Romanowsky of San Jose State University, and Jielai Zhang of the University of Toronto. Explore further: Astronomers find seven dwarf galaxies with new telescope More information: "A High Stellar Velocity Dispersion and ~100 Globular Clusters for the Ultra Diffuse Galaxy Dragonfly 44," Pieter van Dokkum et al., 2016 Sept. 1, Astrophysical Journal Letters: iopscience.iop.org/article/10.3847/2041-8205/828/1/L6 , Arxiv: arxiv.org/abs/1606.06291


News Article
Site: http://www.rdmag.com/rss-feeds/all/rss.xml/all

PASADENA, CA — Promising new calibration tools, called laser frequency combs, could allow astronomers to take a major step in discovering and characterizing earthlike planets around other stars. These devices generate evenly spaced lines of light, much like the teeth on a comb for styling hair or the tick marks on a ruler — hence their nickname of "optical rulers." The tick marks serve as stable reference points when making precision measurements, such as those of the small shifts in starlight caused by planets pulling gravitationally on their parent stars. Yet today's commercially available combs have a significant drawback. Because their tick marks are so finely spaced, the light output of these combs must be filtered to produce useful reference lines. This extra step adds complexity to the system and requires costly additional equipment. To resolve these kinds of issues, Caltech researchers looked to a kind of comb not previously deployed for astronomy. The novel comb produces easily resolvable lines, without any need for filtering. Furthermore, the Caltech comb is built from off-the-shelf components developed by the telecommunications industry. "We have demonstrated an alternative approach that is simple, reliable and relatively inexpensive," says paper coauthor Kerry Vahala, the Ted and Ginger Jenkins Professor of Information Science and Technology and Applied Physics, as well as the executive officer for Applied Physics and Materials Science in Caltech's Division of Engineering and Applied Science. The kind of frequency comb used by the researchers previously has been studied in the Vahala group in a different application, the generation of high-stability microwaves. "We believe members of the astronomical community could greatly benefit in their exoplanet hunting and characterization studies with this new laser frequency comb instrument," says Xu Yi, a graduate student in Vahala's lab and the lead author of a paper describing the work published in the January 27, 2016, issue of the journal Nature Communications. Scientists first began widely using laser frequency combs as precision rulers in the late 1990s in fields like metrology and spectroscopy; for their work, the technology's developers (John L. Hall of JILA and the National Institute of Standards and Technology (NIST) and Theodor Hänsch of the Max Planck Institute of Quantum Optics and Ludwig Maximilians University Munich) were awarded half of the Nobel Prize in Physics in 2005. In astronomy, the combs are starting to be utilized in the radial velocity, or "wobble" method, the earliest and among the most successful methods for identifying exoplanets. The "wobble" refers to the periodic changes in a star's motion, accompanied by starlight shifts owing to the Doppler effect, that are induced by the gravitational pull of an exoplanet orbiting around the star. The magnitude of the shift in the starlight's wavelength — on the order of quadrillionths of a meter — together with the period of the wobble can be used to determine an exoplanet's mass and orbital distance from its star. These details are critical for assessing habitability parameters, such as surface temperature and the eccentricity of the exoplanet's orbit. With exoplanets that pass directly in front of (or "transit") their host star, allowing their radius to be determined directly, it is even possible to determine the bulk composition — for example, if the planet is built up primarily of gas, ice or rock. In recent years, so-called mode-locked laser combs have proven useful in this task. These lasers generate a periodic stream of ultrashort light pulses to create the comb. With such combs, however, approximately 49 out of every 50 tick marks must be blocked out. This requires temperature- and vibration-insensitive filtering equipment. The new electro-optical comb that the Caltech team studied relies on microwave modulation of a continuous laser source, rather than a pulsed laser. It produces comb lines spaced by tens of gigahertz. These lines have from 10 to 100 times wider spacing than the tick marks of pulsed laser combs. To see how well a prototype would work in the field, the researchers took their comb to Mauna Kea in Hawaii. In September 2014, the instrument was tested at the NASA Infrared Telescope Facility (IRTF); in March 2015, it was tested with the Near Infrared Spectrometer on the W. M. Keck Observatory's Keck II telescope with the assistance of UCLA astronomer Mike Fitzgerald (BS '00) and UCLA graduate student Emily Martin, coauthors on the paper. The researchers found that their simplified comb (the entire electro-optical comb apparatus requires only half of the space available on a standard 19-inch instrumentation rack) provided steady calibration at room temperature for more than five days at IRTF. The comb also operated flawlessly during the second test — despite having been disassembled, stored for six months, and reassembled. "From a technological maturity point of view, the frequency comb we have developed is already basically ready to go and could be installed at many telescopes," says paper coauthor Scott Diddams of NIST. The Caltech comb produces spectral lines in the infrared, making it ideal for studying red dwarf stars, the most common stars in the Milky Way. Red dwarf stars are brightest in infrared wavelengths. Because red dwarfs are small, cool and dim, planets orbiting these types of stars are easier to detect and analyze than those orbiting hotter sun-like stars. NASA's Kepler space observatory has shown that almost all red dwarf stars host planets in the range of one to four times the size of Earth, with up to 25 percent of these planets located in the temperate, or "habitable," zone around their host stars. Thus, many astronomers predict that red dwarfs provide the best chance for the first discovery of a world capable of supporting life. "Our goal is to make these laser frequency combs simple and sturdy enough that you can slap them onto every telescope, and you don't have to think about them anymore," says paper coauthor Charles Beichman, senior faculty associate in astronomy and the executive director of the NASA ExoPlanet Science Institute at Caltech. "Having these combs routinely available as a modest add-on to current and future instrumentation really will expand our ability to find potentially habitable planets, particularly around very cool red dwarf stars," he says. The research team is planning to double the frequency of the prototype comb's light output — now centered around 1,550 nanometers, in the infrared — to reach into the visible light range. Doing so would allow the comb also to calibrate spectra from sun-like stars, whose light output is at shorter, visible wavelengths and, thus, seek out planets that are Earth's "twins." Other authors of the paper are Jiang Li, a visitor in applied physics and materials science, graduate students Peter Gao and Michael Bottom, and scientific research assistant Elise Furlan, all from Caltech; Stephanie Leifer, Jagmit Sandhu, Gautam Vasisht, and Pin Chen of JPL; Peter Plavchan (BS '01), formerly at Caltech and now a professor at Missouri State University; G. Ycas of NIST; Jonathan Gagne of the University of Montréal; and Greg Doppmann of the Keck Observatory. The paper is titled "Demonstration of a near-IR line-referenced electro-optical laser frequency comb for precision radial velocity measurements in astronomy." The research performed at Caltech and JPL was funded through the President's and Director's Fund Program, and the work at NIST was funded by the National Science Foundation.


News Article
Site: http://phys.org/space-news/

GN-z11, as they named it, seemed small, reddish and unexpectedly bright. It appeared far away even by cosmic standards. But because it was beyond the optimal reach of NASA's Hubble Space Telescope, it left them puzzled. Now they're certain it represents history. The international team, which includes an astronomer based in Baltimore, pushed Hubble to its limits this year to demonstrate that GN-z11 is the most distant galaxy ever observed. "The light that left this galaxy that we're observing now left the galaxy 13.4 billion years ago," said Gabriel Brammer, an astronomer at the Space Telescope Science Institute in Baltimore and the study's second author. "As far as we know, the universe itself is about 13.8 billion years old. We're seeing a galaxy as it was when the universe was about 3 percent of its current age." The light from GN-z11 is 200 million years closer to the Big Bang than that of the previous record-holder, a galaxy called EGSY8p7 that was found last year. That puts GN-z11 about 32 billion light years away. Because expansion of the universe over billions of years makes distance calculation complex, astronomers generally represent distance as a function of time -how long it takes light rays originating at a given object to reach us. Another way they express distance is through a unit of measurement called redshift. The farther away an object, the longer - and therefore redder - the light wavelengths are when they reach us. The spectroscopic redshift of EBSY8p7 was measured at a sizable 8.8, then believed to be at or beyond the outer edge of Hubble's range. GN-z11 has a redshift of 11.1, such a big jump that few saw it coming. The findings - described in a recent article in The Astrophysical Journal - give scientists what appears to be their best view yet of conditions near the end of the so-called Dark Ages of the Universe, when the cosmos was still opaque and just before the first stars and quasars formed. "We've taken a major step back in time, beyond what we'd ever expected to be able to do with Hubble," said Pascal Oesch, a Yale University astronomer and the study's principal investigator. Oesch and his team discovered GN-z11 in 2014 during a routine survey of a small patch of sky. In addition to taking note of the galaxy, they used imaging from both the orbiting Hubble - the most powerful telescope in history - and NASA's Spitzer Space Telescope, an infrared instrument in Pasadena, Calif., to ascertain its color to estimate its distance. They came up with an estimated redshift of 10.2, which in itself would have been a record for Hubble, but the image came with enough visual interference, or "noise," that the number had a sizable margin of error. Also, Brammer said, team members couldn't be sure they weren't seeing an "interloper" - a much closer object - by mistake. But the galaxy's unusual brightness gave investigators a lucky second option: to use a more exacting measurement method known as spectroscopy - a way of splitting the visible light into its component colors - to firm up the distance estimate. Analyzed with this method, GN-z11 registered the record redshift of 11.1 - and it exhibited many of the clear properties of an infant galaxy, not an interloper. For one thing, the team found, even though it's only 0.04 percent the size of our Milky Way galaxy, GN-z11 appears to be forming stars at a staggering rate, about three times more rapidly than expected and 20 times more quickly than the Milky Way. That, they say, is why it's so much more luminous than many models predicted. "Our earlier work had suggested that such bright galaxies should not exist so early in the universe," Marijn Franx, a team member from the University of Leiden in the Netherlands, told Astronomy Magazine. "What we're seeing is young stars, massive stars, stars just being formed. At first glance, this galaxy appeared to be red, but that was because it's so far away. On closer look, it's actually very blue," Oesch said. Hubble has amassed hundreds of images of galaxies in the range of redshift 7 or 8 in its 26-year existence, Brammer said, allowing astronomers to develop a relatively clear picture of those galaxies' general properties - their star formation rates, their chemical makeup, their brightness - at those times and distances. That has helped scientists create a fuller, more credible map of how the universe evolved back to about half a billion years after the Big Bang. It's harder to extrapolate such a clear picture from a single example of a redshift higher than 11, but astronomers say it's still striking to see evidence that at least one galaxy was up, running and fully active so much earlier than many previously believed. Astronomers believed there had to be a sizable time gap between the Big Bang and the eras in which the first stars took shape, forming the groups that would become galaxies, Oesch said. The team's work suggests the gap is smaller and the primordial population more active. Some in the field remain skeptical of the findings. Astronomer Richard Ellis of the European Southern Observatory said in an email that the luminosity the group claims is three times higher than that of similar bodies "at much later times," and that astronomers seeking to measure distances greater than redshift 10 usually do so in conjunction with powerful ground-based telescopes such as the ones at the W.M. Keck Observatory in Hawaii. Ellis said, "The ultimate proof can only come from a higher resolution spectrum such as those published for previous record-holders, either via a long integration with a ground-based telescope or, shortly, with the James Webb Space Telescope" - the Hubble's more powerful successor, which is now under construction and expected to be launched in 2018. Everyone agrees that the Hubble has looked as far off in the universe as it's going to, given the size of its primary mirror (2.4 meters in diameter) and other limitations. The Space Telescope Science Institute, which calibrates Hubble's instruments and interprets its raw data, is well along in the process of helping NASA build the Webb telescope, with a 6.5-meter mirror. Astronomers say Hubble's recent feats suggest the Webb will routinely be able to look farther, providing better answers to what Oesch calls "the very, very big" questions. "Where do these galaxies come from? Where did we all come from? Where did everything start?" he asked. "That's what we're really asking. We're getting closer all the time." Explore further: Spitzer and Hubble telescopes find rare galaxy at dawn of time


News Article | August 24, 2016
Site: http://phys.org/space-news/

The international University of California, Riverside-led SpARCS collaboration has discovered four of the most distant clusters of galaxies ever found, as they appeared when the universe was only 4 billion years old. Clusters are rare regions of the universe consisting of hundreds of galaxies containing trillions of stars, as well as hot gas and mysterious dark matter. Spectroscopic observations from the ground using the W. M. Keck Observatory in Hawaii and the Very Large Telescope in Chile confirmed the four candidates to be massive clusters. This sample is now providing the best measurement yet of when and how fast galaxy clusters stop forming stars in the early Universe.


News Article
Site: http://phys.org/space-news/

Yet today's commercially available combs have a significant drawback. Because their tick marks are so finely spaced, the light output of these combs must be filtered to produce useful reference lines. This extra step adds complexity to the system and requires costly additional equipment. To resolve these kinds of issues, Caltech researchers looked to a kind of comb not previously deployed for astronomy. The novel comb produces easily resolvable lines, without any need for filtering. Furthermore, the Caltech comb is built from off-the-shelf components developed by the telecommunications industry. "We have demonstrated an alternative approach that is simple, reliable, and relatively inexpensive," says paper coauthor Kerry Vahala, the Ted and Ginger Jenkins Professor of Information Science and Technology and Applied Physics as well as the executive officer for Applied Physics and Materials Science in Caltech's Division of Engineering and Applied Science. The kind of frequency comb used by the researchers previously has been studied in the Vahala group in a different application, the generation of high-stability microwaves. "We believe members of the astronomical community could greatly benefit in their exoplanet hunting and characterization studies with this new laser frequency comb instrument," says Xu Yi, a graduate student in Vahala's lab and the lead author of a paper describing the work published in the January 27, 2016, issue of the journal Nature Communications. Scientists first began widely using laser frequency combs as precision rulers in the late 1990s in fields like metrology and spectroscopy; for their work, the technology's developers (John L. Hall of JILA and the National Institute of Standards and Technology (NIST) and Theodor Hänsch of the Max Planck Institute of Quantum Optics and Ludwig Maximilians University Munich) were awarded half of the Nobel Prize in Physics in 2005. In astronomy, the combs are starting to be utilized in the radial velocity, or "wobble" method, the earliest and among the most successful methods for identifying exoplanets. The "wobble" refers to the periodic changes in a star's motion, accompanied by starlight shifts owing to the Doppler effect, that are induced by the gravitational pull of an exoplanet orbiting around the star. The magnitude of the shift in the starlight's wavelength—on the order of quadrillionths of a meter—together with the period of the wobble can be used to determine an exoplanet's mass and orbital distance from its star. These details are critical for assessing habitability parameters such as surface temperature and the eccentricity of the exoplanet's orbit. With exoplanets that pass directly in front of (or "transit") their host star, allowing their radius to be determined directly, it is even possible to determine the bulk composition—for example, if the planet is built up primarily of gas, ice, or rock. In recent years, so-called mode-locked laser combs have proven useful in this task. These lasers generate a periodic stream of ultrashort light pulses to create the comb. With such combs, however, approximately 49 out of every 50 tick marks must be blocked out. This requires temperature- and vibration-insensitive filtering equipment. The new electro-optical comb that the Caltech team studied relies on microwave modulation of a continuous laser source, rather than a pulsed laser. It produces comb lines spaced by tens of gigahertz. These lines have from 10 to 100 times wider spacing than the tick marks of pulsed laser combs. To see how well a prototype would work in the field, the researchers took their comb to Mauna Kea in Hawaii. In September 2014, the instrument was tested at the NASA Infrared Telescope Facility (IRTF); in March 2015, it was tested with the Near Infrared Spectrometer on the W. M. Keck Observatory's Keck II telescope with the assistance of UCLA astronomer Mike Fitzgerald (BS '00) and UCLA graduate student Emily Martin, coauthors on the paper. The researchers found that their simplified comb (the entire electro-optical comb apparatus requires only half of the space available on a standard 19-inch instrumentation rack) provided steady calibration at room temperature for more than five days at IRTF. The comb also operated flawlessly during the second test—despite having been disassembled, stored for six months, and reassembled. "From a technological maturity point of view, the frequency comb we have developed is already basically ready to go and could be installed at many telescopes," says paper coauthor Scott Diddams of NIST. The Caltech comb produces spectral lines in the infrared, making it ideal for studying red dwarf stars, the most common stars in the Milky Way. Red dwarf stars are brightest in infrared wavelengths. Because red dwarfs are small, cool, and dim, planets orbiting these types of stars are easier to detect and analyze than those orbiting hotter sun-like stars. NASA's Kepler space observatory has shown that almost all red dwarf stars host planets in the range of one to four times the size of Earth, with up to 25 percent of these planets located in the temperate, or "habitable," zone around their host stars. Thus, many astronomers predict that red dwarfs provide the best chance for the first discovery of a world capable of supporting life. "Our goal is to make these laser frequency combs simple and sturdy enough that you can slap them onto every telescope, and you don't have to think about them anymore," says paper coauthor Charles Beichman, senior faculty associate in astronomy and the executive director of the NASA ExoPlanet Science Institute at Caltech. "Having these combs routinely available as a modest add-on to current and future instrumentation really will expand our ability to find potentially habitable planets, particularly around very cool red dwarf stars," he says. The research team is planning to double the frequency of the prototype comb's light output—now centered around 1,550 nanometers, in the infrared—to reach into the visible light range. Doing so would allow the comb also to calibrate spectra from sun-like stars, whose light output is at shorter, visible wavelengths, and thus seek out planets that are Earth's "twins." Other authors of the paper are Jiang Li, a visitor in applied physics and materials science, graduate students Peter Gao and Michael Bottom, and scientific research assistant Elise Furlan, all from Caltech; Stephanie Leifer, Jagmit Sandhu, Gautam Vasisht, and Pin Chen of JPL; Peter Plavchan (BS '01), formerly at Caltech and now a professor at Missouri State University; G. Ycas of NIST; Jonathan Gagne of the University of Montréal; and Greg Doppmann of the Keck Observatory. Explore further: Future 'comb on a chip': NIST's compact frequency comb could go places More information: X. Yi et al. Demonstration of a near-IR line-referenced electro-optical laser frequency comb for precision radial velocity measurements in astronomy, Nature Communications (2016). DOI: 10.1038/ncomms10436

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