Posts tagged astronomers
CU-Boulder study: Spiral galaxies like Milky Way bigger than thought
Jun 27th
Let’s all fist bump: Spiral galaxies like our own Milky Way appear to be much larger and more massive than previously believed, according to a new University of Colorado Boulder study by researchers using the Hubble Space Telescope.
CU-Boulder Professor John Stocke, study leader, said new observations with Hubble’s $70 million Cosmic Origins Spectrograph, or COS, designed by CU-Boulder show that normal spiral galaxies are surrounded by halos of gas that can extend to over 1 million light-years in diameter. The current estimated diameter of the Milky Way, for example, is about 100,000 light-years. One light-year is roughly 6 trillion miles.
The material for galaxy halos detected by the CU-Boulder team originally was ejected from galaxies by exploding stars known as supernovae, a product of the star formation process, said Stocke of CU-Boulder’s astrophysical and planetary sciences department. “This gas is stored and then recycled through an extended galaxy halo, falling back onto the galaxies to reinvigorate a new generation of star formation,” he said. “In many ways this is the ‘missing link’ in galaxy evolution that we need to understand in detail in order to have a complete picture of the process.”
Stocke gave a presentation on the research June 27 at the University of Edinburgh’s Higgs Centre for Theoretical Physics in Scotland at a conference titled “Intergalactic Interactions.” The CU-Boulder research team also included professors Michael Shull and James Green and research associates Brian Keeney, Charles Danforth, David Syphers and Cynthia Froning, as well as University of Wisconsin-Madison Professor Blair Savage.
Building on earlier studies identifying oxygen-rich gas clouds around spiral galaxies by scientists at the Space Telescope Science Institute in Baltimore, the University of Massachusetts, Amherst College and the University of California, Santa Cruz, Stocke and his colleagues determined that such clouds contain almost as much mass as all the stars in their respective galaxies. “This was a big surprise,” said Stocke. “The new findings have significant consequences for how spiral galaxies change over time.”
In addition, the CU-Boulder team discovered giant reservoirs of gas estimated to be millions of degrees Fahrenheit that were enshrouding the spiral galaxies and halos under study. The halos of the spiral galaxies were relatively cool by comparison — just tens of thousands of degrees — said Stocke, also a member of CU-Boulder’s Center for Astrophysics and Space Astronomy, or CASA.
Shull, a professor in CU-Boulder’s astrophysical and planetary sciences department and a member of CASA, emphasized that the study of such “circumgalactic” gas is in its infancy. “But given the expected lifetime of COS on Hubble, perhaps another five years, it should be possible to confirm these early detections, elaborate on the results and scan other spiral galaxies in the universe,” he said.
Prior to the installation of COS on Hubble during NASA’s final servicing mission in May 2009, theoretical studies showed that spiral galaxies should possess about five times more gas than was being detected by astronomers. The new observations with the extremely sensitive COS are now much more in line with the theories, said Stocke.
The CU-Boulder team used distant quasars — the swirling centers of supermassive black holes — as “flashlights” to track ultraviolet light as it passed through the extended gas haloes of foreground galaxies, said Stocke. The light absorbed by the gas was broken down by the spectrograph, much like a prism does, into characteristic color “fingerprints” that revealed temperatures, densities, velocities, distances and chemical compositions of the gas clouds.
“This gas is way too diffuse to allow its detection by direct imaging, so spectroscopy is the way to go,” said Stocke. CU-Boulder’s Green led the design team for COS, which was built by Ball Aerospace & Technologies Corp. of Boulder for NASA.
While astronomers hope the Hubble Space Telescope keeps on chugging for years to come, there will be no more servicing missions. And the James Webb Space Telescope, touted to be Hubble’s successor beginning in late 2018, has no UV light-gathering capabilities, which will prevent astronomers from undertaking studies like those done with COS, said Green.
“Once Hubble ceases to function, we will lose the capability to study galaxy halos for perhaps a full generation of astronomers,” said Stocke. “But for now, we are fortunate to have both Hubble and its Cosmic Origins Spectrograph to help us answer some of the most pressing issues in cosmology.”
The study was supported by a NASA/Hubble Space Telescope contract to the Cosmic Origins Spectrograph science team, general NASA/Hubble Space Telescope observing grants to Stocke and a National Science Foundation grant to Keeney.
-CU-
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CU joins Sloan Digital Sky Survey to map stars, galaxies and quasars in 3D
Jun 26th
The University of Colorado Boulder has become a full institutional member of the Sloan Digital Sky Survey-IV, an ambitious effort by some of the world’s top astronomers to map the celestial sky in three dimensions to learn more about the structure and evolution of the universe.
The survey, known as SDSS-IV, is the fourth stage of an effort that began with SDSS-I in 2000 to create the largest digital color image of the northern sky, said CU-Boulder Professor Michael Shull of the astrophysical and planetary sciences department, lead scientist in the effort by CU-Boulder to join the survey. Since 2000, astronomers have mapped about one-half of the visible northern sky in three dimensions as part of the three prior Sloan sky surveys, discovering nearly half a billion astronomical objects ranging from asteroids and stars to galaxies and distant quasars in the process.
“We got into this because we think it is going to be a great recruitment tool for new students, and we have one of the best undergraduate majors in the country,” Shull said. “We also want to recruit high-caliber graduate students and postdoctoral researchers.”
The SDSS 2.5-meter telescope is located at the Apache Point Observatory in Sunspot, N.M., and is owned by the Astrophysical Research Consortium, or ARC, an organization of eight research institutions including CU-Boulder. The Sloan telescope sky-mapping project is funded by the Alfred P. Sloan Foundation, the participating institutions, the National Science Foundation and the U.S. Department of Energy Office of Science. Apache Point also hosts several other telescopes, including a 3.5-meter optical telescope owned and operated by ARC and routinely used by CU-Boulder.
ARC was formed in 1984 to create a national observatory that could provide telescope time to each member university based on its investment. Current ARC members in addition to CU-Boulder are the University of Chicago, Johns Hopkins University, Princeton University, the Institute of Advanced Study in Princeton, N.J., the University of Washington, the University of Virginia and New Mexico State University. CU-Boulder owns a one-eighth share of each of the two telescopes.
The costs to build new instruments, make observations and analyze data from the SDSS-IV from 2014 to 2020 is estimated to be between $50 million and $60 million, said Shull. The Sloan Foundation is contributing roughly $10 million, while additional funds are coming from more than 10 full institutional members, including CU, and from scientists with individual and small group memberships from various institutions.
Full institutional partners like CU-Boulder are paying roughly $1 million to join part four of the Sloan sky survey effort. CU-Boulder’s member fee was supported by university grants, awards, donations, general funds and indirect cost recovery savings. As an early institutional partner joining the Sloan IV survey before the end of the current fiscal year, CU received a $350,000 discount from ARC, said Shull.
Light from the Sloan telescope is directed to two powerful new instruments — a dual-channel visible light, or optical spectrograph, and a near-infrared spectrograph. Astronomical spectrographs break light into telltale colors much like a prism, revealing information about the size, temperature, composition and motion of celestial objects, said Shull.
The Sloan spectrographs will carry out a massive survey of galaxies and quasars in the distant universe, as well as stars in the Milky Way and thousands of nearby galaxies, said Shull, who also is a member of CU-Boulder’s Center for Astrophysics and Space Astronomy.
The new optical spectrograph on the Sloan telescope can take data from up to 1,000 galaxies or quasars simultaneously, he said. The instrument includes a circular aluminum plate roughly the size of a large pizza pan with 1,000 small perforations precisely drilled to match up with known astronomical objects in the sky. Each hole is plugged with an optical fiber attached to the spectrograph.
“I think this is going to be a perfect way for undergraduates to get their hands dirty working with ‘big data,’ said Shull. “A lot of undergraduates are better at computers than we are, so hiring a freshman or a sophomore who really wants to get into computing and big data sets in the field of astronomy is one of our goals.”
One of the biggest discoveries by SDSS-III astronomers came in 2012 when they detected the predicted signature of the first sound waves from matter and radiation in the early universe, said Shull. Sloan researchers used a multi-fiber spectrograph as part of the Baryon Oscillation Sky Survey, or BOSS, to detect the large-scale structures of ancient galaxies — similar in some ways to ripples on a pond — that were preserved after the Big Bang.
Shull, who plans to use the multi-fiber spectrograph to hunt for distant quasars in the early universe going back 13 million years, said the BOSS effort also is expected to reveal new information about so-called “dark energy.” A hypothetical form of energy that makes up the majority of the universe and produces a force that opposes gravity, dark energy is thought to be the cause of the accelerating expansion of the universe.
Another SDSS-IV effort will be a sky survey in the infrared to probe the distribution, dynamics and chemistry of stars and to explore the formation of our Milky Way Galaxy and its two companion galaxies, the Large Magellanic Cloud and the Small Magellanic Cloud, said Shull. Since the two Magellanic Clouds are best viewed from the southern hemisphere, SDSS scientists plan to collaborate with astronomers who are using the 2.5 meter du Pont Telescope at Las Campanas, Chile, on the effort.
SDSS-IV astronomers also will be using the BOSS instrument to study the internal structure of 10,000 nearby galaxies. The data will include precise velocities of stellar motions and chemical abundances for a large range of galaxy masses, types and environments. The data will complement observations of two newly completed American telescopes: the ALMA millimeter and submillimeter array radio telescope in Chile and the Expanded-Very Large Array radio telescope in New Mexico.
SDSS-IV also has had a significant citizen science component since 2007, when a data set of a million galaxies was released to the public, who were asked to classify them in three categories: Elliptical galaxies, merging galaxies and spiral galaxies, including the direction of the spiral arms. An astounding 70,000 classifications were received by SDSS scientists from the public within an hour of the data release, and during the first year more than 150,000 people made more than 50 million galaxy classifications.
CU has a legacy in space dating back nearly 70 years, said CU-Boulder Vice Chancellor for Research Stein Sture. It is the top funded public university by NASA, has a $70 million instrument now flying on the Hubble Space Telescope, is leading a $485 million mission to Mars and controls four NASA satellites from campus.
A video news story on the project is available at http://youtu.be/1Rke59L5cAo.
-CU-
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CU study: ‘Sideline quasars’ helped to stifle early galaxy formation
Mar 21st
Astronomers targeting one of the brightest quasars glowing in the universe some 11 billion years ago say “sideline quasars” likely teamed up with it to heat abundant helium gas billions of years ago, preventing small galaxy formation.
CU-Boulder Professor Michael Shull and Research Associate David Syphers used the Hubble Space Telescope to look at the quasar — the brilliant core of an active galaxy that acted as a “lighthouse” for the observations — to better understand the conditions of the early universe. The scientists studied gaseous material between the telescope and the quasar with a $70 million ultraviolet spectrograph on Hubble designed by a team from CU-Boulder’s Center for Astrophysics and Space Astronomy.
During a time known as the “helium reionization era” some 11 billion years ago, blasts of ionizing radiation from black holes believed to be seated in the cores of quasars stripped electrons from primeval helium atoms, said Shull. The initial ionization that charged up the helium gas in the universe is thought to have occurred sometime shortly after the Big Bang.
“We think ‘sideline quasars’ located out of the telescope’s view reionized intergalactic helium gas from different directions, preventing it from gravitationally collapsing and forming new generations of stars,” he said. Shull likened the early universe to a hunk of Swiss cheese, where quasars cleared out zones of neutral helium gas in the intergalactic medium that were then “pierced” by UV observations from the space telescope.
The results of the new study also indicate the helium reionization era of the universe appears to have occurred later than thought, said Shull, a professor in CU-Boulder’s astrophysical and planetary sciences department. “We initially thought the helium reionization era took place about 12 billion years ago,” said Shull. “But now we think it more likely occurred in the 11 to 10 billion-year range, which was a surprise.”
A paper on the subject by Shull and Syphers was published online this week in the Astrophysical Journal.
The Cosmic Origins Spectrograph used for the quasar observations aboard Hubble was designed to probe the evolution of galaxies, stars and intergalactic matter. The COS team is led by CU Professor James Green of CASA and was installed on Hubble by astronauts during its final servicing mission in 2009. COS was built in an industrial partnership between CU and Ball Aerospace & Technologies Corp. of Boulder.
“While there are likely hundreds of millions of quasars in the universe, there are only a handful you can use for a study like this,” said Shull. Quasars are nuclei in the center of active galaxies that have “gone haywire” because of supermassive black holes that gorged themselves in the cores, he said. “For our purposes, they are just a really bright background light that allows us to see to the edge of the universe, like a headlight shining through fog.”
The universe is thought to have begun with the Big Bang that triggered a fireball of searing plasma that expanded and then become cool neutral gas at about 380,000 years, bringing on the “dark ages” when there was no light from stars or galaxies, said Shull. The dark ages were followed by a period of hydrogen reionization, then the formation of the first galaxies beginning about 13.5 billion years ago. The first galaxies era was followed by the rise of quasars some 2 billion years later, which led to the helium reionization era, he said.
The radiation from the huge quasars heated the gas to 20,000 to 40,000 degrees Fahrenheit in intergalactic realms of the early universe, said Shull. “It is important to understand that if the helium gas is heated during the epoch of galaxy formation, it makes it harder for proto-galaxies to hang on to the bulk of their gas. In a sense, it’s like intergalactic global warming.”
The team is using COS to probe the “fossil record” of gases in the universe, including a structure known as the “cosmic web” believed to be made of long, narrow filaments of galaxies and intergalactic gas separated by enormous voids. Scientists theorize that a single cosmic web filament may stretch for hundreds of millions of light years, an eye-popping number considering that a single light-year is about 5.9 trillion miles.
COS breaks light into its individual components — similar to the way raindrops break sunlight into the colors of the rainbow — and reveals information about the temperature, density, velocity, distance and chemical composition of galaxies, stars and gas clouds.
For the study, Shull and Syphers used 4.5 hours of data from Hubble observations of the quasar, which has a catalog name of HS1700+6416. While some astronomers define quasars as feeding black holes, “We don’t know if these objects feed once, or feed several times,” Shull said. They are thought to survive only a few million years or perhaps a few hundred million years, a brief blink in time compared to the age of the universe, he said.
“Our own Milky Way has a dormant black hole in its center,” said Shull. “Who knows? Maybe our Milky Way used to be a quasar.”
The first quasar, short for “quasi-stellar radio source,” was discovered 50 years ago this month by Caltech astronomer Maarten Schmidt. The quasar he observed, 3C-273, is located roughly 2 billion years from Earth and is 40 times more luminous than an entire galaxy of 100 billion stars. That quasar is receding from Earth at 15 percent of the speed of light, with related winds blowing millions of miles per hour, said Shull.
-CU-
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