Comet Lovejoy can be seen in the video rising just right of the Milky Way.
Here’s a quick but lovely little gem: a time-lapse video taken from the ISS as it passed above central Africa, Madagascar and the southern Indian Ocean on December 29, 2011. The nighttime flyover shows numerous lightning storms and the thin band of our atmosphere, with a layer of airglow above, set against a stunning backdrop of the Milky Way and a barely-visible Comet Lovejoy, just two weeks after its close encounter with the Sun.
This video was made from photos taken by Expedition 30 astronauts. The photos were compiled at Johnson Space Center and uploaded to The Gateway to Astronaut Photography of Earth, an excellent database of… well, of astronauts’ photos of Earth.
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The site’s description of this particular video states:
This video was taken by the crew of Expedition 30 on board the International Space Station. The sequence of shots was taken December 29, 2011 from 20:55:05 to 21:14:09 GMT, on a pass from over central Africa, near southeast Niger, to the South Indian Ocean, southeast of Madagascar. The complete pass is over southern Africa to the ocean, focusing on the lightning flashes from local storms and the Milky Way rising over the horizon. The Milky Way can be spotted as a hazy band of white light at the beginning of the video. The pass continues southeast toward the Mozambique Channel and Madagascar. The Lovejoy Comet can be seen very faintly near the Milky Way. The pass ends as the sun is rising over the dark ocean.
There are lots more time-lapse videos on the Gateway as well, updated periodically. Check them out here.
Video courtesy of the Image Science & Analysis Laboratory, NASA Johnson Space Center.
Spitzer telescope view of the galactic center. (NASA/JPL-Caltech/S. Stolovy)
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“Sgr A* is the right object, VLBI is the right technique, and this decade is the right time.”
So states the mission page of the Event Horizon Telescope, an international endeavor that will combine the capabilities of over 50 radio telescopes across the globe to create a single Earth-sized telescope to image the enormous black hole at the center of our galaxy. For the first time, astronomers will “see” one of the most enigmatic objects in the Universe.
And tomorrow, January 18, researchers from around the world will convene in Tucson, AZ to discuss how to make this long-standing astronomical dream a reality.
During a conference organized by Dimitrios Psaltis, associate professor of astrophysics at the University of Arizona’s Steward Observatory, and Dan Marrone, an assistant professor of astronomy at the Steward Observatory, astrophysicists, scientists and researchers will gather to coordinate the ultimate goal of the Event Horizon Telescope; that is, an image of Sgr A*’s accretion disk and the “shadow” of its event horizon.
“Nobody has ever taken a picture of a black hole. We are going to do just that.”
– Dimitrios Psaltis, associate professor of astrophysics at the University of Arizona’s Steward Observatory
Sgr A* (pronounced as “Sagittarius A-star”) is a supermassive black hole residing at the center of the Milky Way. It is estimated to contain the equivalent mass of 4 million Suns, packed into an area smaller than the diameter of Mercury’s orbit.
Because of its proximity and estimated mass, Sgr A* presents the largest apparent event horizon size of any black hole candidate in the Universe. Still, its size in the sky is about the same as viewing “a grapefruit on the Moon.”
So what are astronomers expecting to actually “see”?
(Read more: What does a black hole look like?)
A black hole's "shadow", or event horizon. (NASA illustration)
Because black holes by definition are black – that is, invisible in all wavelengths of radiation due to the incredibly powerful gravitational effect on space-time around them – an image of the black hole itself will be impossible. But Sgr A*’s accretion disk should be visible to radio telescopes due to its billion-degree temperatures and powerful radio (as well as submillimeter, near infrared and X-ray) emissions… especially in the area leading up to and just at its event horizon. By imaging the glow of this super-hot disk astronomers hope to define Sgr A*’s Schwarzschild radius – its gravitational “point of no return”.
This is also commonly referred to as its shadow.
The position and existence of Sgr A* has been predicted by physics and inferred by the motions of stars around the galactic nucleus. And just last month a giant gas cloud was identified by researchers with the European Southern Observatory, traveling directly toward Sgr A*’s accretion disk. But, if the EHT project is successful, it will be the first time a black hole will be directly imaged in any shape or form.
“So far, we have indirect evidence that there is a black hole at the center of the Milky Way,” said Dimitrios Psaltis. “But once we see its shadow, there will be no doubt.”
Submillimeter Telescope on Mt. Graham, AZ. (Used with permission from University of Arizona, T. W. Folkers, photographer.)
The ambitious Event Horizon Telescope project will use not just one telescope but rather a combination of over 50 radio telescopes around the world, including the Submillimeter Telescope on Mt. Graham in Arizona, telescopes on Mauna Kea in Hawaii and the Combined Array for Research in Millimeter-wave Astronomy in California, as well as several radio telescopes in Europe, a 10-meter dish at the South Pole and, if all goes well, the 50-radio-antenna capabilities of the new Atacama Large Millimeter Array in Chile. This coordinated group effort will, in effect, turn our entire planet into one enormous dish for collecting radio emissions.
By using long-term observations with Very Long Baseline Interferometry (VLBI) at short (230-450 GHz) wavelengths, the EHT team predicts that the goal of imaging a black hole will be achieved within the next decade.
“What is great about the one in the center of the Milky Way is that is big enough and close enough,” said assistant professor Dan Marrone. “There are bigger ones in other galaxies, and there are closer ones, but they’re smaller. Ours is just the right combination of size and distance.”
An image of one of the Milky Way analogs found by Timothy Licquia and Jeffrey Newman. This galaxy, known to astronomers as SDSS J083909.27+450747.7, has properties which closely match those of the galaxy we live in. Credit: Sloan Digital Sky Survey
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What color would the Milky Way appear to alien civilizations looking at our galaxy through their telescopes? It turns out the Milky Way has approximately the right name – but for all the wrong reasons. “The true color of the Milky Way is as white as fine-grained new spring snow seen in early morning light,” said Dr. Jeffrey Newman, from the University of Pittsburgh, speaking at a press conference from the American Astronomical Society (AAS) Meeting.
Our ancestors gave our galaxy the name “Milky Way” because when they looked up and saw the band of the stars that stretches from one horizon to the other, it appears white to our human eyes. “But that’s only because our low-light vision isn’t sensitive to color,” said Newman. “There are portions of the Milky Way that are more yellow or red versus more blue, but our eyes can’t pick that up. But a sensitive instrument or photograph can.”
When we look at other galaxies, we can see them in their entirety, and can examine them for color and luminosity. Color and luminosity have been great tool for astronomy, helping us to understand stars and galaxies.
“Unfortunately we can’t get a complete picture of the Milky Way from outside, so we have had to resort to other methods,” said Newman. “Not only are we looking at Milky Way from the inside, but it’s even worse than that — our view is blocked by dust, both in clouds and diffuse dust. We can only see about 1,000 -2,000 light years in any direction, even though our galaxy is a 100,000 light years across.”
A digital all-sky mosaic of our view of the Milky Way from Earth, assembled from more than 3,000 individual CCD frames. Credit: Axel Mellinger. Click on image to view a zoomable panorama.
So if you ask, ‘what is the integrated color of the Milky Way,’ we can can’t tell from a picture like the one above, we can only tell what color the local neighborhood is.
“We have had to resort to different techniques, and rather than looking at the Milky Way directly, we look at other galaxies that should be like the Milky Way and we can determine what their color and luminosity are,” Newman said.
Newman, along with Timothy Licquia, a PhD student in physics at Pitt, used images from the Sloan Digital Sky Survey — which contains detailed properties of nearly a million galaxies — and looked for galaxies with similar properties to the Milky Way in regards to total mass and star formation rates. The Milky Way Galaxy should then fall on a plot somewhere within the range of colors of these matching objects.
While the composite color of the Milky Way is snowy-white, our galaxy appears more yellow towards the center and more blue out in the spiral arms.
Newman and Licquia determined the light color temperature of the Milky Way is 4,840 K, which closely matches the light from a standard light bulb with a color temperature of 4,700-5,000K. “It is well within the range our eye can perceive as white—roughly halfway between the light from old-style incandescent light bulbs and the standard spectrum of white on a television,” said Newman. “Our eyes treat both as white.”
The color of new snow is the whitest natural color on Earth. While milk has a more bluish color than snow, the association of our Milky Way to milk has proven to be very appropriate, given the Milky Way’s true color.
Newman even wrote a Haiku about the color:
Look at new spring snow
See the River of Heaven
An hour after dawn
The Milky Way’s color could be on either side of a standard dividing line between red and blue galaxies: relatively red galaxies rarely form new stars and blue galaxies have stars still being born. This adds to the evidence that although the Milky Way is still producing stars, it is “on its way out,” according to Newman. “A few billion years from now, our Galaxy will be a much more boring place, full of middle-aged stars slowly using up their fuel and dying off, but without any new ones to take their place. It will be less interesting for astronomers in other galaxies to look at, too: The Milky Way’s spiral arms will fade into obscurity when there are no more blue stars left.”
The BRAVA fields are shown in this image montage. For reference, the center of the Milky Way is at coordinates L= 0, B=0. The regions observed are marked with colored circles. This montage includes the southern Milky Way all the way to the horizon, as seen from CTIO. The telescope in silhouette is the CTIO Blanco 4-m. (Just peaking over the horizon on the left is the Large Magellanic Cloud, the nearest external galaxy to our own.) Image Credit: D. Talent, K. Don, P. Marenfeld & NOAO/AURA/NSF and the BRAVA Project
[/caption]You may have heard about the restaurant at the end of the Universe, but have you heard of the bar in the middle of the Milky Way?
Nearly 80 years ago, astronomers determined that our home, the Milky Way Galaxy, is a large spiral galaxy. Despite being stuck inside and not being able to see what the entire the structure looks like — as we can with the Pinwheel Galaxy, or our nearest neighbor, the Andromeda Galaxy — researchers have suspected our galaxy is actually a “barred” spiral galaxy. Barred spiral galaxies feature an elongated stellar structure , or bar, in the middle which in our case is hidden by dust and gas. There are many galaxies in the Universe that are barred spirals, and yet, there are numerous galaxies which do not feature a central bar.
How do these central bars form, and why are they only present in some, but not all spiral galaxies?
A research team led by Dr. R. Michael Rich (UCLA), dubbed BRAVA (Bulge Radial Velocity Assay), measured the velocity of many old, red stars near the center of our galaxy. By studying the spectra (combined light) of the M class giant stars, the team was able to calculate the velocity of each star along our line of sight. During a four-year time span, the spectra for nearly 10,000 stars was acquired with the CTIO Blanco 4-meter telescope located in Chile’s Atacama desert.
Analyzing the velocities of stars in their study, the team was able to confirm that the Milky Way’s central bulge does contain a massive bar, with one end nearly pointed right at our solar system. One other discovery made by the team is that while our galaxy rotates like a wheel, the BRAVA study found that the rotation of the central bar is more like that of a roll of paper towels in a dispenser. The team’s discoveries provide vital clues to help explain the formation of the Milky Way’s central region. BRAVA data. Image Credit: D. Talent, K. Don, P. Marenfeld & NOAO/AURA/NSF and the BRAVA Project
The spectra data set was compared to a computer simulation created by Dr. Juntai Shen (Shanghai Observatory) showing how the bar formed from a pre-existing disk of stars. The team’s data fits the model quite well, suggesting that before the central bar existed, there was a massive disk of stars. The conclusion reached by the team is in stark contrast to the commonly accepted model of formation of our galaxy’s central region – a model that predicts the Milky Way’s central region formed from an early chaotic merger of gas clouds. The “take-away” point from the team’s conclusions is that gas did play some role in the formation of our galaxy’s central region, which organized into a massive rotating disk, and then turned into a bar due to the gravitational interactions of the stars.
One other benefit to the team’s research is that stellar spectra data will allow the team to analyze the chemical composition of the stars. All stars are composed of mostly hydrogen and helium, but the tiny amounts of other elements (astronomers refer to anything past helium as “metals”) provides insight into the conditions present during a star’s formation.
The BRAVA team found that stars closest to the plane of the Milky Way Galaxy have fewer “metals” than stars further from its galactic plane. The team’s conclusion does confirm standard views of stellar formation, yet the BRAVA data covers a significant area of the galactic bulge that can be chemically analyzed. If researchers map the metal content of stars throughout the Milky Way, a clear picture of stellar formation and evolution emerges, similar to how mapping CO2 concentrations in the Antarctic ice shelf can reveal the past weather patterns here on Earth.
A true heart of darkness lies at the center of our galaxy: Sagittarius A* (pronounced “A-star”) is a supermassive black hole with the mass of four million suns packed into an area only as wide as the distance between Earth and the Sun. Itself invisible to direct observation, Sgr A* makes its presence known through its effect on nearby stars, sending them hurtling through space in complex orbits at speeds upwards of 600 miles a second. And it emits a dull but steady glow in x-ray radiation, the last cries of its most recent meals. Gas, dust, stars… solar systems… anything in Sgr A*’s vicinity will be drawn inexorably towards it, getting stretched, shredded and ultimately absorbed (for lack of a better term) by the dark behemoth, just adding to its mass and further strengthening its gravitational pull.
Now, for the first time, a team of researchers led by Reinhard Genzel from the Max-Planck Institute for Extraterrestrial Physics in Germany will have a chance to watch a supermassive black hole’s repast take place.
About a decade ago, standard cosmological models encountered a slight problem when applied to the Milky Way… missing satellite galaxies. While the calculations predicted as many as 500, only 10 are documented and modern figures state as many as 20. So what happened to the other 480 that should be out there? Either they don’t exist – or we can’t see them for some reason. Thanks to research done by the LIDAU project and two researchers from Observatoire Astronomique de Strasbourg, we might just have an answer.
About 150 million years after the Big Bang, the Universe’s first stars began to appear out of the cold, electrically neutral hydrogen and helium gas which filled it. As their intense light cut through the hydrogen atoms, it returned them to their plasma state in a process called reionisation. Things really began to heat up from there… gas began escaping the gravity of low-mass galaxies and as a consequence, they lost their star-forming abilities. By computing the observable consequences of this process, Pierre Ocvirk and Dominique Aubert demonstrated that the Milky Way’s first stars had the power of reionisation and it “is indeed an essential process in the standard model of galaxy formation.” This photo-evaporation state neatly explains the sparsity and age of Milky Way companions and offers up the reason satellite galaxies are rare in this neighborhood.
“On the other hand, their sensitivity to UV radiation means satellite galaxies are good probes of the reionisation epoch. Moreover, they are relatively nearby, from 30000 to 900000 light-years, which allows us to study them in great details, especially with the forthcoming generation of telescopes.” says Ocvirk. “In particular, the study of their stellar content with respect to their position could give us precious insight into the structure of the local UV radiation field during the reionisation.”
Current theory states this photo-evaporation was simply caused by nearby galaxies, resulting in a uniform event – but the new model built by the two French researchers proves this assumption wrong. Their high resolution numerical simulation accounts for the dynamics of the dark matter haloes from beginning to end, as well as their resultant gas impacted star formation and UV radiation.
“It is the first time that a model accounts for the effect of the radiation emitted by the first stars formed at the center of the Milky way, on its satellite galaxies. Indeed, contrary to previous models, the radiation field produced in this configuration is not uniform, but decreases in intensity as one moves away from the source.” explains Ocvirk. “On one hand, the satellite galaxies close to the galactic center see their gas evaporate very quickly. They form so few stars that they can be undetectable with current telescopes. On the other hand, the more remote satellite galaxies experience on average a weaker irradiation. Therefore they manage to keep their gas longer, and form more stars. As a consequence they are easier to detect and appear more numerous.”
Where did initial assumptions fall short? In previous models reionisation was thought to occur over an evenly distributed UV background, but the MIlky Way’s first stars had already done its damage by consuming its satellites. As the study suggests, our own galaxy is responsible for the lack of smaller companions.
Says Ocvirk; “This new scenario has deep consequences on the formation of galaxies and the interpretation of the large astronomical surveys to come. Indeed, satellite galaxies are affected by our galaxy’s tidal field, and can be slowly digested into our galaxy’s stellar halo. They can also be stretched into filaments and form stellar streams.”
It’s a very interesting new concept and will be one of the main science goals of the Gaia space mission, scheduled for launch in 2013. Until then, the Observatoire Astronomique de Strasbourg team will continue in their efforts to further understand radiative processes during reionisation.
Computer model of the Milky Way and its smaller neighbor, the Sagittarius dwarf galaxy. The flat disk is the Milky Way, and the looping stream of material is made of stars torn from Sagittarius as a result of the strong gravity of our galaxy. The spiral arms began to emerge about two billion years ago, when the Sagittarius galaxy first collided with the Milky Way disk. Image by Tollerud, Purcell and Bullock/UC Irvine
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For a good number of years, astronomers have hypothesized the Sagittarius Dwarf Galaxy has been loaded up with dark matter. As one of our nearest neighboring galaxies and part of our local group, Sag DEG has been hanging around for billions of years and may have orbited us as many as ten times. However, in order to survive the tidal strain of such interaction, this loop-shaped elliptical has got to have some muscle. Now UC Irvine astronomers are speculating on how these close encounters may have shaped the Milky Way’s spiral arms.
In a study released in today’s Nature publication, astronomers are citing telescopic data and computer modeling to show how our local galactic collision has sent streams of stars out in loops in both galaxies. These long streamers continue to collect stellar members and the rotation of the Milky Way forms them into our classic spiral pattern. The news is the presence of dark matter in Sag DEG is responsible for the initial push.
“It’s kind of like putting a fist into a bathtub of water as opposed to your little finger,” said James Bullock, a theoretical cosmologist who studies galaxy formation.
But the little Sagittarius Dwarf, as strong as the dark matter might be, isn’t going to win this cosmic arm wrestling match. Each time we interact, the small galaxy gets further torn apart and about all that’s left is four globular clusters and a smattering of old stars which spans roughly 10,000 light-years in diameter.
“When all that dark matter first smacked into the Milky Way, 80 percent to 90 percent of it was stripped off,” explained lead author Chris Purcell, who did the work with Bullock at UCI and is now at the University of Pittsburgh. “That first impact triggered instabilities that were amplified, and quickly formed spiral arms and associated ring-like structures in the outskirts of our galaxy.”
Will we meet again? Yes. The Sagittarius galaxy is due to strike the southern face of the Milky Way disk fairly soon, Purcell said – in another 10 million years or so.
New research shows that some old stars known as white dwarfs might be held up by their rapid spins, and when they slow down, they explode as Type Ia supernovae. Thousands of these "time bombs" could be scattered throughout our Galaxy. In this artist's conception, a supernova explosion is about to obliterate an orbiting Saturn-like planet. Credit: David A. Aguilar (CfA)
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According to new research, the only thing that may be keeping elderly stars from exploding is their rapid spin. In a galaxy filled with old stars, this means we could literally be sitting on a nearby “time bomb”. Or is this just another scare tactic?
“We haven’t found one of these ‘time bomb’ stars yet in the Milky Way, but this research suggests that we’ve been looking for the wrong signs. Our work points to a new way of searching for supernova precursors,” said astrophysicist Rosanne Di Stefano of the Harvard-Smithsonian Center for Astrophysics (CfA).
In light of the two recently discovered supernova events in Messier 51 and Messier 101, it isn’t hard to imagine the Milky Way having more than one candidate for a Type Ia supernova. This is precisely the type of stellar explosion Di Stefano and her colleagues are looking for… and it happens when a white dwarf star goes critical. It has reached Chandrasekhar mass. Add any more weight and it blows itself apart. How does this occur? Some astronomers believe Type Ia supernova are sparked by accretion from a binary companion – or a collision of two similar dwarf stars. However, there hasn’t been much – if any – evidence to support either theory. This has left scientists to look for new answers to old questions. Di Stefano and her colleagues suggest that white dwarf spin might just be what we’re looking for.
“A spin-up/spin-down process would introduce a long delay between the time of accretion and the explosion. As a white dwarf gains mass, it also gains angular momentum, which speeds up its spin. If the white dwarf rotates fast enough, its spin can help support it, allowing it to cross the 1.4-solar-mass barrier and become a super-Chandrasekhar-mass star. Once accretion stops, the white dwarf will gradually slow down. Eventually, the spin isn’t enough to counteract gravity, leading to a Type Ia supernova.” explains Di Stefano. “Our work is new because we show that spin-up and spin-down of the white dwarf have important consequences. Astronomers therefore must take angular momentum of accreting white dwarfs seriously, even though it’s very difficult science.”
Sure. It might take a billion years for the spin down process to happen – but what’s a billion years in cosmic time? In this scenario, it’s enough to allow accretion to have completely stopped and a companion star to age to a white dwarf. In the Milky Way there’s an estimated three Type Ia supernovae every thousand years. If figures are right, a typical super-Chandrasekhar-mass white dwarf takes millions of years to spin down and explode. This means there could be dozens of these “time bomb” systems within a few thousand light-years of Earth. While we’re not able to ascertain their locations now, upcoming wide-field surveys taken with instruments like Pan-STARRS and the Large Synoptic Survey Telescope might give us a clue to their location.
“We don’t know of any super-Chandrasekhar-mass white dwarfs in the Milky Way yet, but we’re looking forward to hunting them out,” said co-author Rasmus Voss of Radboud University Nijmegen, The Netherlands.
This artist's concept illustrates a quasar, or feeding black hole, similar to APM 08279+5255, where astronomers discovered huge amounts of water vapor. Gas and dust likely form a torus around the central black hole, with clouds of charged gas above and below. Image credit: NASA/ESA
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From a Caltech Press Release:
Water really is everywhere. Two teams of astronomers, each led by scientists at the California Institute of Technology (Caltech), have discovered the largest and farthest reservoir of water ever detected in the universe. Looking from a distance of 30 billion trillion miles away into a quasar—one of the brightest and most violent objects in the cosmos—the researchers have found a mass of water vapor that’s at least 140 trillion times that of all the water in the world’s oceans combined, and 100,000 times more massive than the sun.
Because the quasar is so far away, its light has taken 12 billion years to reach Earth. The observations therefore reveal a time when the universe was just 1.6 billion years old. “The environment around this quasar is unique in that it’s producing this huge mass of water,” says Matt Bradford, a scientist at NASA’s Jet Propulsion Laboratory (JPL), and a visiting associate at Caltech. “It’s another demonstration that water is pervasive throughout the universe, even at the very earliest times.” Bradford leads one of two international teams of astronomers that have described their quasar findings in separate papers that have been accepted for publication in the Astrophysical Journal Letters.
Read Bradford & team’s paper here.
A quasar is powered by an enormous black hole that is steadily consuming a surrounding disk of gas and dust; as it eats, the quasar spews out huge amounts of energy. Both groups of astronomers studied a particular quasar called APM 08279+5255, which harbors a black hole 20 billion times more massive than the sun and produces as much energy as a thousand trillion suns.
Since astronomers expected water vapor to be present even in the early universe, the discovery of water is not itself a surprise, Bradford says. There’s water vapor in the Milky Way, although the total amount is 4,000 times less massive than in the quasar, as most of the Milky Way’s water is frozen in the form of ice.
Nevertheless, water vapor is an important trace gas that reveals the nature of the quasar. In this particular quasar, the water vapor is distributed around the black hole in a gaseous region spanning hundreds of light-years (a light-year is about six trillion miles), and its presence indicates that the gas is unusually warm and dense by astronomical standards. Although the gas is a chilly –53 degrees Celsius (–63 degrees Fahrenheit) and is 300 trillion times less dense than Earth’s atmosphere, it’s still five times hotter and 10 to 100 times denser than what’s typical in galaxies like the Milky Way.
The water vapor is just one of many kinds of gas that surround the quasar, and its presence indicates that the quasar is bathing the gas in both X-rays and infrared radiation. The interaction between the radiation and water vapor reveals properties of the gas and how the quasar influences it. For example, analyzing the water vapor shows how the radiation heats the rest of the gas. Furthermore, measurements of the water vapor and of other molecules, such as carbon monoxide, suggest that there is enough gas to feed the black hole until it grows to about six times its size. Whether this will happen is not clear, the astronomers say, since some of the gas may end up condensing into stars or may be ejected from the quasar.
Bradford’s team made their observations starting in 2008, using an instrument called Z-Spec at the Caltech Submillimeter Observatory (CSO), a 10-meter telescope near the summit of Mauna Kea in Hawaii. Z-Spec is an extremely sensitive spectrograph, requiring temperatures cooled to within 0.06 degrees Celsius above absolute zero. The instrument measures light in a region of the electromagnetic spectrum called the millimeter band, which lies between infrared and microwave wavelengths. The researchers’ discovery of water was possible only because Z-Spec’s spectral coverage is 10 times larger than that of previous spectrometers operating at these wavelengths. The astronomers made follow-up observations with the Combined Array for Research in Millimeter-Wave Astronomy (CARMA), an array of radio dishes in the Inyo Mountains of Southern California.
This discovery highlights the benefits of observing in the millimeter and submillimeter wavelengths, the astronomers say. The field has developed rapidly over the last two to three decades, and to reach the full potential of this line of research, the astronomers—including the study authors—are now designing CCAT, a 25-meter telescope to be built in the Atacama Desert in Chile. CCAT will allow astronomers to discover some of the earliest galaxies in the universe. By measuring the presence of water and other important trace gases, astronomers can study the composition of these primordial galaxies.
The second group, led by Dariusz Lis, senior research associate in physics at Caltech and deputy director of the CSO, used the Plateau de Bure Interferometer in the French Alps to find water. In 2010, Lis’s team was looking for traces of hydrogen fluoride in the spectrum of APM 08279+5255, but serendipitously detected a signal in the quasar’s spectrum that indicated the presence of water. The signal was at a frequency corresponding to radiation that is emitted when water transitions from a higher energy state to a lower one. While Lis’s team found just one signal at a single frequency, the wide bandwidth of Z-Spec enabled Bradford and his colleagues to discover water emission at many frequencies. These multiple water transitions allowed Bradford’s team to determine the physical characteristics of the quasar’s gas and the water’s mass.
Here on Earth we play around with CCD cameras that boast a million pixels. But, can you imagine what a billion pixels could do? That’s the plan for ESA’s Galaxy-mapping Gaia mission. One hundred six electronic plates are being carefully integrated together to add up to the largest digital camera ever built for space… and its mission is to chart the Milky Way.
Beginning in 2013, Gaia’s five year mission will be to photograph a billion stars within our own galaxy – determining magnitude, spectral characteristics, proper motion and dimensional positioning. This information will be gathered by its charge coupled device (CCD) sensor array. Each of the 106 detectors are smaller than a normal credit card and thinner than a human hair. Put simplistically, each plate holds its own array of light-sensitive cells called photosites. Each photosite is its own pixel – just one tiny cell in the whole body of a photograph that could contain hundreds of thousands of pixels! When incoming light strikes the photosite, the photoelectric effect occurs and creates electrons for as long as exposure occurs. The electrons are then kept “stored” in their individual cells until a computer unloads the array, counts the electrons and reassembles them into the “big picture”.
And what a picture it will be…
In a period of a month, technicians managed to delicately assemble the CCD plates onto the support structure, leaving only a 1 mm gap between them. “The mounting and precise alignment of the 106 CCDs is a key step in the assembly of the flight model focal plane assembly,” said Philippe Garé, ESA’s Gaia payload manager. Upon completion, there will be seven rows of CCD composites with a main bank of 102 strictly dedicated to star detection. The remaining four will monitor image quality of each telescope and the stability of the 106.5º angle between the two telescopes that Gaia uses to obtain stereo views of stars. And, just like cooling a smaller CCD camera, the temperature needs to be maintained at -110ºC to keep up the sensitivity.
Gaia might be heavy on imaging capabilities, but she’s light on weight. The majority of the spacecraft, including the support structure is crafted from a ceramic-like material called silicon carbide. Resistant to warping in extreme temperature conditions, the whole support structure with its detectors weighs in at only 20 kg. She’ll sail out to Lagrange Point L2 – 1.5 million kilometers behind the Earth – where twin telescopes will capture perhaps 1% of our galaxy’s stellar population. While that may seem like a small amount, the information that Gaia’s three-dimensional star map will provide can reveal much more than we already know about the composition, formation and evolution of the Milky Way.
