[/caption]The traditional picture of galaxy growth is not pretty. In fact, it’s a kind of cosmic cannibalism: two galaxies are caught in ominous tango, eventually melding together in a fiery collision, thus spurring on an intense but short-lived bout of star formation. Now, new research suggests that most galaxies in the early Universe increased their stellar populations in a considerably less violent way, simply by burning through their own gas over long periods of time.
The research was conducted by a group of astronomers at NASA’s Spitzer Science Center in Pasadena, California. The team used the Spitzer Space Telescope to peer at 70 distant galaxies that flourished when the Universe was only 1-2 billion years old. The spectra of 70% of these galaxies showed an abundance of H alpha, an excited form of hydrogen gas that is prevalent in busy star-forming regions. Today, only one out of every thousand galaxies carries such an abundance of H alpha; in fact, the team estimates that star formation in the early Universe outpaced that of today by a factor of 100!
Not only did these early galaxies crank out stars much faster than their modern-day counterparts, but they created much larger stars as well. By grazing on their own stores of gas, galaxies from this epoch routinely formed stars up to 100 solar masses in size.
These impressive bouts of star formation occurred over the course of hundreds of millions of years. The extremely long time scales involved suggest that while they probably played a minor role, galaxy mergers were not the main precursor to star formation in the Universe’s younger years. “This type of galactic cannibalism was rare,” said Ranga-Ram Chary, a member of the team. “Instead, we are seeing evidence for a mechanism of galaxy growth in which a typical galaxy fed itself through a steady stream of gas, making stars at a much faster rate than previously thought.” Even on cosmic scales, it would seem that slow and steady really does win the race.
Today at the American Astronomical Society conference in Boston, the Kepler team announced the confirmation of a new rocky planet in orbit around Kepler-10. Dubbed Kepler-10c, this planet is described as a “scorched, molten Earth.”
2.2 times the radius of Earth, Kepler-10c orbits its star every 45 days. Both it and its smaller, previously-discovered sibling 10b are located too close to their star for liquid water to exist.
Kepler-10c was validated using a new computer simulation technique called “Blender” as well as additional infrared data from NASA’s Spitzer Space Telescope. This method can be used to locate Earth-sized planets within Kepler’s field of view and could also potentially help find Earth-sized planets within other stars’ habitable zones.
This is the first time the team feels sure that it has exhaustively ruled out alternative explanations for dips in the brightness of a star… basically, they are 99.998% sure that Kepler-10c exists.
The Kepler-10 star system is located about 560 light-years away near the Cygnus and Lyra constellations.
Looking out my own window this morning provides a gloomy overcast view, so this new image from the Spitzer Space Telescope provides a day-brightener: a pink sunflower! This is the Sunflower galaxy, also known as Messier 63, and with Spitzers’ infrared eyes, the arms of the galaxy show up vividly. Infrared light is sensitive to the dust lanes in spiral galaxies, which appear dark in visible-light images. Spitzer’s view reveals complex structures that trace the galaxy’s spiral arm pattern.
This galaxy is about 37 million-light years away from Earth, and lies close to the well-known Whirlpool galaxy and the associated Messier 51 group of galaxies.
Time for another action-packed double episode of Astronomy Cast. This week we focus on the Lyman Spitzer, a theoretical physicist and astronomer who worked on star formation and plasma physics. Of course, this will lead us into next week’s episode where we talk about the mission that bears his name: the Spitzer Space Telescope.
New research from NASA’s Spitzer Space Telescope reveals that asteroids somewhat near Earth, termed near-Earth objects, are a mixed bunch, with a surprisingly wide array of compositions. Like a piñata filled with everything from chocolates to fruity candies, these asteroids come in assorted colors and compositions. Some are dark and dull; others are shiny and bright. The Spitzer observations of 100 known near-Earth asteroids demonstrate that the objects’ diversity is greater than previously thought.
The findings are helping astronomers better understand near-Earth objects as a whole — a population whose physical properties are not well known.
“These rocks are teaching us about the places they come from,” said David Trilling of Northern Arizona University, Flagstaff, lead author of a new paper on the research appearing in the September issue of Astronomical Journal. “It’s like studying pebbles in a streambed to learn about the mountains they tumbled down.”
After nearly six years of operation, in May 2009, Spitzer used up the liquid coolant needed to chill its infrared detectors. It is now operating in a so-called “warm” mode (the actual temperature is still quite cold at 30 Kelvin, or minus 406 degrees Fahrenheit). Two of Spitzer’s infrared channels, the shortest-wavelength detectors on the observatory, are working perfectly.
One of the mission’s new “warm” programs is to survey about 700 near-Earth objects, cataloging their individual traits. By observing in infrared, Spitzer is helping to gather more accurate estimates of asteroids’ compositions and sizes than what is possible with visible light alone. Visible-light observations of an asteroid won’t differentiate between an asteroid that is big and dark, or small and light. Both rocks would reflect the same amount of visible sunlight. Infrared data provide a read on the object’s temperature, which then tells an astronomer more about the actual size and composition. A big, dark rock has a higher temperature than a small, light one because it absorbs more sunlight.
Trilling and his team have analyzed preliminary data on 100 near-Earth asteroids so far. They plan to observe 600 more over the next year. There are roughly 7,000 known near-Earth objects out of a population expected to number in the tens to hundreds of thousands.
“Very little is known about the physical characteristics of the near-Earth population,” said Trilling. “Our data will tell us more about the population, and how it changes from one object to the next. This information could be used to help plan possible future space missions to study a near-Earth object.”
The data show that some of the smaller objects have surprisingly high albedos (an albedo is a measurement of how much sunlight an object reflects). Since asteroid surfaces become darker with time due to exposure to solar radiation, the presence of lighter, brighter surfaces for some asteroids may indicate that they are relatively young. This is evidence for the continuing evolution of the near-Earth object population.
In addition, the fact that the asteroids observed so far have a greater degree of diversity than expected indicates that they might have different origins. Some might come from the main belt between Mars and Jupiter, and others could come from farther out in the solar system. This diversity also suggests that the materials that went into making the asteroids — the same materials that make up our planets — were probably mixed together like a big solar-system soup very early in its history.
The research complements that of NASA’s Wide-field Infrared Survey Explorer, or WISE, an all-sky infrared survey mission also up in space now. WISE has already observed more than 430 near-Earth objects — of these, more than 110 are newly discovered.
In the future, both Spitzer and WISE will tell us even more about the “flavors” of near-Earth objects. This could reveal new clues about how the cosmic objects might have dotted our young planet with water and organics — ingredients needed to kick-start life.
How do massive stars form? This has been one of the more hotly debated questions in astronomy. Do big stars form by accretion like low-mass stars or do they form through the merging of low mass protostars? Since massive stars tend to be quite far away and usually are surrounded by a shroud of dust, they are difficult to observe, said Stefan Kraus from the University of Michigan. But Kraus and his team have obtained the first image of a dusty disc closely encircling a massive baby star, providing direct evidence that, big or small, all stars form the same way.
“Our observations show a disc surrounding an embryonic young, massive star, which is now fully formed,” said Kraus. “It’s the first time something like this has been observed, and the disk very much resembles what we see around young stars that are much smaller, except everything is scaled up and more massive.”
Not only that, but Kraus and his team found hints at a potential planet-forming region around the nascent star.
Using ESO’s Very Large Telescope Interferometer Kraus and his team focused on IRAS 13481-6124, a star located about 10,000 light-years away in the constellation Centaurus, and about 20 times more massive than our sun. “We were able to get a very sharp view into the innermost regions around this star by combining the light of separate telescopes,” Kraus said, “basically mimicking the resolving power of a telescope with an incredible 85-meter (280-foot) mirror.”
Kraus added that the resulting resolution is about 2.4 milliarcseconds, which is equivalent to picking out the head of a screw on the International Space Station from Earth, or more than ten times the resolution possible with current visible-light telescopes in space.
They also made complementary observations with the 3.58-meter New Technology Telescope at La Silla. The team chose this region by looking at archived images from the Spitzer Space Telescope as well as from observations done with the APEX 12-meter submillimeter telescope, where they discovered the presence of a jet.
“Such jets are commonly observed around young low-mass stars and generally indicate the presence of a disc,” says Kraus.
From their observations, the team believes the system is about 60,000 years old, and that the star has reached its final mass. Because of the intense light of the star — 30,000 times more luminous than our Sun — the disc will soon start to evaporate. The disc extends to about 130 times the Earth–Sun distance — or 130 astronomical units (AU) — and has a mass similar to that of the star, roughly twenty times the Sun. In addition, the inner parts of the disc are shown to be devoid of dust, which could mean that planets are forming around the star.
“In the future, we might be able to see gaps in this and other dust disks created by orbiting planets, although it is unlikely that such bodies could survive for long,” Kraus said. “A planet around such a massive star would be destroyed by the strong stellar winds and intense radiation as soon as the protective disk material is gone, which leaves little chance for the development of solar systems like our own.”
Kraus looks forward to observations with the Atacama Large Millimeter/submillimeter Array (ALMA), currently under construction in Chile, which may be able to resolve the disks to an even sharper resolution.
Previously, Spitzer detected dusty disks of planetary debris around more mature massive stars, which supports the idea that planets may form even in these extreme environments. (Read about that research here.) .
The Spitzer Space Telescope has found what appear to be two of the earliest and most primitive supermassive black holes known. “We have found what are likely first-generation quasars, born in a dust-free medium and at the earliest stages of evolution,” said Linhua Jiang of the University of Arizona, Tucson, lead author of a paper published this week in Nature.
A quasar is a compact region in the center of a massive galaxy surrounding the central supermassive black hole.
As shown by the image we posted earlier today from the Planck mission, our galaxy – and the Universe – is littered with dust. But scientists believe the very early universe didn’t have any dust — which tells them that the most primitive quasars should also be dust-free. But nobody had seen any “clean” quasars — until now.
Spitzer has identified two — the smallest on record — about 13 billion light-years away from Earth. The quasars, called J0005-0006 and J0303-0019, were first unveiled in visible light using data from the Sloan Digital Sky Survey. That discovery team, which included Jiang, was led by Xiaohui Fan, a coauthor of the recent paper. NASA’s Chandra X-ray Observatory had also observed X-rays from one of the objects. X-rays, ultraviolet and optical light stream out from quasars as the gas surrounding them is swallowed.
“Quasars emit an enormous amount of light, making them detectable literally at the edge of the observable universe,” said Fan.
When Jiang and his colleagues set out to observe J0005-0006 and J0303-0019 with Spitzer between 2006 and 2009, their targets didn’t stand out much from the usual quasar bunch. Spitzer measured infrared light from the objects along with 19 others, all belonging to a class of the most distant quasars known. Each quasar is anchored by a supermassive black hole weighing more than 100 million suns.
Of the 21 quasars, J0005-0006 and J0303-0019 lacked characteristic signatures of hot dust, the Spitzer data showed. Spitzer’s infrared sight makes the space telescope ideally suited to detect the warm glow of dust that has been heated by feeding black holes.
“We think these early black holes are forming around the time when the dust was first forming in the universe, less than one billion years after the Big Bang,” said Fan. “The primordial universe did not contain any molecules that could coagulate to form dust. The elements necessary for this process were produced and pumped into the universe later by stars.”
The astronomers also observed that the amount of hot dust in a quasar goes up with the mass of its black hole. As a black hole grows, dust has more time to materialize around it. The black holes at the cores of J0005-0006 and J0303-0019 have the smallest measured masses known in the early universe, indicating they are particularly young, and at a stage when dust has not yet formed around them.
The Spitzer observations were made before the telescope ran out of its liquid coolant in May 2009, beginning its “warm” mission.
It goes by the super-catchy (not!) title “A Catalog of MIPSGAL Disk and Ring Sources”. I chose it, over 213 competitors, because it’s pure astronomy, and because it’s something you don’t need a PhD to be able to do, or even a BSc.
Oh, and also because Don Mizuno and co-authors may have found two, quite local, spiral galaxies that no one has ever seen before!
Some quick background: arXiv has been going for several years now, and provides preprints, on the web, of papers “in the fields of physics, mathematics, non-linear science, computer science, quantitative biology and statistics”. It’s owned, operated and funded by Cornell University. astro-ph is the collection of preprints classified as astro physics; the “recent” category in astro-ph is the new preprints submitted in the last week.
When I have any, one of my favorite spare-time activities is browsing astro-ph (Hey, I did say, in my profile, that I am hooked on astronomy!)
Briefly, what Mizuno and his co-authors did was get hold of some of the images from Spitzer (something that anyone can do, provided their internet connection has enough bandwidth), and eyeball them, looking for things which look like disks and rings. Having found over 400 of them, they did what the human brain does superbly well: they grouped them by similarity of appearance, and gave the groups names. They then checked out other images – from different parts of Spitzer’s archive, and from IRAS – and checked to see how many had already been cataloged.
And what did they find? Well, first, that most of the objects they found had not been cataloged before, and certainly not given definite classifications! Many, perhaps most, of the new objects are planetary nebulae, and their findings may help address a long-standing puzzle in this part of astronomy.
But they also may have found two local spiral galaxies, which had not been noticed before because they are obscured by the gas-and-dust clouds in the Milky Way plane. How cool is that!
Here’s the ‘credits’ section of the preprint: “This work is based on observations made with the Spitzer Space Telescope, which is operated by the Jet Propulsion Laboratory, California Institute of Technology under a contract with NASA. Support for this work was provided by NASA in part through an award issued by JPL/Caltech. This research made use of the SIMBAD database and the Vizier catalog access tool, operated by the Centre de Donnees Astronomique de Strasbourg. This research has also made use of NASA’s Astrophysics Data System Bibliographic Services.”
And here’s the preprint itself: arXiv:1002.4221 A Catalog of MIPSGAL Disk and Ring Sources; D.R. Mizuno(1), K. E. Kraemer(2), N. Flagey(3), N. Billot(4), S. Shenoy(5), R. Paladini(3), E. Ryan(6), A. Noriega-Crespo(3), S. J. Carey(3). ((1) Institute for Scientific Research, (2) Air Force Research Laboratory, (3) Spitzer Science Center, (4) NASA Herschel Science Center, (5) Ames Research Center, (6) University of Minnesota)
PS, going over the Astronomy Cast episode How to be Taken Seriously by Scientists is what motivated me to pick this preprint (however, I must tell you, in all honesty, that there are at least ten other preprints that are equally pickable).
At the end of the proverbial day, space-based missions like Spitzer produce millions of observations of astronomical objects, phenomena, and events. And those terabytes of data are used to test hypotheses in astrophysics which lead to a deeper understanding of the universe and our home in it, and perhaps some breakthrough whose here-on-the-ground implementation leads to a major, historic improvement in human welfare and planetary ecosystem health.
But such missions also leave more immediate legacies, in terms of the pleasure they bring millions of people, via the beauty of their images (not to mention posters, computer wallpaper and screen savers, and even inspiration for avatars).
Some recent results from one of Spitzer’s programs – SAGE-SMC – are no exception.
The image shows the main body of the Small Magellanic Cloud (SMC), which is comprised of the “bar” on the left and a “wing” extending to the right. The bar contains both old stars (in blue) and young stars lighting up their natal dust (green/red). The wing mainly contains young stars. In addition, the image contains a galactic globular cluster in the lower left (blue cluster of stars) and emission from dust in our own galaxy (green in the upper right and lower right corners).
The data in this image are being used by astronomers to study the lifecycle of dust in the entire galaxy: from the formation in stellar atmospheres, to the reservoir containing the present day interstellar medium, and the dust consumed in forming new stars. The dust being formed in old, evolved stars (blue stars with a red tinge) is measured using mid-infrared wavelengths. The present day interstellar dust is weighed by measuring the intensity and color of emission at longer infrared wavelengths. The rate at which the raw material is being consumed is determined by studying ionized gas regions and the younger stars (yellow/red extended regions). The SMC is one of very few galaxies where this type of study is possible, and the research could not be done without Spitzer.
This image was captured by Spitzer’s infrared array camera and multiband imaging photometer (blue is 3.6-micron light; green is 8.0 microns; and red is combination of 24-, 70- and 160-micron light). The blue color mainly traces old stars. The green color traces emission from organic dust grains (mainly polycyclic aromatic hydrocarbons). The red traces emission from larger, cooler dust grains.
The image was taken as part of the Spitzer Legacy program known as SAGE-SMC: Surveying the Agents of Galaxy Evolution in the Tidally-Stripped, Low Metallicity Small Magellanic Cloud.
The Small Magellanic Cloud (SMC), and its larger sister galaxy, the Large Magellanic Cloud (LMC), are named after the seafaring explorer Ferdinand Magellan, who documented them while circling the globe nearly 500 years ago. From Earth’s southern hemisphere, they can appear as wispy clouds. The SMC is the further of the pair, at 200,000 light-years away.
Recent research has shown that the galaxies may not, as previously suspected, orbit around our galaxy, the Milky Way. Instead, they are thought to be merely sailing by, destined to go their own way. Astronomers say the two galaxies, which are both less evolved than a galaxy like ours, were triggered to create bursts of new stars by gravitational interactions with the Milky Way and with each other. In fact, the LMC may eventually consume its smaller companion.
Karl Gordon, the principal investigator of the latest Spitzer observations at the Space Telescope Science Institute in Baltimore, Maryland, and his team are interested in the SMC not only because it is so close and compact, but also because it is very similar to young galaxies thought to populate the universe billions of years ago. The SMC has only one-fifth the amount of heavier elements, such as carbon, contained in the Milky Way, which means that its stars haven’t been around long enough to pump large amounts of these elements back into their environment. Such elements were necessary for life to form in our solar system.
Studies of the SMC therefore offer a glimpse into the different types of environments in which stars form.
“It’s quite the treasure trove,” said Gordon, “because this galaxy is so close and relatively large, we can study all the various stages and facets of how stars form in one environment.” He continued: “With Spitzer, we are pinpointing how to best calculate the numbers of new stars that are forming right now. Observations in the infrared give us a view into the birthplace of stars, unveiling the dust-enshrouded locations where stars have just formed.”
This image shows the main body of the SMC, which is comprised of the “bar” and “wing” on the left and the “tail” extending to the right. The tail contains only gas, dust and newly formed stars. Spitzer data has confirmed that the tail region was recently torn off the main body of the galaxy. Two of the tail clusters, which are still embedded in their birth clouds, can be seen as red dots.
Astronomers have found numerous Jupiter-like planets orbiting other stars. But because of the limits of our current technology, they haven’t yet found any other terrestrial Earth-like planets out in the universe. But new findings from the Spitzer Space Telescope suggest that terrestrial planets might form around many, if not most, of the nearby sun-like stars in our galaxy. So perhaps, other worlds with the potential for life might be more common than we thought.
A group of astronomers led by Michael Meyer of the University of Tucson, Arizona used Spitzer to survey six sets of stars with masses comparable to our sun, and grouped them by age.
“We wanted to study the evolution of the gas and dust around stars similar to the sun and compare the results with what we think the solar system looked like at earlier stages during its evolution,” Meyer said. Our sun is about 4.6 billion years old.
They found that at least 20 percent, and possibly as many as 60 percent, of stars similar to the sun are candidates for forming rocky planets.
The Spitzer telescope does not detect planets directly. Instead, using its infrared capability, it detects dust — the rubble left over from collisions as planets form — at a range of infrared wavelengths. Because dust closer to the star is hotter than dust farther from the star, the “warm” dust indicates material orbiting the star at distances comparable to the distance between Earth and Jupiter.
Meyer said that about 10 to 20 percent of the stars in the four youngest age groups shows ‘warm’ dust, but not in stars older than 300 million years. That is comparable to the theoretical models of our own solar system, which suggests that Earth formed over a span of 10 to 50 million years from collisions between smaller bodies.
But the numbers are vague on how many stars are actually forming planets because there’s more than one way to interpret the Spitzer data. “An optimistic scenario would suggest that the biggest, most massive disks would undergo the runaway collision process first and assemble their planets quickly. That’s what we could be seeing in the youngest stars. Their disks live hard and die young, shining brightly early on, then fading,” Meyer said.
“However, smaller, less massive disks will light up later. Planet formation in this case is delayed because there are fewer particles to collide with each other.”
If this is correct and the most massive disks form their planets first and then the smaller disks take 10 to 100 times longer, then up to 62 percent of the surveyed stars have formed, or may be forming, planets. “The correct answer probably lies somewhere between the pessimistic case of less than 20 percent and optimistic case of more than 60 percent,” Meyer said.
In October 2007, another group of astronomers used similar Spitzer data to observe the formation of a star system 424 light-years away, with another possible Earth-like planet being created.
More definitive data on formation of rocky planets will come with the launch the Kepler mission in 2009, which will search to find if terrestrial planets like Earth could be common around stars like the sun.