STARS REVEAL THE SECRETS OF LOOKING YOUNG
Some people are in great shape at the age of 90, while others are decrepit before they’re 50. We know that how fast people age is only loosely linked to how old they actually are — and may have more to do with their lifestyle. A new study using both the MPG/ESO 2.2-meter telescope at ESO’s La Silla Observatory and the NASA/ESA Hubble Space Telescope reveals that the same is true of star clusters.
Globular clusters are spherical collections of stars, tightly bound to each other by their mutual gravity. Relics of the early years of the universe, with ages of typically 12-13 billion years (the Big Bang took place 13.7 billion years ago), there are roughly 150 globular clusters in the Milky Way and they contain many of our galaxy’s oldest stars.
But while the stars are old and the clusters formed in the distant past, astronomers using the MPG/ESO 2.2-meter telescope and the NASA/ESA Hubble Space Telescope have found that some of these clusters are still young at heart. The research is presented in the 20 December 2012 issue of the journal Nature.
“Although these clusters all formed billions of years ago,” says Francesco Ferraro (University of Bologna, Italy), the leader of the team that made the discovery, “we wondered whether some might be aging faster or slower than others. By studying the distribution of a type of blue star that exists in the clusters, we found that some clusters had indeed evolved much faster over their lifetimes, and we developed a way to measure the rate of aging.”
Star clusters form in a short period of time, meaning that all the stars within them tend to have roughly the same age. Because bright, high-mass stars burn up their fuel quite quickly, and globular clusters are very old, there should only be low-mass stars still shining within them.
This, however, turns out not to be the case: in certain circumstances, stars can be given a new burst of life, receiving extra fuel that bulks them up and substantially brightens them. This can happen if one star pulls matter off a close neighbor, or if they collide. The re-invigorated stars are called blue stragglers [1], and their high mass and brightness are properties that lie at the heart of this study.
Heavier stars sink towards the center of a cluster as the cluster ages, in a process similar to sedimentation. Blue stragglers’ high masses mean they are strongly affected by this process, while their brightness makes them relatively easy to observe [2].
To better understand cluster aging, the team mapped the location of blue straggler stars in 21 globular clusters, as seen in images from the MPG/ESO 2.2-meter telescope and Hubble, among other observatories [3]. Hubble provided high resolution imagery of the crowded centers of 20 of the clusters, while the ground-based imagery gave a wider view of their less busy outer regions.
Analyzing the observational data, the team found that a few clusters appeared young, with blue straggler stars distributed throughout, while a larger group appeared old, with the blue stragglers clumped in the center. A third group was in the process of aging, with the stars closest to the core migrating inwards first, then stars ever further out progressively sinking towards the center.
“Since these clusters all formed at roughly the same time, this reveals big differences in the speed of evolution from cluster to cluster,” said Barbara Lanzoni (University of Bologna, Italy), a co-author of the study. “In the case of fast-aging clusters, we think that the sedimentation process can be complete within a few hundred million years, while for the slowest it would take several times the current age of the universe.”
As a cluster’s heaviest stars sink towards the center, the cluster eventually experiences a phenomenon called core collapse, where the center of the cluster bunches together extremely densely. The processes leading towards core collapse are quite well understood, and revolve around the number, density and speed of movement of the stars. However, the rate at which they happened was not known until now [4]. This study provides the first empirical evidence of how quickly different globular clusters age.
Notes
[1] Blue stragglers are so called because of their blue color, and the fact that their evolution lags behind that of their neighbors.
[2] Blue stragglers combine being relatively bright and high mass by the standards of globular cluster stars, but they are not the only stars within these clusters that are either bright or massive.
Red giant stars are brighter, but they have a much lower mass, and therefore are not affected by the sedimentation process in the same way. (It is easy to distinguish these from blue stragglers because their color is very different.)
Neutron stars, the extremely dense cores of stars much bigger than the Sun that exploded billions of years ago in the early history of globular clusters, have a similar mass to blue stragglers, and are affected by the sedimentation process, but they are incredibly difficult to observe and therefore do not make a useful subject for this study.
Blue stragglers are the only stars within clusters that combine high mass and high brightness.
[3] Of the 21 clusters covered by this research, 20 were studied with Hubble, 12 with the MPG/ESO 2.2-meter telescope, eight with the Canada-France-Hawaii telescope and one with NAOJ’s Subaru Telescope.
[4] Such a rate depends in a complex manner on the number of stars, their density and their velocity within a cluster. While the first two quantities are relatively easy to measure, velocity is not. For these reasons, previous estimates of the rate of globular cluster dynamical aging were based only on theoretical arguments, while the new method allows a totally empirical measurement.
IMAGE…Some people are in great shape at the age of 90, while others are decrepit before they’re 50. We know that how fast people age is only loosely linked to how old they actually are — and may have more to do with their lifestyle. A new study with the NASA/ESA Hubble Space Telescope reveals that the same is true of star clusters.
![abcstarstuff:
STARS REVEAL THE SECRETS OF LOOKING YOUNG
Some people are in great shape at the age of 90, while others are decrepit before they’re 50. We know that how fast people age is only loosely linked to how old they actually are — and may have more to do with their lifestyle. A new study using both the MPG/ESO 2.2-meter telescope at ESO’s La Silla Observatory and the NASA/ESA Hubble Space Telescope reveals that the same is true of star clusters.
Globular clusters are spherical collections of stars, tightly bound to each other by their mutual gravity. Relics of the early years of the universe, with ages of typically 12-13 billion years (the Big Bang took place 13.7 billion years ago), there are roughly 150 globular clusters in the Milky Way and they contain many of our galaxy’s oldest stars.
But while the stars are old and the clusters formed in the distant past, astronomers using the MPG/ESO 2.2-meter telescope and the NASA/ESA Hubble Space Telescope have found that some of these clusters are still young at heart. The research is presented in the 20 December 2012 issue of the journal Nature.
“Although these clusters all formed billions of years ago,” says Francesco Ferraro (University of Bologna, Italy), the leader of the team that made the discovery, “we wondered whether some might be aging faster or slower than others. By studying the distribution of a type of blue star that exists in the clusters, we found that some clusters had indeed evolved much faster over their lifetimes, and we developed a way to measure the rate of aging.”
Star clusters form in a short period of time, meaning that all the stars within them tend to have roughly the same age. Because bright, high-mass stars burn up their fuel quite quickly, and globular clusters are very old, there should only be low-mass stars still shining within them.
This, however, turns out not to be the case: in certain circumstances, stars can be given a new burst of life, receiving extra fuel that bulks them up and substantially brightens them. This can happen if one star pulls matter off a close neighbor, or if they collide. The re-invigorated stars are called blue stragglers [1], and their high mass and brightness are properties that lie at the heart of this study.
Heavier stars sink towards the center of a cluster as the cluster ages, in a process similar to sedimentation. Blue stragglers’ high masses mean they are strongly affected by this process, while their brightness makes them relatively easy to observe [2].
To better understand cluster aging, the team mapped the location of blue straggler stars in 21 globular clusters, as seen in images from the MPG/ESO 2.2-meter telescope and Hubble, among other observatories [3]. Hubble provided high resolution imagery of the crowded centers of 20 of the clusters, while the ground-based imagery gave a wider view of their less busy outer regions.
Analyzing the observational data, the team found that a few clusters appeared young, with blue straggler stars distributed throughout, while a larger group appeared old, with the blue stragglers clumped in the center. A third group was in the process of aging, with the stars closest to the core migrating inwards first, then stars ever further out progressively sinking towards the center.
“Since these clusters all formed at roughly the same time, this reveals big differences in the speed of evolution from cluster to cluster,” said Barbara Lanzoni (University of Bologna, Italy), a co-author of the study. “In the case of fast-aging clusters, we think that the sedimentation process can be complete within a few hundred million years, while for the slowest it would take several times the current age of the universe.”
As a cluster’s heaviest stars sink towards the center, the cluster eventually experiences a phenomenon called core collapse, where the center of the cluster bunches together extremely densely. The processes leading towards core collapse are quite well understood, and revolve around the number, density and speed of movement of the stars. However, the rate at which they happened was not known until now [4]. This study provides the first empirical evidence of how quickly different globular clusters age.
Notes
[1] Blue stragglers are so called because of their blue color, and the fact that their evolution lags behind that of their neighbors.
[2] Blue stragglers combine being relatively bright and high mass by the standards of globular cluster stars, but they are not the only stars within these clusters that are either bright or massive.
Red giant stars are brighter, but they have a much lower mass, and therefore are not affected by the sedimentation process in the same way. (It is easy to distinguish these from blue stragglers because their color is very different.)
Neutron stars, the extremely dense cores of stars much bigger than the Sun that exploded billions of years ago in the early history of globular clusters, have a similar mass to blue stragglers, and are affected by the sedimentation process, but they are incredibly difficult to observe and therefore do not make a useful subject for this study.
Blue stragglers are the only stars within clusters that combine high mass and high brightness.
[3] Of the 21 clusters covered by this research, 20 were studied with Hubble, 12 with the MPG/ESO 2.2-meter telescope, eight with the Canada-France-Hawaii telescope and one with NAOJ’s Subaru Telescope.
[4] Such a rate depends in a complex manner on the number of stars, their density and their velocity within a cluster. While the first two quantities are relatively easy to measure, velocity is not. For these reasons, previous estimates of the rate of globular cluster dynamical aging were based only on theoretical arguments, while the new method allows a totally empirical measurement.
IMAGE…Some people are in great shape at the age of 90, while others are decrepit before they’re 50. We know that how fast people age is only loosely linked to how old they actually are — and may have more to do with their lifestyle. A new study with the NASA/ESA Hubble Space Telescope reveals that the same is true of star clusters.](http://25.media.tumblr.com/bd9e3834d07393ef8619939ab392daf5/tumblr_mfha0ffenA1qg9lvdo1_500.jpg)
![ikenbot:
NASA Plans for 3-D Printing Rocket Engine Parts Could Boost Larger Manufacturing Trend
There is a lot riding on NASA’s Space Launch System (SLS). Not only does the agency’s first new heavy-lift booster since the Saturn 5 that took U.S. astronauts to the moon play a central role in the future of the American spaceflight, it also provides a critical test for technology expected to figure prominently in revamping the country’s ailing manufacturing industry.
NASA’s Marshall Space Flight Center in Huntsville, Ala., is testing an approach called selective laser melting (SLM) to create parts for the J-2X and RS-25 rocket engines that will power the SLS, whose maiden voyage is slated for 2017 (pdf). The space agency expects SLM to simplify the process of making certain parts and in some cases halve the cost of producing them—a huge advantage for NASA, provided the components can withstand the rigors of lifting the largest launch vehicle ever built into space.
The first version of the SLS is a 70-metric-ton rocket that will lift around 70,000 kilograms while providing 10 percent more thrust than the Saturn 5. This SLS will power the 2017 Exploration Mission 1, which will launch an unmanned Orion spacecraft on a circumlunar voyage as a precursor to Exploration Mission 2. That mission, scheduled for 2021, will use a 130-metric-ton version of the SLS to launch Orion and a crew of up to four astronauts. This second SLS will be capable of lifting more than 130,000 kilograms and provide 20 percent more thrust than the Saturn 5.
Cash-strapped NASA is counting on SLM to speed SLS’s development and reduce the program’s costs. SLM is a type of additive manufacturing technology, which uses computer-aided design (CAD) files to build parts layer by layer (3-D printing is perhaps the most well known example of additive manufacturing). With SLM, a finely powdered alloy is deposited in a layer as thin as 20 microns and then fused together by a focused laser beam inside a chamber containing inert gas such as argon or nitrogen. Once the laser has turned that layer into solid metal, another layer of powder is deposited and the process is repeated.
NASA is testing the viability of making engine parts from nickel-based alloys using an SLM machine (pdf) with a square cubical build chamber measuring 250 millimeters on each side and a depth of 280 millimeters. These same alloys are already used to make 90 percent of the parts in the RS-25 and J-2X engines. The key difference is that the engines’ current elements are forged and then milled into their final shapes. Often several pieces must be welded together to create a part.
Marshall engineers began evaluating alternative approaches to building parts for the next-generation J-2X engine a few years ago. In late 2010 they turned to SLM to create a duct for a gas generator in the engine. “The part itself is not necessarily complex—it’s a [10-centimeter] in diameter duct that’s bent in a U-shape,” says Andy Hardin, SLS Liquid Engines Office engine integration hardware lead. However, “because of the thickness and the radius of the bend, it’s very difficult to make. We were having trouble getting vendors to do this properly.”
After printing the duct, the engineers set about deconstructing it to study its metallurgy and microscopic structure. They found that although the part was not as strong as a forged and milled duct, it fell within the “minimal acceptable range,” Hardin says. “If you made a part [using SLM], the material properties would be degraded somewhat but not much.” One structural advantage is that the part required no welding. “When you make a part out of multiple pieces, welds are always the weakest points,” he adds. This opened the door for the engineers to consider using SLM to make other engine parts as well.
SLM, and additive manufacturing in general, is not a viable option for all J-2X or RS-25 engine parts. For starters, the printed parts must be small enough to fit in the machine’s build chamber. And a lot more testing is required to determine whether components such as turbines, which operate under the most intense conditions, could be made properly using SLM, Hardin says. Good candidates for SLM are those with complex geometries that are difficult to make and require multiple welds to achieve those geometries. Depending on how well printed J-2X parts fare in tests, Marshall engineers hope to at some point use SLM to likewise make parts for the older RS-25, which served as the space shuttle’s main engine throughout its 30-year history.
Another incentive for NASA to transition to additive-manufactured parts: their contractors are beginning to adopt the technology in their factories. “As a big customer for many of these manufacturers, we thought it was important that we understand the technology,” Hardin says. NASA does not want to hold manufacturers back by failing to create specifications for parts made using SLM or some other additive process, he adds.
As such, NASA’s success with SLM could be a boon to a flagging U.S. manufacturing industry that seeks to create more domestic jobs but has been reluctant do so because of high costs.](http://24.media.tumblr.com/tumblr_mdfy60KwwB1qbn5m1o1_500.jpg)
