by Paul Gilster | Jul 17, 2014 | Missions |
In mid-June, NASA announced the award of two contracts with Deep Space Industries in conjunction with the agency’s plans to work with private industry in the exploration and harvesting of asteroids. One of these contracts caught my eye immediately. It involves small payloads that can ride along to supplement asteroid missions, and it’s in the hands of NASA’s former Chief Technologist, Mason Peck, a Cornell University aerospace engineer. Peck’s work at Cornell’s Space Systems Design Studio has led to the development of Sprites, fully functional spacecraft each weighing less than a penny. You can think of a Sprite as a spacecraft on a chip without any constraints from onboard fuel.
You can see where this fits in with the current theme of building smaller spacecraft and sending them in swarms to investigate a particular target. You may have already run into KickSat, a citizen science project involving hundreds of proof-of-concept spacecraft in low Earth orbit for assessment of their performance and re-entry characteristics. KickSat grew out of a KickStarter campaign from 2011. The diminutive spacecraft are 32x32x4mm in size, each weighing less than 7.5 grams, designed to be released from the larger KickSat, a CubeSat modified and enhanced for Sprite deployment, on command from the ground.
Image: Aerospace engineer Mason Peck, whose Sprite concept shrinks spacecraft to the size of micro-chips. Credit: NASA/Bill Ingalls.
KickSat was launched on April 18th of this year, the plan being to release more than 100 Sprites, which would have become the smallest satellites ever to orbit the Earth. Unfortunately, the KickSat satellite reentered the atmosphere without Sprite deployment, leading to talk of building KickSat-2. The latest KickSat-2 update from Zachary Manchester, a member of Mason Peck’s lab at Cornell, is here. But as the new satellite takes shape, let’s talk about those Sprites. For while the KickSat experiments could provide broad spatial coverage of near-Earth phenomena, there is nothing to prevent the use of sprites to create sensor nets for deep space.
Modes of Propulsion
In Exploring Space with Chip-sized Satellites, an article in IEEE Spectrum in 2011, Peck explained that radiation pressure from the Sun offers one way for Sprites to move around the Solar System. They’re too small for onboard propellant, but the ratio of surface area to volume ensures that they can be driven just like a tiny sail. Peck explains the idea in relation to a much larger sail, the Japanese IKAROS:
If a Sprite could be made thin enough, then its entire body could act as a solar sail. We calculate that at a thickness of about 20 micrometers—which is feasible with existing fabrication techniques—a 7.5-mg Sprite would have the right ratio of surface area to volume to accelerate at about 0.06 mm/s2, maybe 10 times as fast as IKAROS. That should be enough for some interplanetary missions. If Sprites could be printed on even thinner material, they could accelerate to speeds that might even take them out of the solar system and on toward distant stars.
Image: Size of the Sprite satellite. Credit: Space Systems Design Studio.
Earlier this week we looked at Jordin Kare’s work on SailBeam, a concept involving vast numbers of tiny ‘micro-sails’. The Sprite has an affinity with Kare’s thinking, but unlike Kare, who was going to drive his microsails with a multi-billion watt orbiting laser, Peck is also exploring how charged Sprites might interact with the magnetic fields that surround planets. The Lorentz force bends the trajectory of a charged particle moving through a magnetic field. Can we put a charge on a Sprite?
In his lab work at Cornell, Peck and colleagues have tested ways of exposing Sprites to xenon plasma, mimicking conditions in Earth’s ionosphere. The Sprite can use a power supply to put a potential between two wires extending from the chip, letting plasma interactions charge the device. The charge is maintained as long as the Sprite continues to power its wires, so we can turn it on and off. If we can manipulate the charge aboard a Sprite at will, then imagine exposing a stream of charged Sprites to Jupiter’s magnetic field, 20,000 times the strength of Earth’s.
Jupiter as particle accelerator? The idea seems made to order, particularly since we’ve been examining particle accelerators of a vastly different order of magnitude — remember the 105 kilometer accelerators we talked about in relation to Cliff Singer’s pellet propulsion concepts. The nice thing about Jupiter is that we don’t have to build it. Here we have a way to accelerate one Sprite or 10,000 of them to speeds of thousands of kilometers per second, at which point the chips could shed their charge and be flung off on an interstellar journey.
Peck adds that getting the Sprites up to speed might itself take decades, and the journey to the nearest star would still be a matter of several centuries. But 300 years to Alpha Centauri beats any solar-sail-plus-Sundiver-maneuver mission I’ve ever seen, and unlike the admittedly faster beamed lightsail missions (some of Forward’s missions get down to decades), the Sprites take advantage of a form of propulsion that doesn’t require vast infrastructure in space.
Near-Term Issues
We’re talking, of course, about future generation Sprites, tiny spacecraft that have been built to surmount the problems Peck’s team is now trying to solve. Take the issue of damage along the way, which we had to think about both with Cliff Singer’s pellets and Gerald Nordley’s self-steering ‘snowflake’ craft. Better build many and be prepared for some losses. Lightweight Sprites have no radiation shielding, leaving the electronics vulnerable, and micrometeorites within the Solar System pose their own threat. The way to overcome such problems in the near-term is to send Sprites in large numbers, assuming a degree of loss during the mission.
Image: Artist’s conception of a cloud of Sprite satellites over the Earth. Credit: Space Systems Design Studio.
For missions deep into the Solar System and beyond it, though, we have to solve these problems. But I love the idea of using sunlight or the Lorentz force to accelerate these tiny payloads, which also have a natural synergy with CubeSats. Remember that The Planetary Society’s LightSail-1 is testing sail deployment from CubeSats, potentially creating a way to deliver a CubeSat laden with Sprites to other planets in the Solar System. Before we think of scaling to interstellar, why not think in terms of legions of Sprites sending back data from the surface of Mars, or placed into orbits that could provide deeply detailed maps of the solar wind and flare activity?
As we do this, we can be learning how best to deploy future Sprites, and how to fabricate everything from spectrometers to load sensors and basic cameras on a chip. Peck notes in the IEEE article that almost everything a spacecraft has to do can be managed with semiconductors, from solar cells for power, capacitors for energy storage and the various requirements of memory and processing. Take these ideas down to much smaller scales and the idea of swarm probes exploring the outer planets begins to resonate, with obvious implications for the kind of payloads we will one day want to send to Alpha Centauri.
by Paul Gilster | Jul 16, 2014 | Sail Concepts |
When Clifford Singer proposed in his 1980 paper that a stream of pellets could be used to drive an interstellar vehicle, the idea emerged at a time when Robert Forward had already drawn attention to a different kind of beamed propulsion. Forward’s sail missions used a beamed laser from an array near the Sun, and he explored the possibility of building a Fresnel lens in the outer Solar System to keep the beam tightly collimated; i.e., we want the narrowest possible beam to put maximum energy on the sail.
It was an era when huge structures in space defined interstellar thinking. Forward’s lasers were vast and he envisioned a 560,000-ton Fresnel lens in deep space, a structure fully one-third the diameter of the Moon. Such a lens made collimating the laser beam a workable proposition, to say the least — at 4.3 light years, the distance of Alpha Centauri A and B, such a beam is still converging, and would not reach the size of its 1000 kilometer transmitting aperture until an amazing 44 light years out.
Singer’s ideas were just as big, of course, and we saw yesterday that they demanded not only a series of stations to keep the pellet beam collimated but also an accelerator in the outer Solar System that would be 105 kilometers long. If we’re building enormous structures to begin with, wouldn’t it be easier to just send laser photons than a stream of particles or pellets? The answer, and it’s surely one that occurred to Singer as he examined Forward’s ideas, is that there is an inherent downside to photon propulsion. Let Gerald Nordley explain it:
The pellet, or particle, beam propulsion system is conceptually similar to photon beam propulsion systems discussed by Forward and others. While the concept is feasible, the reflected photons must still move at the speed of light and so carry away much of the energy used to generate them. The velocity of a beam of particles, however, can be varied so that the reflected particles are left dead in space and thus waste much less energy.
Geoffrey Landis described the same problem in his 2004 paper “Interstellar Flight by Particle Beam.” For all their size, Forward’s laser-propelled lightsails have extremely low energy efficiency, which is why the laser installations have to be so large in the first place. Some of Forward’s proposals reach lasers with power in the range of 7.2 terawatts. So we have an inefficient mechanism forcing not just huge lasers but spectacular lenses in the outer system. I don’t rule out huge structures in space — nanotech assemblers may some day make this possible — but finding ways to eliminate the need for them may bring the day of actual missions closer.
The Nordley quote above is drawn from his website, where slides from a presentation he made at a workshop in 1993 are made available. Nordley had already addressed the matter of particle beam propulsion in a 1993 paper in the Journal of the British Interplanetary Society, in which he discussed a magnetic sail, or ‘magsail,’ as the reflector for the incoming particles. The magsail reflects the particles and, as Nordley notes, thereby gains some fraction of twice their momentum, although he adds that reflector concepts are not limited to magnetic sails.
A retired Air Force officer, Nordley is an astronautical engineer who also writes science fiction (under the name G. David Nordley), author of the highly regarded novella “Into the Miranda Rift” along with numerous other stories mostly in Analog. It was in that magazine in 1999 that he pursued the work on magnetic sails that Dana Andrews and Robert Zubrin had developed, combining their insights with Clifford Singer’s pellet concepts. The result: Mass beam drivers driven by solar power that shoot pellets to a spacecraft whose laser system ionizes them, reflecting the resultant plasma by a magnetic mirror to produce thrust. Or perhaps a self-destruct mechanism within each pellet that would be triggered by proximity to the starship.
Image: Pushing pellets to a starship, where the resulting plasma is mirrored as thrust. Credit: Gerald Nordley.
Nordley’s pellet stream added a significant new wrinkle to Singer’s in that it would be made up of pellets that could steer themselves to the beam-riding spacecraft. Remember the scope of the problem: Singer needed those stations in deep space to make course adjustments for the pellet stream, which had to hit the spacecraft at distances of several hundred AUs. Nordley talks about nanotech-enabled pellets in the shape of snowflakes capable of carrying their own sensors and thrusters, tiny craft that can home in on the starship’s beacon. Problems with beam collimation thus vanish and there is no need for spacecraft maneuvering to stay under power.
In “Beamriders,” a non-fiction article in the July/August, 1999 Analog, he sees these pellets as weighing no more than a few micrograms, although here again the question of interstellar dust comes into play. Singer had found in his second JBIS paper (see citation at the end of yesterday’s entry) that pellets over a gram in size should be impervious to large-scale dispersion. It would obviously have to be demonstrated that much lighter ‘smart pellets’ like these would not suffer from dust strikes. But the beauty of lighter pellets is that they would rely on shorter accelerators than the 100,000 kilometer behemoth Singer described.
Efficient delivery of the pellet stream can also make for smaller magsails because the incoming stream is tightly concentrated. The pellet concept Singer introduced is thus significantly enhanced by Nordley’s application of nanotechnology, and forces us to ask the question that has infused this entire series of posts: Given the rapid pace of miniaturization and computing, can we imagine a paradigm shift that takes us from smart pellets all the way to self-contained probes the size of bacteria? Developing the technologies by which such minuscule craft would travel in swarms, combining resources for scientific study and communications, will surely energize one stream of interstellar studies in coming decades.
The Geoffrey Landis paper cited above is “Interstellar Flight by Particle Beam,” in Acta Astronautica Vol. 55, pp. 931-934 (2004). The earlier Nordley paper on particle beam propulsion is “Relativistic Particle Beams for Interstellar Propulsion,” JBIS, 46-4, April 1993. See also his “Interstellar Probes Propelled by Self-steering Momentum Transfer Particles” (IAA-01-IAA.4.1.05, 52nd International Astronautical Congress, Toulouse, France, 1-5 Oct 2001).
by Paul Gilster | Jul 15, 2014 | Sail Concepts |
Small payloads make sense if we can extract maximum value from them. But remember the problem posed by the rocket equation: It’s not just the size of the payload that counts. A chemical rocket has to carry more and more propellant to carry the propellant it needs to carry more propellant, and so on, up the dizzying sequence of the equation until the kind of mission we’re interested in — deep space in reasonable time frames — is ruled out. That’s why other forms of rocket using fission or fusion make a difference. As the saying goes, they get more bang for the buck.
But the idea of carrying little or no propellant at all has continued to intrigue the interstellar community, and numerous ways of doing so have been proposed. One early contender was a particle beam, which would be used to push a magnetic sail. Strip electrons from atomic nuclei and accelerate the positively charged particles close to the speed of light. There’s a benefit here over laser-beamed sail concepts, for the magnetic field creating the magsail has no heat limit. We’re less concerned about sail degradation under the beam and, unlike some of Robert Forward’s laser concepts, we don’t require a huge laser lens in the outer Solar System.
At first glance, the idea stacks up favorably when compared to lasers. What it demands is a particle accelerator powered by solar energy sufficient to accelerate the charged particle beam, just as laser beaming to a sail would require large laser installations in an inner system orbit. But physicist Clifford Singer noticed early on that a stream of charged particles has an inherent problem — it will spread as it travels because particles with the same charge repel each other. Singer’s idea was to use a stream of pellets to replace the charged particles, each of them a few grams in size. The pellet stream does not ‘bloom’ as it travels. Singer believed that the pellets, accelerated to perhaps as much as a quarter of the speed of light, would be vaporized into a plasma when they reached the interstellar craft, turning into a hot plasma exhaust.
Image: Clifford Singer, whose work on pellet propulsion in the late 1970s has led to interesting hybrid concepts involving on-board intelligence and autonomy. Credit: University of Illinois.
When he came up with the proposal in 1979, Singer was at Princeton University’s Plasma Physics Laboratory, and it’s interesting to consider his work a kind of hybrid between beamed power and nuclear pulse propulsion, which is how Gregory Matloff and Eugene Mallove approach it in The Starflight Handbook. Singer envisioned pellets for acceleration, after which there would be a long coasting phase of the interstellar mission. Looking at laboratory work involving so-called ‘rail gun’ accelerators, he thought of scaling up the idea to an accelerator 105 kilometers long deployed somewhere in the outer Solar System.
Singer’s ideas, first broached in a paper called “Interstellar Propulsion Using a Pellet Stream for Momentum Transfer” in The Journal of the British Interplanetary Society drew their share of criticism. Could the stream of pellets really be collimated so as to remain a single, coherent beam? One problem was that pellets might be dispersed due to interactions with dust grains in the interstellar medium. Singer would defend the concept in a second paper one year later in JBIS, acknowledging the dispersion problem for lighter particles but concluding that particles heavier than one gram should not be affected. Nor would interactions with the galactic magnetic field be a serious impediment.
Interstellar thinking of this era demanded thinking big, and while Singer’s pellets were tiny, they demanded not only that enormous accelerator but a series of deep space facilities spaced 340 AU apart — several dozen of them — to help keep the beam fully collimated. Such stations might be deployed from the departing starship itself, each of them measuring particle locations and correcting the particle flight path through the use of magnetic or electrostatic fields. Singer’s ideas have been enormously fruitful, leading to ideas the technology of the day would not render obvious, but as we’ll see tomorrow, they point to a fusion of digital tech and nanotechnology.
I like what Matloff and Mallove have to say about pellet propulsion in The Starflight Handbook:
Workable concept or not, the advent of the pellet-stream propulsion idea several decades after the beginning of serious starship speculation illustrates again how easy it is to overlook ‘obvious’ interstellar flight concepts. What other propulsion gems may be waiting to be found, buried in the armamentarium of twentieth-century technology!
Now a professor of nuclear, plasma, and radiological engineering at the University of Illinois, Singer is no longer active in interstellar work but keeps an interested eye on the propulsion method he created. The pellet concept is indeed a gem, and one whose facets keep changing as we hold it up to the light. For we’re seeing a metamorphosis away from the idea that the only kind of particles we can send are dumb objects. Gerald Nordley would enhance the particle stream with active intelligence that would allow collimation through course correction at the particle level.
No need for starship maneuvering or course correction stations along the way if we can deploy Nordley’s ‘snowflake’ pellets, which we’ll look at more closely tomorrow. I argue that an enhanced ‘smart pellet’ is one step away from becoming not just the propellant but the spacecraft itself. In any case, it’s into the interesting synergy between driving small objects — particles, pellets, micro-sails — to a spacecraft and the extremely rapid advance of digital tools and miniaturization that 21st Century interstellar thinking seems to be expanding.
Clifford Singer’s key paper is “Interstellar Propulsion Using a Pellet Stream for Momentum Transfer,” JBIS 33 (1980), pp. 107-115. He followed this up with “Questions Concerning Pellet-Stream Propulsion,” JBIS 34 (1981), pp. 117-119.
by Paul Gilster | Jul 14, 2014 | Autonomy and Robotics |
We’ve all imagined huge starships jammed with human crews, inspired by many a science fiction novel or movie. But a number of trends point in a different direction. As we look at what it would take to get even a robotic payload to another star, we confront the fact that tens of thousands of tons of spacecraft can deliver only the smallest of payloads. Lowering the mass requirement by miniaturizing and leaving propellant behind looks like a powerful option.
Centauri Dreams regular Alex Tolley pointed to this trend in relation to The Planetary Society’s LightSail-1 project. In a scant ten years, we have gone from the earlier Cosmos 1 sail with an area of 600 square meters to LightSail-1, with 32 square meters, but at no significant cost in scientific return because of continuing miniaturization of sensors and components. We can translate that readily into interstellar terms by thinking about future miniature craft that can be sent out swarm-style to reach their targets. Significant attrition along the way? Sure, but when you’re building tiny, cheap craft, you can lose some and count on the remainder to arrive.
The Emergence of SailBeam
I inevitably think about Jordin Kare’s SailBeam concepts when I hear thinking like this. Kare, a space systems consultant, had been thinking in terms of pellet propulsion of the kind that Clifford Singer and, later, Gerald Nordley have examined. The idea here was to replace a beam of photons from a laser with a stream of pellets fired by an accelerator — the pellets (a few grams in size) would be vaporized into plasma when they reached the spacecraft and directed back as plasma exhaust. Nordley then considered lighter ‘smart’ pellets with onboard course correction.
I’m long overdue for a re-visit to both Singer and Nordley, but this morning I’m thinking about Kare’s idea of substituting tiny sails for the pellets, creating a more efficient optical system because a stream of small sails can be accelerated much faster close to the power source. Think of a solar sail, as Kare did, divided into a million pieces, each made of diamond film and being accelerated along a 30,000 kilometer acceleration path, all of them shot off to drive a larger interstellar probe by being turned into a hot plasma and pushing the probe’s magnetic sail.
Image: Jordin Kare’s ‘SailBeam’ concept. Credit: Jordin Kare/Dana G. Andrews.
Kare, of course, was using his micro-sails for propulsion, but between Nordley and Kare, the elements are all here for tiny smart-probes that can be pushed to a substantial fraction of the speed of light while carrying onboard sensors shrunk through the tools of future nanotechnology. Kare’s sails, in some designs, get up to a high percentage of c within seconds, pushed by a multi-billion watt orbiting laser. Will we reach the point where we can make Kare’s sails and Nordley’s smart pellets not the propulsion method but the probes themselves?
In that case, the idea of a single probe gives way to fleets of tiny, cheap spacecraft sent out at much lower cost. It’s a long way from LightSail-1, of course, but the principle is intact. LightSail-1 is a way of taking off-the-shelf Cubesat technology and giving it a propulsion system. Cubesats are cheap and modular. Equipped with sails, they can become interplanetary exploration tools, sent out in large numbers, communicating among themselves and returning data to Earth. LightSail’s cubesats compel anyone thinking long-term to ask where this trend might lead.
A Gravitational Lensing Swarm
In Existence, which I think is his best novel, David Brin looks at numerous scenarios involving miniaturization. When I wrote about the book in Small Town Among the Stars, I was fascinated with what Brin does with intelligence and nanotechnology, and dwelled upon the creation of a community of beings simulating environments aboard a starship. But Brin also talks about a concept that is much closer to home, the possibility of sending swarms of spacecraft to the Sun’s gravitational focus for observation prior to any star mission.
We normally speak about the distance at which the Sun’s gravity bends light from objects on the other side of it as being roughly 550 AU, but effects begin closer than this if we’re talking about gravitons and neutrinos, and in Brin’s book, early probes go out here, between Uranus and Neptune, to test the concept. But get to 550 AU and beyond and photon lensing effects begin and continue, for the focal line goes to infinity. We have coronal distortion to cope with at 550 AU, but the spacecraft doesn’t stop, and as it continues ever further from the Sun, we can be sampling different wavelengths of light to make observations assisted by this hypothesized lensing.
Before committing resources to any interstellar mission, we want to know what targets are the most likely to reward our efforts. Why not, then, send a swarm of probes. Claudio Maccone, who has studied gravitational lensing more than any other physicist, calls his design the FOCAL probe, but I’m talking about its nanotech counterpart. Imagine millions of these sent out to use the Sun’s natural lens, each with an individual nearby target of interest. Use the tools of future nanotech and couple them with advances in AI and emulation and you open the way for deep study of planets and perhaps civilizations long before you visit them.
The possibilities are fascinating, and one of the energizing things about them is that while they stretch our own technology and engineering well beyond the breaking point, they exceed no physical laws and offer solutions to the vast problems posed by the rocket equation. Perhaps we’ll build probes massing tens of thousands of tons to deliver a 100 kilogram package to Alpha Centauri one day, but a simultaneous track researching what we can do at the level of the very small could pay off as our cheapest, most effective way to reach a neighboring star.
More on this tomorrow, as I take a longer look at Clifford Singer and Gerald Nordley’s ideas on pellet propulsion. I want to use that discussion as a segue into a near term concept, Mason Peck’s ideas on spacecraft the size of computer chips operating in our Solar System.
And today’s references: Cliff Singer’s first pellet paper is “Interstellar Propulsion Using a Pellet Stream for Momentum Transfer,” JBIS 33 (1980), pp. 107-115. Gerald Nordley’s ideas can be found in “Beamriders,” Analog Vol. 119, No. 6 (July/August, 1999). Jordin Kare’s NIAC report “High-Acceleration Micro-Scale Laser Sails for Interstellar Propulsion,” (Final Report, NIAC Research Grant #07600-070, revised February 15, 2002) can be found on the NIAC site.
by Paul Gilster | Jul 11, 2014 | Deep Sky Astronomy & Telescopes |
Not long ago we talked about what the Milky Way would look like when seen from afar. I had mentioned Poul Anderson’s World Without Stars, which appeared in Analog in 1966 under the title The Ancient Gods. In the Anderson tale, a starship crew is sent to make contact with a recently discovered technological civilization that lives on a world hundreds of thousands of light years from the galactic core. Now a recent paper deepens our understanding of this environment deep in the galaxy’s outer halo.
Recall that the Milky Way is about 100,000 light years in diameter, and that the distance to the nearest large galaxy is roughly 2,500,000 light years. Anderson’s crew is over 200,000 light years from the core, which puts them in the outer halo, a sparse spherical volume of space that stretches out 500,000 light years, well beyond the familiar, highly visible disk. While the stars in the galactic disk are on nearly circular orbits in the plane of the galaxy, the halo stars are on more elliptical orbits that are randomly oriented, so that while inner halo stars can pass through the disk, most of their lives are spent well above or below the plane of the galaxy. The inner, visible part of the halo is where we find the ancient, metal-poor globular clusters.
Image: Structure of the Milky Way, showing the inner and outer halo. Credit: NASA, ESA, and A. Feild (STScI).
Astronomer John Bochanski (Haverford College, PA) and team, however, are looking out well beyond the globular clusters. The researchers note in their paper in The Astrophysical Journal Letters that there are few known outer halo stars at distances over 120 kiloparsecs, which works out to about 390,000 light years — in fact, the list of known halo stars at this distance yields a grand total of seven, with the paper adding an additional two. The galaxy’s outer halo, we learn, is largely unexplored, but as we’ll see, it holds implications for galaxy formation theories.
The team’s recent paper outlines the discovery of two cool red giants — ULAS J0744+25 and ULAS J0015+01 — that appear to be the most distant Milky Way stars yet detected, at distances of 775,000 and 900,000 light years respectively. The work draws on observations from the UKIRT Infrared Deep Sky Survey and Sloan Digital Sky Survey, with spectroscopic studies using the 6.5m telescope at the MMT Observatory in Arizona. The newly discovered stars are five times more distant than the Large Magellanic Cloud and almost a third of the way to the Andromeda galaxy. At these distances, both Andromeda and the Milky Way should appear quite faint in the visible spectrum. If Anderson’s crew were here, the night sky would be dark indeed.
The image below brightens the Milky Way to give some sense of its distance from these stars.
Image: This simulated image demonstrates how small the Milky Way would look from the location of ULAS J0744+25, nearly 775,000 light years away. This star, along with ULAS J0015+01, are the most distant stars ever associated with our Galaxy, and are about five times further away than the Large Magellanic Cloud, one of the Milky Way’s closest galactic neighbors. Credits: Visualization Software: Uniview by SCISS Data: SOHO (ESA & NASA), John Bochanski (Haverford College) and Jackie Faherty (American Museum of Natural History and Carnegie Institute’s Department of Terrestrial Magnetism).
Bochanski’s team has been looking at formation models for the Milky Way, an interesting issue given that, as he explains, “Most models don’t predict many stars at these distances. If more distant red giants are discovered, the models may need to be revised.” The halo itself may be the result of mergers over the galaxy’s lifetime with numerous smaller galaxies, with outer stars the remnant population of what had once been intact dwarf galaxies. If this is correct, we can study these outer halo stars as a way of probing the formation history of the entire spiral. The team hopes to identify up to 70 red giants in the halo, refining its selection criteria and aiding next generation surveys like Gaia that will help us deepen our catalog in this distant region.
The paper is Bochanski et al., “The Most Distant Stars in the Milky Way,” The Astrophysical Journal Letters, Volume 790, Issue 1, article id. L5 (abstract / preprint).
