Weekend Reading from Triton to Kentucky

The Kentucky space program may get back to the Moon before NASA or the Chinese. If that sounds cryptic, do visit the latest Carnival of Space, held on Wayne Hall’s KySat Online site, which supports this innovative and student-led program to get the educational system into the business of designing, building, and operating small satellites. Wayne writes:

The very first project of this ambitious enterprise is a cooperative, student-led effort to design, build and fly a CubeSat that kids from the eastern mountains to the western Mississippi river shore can figuratively reach out and touch from classrooms all over the state. The first of many planned efforts, it will rocket to orbit sometime late this year or early next.

Good fortune accompany the attempt! I hope many states are watching what Kentucky is doing, an educational activity that spreads interest and enthusiasm for space projects to the next generation of scientists.

As to the Carnival itself, I normally choose one post of particular interest to Centauri Dreams readers, and this week I send you to Colony World‘s musings on Triton, Neptune’s largest moon, famous for the retrograde orbit that seems to argue that it is a captured object. Darnell Clayton is intrigued by the proximity of Neptune’s helium-3, and the possibilities for future human settlements in this remote part of the Solar System. Just how much might Triton be worth to us?

I also want to note Adam Crowl’s comment about Triton in a recent post, which notes a paper by Paul Schenk and Kevin Zahnle that implies even more melting of the moon’s crust than we see around Enceladus’ southern pole. Is a sub-surface ocean possibly bursting through in cryovolcanic events, as Adam speculates? So far we have all too little data from spacecraft, but the Voyager imagery tells us how rich a Neptune orbiter mission would be. Fraser Cain at Universe Today offers a nice chart of the known trans-Neptunian objects in the context of a backgrounder on how we have come to define the word ‘planet.’ Useful stuff in these confusing times, and helpful to those of us who speculate about the discoveries yet to be made in the Edgeworth/Kuiper belt.

Although not in this week’s Carnival (well, for that matter, neither is Adam’s Triton post, but bear with me as I collate various things I’ve been meaning to write about), Brian Wang looks at an electric solar sail concept developed at the Finnish Meteorological Institute and the plans for a test mission. This one uses an electron gun to charge long metallic tethers, riding not the momentum imparted by photons but the solar wind, an interesting variation on existing magsail concepts.

Star Formation in the Hinterlands

Centauri Dreams always thinks it’s important to talk about images like the one below. Not the specific subject matter — this is the Southern Pinwheel galaxy M83, about which more in a moment — but about the beauty of the image. Casual browsers of astronomy photos often tell me they never realized how colorful space actually is, which is why I want to say periodically that images like these are doctored to reveal information. In this case, far-ultraviolet light is intentionally shown in blue, near-ultraviolet light in green, and radio emissions — at the 21 centimeter wavelength of gaseous hydrogen — are shown in red.

M83 galaxy in false colors

Space is undoubtedly beautiful, but what you see in many of these photos is not what you would get if you were there. In fact, not only are the colors doctored here, but this is a composite image, incorporating observations from the Very Large Array and the Galaxy Evolution Explorer (GALEX), an orbiting ultraviolet survey telescope.

Image: The outlying regions around the Southern Pinwheel galaxy, or M83, are highlighted in this composite image from NASA’s Galaxy Evolution Explorer and the National Science Foundation’s Very Large Array in New Mexico. The blue and pink pinwheel in the center is the galaxy’s main stellar disk, while the flapping, ribbon-like structures are its extended arms. Credit: NASA/JPL-Caltech/VLA/MPIA.

So what would you see if you were actually viewing M83 from the viewport of an intergalactic spaceship? Greg Laughlin wrote up this question a few years back with regard to the Sombrero Galaxy, M104, noting that if you could somehow place yourself 300,000 light years from it, your human eyes would see a galaxy so dim that it would appear only as a faint, glowing patch. For that matter, try to see M31, the Andromeda Galaxy, subtending an angle larger than the full Moon in the sky, and you’ll see precisely nothing there. Laughlin describes this key fact:

The storms from earlier this week have blown through. The sky sparkles with brilliant clarity. Yet when I step outside and look up, I can’t see the Andromeda Galaxy at all. It’s too faint. In a 1:10,000,000,000,000 scale model of M31, the stars are like fine grains of sand separated by miles. Our Galaxy, the Andromeda Galaxy, and the Sombrero Galaxy are all essentially just empty space. To zeroth, to first, to second approximation, a galaxy is nothing at all.

All of which is prelude to the real point of this post, which is that the image above lets us see things we would otherwise find invisible, in this case the Southern Pinwheel galaxy itself and the extended galactic arms in which astronomers have now identified new stars forming. Their distance from the primary disk of M83 is impressive, even startling, for M83 is only some 40,000 light years across, while the young star formation area runs up to 140,000 light years away from the center of the galaxy, a phenomenon Frank Bigiel (Max Planck Institute for Astronomy) calls ‘absolutely stunning.’

Shouldn’t these galactic outskirts be deficient in star-forming materials? You would think so, but the radio observations from the Very Large Array pinpointed the location of the necessary hydrogen, findings that mesh with what the Galaxy Evolution Explorer saw. Thus we may be looking at the kind of star formation that occurred early in the history of the cosmos, when dust and heavier elements were not plentiful. That makes M83, some 15 million light years away in the constellation Hydra, a helpful proving ground for our theories of early star formation, as per this GALEX news release. Such a relatively nearby laboratory (in cosmic terms, at least) will help us develop useful data for comparison with what we see much further out in space and, by extension, back in time.

Bach’s Flare: Brightening the Galactic Core

Looking at the central black holes in galaxies other than our own has forced a question: What’s going at Milky Way galactic central? We know there is a black hole there, and a big one, weighing in at about four million solar masses. But the Milky Way’s black hole, called Sagittarius A* (pronounced ‘A-star’) seems quiet compared to what we see in other galaxies, emitting but a trace of the radiation they are pushing into the cosmos. A new study from a Japanese team proposes an answer. Three hundred years ago, Sgr A* put out a huge flare, making it a million times brighter than today. Today’s quiet black hole may simply be the slumbering aftermath of what must have been a frenetic round of activity.

“We have wondered why the Milky Way’s black hole appears to be a slumbering giant,” says team leader Tatsuya Inui of Kyoto University in Japan. “But now we realize that the black hole was far more active in the past. Perhaps it’s just resting after a major outburst.”

X-ray panels of Sagittarius A*

Figuring out this possibility involved measuring the brightening of clouds of gas near the black hole, so-called ‘light echoes’ that resulted from the clouds being bathed in X-ray pulses from just outside Sgr A*. The pulses would have been the result of gases spiraling in toward the black hole, being heated to millions of degrees, and emitting X-rays. The observed brightening involved the large cloud called Sagittarius B2, which is about 300 light years from the black hole, its iron atoms emitting X-rays of their own as a result of a flare that went off, in relative terms, when Bach was still writing fugues.

Image: Four X-ray satellites imaged a small region in the gas cloud Sagittarius B2, and saw pockets brighten and fade over the course of nearly 12 years. These light echoes are caused by varying X-ray output from our galaxy’s central black hole. Credits: ASCA and Suzaku: JAXA; Chandra: NASA/CXC; XMM-Newton: ESA.

The actual event, of course, occurred long before that. The Milky Way’s center is 26,000 light years from Earth; we’re looking at ancient history, but able to make sense out of the sequence of events to parse out at least a bit of Sagittarius A*’s activity. This particular flare lit up the Sagittarius B2 cloud in a region ten light years across, with results varying widely over a five year period. The work follows on an earlier study of Sagittarius A* that tracked an X-ray burst some fifty years ago. The recently discovered flare was ten times stronger than that event.

Working in these wavelengths involved using archival data over an eleven year period from the major X-ray observatories — Japan’s Suzaku and ASCA X-ray satellites, NASA’s Chandra X-ray Observatory, and the European Space Agency’s XMM-Newton X-ray Observatory. The study is Inui et al., “Time Variability of the Neutral Iron Lines from the Sgr B2 Region and its Implication of a Past Outburst of Sgr A*,” slated to appear in Publications of the Astronomical Society of Japan (abstract).

Addendum: A light echo preserving an enormous X-ray flare has been observed in the galaxy SDSSJ0952+2143, as per this news release from the Max Planck Institute for Extraterrestrial Physics. The flare seems to have been produced when a single star was disrupted by a supermassive black hole. In this study, light echoes are used both to study the disruption of the star and also to map the galactic nucleus. “Reverberation-mapping of light echoes opens up new possibilities to study galaxies,” says the Planck Institute’s Stefanie Komossa, leader of the team on this work. Abstract of their paper here.

Ringing the Stellar Bell

56 light years from Earth, the star Iota Horologii is a member of the ‘Hyades stream,’ a number of stars moving in a similar direction with respect to the rest of the galaxy. It’s also an exoplanet host star, known to have a planet twice the mass of Jupiter in a 320-day orbit. The two factors — the position of the star within the stream and the planet that accompanies it — play into an unusual application of asteroseismology, the study of the sound waves that move through a star.

The star Iota Horologii

I want to note this work particularly because it has a bearing on planet formation, about which the more we learn the better as we continue the hunt for exoplanets. But let’s pause on asteroseismology itself. You may recall that using this technique for studying the interiors of stars is one of the purposes of the COROT mission, the other being the detection of planetary transits. Asteroseismology is invariably explained with musical metaphors, likening the sound moving within a star to the ringing of a bell.

Just how the bell rings can tell us much about the star. In the case of Iota Horologii, the team studying the star (led by Sylvie Vauclair of the University of Toulouse) was able to pick out the signature of 25 separate waves, as if the ringing bell had produced 25 ‘notes.’ Out of that data come measurements that are quite precise. Iota Horologii is now believed to have a mass 1.25 times that of the Sun, with a temperature of 6150 K and an age of 625 million years.

Image: Using HARPS on ESO’s 3.6-m telescope at La Silla, astronomers were able to study in great detail the star Iota Horologii, known to harbour a giant planet, and make a very precise portrait of it: its temperature is 6150 K, its mass is 1.25 times that of the Sun, and its age is 625 million years. Moreover, the star is found to be more metal-rich than the Sun by about 50%. This means the star must have drifted from the Hyades cluster where it formed. Credit: Digital Sky Survey/VirGO.

And note this: The star is about fifty percent more metal-rich than the Sun. That’s useful information because it tell us that Iota Horologii has the same metal abundance and age as the Hyades cluster, located 151 light years away. Note the distance — the star has drifted about 130 light years from its apparent birthplace, although it continues to move in the general direction of the cluster. The paper on this work makes the claim that Iota Horologii is one of the 15 percent of stars in the Hyades stream that share this origin, the others being simply “…field-like stars sharing the Hyades galactic velocities because of galactic dynamical effects.”

The high metal content of this star is significant in its own right. Metals in astrophysical terms are elements higher than hydrogen and helium, and the question of how they play into planetary development remains a thorny one. If you take an average of the stars known to have exoplanets, they turn out to be far more laden with metals than our own Sun. Is this because the clouds that gave birth to these stars already contained high levels of metals, or because planets and planetesimals accrete around these stars early on, increasing their metallicity?

This is a testable issue, for if the metals come from the original cloud, then they extend throughout the star, whereas if they’re the result of accretion, only the star’s outer layers should show high metal levels. You can see how asteroseismology ties in to all this. The paper summarizes the result, noting that this is the first time these methods have been able to deliver unambiguous results, despite studies of the star Mu Arae, which was observed with the same HARPS spectrograph:

In the case of ? Hor, the question may be approached in a different way. Asteroseismology leads to the conclusion that this star was evaporated from the primordial Hyades cluster, sharing the same age, helium abundance and overmetallicity. This is one proof that the origin of this overmetallicity is primordial, from the original cloud. This result has important consequences for the formation and subsequent evolution of galactic clusters and the theories of exoplanets formation and migration.

Or as Vauclair herself puts it in this ESO news release:

“The chicken and egg question of whether the star got planets because it is metal-rich, or whether it is metal-rich because it made planets that were swallowed up is at least answered in one case.”

What we need, of course, are many, many cases as we continue to investigate how planets form. As that work continues, expect asteroseismology to play a significant role. The idea that we can use a spectrograph to study the motions on stellar surfaces and translate that information into solid data about the interior of stars — age, helium abundance, gravity, mass — is striking, and in this case led to an identification of origins that feeds into broader exoplanet questions. As the paper summarizes the issue:

This work shows how powerful asteroseismology can be in deriving the characteristic parameters of a star with the help of spectroscopic analysis, but ?nally obtaining much more precise results than with spectroscopy alone.

The paper is Vauclair et al., “The exoplanet-host star iota Horologii: an evaporated member of the primordial Hyades cluster,” accepted by Astronomy and Astrophysics and available online.

John Wheeler and the Umpires

Is observation critical to existence? Niels Bohr believed that it was the collapse of the wave function that gave particles like electrons their distinct reality. John Wheeler, who knew and worked with the great figures of quantum mechanics, summarized the gap between that point of view and Einstein’s by quoting three baseball umpires:

Number 1: I calls ’em like I see ’em.
Number 2: I calls ’em the way they are.
Number 3: They ain’t nothing till I calls ’em.

Michio Kaku reports this story in his book Parallel Worlds, noting this:

“To Wheeler, the second umpire is Einstein,who believed there was an absolute reality outside human experience. Einstein called this ‘objective reality,’ the idea that objects can exist in definite states without human intervention. The third umpire is Bohr, who argued that reality existed only after an observation was made.”

John Wheeler and friends

Image: Albert Einstein, Hideki Yukawa and John A. Wheeler. Credit: Johns Hopkins University.

Out of such conundrums John Wheeler made a career richly summarized in this New York Times obituary. I send you there for the details, from general relativity to black holes, but do want to preserve this quote:

“If there’s one thing in physics I feel more responsible for than any other, it’s this perception of how everything fits together. I like to think of myself as having a sense of judgment. I’m willing to go anywhere, talk to anybody, ask any question that will make headway.

“I confess to being an optimist about things, especially about someday being able to understand how things are put together. So many young people are forced to specialize in one line or another that a young person can’t afford to try and cover this waterfront — only an old fogy who can afford to make a fool of himself.

“If I don’t, who will?”

Addendum: Don’t miss Cosmic Variance‘s beautiful tribute.