ASTRONOMY UPDATES

ASTRONOMY UPDATE 2003

James B. Kaler

Department of Astronomy, University of Illinois

First published in the Proceedings of the 39th Annual GLPA Conference, Cleveland, OH, October 22-25, 2003. Reprinted by permission.

Abstract

As always, the year was marked by dramatic gains and losses, the worst of which was that of our Shuttle Crew. Beyond that, our astronomers explained solar faculae, got more information on Martian water, and reversed our ideas about Jupiter's cloud belts. We saw some magnificent imagery from our telescopes, watched a non-lethal meteorite strike, and witnessed more records regarding brown dwarfs and planets, whose properties and limits are no more understood than dark matter or the dark energy that is making our Universe's expansion accelerate.

Entries and Passages

The year was marked by fine discoveries, but also by fine beginnings and sad endings. The National Virtual Observatory is underway, again it seems, since it was reported on last year. Nevertheless, it is a major development in astronomy, wherein the vast amounts of data from many monstrous surveys will be compiled and housed for access to any astronomer who cares to do the research. Neither good nor bad, we will slowly raise a new breed of observational astronomer who will never go near a real telescope, nor even use it remotely. Photography, a dying means of data acquisition, is really seeing the end of its days, as its last bastion -- wide field recording -- is quickly being replaced by large format CCDs. Such advances are epitomized by the Hubble's new Advanced Camera for Surveys, which can now reach to 31st magnitude. And the contract for the Next Generation Space (= James T. Webb) Telescope has been let to TRW. But the fight is on for the budget, as the Hubble has been so very successful that few want to see it go, to be replaced (around 2010) by the infrared high-redshift telescope that is the NGST. Stay tuned.

Three passages of note include the deliberate destruction of the Galileo spacecraft by the object of its vision, Jupiter, this wonderful satellite having had a decade to revise our view of the giant planet. A similar fiery fate visited the Mt. Stromlo Observatory in Australia, which was burned by a wildfire. Nothing, though, can compare with the loss of our astronauts aboard the Columbia.

Turn now to rebirth with the ancient Jodrell Bank 250-foot radio telescope, renewed with a surface good to 1-2 mm. And to the re- opening of the Super Kamiokande neutrino detector, whose phototubes had exploded.

That Old Sun

Neutrinos, whose count had been falling short in observations from older detectors, have been found to be in the right number upon observation of all three "flavors" (electron, mu, and tau). They change their form upon flight to the Earth, which can happen only if neutrinos have mass, which recent observations report.

Data from our nearest star pour in. Even as the current cycle is winding down, we have the appearance of not one, but two naked- eye sunspot groups. The umbras (cores) of sunspots are depressions in the solar "surface" (the hot, opaque gases of the photosphere), while the penumbras are upward slopes, which to the surprise of the astronomers at the Swedish Vacuum Telescope have filaments with dark cores whose significance is unknown.

And who of us, upon observing the Sun in white light has not seen the bright faculae near the limb? Nowhere could one find a real explanation of them. Because, while it was not really admitted, nobody knew what caused them. Until now. They are the bright slopes of granules that are visible only when the granules are seen at an angle close to the solar edge. Mystery solved.

Mars Mania (and the other planets too)

What can one say? For being less than one percent closer than it was two favorable oppositions ago, we get great press! And it sure was bright. "As big as the Moon" said one release (but shhh, only when seen at 70 power). And even then it was not THAT great, as good eyes have 30 picture elements across the Moon, whereas with typical non-mountain seeing you might have but a few for Mars.

Nevertheless, one could write a book, or at least a good article, on what's new for the red planet (as is being done). Couple highlights: crater gullies are back to being created by water. High water content near the equator -- "wet poles" -- may be due to the shifting of rotation poles, which are central to subsoil water, and which may in fact be rather close to the surface.

The giant planets show that what seemed obvious is not always so. The dark Jovian cloud belts were long thought to be falling, the bright zones rising. Uh, it may be the other way around, as Cassini found rising columns in the belts. And thanks to new technologies, it's hard to keep up with the satellite number. Jupiter is up to 61, Saturn (which once held the lead) up to 31. Many of these are probably the smashed remains of larger moons. One, Amalthea (inside Io's orbit) is little more than a reformed rubble pile. Io itself was found to have a violent volcanic eruption, with temperatures hitting 1500 Kelvin. Saturn's large moon Titan displayed specular radar reflection suggesting that the purported ethane ocean may really be there. We will soon know when Cassini drops its probe through the thick hydrocarbon haze.

At the edge of the Solar System, in the infrared, Uranus (which is showing us more of its equator and less of its poles) looks remarkably like Saturn. And the discovery of Neptune (from its perturbations of Uranus) seems to go now more to Leverrier and Galle, as there is evidence that Adams's calculations were not very good, the facts of the case long covered up. And to our surprise, Pluto, though getting farther from the Sun, is heating up (though not a lot when you are near 40 Kelvin). It seems to be just a phase lag, rather like the hottest northern days being in July and August rather than in June.

Astrotrash

The Planetary System, as we have long known, is not synonymous with the SOLAR System, which contains far more than just the planets. Beyond Neptune lies the Kuiper Belt, which at last count contained 654 known objects (i.e., KBOs). Of these, 131 are "Plutinos" that are caught by Neptune in resonant orbits, in which they go around the Sun twice for every time Neptune circuits thrice (leaving 523 non-resonant KBOs farther out). Pluto, a clear member of the Kuiper belt, is but one of them (though the largest, which is why you still get to call it a planet). Giant-planet gravity slowly works KBOs inward, where between Neptune and Jupiter they wind up as Centaurs in unstable orbits (190 now known) that bring them toward us to be seen as short-period comets.

Between Jupiter and Mars lies a zone of stability, the home where the asteroids roam (ok, orbit). Even these can be moved inward, however, where upon hitting the Earth they are called meteorites (or in the case of big ones, "hazardous objects"). To our relief, modestly big hits of the 1908 Tunguska variety are much rarer than thought, about once every thousand years (though like supernovae you can get none for a long time followed by two in a row). Never mind the big hits. Watch for the smaller ones, the like of which sent a shower of stones over the Chicago suburbs on March 26 that nailed six houses and three cars within a 10-km strewn field, the "rock" an ordinary chondrite that may have weighed as much as 25 tons. Who says astronomy is a "pure" science!

And how about the last of the Leonids. For now. Maybe.

More significant is the age of the stuff from both comets and meteorites. The oldest known things are said to be the carbonaceous chondrites, which date to 4.5 or so billion years ago. But within them are interstellar grains that predate the solar system, dust grains from the stars that were in the neighborhood of the new Sun. They have been found in tiny interplanetary dust grains as well.

Interstellar, Star Formation, and Low Mass Stars

The interplanetary dust provides a fine transition to the interstellar medium, its dust epitomized by such Hubble shots as the interior of M 17, the Omega Nebula. Within these dust clouds works a cold chemistry that has produced the 120 now-known interstellar molecules. One of these, acetic acid, seems to be found closer in to the center of the Galaxy, odd since it is widely assumed that the substance is important in building life- giving molecules. Closer to us, the black clouds of the Milky Way become very obvious. They are not static, but dynamic. Bok globules such as much photographed B 68 seem to be pulsing, probably from being hammered by interstellar shock waves. (Yes, there IS sound in space. You just could not hear it.) The globule probably contains little more than a solar mass.

Stars form from such clouds. The maximum mass of a star is around 100-120 times solar. Above that, the odds of formation drop to near zero (since the greater the mass, the fewer the stars), and in any case, very high mass stars tear themselves quickly apart as a result of their high luminosities, which generate fierce winds. The low mass limit, in the realm of the brown dwarfs (BDs, substars below 0.075 solar mass that cannot run the proton-proton fusion chain), is simply not known. The nearest of the BDs orbits Epsilon Indi, and is a 40-60 Jupiter- mass class T star 12 light years away with a temperature of but 1000 Kelvin. The coolest of the BDs is a mere 683 Kelvin, not a lot hotter than your oven. (Note that brown dwarfs fall into new classes L and T that are cooler than classic class M, and below 2000 Kelvin. Class L, which contains real stars as well, is characterized by hydride absorptions and powerful resonance lines of the alkali metals. Class T displays methane bands.)

The record low mass is said to be about 3 Jupiters for a "star" in the Sigma Orionis complex (assuming an age of 3 million years, necessary since BDs dim with time, so the age must be known to get a mass from the luminosity). Or perhaps it is some kind of "planet." Apparently, planets (made from the bottom up by accumulation of dust) overlap stars (made from he top down by contraction). But maybe companion stars in binaries can be made by accretion, just as are planets, and maybe "planets" can descend directly from interstellar clouds. We simply do not know. And yes it IS confusing. Add to that "free floating planets" in the Orion Nebula Cluster. Terrible name, as they do not "float," and are probably not planets, whatever that now means, but low mass class T BDs, 5-15 Jupiters that orbit chaotically within the cluster.

One criticism held against the accumulation of dust grains in the formation of Jupiter-like planets is that the disks of young T Tauri stars seemed to dissipate too fast for them to develop (producing "naked T Tau stars.") Evidence now is that the naked T Tau stars DO have disks, but that the particles are larger so that they do not radiate in the infrared, thus saving this standard planet formation idea.

Exo-planets

What then about actual planets surrounding real stars? There are now 102 planetary systems with 117 planets (13 are multiple). More transits have been detected, and in the classic case of HD 209458, the spectrum of the star shows the effect of evaporation from the planetary atmosphere. Hollows in disks around mature stars reveal the effects of planets as well; among the best cases is Fomalhaut. That planets at least tend to be the spawn of high-metal stars is holding up. One idea had it that the high- metals are coming from metal-laden planets that are devoured by their stars, but the original notion, that the stars really are originally metal-rich, is now ascendant.

That idea, however, was challenged by the discovery of a Jupiter- mass planet orbiting a binary white dwarf-neutron star (pulsar) combination in the ancient, low-metal globular cluster M 4. The "planet" orbits the binary. How the situation developed can only be speculated upon, but it is hardly "normal," and should probably not be used as any kind of paradigm for current (or even past) planet formation. Planets form around neutron stars by accumulating from the debris of a destroyed binary companion to the neutron star (or so we think). Add to that a propensity for star-swapping among binaries in dense clusters, and any history of the new "planet" is pretty problematic. What nature gives, and what we do not know, is fascinating nonetheless.

Stars

Last year gave you an oblate Altair. Now we get REALLY oblate Achernar, which is spinning at least 225 km/s at the equator, and is a "Be" (B-emission) star with a surrounding radiating disk. Such disks seem to be caused in a complex way by a combination of spins and stellar winds. The best thing here is our ability to actually measure the shape of a stellar disk through interferometry. And speaking of Be stars, keep your eye on Delta Sco (admittedly a bit difficult this time of year), which turned into a Be star a few years ago, brightened, and now hovers just under first magnitude, making the constellation look rather weird to the practiced eye (and unlike that in your dome).

Then go back to the interferometer to see that the techniques are so good they can measure the angular size of Proxima Centauri! It's 1.03 milliarcseconds across, just 1.4 times the size of Jupiter. (Jupiter is close to being the largest size possible for a hydrogen-helium planet; much more massive and such bodies would squeeze themselves to smaller radii. Proxima is held to larger than Jupiter because it creates its own energy from nuclear fusion.)

At the other end of the evolutionary scale, we are finding more dusty dark knots within planetary nebulae (which are the compressed, ionized remains of mass ejected from giant stars). The Dumbbell (M 27) contains those similar to the famed Helix (NGC 7293). For all the work done on them, the immensely complex shapes of planetaries still defy ready explanation. They may be caused by some combination of binary activity in the mass-losing stars, by rotation, even by magnetic fields. Such fields have been found in the predecessor giants. One protoplanetary nebula, the "Boomerang," is (allowing for some hyperbole) the coldest (natural) place in the Universe. For the most part, things can get no colder than the three degree temperature of the cosmic background radiation, but expansion in a dense nebula can act as a refrigerator. And what happens to planets during the stellar ejections that make the planetary nebulae? Mass loss may make orbits elliptical and destabilize them, causing them to be kicked out of their planetary systems. Are there really free planets?

The successors to planetary nebulae are the burned out carbon- oxygen cores that used to be the stellar nuclear furnaces. The carbon is formed by the triple-alpha reaction (3 He go to C), then C plus He makes O. But the reaction rate is very poorly known. Measures of the C/O ratio in a white dwarf through measurements of seismic vibrations allow the rate to be found: a laboratory in space!

The shells of Wolf-Rayet stars (NGC 6888 and the like) are similar to planetary nebulae, but of higher mass, wherein a fast wind acts on earlier stages of mass loss to produce a ring structure.

Somehow related to all this active evolution is V 838 Monocerotis, which suddenly turned itself into a supergiant and sent a blast of radiation that was reflected from a surrounding shroud caused by earlier phases of mass loss, creating a beautiful hollow structure. Nobody understands it.

At yet higher mass, X-ray observations support the idea that Eta Carinae, the best candidate we have for a core-collapse supernova, really is a binary, with 30 and 80 solar mass stars orbiting each other every 5.52 years. Fortunately, the pair is some 6000 light years away. Hubble and Chandra combined to produce a wonderful composite of the Crab Nebula, with which we see a ring around the neutron star created by shock waves from the electrically-generated stellar wind. Supernovae are apparently the generators of cosmic rays. The bulk of high- energy ones seem now to come from the huge "Monogem" (Monoceros+Gemini) structure that is 25 degrees across, only 1000 light years away, and connected to a known pulsar.

We "see" stellar black holes (Cygnus X-1, around 10 solar or so), supermassive black holes (millions of solar masses, within cores of galaxies), but how about something in between? Last year M 15 was "found" to have a black hole that contained 4000 solar masses. Further analysis shows maybe not. Some galaxies may contain them however, a subject that is not at all now clear. At the top of the pile are gamma ray bursts (GRBs) that apparently come from vastly powerful supernovae (SN) in distant galaxies. The connection between GRBs and SN grew when one GRB afterglow turned into the glow of an SN. (The collapse of massive Eta Carinae could produce a gamma-ray burst beam that could affect the Earth, but fortunately again, the orientation of the star seems to preclude any danger.)

The Big Bang produced our hydrogen, helium, and a smattering of lithium. The stars produced the rest. But they had to start out as zero-metal stars. So where are they, these "Population III" stars? They probably formed as high mass stars only. Exploding as supernovae, they seeded space with the first metals, creating dust, and allowing stars to be born in the "normal" way. Though we cannot find zero-metal stars (as there may no longer be any), we can get to very low metal levels. The new record is 1/200,000 that of the Sun. Such stars in fact show the chemical signatures of having been salted by the first ancient supernovae. The metal content must have risen quickly to produce the higher metal contents (still down to 1/100 solar) of the ancient globular clusters.

The greatest cluster, Omega Centauri, however, seems more and more to be not of the ordinary variety, but the core of a small, dwarf galaxy that merged with our big one. (Among other things, Omega Cen's stars show variations in chemical composition and HR diagrams.) M 53, also one of the great globulars, may be the core of the Sagittarius dwarf galaxy, which is now merging with our own.

Galaxies

Beginning with our own Galaxy, we get better and better at measuring the mass of the supermassive black hole at its center. Even at a distance of 25,000 or so light years, we can see a star called S2 orbit the black hole, and can apply Kepler's laws to find a black hole mass of 2.6 million solar masses. Even at an average distance of 950 Astronomical Units, the star takes a mere 15 years to orbit.

The history of a galaxy seems more and more to deal with that of its mergers (witness Omega Cen and M 53). For example, we observe rings of gas surrounding the galaxy Centaurus A (NGC 5128) that probably are the debris of merged satellite galaxies. Something of the same thing is seen around our own, 60,000 light years in radius. Mergers are clearly observed in close clumps of galaxies like Seyfert's Sextet, and they even seem to form double massive black holes at the merged centers.

Among the most spectacular of images was the X-ray picture of the sound waves in the Perseus cluster from the effect of the supermassive black hole in Perseus A. If only you were there, and could go another 57 octaves down from middle C, you might hear them.

Dark matter in and surrounding galaxies and their clusters is no more understood now than it was last year -- or the year before -- or... It does, however, seem to be tracked by bright matter (or stars). Explanations based on variations on Newtonian dynamics keep popping up, and being knocked down. Oddly, some galaxies to do not exhibit it.

All That There IS

A quick summary of the Universe is all that is needed. Variations in the Cosmic Microwave Background Radiation (CMB) tell that 4 percent of the Universe is in ordinary matter ("baryonic": protons, neutrons, and the like), 23 percent in the mysterious non-baryonic dark matter, and 73 percent in "dark energy," which is causing the expansion rate of the Universe to accelerate. The acceleration is also clearly seen in looking at the Hubble diagram of redshift vs. distance. Moreover, the time of change-over from deceleration from gravity to acceleration from dark energy has apparently been identified by a high redshift Type Ia supernova as taking place about 5 billion years ago, roughly when the Sun was being born. (Such supernovae are produced by white dwarfs that accrete enough matter from a companion to cause them to overflow the 1.4 solar mass white dwarf limit and to explode. The result is a set of very similar supernovae that make excellent "standard candles" for measuring vast distances.) No one know what any of this "dark stuff" is.

Going back to just after the Big Bang, the idea grows that the first massive stars (those that produced the first heavy elements) were created before there were any galaxies, and that these became the first black holes around which the first galaxies were organized. Our observations even are perhaps beginning to show us the ending of the "dark ages," when the first stars and galaxies re-ionized the gas and lit the gloom following the neutralization of the growing Universe, from which the CMB had been released. That long ago time resounds yet today. As the early stars re-ionized the Universe, you, the planetarians, now light the minds of the children and the public, allowing us in our beautiful fall to have our "glippa time."