ASTRONOMY UPDATES

ASTRONOMY UPDATE 2004

James B. Kaler

Department of Astronomy, University of Illinois

First published in the Proceedings of the 40th Annual GLPA Conference, Detroit, MI, October 20-23, 2004. Reprinted by permission.

Abstract

The year again saw the reversals of astronomical life, from the crash of Genesis to the success of the Spitzer Space Telescope, with the worries about Hubble in between. From an amazing array of instruments and computers we saw spectacular solar flares, viewed a comet close-up, probed further into the Kuiper Belt, found new exo-planets and brown dwarfs, watched galaxies merge and being stripped of matter, and extended our view of infant galaxies nearly to the time of the Big Bang itself.

Comings and Goings

At the pinnacle of discovery might be the Hubble Ultra Deep Field (UDF). The successor to 1995's Hubble Deep Field and 1998's Southern Deep Field (which are among the most used scientific images of all time), the UDF, made with a combination of the Advanced Camera for Surveys (ACS) and the Near Infrared Camera and Multi-object Spectrometer (NICMOS), crammed 10,000 galaxies into an area of sky a mere three minutes of arc across. Gazing at the image, realizing that on the average the smaller galaxies are the more distant, one comes away with a near-three-D picture of the Universe and of the spectacular number of galaxies that surround us, each carrying hundreds of billions of stars. And these are just the brightest -- the fainter ones, the dwarfs, do not show up at all.

Given Hubble's success, it seems barely believable that NASA would decide to pull the plug, and not allow a Shuttle Crew to upgrade and repair it as its instruments and controlling gyroscopes continue to degrade. The only hope now seems to be robotic repair.

But that is in the future. For immediate disaster, try Genesis, the spacecraft that was to measure directly the chemical composition of the Solar wind. As well documented, its parachute failed as a result of a design flaw, and the craft pounded straight into Earth at close to 200 miles per hour, seriously damaging hope of recovering pristine solar matter that tells of us more of the Sun's chemistry.

On the personal side, we mourn Janet Mattei, the vigorous leader of the American Association of Variable Star Observers, whose collective work has long aided professional research through the monitoring of countless variable stars. Janet was kind, generous, and dedicated to her craft; she will be greatly missed.

Back to the brighter side, and to home, how about that transit of Venus? Long awaited, it was watched and photographed wherever it was visible, and provided us all with another great chance to bring people out to look and into our observatories and planetaria.

On a vastly higher plane were the successes of Cassini and of the Spitzer Space Telescope. Cassini rendezvoused with Saturn and has already returned a richness of sights of the planet, its rings, and even some on hazy Titan. The next year will provide endless fascination as the craft continues to round Saturn and to drop a probe into the Titanian atmosphere. Spitzer, on the other hand, looks out into the cosmos in the infrared, and will revolutionize our knowledge of the interstellar medium, star formation, galaxies, and the Universe at large.

As an aside, Cassini provided us with yet another successful test of relativity, as frequency-shifts from its radio transmission as it went nearly in back of the Sun gave the predicted time dilation. Yet another relativistic experiment, Gravity Probe B, was launched, its mission to observe "frame dragging," in which the fabric of spacetime is shifted around with the rotation of a gravitating body.

To the Sun...

Among the greater solar mysteries were "spicules," projections of cool gas that stick up from the solar chromosphere. They last about 5 minutes, which is the principal period of the solar (photospheric) oscillation, and is also the period of waves that appear in the corona. Putting them all together suggests that solar oscillations drive gas through conduits made by solar magnetism, and thereby allow spicule formation.

About a year ago, the downslope of the solar cycle produced two amazingly large "naked-eye" sunspots (but don't dare try to see such unless you know what you are doing). These were associated with a series of immense flares, one of which was the most powerful in decades. Related coronal mass ejections in turn interacted with the Earth's magnetic field to produce wonderful terrestrial aurorae.

The Earth's field has been slowly weakening over the years. Is this a cyclic effect, or is the field preparing to reverse itself, which it does every several hundred thousand years or so? The latter would temporarily allow solar wind particles to impact the atmosphere to the point of damage. Only time and a great deal of human patience will tell.

The Sun is the seat of the solar wind, which spreads itself throughout the Solar System. The last remaining task of the Voyager spacecraft is to locate the heliopause, where the wind collides into the gases of interstellar space. Though expected to cross the heliopause around 2020, Voyager I is watching the wind slow down as this boundary is approached.

Want to see our Sun from a distance? The search for the solar twin led to 18 Scorpii, a sixth magnitude G2 star 46 light years away that lies near the Ophiuchus border and that has about the same mass, age, rotation period, etc. as our own star.

And Moon...

Which now seems, by radar, to have no water at the poles, as opposed to seeming to have it, which was opposed to NOT having it before that, and ... you get the idea. At this point nobody knows.

And Planets

At long last, an orbiter will encounter the innermost planet, Mercury, which has not been visited since 1975 (by Mariner 10). After one flyby past the Earth, two past Venus, and three past Mercury to slow the craft, Mercury Messenger will enter Mercurian orbit in 2011, whence we may begin truly to understand the enigmatic planet.

Mars Mania of course is in full swing, and there is little need to tabulate the craft that are orbiting and running around on it: needless to say, we will soon need parking lots. A few items of special interest suffice. The evidence for water continues to build, and includes hematite and other minerals formed in association with water, the small "blueberries" of hematite, layered deposits, and runoffs. Volcano slopes also show evidence for once having harbored glaciers, which implies a once-high obliquity of the Martian ecliptic that could have changed climate patterns. There also seems to be a consensus on the existence of an iron core similar to that of Earth, one that may still be partially molten.

Up up and away to the atmosphere, we find methane, whose origin is uncertain. (Cows on Mars?) More significant is the idea that the early Martian atmosphere was stripped by a more vigorous active Sun caused by a higher rotation rate, discussed more below. Farther out yet, "Opportunity" showed us annular eclipses of the Sun (transits if you like) by the two Martian moons, Deimos and Phobos.

Speaking of Which...

The Moon count increases by quantum leaps it seems. Jupiter now has 61, Saturn 33, Uranus 27, Neptune 13. At some point "the count" becomes pointless, as there must be thousands, if not more, tiny rocks too small to be named.

More Small Things...

Some of the Jovian moons must be captured asteroids (some of these orbiting backwards), as might even be the Martian moons, though that issue is contended. While the asteroids lie mostly between Mars and Jupiter, many stray beyond, sent inward largely by Jove himself, many to plague the Earth and hit us as meteorites. Not only do Jupiter and the other planets shift asteroid orbits, but so does the Sun! Rotating asteroids, heated on one side and radiating on the other, will change orbits under the relentless pressure of radiation (directly rotating ones moving farther away, retrograde rotators moving inward). Have a problem with the killer asteroid taking a bead on Earth? Send out a crew to paint one side white.

We are not the only planet threatened. Both Venus and Mercury are covered with craters. And now we see living proof of the damage that can be wrought on the inferior planets with an asteroid that not only comes inside Mercury's orbit, but is entirely within Earth's. Could there be a whole belt of "Vulcanoids" (annoyed Vulcans?) inside the Mercurian orbit? No one knows, but we will look.

Out in the main belt lies asteroid 17851 Kaler, otherwise known as 1998 JK, named at the behest of Jeanne Bishop, and a special thanks to her and to GLPA for making such possible. It really is in your honor. Unfortunately, this namesake, this "lifeless hunk of rock floating aimlessly about the Solar System" (as one friend put it) is well behaved, so there will be no screaming headlines: "Kaler threatens Earth."

Including Those With Tails

Yet another asteroid has been found with a comet tail, blurring the line between the two. Yet another of these, an "asteroid" but really a dead comet, 2003 EH1, has been identified as the perpetrator of January's Quadrantid meteor shower, named after a defunct constellation near the Big Dipper called Quadrans (the Quadrant: who needs one with Sextans and Octans to guide our way?). Though the Quadrantids is one of the best showers of the year, putting out as many as 100 meteors a minute, it's not so well known because of the January cold.

Two of these critters have been seen close up. Halley's was the first. Still being imaged, though at a distance of 28 AU and 28th magnitude, it is totally frozen with no hint of coma or tail. To the Stardust probe, Comet Wild 2 looked battered and beaten. Stardust is collecting cometary material and will return to Earth with its treasure in January of 2006.

While debris belts between Jupiter and Saturn and among the outer planets are unstable, beyond Neptune, in the Kuiper Belt, we again find some permanence. Over 700 Kuiper belt objects (KBOs) -- the smaller of which if moved inward would appear as short period comets -- are known, the largest of them Pluto. Pluto is an evolved body and can hardly be classed as a comet. Nor can several other large KBOs that come close to Pluto in size, including newly- discovered Sedna, which is probably over half Pluto's size. The Kuiper Belt appears to end rather abruptly at around 50 AU. Yet here is Sedna, which holds some kind of distance record as it orbits from 76 AU out to as far as an astounding 950 (implying a period of 11,500 years). How did it get there, and what else may lie at such distances? Just how big is our Solar System anyway (ignoring the invisible Oort Comet Cloud that may extend to 50,000 AU or more)? There seems to be too little matter in the Kuiper Belt to have formed these bodies in situ, so maybe they were formed closer and moved outward.

Interstellar Matter and Star Formation...

Planets and stars ultimately come from the cold dusty molecular clouds of interstellar space. Massive new stars ionize, hence illuminate, their surroundings. Impressive as it is, the Orion Nebula (lit mostly by a single O star) is tiny compared to some diffuse nebulae. The record holder seems to be NGC 604, a "giant HII region" in the nearby galaxy M 33. Some 1300 light years in diameter, lit by a cluster of O stars, if it replaced the Orion Nebula it would stretch half way to the Sun.

The subject of star formation shows the wonderful contributions that amateur astronomers can make. A particular case in point is "McNeils Nebula," discovered by Jay McNeil. It seems to be a new entry into the class of FU Orionis stars, which are protostars that suddenly increase their accretion rates from surrounding disks, hence greatly increase their brightness as well.

Star birth is cyclic. Evolved windy and exploding stars dump energy and chemically enriched matter back into the interstellar medium, which increases the metal content of space and also causes the interstellar clouds to compress and collapse, the result being new stars. The star formation rate appears to have come to a maximum in our Galaxy about five billion years ago, about the time that our Sun was being born. Even though stellar gases are recycled, the rate must eventually slow down, and now it seems to be about 15 percent of what it once was.

Which Leads to Exoplanets...

The disks that surround protostars, from which baby stars accrete their final masses, also form orbiting planets. Unless something disrupts such a disk, planet formation should be a natural by- product of star formation. Over 100 such planets, mostly Jupiter- size bodies, have been found through Doppler techniques (in which the orbiting planet causes the star to shift slightly back and forth). The leading system is sixth magnitude 55 Cancri, a G8 dwarf 41 light years away, which now is found to have FOUR planets, including a new Neptune-mass one in a 3.8 day period only 0.038 AU out from the star.

Occultations provide another route to planetary discovery (the planet passing in front of the star), and also allow some measure of the planet's chemistry. In addition to sodium and hydrogen, carbon and nitrogen have been found in the atmosphere of the planet that belongs to HD 209548. More planets are being found solely through such transits and also by gravitational lensing, which involves relativity and the bending of spacetime around an intervening star.

The manufacture of giant planets is contended. The long-time standard theory is that such a planet begins with a core made by the accumulation of dust grains in the primitive circumstellar disk (the core then attracting gas from the disk), which takes millions of years. Planet production through instabilities in the gaseous disks can do it much faster, which is in line with a gap in the disk around a star called CoKu Tau 4, and which implies planets far too young to be made by the core-buildup theory.

Debris disks around mature stars, which might contain planets, were thought to be confined to those of higher mass (Vega, Fomalhaut, Beta Pictoris and the like), and now comes along one around AU Microscopii, an active M1 dwarf.

And to Brown Dwarfs

The major problem with these "substars" (which weigh in at less than 0.08 solar mass, the low mass suppressing fusion) is in the measurement of their masses, which is usually done indirectly through measures of age (they fade as they get older) and luminosity (higher mass ones the brighter). We need binaries, and now we have some nice ones. Epsilon Indi, a fifth magnitude K dwarf only 12 light years away, has a distant companion (1500 AU away from it) that has been resolved into a pair of low mass class T brown dwarfs (T1 and T6, 1240 and 850 Kelvin) separated by a mere 2.6 AU. Analysis of the observed orbit will eventually test the assumed masses of 45 and 30 Jupiters. Real measurements of a faint infrared pair give a record low total mass of 15 percent that of the Sun, which from luminosities suggest individual masses of 8.5 and 6.5 percent solar.

Any port in the storm is fine where masses are concerned. The widths of spectral lines are sensitive to the pressure in the line- forming stellar atmospheres, which in turn are sensitive to gravities, which in turn depend on masses and radii. Distances and apparent luminosities yield radii, then masses down to a hundredth that of the Sun, just nine times that of Jupiter. The line between higher mass planets and lower mass brown dwarfs is blurred, as maybe the two overlap in both formation process and mass. The popular term "free-floating planet" for such low mass objects is probably a misnomer, however, since planets and brown dwarfs may still have very different origins.

"Real" Stars

Have you reconnoitered the RECONS web site that specializes in nearby stars? A principal goal of astronomy is to find the numbers of different types of stars within a volume-limited sample of space. Within 10 parsecs (32.6 light years) RECONS gives us NO O or B stars, only 4 of class A (Vega, Sirius...), 6 F stars (think Procyon), 21 class G solar types, 45 K stars, and an amazing 236 M stars. Several lower mass L and T stars are also known.

Just as the lower mass stars have new mass records from binary stars, so do those of higher mass, a Wolf-Rayet (stars with stripped envelopes) binary in Carina coming in at 82 and 83 solar masses. Unfortunately, the discovery does not help to extend the crucial mass-luminosity relation upward, since the distance and interstellar extinction, hence the stellar luminosities, are not known. At least we know such high-mass stars really exist, which gives credence to our extrapolation that masses top out near 120 times that of the Sun. Such measures are of great importance in the determining the evolution of massive stars.

Much lower mass solar types are known to slow down their rotations as a result of magnetic braking, wherein stellar winds drag outward magnetic fields that are still attached to their stars. Stellar magnetic activity thereby declines with age, an effect now dramatically confirmed through comparison of spectral activity indicators with stellar ages. The Sun was vastly more active in the past (see Mars above), while in another few billion years sunspots will effectively disappear forever.

Binary stars are drawn closer together when one of the pair evolves and spreads a common envelope around the two. The effect is nicely confirmed by V 471 Tauri, in which an ordinary dwarf has clearly been contaminated by chemically altered gas (through interior nuclear reactions) from the evolved, now dead, star.

Among the great puzzles of stellar astronomy are the origins of the spectacular forms of planetary nebulae. The consensus grows that strong bi-polar structures are caused by the influences of binary companions. Or magnetic fields. Or none of the above. That's why it's still a puzzle. That aside, many planetaries show evidence for episodic mass ejections from the parent giant stars, whose origins are also puzzles. NGC 6302, a planetary with one of the hottest central stars known (250,000 Kelvin), perversely may have water ice in the nebula.

Mass loss is among the most profound of all stellar processes, as it allows white dwarfs to emerge from giants, which brings us again to V 838 Monocerotis. Erupting to near naked-eye brilliance some three years ago, it bounced light echoes from aeons of previous mass loss. The star, now 15th magnitude, has cooled itself into a giant or supergiant of class L (cooler than M), the first non-dwarf L star such ever seen. While theories abound, nobody knows the origin of the weird behavior.

Explosions and Aftermaths

A half-dozen years ago, the mass ejected from Supernova 1987A made the first impact on the surrounding ring of matter that the star had ejected when it was a supergiant. Now the whole thing, half a light year from the destroyed star, is lit like a string of pearls.

The highest mass progenitors of supernovae may be responsible for creating highly directional gamma ray bursts (GRBs) we see coming from distant galaxies. A gamma ray burst seems to be formed by conical shock waves from the collapse acting on the stellar envelope. Our own Galaxy should have harbored such bursts. If we are in the way of the energy flow, Earth could be badly damaged, and there are speculations that such an event might have produced a mass extinction 400 million years ago. A Galactic supernova remnant called W49B may have been associated with such a GRB.

In the act of becoming supernovae, the collapsing cores of massive stars above 8 to 10 times solar become neutron stars, while in the very upper range they may produce black holes. Several binary neutron stars -- including one binary pulsar -- are now known. Through gravitational radiation, the components of a newly- discovered one should spiral closer together and merge within a few tens of millions of years. The possible frequency of such events make the creators of LIGO (the Laser Interferometer Gravitational Wave Observatory) smile, as the waves should be detectable by the device within the distance of the Virgo cluster.

Among the first of the breed of "microquasars" discovered was SS 433, which spews matter at outward at a quarter the speed of light. Long thought to be powered by a hot supergiant orbiting a neutron star, the compressed companion now seems to have a mass greater than the neutron star limit, and may be a black hole instead (as are more energetic microquasars whose flows approach the speed of light).

Does a black hole preserve the information of things that fall into it. Steven Hawking said no. Now he says he lost his bet and that they do. Or maybe they don't. It's not a simple subject.

Our Very Own Galaxy...

Larger galaxies, including ours, seem to grow through successive mergers with other systems. As part of the process, the Galaxy destroys smaller neighbors, including the newly-discovered Canis Major galaxy, which, 25,000 light years away from us, is being shredded. Thus many of the Galaxy's stars have come from elsewhere. The motion and metal content of Arcturus -- and stars with similar motions -- suggest that it may be one of them.

The Galaxy also continues to "grow" through discovery. Astronomers have now found a distant spiral arm that curves 60,000 to 80,000 light years out in the direction of the summer-autumn northern hemisphere Milky Way.

And Other Galaxies as Well

A similar but much more dramatic merger seems to have emplaced a spiral galaxy within the central region of NGC 5128, more commonly called Centaurus A (for its powerful radio emission).

Pause now to admire the HST's Sombrero, M 104. Nearly edge-on, split by a dark "hat band," this immense galaxy features 800 billion stars, 2000 globular clusters, and a billion solar mass central black hole.

Much closer, the Large Magellanic Cloud has something of an old- star halo vaguely similar to our own. While our Galaxy has only old globular clusters, whose ages approach that of the Universe itself, the LMC also has some young ones a mere three billion years old that may have been induced to form by an interaction with the Small Magellanic Cloud.

Other galaxy clusters (as opposed to our Local Group) show the effects of similar mergers and destructive forces. The Fornax cluster (60 million light years away), for example, contains bunches of 100-light-year-wide ultracompact galaxies, which appear to be the cores of once-larger systems that have been stripped by gravitational encounters with neighbors. Omega Centauri may be such a remnant in our own system. We can even watch galaxies being stripped of their gas by ram pressure as they sail through much hotter intracluster (X-ray-emitting) gas.

Like the Sombrero, all large galaxies seem to contain central supermassive black holes, our own weighing in at only about 3 million solar masses. We even "watched" a central black hole appear to devour a close-passing star, the event producing an X-ray flare that went on for 10 years. Disturbances caused by jets from the central black hole in NGC 1275 apparently send sound waves into the hot gas that resides within the Perseus cluster and that have wavelengths greater than 10,000 light years. As so often demonstrated, there IS sound in space; you just can't hear it. A deep view with the Chandra X-ray satellite turned up lots of X-ray sources that may be central black holes but that had no galaxy counterparts in the Hubble view. They did, however, show up with Spitzer infrared observations. Blockage of optical radiation by dust? No one really knows.

Superactive black holes in distant, and thereby young, galaxies produce the quasars. Such brilliant objects provide backlighting for locating intervening dark matter when light from the quasars is lensed by the dark matter to produce multiple images. A record image separation for such a lens hit 33 seconds of arc for a quasar 11 billion light years away, revealing a LOT of invisible mass between it and us.

Everything

Galaxy mapping grows apace, the Sloan Survey of 35,000 galaxies revealing another Great Wall a billion light years away, one nearly a billion and a half light years long.

Galaxy clusters can used to get information on the parameters of the expanding Universe by estimating the amount of bright matter, assuming a fixed ratio of dark-to-bright matter, estimating the diameter needed to bind all of it together, and comparing that to the angular diameter to get the distance. No supernovae need apply. What we find is even more evidence for dark energy.

Updated parameters of the Universe from all sources: Age = 13.5 billion years; Hubble constant = 70 km/s/Mpc; Omega (ratio of average density to density needed to flatten the Universe) = 1.01 +/- 0.02 (or, basically, 1, such that the Universe is geometrically flat); fraction of normal (baryonic) matter = 4.8%; fraction of dark matter = 25%; fraction of dark energy (which acts like matter to flatten the Universe) = 75%. Not only is the Universe expanding, but the expansion is accelerating, the latter process seeming to have kicked in about 5 billion years ago when self- gravity from lower and lower average matter-density began to drop off. New data suggest that the acceleration is coming from a basic property of space itself, that is, Einstein (who first suggested this "cosmological force") may have been right! (though for the wrong reason). If that is all correct, then the "Big Rip," in which everything finally gets torn apart by the accelerating expansion, will not happen. Relief prevails. Moreover, from WMAP's (Wilkinson Microwave Anisotropy Probe) observations of the temperature fluctuations of the Cosmic Background Radiation, the Universe is not closed on itself, that is you cannot (fortunately perhaps) look to the distant Universe and see the back of your head.

Perhaps the most amazing thing now is to return to the top, to the HUDF to see galaxies so far away that they were formed less than a billion years after the Big Bang, and in one additional case to redshift 10, to within half a billion years after the event that created our present Universe.

Far away. But if you were out there on one of those distant galaxies, you would be able to look back to see us just as young, our Galaxy only beginning to form, the Sun not yet born. In your mind, then travel to more nearby galaxies to see us age until you see the Sun come into being, and finally arrive here among the trees and flowers, showing vividly that the Universe is not just "out there," but a profound part of our very selves.