ASTRONOMY UPDATES

ASTRONOMY UPDATE 1997

James B. Kaler

Department of Astronomy, University of Illinois

First published in the Proceedings of the 33rd Annual GLPA Conference, Cleveland, OH, October 22-25, 1997. Reprinted by permission.

Abstract

From the Moon to the distant Universe, astronomers solved mysteries, puzzled over others, and found new ones to examine. Mars revealed some of its secrets thanks to the Pathfinder mission, and the Universe became more understandable as the values of the Hubble constant and age approached consensus, we began to understand the formation of galaxies, and gamma ray bursts were seen optically. In between we delighted in a comet of the century, asteroids that act like comets and vice versa, the extension of the Solar System deeper into the Kuiper belt, new extrasolar planets, high-resolution probing of stars, an antimatter cloud near the galactic center, massive galactic black holes, and puzzlement about matter that falls into galaxies.

Good morning. (Good morning.) Thank you.

Mission to Mars

Your first quiz is: what constellation are we looking at that has a supernova in it? That's no supernova, it's Mars in Taurus. You can just see the Pleiades at the top. This is the year of Mars, and as usual I don't get to talk about the really hot topic. You get somebody else to do that, and then give me the sludge, which is the rest of the stuff, about what galaxies are the most massive and that sort of thing. But I'm darned if I'm going to pass up this opportunity. That (Sojourner) is just a marvelous little critter walking around on Mars; it is just a riveting thing to watch. Mars is beautiful in Scorpius right now, near Venus, and the conjunction with Venus is coming up. Here it is near opposition in 1989 in Taurus. The Hubble Space Telescope, of course, is focusing in on this planet and getting beautiful views, including dust storms; there are differences from one picture to another - we can actually watch the weather phenomena taking place on this beautiful planet, which looks so much like Earth. Looking even closer, you go from the sublime to the ridiculous with this rather large ugly rock.

One of the reasons that we sending spacecraft to Mars is the possibility of life. Well, so it's that NASA can have money from Congress to launch more space programs. You notice perhaps that every time something interesting comes up, Galileo to Jupiter, or whatever, they say maybe there's life there. That makes everybody sit up, and they hope that it loosens up the money pockets.

This is another meteorite, one not really that big, from Mars. The issue of the microtubules in the earlier meteorite have still not been resolved. Some geologists say that no life forms are involved. This rock has a very high carbon content, which is indicative of life forms; but then other geologists say that it is still sort of normal. The only way we are going to find out is to go there and take core samples, to bring stuff back, and really look at them in the laboratory.

I just love these pictures. The panorama was just marvelous and looks a lot like the Viking pictures. You see boulders that have been kicked out of nearby meteorite craters. One of the marvelous things that this instrument has found is that there really are differences among the rocks, and that some of them bear a close relationship to what we find on Earth.

Here's the little guy himself kissing a rock. It's not just the Sojourner that irradiates the rocks - it is the MICROWAVE SIZED SOJOURNER, all in capital letters, as taken from the press releases. It can determine something of the chemical compositions of the rocks it examines.

There is a weather station aboard. Here is a day-to-day temperature graph. You can see it almost gets up to 0 degrees, perfect weather for a baseball game, fitting very nicely with what Viking found. The spacecraft is doing marvelous work. It's another piece of truly brilliant NASA engineering that long outlived its putative lifetime. It was only supposed to last for a short time, but it went into an extended mission phase and just keeps going and going. (I'll leave that phrase were it lies.)

The view at sunset, looking over the low hills off in the distance, shows you perhaps more than anything that this is really an Earthlike planet. You could almost imagine yourself out at some south sea island looking at the red sunset off in the distance. Sadly, it was also sunset for Carl Sagan, who probably did more than any other person in this country to popularize science with one book after the other and with television programs. I think all of us owe a great deal to what he did over the many years with accurately, exceedingly reported science.

Several other people left us this year, including Clyde Tombaugh, either the discoverer of the last planet, or, as he put it shortly before his death, the discoverer of the first object of the Kuiper Belt. I think he was quite proud of that. Gene Shoemaker as well left us in an auto accident in Australia. He is here seen standing here at the edge of Barringer Crater in Arizona. Go see it, this magnificent sight in northern Arizona. You really get the sense of what a target the Earth is.

Comets

Shoemaker has lasting memorials, such as Comet Shoemaker-Levy. I also thought it was appropriate to look outward at a comet that bears his name, and I think his legacy will live on long after he is gone, as did his comet. You can just barely see it here in an enhanced view. It's 12 astronomical units from the Sun and it still has a tail, still leaving a path behind it, probably not by outgassing water but by outgassing carbon monoxide. The remarkable thing is that even though near the orbit of Saturn you can see that comet's tail.

Speaking of comets (how's that for a segue?), what a magnificent sight this was. I imagine we would be rich if we could pool the amount of money spent on film to take pictures of comet Hale-Bopp. This is a picture by an old friend, Gary Goodman, in California, who developed a nifty tracking program. Here in the morning we see the North America Nebula. This really quite wonderful ion tail is directed away from the Sun, and here's the dust tail. This is one of the best separations I have ever seen of a dust tail and an ion tail. Halley's was nowhere as good as this. Most comets have powerful ion tails and not much in the way of dust tails or vice versa. West, for example, had a beautiful dust tail and little ion tail. Set in the middle of the Milky Way, you couldn't ask for a better picture and better contrast between the Solar System and the Galaxy. The comet was quite a chemical factory. At last count there were 32 or 33 molecules, including methyl alcohol, and formaldehyde.

Here we see a new discovery: a sodium tail from sodium ions ejected from molecules in dust particles after they were ejected from the comet. Who liked Hyakutake the better of the two? I was kind of a Hyakutake fan because it was so close and the tail was so beautiful; and because you could see a disconnection event with the naked eye (produced when the comet changed sectors in the solar magnetic field).

On the other hand, what's a great comet? Hyakutake just happened to be nearby. Hale-Bopp was an astronomical unit away. The tail stretched several tenths of an astronomical unit. I heard one report of a 40 degree tail. Imagine if Hale-Bopp had been as close as Hyakutake: there probably would have been several new religions founded on it.

This Hubble Space Telescope image shows dust shells being flung from Hale-Bopp. You could even see this through a small telescope. As for other comets, notably Hyakutake, X-rays were found coming from Hale-Bopp's head. We are still not sure why, though they may be produced by shock-interaction with the solar wind. But that's still something of a guess.

The Hubble, which took this picture, has been re-outfitted with an infrared camera, NICMOS, and with STIS, the multiple object-long slit spectrograph. With these instruments, Hubble has made a number of fascinating discoveries. Once you get a camera that can operate out at two microns with this kind of resolution, all kinds of things in the Universe begin to pop out at you. For example, here's the Cone Nebula off to the left. This little blank box has nothing in it at all, but when you look through the dust clouds at 2.2 microns, here's this beautiful bright star with a whole bunch of little ones near it. They are brand new, having just been born around the high mass one. It posed something of a problem because these are so close to the bright one, one wonders how they could have survived. But, of course, nature knows how to produce stars a lot better than astronomers do.

Radio Astronomy

Hubble is not the only great spacecraft out there. We've finally really gotten off the earth with radio astronomy and an interferometer working from space. One of the elements is on Earth and the other is in orbit around it to make a telescope approximately twice the Earth's diameter, at least in terms of resolution. Here's the VLBA (Very Long Baseline Array) image of a distant quasar. Look here at the way detail pops out here with the space-based radio telescope. I think you're going to see a lot more of this sort of thing over the next decade or two.

Hipparcos

Hipparcos finally released some of its parallax results. This is a color magnitude, or HR, diagram made with Hipparcos's high precision parallaxes. Back when I was a boy, they said nobody will ever get beyond 100 parsecs. Now we're pushing in the order of 400 or 500 parsecs, to the point where getting absolute parallaxes becomes somewhat difficult because everything in the background is moving a little bit as well.

This diagram is high precision in terms of absolute magnitude and color, but notice the selection effects. Most of the main sequence stars are sit around class G, and there are hardly any dwarf M stars at all. Hipparcos did not provide a volume-limited sample, which we rarely get in astronomy. Seventy percent of all stars are actually dwarf M, so when you look at diagrams like these you've got to be very careful.

Here's the "clump" up here. The red giants evolve from the main sequence, then fire their helium, and come halfway back down and sit there, well, in a clump. It just pops out beautifully here and is the Population I horizontal branch, except that it's not horizontal and it's not a branch. But we never let things like that, the odd vocabulary, bother us much in astronomy.

Cassini

Cassini is finally on its way out to Saturn, with its 258,000 tons of plutonium, which we all know is going to destroy the Earth and all life when it gets back here for its gravitational boost (ok it's a LOT less than that).

We're going to get some good views. The flight time sort of stunned me. It will arrive in the year 2004, the year I am supposed to retire! I may spend the rest of my professional life with that thing in cruise toward Saturn; if nothing else, it shows the enormity of the Solar System, a continuing problem in teaching this subject. Typically you go into a grade school class and see the usual poster, with the Sun and all the huge planets all lined up in a row right next to it. It's so important to give a sense of reality. Go visit Sheldon Schafer and Peoria's model Solar System; you really get the news when you try to bicycle from one planet to another.

Impacts

Iceballs, ladies and gentlemen, iceballs! We're being pelted (maybe) with 10 several-ton iceballs a minute from outer space. This is a superimposed image of the Earth and of what appears to be a large fragile iceball entering the upper atmosphere. There are strong arguments against their reality. But if they are real, they may add an inch of water to the oceans every ten thousand years or so. It's quite a startling thought. The chief critic says that something is hitting us, but he doesn't know what. This could be major news over the next few years or it could just fizzle.

The water on the Earth is thought to have come from comets in the early days of the solar system when the impact rate was much higher than it is today. Yet certainly comets still add ice to the inner Solar System. The case for ice on the planet Mercury is relatively good, but that for the Moon seems to have dissipated much like the ice itself. You are looking here at the Aitken South Polar Basin. These are spots of high radar reflectivity, and I came in last year and very excitedly said, "Ice on the Moon, Water on the Moon." I had just given an hour exam (maybe you remember) and had a multiple choice question on it about the Moon having no water. Within a week somebody "discovered" water on the Moon, so I had to go back and tell the class "those of you who actually got it wrong got it right, except that you're not going to be regraded because then it was wrong, and now it's right, so too bad. And now I guess I have to track all down that got it wrong or right or whatever, and tell them that there is no water on the Moon because now they've decided that it's not really ice. It's just some kind of high mineral reflectivity. But if there is no water on the Moon, why not? If we're being hit by iceballs fifteen times a minute, there should be a lot of ice on the Moon. So where is it? It probably just evaporate under intense sunlight.

But we do get hit a lot. This is an impact map of the United States showing its big meteor craters. Notice where most of them are. Notice where the center of the distribution is right here (in Indiana). You might have a very exciting time at next year's GLPA meeting, so by all means, come and just keep looking up. This distribution, of course, means that the craters are just easy to find in certain places.

But meteorite strikes really do have a powerful impact on life on Earth. Remember that the demise of the dinosaurs is supposedly due to the impact of an enormous asteroid off the coast of the Yucatan Peninsula. There have been many attempts at trying to track other mass extinctions with infalls and meteor craters. Here we have a graph of the cratering rate. These bars represent mass extinctions. The two seem to be correlated with each other. Periodic disasters may really have a strong effect on the development of life on Earth.

Astronomers have gone back to wondering why periodic infalls may happen. It may be that comets fall on Earth with a periodic distribution that depends on how badly the Oort Cloud is stirred up. You may remember that several years ago, somebody got relatively rich writing a book called, "Death Star." The idea was that there was a dim red dwarf in a highly elliptical orbit about the Sun. It kept passing through the Oort Cloud and tossing comets toward us. That seems to have died a welcome death, partly because infrared cameras in space have not shown up any kind of dim M star. There may indeed be stars that pass through the Oort Cloud and send comets toward the Earth, or they may be sent by interactions with giant molecular clouds, which have a stronger gravitational effects.

But the cause may in fact be tides produced by the entire Galaxy that send in the comets as the Sun passes in and out of the galactic plane. The entire Galaxy took part in the creation of the Sun in the first place. We cannot separate our own little Sun from everything that's out there. This message, which we can tell our students, helps removes the isolation of the Earth from the Universe. Sorry for the editorial opinion, but I get excited about such concepts.

The Sun

This doesn't look like the Sun, but it is. Its an X-ray picture of a coronal mass ejection. There has been a great shift in opinion over the last few years as to what causes aurorae on Earth. We used to believed they are caused by solar flares. Now we know the cause is the coronal mass ejection with which flares are sometimes associated. A collapse of magnetic field on the Sun releases a huge blob of corona into the solar wind, and if the Earth is in the way, it gets slammed. With space observatories we can follow the ejections from birth to death. A person at NASA got a little excited about this one, and put out a major press release that somewhat frightened the public, and we started getting calls asking "Is it going to kill us?"

Such ejections have been going on for billions of years, and nobody paid much attention to them, except that they produce nice northern lights displays. We now have other reasons, as they can have strong impacts on spacecraft; spacecraft have been disabled as a result of ejections from the Sun. A very high particle flux simply knocks the spacecraft out. The electrical disturbances can also bring down power grids, as one did several years ago. So it's nice to have predictive power. But the ejections don't kill anybody. This event though shows our advances in solar astronomy, as we can follow the ejections from start to finish.

Quite a few other things have been discovered about the Sun. We now know where the magnetic field has its origin, apparently way down here at the base of the convective zone, which is about a third of the way in. A good portion of the Sun takes part in producing the magnetic field. The solar wind from the equator is different from the solar wind from the poles. The equatorial solar wind seems to flow out as a result of solar luminosity. The polar solar wind, which flows faster, is apparently produced by the magnetic field. The whole thing is much more complicated than we had thought.

Last year we went months with no sunspots at all. If you had a class and were trying to show the beauty of the Sun and the sunspots, you were mightily disappointed, as they were gone. It was the biggest drought since the 1930s. You think, my goodness, there's a new Maunder minimum coming along. If you look outside today at the miserable weather, it's almost believable. But the spots are activating again, and we're heading toward a nice peak somewhere around the year 2000 or 2001 as the new cycle comes in.

The Planets

Moving off with the solar wind toward Jupiter was the Galileo spacecraft, which is now in orbit about the planet. A famous theoretician once asked a friend of mine, long before the advent of spacecraft, what he was studying. And he said, "Oh, I'm doing some work on Jupiter right now." And the theoretician said "Isn't that the one with the rings?" Ah, well. Shortly thereafter, we discovered rings around Jupiter. Here is an image of Jupiter's ring, taken by the Galileo spacecraft. It's quite a beautiful image, much better than anything that had been done before. The ring is a kind of way station, is probably made of particles smashed from the satellites, and is probably quite different from Saturn's rings. Of course, it's wise to remember that all these Jovian planets have their rings and that they're all different, one of the marvelous things about them.

The Pioneer spacecraft, which first imaged Jupiter up close, has been turned off. It's one of four spacecraft to be launched by us into interstellar space. Their engineering just amazes me. Even though it was outside the orbits of Neptune and Pluto, we were still getting results from an 8 watt transmitter.

The Galileo craft has done some beautiful work on Jupiter. This is an image of Europa, which apparently really does have a deep water ocean with an icy crust on the top. Of course, NASA people still say, "Maybe there's life there, in the warm ocean beneath." But you can see that it looks kind of like a frozen Lake Erie. You can see rafting and what appear to be consolidated ice flows on the surface. When we move out to Ganymede, we see what appears to be ice in the craters. Now these outer satellites are about half water ice. The amount is really quite phenomenal. Water ice at temperatures like those here has the structural strength of steel, and if you get a crater in it, the crater will last forever. So it's rather like having rock except that the density is relatively low.

This isn't news, but I just saw these pictures of Neptune from the Hubble and was so taken by them that I just wanted to show them. These are methane clouds in Neptune's atmosphere. We can follow the weather on Neptune from the Earth. Have you ever seen Neptune in a small telescope with its two-second of arc diameter? Here we are looking at the "last planet" of the planetary system, Pluto no longer really counting as such.

Asteroids and the Kuiper belt

The minor stuff has been making news as well. This is a color- enhanced view of Vesta, an altitude map that shows an enormous crater with a large mountain peak in the middle. It probably came close to tearing Vesta apart, and accounts for many meteorites from Vesta that we have on the Earth. We have in fact identified a number of asteroids as parents of meteorite families. You can pick up pieces of known asteroids and compare our view in space with what we have on the ground. It's a nice way of identifying various parts of the debris belt of the planetary system.

What a collection of asteroids! Here's Mathilde, observed by the NEAR probe. It's actually an enhanced view. If they actually showed the thing as dark as it was, you wouldn't be able to see it. You probably couldn't even see the thing if you were riding in the nose cone of the spacecraft. Compare it with brighter Gaspra and Ida. These are all at the proper relative sizes, although obviously not that close together. The picture reveals the darkness of the outer solar system. Things get very black. You could not, for another example, see the rings of Uranus. They're as dark as velvet. Just think of what a painting of Elvis you could make.

I really hate this. Back when I was a boy, some distant time ago, there were asteroids and there were comets, and you didn't mix them up. Well, here's an asteroid coming in from the Oort Cloud. No tail, no nothing. It looks just like an asteroid, except it's in a highly elliptical orbit like a comet. And over here is a comet dead in the main asteroid belt. It's got a nice tail. They do apparently overlap. It may depend upon where in the asteroid belt you are talking about, because the water content goes up as you go out. It's getting more and more confusing. This asteroid could have been kicked into the Oort cloud by the planets just like comets were. It's neat having what appears to be an asteroid leaking back in. Or maybe it really is a comet, just one with the water baked out of it. And maybe the comet just got trapped into the asteroid belt. There are a lot of unknowns in dealing with the little bodies of the planetary system.

The planetary system is being greatly extended. This is 1996 TL66. It's WAY out, and is the farthest body from the Sun now known. It's probably in the Kuiper belt and out-plutos Pluto. Here is its orbit. Look at how far it goes, with a semimajor axis of 84.5 AU. These are all of the new bodies that have been found in the Kuiper Belt. Many of them, like Pluto, are trapped by Neptune into an orbit 1.5 times Neptune's period. It's a true trapping. If you look in your textbook and take the ratio of the orbital period of Pluto relative to that of Neptune, it's not exactly 1.5 because of planetary perturbations. But if you look at the calculations in the orbits over say a couple of million years, the ratio averages out to 1.50000. The group of trapped bodies are called Plutinos - I know, I know! It's pretty clear that Pluto is a member of the Kuiper belt. There are now various attempts underway to really try to map the outer parts of the Kuiper belt to see just see how many bodies are out there.

Interstellar material

All of this stuff was created from the dark dust clouds of interstellar space. Now I give you yet another horrible acronym. These are DIBs. What's a DIB? It's a "diffuse interstellar band." Why should you care? Well, they really are quite important. The strongest one is at 4420 Angstroms. It's very difficult to take a stellar spectrum and not find one of them. They're broad shallow interstellar absorption lines, very unlike the typical calcium K line discovered in 1904. DIBs have been known since the 1920s and they represent one of the greatest of all interstellar mysteries. We don't know what makes them. There was a growing feeling that they were caused by PAHs. I'm going to load as many of these acronyms on you as I can: PAH stands for polycyclic aromatic hydrocarbon. They are polycyclic because they consist of linked benzene rings, benzene itself not found. "Aromatic" is used for fairly obvious reasons - they stink. Their infrared spectra have been found in interstellar space, and they show up in meteorites as well. They help reveal a very complex organic chemistry in interstellar space. But the DIBS might just be produced by molecular hydrogen, which is kind of disappointing, but still a nice solution of a really deep and dark interstellar mystery.

Trionium, H3+! You don't have to write this down and memorize it. It's a theoretician's view of how complex interstellar molecules are formed from interstellar space. First by adsorption of the atoms on the dust grains where the chemical reactions take place to make H2, which then gets kicked off. The H2 becomes ionized by cosmic rays, and after another reaction you should wind up with trionium, certainly a strange molecule, but one that is extremely important in creating the chains that produce other heavy stuff out there. We finally found the trionium itself, and added it to the list of somewhere around 110 interstellar molecules, including such wonders as glycine and vinegar. But the trionium was really quite an exciting discovery, as it shows that the theoreticians were quite right.

Brown dwarfs

Virginia Trimble came up with a basic principle for astronomy, that all problems are solved in twenty years. It seems kind of true. (What negates that is the solution for the solar neutrino mystery, which is still with us. It's one of these things that I think we will miss when it's solved because it's been with us for so long.) For twenty years, astronomers have been looking for brown dwarfs. Now they are starting to pop out. Several seem to have been found in the Pleiades. Yet you can't really prove it though without orbital data. They are identifying the brown dwarfs simply from the temperatures, luminosities, and colors and by applying a little theory that says to produce what is observed, you need a star, a non-star really, below the hydrogen fusion limit of 0.08 solar masses. But I think, we're really starting to find them. Still, it's remarkable that there are so few of them. If there were a lot, you should be able to see them all over the place.

Going back to the Hipparcos diagram, it has long been known that 70% of the stars seemed to be M dwarfs, and it was expected that the lack of very late type M dwarfs down around M8 or M10 was a result of selection, yet we expected the numbers simply to keep increasing, which meant there should be huge numbers of brown dwarfs. But the number really does seem to drop off. Brown dwarfs are relatively rare, and the Hubble has shown that very late type, very cool M dwarfs are in fact remarkably rare as well. We're not finding anywhere near as many as expected. The population of stars seems to peak around M5 or so. We have no idea why.

Nature seems not to like to make very small stars, though some are being picked up in orbit by the reflexive motion on stellar companions. The mass that divides planets from brown dwarfs is about 13 times that of Jupiter, although there may be overlap, as there is between comets and asteroids. Above that limit, you can fuse natural deuterium into helium. Brown dwarfs can't really exist below that. But then there's another definition, that brown dwarfs are made directly from the interstellar medium, whereas planets are assembled from the dust in disks around new stars. Again, the two kinds of bodies may overlap. There have been a number of bodies in the range of several tens of Jupiter masses, probably brown dwarfs, found from Doppler shifts of their associated companion stars.

Extrasolar planets

But true planets seem to be in some abundance as well. The first planet orbiting a double star was found last year going around 16 Cygni B, the fainter member of a fairly wide binary. The orbit is highly elliptical, maybe the result of the binary companion. Nobody really knows.

This figure shows all but two of the new planets that have been found. Again, this is not news as such, that Jupiter-mass bodies seem to be tucked right up close to their parent stars. We've got a new kind of planetary system. Mind you, these are all lower limits, as in effect the stars are single line spectroscopic binaries, and you've got to do some handwaving to estimate real masses. The orientation of the orbits would be too severe to produce brown dwarfs, so they that are probably true planets. Outside of these presented here, we also now have Rho Cancri and also 16 Cygni B.

It's still a mystery as to how these Jupiter size bodies got so close to their stars. They shouldn't form there because the star, as it was being born, should have been so hot that you should not get accretion of hydrogen into a Jupiter-sized body. You should get terrestrial planets instead. The best suggestion is that they are in fact being forming in the outer part of the stars' planetary systems and were dragged in by relatively thick residual disks that had yet to dissipate. The theory is getting pretty good. An orbiting disk should produce spiral density waves much as does a galaxy. The gravity from these waves would bring the planet inward. Once the planet gets close to the star, the disk dissipates as a result of the star's wind, and you leave the planet in close orbit. I guess it makes sense, because some stars are going to have very thick protoplanetary disks and others are not, and the ones that have them may wind up with planets that are close to their parent stars. But it does demonstrate the variety of planetary systems we are going to find once we really are able to track them all down. Right now we are not in a position to find our own kind of planetary system out there. We're just finding the ones in which the Jupiters are close to their stars.

We are, however, finding more planetary disks. Here's Beta Pictoris - many many pictures have been taken of this southern A star and of its famous disk, which is about 400 astronomical units in radius. Here is a binary star that has a similar disk. It may well have planets embedded in it. We can't tell yet. Here's another one seen more face-on. Many stars may have residual disks and so do we. If were somebody were looking back on us, they might, with sufficient technology, see our Kuiper belt.

But not all stars may have such disks. This is a marvelous picture of the Trapezium in the Orion Nebula taken with the Hubble. Theta- 1 Orionis C, right here, is the big guy, an O6 star that controls everything. Here we see disks around brand new stars, maybe T Tauri stars, and look what's happening to them. They all look like little comets pointing away from Theta-1. This star is so hot and bright that it is simply eroding away the planetary disks, and none of the stars that are formed within the diffuse nebula, rather none close to the power of a bright O, is likely to survive. The O stars just kill them off. They are very rare stars by the way - only something like 0.0001 percent of all stars are O stars. It's a good thing, because otherwise they would be blowing up all over the place and we'd see a sky full of supernovae. That would probably not be healthy for life on Earth.

Stars

Not only can we dissect stellar disks, but we are also beginning to dissect stars. This is Kruger 60B, otherwise known as UV Ceti, a well known M5 dwarf flare star. You've seen pictures of flares on the Sun. Think of the entire Sun going off with in a flare. It would not do life on Earth any good, producing terrible X-ray radiation as well. These dim M stars can brighten by a factor of two. Think of this wonderful weather forecast: "the Sun is going to be twice as bright tomorrow as it is today." This is the star; these are radio images of magnetic field loops around it. You are actually seeing a magnetic field surrounding another star. The Sun has the same general field, but in a much reduced way - it's what produces the coronal loops. But these in UV Ceti are incredibly powerful, and when they collapse, they brighten the whole star by a huge amount.

We're also able to look into the giant stars. These are silicon monoxide masers. These are the magnetic field directions in the stars. The blue spots here are silicon monoxide patches. R Cassiopeiae, a Mira variable, is compared here with an ordinary star, 51 Andromedae. You see here in this speckle interferometry picture that R Cas is not round. These huge stars are not spherical. You might think of a Mira variable as a water balloon thrown in the air oscillating all over the place. There's no theory for this. We do not know why such stars are not spherical.

Here's another one, Mira itself, resolved beautifully by the Hubble Space Telescope. Here's the raw picture - Mira A, the long period variable star we all know and love, and Mira B, a white dwarf. This is not an uncommon situation. The white dwarf was originally the more massive star; it evolved and lost its outer layers, and is now the dead white dwarf. Because it is so small, it is a true point source for the Hubble Space Telescope, and gives the telescope's point-spread function. You can then use it to computer-enhance Mira A to produce a beautiful image. Mira A is a big blobby thing as well that has a projection on it. We have no idea why. It's then no surprise that many planetary nebulae, which come from the mass being lost by these Miras, are aspherical and have some very strange appearances.

Planetary Nebulae and White Dwarfs

This is the coldest spot known in the universe. The World Series takes place right here (laughter), and these are the suburbs. This is the Boomerang Nebula. Raise your hands if you know what the Boomerang Nebula is. Notice that mine didn't go up. It was reported as the coldest spot, but nobody ever said what it was. You had to go on the web and start looking. It's another one of these silly names that frequently pops up and I'm getting tired of them. I wish they'd quit. It's also called the Centaurus Infrared Source, so now we know where it is. It apparently used to be a Mira, and this is the mass being lost by the star. Look how asymmetric it is, rather note that it is not spherically symmetric. Measurements show 0.3 degrees Kelvin in center. You don't expect that because the background temperature of the universe is 2.7 Kelvin. The amount of dust is so great that it apparently shields the cosmic background radiation. Mass loss rates probably hit a thousandth of a solar mass per year, producing a whopping amount of dust. These things ultimately generate planetary nebulae.

I love this picture of the Egg Nebula in Cygnus. There is an F supergiant in the center of a disk that probably was once a Mira variable, and it's beaming light through the polar holes, revealing dust rings. The origin of the dust rings isn't really understood. One theory suggests that they might be due to periodic helium detonations deep in the star, another that they might be produced by an orbiting companion. Hubble's new NICMOS camera showed the same thing. Now you can see the disk in molecular hydrogen; set perpendicular it is we see stellar radiation beamed outward reflected from dust grains mixed in with more molecular hydrogen. Ultimately, the star in the center will heat up as it loses its mass, and then the system will turn into a planetary nebula.

William Herschel discovered planetary nebulae in 1786. The Saturn Nebula in Aquarius was the first one. He named them planetary nebulae not because they looked like Uranus, which you'll find in most books, but just "planetary" as a synonym for "disk-like." But under high resolution, they're hardly disk-like. These are two newly discovered planetaries. In this picture you are looking down the pole into a disk similar to the ones you saw in earlier images. This one is turned edgewise. There's a growing theory that some of these structures are produced by orbiting binary companions that stir up the mass lost by progenitor Miras. But you might also do that with orbiting planets! If you get a Jupiter-sized body in orbit about a Mira variable star, the disturbance may be enough to produce some of these funny shapes. How ironic that the shapes of planetary nebulae might really be produced by planets. I'm sure that William Herschel would be delighted to know that. Maybe we can stop telling our students that planetary nebulae have nothing at all to do with planets. We may also be watching the deaths of planets, which might be vaporized in the process.

Abell 30 is an old planetary nebula, and the only planetary known with X-ray emission. If you look in the middle, you see a funny looking set of blobs that have no hydrogen in them. They have been ejected by the star in the last 3000 years. This is an example of a "born again" planetary nebula. The thing was on its way to becoming a white dwarf. The helium in the stellar interior then popped off in a big nuclear reaction, and that made the star a giant again. By that time, the stellar surface had lost its hydrogen. It then began to eject hydrogen-free matter that became shocked to a high temperature when it hit the surrounding gas. Here we see polar blobs centered on a disk. The system shows some of the bizarre nature of stellar evolution, of how you can transform one kind of star into another, a giant into a white dwarf, and a white dwarf back into a giant, revealing the power of nuclear reactions and of gravity.

I never thought I would see a picture of a white dwarf as good as this one, as the Hubble picture of Procyon and Procyon B. In images of Sirius it is quite difficult to see Sirius B. Look at the beautiful separation. We finally have decent enough data to conclude that Procyon B's mass is normal. If you've been worried about Procyon over the years, you can put it aside and find something else to be concerned about.

Massive stars and supernovae

Perhaps you could worry about the Pistol Star (the name based on the shape of the surrounding nebula), which has been given another irritating silly name. Another irritation involves the Hubble press releases that tout a star like this and ignore known systems like Eta Carinae, which is pretty much the same, and a star that has been observed since John Herschel's time. That did not come out in the press release.

Yet it's nice to have another one. The "Pistol Star" is near the center of the Galaxy and is apparently a "luminous blue variable," a hot evolved star of about a hundred solar masses that is pumping out enormous quantities of matter. Eta Carinae is the archetypal luminous blue variable. They're called that in the logic of astronomy because they are luminous, they're blue, and they vary. Eta Carinae was one of the brightest stars in the sky shortly before the American Civil War, but now it's around sixth magnitude. At that time it pumped out probably a solar mass of material that buried the star in a dust cloud. The rings associated with the "Pistol" were pumped out over the last few thousands of years. It's been suggested that the Pistol Star might once have contained as much as 200 solar masses, which would have made it the most massive star in the Galaxy. But it really falls into the company of half a dozen others like P Cygni, which you can see with the naked eye. Such stars are rare, but so bright they can be seen over enormous distances.

Luminous blue variables are prime candidates for supernovae, and we therefore have at least one more. Here are two supernova that took place close to each other in a distant spiral galaxy at about the same time. We haven't seen one in our own Galaxy since Kepler's star of 1604, and I'm getting tired of it. I want to see a supernova before I pass off. And some lucky people in this Galaxy got to see two of them. Supernova are thought to be very important in producing the compressive forces in interstellar space that cause the birth of stars. You do in fact see in the Large Magellanic Cloud big superbubbles that have been blown in the interstellar medium by supernovae; these then create more superbubbles as newly formed massive stars explode.

Here is a lovely example of what appears to be two supernova remnants, the expanding remains of exploding stars, colliding. They demonstrate that supernova shells - these are really blast waves - intersect and interlock with each other and punch enormous bubbles in the interstellar medium that are filled with exceedingly hot gas with temperatures up to 500,000 degrees Kelvin, producing X-rays.

Here is a pulsar from the Vela supernova remnant moving along at somewhere around 90 kilometers per second; it has a bow shock in front of it, a sonic boom as it moves along through the thin gas of interstellar space. Pulsars and neutron stars tend to have very high velocities. They are Population I disk stars that should be moving at ten or twenty kilometers per second like the massive stars from which they came. Not these. The standard theory is that when a supernova blows up, the blast is slightly off center. We don't know why. But the off-center detonation gives the resulting neutron star an incredible kick, one strong enough to knock the star right out of the disk of the Galaxy. For this reason, a pulsar may not at the center of its remnant.

This is a Hubble picture of what seems to be the first known bare neutron star, one not observed as a pulsar. It was first seen as an X-ray source. Hubble focused on its location and found this very dim 25th magnitude star. Comparison of the optical emission with that in the X-ray yields a temperature of 1.2 million degrees Kelvin at the star's surface, making it the hottest star known. Most of the radiation is coming out in the X-ray and ultraviolet. If your eyes were sensitive to this, you could see it with a small telescope even though it is only something like 20 kilometers across. It may be a pulsar that is simply aligned so that the magnetic field doesn't sweep across the Earth.

Another newspaper scare story announced the discovery of an anti-matter cloud or jet coming out of the galactic plane. Someone asked "Is it going to hit us?" It's 8 kiloparsecs away. It was discovered through the 511 kilovolt spectral signature of the annihilation of electrons and positrons. There's therefore no question that it's really an anti-matter cloud of positrons being annihilated. We have no idea why. The best guess is that a whole bunch of supernova probably ejected some of the stuff. The cloud really is very thin and not very dangerous. But the observation shows that anti-matter really does exist in nature, and not just in the middle of stars where it is part of the generation of nuclear energy.

Galaxies and galaxy formation

With infrared cameras, we are able to probe deeply into the galactic center. These are red giant stars. From their velocities, and now even their proper motions, we can get a good fix on the mass of the galactic nucleus, which comes in at about two and a half million solar masses - that's a boost to the putative black hole at the center of the Galaxy. Of course, the nucleus could consist of a lot of black holes in orbit around each other. It could also be a bunch of really massive stars, a big cluster. The issue still isn't resolved. But the great masses at the centers of other galaxies give credence to a black hole at the center of ours.

Here is the Antlia dwarf. This is not exactly hot news, but it is at least apparently a newly placed member of the Local Group. The so called "new galaxy," however, had actually been "discovered" three times before, showing the difficulty of keeping up in astronomy even for professionals researchers. It is just a shard; it may be absorbed into a galaxy, perhaps was kicked out of one, or both. Galactic collisions are the modern paradigm for the formation of galaxies. Sometimes small ones get ripped away as a result of tides; other galaxies then accumulate them, giving us a picture of closely-spaced galaxies trading matter back and forth.

When I was learning this stuff, barred spirals were thought to be relatively rare. Now we are finding that probably most galaxies are barred, maybe even our own, as seen in evidence drawn from the MACHO project. MACHO was designed to find the dark matter in our Galaxy by observing gravitational lensing events by small bodies. The bar has solved problems in galactic dynamics. I'm not sure when this will hit the textbooks, because they're still plotting out the distribution of the bar itself. Bars may be naturally produced, and only in some galaxies may be destroyed by fast accumulation of matter. But you might also create them by the cannibalization of matter torn from other galaxies. The subject is becoming a fruitful line of research.

Here is a nice picture of M 82 showing supernovae popping off about every 30 years within a relatively small volume. They seem to produce huge fountains of matter. It was long thought that in our own Galaxy supernovae simply blast holes in the interstellar medium. Remember the picture of the colliding supernova remnants shown earlier? The supernovae also raise enormous fountains out of the galactic plane that then flow back into the galactic disk, creating huge circulation patterns. Now we're getting a bit of a different picture. Here's a edge-on spiral, M 108, which is surrounded by a cloud of X-ray emitting gas. The gas appears to be produced by flows from supernovae, but there's too much of the stuff. Now some astronomers are reversing opinions saying that, no the gas is not being produced by fountains, but that it has been torn from other galaxies and is flowing into this one. So we're not entirely sure which direction the matter is going. These studies are in a great state of flux. In fact, our own Galaxy may still be accumulating matter from intergalactic space, and the high velocity clouds we find flowing into our galactic disk may be shards from other galaxies that we're cannibalizing. Both processes may be operating, showing the complexity of the problem. Galaxy formation has been a very difficult matter. The feeling now is that there is an enormous amount of cannibalization that goes on, galaxies built from smaller pieces.

Well, we've got to show some records. NGC 5084 here is apparently the most massive galaxy known, probably again demonstrating cannibalization. These little things are galaxies whose velocities have been measured. You then use, in a sense anyway, Kepler's laws to find something like 6 to 10 trillion solar masses in this single large galaxy. It probably has just eaten a lot of other galaxies that are near it.

The black hole business is thriving. The slit of the Hubble's new STIS spectrograph was set across M 84. You can see large Doppler shifts in the emission line from the center, showing velocities of over 300 hundreds of kilometers per second close to the core. The velocities give an accurate mass on the order of about two or three hundred million solar masses packed into the galaxy's middle. What else could be there but a black hole? That's not much of a scientific argument, but it's the only one we have. You see ejecta coming from the centers of such galaxies, jets that can go for millions of parsecs before coming to a halt. So the black holes in the centers of galaxies do seem to be real. The deeper we look, the more we confirm them.

The galaxies themselves interact so much that there's a growing feeling that there are lots of stars between them. We all thought, or at least I always told my students, that all stars are in galaxies and between galaxies there isn't much of anything except a thin gas. But now with the power of the telescopes available, we're beginning to find intergalactic stars. Perhaps 10-30% of the stars in a rich cluster are actually in intergalactic space. They get ripped out of their forming galaxies. Collisions and violence, graphic violence! You have to be eighteen these days to go to an astronomy lecture.

Quasars seem now to be really just galaxies, albeit galaxies with ultrabright nuclei. We're finding that almost all quasars have some kind of fuzz around them, and they seem to be galaxies in formation. Why some galaxies formed quasars, which are the brilliant nuclei, and why some did not, we don't know; maybe it depends on the amount of matter available to fuel a black hole in the middle, and whether there are nearby companions that can be cannibalized. The problem is difficult because you're looking out at large redshifts and therefore to great distances.

Here's a cluster of galaxies. The funny looking thing down here is a gravitationally lensed galaxy in back of the cluster. That is, the gravitational field of the cluster bends spacetime and lenses the distant object, making it appear as if you were looking at it through the bottom of a wine glass. Such lensing can magnify the brightnesses of distant galaxies, allowing us to see more distant parts of the Universe than we ordinarily could. Keck measured a redshift of 4.92 for this the galaxy, making the most distant one ever observed, one only about a billion years old following the Big Bang. How galaxies can form that quickly has become one of the Big Bang's Big Problems. Distant objects also have carbon lines. How was the element created so quickly? We don't know. With high- speed computers, astronomers can map out the gravitational field and reconstruct what the distant galaxy probably looks like.

If you look at these pictures of the distribution of galaxies, you immediately notice long fingers pointing right at the Earth. It is also bothersome that the Great Wall, which contains the Coma cluster, extends all the way around the sky into a Southern Wall. It looks as if we are at the center of a bull's-eye, making the Earth look special. The Great Wall itself may not exist. If you take a random collection of galaxies, and then apply flows and true Doppler motions caused by gravity (as opposed to the redshift, which is caused by the expansion of the Universe and is not a Doppler shift), and do a computer analysis, you get something like this picture, which looks like what the observers are finding: great walls. We have to be very careful in interpreting redshift data in terms of the distribution of galaxies. So maybe the "great walls" don't exist at all. Or maybe they do. We do not yet really know.

The Hubble Space Telescope is being used to examine the evolution of galaxies. This picture is not the Deep Field, but another similar picture with a shorter exposure. Hubble can look to such great distances with clarity that we see galaxies in different shapes and forms back in earlier times. Anybody who teaches astronomy gets the common: "Well Alpha Centauri is four light years away, so you see it as it was four years ago. Doesn't that bother you, that you don't see it as it is now?" It does really bother beginning students. I say, compared to the ages of the stars, who cares? You can then point out that we don't see each other as we are either. I see you as you were a trillionth of a second ago, so you could get up and run out of the room, and I wouldn't know it until the light gets to me. (laughter) You never see anything in the universe as it is NOW. You don't want to think about that too much or you'll go nuts. To me standing here, people at the back of the room are at a different age than the people in the front of the room.

The only time this really matters is when you go out to great distances, and then it becomes VERY important because you're looking SO far back in time. You're now actually able to see these dim, distant shards, what appear to be almost star clusters, which apparently began to accumulate to form bigger and bigger galaxies, galaxies like ours. They form from accumulation and cannibalization of relatively small companions, the interactions pulling out other shards to produce dwarf galaxies in a sort of a grand design of constant collision and cannibalization.

The Deep Field: I love this picture. I saw this for the first time at an American Astronomical Society meeting where they had it set up as an eight foot wide mural. As you stood in front of it, it was even in your peripheral vision, like you were floating off in space. It's great to use your imagination and realize that the big galaxies are close to you, and the small ones are more distant, giving something of a three-dimensional effect. You can see off into the distance, and off into the distant past as well.

The Hubble constant

I put this slide in here more to show that way we're beginning to normalize something of the problem of Hubble constant. There's been a constant theme of two camps, that of the high Hubble constant of about 80 and the Sandage crowd that likes 50 or so. Type Ia (white dwarf) supernovae seem to have constant upper brightness limits, and they are so bright you can go to great distances. From these and other studies, as well as a new Cepheid distance scale from Hipparcos (which places galaxies somewhat farther away), the Hubble Constant is coming in at around 65 to 68 kilometers per second per megaparsec. Sandage is still hanging in at 55-60, but the camps are coming closer together. That makes the Universe a little bit older as well, 10 to 15 billion years (the number depending on the curvature assumed for the Universe).

At the same time, Hipparcos showed that maybe our distances for the globular clusters were off a little bit, and that maybe they are a somewhat younger than the previously estimated 15 to 18 billion years. The numbers are therefore ALL starting to come closer together. If you want to push things a little, you can begin to get an overlap between the two (the ages of the Universe from the Hubble constant and from the globular clusters), so that the stars are not older than the Universe itself, which was a bit of an embarrassment to the astronomers.

But not really. Look instead at the agreement. There are two completely different ways of getting the age of the Universe, and even if they are within a factor of two of each other, I consider it remarkable, let alone a few tens of percent.

Gamma ray bursts

Deep mysteries still remain. But maybe even this one will be resolved. About once a day another gamma ray burst goes off in the sky. Theories of the origin of the gamma ray bursts have ranged from comets colliding in the Oort cloud, which is a little silly perhaps, to something popping off in the halo of our Galaxy, to colliding neutron stars in distant galaxies. The observations favor a distant scenario, as the bursts are evenly distributed across the whole sky and do not show a distribution peculiar to the structure of our Galaxy, Local Group, or any local supercluster. Neutron stars should not collide or merge very often. But over the whole observable Universe of trillions of galaxies, containing perhaps 10**22 stars (10 raised to the 22 power), you might have quite a number of events, their violence visible across most of space. That "distant scenario" was supported this year, as three gamma ray bursts have now been imaged with Hubble and with Keck. One had a redshift of close to 1, showing that gamma ray bursts really are cosmological in nature, that is, they take place at great distances. In one case, there may even be an associated galaxy.

Conclusion

We now need to come back to home to this picture of Hale-Bopp. Here you can look at the distant Universe, can contemplate the grand theories, and perhaps realize that all of our ideas start here. Hale-Bopp, epitomizing the Solar System, is set against distant space, here against the globular cluster M 14 and the stars of our Galaxy. If you can take the picture even deeper, you would see the galaxies themselves off in the background, our own solar system superimposed upon the Universe at large to which it is inextricably locked.

This picture also shows the problems that we face with telling people about the sky and the Universe, because, you may remember, M 14 was taken as one of the "UFOs" that were accompanying Comet Hale-Bopp toward the Earth. The most famous example was a bright SAO star, showing the difficulty faced in educating the public, in trying to separate out silliness from genuine beautiful mystery and from the extraordinary cosmos in which we live.

I think it's a good time to thank you all for being at the forefront of astronomical education: those in the high schools, colleges, universities, and in the planetaria, in which you can show the sky as it really is, not with the silliness of the UFOs, but with the real M 14s and what the Universe is really about, helping us all to stand under a nighttime sky and really appreciate the beauty of what is out there.

Thank you.

Questions.

(What are the ages converging to?)

About 10-13 billion years. If you have a Hubble Constant of 75, you essentially tip it upside down for about 13 billion years; if you have 65, the age is about 15 billion, and if you bring the globular clusters down to 15 billion, then everything sort of fits. The problem is that inverting the Hubble constant works only for an empty universe, one without any deceleration. But you must have deceleration because of gravity. If the Universe is "spherical," just barely closed with an Omega (the ratio of the average density of the Universe to that required to close it) of one, then the age is two-thirds of the age you get without deceleration. So then you drop the age to 9 or 10 billion years. Some theoreticians suggest that the globulars may be this young, but that is not widely believed. But the cosmologists seem to think that now Omega may in fact not be 1. Observationally, the numbers are coming in at 0.1, 0.2, and that is hard to shake. Even the theoreticians now suggest that Omega can be 1 even with inflation ("inflationary" theory, which requires a superfast expansion just after the Big Bang, had strongly suggested 1). Maybe the Universe is really open, which means the age is greater than the two thirds value of the non- deceleration age.

(You talked about the coldest spot in the universe. How can they get that cold?)

I don't know. It's bothersome to me. There should be shocks, there should be something in there that's heating it up. This is simply a measurement, and I'm not sure that the theory is up to saying how it can do that. Or maybe the observers are somehow being fooled.

(Question on the supersize planets and whether they are a selection effect.)

The big Jupiters tucked close to their stars clearly seems to be a selection effect. You're going to pick out them out first, as they will produce the biggest Doppler shifts in their parent stars. We do not know enough yet to do statistics on other planetary systems. Detecting our kind of Jupiter is marginal, and if you tip the system a bit to the line of sight, the problem gets worse. The fun will be to see different kinds of systems that exist. No one has any idea about what kind of variety we're going to find.

(question on whether the Jupiters are really there or are an artifact?)

Thank you. I meant to mention this. David Gray at Western Ontario studied 51 Pegasi, which is the first star with a presumed planet. He found asymmetries in the spectrum lines that vary with the same period as the planet. He didn't have as good data as the "planet people" had, but he immediately wrote a paper saying that there is no planet orbiting 51 Pegasi. The people who discover planets then used the Web to write their own note back, which to me is not the way you should be doing science. I'm not sure the issue has been resolved. Perhaps the planet is stirring up the atmosphere of the star that's producing the Doppler shifts and the spectrum lines. Others say a planet can't do that. We need just wait and watch the new data come in. Of one thing we can be certain, that our perceptions of the Universe will continue to change as we learn more about the world we live in.

Thank you all very much.