ASTRONOMY UPDATES

ASTRONOMY UPDATE 1996

James B. Kaler

Department of Astronomy, University of Illinois

First published in the Proceedings of the 32nd Annual GLPA Conference, Minneapolis, MN, October 23-26, 1996. Reprinted by permission.

Abstract

The year was topped by the Hubble Deep Field, which revealed a spectacular number of galaxies within an area of sky 2.5 minutes of arc wide, a cascade of new planets (the result of dramatically improved technology), the resuscitation of the possibility of life on Mars, and of course the wonderfully popular Comet Hyakutake. The Deep Field and other deep imaging is allowing us to see the evolution and development of the Universe; the other discoveries allow us to begin to find our own places in and among the stars.

Introduction

While driving here yesterday morning I heard this delightful oboe concerto on a PBS station. The announcer said it was the Oboe Concerto in D by William Herschel. He was not playing it because Herschel was the astronomer, he was playing it because it was good music. What a wonderful lead-in to this conference, because to a large degree it was William Herschel who began to show us the natures of this variety of objects we see in the sky. He and his son John discovered half the NGC objects and began to sort out the differences among star clusters, nebulae, and ultimately galaxies.

When I have given these talks in the past, I've generally started with nearest bodies and have moved my way out, but there have been so many wonderful discoveries that I just can't wait to get to them. Though everyone is aware of these, I want to revisit them and to review what a truly remarkable year this has been.

Hubble deep field galaxies

If I can have the first slides ... can we douse all the lights? These pictures deserve utter darkness. At the AAS meeting last January they had a mural 8 feet high and 8 feet wide. You just stood there in amazement looking at it as if you were floating among these galaxies yourself. There are sixteen hundred galaxies in this picture; all in a frame only a couple minutes of arc wide, a tiny piece of sky. If you look at it on ground-based pictures, these two bright galaxies up here are the only ones that are readily visible. The others have not been seen before.

It took a hundred hours' exposure time with Hubble Space Telescope. It was taken in four colors and put together to resemble real color. What's truly remarkable is that if you gaze at it for a while, you almost get a three dimensional sense; you can see the bright galaxies in front of you and the faint galaxies off in the distance. There are more galaxies in the nighttime sky than there are stars in our own Galaxy. You could probably count ten trillion if you kept the Hubble Space Telescope busy for the next hundred or so thousand years. These images are a gold mine in their own right. You can apply to the Space Telescope simply to study the Deep Field image. There is a wealth of information that's going to reveal new science for years to come.

I kept wondering what kind of transition I'm going to use to jump from this Deep Field into the next picture. We are going from the galaxies to look at the stars themselves. The next picture I am going to show you is a graph. Can a graph be as spectacular? We know something about the galaxies of the Universe and about the expanding Universe from their spectra. We know that these galaxies are moving away from us at enormously high speeds. The redshift of the most distant galaxy, the very faintest specks that you can see here, is about z = 3.5. The ultraviolet part of the spectrum is shifted way up into the optical portion.

Planets orbiting other stars

Radial velocities also yield information on planets that orbit other stars. This is a graph of the radial velocity of 51 Pegasi, the best one now available. Take a very close look at the error bars. They are in meters per second. I remember growing up in this business when a radial velocity error of a km/s was considered accurate. Now the accuracy is down to about 5 meters per second. You can see the star going back and forth in a reflexive motion. There is something going around it. We're now living in an era in which we are discovering planets orbiting other stars. If there is anything more astonishing to me than that, I'm not sure what it is. The discoveries are coming in at a rate that's almost impossible to keep up with. I'm sure that since I got this slide, there have been probably one or two more found. It's been a cascade, beginning with 51 Pegasi then proceeding to 47 Ursae Majoris, 55 Cancri, Tau Bo÷tis, Upsilon Andromedae, 70 Virginis and HD whatever down at the bottom of the slide.

What is even more astonishing is that if you look across the top you can see the terrestrial planets of our Solar System: Mercury, Venus, Earth and Mars; Jupiter is way out there on the other side of the building. We're finding a whole bunch of Jupiters and they are tucked right up next to their stars. Look at 51 Pegasi for example. Here is a half-Jupiter-mass body (actually a lower limit) sitting right next to the star. How on earth can a Jovian planet like that survive? How can it possibly have formed? The heat of our own solar system is thought to be much too great to have allowed a Jovian type planet, with all the hydrogen and helium, to develop in this region. That's why we -- the terrestrial planets - - are big rock balls and why the Jovian planets are filled with hydrogen and helium. The general feeling seems to be that through some gravitational interaction that is yet unspecified, these planets have moved their way inward. [There's some evidence that Neptune perhaps moved its way inward from a more distant point in the Solar System to its present location.] But there is really no theory for why these planets are sitting there. We expected, in our own parochial view, that most of the other planets we would find would be much like our system. But they turned out to be incredibly different. We're finding a whole different style of planetary-system structure.

Now you have to be very careful because there are going to be selection effects. It is more difficult to detect Jupiters at 5 AU orbiting these other stars. The first ones we're going to pick up will be those that are closest to their stars, the ones that are moving their stars with the highest velocities. These systems may not be at all typical. Yet it won't be too long before we stretch our reach. NASA already has an initiative to try to detect even "earths" orbiting other stars sometime early in the next millennium. (We get to say that now ,since the next century is also the next millennium. We don't want to get into an argument here or take a vote as to whether it's 2000 or 2001, as if anyone really cares. You of all people are going to be plagued with telephone calls about it.) The idea is to orbit a telescope out around Jupiter and also to start looking at spectroscopic signatures of the kinds of gases that exist in earth-type atmospheres. I think that within the next ten or twenty years we are going to have a marvelous inventory of other planetary systems. The next question is what is on them.

Evidence for life on Mars

I couldn't wait until we got to Mars to talk about the possibility of life. You know all about it at this point; everybody knows all about the life on Mars "discovery." The first evidence, of course, is the "face on Mars," which according to the supermarket tabloids is actually a statue of Elvis. OK, enough of that. What is truly remarkable is that there may actually BE life on Mars. The question I ask when teaching this subject has been "Why ISN'T there life on Mars?" Life couldn't wait to get started on the Earth. Mars had a thick atmosphere at one time; there's evidence for water having vigorously flowed across the planet's surface, so one might think there ought to have been life too. Roberta Score, who discovered this rock (ALH 84001) in Antarctica, thought it looked rather odd. It turned out to be one of a dozen or so known Martian meteorites that were blasted off the planet in a very large meteoric impact. There are about an equal number of lunar meteorites. You can tell it's a Martian meteorite by analyzing the trapped gases, which turn out to be similar to those found in Martian atmosphere by Viking; there is no question that this thing came from Mars.

If you slice it open, you find some very interesting stuff inside. You find small globules with chemical compositions similar to the kinds of metallic compositions produced by anaerobic bacteria; they have high sulfur and iron contents. These may have been produced by early microbial life forms that also produced these microtubules. We find life forms on Earth that have produced structures like this, albeit of a considerably larger size.

The question is clearly still open. Everybody now is scrambling to look at other Martian meteorites. They need to open up these little tubules to find out whether or not (to put it lightly) there're critters inside, or at least to see whether or not there HAD been something that produced the tubules. I think it's probably going to take several years before all of this is settled. It's a wonderful excuse to go back to Mars, and NASA is just dripping with excitement. We need to take core samples from areas where we know there had been water, not just dust from the northern plains where the Vikings landed. There was a fascinating article in Scientific American within the past couple of months about life forms living deep in the solid rock of the Earth. Life on our planet seems to be everywhere. Maybe if we dig deeply enough, we'll find that life may have started on Mars and simply died out because Mars is too small to have been able to sustain its atmosphere for very long.

Comets

And now for the ever popular -- OK everybody pronounce it for me. We had a Japanese woman working for the local TV station and she drilled me on the phone for five minutes on how to say Hya-ku-tak- eh (Hyakutake). She said it's not too bad, at least it's acceptable.

What a glorious sight this was. We all had such a wonderful time with this comet, with open houses for hundreds if not thousands of people glorying in the Great Comet of 1996. Whether it falls into the "Great January" or Halley-1910 categories is arguable, but it's the first time since Ikeya-Seki back in 1965 that I've been able to see a tail this long. Here you are seeing a beautiful disconnection event that took place when the comet apparently moved into a different sector of the solar magnetic field, in which the magnetic field direction reversed; and that snapped the tail off. A comet's gas tail is a creature of the solar wind, which carries the Sun's magnetic field and wraps it around it the comet's ionized gas much like a wind sock. Without the solar wind and the Sun's magnetic field, all you'd have is a big fuzzy ball with no tail at all. Close up, it just amazed me; it looks just like it looked through my telescope. You could see all of this structure here with the eye with no problem at all.

OK, sit still, because I'm going to show you one of the pictures I took. I put this in here just because this is one of the few chances I get to show it. It's a wide angle view. Over here is the Little Dipper, and here the Big Dipper. The comet's tail just kept going like the Energizer Bunny. You could even see the disconnection event with the naked eye. I remember being out in the country (such as it is). This is the light of Champaign-Urbana over here near the Little Dipper. With a little averted vision the tail went through Canes Venatici all the way to Coma Berenices over here, which is absolutely amazing.

To the astonishment of astronomers everywhere, the darn thing produced X-rays. The ROSAT satellite captured it accidentally on a frame. This is an X-ray image of Comet Hyakutake; no one yet knows what produces the X-rays. It was thought at first that it might be a fluorescent phenomenon from solar radiation, but that was knocked down. It might be part of the shock wave phenomenon, of the solar magnetic field and wind hitting the comet's head. But there is really no theory at the present time. I love it when the theoreticians are scratching their heads and simply cannot figure out what is going on. This is what drives the science. They then looked at other comets that had been captured accidentally in ROSAT frames and there are at least two others that produced X-rays, two that weren't even visible with the naked eye. Apparently it's a common phenomenon.

As it went around the Sun, the comet was viewed with an orbiting satellite; it produced some stunning dust tails. Astronomers have identified over 20 molecules; the comet appears to have chilled to around 20 Kelvin, rather the molecules imply that they existed at about 20 Kelvin when the comet was in the Oort cloud. The last orbital calculation suggested that the period was about one hundred thousand years. So it's going to be a long, long time before we see it again. The molecules included methanol, water, HDO (deuterated water), methane, ammonia, and (now you get to say "that stinking comet") hydrogen sulfide.

Hale-Bopp is coming along, and you'll be hearing all about that tomorrow. I just want to show this picture of it. This looks just like it looked through my telescope. It's a pretty little sight right now, and may be the NEXT comet of the century. I think everybody is looking forward to seeing what this one is going to do.

International Ultraviolet Explorer

Now let's get back to the Earth and the stars in a traditional format. I hate to tell you something perhaps you already know: they pulled the plug on IUE, the International Ultraviolet Explorer. It was sent up in 1976 for three years and until just recently was still obtaining data. It is a testimony to NASA engineering if ever there was one. Yoji Kondo, who had been the spirit in the operation of IUE for many years, had to push the button and release all of the hydrazine propellent out into space so that it could not ever be used again. IUE took over 100,000 ultraviolet spectra, all of which are archived away in another gold mine of data. IUE was superseded by the Hubble Space Telescope, yet it had capabilities that the Hubble did not; for one, it had time available. It's still up there in geosynchronous orbit, and will be for a VERY long time; perhaps even when Comet Hyakutake comes back.

IUE is replaced (in spirit of not in wavelength capability) by several other satellites. The best-known is probably the infrared observatory ISO. Here is a picture of M 51's dust emission. At the center is a structure that almost looks like a bar and which probably helps generate the spiral structure. Here too is M 51's small companion. ISO will be an enormous help in studying star formation and the interstellar medium.

Optical interferometry

Keck 2 is now in operation. Keck 1 and Keck 2 are linked as an interferometer. We are going to be able to beat Hubble Space Telescope at its own game before too terribly long. In fact, we're already doing that by employing optical interferometers on the ground to achieve high resolution, a theme that I come back to in this talk over and over, since the first time I gave it in Champaign several years ago.

For a remarkable view, look at this: Capella is just barely visible as a binary star under the best conditions with the human eye in the best telescopes. George van Biesbrock saw it as slightly elliptical, but could not get the observing time to examine it. Look at Capella through the eyes of the interferometer. You can watch the components orbit. If you are going to show the public something through the telescope on a semi-cloudy night, you can always look at Mizar and Alcor. You split Mizar into Mizar A and Mizar B and tell everybody they are both spectroscopic binaries -- not any more! There's the orbit of one of the visual components as viewed with the interferometer; the components of this star are only a few thousandths of a second of arc apart. This is again a revolution in astronomy -- it will be more difficult to write textbooks in which we divide binary stars into their traditional visual, spectroscopic, and eclipsing categories; the lines are now being blurred.

Earth's inner core

Once again, here is the beautiful Apollo picture of the Earth. Earth is an astronomical body, although we don't view it that way very often. Like the other terrestrial planets, it has a crust, mantle, and core. The core is now being explored directly. A liquid outer iron core produces our magnetic field. Buried within it should be a solid iron core. It has recently been "seen" because apparently it's in crystalline form. It may in fact be one big crystal somewhere around 2000 miles across and approximately the mass of the Moon. We can follow the slow motion of the earthquake waves through it and see that the inner core rotates slightly faster than the outer part of the Earth, the difference about one day in 400 or so years. We are picking our planet apart from the inside out, a remarkable accomplishment.

Asteroid impacts

What would these talks be without the latest asteroid that almost crashed into the Earth? I've shown one every time; there goes yet another one. I didn't bother to write down its name, but it was 220 meters across and passed 1.2 times the distance to the Moon. If it had hit, it would have produced devastation somewhere on Earth. These things are coming by us all the time and we are beginning to feel as if we are a target in a shooting gallery. And sure enough, once in a while one will hit. About 30 million years ago we were struck by a really big one. There is an enormous meteorite crater under Chesapeake Bay. It is around 90 kilometers wide. That would not have done Washington D.C. any good. There are people who think it would have done a lot of good actually (laughter). There are many of these things all over the world, but this one solved the Georgia tektite problem. We find glassy spherules all throughout the Southeast. Here is a picture of one of them. They apparently were produced by this collision, which splashed impact melts and the like across a good part of the United States.

Speaking of impacts, let's look very briefly at a Clementine result. I hate to show pictures like this in public talks because of the horrible garish false color. Everyone here recognizes this is the Moon, but it's the south pole, a view we cannot have from here. Here is the biggest basin on the Moon, the Aitken Basin. It is somewhere around 2300 kilometers across and 8 kilometers deep. The edge of it -- its encircling mountain range -- is just barely visible from here near the Moon's south pole. It probably would not have taken a much bigger impact than this to have split the Moon in half, testimony again to the awesome violence in the Solar System and supportive of the modern view of formation of the Moon, that it was produced in a giant impact between the primitive Earth and a body about the size of Mars. The iron core of the impacting body merged with that of the Earth and then the debris reassembled in space without a core, producing a body, our Moon, with very little iron in it.

Planets

The first radar examinations of Venus indicated that the surface was a single plate and that there was no "continental drift." However, now we find evidence for at least some subduction in 10,000 miles of trenches.

Jumping past Mars, discussed above, to Jupiter, we see the impact of the Galileo spacecraft. Look here at the detail in the Great Red Spot. Galileo discovered evidence for an iron core in Io, saw more volcanic eruptions, and has imaged tidal fractures and stresses on Europa that support the notion that the satellite has an icy crust covering a liquid water ocean. Ganymede looks almost smooth in images taken by Voyager, as if you could almost skate on it, but after looking at these images, which show these huge ridges, I doubt anyone could. As we speak, the satellite is about to visit Callisto.

Hubble has been busy with Saturn and the ring-plane crossings looking for new satellites. The number is uncertain; here we see what appear to be temporary "rubble satellites" formed by the conglomeration of ring particles.

And finally, look at this wonderful Hubble image of Pluto. You can see what is probably nitrogen-carbon monoxide-methane "snow" at the poles, and what may be some kind of large basin.

Diffuse nebulae and star formation

Well, the Solar System, the Sun, planets, and the rest, had to come from somewhere. We are learning what happened to make them. Look first at the aftermath, at the HST composite of the Orion Nebula with its ionization and shock fronts and dust clouds. Here is the Trapezium. Then jump to M 33 to examine an incredible view of NGC 604, as good a picture of a diffuse nebulae in another galaxy as we can get in our own Galaxy from the ground. Here you can see great loops produced by generations of star formation that have produced winds and supernovae.

Back closer to home, radio astronomers (in my own department actually) discovered the spectral signatures of interstellar vinegar, of acetic acid. The discovery is important as, theoretically, acetic acid is needed to make glycine, which appears to be present in molecular clouds. The acetic acid supports the existence of this amino acid, the first known "biomolecule" in interstellar space.

And who has not seen these? Here is a ground-based photograph of the Eagle Nebula. See the three "elephant trunks?" These were dramatically imaged by Hubble, the great so-called "towers." Hot stars off the picture are cooking the dust away, evaporating it to reveal new stars buried within, which you can see here. The ridges here show a three-dimensional structure to it all.

This image shows the probable creation of a binary star within a collapsing cloud. Binary formation is, in some cases, a way in which a collapsing new star gets rid of its angular momentum, allowing the stars to form. Ejection from binary systems may have produced these "runaway stars," which are leaving wakes behind them in the interstellar medium.

And if you want resolution, look at this, starspots on the T Tauri star V410 Tauri. Well, it's not a real direct picture, but one constructed from Doppler imaging, from analysis of the shapes of spectrum lines as the starspots move across the apparent face of the star. The image shows what may be extraordinary magnetic activity, perhaps of the kind that may have kept our Earth warm when the Sun was young and 30% fainter than it is today.

More evidence for the existence of planets, and for the way in which we think our Solar System formed is seen when we probe inside the Hubble images of the Orion Nebula to see these disks, this one edge on. The star is hidden by a disk of dust, perhaps one similar to that which formed our planetary system. We can see reflection of the starlight at the edge of the disk. More evidence for planets is revealed by the warping of the disk around Beta Pictoris, possibly produced by an orbiting planet.

Finally, the search for brown dwarfs, different from planets in that they are believed to have been created whole instead of by accretion from dust (and are also generally more massive than planets), may be breaking open. This dim body, Gliese 229B, has methane in its atmosphere, suggesting a temperature of only about 1000 K, too cool to be a star. It probably has a mass of around 20 to 50 times that of Jupiter, and appears to be the first real brown dwarf. Only orbital observations will tell for sure.

Old stars and planetary nebulae

Then, after birth, solar-type the stars begin to age, becoming giants twice, once when their hydrogen cores are used up, and again when the helium cores die. At some point in the second ascent of the giant branch, they begin to vary as Mira, or long-period variables. These stars are apparently far more complicated than we ever guessed. Mira, as seen by the HST, is not round!

Ejection of mass by the Mira variables and their predecessors ultimately produces planetary nebulae. Matter ejected by winds is compressed and then illuminated by what was once the old nuclear burning core of the star, now nearly revealed, covered only by a thin skin of enriched hydrogen. The big problem has been in getting from here to there, in seeing the development of the objects from the Mira stage to the mature planetary. The action is hidden by the dust raised by the mass-losing Mira. But now, with infrared cameras, we can begin to see what takes place and have identified many "protoplanetary nebulae" (not to be confused with the concept of the same name, the rotating disk of dusty gas that circulated around the early Sun and that produced the planets). The Egg Nebula is a lovely example. First, look at a ground-based picture, in which the structure is fuzzy, and then be impressed again with the abilities of Hubble. Now we see that these "projections" are clearly beams of radiation illuminating a hundred or so dust shells caused by successive stages of mass loss. There is an F giant or supergiant at the center, known by its reflected light, a star not yet hot enough to ionize the surrounding gas, but moving to the left on the HR diagram.

After the protoplanetary stage, the star becomes hot enough to turn on the planetary nebula. This one is MyCn-18, also called the Hourglass Nebula. You can actually see a kind of hourglass tilted at you, with the illuminating star in the middle. You might immediately see something strange about that star in the middle. It is not in the center of the structure, perhaps the result of a binary companion, but we don't really know.

The central stars of planetary nebulae are under-appreciated. The typical planetary nebula central star has a luminosity between 1,000 and 10,000 times that of the Sun, making them among the most luminous stars in the Universe. But they are putting most of their energy out in the ultraviolet, so they are thought of as obscure stars. Dim main-sequence companions are therefore difficult to see. Nevertheless, we are beginning to learn the roles played by the binary stars in the formation of the planetaries. Binary action may be producing non-spherical or even asymmetric mass loss. A recent paper even suggested that bodies as small as Jupiter could seriously influence the distribution of mass loss in a Mira variable star.

Well, yet another Hubble Space Telescope picture: this is one of NGC 7027 in Cygnus, one of the brightest planetaries in the sky. Here we again see aeons of mass loss. This inner part is carbon rich. The stuff out here is filled with molecular hydrogen. We see here that the planetary nebulae are the last mass-losing gasps of the stars and that they are centered within much larger volumes of space filled with earlier generations of mass loss. These bodies produce most of the dust, or at least the seeds of the dust, that inhabits interstellar space. Supernovae produce some, but the Mira variables, through their agents the planetary nebula, produce most of it. And it's those dust grains that hide the starlight within the dark globules of the Milky Way that allow star formation to proceed in the first place. Thus mass loss ultimately drives much of star formation. Maybe William Herschel was more perspicacious than we thought: his mis-named "planetary nebulae" actually play a role in the formation of planets.

Planetary nebulae are turning out to be marvelously complex affairs. The first planetary found by William Herschel we now call NGC 7009. It's also called the Saturn nebula because of these two odd ansae. Such features have been found in many planetaries, and are now called FLIERS. They appear to be zooming outward asymmetrically, and nobody knows why, but they imply a disk around the star that propelled the FLIERS through the disk's poles. Think again of the Egg Nebula, the protoplanetary in which you can see the disk. We are beginning to put these structures together, but still do not know the origins of many of the phenomena. As Bruce Balick, who took this picture, commented, "only the central star central star knows for sure." The same kinds of "bipolar flows" are produced by stars that are being formed, flows that create the famous Herbig-Haro objects, the globs of illuminated matter that we see symmetrically displaced from the poles of T Tauri stars. When stars die, they do the same thing all over again, star death simulating aspects of star birth.

The planetary nebulae continue to expand and dissolve into space. Here is David Malin's picture of the Helix Nebulae (NGC 7293) in Aquarius. If you've got good binoculars and a dark sky, you can pick it out. It's about half the angular diameter of the full Moon. The nebula has a very hot central star, 120,000 degrees or so, and is starting to fade away into interstellar space. Back in the 1950s, Walter Baade at Mt. Wilson-Palomar took exquisite pictures of the Helix that showed these odd radial cometary features, hundreds of them, all pointing away from central star. Nobody knew what they were, but they are obviously generated by the central star.

Bob O'Dell at Rice, who also spearheaded the mosaic of the Orion Nebula seen earlier, went into the Helix with the Hubble, and look at the little features now. They appear to be simply instabilities in the gas. The hot wind from the central star shovelled the mass lost by the Mira and swept past some of it, leaving molecule- and dust-rich globules on the inside. Energetic starlight is now evaporating the dusty gas away. These little cometary features are not dissimilar from the elephant trunk structures that you saw in the Eagle Nebula, although they are on a much smaller scale. I've got to hand to O'Dell because he went out on the limb a little, and suggested that maybe these really are little comets that had orbited around the star, and were in the star's Oort cloud. Now they are being swept away by the evolving star. However, you can make a measurement of their masses, and they would be Earth-size comets, that is, awfully big. On the other hand, look at the newly-discovered planetary systems, at their variety. Maybe there are stars with Earth size comets. We simply don't know. Though they are probably just instabilities, as much as anything, they reveal our level of ignorance. Hubble investigators are now trying to find the same structures surrounding other stars. Here is a close up here (in the Helix). They almost look like they swimming upstream toward the star except they are gradually being blown away. You can see the ionization fronts that are gradually eating away at the dark cores at their centers.

White dwarfs

Eventually the planetary nebulae will dissipate, leaving behind white dwarfs. The central star of Helix Nebula in fact already is one. It will gradually cool down through the HR diagram, dimming away, eventually dropping off the diagram some trillions of years hence. Every white dwarf made, however, is still shining. You will still occasionally pick up a text or science book that will talk about black dwarfs and stars that are now truly dead. There aren't any such things; they do not exist. The cooling of the white dwarfs is by conduction and is very slow. The coolest white dwarf born at the earliest stage of the Galaxy may be down now around about 4500 degrees, all adding to the wonderful vocabulary of astronomy: we see blue white dwarfs, white white dwarfs, yellow white dwarfs, orange white dwarfs, and red white dwarfs.

This is a picture of the globular cluster M 4 taken with the Hubble Space Telescope. Maybe 20-30 percent of the stars in these ancient globular clusters are white dwarfs. They are still shining. They give us a marvelous opportunity to measure the age of the Universe. From theory we know how long it takes white dwarfs to develop and then cool. You then need only find the faintest and reddest white dwarfs, and you have a measurement of the age of, at least, the Galaxy. The age of the galactic disk found from the white dwarfs comes out to be about 10 billion years. As we work our way into the halo of the Galaxy, we'll be able to refine this measurement and learn more about the age of the whole galactic system.

Supergiants and supernovae

Supergiants, of course, don't die this way. Instead of producing white dwarfs, they explode. Here is a picture of Betelgeuse made with the Hubble Space Telescope in which we can see the star's disk. It is similar to an image made earlier using different techniques. The pictures are nearly the same, both showing a hot spot on the star's surface. It's an asymmetric star, and no one knows why. Perhaps the bright feature is related to some kind of magnetic activity or is a convective bubble coming up from below. We don't have a clue. But it's consistent with the fact that in close up views of very luminous stars, we see mass ejected asymmetrically, to one side and not the other. We have no idea why.

Has anybody read this year's book called "The End of Science" by the Scientific American writer John Horgan? I don't think we're seeing the end of science in these pictures. I'm beginning to think that as the millennium comes (in whatever year), if anything we are more seeing the BEGINNING of science rather than its end. We are only beginning to understand something about what is out there.

These stars eventually blossom through huge quantities of lost mass. Here is a Hubble view of Eta Carinae that shows a waistband, a disk in the middle, and flows from the poles, the same sort of thing that we see in almost all mass loss phenomena. Stand back because she's gonna blow, and when it goes off in a supernovae, are we ever going to know it! You could probably take your newspaper outdoors and read about it by the light of the destroyed star.

The Crab Nebula flickers inside. The Crab pulsar produces a powerful wind of electrons and protons that interact with the surrounding nebula and are focused into these jets. You can get on the Web and watch the "movie" of the flickering and can see variations that take place only over a few weeks. Some of the ejected particles become cosmic rays, apparently bouncing back and forth and accelerating within the expanding cloud and then being launched to near the speed of light out into the Galaxy. The energetic outflowing wind ablates the gas of the Crab, shredding it; that of course is why it is called the "Crab Nebula."

We are watching the expansion of Supernovae 1993J in M 81. The expansion of supernovae actually gives us a way to independently determine distance from the angular size of the image and the velocity of expansion. Supernovae 1987a now provides the fundamental distance calibration for the Cepheid variables. So the supernovae are beginning to lead us into a measure of the dimensions of the Universe.

The Milky Way Galaxy

Looking into the center of the Galaxy itself, we think we finally have imaged Sagittarius A in the infrared, the object that is thought to be the actual core of the Galaxy. We can take a look at matter that is in orbit around it, specifically emission line stars, and derive the mass of the presumed black hole in the center from Kepler's laws. The measurement suggests that within a half a light year of the center, there is no velocity drop off, which implies about a 3 million solar mass black hole. We have a little tiny "quasar" at the center of our Galaxy.

Look at the entire picture and then back at the white dwarfs. This is an image of the Galaxy taken by Voyager 2 on its way out (laughter). It is, of course, the "Portrait of the Milky Way" by Jon Lomberg. The halo is way up here. Some astronomers have suggested that much of the "dark matter" (mass detected only by its gravitational effects) may be no more than a huge collection of dim white dwarfs. Recall how difficult they are to see in that picture of M 4 that I showed before. That may solve at least part of the dark matter problem, although no one has as yet proven it.

Galaxy mergers, filament structure, and lensing

Now move farther out: the galaxies are beginning to tell something of their own story. Older research papers on the origin of our Galaxy tout a monotonic progression of metallicity and orbit, picturing a progressive collapse of the Galaxy into a disk. As stars die, their mass loss seeded the Galaxy with more metals; at the same time, the orbits of new stars become more flattened and circular. Consequently there was a strict relationship between the metal content of a component of a galaxy, its location, and its orbit. Much of that has been knocked into the garbage can. There seem to be two extremes and not much in between. The Galaxy seems to have evolved in a way that is much more complex than anybody dreamed.

You can begin to see how we developed by looking at other galaxies. Here are pictures of four galaxies imaged at various wavelengths. The blue is neutral hydrogen, the red is ionized hydrogen, and the yellow is starlight. See how the galaxies are merging. This is not a time lapse image of one galaxy, of course, but four pictures put together to show how one pair of galaxies may merge to create the final image, in which we see that elliptical galaxies may be the products of spirals. If you look into the far distance you see more spirals than we see nearby today. So our own Galaxy is probably in part the result of mergers with other systems, albeit smaller systems that were in different stages of evolution; such events really foul up the evolutionary patterns.

Yet, at the same time, the process works in reverse. Here are several galaxies that are in the process of colliding. The tidal streamers carry these knots, which will ultimately become dwarf galaxies. They will evolve in a different way, and may eventually re-collide with their parent galaxies, messing up the evolutionary sequences for the astronomers of that galaxy who may someday try to figure out what happened. So we have mergers that produce one kind of galaxy from another, and then mergers that produce yet more independent galaxies, the whole affair becoming terribly complex.

The Universe is expanding, but so is our view of it. The Center for Astrophysics survey has been approximately doubled in scale. Here's the Great Wall again; we see yet more walls and see more evidence for the filamentary structure of the Universe that seems to go and go. We are not entirely sure where any kind of uniformity begins to take over.

This is a spectacular picture of gravitational lensing. You look into a distant cluster of galaxies and can see funny little shapes surrounding it. The shapes are made from an extremely distant blue galaxy whose light is passing through the cluster of galaxies and is being multiply lensed. By surmising the mass distribution in the cluster, you can take these lensed galaxies -- they're not only lensed, but they're amplified -- and can reconstruct what the original galaxy looked like. It's a primitive looking thing. The natural lensing by clusters of galaxies gives us a kind of gravitational telescope for looking at things that we cannot see from Earth. Yet at the same time, the image shows the distorting nature of gravity. You begin to realize that looking at the distant universe is something like looking through the bottom of a Coke bottle. You get a very distorted view. Yet with modern high speed computers, we can overcome the problem and can actually begin to reconstruct what the distant galaxies look like.

Active galaxies and quasars

The active galaxy NGC 4261 was imaged again with Hubble. It now seems to contain a 3 billion solar mass black hole. This is probably the accretion disk. But the black hole is not centered within it. It may be in orbit around something, or a jet phenomenon may be involved that is propelling the black hole through space.

These black holes appear to power quasars. Last year I reported on the existence of fuzz around many quasars, and now we see more of the same. It's looking more and more like quasars are simply hyperactive nuclei of real galaxies. Here you can begin to see the galaxy that surrounds the quasar. Why the quasars die out and where they come from, we do not know. But now we are finding even more complexity. There are two quasars in which there appear to be double black holes evidenced by slow Doppler shifts in the emission lines. Can you imagine the bizarre nature of a 4.4 billion-sun black hole orbiting a mere 2 billion-sun black hole, and the enormous amount of activity the interaction might produce?

The Big Bang

The standard picture of the Big Bang seems to be intact, at least in some quarters. The Hubble Telescope continues to pop away at Cepheid variable stars in yet more distant galaxies. This one is at the edge of the Virgo Cloud. You can see a number of Cepheid variables, and the point is that no matter where Hubble looks for the Cepheid variables -- we're out now to a little over twenty million parsecs away from Earth -- the Hubble constant is hanging in there at a pretty firm 70-80 kilometers per second per megaparsec. The same seems to be true when we measure distances to galaxies with planetary nebulae. The planetary nebulae have a sharp upper luminosity cutoff and therefore serve as good distance indicators.

The old problem is still with us, however: when you invert the Hubble Constant and get the age of the Universe, even if you assume that the Universe is closed, the globular clusters still seem older than the Universe itself. You can say that the stellar theoreticians don't know what they are doing (don't say that around my department) or that the observers are somehow making errors. Nevertheless, the ages ARE within a factor of two of each other, and no one is excluding the Big Bang.

You can use the Hubble Space Telescope, and now Keck, to look back in time. When we look at the most distant galaxies, we are looking far, far back, billions of light years away. You can therefore see the way the Universe used to be all that distant time ago. We see that galaxies have different shapes compared with those we see today: we see ragged looking systems, smaller systems, and a greater abundance of spirals, again suggesting that spirals are merging to produce today's ellipticals. This picture is the Young Galaxy Survey; it rather looks like the Deep Field we saw before. We're looking back in time again and seeing little shredded, young galaxies. The Young Galaxy Survey used a filter that was centered on the Lyman alpha line so that the investigators could pick up very distant galaxies that were emitting radiation as a result of their young stars. You can see little shreds of galaxies that may just be beginning; we are seeing the evolution of the galaxies.

All of this fits in reasonably well with the Big Bang. These small systems are only about a tenth the size of our own Galaxy. Their mergers may produce galaxies much like our own. Then, looking into the cosmic background radiation, close to the time of the Big Bang itself, we're now seeing only ten-arc-minute structures, tiny ripples that really could have produced the clusters of galaxies we see today. Everything looks very nice about the Big Bang at this point, except that when you go back into the Deep Field there's a little galaxy here that is visible only in the infrared and that appears to have been born just after the formation of the Universe; But there should not have been enough time, indicating a growing serious problem among cosmologists. Galaxies seem to have formed almost at the same time the Big Bang was able to cool off to the point of allowing star formation. Galaxies formed too fast. We don't know how these galaxies could have developed as quickly as they did from the ripples that we saw before.

We also have problems with flows and have yet to find the needed uniformity to the Universe. You are here looking out to a billion light years, and see the local galaxies moving more off to one side than to the other side. We begin to wonder what this means for the Hubble constant. Is it just local? What would happen if we would calculate the Hubble constant over 3 or 4 billion light years, which we can't do, because we can't get the required accurate distances. Although many cosmologists, and those who study the Hubble constant, think everything is fine, right around the corner are astronomers who look at the giant flows that are taking the galaxies one way or the other, and are saying if we don't understand them, then we know less than nothing about the Universe.

Nevertheless, the Universe knew how to do it even if we don't. We look back into the distant past with the Hubble Deep Field and we know that all of it that we see out there ultimately led to here. Thank you.

Special presentation

Following Dr. Kaler's address, Dr. Jeanne Bishop, on behalf of GLPA, presented him with a needlepoint creation of a butterfly she had made:

Every year, Dr. Kaler, you have honored us with a wonderful astronomy update. For eight years this has happened. As we talk with you informally, we also learn about your extracurricular interests. One year we learned of the cooking and the hot peppers. We also know about your interest in music, and one of these years we are going to get him to sing. But last year in an informal conversation I learned that he is interested in butterflies. We are very grateful to you for all that you have done for us. Just as this butterfly unfolds its wings and shows the detail and beauty of those wings, each year you show us the unfolding detail and beauties of the Universe. So this year, Jim, as a memento of our appreciation, we present this to you.

Dr. Kaler: Thank you. I am so grateful to you all for this, and hardly know what to say. I don't collect Butterflies; instead I keep them alive in photographs. I planted a garden this year to attract more of them. But for some reason, perhaps the late frost, there were very few, to my disappointment, almost none at all except for a few sulphurs and monarchs. Now perhaps I know why. They are all right here in your gift.
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