ASTRONOMY UPDATES

ASTRONOMY UPDATE 1995

James B. Kaler

Department of Astronomy, University of Illinois

First published in the Proceedings of the 31st Annual GLPA Conference, Grand Rapids, MI, October 25-28, 1995. Reprinted by permission.

Abstract

A review of astronomical discoveries during the past year, including the solar system, stars and the Universe. Special emphasis is placed on Kuiper belt objects, on questions of star formation and the final stages of star life, and on the distant, early Universe.

Introduction

It's really nice to be back with you again and back in Michigan. I'd forgotten how wonderfully dark it is at eight o'clock in the morning this time of year. I should point out to everybody that my second cousin's wife's father was mayor of Grand Rapids. I think by Michigan tradition that makes me the tax collector, so I'll be seeing everybody on his or her way out.

Earth-approaching objects

We'll start with the good news. Comet Swift-Tuttle is not going to hit the Earth in the year 2126. It was supposed to, but some interesting new orbital calculations show that it's going miss. The comet is supposed to have a wild rocket effect, yet it doesn't seem to make any difference at all in the orbital calculations. You do them straightforwardly in terms of Newtonian mechanics and they work just fine. So I'm not sure that anyone can predict very well whether it's going to miss or not.

The other good news is that 1995XM1, yet another asteroid that passed between the Earth and the Moon, did miss the Earth by about a hundred thousand miles. The scary part was that this year there was another one of them, 1995XL1.

Some of the smaller ones that nobody can see coming in actually hit. This is yet another meteorite crash onto a car. They seem to come in pairs. So, in addition, to collecting your taxes, I'm going to be selling meteorite insurance in the lobby. There doesn't seem to be any real evidence for any of these things killing anyone, however.

The Solar Cycle

The other bad news involves the most convincing evidence I've ever seen for the effect of the solar cycle on the Earth. The effect seems to be that the closer the cycle peaks are together, the warmer the Earth. It seems to make a difference of a couple of degrees. We speak of the 11 year solar cycle, but it varies between nine and fourteen years. The farther apart the cycles, the cooler the Earth. Between 1645 and 1715 the solar cycle shut down, and the Earth chilled off in the Little Ice Age. It may be coincidence, but a variety of other evidence has shown that it is probably true that as the solar cycle shuts down, the Earth chills off by several degrees. We don't know when it's going to happen again.

There are now long-term studies of cycles in other stars. It seems that about a third of the G-type stars have no cycles. This could mean that the cycle shuts down about a third of the time; about one century out of three, the cycle disappears. The Sun's cycle has been on now for over two centuries, so we may expect it to shut down sometime within the next couple hundred years.

Venus

Magellan died last year. As one of the newscasters put it, "Magellan, which has been going around Venus for several years, finally fell into the gravity of Venus and crashed on the surface." So we have nothing in orbit above the planet now, but the Hubble Space Telescope has provided us with a superlative way of examining the planets and looking at them in continuing time rather than in just one-shot affairs. This is a beautiful image made with the Hubble Space Telescope.

Using spectroscopy, you can tell that the sulfur dioxide in Venus is decreasing, that is, the atmosphere is changing, providing considerable support for the notion that volcanic activity is continuing on the planet, that is, the planet is not dead. There was apparently a major volcanic eruption about 1976; the sulfur level in the atmosphere has been decreasing steadily since then. The same thing happens when a volcanic eruption occurs on Earth.

Mars

The Hubble also took some magnificent images of Mars. This one almost looks like some of the Viking pictures taken from a fair distance. You can see some of the features, like Valles Marineris. You can also begin to see why some of the old observers -- especially if you are somewhat near-sighted and take your glasses off -- thought there were canals on Mars. You do have these linear features, but they have nothing to do with artificial waterways; they do, however, have a lot to do with real waterways.

The one-time presence of water on Mars is aptly demonstrated by the SNC meteorites. There are a few pieces of Mars on the Earth. The evidence is pretty strong. This is a picture of one recovered this year. These meteorites are produced by a violent meteorite crash on the planet that accelerates some of the particles to the escape velocity, placing them into orbit around the Sun. After a few million years, one of them will hit the Earth and we can pick up a piece of Mars. There are several lunar meteorites of the same variety, and they are free.

How can you tell that it's from Mars? You can look at the gases dissolved within it and find that they are similar to the Martian atmosphere as determined by the Viking landers. So there is very little doubt that these are actually Martian meteorites. They are loaded with water. If you slice one, you find water-soaked clays. It looks as though the thing has been soaked in water for a million years or more, direct chemical proof that water was once abundant on the planet.

Liquid water is not there any more because there's no atmosphere to hold it down. Once you release your atmosphere, you sublime the water, it flies up to the upper part of what little atmosphere there is, and gets broken down by sunlight. You can't have liquid water at the Martian pressure of less than 0.01 bar. So where did the atmosphere go? Mars is pretty small, it doesn't have much gravity, and the Sun can heat up the atmosphere. But there has been some new theory done on the planet. The planet cooled off quickly and has no measurable magnetic field. A magnetic field holds the solar wind at bay, the same solar wind that produces the Aurora Borealis (or the Aurora Australis for the penguins). The Aurora is produced by the solar wind and the Earth's magnetic field. If you could remove the Earth's magnetic field you would have no aurora because the magnetic field traps the incoming particles from the Sun, and it prevents these particles actually from getting to the surface of the Earth, fortunately for life. But since there is no magnetic field on Mars, the solar wind can abrade the atmosphere, and may be that the chief factor that has been responsible for removing the Martian atmosphere and making it so much less Earthlike.

Vesta

Here's a Hubble picture of Vesta. Vesta is supposed to be just a little dot against the starry sky. You are not supposed to see it as a disk. When I first started studying about asteroids, there was a suggestion that some asteroids could just barely be seen as something other than stellar images. Now the Hubble Space Telescope has mapped Vesta; you can see surface features on it. With filter photometry you can even begin to say something about what the surface is like. It looks as if there are deep pits here that might take you down to the mantle area, and then some iron-rich or metal-rich silicates over here. What nailed me about Vesta, however, was the newspaper headline: Hubble Space Telescope Discovers New Terrestrial Planet. It found Vesta. What it found, was that it had a silicate outer mantle and it might even have a metallic core. Anybody who has gone to a museum and found iron and stony asteroids knows that asteroids have metallic cores.

Europa

Europa: another Hubble Space Telescope picture. I just love looking at these things because now we are seeing details, the same details that the Voyager craft showed. Europa has an atmosphere, surprisingly enough. We thought for a long time that Titan was the only satellite that had an atmosphere. Now it turns out there are several: Triton as well, and now Europa. with its thin oxygen atmosphere. I think that's what surprised everybody. I don't think anybody really knows where it's coming from. Its atmosphere is actually thicker than Mercury's, which is pretty light. There are very few bodies that don't have at least some kind of minimal atmosphere: no surprise because after all they have been active geologically in the past, at least to some tiny degree. And Europa certainly is active because it is close enough to Jupiter to have experienced some tidal heating.

Io

But not as much as Io. Outside of Venus, Io is the nastiest place in the solar system, with sulfur-loaded silicate volcanoes going off all over the place. Not only that, it so deeply buried within Jupiter's magnetic field and Jupiter's magnetosphere that the particle radiation field is lethal within a very short period of time. You will probably never see an astronaut walking on Io unless he or she has an enormous amount of shielding.

The Hubble Space Telescope is showing you yet some more activity on Io: another volcano seems to have gone off. But in general it is actually relatively quiet. Of course you can say that of the Earth; it's relatively quiet, but every few years, a big volcano goes off. Io has a great deal of other activity associated with it. The sulfurous surface gets abraded away by particles orbiting within Jupiter's magnetic field, and that produces a sulfur and sodium ring around the planet.

The first video gives you an idea of just how active this body is; here is an actual movie of Io going around Jupiter and of the Io torus. [video narration: "Jupiter's moon Io loses about a ton of sulfur and oxygen every second, an indirect result of Io's astonishing volcanic activity. This video shows what happens to that material after it escapes from Io. Some of the atoms will be ionized, picked up Jupiter's strong magnetic field and swept into a ring around Jupiter around Io's orbit. This ring of plasma is tilted because of the tilt of Jupiter's magnetic field. Jupiter and its plasma torus rotate in ten hours,.which is the length of the observing sequence shown here. The illusion of continuous rotation comes from repeating the sequence. From a video tape associated with an article in the Astrophysical Journal by N. M. Schneider and J. T. Trauger]. It's quite a little body isn't it? That was ground-based work. I am still in awe over the ability of the astronomers to do that.

Saturn's Ring Plane Crossing

We are going through Saturn's ring plane this year. I think this is the only audience in the world that actually gets excited by looking at Saturn and not seeing the rings. It gives us the real sense of just how thin they are. But the ring crossing also gives you the opportunity to examine Saturn for additional satellites. Saturn is about almost a magnitude brighter when the rings are fully open than when we are passing through the plane. If Mars had rings the size of Saturn, they'd be visible to the naked eye. The things are really huge.

During the ring plane crossing, Hubble found some of the satellites that had been seen by the Voyager spacecraft. The idea was to look for new satellites, and the press release came through over the internet saying,"Two new satellites discovered by Saturn." Maybe they were the old satellites, but then there may have been four satellites, but we're not entirely sure; we're going to have to look at it again during the next ring plane crossing. Then it got even more confusing during the second one when it turned out that at least one of them had been one seen by Voyager. But they also found something that they claimed looked like a rubble satellite. It may be that either the ring particles accumulate into a quasi satellite, or that this was a satellite that had recently suffered a collision and was broken up. This is not a criticism; these observations are very difficult. So Saturn up to this year had 18 recognized satellites. It may be up to 20, it may be up to 22, it may be up to 23, and nobody is quite sure at this point, which makes this subject extremely difficult to write about. I changed a textbook draft three times and finally just gave up.

Magnetic fields of planets

Aurorae have been seen on Jupiter, but this is the first time that an aurora has been seen on Saturn. This is another Hubble Space Telescope picture, one taken in the ultraviolet. The odd thing about Saturn is that the magnetic field is aligned with the rotation axis. You can see that the aurora is sitting right up there at the pole. In all the other cases I know of, the magnetic field axis is always tilted relative to the rotation axis. This seems to be a result of the way in which rotation interacts with convection in some kind of a liquid core. The Earth's is tilted by about eleven degrees, Jupiter's by about the same amount. Pulsar magnetic fields may be tilted by nearly 90 degrees. Those of Uranus and Neptune are tilted over by about fifty degrees. And here Saturn is sitting with the thing up and down. So the hard part is to explain something that looks perfectly normal but isn't. Nobody knows why. Uranus's and Neptune's fields are not only wildly tilted, but are off-center by about thirty percent. Nobody really understands them.

Satellites of Saturn

Titan: the largest moon in the solar system after Ganymede. This is the one with the thick atmosphere; to the consternation of the Voyager scientists. They sent the Voyager 1 screaming past Titan instead of toward Pluto. To everybody's disappointment, it showed us just a bland atmosphere that is twice as thick as the Earth's. There have been predictions of both methane and ethane oceans or lakes on this satellite. You couldn't see anything of the surface at all, but now the Hubble Telescope can actually image it. It's in synchronous rotation relative to Saturn, which is no great surprise. Unfortunately, nobody has any clue as to what these features are. It's the first step; there are certainly going to be other studies made of it. At least we're able to get through the atmosphere; in the infrared of course, not in the optical.

Iapetus: the one with the bright side and the dark side. This is a Voyager image. It's a strange little body, and it looks like it's picking up matter knocked off Phoebe. This just startled me too. You are looking into the outer part of the solar system and here is a map of the satellite showing the bright (trailing) side and the dark leading side. Since Iapetus is in synchronous rotation, it's the leading side that's picking up all the junk being kicked off Phoebe. This whole issue, which has been hanging around for a couple of decades, seems to be pretty well solved. These are from composites from the Voyager images, not from the Hubble Space Telescope: it's not quite that good.

Pluto

(When I was doing the short version of the textbook that Dave told you about, I had made some comment about Hubble soon being able to see surface features on Pluto. One reviewer wrote back a scathing comment to the effect that nobody is ever going to see surface features on Pluto from Earth. So the following felt good.)

Surface features on Pluto: can you imagine that? Pluto is about a tenth of second of arc across and effectively unresolvable from the ground. The Hubble, however, can see surface features on the planet. Again we do not know what they are, but they do match up with the occultation features. They are real. Each one supports the other. In fact, the occultation map is a little bit better than this. They may be frost deposits, perhaps near the poles.

This planet looks, or should look, a lot like Triton. It's the same size, the same mass, the same density. What is more intriguing is that Pluto and Triton have both been captured by Neptune. Triton orbits Neptune in the backward direction and, as clear as things can be, is a captured body. But Pluto is captured too. If you look at the orbital periods, you find that Pluto's sidereal period is about 1.5 times Neptune's. If you do sufficient orbital calculations over a million years or so and look at the perturbations that Pluto is subject to, the sidereal periods are in the exact ratio of 1.500. That is, Pluto has been captured into a gravitational resonance by Neptune. So Neptune got them both. They apparently drifted inward and got caught by Neptune, so there may be more Plutos orbiting way outside, in the Kuiper disk.

Kuiper disk and comets

The Kuiper disk is filled with comets. Comets are coming in from the outer parts of the solar system, either from this extended disk around the Sun, or from way out in the Oort cloud, which may extend halfway to the nearest star.

We have a new comet on its way in, a brand new "comet of the century," so they say, Comet Hale-Bopp. Have you seen it yet,? I think I saw it with my backyard telescope, but I'm not quite sure. That's usually the way it is when they are almost stellar, but it had a little bitty haze around it. Hubble nailed the thing quite recently and found it to be spinning. In fact, it's throwing off these arc-shaped blobs. It has been estimated to be a hundred kilometers across. Now consider that Halley's is of the order of ten kilometers across. This is a big body and if it continues on its present course of brightening, it will be an extremely bright comet, perhaps visible in daylight. (Not the whole comet, but the nucleus.) It may produce something like this, one of the classic 19th century comets. There were three or four that were just beautiful, in part of course because it was a lot darker in the 19th century, but we may yet see another one like Donati's here in 1858.

This is a picture of Comet Kohoutek. I remember seeing a painting or a drawing of it in a newspaper as it might be seen during daylight above the Golden Gate Bridge. Well, we've all been through three or four of these episodes in which you put your coat up over your head and pretend you are not an astronomer; like after the discovery of the flawed Hubble Space Telescope mirror, not to mention the great "Perseid meteor storm" of a few years ago. But maybe keep your eye open for Hale-Bopp. I'm not going to let this joke pass. For all you Kohoutek fans, the next comet of the century is supposed to reach perihelion on April 1, 1996.

I think one of the most exciting things in planetary science, other than the genuine examinations of the planets that have been done with the Hubble Space Telescope [see also the paper "New Views of Gas Giants" by Heidi Hammel elsewhere in these Proceedings], is the extension of the Solar System. When I was a kid growing up, the Solar System went to Pluto at a distance of 40 astronomical units. And that was it. There was the Oort cloud, of course, but we cannot see that, and it was not usually considered part of the "Solar System." But of course it is, as it's under the gravitational influence of the Sun. So you really have to distinguish between the Planetary System and the Solar System. They are not the same thing. You can extend the Solar System beyond the planetary system with bodies like this: 1994 TG2, a body 42 astronomical units away, out beyond the average orbit of Pluto.

The long period comets, those with periods greater than 200 years, can be found anywhere. You will find them in the Little Dipper as easily as you'll find them in Capricornus. Half of them go backwards and half of them forwards. But the short period ones tend toward prograde orbits and they tend to stick to the plane of the Solar System. That means they must be coming in from some extended disk beyond the planetary system. And if they are out there, we should see them. A few years ago, we began to pick up these Kuiper belt objects, and the count is now up to 23 and growing. There seems to be a bunch just inside Neptune's orbit, and then a bunch just outside.

We're looking here at bodies near the limit of ground-based observation. But the Hubble astronomers did a really interesting trick. They pointed the telescope toward one of the dark clouds of Taurus, so that there was very little stellar background. As Herschel found to his surprise, there are these areas in the sky in the Milky Way that are devoid of stars. They are really quite startling to come across. With no background, Hubble should have been able to pick out faint Kuiper belt objects, and it did; I think we're going down to close to 28th magnitude.

You have to work statistically. This thing may as well be a cosmic ray hit as a real body. But they took multiple images and then overlapped them. They found that most of these little blips were proceeding in the prograde direction. If they were accidental, as many of them would be going backwards as forwards. So using statistics, you can determine the number that are real. Whether this one is real or not is irrelevant. If it is real, it's only 20 or so kilometers across. Twenty kilometers at over 40 AU away! It's amazing, and from this little area surveyed, they estimated there should be around 200 million Kuiper belt objects, which is consistent with the number of short period comets that are being perturbed in long elliptical orbits around the Sun.

So we are working our way out into the far distant reaches of the Solar System, beyond the planetary system. I just find this wildly exciting because we are starting to get a real census of our surroundings. It turns out that even with the number of Kuiper belt objects you see, there are too few to make a major planet. The suggestion is that when the major planets were being built, there must have been ten or one hundred times more small bodies. You have to have many more to produce a planet like Uranus or Neptune in the short period, one hundred million years or so, it took to make the planets. So most of things probably got absorbed making the planets or got kicked out of the Solar System altogether. Of those kicked out, many of them should have been placed on interstellar orbits. Other stars should have done the same thing, and we should be able to find comets coming in on hyperbolic orbits. Not one has yet been found. This is turning into a major problem in planetary astronomy. Where are the hyperbolic comets? Are we the only solar system, at least of our kind? Nobody knows.

The Sun

Well, you can't have a Solar System without a Sun. (That was a pretty good segue, huh? Not bad.) The new solar cycle is starting, so we can all breathe a sigh of relief. There's no way to predict what it's going to be like of course. The last one was really neat. If you've been looking at the Sun recently, it has its absolute blank days. And it's pretty scary to tell a thousand students, "We're going to look at the Sun this week," and then there's nothing there at all. It's like the ring plane crossing of Saturn. This is a wonderful year for public demonstrations.

GONG got started looking at solar oscillations. This has been wildly exciting too. The Sun vibrates with multiple frequencies much as a bell. You can use them to probe all the way through the convection layer, almost all the way down to core, and even examine such things as the solar helium abundance, which is difficult spectroscopically because the helium lines are produced only in the chromosphere. Or you use the solar wind and then you have acceleration problems between hydrogen and helium. But you can get the helium abundance of the Sun to be around 0.08 by using the oscillations. You can also determine the rotational characteristics all the way down close to the core. You need this information to understand the solar magnetic field. With GONG, we can examine the Sun all day long by looking from different observing stations all the way around the Earth.

The Sun is also being examined by Ulysses. Ulysses flew under the south pole of the Sun last year. Next year it will go over the north pole and back to Jupiter; then it will return during the next solar maximum. This has been a very exciting satellite to watch. What we have seen is that the solar wind speed goes up and up toward the pole. These oscillations are not caused by any kind of error but by a Sunspot group that kept rotating in and out of Ulysses' field of view. Every time it was in the field of view, the wind speed changed, so what you are seeing here is solar rotation.

Star formation

We have achieved a remarkable understanding of the formation of sunlike stars in the last ten years or so with the aid of infrared and radio instrumentation. (O stars are still really problematic.) The most remarkable thing is the understanding of the Herbig-Haro objects. If you look in Orion and Taurus and the dark clouds of Ophiuchus, you see these blobs of gas. With no apparent source of illumination, they just hang against the dark clouds of these constellations. Then about ten years ago, we found that these blobs come in pairs that should be associated with jet-like phenomenon. Then we found actual jets and the stars in the middle between the pairs of blobs.

Here you see the jets coming from the stars. These are T Tauri stars, brand new stars, stars that are above and contracting on to the main sequence, shooting out jets of gas in both directions in a bi-polar flow. The flows ram into the interstellar medium, sweep it up, and produce shock waves, sonic booms that raise the temperature of the surrounding gas. And aha, you see these symmetrical blobs of gas on each side of the star.

What is remarkable is that a new star is supposed to be accreting matter from interstellar space; that's how it's growing. No theoretician realized that as the stars accrete mass, they lose mass at the same time. They are accreting mass from a surrounding disk, and then some of the mass gets thrown off in the perpendicular direction to create the Herbig-Haro objects. This may be an important way for a star to lose some of its angular momentum, so that as it contracts it doesn't start spinning so fast that it tears itself apart.

The accretion disk itself has been difficult to see; then Hubble nailed it. That is actually a disk, and you can see the jet pouring out of it in both directions. Way out here in the distance, the jet will create a Herbig-Haro object. We're looking at what may be a nascent solar system. There is a new star right here; the disk is several times our planetary system. Our planetary system is about this size, and quite possibly planets will be forming from the circumstellar disk from which the star is accreting its mass. We're beginning to get a handle not only on the formation of stars, but even on the formation of planetary systems.

Planetary systems and the stellar systems are created from molecular clouds. Bok globules are tiny molecular clouds. You can see a few faint red stars, but nothing in here at all. The dust is so thick you can't see through to the background. The dust blocks the incoming ultraviolet light from other stars, and turns the globule into a natural refrigerator. The temperature goes way down, almost to absolute zero. In fact some molecular clouds get down to the point of the cosmic background radiation of 2.7 degrees. You can't get them any colder than that.

At these temperatures, you have a wonderful way of producing molecules, including some very fragile molecules. The count of interstellar molecules plus circumstellar molecules, now stands at 109 different species (including ions). Almost all of them are visible only in the radio spectrum, but a few are visible from the infrared and even the ultraviolet. An astronomer at the University of Illinois discovered interstellar nitrous oxide -- laughing gas - - I have to tout the home institution at least once.

Mass limits of stars

The Hubble, and ground based telescopes as well, have achieved marvelous resolution. It almost seems that as soon as Hubble has resolved something, somebody does it almost as well from the ground with adaptive optics techniques that offset the shimmering effects of the Earth's atmosphere. Here's an example. We've long wondered what the limits of stars are. I've always defined a star as something that has gone, that will go, or is going through full thermonuclear fusion, the creation of helium out of hydrogen. That allows you to throw in white dwarfs, protostars, and all kinds of things like that. But what's the limit? The lower limit seems to be 0.08 solar masses. Below that, it's been theoretically determined that you can't get full fusion from hydrogen to helium. You can get some deuterium fusion, but you can't get the deuterium out of hydrogen. That should represent the lowest limit to stars; and we do see stars down to 0.08 solar masses.

What's the upper limit? Nobody really knows. It's generally been thought to be around 100 to 120 solar masses. Nobody really knows why that upper limit should exist. It just seems to be reasonable, based on the luminosities of the brightest stars, on extrapolating the mass-luminosity relation. That's not a very good argument. We can't analyze such ultraluminous stars in binary systems. There are too few of them, and they are too far away. It just seems to get harder and harder for nature to make higher and higher mass stars. In a galaxy of 200 billion solar masses the odds of making anything bigger than a 100-solar-mass star are just so small you don't have them.

Here's one that was thought to be 150 to 200 solar masses, a superstar like R136A was thought to be several years ago. But when you look at it with high enough resolution, it breaks down into a cluster. In the seven wonderful years I've talked to GLPA, if there has been one constant theme it's been in using telescopes not as light buckets but as resolution machines. There is nothing that will replace resolution. The brightest star in this cluster may indeed by up to 100 solar masses, but the latest superstar, so to speak, fell apart.

Down at the low end, astronomrs have been looking for bodies below 0.08 solar masses, for the brown dwarfs. Here's yet another brown dwarf candidate imaged by Hubble. It's been a constant theme, "New Brown Dwarf Discovered; this one is about .08 solar masses; we think maybe it's underneath that, but maybe not." That's the way the press release usually goes and then nobody else ever talks about it again because it turned out to be a real star. You're going to have to watch several orbits to be able to actually measure the mass of this one. At least they will know one way or the other after they have looked at it long enough and made the gravitational analysis.

But the fact is that the discovery has been so difficult that's it's showing us that there are precious few brown dwarfs out there. Either that or they're not illuminated at all. They should radiate for a while not only on gravitational contraction, but also on the nuclear burning of their natural deuterium into helium. And they should be visible. But where are they? The luminosity function (the number of stars per unit luminosity as you go down the main sequence) drops off, but for a long time we thought it just kept going up and up and up. And the brown dwarfs were taken as maybe being the solution to the dark matter problem. It certainly looks now as if they aren't. Here's another brown dwarf candidate in the Pleiades. There's an optical picture here; there's another in the infrared. You can see how red it is. But again it's right down there at about 0.08 or maybe a little bit under; if they exist in any number somebody would be coming up with them at 0.05 solar masses or so, but they're all hovering right at the limit. Here's just a wonderful puzzle. Why would nature stop making bodies from the interstellar medium right at the point at which they stop nuclear burning? This is a remarkable coincidence as one thing should have nothing to do with the other.

Planetary nebulae, neutron stars, and black holes

At the other end of stellar evolution are these beautiful planetary nebulae. This is NGC 6543, sometimes known at the Cat's Eye Nebula. It has a wonderful history, as it was the first nebula spectroscopically observed. It's in Draco, quite far north, so nothing much was done with it, mostly because the 100-inch could not reach it. This Hubble image is enormously complex, with ejected "bullets" seeming to punch holes in the surrounding rings. The astronomer who was in charge of the project, a theoretician who models planetaries, said that if he knew the planetaries would be this complicated, he would have gone into another line of work.

Planetaries become white dwarfs, and it is was sad to hear that S. Chandrasekhar had died. He had applied the theory of relativity to white dwarfs and realized that there was an upper limit to the mass that could be supported by degenerate electrons, the limit of 1.4 solar masses now carrying his name. He would likely have been pleased with the initiation of the "Whole Earth Telescope," which can continuously monitor variable stars, and obtained this observation of a pulsating white dwarf, observed for 11 days in 180 vibration modes, astroseismology at its current best (showing the helium shell to be very thin). And speaking of pulsations, in spite of last years' prediction, Polaris is still pulsing.

Moving to higher mass stars, the supernova problem is now being solved. The theoreticians have had great difficulty getting the things to blow up, as in one-dimensional calculations, the shocks pushing out on the star would stall against the gas pushing inward. Two-D calculations solved the problem as the outgoing matter could spread around the infalling, allowing the star to explode, as in this video. The next step will be 3-D calculations, which increases the complexity by another order of magnitude. I think we're well away from being able to do anything like that.

These turbulent ejecta show that you're not going to have a symmetric explosion. It wouldn't take much to produce a supernova explosion that's stronger on one side than it is on the other. And what's that going to do to the neutron star? Well look at the central neutron star of Puppis A. It's not in the middle of the supernova remnant! Proper motions show some pulsars to be moving at hundreds of kilometers per second, above the escape velocity of the Galaxy. They have received a kick that might have been caused by binary interaction, or by off-center detonation that could drive a pulsar like a rocket. By the way, nobody has found the Supernova 1987a pulsar. It should be there. But then you're not going to see all the pulsars. If the magnetic field isn't aligned properly, it will miss the Earth. We may never find the pulsar to 1987a. It might also be a black hole.

But we sure do see activity in other bodies that involve neutron stars and black holes. Up until this year, we have seen superluminal velocities only in quasars, where you see gas blobs seemingly ejected above the speed of light. This effect is an illusion caused by a beam of matter ejected nearly toward the observer at nearly the speed of light; geometrical effects will make it seems like it's superluminal. We've found some of superluminal sources that are apparently caused by matter being ejected by neutron stars and black holes within our own Galaxy. This one is from an X-ray nova, which involves the eruption of helium burning on the surface of a neutron star. If you have a neutron star in a binary, and the binary companion dumps gas onto it, the gas is compressed and you get a high energy runaway thermonuclear explosion. From this X-ray nova stream blobs in a bi-polar flow at seemingly greater than the speed of light. The blobs should be coming out at something like 0.95c at an angle of about 85 degrees toward the line of sight.

I think one of the remarkable things about stars and stellar evolution, star birth, even galaxies, is the ubiquitous nature of the bi-polar flow. You see it everywhere. You even see it in the Sun a little bit. The solar wind is coming out at a higher speed at the poles than it is at the equator. A kind of magnetic focusing is almost certainly involved. You see the Herbig-Haro objects, you see these flows here from neutron stars, you see the same kind of flows from black holes at the centers of galaxies. They should be linked somehow, probably as a result of rotation and magnetic fields.

You might remember supernova 1993J in M81. It was examined with very long baseline interferometry. This colored blob is only 0.002 milli-arc seconds across. We're looking at the supernova remnant of 1993J. We can see the expanding cloud of gas around it. It's just incredible! Resolution again, resolution, resolution, there's nothing like resolution. I won't say it again.

Star formation mechanisms

Look at star formation again. We are beginning to understand a little bit about the distribution of new stars and galaxies, and about how stars are created. There may be a variety of mechanisms that compress the interstellar medium; one could be a supernova erupting in a nearby cloud. In meteorites we find isotopes that are daughter products of plutonium. So plutonium existed naturally in the solar system at one point, which requires input from a supernova. Compression from a supernova may have created us.

We find other galaxies where various disturbances create stars. The Cartwheel Galaxy is a good example. It looks like this little guy punched right through the big guy, and produced a tremendous expanding disturbance filled with blue O-stars that are still collapsing out of the interstellar medium. This little starburst galaxy -- the one that collided with the big one -- suffered the same effect, whereas this one up here didn't have anything to do with it and is just watching the action.

Interactions produce star formation. Interactions -- mergers and collisions -- are going on in galaxies all the time. The Ring- Tail Galaxy (the "Antennae") is another example. A collision between two galaxies tidally swept out these huge clouds of intergalactic gas. We understand pretty well how that happens through gravitational tides. Within the antennae themselves, you see great star formation in progress. These interactions are critical in generating stars in a wide variety of galaxies.

In the center of this galaxy groweth a black hole -- we think. We still don't know whether there are black holes in the center of galaxies. We think we have one of a million solar masses in the center of our Galaxy. Hubble looked at M87 and found very high velocities right down at the core, implying a hundred-million solar mass black hole. But some of the best evidence comes from arcane data. They looked at this thing with an X-ray instrument and found an X-ray spectrum line. The asymmetry shows gravitational redshifting of the X-ray line as matter falls into the black hole. This is some of the best evidence available for the existence of black holes in the centers of galaxies.

Dark matter

Maybe we can find the black holes, but we're still in the dark on dark matter. This is NGC 5907. (How do we remember all these numbers? I have it written down. We had a wonderful man I studied with at Michigan named Dean McLaughlin. When I was a graduate student, we played pin-the-star-on-the-HR-diagram. They gave Arcturus to the radio astronomer, who had no idea of what to do with it. At random -- cross my heart, this is true -- they picked a star out of the HD catalog and gave it to Dean McLaughlin, and he put it in the right place.) Anyway, this is a disk galaxy seen edge on. Like our own Galaxy, it should have a halo, and it does. You can see it. From its luminosity, the halo is more massive than expected. It may be that some dark matter simply consists of dim red dwarf stars.

Yet, here Hubble (the name comes up an awful lot doesn't it -- the thing is doing incredible work) looks into a patch of our own Galaxy's halo away from the Milky Way. The diamonds are a random pattern of expected stars based upon what we think the luminosity function (the number of stars per unit luminosity) should be. We should see an awful lot of M dwarfs. But they are not there. If the dark matter were being produced by an overabundance of M dwarfs, or even brown dwarfs, this picture should be filled with images. And yet we don't even see the number that we expect to see on the basis of the number in the galactic disk. There are even fewer M dwarfs in the halo than there are in the disk. There seems to be a cutoff at 0.2 solar masses and nobody knows why. It may be abundance-related because the halo is metal-poor. But we really don't understand it. And it really does seem as if the overabundance of M dwarfs is not a solution to the dark matter problem. You see the same thing here. You look into a little patch of a globular cluster. This image should be filled wall to wall with stars, and it isn't. There are a lot of them, but you should see ten times as many if dark matter were due to low mass stars, and we don't. So we still have the problem.

Quasars

This is the famous quasar 3C273; you can recognize it by its jet; and it has a host galaxy. This isn't just flaring, this is actual material surrounding 3C273. We've recovered the galaxy around it and begin to understand something of what feeds the purported black hole at the center. If quasars are the over- brilliant nuclei of active galaxies, that is if they are just active galaxies at a great distance at an early time (since you're looking back into the history of the Universe), they ought to have big black holes with matter flowing into them. But where's the matter? In some instances you can see the host galaxy, but what's remarkable is that in a good percentage of quasars you see nothing at all except the naked quasar. What's feeding it? We don't know. Maybe interactions are involved. Here's a naked quasar, and this is actually flaring on the image; it is not real. But there is a galaxy near the quasar, and the quasar may be extracting mass, food so to speak, from it. You can't get away from the interactions.

As much as people would like to see Halton Arp go away, he won't. He still keeps throwing things at us from Switzerland. Now we've got an X-ray image of quasars with very different redshifts surrounding Markarian 205. They all seem to be part of the same X-ray patch, and yet they have very different redshifts. He won't give up on it, and it's probably a good thing, because he keeps making people think, whether he's right or not. Burbidge is in the same gang. You've got two quasars here. They're symmetrical around the galaxy M106, and it looks as if they've been somehow kicked out of the black hole at the center. We don't know. The theoretical work done on Arp's coincidences (or Arp's relationships) tend to show that they are consistent with coincidence. If you have enough objects, you're going to get coincidences and that's probably all it's about. I think that's what most astronomers believe. Yet Arp keeps everybody on their toes attempting to demonstrate that, yes, Big Bang theory really does work, that there is a uniform expansion in the Universe; and if they keep looking, maybe someday we'll find that something else is involved. We don't really know, do we?

Distant, early Universe

I always have a picture of the most distant galaxy yet found; it's traditional. You have to find the most distant galaxy because you can get publicity and thus NSF money. Then I have the slide up and I forget what it is. That's a galaxy at z =4.25! Now why they distinguish between galaxies at high z and quasars at high z, I have no idea, because quasars are now believed to be nascent galaxies. It all seems to be a matter of semantics and who can get the biggest record.

Looking into the vast distances like this, though, you begin to see a little bit more of the nature of the Universe. Look at these arc-shaped structures. You're looking at the images of distant galaxies and quasars through the gravitational lens of a closer galaxy cluster. And how are you ever really going to see to great distances? It's rather like (this is someone else's metaphor) trying to see the Universe through the bottom of a Coke bottle. The gravity in the far distance acts as a very disturbing medium. It distorts the far distant universe, making it almost impossible to see in some cases. You can't tell anything about the natures of these distant galaxies here; they're all just horribly distorted. Gravity is in a sense akin to the Earth's atmosphere, which makes stars twinkle. This isn't twinkling but it's producing a natural distortion that cannot be overcome.

Yet we're still able to look at the evolution of galaxies. As you look to great distances, you are seeing galaxies as they were in the past. The Hubble begins to make the natural time machine of the Universe real. You find that our more or less symmetrically beautiful galaxies were very ragged funny looking things way back in the past. You can also begin to see something of the evolution of elliptical galaxies. This is only a vague beginning. If you look off into the distant past, you also see huge numbers of these blue galaxies. They're all over the place. If you look near us, you don't see blue galaxies; they've all gone away. One of the press releases commented that blue galaxies dominate all other galaxies -- in the past, but not now.

We're looking in the past. You really need to keep repeating that. I think it is such a stunning concept that you can look into the past. I see you as you were in the past a hundred millionth of a second ago. We never see reality as it is. On the Earth, who cares, because the speed of light is so great. But now you're actually looking at the early Universe itself. Nobody understands why these galaxies were blue and what happened to them; great star formation seems to be involved. We see then that it gets difficult to do anything with the Hubble constant over great distances because we can't easily correct for magnitude changes due to galaxy evolution.

That brings us really back to the evolution of our own Galaxy which looks so symmetrical and beautiful. We're beginning more and more to understand that it has a very complex history and may be the result of many different mergers of different kinds of galaxies at different states of evolution. We do not see, for example, a steady monotonic change of metallicity with age. It's very jerky and it's probably different in different parts of the Galaxy. It's an awful mess. And we're beginning to see why.

Hubble "discovered" a new class of gravitational lenses, though these Einstein crosses have been seen before. But Hubble was able to look at them and measure CO in absorption against them, showing that star formation took place. Star formation had to take place to develop the carbon out of the hydrogen of the Big Bang very early in the Universe. This segues into the missing Population III of our Galaxy. The creation of the globular cluster stars with their low metallicity at some point took a star of zero metallicity. You had to have early supernovae to create even the few metals that we see in globular clusters. Yet none of these stars can be found. We had to have an early burst of star formation that produced heavy elements and we can see by looking at distant quasars that gas was there early on. It is consistent with the existence of Population III.

I think this is remarkable too. We can use these carbon lines to measure the temperature of the carbon gas. It should be at a temperature of the background radiation, which in our own time is three degrees. Here are the measurements of the higher temperature in the earlier Universe. They fit theory!

Hubble Constant and Omega

Hubble -- Hubble Constant, not the Hubble Telescope. From the ground, a Cepheid variable is giving us a new Hubble constant of 87 km/sec/Mpc for the Virgo cloud. Then Hubble looked at M100 and they got 80 plus or minus 17. Here you are looking at the Cepheid pulsing in M100.

But it is dangerous to get the Hubble constant from something that is so gravitational involved with our own Galaxy. You've got to account for the gravitational pull, for real Doppler shifts, as opposed to the redshift of the Universe. If you've got a Universe as big as this room and you're measuring the Hubble constant over the size of this dot from my laser pointer, we ought to be a little uncomfortable. It doesn't seem to make uncomfortable the people who are doing the measurements. Sidney van den Bergh in Canada used all the markers he could find and derived a Hubble constant of 75. This is M106 in Leo at 11.6 megaparsecs; you can use the ratio of the Coma cluster to M106 using other indicators, and you come up with a Hubble constant of 69. We're ranging from 69 to 87. And then Joseph Silk, a theoretician at Santa Cruz,derived 30 from theory and globular cluster ages. Sandage probably loved that one. But, of course, there's a lot of theory that goes into that value, and you've got to be very uncomfortable with that. The fact is that I don't think anybody's got it nailed down. The fact is that nobody really seems to understand what is going on.

Neither do we seem to understand Omega (the ratio of the density of the universe to that required to close it and stop the expansion). This is a Keck galaxy count that suggests an open universe and an Omega of one tenth, so the Universe seems to be open and expanding. The Keck has been doing work equal to the Hubble, just in a different way. This little thing here is a cluster surrounded by X-rays. The chemical composition of the Universe gives you roughly a baryon (a neutron or proton) Omega of about 0.05. Then you can use the captured X-ray gas to measure the actual dark matter and everything else of the galaxy cluster in the middle because it takes gravity to hold the X-ray gas down. From that, they derived an Omega of 0.20 at most.

The theoreticians claim Omega must be exactly 1 from the expansion of the Universe and the inflationary Big Bang . But the observers are beginning to find less than 1. It was only in the 1920s that we really understood observationally that there WAS such a thing as an expanding Universe . So we've only been at this 60 years or so. There's an awful lot of work to do, and I think this demonstrates our ignorance as much as anything else.

Gamma ray bursts

But if you want a demonstration of ignorance, true unadulterated absolutely pure ignorance, it's this. The Compton Gamma Ray Telescope has found gamma ray bursts all over the sky. The video will show them. This is a map of the whole sky. Watch, this can be mesmerizing. Look at the gamma ray bursts. The color shows you the energy and the size the intensity. They're randomly distributed. There is just no predicting where the next one is going to occur.

They appear in a uniform, isotropic distribution around the Earth. They can't therefore be in the disk of the Galaxy. So they should not caused by neutron stars or black holes, which are expected to be in the galactic disk. They have to be produced by something distributed uniformly around us. What's distributed around us? I've heard theories that take us from the Oort comet cloud (believe me!) through the halo of the Galaxy, a huge extended halo that would appear isotropic to us on Earth, to bodies at immense cosmological distances, to the limit of the distribution of things that we would call galaxies. The burts somehow probably involve neutron stars or black holes. They might be coming from neutron stars ejected from the Galaxy into a huge halo. Some have suggested they might even involve the collisions between neutron stars or between neutron stars and black holes in the distant Universe. What are the chances of two neutron stars colliding with each other? Good heavens. But over the whole Universe, it could happen with reasonable frequency. The fact is, nobody knows.

That's what makes this subject so wonderful, isn't it? You see something in the newspaper, "Astronomers worried that the age of the stars is greater than the age of the Universe." I think that's wonderful, not worrisome, because that drives the science. Not only that, you hear theoreticians saying, "Gamma rays can only be produced in very high energy processes involving magnetic fields;" then you come back to Earth and find gamma rays from lightning storms. These bring us back from the edge of the Universe all the way back home, showing the integrated nature of this subject, where gamma ray bursts may be produced in the outer regions of the Universe, and here are gamma rays being produced right back home as well. And neither kind is understood. It's a way of relating ourselves and our GLPA Conferences to all of our surroundings, not just to the Solar System and the Galaxy, but to the Universe at large.

Following his lecture, Dr. Kaler was awarded the rank of Fellow of the Great Lakes Planetarium Association. The award was conferred by Dr. David Batch, President of GLPA:

(Batch) Many of the newcomers now see why so many of us consider this one of the highlights for the last seven years of the GLPA Conferences. It occurred to me too as I was sitting there listening that we try to keep up during the year, but it's very difficult. We'll catch a few of these excitements throughout the year, but sitting here and hearing them all presented together puts that excitement in me that makes me remember why I got in this profession in the first place. It's really marvelous.

(Kaler) I need to interject something too because it has been one of the glories of my life to be able to do this, because it shows me why I became an astronomer and it gives me the chance to look at everything within astronomy. Researchers tend to get involved in their own little areas and know little outside it; doing something like this just integrates the whole thing. I want to thank everybody here for the opportunity to do this. I appreciate it.

(Batch) The Executive Committee has decided that we needed in a more formal way to recognize Dr. Kaler's efforts on our behalf over the last seven years, so I have a certificate here I'd like to present to you that confers upon you the rank of Fellow of the Great Lakes Planetarium Association.

(Kaler) When I don't know what to say, it's deeply meaningful. Thank you so much. This is perhaps the highest honor I have ever received. It means so much because it's from a group of people that I admire a great deal and always have. I grew up going to Hayden Planetarium in New York City and learned a lot of astronomy with the Junior Astronomy Club that operated out of Hayden, although I was a hundred and fifty miles away. I made my own planetarium when I was 13 or so years old and learned to love the sky in the way that you have, in the way that many professional astronomers and research astronomers don't understand. This is how you bring this subject to the children, the coming generations of astronomers and to the public at large, who support you and astronomy. You are the people who bring the beauty of the night sky back to people, the beauty of the night sky that has been lost to so many of us because of the bright lights, and the beauty of the research astronomy back to people who are supporting it. I want to thank you for this deep connection with you. To say I truly appreciate doesn't do justice to the way I feel. I'll treasure this moment always. Thank you very much.