ASTRONOMY UPDATES

ASTRONOMY UPDATE 2002

James B. Kaler

Department of Astronomy, University of Illinois

First published in the Proceedings of the 38th Annual GLPA Conference, Menasha, WI, October 23-26, 2002. Reprinted by permission.

Abstract

New discoveries continue to flood in, from the Earth's symmetrical aurorae to the huge redshifts of the most distant galaxies and theories of the origin of Big Bang itself. Along the way we imaged a comet, found more of Pluto's Kuiper Belt company, discovered lots more planets in orbit around other stars, heard that pulsar ages are not as well known as we thought, located medium-sized black holes, and ran up against quark stars, changes in fundamental constants, a green Universe, and BRANES. Sir Fred would have loved it.

Goodbye and Hello

Beginnings and endings are an intimate part of astronomy, and so it is with astronomers as well, as we say farewell to one of the great ones, Fred Hoyle (1915-2001), who helped pioneer cosmology and the science of the origins of the elements. Goodby too to the CONTOUR Spacecraft, whose rocket blew it apart, and to 11,000 vacuum tubes of the Super-Kamiokande neutrino detector, completely disabling it.

On the other hand, hello to the Sloan Sky Survey data at their website at http://skyserver.fnal.gov, as well as to the new Hubble Advanced Camera for Surveys and the new NICMOS camera. A hello too to the contract for the Next Generation Space Telescope (renamed the James T. Webb Telescope) and to the National Virtual Observatory, which will compile a vast amount of survey data for astronomers to use without observing for themselves (rather sad in a way...).

Earth-Moon-Sun

For the first time, aurorae have been seen to be mirror images of each other, as long suspected. Other than the Moon being hit with some Leonids, the big news is that we are finally doing something with Earthshine (rather than with Moonshine, which is in SEPA territory). The brightness of Earthlight is useful in determining the global state of the Earth's reflectivity, which factors into climate studies. And for all those who are impressed with such things (including myself), we have the stunning news of Saturn being in that famous constellation of the Zodiac, Orion. Really! A little piece of the modern boundary sticks up toward the ecliptic, while Saturn is a bit below the ecliptic, and there we are.

The biggest news of the decade (which is still young yet) must be the solution to the solar neutrino problem. The Sudbury neutrino detector can pick up all the different kinds of neutrinos (electron, muon, and tau), which the earlier detectors (limited to electron neutrinos) could not. They are all now accounted for, but a good fraction of them change their flavors on their flight to the Earth, rendering them invisible to Ray Davis's original telescope and showing that they have mass, thus turning physics once again on its head. Davis, the originator of it all, was one of the recipients of the 2002 Nobel Prize in Physics. Advances in solar physics stretched to the solar surface as well, as solar oscillations reveal downflows that help keep solar magnetic fields and sunspots together, sunspots no longer quite so mysterious (except insofar as how they affect the stock market...)

Planets

Outward bound to the planets, we encounter Mercury first, whose surface features are finally falling to radar. Unfortunately, spacecraft have not approached Mercury since the 1975. That may change with the planning of new missions, Messenger (2009) and BeppiColumbo (2011 or so), the latter with a lander.

Venus put on a lovely evening display for us during 2002. Its backwards rotation is now being explained by the effects of solar tides on its thick atmosphere, and the coupling of the atmosphere with the surface.

There is more on Mars than we know what to do with. A few points suffice, including the appearance of the best picture ever taken from Earth (with the Hubble of course). The planet did its best to hide itself in a grand global 2001 dust storm, with little ones popping up all the time. The gamma ray spectrometer aboard Odyssey revealed hydrogen near the poles, strongly implying the existence of subterranean water. The touted layered deposits on the other hand, rather than coming from lake beds, appear now to be from volcanic ash.

OH NO, the Great Red Spot is shrinking (!), now 21 degrees across, marked down from the 35 degrees of a century ago. It does vary with time, and will probably grow back to its former glory. X-ray observations show unexplained bright spots at the Jovian poles, while the Ice Spires of Callisto (a great title for a novel) remain unexplained as well, except in vague terms as evaporating ice.

And as Cassini approaches Saturn, the Feds seem to care less about the Pluto mission, which seems constantly on again, off again, but perhaps may still go. Watch this space.

So is Pluto or isn't it? The answer is Yes. Or maybe No. Whatever the emotional connection with planethood, there is no longer much doubt that Pluto is the Great Body of the Kuiper Belt, that vast ring of debris that lies between Neptune and roughly 50 Astronomical Units out. In the ten years since the first Kuiper Belt Object (KBO) (other than Pluto) was found, over 600 have been discovered, about a third of them Plutinos that share Pluto's 2:3 resonance with Neptune. KBO 2001KX76 is 1200 km in diameter, larger than Ceres, and the unpronounceable Quaoar (go ahead, try it), found in 2002, is even bigger, 1300 km, 55 percent Pluto's diameter, and averaging 44 AU out. In a broad sense it's fair to lump them with the planets, as there were just too few of them, and they were too disrupted by Neptune, to form one. Pluto (along with Triton of Neptune) at least tried hard, and probably -- as a crossover -- deserves the appellation of planet as well.

Other Junk

But we probably should draw the planetary line at the asteroids, none big enough to be crossovers. Of this debris of what might have been a planet had Jupiter not gotten them so messed up, the biggest, Ceres, has been imaged by Hubble, showing not much except a basin (?) of some sort. More data now also confirm the existence of asteroid families that share orbital and physical characteristics, and which are the broken debris of collisions among larger bodies.

A primitive rocky asteroid hits the Earth, and we admire what might be a 4.5 billion year old carbonaceous chondrite made largely of tiny flash-heated chondrules. A leading theory contends that the chondrules were made very close to a highly active Sun in the early days of the Solar System, and then were blown outward by winds controlled by the primitive disk and a magnetic field. Maybe. Such theories come and go, though this one is supported by the shapes of disks around other young stars. Related are the tiny diamonds found in meteorites, which might come from near the Sun rather than from interstellar space.

It weren't no Hale-Bopp, but Ikeya-Zhang was still a lovely cometary sight. Even better was the close-up of Comet Borrelly made by Deep Space 1. Only 8 by 4 km across, the Comet is very dark, some of it down to one percent albedo. Nobody knows the nature of the covering material.

Comets eject meteoroids, which become meteors. The 2002 Leonids were very nice indeed. What will happen this year?

Interstellar Medium and Star Formation

Before we form planets, we must form stars, which are made in the dark cold dust clouds of interstellar space. A public vote gave us a beautiful Hubble picture of the famed Horsehead Nebula, which shows a small Herbig-Haro object (a small nebula formed by a jet from a new star and focussed by a circumstellar disk) at its top, a giveaway of a developing star. These dust clouds are filled with molecules. Some 120 of them have now been found.

From the disks around new stars come planets, their numbers not all that far behind those of the KBOs. Just over 100 extrasolar planets are now know (from radial velocity studies) to be in orbit around other stars, which include 11 multiple planet systems. Among the most interesting are the first planet known to be orbiting a giant star, Iota Draconis, another orbiting the principal star in a fairly compact binary system, Gamma Cephei, and one with a record short period, 2.98 days. Another 46 planets have been found by the OGLE project, which discovered subtle brightness variations caused by planetary transits.

Indirect evidence abounds as well. Vega has two condensations in its surrounding face-on disk, which suggests disturbance by a planet. (Speaking of which, the "twinkling" of a background quasar shows a Vegan wind extending 1.5 light years from this classic A star). Hubble sees similar evidence in Beta Pictoris's distorted disk. Even brown dwarfs (substars below 0.08 solar mass that cannot run full hydrogen fusion) are seen to have disks! Do such miserable stars have planets of their own? Then there are what appear to be isolated planets, or bodies of planetary mass, in the Orion Nebula complex as well as in the globular cluster (this from gravitational microlensing) M 22. Digging deeper, when the planet of HD 209548 crosses in front of its star, we see evidence for planetary sodium, marking the first spectrum available, however limited, of another planet. All these planets are Jupiters or Saturns (or much larger, some even brown dwarfs).

Are there Earths? None is yet found, nor is there any trace of intelligent signals. Maybe we are among the first to walk any planet, as the stars with planets are on the whole more-metal rich than the Sun. Early stars, with low metallicity, may not have been able to make them. Only time, and perhaps higher SETI doses, will tell.

For sheer strangeness, however, try on Pulsar B1257+12, which is now found to have four low-mass planets around it. Hardly "earths," however. The planets were probably created from the debris of a companion star evaporated by the pulsar.

Stars

One of the more futile arguments one can get into regards star colors, as we all see them somewhat differently. That did not stop someone from calculating brown dwarf colors. If only our eyes could see infrared...

Another argument involves the mass of the most massive star in the Galaxy. It is commonly taken as around 100 to 120 solar masses. But that is from a theoretical extension of the mass- luminosity relation. The most massive star ever actually measured from a binary orbit now comes in at 57 solar, moving us farther up the scale.

Among better known stars:

Delta Scorpii, a developing Be (emission) star got brighter, and is near first magnitude. The famed double Castor A and B (a quadruple A star) is (from the stars' temperatures and luminosities) 379 million years old, while a distant companion, the eclipsing double Castor C (a pair of class M stars also called YY Gem) seems only a tenth as old. Something may be very wrong with the theory of red dwarfs. Altair, a rapid rotator (over 210 km/s), is observed to be, as expected, oblate. Mira is a "mild symbiotic," as it passes mass to a white dwarf companion via its wind. Then there is "Gomez's Hamburger," a star with a thick dusty disk that is becoming a planetary nebula (and that also reminds us that lunch is coming soon.)

And then there are new pictures of what the Hamburger will become when fully matured, as Hubble took beautiful pictures of the planetary nebulae IC 4406 with its dusty lanes and NGC 6537 with its amazing loops. The always-popular planetaries are being augmented by the discovery of 1000 more, thanks to new surveys.

The central stars of the planetary nebulae are on their way to becoming white dwarfs. Most are ordinary, but some are highly magnetic with field strengths hundreds of millions of times that of Earth. Then there is a bizarre ELECTRIC double white dwarf. The stars are so close together that they have an orbital period of only 9.5 minutes. The two are not spinning at quite the same period, so the magnetic white dwarf induces an electric field in the other, which causes a current loop to flow back to the magnetic white dwarf. The spots where the loop hits radiate powerful X-rays. There seems no limit to the wonders nature provides. For the record, the record white dwarf orbital period is only 5.4 minutes, the stars only about 6 Earth diameters apart.

Massive stars above about 10 solar masses explode as their iron cores (created by millions of years of nuclear fusion) collapse into neutron stars (or even black holes), but no one has been able to figure out exactly what mechanism actually gets the blast wave going so as to lift the huge outer stellar envelope away. Apparently, neutrino heating and turbulent convection in the nascent neutron star does the job.

Neutron stars, even black holes, but quark stars? (Quarks are the particles that make protons and neutrons.) The announcement of the first "quark star," suggested because an isolated non- pulsar neutron star seemed too small and cool, was quickly quashed with more realistic neutron star models.

Not that we really understand neutron stars/pulsars. We derive ages from pulsar rotations and spin-down rates. However, we are now finding that spin-down rates can give ages much too long. Clearly we know the age of the pulsar associated with the Supernova of the year 386. Spin-down, however, gives 24,000 years, which is more than a bit out of line. Another ancient supernova, CTB 80, gives the same wacky result. A supernova can kick its resulting pulsar away from the point of explosion at high speed. The pulsar motion gives an age of 54,000 years for the event, while the spindown gives 107,000 years. Woops.

Ancient supernovae are recognized by their long-lasting expanding remnants. The famed Cygnus loop may be part of a pair of colliding remnants. Whatever, the main portion of the loop, 1500 light years away and 80 light years across, now seems to be much younger than previously thought, only 5000 years old. And just for the glory of it, look at the combined optical-X ray image of the Crab Nebula (the remnant the supernova of 1054), which shows a ring-shaped shock wave created by the powerful pulsar wind.

The most massive stars are expected to collapse into black holes, which are hard to identify. The evidence for supermassive black holes at the cores of galaxies (with millions of solar masses) is actually better. Globular clusters seem to create something in the middle, the core of the highly condensed globular M 15 containing one of around 4000 solar masses (derived from star motions), adding further credence to the reality of all these weird critters.

The most luminous supernovae, the "hypernovae," those from the highest mass stars, produce black holes (or so we believe), and also create (so goes the theory) extreme bipolar jets that produce the gamma ray bursts that come at us from the distant reaches of the Universe. If you are in line with the jet, you get the burst, if not, you see little expect perhaps an optical afterglow. It has been suggested that directed gamma ray bursts in our Galaxy could produce extinctions of life on Earth. The best known candidate for such a violent event is Eta Carinae, which lies 8000 light years away. Fortunately, the rotation axis of the star (along which the bursts would be focussed) is tilted well away from us, thus averting possible disaster.

Galaxies (Including Ours)

The supermassive black hole at the center of our own Galaxy received additional confirmation from variations in the X-ray flux. (A body cannot be larger in light travel time than the time-scale of its variations.) Two and a half million solar masses tucked into a radius of 1 AU can only harbor a black hole. Within one light year of the Galaxy's center lie an estimated 10 million stars, providing plenty for the black hole to feed on to make its surroundings bright. Mergers of double supermassive black holes in active galaxies may be responsible for distortions in the jets that pour out of them.

Since galaxies seem to have formed very quickly after the Big Bang, the age of our Galaxy gives a good measure of the age of the Universe. An eclipsing double star (from which a vast amount of stellar information, including the radii of the stars, can be obtained) in Omega Centauri makes it to be 17,000 light years away and 11.8 billion years old, confirming Omega Cen's ancient age from its HR diagram. In another globular, M 4, the coolest white dwarfs give an age of 12.7+/-0.7 billion years and the main-sequence turnoff gives 13.2+/-1.5 billion for excellent agreement. By comparison, because they have different decay rates, the thorium to uranium ratio in the oldest star known in the Galaxy's halo gives 12.5+/-3 billion years, while the white dwarfs in the younger Galactic disk give 7.3+/-1.5 billion. These fit well with the current estimate of the age of the Universe itself of around 13-14 billion years. All seems right with the world.

However, if all this seems too exotic, go look at M 51, one of the few galaxies that shows its spiral arms to the visual observer. The outer arms are caused by density waves, while the inner ones near the core seem to be made from acoustic waves.

Dark Matter

It remains dark. But surveys show that it tracks bright matter very well, that is, it is "unbiased." One scientist has suggested that we can do away with it if we tweak Newton's laws. The idea has not gained much acceptance and will likely go the way of quark stars.

Finally, the Universe

It's not dark, it's green! In spite of all the wonderful discoveries made over the past year, the average color of the Universe got close to the most press. Then, woops, no it's BLUE. Thank goodness.

Time for records. The highest redshift (z, which equals the wavelength shift divided by the true wavelength) for a quasar is now 6.28, implying an age of but 800 million years since the Big Bang. In its spectrum is found evidence for neutral hydrogen, suggesting that we can locate the re-ionization of the Universe (the end of the so-called neutral "dark ages") between z = 5 and 6. How can a quasar be this young? How could the Universe create a billion solar mass black hole so quickly? Nobody knows. In other weird news, quasar absorption lines suggested to one research group a change in fundamental physical constants (in this case, the "fine structure constant"). It's hardly accepted, so add this one to quark stars and changes in Newton's laws.

But we are not at the end. A galaxy, visible only because it is gravitationally lensed, has z = 6.56.

Digging deeper, we still battle over the Hubble constant, one camp claiming 58+/-6, the other 74+/-7. The error bars almost overlap, so slowly we are coming to some agreement.

The push in cosmology, however, is toward the study of the ripples in the cosmic background radiation (the three-degree remnant of the Big Bang fireball), from which a variety of cosmological parameters can be measured. As of now, less than one percent (0.6) of the stuff of the Universe is made of things visible (stars and the like). Another 3.4 percent is made of "baryonic dark matter," normal matter composed of protons, neutrons, but not easily or directly detected. Of the rest, a quarter (26 percent) is "non-baryonic dark matter," whose form is entirely unknown. That adds up to 30 percent. The observed acceleration of the Universe (along with the cosmic background radiation ripples) implies that the remaining 70 percent is made of "dark energy," whose origin is even more mysterious, if such is possible.

And where does that all leave us? In confusion. Yet in spite of not knowing what the Universe is entirely composed of, the human mind pushes back farther and farther to the limit to look into the origin of the Big Bang itself, which may involve cosmic "branes" that are parallel universes that occasionally "bang together" to re-create Universes like ours within a vaster structure that in the grandest sense may never have had a beginning and may never have an end, which Fred Hoyle said all along.