ASTRONOMY UPDATE 2003
James B. Kaler
Department of Astronomy, University of
First published in the Proceedings of the 39th Annual GLPA
Conference, Cleveland, OH, October 22-25, 2003. Reprinted by
As always, the year was marked by dramatic gains and losses, the
worst of which was that of our Shuttle Crew. Beyond that, our
astronomers explained solar faculae, got more information on
Martian water, and reversed our ideas about Jupiter's cloud
belts. We saw some magnificent imagery from our telescopes,
watched a non-lethal meteorite strike, and witnessed more records
regarding brown dwarfs and planets, whose properties and limits
are no more understood than dark matter or the dark energy that
is making our Universe's expansion accelerate.
Entries and Passages
The year was marked by fine discoveries, but also by fine
beginnings and sad endings. The National Virtual Observatory is
underway, again it seems, since it was reported on last year.
Nevertheless, it is a major development in astronomy, wherein the
vast amounts of data from many monstrous surveys will be compiled
and housed for access to any astronomer who cares to do the
research. Neither good nor bad, we will slowly raise a new breed
of observational astronomer who will never go near a real
telescope, nor even use it remotely. Photography, a dying means
of data acquisition, is really seeing the end of its days, as its
last bastion -- wide field recording -- is quickly being replaced
by large format CCDs. Such advances are epitomized by the
Hubble's new Advanced Camera for Surveys, which can now reach to
31st magnitude. And the contract for the Next Generation Space
(= James T. Webb) Telescope has been let to TRW. But the
fight is on for the budget, as the Hubble has been so very
successful that few want to see it go, to be replaced (around
2010) by the infrared high-redshift telescope that is the NGST.
Three passages of note include the deliberate destruction of the
Galileo spacecraft by the object of its vision, Jupiter, this
wonderful satellite having had a decade to revise our view of the
giant planet. A similar fiery fate visited the Mt. Stromlo
Observatory in Australia, which was burned by a wildfire.
Nothing, though, can compare with the loss of our astronauts
aboard the Columbia.
Turn now to rebirth with the ancient Jodrell Bank 250-foot radio
telescope, renewed with a surface good to 1-2 mm. And to the re-
opening of the Super Kamiokande neutrino detector, whose
phototubes had exploded.
That Old Sun
Neutrinos, whose count had been falling short in observations
from older detectors, have been found to be in the right number
upon observation of all three "flavors" (electron, mu, and tau).
They change their form upon flight to the Earth, which can happen
only if neutrinos have mass, which recent observations report.
Data from our nearest star pour in. Even as the current cycle is
winding down, we have the appearance of not one, but two naked-
eye sunspot groups. The umbras (cores) of sunspots are
depressions in the solar "surface" (the hot, opaque gases of the
photosphere), while the penumbras are upward slopes, which to the
surprise of the astronomers at the Swedish Vacuum Telescope have
filaments with dark cores whose significance is unknown.
And who of us, upon observing the Sun in white light has not seen
the bright faculae near the limb? Nowhere could one find a real
explanation of them. Because, while it was not really admitted,
nobody knew what caused them. Until now. They are the bright
slopes of granules that are visible only when the granules are
seen at an angle close to the solar edge. Mystery solved.
Mars Mania (and the other planets too)
What can one say? For being less than one percent closer than it
was two favorable oppositions ago, we get great press! And it
sure was bright. "As big as the Moon" said one release (but
shhh, only when seen at 70 power). And even then it was not THAT
great, as good eyes have 30 picture elements across the Moon,
whereas with typical non-mountain seeing you might have but a few
Nevertheless, one could write a book, or at least a good article,
on what's new for the red planet (as is being done). Couple
highlights: crater gullies are back to being created by water.
High water content near the equator -- "wet poles" -- may be due
to the shifting of rotation poles, which are central to subsoil
water, and which may in fact be rather close to the
The giant planets show that what seemed obvious is not always so.
The dark Jovian cloud belts were long thought to be falling, the
bright zones rising. Uh, it may be the other way around, as
Cassini found rising columns in the belts. And thanks to new
technologies, it's hard to keep up with the satellite number.
Jupiter is up to 61, Saturn (which once held the lead) up to 31.
Many of these are probably the smashed remains of larger moons.
One, Amalthea (inside Io's orbit) is little more than a reformed
rubble pile. Io itself was found to have a violent volcanic
eruption, with temperatures hitting 1500 Kelvin. Saturn's large
moon Titan displayed specular radar reflection suggesting that
the purported ethane ocean may really be there. We will soon
know when Cassini drops its probe through the thick hydrocarbon
At the edge of the Solar System, in the infrared, Uranus (which
is showing us more of its equator and less of its poles) looks
remarkably like Saturn. And the discovery of Neptune (from its
perturbations of Uranus) seems to go now more to Leverrier and
Galle, as there is evidence that Adams's calculations were not
very good, the facts of the case long covered up. And to our
surprise, Pluto, though getting farther from the Sun, is heating
up (though not a lot when you are near 40 Kelvin). It seems to
be just a phase lag, rather like the hottest northern days being
in July and August rather than in June.
The Planetary System, as we have long known, is not synonymous
with the SOLAR System, which contains far more than just the
planets. Beyond Neptune lies the Kuiper Belt, which at last
count contained 654 known objects (i.e., KBOs). Of these, 131
are "Plutinos" that are caught by Neptune in resonant orbits, in
which they go around the Sun twice for every time Neptune
circuits thrice (leaving 523 non-resonant KBOs farther out).
Pluto, a clear member of the Kuiper belt, is but one of them
(though the largest, which is why you still get to call it a
planet). Giant-planet gravity slowly works KBOs inward, where
between Neptune and Jupiter they wind up as Centaurs in unstable
orbits (190 now known) that bring them toward us to be seen as
Between Jupiter and Mars lies a zone of stability, the home where
the asteroids roam (ok, orbit). Even these can be moved inward,
however, where upon hitting the Earth they are called meteorites
(or in the case of big ones, "hazardous objects"). To our
relief, modestly big hits of the 1908 Tunguska variety are much
rarer than thought, about once every thousand years (though like
supernovae you can get none for a long time followed by two in a
row). Never mind the big hits. Watch for the smaller ones, the
like of which sent a shower of stones over the Chicago suburbs on
March 26 that nailed six houses and three cars within a 10-km
strewn field, the "rock" an ordinary chondrite that may have
weighed as much as 25 tons. Who says astronomy is a "pure"
And how about the last of the Leonids. For now. Maybe.
More significant is the age of the stuff from both comets and
meteorites. The oldest known things are said to be the
carbonaceous chondrites, which date to 4.5 or so billion years
ago. But within them are interstellar grains that predate the
solar system, dust grains from the stars that were in the
neighborhood of the new Sun. They have been found in tiny
interplanetary dust grains as well.
Interstellar, Star Formation, and Low Mass
The interplanetary dust provides a fine transition to the
interstellar medium, its dust epitomized by such Hubble shots as
the interior of M 17, the Omega Nebula. Within these dust clouds
works a cold chemistry that has produced the 120 now-known
interstellar molecules. One of these, acetic acid, seems to be
found closer in to the center of the Galaxy, odd since it is
widely assumed that the substance is important in building life-
giving molecules. Closer to us, the black clouds of the Milky
Way become very obvious. They are not static, but dynamic. Bok
globules such as much photographed B 68 seem to be pulsing,
probably from being hammered by interstellar shock waves. (Yes,
there IS sound in space. You just could not hear it.) The
globule probably contains little more than a solar mass.
Stars form from such clouds. The maximum mass of a star is
around 100-120 times solar. Above that, the odds of formation
drop to near zero (since the greater the mass, the fewer the
stars), and in any case, very high mass stars tear themselves
quickly apart as a result of their high luminosities, which
generate fierce winds. The low mass limit, in the realm of the
brown dwarfs (BDs, substars below 0.075 solar mass that cannot
run the proton-proton fusion chain), is simply not known. The
nearest of the BDs orbits Epsilon Indi, and is a 40-60 Jupiter-
mass class T star 12 light years away with a temperature of but
1000 Kelvin. The coolest of the BDs is a mere 683 Kelvin, not a
lot hotter than your oven. (Note that brown dwarfs fall into new
classes L and T that are cooler than classic class M, and below
2000 Kelvin. Class L, which contains real stars as well, is
characterized by hydride absorptions and powerful resonance lines
of the alkali metals. Class T displays methane bands.)
The record low mass is said to be about 3 Jupiters for a "star"
in the Sigma Orionis complex (assuming an age of 3 million years,
necessary since BDs dim with time, so the age must be known to
get a mass from the luminosity). Or perhaps it is some kind of
"planet." Apparently, planets (made from the bottom up by
accumulation of dust) overlap stars (made from he top down by
contraction). But maybe companion stars in binaries can be made
by accretion, just as are planets, and maybe "planets" can
descend directly from interstellar clouds. We simply do not
know. And yes it IS confusing. Add to that "free floating
planets" in the Orion Nebula Cluster. Terrible name, as they do
not "float," and are probably not planets, whatever that now
means, but low mass class T BDs, 5-15 Jupiters that orbit
chaotically within the cluster.
One criticism held against the accumulation of dust grains in the
formation of Jupiter-like planets is that the disks of young T
Tauri stars seemed to dissipate too fast for them to develop
(producing "naked T Tau stars.") Evidence now is that the naked
T Tau stars DO have disks, but that the particles are larger so
that they do not radiate in the infrared, thus saving this
standard planet formation idea.
What then about actual planets surrounding real stars? There are
now 102 planetary systems with 117 planets (13 are multiple).
More transits have been detected, and in the classic case of HD
209458, the spectrum of the star shows the effect of evaporation
from the planetary atmosphere. Hollows in disks around mature
stars reveal the effects of planets as well; among the best cases
is Fomalhaut. That planets at least tend to be the spawn of
high-metal stars is holding up. One idea had it that the high-
metals are coming from metal-laden planets that are devoured by
their stars, but the original notion, that the stars really are
originally metal-rich, is now ascendant.
That idea, however, was challenged by the discovery of a Jupiter-
mass planet orbiting a binary white dwarf-neutron star (pulsar)
combination in the ancient, low-metal globular cluster M 4. The
"planet" orbits the binary. How the situation developed can only
be speculated upon, but it is hardly "normal," and should
probably not be used as any kind of paradigm for current (or even
past) planet formation. Planets form around neutron stars by
accumulating from the debris of a destroyed binary companion to
the neutron star (or so we think). Add to that a propensity for
star-swapping among binaries in dense clusters, and any history
of the new "planet" is pretty problematic. What nature gives,
and what we do not know, is fascinating nonetheless.
Last year gave you an oblate Altair. Now we get REALLY oblate
Achernar, which is spinning at least 225 km/s at the equator, and
is a "Be" (B-emission) star with a surrounding radiating disk.
Such disks seem to be caused in a complex way by a combination of
spins and stellar winds. The best thing here is our ability to
actually measure the shape of a stellar disk through
interferometry. And speaking of Be stars, keep your eye on Delta
Sco (admittedly a bit difficult this time of year), which turned
into a Be star a few years ago, brightened, and now hovers just
under first magnitude, making the constellation look rather weird
to the practiced eye (and unlike that in your dome).
Then go back to the interferometer to see that the techniques are
so good they can measure the angular size of Proxima Centauri!
It's 1.03 milliarcseconds across, just 1.4 times the size of
Jupiter. (Jupiter is close to being the largest size possible
for a hydrogen-helium planet; much more massive and such bodies
would squeeze themselves to smaller radii. Proxima is held to
larger than Jupiter because it creates its own energy from
At the other end of the evolutionary scale, we are finding more
dusty dark knots within planetary nebulae (which are the
compressed, ionized remains of mass ejected from giant stars).
The Dumbbell (M 27) contains those similar to the famed Helix
(NGC 7293). For all the work done on them, the immensely complex
shapes of planetaries still defy ready explanation. They may be
caused by some combination of binary activity in the mass-losing
stars, by rotation, even by magnetic fields. Such fields have
been found in the predecessor giants. One protoplanetary nebula,
the "Boomerang," is (allowing for some hyperbole) the coldest
(natural) place in the Universe. For the most part, things can
get no colder than the three degree temperature of the cosmic
background radiation, but expansion in a dense nebula can act as
a refrigerator. And what happens to planets during the stellar
ejections that make the planetary nebulae? Mass loss may make
orbits elliptical and destabilize them, causing them to be kicked
out of their planetary systems. Are there really free planets?
The successors to planetary nebulae are the burned out carbon-
oxygen cores that used to be the stellar nuclear furnaces. The
carbon is formed by the triple-alpha reaction (3 He go to C),
then C plus He makes O. But the reaction rate is very poorly
known. Measures of the C/O ratio in a white dwarf through
measurements of seismic vibrations allow the rate to be found: a
laboratory in space!
The shells of Wolf-Rayet stars (NGC 6888 and the like) are
similar to planetary nebulae, but of higher mass, wherein a fast
wind acts on earlier stages of mass loss to produce a ring
Somehow related to all this active evolution is V 838
Monocerotis, which suddenly turned itself into a supergiant and
sent a blast of radiation that was reflected from a surrounding
shroud caused by earlier phases of mass loss, creating a
beautiful hollow structure. Nobody understands it.
At yet higher mass, X-ray observations support the idea that Eta
Carinae, the best candidate we have for a core-collapse
supernova, really is a binary, with 30 and 80 solar mass stars
orbiting each other every 5.52 years. Fortunately, the pair is
some 6000 light years away. Hubble and Chandra combined to
produce a wonderful composite of the Crab Nebula, with which we
see a ring around the neutron star created by shock waves from
the electrically-generated stellar wind. Supernovae are
apparently the generators of cosmic rays. The bulk of high-
energy ones seem now to come from the huge "Monogem"
(Monoceros+Gemini) structure that is 25 degrees across, only 1000
light years away, and connected to a known pulsar.
We "see" stellar black holes (Cygnus X-1, around 10 solar or so),
supermassive black holes (millions of solar masses, within cores
of galaxies), but how about something in between? Last year M 15
was "found" to have a black hole that contained 4000 solar
masses. Further analysis shows maybe not. Some galaxies may
contain them however, a subject that is not at all now clear. At
the top of the pile are gamma ray bursts (GRBs) that apparently
come from vastly powerful supernovae (SN) in distant galaxies.
The connection between GRBs and SN grew when one GRB afterglow
turned into the glow of an SN. (The collapse of massive Eta
Carinae could produce a gamma-ray burst beam that could affect
the Earth, but fortunately again, the orientation of the star
seems to preclude any danger.)
The Big Bang produced our hydrogen, helium, and a smattering of
lithium. The stars produced the rest. But they had to start out
as zero-metal stars. So where are they, these "Population III"
stars? They probably formed as high mass stars only. Exploding
as supernovae, they seeded space with the first metals, creating
dust, and allowing stars to be born in the "normal" way. Though
we cannot find zero-metal stars (as there may no longer be any),
we can get to very low metal levels. The new record is 1/200,000
that of the Sun. Such stars in fact show the chemical signatures
of having been salted by the first ancient supernovae. The metal
content must have risen quickly to produce the higher metal
contents (still down to 1/100 solar) of the ancient globular
The greatest cluster, Omega Centauri, however, seems more and
more to be not of the ordinary variety, but the core of a small,
dwarf galaxy that merged with our big one. (Among other things,
Omega Cen's stars show variations in chemical composition and HR
diagrams.) M 53, also one of the great globulars, may be the
core of the Sagittarius dwarf galaxy, which is now merging with
Beginning with our own Galaxy, we get better and better at
measuring the mass of the supermassive black hole at its center.
Even at a distance of 25,000 or so light years, we can see a star
called S2 orbit the black hole, and can apply Kepler's laws to
find a black hole mass of 2.6 million solar masses. Even at an
average distance of 950 Astronomical Units, the star takes a mere
15 years to orbit.
The history of a galaxy seems more and more to deal with that of
its mergers (witness Omega Cen and M 53). For example, we
observe rings of gas surrounding the galaxy Centaurus A (NGC
5128) that probably are the debris of merged satellite galaxies.
Something of the same thing is seen around our own, 60,000 light
years in radius. Mergers are clearly observed in close clumps of
galaxies like Seyfert's Sextet, and they even seem to form double
massive black holes at the merged centers.
Among the most spectacular of images was the X-ray picture of the
sound waves in the Perseus cluster from the effect of the
supermassive black hole in Perseus A. If only you were there,
and could go another 57 octaves down from middle C, you might
Dark matter in and surrounding galaxies and their clusters is no
more understood now than it was last year -- or the year
before -- or... It does, however, seem to be tracked by bright
matter (or stars). Explanations based on variations on Newtonian
dynamics keep popping up, and being knocked down. Oddly, some
galaxies to do not exhibit it.
All That There IS
A quick summary of the Universe is all that is needed.
Variations in the Cosmic Microwave Background Radiation (CMB)
tell that 4 percent of the Universe is in ordinary matter
("baryonic": protons, neutrons, and the like), 23 percent in the
mysterious non-baryonic dark matter, and 73 percent in "dark
energy," which is causing the expansion rate of the Universe to
accelerate. The acceleration is also clearly seen in looking at
the Hubble diagram of redshift vs. distance. Moreover, the time
of change-over from deceleration from gravity to acceleration
from dark energy has apparently been identified by a high
redshift Type Ia supernova as taking place about 5 billion years
ago, roughly when the Sun was being born. (Such supernovae are
produced by white dwarfs that accrete enough matter from a
companion to cause them to overflow the 1.4 solar mass white
dwarf limit and to explode. The result is a set of very similar
supernovae that make excellent "standard candles" for measuring
vast distances.) No one know what any of this "dark stuff" is.
Going back to just after the Big Bang, the idea grows that the
first massive stars (those that produced the first heavy
elements) were created before there were any galaxies, and that
these became the first black holes around which the first
galaxies were organized. Our observations even are perhaps
beginning to show us the ending of the "dark ages," when the
first stars and galaxies re-ionized the gas and lit the gloom
following the neutralization of the growing Universe, from which
the CMB had been released. That long ago time resounds yet
today. As the early stars re-ionized the Universe, you, the
planetarians, now light the minds of the children and the public,
allowing us in our beautiful fall to have our "glippa
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