ASTRONOMY UPDATE 2008
James B. Kaler
Department of Astronomy, University of
First published in the Proceedings of the 44th Annual GLPA
Conference, Milwaukee, WI, October 29-November 1, 2008, reprinted
The year presented us more with numerous small things rather than
blockbuster events. There were exceptions of course, notably the
Phoenix landing on Mars and the Mercury flybys. Highlights include
the continuing Hubble saga, no or few spots on the Sun, the
centenary of the Tunguska impact, the inscrutable Comet Holmes, the
discovery of numerous superearths, a number of confusing anomalies,
and quite a lot on supergiants and supernovae.
All must pass. Nothing, not even the stars, lasts forever. Not
even GLPA talks. Before going on, I need to express my deepest
thanks to one of the best groups of people I can imagine for an
amazing 20-year run that has brought far more to me than I ever
gave. Thanks to Dave Linton who got me started giving the Updates
in 1989 and to Dave Leake for his continued ideas and
encouragement. Thanks to Bob Bonadurer and Dave DeRemer for "The
Stargazer." Thanks to Dale Smith for his editorial patience and to
Jeanne Bishop for just about everything. Thanks for the
opportunity to show my old hand-made planetarium in a real dome,
and for granting me the Spitz Lecture. Thanks to the University of
Illinois Department of Astronomy for the many years of helping to
support these lectures. And above all, thanks for the friendship
and bubbling enthusiasm from all.
We've traditionally started this review with comings and goings of
note, and this year is no different. Among the saddest is watching
the big old observatories of yesteryear fade into the twilight.
Over the last couple years it was Yerkes, and now it's David Dunlap
Observatory, which the University of Toronto wishes to close. It's
hard to maintain a top institution within sight of a large
community (and when I worked there once, a driving range). The
family contends, so stay tuned.
Then NASA blew a FUSE, the Far UV Spectroscopic Explorer failing
mechanically after an eight-year run. And Ulysses, the "over the
top" solar satellite that examined the Sun's fast (750 km/sec) but
constant polar wind (compliments of a gravitational boost from
Jupiter), went to join the gods at Olympus, its transmitter going
off for good. On the plus side, GLAST, the "Gamma Ray Large Area
Space Telescope," mercifully renamed after Enrico Fermi, was
successfully launched on June 3 and quickly bagged its first
discovery, an all-gamma-ray pulsar.
Even more positively speaking, Salvation is at hand for one of the
greatest scientific instruments ever built, the Hubble Space
Telescope. Last October (clearly in honor of the GLPA meeting),
Shuttle astronauts were to service the Imaging Spectrograph, the
Advanced Camera for Surveys, the guidance sensor, all batteries and
gyros, and then add the new Wide Field Camera 3 and the Cosmic
Origins Spectrograph. Then the data transmission system went out
(fortunately BEFORE the mission was launched), resulting in a new
launch date in February of 2009. Farther out in the Solar System,
the Pioneer Problem, in which the spacecraft motion indicated an
unknown gravitational influence, is solved. Just uneven heating.
No planet X, no dark companion, no DeathStar. No aliens. But we
Back on Earth, the Large Binocular Telescope (too bad not the
Binocular Large Telescope, as then we could have had the BLT) saw
first light last January with its twin 8.4 meter mirrors, which
together give the light-gathering power of an 11.8 meter telescope
and, as an interferometer, the resolution of a 22.8 meter.
We tell all, "don't look at the Sun." Right now there is not even
much point. There have been preciously few spots for over a year.
Are we seeing just a long wait for the new cycle, or are we
entering a new Maunder Minimum, wherein the lack of spots between
1645 and 1715 coincided with the Little Ice Age? That would
certainly counter global warming. If so, though, we'd best prepare
for when the cycle roars back. More mystery resides in the corona.
In spite of unprecedented space imagery and measurement, we still
do not know how the solar magnetic field heats the gas to such high
We commonly define the "Solar System" by the extent of the
planetary system, which stretches to 30 Astronomical Units, 40 if
you count Pluto. It's more accurate, however, to include the
Kuiper Belt of comets, which takes us to 55 AU or greater. Another
definition involves the domain of the solar wind, which we are
starting to breach. At a distance of 84 AU, Voyager 2 went through
the "termination shock" (where the wind goes subsonic as it pushes
against the interstellar medium), a lesser distance than for
Voyager 1, which was 94 AU away. The system is clearly flattened.
We hope the Voyagers' power supplies last long enough for them to
hit the heliopause, where the wind finally slows a halt.
More here than usual. Long before it reaches the heliopause, the
solar wind slams past Earth, it and the solar magnetic field
seemingly carrying echoes of the five-minute solar oscillation.
There is evidence of its imprint on undersea cable and cell phone
communications. The effect -- if real -- is the ultimate subtlety
in solar-terrestrial relations.
It's nothing compared with the whammy from the asteroid belt.
Celebrate then the centenary of the mighty Tunguska impact, whose
energy has been downgraded to a "mere" 3 to 8 megatons. (Celebrate
more that it has not happened again!) That number of course pales
in comparison to the K-T impact of 65 million years ago, the one
that took out the dinosaurs. Orbital simulations (that include the
"interplanetary superhighway," along which planets can toss things
around in a predictable way) suggest that the impactor was a chip
from the 198 Baptistina asteroid family (the main belt asteroid
itself roughly 20 km in diameter and a piece of a once much larger
In a triumph of measurement, the GRACE polar satellites have
measured the geoid (the Earth's real shape) to a precision of one
centimeter, which allows us to see the rebound of Greenland from
the glacial pressures of the last ice age.
Our oxygen isotopes do not match solar or meteoritic values.
Nobody knows why. But at least the "faint young Sun" paradox may
be resolved. At the time of solar birth, the Sun is calculated to
have been only 70 percent as bright as now. How could life have
begun on a frozen planet? Perhaps by greater solar magnetic
activity caused by youthful fast rotation, or -- as posed recently
-- by an increased carbon dioxide content and greenhouse effect,
the new work finding that less CO2 is needed than once thought.
... and Moon
Water on the Moon or not? Ice at the poles, ice not at the poles,
back and forth. Well, water has finally been found in microscopic
amounts in glassy regolith from Apollo 15. So drink up. Then its
on to the planets.
With the January and October Messenger flybys (needed to slow the
craft down for orbital insertion in March of 2011), Mercury finally
takes top billing. We see heavy cratering set within volcanic
plains and mysterious radial cracks ("The Spider") at the center of
the Caloris Basin, which seem to come out of a large crater at dead
center (the latter likely coincidental). At just over 1500
kilometers diameter, Caloris is 20 percent bigger than thought.
There is an argued possibility of Mercurian meteorites blasted off
the surface. But that is nothing compared to the calculation that
there is a 1-2 percent possibility that Jupiter could so change the
orbit that whole dang planet could hit us. Fortunately, that would
be long after the Sun, expanding as a red giant (5 billion years
hence), vaporizes it. And maybe us as well.
Lightning on Venus? So suggests static observed by Venus Express,
and originally indicated by the old Soviet Venera craft. New
simulations show that our Sister Planet could have had oceans for
its first two billion years. And thus maybe life. But all
evidence for Venusians (whatever form they might have taken, if
any) would have been destroyed by the planet-wide volcanic turnover
that took place within the past billion years, not to mention the
effect of the runaway Venusian heat.
Mars merits a book. Indeed, several books. So we will note just
a few returns from the red planet. The Recon Orbiter sees huge
holes, caves hundreds of feet wide, of unknown origin or depth,
plus active avalanches across a kilometer-wide scarp and evidence
for long-gone glaciers and clays in ancient river deltas. But
there is a suggestion that early Martian water was just too salty
for life. Back to now, is there a more dramatic picture than the
one that spotted the Phoenix Lander coming down under its
parachute? It then gave us a magnificent view of the northern
Martian plains and more evidence for ice. And then Move Over
Mercury, as Caloris pales beside the "Big One." The Martian
hemispheric anomaly (volcanos, plains, in the north, cratered
highlands in the south) can be explained by a 10,600-kilometer-long
"crater" in the north caused by an off-center sideways collision
with a 1900-kilometer-wide impactor some four billion years ago
that ripped off part of the Martian crust.
Well, not really. Jupiter and Saturn are mostly liquid molecular
hydrogen, whereas Uranus and Neptune contain not only H and He but
a lot of water and other volatiles such as methane and ammonia.
All of a sudden Jupiter had not one, but three red spots. But the
GRS is eating the others. No wonder it's so big.
Saturn's ring system seems to have a lot more heft than thought,
some three times the "old" mass and about triple that of Mimas.
It's mostly the moons that make the press, though, topped by
Titan's huge northern methane lake the size of Superior, with
tributaries and all. The satellite's rotation suggests a 100-km-
thick crust floating on a warmer ocean, reminiscent of Europa.
Then we can't seem to get enough of the "tiger stripes" and the icy
geysers of Enceladus. Not only have the geysers' origins been
seen, but Cassini flew right through them, revealing relatively
high temperatures and a complex mix of water and carbon compounds,
all possibly the result of tidal heating. The phenomenon suggests
subsurface liquid water. And Rhea's got subtle debris rings, the
first satellite known to have them. Don't believe in "flying
saucers"? You will when you see the nutty shapes of some of
Saturn's small moons, which exchange particles with the rings,
suggesting that the rings might not be as young as thought.
Speeding along past Uranus, we arrive at Neptune, whose south pole
is weirdly hotter (10 K out of 60 K average) than the rest of the
planet. Watch out for the resulting strong winds.
Pluto and the Iceballs
Comets, that is. And none captured attention like Comet Holmes.
The thing is in a modest 6.9 year period with a perihelion of 2 AU.
Who would expect an outburst that raised it from 17th magnitude to
3rd (an increase in visual brightness of a factor of more than a
quarter million), whereupon it became an important modifier to
Perseus (and a seeming threat to Alpha Persei!). It did the same
thing in 1892. Nobody knows what could trigger such an event.
Among the best iceballs of the past century, though, was Comet
Hale-Bopp, which came to us from the vast Oort Comet Cloud and
brought so many out to look. Even though it is now 26 AU out from
the Sun and 20th magnitude, it's still puffing a coma. The stuff
that the Stardust spacecraft returned from Comet Wild 2 adds to
cometary mystery by revealing olivine, suggesting that comets -- at
least some comets -- may not have formed so far out as thought.
Circulating among the comets in the Kuiper Belt is our "last
planet," Pluto. Now comes along another near-Pluto-sized body,
Makemake, touted as the next Plutoid. NOOOOOO, don't let that
awful word catch on! Pluto, the first body of the Kuiper Belt, is
to my mind an "honorary planet" if nothing else. We'll know more
when New Horizons (which has passed the orbit of Saturn) gets there
in 2015. (That's only 7 years from now, about a third of the time
I've been doing the GLPA Updates.)
Winter's coming, and so is the Orion Nebula. We have a new and
improved distance from parallaxes of related small radio sources as
found by the Very Large Array, which give 1350 light years good to
2 percent. I've had it at 1400 l-y, not bad. The Nebula is now
seen as an ionization blister on the front side of the huge and
very dark Orion Molecular Cloud, which lies in back of it, the
ionizing radiation coming from the hot stars of the Trapezium
(notably Theta-1 Orionis C). While the "OMC" is rich in molecules,
the best place to find them is the "Heimat Source," Sagittarius B2
North, near the Galactic Center. Radio astronomers have now found
it to contain acetonitrile (NH2CH2CN), a possible precursor to
glycine (which was once discovered, then undiscovered). The total
number of interstellar molecules is closing in on 150, and there
are far more when isotopic variations are included.
Among the most exciting discoveries since Galileo is the existence
of other planets, and even planetary systems, around other stars.
They are topped by 55 Cancri (a sixth magnitude G8 dwarf), which
has (at least) five planets. The biggest news is the lowering of
planetary masses into the realm of "superearths" as a result of
dramatically improving technologies. The smallest in the 55 Cancri
system carries only 11 Earth masses, while HD 40307 in Pictor has
three such planets, the lightest of which carries but 4.2 Earth
masses. It goes around its star in 4.3 days. And you think summer
speeds by HERE. The current record is 3.3 Earths (in Sagittarius)
for a planet found through gravitational lensing.
Going up the mass scale from planets takes us into the realm of the
brown dwarfs, "substars" that cannot run the proton-proton fusion
chain (though above 13 Jupiters they can fuse their natural
deuterium.) At the low end it's difficult to tell these from
planets, though planets are presumed to accumulate from proto-
stellar disks, while brown dwarfs collapse directly from
interstellar clouds. Or not. Remember that the spectral sequence
is now OBAFGKMLT, where class M has a few BD's, class L lots of
them, and ALL of class T is made of the little guys. We now have
new, and lowest, brown dwarf masses for a T5.0/T5.5 binary of
0.029/0.027 solar masses, far below the 0.075 solar mass fusion
cutoff. Each running about 1000 Kelvin, they are "visible" only in
the infrared. But that's nothing compared to a new low record
temperature of 620 Kelvin (657 degrees F, lower than your self-
cleaning oven) for a star that seems to have ammonia bands and has
been touted as the first of a proposed new and cooler spectral
class Y (though it is more likely very late T).
Climbing the mass-mountain even higher, we arrive at real stars.
Among the more interesting news notes is the re-determination of
the Hipparcos parallaxes by Floor van Leeuwen, resulting in
improved values and lower errors, especially for very distant
Then there are various odds and ends that show fascinating progress
in stellar techniques and research. Going more or less from lower
masses on up, we encounter, for example, BO Microscopii, a K0 dwarf
145 light years away in which Doppler imaging (from the changing
shapes of spectrum lines as the star rotates) actually revealed the
location of a stellar flare. More dramatic is EV Lacertae, a red
dwarf that popped a global flare that brightened it from 10th
magnitude to a naked-eye fifth! So much for life and sunbathing
under red dwarf skies. How would you like to see the Sun suddenly
100 times brighter! And since today is Halloween, we have to say
"BOO!" Tau Boo that is, a class F6 dwarf/subgiant with a hot
Jupiter, for which the stellar magnetic field was found to reverse
-- rather like it does in the Sun.
Much higher on the mass scale we find familiar Regulus. Long known
to be a wide double (triple, really, as its distant companion is
also binary), we now see that it has a white dwarf companion with
a 40-day orbital period, making it a quadruple star. Mass transfer
from the evolving close companion to Regulus proper is suggested as
the source of Regulus's rapid rotation and (as a result) its
clearly oval shape (though there is nothing unusual about the rapid
rotations of B stars).
White dwarfs evolve from stars with initial masses under 8 to 10
solar, and they are found in abundance not just in the general
field, but, as expected, in clusters as well. A search for the
oldest open clusters leads to an age for the Galactic disk. Among
the oldest open clusters is NGC 6791 in Lyra. All the stars of a
cluster are presumed to form at the same time. But two different
sets of the cluster's white dwarfs give ages of 4 and 6 billion
years, whereas the rest of the stars give 8 billion. Something is
amiss, probably with the theory. If it's with the cluster, we
clearly have an interesting problem to solve.
R Coronae Borealis stars are a collective form of carbon star
without much in the way of hydrogen envelopes. The prototype, R
CrB (a G0 supergiant), will suddenly drop from 5th magnitude to as
dim as 15th as a dust cloud is ejected along the line of sight.
Now we've confirmed the scenario by actually seeing such a cloud,
compliments of RY Sagittarii. Of mysterious origins, R CrB stars
may result from the mergers of double white dwarfs.
Are you ready for Epsilon Aurigae, the northernmost of Auriga's
Kids? Every 27.1 years, a mysterious immense cloud that seems to
surround an internal star or stars eclipses a class F0 supergiant,
which is quite a feat. The next event begins in August of 2009 and
lasts until May of 2011, during which time the star dims by nearly
Then look to the north for another supergiant, Polaris, the
brightest Cepheid variable in the sky. Not that you would notice,
since the amplitude of variation shrunk in the 20th century to
almost nothing. We thought the star was converting itself from a
first overtone 4.0-day pulsator to a 5.7-day fundamental mode, but
no, the amplitude now seems to be increasing, making us all wonder
what is going on. A much fainter Cepheid, RS Puppis, had its
distance accurately measured at 6500 light years using the echo of
its light from its surroundings. Such measures are deeply
important in calibrating Cepheids for their use as primary distance
And are you ready for the coming variation in the grandest of all
hypergiants, Eta Carinae? Every 5.5 years an unseen companion
makes rather a mess of the Eta Car's wind, spectrum, and X-ray
radiation as it loops past its periastron. Keep watch in January
of 2009 (though you would need to go to the southern hemisphere and
have a lot of fancy equipment to do it). This magnificent star is
always worth watching. Around 1840, Eta Car erupted to become the
second brightest star in the sky after Sirius as it released a vast
cloud now seen as the famed Homunculus. Shining near 5 million
solar luminosities, it is a prime candidate for a supernova, or an
even greater hypernova.
We look at other galaxies to see active "starburst" star formation.
But it's here too, as observed by Hubble in the spectacular open
cluster/nebular complex NGC 3603, which lies 20,000 light years
away in the Milky Way in Carina. Just two million years old, the
cluster is loaded with class O3 and already-evolving Wolf-Rayet
stars, which have stripped their hydrogen envelopes, allowing us to
see by-products of nuclear fusion. (The nitrogen-rich variety is
supposed to precede the carbon-rich, but in a nearby galaxy, IC 10,
the former are mysteriously missing, suggesting we do not
understand such stars all that well.) Measurement of a binary in
the cluster gives us the most massive star known to date, 115 solar
masses, topping the old value of 85 (and close to the old predicted
maximum of 120). Such massive stars may need the heat from less
massive "helper stars" to allow them birth, which means they can
form only in clusters. This connection is supported by the
Galactic motions of a large fraction of field O stars that take
them back to their parent clusters. The best known of these is the
second magnitude class O star, Zeta Puppis, which left a cluster
called Trumpler 10 two and a half million years ago and is now some
8 degrees away from it.
Supernovae and their Leavings
Along with Eta Car, NGC 3603's O and WR stars are destined to
develop iron cores that collapse into neutron stars or (in the case
of the highest mass stars) into black holes. The remainder of the
star is then blown apart in a grand supernova. A first: the SWIFT
gamma ray burst telescope spotted the initial X-ray burst from
Supernova 2008d in the galaxy NGC 2770 (88 million light years
away), the first such observation ever.
A couple years ago, we introduced "RRATS" (Rotating Radio
Transients), that can temporarily become the brightest known radio
sources in their 0.1 to 1 second bursts. They are apparently
another form of neutron star, whose variety boggles the mind. And
now we have accurate measures of neutron star dimensions from
relativistic effects on hot circumstellar X-ray emitting gas,
placing them, as expected, in the range of 29-33 kilometers across.
Then it's back to the galaxy IC 10, which contains an eclipsing
binary that tells of the largest known stellar black hole,
estimated at 24 to 33 solar masses.
Core-collapse ("Type II") supernovae are almost always exceeded in
their power by the Type Ia variety, caused when white dwarfs are
forced to go past the Chandrasekhar "degeneracy" limit of 1.4 solar
masses and then flame out in gigantic nuclear bombs. There are (as
seemingly always) two possibilities: overflow onto a massive white
dwarf from a binary companion, or the merger of two white dwarfs.
The first is the more accepted, but now we have good evidence from
the spectrum of ultrabright supernova 2006gz of the merger
scenario. Probably it's both, and it's important to understand
because the Ia SN's are used as the principal distance indicators
in demonstrating the acceleration of the Universe.
At the top are the GRBs, which are (we think) caused by high mass
hypernovae, which, because of their increasingly fast rotation as
they collapse, produce focused bi-polar bursts of gamma rays.
These in turn light up their surroundings in visual "afterglows."
That from GRB 089319B hit an all time record of visual magnitude
5.4 even though 7.5 billion light years away! All things being
equal (which of course they are not), the absolute magnitude must
have been around -35. Don't get too close. Eta Carinae may blast
out an energetic GRB. The rotation axis, however, happily points
Well, just one. Hubble spotted a transient that went from fainter
than magnitude 26 to 21 in 100 days, then disappeared. We have no
idea where to place it within this presentation, so it might just
as well go here.
Galaxies, Including Ours
The Spitzer infrared space telescope's observation of 110 million
stars resulted in yet another, but greatly detailed, map of our
Galaxy, clearly revealing its central bar. Yes, we are a barred
spiral (a concept that goes back at least 40 years).
Galaxies build themselves up by mergers. We see, for example, the
Sagittarius dwarf now passing through our own. The great globular
cluster Omega Centauri seems to be the stripped core of a long-
since merged small galaxy, and apparently contains a middling
central black hole of some 40,000 solar masses. (Even the Large
Magellanic Cloud, which we are tidally tearing apart, may have one.
A hot star shot out of the LMC at 1000 km/s can be explained by a
binary star being disrupted by passing a 1000 solar mass black
hole.) There is also evidence that the mergers of spiral galaxies
can create ellipticals. Will that happen to us if and when the
Andromeda Galaxy hits us? Even multiple events can take place,
Spitzer showing four distant galaxies merging at once within a
It's standard dogma that stars form within a galaxy's dense spiral
arms. But apparently not always. We find stars being born also
within thin, tidally-formed streamers. In the magnificent spiral
galaxy M 83, star formation extends to vast distances out, more
than five times distant from the center than the "edge" of the
visible disk. But don't expect life. The low metal content of
these outlier stars leads to excess ionizing radiation, which kills
off interstellar molecules (as observed in M 101). That is, if
interstellar molecules really have anything to do with life. And
close to the center, we have too many supernovae, resulting in an
intermediate ring that may be friendly to life forms. The bulges
of spiral galaxies correlate with the masses of their central black
holes. And now, so do the pitch angles of the spiral arms. Once
more, nobody knows why.
BL Lacertae does it again. Once thought to be a variable star
(hence the name), it's a quasar (now known to be a galaxy's central
black hole) with one of its bipolar jets pointing right at us,
which gives the light a relativistic boost. An ejected blob shows
that twisted magnetic fields really do power the jets. And it's
hard to ignore OJ 287, in which an orbiting star points to a
central black hole of an amazing 18 billion solar masses.
Finally, out there in the great distance, more than 10 billion
light years away, are ultradense galaxies that carry our Galaxy's
mass but measure only a few percent of our size. No one knows yet
what to make of them or how they fit in.
Dark Matter, Dark Energy, and Everything Else
We still do not know what the two "darks" are, though observations
continue to point to dark matter as WIMPS (weakly interacting
massive particles). From Hubble and the Chandra X-ray observatory,
we see the results of yet another collision of galaxy clusters in
which the normal matter is stripped and radiates X-rays, while the
dark matter, whose distribution is given by gravitational lensing
of distant sources, just sails on along with the parent clusters.
In the last category, further analysis of the Wilkinson Microwave
Anisotropy Explorer (WMAP) observations of the variations in the
cosmic background radiation produced by the Big Bang lead to an age
to the Universe of 13.73 billion years, a Hubble constant of 70.1
kilometers per second per megaparsec, a baryonic (normal matter)
contribution to the mass-energy of the Universe of 4.6 percent,
dark matter and dark energy respectively coming in at 23 and 72
percent. Numbers may vary, depending on what set of observations
one uses. The message, though, is clear. We don't understand 95
percent of it all.
Such is the excitement of our field. We never know what is going
to turn up with the next observation. We may solve these problems,
we may not, but if we do we'll surely encounter more. It's been an
exciting and fun ride along the GLPA trail. Thank you for
everything. Paraphrasing Edward R. Murrow, "Good Night and 217-
555-1212," we end with a lovely sunset that will surely turn for
both of us into a golden sunrise.