ASTRONOMY UPDATE 2007
James B. Kaler
Department of Astronomy, University of
First published in the Proceedings of the 43rd Annual GLPA
Conference, Wheeling, WV, October 9-13, 2007, reprinted by
The year was led by Cassini's Saturn and methane-filled Titan, as
well as by Hubble, which will indeed get its repair (if all goes
well) in 2008. And let's not forget the Rovers' Mars, on which
the little guys continue to roam and discover. Plan on parties
for Uranus's equinox on December 7, and for new views of Pluto in
2015. Pluto gets a minor planet number, but so too does Eris.
Our planets and their debris remind us of the remarkable number
of discoveries that bring the exo-planet count to 255 (and
counting) that include a five-earth-mass measure. Brown dwarfs
continue to fall from the sky, Altair now has an actual image,
and a record super-supernova lit someone's distant sky. At least
we do not have to be so afraid of a nearby gamma-ray burst. Dark
matter is more real than ever, while we can now make out some
structure in the time-history of dark energy. Huge surveys also
begin to show us not just the nature of the Universe, but our
place in it as well.
Though most passages are quick, others, like that of the Yerkes
Observatory, seem to linger over the years. Now the deal with
the developer (to whom the University of Chicago wanted to sell
it), who was to maintain the Observatory as an educational site,
fell through. Check back with these pages in 2008. The end of
the story did, though, catch up with the Mars Global Explorer,
which passed away to that great orbit in the sky as a result of a
Now a piece of space junk, the MGS, is at least not orbiting OUR
world, where debris is becoming a serious problem. Collision
with even a small bit of the dregs of the space age moving at
orbital speed can cause massive damage to a live satellite, let
alone an astronaut. The Chinese government did not help the
situation by destroying one of their own satellites, the mess
from which added mightily to the danger. One hopes nobody else
will try a repeat. It reminds one of the ancient Air Force's
circa-1950 Project West Ford, in which it was proposed to launch
500 million copper needles to act as a global radio reflector.
Hare-brained schemes are nothing new.
But all is not lost, indeed far from it. The infrared
observatory SOFIA (built into a Boeing 747), though years behind
schedule (the FAA seems to think that flying a plane at 40,000
feet with a huge hole in its side is unsafe), finally flew, and
should be ready to make observations from the optical through 65
microns before long (in dog years). The best news, though, is of
Hubble, which is to be serviced next year and outfitted with new
cameras, gyros, batteries, coverlets, and so on, in the most
complex Hubble repair mission yet. It's a "go" now for perhaps
To the rebirth of Hubble add two real births that involve our own
The Japanese satellite "Hinode" ("Sunrise") has risen to observe
the Sun in the X-ray spectrum, where so much energetic action
takes place. STEREO goes "one better." The observatory consists
of TWO satellites that lead and follow Earth in orbit and that
can then observe Sun and solar activity in three dimensions.
While we are now within a long "sunspot desert" (nothing seen
from August through at least mid-November of 2007) at the low end
of the solar cycle, we did catch one flare last December that
literally rocked the Sun as it sent a "tsunami" of massive
proportions skimming around both sides of the solar sphere. Keep
a watch, as the next cycle is on its way (remember the naked-eye
pair of 2003?). It's predicted to be a whopper. Then let the
Sun set, allowing us to admire
Not only does one face now point at the Earth, but it has odd
bulges on it too. Rotation alone (before it became tidally
locked to us) can't do it, but a once-high eccentricity might.
Closer to us in the astronomically distant past, the tides raised
by each upon the other must have been highly variable humdingers.
And here we go again with "ice" in shadowed craters at the lunar
poles, where it is presumably mixed with the lunar regolith.
Water ice has been discovered, undiscovered, and discovered once
again. Now it's the undiscoverer's turn, wherein the ice does
not show via radar reflection. Then again, who knows at this
point. One thing for sure has been some sort of volcanic
outgassing from crater Ina. Those who were once derided for
seeing "flaring" on the Moon have been vindicated. We've even
seen impacts from Leonids. Things DO happen there.
As they do here and on our brother/sister rock-balls. Mercury
leads us with more proof of a liquid iron interior. By rights,
the huge iron core, which contains 60 percent of the mass, should
be frozen, the result of small Mercurian size. Yet there is a
magnetic field suggesting a fluid core. Radar observations of
the planet's librations reveal the same thing. The core is
probably "polluted" with something, sulphur perhaps, to maintain
at least a slushy state. And let's hear it for last November's
great Mercury transit.
Venus's nighttime side has long been seen to glow with the
controversial "ashen light." It really does glow, though, in the
infrared, with light from the recombination of atomic oxygen into
molecular form, the O-atoms separated from their molecules by
sunlight on the other side. More dramatic may be an explanation
for the planet's backward rotation, which may have been the
result of a pair of impacts that created two moons, one of which
escaped, the other of which crashed into Venus and reversed its
spin. Best idea so far. If you don't like ad-hoc collision
hypotheses, just look at the huge basins on Mercury, the Moon,
Speaking of which, someone could write a book on Mars. And they
have. More than one. Someone could write a book just on the
Mars Rovers, which have now exceeded their 90-day design lifetime
by a factor of nearly 15. You'd like your car to do that, though
you would have to drive in the slow lane. All we can do here is
sample the news. The smoother northern hemisphere, which appears
so different from the cratered southern, may not be so divergent,
as lots of buried craters are being noted. The most amazing
thing (among many amazing things) might be fresh running water,
evidence for which lies in a crater-wall gully observed in 2005
that was not there in 2001. Magma intrusions make the planet
even more earthlike. Except of course, for any evidence for
That leaves us, our Earth. Plenty of life here, and it's having
an impact by continuing to warm our planet through carbon dioxide
(and other) emissions. Summer arctic waters are in massive
retreat, as are glaciers. "Global warming" seems to mean
intensification of storm systems. And possible further
humidification. But studies seem to rule out any sort of
variable solar luminosity.
As big as Earth storms are, they pale beside those of the "big
guys." Last year Jupiter's "Oval BA" turned itself into "Red
Spot Junior." Though roughly a half the size of the Great Red
Spot itself, RSJ is as big as Earth. Passing to the south in
2006, RSJ hailed its bigger brother without destruction, and it
was still kicking in 2007 when New Horizons took a shot at it.
The origins and colors of such spots are not understood.
Saturn is the outer "new Mars," not in terms of form, but as a
result of massive information flow from passing and orbiting
spacecraft. Cassini has simply transformed what we know about
the planet and its satellites, enough for more books. A sampling
is all we can do. The famed "spokes" in the ring system observed
by the Voyager craft may be the result of electrical charge
induced by lightning in Saturn's cloudy atmosphere. The rings
are flat enough to disappear when edge on: not true, though, of
the D ring, which is rippled, the likely cause of which was an
impact with a small body a dozen or so years ago. A spectacular
image taken with Cassini in Saturn's shadow, the planet eclipsing
the Sun, revealed a distant Earth and Moon. The backlighting and
resulting forward scattering of sunlight allowed the detection of
very faint rings associated with the satellites Janus and
Epimetheus at respective distances of 151,000 and 212,000 km.
Light scattered from the rings is so bright that it lights
Saturn's nighttime side.
Speaking of satellites, Saturn is up to 56 (not counting ring
particles!), Jupiter to 63. And it is the satellites that are
getting the press. The nitrogen-ammonia geysers of Enceladus are
spraying from the "tiger stripes," which seem to be faults.
Tidal flexure makes them rub against each other to produce the
needed heat. Tethys and Dione also seem to be ejecting gas into
Saturn's whipping magnetic field. And Sponge Bob lives! in the
form of Hyperion, on which impacts onto a very low density object
create a weird spongy-appearing terrain. That "leaves" Titan, a
subject for yet more books. Among other discoveries were a huge
cloud from which methane may rain, a low mountain range that may
be like our mid-Atlantic ridge, a northern methane lake district,
a lake that outranks Superior, sand dunes, and a probable
"hydrological cycle." It's enough to wear one out.
On now to Uranus and party time, as the planet will see the Sun
crossing its celestial equator next December 7. Voyager 2 saw
only a drab cloud deck when the Sun shone overhead near the south
pole, but as the Sun (from the planet's perspective) crept toward
its equinox, Uranus has developed wonderful weather patterns and
"storms." Since there is "nothin' for Neptune," we move on to
Pluto and the KBOs
In spite of its new minor planet number 134340, most of us will
remain calling the little body the "ninth planet." Sure, Eris
(136108) is larger, and from Hubble observations of its
satellite, 1.27 times more massive. But it's also a lot farther
away (90 AU) and a lot fainter. Pluto indeed is a member of the
Kuiper Belt of debris out beyond Neptune. Traditionally, Pluto
has been a planet, and given its terrific importance as a
transition body, surely can remain so, at least in our minds.
We'll know more about it when New Horizons gets there in 2015.
An eighth of the way out, the craft passed Jupiter and (as we saw
above) took a good look at the colorful cloud belts and the dusty
ring, which appeared greatly enhanced when backlit by the Sun
(which allows for further exploration of particle size). Even
Charon got into the act with the discovery of watery
The Kuiper Belt extends more or less between 30 and 50 AU from
the Sun. More than 1000 Kuiper Belt objects are known, and it is
estimated that there may be 70,000 with diameters of at least 100
Discussion of the Kuiper Belt of course leads us to comets, as
the Belt is the source of those comets with periods under a
couple (or a few) hundred years. We've found that far from being
monolithic, comets show great diversity. From observation of
Deep Impact debris, we see processed matter: carbonates and
clays. The return of "comet stuff" by the Stardust craft shows a
body in which some 10 percent seems to have been formed under
high-temperature conditions. If so, the finding supports the "X-
wind" hypothesis, in which meteoric chondrules were heated near
the primitive Sun and then flung outward in part through magnetic
interactions with the inner solar nebula. Comet McNaught was
great if you could see it. I didn't. (We'll do the
extraordinary Comet Holmes next year.)
All of the above came from "out there," when the Sun was birthed
from an interstellar cloud. Hubble's 17th anniversary picture
was a fabulous 48-image mosaic of the amazing Carina Nebula, in
which star formation and death go on at a frantic pace. At the
head of the class is Eta Carinae, a binary that is among the most
massive in the Galaxy and whose stars may be candidates for the
creation of deadly gamma ray bursts (but see below) and black
Contemplation of the interstellar medium brings us to the
discovery of another eight interstellar molecules in Sagittarius
B2 (the "Heimat [home] Source") near the Galactic Center. The
count of all molecules everywhere, including isomeric variations,
is up to 141. Not bad considering that the number was TWO when I
was in grad school.
Another, though smaller, source is the Orion Nebula, whose
distance (derived mostly from the assumed luminosity of the
Trapezium stars) has long been somewhat uncertain. Radio
parallaxes of young embedded T Tauri stars (stars in formation)
nails them at 1350 light years (the nebula a bit farther than the
stars), very close to the 1400-1500 light years generally
adopted. The radiation from "killer O stars," like the one that
lights Orion's nebula, and this year in IC 1396 (as seen with the
Spitzer Space Telescope), acts to destroy the protostellar disks
of lower mass stars. Don't expect any planets from stars born in
One of the more contentious star-formation problems involves the
creation of binary stars. The old idea that stars bifurcate
through rotation is not correct. Binaries may come from
fragmentation of the collapsing cloud, multiples from
fragmentation of disks.
As Mars and Saturn are to their respective planetary groups, exo-
planets are to stars, as there is so much new that we can but
sample. As of October of '07, we've found a total of 255
planets. The main radial velocity technique has uncovered 242
planets in 207 systems that include 25 multiple planet systems.
From transits we get another 28 planets, including 16 that Hubble
nailed in one small area in the Galactic bulge.
Records fall every year. This year we get a "super-earth" of
five (at least) earth masses orbiting the class M3 dwarf Gliese
581c every 12.9 days at a distance of 11 million km. Sandwiched
between two other planets, (Gl 581b: 5.4 days, and Gl 581d: 83.6
days, the star itself Gl 581a), "c" may be in the life-giving
liquid-water zone. Unfortunately, M dwarfs tend to be flare
stars, which would not help life along very much. Oddly, M
dwarfs with planets seem to have LOWER metal abundances than
solar, rather than the usual higher metals as seen for more
Then there are the puffy planets that are too large for their
masses, planets in which hot spots are detected through infrared
radiation, and famed Epsilon Eridani, for which a combination of
radial velocity and proper motion variations show an orbital tilt
similar to that of the dusty disk, firmly tieing planets and
Planets lead us on to failed stars, brown dwarfs with masses
under about 0.075 solar, which are too small to fire
thermonuclear fusion of hydrogen to helium via the full proton-
proton chain. Their bottom limit is assumed to be 13 Jupiters,
below which even deuterium will not fuse, but nobody knows, and
they may well overlap planetary masses (planets forming from
dusty disks from the bottom up, stars forming top down directly
from interstellar clouds. Maybe).
Remember now that it's OBAFGKMLT. Gimme an "O" and all that.
Young brown dwarfs may appear at first to be in class M, and then
cool through L. All the T stars are BD's, the record for which
is but a few hundred Kelvin. And there are a lot of them. There
may be as many class L brown dwarfs as there are between class M7
and M9.5. Some are in binaries, and a tiny number reside in
cataclysmic variables. (In a CV, a star donates matter drawn by
tides into an accretion disk around a white dwarf. Instabilities
in the disk cause flaring and a "dwarf nova." At the extreme,
the accreted matter can explode to create a nova.) In an
outstandingly odd case, we see an eclipsing binary with a star
whittled down to the point in which it is making the transition
Now to more familiar territory, to some things we can go outside
to see! Our local solar clone, Alpha Centauri A (in an 80-year
binary orbit with Alpha B), seems to be losing its activity,
hence its magnetic field, which is down by a factor of 80. Is
the star going through a Maunder minimum, in which sunspots fell
off between 1645 and 1715 and seem to have promoted a "little ice
age"? Alpha Cen C, the M5 dwarf far better known as Proxima,
turns out to have a solar cycle all its own of 1.2 years. Even
with a long rotation period of 84 days, it's active and a flare
Hubble has directly imaged the disks of giants and supergiants
(including Mira and Betelgeuse), and now we have an image (made
by optical interferometry) of a famed dwarf, Altair, which
directly reveals the oblateness that comes from its high rotation
speed and short rotation period of 6.5 hours. To conclude naked-
eye star news, Mira is trailing a 13-light-year long shock-heated
tail from its wind as it plows through interstellar
Then there is the nutty eclipsing double in Orion with stars of
similar mass, yet one is twice the size of the other. Nobody
knows why. And the debris disk surrounding the central star of
the Helix Nebula (NGC 7293). The hypothesis is that as the star
rapidly lost mass in the creation of the nebula, chaotic motion
in its orbiting bodies helped to stir up its Kuiper Belt,
resulting in massive collisions and debris. And the perfect "Red
Square" that seems to be a planetary nebula in formation. And a
old shell around the dwarf nova Z Camelopardalis, which strongly
indicates that it is an old nova and that the theory that dwarf
novae (see above) eventually produce real novae when the white
dwarfs accumulate sufficient mass for a surface nuclear
Clusters segregate stars according to their masses, higher mass
stars sent to the center under the force of combined stellar
gravity, lower mass ones to the outside where they can
"evaporate" out of the cluster. Further proof of mass
segregation was provided by the globular 47 Tucanae, in which
more massive "blue stragglers" have sunk more toward the
Blue stragglers are stars the lie above a cluster's main
sequence-to-giant turnoff, stars that should have evolved but
have not. They are believed to be formed by binary star merger
or even direct collision, which gives them their excess masses.
And here it is:
Poor Blue Straggler
By Ol' Jim
To be sung to a blues tune.
I'm a poor blue straggler
On the HR diagram...
I don't know where I came from
And I don't know who I am...
Oh blue...poor blue blue blue straggler...
Too high on the main sequence,
Far above the giant turn...
I should now be brightening
My helium for to burn...
Oh blue...poor blue blue blue straggler...
Born in a collision
In an ancient glob-u-lar...
Or maybe by the merger
Of an old bi-nary star...
Oh blue...poor blue blue blue straggler...
When WILL I start evolving,
My stellar mates to join...
It could be in a billion,
With this core H yet to burn...
Oh blue...poor blue blue blue straggler...
Someday though I'll get there,
Be a big old AGB,
Pop a pretty neb'la,
And end degenerately.
Oh blue...poor blue blue blue straggler...
Oh blue...poor blue blue blue straggler.
Supergiants, supernovae, superdense
The wacky variable V838 Mon, the only evolved star ever seen to
cross over into class L, still lights its surrounding nebula. In
2002, the star went from 12th magnitude to 6th, as it turned
itself into a supergiant, and by reflection (a "light echo")
illuminated a cloud of mass previously lost to the star through
its wind. V838 is not understood, but with the discovery of
another one in the galaxy M 85, it has now has a "class" as one
of two "Luminous Red Novae." (See the 2003 update.)
Massive-star core-collapse (Type II) supernovae have left their
mark in the Eagle Nebula (M 16) with hot dust revealed by
Spitzer, the hot stars carving vast bubbles. These are supposed
to be less powerful than the Type Ia supernovae (caused by white
dwarfs in binaries exceeding the 1.4 solar mass limit), with
absolute visual magnitudes of -17 to -19 as opposed to -19.5 for
the Type Ia. Imagine everyone's surprise at seeing a core-
collapse event in the galaxy NGC 1260 that hit an amazing -22.
It remained brighter than the Ia maximum for nearly a third of a
year. Could it be the first example of a "pair-production"
supernova in a supermassive 100-150 solar mass star? In such an
event, the core collapse is not caused by creation of an iron
core, but by the creation of electron-positron pairs from gamma
ray collisions that suck the energy from the core, leading to
ultimate catastrophe. The result may be total annihilation
The nature of Kepler's Star of 1604 has long been contended.
High iron and low oxygen content in the ejecta now clearly show
it to be a Type Ia white dwarf supernova, as expected from its
distance from the Galactic plane. The reality of the oldest
recorded supernova (with an estimated apparent visual magnitude
of -2), that of the year 185, has been contended too. Connection
with its remnant, RCW 86, confirms that it really happened. To
complete the supernova story, X-rays from Cassiopeia A (the
brightest radio source beyond the Solar System) reveal particles
accelerated by shocks, confirming it and other supernovae as
sources of cosmic rays.
Type II supernovae collapse (so far as we know) into neutron
stars (lower masses), black holes (in the tens of masses), or
even into nothing (for the most massive stars). Don't take any
of these limits too seriously. A neutron-star subset, the
millisecond pulsars, are spun up to rotation frequencies of more
than 700 spins per second by accretion of matter from a
companion. It seems that black holes can do the same thing, one
rotating 950 times per second as derived from the nature of the
accretion disk. The X-rays from the accretion disk have also
allowed the mass of the collapsed object in Cygnus X-1 to be
nailed at 8.7 solar masses with an uncertainty of only 0.8 solar,
confirming once again, that (given a mass greater than the
neutron star limit of about three solar) it is indeed a black
Gamma Ray Bursts
Core collapse in ultramassive stars seems to be responsible for
ultrapowerful long-duration (more than two seconds) beamed gamma-
ray bursts that more than once a day come from distant galaxies.
One in our Galaxy even thousands of light years away could cause
damage to Earth. But Hubble observations suggest that we might
be safe, since the long bursts tend to take place in low-metal
galaxies. High metals help produce strong stellar winds that
whittle down high-metal supergiants to lower masses, hence lower
supernova power. Short-duration bursts are not linked to
supernovae. That and their presence in elliptical galaxies
(where there are no massive stars) suggest that they come from
mergers of binary neutron stars (or neutron stars and black
holes). But then to cross it all up there was the long burst
with NO supernova.
The globular clusters of the outer halo have long been the oldest
things known, 12 to nearly 13 billion years old. Now we have the
oldest-known single star, which from thorium-uranium dating comes
in at 13.2 billion years. Seemingly born only a few hundred
million years after the Big Bang, the heavy element content (all
from an earlier generation of supernovae) is quite low, a
thousandth that of the Sun, though far from the lowest (which
brings the age into some question).
Our Galaxy, and all the others, is a complex system. Not only
was it apparently built from mergers, but collections of its
supernovae blow superbubbles and chimneys of gas into the halo,
from which it flows back. The nearest of these is found to be in
Ophiuchus, 100 supernovae having blown a multi-million solar-mass
bubble 13,000 light years into the halo.
Galaxies and their Clusters
While not an actual merger, some 200 million years ago, the
Andromeda galaxy (M 31) seems to have taken a hit from M 32 that
left ripples in its disk. Within clusters, individual galaxies
apparently are swept of much of their interstellar star-forming
gas from tides and from plowing through the hot intergalactic
medium. Younger, high redshift, galaxies do not yet show the
effect. Our own Local Group, not much as clusters go, is however
growing, not with forming systems but with more discoveries.
There may be as many as 50 dwarfs, though this number is far
below that theoretically expected. Faint ones seem to be loaded
with dark matter.
Active Galaxies and Quasars
The largest galaxies are centered on supermassive black holes,
some of which may reach a billion or more solar masses.
Accretion of surrounding matter leads to relativistic bipolar
flows, the most famed of which is the jet coming out of the Virgo
Cluster's M 87. If the jet comes more or less toward the
observer, it's amplified by relativistic effects, and the
counter-jet (the one going away from us) visually suppressed. M
87's counterjet has now been confirmed. The outbound flows are
so strong that they are seen to power the entire cluster with
filaments and loops that come from periodic outbursts that may
even inhibit star formation. In another instance we can see the
flow from the supermassive black hole in 3C 321 directly blasting
and bending around a neighboring galaxy. A two-year flare in a
distant galaxy revealed the central black hole to be swallowing a
star. Even our own, as evidenced by X-rays, consumed a Mercury-
mass some 50 years ago.
Mergers are a major paradigm in galaxy formation and maturation.
We even sort of see the process producing bigger supermassive
black holes from smaller ones. Ten billion light years off --
that far into the past -- is a triple quasar (quasars young,
active, central black holes). Separated by but 100,000 light
years, the trio seems to be in the act of merging to produce a
more massive black hole. We've even learned how they can align
themselves and their surrounding accretion disks so that they
actually come together rather than slinging themselves apart.
Dark Matter and Energy
It's still dark. Nobody really has a clue. But dark matter, at
least, is surely there. Colliding clusters of galaxies show that
normal intergalactic matter was stopped dead, whereas the dark
matter, revealed by gravitational lensing (in which dark matter
distorts the light from more distant galaxies), stays centered on
the clusters. Another huge ring of dark matter may be the result
of yet another cluster collision, and seems to represent a DM-
ripple much like a stone dropped into a pond. Using lensing,
Hubble (with X-ray observations from XMM-Newton) even produced a
three-dimensional dark matter map of two trillion solar masses
that stretches from near here to halfway back to the Big Bang and
reveals increasing clumpiness with time.
Dark energy (if real, as some think it can be explained by
messing with gravitational theory) is accelerating the expansion
of the Universe. Observations of distant Type Ia supernovae show
that it goes back at least 9 billion years and took over from
gravitational deceleration 5-6 billion years ago, shortly before
the Sun was born.
The Whole Thing
Great distances pose anomalies and puzzles. Did Spitzer find the
earliest objects, the mysterious Population III stars that were
the first to come along? Spitzer's puzzling objects may also be
accreting black holes. A redshift of between around 6 (age of
Universe 900 million years) and 7 to 8 (700 million years) may be
some sort of great divide, as there are many mature galaxies at
the 900 megayear mark, but far fewer at earlier times. And of
course there is the usual redshift record, up to 10 (a Universe
only 500 million years old), using galaxies brightened by
Far out we do go. The Sloan survey now has 60,000 giant
elliptical galaxies mapped to a distance of five billion light
years. Farther yet, we see a huge void 6-10 billion light years
away and a billion light years wide, in which there seems to be
nothing, the void appearing as a dark spot on maps of the Cosmic
At the end of story is AEGIS, the "All-Wavelength Extended Groth
Strip International Survey" (whatever would we do without
acronyms?). It's a 150,000-galaxy, 1.1 X 0.15 degree, panorama
that takes us back to eight billion light years. In a different
broad panoramic sense, we are one of them, as we can see what we
were ourselves only a few billion years after our galaxy formed,
giving us yet another dramatic glimpse of our place in the beauty
of our wide-ranging and still-mysterious Universe.