2011
Department of Astronomy, University of
Illinois
Mixed Beginnings
We start with a disturbing note, that the long-awaited James
Webb Space Telescope (formerly the Next Generation Space
Telescope) might be scratched by Congress. There are large
cost overruns that are draining the NASA budget. It's in line
with the decline of the whole space program, as evidenced quite
publicly by the end of the orbiting Shuttle flights. We still
hope for a JWST launch in 2015.
On the plus side, the historic horn antenna used in the discovery
of the Cosmic Microwave Background (the fireball remnant of the
Big Bang) has been restored. Better yet, SOFIA, the
flying high-altitude infrared observatory,
has taken its first science data. Just as good, the WISE
("Wide Field Infrared Survey Explorer") has released its first
data set. In the first year of observation, it discovered 20
comets and 33,000 asteroids, and has since plotted a fine map of
the infrared sky. More obscure, Gravity Probe B has found
the appropriate evidence for spacetime distortion and frame
dragging.
The Sun
The sky is of course dominated by the Sun, which is now being observed by a
new 63-inch telescope at the Big Bear observatory in California.
The largest of its kind, it is also equipped with adaptive optics
to produce spectacular images. Space imagery both adds and
supplements. SOHO keeps going, STEREO is a marvel,
and the Solar Dynamics Observatory has been wildly
successful.
Sunspots are related to solar meridional flows, which slowed
during the last maximum and supposedly led to the great "sunspot
desert" of the last minimum. The prediction of a weak next peak
did not seem to come true, as the Sun has been pretty active.
There is some indication from weakening magnetic fields and
large-scale solar gas motions that we might be approaching a new
"Maunder Minimum" of the kind in which sunspots disappeared
between roughly 1645 and 1715 and is associated with a "Little
Ice Age." (Not everyone agrees. The period of cold weather has
also been ascribed to intense volcanism.) In any case, it seems
that anyone who predicts solar behavior is usually wrong and in
for a big surprise.
Ourselves: The Earth...
Water: something of a theme that streams through this account.
Water was (and is) thought to have been brought to Earth by
crashing comets shortly after Solar System formation. But Ceres,
the largest (and first discovered) of the asteroids, is best
understood by presuming a layer of internal ice, so maybe
crashing asteroids brought a lot of the wet stuff too. Impactors
may well have also brought us heavy metals that are incorporated
into the terrestrial surface, as earlier stuff would have sunk
(and did sink) into the interior.
Earth is hardly isolated. Cosmic Rays (presumably from supernova
explosions) may in part be responsible for triggering lightning.
Looking down, the Fermi Gamma Ray Telescope found that
thunderstorms can create antimatter and gamma rays that are
probably linked to upward "sprites" associated with lightning and
first seen by airplane pilots.
And oh, Earth not only has its own satellite (the Moon, see the
next title), it also has its own asteroid, a "Trojan" stuck in a
gravitational "well" 60 degrees ahead of us in orbit. Welcome
aboard. At least it can't hit us.
...and Moon
We are finally coming to grips with the structure and origin of
the Moon. The latest reasoning
has it rather like Earth, with a molten iron core 350 km in
radius, with maybe a solid core inside and a 60-80 km crust that
is (and has long been known to be) thinner on the near side (that
facing Earth) than on the far side. Almost all agree that the
Moon was formed when a Mars-sized competing planet hit us shortly
after formation. The dichotomy in crustal depth might be due to
a second hit that thickened the far side and promoted lava flows
on the near side to create the dark maria. With a newly-determined age
of 4.36 billion years (from the latest dating of Moon rocks), the
cooling time may have been longer than expected due to tidal
heating by Earth (the Moon much closer to us in early
days).
More water: LCROSS showed it in pockets, but also found other
volatiles like methane and ammonia. Curiously, the old Apollo
moon rocks now are revealing an unexpected water content, the
extra water counter to the standard formation theory, which
involved the accumulation of debris after the Big Hit.
OH NO, the Moon is shrinking! Rather has shrunk. Lunar
Reconnaissance Orbiter finds scarps that date to within the
past billion years (the shrinkage not all that much).
Inner Planets
Mercury probably made more news than any of the others (well,
there is Mars...) because of the orbit insertion of
Messenger on March 18, 2011. Great numbers of images and
amounts of other data reveal a planet unlike any other or
expected. (But then, none is like any other.) We see heavily
cratered areas, smooth volcanic plains, and polar craters that
are indeed deep and dark enough to shield water (there it is
again) ice against the solar heat. The surprising surface is
rich in sodium and sulfur but poor in iron, the latter bound up
in a huge iron core whose origins remain mysterious, though the
theory of a collision that ripped off the outer rocky mantle is
still viable. Oddest of all perhaps is the magnetic field, which
is offset from the planet's rotation axis. One wonders why this
small body, which should have cooled, should have a magnetic
field at all.
Venus is known more for its possible future neglect. But not
Mars. We find evidence for recent (within the past 200 million
years) volcanism (which helps generate atmospheric carbon
dioxide) and, from apparent rivulets, for occasional running
water(!). Perhaps the best news is the launch of the
Curiosity rover in November of 2011, the complex craft
scheduled to land in August of 2012. It's to be lowered to the
ground by a novel "sky crane."
Outer Ones
Planets seem to have shifted and migrated in the early Solar
System. One idea is that an ancient 3:2 (ratio of periods)
orbital resonance between Jupiter and Saturn kept Jupiter from
invading the inner planetary system. Perhaps we owe our lives to
it. Remember Comet Shoemaker-Levy 9 that hit Jupiter in 1994?
The planet got it again in 2009 when hit by an asteroid perhaps
50 meters or more across. Spectra of the spot caused by the
strike revealed iron and silicates from the impactor. If it can
happen there, it can surely happen here. The best Jovian news is
the launch to Jupiter of JUNO on August 5. The probe, to
arrive in 2016, will examine the Jovian atmosphere and map the
planet's gravitational and magnetic fields to determine its
interior structure.
Cassini continues to bring back the riches of Saturn. The
Great White Storm returned to the southern hemisphere, which it
does periodically. Once again, the rings are explained. Both
Cassini and ground-based data suggest that the rings are nearly
pure (you guessed it) water ice. They are thus caused by the
breakup of an icy satellite. The gravitational tidal limit is
less restrictive for ice than for rock. Ice and rock were
therefore separated. The ice then went around the planet and the
rock crashed downward into it. The rings may therefore be nearly
as old as the Solar System and not a recent acquisition.
Titan's atmosphere has some oxygen in it. Lab experiments
suggest that the Titanic air could form chemicals of life. The
satellite also exhibits high cirrus. Except (and they are big
exceptions) for the cold and the dominance of methane, there is a
remarkable similarity to Earth.
The water (a real theme) plumes of Enceladus come in part from
heat produced by tidal flexing, but also by forced librations
that arise from its irregular shape. Like Io to Jupiter,
Enceladus has an electrical connection to Saturn, the base of it
now found on the planet.
And then there is Iapetus. The old idea is that the dark side is
the result of the satellite sweeping up dust blown off of others,
and that the bright side is covered with snow. That is currently
out. Another idea is that the ice on the dark side evaporated
away, leaving a dark tarry substance. But why? Then there is
the problem of the synchronous 79-day rotation, which should not
be, as the satellite is too far from the planet for such a
locking. That, the oblateness, and an equatorial ridge 15
kilometers high, may be the result of a collision. The debris
rained back down to form the ridge, and a temporary moonlet
gravitationally slowed the satellite and allowed the synchronous
spin.
In July of 2011 Neptune finally completed its first orbit since
discovery (which came from the perturbations it induces on the
orbit of Uranus). The sea-god's planet has half a dozen captured
trojans in the stable 60-degree points (ahead and behind in
orbit), in addition of course to having synchronously captured
Pluto into a 3:2 resonance.
Comets, Asteroids, KBOs, and Pluto
Deep Impact's imagery of Comet Hartley-2 shows that jets
from the ends of the body are driven not by water (for a change)
but by carbon dioxide (which sublimes quietly from the smooth,
narrow, dusty center), big 10-20 centimeter aggregates of smaller
pieces flying off. Then NASA did it again, when Stardust
passed Comet Tempel-1, its camera revealing Deep Impact's
150-meter crater. The probe got hit with lots of dust, as the
comet had just passed perihelion. Stardust then found
minerals in Comet Wild that suggest liquid water. December of
2010 saw a veritable storm of two dozen Kreutz-group comets
plowing into the Sun, with of course no damage to our star.
Probe Dawn imaged Vesta, the 550-km-wide asteroid (the only one
visible to the naked eye). It's covered with craters that
include a 450-km-wide monster at the south pole. The collision
that caused it was perhaps the source of Vesta meteorites. Large
grooved ridges near the equator are unexplained. Noted last year
was the first recorded asteroid collision, which produced dust
streaming away (but no gas) and a mysterious X-shaped head. New
is a measure of 100,000 tons of the stuff in millimeter to
centimeter sizes.
From asteroids cometh meteorites. A rare sighting of a pre-
strike meteoroid resulted in a meteorite found to hold 19 amino
acids. The Tagish Lake meteorite had amino and other organic
acids that were formed within the meteorite itself (not in the
interstellar medium) with the aid of water and heat generated by
radioactive aluminum. In other meteorites, guanine and adenine
(components of DNA) are found with non-DNA analogues, showing
that they are made in space and are not contaminants.
The Solar System, like those of exoplanet systems, has a dust
ring from smashed Kuiper Belt Objects. Among the biggest of the
KBOs is Pluto, which sort of regained "largest" status, and is,
with additional measures, now in a virtual tie with Eris. Pluto
also added to its family with a fourth moon, "P4," its 32-day
orbit between those of Hydra and Nix and well outside that of the
innermost and (relatively) large satellite Charon.
Interstellar
We now launch outward from our local planetary system to the stars, wherein we first deal with the
interstellar medium and star formation. Infrared
radiation from dense cores (the first observational evidence of
star formation) shows larger particles than we find in the ISM
proper, suggesting that planet formation is already underway even
as the parent star develops.
Such cores and birthing stars develop strong bipolar jets that
sweep up and shock the local ISM to create Herbig-Haro Objects.
Magnetic fields found in the jets may help reveal the jets' power
sources. Could it be then that all such flows, including those
associated with advanced-evolution (Mira) giants and planetary nebulae, be magnetically
driven as well? Even outflows from supermassive black holes at
the centers of galaxies may be included.
Exoplanets
The end result of the process are planets and planetary systems orbiting
the parent stars. The numbers of them found, and their
incredible variety, are daunting. We can but scratch the
surface. Doppler
measures have given us more than 700 exoplanets, while the
Kepler satellite (which looks for transits) notes as many
as 3000 candidates, 200 in habitable zones. As many as half of
the solar-type stars may have "terrestrial" planets. There are
good odds that if a star has a planet there is another, perhaps
in orbital resonance with it. A downside is that stellar
oscillations, which cause the star to vary slightly, can confuse
the dips in brightness caused by the transits. The upside is a
treasury of information on the stars, the oscillations acting as
internal probes. As a result, Kepler needs more time than
designed so as to untangle the two effects.
Among the interesting results are more hot Jupiters, wrong-way
planets (both possibly caused by gravitational interactions with
other planets), one that encircles an inner binary star, various
"superearths" (but none quite yet down to our mass), one hot
Jupiter found speeding up in orbit in preparation for being
swallowed by its star, systems of up to 6 or 7 planets, a
superdense superearth, an "iron planet," a "diamond planet"
(actually a star stripped to its core orbiting a millisecond
pulsar), a "black Jupiter" for which there is no explanation, and
several "free-floating" bodies, perhaps planets ejected from
their systems, which with low mass brown dwarfs (substars not
capable of full nuclear fusion of hydrogen to helium) may
outnumber actual stars. Among the more remarkable observations
is the first spectroscopy of a superearth in orbit around a red
dwarf. Continuing the theme, the spectrum shows a water
haze.
But don't look to globular clusters to
find exoplanets, as the clusters have low metals (planet-holding
stars tending to have high metal contents). Strong gravitational
interactions within the clusters would also eject such small
bodies.
Stars
We finally arrive at the stars
themselves (probably something no spacecraft will ever do).
Class Y, cooler than L and
T (the latter exclusively made of brown dwarfs), is still
empty, but may be on the verge of fulfillment. The coolest BD's
run down to 400 Kelvin but we need to see ammonia and water to
classify one as "Y." It's an important consideration, as class Y
would close the gap between brown dwarfs and planets.
We've tripled the number of red dwarfs in elliptical galaxies,
seeing far more than here, so star formation may have worked
differently there. Oddly, even old red dwarfs, for which
rotation and magnetic fields should have declined, show flaring
activity (all the way into class L). Harkening to earlier
comments, oscillation data from Kepler is transforming the
asteroseismology business.
The vibrations of some 500 Kepler stars reveal radii and masses,
the former in good shape, the latter lower than expected.
Remarkably, imagers aboard the solar observatory STEREO
have been able to check out background stars, resulting in the
discovery of more than 100 eclipsing binaries.
Advanced evolution draws more attention. The wind from Delta Cephei (the prototype of
Cepheids) blows
with a strength a million times that of the solar wind, creating
a shock wave half a light year across. And nobody expected gamma
rays from a 2.5 magnitude symbiotic star outburst ("symbiotics"
combinations of windy a
href="../sow/star_intro.html#giants">giants and dense white dwarfs).
Then there is yet more water, seen in extraordinary, molecule-
rich IRC+10216 (centered on the Mira star CW Leonis); at 1000
Kelvin, it should not be there. It's presumably formed in the
star itself.
Further along, we find the structure of a carbon-rich
protoplanetary nebula (the leavings of an advanced red giant
whose core is not yet hot enough to create a true planetary) to be apparently
related to a binary
companion in an 800 year orbit. It could then be that much
of the varied structures among real planetaries, a subject that
has long confused astronomers, is caused by such companions (note
the rings in the Cat's Eye and
others).
Supernovae, Pulsars, and Stellar Black
Holes
The final product of the evolution of lower mass stars (below 8
or 9 solar masses) is the white dwarf state. Binary white dwarfs
can be in incredibly tight orbit. One pair consists of mutually-
stripped helium wd's (most are carbon/oxygen) that whirl around
each other in 2.8 hours at 1.5 times the distance from here to
the Moon. Binary white dwarfs are significant, because if they
merge and have enough mass to exceed the 1.4 solar mass support
limit, they will collapse and violently flame out in Type Ia supernova
explosions.
A roughly equal number of supernovae are of Type II, in which
the core of a massive star (one born with greater than 8 to 10
times the solar mass) fuses to iron and implodes, an outbound
shock wave exploding the vast stellar envelope. A prime
candidate is familiar Betelgeuse, which has an outer
envelope even bigger than expected, its oxygen-rich dust
extending to 400 AU.
Famed Messier 101 made special news with a nearby ninth magnitude
Type Ia supernova that was easily accessible from the back yard
with a small telescope. Adding to the mix of supernovae (which
include the core-collapse Ibc's) is a new class of ultra-bright
hydrogen-less (like the Ia's) supernovae that nobody really knows
anything about.
It's long been thought that cosmic rays (see above) are produced
by acceleration of ambient particles by supernova explosions.
The different energy spectra of protons and alpha particles
(helium nuclei) suggest otherwise. The issue needs further
resolution.
The origins of Type II core-collapse supernovae are more or less
understood (except for the "minor details" of the energy source
of the explosion). The detailed origins of the Ia's, however,
are still controversial, there being two roads to success, the
merger of a double white dwarf or the tidal overflow from a
normal star onto a white dwarf companion, either of which can
cause the result to exceed the 1.4 solar mass Chandrasekhar
limit. There is evidence on both sides. Note the double white
dwarf in tight orbit above, which supports the merger theory. On
the other hand the spectral signature of sodium in Ia supernovae
supports mass transfer.
The expanded leavings of supernovae, the blown-out clouds (the
gaseous "supernova
remnants"), dot the sky. The outbound remnant of Supernova
1987a in the Large Magellanic
Cloud is filled with half a solar mass of dust, much more
than expected. The best-known supernova remnant of all is the
easily accessible Crab Nebula, Messier 1, in Taurus. It's long been used as a
standard source for X-ray intensities (in units of "crabs"). But
the standard is hardly that, as we find the X-ray Crab to vary by
several percent a year. Moreover it has been dimming and has
been seen to pop gamma-ray flares.
The final by-products of core-collapse Type II's are either neutron stars
(which include pulsars) or black holes (the
Ia's annihilating themselves). Within the pulsar class are the
magnetars with fields 100 or so times "normal." One such seems
to have come from a star with an initial mass of more than 40
times that of the Sun, which provides a lower limit to black hole
formation.
Gamma Ray Bursts
At the extreme energetic end are distant gamma ray bursts
(GRB's), of which there are two kinds,"short" and "long," divided
at about two-second duration. Computer simulations suggest that
short bursts are caused by tangled magnetic fields that derive
from the merger of orbiting neutron stars as they form black
holes. The long bursts have long been known (so far as we can
know) to be caused by "hypernovae" collapsing to black holes,
both kinds of bursts producing their radiation in narrow cones.
We see the GRBs only when the cone-shaped jets are pointed at us.
Also at the energetic edge was the observation of a supermassive
black hole in the center of a distant galaxy that apparently
swallowed an orbiting star, which produced a third kind of gamma-
ray burst that poured out in bipolar jets quite like the usual
short and long bursts.
The Galaxy
Every year seems to include a new idea for the structure of our
Galaxy. Now we are
apparently in a three-arm spiral (and from much prior data, a
barred one).
Of more dramatic interest is observation by the Fermi Gamma
Ray Observatory of huge gamma-ray bubbles that spring in
bipolar flows from the Galactic center perpendicular to the plane
that are 25,000 light years long. We might speculate that they
are caused by some kind of burp from the central supermassive
black hole or are expanding superbubbles that arise from a high
star formation rate that results in powerful winds and great
supernova rates. But nobody really knows their origins.
Galaxies, Quasars, and the Distant Universe
First we had another galaxy redshift record of z = 8.6 ("z" the
shift in wavelength relative to the rest wavelength), which took
us back 13.1 billion light years, some 600 million years after
the Big Bang, which restricts the time of re-ionization of the
Universe following the so-called "dark ages" of neutrality. Then
a bit later comes the news of z = 10.3, taking us to a look-back
time of 13.2 billion light years, 500 megayears after the
creation event. We are slowly getting there, back to origins,
which is why we need the JWST (see the opening paragraph).
The most distant galaxy cluster comes in at z = 5.3, at an age of
1.1 billion years. The hot gas touted to be within galaxy
clusters is being increasingly revealed, PLANCK (the CMB
satellite) finding a hot medium with temperatures in the tens to
hundreds of millions Kelvin. A record of sorts among clusters is
set by the merger of not just a pair of them but by four at the
same time to make Abell 2744, the results very visible in X-ray
radiation.
Then there is the 770 megayear fully functional quasar (a forming
galaxy surrounding a superenergetic supermassive black hole).
How on Earth (or in the Heavens) could it develop so quickly?
Another distant QSO at 11 billion years in time from us is seen
to be surrounded by a cloud of (yet more) water vapor. Outflows
from the supermassive black holes that make the quasars drive
away the infalling galactic gas, and therefore are self-limiting
systems that shut themselves down, which explains why quasars are
all so far away (distant in time). In that sense there is a
small (it's all relative) nearly dead quasar at the center of our
of Milky Way Galaxy.
Massive ionization in the early Universe is seen through the
observation of nearly three dozen "supernebulae." Seen through
their Lyman-Alpha radiation, the biggest of the blobs, at z = 3.1
(2.1 billion years after the Big Bang), is 300,000 light years
across, thrice the size of our own Galaxy. They represent one
more still-obscure step in the creation of what we see around us
today. (Lyman Alpha is the fundamental emission line of
hydrogen. Produced by electron jumps from the second energy
level down to the lowest energy state, at rest (no large radial
motion) it is found in the middle ultraviolet, but at high
redshift lies in the optically-observable realm.)
But which actually came first, black holes that acted as
nucleating cores of galaxies, or early galaxies that then formed
the black holes? The opinions fall on the former side, supported
by the discovery of a distant, early, small galaxy that already
has a massive black hole at its core. That said, did early
galaxies form through mergers of smaller ones, or more slowly
from infalling gas? We get both sides, and no decision. Only
the galaxies themselves seem to know.
Dark Matter, Dark Energy, and the Hubble
Constant
At the end, we search for the origins of most of the mass-energy
of the Universe. Normal matter, including hot intergalactic gas,
seems to make up a mere four percent of it, while 22 percent is
in dark matter and 74 percent in dark energy (these numbers
somewhat dependent on the mode of research). Dark matter is
"visible," its distribution measurable, only through its gravity.
The leading candidate for it is a vast collection of exotic,
weakly interacting massive particles ("WIMPS") that have yet to
be found.
Dark energy (and its mass equivalence) is known through the
deviation of the Hubble Law (redshift versus distance) from a
straight line. The weight of evidence is that DE is a property
of spacetime itself as first suggested (for the wrong reason) by
Einstein. Support comes from observations of gravitational
lensing, in which light from background galaxies is split into
different paths through a closer cluster 2.2 billion light years
away, allowing the structure of spacetime to be examined.
The Hubble Telescope era (which includes a lot of other
instrumentation) finally led to the resolution of the Hubble
Constant, the rate at which the Universe is expanding. The value
currently ranges from 70.4 to 74.2 kilometers per second per
megaparsec, quite a change from earlier years when the range from
different observers went from under 50 to near 100. Taking
everything into account, the age of the Universe, the time since
the Big Bang, comes in close to 13.7 billion years. Included
within it almost immediately after the event were the atoms of
our own Earth and our own selves, all of us the produced by
everything that is out there.