2009-2010
Department of Astronomy, University of
Illinois
The New "Advances"
For two decades, I gave "Astronomy Update" talks to annual
conference of the Great Lakes
Planetarium Association, after which the lectures were written up
for publication both in their Conference Proceedings and on the
Web, the last one for 2008. After a hiatus of two years, this
long-term project on astronomy news is continued here in written
form only and with a different name, "Advances in Astronomy."
The first of these covers the two year period, 2009-2010
(actually November 2008 - October 2009, consistent with the GLPA
talks). Deep thanks go to past and potential readers, to GLPA,
and to Dale Smith for scanning the updates for 1989 through 1994.
I am also indebted to Sky and Telescope, Astronomy,
the Hubble NewsCenter, and to numerous other sources.
Flying High ... and Low
IT'S BEEN SAID that there are only two telescopes,
Galileo's and the Hubble with only improvements in between. We
are going to have the latter for awhile, as at the top of this
double-years' worth of news, the HST saw new life with a
magnificent repair job and the installation of a new camera and
imaging spectrograph. The great machine should be good for many
more years of service.
But there ARE others. A brief rundown includes the Gamma Ray
Large Area Telescope (GLAST, now the Fermi Gamma Ray
Telescope), the Spitzer Space Telescope (having run
out of coolant now in "warm phase"), and the Herschel
infrared telescope (which has seen first light). Down on the
ground is Pan-STARRS (the Panoramic Survey Telescope and Rapid
Response System, whose 3-degree field will be used to image
1/5 of the sky every night to spot approaching asteroids and to
detect ephemera, and the Auger Cosmic Ray Observatory,
which will use the air to detect high-energy particles from
space. In between, SOFIA (the Stratospheric Observatory for
Infrared Astronomy built into a Boeing 747 aircraft) finally
saw first light, and then back up into space is PLANCK, which is
examining subtle fluctuations in the Cosmic Microwave Background
radiation to probe the origins of the Universe. Meanwhile,
looking back into EARTHLY past, the historic David Dunlap
Observatory of the University of Toronto has been spared to
become a public facility.
The Sun
Specific to our own star, we saw
the launch and opening of the Solar Dynamics Observatory, which
should re-define our knowledge of space weather and solar
activity, much as SOHO did in the past. Maybe it will help tell
us why the "sunspot desert" has continued in an extended solar
minimum. When will the spots and activity return? Are we
approaching a new Maunder Minimum and "little ice age?" We have
made some progress in the idea that small numerous nanoflares are
responsible for heating the two-million Kelvin corona. Just how
they do that, though, remains a mystery.
In the solar subtlety category, the Sun is seen to have a tiny,
8-milliarcsecond equatorial bulge that goes to 11 at high
activity, suggesting the bulge to be magnetic in origin. Second,
new radar observations have refined the Astronomical Unit to
149,597,870.696 kilometers (accurate to 10 centimeters), and show
that as a result of mutual tides, the Sun is getting farther away
by 15 cm per year (which is not enough to offset global
warming!).
Moon
You can't speak of the Sun without calling to the Moon. The BIG ISSUE of course is
water, which now seems to be all over, though in minuscule
amounts. It was seen in the LCross impact, which dredged up
minimally "wet" debris from a dark, cold crater near the lunar
south pole, by an Indian orbiter that found ice in north polar
craters, and through various other studies that showed it locked
as hydroxyl in surface minerals.
And, as already known, the Moon is OLD, a new study dating the
solidification of small crystals to 4.42 billion years ago.
Little Planets
Finally, after a hugely long hiatus, Mercury is under intense
scrutiny from MESSENGER, which has flown past the planet three
times and is headed for orbit insertion. It's found the second
largest basin in the solar system, 715 km across, and depressions
in craters that appear to be volcanic calderas. Oddly, the
planet has an internally-generated magnetic field rather like
Earth's, implying a "dirty," hence partially molten, iron core.
Here, Venus Express does the job. Infrared observations
of the surface reveal shield volcanoes topped with rock that is
different from that down in the plains, suggesting that the
volcanoes were recently active. Similar data from the southern
hemisphere also points to different kinds of rock, including
granite, that suggests both an ancient ocean and plate tectonics.
Could the runaway greenhouse planet once have been more
earthlike, and is there a lesson here?
Books of course could be written from the Rovers' adventures
alone (which are in their seventh year, long past warranty),
never even minding Mars Reconnaissance Orbiter and various other
craft. "Sprite" got famously stuck, but "Opportunity" lumbers
on.
Water seems to dominate the themes. Phoenix died, but found lots
of buried ice in the far-northern plains, plus clays and salts.
Farther north, the polar cap seems to have been carved in its
curving forms by winds. Meanwhile, Mars Express found
subsurface southern-hemisphere ice that evokes ancient glaciers.
Surface mineralogy suggests an ancient ocean (as do long-known
shorelines). Methane plumes intriguingly suggest (perhaps
wishful) biological activity, but are more likely geological in
origin.
Big Ones
Whacked again in 2009, an asteroid or comet impact left a
southern-hemisphere scar thousands of kilometers wide, the
colliding body thus several hundred meters across. Modelling
shows that Jupiter's rocky-metallic core (though in form vastly
unlike the rock we know) is larger than thought, its mass
somewhere between 14 and 18 Earths.
With Cassini still in orbit, the data keep flooding in, so much
that only a sample of discovery is possible. Like Earth and
Jupiter, Saturn has a magnetically-induced aurora. But for no
known reason, it's different. Rather than being ring-like, its
infrared glow covers the whole pole. Lightning bolts strike 300
km long, while storms can last for months.
The focus seems to be more on the intriguing satellites,
particularly on Titan, with its methane lakes and hydrologic
cycle that causes the lake levels to go up and down in response
to evaporation and rains. The amazingly satellite also seems to
have watery volcanoes. Meanwhile the famed geysers of Enceladus
are apparently caused by heat produced by a tidal resonance with
Dione, the debris feeding the E ring. The continuing geysers
plus salts in the E Ring point to a possible liquid water ocean
beneath the moon's rocky surface. Is it yet, along with
Jupiter's Europa, another site for life?
Satellite-ring interactions continue with the 61st-known moon
feeding the G ring (which lies just past the A ring), and with
backwards-orbiting Phoebe (which probably is a captured Kuiper
Belt Object) creating a newly-found (from Spitzer) giant
tilted outer dust ring. Iapetus then sweeps up the dust on one
hemisphere to give it its two-sided nature. Various embedded
moonlets disturb ring particles to help create the rings'
structures.
Finally, start the party. Neptune will complete one full orbit since
discovery on July 12, 2011.
Really Small Stuff: Asteroids, Comets, and
KBOs
Huge numbers: asteroids with known orbits around half a million.
And the total number there are now has but a thousandth the
original mass thanks to gravitational scattering by the planets.
They may have been born large and then have ground themselves
down through collisions that are still going on. Indeed, we seem
to have witnessed the aftermath of a direct hit of one on
another, which created a streaming dust tail with an unexplained
X-shaped head.
They of course hit us as well, asteroid 2008 TC3 was observed
before it burst in the air over the African Sudan. Three-
hundred-meter-wide Apophis, though, will not, at least not soon,
but it is expected to pass close enough to reach easily-visible
third magnitude in April of 2029. It ought to present quite a
sight.
Turning the tables, we continue to visit them. The Rosetta
spacecraft visited both three-mile-wide asteroid 2867 Steins and
larger (100 X 131 km) 21 Lutetia (both of which are badly beaten
up) on its way to land on Comet 67P in 2014. Sadly, Hyabusa
returned from asteroid 25143 Itakawa with no known samples
(though the craft is being examined for traces).
Comets are another matter. The Deep Impact strike revealed
amorphous ice. Disintegrations of short-period comets seem to be
responsible for the Zodiacal light, which makes sense since they
come from the trans-Neptune Kuiper Belt and strongly tend to
stick to the ecliptic. In the most exciting of findings, the
STARDUST mission seems to have uncovered the amino acid glycine,
a building-block of life, in Comet Wild 2. Since early comet
impacts s are thought to have brought our water, they have
supplied a rich pre-biotic chemistry as well.
But not all Kuiper Belt Objects (KBOs) are regular. At least one
(like Halley's Comet, which is not a KBO) orbits retrograde.
They confuse further. A stellar occultation of another showed it
to be smaller than expected, and thus bright, in violation of the
expectation that such objects are covered with dark chemicals.
"Retired planet" Pluto is the most famed of the KBOs.
Exquisitely-processed HST observations reveal a changing,
variegated surface with methane-nitrogen frosts as the atmosphere
freezes out, combined with dark areas in which methane has been
processed into dark carbon compounds. We avidly anticipate New
Horizons' visit in 2015.
Exoplanets
More books could be written about extrasolar planets. And are. All we
can do is sample the discoveries to give flavor to the subject.
We passed 400 of them, the number increasing with great rapidity.
Kepler (the transit-finding spacecraft) alone quickly found some
700 candidates, the number destined to rise fast. At least one-
third, maybe a half, of all stars may have planets, the
percentage apparently going up with stellar mass. While planet-
holding stars tend to be more metal-rich than those without, they
are notably lithium-poor, the possible result of downward
circulation of the element where it is destroyed by high interior
heat, possibly as a result of stellar rotation spun up by the
planets.
While most planets are discovered through the Doppler effect, we
now have finally SEEN them orbiting Fomalhaut (one Jupiter-like
planet in a 115 AU orbit), HR 8799
Pegasi (three "Jupiters" within a few dozen AU), and famed Beta Pictoris (one "Jupiter" in
which we have seen orbital motion, which is consistent with Beta
Pic's beautiful large dusty disk).
Equally big news is the discovery of lower mass bodies that
approach Earth in mass and size. Gliese 581 sets the current
record. A red (class M) dwarf 20 light years away, Gl 581 is
orbited by at least four planets (and maybe as many as six) that
range from around 2.5 Earth masses to perhaps half a Neptune
mass. The little one, Gl 581e, is in a 3-day, 0.03 AU orbit.
More massive (but still rather earthlike) Gl 581d circles close
to the habitable temperature zone of the dim star -- if that
means much.
Other highlights include 61
Virginis with three "superearths," GJ 1214b, a low density
superearth "water world" (or some such), a huge eccentric (e =
0.93) jupiter going around HD 80806, backward orbits, non-
coplanar orbits (Upsilon
Andromedae), planets that interact with each other (24
Sextantis), which may explain such systems as Ups And, and more,
showing that our more or less regular Solar System is hardly the
paradigm we thought it would be.
Add to these, nearby planet-holding Epsilon Eridani, which appears to
have two infrared-radiating "asteroid belts, one 3 AU out,
another at 20, all within an outer disk at around 100. The
planet is associated with the inner belt, suggesting that the
other two belts might hold more.
Brown Dwarfs
It's just a step up (from planets) or, if you like, down (from
stars) to the brown
dwarfs. Faint VB 10 near the
bottom of the main sequence provides a transition as the lowest
mass star known to have a planet, one near the brown dwarf cutoff
around 0.08 of a solar mass, below which full core hydrogen-
burning is not possible.
And there are not as many brown dwarfs as once believed. As we
drop in mass along the main sequence of the HR diagram, stars become more
numerous. But instead of steadily increasing all the way down,
their numbers seem to turn over and reverse somewhere in late
(cool) class M. Among the cooler set is a puzzling eclipsing double
brown dwarf in Orion in which
the larger is the cooler rather than the warmer, which is
explained by having the larger covered with starspots, which in
turn goes along with some brown dwarfs being magnetically active
flare stars (for which there is little explanation). Among them
too is the coolest class T brown dwarf, just 620 Kelvin, not much
warmer than your baking oven. It may be a transition object into
still-empty class Y.
Stars
Real stars are hardly neglected. It seems that Alcor has an M dwarf companion about
a second of arc away. Given that Mizar is already quadruple (each of
the stars of the visual
double also a pair), the Mizar-Alcor system is now known to
be sextuple both similar to, yet very different from, Castor. Moving up in mass, Spica, a close "ellipsoidal binary"
that varies as a result of tidally distorted stars baring
different cross sections as they orbit, does indeed seem to very
slightly eclipse. Moving up farther, satellite infrared
observations show that Betelgeuse is producing a shock
wave as it plows through an interstellar cloud at 30 km/s, double
the speed of its wind. The star is violently convective, non-
spherical, irregularly losing mass at a rate of some five hundred
thousandths of a solar mass a year, and for now getting smaller,
the diameter down by 15 percent between 1993 and 2010. Given its
known long-term behavior, the trend will probably eventually
reverse.
Staying big, the strangeness of Epsilon Aurigae nears a final
explanation. Every 27 years, the readily visible class F
supergiant (one of Auriga's
"Kids"), comparable to the Earth's orbit in size, is eclipsed
for an amazing two years as a giant disk of dust some 10 AU in
diameter surrounding an accreting B star passes in front of it,
cutting the total light by 0.8 magnitudes. The last eclipse
began in August of 2009, and will go on until May of 2011. Go
watch.
And going up more, Eta Carinae
(which in the 19th century erupted to become the second brightest
star in the sky) is brightening again, and is now up to magnitude
4.7. Is it returning to normal, or preparing to erupt again?
And at the peak of the pile, THEY'RE BACK. Supermassive stars. Models show one
of 170 solar masses (topping the supposed upper limit of 120
Suns) in NGC 3603, another in the Tarantula Nebula complex (R
136a1) of 320 suns. But watch out, as the history of the subject
says no. Near the bottom end, the Kepler satellite found an
eclipsing pair of low mass white dwarfs, each
(from their sizes) about 0.2 solar masses, far lower than
seemingly possible, suggesting once-strong mass loss.
A handful of "hypervelocity stars" have been flung out of the Galaxy compliments of
the gravitational action (so thought) of the central supermassive black hole. A
record of 817 km/s relative to the Sun (55 times normal for local
disk stars) seems to have been originated by a triple, when the
black hole absorbed a distant companion to a close inner double
that then got tossed out and subsequently merged to become a
class B "blue
straggler," a star that is too massive and unevolved for its
supposed age.
Clusters
Clusters of stars, that is, of the globular persuasion. The
first gamma rays have been found coming from a globular cluster, from
massive 47 Tucanae. They may be
have their origins in the cluster's set of millisecond
pulsars.
And just what are these clusters anyway? Terzan 5 joins giant Omega Centauri as a possible
stripped dwarf galaxy that merged with ours, the evidence lying
in two distinct generations of stars. It's also suspected that a
quarter of all globulars actually came to us from galaxy mergers,
including Messier 80 -- which is what M 54 is doing now as it
arrives compliments of the Sagittarius dwarf.
Supernovae, Pulsars, and Stellar Black
Holes
Light echoes, which were wonderfully visible in creating various
phenomena around
Supernova 1987a, are becoming a powerful observing tool for
probing historical SN. The spectrum of a 436-year-old echo off
an interstellar dust cloud confirmed that Tycho's Star was a normal Type Ia supernova (produced
by a white dwarf in a binary system that accreted more mass from
its companion than it could support). Multiple echoes from 330-
year-old Cassiopeia A also allowed a three-dimensional
reconstruction that shows an asymmetric blast, the central pulsar (neutron
star) going off at 350 km/s opposite a jet.
The remnant pulsar is essentially the progenitor star's old iron
core that has been compressed into neutrons. X-ray observations
yield an expected diameter of 30 or so kilometers only if Tycho's
pulsar/neutron star has a carbon atmosphere, the result of
nuclear "burning" of helium, which in turn came from hydrogen.
The Sun's "atmosphere," from which its radiation is emitted, is a
thousand kilometers deep. The gravitational force at the surface
of a neutron star is so great that the carbon layer is squeezed
to a depth of only 10 centimeters! Or so goes the
theory.
New, energetic pulsars like the one in the Crab Nebula radiate
across the spectrum, while spun-down old ones emit only radio.
It came as a surprise then when Fermi/GLAST (see the note at the
top) discovered that a handful of pulsars radiate ONLY gamma
rays. Apparently, the cone with which they sweep the sky is
wider for gamma rays than it is for optical or radio, and if we
are on the edge, we get just the gammas.
Astronomers keep anticipating a wider variety of exploding stars.
Among the theoretically expected are "pair-instability"
supernovae. In these, the stars are so massive that highly
energetic gamma ray collisions in the deep interiors create
electron/positron pairs that causes sudden cooling and thus
collapse. A superenergtic blast from ultradistant SN 2007bi
suggests it might be a long-searched-for example that came from
the collapse of a 100-solar-mass helium core. But we do not yet
have a definitive answer.
Normal supernovae, though, still have the standard two routes to
success, collapse of an iron core (Type II, Ib, Ic) or a white
dwarf that are pushed beyond the "Chandrasekhar Limit" of 1.4
solar masses (Type Ia).
The latter have two sub-routes, overflow from a binary companion
or merger of the stars in a double white dwarf, which could
produce mergers far beyond the limit and super-luminous Type
Ia's, which in turn would confuse the Universe's distance scale,
for which Ia SN are standard candles because of their uniformity.
SN 2007if might have been an example.
Pulsars have varieties too that include millisecond versions that
are spun up by accretion from a companion, and magnetars that
have fields 100 times that of a normal pulsar and that are
visible in the gamma ray and X-ray spectral domains. Surface
adjustments of the magnetars can radiate so intensely that they
effect the Earth even from thousands of light years away. Now
the first optical/infrared magnetar has been found, studies of
which will help untangle their mystery.
The Galaxy
That is, OUR Galaxy. It has a well-studied supermassive black
hole at its center that lies some 27,000 light years away from
us. Only 0.3 Astronomical Units across, less than the size of
Mercury's orbit, from motions and orbits of surrounding stars its
mass has been refined to 4.3 million times that of the Sun.
Oddly, in spite of its disruptive nature, star formation still
goes on only 10 or so light year away from it.
Moving on out, studies of radio radiation from star-forming
regions suggest that the Sun is orbiting the Galaxy fifteen
percent faster (at 255 kilometers per second) than once thought,
which boosts the Galactic mass upward by 35 percent or more.
Galaxies
For which there is another hodge-podge of various discoveries.
Our Galaxy is filled with high-speed particles, cosmic rays
accelerated to near the speed of light by supernova shock waves.
They constantly hammer into Earth, produce carbon-14, and
possibly even initiate lightning and rain. If you think it is
violent here, try Messier 82, a "starburst" galaxy in which the
supernova rate is so high that the whole galaxy was once thought
to be exploding. The resultant cosmic ray flux is 500 times what
we have here, which, speculating, might make life near-
impossible.
When we look outward, we also look back in time. This effect
matters not for stars and nearby galaxies, but at the extreme, it
allows us to see distant galaxies and the far reaches of the
Universe as they once were. There is thus a constant search for
the "youngest galaxy," that is, the most distant. We are down
to 600 million years after the Big Bang, showing that galaxies
formed VERY fast indeed. The most distant cluster of galaxies
has been moved back to 9.5 to 10 billion light years
away.
All more or less local galaxies, though, are expected to be about
the same age. Since their metal content comes from stellar
evolutionary processes, large galaxies have higher metallicities
than low-mass ones. It comes as a surprise then to find large
galaxies with low metals. Either galaxies can form late, well
after the Big Bang, or, more likely, the effect is due to mergers
of smaller galaxies into the low-metal big ones we now
see.
All large, even some small, galaxies seem to be organized about a
central supermassive black hole of the sort that occupies our own
central region, many far more massive than ours, topping out in
the low billions of solar masses. There is a growing consensus
that the black holes came first and that the galaxies
subsequently organized around them. That the masses of central
bulges of galaxies are tied to the mass of the central black hole
(in a local 700-to-1 ratio) suggests that the latter limits the
former by blowing away potentially accreting matter. Moreover,
very young, distant galaxies show a bulge-to-black-hole ratio of
only 300:1, suggesting continued and later galaxy growth.
Lying at the cores of faint young galaxies, quasars are the
youngest, most distant, and most wildly active of the
supermassive black holes, from which pour vast amounts of energy
and flows of matter in the form of jets. Occasionally, we find
double black holes at the centers of galaxies as a result of
galactic mergers, nearly three dozen now known. At the extreme
is a double quasar in which the individuals, only 0.3 light years
apart, orbit in a mere century and are probably destined to
merge. In one case, a merger was apparently so violent that it
seems to have actually ejected the black hole from the galaxy's
center.
Gamma Ray Bursts
At the fringe of the Universe, the most distant galaxies contain
the most violent of supernovae, "hypernovae" from very massive
stars that radiate massive bursts of gamma rays, which in turn
produce optical afterglows that can be so bright as to be visible
to the naked eye. The highest confirmed red shift is in the
neighborhood of 8.2, the instigator just over 600 million years
old and some 13 billion light years away. A GRB may result from
intense magnetic fields generated in the stellar collapse that
produces the hypernova.
We are getting close to the era of the zero-metal "Population
III" stars that were formed from only the hydrogen and helium
that came from the Big Bang, their ages expected to be in the
range of 200-400 million years (the time after the Bang itself).
Dark matter, Dark Energy, and Everything
Else
We still of course do not know what dark matter and energy are in
spite of the DM mystery being with us since the 1930s. Is DM
made of exotic particles? Are there viable alternative theories
of gravity that explain them? Whatever they may be, dark matter
exceeds the normal stuff in galaxies by a factor of 5 or so, and
seems to love dwarf galaxies more than large ones, as the smaller
galaxies have relatively up to 20 times more. Theory suggests
that the small ones lost a lot of normal matter through supernova
explosions, which do not affect the DM, and which helps protect
smaller systems against gravitational shredding by larger ones.
Not to be left out, dark energy makes its mark locally as well,
seeming to become significant by the time we reach the outer edge
of the Local Group, our own small cluster of galaxies. Whatever
it is, it seems to be an inherent property of space.
At the end, the seven-year WMAP (Wilkinson Microwave Explorer)
results are in, which give an age to the Universe of 13.75
billion years (since the Big Bang), a Hubble constant of 70.4
kilometers per second per Megaparsec, the Universe "flat,"
Euclidean, and closed to within 0.23 percent. The mass-energy
mix that achieves such flatness is made of 73 percent dark
energy, 22 percent dark matter, and just five percent normal
matter. Of the last, a mere half percent is in stars, leaving
3.5 percent or so (the numbers all subject to minor change)
presumed to be in hot intergalactic gas, some of which was
observed, but the rest actually missing. It's just been found as
the cooler WHIM (the "warm-hot intergalactic medium"), leaving
our story satisfyingly complete. If only we knew what makes some
95 percent of it all. Whatever it all is, without it we
undoubtedly would not be here.