Topic: Early Julyl Astronomy Bulletin

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JUPITER NOW HAS 69 KNOWN MOONS
Nature World News

A new study has shown that Jupiter, the biggest planet in the Solar
System, has at least 69 moons.  The U.S. Department of Terrestrial
Magnetism said that the study, which was originally conducted to
survey distant objects within the Kuiper Belt and beyond Pluto, also
aimed to look for new planets such as Planet X.  It just so happened
that Jupiter was within the area in which the research was conducted
in March 2016 and March 2017.  The research imaged fields near
Jupiter, offering a chance to examine the regions near the planet and
to look for its moons.  The already-known moons were detected as well
as new ones.  Some previously-detected ones had been 'lost' but were
re-discovered, and some not previously known were seen for the first
time.  In March 2016 and 2017, S/2016 J1 and S/2017 J1 were observed,
respectively.  It has been confirmed that those are not already-
observed but 'lost' objects, but are two 'new' moons that are now
included in the total of 69.  There could still be other new Jupiter
moons detected in the observations, but the researchers want to re-
observe and confirm them first in 2018 to know for sure.

In 2003, there were several known Jupiter moons that were believed to
have been lost and were never recognized again until now.  There was
too little information available about their orbits, so it was not
possible to predict where they should be at any given time.  In 2016,
there were 14 'lost' Jupiter moons.  In the new study, five of the 14
lost moons were found.  The researchers believe that they could have
found all 14 of them, but it would require further analysis to cross-
check if they were indeed the lost ones or were newly discovered ones.


DID OUR SUN HAVE A TWIN?
University of California at Berkeley

Did our Sun have a twin when it was born 4.5 billion years ago?
Almost certainly yes -- though not an identical twin.  And so did
every other Sunlike star in the Universe, according to a new analysis
by a theoretical physicist from the University of California at
Berkeley, and a radio astronomer from the Smithsonian Astrophysical
Observatory at Harvard.  Many stars have companions, including our
nearest neighbour, Alpha Centauri, a triple system.  Astronomers have
long sought an explanation.  Are binary and triple star systems born
that way?  Did one star capture another?  Do binary stars sometimes
split up and become single stars?  Astronomers have even searched for
a companion to our Sun, a star dubbed Nemesis because it was supposed
to have kicked into the Earth's orbit an asteroid that collided with
our planet and exterminated the dinosaurs.  But it has never been
identified.  The new assertion is based on a radio survey of a giant
molecular cloud filled with recently formed stars in the constellation
Perseus, and a mathematical model that can explain the Perseus
observations only if all Sun-like stars are born with a companion. 
The astronomers ran a series of statistical models to see if they
could account for the relative populations of young single stars and
binaries of all separations in the Perseus molecular cloud, and the
only model that could reproduce the data was one in which all stars
form initially as wide binaries.  Those systems then either shrink or
break apart within a million years.  In that study, 'wide' means that
the two stars are separated by more than 500 astronomical units (AU).
(1 AU is the average distance between the Sun and the Earth.)  A wide
binary companion to the Sun would have been at least 17 times farther
from the Sun than Neptune.  On the basis of that model, the Sun's
sibling most likely escaped and mixed with all the other stars in our
region of the Milky Way galaxy, never to be recognized.  Astronomers
have speculated about the origins of binary- and multiple-star systems
for hundreds of years, and in recent years have created computer simu-
lations of collapsing masses of gas to understand how they condense
under gravity into stars.  They have also simulated the interaction of
many young stars recently freed from their gas clouds.  Several years
ago, one such simulation at the University of Bonn led astronomers to
conclude that all stars are born as binaries.

Yet direct evidence from observations has been scarce.  As astronomers
look at younger and younger stars, they find a greater proportion of
binaries, but why is still a mystery.  Astronomers have known for
several decades that stars are born inside egg-shaped cocoons called
dense cores, which are sprinkled throughout immense clouds of cold,
molecular hydrogen that are the nurseries for young stars.  Through an
optical telescope, such clouds look like holes in the starry sky,
because the dust accompanying the gas blocks light from both the stars
forming inside and the stars behind.  The clouds can, however, be
probed by radio telescopes, since the cold dust grains in them emit at
radio wavelengths, and radio waves are not blocked by the dust.  The
Perseus molecular cloud is one such stellar nursery, about 600 light-
years away and about 50 light-years long.  Last year, a team of
astronomers completed a survey that used the Very Large Array, a
collection of radio dishes in New Mexico, to look at star formation
inside the cloud.  Called VANDAM, it was the first complete survey of
all young stars in a molecular cloud, that is, stars less than about
4 million years old, including both single and multiple stars down to
separations of about 15 astronomical units.  It captured all multiple
stars with a separation of more than about the radius of Uranus' orbit
-- 19 AU -- in the Solar System.  The VANDAM survey produced a census
of all Class 0 stars -- those less than about 500,000 years old -- and
Class I stars -- those between about 500,000 and 1 million years old.
Both types of stars are so young that they are not yet burning
hydrogen to produce energy.  The results from VANDAM were combined
with additional observations that reveal the egg-shaped cocoons around
the young stars.  Those additional observations come from the Gould
Belt Survey with SCUBA-2 on the Maxwell Telescope in Hawaii.  From
those data, it was discovered that all of the widely separated binary
systems -- those with stars separated by more than 500 AU -- were very
young systems, containing two Class 0 stars.  Those systems also
tended to be aligned with the long axis of the egg-shaped dense core.
The slightly older Class I binary stars were closer together, many
separated by about 200 AU, and showed no tendency to align along the
egg's axis.  There is an implication that each dense core, which
typically comprises a few solar masses, converts twice as much
material into stars as was previously thought.


TEN EARTH-SIZE PLANETS WITHIN HABITABLE ZONE
NASA

The Kepler space-telescope team has produced a catalogue that lists
219 new planet candidates, 10 of which are of near-Earth size and
orbiting in their respective stars' habitable zones -- the range of
distance from a star where liquid water could pool on the surface of a
rocky planet.  It is a comprehensive and detailed catalogue of candi-
date exo-planets (planets outside the Solar System), from Kepler's
first four years of data.  It is also the final catalogue from the
spacecraft's view of a patch of sky in the constellation Cygnus.  With
the release of that catalogue, derived from data publicly available on
the NASA Exo-planet Archive, there are now 4,034 planet candidates
identified by Kepler, of which 2,335 have been verified as exo-planets.
Of roughly 50 near-Earth-size habitable-zone candidates detected by
Kepler, more than 30 have been verified.  Additionally, results using
Kepler data suggest two distinct size groupings of small planets.
Both results have significant implications for the search for life.
The final Kepler catalogue will serve as the foundation for more study
to determine the prevalence and demographics of planets in the Galaxy,
while the discovery of the two distinct planetary populations shows
that about half the planets we know of in the Galaxy either have no
surface, or one that lies beneath a deep, crushing atmosphere --
environments unlikely to encourage life.  The Kepler space telescope
hunts for planets by detecting the minuscule drop in a star's
brightness that occurs during a transit, when a planet crosses in
front of it.

This is the eighth instalment of the Kepler candidate catalogue,
gathered by re-processing the entire set of data from Kepler's
observations during the first four years of its primary mission. 
The data are expected to go some way towards enabling scientists to
determine what planetary populations -- from rocky bodies the size of
the Earth, to gas giants the size of Jupiter -- make up the Galaxy's
planetary demographics.  To try to ensure that many planets were not
missed, the team introduced their own simulated planet-transit signals
into the data set and determined how many their software identified as
planets.  Then they added spoof data such as might appear to come from
a planet, but were actually false signals, and checked how often the
analysis mistook them for actual planet candidates.  Those experiments
indicated which types of planets were over-counted and which were
under-counted by the Kepler team's data-processing methods.


FIRST BLACK-HOLE VISUAL BINARY?
National Radio Astronomy Observatory

Astronomers using the Very-Long-Baseline Array (VLBA) have made the
first detection of orbital motion in a pair of super-massive black
holes in a galaxy some 750 million light-years away.  The object, an
elliptical galaxy, called 0402+379 after its location in the sky, was
first observed in 1995.  The two black holes, with a combined mass
15 billion times that of the Sun, are probably separated by 'only'
about 24 light-years, extremely close for such a system.  This is the
first pair of black holes to be seen as separate objects that are
moving with respect to each other, so this is the first black-hole
'visual' binary.  Super-massive black holes, with millions of times
the mass of the Sun, are thought to reside at the cores of most
galaxies.  The presence of two such monsters at the centre of a single
galaxy is taken to mean that two galaxies merged with one another some
time in the past.  In such a case, the two black holes themselves may
eventually merge in an event that would produce gravitational waves
that would ripple out across the Universe.  Researchers believe that
millions of years into the future the two super-massive black holes in
0402+379 will merge.  The latest research incorporates new VLBA
observations from 2009 and 2015, along with re-analysis of earlier
VLBA data.  This work has revealed motion of the two cores, confirming
that the two black holes are orbiting one another.  The scientists'
initial calculations indicate that they complete a single orbit in
about 30,000 years.  The astronomers also hope to discover other such
systems. The galaxy mergers that bring two super-massive black holes
close together are considered to be a common process in the Universe,
so astronomers expect that such binary pairs ought to be common.
 

MASSIVE DEAD DISC GALAXY FOUND
NASA/Goddard Space Flight Center

By combining the power of a 'natural lens' in space with the capabil-
ity of the Hubble telescope, astronomers made a surprising discovery
-- the first example of a compact yet massive, fast-spinning, disc-
shaped galaxy that stopped making stars 'only' a few thousand million
years after the 'Big Bang'.  Finding such a galaxy early in the
history of the Universe challenges the current understanding of how
massive galaxies form and evolve.  When Hubble photographed the
galaxy, astronomers expected to see a chaotic ball of stars formed
through galaxies merging together.  Instead, they saw evidence that
the stars were born in a pancake-shaped disc.  This is the first
direct observational evidence that at least some of the earliest
so-called 'dead' galaxies -- where star formation stopped -- somehow
evolve from Milky-Way-shaped discs into the giant elliptical galaxies
we see today.  This is a surprise because elliptical galaxies contain
older stars, while spiral galaxies typically contain younger blue
stars.  At least some of the early 'dead' disc galaxies must have gone
through major make-overs.  They not only changed their structure, but
also the motions of their stars to make the shape of an elliptical
galaxy.  Previous studies of distant dead galaxies have assumed that
their structure is similar to the local elliptical galaxies they will
evolve into.  Confirming that assumption in principle requires more
powerful space telescopes than are currently available.  However,
through the phenomenon known as gravitational lensing, a massive,
foreground cluster of galaxies acts as a natural lens in space by
magnifying and stretching images of more-distant background galaxies.
By supplementing such a natural lens with the resolving power of
Hubble, scientists were able to see into the centre of the dead
galaxy.

The remote galaxy is three times as massive as the Milky Way but only
half the size.  Rotational-velocity measurements made with the
European Southern Observatory's Very Large Telescope (VLT) showed that
the disc galaxy is spinning more than twice as fast as the Milky Way.
Using archival data from the Cluster Lensing And Supernova survey with
Hubble (CLASH), astronomers were able to determine the stellar mass,
star-formation rate, and the ages of the stars.  Why that galaxy
stopped forming stars is still unknown.  It may be the result of an
active galactic nucleus, where energy is gushing from a super-massive
black hole; such energy inhibits star formation by heating the gas or
expelling it from the galaxy.  Or it may be the result of the cold gas
streaming onto the galaxy being rapidly compressed and heated up, pre-
venting it from cooling down into star-forming clouds in the galaxy's
centre.  But how do young, massive, compact discs evolve into the
elliptical galaxies we see in the present-day Universe?  If those
galaxies grow through merging with minor companions, and the minor
companions come in large numbers and from all sorts of different
angles onto the galaxy, that would eventually randomize the orbits of
stars in the galaxies.  Major mergers would definitely also destroy
the ordered motion of the stars.