EVIDENCE OF A REAL NINTH PLANET
California Institute of Technology
Caltech researchers have found evidence of a giant planet tracing a
bizarre, highly elongated orbit in the outer Solar System. The
object, which the researchers have nicknamed Planet Nine, is supposed
to have a mass about 10 times that of the Earth and orbits about 20
times further from the Sun on average than Neptune (which does so at
an average distance of 2800 million miles). In fact, it would take
the (still-hypothetical) planet between 10,000 and 20,000 years to
orbit round the Sun. The researchers' evidence for the planet's
existence came through mathematical modelling and computer simulations;
they have not observed the object directly. There have been only two
true planets discovered since ancient times, and this would be a
third. The putative ninth planet -- at 5,000 times the mass of Pluto
-- is sufficiently large that there should be no debate about whether
it is a true planet. Unlike the class of smaller objects now known as
dwarf planets, Planet Nine gravitationally dominates its neighbourhood
of the Solar System. In fact, it dominates a region larger than any
of the known planets.
The road to the theoretical discovery was not straightforward. In
2014, astronomers noted that 13 of the most distant objects in the
Kuiper Belt are similar with respect to an obscure orbital feature.
To explain that similarity, they suggested the possible presence of a
small planet. A year-and-a-half-long collaboration began to
investigate the distant objects. Fairly quickly it was realized that
the six most distant objects from the original 13 under study all
follow elliptical orbits that point in the same direction in space.
That is particularly surprising because the outermost points of their
orbits move around the Solar System, and they travel at different
rates. It is almost like having six hands on a clock all moving at
different rates, and when you happen to look up, they're all in
exactly the same place. The odds of having that happen are something
like 1 in 100. But on top of that, the orbits of the six objects are
also all tilted in the same way -- pointing about 30 degrees downward
in the same direction relative to the plane of the eight known
planets. The probability of that happening is about 0.007%. It could
not happen randomly, so something must be shaping the orbits.
The first possibility investigated by astronomers was that perhaps
there are enough distant Kuiper-Belt objects -- some of which have not
yet been discovered -- to exert the gravity needed to keep that
sub-population clustered together. The researchers quickly ruled that
out when it turned out that such a possibility would require the
Kuiper Belt to have about 100 times the mass that it actually has.
That left them with the idea of a planet. Their first instinct was to
run simulations involving a planet in a distant orbit that encircled
the orbits of the six Kuiper-Belt objects, acting like a giant lassoo
to wrangle them into their alignment. That almost works but does not
provide the observed eccentricities precisely. Then, effectively by
accident, the team noticed that if they ran their simulations with a
massive planet in an anti-aligned orbit -- an orbit in which the
planet's closest approach to the Sun, or perihelion, is 180 degrees
away from the perihelion of all the other objects and known planets --
the distant Kuiper-Belt objects in the simulation assumed the
alignment that is actually observed. Through a mechanism known as
mean-motion resonance, the anti-aligned orbit of the ninth planet
actually prevents the Kuiper-Belt objects from colliding with it and
keeps them aligned. As orbiting objects approach each other they
exchange energy. So, for example, for every four orbits Planet Nine
makes, a distant Kuiper-Belt object might complete nine orbits.
They never collide. Instead, like a parent maintaining the arc of a
child's swing by periodic pushes, Planet Nine nudges the orbits of
distant Kuiper-Belt objects such that their configuration with
relation to the planet is preserved.
Planet Nine's existence helps to explain more than just the alignment
of the distant Kuiper-Belt objects. It also provides an explanation
for the curious orbits that two of them trace. The first of those
objects, dubbed Sedna, was discovered in 2003. Unlike standard-
variety Kuiper-Belt objects, which can get gravitationally 'kicked
out' by Neptune but can then return back to it, Sedna never gets very
close to Neptune. A second object like Sedna, known as 2012 VP113,
was announced in 2014. The presence of Planet Nine in its proposed
orbit naturally produces Sedna-like objects by taking a standard
Kuiper-Belt object and slowly pulling it away into an orbit less
connected to Neptune. But the real clincher for the researchers was
the fact that their simulations also predicted that there would be
objects in the Kuiper Belt on orbits inclined perpendicularly to the
plane of the planets. In the last three years, observers have
identified four objects tracing orbits roughly along one perpendicular
line from Neptune and one object along another. Where did Planet Nine
come from and how did it end up in the outer Solar System? Scientists
have long believed that the early Solar System began with four planet-
ary cores that went on to grab all of the gas around them, forming the
four gas planets -- Jupiter, Saturn, Uranus, and Neptune. Over time,
collisions and ejections shaped them and moved them out to their
present locations. But there is no reason why there could not have
been five cores, rather than four. Planet Nine could represent that
fifth core, and if it got too close to Jupiter or Saturn, it could
have been ejected into its distant, eccentric orbit. Researchers
continue to refine their simulations and learn more about the planet's
orbit and its influence on the distant Solar System. Meanwhile,
astronomers have begun searching the skies for it. Only a rough orbit
is indicated, not the precise location of the planet. If the planet
happens to be close to its perihelion, astronomers should be able to
find it in images captured by previous surveys. If it is in the most
distant part of its orbit, the world's largest telescopes will be
needed to see it. If, however, Planet Nine is now located anywhere in
between, many telescopes might have a shot at finding it.
ETA CARINAE 'TWINS' FOUND IN OTHER GALAXIES
Space Telescope Science Institute (STScI)
Eta Carinae, the most luminous and massive stellar system within
10,000 light-years of us, is best known for an enormous eruption seen
in 1843 that ejected an amount of material at least 10 times the Sun's
mass into space. That expanding veil of gas and dust, which still
shrouds Eta Carinae, makes it the only object of its kind known in our
Galaxy. Now a study using archival data from the Spitzer and Hubble
space telescopes has found five similar objects in other galaxies.
The most massive stars are always rare, but they have tremendous
impact on the chemical and physical evolution of their host galaxy.
Such stars produce and distribute large amounts of different chemical
elements and eventually explode as supernovae. Located about 7,500
light-years away in the southern constellation of Carina, Eta Carinae
outshines the Sun by 5 million times. It is a binary system that
consists of two massive stars in a 5.5-year orbit. Astronomers
estimate that the more massive star has about 90 times the Sun's mass,
while the smaller companion may exceed 30 solar masses. As one of the
nearest laboratories for studying high-mass stars, Eta Carinae has
been a unique astronomical touchstone since its eruption in 1843.
To try to understand why the eruption occurred and how it relates to
the evolution of massive stars, astronomers needed to see additional
examples. Catching rare stars during the short-lived aftermath of a
major outburst approaches needle-in-a-haystack levels of difficulty,
and nothing matching Eta Carinae had been found previously.
Astronomers felt sure that others must be out there, it was really a
matter of deciding what to look for and of being persistent.
The researchers developed an optical and infrared fingerprint for
identifying possible Eta Carinae twins. Dust forms in gas ejected by
a massive star. The dust dims the star's ultraviolet and visible
light, but it absorbs and re-radiates that energy as heat at longer,
mid-infrared wavelengths. With Spitzer, a steady increase in
brightness starting at around 3 microns and peaking between 8 and 24
microns could be seen. By comparing that emission to the dimming seen
in Hubble's optical images, it could be determined how much dust was
present and compare it to the amount seen around Eta Carinae. An
initial survey of seven galaxies from 2012 to 2014 did not turn up any
Eta twins, underlining their rarity. It did, however, identify a
class of less-massive and less-luminous stars of scientific interest,
demonstrating that the search was sensitive enough to find Eta-like
stars had they been present. In a follow-up survey in 2015, the team
found two candidate Eta twins in the galaxy M83, located 15 million
light-years away, and one each in NGC 6946, M101, and M51, between 18
and 26 million light-years away. Those five objects mimic the optical
and infrared properties of Eta Carinae, indicating that each very
likely contains a high-mass star buried in five to 10 solar masses of
gas and dust. Further study should enable astronomers to estimate
more precisely their physical properties.
SECOND-LARGEST BLACK HOLE IN MILKY WAY
National Astronomical Observatory of Japan
Astronomers using the Nobeyama 45-m radio telescope have detected
signs of an invisible black hole with a mass of 100,000 solar masses
near the centre of the Milky Way. The team assumes that that possible
'intermediate-mass' black hole is a key to understanding the birth of
the super-massive black holes located in the centres of galaxies. The
observers found an enigmatic gas cloud, called CO-0.40-0.22, only 200
light-years away from the centre of the Milky Way. What makes
CO-0.40-0.22 unusual is its surprisingly great velocity dispersion:
the cloud contains gas with a very wide range of velocities. To
investigate the detailed structure, the team observed CO-0.40-0.22
again to obtain 21 emission lines from 18 molecules. The results show
that the cloud has an elliptical shape and consists of two components:
a dense component extending 10 light-years with a small velocity
dispersion, and a compact but low-density component with the very
large velocity dispersion of 100 km/s. What makes that velocity
dispersion so wide? There are no holes inside the cloud. Also, X-ray
and infrared observations did not find any compact objects. Those
features indicate that the velocity dispersion is not caused by a
local energy input, such as supernova explosions. The team performed
a simple simulation of gas clouds flung out by a strong-gravity
source. In the simulation, the gas clouds are first attracted by the
source and their speeds increase as they approach it, reaching maxima
at the closest point to the object. After that the clouds continue
past the object and their speeds decrease. The team found that a
model using a gravity source with 100,000 times the mass of the Sun in
a region with a radius of 0.3 light-years provided the best fit to the
observed data. In view of the fact that no compact objects are seen
in X-ray or infrared observations, the best candidate for the compact
massive object seems to be a black hole.
If that is the case, this is the first detection of an intermediate-
mass black hole. Astronomers already know about two sizes of black
holes: stellar-mass black holes, formed after the explosions of very
massive stars; and super-massive black holes (SMBH) often found at the
centres of galaxies. The masses of SMBHs range from several million
to billions of times the mass of the Sun. A number of SMBHs
has been found, but no one knows how they are formed. One idea is
that they are formed from mergers of many intermediate-mass black
holes. But that raises a problem, because so far no firm
observational evidence for intermediate-mass black holes has been
found. If the cloud CO-0.40-0.22, located 'only' 200 light-years away
from Sgr A* (the 400-million-solar-mass SMBH at the centre of the
Milky Way), contains an intermediate-mass black hole, it might support
the intermediate-mass-merger scenario of SMBH evolution. The results
open a new way to search for black holes with radio telescopes.
Recent observations have revealed that there is a number of wide-
velocity-dispersion compact clouds similar to CO-0.40-0.22. The team
proposes that some of those clouds might contain black holes. A study
suggested that there are 100 million black holes in the Milky Way
Galaxy, but X-ray observations have found only dozens so far. Most of
the black holes may be 'dark' and very difficult to see directly at
any wavelength. Investigations of gas motion with radio telescopes
may provide a complementary way to search for dark black holes.
'GREEN PEA' GALAXIES AND EARLY UNIVERSE EVOLUTION
University of Virginia
Newly formed dwarf galaxies may have caused the Universe to heat up
about 13 billion years ago, according to new work by an international
team of scientists. The finding opens an avenue to better understand-
ing of the early period of the Universe's 14-billion-year history.
In the period of several hundred thousand years after the Big Bang,
the Universe was so hot and dense that matter was ionized instead of
being in a neutral form. But 380,000 years later, the expansion of
the Universe had cooled it enough for matter to become neutral and for
the first structures of the Universe to form -- gas clouds of hydrogen
and helium. Gravity then made such gas clouds grow in mass and
collapse to form the first stars and galaxies. Then, about one
billion years after the Big Bang, another important transformation
occurred: the Universe re-heated, and hydrogen -- the most abundant
element -- became ionized again, as it had been shortly after the Big
Bang, an event which astronomers call 'cosmic re-ionization'. How
that happened is still debated. Astronomers have long thought that
galaxies were responsible for that transformation.
Using data from an ultraviolet spectrometer on the Hubble space tele-
scope, the team discovered a 'nearby' compact dwarf galaxy emitting a
large number of ionizing photons into the intergalactic medium (the
space between galaxies). Scientists believe that such photons are
responsible for the Universe's re-ionization. The galaxy appears to
be an excellent local analogue of the numerous dwarf galaxies thought
to be responsible for the re-ionization of the early Universe. The
finding is significant, because it gives us a good idea of where to
look to learn about the re-ionization phenomenon, which took place
early in the formation of the universe that became the Universe we
have today. Normal matter in the early Universe consisted mostly of
gas. Stars and star clusters are born from clouds of gas, forming the
first galaxies. Ultraviolet radiation emitted by those stars contains
numerous ionizing photons. For that reason, scientists have long
suspected that galaxies were responsible for cosmic re-ionization.
However, for re-ionization to occur, galaxies must eject the photons
into the intergalactic medium; otherwise, they are easily absorbed by
the gas and dust in the galaxies where they originate before they can
escape.
Despite 20 years of intensive searching, no galaxy emitting sufficient
ionizing radiation had been found, and the mechanism by which the
Universe became re-ionized remained a mystery. In an effort to solve
that problem, the international research team proposed to observe
'green-pea' galaxies. Discovered in 2007, those galaxies represent a
special and rare class in the nearby Universe. They appear green to
light sensors, and are round and compact, like a pea. They are
believed to host stellar explosions or winds strong enough to eject
ionizing photons. The team examined data from the Sloan Digital Sky
Survey -- a data base of more than a million galaxies. From that
survey, they identified approximately 5,000 galaxies that match their
criteria: very compact galaxies emitting very intense UV radiation.
Researchers selected five galaxies for observation with the Hubble
telescope. Using Hubble's UV-radiation-detecting capabilities, the
research team found that the 'green-pea' galaxy J0925+1403, located at
a distance of three billion light-years, was ejecting ionizing photons
with an intensity never seen before -- about an 8% ejection. That
fundamental discovery shows that galaxies of that type could explain
cosmic re-ionization, supporting the most common hypothesis for that
phenomenon.
COLOSSAL STAR EXPLOSION
BBC Science
Astronomers have seen what could be the most powerful supernova ever
detected. The exploding star was first observed in June last year but
is still radiating vast amounts of energy. At its peak, the event was
200 times more powerful than a typical supernova, making it shine with
570 billion times the brightness of the Sun (absolute magnitude about
-20). Researchers think that the explosion and ongoing activity have
been boosted by a very dense, very strongly magnetized, remnant object
called a magnetar. That object, created as the supernova got going,
is probably no bigger than a city such as London, and is probably
spinning at a fantastic rate -- perhaps a thousand times a second.
But it probably also is slowing, and as it does so, it is dumping that
rotational energy into the expanding shroud of gas and dust thrown
off in the explosion. The super-luminous supernova was observed
some 3.8 billion light-years away by the 'All-Sky Automated Survey for
SuperNovae' (ASAS-SN). That uses a suite of camera lenses at Cerro
Tololo, Chile, to sweep the sky for sudden brightenings. Follow-up
observations with larger facilities are then used to investigate
objects in more detail. The intention of ASAS-SN is to get better
statistics on the different types of supernovae and where they are
occurring in the cosmos.
Astronomers have long been fascinated by those monster explosions and
have come to recognize just how important they are to the story of how
the Universe has evolved. Not only do they forge the heavier chemical
elements in nature but their shock waves disturb the space environ-
ment, stirring up the gas and dust from which the next generation of
stars will be formed. The source star for the recent supernova must
have been 50 to 100 times the mass of the Sun. Such stars begin very
voluminous but then shed a lot of mass in great winds that blow out
into space. So, by the time that star blew up, it was probably much
reduced in size. It would have been very hot, however, about 100,000°
at the surface. Basically, it would have got rid of all of its
hydrogen and helium, leaving just the material that had been 'burnt'
into carbon and oxygen. There are signs that the supernova may be
about to fade, and the team has observing time on the Hubble telescope
in the coming weeks to try to understand the mechanisms driving the
supernova.
ANCIENT GAS CLOUD MAY BE RELIC FROM FIRST STARS
RAS
Researchers have discovered a distant, ancient cloud of gas that may
contain the signature of the very first stars that formed in the
Universe. The gas cloud has an extremely small percentage of heavy
elements, such as carbon, oxygen and iron -- less than a thousandth
the fraction observed in the Sun. It is many billions of light-years
away from the Earth, and is observed as it was just 1.8 billion years
after the Big Bang. The observations were made by the Very Large
Telescope in Chile. Heavy elements were not manufactured during the
Big Bang; they were made later by stars. The first stars were made
from completely pristine gas, and astronomers think that they formed
quite differently from stars today. The researchers say that soon
after forming, those first stars -- known as Population III stars --
exploded as powerful supernovae, spreading their heavy elements into
the surrounding clouds of gas. Those clouds then carried a chemical
record of the first stars and their deaths, and that record can be
read like a fingerprint. Previous gas clouds found by astronomers
show a higher enrichment level of heavy elements, so they were
probably polluted by more recent generations of stars, obscuring any
signature from the first stars. The newly observed cloud is the first
one to show the tiny heavy-element fraction expected for a cloud
enriched only by the first stars. The researchers hope to find more
such systems, where they can measure the ratios of several different
elements. By finding new clouds where more elements can be detected,
astronomers may be able to test for the unique pattern of abundances
expected for enrichment by the first stars.
FOUR NEW ELEMENTS FOR PERIODIC TABLE
Chemistry World
Confirmation that four new elements -- those with atomic numbers 113,
115, 117 and 118 -- have been synthesized has come from the
International Union of Pure and Applied Chemistry (IUPAC), completing
the seventh row of the Periodic Table. The groups credited for
creating them, in Japan, Russia and the US, have spent several years
gathering enough evidence to convince experts from IUPAC and its
physics equivalent, the International Union of Pure and Applied
Physics, of the elements' existence. All four are highly unstable
super-heavy metals that exist only for a fraction of a second. They
are made by bombarding heavy-metal targets with beams of ions, and can
usually only be detected by measuring the radiation and other nuclides
produced as they decay. Element 113, currently known by its place-
holder name ununtrium, is the first to be discovered in East Asia.
It was created by firing a beam of zinc-70 at a target made of
bismuth-209. Elements 115 (ununpentium) and 117 (ununseptium) were
discovered by groups collaborating across institutions in the US and
Russia. Element 118 (ununoctium) was discovered in the US. Now that
the elements have been officially discovered, the institutions
responsible will get to choose permanent names for them. But it will
be a while before the textbooks and posters can be updated, as the new
names and symbols will have to be approved by the inorganic chemistry
division of IUPAC and submitted for public review. Various rules
govern the names that can be given to new elements, which can be
inspired by nature, mythology, people or place.
Topic: Late January Astronomy Bulletin (Read 1715 times)