CURIOUS TILT OF SUN'S AXIS ATTRIBUTED TO PLANET 9
Europlanet Media Centre
'Planet Nine' -- the undiscovered planet that was predicted by
astronomers in January this year to exist at the edge of the Solar
System -- has been held responsible for the tilt of the Sun's axis,
according to a new study. The large and distant planet may be adding
a wobble to the Solar System, giving the appearance that the Sun is
tilted slightly. The argumemt goes that, because Planet Nine is so
massive and has an orbit tilted with respect to the orbits of the
other planets, the Solar System is slowly twisted out of alignment.
All of the known planets' orbits lie close to a particular plane,
roughly within a couple of degrees of each other. That plane,
however, has a six-degree tilt with respect to the Sun, giving the
impression that the Sun's axis of rotation is at that angle from the
normal to the planetary orbits. Until now, no one had found a good
explanation for that. The discovery of evidence that the Sun is
orbited by an as-yet-unseen planet that is about 10 times the size of
the Earth, in an orbit that is about 20 times farther from the Sun on
average than Neptune's, changes the physics. Planet Nine,according to
the calculations, appears to orbit in a plane at about 30 degrees from
that of the other planets, influencing the orbits of a large popula-
tion of objects in the Kuiper Belt, which is how astronomers came to
suspect that a planet existed there in the first place.
The tilt of the Solar System's orbital plane has long been a puzzle to
astronomers because of the way the planets formed: as a spinning cloud
slowly collapsing first into a disc and then into objects orbiting the
central star. Planet Nine's angular momentum is having an outsized
impact on the Solar System on account of its location and size.
A planet's angular momentum equals the mass of the object multiplied
by its distance from the Sun, and represents the contribution that the
planet makes to the overall system's spin. Because the other planets
in the Solar System all orbit in practically the same plane, their
angular momenta work to keep the whole disc spinning smoothly.
Planet Nine's unusual orbit, however, adds a wobble to the system.
Mathematically, given the hypothesized size and distance of Planet
Nine, a six-degree tilt fits perfectly. The next question, then, is
how did Planet Nine achieve its unusual orbit? Though that remains to
be determined, it is suggested that the planet may have been ejected
from the neighbourhood of the gas giants by Jupiter, or perhaps may
have been influenced by the gravitational pull of other stellar bodies
in the Solar System's extreme past. For now, astronomers will be
searching the sky for signs of Planet Nine along the path that they
predicted in January. That search may take some time.
UNUSUAL 'BINARY BINARY' SYSTEM
Science News
A team of scientists has discovered a new 'binary-binary' system --
two massive companions around one star in a close binary system.
HD 87646 is a binary stellar system approximately 240 light-years
away. The primary, HD 87646A, is an 8th-magnitude solar-type star in
the constellation Leo, and has a mass about 1.12 times that of the
Sun. It is only 22 AU (astronomical units) away from the secondary
star, HD 87646B, a fainter K-type star with about 0.9 times the mass
of the Sun. HD 87646 is the first known system to have two massive
sub-stellar objects (a giant planet and a brown dwarf) orbiting a star
in a close binary system. The newly-discovered giant planet, called
MARVELS-7b, is 12 times the mass of Jupiter, while the brown dwarf,
MARVELS-7c, is 57 times Jupiter's mass. The two companions respect-
ively take 13.5 and 674 days to orbit their parent star, HD 87646A,
and are about 0.1 and 1.5 AU from it. In HD 87646, the two giant
companions are close to the minimum masses for burning deuterium and
hydrogen, implying that they have accumulated far more dust and gas
than a typical collapsed disc-like gaseous cloud can provide. They
were probably formed by a different mechanism. The interest of
HD 87646 was recognised in 2006 during the pilot survey of the
'Multi-object APO Radial Velocity Exoplanet Large- area Survey'
(MARVELS) of the SDSS-III programme. It has taken eight years of
follow-up data collection through collaboration with over 30
astronomers at seven other telescopes around the world and careful
data analysis to confirm what they call a "very bizarre" finding.
'HEARTBEAT STARS' UNLOCKED IN NEW KEPLER STUDY
NASA
Heartbeat stars, discovered in large numbers by the Kepler space
telescope, are binary stars (systems of two stars orbiting one
another) that got their name because a graph of their brightness over
time would look like an electrocardiogram, a graph of the electrical
activity of a human heart. Scientists are interested in them because
they are binary systems in elongated elliptical orbits. That makes
them natural laboratories for studying the gravitational effects of
stars on one another. In a heartbeat star system, the distance
between the two stars varies enormously as they orbit one another.
They can get as close together as a few stellar radii, and as far
apart as 10 times that distance during the course of one orbit. At
the point of their closest encounter, the stars' mutual gravitational
pull causes them to become slightly ellipsoidal in shape, which is one
of the reasons that their light is variable. They experience the same
type of 'tidal force' that causes ocean tides on the Earth. Tidal
forces also cause heartbeat stars to vibrate or 'ring' -- in other
words, the diameters of the stars fluctuate rapidly as they orbit one
another. The effect is most noticeable at the point of closest
approach, periastron. Once every orbital revolution, when the stars
reach periastron, it is as if they hit one another with a hammer. One
or both stars vibrate throughout their orbits, and when they get near
together, it is as though they are ringing very loudly.
Kepler discovered large numbers of heartbeat stars in the last several
years. A 2011 study discussed a star called KOI-54 that shows an
increase in brightness every 41.8 days. In 2012, a subsequent study
characterized 17 additional objects in the Kepler data and dubbed them
'heartbeat stars'. To characterise them, further data and research
were required. The study involved observations of 19 heartbeat star
systems with the Keck Telescope in Hawaii, using an instrument called
the High-Resolution Echelle Spectrometer (HIRES), to measure the
radial velocities of the stars from time to time and thereby determine
their orbits. It was found that the heartbeat stars in the sample
tend to be hotter and bigger than the Sun. Astronomers also postulate
that some binary systems of heartbeat stars could include a third star
that has not yet been detected, or even a fourth star. The mere
existence of heartbeat stars is a bit of a puzzle. The repeated tidal
stretching of heartbeat stars should quickly cause the systems to
evolve into circular orbits. A third star in a system is one way to
create the high-eccentricity elliptical orbits that are observed.
Researchers are currently pursuing follow-up studies to search for
third components in heartbeat star systems.
NEW CLASS OF EXPLOSIVE EVENTS
University of Alabama
Space energy anomalies more than 50 million light-years from our
Galaxy are creating conditions that should be destroying stars, but
instead are regenerating them. A team of researchers has detected
seven instances of massive flares of energy in X-ray binary stars in
two separate galaxies after poring through more than a decade of
Chandra X-ray Observatory data. But, unlike supernovae or gamma ray
bursts in other galaxies, which collapse and are destroyed by huge
increases in energy, the two stars detected by the researchers flare
to the verge of exploding, only to simmer down back to baseline energy
in an hour. They repeat the process every few days. Whatever these
objects are, there is evidently some sort of undiscovered mechanism by
which compact objects can accrete matter from a companion star.
It could be a black hole or a neutron star, but it is not something
observed in our own Galaxy. It must be rare enough that our Galaxy
does not contain an example as far as we know, and we have to look at
other galaxies to find any of them.
The team was looking for any types of variability in the X-ray sources
around distant galaxies, which can contain more than 100 different
sources per galaxy. An X-ray detector on the telescope provides a
photon-by-photon account of the X-rays that reach the detector.
Astronomers were looking for mild variations, maybe factors of three
over a time-scale of an hour, but they found sources that were varying
by a hundred on time-scales of a minute! The flares occurred in a
globular cluster, a system of a few hundred thousand stars associated
with the observed galaxy. The Milky Way Galaxy, for instance, has
roughly 150 globular clusters scattered throughout it. The fact that
the flares are occurring in globular clusters implies that there is
some sort of neutron star or a small- or intermediate-mass black hole
causing the cycle. It is possible that it is a somewhat larger
intermediate-mass black hole, tens of thousands times the mass of the
Sun. There could be material raining down onto the event horizon of
an intermediate-mass black hole in the star clusters. Scientists have
hypothesized for a long time that intermediate-mass black holes exist,
but there is really no good evidence for their existence. Additional
wavelengths, such as ultraviolet and radio, could help the team
determine what the objects could be. They are atypical -- the time-
scale and energy output is the second known category with those
characteristics in astronomy -- but access to high-powered telescopes
is limited. The time between bursts is uncomfortably long, about one
and a half to two days, and we do not know when it is going to happen
again. It is hard to go to a committee that allocates observing time
on a large telescope and say 'we want to observe this object for two
straight days, uninterrupted', in the hope that the time would be
allocated and then that an event of interest would actually happen
then. So the team is trying to come up with ways to predict -- given
the six bursts now known-- when the next one is going to be.
GLOWING HALOES AROUND DISTANT QUASARS
ESO
An international collaboration of astronomers has used the Very Large
Telescope (VLT) at the Paranal Observatory to study gas around distant
active galaxies (quasars), less than two billion years after the
Big Bang. The quasars contain in their centres super-massive black
holes, which consume stars, gas, and other material at extremely high
rates. That, in turn, causes the galaxy centres to emit huge amounts
of radiation, making quasars the most luminous and active objects in
the Universe. The new study involved 19 quasars, selected from among
the brightest that are observable with the MUSE spectrograph. Earlier
studies showed that around 10% of all quasars examined were surrounded
by haloes, made of gas known as the intergalactic medium. The haloes
extend up to 100 kiloparsecs (300,000 light-years) away from the
centres of the quasars. The study, however, has thrown up a surprise,
with haloes detected around all 19 quasars observed -- far more than
the two that were expected statistically. The team suspects that that
is due to the vast increase in the observing power of MUSE over
previous similar instruments, but further observations are needed to
determine whether that is really the case.
The original goal of the study was to analyse the gaseous components
of the Universe on the largest scales -- a structure sometimes
referred to as the cosmic web, in which quasars form bright nodes.
The gaseous components of the web are normally extremely difficult to
detect, so the illuminated haloes of gas surrounding the quasars
represent an almost unique opportunity to study the gas in that large-
scale cosmic structure. The 19 newly-detected haloes also produced
another surprise: they consist of relatively cool intergalactic gas --
approximately 10,000 degrees C. That revelation is in strong
disagreement with currently accepted models of the structure and
formation of galaxies, which suggest that gas in such close proximity to
galaxies should have temperatures upwards of a million degrees.
DOUBT CAST ON DARK ENERGY
University of Oxford
Five years ago, the Nobel Prize in Physics was awarded to three
astronomers for their discovery, in the late 1990s, that the Universe
is expanding at an accelerating pace. Their conclusions were based on
analysis of Type-Ia supernovae -- the spectacular thermonuclear
explosions of dying stars -- picked up by the Hubble space telescope
and large ground-based telescopes. It led to the widespread acceptance
of the idea that the Universe is dominated by a mysterious substance
named 'dark energy' that drove the alleged accelerating expansion.
Now, a team of scientists at Oxford University's Department of Physics
has cast doubt on that now-standard cosmological concept. Making use
of a vastly increased data set -- a catalogue of 740 Type-Ia super-
novae, more than ten times the original sample size -- the researchers
have found that the evidence for acceleration may be flimsier than has
been thought, the data actually being consistent with a constant rate
of expansion. The assertion of the accelerating expansion of the
Universe won for its promoters the Nobel Prize, the Gruber Cosmology
Prize, and the Breakthrough Prize in Fundamental Physics. It led to
the widespread acceptance of the idea that the Universe is dominated
by 'dark energy' that behaves like a cosmological constant -- this is
now the 'standard model' of cosmology. However, there now exists a
much bigger data base of supernovae on which to perform rigorous and
detailed statistical analyses. The team analysed the latest catalogue
of supernovae -- over ten times bigger than the original samples on
which the discovery claim was based -- and found that the evidence for
accelerated expansion is, at most, what physicists call '3 sigma' --
far short of the 5-sigma standard required to claim a discovery of
fundamental significance. An analogous example in this context would
be the recent suggestion of a new particle of 'mass' 750 GeV based on
data from the Large Hadron Collider at CERN. It initially had even
higher significance -- 3.9 and 3.4 sigma in December last year -- and
stimulated over 500 theoretical papers. However, it was announced in
August that new data show that the significance has dropped to less
than 1 sigma. It was just a statistical fluctuation, and there is no
such particle. Any facial redness, or other reaction or even apology,
of any of the authors of the 500-odd papers who were so quick off the
mark to explain something that was not really there has not been
disclosed.
There are other data available that appear to support the idea of an
accelerating Universe, such as information on the cosmic microwave
background -- the faint afterglow of the Big Bang -- from the Planck
satellite. However, all of such tests are indirect, carried out in
the framework of an assumed model, and the cosmic microwave background
is not directly affected by 'dark energy'. Actually, there has been
suggested a subtle effect (called 'the late-integrated Sachs-Wolfe
effect'; it is not worth trying to explain it here, especially since
it has not been convincingly detected.) So it is only too possible
that we are being misled, and that such apparent manifestation as
there may have been of 'dark energy' is a consequence of analysing the
data in an oversimplified theoretical model -- one that was in fact
constructed in the 1930s, long before there were any real data. A
more sophisticated theoretical framework, accounting for the fact that
the Universe is not exactly homogeneous and that its matter content
may not behave as an ideal gas -- two key assumptions of standard
cosmology -- may well be able to account for all observations without
requiring dark energy. Indeed, vacuum energy is something of which
scientists have absolutely no understanding in fundamental theory.
Naturally, a lot of work will be necessary to convince the physics
community of that, but the work serves to demonstrate that a key
pillar of the standard cosmological model is rather shaky. We may
hope that this will motivate better analyses of cosmological data, as
well as inspiring theorists to investigate more nuanced cosmological
models. Significant progress may be made when the European Extremely
Large Telescope makes observations with an ultra-sensitive 'laser
comb' to try to measure diectly, over a 10- to 15-year interval,
whether the expansion rate is indeed accelerating.
MARS ORBITER CAMERA REVEALS SIGNS OF SCHIAPARELLI
NASA
The Mars Reconnaissance Orbiter (MRO) has identified new markings on
the surface that are believed to be related to Europe's 'Schiaparelli'
test lander, which arrived at Mars on October 19. The new image shows
a bright spot that may be the lander's parachute, and a larger dark
spot interpreted as resulting from the impact of the lander itself
following a free fall much longer than planned, after thrusters
intended to brake its descent switched off prematurely. It was taken
by the Context Camera (CTX) on MRO and is available online, as a
before-and-after comparison with an image from 2016 May, at:
http://mars.nasa.gov/multimedia/images/?ImageID=8131The location information gained from acquiring the CTX image will be
used for imaging the site with MRO's 'High Resolution Imaging Science
Experiment' (HiRISE) camera. (With CTX, HiRISE and four other
instruments, MRO has been investigating Mars since 2006.) ESA and
NASA researchers will analyse the images for information about the
sequence of events on Schiaparelli's landing, possibly supplementing
data transmitted from the test module during its descent.
The location of the bright spot interpreted as the parachute is 353.79
degrees east longitude, 2.07 degrees south latitude, closely matching
ESA's calculation for the landing location based on landing-day data.
It is within the planned landing area and about 5.4 km west of the
centre of the landing target. The dark spot is larger and elliptical,
approximately 15 by 40 metres. It may be where the lander hit the
surface and exposed darker ground. The test lander is part of ESA's
ExoMars 2016 mission, which placed the 'Trace Gas Orbiter' into orbit
around Mars. The orbiter will investigate Mars' atmosphere and provide
relay communications capability for landers and rovers on the surface.
AUSTRALIAN RADIO TELESCOPE VIEWS SKY IN COLOUR
RAS
A telescope located deep in the West Australian outback has shown what
the Universe would look like if human eyes could see radio waves. The
GaLactic and Extragalactic All-sky MWA, or 'GLEAM' survey, has
produced a catalogue of 300,000 galaxies observed by the Murchison
Widefield Array (MWA), a $50 million radio telescope located at a
remote site north-east of Geraldton. It is the first radio survey to
image the sky in colour. The human eye sees brightness in three
different primary colours -- red, green and blue. GLEAM does much
better than that, viewing the sky in 20 primary colours. That beats
the very best in the animal kingdom, the mantis shrimp, which can see
12 different primary colours. GLEAM is a large-scale, high-resolution
survey of the radio sky observed at frequencies from 70 to 230 MHz,
observing radio waves that have in some cases been travelling through
space for thousands of millions of years. The survey is being used to
find out what happens when clusters of galaxies collide and to see the
remnants of explosions from the most ancient stars in our Galaxy, and
find the first and last gasps of supermassive black holes. GLEAM is
one of the biggest radio surveys of the sky ever assembled.
Completing the GLEAM survey with the Murchison Widefield Array is a
big step on the path to 'SKA-low', the low-frequency part of the
international Square Kilometre Array radio telescope to be built in
Australia in the coming years.
Topic: Early November Astronomy Bulletin (Read 1262 times)