WILL THE EARTH STILL EXIST FIVE BILLION YEARS FROM NOW?
Catholic University of Leuven
What will happen to the Earth when, in a few billion years' time, the
Sun is a hundred times bigger than it is today? Using the most powerful
radio telescope in the world, an international team of astronomers has
set out to look for answers in the star L2 Puppis. Five billion years ago,
that star was very similar to the Sun as it is today. Five billion years from
now, the Sun will have grown into a red giant star, more than a hundred
times larger than its current size. It will also experience intense mass
loss through a very strong stellar wind. The end product of its
evolution, 7 billion years from now, will be a tiny white-dwarf star.
That will be about the size of the Earth, but much more massive:
a teaspoonful of white-dwarf material has a mass of about 5 tons.
That metamorphosis will have a dramatic impact on the planets of
the Solar System. Mercury and Venus will be engulfed by the giant
Sun and destroyed, but the fate of the Earth is still uncertain.
We already know that the Sun will be much bigger and brighter, so it
will probably destroy all forms of life on our planet. But will the
Earth's rocky core survive the red-giant phase and continue orbiting
the white dwarf?
In an effort to answer that question, an international team of astro-
nomers observed the evolved star L2 Puppis. That star is 208 light-
years away -- which in astronomical terms is nearby. The researchers
used the ALMA radio telescope, which consists of 66 individual radio
antennae that together contitute a telescope with a diameter of 16
kilometres. They discovered that L2 Puppis is about 10 billion years
old. Five billion years ago, that star was an almost perfect twin of
the Sun as it is today, with the same mass. One third of its mass was
lost during the evolution of the star. The same will happen with the
Sun in the very distant future. 300 million kilometres from L2 Puppis
-- twice the distance between the Sun and the Earth -- the researchers
detected an object orbiting the giant star. In all likelihood, it is
a planet that offers a unique preview of our Earth five billion years
from now. A deeper understanding of the interactions between L2
Puppis and its planet should yield interesting information on the
final evolution of the Sun and its impact on the planets in the Solar
System. Whether the Earth will eventually survive the Sun or be
destroyed is still uncertain; L2 Puppis may be the key to answering
that question.
SATURN'S MOONS YOUNGER THAN WAS THOUGHT
Cornell University
Freshly harvested data from the Cassini mission reveal that Saturn's
moons may be younger than previously thought. Members of the Europe-
based Encelade scientific team that pored over the Cassini data
provided two key measurements in the research: the rigidity of the
tidal bulge, or the Love number -- named for Augustus E.H. Love, a
distinguished British mathematician who studied elasticity -- and the
dissipation factor, which controls the speed at which moons move away.
While Saturn is mostly a gigantic shroud of liquid hydrogen and liquid
helium, it contains a rocky core about 18 times the size of the Earth,
which responds to tidal forces from all of Saturn's major moons by
bulging. The forces of the bulging core, in turn, push the moons
slightly away. The two parameters -- the Love number and dissipation
factor -- are difficult to separate. So the team detected and exam-
ined the orbits of four tiny moons associated with the larger moons
Tethys (Telesto and Calypso) and Dione (Helene and Polydeuces). While
those tiny moons produce neglible tidal forces on Saturn, their orbits
are disturbed by the tidal bulges of Saturn's core. By monitoring the
disturbances, the team managed to obtain the first measurement of
Saturn's Love number and distinguish it from the dissipation factor.
The moons are migrating away much faster than was expected.
Experts believe that if Saturn's moons actually formed 4.5 billion
years ago, soon after the birth of the Solar System, their
current distances from the planet should be greater. Thus, the new
research implies that the moons are younger than 4.5 billion years,
favouring a theory that the moons formed from Saturn's rings. The
team also found that the moon Rhea is moving away 10 times faster
than the other moons, which is the first evidence that a planet's
dissipation factor can vary with its distance in relation to the moon.
The scientists have no good explanation; what is believed about the
history of Saturn's moons might still change in the coming years with
the conclusion of the Cassini mission.
CASSINI MISSION APPROACHES FINALE
BBC SCIENCE
The Cassini space probe was launched in 1997 and arrived at Saturn in
2004 July. Since then it has been in orbit around the planet and has
sent back a stream of images of the surface as well as of the moons.
Its principal discoveries have included the observation that Enceladus
is spewing water into space from a sub-surface ocean, and that Titan
is a strange Earth-like world where lakes and seas are fed by rivers
and rain -- except that it is frightfully cold, and the liquid is not
water but is a mixture of hydrocarbons such as methane.
Having spent 12 years orbiting around Saturn and seeing its moons at a
relatively safe distance, the Cassini probe is now about to undertake
a series of dare-devil manoeuvres. They will make the satellite dive
repeatedly extremely close to - and through - the rings over the next
nine months. The manoeuvres will culminate in Cassini ditching itself
in Saturn's atmosphere. That destructive ending is necessary because
the spacecraft is running low on fuel. NASA, which leads the Cassini
mission, wants to make sure that an out-of-control probe does not at
some future date crash into any of Saturn's moons - in particular,
Enceladus and Titan. There is a chance that those moons harbour life,
and a colliding satellite could introduce contamination from the
Earth. That must not be allowed to happen. But in the lead-up to its
safe disposal - set for September 15 next year - Cassini should gather
some remarkable science. Starting on Wednesday, Cassini will repeat-
edly climb high above Saturn's north pole and then plunge to a point
just outside the F ring (the outer boundary of the main ring system).
The probe will do 20 such orbits, even sampling some of the particles
and gases associated with the F ring. Then, starting on April 22
next year, Cassini will initiate a series of dives that will take it
between the inner edge of the rings and the planet's atmosphere. On
occasion, it could pass less than 2,000 km above Saturn's cloud tops.
As well as returning some spectacular imagery of the rings and of
moonlets previously seen only from a great distance, the upcoming
manoeuvres are designed to permit investigation of Saturn's interior.
NEW EVIDENCE ON THE FORMATION OF THE SOLAR SYSTEM
Monash University
Scientists find that new computer models and evidence from meteorites
show that a low-mass supernova triggered the formation of the Solar
System. About 4.6 billion years ago, a cloud of gas and dust that
eventually formed the Solar System was disturbed. The ensuing
gravitational collapse formed the proto-Sun with a surrounding disc
where the planets were born. A supernova would have enough energy to
induce the collapse of such a gas cloud. The research team decided to
focus on short-lived radioactive nuclei that were present only in the
early Solar System. Owing to their short lifetimes, those nuclei
could have come only from the triggering supernova. Their abundances
in the early Solar System have been inferred from their decay products
in meteorites. As the debris from the formation of the Solar System,
meteorites are comparable to the leftover bricks and mortar in a
construction site. They tell us what the system is made of and, in
particular, what short-lived nuclei the triggering supernova provided.
Identification of those 'fingerprints' of the supernova is what was
needed for an understanding of how the formation of the Solar System
was initiated. The fingerprints point uniquely to a low-mass super-
nova as the trigger. In addition to explaining the abundance of
beryllium-10, the low-mass-supernova model would also explain the
short-lived nuclei calcium-41, palladium-107, and a few other isotopes
found in meteorites.
EXPLANATION OF SUPERLUMINOUS EVENT
ESO
In 2015, the All-Sky Automated Survey for SuperNovae (ASAS-SN)
detected an event, named ASASSN-15lh, that was recorded as the
brightest supernova ever seen, and categorised as a superluminous
supernova -- the explosion of an extremely massive star at the end of
its 'life'. It was twice as bright as the previous record-holder, and
at its peak was 20 times brighter than the total light output of the
entire Milky Way. An international team has now made additional
observations of the distant galaxy, about 4 billion light-years away,
where the explosion took place and they have proposed a new explanation
for this extraordinary event. The source was observed for 10 months
following the event and it has been concluded that the explanation is
unlikely to lie with an extraordinarily bright supernova. The results indicate
that the event was probably caused by a rapidly spinning super-massive
black hole as it destroyed a low-mass star. In that scenario, the
extreme gravitational forces of a supermassive black hole, located in
the centre of the host galaxy, ripped apart a Sun-like star that came
too close -- a so-called tidal disruption event, something so far only
observed about 10 times. In the process, the star was 'spaghettified',
and shocks in the colliding debris as well as heat generated in
accretion led to a burst of light. That gave the event the appearance
of a very bright supernova explosion, even though the star would not
have become a supernova on its own as it did not have enough mass.
The team based its new conclusions on observations from a selection of
telescopes, both on the ground and in space. Among them was the Very
Large Telescope at the Paranal Observatory, the New Technology Tele-
scope at La Silla, and the Hubble Space Telescope. The observations
with the NTT were made as part of the Public ESO Spectroscopic Survey
of Transient Objects (PESSTO).
There are several independent aspects of the observations that suggest
that the event was indeed a tidal disruption and not a super-luminous
supernova. In particular, the data showed that the event went through
three distinct phases over the 10 months of follow-up observations.
Overall, those data resemble more closely what would be expected for a
tidal disruption rather than a supernova. An observed re-brightening
in ultraviolet light, as well as a temperature increase, further
reduce the likelihood of a supernova event. Furthermore, the location
of the event, in a red, massive and passive galaxy, would be unusual
for a super-luminous supernova explosion; such events normally occur
in blue, star-forming dwarf galaxies. Although the team says that a
supernova source is therefore very unlikely, it accepts that a
classical tidal-disruption event would not be an adequate explanation
for the event either. The tidal-disruption event proposed cannot be
explained with a non-spinning super-massive black hole. The team
argues that ASASSN-15lh was a tidal-disruption event arising from a
very particular kind of black hole. The mass of the host galaxy
implies that the black hole at its centre has a mass of at least 100
million times that of the Sun. A black hole of such a mass would
normally be unable to disrupt stars outside its event horizon -- the
boundary within which nothing is able to escape its gravitational
pull. However, if the black hole is a particular kind that happens to
be rapidly spinning -- a so-called Kerr black hole -- the situation
changes and that limit no longer applies.
SECOND-GENERATION STARS IDENTIFIED
University of Notre Dame
Astronomers have identified what they believe to be the second
generation of stars, shedding light on the nature of the Universe's
first stars. A sub-class of carbon-enhanced metal-poor (CEMP) stars,
the so-called CEMP-no stars, are ancient stars that have large amounts
of carbon but little of the heavy metals (such as iron) common to
later-generation stars. Massive first-generation stars made up of
pure hydrogen and helium produced and ejected heavier elements by
stellar winds during their lifetimes or when they exploded as super-
novae. Those metals -- anything heavier than helium, in astronomical
parlance -- polluted the nearby gas clouds from which new stars
formed. The team has shown that the lowest-metallicity stars, the
most chemically primitive, include large fractions of CEMP stars.
The CEMP-no stars, which are also rich in nitrogen and oxygen, are
probably the stars born out of hydrogen and helium gas clouds that
were polluted by the elements produced by the Universe's first stars.
The CEMP-no stars we see today, or at least many of them, were born
shortly after the Big Bang, 13.5 billion years ago, out of almost
completely unpolluted material. Those stars, located in the halo of
our Galaxy, are true second-generation stars, born out of the nucleo-
synthesis products of the very first stars.
It is unlikely that any of the Universe's first stars still exist,
but much can be learned about them from detailed studies of the next
generation of stars. Astronomers are analyzing the chemical products
of the very first stars by looking at what was locked up by the
second-generation stars. They can use that information to tell the
story of how the first elements were formed, and determine the
distribution of the masses of those first stars. If we know how their
masses were distributed, we can model the process of how the first
stars formed and evolved from the very beginning. The authors used
high-resolution spectroscopic data gathered by many astronomers to
measure the chemical compositions of about 300 stars in the halo of
the Milky Way. More and heavier elements form as later generations of
stars continue to contribute additional metals. As new generations of
stars are born, they incorporate the metals produced by the earlier
generations. Hence, the more heavy metals a star contains, the more
recently it was born. Our Sun, for example, is relatively young, with
an age of only 4.5 billion years.
DARK MATTER MAY BE SMOOTHER THAN EXPECTED
RAS
Analysis of a great new galaxy survey, made with ESO's VLT Survey
Telescope in Chile, suggests that dark matter may be less dense and
more smoothly distributed throughout space than has previously been
thought. An international team used data from the Kilo Degree Survey
(KiDS) to study how the light from about 15 million distant galaxies
was affected by the gravitational influence of matter on the largest
scales in the Universe. The results appear to be in disagreement with
earlier findings from the Planck satellite. For their analysis,
researchers used survey images that covered five patches of the sky
covering a total area of about 2200 times the size of the Full Moon
and containing around 15 million galaxies. They were able to carry
out one of the most precise measurements ever made of an effect known
as cosmic shear -- a subtle variant of weak gravitational lensing, in
which the light emitted from distant galaxies is slightly warped by
the gravitational effect of large amounts of matter, such as galaxy
clusters. In cosmic shear, it is not galaxy clusters but large-scale
structures in the Universe that warp the light -- they produce an even
smaller effect. Very wide and deep surveys, such as KiDS, are needed
to ensure that the very weak cosmic-shear signal is strong enough to
be measured and can be used by astronomers to map the distribution of
gravitating matter. The presently described study relates to the
largest area of the sky ever to be mapped with that technique so far.
Intriguingly, the results of the analysis appear to be inconsistent
with deductions from the results of ESA's Planck satellite, the
leading space mission probing the fundamental properties of the
Universe. In particular, the KiDS team's measurement of how clumpy
matter is throughout the Universe -- a key cosmological parameter --
is significantly lower than the value derived from the Planck data.
This latest result indicates that dark matter in the cosmic web, which
accounts for about one-quarter of the content of the Universe, is less
clumpy than we previously believed. Despite making up about 85% of
the matter in the Universe, dark matter remains elusive, and rather
than being detected directly, its presence is only inferred from its
gravitational effects. Studies like these are the best current way to
determine the shape, scale and distribution of the invisible material.
The surprise result of this study also has implications for our wider
understanding of the Universe, and how it has evolved during its
almost-14-billion-year history. Such an apparent disagreement with
previously established results from Planck means that astronomers may
now need to re-formulate their understanding of some fundamental
aspects of the development of the Universe. The findings will help to
refine our theoretical models of how the Universe has grown from its
inception up to the present day. The KiDS analysis of data from the
VST is an important step, but future telescopes are expected to make
even wider and deeper surveys of the sky. Unravelling what has
happened since the Big Bang is a complex challenge, but by continuing
to study the distant skies, we can build a picture of how our modern
Universe has evolved. We see an intriguing discrepancy with Planck
cosmology at the moment. Future missions such as the Euclid satellite
and the Large Synoptic Survey Telescope will allow us to repeat these
measurements and perhaps understand better what the Universe is really
telling us.
FIRST SIGNS OF WEIRD QUANTUM PROPERTY IN EMPTY SPACE?
RAS
By studying with the VLT the light emitted from an extraordinarily
dense and strongly magnetized neutron star, astronomers may have found
the first observational indications of a strange quantum effect, first
predicted in the 1930s. The polarisation of the observed light
suggests that the empty space around the neutron star is subject to a
quantum effect known as vacuum birefringence. Astronomers used the
Very Large Telescope (VLT) at the Paranal Observatory in Chile to
observe the neutron star RX J1856.5-3754, about 400 light-years away.
Despite being amongst the closest neutron stars, its extreme dimness
meant that the astronomers could only observe the star in visible
light with the FORS2 instrument on the VLT, at the limits of current
telescope technology. Neutron stars are the very dense remnant cores
of massive stars (at least 10 times the mass of the Sun) that have
exploded as supernovae at the ends of their 'lives'. They also have
extreme magnetic fields, billions of times stronger than that of the
Sun, which permeate their outer surfaces and surroundings. The fields
are so strong that they even affect the properties of the empty space
around the star. Normally a vacuum is thought of as being completely
empty, and light can travel through it without being changed. But in
quantum electrodynamics (QED), the quantum theory describing the
interaction between photons and charged particles such as electrons,
space is full of virtual particles that appear and vanish all the
time. Very strong magnetic fields can modify the space so that it
affects the polarization of light passing through it.
According to QED, a highly magnetized vacuum behaves as a prism for
the propagation of light, an effect known as vacuum birefringence.
Among the many predictions of QED, however, vacuum birefringence so
far lacked a direct experimental demonstration. Attempts to detect it
in the laboratory have not yet succeeded in the 80 years since it was
predicted in a paper by Werner Heisenberg (of uncertainty-principle
fame) and Hans Heinrich Euler. The effect can be detected only in the
presence of enormously strong magnetic fields, such as those around
neutron stars. After careful analysis of the VLT data, the team
detected linear polarization, at a significant level of around 16%,
that they say is most probably due to the boosting effect of vacuum
birefringence occurring in the area of empty space surrounding
RX J1856.5-3754. That is the faintest object for which polarization
has ever been measured. The high linear polarization measured with
the VLT can not easily be explained by models unless the vacuum
birefringence effects predicted by QED are included. Further improve-
ments to this area of study could come about with more advanced
telescopes. Polarization measurements with the next generation of
telescopes, such as ESO's E-ELT, could play a crucial role in testing
QED predictions of vacuum birefringence effects around many more
neutron stars. The presently described measurement, made for the
first time now in visible light, also paves the way to similar
measurements to be carried out at X-ray wavelengths.
FOUR NEW ELEMENTS NAMED
SCIENCE DAILY
Four more elements have officially been added to the seventh row of
the Periodic Table. They are 113 nihonium (Nh), 115 moscovium (Mc),
117 tennessine (Ts), and 118 oganesson (Og). There have been mentions
of those four new elements since January, but the International Union
of Pure and Applied Chemistry (IUPAC) has finally announced that the
names have been officially approved. In keeping with tradition, the
new elements have been named after a place or geographical region, or
else a scientist. The endings of the names also reflect and maintain
historical and chemical consistency: '-ium' for elements 113 and 115,
as for all new elements of groups 1 to 16, '-ine' for element 117 and
belonging to group 17 and '-on' for element 118 belonging to group 18.
Nihonium is derived from Nihon, a Japanese word for Japan, and mosco-
vium honours the Russian capital city, Moscow. Tennessine is named
after the U.S. state of Tennessee, known for its pioneering research
in chemistry. It is the second state to be honoured in the periodic
table; the first was California, referenced by californium (element
98). Oganesson is named after the 83-year-old Russian physicist Yuri
Oganessian. This is only the second time that a new element has been
named after a living scientist.
Topic: Mid December Astronomy Bulletin (Read 2108 times)