STAR IS ROSETTA STONE FOR UNDERSTANDING SUN
Aarhus University
The spots on the surface on the Sun come and go with an 11-year periodicity
known as the solar cycle. The solar cycle is driven by the solar dynamo,
which is an interplay between magnetic fields, convection and rotation.
However, our understanding of the physics underlying the solar dynamo is far
from complete. One example is the so-called Maunder Minimum, a period in
the 17th century, when spots almost disappeared from the surface of the Sun
for a period of over 50 years. Now, a large international team has found a
star that can help shed light on the physics underlying the solar dynamo.
The star is located 120 light-years away in the constellation Cygnus, and
on the surface, the star looks just like the Sun: it has the same mass,
radius and age -- but inside, the chemical composition of the star is very
different. It has around twice as much mass in heavy elements as the Sun.
Heavy elements here means elements heavier than hydrogen and helium. The
team has succeeded in combining observations from the Kepler spacecraft
with ground-based observations dating as far back as 1978, and have
reconstructed a 7.4-year cycle in the star. The unique combination of a
star almost identical to the Sun, except for the chemical composition, with
a cycle that has been observed from both the Kepler spacecraft and from the
ground, makes this star a Rosetta Stone for the study of stellar dynamos.
By combining photometric, spectroscopic and astero-seismic data, the team
collected the most detailed set of observations for a solar-like cycle in
any star other than the Sun. The observations revealed that the amplitude
of the cycle seen in the star's magnetic field is more than twice as strong
as that seen on the Sun, and the cycle is even stronger in visible light.
The team jumped to the conclusion that more heavy elements make a stronger
cycle. On the basis of models of the physics taking place in the deep
interior and the atmosphere of the star, the team was also proposed an
explanation of the stronger cycle. Actually, it came up with a two-part
explanation. First, the heavy elements make the star more opaque, which
changes the energy transport deep inside the star from radiation to
convection. That makes the dynamo stronger, affecting both the amplitude of
the variability in the magnetic field and the rotation pattern near the
surface. The latter effect was also measured. Second, the heavy elements
affect the processes on the surface and in the atmosphere of the star.
Specifically, the contrast between diffuse bright regions called faculae and
the quiet solar background increases as the mix of heavy elements is
increased. That makes the cyclic photometric variability of the star
stronger. The new study can help us to understand how the irradiance of the
Sun has changed over time, which is likely to have an effect on our climate.
Special attention is paid to the Maunder Minimum, which coincided with a
period of relatively cold climate, especially in Northern Europe. The new
measurements offer an important constraint on the models trying to explain
the weak activity and possible reduced brightness of the Sun during the
Maunder Minimum.
SITES RICH IN WATER ICE FOUND ON MARS
American Association for the Advancement of Science
Erosion on Mars is exposing deposits of water ice, starting at depths as
shallow as one to two metres below the surface and extending 100 metres or
more. The ice is a critical target for science and exploration: it affects
modern geomorphology, is expected to preserve a record of climate history,
influences the planet's habitability, and may be a potential resource for
future exploration. Whilst water ice is known to be present in some
locations on Mars, many questions remain about its layering, thickness,
purity, and extent. Now, astronomers have pinpointed eight locations, using
the Mars Reconnaissance Orbiter (MRO), where steep, pole-facing slopes
created by erosion expose substantial quantities of sub-surface ice. The
fractures and steep angles indicate that the ice is cohesive and strong.
What's more, bands and variations in colour suggest that the ice contains
distinct layers, which could be used to understand changes in Mars' climate
over time (the ice sheets themselves probably formed as snow accumulated
over time). Since there are few craters on the surface at those sites, it
is proposed that the ice was formed relatively recently. Images taken over
the course of three Martian years reveal massive chunks of rock that fell
from the ice as erosion occurred, leading the researchers to estimate that
the ice is retreating a few millimetres each summer. Because the ice is
only visible where surface soil has been removed, astronomers say it is
likely that ice near the surface is even more extensive than detected in
this study. The ice could be a useful source of water for future missions
to Mars.
PLANETS ORBITING OTHER STARS ARE SIMILAR
University of Montreal
An international research team has discovered that exoplanets orbiting the
same star tend to have similar sizes and a regular orbital spacing. That
pattern, revealed by new Keck Observatory observations of planetary systems
discovered by the Kepler telescope, could suggest that most planetary
systems have a formation history different from that of the Solar System.
Thanks in large part to the Kepler telescope, launched in 2009, many
thousands of exoplanets are now known. The large sample allows researchers
not only to study individual systems, but also to draw conclusions on
planetary systems in general. The team obtained high-resolution spectra of
1305 stars hosting 2025 transiting planets originally discovered by Kepler.
From those spectra, precise sizes of the stars and their planets were
measured. In this new analysis, the team focused on 909 planets belonging
to 355 multi-planet systems. The planets are mostly located between 1,000
and 4,000 light-years away from us. By statistical analysis, the team found
two surprising patterns. It found that exoplanets tend to be the same sizes
as their neighbours. If one planet is small, the next planet around that
same star is very likely to be small as well, and if one planet is big, the
next is likely to be big. It also found that planets orbiting the same
star tend to have a regular orbital spacing.
The similar sizes and orbital spacing of planets have implications for how
most planetary systems form. In classical planet-formation theory, planets
form in the protoplanetary disc that surrounds a newly formed star. The
planets might form in compact configurations with similar sizes and a
regular orbital spacing, in a manner similar to the newly observed pattern
in exoplanetary systems. However, in our Solar System, the inner planets
have surprisingly large spacing and diverse sizes. Abundant evidence in the
Solar System suggests that Jupiter and Saturn disrupted our system's early
structure, resulting in the four widely-spaced terrestrial planets we have
today. That planets in most systems are still similarly sized and regularly
spaced suggests that perhaps they have been mostly undisturbed since their
formation. To test that hypothesis, the team is conducting a new study at
the Keck Observatory to search for Jupiter analogues around Kepler's multi-
planet systems. The planetary systems studied by the team have multiple
planets quite close to their star. Because of the limited duration of the
Kepler Mission, little is known about what kind of planets, if any, exist
at larger orbital distances around those systems. It hopes to test how
the presence or absence of Jupiter-like planets at large orbital distances
relate to patterns in the inner planetary systems. Regardless of their
outer populations, the similarity of planets in the inner regions of
extrasolar systems requires an explanation. If the deciding factor for
planet sizes can be identified, it might help to determine which stars are
likely to have terrestrial planets that are suitable for life.
OBSERVATORIES TEAM UP TO FIND FARTHEST KNOWN GALAXY
NASA
An intensive survey deep into the Universe by the Hubble and Spitzer space
telescopes has yielded the farthest galaxy yet seen in an image that has
been stretched and amplified by gravitational lensing. The embryonic galaxy
named SPT0615-JD existed when the Universe was just 500 million years old.
Though a few other primitive galaxies have been seen at that early epoch,
they have all looked merely like red dots, owing to their small size and
tremendous distances. However, in this case, the gravitational field of a
massive foreground cluster of galaxies not only amplified the light from the
background galaxy but also smeared its image it into an arc about 2
arcseconds long. First predicted by Einstein a century ago, the warping of
space by the gravity of a massive foreground object can brighten and distort
the images of far-more-distant background objects. SPT0615-JD was identified
in Hubble's Reionization Lensing Cluster Survey (RELICS) and the companion
S-RELICS Spitzer program. RELICS was designed to discover distant galaxies
like these that are magnified brightly enough for detailed study. RELICS
observed 41 massive galaxy clusters for the first time in infrared with
Hubble to search for such distant lensed galaxies. By combining the Hubble
and Spitzer data, astronomers calculated the lookback time to the galaxy of
13.3 billion years. Preliminary analysis suggests the diminutive galaxy
weighs in at no more than 3 billion solar masses (roughly 1/100th the
mass of our fully grown Milky Way galaxy). It is less than 2,500 light-
years across, half the size of the Small Magellanic Cloud, a satellite
galaxy of the Milky Way. The object is considered prototypical of young
galaxies that emerged during the epoch shortly after the big bang. The
galaxy is right at the limits of Hubble's detection capabilities, but just
the beginning for the upcoming James Webb Space Telescope's powerful
capabilities.
BENZONITRILE FOUND IN INTERSTELLAR SPACE
National Radio Astronomy Observatory
Astronomers using the Green Bank telescope have made the first definitive
interstellar detection of benzonitrile, an intriguing organic molecule that
helps chemically to link simple carbon-based molecules with truly massive
ones known as polycyclic aromatic hydrocarbons. The discovery is a vital
clue in a 30-year-old problem: identifying the source of a faint infrared
glow that permeates the Milky Way and other galaxies. Astronomers had a
mystery on their hands. No matter where they looked, from inside the Milky
Way to distant galaxies, they observed a puzzling glow of infrared light.
That faint cosmic light, which presents itself as a series of spikes in the
infrared spectrum, had no easily identifiable source. It seemed unrelated
to any recognizable cosmic feature, like giant interstellar clouds, star-
forming regions, or supernova remnants. It was ubiquitous and baffling.
The probable culprit, scientists eventually deduced, was the intrinsic
infrared emission from a class of organic molecules known as polycyclic
aromatic hydrocarbons (PAHs), which, scientists would later discover, are
amazingly plentiful; nearly 10% of all the carbon in the Universe is tied
up in PAHs. Even though, as a group, PAHs seemed to be the answer to this
problem, none of the hundreds of PAH molecules known to exist had ever been
conclusively detected in interstellar space. New data from the Green Bank
Telescope (GBT) show, for the first time, the convincing radio fingerprints
of a close cousin and chemical precursor to PAHs, the molecule benzonitrile
(C6H5CN). That detection may finally provide the 'smoking gun' that PAHs
are indeed spread throughout interstellar space and account for the infra-
red light that astronomers had been observing. The science team detected
that molecule's telltale radio signature coming from a nearby star-forming
nebula known as the Taurus Molecular Cloud 1 (TMC-1), which is about 430
light-years away.
MASSIVE STARS ARE SURPRISINGLY ABUNDANT
University of Oxford
An international team of astronomers has revealed an 'astonishing' over-
abundance of massive stars in a neighbouring galaxy. The discovery, made in
the gigantic star-forming region 30 Doradus in the Large Magellanic Cloud
galaxy, has 'far-reaching' consequences for our understanding of how stars
transformed the pristine Universe into the one we live in today. As part
of the VLT-FLAMES Tarantula Survey (VFTS), the team used ESO's Very Large
Telescope to observe nearly 1,000 massive stars in 30 Doradus, a gigantic
stellar nursery also known as the Tarantula nebula. The team used detailed
analyses of about 250 stars with masses between 15 and 200 times the mass of
the Sun to determine the distribution of massive stars born in 30 Doradus --
the so-called initial mass function (IMF). Massive stars are particularly
important for astronomers because of their enormous influence on their
surroundings (known as their 'feedback'). They can explode in spectacular
supernovae at the end of their lives, forming some of the most remarkable
objects in the Universe -- neutron stars and black holes. Until recently,
the existence of stars up to 200 solar masses was highly disputed, but the
study shows that a maximum birth mass of stars of 200-300 solar masses
appears likely. In most parts of the Universe studied by astronomers to
date, stars become rarer the more massive they are. The IMF predicts that
most stellar mass is in low-mass stars and that less than 1% of all stars
are born with masses in excess of ten times that of the Sun. Measuring the
proportion of massive stars is extremely difficult -- primarily because of
their scarcity -- and there is only a handful of places in the local
Universe where that can be done. The team turned to 30 Doradus, the biggest
local star-forming region, which hosts some of the most massive stars ever
found, and determined the masses of massive stars with unique observational,
theoretical and statistical tools. The large sample allowed the scientists
to derive the most accurate high-mass segment of the IMF to date, and to
show that massive stars are much more abundant than was previously thought.
Stars are cosmic engines, and have produced most chemical elements heavier
than helium, from the oxygen we breathe every day to the iron in our blood.
During their lives, massive stars produce copious amounts of ionizing
radiation and kinetic energy through strong stellar winds. The ionizing
radiation of massive stars was crucial for the re-brightening of the
Universe after the so-called Dark Ages, and their mechanical feedback drives
the evolution of galaxies. The results have far-reaching consequences for
our understanding of the cosmos: there might be 70% more supernovae, a
tripling of the chemical yields and nearly four times the ionizing
radiation from massive star populations. Also, the formation rate of black
holes might be increased by 180%, directly translating into a corresponding
increase of binary black-hole mergers that have recently been detected by
their gravitational-wave signals. The team's research leaves many open
questions, which it intends to investigate in the future: how universal are
the findings, and what are the consequences for the evolution of our cosmos
and the occurrence of supernovae and gravitational-wave events?
REPEATING FAST RADIO BURST
McGill University
New detections of radio waves from a repeating fast radio burst have
revealed an astonishingly potent magnetic field in the source's environment,
indicating that it is situated near a massive black hole or within a nebula
of unprecedented power. A year ago, astronomers pinpointed the location of
the enigmatic fast radio burst (FRB) source named FRB 121102 and reported
that it lies in a star-forming region of a dwarf galaxy more than three
billion light-years away. The vast distance to the source implies that it
releases an enormous amount of energy in each burst -- roughly as much
energy in a single millisecond as the Sun releases in an entire day. Now,
using data from the Arecibo Observatory (Puerto Rico) and the Green Bank
Telescope (West Virginia), the researchers have shown that the radio bursts
from FRB121102 are highly polarized. The behaviour of the polarized
emission enables scientists to probe the source's environment in a new way.
When polarized radio waves pass through a region with a magnetic field, the
polarization gets `twisted' by Faraday rotation: the stronger the magnetic
field, the greater the twisting. The amount of twisting observed in FRB
121102's radio bursts is among the largest ever measured in a radio source,
leading the researchers to conclude that the bursts are passing through an
extraordinarily strong magnetic field in a dense plasma.
One possible explanation for the hugely magnetized environment is that FRB
121102 is located close to a massive black hole in its host galaxy. Such
highly magnetized plasmas have so far been seen only near the centre of the
Milky Way, which has its own massive black hole. But the authors also
speculate that the twisting of the radio bursts could be explained if FRB
121102 is located in a powerful nebula (an interstellar cloud of gas and
dust) or amid the remains of a dead star. FRBs are a recently discovered
class of transient astrophysical events, originating from deep in extra-
galactic space. Their physical nature remains unknown. FRB 121102 is the
only known repeating FRB, and that has also raised the question of whether
it has a different origin from the apparently non-repeating FRBs. With a
number of wide-field radio telescopes now coming online, more such sources
are expected to be discovered in the coming year, and astronomers are poised
to answer some fundamental questions about FRBs.
BLACK HOLES PREVENT STAR FORMATION
University of Portsmouth
Scientists have solved a cosmic problem by finding evidence that super-
massive black holes prevent stars forming in some smaller galaxies. Such
giant black holes are over a million times more massive than the Sun and sit
in the centres of galaxies, sending out powerful winds that quench the star-
making process. Astronomers previously thought that they had no influence
on the formation of stars in dwarf galaxies, but a new study has proved
their role in the process. The results are particularly important because
dwarf galaxies (those composed of one billion to several billion stars}
outnumber larger galaxies like the Milky Way 50 to one, so they are far more
numerous than bigger systems and what happens in them is likely to give a
more typical picture of the evolution of galaxies. In any galaxy stars are
born when clouds of gas collapse under the force of their own gravity. But
stars do not keep being born for ever -- at some point star formation in a
galaxy shuts off. The reason for that differs in different galaxies but
sometimes a supermassive black hole is the culprit.
Supermassive black holes can regulate their host galaxy's ability to form
new stars through a heating process. The black hole drives energy through
powerful winds. When its wind hits the giant molecular clouds in which
stars would form, it heats the gas, preventing its collapse into new stars.
Previous research has shown that that process can prevent star formation in
larger galaxies containing hundreds of billions of stars -- but it was
believed that a different process could be responsible for dwarf galaxies
ceasing to produce stars. Scientists previously thought that the larger
galaxies could have been interacting gravitationally with the dwarf systems
and pulling the star-making gas away. Data, however, showed the researchers
that the dwarf galaxies under observation were still accumulating gas which
should re-start star formation in a red, dead galaxy, but didn't. That led
the team to the supermassive-black-hole discovery. The team of internation-
al scientists used data from the Sloan Digital Sky Survey (SDSS), which has
a telescope in New Mexico, to make their observations. Using SDSS's
'Mapping Nearby Galaxies' at Apache Point Observatory (MaNGA) survey, they
were able to map the processes acting on the dwarf galaxies through the star
systems' heated gas, which could be detected. The heated gas revealed the
presence of a central supermassive black hole, or active galactic nucleus
(AGN), and through MaNGA the team was able to observe the effect that AGNs
had on their host dwarf galaxies.
SWIRLING GASES DETECTED SOON AFTER BIG BANG
University of Cambridge
Astronomers have looked back to a time soon after the Big Bang, and have
discovered swirling gas in some of the earliest galaxies to have formed in
the Universe. Those 'newborns' -- observed as they appeared nearly 13
billion years ago -- spun like a whirlpool, similar to our own Milky Way.
This is the first time that it has been possible to detect movement in
galaxies at such an early point in the Universe's history. The team used
the Atacama Large Millimeter/submillimeter Array (ALMA) in Chile to open a
new window onto the distant Universe, and have for the first time been able
to identify normal star-forming galaxies at a very early stage in cosmic
history. Light from distant objects takes time to reach the Earth, so
observing objects that are billions of light-years away enables us to look
back in time and observe directly the formation of the earliest galaxies.
The Universe at that time, however, was filled with an obscuring 'haze' of
neutral hydrogen gas, which makes it difficult to see the formation of the
very first galaxies with optical telescopes. Astronomers used ALMA to
observe two small newborn galaxies, as they existed just 800 million years
after the Big Bang. By analyzing the spectral 'fingerprint' of the far-
infrared light collected by ALMA, they were able to establish the distance
to the galaxies and, for the first time, to see the internal motion of the
gas that fuelled their growth.
The researchers found that the gas in the newborn galaxies swirled and
rotated in a whirlpool motion, similar to our own galaxy and other more
mature galaxies much later in the Universe's history. Despite their
relatively small size -- about a fifth the size of the Milky Way -- those
galaxies were forming stars at a higher rate than other young galaxies, but
the researchers were surprised to discover that the galaxies were not as
chaotic as expected. In the early Universe, gravity caused gas to flow
rapidly into the galaxies, stirring them up and forming lots of new stars --
violent supernova explosions also made the gas turbulent. It was expected
that young galaxies would be dynamically 'messy', owing to the havoc caused
by exploding young stars, but the mini-galaxies show an ability to retain
order and appear well regulated. Despite their small size, they are already
rapidly growing to become 'adult' galaxies like the one we live in today.
FIRST ELT MIRROR SEGMENTS CAST
ESO
The first six hexagonal segments for the main mirror of ESO's Extremely
Large Telescope (ELT) have been successfully cast by the German company
SCHOTT. The segments will form parts of the ELT's 39-metre main mirror,
which will be by far the largest ever made for an optical-infrared
telescope. Such a giant is much too large to be made from a single piece
of glass: it will consist of 798 individual hexagonal segments, each
measuring 1.4 metres across and about 5 centimetres thick. The segments will
work together as a single huge mirror to collect tens of millions of times
as much light as the human eye. As with the telescope's secondary-mirror
blank, the ELT main-mirror segments are made from the low-expansion ceramic
material Zerodur*. The first segment castings are important, as they allow
the engineers at SCHOTT to validate and optimise the manufacturing process
and the associated tools and procedures.
The casting of the first six segments is a major milestone, but the road
ahead is long -- in total more than 900 segments will need to be cast and
polished (798 for the main mirror itself, plus a spare set of 133). When
fully up to speed, the production rate will be about one segment per day.
After casting, the mirror-segment blanks will go through a slow cooling and
heat-treatment sequence and will then be ground to the right shape and
polished to a precision of 15 nanometres across the entire optical surface.
*Zerodur was originally developed for astronomical telescopes in the late
1960s. It has an extremely low coefficient of thermal expansion.
Topic: Late January Astronomy Bulletin (Read 1314 times)