Topic: Early April Astronomy Bulletin

[Clive]

INSIGHT TO STUDY CENTRE OF MARS

NASA

InSight -- short for Interior Exploration using Seismic Investigations,
Geodesy and Heat Transport -- is a stationary lander scheduled to be
launched towards Mars as soon as May 5. It will be the first mission ever
dedicated to Mars' deep interior, and the first NASA mission since the
Apollo moon landings to place a seismometer on the soil of another planet.
Scientists hope that by detecting marsquakes and other phenomena inside the
planet, InSight can enable them to understand how Mars formed. InSight
carries a suite of sensitive instruments to gather such data; unlike a rover
mission, they require a spacecraft that sits still and carefully places its
instruments on the Martian surface. NASA is not the only agency excited
about the mission. Several European partners contributed instruments, or
instrument components. For example, France's Centre National d'Etudes
Spatiales (CNES) led a multinational team that built an ultra-sensitive
seismometer for detecting marsquakes. The German Aerospace Center (DLR)
developed a thermal probe that can bury itself up to 5 metres underground
and measure heat flowing from inside the planet. Looking deep into Mars
will let scientists understand how different its crust, mantle and core are
from their counterparts on Earth. In a sense, Mars is the exo-planet next
door -- a nearby example of how gas, dust and heat combine and arrange
themselves into a planet.


'OUMUAMUA PROBABLY CAME FROM BINARY SYSTEM
RAS

New research finds that 'Oumuamua, the rocky object identified as the first
confirmed interstellar asteroid, very likely came from a binary-star system.
For the new study, astronomers set about testing how efficient binary-star
systems are at ejecting objects. They also looked at how common such star
systems are in the Galaxy. They found that rocky objects like 'Oumuamua are
far more likely to come from binary- than single-star systems. They were
also able to determine that rocky objects are ejected from binary systems in
comparable numbers to icy objects. Astronomers claim that it is really odd
that the first object we would see from outside our system would be an
asteroid, because a comet would be a lot easier to spot and the Solar System
ejects many more comets than asteroids. Once they determined that binary
systems are very efficient at ejecting rocky objects, and that a sufficient
number of them exists, they were satisfied that 'Oumuamua very likely came
from a binary system. They also concluded that it probably came from a
system with a relatively hot, high-mass star, since such a system would have
a greater number of rocky objects closer in. The team suggests that the
asteroid was very likely to have been ejected from its binary system some
time during the formation of planets.

'Oumuamua, which is Hawaiian for 'scout', was first observed by the
Haleakala Observatory in Hawaii on 2017 October 19. With a radius of 200
metres and travelling at 30 kilometres per second, at its closest it was
about 33 million km from the Earth. When it was first discovered,
researchers assumed that it was a comet. But it did not show any comet-like
activity as it neared the Sun, so it seemed that it must be rocky, and it
was quickly re-classified as an asteroid. Researchers were also fairly sure
it was from outside the Solar System, on the basis of its trajectory and
speed. An eccentricity of 1.2 -- which classifies its path as an open-ended
hyperbolic orbit -- and such a high speed meant that it was not bound by the
gravity of the Sun. In fact, 'Oumuamua's orbit has the highest eccentricity
ever observed in an object passing through the Solar System. Major
questions about 'Oumuamua remain. For planetary scientists, being able to
observe such objects may yield important clues about how planet formation
works in other star systems.


COMETS DISTURBED 70,000 YEARS AGO
FECYT - Spanish Foundation for Science and Technology

About 70,000 years ago, a small reddish star approached the Solar System and
gravitationally disturbed comets and asteroids. Astronomers have verified
that the movement of some of those objects is still marked by that stellar
encounter. At a time when modern humans were beginning to leave Africa and
the Neanderthals were living on our planet, Scholz's star -- named after the
German astronomer who discovered it -- approached within less than a light-
year from the Sun. Nowadays it is almost 20 light-years away, but 70,000
years ago it entered the Oort cloud, a reservoir of trans-Neptunian objects
located in the confines of the Solar System. Now astronomers have analyzed
for the first time the nearly 340 objects of the Solar System with hyper-
bolic orbits, and in doing so they have detected that the trajectories of
some of them are influenced by the passage of Scholz's star. Using numerical
simulations they calculated the radiants or positions in the sky from which
all these hyperbolic objects seem to come. In principle, one would expect
such positions to be evenly distributed in the sky, particularly if the
objects come from the Oort cloud; however, what is found is very different:
a statistically significant accumulation of radiants. The pronounced over-
density appears projected in the direction of the constellation of Gemini,
which fits the close encounter with Scholz's star.

The time at which that star passed close to us and its position during
prehistory coincide with the data of the new investigation. It could be a
coincidence, but it is unlikely that both location and time would be
compatible just by coincidence. The simulations suggest that Scholz's star
approached even closer than the 0.6 light-years pointed out in a 2015 study
as the lower limit. The close fly-by of the star 70,000 years ago did not
disturb all the hyperbolic objects of the Solar System, only those that were
closest to it at that time. For example, the radiant of the interstellar
asteroid `Oumuamua is in the constellation Lyra, very far from Gemini, so it
is not part of the detected over-density. Scholz's star is actually a
binary system formed by a small red dwarf, with about 9% of the mass of the
Sun, around which a still less bright and smaller brown dwarf orbits. Some
of our distant ancestors may have seen its faint reddish light with their
naked eyes in the nights of prehistory.

ASTRONOMERS FIND 72 BRIGHT AND FAST EXPLOSIONS
RAS

A team of astronomers found 72 very bright, but quick, events in a recent
survey, and are still struggling to explain their origin. The scientists
found the transients in data from the Dark Energy Survey Supernova Programme
(DES-SN). That is part of a global effort to understand dark energy, an
entity that seems to be driving an acceleration in the expansion of the
Universe. DES-SN uses a large camera on the 4-metre telescope at the Cerro
Tololo Inter-American Observatory (CTIO) in the Chilean Andes. The survey
looks for supernovae, the explosion of massive stars at the end of their
lives. A supernova explosion can briefly be as bright as a whole galaxy.
The team found the largest number of those quick events to date. Even for
transient phenomena, they are very peculiar: while they have a similar
maximum brightness to different types of supernovae they are visible for
shorter times, from a week to a month. In contrast, supernovae last for
several months or more. The events appear to be both hot, with temperatures
from 10,000 to 30,000 degrees Celsius, and large, ranging in size from
several up to a hundred times the distance from the Earth to the Sun. They
also seem to be expanding and cooling as they evolve in time, as would be
expected from an exploding event such as a supernova. There is still debate
on the origin of these transients. One possible scenario is that the star
sheds a lot of material before a supernova explosion, and in extreme cases
could be completely enveloped by a shroud of matter. The supernova itself
may then heat the surrounding material to very high temperatures. In that
case astronomers see the hot cloud rather than the exploding star itself.
To confirm any of that, the team will need a lot more data. For the future,
the team plans to continue its search for transients, and estimate how often
they occur compared with more 'routine' supernovae.


SUPERNOVA MAY HAVE 'BURPED':
University of Notre Dame

The slow fade of radioactive elements in a supernova allows astrophysicists
to study them at length. But the Universe is full of flash-in-the-pan
transient events lasting only a brief time, so quick and hard to study that
they remain a mystery. Only by increasing the rate at which telescopes
monitor the sky has it been possible to catch more Fast-Evolving Luminous
Transients (FELTs) and begin to understand them. According to a new study,
researchers say that the Kepler space telescope captured one of the fastest
FELTs to date. The FELT, captured in 2015, rose in brightness over just 2.2
days and faded completely within 10 days. Most supernovae can take 20 days
to reach peak brightness and weeks to become undetectable. Researchers
debated what could be causing these particularly fast events but ultimately
settled on a simple explanation: the stars 'burp' before exploding and do
not generate enough radioactive energy to be seen later. As the supernova
runs into the gas expelled in the burp, astrophysicists observe a flash.
The supernova then fades beyond their ability to detect it.

Astronomers conclude that this was a massive star that exploded, but it had
a mass loss -- a wind -- that started a couple of years before it exploded.
A shock ran into that wind after the explosion, and that is what caused the
big flash. But it turns out to have been a rather weak supernova, so within
a couple of weeks we did not see the rest of the light. The only visible
activity was from the quick collision of the gas and the exploding star,
where some of the kinetic energy was converted into light. One mystery that
remains is why the 'burp' would happen such a short time before the super-
nova explosion. Astrophysicists want to know how the outside of the star
reacts to what is happening deep in the core. While the Kepler telescope
and its K2 mission is expected to run out of fuel and end in the coming
months, NASA's Transiting Exoplanet Survey Satellite (TESS) is planned for
launch following the K2 mission. Data retrieved during the TESS mission
could also be used to study FELTs.


ANCIENT GALAXY FOUND IN COSMIC BACKYARD
NASA/Goddard Space Flight Center

Astronomers using the Hubble Space Telescope have uncovered an ancient
'relic galaxy' in our own cosmic backyard. The very rare and odd assemblage
of stars has remained essentially unchanged for the past 10 billion
years and provides valuable new insights into the origin and evolution of
galaxies billions of years ago. The galaxy, NGC 1277, started its life with
a bang long ago, churning out stars a thousand times faster than happens
in our own Milky Way today. But it abruptly went quiescent as the early
stars aged and grew ever redder. Though Hubble has seen such 'red and dead'
galaxies in the early Universe, one has never been conclusively found
nearby. While the early galaxies are so distant, they are just red dots in
Hubble deep-sky images. NGC 1277 offers a unique opportunity to see one up
'close'. The researchers learned that the relic galaxy has twice as many
stars as our Milky Way, but physically it is only one quarter the size of
our galaxy. Essentially, NGC 1277 is in a state of 'arrested development'.
Perhaps, like all galaxies, it started out as a compact object but failed to
accrete more material to grow in size to form a pinwheel-shaped galaxy.
Researchers say that approximately one in 1,000 massive galaxies is expected
to be a relic galaxy like NGC 1277. They were not surprised to find it, but
simply consider that it was in the right place at the right time to evolve
-- or rather not evolve -- the way it did.

The telltale sign of the galaxy's state lies in the ancient globular
clusters of stars that swarm around it. Massive galaxies tend to have both
metal-poor (appearing blue) and metal-rich (appearing red) globular
clusters. The red clusters are believed to form as the galaxy forms, while
the blue clusters are later brought in as smaller satellites are swallowed
by the central galaxy. However, NGC 1277 is almost entirely lacking in blue
globular clusters. The red clusters are the strongest evidence that the
galaxy went out of the star-making business long ago. However, the lack of
blue clusters suggests that NGC 1277 never grew further by accreting
surrounding galaxies. By contrast, our Milky Way contains approximately 180
blue and red globular clusters. That is due partly to the fact that our
Milky Way continues cannibalizing galaxies that come too close by in our
Local Group of a few dozen small galaxies. It is a markedly different
environment for NGC 1277. That galaxy lives near the centre of the Perseus
cluster of over 1,000 galaxies, located 240 million light-years away. But
NGC 1277 is moving so fast through the cluster, at 2 million miles per hour,
that it cannot merge with other galaxies to collect stars or pull in gas to
fuel star formation. In addition, near the galaxy cluster centre, inter-
galactic gas is so hot that it cannot cool to condense and form stars.
The team started looking for 'arrested development' galaxies in the Sloan
Digital Sky Survey and found 50 candidate massive compact galaxies. Using a
similar technique, but from a different sample, NGC 1277 was identified as
unique in that it has a central black hole that is much more massive than it
should be for a galaxy of that size. That reinforces the scenario that the
supermassive black hole and dense hub of the galaxy grew simultaneously, but
the galaxy's stellar population stopped growing and expanding because it was
starved of outside material. The team has 10 other candidate galaxies to
look at with varying degrees of 'arrested development'.


MOST DISTANT STAR EVER SEEN
University of California - Berkeley

Thanks to a rare cosmic alignment, astronomers have observed the most
distant normal star ever observed, some 9 billion light years away.
While astronomers routinely study galaxies much farther away, they are
visible only because they glow with the brightness of millions of stars.
And a supernova, often brighter than the galaxy in which it sits, also can
be visible across the entire Universe. In galaxies beyond a distance of
about 100 million light-years, however, the stars are impossible to make out
individually. But gravitational lensing -- the bending of light by massive
galaxy clusters in the line of sight -- can magnify the distant universe and
make dim and distant objects visible. Typically, lensing magnifies galaxies
by up to 50 times, but in this case, the star was magnified more than 2,000
times. It was discovered in Hubble telescope images taken in late April
2016. The discovery of the star, which astronomers often refer to as Icarus
rather than by its formal name, MACS J1149 Lensed Star 1 (LS1), initiates a
new technique for astronomers to study individual stars in galaxies formed
during the earliest days of the Universe. Such observations can provide a
rare look at how stars evolve, especially the most luminous ones. The
astronomy team also used Icarus to test and reject one theory of dark matter
-- that it consists of numerous primordial black holes lurking inside galaxy
clusters -- and to probe the make-up of normal matter and dark matter in the
galaxy cluster.

The star was noticed while the observers were monitoring a supernova that
they had discovered in 2014 while using Hubble to look through a
gravitational lens in the constellation Leo. That supernova, dubbed
SN Refsdal in honour of the late Norwegian astrophysicist Sjur Refsdal, a
pioneer of gravitational lensing studies, was split into four images by the
lens, a massive galaxy cluster called MACS J1149+2223, located about 5
billion light years away. Suspecting that Icarus might be more highly
magnified than SN Refsdal, astronomers analyzed the colours of the light
coming from it and discovered it was a single star, a blue supergiant. This
B-type star is much larger, more massive, hotter and possibly hundreds of
thousands of times intrinsically brighter than the Sun, though still much
too far away to see without the amplification of gravitational lensing. By
modelling the lens, they concluded that the tremendous apparent brightening
of Icarus was probably caused by a unique effect of gravitational lensing.
While an extended lens, like a galaxy cluster, can only magnify a background
object up to 50 times, smaller objects can magnify much more. A single star
in a foreground lens, if precisely aligned with a background star, can
magnify the background star thousands of times. In this case, a star about
the size of our Sun briefly passed directly through the line of sight
between the distant star Icarus and Hubble, boosting its brightness more
than 2,000 times. In fact, if the alignment was perfect, that single star
within the cluster turned the light from the distant star into an 'Einstein
ring' -- a halo of light created when light from the distant star bends
around all sides of the lensing star. The ring is too small to discern from
this distance, but the effect made the star easily visible by magnifying its
apparent brightness. The team saw a second star in the Hubble image, which
could either be a mirror image of Icarus, or a different star being gravi-
tationally lensed. There are analogous alignments all over the place as
background stars or stars in lensing galaxies move around, offering the
possibility of studying very distant stars dating from the early universe,
just as we have been using gravitational lensing to study distant galaxies.
For this type of research, nature has provided us with a larger telescope
than we can possibly build! As for Icarus, the astronomers predict that it
will be magnified many times over the next decade as cluster stars move
around, perhaps increasing its brightness as much as 10,000 times.


DARK MATTER MAY NOT BE INTERACTIVE AFTER ALL
RAS

Astronomers are back in the dark about what dark matter might be, after new
observations showed that the mysterious substance may not be interacting
with forces other than gravity after all. Three years ago, a Durham-led
international team of researchers thought that they had made a breakthrough
in ultimately identifying what dark matter is. Observations from the
Hubble telescope appeared to show that a galaxy in the Abell 3827 cluster --
approximately 1.3 billion light-years away -- had become separated from
the dark matter surrounding it. Such an offset is predicted during
collisions if dark matter interacts with forces other than gravity,
potentially providing clues about what the substance might be. The chance
orientation at which the Abell 3827 cluster is seen from the Earth makes
it possible to conduct highly sensitive measurements of its dark matter.
However, the same group of astronomers now says that new data from more
recent observations show that dark matter in the Abell 3827 cluster has not
separated from its galaxy after all. The measurement is consistent with
dark matter feeling only the force of gravity.

The Universe is composed of approximately 27 per cent dark matter, with the
remainder largely consisting of the equally mysterious dark energy. Normal
matter, such as planets and stars, contributes a relatively small five per
cent of the Universe. There is believed to be about five times more dark
matter than all the other particles understood by science, but nobody knows
what it is. However, dark matter is an essential factor in how the Universe
looks today, as without the constraining effect of its extra gravity,
galaxies like our Milky Way would fling themselves apart as they spin. In
this latest study, the researchers used the Atacama Large Millimetre Array
(ALMA) in Chile to view the Abell 3827 cluster. ALMA picked up on the
distorted infra-red light from an unrelated background galaxy, revealing the
location of the otherwise invisible dark matter that remained unidentified
in the previous study. While the new results show dark matter staying with
its galaxy, the researchers said it did not necessarily mean that dark
matter does not interact. Dark matter might just interact very little, or
this particular galaxy might be moving directly towards us, so we would not
expect to see its dark matter displaced sideways, the team added. Several
new theories of non-standard dark matter have been invented over the past
two years and many have been simulated at Durham University with high-
powered computers. With a view to measuring the dark matter in hundreds of
galaxy clusters and continuing this investigation, Durham University has
just finished helping to build the new SuperBIT telescope, which gets a
clear view by rising above the Earth's atmosphere under a giant helium
balloon.