Releases from NASA, HubbleSite, Spitzer, ESO, ESA, NASA’s Chandra X-ray Observatory, Royal Astronomical Society, Harvard-Smithsonian Center For Astrophysics, Max Planck Institute, Gemini Observatory, Subaru Telescope, W. M. Keck Observatory, JPL-Caltech, ICRAR, Webb Space Telescope, etc
Resembling an opulent diamond tapestry, this image
from NASA’s Hubble Space Telescope shows a glittering star cluster that
contains a collection of some of the brightest stars seen in our Milky
Way galaxy. Credits: NASA, ESA, and J. Maíz Apellániz
(Institute of Astrophysics of Andalusia, Spain), Acknowledgment: N.
Smith (University of Arizona)
Resembling an opulent diamond tapestry, this image from NASA’s Hubble
Space Telescope shows a glittering star cluster that contains a
collection of some of the brightest stars seen in our Milky Way galaxy.
Called Trumpler 14, it is located 8,000 light-years away in the Carina
Nebula, a huge star-formation region. Because the cluster is only
500,000 years old, it has one of the highest concentrations of massive,
luminous stars in the entire Milky Way. The small, dark knot left of
center is a nodule of gas laced with dust, and seen in silhouette.
These blue-white stars are burning their hydrogen fuel so ferociously
they will explode as supernovae in just a few million years. The
combination of outflowing stellar “winds” and, ultimately, supernova
blast waves will carve out cavities in nearby clouds of gas and dust.
These fireworks will kick-start the beginning of a new generation of
stars in an ongoing cycle of star birth and death.
This composite image of Trumpler 14 was made with data taken in
2005-2006 with Hubble's Advanced Camera for Surveys. Blue, visible and
infrared broadband filters combine with filters that isolate hydrogen
and nitrogen emission from the glowing gas surrounding the open cluster.
For images and more information about Hubble, visit:
A new theory developed by the Brookhaven National Laboratory suggests that, after the Big Bang, there was a secondary inflation, able to explain the quantity of dark matter present in the Universe
A dense, boiling hot primordial nucleus, extremely rapid expansion and a progressive and increasingly slow cooling period. These are the main stages that, according to standard cosmological theory, mark our Universe's very first “action” after the Big Bang: inflation.
The inflation theory is in fact the theory stating that the Universe inflated exponentially a few moments after its birth (to be precise, over an interval of time equal to 10 to the power of minus 35 seconds) and is still expanding today. Most scientists agree with this theory, because it can explain a great many known physical phenomena. Nevertheless, it does not explain all of them: for example, it does not explain one of the greatest mysteries of modern cosmology - that of the quantity of dark matter present in the Universe.
For this reason, a group of physicists from the American Brookhaven National Laboratory has speculated that there could be a passage missing from standard cosmological theory. An intermediate stage, something that happened after the first, great expansion of the Universe: a smaller and shorter expansion that researchers have called “secondary inflation”.
This theory, which will be published on 18 January in the Physical Review Letters magazine, could offer a more precise explanation of what Hooman Davoudiasl, the first author of the study, calls “dilution of dark matter”.
In fact, this phenomenon cannot be explained by the many theories branching from the standard cosmological model, which envisage more dark matter than can be demonstrated by empirical observations.
This is where the idea of “adding” another cosmic inflation came from - an inflation that took place between the great expansion and the beginning of the Universe's cooling period. It is believed that this second inflation took place when temperatures were still very high: this is a fundamental feature, because it is precisely the heat that would have made it possible for the particles of dark matter to collide with each other and annihilate one another, thus creating particles like electrons and quarks. Above all, this makes sense with regard to the quantity of dark matter calculated today.
The secondary inflation suggested by the Brookhaven National Laboratory was much gentler than the primary one, but crucial in taking the primordial particles to conditions of temperature, volume and density consistent with what we can observe almost 14 billion years later.
Therefore, this is a potentially simple and coherent theory. Nevertheless, we are still a long way from moving from theory to practice, as Hooman Davoudiasl, the father of the inflation theory himself, asserts: the next step will be to try to identify particle interactions according to the new theory through experiments within the scope of the LHC. Thus, empirical proof of this double inflation at the origin of our Universe can be found.
“The best explanations in physics are the simple ones – explains the president of the Italian Space Agency (ASI), Roberto Battiston - but in the Universe's case the simplest one may not be the best! In order to make sense of the quantity of dark matter observed in our universe, which is approximately 6 times more abundant than normal matter, according to this new theory, the hyper-fast phase of expansion that accompanied the big-bang (called inflation, editor’s note) had a sort of hiccup and repeated itself a second time, in quick succession to the first. There was much less intensity in this phase, but it was sufficient to dilute the dark matter produced in the first phase and reach a figure compatible with that measured.”
Battiston points out that “This is a theory and, as such, requires verification. For this reason - he concludes - a new generation of instruments will be needed, able to observe the effect of what happened during the initial moments, such as, for example, the impression made in the radiation of the Big Bang, due to the effect of the gravitational waves produced during the initial phases of the great explosion”.
This
artistic rendering shows the distant view from Planet Nine back towards
the sun. The planet is thought to be gaseous, similar to Uranus and
Neptune. Hypothetical lightning lights up the night side. Credit: Caltech/R. Hurt (IPAC)
The
six most distant known objects in the solar system with orbits
exclusively beyond Neptune (magenta) all mysteriously line up in a
single direction. Also, when viewed in three dimensions, they tilt
nearly identically away from the plane of the solar system. Batygin and
Brown show that a planet with 10 times the mass of the earth in a
distant eccentric orbit anti-aligned with the other six objects (orange)
is required to maintain this configuration.Credit: Caltech/R. Hurt (IPAC); [Diagram created using WorldWide Telescope.]
Caltech's
Konstantin Batygin, an assistant professor of planetary science, and
Mike Brown, the Richard and Barbara Rosenberg Professor of Planetary
Astronomy, discuss new research that provides evidence of a giant planet
tracing a bizarre, highly elongated orbit in the outer solar system.Credit: Caltech AMT
A predicted
consequence of Planet Nine is that a second set of confined objects
should also exist. These objects are forced into positions at right
angles to Planet Nine and into orbits that are perpendicular to the
plane of the solar system. Five known objects (blue) fit this prediction
precisely. Credit: Caltech/R. Hurt (IPAC) [Diagram was created using WorldWide Telescope.]
Caltech
professor Mike Brown and assistant professor Konstanin Batygin have
been working together to investigate distant objects in our solar system
for more than a year and a half. The two bring very different
perspectives to the work: Brown is an observer, used to looking at the
sky to try and anchor everything in the reality of what can be seen;
Batygin is a theorist who considers how things might work from a physics
standpoint. Credit: Credit: Lance Hayashida/Caltech
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, has a mass about 10
times that of Earth and orbits about 20 times farther from the sun on
average than does Neptune (which orbits the sun at an average distance
of 2.8 billion miles). In fact, it would take this new planet between
10,000 and 20,000 years to make just one full orbit around the sun.
The researchers, Konstantin Batygin and Mike Brown,
discovered the planet's existence through mathematical modeling and
computer simulations but have not yet observed the object directly.
"This
would be a real ninth planet," says Brown, the Richard and Barbara
Rosenberg Professor of Planetary Astronomy. "There have only been two
true planets discovered since ancient times, and this would be a third.
It's a pretty substantial chunk of our solar system that's still out
there to be found, which is pretty exciting."
Brown notes that 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 neighborhood of the solar system. In
fact, it dominates a region larger than any of the other known planets—a
fact that Brown says makes it "the most planet-y of the planets in the
whole solar system."
Batygin and Brown describe their work in the current issue of the Astronomical Journal
and show how Planet Nine helps explain a number of mysterious features
of the field of icy objects and debris beyond Neptune known as the
Kuiper Belt.
"Although we were initially quite skeptical that this
planet could exist, as we continued to investigate its orbit and what
it would mean for the outer solar system, we become increasingly
convinced that it is out there," says Batygin, an assistant professor of
planetary science. "For the first time in over 150 years, there is
solid evidence that the solar system's planetary census is incomplete."
The
road to the theoretical discovery was not straightforward. In 2014, a
former postdoc of Brown's, Chad Trujillo, and his colleague Scott
Shepherd published a paper noting 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. Brown thought the planet solution was unlikely, but his
interest was piqued.
He took the problem down the hall to Batygin,
and the two started what became a year-and-a-half-long collaboration to
investigate the distant objects. As an observer and a theorist,
respectively, the researchers approached the work from very different
perspectives—Brown as someone who looks at the sky and tries to anchor
everything in the context of what can be seen, and Batygin as someone
who puts himself within the context of dynamics, considering how things
might work from a physics standpoint. Those differences allowed the
researchers to challenge each other's ideas and to consider new
possibilities. "I would bring in some of these observational aspects; he
would come back with arguments from theory, and we would push each
other. I don't think the discovery would have happened without that back
and forth," says Brown. " It was perhaps the most fun year of working
on a problem in the solar system that I've ever had."
Fairly
quickly Batygin and Brown realized that the six most distant objects
from Trujillo and Shepherd's original collection all follow elliptical
orbits that point in the same direction in physical space. That is
particularly surprising because the outermost points of their orbits
move around the solar system, and they travel at different rates.
"It's
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,"
says Brown. The odds of having that happen are something like 1 in 100,
he says. 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 percent. "Basically it
shouldn't happen randomly," Brown says.
"So we thought something else
must be shaping these orbits."
The first possibility they
investigated 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 subpopulation clustered together. The researchers
quickly ruled this out when it turned out that such a scenario would
require the Kuiper Belt to have about 100 times the mass it has today.
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 lasso to
wrangle them into their alignment. Batygin says that almost works but
does not provide the observed eccentricities precisely. "Close, but no
cigar," he says.
Then, effectively by accident, Batygin and Brown
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 across 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.
"Your
natural response is 'This orbital geometry can't be right. This can't
be stable over the long term because, after all, this would cause the
planet and these objects to meet and eventually collide,'" says Batygin.
But 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 on a swing with periodic pushes, Planet
Nine nudges the orbits of distant Kuiper Belt objects such that their
configuration with relation to the planet is preserved.
"Still, I was very skeptical," says Batygin. "I had never seen anything like this in celestial mechanics."
But
little by little, as the researchers investigated additional features
and consequences of the model, they became persuaded. "A good theory
should not only explain things that you set out to explain. It should
hopefully explain things that you didn't set out to explain and make
predictions that are testable," says Batygin.
And indeed Planet
Nine's existence helps explain more than just the alignment of the
distant Kuiper Belt objects. It also provides an explanation for the
mysterious orbits that two of them trace. The first of those objects,
dubbed Sedna, was discovered by Brown in 2003. Unlike standard-variety
Kuiper Belt objects, which get gravitationally "kicked out" by Neptune
and then return back to it, Sedna never gets very close to Neptune. A
second object like Sedna, known as 2012 VP113, was announced by Trujillo
and Shepherd in 2014. Batygin and Brown found that 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 kicker 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. Batygin kept
finding evidence for these in his simulations and took them to Brown.
"Suddenly I realized there are objects like that," recalls Brown. In the
last three years, observers have identified four objects tracing orbits
roughly along one perpendicular line from Neptune and one object along
another. "We plotted up the positions of those objects and their orbits,
and they matched the simulations exactly," says Brown. "When we found
that, my jaw sort of hit the floor."
"When the simulation aligned
the distant Kuiper Belt objects and created objects like Sedna, we
thought this is kind of awesome—you kill two birds with one stone," says
Batygin. "But with the existence of the planet also explaining these
perpendicular orbits, not only do you kill two birds, you also take down
a bird that you didn't realize was sitting in a nearby tree."
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 planetary 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 that there could not
have been five cores, rather than four," says Brown. 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.
Batygin
and Brown continue to refine their simulations and learn more about the
planet's orbit and its influence on the distant solar system.
Meanwhile, Brown and other colleagues have begun searching the skies for
Planet Nine. Only the planet's rough orbit is known, not the precise
location of the planet on that elliptical path. If the planet happens to
be close to its perihelion, Brown says, astronomers should be able to
spot it in images captured by previous surveys. If it is in the most
distant part of its orbit, the world's largest telescopes—such as the
twin 10-meter telescopes at the W. M. Keck Observatory and the Subaru
Telescope, all on Mauna Kea in Hawaii—will be needed to see it. If,
however, Planet Nine is now located anywhere in between, many telescopes
have a shot at finding it.
"I would love to find it," says Brown.
"But I'd also be perfectly happy if someone else found it. That is why
we're publishing this paper. We hope that other people are going to get
inspired and start searching."
In terms of understanding more
about the solar system's context in the rest of the universe, Batygin
says that in a couple of ways, this ninth planet that seems like such an
oddball to us would actually make our solar system more similar to the
other planetary systems that astronomers are finding around other stars.
First, most of the planets around other sunlike stars have no single
orbital range—that is, some orbit extremely close to their host stars
while others follow exceptionally distant orbits. Second, the most
common planets around other stars range between 1 and 10 Earth-masses.
"One
of the most startling discoveries about other planetary systems has
been that the most common type of planet out there has a mass between
that of Earth and that of Neptune," says Batygin. "Until now, we've
thought that the solar system was lacking in this most common type of
planet. Maybe we're more normal after all."
Brown, well known for
the significant role he played in the demotion of Pluto from a planet to
a dwarf planet adds, "All those people who are mad that Pluto is no
longer a planet can be thrilled to know that there is a real planet out
there still to be found," he says. "Now we can go and find this planet
and make the solar system have nine planets once again."
The paper is titled "Evidence for a Distant Giant Planet in the Solar System."
Artists
impression of the power of background galaxies to measure the size of
gas clouds as compared to the conventional method of using quasars. The
plane to the far right shows the background galaxy and overlaid in the
center of the galaxy is a bright white light representing a quasar. The
DLA gas cloud is shown at the center of the plane in between the galaxy
and Earth. The blue/white narrow beam indicates the small area of the
DLA gas cloud probed by quasars, the wider red cone of light indicates
the large area of the DLA probed by galaxies, which is a 100
million-fold increase in area.
Credit: Adrian Malec (Swinburne University) and Marie Martig (Max Planck Institute for Astronomy, Heidelberg)
MAUNAKEA, Hawaii – Using the world’s largest
telescopes, researchers discovered ancient cold gas clouds larger than
galaxies in the early Universe. The discovery was announced today at a
press conference at the 227th meeting of the American Astronomical
Society in Orlando, Florida.
The discovery, led by Associate
Professor Jeff Cooke, Swinburne University of Technology, and Associate
Professor John O’Meara, St. Michael’s College, has helped solve a
decades-old puzzle on the nature of gas clouds, known as damped Lyman
alpha systems, or DLAs.
Cooke and O’Meara realized that finding
DLA gas clouds in the line of sight to background galaxies would enable
measurements of their size by determining how much of the galaxy they
cover.
“Our new method first identifies galaxies that are more
likely to have intervening DLA gas clouds and then searches for them
using long, deep exposures on the powerful Keck Observatory 10m
telescopes on Maunakea and deep data from the VLT 8m telescopes in
Chile,” Cooke said. “The technique is timely as the next generation of
giant 30m telescopes will be online in several years and are ideal to
take advantage of this method to routinely gather large numbers of DLAs
for study.”
DLA clouds contain most of the cool gas in the
Universe and are predicted to contain enough gas to form most of the
stars we see in galaxies around us today, like the Milky Way. However,
this prediction has yet to be confirmed.
DLAs currently have
little ongoing star formation, making them too dim to observe directly
from their emitted light alone. Instead, they are detected when they
happen to fall in the line of sight to a more distant bright object and
leave an unmistakeable absorption signature in the background object’s
light.
Previously, researchers used quasars as the background
objects to search for DLAs. Although quasars can be very bright, they
are rare and are comparatively small, only a fraction of a light year
across, whereas galaxies are quite common and provide a 100 million-fold
increase in area to probe DLAs.
“Using the galaxy technique,
DLAs can be studied in large numbers to provide a 3-D tomographic
picture of distribution of gas clouds in the early Universe and help
complete our understanding of how galaxies formed and evolved over
cosmic time,” O’Meara said.
The W. M. Keck Observatory operates
the largest, most scientifically productive telescopes on Earth. The
two, 10-meter optical/infrared telescopes near the summit of Maunakea on
the Island of Hawaii feature a suite of advanced instruments including
imagers, multi-object spectrographs, high-resolution spectrographs,
integral-field spectrographs and world-leading laser guide star adaptive
optics systems.
Keck Observatory is a private 501(c) 3 non-profit
organization and a scientific partnership of the California Institute
of Technology, the University of California and NASA.
A
false-color infrared image of a young, star-forming dust cloud with
several embedded cores (identified in red). A new infrared study of 3218
cores in various stages of development has enabled astronomers to
categorize the temperatures, densities, and evolutionary characters of
young stellar nurseries. Credit: ASA/Spitzer and P. Myers
Stars
like the Sun begin their lives as cold, dense cores of dust and gas
that collapse under the influence of gravity until nuclear fusion is
ignited. These cores contain hundreds to thousands of solar-masses of
material and have gas densities about a thousand times greater than
typical interstellar regions (the typical value is about one molecule
per cubic centimeter). How the collapse process occurs in these embryos
in poorly understood, from the number of stars that form to the factors
that determine their ultimate masses, as well as the detailed timescale
for stellar birth. Material, for example, might simply fall freely to
the center of the core, but in most realistic scenarios the infall is
inhibited by pressure from warm gas, turbulent motions, magnetic fields,
or some combination of them.
Astronomers are actively studying these issues by observing young
stars in the process of being born. The dust in these natal cores (or
clumps), however, makes them opaque in the optical, thus requiring
observations at other wavelengths, in particular infrared,
submillimeter, and radio. In the early stages of star formation, an
embryonic star heats the surrounding dust cloud to temperatures between
about ten and thirty degrees kelvin before stellar winds and radiation
blow the material away and expose the newborn star. CfA astronomers
Andres Guzman and Howard Smith, together with their colleagues, have
completed an analysis of 3246 star-forming cores, the largest sample
ever done. The cold cores themselves were discovered with the APEX
submillimeter-wavelength sky survey and then observed in sixteen
submillimeter spectral lines; the spectral information enabled the
astronomers to determine the distance to each core as well as to probe
its chemistry and internal gas motions. The new paper combines these
results with far-infrared measurements taken by Herschel Space
Observatory surveys. The Herschel data allow the scientists to calculate
the dust density, mass, and temperature of each core; the large dataset
then permits useful statistical comparisons between cores with varyious
parameters.
Sources in the sample fall generically into four categories:
quiescent clumps, which have the coldest temperatures (16.8K) and the
least infrared emission, protostellar clumps, which are sources with the
youngest identifiable stellar objects, ionized hydrogen regions, which
are cores within which the stars have ionized some of the surrounding
gas, and "photo-dissociation" cores, the warmest of the set, which have
dust temperatures around 28K, are slightly more evolved and brighter
than the ionized hydrogen cores. Although the groups overlap in their
properties, the large sample enables the scientists to conclude that, on
average, in the quiescent clumps the dust temperature increases towards
the outer regions, whereas the temperatures in protostellar and ionized
hydrogen cores increase towards the inner region, consistent with the
idea that they are being internally heated. The latter also tend to have
dust densities that increase more steeply than the quiescent cores.
This study has also identified a population of particularly cold and
infrared-dark objects that are probably still in the stages of
contraction, or else for some reason have had their star formation
aborted.
The new paper and its catalog are just the beginning: now that
the dust in all these cores has been well characterized, astronomers can
associate chemistry with dust temperature, for example, and study
subgroups that might represent different stellar masses in gestation.
Reference(s):
"Far-Infrared
Dust Temperatures and Column Densities of the MALT90 Molecular Clump
Sample," Andrés E. Guzmán, Patricio Sanhueza, Yanett Contreras, Howard
A. Smith, James M. Jackson,Sadia Hoq, and Jill M. Rathborne,ApJ 815, 130, 2015.
The interstellar medium fills the ‘empty’ space between the stars in
our galaxy. It is a mix of molecular clouds, cold and warm gases,
regions of electrically charged hydrogen, and more.
Molecular clouds are the densest part of the interstellar medium, holding most of its mass in the form of hydrogen gas. ESA’s Herschel space observatory has revealed that many are built around filaments,
with dense threads snaking throughout each cloud. These filaments
potentially transport material, and, when massive enough, are known to
form new stars.
This Herschel image shows the Serpens Core, the
heart of a giant molecular cloud. The Core is the bright clump towards
the upper right, with a more diffuse secondary cluster, named Ser G3-G6,
shown at the bottom right. Also visible as a faint yellow glow towards
the upper left of the frame is a region known as LDN 583 that shines
brightly in the far-infrared.
Giant molecular clouds contain up to
10 million times the mass of the Sun, and can stretch for hundreds of
light-years. Compared to the rest of space they are dense, holding up to
a thousand atoms per cubic centimetre – and even more in star-forming
regions. However, these properties are relative: even at their densest,
these clouds are more than 10 times emptier than the best laboratory
vacuums we can produce on Earth.
These giant clouds are complex
formations, most often made up of filaments mixed with clumpy and
irregular folds, sheets and bubble-like structures. A typical spiral
galaxy like the Milky Way can contain thousands of them, accompanied by
many of their smaller relatives.
Serpens is an ideal target for
scientists wanting to know more about giant molecular clouds, because it
lies just 1400 light-years from us. Scientists compared Herschel’s
observations of this cloud to a state-of-the-art simulation to find out
more about the cloud’s properties, and to test the accuracy of their
model.
They discovered
a radial network of filaments stretching throughout the Serpens Core,
filaments that are predicted to break and fragment to form the cores of
new stars. These filaments resemble the spokes of a wheel, with the Core
forming the hub.
This three-colour image is made from
observations with Herschel’s PACS camera (blue and green) and SPIRE
camera (red). The size of the region shown is 1.7x1.9º on the sky, where
1º corresponds to about 25 light-years.
At first glance, this scene may look like a reptilian eye or a
textured splash of orange paint, but it is actually a fish-eye view of
Saturn’s moon Titan. It was acquired at a height of about 5 km as ESA’s
Huygens probe, part of the international Cassini–Huygens mission,
descended through Titan’s atmosphere before landing.
In the late
afternoon of 14 January 2005, engineers and scientists at ESA’s ESOC
operations centre in Darmstadt, Germany, waited anxiously for data to
arrive from Huygens, which touched down on Titan at around 12:34 GMT –
the most distant landing of any craft.
Following its release from
NASA’s Cassini on 25 December, Huygens reached Titan’s outer atmosphere
after 20 days and a 4 million km cruise. The probe started its descent
through Titan’s hazy cloud layers from an altitude of about 1270 km at
10:13 GMT. During the following three minutes Huygens decelerated from
18 000 km/h to 1400 km/h.
A sequence of parachutes then slowed it
down to less than 300 km/h. At a height of about 160 km the probe’s
scientific instruments were exposed to Titan’s atmosphere. Around 120
km, the main parachute was replaced by a smaller one to complete the
descent.
The probe began transmitting data to Cassini four minutes
into its descent and continued to transmit after landing at least as
long as Cassini was above Titan’s horizon. The signals, relayed by
Cassini, were picked up by NASA’s Deep Space Network and delivered
immediately to ESOC. The first science data arrived at 16:19 GMT.
Huygens
was humankind’s first attempt to land a probe on another world in the
outer Solar System. “This is a great achievement for Europe and its US
partners in this ambitious international endeavour to explore Saturn
system,” said Jean-Jacques Dordain, then ESA’s Director General.
This image is a stereographic (fish-eye) projection taken with the descent imager/spectral radiometer on Huygens.
More information and a high-res TIFF version of the image is available at theNASA JPL website.
The most luminous galaxy known in the
Universe — the quasar W2246-0526, seen when the Universe was less than
10% of its current age — is so turbulent that it is in the process of
ejecting its entire supply of star-forming gas, according to new
observations with the Atacama Large Millimeter/submillimeter Array
(ALMA).
Quasars are distant galaxies with very active supermassive black holes at their centres that spew out powerful jets of particles and radiation. Most quasars shine brightly, but a tiny fraction [1]
of these energetic objects are of an unusual type known as Hot DOGs, or
Hot, Dust-Obscured Galaxies, including the galaxy WISE
J224607.57-052635.0 [2], the most luminous known galaxy in the Universe.
For the first time, a team of researchers led by Tanio Díaz-Santos of
the Universidad Diego Portales in Santiago, Chile, has used the unique
capabilities of ALMA[3] to peer inside W2246-0526 and trace the motion of ionised carbon atoms between the galaxy’s stars.
“Large amounts of this interstellar material were found in an
extremely turbulent and dynamic state, careening throughout the galaxy
at around two million kilometres per hour,” explains lead author Tanio Díaz-Santos.
The astronomers believe that this turbulent behaviour could be linked
to the galaxy’s extreme luminosity. W2246-0526 blasts out as much light
as roughly 350 trillion Suns. This startling brightness is powered by a
disc of gas that is superheated as it spirals in on the supermassive
black hole at the galaxy’s core. The light from the blazingly bright accretion disc
in the centre of this Hot DOG does not escape directly, it is absorbed
by a surrounding thick blanket of dust, which re-emits the energy as
infrared light [4].
This powerful infrared radiation has a direct and violent impact on
the entire galaxy. The region around the black hole is at least 100
times more luminous than the rest of the galaxy combined, thus releasing
intense yet localised radiation in W2246-0526 that is exerting
tremendous pressure on the entire galaxy [5].
“We suspected that this galaxy was in a transformative stage of its life because of the enormous amount of infrared energy,” said co-author Peter Eisenhardt, Project Scientist for WISE at NASA's Jet Propulsion Laboratory in Pasadena, California.
“ALMA has now shown us that the raging furnace in this galaxy is making the pot boil over,” adds Roberto Assef, also from Universidad Diego Portales and leader of the ALMA observations.
If these turbulent conditions continue, the intense infrared
radiation would boil away all of the galaxy’s interstellar gas. Models
of galaxy evolution based on the new ALMA data indicate that the
interstellar gas is already being ejected from the galaxy in all
directions.
“If this pattern continues, it is possible that W2246 will eventually mature into a more traditional quasar,” concludes Manuel Aravena, also from the Universidad Diego Portales. “Only
ALMA, with its unparalleled resolution, can allow us to see this object
in high definition and fathom such an important episode in the life of
this galaxy.”
Notes
[1] Only one of every 3000 quasars observed are classified as Hot DOGs.
[2] The full name of this remarkable object is WISE J224607.57-052635.0, it was found byNASA’s Wide-field Infrared Survey Explorer (WISE)spacecraft and the rest of the name gives the precise location of the quasar on the sky.
[3] ALMA is uniquely capable of detecting the faint, millimetre-wavelength light naturally emitted by atomic carbon.
[4] Because of the expansion of the
Universe the infrared radiation from W2246-0526 is redshifted to longer
millimetre wavelengths — where ALMA is very sensitive — when it is
observed from Earth.
[5] In most other quasars this ratio
is much more modest. This process of mutual interaction between the
central black hole of a galaxy and the rest of its material is known to
astronomers as feedback.
More Information
This research was presented in a paper "The Strikingly Uniform,
Highly Turbulent Interstellar Medium of The Most Luminous Galaxy in the
Universe”, by T. Díaz-Santos et al., and will be published in the
journal Astrophysical Journal Letters.
The team is composed of T. Díaz-Santos (Universidad Diego Portales,
Santiago, Chile), R. J. Assef (Universidad Diego Portales, Santiago,
Chile), A. W. Blain (University of Leicester, UK) , C.-W. Tsai (Jet
Propulsion Laboratory, California Institute of Technology, Pasadena,
California, USA) , M. Aravena (Universidad Diego Portales, Santiago,
Chile), P. Eisenhardt (Jet Propulsion Laboratory, California Institute
of Technology, Pasadena, California, USA), J. Wu (University of
California Los Angeles, California, USA), D. Stern (Jet Propulsion
Laboratory, California Institute of Technology, Pasadena, California,
USA) and C. Bridge (Jet Propulsion Laboratory, California Institute of
Technology, Pasadena, California, USA).
ESO is the foremost intergovernmental astronomy organisation in
Europe and the world’s most productive ground-based astronomical
observatory by far. It is supported by 16 countries: Austria, Belgium,
Brazil, the Czech Republic, Denmark, France, Finland, Germany, Italy,
the Netherlands, Poland, Portugal, Spain, Sweden, Switzerland and the
United Kingdom, along with the host state of Chile. ESO carries out an
ambitious programme focused on the design, construction and operation of
powerful ground-based observing facilities enabling astronomers to make
important scientific discoveries. ESO also plays a leading role in
promoting and organising cooperation in astronomical research. ESO
operates three unique world-class observing sites in Chile: La Silla,
Paranal and Chajnantor. At Paranal, ESO operates the Very Large
Telescope, the world’s most advanced visible-light astronomical
observatory and two survey telescopes. VISTA works in the infrared and
is the world’s largest survey telescope and the VLT Survey Telescope is
the largest telescope designed to exclusively survey the skies in
visible light. ESO is a major partner in ALMA, the largest astronomical
project in existence. And on Cerro Armazones, close to Paranal, ESO is
building the 39-metre European Extremely Large Telescope, the E-ELT,
which will become “the world’s biggest eye on the sky”.
The subject of this NASA/ESA Hubble Space Telescope image is known as
NGC 3597. It is the product of a collision between two good-sized
galaxies, and is slowly evolving to become a giant elliptical galaxy.
This type of galaxy has grown more and more common as the Universe has
evolved, with initially small galaxies merging and progressively
building up into larger galactic structures over time.
NGC 3597 is
located approximately 150 million light-years away in the constellation
of Crater (The Cup). Astronomers study NGC 3597 to learn more about how
elliptical galaxies form — many ellipticals began their lives far
earlier in the history of the Universe. Older ellipticals are nicknamed
“red and dead” by astronomers because these bloated galaxies are not
anymore producing new, bluer, stars in ages, and are thus packed full of
old and redder stellar populations.
Before infirmity sets in,
some freshly formed elliptical galaxies experience a final flush of
youth, as is the case with NGC 3597. Galaxies smashing together pool
their available gas and dust, triggering new rounds of star birth. Some
of this material ends up in dense pockets initially called
proto-globular clusters, dozens of which festoon NGC 3597. These pockets
will go on to collapse and form fully-fledged globular clusters, large spheres that orbit the centres of galaxies like satellites, packed tightly full of millions of stars.
ESA’s XMM-Newton has found a wind of high-speed gas streaming from the
centre of a bright spiral galaxy like our own that may be reducing its
ability to produce new stars.
It is not unusual to find hot winds blowing from the swirling discs of
material around supermassive black holes at the centre of active
galaxies.
If powerful enough, these winds can influence their surroundings in
various ways. Their primary effect is to sweep away reservoirs of gas
that might otherwise have formed stars, but it is also possible that
they might trigger the collapse of some clouds to form stars.
Such processes are thought to play a fundamental role in galaxies and black holes throughout the Universe’s 13.8 billion years.
But they were thought to affect only the largest objects, such as
massive elliptical galaxies formed through the dramatic collision and
merging of two or more galaxies, which sometimes trigger the winds
powerful enough to influence star formation.
Now, for the first time, these winds have been seen in a more normal
kind of active galaxy known as a Seyfert, which does not appear to have
undergone any merging.
When observed in visible light, almost all Seyfert galaxies have a
spiral shape similar to our own Milky Way.
However, unlike the Milky
Way, Seyferts have bright cores that shine across the entire
electromagnetic spectrum, a sign that the supermassive black holes at
their centres are not idle but are devouring their surroundings.
The supermassive black hole at the heart of this particular Seyfert,
known as IRAS17020+4544 and located 800 million light-years from Earth,
has a mass of nearly six million Suns, drawing in nearby gas and making
it shine moderately.
XMM-Newton has found that the winds from around the black hole are moving at 23 000–33 000 km/s, about 10% the speed of light.
An important finding is that the wind from the centre is sufficiently
energetic to heat the gas in the galaxy and suppress star formation –
the first time it has been seen in a relatively normal spiral galaxy.
“It’s the first solid case of an ultra-fast X-ray outflow observed in a
‘normal’ Seyfert galaxy,” says Anna Lia Longinotti from the Instituto
Nacional de Astrofísica, Óptica y Electrónica of Puebla, Mexico, lead
author of the paper describing the results in Astrophysical Journal Letters.
The peculiar wind of a spiral galaxy
Copyright: Image: Sloan Digital Sky Survey; Spectrum: Longinotti et al (2015)
The galaxy has another surprise: the X-ray emission from the fast winds
from galactic cores are usually dominated by iron atoms with many of
their electrons stripped off, but this galaxy’s winds turn out to be
rather unusual, exhibiting lighter elements like oxygen, with no iron
detected
“I was actually very surprised to discover that this wind is made mostly
of oxygen because nobody has seen a galaxy like this before,” says Anna
Lia.
Because the galaxy is broadly similar to our own, it raises questions
about the history of the Milky Way and the role that our own central
black hole may have played.
“We know, also thanks to recent results obtained by XMM-Newton, that the
four-million-solar-mass black hole in our own galaxy has undergone
phases of much stronger activities, even only a few hundred years ago,”
says co-author Matteo Guainazzi, ESA astronomer currently at the
Institute of Space and Astronautical Science of the Japan Aerospace
Exploration Agency.
“Of course we cannot be sure, but our discovery implies that fast
outflows like those found in IRAS17020+4544 may have once swept through
our own Galaxy during one of these active phases.
“This possibility was not considered before, because this ‘feedback’
from X-ray winds was previously observed only in galaxies very different
from the Milky Way.”
“XMM-Newton continues to make discoveries with the potential to question
our understanding of how the stars in a galaxy and the supermassive
black hole at its centre co-evolve throughout the history of the
Universe,” says Norbert Schartel, ESA’s XMM-Newton project scientist.
Notes for Editors
“X-ray high-resolution spectroscopy reveals feedback in a Seyfert Galaxy
from an ultra fast wind with complex ionization and velocity
structure,” by A.L Longinotti et al is published inThe Astrophysical Journal Letters.
The findings are based on measurements by XMM-Newton’s Reflection
Grating Spectrometer and the European Photon Imaging Camera in 2004 and
2014.
For more information, please contact: Markus Bauer
ESA Science and Robotic Exploration Communication Officer
Tel: +31 71 565 6799
Mob: +31 61 594 3 954 Email:Markus.Bauer@esa.int
Anna Lia Longinotti
Catedrática CONACYT
Instituto Nacional de Astrofísica, Óptica y Electrónica (INAOE Puebla, Mexico) Email: annalia@inaoep.mx
Matteo Guainazzi
ESA ASTRO-H Resident Astronomer
Institute of Space and Astronautical Science
Japan Aerospace Exploration Agency Email:Matteo.Guainazzi@sciops.esa.int
Copyright: Comet images: ESA/Rosetta/NavCam–CC BY–SA IGO 3.0;
VIRTIS images and data: ESA/Rosetta/VIRTIS/INAF-IAPS, Rome/OBS DE
PARIS-LESIA/DLR; G. Filacchione et al (2016).Hi-res image
Ice in Imhotep Copyright: ESA/Rosetta/NavCam – CC BY-SA IGO 3.0 Hi-res image
Observations made shortly after Rosetta’s arrival at its target comet in
2014 have provided definitive confirmation of the presence of water
ice.
Although water vapour is the main gas seen flowing from comet
67P/Churyumov–Gerasimenko, the great majority of ice is believed to come
from under the comet’s crust, and very few examples of exposed water
ice have been found on the surface.
However, a detailed analysis by Rosetta’s VIRTIS infrared instrument
reveals the composition of the comet’s topmost layer: it is primarily
coated in a dark, dry and organic-rich material but with a small amount
of water ice mixed in.
In the latest study, which focuses on scans between September and
November 2014, the team confirms that two areas several tens of metres
across in the Imhotep region that appear as bright patches in visible light, do indeed include a significant amount of water ice.
The ice is associated with cliff walls and debris falls, and was at an average temperature of about –120ºC at the time.
In those regions, pure water ice was found to occupy around 5% of each
pixel sampling area, with the rest made up of the dark, dry material.
The abundance of ice was calculated by comparing Rosetta’s VIRTIS
infrared measurements to models that consider how ice grains of
different sizes might be mixed together in one pixel.
The data reveal two different populations of grains: one is several tens
of micrometres in diameter, while the other is larger, around 2 mm.
These sizes contrast with the very small grains, just a few micrometres
in diameter, found in the Hapi region on the ‘neck’ of the comet, as
observed by VIRTIS in a different study.
“The various populations of icy grains on the surface of the comet imply
different formation mechanisms, and different time scales for their
formation,” says Gianrico Filacchione, lead author of the new study,
published in the journal Nature.
At Hapi, the very small grains are associated with a thin layer of
‘frost’ that forms as part of the daily ice cycle, a result of fast
condensation in this region over each comet rotation of just over 12
hours.
“By contrast, we think that layers of the larger millimetre-sized grains
we see in Imhotep have a more complex history. They likely formed
slowly over time, and are only occasionally exposed through erosion,”
says Gianrico.
Assuming a typical grain size of tens of micrometres for ice grains on
the surface, as inferred on other comets as well as Rosetta’s comet,
then observations of millimetre-sized grains can be explained by the
growth of secondary ice crystals.
One way this can occur is via ‘sintering’, whereby ice grains are
compacted together. Another method is ‘sublimation’, in which heat from
the Sun penetrates the surface, triggering the evaporation of buried
ice. While some of the resulting water vapour may escape from the
nucleus, a significant fraction of it recondenses in layers beneath the
surface.
This idea is supported by laboratory experiments that simulate the
sublimation behaviour of ice buried under dust, heated from above by
sunlight.
These tests show that more than 80% of the released water vapour does
not make it up through the dust mantle, but rather is redeposited below
the surface.
Additional energy for sublimation could also be provided by a
transformation in structure of the ice at a molecular level. At the low
temperatures observed on comets, amorphous ice can change into
crystalline ice, releasing energy as it does so.
“Ice grain growth can lead to ice-rich subsurface layers several metres
thick, that can then affect the large-scale structure, porosity and
thermal properties of the nucleus,” says Fabrizio Capaccioni, VIRTIS
principal investigator.
“The thin ice-rich layers that we see exposed close to the surface may
be a consequence of cometary activity and evolution, implying that
global layering did not necessarily occur early in the comet’s formation
history.”
“Understanding which features on the comet are left over from its formation
and which have been created during its evolution is somewhat
challenging, but this is why we are studying a comet up close: to try to
discover what processes are important at different stages of a comet’s
lifetime,” adds Matt Taylor, ESA’s Rosetta project scientist.
The Rosetta scientists are now analysing data captured later in the
mission, as the comet moved closer to the Sun in mid-2015, to see how
the amount of ice exposed on the surface evolved as the heating
increased.
Notes for Editors
“Exposed water ice on the nucleus of comet 67P/Churyumov–Gerasimenko,” by G. Filacchione et al is published in the journalNature.
GRAVITY discovers new double star in Orion Trapezium Cluster
Successful commissioning of GRAVITY at the VLTI
Zooming in on black holes is the main
mission for the newly installed instrument GRAVITY at ESO’s Very Large
Telescope in Chile. During its first observations, GRAVITY successfully
combined starlight using all four Auxiliary Telescopes. The large team
of European astronomers and engineers, led by the Max Planck Institute
for Extraterrestrial Physics in Garching, who designed and built
GRAVITY, are thrilled with the performance. During these initial tests,
the instrument has already achieved a number of notable firsts. This is
the most powerful VLT Interferometer instrument yet installed.
The GRAVITY
instrument combines the light from multiple telescopes to form a
virtual telescope up to 200 metres across, using a technique called interferometry. This enables the astronomers to detect much finer detail in astronomical objects than is possible with a single telescope.
Since the summer of 2015, an international team of astronomers and engineers led by Frank Eisenhauer (MPE,
Garching, Germany) has been installing the instrument in specially
adapted tunnels under the Very Large Telescope at ESO’s Paranal
Observatory in northern Chile [1].
This is the first stage of commissioning GRAVITY within the Very Large
Telescope Interferometer (VLTI). A crucial milestone has now been
reached: for the first time, the instrument successfully combined
starlight from the four VLT Auxiliary Telescopes [2].
“During its first light, and for the first time in the history of
long baseline interferometry in optical astronomy, GRAVITY could make
exposures of several minutes, more than a hundred times longer than
previously possible,” commented Frank Eisenhauer. “GRAVITY will
open optical interferometry to observations of much fainter objects,
and push the sensitivity and accuracy of high angular resolution
astronomy to new limits, far beyond what is currently possible.”
As part of the first observations the team looked closely at the bright, young stars known as the Trapezium Cluster,
located in the heart of the Orion star-forming region. Already, from
these first commissioning data, GRAVITY made a small discovery: one of
the components of the cluster was found to be a double star [3].
The key to this success was to stabilise the virtual telescope for
long enough, using the light of a reference star, so that a deep
exposure on a second, much fainter object becomes feasible. Furthermore,
the astronomers also succeeded in stabilising the light from four
telescopes simultaneously — a feat not achieved before.
GRAVITY can measure the positions of astronomical objects on the
finest scales and can also perform interferometric imaging and
spectroscopy [4].
If there were buildings on the moon, GRAVITY would be able to spot
them. Such extremely high resolution imaging has many applications, but
the main focus in the future will be studying the environments around
black holes.
In particular, GRAVITY will probe what happens in the extremely
strong gravitational field close to the event horizon of the
supermassive black hole at the centre of the Milky Way — which explains
the choice of the name of the instrument. This is a region where
behaviour is dominated by Einstein's theory of general relativity.
In addition, it will uncover the details of mass accretion and jets —
processes that occur both around newborn stars (young stellar objects)
and in the regions around the supermassive black holes at the centres of
other galaxies. It will also excel at probing the motions of binary
stars, exoplanets and young stellar discs, and in imaging the surfaces
of stars.
So far, GRAVITY has been tested with the four 1.8-metre Auxiliary
Telescopes. The first observations using GRAVITY with the four 8-metre
VLT Unit Telescopes are planned for later in 2016.
The GRAVITY consortium is led by the Max Planck Institute for
Extraterrestrial Physics, in Garching, Germany. The other partner
institutes are:
LESIA, Observatoire de Paris, PSL Research University, CNRS,
Sorbonne Universités, UPMC Univ. Paris 06, Univ. Paris Diderot, Sorbonne
Paris Cité, Meudon, France
Max Planck Institute for Astronomy, Heidelberg, Germany
1. Physikalisches Institut, University of Cologne, Cologne, Germany
IPAG, Université Grenoble Alpes/CNRS, Grenoble, France
Centro Multidisciplinar de Astrofísica, CENTRA (SIM), Lisbon and Oporto, Portugal
ESO, Garching, Germany
Notes
[1] The VLTI tunnels and beam-combining room have recently undergone
significant construction work to accommodate GRAVITY as well as to
prepare for other future instruments.
[2] It would be more accurate to call
this step “first fringes” as the milestone was the first successful
combination of light from the different telescopes so that the beams
interfered and fringes were formed and recorded.
[3] The newly discovered double star is Theta1 Orionis F, and the observations were made using the nearby brighter star Theta1 Orionis C as the reference.
[4] GRAVITY aims to measure the
positions of objects on scales of order ten microarcseconds, and perform
imaging with four milliarcsecond resolution.
