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
False-color image of SPT-CL J0546–5345 at z = 1:067. Gemini GeMS/GSAOI
Ks (this work) = red, HST ACS F814W = green, HST ACS F606W = blue. The
red polygon shows the approximate sky coverage of the GSAOI pointings.
PSF stars are indicated by white circles. The star near the top of the
image with two circles is a binary star. The inset at lower left is a
zoom-in of the cluster core. The scale bars at lower right of the inset
and full image show the angular and physical projected distances at the
cluster redshift. The red, green and blue spots on the scale bar in the
inset show the PSF FWHM for each band. N is up and E is left.
Credit: Gemini Observatory/AURA.Full Resolution PNG
Summary: A team using the Gemini Multi-Conjugate Adaptive Optics System
(GeMS) with the Gemini South Adaptive Optics Imager (GSAOI) have, for
the first time, measured the stellar masses relative to the physical
sizes of several galaxies in a cluster at a lookback time of about 5
billion years. The data suggest that the relationship between stellar
mass and size has a constant slope over time. This leads to the
conclusion that the most likely evolutionary course for the larger (more
expansive) galaxies we see in the nearby Universe is either from the
combination of smaller galaxies and/or outflows from black holes at
galactic cores.
During the past 20 years astronomers have developed a picture for the
evolution of the size and structure of galaxies – from the formation of
the first galaxies in the early Universe, to what we see today. One of
the most important discoveries is that the most massive galaxies in the
early Universe, at z > 1 (i.e. when the universe was about 5 billion
years old), were much smaller in physical size (for their stellar mass,
by a factor of between 2 to 6) when compared to galaxies we see in the
local Universe today.
It is still unclear what the main physical mechanism(s) is/are that
allow this extraordinary growth in the size of these galaxies over time.
Mergers of galaxies with similar stellar masses (major mergers),
accretion of small satellite galaxies (minor mergers), or the rapid loss
of mass caused by active galactic nuclei (AGN), or supernova winds
(adiabatic expansion) could all potentially be responsible for the
dramatic growth in the size of these galaxies. To distinguish between
these proposed physical mechanisms, astronomers use the stellar mass –
size relation (i.e. the relation between the mass of the galaxies
measured from light of the stars and the intrinsic size of the galaxies
represented by their effective radii).
The accuracy in determining the stellar mass - size relation for a
galaxy depends most strongly on the resolution of the images and the
rest-frame wavelength (assuming no redshift due to the expansion of the
Universe) of the observations. The resolution is required to measure
accurately the sizes of the most compact galaxies.
Using the most advanced adaptive optic system on the planet, the Gemini
Multi-Conjugate Adaptive Optics System (GeMS), and the Gemini South
Adaptive Optics Imager (GSAOI), an international team of astronomers,
led by Sarah Sweet from the Australian National University in Canberra,
Australia, have measured, for the first time, the stellar mass – size
relation for several galaxies in a cluster environment (SPT-CL
J0546−5345 at a redshift of z = 1.067), with an average resolution of
450 parsecs in radius at the cluster redshift, and at the rest-frame
wavelength dominated by an old (redder) stellar population. The authors
of this study find that the stellar mass - size relation at the redshift
of the cluster (z ~ 1) is offset from that at z ~ 0. The result is
consistent with previous findings, where the primary mechanism for
galaxy growth in size is minor mergers.
One of the most important results presented in this study is that the
slope of the stellar mass – size relation plot of the massive galaxies
at z ~ 1 is consistent with the slope seen for the galaxies with same
stellar masses in the local Universe. This result suggests that the
massive galaxies in the cluster SPT-CL J0546-5345 has ceased its early,
rapid growth via major mergers, leaving the accretion of small satellite
galaxies (minor mergers) and/or the rapid loss of mass caused by active
galactic nuclei (AGN), as the principal mechanism to increase the size
of the galaxies.
This work is accepted for publication in Monthly Notices of the Royal Astronomical Society and a preprint is available here.
Core accretion: A 10 Jupiter-mass planet is formed and is placed at 50 AU from the star.
The planet has opened a gap in the circumstellar disk.
Image: J. Szulagyi, JUPITER code
Gravitational instability simulation: Two snapshots in the early and late stage of the simulation at 780 years and 1942 years.
The second snapshot shows only 4 clumps remaining among those initially formed.
Image: Lucio Mayer & T. Quinn, ChaNGa code
Animationby J. Szulagyi, L. Mayer, T. Quinn and C. Gheller/ETH Zurich/University of Zurich/CSCS.
Young giant planets are born from gas and dust. Researchers of
ETH Zürich and the Universities of Zürich and Bern simulated different
scenarios relying on the computing power of the Swiss National
Supercomputing Centre (CSCS) to find out how they exactly form and
evolve. They compared their results with observations and were able to
show amongst others a big difference between the postulated formation
mechanisms.
Astronomers set up two theories explaining how gaseous giant planets like Jupiter or Saturn could be born. A bottom-up formation mechanism states that first, a solid core is aggregated of roughly ten times the size of the Earth. «Then, this core is massive enough to attract a significant amount of gas and keep it,» explains Judit Szulágyi, post-doctoral fellow at the ETH Zürich and member of the Swiss NCCR PlanetS. The second theory is a top-down formation scenario: Here the gaseous disk around the young star is so massive, that due to self-gravity of the gas-dust, spiral arms are forming with clumps inside. Then, these clumps collapse via their own gravity directly into a gaseous planet, similar to how stars form. The first mechanism is called «core-accretion», the second one «disk instability». In both cases, a disk forms around the gas-giants, called the circumplanetary disk, which will serve as a birth-nest for satellites to form.
To find out which mechanism actually takes place in the Universe, Judit Szulágyi and Lucio Mayer, Professor at the University of Zürich, simulated the scenarios on Piz Daint supercomputer at the Swiss National Supercomputing Centre (CSCS) in Lugano. «We pushed our simulations to the limits in terms of the complexity of the physics added to the models,» explains Judit Szulágyi: «And we achieved higher resolution than anybody before.» In their studies published in the «Monthly Notices of the Royal Astronomical Society» the researchers found a big difference between the two formation mechanisms: In the disk instability scenario the gas in the planet’s vicinity remained very cold, around 50 Kelvins, whereas in the core accretion case the circumplanetary disk was heated to several hundreds of Kelvins. «The disk instability simulations are the first that can resolve the circumplanetary disk around multiple protoplanets, using tens of millions of resolution elements in the computational domain. We exploited Piz Daint to accelerate the calculations using Graphics Processing Units (GPUs)” adds Mayer.
This huge temperature difference is easily observable. «When astronomers look into new forming planetary systems, just measuring the temperatures in the planet’s vicinity will be enough to tell which formation mechanism built the given planet,» explains Judit Szulágyi. A first comparison of the calculated and observed data seems to favour the core accretion theory. Another difference that was expected didn’t show up in the computer simulation. Before, astrophysics thought that the circumplanetary disk significantly differs in mass in the two formation scenarios. «We showed that this is not true,» says the PlanetS member.
Luminous shock front detected
Regarding the size of the new born planet, observations can be misleading as the astrophysicist found in a second study together with Christoph Mordasini, Professor at the University of Bern. In the core accretion model the researchers had a closer look at the disk around planets with masses three to ten times bigger than Jupiter’s. The computer simulations showed that gas falling on the disk from the outside heats up and creates a very luminous shock front on the disk’s upper layer. This significantly alters the observational appearance of young, forming planets.
«When we see a luminous spot inside a circumplanetary disk, we cannot be sure whether we see the planet luminosity, or also the surrounding disk luminosity,» says Judit Szulágyi. This may lead to an overestimation of the planet’s mass of up to four times. «So maybe an observed planet has only the same mass as Saturn instead of some Jupiter masses,» concludes the scientist.
In their simulations the astrophysicists mimicked the formation processes by using the basic physical laws such as gravity or the hydrodynamical equations of the gas. Because of the complexity of the physical models the simulations were very time consuming, even on Europe’s fastest supercomputer at CSCS: «On the order of nine months running time on hundreds to several thousands of computing cores» estimates Judit Szulágyi: «This means that on one computing core it would have taken longer than my entire lifetime.»
Yet there are still challenges ahead. Simulations of disk instability still do not cover a long timescale. It is possible that after the protoplanet has collapsed to the density of Jupiter its disk will heat up more like in core-accretion. Likewise, the hotter gas found in the core-accretion case would be partially ionized, a favourable environment for effects of magnetic fields, completely neglected so far. Running even more expensive simulations with a richer description of the physics will be the next step. (bva)
Publications:
Szulagyi; L. Mayer; T. Quinn: Circumplanetary disks around young giant planets: a comparison between core-accretion and disk instability, Monthly Notices of the Royal Astronomical Society 2016;
Szulagyi; C. Mordasini: Thermodynamics of Giant Planet Formation: Shocking Hot Surfaces on Circumplanetary Disks, Monthly Notices of the Royal Astronomical Society: Letters 2016;
Globular clusters
offer some of the most spectacular sights in the night sky. These
ornate spheres contain hundreds of thousands of stars, and reside in the
outskirts of galaxies. The Milky Way contains over 150 such clusters —
and the one shown in this NASA/ESA Hubble Space Telescope image, named NGC 362, is one of the more unusual ones.
As
stars make their way through life they fuse elements together in their
cores, creating heavier and heavier elements — known in astronomy as metals
— in the process. When these stars die, they flood their surroundings
with the material they have formed during their lifetimes, enriching the
interstellar medium with metals. Stars that form later therefore contain higher proportions of metals than their older relatives.
By
studying the different elements present within individual stars in NGC
362, astronomers discovered that the cluster boasts a surprisingly high
metal content, indicating that it is younger than expected. Although
most globular clusters are much older than the majority of stars in
their host galaxy, NGC 362 bucks the trend, with an age lying between 10
and 11 billion years old. For reference, the age of the Milky Way is
estimated to be above 13 billion years.
This image, in which you can view NGC 362’s individual stars, was taken by Hubble’s Advanced Camera for Surveys (ACS).
Astronomers using observations from NASA's Kepler and Swift missions
have discovered a batch of rapidly spinning stars that produce X-rays at
more than 100 times the peak levels ever seen from the sun. The stars,
which spin so fast they've been squashed into pumpkin-like shapes, are
thought to be the result of close binary systems where two sun-like
stars merge.
Dive into the Kepler field and learn more about the origins of these rapidly spinning stars.
Credits: NASA's Goddard Space Flight Center/Scott Wiessinger, producer
"These 18 stars rotate in just a few days on average, while the sun
takes nearly a month," said Steve Howell, a senior research scientist at
NASA's Ames Research Center in Moffett Field, California, and leader of
the team. "The rapid rotation amplifies the same kind of activity we
see on the sun, such as sunspots and solar flares, and essentially sends
it into overdrive."
The most extreme member of the group, a K-type orange giant dubbed
KSw 71, is more than 10 times larger than the sun, rotates in just 5.5
days, and produces X-ray emission 4,000 times greater than the sun does
at solar maximum.
This artist's concept illustrates how the most
extreme "pumpkin star" found by Kepler and Swift compares with the sun.
Both stars are shown to scale. KSw 71 is larger, cooler and redder than
the sun and rotates four times faster. Rapid spin causes the star to
flatten into a pumpkin shape, which results in brighter poles and a
darker equator. Rapid rotation also drives increased levels of stellar
activity such as starspots, flares and prominences, producing X-ray
emission over 4,000 times more intense than the peak emission from the
sun. KSw 71 is thought to have recently formed following the merger of
two sun-like stars in a close binary system.Credits: NASA's Goddard Space Flight Center/Francis Reddy
These rare stars were found as part of an X-ray survey of the
original Kepler field of view, a patch of the sky comprising parts of
the constellations Cygnus and Lyra. From May 2009 to May 2013, Kepler
measured the brightness of more than 150,000 stars in this region to
detect the regular dimming from planets passing in front of their host
stars. The mission was immensely successful, netting more than 2,300 confirmed exoplanets and nearly 5,000 candidates to date.
An ongoing extended mission, called K2, continues this work in areas of
the sky located along the ecliptic, the plane of Earth's orbit around
the sun.
"A side benefit of the Kepler mission is that its initial field of
view is now one of the best-studied parts of the sky," said team member
Padi Boyd, a researcher at NASA's Goddard Space Flight Center in
Greenbelt, Maryland, who designed the Swift survey. For example, the
entire area was observed in infrared light by NASA's Wide-field Infrared Survey Explorer, and NASA's Galaxy Evolution Explorer
observed many parts of it in the ultraviolet. "Our group was looking
for variable X-ray sources with optical counterparts seen by Kepler,
especially active galaxies, where a central black hole drives the
emissions," she explained.
Using the X-ray and ultraviolet/optical telescopes aboard Swift, the researchers conducted the Kepler–Swift Active Galaxies and Stars Survey (KSwAGS), imaging about six square degrees, or 12 times the apparent size of a full moon, in the Kepler field.
"With KSwAGS we found 93 new X-ray sources, about evenly split
between active galaxies and various types of X-ray stars," said team
member Krista Lynne Smith, a graduate student at the University of
Maryland, College Park who led the analysis of Swift data. "Many of
these sources have never been observed before in X-rays or ultraviolet
light."
For the brightest sources, the team obtained spectra using the
200-inch telescope at Palomar Observatory in California. These spectra
provide detailed chemical portraits of the stars and show clear evidence
of enhanced stellar activity, particularly strong diagnostic lines of
calcium and hydrogen.
The researchers used Kepler measurements to determine the rotation
periods and sizes for 10 of the stars, which range from 2.9 to 10.5
times larger than the sun. Their surface temperatures range from
somewhat hotter to slightly cooler than the sun, mostly spanning
spectral types F through K. Astronomers classify the stars as subgiants
and giants, which are more advanced evolutionary phases than the sun's
caused by greater depletion of their primary fuel source, hydrogen. All
of them eventually will become much larger red giant stars.
A paper detailing the findings will be published in the Nov. 1 edition of the Astrophysical Journal and is now available online.
Forty years ago, Ronald Webbink at the University of Illinois,
Urbana-Champaign noted that close binary systems cannot survive once the
fuel supply of one star dwindles and it starts to enlarge. The stars
coalesce to form a single rapidly spinning star initially residing in a
so-called "excretion" disk formed by gas thrown out during the merger.
The disk dissipates over the next 100 million years, leaving behind a
very active, rapidly spinning star.
Howell and his colleagues suggest that their 18 KSwAGS stars formed
by this scenario and have only recently dissipated their disks. To
identify so many stars passing through such a cosmically brief phase of
development is a real boon to stellar astronomers.
"Webbink's model suggests we should find about 160 of these stars in
the entire Kepler field," said co-author Elena Mason, a researcher at
the Italian National Institute for Astrophysics Astronomical Observatory
of Trieste. "What we have found is in line with theoretical
expectations when we account for the small portion of the field we
observed with Swift."
The team has already extended their Swift observations to additional fields mapped by the K2 mission.
Ames manages the Kepler and K2 missions for NASA’s Science Mission
Directorate. NASA's Jet Propulsion Laboratory in Pasadena, California,
managed Kepler mission development. Ball Aerospace & Technologies
Corp. operates the flight system with support from the Laboratory for
Atmospheric and Space Physics at the University of Colorado in Boulder.
Goddard manages the Swift mission in collaboration with Pennsylvania
State University in University Park, the Los Alamos National Laboratory
in New Mexico and Orbital Sciences Corp. in Dulles, Virginia. Other
partners include the University of Leicester and Mullard Space Science
Laboratory in the United Kingdom, Brera Observatory and the Italian
Space Agency in Italy, with additional collaborators in Germany and
Japan.
The eerie glow of a dead star, which exploded long ago as a supernova,
reveals itself in this NASA Hubble Space Telescope image of the Crab
Nebula. But don't be fooled. The ghoulish-looking object still has a
pulse. Buried at its center is the star's tell-tale heart, which beats
with rhythmic precision.
Astronomers discovered a real "tell-tale heart" in
space, 6,500 light-years from Earth. The "heart" is the crushed core of a
long-dead star, called a neutron star, which exploded as a supernova
and is now still beating with rhythmic precision. Evidence of its
heartbeat are rapid-fire, lighthouse-like pulses of energy from the
fast-spinning neutron star. The stellar relic is embedded in the center
of the Crab Nebula, the expanding, tattered remains of the doomed star. Credits: NASA and ESA, Acknowledgment: M. Weisskopf/Marshall Space Flight Center
This time-lapse movie of the Crab Nebula, made from
NASA Hubble Space Telescope observations, reveals wave-like structures
expanding outward from the "heart" of an exploded star. The waves look
like ripples in a pond. The heart is the crushed core of the exploded
star, or supernova. Called a neutron star, it has about the same mass as
the sun but is squeezed into an ultra-dense sphere that is only a few
miles across and 100 billion times stronger than steel. This surviving
relic is a tremendous dynamo, spinning 30 times a second. The rapidly
spinning neutron star is visible in the image as the bright object just
below center. The bright object to the left of the neutron star is a
foreground or background star. The movie is assembled from 10 Hubble
exposures taken between September and November 2005 by the Advanced
Camera for Surveys. Credits: NASA and ESA, Acknowledgment: J. Hester (Arizona State University)
The "heart" is the crushed core of the exploded star. Called a neutron
star, it has about the same mass as the sun but is squeezed into an
ultra-dense sphere that is only a few miles across and 100 billion times
stronger than steel. The tiny powerhouse is the bright star-like object
near the center of the image.
This surviving remnant is a tremendous dynamo, spinning 30 times a
second. The wildly whirling object produces a deadly magnetic field that
generates an electrifying 1 trillion volts. This energetic activity
unleashes wisp-like waves that form an expanding ring, most easily seen
to the upper right of the pulsar.
The nebula's hot gas glows in radiation across the electromagnetic
spectrum, from radio to X-rays. The Hubble exposures were taken in
visible light as black-and-white exposures. The Advanced Camera for
Surveys made the observations between January and September 2012. The
green hue has been added to give the image a Halloween theme.
The Crab Nebula is one of the most historic and intensively studied
supernova remnants. Observations of the nebula date back to 1054 A.D.,
when Chinese astronomers first recorded seeing a "guest star" during the
daytime for 23 days. The star appeared six times brighter than Venus.
Japanese, Arabic, and Native American stargazers also recorded seeing
the mystery star. In 1758, while searching for a comet, French
astronomer Charles Messier discovered a hazy nebula near the location of
the long-vanished supernova. He later added the nebula to his celestial
catalog as "Messier 1," marking it as a "fake comet." Nearly a century
later British astronomer William Parsons sketched the nebula. Its
resemblance to a crustacean led to M1's other name, the Crab Nebula. In
1928 astronomer Edwin Hubble first proposed associating the Crab Nebula
to the Chinese "guest star" of 1054.
The nebula, bright enough to be visible in amateur telescopes, is located 6,500 light-years away in the constellation Taurus.
Ray Villard Space Telescope Science Institute, Baltimore, Maryland Villard@stsci.edu 410-338-4514 Editor: Karl Hille
An international team of astronomers has
discovered glowing gas clouds surrounding distant quasars. This new
survey by the MUSE instrument on ESO’s Very Large Telescope indicates
that halos around quasars are far more common than expected. The
properties of the halos in this surprising find are also in striking
disagreement with currently accepted theories of galaxy formation in the
early Universe.
An international collaboration of astronomers, led by a group at the Swiss Federal Institute of Technology (ETH) in Zurich, Switzerland, has used the unrivalled observing power of MUSE on the Very Large Telescope
(VLT) at ESO’s Paranal Observatory to study gas around distant active
galaxies, less than two billion years after the Big Bang. These active
galaxies, called quasars, contain supermassive black holes
in their centres, which consume stars, gas, and other material at an
extremely high rate. This, in turn, causes the galaxy centre to emit
huge amounts of radiation, making quasars the most luminous and active
objects in the Universe.
The study involved 19 quasars, selected from among the
brightest that are observable with MUSE. Previous studies have shown
that around 10% of all quasars examined were surrounded by halos, made
from gas known as the intergalactic medium.
These halos extend up to 300 000 light-years away from the centres of
the quasars. This new study, however, has thrown up a surprise, with the
detection of large halos around all 19 quasars observed — far more
than the two halos that were expected statistically. The team suspects
this is due to the vast increase in the observing power of MUSE over
previous similar instruments, but further observations are needed to
determine whether this is the case.
“It is still too early to say if this is due to our new
observational technique or if there is something peculiar about the
quasars in our sample. So there is still a lot to learn; we are just at
the beginning of a new era of discoveries”, says lead author Elena Borisova, from the ETH Zurich.
The original goal of the study was to analyse the gaseous
components of the Universe on the largest scales; a structure sometimes
referred to as the cosmic web, in which quasars form bright nodes [1].
The gaseous components of this web are normally extremely difficult to
detect, so the illuminated halos of gas surrounding the quasars deliver
an almost unique opportunity to study the gas within this large-scale
cosmic structure.
The 19 newly-detected halos also revealed another surprise:
they consist of relatively cold intergalactic gas — approximately 10
000 degrees Celsius. This revelation is in strong disagreement with
currently accepted models of the structure and formation of galaxies,
which suggest that gas in such close proximity to galaxies should have
temperatures upwards of a million degrees.
The discovery shows the potential of MUSE for observing this type of object [2]. Co-author Sebastiano Cantalupo is very excited about the new instrument and the opportunities it provides: “We
have exploited the unique capabilities of MUSE in this study, which
will pave the way for future surveys. Combined with a new generation of
theoretical and numerical models, this approach will continue to provide
a new window on cosmic structure formation and galaxy evolution.”
Notes
[1] The cosmic web is the structure of the Universe at the largest scale. It is comprised of spindly filamentsof primordial material (mostly hydrogen and helium gas) anddark matterwhich connect galaxies and span the chasms between them. The material
in this web can feed along the filaments into galaxies and drive their
growth and evolution.
[2]MUSE
is an integral field spectrograph and combines spectrographic and
imaging capabilities. It can observe large astronomical objects in their
entirety in one go, and for each pixel measure the intensity of the
light as a function of its colour, or wavelength.
More Information
This research was presented in the paper "Ubiquitous giant
Lyα nebulae around the brightest quasars at z ~ 3.5 revealed with MUSE",
to appear in the Astrophysical Journal.
The team is composed of Elena Borisova, Sebastiano
Cantalupo, Simon J. Lilly, Raffaella A. Marino and Sofia G. Gallego
(Institute for Astronomy, ETH Zurich, Switzerland), Roland Bacon and
Jeremy Blaizot (University of Lyon, Centre de Recherche Astrophysique de
Lyon, Saint-Genis-Laval, France), Nicolas Bouché (Institut de Recherche
en Astrophysique et Planétologie, Toulouse, France), Jarle Brinchmann
(Leiden Observatory, Leiden, The Netherlands; Instituto de Astrofísica e
Ciências do Espaço, Porto, Portugal), C Marcella Carollo (Institute for
Astronomy, ETH Zurich, Switzerland), Joseph Caruana (Department of
Physics, University of Malta, Msida, Malta; Institute of Space Sciences
& Astronomy, University of Malta, Malta), Hayley Finley (Institut de
Recherche en Astrophysique et Planétologie, Toulouse, France), Edmund
C. Herenz (Leibniz-Institut für Astrophysik Potsdam, Potsdam, Germany),
Johan Richard (Univ Lyon, Centre de Recherche Astrophysique de Lyon,
Saint-Genis-Laval, France), Joop Schaye and Lorrie A. Straka (Leiden
Observatory, Leiden, The Netherlands), Monica L. Turner (MIT-Kavli
Center for Astrophysics and Space Research, Massachusetts Institute of
Technology, Cambridge, Massachusetts, USA), Tanya Urrutia
(Leibniz-Institut für Astrophysik Potsdam, Potsdam, Germany), Anne
Verhamme (University of Lyon, Centre de Recherche Astrophysique de Lyon,
Saint-Genis-Laval, France), Lutz Wisotzki (Leibniz-Institut für
Astrophysik Potsdam, Potsdam, Germany).
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”.
Artist’s impression of Earth-sized planets orbiting a red dwarf star.
(Image: NASA, ESA, and G.Bacon (STScI)
Computer simulations by astrophysicists at the University of
Bern of the formation of planets orbiting in the habitable zone of low
mass stars such as Proxima Centauri show that these planets are most
likely to be roughly the size of the Earth and to contain large amounts
of water.
In August 2016, the announcement of the discovery of a terrestrial exoplanet orbiting in the habitable zone of Proxima Centauri stimulated the imagination of the experts and the general public. After all this star is the nearest star to our sun even though it is ten times less massive and 500 times less luminous. This discovery together with the one in May 2016 of a similar planet orbiting an even lower mass star (Trappist-1) convinced astronomers that such red dwarfs (as these low mass stars are called) might be hosts to a large population of Earth-like planets.
How could these objects look like? What could they be made of? Yann Alibert and Willy Benz at the Swiss NCCR PlanetS at the University of Bern carried out the first computer simulations of the formation of the population of planets expected to orbit stars ten times less massive than the sun.
“Our models succeed in reproducing planets that are similar in terms of mass and period to the ones observed recently,” Yann Alibert explains the result of the study that has been accepted for publication as a Letter in the journal “Astronomy and Astrophysics”. “Interestingly, we find that planets in close-in orbits around these type of stars are of small sizes. Typically, they range between 0.5 and 1.5 Earth radii with a peak at about 1.0 Earth radius. Future discoveries will tell if we are correct!” the researcher adds.
Ice at the bottom of the global ocean
In addition, the astrophysicists determined the water content of the planets orbiting their small host star in the habitable zone. They found that considering all the cases, around 90% of the planets are harbouring more than 10% of water. For comparison: The Earth has a fraction of water of only about 0,02%. So most of these alien planets are literally water worlds in comparison! The situation could be even more extreme if the protoplanetary disks in which these planets form live longer than assumed in the models. In any case, these planets would be covered by very deep oceans at the bottom of which, owing to the huge pressure, water would be in form of ice.
Water is required for life as we know it. So could these planets be habitable indeed? “While liquid water is generally thought to be an essential ingredient, too much of a good thing may be bad,“ says Willy Benz. In previous studies the scientists in Bern showed that too much water may prevent the regulation of the surface temperature and destabilizes the climate. “But this is the case for the Earth, here we deal with considerably more exotic planets which might be subjected to a much harsher radiation environment, and/or be in synchronous rotation,” he adds.
Following the growth of planetary embryos
To start their calculations, the scientists considered a series of a few hundreds to thousands of identical, low mass stars and around each of them a protoplanetary disk of dust and gas. Planets are formed by accretion of this material. Alibert and Benz assumed that at the beginning, in each disk there were 10 planetary embryos with an initial mass equal to the mass of the Moon. In a few day’s computer time for each system the model calculated how these randomly located embryos grew and migrated.
What kind of planets are formed depends on the structure and evolution of the protoplanetary disks. “If the protoplanetary disk lives long, then planets have a long time to migrate,” explains Yann Alibert. Before landing in the habitable zone, they started their migration beyond the so called ice line where water is frozen, and they accreted a lot of icy particles. Therefore, the overwhelming majority of these planets have a fraction of water larger than 10 %.
“Habitable or not, the study of planets orbiting very low mass stars will likely bring exciting new results, improving our knowledge of planet formation, evolution, and potential habitability,” summarizes Willy Benz. Because these stars are considerably less luminous than the sun, planets can be much closer to their star before their surface temperature becomes too high for liquid water to exist. If one considers that these type of stars also represent the overwhelming majority of stars in the solar neighbourhood and that close-in planets are presently easier to detect and study, one understands why the existence of this population of Earth-like planets is really of importance.
Publications: Y. Alibert and W. Benz: Formation and composition of planets around very low mass stars, A&A https://arxiv.org/abs/1610.03460
This artist's concept depicts "heartbeat stars," which have been detected by NASA's Kepler Space Telescope and others. Credits: NASA/JPL-Caltech.Full image and caption
Matters of the heart can be puzzling and mysterious -- so too with unusual astronomical objects called heartbeat stars.
Heartbeat stars, discovered in large numbers by NASA's Kepler space
telescope, are binary stars (systems of two stars orbiting each other)
that got their name because if you were to map out their brightness over
time, the result would look like an electrocardiogram, a graph of the
electrical activity of the heart. Scientists are interested in them
because they are binary systems in elongated elliptical orbits. This
makes them natural laboratories for studying the gravitational effects
of stars on each other.
In a heartbeat star system, the distance between the two stars varies
drastically as they orbit each other. Heartbeat stars can get as close
as a few stellar radii to each other, and as far as 10 times that
distance during the course of one orbit.
At the point of their closest encounter, the stars’ mutual
gravitational pull causes them to become slightly ellipsoidal in shape,
which is one of the reasons their light is so variable. This is the same
type of "tidal force" that causes ocean tides on Earth. By studying
heartbeat stars, astronomers can gain a better understanding of how this
phenomenon works for different kinds of stars.
Tidal forces also cause heartbeat stars to vibrate or "ring" -- in
other words, the diameters of the stars rapidly fluctuate as they orbit
each other. This effect is most noticeable at the point of closest
approach.
“You can think about the stars as bells, and once every orbital
revolution, when the stars reach their closest approach, it's as if they
hit each other with a hammer,” said Avi Shporer, NASA Sagan
postdoctoral fellow at NASA's Jet Propulsion Laboratory, Pasadena,
California, and lead author of a recent study on heartbeat stars. "One
or both stars vibrate throughout their orbits, and when they get nearer
to each other, it's as though they are ringing very loudly."
Kepler, now in its K2 Mission, discovered large numbers of heartbeat stars just in the last several years. A 2011 study discussed a star called KOI-54 that shows an increase in brightness every 41.8 days. In 2012, a subsequent study
characterized 17 additional objects in the Kepler data and dubbed them
"heartbeat stars." To characterize these unique systems, further data
and research were required.
Shporer's study,
published in the Astrophysical Journal, measured the orbits of 19
heartbeat star systems -- the largest batch ever characterized in a
single study. The authors followed up on known heartbeat stars,
previously identified by the Kepler mission. Specifically, they used an
instrument on the W.M. Keck Observatory telescope in Hawaii called the
High Resolution Echelle Spectrometer (HIRES), which measures the
wavelengths of incoming light, which are stretched out when a star is
moving away from us and shorter in motion toward us. This information
allows astronomers to calculate the speed of the objects along the line
of sight, and measure the shape of the orbit.
"We found that the heartbeat stars in our sample tend to be hotter
than the sun and bigger than the sun," Shporer said. "But it is possible
that there are others with different temperature ranges that we did not
yet measure."
Study authors also postulate that some binary systems of heartbeat
stars could have a third star in the system that has not yet been
detected, or even a fourth star.
“The mere existence of heartbeat stars is a bit of a puzzle," said
Susan Mullally (formerly Thompson), a SETI Institute scientist working
for the Kepler Mission at NASA's Ames Research Center in Moffett Field,
California, and co-author of the study. "All the tidal stretching of
these heartbeat stars should have quickly caused the system to evolve
into a circular orbit. A third star in the system is one way to create
the highly stretched-out, elliptical orbits we observe."
Researchers are currently pursuing follow-up studies to search for third-star components in heartbeat star systems.
"We look forward to continued collaboration between ground and space
observatories to better understand the complex inner workings of
heartbeat stars," Shporer said.
NASA Ames manages the Kepler and K2 missions for NASA's Science
Mission Directorate. JPL managed Kepler mission development. Ball
Aerospace & Technologies Corporation operates the flight system with
support from the Laboratory for Atmospheric and Space Physics at the
University of Colorado in Boulder. Work on this study was performed in
part under contract with JPL funded by NASA through the Sagan Fellowship
Program executed by the NASA Exoplanet Science Institute.
Scientists used data from NASA’s Solar Dynamics
Observatory, NASA’s Interface Region Imaging Spectrograph, and the Big
Bear Solar Observatory to track a solar wave as it channeled upwards
from the sun’s surface into the atmosphere. Credits: Zhao et al/NASA/SDO/IRIS/BBSO.Hi-res image
Scientists analyzed sunspot images from a trio of
observatories -- including the Big Bear Solar Observatory, which
captured this footage -- to make the first-ever observations of a solar
wave traveling up into the sun’s atmosphere from a sunspot. Credits: BBSO/Zhao et al
Tracking solar waves like this provides a novel tool for scientists
to study the atmosphere of the sun. The imagery of the journey also
confirms existing ideas, helping to nail down the existence of a
mechanism that moves energy – and therefore heat – into the sun’s
mysteriously-hot upper atmosphere, called the corona. A study on these
results was published Oct. 11, 2016, in The Astrophysical Journal Letters.
“We see certain kinds of solar seismic waves channeling upwards into
the lower atmosphere, called the chromosphere, and from there, into the
corona,” said Junwei Zhao, a solar scientist at Stanford University in
Stanford, California, and lead author on the study. “This research gives
us a new viewpoint to look at waves that can contribute to the energy
of the atmosphere.”
The study makes use of the wealth of data captured by NASA’s Solar
Dynamics Observatory, NASA’s Interface Region Imaging Spectrograph, and
the Big Bear Solar Observatory in Big Bear Lake, California. Together,
these observatories watch the sun in 16 wavelengths of light that show
the sun’s surface and lower atmosphere. SDO alone captures 11 of these.
“SDO takes images of the sun in many different wavelengths at a high
time resolution,” said Dean Pesnell, SDO project scientist at NASA’s
Goddard Space Flight Center in Greenbelt, Maryland. “That lets you see
the frequencies of these waves – if you didn’t have such rapid-fire
images, you’d lose track of the waves from one image to the next.”
Though scientists have long suspected that the waves they spot in the
sun’s surface, called the photosphere, are linked to those seen in the
lowest reaches of the sun’s atmosphere, called the chromosphere, this
new analysis is the first time that scientists have managed to actually
watch the wave travel up through the various layers into the sun’s
atmosphere.
When material is heated to high temperatures, it releases energy in
the form of light. The type, or wavelength, of that light is determined
by what the material is, as well as its temperature. That means
different wavelengths from the sun can be mapped to different
temperatures of solar material. Since we know how the sun’s temperature
changes throughout the layers of its atmosphere, we can then order these
wavelengths according to their height above the surface – and
essentially watch solar waves as they travel upwards.
The implications of this study are twofold – first, this technique
for watching the waves itself gives scientists a new tool to understand
the sun’s lower atmosphere.
“Watching the waves move upwards tells us a lot about the properties
of the atmosphere above sunspots – like temperature, pressure, and
density,” said Ruizhu Chen, a graduate student scientist at Stanford who
is an author on the study. “More importantly, we can figure out the
magnetic field strength and direction.”
The effect of the magnetic field on these waves is pronounced.
Instead of traveling straight upwards through the sun, the waves veer
off, taking a curved path through the atmosphere.
“The magnetic field is acting like railroad tracks, guiding the waves
as they move up through the atmosphere,” said Pesnell, who was not
involved in this study.
The second implication of this new research is for a long-standing question in solar physics – the coronal heating problem.
The sun produces energy by fusing hydrogen at its core, so the
simplest models suggest that each layer of the sun should be cooler as
you move outward. However, the sun’s atmosphere, called the corona, is
about a hundred times hotter than the region below – counter to what you
would expect.
No one has as-yet been able to definitively pinpoint the source of
all the extra heat in the corona, but these waves may play a small role.
“When a wave travels upwards, a number of different things can
happen,” said Zhao. “Some may reflect back downwards, or contribute to
heating – but by how much, we don’t yet know.”
NASA Goddard built, operates and manages the SDO spacecraft for
NASA's Science Mission Directorate in Washington. Lockheed Martin
designed the IRIS observatory and manages the mission for NASA. The Big
Bear Solar Observatory is operated by the New Jersey Institute of
Technology in Newark, New Jersey.
Images of Ioat different near-infrared wavelengths show bright spots that are thermal emissions from the moon’s myriad volcanoes. Click on image to see the entire set, with the name of the near-infrared filter indicated in the black box at the start of each section. Note the increasing number of hot spots detected at longer wavelengths, i.e. towards the bottom of the figure. (Katherine de Kleer and Imke de Pater image, from Gemini Observatory/AURA & Keck Observatory).
All hot spots detected are shown on amap of Io. Each circle represents a
new detection; the size of the circle corresponds logarithmically to
the intensity, and more opaque regions are where a hot spot was detected
multiple times. The color and symbol indicate the type of eruption,
following the legend. Loki Patera is at 310 West, 10 North and
Kurdalagon Patera is at 220 West, 50 South.
Video showing all hot spots detected from August 2013 through
December 2015, displayed on a full map of Io and illustrating the
approximate length of time they were visible. The size of the circle
corresponds logarithmically to the intensity. Loki Patera is at 310 West
longitude, 10 North latitude and Kurdalagon Patera is at 220 West
longitude, 50 South latitude. (Credit: Katherine de Kleer and Imke de
Pater, UC Berkeley).Youtube
High-resolution image of Io, showing hot spots — Loki Patera and
Amaterasu Patera — visible from Earth only with adaptive optics on the
planet’s largest telescopes, Keck and Gemini.
Press release issued by the University of Berkeley to
coincide with presentation at the joint 48th annual meeting of the
Division for Planetary Sciences (DPS) of the American Astronomical
Society (AAS) and 11th annual European Planetary Science Congress
(EPSC).
Jupiter’s moon Io continues to be the most volcanically active body
in the solar system, as documented by the longest series of frequent,
high-resolution observations of the moon’s thermal emission ever
obtained.
Using near-infrared adaptive optics on two of the world’s largest
telescopes — the 10-meter Keck II and the 8-meter Gemini North, both
located near the summit of the dormant volcano Mauna Kea in Hawaii —
University of California, Berkeley, astronomers tracked 48 volcanic
hotspots on the surface over a period of 29 months from 2013 through the
end of 2015.
Without adaptive optics — a technique that removes the atmospheric
blur to sharpen the image — Io is merely a fuzzy ball. Adaptive optics
can separate features just a few hundred kilometers apart on Io’s
3,600-kilometer diameter surface.
“On a given night, we may see half a dozen or more different hot
spots,” said Katherine de Kleer, a UC Berkeley graduate student who led
the observations. “Of Io’s hundreds of active volcanoes, we have been
able to track the 50 that were the most powerful over the past few
years.”
She and Imke de Pater, a UC Berkeley professor of astronomy and of
Earth and planetary science, observed the heat coming off of active
eruptions as well as cooling lava flows and were able to determine the
temperature and total power output of individual volcanic eruptions, as
well as track their evolution over days, weeks and sometimes even years.
Interestingly, some of the eruptions appeared to progress across the
surface over time, as if one triggered another 500 kilometers away.
“While it stretches the imagination to devise a mechanism that could
operate over distances of 500 kilometers, Io’s volcanism is far more
extreme than anything we have on Earth and continues to amaze and baffle
us,” de Kleer said.
De Kleer and de Pater will discuss their observations at a media
briefing on Oct. 20 during the joint 48th meeting of the American
Astronomical Society’s Division for Planetary Sciences and 11th European
Planetary Science Congress in Pasadena, California. Papers describing
the observations have been accepted for future publication by the journal Icarus.
Tidal Heating
Io’s intense volcanic activity is powered by tidal heating: heating
from friction generated in Io’s interior as Jupiter’s intense
gravitational pull changes by small amounts along Io’s orbit. Models for
how this heating occurs predict that most of Io’s total volcanic power
should be emitted either near the poles or near the equator, depending
on the model, and that the pattern should be symmetric between the
forward- and backward-facing hemispheres in Io’s orbit (that is, at
longitudes 0-180 vs. 180-360).
That’s not what they saw. Over the observational period, August 2013
through December 2015, the team obtained images of Io on 100 nights.
Though they saw a surprising number of short-lived but intense eruptions
that appeared suddenly and subsided in a matter of days, every single
one took place on the trailing face of Io (between 180 and 360 degrees
longitude) rather than the leading face, and at higher latitudes than
more typical eruptions.
“The distribution of the eruptions is a poor match to the model
predictions,” de Kleer said, “but future observations will tell us
whether this is just because the sample size is too small, or because
the models are too simplified. Or, perhaps we’ll learn that local
geological factors play a much greater role in determining where and
when the volcanoes erupt than the physics of tidal heating do.”
One key target of interest was Io’s most powerful persistent volcano,
Loki Patera, which brightens by more than a factor of 10 every 1-2
years. A patera is an irregular crater, usually volcanic.
Many scientists believe that Loki Patera is a massive lava lake, and
that these bright episodes represent its overturning crust, like that
seen in lava lakes on Earth. In fact, the heat emissions from Loki
Patera appear to travel around the lake during each event, as if from a
wave moving around a lake triggering the destabilization and sinking of
portions of crust. Prior to 2002, this front seemed to travel around the
cool island in the center of the lake in a counter-clockwise direction.
After an apparent cessation of brightening events after 2002, de Pater observed renewed activity in 2009.
“With the renewed activity, the waves traveled clockwise around the lava lake,” she noted.
Another volcano, Kurdalagon Patera, produced unusually hot eruptions
twice in the spring of 2015, coinciding with the brightening of an
extended cloud of neutral material that orbits Jupiter. This provides
circumstantial evidence that eruptions on the surface are the source of
variability in this neutral cloud, though it’s unclear why other
eruptions were not also associated with brightening, de Kleer said.
De Kleer noted that the Keck and Gemini telescopes, both atop the
dormant volcano Mauna Kea, complement one another. Gemini North’s queue
scheduling allowed more frequent observations — often several a week —
while Keck’s instruments are sensitive also to longer wavelengths (5
microns), showing cooler features such as older lava flows that are
invisible in the Gemini observations.
The astronomers are continuing their frequent observations of Io,
providing a long-term database of high spatial resolution images that
not even Galileo, which orbited Jupiter for eight years, was able to
achieve.
Media Contacts:
Robert Sanders
UCB Media Relations
+1 510-643-6998
rlsanders@berkeley.edu Anita Heward
EPSC Press Officer
+44 (0)77 5603 4243 anita.heward@europlanet-eu.org
Science Contacts:
Katherine de Kleer
kdekleer@berkeley.edu Imke de Pater imke@berkeley.edu
References:
* “Time Variability of Io’s Volcanic Activity from Near-IR Adaptive
Optics Observations on 100 Nights in 2013-2015” (accepted by Icarus).
* “Spatial Distribution of Io’s Volcanic Activity from Near-IR Adaptive
Optics Observations on 100 Nights in 2013-2015” (accepted by Icarus).
Further information:
The joint 48th meeting of the Division for Planetary Sciences (DPS) and
11th European Planetary Science Congress (EPSC) in Pasadena, California,
is second time DPS and EPSC have been joined into one meeting. The goal
of the joint meeting is to strengthen international scientific
collaboration in all areas of planetary science. This is the first time
that EPSC, which provides the dissemination platform for the Europlanet
2020 Research Infrastructure, is held outside Europe. For more
information, see: https://aas.org/meetings/dps48. Follow: #dpsepsc,
@DPSMeeting, @europlanetmedia, and @AAS_Press on Twitter.
It may be famous for hosting spectacular sights such as the Tucana Dwarf Galaxy and 47 Tucanae (heic1510), the second brightest globular cluster in the night sky, but the southern constellation of Tucana (The Toucan) also possesses a variety of unsung cosmic beauties.
One such beauty is NGC 299, an open star cluster located within the Small Magellanic Cloud just under 200 000 light-years away. Open clusters such as this are collections of stars weakly bound by the shackles of gravity, all of which formed from the same massive molecular cloud
of gas and dust. Because of this, all the stars have the same age and
composition, but vary in their mass because they formed at different
positions within the cloud.
This unique property not only ensures a
spectacular sight when viewed through a sophisticated instrument
attached to a telescope such as Hubble’s Advanced Camera for Surveys,
but gives astronomers a cosmic laboratory in which to study the
formation and evolution of stars — a process that is thought to depend
strongly on a star’s mass.
This image shows the location of a remarkable source that dramatically flares in X-rays
unlike any ever seen. Along with another similar source found in a
different galaxy, these objects may represent an entirely new
phenomenon, as reported in our latest press release [link to PR].
These two objects were both found in elliptical galaxies, NGC 5128 (also known as Centaurus A) shown here and NGC 4636. In this Chandra X-ray Observatory image of NGC 5128, low, medium, and high-energy X-rays are colored red, green, and blue, and the location of the flaring source is outlined in the box to the lower left.
Both of these mysterious sources flare dramatically - becoming a
hundred times brighter in X-rays in about a minute before steadily
returning to their original X-ray levels about an hour later. At their
X-ray peak, these objects qualify as ultraluminous X-ray sources (ULXs)
that give off hundreds to thousands of times more X-rays than typical
X-ray binary systems where a star is orbiting a black hole or neutron star.
Five flares were detected from the source located near NGC 5128, which is at a distance of about 12 million light years
from Earth. A movie showing the average change in X-rays for the three
flares with the most complete Chandra data, covering both the rise and
fall, is shown in the inset.
The source associated with the elliptical galaxy NGC 4636, which is
located about 47 million light years away, was observed to flare once.
The only other objects known to have such rapid, bright, repeated
flares involve young neutron stars such as magnetars, which have
extremely powerful magnetic fields. However, these newly flaring sources
are found in populations of much older stars. Unlike magnetars, the new
flaring sources are likely located in dense stellar environments, one
in a globular cluster and the other in a small, compact galaxy.
When they are not flaring, these newly discovered sources appear to
be normal binary systems where a black hole or neutron star is pulling
material from a companion star similar to the Sun. This indicates that
the flares do not significantly disrupt the binary system.
While the nature of these flares is unknown, the team has begun to
search for answers. One idea is that the flares represent episodes when
matter pulled away from a companion star falls rapidly onto a black hole
or neutron star. This could happen when the companion makes its closest
approach to the compact object in an eccentric orbit. Another
explanation could involve matter falling onto an intermediate-mass black
hole, with a mass of about 800 times that of the Sun for one source and
80 times that of the Sun for the other.
This result is describing in a paper appearing in the journal Nature
on October 20, 2016. The authors are Jimmy Irwin (University of
Alabama), Peter Maksym (Harvard-Smithsonian Center for Astrophysics),
Gregory Sivakoff (University of Alberta), Aaron Romanowsky (San Jose
State University), Dacheng Lin (University of New Hampshire), Tyler
Speegle, Ian Prado, David Mildebrath (University of Alabama), Jay
Strader (Michigan State University), Jifeng Lui (Chinese Academy of
Sciences), and Jon Miller (University of Michigan).
NASA's Marshall Space Flight Center in Huntsville, Alabama, manages
the Chandra program for NASA's Science Mission Directorate in
Washington. The Smithsonian Astrophysical Observatory in Cambridge,
Massachusetts, controls Chandra's science and flight operations.
Fast Facts for NGC 5128: Scale: Main image is 16.7 arcmin across (about 58,000 light years); Inset image is 1 arcmin across (about 3,500 light years) Category:Quasars & Active Galaxies Coordinates (J2000): RA 13h 25m 52.7s | Dec -43° 05' 46.00" Constellation:Centaurus Observation Date: 21 pointings between 05 Dec 1999 and 29 Aug 2012 Observation Time: 229 hours 57 min (9 days 13 hours 57 min). Obs. ID: 316, 962, 2978, 3965, 7797-7799, 7800, 8489, 8490, 10722, 10723, 10724-10726, 11846, 11847, 12155, 12156, 13303, 13304 Instrument:ACIS Also Known As: Centaurus A, Cen A References: Irwin, J. et al, 2016, Nature (in press) Color Code: X-ray (Red, Green, Blue) Distance Estimate: 12 million light years
http://chandra.harvard.edu/photo/2016/ngc5128/
