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Weather forecasters on exoplanet GJ 1214b would have an easy job.
Today's forecast: cloudy. Tomorrow: overcast. Extended outlook: more
Two teams of scientists using NASA's Hubble Space Telescope report
they have characterized the atmospheres of a pair of planets with
masses intermediate between gas giants, like Jupiter, and smaller,
rockier planets, like Earth. A survey by NASA's Kepler space telescope
mission showed that objects in this size range are among the most
common type of planets in our Milky Way galaxy. The researchers
described their work as an important milestone on the road to
characterizing potentially habitable, Earth-like worlds beyond the solar
The findings appear in separate papers in the January 2 issue of the journal Nature.
The two planets studied are known as GJ 436b and GJ 1214b. GJ 436b is
categorized as a "warm Neptune" because it is much closer to its star
than frigid Neptune is to our Sun. The planet is located 36 light-years
away in the constellation Leo.
GJ 1214b is known as a "super-Earth" type planet. Super-Earths are
planets with masses between that of Earth and Neptune. Because no such
planet exists in our solar system, the physical nature of super-Earths
is largely unknown. GJ1214b is located just 40 light-years from Earth,
in the constellation Ophiuchus.
Both GJ 436b and GJ 1214b can be observed passing in front of, or
transiting, their parent stars. This provides an opportunity to study
these planets in more detail as starlight filters through their
An atmospheric study of GJ 436b based on such transit observations
with Hubble over the last year is presented in one of the papers, led
by Heather Knutson of the California Institute of Technology in
Pasadena, Calif. The news is about what they didn't find. The Hubble
spectra were featureless and revealed no chemical fingerprints
whatsoever in the planet's atmosphere. "Either this planet has a high
cloud layer obscuring the view, or it has a cloud-free atmosphere that
is deficient in hydrogen, which would make it very unlike Neptune,"
said Knutson. "Instead of hydrogen, it could have relatively large
amounts of heavier molecules such as water vapor, carbon monoxide, and
carbon dioxide, which would compress the atmosphere and make it hard
for us to detect any chemical signatures."
Observations similar to those obtained for GJ 436b had been
previously obtained for GJ 1214b. The first spectra of this planet were
also featureless and presented a similar puzzle: The planet's
atmosphere either was predominantly water vapor or hydrogen-dominated
with high-altitude clouds.
A team of astronomers led by Laura Kreidberg and Jacob Bean of the
University of Chicago used Hubble to obtain a deeper view of GJ 1214b
that revealed what they consider definitive evidence of high clouds
blanketing the planet. These clouds hide any information about the
composition and behavior of the lower atmosphere and surface. The new
Hubble spectra also revealed no chemical fingerprints whatsoever in the
planet's atmosphere, but the high precision of the new data enabled
them to rule out cloud-free compositions of water vapor, methane,
nitrogen, carbon monoxide, or carbon dioxide for the first time.
"Both planets are telling us something about the diversity of planet
types that occur outside of our own solar system; in this case we are
discovering that we may not know them as well as we thought," said
Knutson. "We'd really like to determine the size at which these planets
transition from looking like mini-gas giants to something more like a
water world or a rocky, scaled-up version of the Earth. Both of these
observations are fundamentally trying to answer that question."
Models of GJ 436b and GJ 1214b predict clouds that could be made out
of potassium chloride or zinc sulfide at the scorching temperatures of
several hundred degrees Fahrenheit predicted to be found in these
atmospheres. "You would expect very different kinds of clouds to form
on these planets than you would find, say, on Earth," said Kreidberg.
The Chicago team had to make a big effort to conclusively determine
the nature of GJ 1214b's cloudy atmosphere. Kreidberg explained, "We
really pushed the limits of what is possible with Hubble to make this
measurement — our work devoted more Hubble time to a single exoplanet
than ever before. This advance lays the foundation for characterizing
other Earths with similar techniques." Added Bean, "I think it's very
exciting that we can use a telescope like Hubble that was never
designed with this in mind, do these kinds of observations with such
exquisite precision, and really nail down some aspect of a super-Earth
Knutson continued, "For exoplanets, clouds are incredibly frustrating
because they can hide the bulk composition of the atmosphere that we
want to measure." However, more will be learned with the launch of the
James Webb Space Telescope later this decade. Said Kreidberg, "Looking
forward, the James Webb Space Telescope will be transformative. The new
capabilities of this telescope will allow us to peer through the
clouds on GJ 1214b and similar exoplanets."
The 1st of March 1780 was a particularly productive night for Charles Messier. Combing the constellation of Leo for additions to his grand astronomical catalogue, he struck on not one, but two, new objects.
One of those objects is seen here: Messier 65. "Nebula discovered in Leo: It is very faint and contains no star," he jotted down in his notebook. But he was wrong — as we now know, Messier 65 is a spiral galaxy containing billions upon billions of stars.
All Messier saw was a faint diffuse light, nothing like the fine detail here, so we can forgive his mistake. If he had had access to a telescope like Hubble, he could have spied these stunning, tightly wound purple spiral arms and dark dust lanes, encircling a bright centre crammed with stars.
Almost exactly 233 years later in March of this year, one of the stars within Messier 65 went supernova (not seen in this image), rivalling the rest of the entire galaxy in brightness. This, the first Messier supernova of 2013, is now fading, and the serene beauty of M65 is returning.
Located some 25 million light-years away, this new Hubble image shows spiral galaxy ESO 373-8. Together with at least seven of its galactic neighbours, this galaxy is a member of the NGC 2997 group. We see it side-on as a thin, glittering streak across the sky, with all its contents neatly aligned in the same plane.
We see so many galaxies like this — flat, stretched-out pancakes — that our brains barely process their shape. But let us stop and ask: Why are galaxies stretched out and aligned like this?
Try spinning around in your chair with your legs and arms out. Slowly pull your legs and arms inwards, and tuck them in against your body. Notice anything? You should have started spinning faster. This effect is due to conservation of angular momentum, and it’s true for galaxies, too.
This galaxy began life as a humungous ball of slowly rotating gas. Collapsing in upon itself, it spun faster and faster until, like pizza dough spinning and stretching in the air, a disc started to form. Anything that bobbed up and down through this disc was pulled back in line with this motion, creating a streamlined shape.
Angular momentum is always conserved — from a spinning galactic disc 25 million light-years away from us, to any astronomer, or astronomer-wannabe, spinning in his office chair.
artist’s impression shows our Galaxy, the Milky Way, as the spiral
shape in the background. The massive stars referred to in the new study
are indicated by red circles. The position of the Solar System is marked
by a black dot and circle at the top centre. Credit: J. Urquhart et al.
Background image by Robert Hurt of the Spitzer Science Center. Credit:
J. Urquhart et al. Background image by Robert Hurt of the Spitzer
Science Center. Clickherefor a larger image
A 12-year study of massive stars has reaffirmed that our Galaxy has
four spiral arms, following years of debate sparked by images taken by
NASA’s Spitzer Space Telescope that only showed two arms.
The new research, which is published online in the Monthly Notices of
the Royal Astronomical Society, is part of the RMS Survey, which was
launched by academics at the University of Leeds.
Astronomers cannot see what our Galaxy, which is called the Milky
Way, looks like because we are on the inside looking out. But they can
deduce its shape by careful observation of its stars and their distances
"The Milky Way is our galactic home and studying its structure gives
us a unique opportunity to understand how a very typical spiral galaxy
works in terms of where stars are born and why," said Professor Melvin
Hoare, a member of the RMS Survey Team in the School of Physics &
Astronomy at the University of Leeds and a co-author of the research
In the 1950s astronomers used radio telescopes to map our Galaxy.
Their observations focussed on clouds of gas in the Milky Way in which
new stars are born, revealing four major arms. NASA’s Spitzer Space
Telescope, on the other hand, scoured the Galaxy for infrared light
emitted by stars. It was announced in 2008 that Spitzer had detected
about 110 million stars, but only found evidence of two spiral arms.
The astronomers behind the new study used several radio telescopes in
Australia, USA and China to individually observe about 1650 massive
stars that had been identified by the RMS Survey. From their
observations, the distances and luminosities of the massive stars were
calculated, revealing a distribution across four spiral arms.
“It isn’t a case of our results being right and those from Spitzer’s
data being wrong – both surveys were looking for different things,” said
Professor Hoare. “Spitzer only sees much cooler, lower mass stars –
stars like our Sun – which are much more numerous than the massive stars
that we were targeting.”
Massive stars are much less common than their lower mass counterparts
because they only live for a short time – about 10 million years. The
shorter lifetimes of massive stars means that they are only found in the
arms in which they formed, which could explain the discrepancy in the
number of galactic arms that different research teams have claimed.
“Lower mass stars live much longer than massive stars and rotate
around our Galaxy many times, spreading out in the disc. The
gravitational pull in the two stellar arms that Spitzer revealed is
enough to pile up the majority of stars in those arms, but not in the
other two,” explains Professor Hoare. “However, the gas is compressed
enough in all four arms to lead to massive star formation.”
Dr James Urquhart from the Max Planck Institute for Radio Astronomy
in Bonn, Germany, and lead author of the paper, said: “It's exciting
that we are able to use the distribution of young massive stars to probe
the structure of the Milky Way and match the most intense region of
star formation with a model with four spiral arms.”
Professor Hoare concludes, “Star formation researchers, like me, grew
up with the idea that our Galaxy has four spiral arms. It’s great that
we have been able to reaffirm that picture.”
(To arrange interviews with Professor Melvin Hoare) Sarah Reed Press Officer University of Leeds Tel: +44 (0)113 343 4196 firstname.lastname@example.org
Robert Massey Royal Astronomical Society Tel: +44 (0)20 7734 3307 x214 Mob: +44 (0)794 124 8035 email@example.com
The new work appears in the paper “The RMS survey: galactic
distribution of massive star formation”, J. S. Urquhart, C. C. Figura,
T. J. T. Moore, M. G. Hoare, S. L. Lumsden, J. C. Mottram, M. A.
Thompson and R. D. Oudmaijer, Monthly Notices of the Royal Astronomical
Society, published by Oxford University Press. The paper is available
Notes for editors
University of Leeds
The University of Leeds is one of the largest higher education
institutions in the UK and a member of the Russell Group of
The 2008 Research Assessment
Exercise showed the University of Leeds to be the UK's eighth biggest
research powerhouse and the University's vision is to secure a place
among the world's leading universities by 2015.www.leeds.ac.uk
Royal Astronomical Society
The Royal Astronomical Society (RAS, www.ras.org.uk), founded in 1820, encourages and promotes the study of astronomy,
solar-system science, geophysics and closely related branches of
science. The RAS organizes scientific meetings, publishes international
research and review journals, recognizes outstanding achievements by the
award of medals and prizes, maintains an extensive library, supports
education through grants and outreach activities and represents UK
astronomy nationally and internationally. Its more than 3500 members
(Fellows), a third based overseas, include scientific researchers in
universities, observatories and laboratories as well as historians of
astronomy and others.
NASA's NEOWISE spacecraft opened its "eyes"
after more than two years of slumber to see the starry sky. Image
credit: NASA/JPL-Caltech.Full image and caption
This is one of the first images captured by
the revived NEOWISE mission, after more than two years of hibernation.
Image credit: NASA/JPL-Caltech.Full image and caption-enlarge image
Probe Will Assist Agency in Search for Candidates to Explore
NASA's Near-Earth Object Wide-field Infrared Survey Explorer (NEOWISE), a
spacecraft that made the most comprehensive survey to date of asteroids
and comets, has returned its first set of test images in preparation
for a renewed mission.
NEOWISE discovered more than 34,000 asteroids and characterized 158,000
throughout the solar system during its prime mission in 2010 and early
2011. It was reactivated in September following 31 months in
hibernation, to assist NASA's efforts to identify the population of
potentially hazardous near-Earth objects (NEOs). NEOWISE also can assist
in characterizing previously detected asteroids that could be
considered potential targets for future exploration missions.
"NEOWISE not only gives us a better understanding of the asteroids and
comets we study directly, but it will help us refine our concepts and
mission operation plans for future, space-based near-Earth object
cataloging missions," said Amy Mainzer, principal investigator for
NEOWISE at NASA's Jet Propulsion Laboratory in Pasadena, Calif. "The
spacecraft is in excellent health, and the new images look just as good
as they were before hibernation. Over the next weeks and months we will
be gearing up our ground-based data processing and expect to get back
into the asteroid hunting business, and acquire our first previously
undiscovered space rock, in the next few months."
Some of the deep-space images taken by the spacecraft include a
previously detected asteroid named (872) Holda. With a diameter of 26
miles (42 kilometers), this asteroid orbits the sun between Mars and
Jupiter in a region astronomers call the asteroid belt. The images tell
researchers the quality of the spacecraft's observations is the same as
during its primary mission.
The spacecraft uses a 16-inch (40-centimeter) telescope and infrared
cameras to seek out and discover unknown NEOs and characterize their
size, albedo or reflectivity, and thermal properties. Asteroids reflect,
but do not emit visible light, so data collected with optical
telescopes using visible light can be deceiving.
Infrared sensors, similar to the cameras on NEOWISE, are a powerful tool
for discovering, cataloging and understanding the asteroid population.
Some of the objects about which NEOWISE will be collecting data could
become candidates for the agency's announced asteroid initiative.
NASA's initiative will be the first mission to identify, capture and
relocate an asteroid. It represents an unprecedented technological feat
that will lead to new scientific discoveries and technological
capabilities that will help protect our home planet. The asteroid
initiative brings together the best of NASA's science, technology and
human exploration efforts to achieve President Obama's goal of sending
humans to an asteroid by 2025.
"It is important that we accumulate as much of this type of data as
possible while the spacecraft remains a viable asset," said Lindley
Johnson, NASA's NEOWISE program executive in Washington. "NEOWISE is an
important element to enhance our ability to support the initiative."
NEOWISE began as WISE. The prime mission, which was launched in December
2009, was to scan the entire celestial sky in infrared light. WISE
captured more than 2.7 million images in multiple infrared wavelengths
and cataloged more than 747 million objects in space, ranging from
galaxies faraway to asteroids and comets much closer to Earth. NASA
turned off most of WISE's electronics when it completed its primary
mission in February 2011.
Upon reactivation, the spacecraft was renamed NEOWISE, with the goal of
discovering and characterizing asteroids and comets whose orbits
approach within 28 million miles (45 million kilometers) from Earth's
path around the sun.
JPL manages the project for NASA's Science Mission Directorate in
Washington. The Space Dynamics Laboratory in Logan, Utah, built the
science instrument. Ball Aerospace & Technologies Corp. of Boulder,
Colo., built the spacecraft. Science operations and data processing take
place at the Infrared Processing and Analysis Center at the California
Institute of Technology in Pasadena. Caltech manages JPL for NASA.
The collection of red dots seen near the center of this image show
one of several very distant galaxy clusters discovered by combining
ground-based optical data from the National Optical Astronomy
Observatory's Kitt Peak National Observatory with infrared data from
NASA's Spitzer Space Telescope. This galaxy cluster, named ISCS
J1434.7+3519, is located about 9 billion light-years from Earth.
large white and yellow dots in this picture are stars in our galaxy,
while the rest of the smaller dots are distant galaxies. The cluster,
comprised of red dots near the center, includes more than 100 massive
Spitzer was able to capture prodigious levels of star
formation occurring in the galaxies that live in this cluster. Some of
them are forming stars hundreds of times faster than our own Milky Way
Infrared light in this image has been colored red; and visible light, blue and green. Credit: NASA/JPL-Caltech/M. Brodwin (UMKC)
In the fable of the town and country mice, the country mouse visits
his city-dwelling cousin to discover a world of opulence. In the early
cosmos, billions of years ago, galaxies resided in the equivalent of
urban or country environments. Those that dwelled in crowded areas
called clusters also experienced a kind of opulence, with lots of cold
gas, or fuel, for making stars.
Today, however, these galactic
metropolises are ghost towns, populated by galaxies that can no longer
form stars. How did they get this way and when did the fall of galactic
A new study from NASA's Spitzer Space Telescope
finds evidence that these urban galaxies, or those that grew up in
clusters, dramatically ceased their star-making ways about 9 billion
years ago (our universe is 13.8 billion years old). These galactic
metropolises either consumed or lost their fuel. Galaxies in the
countryside, by contrast, are still actively forming stars.
know the cluster galaxies we see around us today are basically dead, but
how did they get that way?" wondered Mark Brodwin of the University of
Missouri-Kansas City, lead author of this paper, published in the
Astrophysical Journal. "In this study, we addressed this question by
observing the last major growth spurt of galaxy clusters, which happened
billions of years ago."
Researchers studying distant galaxies get
a peek into the past since the galaxies' light takes time, sometimes
billions of years, to reach us. Brodwin and his colleagues used Spitzer
to study 16 galaxy clusters that existed between the time our universe
was 4.3 and 6 billion years old. Spitzer's infrared vision allows it see
the dust warmed by new stars, revealing star-formation rates. NASA's
Hubble Space Telescope and the W.M. Keck Observatory were used to
measure the galaxies' distances from Earth.
This is one of the
most comprehensive looks at distant galaxy clusters yet, revealing new
surprises about their environments. Previous observations of relatively
nearby clusters suggested that the urban, cluster galaxies produced all
their stars early in the history of our universe in one big burst. This
theory, called monolithic collapse, predicted that these tight-knit
galaxies would have used all their fuel at once in an early, youthful
frenzy. But the new study shows this not to be the case: The urban
galaxies continued to make stars longer than expected, until suddenly
production came to a halt around 9 billion years ago, or about 3 billion
years later than previously thought.
A second study using
observations from the Herschel Space Observatory, led by Stacey Alberts
at the University of Massachusetts-Amherst and published in the Monthly
Notices of the Royal Astronomical Society journal, finds a similar
transition epoch. Alberts and colleagues observed 300 clusters over a
longer period of time, dating back to when the universe was 4 to 10
billion years old. Herschel, which ran out of coolant in April of 2013
as expected, detected longer wavelengths of infrared light than Spitzer,
which is still up and running. The two telescopes complement each
other, allowing scientists to confirm results and probe different
aspects of cosmic conundrums.
"We find that around 9 billion
years ago, cluster galaxies were as active as their counterparts outside
of clusters; however, their rate of star formation decreases
dramatically between then and now, much more quickly than we see in
isolated galaxies," said Alberts.
Why do the urban galaxies shut
down their star formation sooner and more rapidly than the country
bumpkins? Brodwin says this may have to do with galaxy mergers. The more
crowded a galactic environment, as is the case in young, growing galaxy
clusters, the more often two galaxies will collide and merge. Galaxy
mergers induce bursts of fuel-consuming star formation, and also feed
growing supermassive black holes, which then blast out radiation that
heats up the gas and quickly shuts off the star formation.
as if boom times for galaxies in clusters ended with a sudden widespread
collapse," said Peter Eisenhardt of NASA's Jet Propulsion Laboratory,
Pasadena, Calif., who led a previous study that identified the distant
galaxy cluster sample used by Brodwin and Alberts. "They go from
vibrantly forming new stars to the quiescent state they've been in for
the last half of the history of the universe, and the switch happens
JPL manages the Spitzer Space Telescope
mission for NASA's Science Mission Directorate, Washington. Science
operations are conducted at the Spitzer Science Center at the California
Institute of Technology in Pasadena. Spacecraft operations are based at
Lockheed Martin Space Systems Company, Littleton, Colorado. Data are
archived at the Infrared Science Archive housed at the Infrared
Processing and Analysis Center at Caltech. Caltech manages JPL for NASA.
Look at the bright star in the middle of this image. Achoo! It has
just sneezed. This sight will only last for a few thousand years — a
blink of an eye in the young star's life.
If you could carry on watching for a few years you would realise it's
not just one sneeze, but a sneezing fit. This young star is firing off
salvos of super-hot, super-fast gas — Achoo! Achoo! — before it finally
exhausts itself. These bursts of gas have shaped the turbulent
surroundings, creating structures known as Herbig-Haro objects.
These objects are formed from the star's energetic "sneezes". These
salvos can contain as much mass as our home planet, and cannon into
nearby clouds of gas at hundreds of kilometres per second. Shock waves
form, such as the U-shape below this star. Unlike most other
astronomical phenomena, as the waves crash outwards, they can be seen
moving across human timescales. Soon, this star will stop sneezing, and
grow up to be a star like the Sun.
This region is actually home to several interesting objects. The star
at the centre of the frame is a variable star named V633 Cassiopeiae,
with Herbig-Haro objects HH 161 and HH 164 forming parts of the
horseshoe-shaped loop emanating from it. The slightly shrouded star just
to the left is known as V376 Cassiopeiae, another variable star that
has succumbed to its neighbour's infectious sneezing fits; this star is
also sneezing, creating yet another Herbig-Haro object — HH 162. Both
stars are very young and are still surrounded by dusty material left
over from their formation, which spans the gap between the two
A version of this image was entered into the Hubble's Hidden Treasures image processing competition by contestant Gilles Chapdelaine.
Pasadena, CA— Astronomers, including Carnegie’s Yuri Beletsky, took
precise measurements of the closest pair of failed stars to the Sun,
which suggest that the system harbors a third, planetary-mass object.The
research is published as a letter to the editor in Astronomy &
Astrophysics available online at http://arxiv.org/abs/1312.1303.
Failed stars are known as brown dwarfs and have a mass below 8% of
the mass of the Sun—not massive enough to burn hydrogen in their
centers. This particular system, Luhman 16AB, was discovered earlier
this year and is only 6.6 light-years away.
After the discovery announcement, several teams of astronomers,
including the one with Beletsky, used a variety of telescopes to
characterize the neighbouring couple.
After two-months of observations and extensive data analysis,
Beletsky’s team, led by Henri Boffin of the European Southern
Observatory (ESO), found that both objects have a mass between 30 and 50
Jupiter masses. By comparison, the Sun has a mass of about 1,000
“The two brown dwarfs are separated by about three times the distance
between the Earth and the Sun. Binary brown dwarf systems are
gravitationally bound and orbit about each other. Because these two
dwarfs have so little mass, they take about 20 years to complete one
orbit,” explained Beletsky.
The team used the FORS2 instrument on ESO’s Very Large Telescope at
Paranal to image the brown dwarf couple in the best possible conditions,
every 5 or 6 days over the period April 14, to June 22, 2013. Because
of the instrument enabled the observers to make very precise
measurements, the scientists were already able to detect tiny
displacements of the two objects in their orbit during only this the
The astronomers were able to measure the positions of the two brown
dwarfs with ten times better accuracy than before and thereby detect
even small perturbations of their orbit.
“We have been able to measure the positions of these two objects with
a precision of a few milli-arcseconds,” said Boffin. “That is like a
person in Paris being able to measure the position of someone in New
York with a precision of 10 centimetres.”
The measurements were so fine that the astronomers were able to see
some very small deviations from the expected motion of the two brown
dwarfs around each other. The fact that the deviations appear correlated
is a strong indication that a companion perturbs the motion of one of
the two brown dwarfs. This companion is most likely a planetary-mass
object, which has an orbital period between two months and a year.
“Further observations are required to confirm the existence of a
planet,” concludes Boffin. “But it may well turn out that the closest
brown dwarf binary system to the Sun turns out to be a triple system!”
The team is composed of Henri Boffin, Kora Muzic, Valentin Ivanov,
Andrea Mehner, Jean-Philippe Berger, Julien Girard, and Dimitri Mawet
(ESO, Chile), Dimitri Pourbaix (Université Libre de Bruxelles, Belgium),
Rudy Kurtev (Universidad de Valparaiso, Chile), and Yuri Beletsky
(Carnegie Observatories at Las Campanas Observatory, Chile).
In the middle of the twentieth century, an unusual star was spotted in the constellation of Canes Venatici
(Latin for "hunting dogs"). Years later, astronomers determined that
this object, dubbed AM Canum Venaticorum (or, AM CVn, for short), was,
in fact, two stars. These stars revolve around each other every 18
minutes, and are predicted to generate gravitational waves - ripples in
space-time predicted by Einstein.
The name AM CVn came to represent a new class of objects where one white dwarf star is pulling matter from a very compact companion star, such as a second white dwarf. (White dwarf stars are dense remains of Sun-like stars that have run out of fuel and collapsed
to the size of the Earth.) The pairs of stars in AM CVn systems orbit
each other extremely rapidly, whipping around one another in an hour,
and in one case as quickly as five minutes. By contrast, the fastest
orbiting planet in our Solar System, Mercury, orbits the Sun once every 88 days.
Despite being known for almost 50 years, the question has remained: where do AM CVn systems come from? New X-ray and optical observations
have begun to answer that with the discovery of the first known systems
of double stars that astronomers think will evolve into AM CVn systems.
The two binary systems - known by their shortened names of J0751 and J1741 - were observed in X-rays by NASA's Chandra X-ray Observatory and ESA's XMM-Newton telescope.
Observations at optical wavelengths were made using the McDonald
Observatory's 2.1-meter telescope in Texas, and the Mt. John Observatory
1.0-meter telescope in New Zealand.
The artist's illustration depicts what these systems are like now and
what may happen to them in the future. The top panel shows the current
state of the binary that contains one white dwarf (on the right) with
about one-fifth the mass of the Sun and another much heavier and more
compact white dwarf about five or more times as massive (unlike Sun-like
stars, heavier white dwarfs are smaller).
As the two white dwarfs orbit around each other, gravitational waves
will be given off causing the orbit to become tighter. Eventually the
smaller, heavier white dwarf will start pulling matter from the larger,
lighter one, as shown in the middle panel, forming an AM CVn system.
This process continues until so much matter accumulates on the more
massive white dwarf that a thermonuclear explosion may occur in about
100 million years.
Credit: X-ray: NASA/CXC/Univ of Oklahoma/M.Kilic et al,
One possibility is that the thermonuclear explosion could destroy the
larger white dwarf completely in what astronomers call a Type Ia
supernova (the type of supernova
used to mark large distances across the Universe by serving as
so-called standard candles.) However, it's more likely that a
thermonuclear explosion will occur only on the surface of the star,
leaving it scarred but intact. The resulting outburst is likely to be
about one tenth the brightness of a Type Ia supernova. Such outbursts
have been named - somewhat tongue-in-cheek - as .Ia supernovae. Such
.Ia outbursts have been observed in other galaxies, but J0751 and J1741
are the first binary stars known which can produce .Ia outbursts in the
The optical observations were critical in identifying the two white
dwarfs in these systems and ascertaining their masses. The X-ray
observations were needed to rule out the possibility that J0751 and
J1741 contained neutron stars.
A neutron star - which would disqualify it from being a possible parent
to an AM CVn system - would give off strong X-ray emission due to its
magnetic field and rapid rotation. Neither Chandra nor XMM-Newton
detected any X-rays from these systems.
AM CVn systems are of interest to scientists because they are
predicted to be sources of gravitational waves, as noted above. This is
important because even though such waves have yet to be detected, many
scientists and engineers are working on instruments that should be able
to detect them in the near future. This will open a significant new
observational window to the universe.
The paper reporting these results is available online
and is published in the Monthly Notices of the Royal Astronomical
Society Letters. The authors are Mukremin Kilic, from the University of
Oklahoma in Norman, OK; J.J. Hermes from the University of Texas at
Austin in TX; Alexandros Gianninas from the University of Oklahoma;
Warren Brown from Smithsonian Astrophysical Observatory in Cambridge,
MA; Craig Heinke from University of Alberta, in Edmonton, Canada; Marcel
Agüeros from Columbia University in New York, NY; Paul Chote and Denis
Sullivan from Victoria University of Wellington, New Zealand; and Keaton
Bell and Samuel Harrold from University of Texas at Austin.
NASA's Marshall Space Flight Center in Huntsville, Ala., manages the
Chandra program for NASA's Science Mission Directorate in Washington.
The Smithsonian Astrophysical Observatory in Cambridge, Mass., controls
Chandra's science and flight operations.
Fast Facts for J075141:
Scale: Image is 7 arcmin across (about 11 light years). Category:White Dwarfs & Planetary Nebulas Coordinates (J2000): RA 07h 51m 41.20s | Dec -01° 41' 20.90" Constellation: Monoceros Observation Dates: 22 Dec 2012 Observation Time: 1 hours 7 min Obs. IDs: 14608 Instrument: ACIS References: Kilic, M. et al, 2013, MNRAS Letters (in press);arxiv:1310.6359 Color Code: X-ray (Pink); Optical (Red, Green, Blue) Distance Estimate: About 5,500 light years
The NASA/ESA Hubble Space Telescope has
observed the variable star RS Puppis over a period of five weeks,
showing the star growing brighter and dimmer as it pulsates. These
pulsations have created a stunning example of a phenomenon known as a
light echo, where light appears to reverberate through the murky
environment around the star.
For most of its life, a star is pretty stable, slowly consuming the fuel at its core to keep it shining brightly.
However, once most of the hydrogen that stars use as fuel has been
consumed, some stars evolve into very different beasts – pulsating
stars. They become unstable, expanding and shrinking over a number of
days or weeks and growing brighter and dimmer as they do so.
A new and spectacular Hubble image shows RS Puppis, a type of variable star known as a Cepheid variable .
As variable stars go, Cepheids have comparatively long periods. RS
Puppis, for example, varies in brightness by almost a factor of five
every 40 or so days.
RS Puppis is unusual as it is shrouded by a nebula – thick, dark clouds
of gas and dust. Hubble observed this star and its murky environment
over a period of five weeks in 2010, capturing snapshots at different
stages in its cycle and enabling scientists to create a time-lapse video
of this ethereal object (heic1323a).
The apparent motion shown in these Hubble observations is an example of a phenomenon known as a light echo .
The dusty environment around RS Puppis enables this effect to be shown
with stunning clarity. As the star expands and brightens, we see some of
the light after it is reflected from progressively more distant shells
of dust and gas surrounding the star, creating the illusion of gas
moving outwards. This reflected light has further to travel, and so
arrives at the Earth after light that travels straight from star to
telescope . This is analogous to sound bouncing off surrounding objects, causing the listener to hear an audible echo.
While this effect is certainly striking in itself, there is another
important scientific reason to observe Cepheids like RS Puppis. The
period of their pulsations is known to be directly connected to their
intrinsic brightness, a property that allows astronomers to use them as
cosmic distance markers. A few years ago, astronomers used the light
echo around RS Puppis to measure its distance from us, obtaining the
most accurate measurement of a Cepheid's distance (eso0805). Studying stars like RS Puppis helps us to measure and understand the vast scale of the Universe.
 RS Puppis is over ten times more massive than our
Sun, and around 15 000 times more luminous. It lies around 6500
light-years away from us.
 This light echo enabled astronomers to measure the distance to RS Puppis very accurately back in 2008. This measurement is the most accurate ever calculated for a Cepheid.
 This effect can make it appear that this
propagation of light is happening at speeds greater than the speed of
light, but this is just an illusion.
Notes for editors
The Hubble Space Telescope is a project of international cooperation between ESA and NASA.
image from the Smithsonian's Submillimeter Array maps the projected
density of molecular gas in the central 30 light years of W49A. Brighter
colors mark denser regions. The brightest region at the image center is
less than three light-years across, yet it contains about 50,000 suns'
worth of molecular gas. Roberto Galván-Madrid (ESO), Hauyu Baobab Liu (ASIAA, Taiwan), Tzu-Cheng Peng (ESO). Low Resolution (jpg)
Cambridge, MA -W49A
might be one of the best-kept secrets in our galaxy. This star-forming
region shines 100 times brighter than the Orion nebula, but is so
obscured by dust that very little visible or infrared light escapes.
The Smithsonian's Submillimeter Array (SMA) has peered through the
dusty fog to provide the first clear view of this stellar nursery. The
SMA revealed an active site of star formation being fed by streamers of
"We were amazed by all the features we saw in the SMA images," says
lead author Roberto Galván-Madrid, who conducted this research at the
Harvard-Smithsonian Center for Astrophysics (CfA) and the European
Southern Observatory (ESO).
W49A is located about 36,000 light-years from Earth, on the opposite
side of the Milky Way. It represents a nearby example of the sort of
vigorous star formation seen in so-called "starburst" galaxies, where
stars form 100 times faster than in our galaxy.
The heart of W49A holds a giant yet surprisingly compact star
cluster. About 100,000 stars already exist within a space only 10
light-years on a side. In contrast, fewer than 10 stars lie within 10
light-years of our Sun. In a few million years, the giant star cluster
in W49A will be almost as crowded as a globular cluster.
The SMA also revealed an intricate network of filaments feeding gas
into the center, much like tributaries feed water into mighty rivers on
Earth. The gaseous filaments in W49A form three big streamers, which
funnel star-building material inward at speeds of about 4,500 miles per
hour (2 km/sec).
"Move over, Mississippi!" quips co-author Qizhou Zhang of the CfA.
Being denser than average will help the W49A star cluster to survive.
Most star clusters in the galactic disk dissolve rapidly, migrating
away from each other under the influence of gravitational tides. This is
why none of the Sun's sibling stars remain nearby. Since it is so
compact, the cluster in W49A might remain intact for billions of years.
The Submillimeter Array mapped the molecular gas within W49A in
exquisite detail. It showed that central 30 light-years of W49A is
several hundred times denser than the average molecular cloud in the
Milky Way. In total, the nebula contains about 1 million suns' worth of
gas, mostly molecular hydrogen.
"We suspect that the organized architecture seen in W49A is rather
common in massive stellar cluster-formation," adds co-author Hauyu
Baobab Liu of the Academia Sinica Institute of Astronomy and
Astrophysics (ASIAA) in Taiwan.
The team expects to continue analyzing the SMA data for some time to come.
"It's a mine of information," says Galván-Madrid.
Their research was published in the December 2013 Astrophysical Journal.
in Cambridge, Mass., the Harvard-Smithsonian Center for Astrophysics
(CfA) is a joint collaboration between the Smithsonian Astrophysical
Observatory and the Harvard College Observatory. CfA scientists,
organized into six research divisions, study the origin, evolution and
ultimate fate of the universe.
For more information, contact:
David A. Aguilar
Director of Public Affairs
Harvard-Smithsonian Center for Astrophysics
Public Affairs Specialist
Harvard-Smithsonian Center for Astrophysics
This composite image was obtained through the filters Hα (red, 3×120s),
Sloan r´ (green, 3×30s) and [OIII] (blue, 3×120s) using the Wide Field
Camera on the Isaac Newton Telescope on the 21st of October, 2013.
Images were reduced usingTHELI, and processed usingFITS LiberatorandMATLAB. Field of view is 9×6 arcminutes, North up, East left. Credits: Teo Mocnik (ING) [JPEG|TIFF]
The bipolar planetary nebula (PN) Sh2-71 lies in the constellation of
Aquila at a distance of 1 kpc. It was discovered by Rudolph Minkowski in
1946. Shortly after the discovery, the central star (the brightest star
in the centre of the nebula) was identified to be a variable with a
quasi-sinusoidal lightcurve with an amplitude of 0.8 magnitudes. Later
observations showed sharp brightness dips, possibly eclipses, with a
period of 17.2 days. Besides an unusual lightcurve, it also exhibits
pronounced spectral variations.
Astronomers believe that the central star is a close binary, which
could explain the observed variability as well as the necessary
mechanism for collimating the outflowing material.
However, some astronomers claim that the real central star is
actually a much dimmer star located to the North-West of the bright one.
The true nature of the planetary nebula Sh2-71 will remain veiled until
more data are obtained and new analysis and explanations are provided.
Herschel image and spectrum of the Crab Nebula, with emission lines from the molecular ion argon hydride. Credit: ESA/Herschel/PACS, SPIRE/MESS Key Programme Supernova Remnant Team.Hi-Res Image
Herschel (red) and Hubble (blue) composite image of the Crab Nebula. Credit:
ESA/Herschel/PACS/MESS Key Programme Supernova Remnant Team; NASA, ESA
and Allison Loll/Jeff Hester (Arizona State University).Hi-Res Image
Using ESA's Herschel Space Observatory, a
team of astronomers has found first evidence of a noble-gas based
molecule in space. A compound of argon, the molecule was detected in the
gaseous filaments of the Crab Nebula, one of the most famous supernova
remnants in our Galaxy. While argon is a product of supernova
explosions, the formation and survival of argon-based molecules in the
harsh environment of a supernova remnant is an unforeseen surprise.
Just like a group of people, the periodic table of chemical elements
has its share of team players and loners. While some elements tend to
react more easily with other species, forming molecules and other
compounds, others hardly ever take part in chemical reactions and are
mainly found in isolation. 'Inert' elements par excellence are the noble
gases: helium, neon, argon, krypton, xenon and radon.
The name of one of them – argon – derives from the Greek word for idle,
to emphasise its highly inert nature. But noble gases are not entirely
inactive. While at first scientists doubted that chemical compounds
could even contain noble gases, several such species are now known and
have been extensively studied in the laboratory.
Things are more complex in space. Over the decades, astronomers have
detected atoms and ions of noble gases in a variety of cosmic
environments, ranging from the Solar System to the atmospheres of stars,
from dense nebulae to the diffuse interstellar medium. But the search
for noble-gas based compounds had until now proved unsuccessful,
suggesting that these almost inert elements might have a hard time
reacting with other species in space.
A new study, led by Michael Barlow from University College London, UK,
and based on data from ESA's Herschel Space Observatory, has found the
first evidence of such a compound in space. The results are published in
the journal Science.
The team of astronomers has detected emission from argon hydride (ArH+),
a molecular ion containing the noble gas argon, in the Crab Nebula. A
wispy and filamentary cloud of gas and dust, the Crab Nebula is the
remnant of a supernova explosion that was observed by Chinese
astronomers in the year 1054.
"At first, the discovery seemed bizarre," comments Barlow.
"With hot gas still expanding at high speeds after the explosion, a
supernova remnant is a harsh, hostile environment, and one of the
places where we least expected to find a noble-gas based molecule," he adds.
Argon hydride is produced when ions of argon (Ar+) react with hydrogen molecules (H2),
but these two species are usually found in different regions of a
nebula. While ions form in the most energetic regions, where radiation
from a star or stellar remnant ionises the gas, molecules take shape in
the denser, colder pockets of gas that are shielded from this powerful
"But we soon realised that even in the Crab Nebula, there are
places where the conditions are just right for a noble gas to react and
combine with other elements.
"There, in the transition regions between ionised and molecular gas, argon hydride can form and survive," explains Barlow.
This new picture was supported by the comparison of the Herschel data
with observations of the Crab Nebula performed at other wavelengths,
which revealed that the regions where they had found ArH+ also exhibit higher concentrations of both Ar+ and H2. There, argon ions can react with hydrogen molecules forming argon hydride and atomic hydrogen.
In the partly ionised gas filling these regions, molecules collide
frequently with ions and free electrons. These collisions excite the
molecular structure of ArH+ making it rotate; in turn,
molecular rotations produce the emission features detected in the
spectrum of the Crab Nebula by Herschel.
"The discovery was truly serendipitous: we were observing the Crab
Nebula to study its dust content. But then, on top of the emission from
dust, we found two emission lines that had never been seen before," says co-author Bruce Swinyard, also from University College London.
The identification of these lines was a challenging task. To this end,
the astronomers exploited two extensive databases of molecular spectra
and, after lengthy investigation, they matched the observed features
with two characteristic lines emitted by ArH+.
"And there's icing on the cake: from a molecule's emission, we can
determine the isotope of the elements that form it – something that we
can't do when we see only ions," adds Swinyard.
The Herschel data indicate that the argon hydride found in the Crab Nebula is made up of the argon isotope 36Ar. This is the first time that astronomers could identify the isotopic nature of an element in a supernova remnant.
"Finding that argon in the Crab Nebula consists of 36Ar was not surprising because this is the dominant isotope of argon across the Universe.
"And it's also the main argon isotope to be synthesised in the
nuclear reactions during supernova explosions, so its detection in the
Crab Nebula confirms that this iconic nebula was created by the
explosive death of a massive star," explains Barlow.
The astronomers are planning further observations with other facilities
to seek new emission lines in the Crab Nebula's spectrum, possibly from
molecules containing different isotopes of argon. The detection of such
a molecule would enable them to study the ratio of different isotopes
produced by supernovae and to learn more about the nuclear reactions
that take place when a massive star dies.
"This is not only the first detection of a noble-gas based molecule
in space, but also a new perspective on the Crab Nebula. Herschel has
directly measured the argon isotope we expect to be produced via
explosive nucleosynthesis in a core-collapse supernova, refining our
understanding of the origin of this supernova remnant," concludes Göran Pilbratt, Herschel Project Scientist at ESA.
The results described in this article are reported in "Detection of a Noble Gas Molecular Ion, 36ArH+, in the Crab Nebula", by M. J. Barlow et al., published in Science, 342, 6163, 1343-1345, 13 December 2013. DOI: 10.1126/science.124358213.
The argon isotope found in the Crab Nebula is different from the one that dominates in Earth's atmosphere, 40Ar, which derives from the decay of a radioactive isotope of potassium (40K)
present in our planet's rocks.
At almost one per cent, argon is the
third most abundant gas in the atmosphere of Earth after nitrogen and
oxygen, and was discovered at the end of the 19th century.
The study is based on data collected with the Spectral and Photometric
Imaging Receiver (SPIRE) on board ESA's Herschel Space Observatory. The
team of astronomers detected two emission lines corresponding to the
first two rotational transitions of argon hydride (ArH+) at
frequencies of 617.5 GHz and 1234.6 GHz, respectively. To identify the
lines, they made use of two extensive databases of molecular lines: the
Cologne Database for Molecular Spectroscopy (CDMS) and the Madrid
Molecular Spectroscopy Excitation (MADEX) code.
Herschel is an ESA space observatory with science instruments provided
by European-led Principal Investigator consortia and with important
participation from NASA.
The SPIRE instrument contains an imaging photometer (camera) and an
imaging spectrometer. The camera operates in three wavelength bands
centred on 250, 350 and 500 µm, and so can make images of the sky
simultaneously in three sub-millimetre colours; the spectrometer covers
the wavelength range between 194 and 671 μm. SPIRE has been developed by
a consortium of institutes led by Cardiff Univ. (UK) and including
Univ. Lethbridge (Canada); NAOC (China); CEA, LAM (France); IFSI, Univ.
Padua (Italy); IAC (Spain); Stockholm Observatory (Sweden); Imperial
College London, RAL, UCL-MSSL, UKATC, Univ. Sussex (UK); Caltech, JPL,
NHSC, Univ. Colorado (USA). This development has been supported by
national funding agencies: CSA (Canada); NAOC (China); CEA, CNES, CNRS
(France); ASI (Italy); MCINN (Spain); SNSB (Sweden); STFC, UKSA (UK);
and NASA (USA).
Herschel was launched on 14 May 2009 and completed science observations on 29 April 2013.
Michael J. Barlow
Department of Physics & Astronomy
University College London
Email:firstname.lastname@example.org Phone: +44-20-7679-7160
Herschel Project Scientist
Research and Scientific Support Department
Science and Robotic Exploration Directorate
ESA, The Netherlands
Email:email@example.com Phone: +31-71-565-3621
A composite of space- and ground-based observations in different
wavelengths gathered on the day of the solar eclipse of 3 November 2013.
The result is an overall view of the Sun and its surrounding corona,
extending far out into space.
Close-in views of the solar disc and
its surroundings in extreme-ultraviolet light are covered by the Royal
Observatory of Belgium’s SWAP instrument aboard ESA’s Proba-2
minisatellite and the AIA and HMI instruments aboard NASA’s Solar
Dynamics Observatory mission. The surrounding inner corona is depicted
through a combination of white-light images acquired from the ground
along the path of totality, from Port Gentil in Gabon and Pokwero in
Uganda. The outer corona is depicted through the white-light LASCO-C2
and C3 coronagraph instruments aboard the ESA/NASA SOHO satellite.
planet Saturn is visible at the top left of the picture as a bright
saturated object, coincidentally giving an impression of rings. To see
more of the eclipse in multiple wavelengths, check this video.
The NASA/ESA Hubble Space Telescope has
discovered water vapour erupting from the frigid surface of Jupiter’s
moon Europa, in one or more localised plumes near its south pole.
Europa is already thought to harbour a liquid ocean beneath its icy
crust, making the moon one of the main targets in the search for
habitable worlds away from Earth. This new finding is the first
observational evidence of water vapour being ejected off the moon's
"The discovery that water vapour is ejected near the south pole
strengthens Europa's position as the top candidate for potential
habitability," said lead author Lorenz Roth of the Southwest Research Institute in San Antonio, Texas. "However, we do not know yet if these plumes are connected to subsurface liquid water or not."
The Hubble findings will be published in the 12 December online issue
of Science Express, and are being reported today at the meeting of the
American Geophysical Union in San Francisco, California, USA.
The Hubble discovery makes Europa only the second moon in the Solar
System known to have water vapour plumes. In 2005, plumes of water
vapour and dust were detected by NASA's Cassini orbiter spewing off the
surface of the Saturnian moon Enceladus.
The Europa plumes were discovered by Hubble observations in December
2012. The Space Telescope Imaging Spectrograph (STIS) detected faint
ultraviolet light from an aurora at the moon's south pole. This aurora
is driven by Jupiter's intense magnetic field, which causes particles to
reach such high speeds that they can split the water molecules in the
plume when they hit them, resulting in oxygen and hydrogen ions which
leave their telltale imprint in the colours of the aurora.
So far, only water vapour has been detected — unlike the plumes on Enceladus, which also contain ice and dust particles.
"We pushed Hubble to its limits to see this very faint emission,"
said co-lead author and principal investigator of the Hubble observing
campaign Joachim Saur of the University of Cologne, Germany. "Only
after a particular camera on the Hubble Space Telescope had been
repaired on the last servicing mission by the Space Shuttle did we gain
the sensitivity to really search for these plumes."
Roth suggests long cracks on Europa's surface, known as linea, might
be venting water vapour into space. Similar fissures have been
photographed near Enceladus's south pole by the Cassini spacecraft. It
is unknown how deep inside Europa's crust the source of the water may
be. Roth asks, "Do the vents extend down to a subsurface ocean or
are the ejecta simply from warmed ice caused by friction stresses near
Also like Enceladus, the Hubble team found that the intensity of the
plumes varies with Europa's orbital position. Active geysers have only
been seen when the moon is furthest from Jupiter. But the researchers
could not detect any sign of venting when Europa is closer to Jupiter.
One explanation is that the long fractures in the ice crust
experience more stress as gravitational tidal forces push and pull on
the moon and so open vents at larger distances from Jupiter. The vents
are narrowed or closed when at closest approach to the gas giant planet . Team member Kurt Retherford, also of the Southwest Research Institute, points out that "the
plume variability supports a key prediction that we should see this
kind of tidal effect if there is a subsurface ocean on Europa".
Future space probe missions to Europa could confirm that the exact
locations and sizes of vents and determine whether they connect to
liquid subsurface reservoirs. It is important news for missions such as
ESA's JUpiter ICy moons Explorer,
a mission planned for launch in 2022, and which aims to explore both
Jupiter and three of its largest moons: Ganymede, Callisto, and Europa.
 When Europa orbits around Jupiter,
the moon experiences varying tidal forces at different points in its
orbit. The tidal stresses compress the vents at the south pole region
when Europa is closest to Jupiter, and stretch them when Europa is
furthest away, making it possible for the vents to open up. A subsurface
ocean would allow the stresses on Europa's surface to be much stronger
as the interior would be malleable and flexible.
Notes for editors
The Hubble Space Telescope is a project of international cooperation between ESA and NASA.
The international team of astronomers in this study consists of L.
Roth (Southwest Research Institute, USA; University of Cologne,
Germany), J. Saur (University of Cologne, Germany), K. D. Retherford
(Southwest Research Institute, USA), D. F. Strobel (The Johns Hopkins
University, USA), P. D. Feldman (The Johns Hopkins University, USA), M.
A. McGrath (NASA Marshall Space Flight Center, USA), F. Nimmo
(University of California, USA).
Image credit: NASA, ESA, L. Roth (Southwest Research Institute, USA/University of Cologne, Germany) and M. Kornmesser.