Friday, July 21, 2017

Dim and diffuse

Credit: ESA/Hubble & NASA



Tucked away in the small northern constellation of Canes Venatici (The Hunting Dogs) is the galaxy NGC 4242, shown here as seen by the NASA/ESA Hubble Space Telescope. The galaxy lies some 30 million light-years from us. At this distance from Earth, actually not all that far on a cosmic scale, NGC 4242 is visible to anyone armed with even a basic telescope (as British astronomer William Herschel found when he discovered the galaxy in 1788).

This image shows the galaxy’s bright centre and the surrounding dimmer and more diffuse “fuzz”. Despite appearing to be relatively bright in this image, studies have found that NGC 4242 is actually relatively dim (it has a moderate-to-low surface brightness and low luminosity) and also supports a low rate of star formation. The galaxy also seems to have a weak bar of stars cutting through its asymmetric centre, and a very faint and poorly-defined spiral structure throughout its disc. But if NGC 4242 is not all that remarkable, as with much of the Universe, it is still a beautiful and ethereal sight.



Thursday, July 20, 2017

Billions of new neighbours?

Credit: ESO/Koraljka Muzic (University of Lisbon), Aleks Scholz (University of St Andrews), Rainer Schoedel (Institituto de Astrofísica de Andalucía), Vincent Geers (UKATC), Ray Jayawardhana (York University), Joana Ascenso (Univeristy of Porto & University of Lisbon) & Lucas Cieza (University Diego Portales)



The objects that astronomers call brown dwarfs sit somewhere between the definition of a planet and a star. They are balls of gas with more mass than a planet, but not enough mass to sustain stable hydrogen fusion like a star. Because they hardly emit any visible light, they were only first discovered in 1995 and up until today the majority of known brown dwarfs are within 1500 light-years of us.

Now, astronomers using the NACO adaptive optics infrared camera on ESO’s Very Large Telescope have observed the star cluster RCW 38 in the constellation Vela (the Sail), about 5500 light-years away. This Picture of the Week shows the central part of RCW 38; the inserts on the sides show a subset of the brown dwarf candidates detected within the cluster.

The scientists found half as many brown dwarfs as stars in the cluster. From these results and from studying other star clusters, the astronomers estimate that the Milky Way contains at least between 25 to 100 billion brown dwarfs. RCW 38 probably contains even more less massive, fainter brown dwarfs, which are beyond the detection limits of this image — so this new estimate could actually be a significant underestimation. Further surveys will reveal the true number of brown dwarfs lurking in the Milky Way.



Links 

Source:  ESO/Potw

Wednesday, July 19, 2017

Signals from A Nearby Star System?

 Ross 128

  ATA observation of Ross 128. Screen capture from setiquest.
Info credit: Jon Richards


It’s unlikely that Ross 128 has been big in your life. In fact, it’s unlikely you’ve ever seen it, despite the fact that it’s nestled in the prominent summer constellation, Virgo. That’s because Ross 128 is a dim bulb of a star, a so-called red dwarf. Even on the darkest of moonless nights, it’s 100 times too faint to be seen with the naked eye.

In May, radio astronomers at the Arecibo radio telescope in Puerto Rico pointed their Brobdingnagian antenna in the direction of Ross 128.  The researchers’ interest was to learn if they could measure any natural radio emissions from this very close (11 light-years) dwarf.  Such stars are known to act up, and the turbulent flares that erupt from their surfaces produce radio static.  The hope was that small changes in such emission might offer clues to planets whose magnetic fields might perturb these stellar storms. (Note that Ross 128 does not have any known planets, but that doesn’t guarantee there aren’t any. 

What the Puerto Rican astronomers found when the data were analyzed was a wide-band radio signal.  This signal not only repeated with time, but also slid down the radio dial, somewhat like a trombone going from a higher note to a lower one.

That was odd, indeed. And the discoverers, led by Abel Mendez at the University of Puerto Rico, immediately enlisted the help of other astronomical observatories to keep watch on Ross 128. They suspected one of three possible causes for the radio noise: (1) Flares from the star, as above; (2) other background astronomical source, or (3) terrestrial interference, most likely from some artificial satellite. A deliberate transmission from intelligent beings on a planet near the star is another possibility of course, but was at the bottom of their list.

The Arecibo observers were careful to point out that the intelligent beings explanation – while instinctively more appealing than a barrel of kittens – was the least likely. Still, the facts are that no one yet knows for sure what’s going on in this system.

Beginning last weekend, Jon Richards swung the SETI Institute’s Allen Telescope Arrayin the direction of Ross 128, and so far has collected more than 10 hours of data.  Even using the massive Arecibo antenna, the detected signal was weak, and that makes its detection with other instruments difficult.  But it’s obviously important to check the signal out and, insofar as possible, see if it’s really coming from the Ross 128 star system.

Institute scientist Gerry Harp is looking at the ATA data now, and this page will be updated with whatever findings are made.  Of course it’s possible that Ross 128 will shed its anonymity and become the first star system to show good evidence of extraterrestrial intelligence.  But it’s likely – at least on the basis of past experience – that we will find another, less romantic explanation for the mystery that now enshrouds this object.  That, of course, is a frequent occurrence for anyone doing exploration, and hardly a cause for discouragement, but rather an incentive to continue the search. 


by Seth Shostak, Senior Astronomer

Source: SETI Institute

Tuesday, July 18, 2017

NASA-funded Citizen Science Project Discovers New Brown Dwarf

This illustration shows a close-up view of a Y dwarf. Objects like this, drifting just beyond our solar system, have been imaged by NASA's Wide-field Infrared Survey Explorer and could be discovered by Backyard Worlds: Planet 9. Credit: NASA/JPL-Caltech

This illustration shows the average brown dwarf is much smaller than our sun and low mass stars and only slightly larger than the planet Jupiter. Credits: NASA's Goddard Space Flight Center. Download this image from NASA Goddard's Scientific Visualization Studio

The newly discovered brown dwarf WISEA J110125.95+540052.8 appears as a moving dot (indicated by the circle) in this animated flipbook from the Backyard Worlds: Planet 9 citizen science project. Credits: NASA/WISE.



One night three months ago, Rosa Castro finished her dinner, opened her laptop, and uncovered a novel object that was neither planet nor star. Therapist by day and amateur astronomer by night, Castro joined the NASA-funded Backyard Worlds: Planet 9 citizen science project when it began in February — not knowing she would become one of four volunteers to help identify the project's first brown dwarf, formally known as WISEA J110125.95+540052.8.

After devoting hours to skimming online, publicly available "flipbooks" containing time-lapse images, she spotted a moving object unlike any other. The search process involves fixating on countless colorful dots, she explained. When an object is different, it simply stands out. Castro, who describes herself as extremely detail oriented, has contributed nearly 100 classifications to this specific project.

A paper about the new brown dwarf was published on May 24 in The Astrophysical Journal Letters. Four citizen scientists are co-authors of the paper, including Castro. Since then, Backyard Worlds: Planet 9 has identified roughly 117 additional brown dwarf candidates.

The collaboration was inspired by the recently proposed ninth planet, possibly orbiting at the fringes of our solar system beyond Pluto.

"We realized we could do a much better job identifying Planet Nine if we opened the search to the public," said lead researcher Marc Kuchner, an astrophysicist at NASA's Goddard Space Flight Center in Greenbelt, Maryland. "Along the way, we're hoping to find thousands of interesting brown dwarfs."

It's been roughly two decades since researchers first discovered brown dwarfs, and the scientific community opened its eyes to this new class of objects between stars and planets. Although they are as common as stars and form in much the same way, brown dwarfs lack the mass necessary to sustain nuclear fusion reactions. They therefore do not have the energy to maintain their luminosity, so they slowly cool over the course of their lifetimes. Their low temperatures also render them intrinsically dim.

For years, Kuchner has been fascinated by infrared images of the entire sky captured by NASA's Wide-field Infrared Survey Explorer (WISE), launched in 2009. The space telescope is specially designed to observe cold objects emitting light at long wavelengths — objects like brown dwarfs. With its initial mission complete, WISE was deactivated in 2011. It was then reactivated in 2013 as NEOWISE, a new mission funded by the NEO Observations Program with a different goal: to search for potentially hazardous near-Earth objects (NEOs).

Previously, Kuchner had focused on stationary objects seen by WISE. But the Backyard Worlds: Planet 9 project shows the WISE and NEOWISE data in a way custom-tailored for finding fast-moving objects. His team layers many images of the same location to create a single, comprehensive snapshot. These are then combined with several similarly "co-added" pictures to form flipbooks that show motion over time.

Anyone with internet access can scour these flipbooks and click on anomalies. If they would like to call the science team's attention to an object they found, they can submit a report to the researchers or share their insights on a public forum. Kuchner and his colleagues then follow up the best candidates using ground-based telescopes to glean more information.

According to Backyard Worlds: Planet 9 citizen scientist Dan Caselden, participants are free to dig as deep into the results as they choose. A security researcher by trade, Caselden developed a series of tools allowing fellow participants to streamline their searches and visualize their results, as well as aggregate various user statistics. He also helped identify several of the additional brown dwarf candidates while the first discovery was being confirmed.

Kuchner and his co-author, Adam Schneider of Arizona State University, Tempe, agree WISEA J110125.95+540052.8 is an exciting discovery for several reasons. "What's special about this object — besides the way it was discovered — is that it's unusually faint," Schneider said. "That means our citizen scientists are probing much deeper than anyone has before."
While computers efficiently sift through deluges of data, they can also get lost in details that human eyes and brains easily disregard as irrelevant.

However, mining this information is extremely arduous for a single scientist or even a small group of researchers. That's precisely why collaborating with an enthusiastic public is so effective — many eyes catch details that one pair alone could miss.

While Kuchner is delighted by this early discovery, his ultimate goal for Backyard Worlds: Planet 9 is to find the smallest and coldest brown dwarfs, called Y dwarfs.  Some of these Y dwarfs many even be lurking closer to us than Proxima Centauri, the nearest star to the sun.

Their low temperatures make Y dwarfs extremely dim, according to Adam Burgasser at the University of California San Diego. "They're so faint that it takes quite a bit of work to pull them from the images, that's where Kuchner's project will help immensely," he said. "Anytime you get a diverse set of people looking at the data, they'll bring unique perspectives that can lead to unexpected discoveries."

Kuchner anticipates the Backyard Worlds effort will continue for several more years — allowing more volunteers like Caselden and Castro to contribute.

As Castro put it: "I am not a professional. I'm just an amateur astronomer appreciating the night sky. If I see something odd, I'll admire and enjoy it."

Backyard Worlds: Planet 9 is a collaboration between NASA, UC Berkeley, the American Museum of Natural History in New York, Arizona State University, the Space Telescope Science Institute in Baltimore and Zooniverse, a collaboration of scientists, software developers and educators who collectively develop and manage citizen science projects on the internet.

NASA's Jet Propulsion Laboratory in Pasadena, California, manages the NEOWISE mission for NASA's Planetary Defense Coordination Office within the Science Mission Directorate in Washington. The Space Dynamics Laboratory in Logan, Utah, built the science instrument. Ball Aerospace & Technologies Corp. of Boulder, Colorado, built the spacecraft. Science operations and data processing take place at the Infrared Processing and Analysis Center at Caltech in Pasadena. Caltech manages JPL for NASA.

For more information about Backyard Worlds: Planet 9, visit: http://backyardworlds.org

For more information about NASA's WISE mission, visit:  http://www.nasa.gov/wise




Editor: Rob Garner




Monday, July 17, 2017

Remarkable planet discovery

An artist’s impression of the newly discovered exoplanet around the binary star KIC 5095269.
Credit: USQ Media Design.



A long time ago in a galaxy far, far away, Luke Skywalker lived on a planet circling twin suns.

While Star Wars is science-fiction, two stars in orbit of each other is firmly based in reality.

An astronomy student working with an Australian Astronomical Observatory (AAO) astronomer has uncovered evidence of a new planet orbiting a binary star (two stars that orbit a common centre of mass).

Adding interest to this discovery is the observation that the planet orbits the stars on a tilt – an example of the weird and wonderful diversity of the Universe.

The binary star, KIC 5095269, system was first observed by NASA’s Kepler space telescope.

The newly-discovered planet has a mass 7.7 times more than Jupiter and orbits the binary star every 237.7 days.

“My PhD research involves performing an eclipse timing variation study of binary stars in order to look for any third bodies that may be present, like stars/brown dwarfs or planets,” PhD student Kelvin Getley, who lead authored the journal article announcing the discovery, said.

“I created a program that determined when one star passes in front of another as seen from Earth, and compared them to what we’d expect to see if there was nothing else in the system.

“My PhD supervisors, Professor Brad Carter and Dr Rachel King from the University of Southern Queensland (USQ), and Simon O'Toole from the AAO, guided and advised me, and helped come up with tests that could be done on the system to try to make sure what we were seeing was possible.”

Supervisor and AAO astronomer Dr O’Toole is an expert in exoplanetary systems.

“This is a really neat result,” Dr O’Toole said, “Planets orbiting two stars have been found before, but the cool thing here is that Kelvin has discovered a planet with a tilted orbit, more reminiscent of Pluto than the other planets in our Solar System."

Professor Carter leads USQ’s Astrophysics Research Program Team and commended Mr Getley on his work and discovery.

“Kelvin’s research demonstrates that evidence for new worlds can be gathered through an innovative analysis of the Kepler space telescope's treasure trove of observational data," he said.

Mr Getley is studying a PhD in Astronomy and is an external USQ student living in Charlton, Victoria, with the support of the AAO.

“Being an astronomer is something that I've wanted to be basically my entire life,” he said.

“My granddad was interested in astronomy as a hobby so I grew up reading his books. Doing this research, and making a discovery like this is amazing.”

The AAO is a division of the Department of Industry, Innovation and Science.



Publication details:

A.K. Getley (University of Southern Queensland), B. Carter (University of Southern Queensland), R. King (University of Southern Queensland) and S. O’Toole (Australian Astronomical Observatory), “Evidence for a planetary mass third body orbiting the binary star KIC 5095269”, Published in Monthly Notices of the Royal Astronomical Society (MNRAS) through Oxford University Press. MNRAS, 2017, 468, 2932

https://academic.oup.com/mnras/article/468/3/2932/3070417/Evidence-for-a-planetary-mass-third-body-orbiting



Science Contacts:


Dr. Simon O’Toole

Web & eReseach Administrator, Australian Astronomical Observatory
M: +61 434 916 378
E: simon.otoole@aao.gov.au
 

Prof. Andrew Hopkins 
Head of Research and Outreach, Australian Astronomical Observatory,
M: +61 432 855 049
E:
 
andrew.hopkins@aao.gov.au


Media contact:

AAO – Andrew Hopkins, 
email: andrew.hopkins@aao.gov.au
Phone: 04 3285 5049 

Rhianwen Whitney, 
email: rhianwen.whitney@usq.edu.au
Phone: 07 4631 2977




Sunday, July 16, 2017

Hidden Stars May Make Planets Appear Smaller

This cartoon explains why the reported sizes of some exoplanets may need to be revised in cases where there is a second star in the system. Credits: NASA/JPL-Caltech. Larger labeled view



In the search for planets similar to our own, an important point of comparison is the planet's density. A low density tells scientists a planet is more likely to be gaseous like Jupiter, and a high density is associated with rocky planets like Earth. But a new study suggests some are less dense than previously thought because of a second, hidden star in their systems.

As telescopes stare at particular patches of sky, they can't always differentiate between one star and two. A system of two closely orbiting stars may appear in images as a single point of light, even from sophisticated observatories such as NASA's Kepler space telescope. This can have significant consequences for determining the sizes of planets that orbit just one of these stars, says a forthcoming study in the Astronomical Journal by Elise Furlan of Caltech/IPAC-NExScI in Pasadena, California, and Steve Howell at NASA's Ames Research Center in California's Silicon Valley.

"Our understanding of how many planets are small like Earth, and how many are big like Jupiter, may change as we gain more information about the stars they orbit," Furlan said. "You really have to know the star well to get a good handle on the properties of its planets."

Some of the most well-studied planets outside our solar system -- or exoplanets -- are known to orbit lone stars. We know Kepler-186f, an Earth-size planet in the habitable zone of its star, orbits a star that has no companion (the habitable zone is the distance at which a rocky planet could support liquid water on its surface). TRAPPIST-1, the ultra-cool dwarf star that is home to seven Earth-size planets, does not have a companion either. That means there is no second star complicating the estimation of the planets' diameters, and therefore their densities.

But other stars have a nearby companion, high-resolution imaging has recently revealed. David Ciardi, chief scientist at the NASA Exoplanet Science Institute (NExScI) at Caltech, led a large-scale effort to follow up on stars that Kepler had studied using a variety of ground-based telescopes. This, combined with other research, has confirmed that many of the stars where Kepler found planets have binary companions. In some cases, the diameters of the planets orbiting these stars were calculated without taking the companion star into consideration. That means estimates for their sizes should be smaller, and their densities higher, than their true values.  

Previous studies determined that roughly half of all the sun-like stars in our sun's neighborhood have a companion within 10,000 astronomical units (an astronomical unit is equal to the average distance between the sun and Earth, 93 million miles or 150 million kilometers). Based on this, about 15 percent of stars in the Kepler field could have a bright, close companion -- meaning planets around these stars may be less dense than previously thought. 

The Transit Problem for Binaries

When a telescope spots a planet crossing in front of its star -- an event called a "transit" -- astronomers measure the resulting apparent decrease in the star's brightness. The amount of light blocked during a transit depends on the size of the planet -- the bigger the planet, the more light it blocks, and the greater the dimming that is observed. Scientists use this information to determine the radius -- half the diameter -- of the planet.

If there are two stars in the system, the telescope measures the combined light of both stars. But a planet orbiting one of these stars will cause just one of them to dim. So, if you don't know that there is a second star, you will underestimate the size of the planet.

For example, if a telescope observes that a star dims by 5 percent, scientists would determine the transiting planet's size relative to that one star. But if a second star adds its light, the planet must be larger to cause the same amount of dimming.

If the planet orbits the brighter star in a binary pair, most of the light in the system comes from that star anyway, so the second star won't have a big effect on the planet's calculated size. But if the planet orbits the fainter star, the larger, primary star contributes more light to the system, and the correction to the calculated planet radius can be large -- it could double, triple or increase even more. This will affect how the planet's orbital distance is calculated, which could impact whether the planet is found to be in the habitable zone.

If the stars are roughly equal in brightness, the "new" radius of the planet is about 40 percent larger than if the light were assumed to come from a single star. Because density is calculated using the cube of the radius, this would mean a nearly three-fold decrease in density. The impact of this correction is most significant for smaller planets because it means a planet that had once been considered rocky could, in fact, be gaseous.

The New Study

In the new study, Furlan and Howell focused on 50 planets in the Kepler observatory's field of view whose masses and radii were previously estimated. These planets all orbit stars that have stellar companions within about 1,700 astronomical units. For 43 of the 50 planets, previous reports of their sizes did not take into account the contribution of light from a second star. That means a revision to their reported sizes is necessary.

In most cases, the change to the planets' reported sizes would be small. Previous research showed that 24 of the 50 planets orbit the bigger, brighter star in a binary pair. Moreover, Furlan and Howell determined that 11 of these planets would be too large to be planets if they orbited the fainter companion star. So, for 35 of the 50 planets, the published sizes will not change substantially.

But for 15 of the planets, they could not determine whether they orbit the fainter or the brighter star in a binary pair. For five of the 15 planets, the stars in question are of roughly equal brightness, so their densities will decrease substantially regardless of which star they orbit.

This effect of companion stars is important for scientists characterizing planets discovered by Kepler, which has found thousands of exoplanets. It will also be significant for NASA's upcoming Transiting Exoplanet Survey Satellite (TESS) mission, which will look for small planets around nearby, bright stars and small, cool stars.

"In further studies, we want to make sure we are observing the type and size of planet we believe we are," Howell said. "Correct planet sizes and densities are critical for future observations of high-value planets by NASA's James Webb Space Telescope. In the big picture, knowing which planets are small and rocky will help us understand how likely we are to find planets the size of our own elsewhere in the galaxy."

For more information about exoplanets, visit:  https://exoplanets.nasa.gov


Elizabeth Landau
Jet Propulsion Laboratory, Pasadena, Calif.
818-354-6425

elizabeth.landau@jpl.nasa.gov

Editor: Martin Perez


Saturday, July 15, 2017

Just like home

Credit: ESA/Hubble & NASA


Discovered by British astronomer William Herschel over 200 years ago, NGC 2500 lies about 30  million light-years away in the northern constellation of Lynx. As this NASA/ESA Hubble Space Telescope image shows, NGC 2500 is a particular kind of spiral galaxy known as a barred spiral, its wispy arms swirling out from a bright, elongated core.

Barred spirals are actually more common than was once thought. Around two-thirds of all spiral galaxies — including the Milky Way — exhibit these straight bars cutting through their centres. These cosmic structures act as glowing nurseries for newborn stars, and funnel material towards the active core of a galaxy. NGC 2500 is still actively forming new stars, although this process appears to be occurring very unevenly. The upper half of the galaxy — where the spiral arms are slightly better defined — hosts many more star-forming regions than the lower half, as indicated by the bright, dotted islands of light.

There is another similarity between NGC 2500 and our home galaxy. Together with Andromeda, Triangulum, and many smaller natural satellites, the Milky Way is part of the Local Group of galaxies, a gathering of over 50 galaxies all loosely held together by gravity. NGC 2500 forms a similar group with some of its nearby neighbours, including NGC 2541, NGC 2552, NGC 2537, and the bright, Andromeda-like spiral NGC 2481 (known collectively as the NGC 2841 group).



Friday, July 14, 2017

Distant Galaxies ‘Lift the Veil’ on the End of the Cosmic Dark Ages

False color image of a 2 square degree region of the LAGER survey field, created from images taken in the optical at 500 nm (blue), in the near-infrared at 920 nm (red), and in a narrow-band filter centered at 964 nm (green). The last is sensitive to hydrogen Lyman alpha emission at z ~ 7. The small white boxes indicate the positions of the 23 LAEs discovered in the survey. The detailed insets (yellow) show two of the brightest LAEs; they are 0.5 arcminutes on a side, and the white circles are 5 arcseconds in diameter. Image Credit: Zhen-Ya Zheng (SHAO) & Junxian Wang (USTC).

Milestones in the history of the Universe (not to scale). The intergalactic gas was in a neutral state from about 300,000 years after the Big Bang until light from the first generation of stars and galaxies began to ionize it. The gas was completely ionized after 1 billion years. The LAGER study takes a close look at the state of the Universe at 800 million years (yellow box) to investigate when and how this transformation occurred. Image Credit: NAOJ.



Astronomers studying the distant Universe have found that small star-forming galaxies were abundant when the Universe was only 800 million years old, a few percent of its present age. The results suggest that the earliest galaxies, which illuminated and ionized the Universe, formed at even earlier times.

Long ago, about 300,000 years after the beginning of the Universe (the Big Bang), the Universe was dark. There were as yet no stars and galaxies, and the Universe was filled with neutral hydrogen gas. At some point the first galaxies appeared, and their energetic radiation ionized their surroundings, the intergalactic gas, illuminating and transforming the Universe.

While this dramatic transformation is known to have occurred sometime in the interval between 300 million years and 1 billion years after the Big Bang, determining when the first galaxies formed is a challenge. The intergalactic gas, which is initially neutral, strongly absorbs and scatters the ultraviolet light emitted by the galaxies, making them difficult to detect.

To home in on when the transformation occurred, astronomers take an indirect approach. Using the demographics of small star-forming galaxies to determine when the intergalactic gas became ionized, they can infer when the ionizing sources, the first galaxies, formed. If star forming galaxies, which glow in the light of the hydrogen Lyman alpha line, are surrounded by neutral hydrogen gas, the Lyman alpha photons are readily scattered, much like headlights in fog, obscuring the galaxies. When the gas is ionized, the fog lifts, and the galaxies are easier to detect.

A new study taking this approach has discovered 23 candidate Lyman alpha emitting galaxies (LAEs) that were present 800 million years after the Big Bang (at a redshift of z~7), the largest sample detected to date at that epoch. The study, “Lyman-Alpha Galaxies in the Epoch of Reionization” (LAGER), was carried out by an international team of astronomers from China, the US, and Chile using the Dark Energy Camera (DECam) on the CTIO 4-m Blanco telescope.

While the study detected many LAEs, it also found that LAEs were 4 times less common at 800 million years than they were a short time later, at 1 billion years (at a redshift of z~5.7). The results imply that the process of ionizing the Universe began early and was still incomplete at 800 million years, with the intergalactic gas about half neutral and half ionized at that epoch. The low incidence rate of LAEs at 800 million years results from the suppression of their Lyman alpha emission by neutral intergalactic gas.

The study shows that “the fog was already lifting when the universe was 5% of its current age”, explained Sangeeta Malhotra (Goddard Space Flight Center and Arizona State University), one of the co-leads of the survey.

Junxian Wang (USTC), the organizer of the study, further explained, “Our finding that the intergalactic gas is 50% ionized at z ~ 7 implies that a large fraction of the first galaxies that ionized and illuminated the universe formed early, less than 800 million years after the Big Bang.”

For Zhenya Zheng (Shanghai Astronomical Observatory, CAS), the lead author of the paper describing these results, “800 million years is the current frontier in reionization studies.” While hundreds of LAEs have been found at later epochs, only about two dozen candidate LAEs were known at 800 million years prior to the current study. The new results dramatically increase the number of LAEs known at this epoch.

“None of this science would have been possible without the widefield capabilities of DECam and its community pipeline for data reduction,” remarked coauthor James Rhoads. “These capabilities enable efficient surveys and thereby the discovery of faint galaxies as well as rare, bright ones.”

To build on these results, the team is “continuing the search for distant star forming galaxies over a larger volume of the Universe”, said Leopoldo Infante (Pontificia Catolica University of Chile and the Carnegie Institution for Science), “to study the clustering of LAEs.” Clustering provides unique insights into how the fog lifts. The team is also investigating the nature of these distant galaxies.



Reference: 


Preprint: https://arxiv.org/abs/1703.02985

Cerro Tololo Inter-American Observatory is managed by the National Optical Astronomy Observatory, which is operated by the Association of Universities for Research in Astronomy Inc. (AURA) under a cooperative agreement with the National Science Foundation.



Science Contacts


Dr. Junxian Wang
Department of Astronomy
University of Science and Technology of China
96 Jinzhai Road Hefei, Anhui 230026 China
Email: jxw@ustc.edu.cn

Dr. Sangeeta Malhotra
ASU School of Earth and Space Exploration
and
Astrophysics Science Division,
Goddard Space Flight Center
8800 Greenbelt Road
Greenbelt, Maryland 20771
Email: sangeeta.malhotra@asu.edu


Thursday, July 13, 2017

W51: Chandra Peers into a Nurturing Cloud

W51/G49.5−0.4 
Credit: X-ray: NASA/CXC/PSU/L.Townsley et al; Infrared: NASA/JPL-Caltech


animation




In the context of space, the term 'cloud' can mean something rather different from the fluffy white collections of water in the sky or a way to store data or process information. Giant molecular clouds are vast cosmic objects, composed primarily of hydrogen molecules and helium atoms, where new stars and planets are born. These clouds can contain more mass than a million suns, and stretch across hundreds of light years.

The giant molecular cloud known as W51 is one of the closest to Earth at a distance of about 17,000 light years. Because of its relative proximity, W51 provides astronomers with an excellent opportunity to study how stars are forming in our Milky Way galaxy.

A new composite image of W51 shows the high-energy output from this stellar nursery, where X-rays from Chandra are colored blue. In about 20 hours of Chandra exposure time, over 600 young stars were detected as point-like X-ray sources, and diffuse X-ray emission from interstellar gas with a temperature of a million degrees or more was also observed. Infrared light observed with NASA's Spitzer Space Telescope appears orange and yellow-green and shows cool gas and stars surrounded by disks of cool material.

W51 contains multiple clusters of young stars. The Chandra data show that the X-ray sources in the field are found in small clumps, with a clear concentration of more than 100 sources in the central cluster, called G49.5−0.4 (pan over the image to find this source.)

Although the W51 giant molecular cloud fills the entire field-of-view of this image, there are large areas where Chandra does not detect any diffuse, low energy X-rays from hot interstellar gas. Presumably dense regions of cooler material have displaced this hot gas or blocked X-rays from it.

X-ray Image of W51 (cropped)


One of the massive stars in W51 is a bright X-ray source that is surrounded by a concentration of much fainter X-ray sources, as shown in a close-up view of the Chandra image. This suggests that massive stars can form nearly in isolation, with just a few lower mass stars rather than the full set of hundreds that are expected in typical star clusters.

Another young, massive cluster located near the center of W51 hosts a star system that produces an extraordinarily large fraction of the highest energy X-rays detected by Chandra from W51. Theories for X-ray emission from massive single stars can't explain this mystery, so it likely requires the close interaction of two very young, massive stars. Such intense, energetic radiation must change the chemistry of the molecules surrounding the star system, presenting a hostile environment for planet formation.

A paper describing these results, led by Leisa Townsley (Penn State), appeared in the July 14th 2014 issue of The Astrophysical Journal Supplement Series and is available online.

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 W51:

Scale: Image is about 20 arcmin (100 light years) across
Category: Normal Stars & Star Clusters
Coordinates (J2000): RA 19h 23m 50s | Dec 14° 06´ 00"
Constellation: Aquila
Observation Date: 2 pointings in June 2003
Observation Time: 20 hours 10 min
Obs. ID: 2524, 3711
Instrument: ACIS
References: Townsley, L. et al., 2014, ApJS, 213, 1; arXiv:1403.2576
Color Code: X-ray (Blue), Infrared (Yellow-Orange)
Distance Estimate: About 17,000 light years


Wednesday, July 12, 2017

UA Astronomers Track the Birth of a 'Super-Earth'

This is an artist’s impression of a young star surrounded by a protoplanetary disk in which planets (not shown to scale) are forming. 
Illustration: ESO/L. Calçada


The protoplanetary disk around HL Tau, a million-year-old sunlike star located approximately 450 light-years from Earth in the constellation of Taurus, dwarfs our solar system (right). Taken by the ALMA array, this image reveals a series of concentric and bright rings, separated by gaps — features astronomers have struggled to explain until now. Credit: ALMA (ESO/NAOJ/NRAO)

The protoplanetary disk around HL Tau, a million-year-old sunlike star located approximately 450 light-years from Earth in the constellation of Taurus, dwarfs our solar system (right). Taken by the ALMA array, this image reveals a series of concentric and bright rings, separated by gaps — features astronomers have struggled to explain until now. (Credit: ALMA (ESO/NAOJ/NRAO))

Ruobing Dong, currently the Bart J. Bok Fellow at the UA's Steward Observatory, is interested in exoplanets and, in particular, how they form from protoplanetary disks surrounding newly born stars.



"Synthetic observations" simulating nascent planetary systems could help explain a puzzle that has vexed astronomers for a long time.

A new model giving rise to young planetary systems offers a fresh solution to a puzzle that has vexed astronomers ever since new detection technologies and planet-hunting missions such as NASA's Kepler space telescope have revealed thousands of planets orbiting other stars: While the majority of these exoplanets fall into a category called super-Earths — bodies with a mass somewhere between Earth and Neptune — most of the features observed in nascent planetary systems were thought to require much more massive planets, rivaling or dwarfing Jupiter, the gas giant in our solar system.

In other words, the observed features of many planetary systems in their early stages of formation did not seem to match the type of exoplanets that make up the bulk of the planetary population in our galaxy.

"We propose a scenario that was previously deemed impossible: how a super-Earth can carve out multiple gaps in disks," says Ruobing Dong, the Bart J. Bok postdoctoral fellow at the University of Arizona's Steward Observatory and lead author on the study, soon to be published in the Astrophysical Journal. "For the first time, we can reconcile the mysterious disk features we observe and the population of planets most commonly found in our galaxy."

How exactly planets form is still an open question with a number of outstanding problems, according to Dong.

"Kepler has found thousands of planets, but those are all very old, orbiting around stars a few billion years old, like our sun," he explains. "You could say we are looking at the senior citizens of our galaxy, but we don't know how they were born."

To find answers, astronomers turn to the places where new planets are currently forming: protoplanetary disks — in a sense, baby sisters of our solar system.

Such disks form when a vast cloud of interstellar gas and dust condenses under the effect of gravity before collapsing into a swirling disk. At the center of the protoplanetary disk shines a young star, only a few million years old. As microscopic dust particles coalesce to sand grains, and sand grains stick together to form pebbles, and pebbles pile up to become asteroids and ultimately planets, a planetary system much like our solar system is born.

"These disks are very short-lived," Dong explains. "Over time the material dissipates, but we don't know exactly how that happens. What we do know is that we see disks around stars that are 1 million years old, but we don't see them around stars that are 10 million years old."

In the most likely scenario, much of the disk's material gets accreted onto the star, some is blown away by stellar radiation and the rest goes into forming planets.

Although protoplanetary disks have been observed in relative proximity to the Earth, it is still extremely difficult to make out any planets that may be forming within. Rather, researchers have relied on features such as gaps and rings to infer the presence of planets.

"Among the explanations for these rings and gaps, those involving planets certainly are the most exciting and drawing the most attention," says co-author Shengtai Li, a research scientist at Los Alamos National Laboratory in Los Alamos, New Mexico. "As the planet orbits around the star, the argument goes, it may clear a path along its orbit, resulting in the gap we see."

Except that reality is a bit more complicated, as evidenced by two of the most prominent observations of protoplanetary disks, which were made with ALMA, the Atacama Large Millimeter/submillimeter Array in Chile. ALMA is an assembly of radio antennas between 7 and 12 meters in diameter and numbering 66 of them once completed. The images of HL Tau and TW Hydra, obtained in 2014 and 2016, respectively, have revealed the finest details so far in any protoplanetary disk, and they show some features that are difficult, if not impossible, to explain with current models of planetary formation, Dong says.

"Among the gaps in HL Tau and TW Hya revealed by ALMA, two pairs of them are extremely narrow and very close to each other," he explains. "In conventional theory, it is difficult for a planet to open such gaps in a disk. They can never be this narrow and this close to each other for reasons of the physics involved."

In the case of HL Tau and TW Hya, one would have to invoke two planets whose orbits hug each other very closely — a scenario that would not be stable over time and therefore is unlikely.

While previous models could explain large, single gaps believed to be indicative of planets clearing debris and dust in their path, they failed to account for the more intricate features revealed by the ALMA observations. The model created by Dong and his co-authors results in what the team calls synthetic observations — simulations that look exactly like what ALMA would see on the sky. Dong's team accomplished this by tweaking the parameters going into the simulation of the evolving protoplanetary disk, such as assuming a low viscosity and adding the dust to the mix. Most previous simulations were based on higher disk viscosity and accounted only for the disk's gaseous component.

"The viscosity in protoplanetary disks may be driven by turbulence and other physical effects," Li says. "It's a somewhat mysterious quantity — we know it's there, but we don't know its origin or how large its value is, so we think our assumptions are reasonable, considering that they result in the pattern that has actually been observed on the sky."

Even more important, the synthetic observations emerged from the simulations without the necessity to invoke gas giants the size of Jupiter or larger.

"One super-Earth turned out to be sufficient to create the multiple rings and multiple, narrow gaps we see in the actual observations," Dong says.

As future research uncovers more of the inner workings of protoplanetary disks, Dong and his team will refine their simulations with new data. For now, their synthetic observations offer an intriguing scenario that provides a missing link between the features observed in many planetary infants and their grown-up counterparts.

The study, "Multiple Disk Gaps and Rings Generated by a Single Super-Earth," by Ruobing Dong, Shentai Li, Eugene Chiang and Hui Li, will be published on July 13 in the Astrophysical Journal.

This simulation of a lone super-Earth in a protoplanetary disk takes into account the effects of dust in addition to gas, resulting in a much more realistic picture. After 2,000 orbits, narrow gaps and multiple ring features emerge, just like those seen in actual observations such as the ones by ALMA. Credit: Shengtai Li and Ruobing Dong




Tuesday, July 11, 2017

Re-Making Planets after Star-Death

Data at wavelength of 0.45 mm, combined from SCUBA and SCUBA-2, in a false-colour image. The Geminga pulsar (inside the black circle) is moving towards the upper left, and the orange dashed arc and cylinder show the ‘bow-wave’ and a ‘wake’. The region shown is 1.3 light-years across; the bow-wave probably stretches further behind Geminga, but SCUBA imaged only the 0.4 light-years in the centre. (Credit: Jane Greaves / JCMT / EAO)



Two UK astronomers may have found an answer to the 25-year-old mystery of how planets form in the aftermath of a supernova explosion.

Astronomers Dr Jane Greaves, of the University of Cardiff, and Dr Wayne Holland, of STFC’s UK Astronomy Technology Centre in Edinburgh presented their work this week at the National Astronomy Meeting at the University of Hull.

The first planets outside our solar system were only discovered 25 years ago – not around a normal star like our Sun, but instead orbiting a tiny, super-dense 'neutron star'. These remnants are left over after a supernova, the titanic explosion of a star many times more massive than our own.

Such 'planets in the dark' have turned out to be incredibly rare, and astronomers are puzzled over where they come from. The supernova explosion should destroy any pre-existing planets, and so the neutron star needs to capture more raw materials to form its new companions. These after-death planets can be detected because their gravitational pull alters the times of arrival of radio pulses from the neutron star, or 'pulsar', that otherwise pass us by extremely regularly.

Greaves and Holland believe they have found a way for this to happen. Greaves explains: "We started looking for the raw materials soon after the pulsar planets were announced. We had one target, the Geminga pulsar located 800 light years away in the constellation of Gemini. Astronomers thought they'd found a planet there in 1997, but later discounted it because of glitches in the timing. So it was much later when I went through our sparse data and tried to make an image."

The two scientists observed Geminga using the James Clerk Maxwell Telescope (JCMT), which operates at submillimetre wavelengths, sited on Hawaii. The light the astronomers detected has a wavelength of about half a millimetre, is invisible to the human eye, and struggles to get through the Earth's atmosphere.

Holland, part of the group that built the JCMT camera the team used – called 'SCUBA' – notes: "What we saw was very faint. To be sure, we went back to it in 2013 with the new camera our Edinburgh-based team had built, SCUBA-2, which we also put on JCMT. Combining the two sets of data helped to ensure we weren't just seeing some faint artefacts."

Both images showed a signal towards the pulsar, plus an arc around it. Greaves adds: "This seems to be like a bow-wave – Geminga is moving incredibly fast through our Galaxy, much faster than the speed of sound in interstellar gas. We think material gets caught up in the bow-wave, and then some solid particles drift in towards the pulsar."

Her calculations suggest that this trapped interstellar 'grit' adds up to at least a few times the mass of the Earth. So the raw materials could be enough to make future planets.

Greaves cautions that more data is still needed to tackle this quarter of a century old puzzle: "Our image is quite fuzzy, so we've applied for time on the international Atacama Large Millimetre Array – ALMA – to get more detail. We're certainly hoping to see this space-grit orbiting nicely around the pulsar, rather than some distant blob of Galactic background!"

If ALMA data confirm their new model for Geminga, the team hope to explore some similar pulsar systems, and contribute to testing ideas of planet formation by seeing it happen in exotic environments. This will add weight to the idea that planet birth is commonplace in the universe.



Contact

Jake Gilmore
STFC Media Manager



Further information

The new work appears in: "The Geminga pulsar wind nebula in the mid-infrared and submillimetre", J. S. Greaves and W. S. Holland, Monthly Notices of the Royal Astronomical Society Letters, in press. A preprint of the paper is available here.



UKATC

UKATC Based at the Royal Observatory in Edinburgh and operated by STFC, the UK Astronomy Technology Centre (UK ATC) is the national centre for astronomical technology. The UK ATC designs and builds instruments for many of the world’s major telescopes. It also project manages UK and international collaborations and its scientists carry out observational and theoretical research into questions such as the origins of planets and galaxies. The UK ATC has been at the forefront of previous key initiatives at the VLT, including the construction of KMOS (K-band Multi-Object Spectrograph) which enables 24 objects to be observed simultaneously in infrared light.

Cardiff University School of Physics and Astronomy


Monday, July 10, 2017

Odd planetary system around fast-spinning star doesn't quite fit existing models of planet formation

Image of the planet HIP 65426b (bottom left), produced with the SPHERE instrument. SPHERE has physically blocked out light from the central star (blocked-out region marked by circle) in order for the planets much weaker light to become detectable. The light received from the planet allows deductions about its properties – in this case the presence of water vapor and reddish clouds.Image: Chauvin et al. / SPHERE



Astronomers have discovered a rare, warm, massive Jupiter-like planet orbiting a star that is rotating extremely quickly. The discovery raises puzzling questions about planet formation – neither the planet's comparatively small mass nor its large distance from its host star are expected according to current models. The observations that led to the discovery were made using the SPHERE instrument at ESO's very large telescope. The article describing the results has been accepted for publication in the journal Astronomy & Astrophysics.

Paraphrasing Isaac Asimov, scientific progress is announced not so much by “Eureka!” than by “Hm, this is odd!” The newly discovered planetary system HIP 65426 is a case in point: With a central star in ultrafast rotation, the absence of a gas disk one would have expected for a system 14 million years old and a comparatively light, distant planet, the system doesn't quite fit the existing models for how planetary systems come into being.

Planets are formed in gigantic disks of gas and dust that surround young stars. In the young planetary systems that have been found so far, including all of those observed with the SPHERE instrument, remnants of the disk are usually still visible. There is some degree of correlation in mass: massive stars tend to have more massive disks, forming more massive planets.

Enter HIP 65426b, a planet newly discovered by a group of astronomers that includes researchers from the Max Planck Institute for Astronomy (MPIA), and its host system. HIP 65426b was discovered with the SPHERE instrument at the Very Large Telescope at ESO's Paranal Observatory in Chile, which took a direct image of the planet. The central star, HIP 65426, is part of what might be termed a stellar kindergarten: the Scorpius-Centaurus association which contains between 3000 and 5000 stars that formed at approximately the same time, at a distance of almost 400 light-years from Earth. Applying common astronomical techniques for dating stars both to HIP 65426 individually and to its stellar neighbors, it follows that HIP 65426 is only about 14 million years old.
Gael Chauvin of the University of Grenoble and the University of Chile, the lead author of the study, says: "We would expect a planetary system this young to still have a disk of dust, which could show up in observations. HIP 65426 does not have such a disk known for the moment – a first indication that this system doesn't quite fit our classical models of planetary formation."

An unusual planet

There is, however, the planet HIP 65426b. Comparing the direct observations with suitable models, HIP 65426b is a warm Jupiter-like planet, with a temperature of about 1300-1600 Kelvin (1000-1300 degrees Celsius), about 1.5 times the radius of Jupiter, and between 6 and 12 times Jupiter's mass. This would make HIP 65426b a gas giant, like Jupiter, with a solid core and thick layers of (mostly hydrogen) gas. Indeed, spectral examinations using SPHERE's spectrograph indicate the presence of water vapor and reddish clouds, similar to Jupiter's. The planet is far out, orbiting its host star at 100 astronomical units (100 times the average Earth-Sun distance, and more than four times Neptune's distance from the Sun).

Again, this represents various levels of oddness: Stars of the type of HIP 65426 (spectral class A2V) are expected to have about twice the mass of the Sun; it has long been assumed that such a star would have much more massive giant planets than the 6-12 Jupiter masses of HIP 65426b. On the other hand, such giant planets would not be expected as far out as HIP 65426b.

Last but not least, the host star HIP 65426 is special, as well: According to spectra taken with ESO's HARPS spectrograph, it rotates about 150 times as fast as the Sun. There is only one other star of similar type that is rotating as fast, and that one is part of a binary star system. In such a system, matter transfer from one star to the other can spin up the receiving star. How a single star could have sped up that much requires an explanation.

The origin of HIP 654426b: a system-wide drama?

So far, the astronomers can only speculate about the origin of the newly discovered system's peculiar properties. A possible scenario involves a regular planetary-scale drama: Initially, HIP 65426b would have formed much closer to the star (explaining its comparatively low mass), and at least one other massive body would have formed as well. At some point, HIP 65426b and that other body would have come close enough for HIP 65426b to be catapulted outwards (up to its current great distance) and the other body moving inwards and merging with the star (causing the star's rapid rotation). The planets traversing the system could also have destabilized the disk, explaining why it did not survive long enough to be observed.

An alternative explanation would involve particular dynamics of the protoplanetary disk, with both the star and the planet forming by collapse at the same time by fragmentation – which would still require an explanation for why the disk was so short-lived to have vanished by now.
More definite explanations will have to wait for additional observations and simulations. They could have an impact on our understanding of how gas giants form, evolve, and possibly migrate, in general. This, in turn, is crucial for understanding the formation of planetary systems as a whole: the mass of the host star aside, most of the mass in a planetary system is carried by such giant planets, and the presence and properties of such planets has a decisive influence on the formation of their smaller cousins, such as Earth-like planets or Super-Earths.

For the SPHERE team, the discovery holds an additional special significance. This is the first planet discovered using the SPHERE instrument. MPIA director Thomas Henning, who is one of the fathers of the SPHERE instrument and a co-author of the present study, adds: "Direct images of exoplanets are still very rare, but they contain a wealth of information about planets such as HIP 65426b. The analysis of the direct light of the planet allows us to constrain the composition of the planet's atmosphere with great confidence. " Images exist for less than 20 of the currently known 3600 exoplanets; the common methods of detection are all indirect, relying as they do on how the presence of a planet influences the host star's light. Direct imaging is very difficult, given that stars are so bright their light drowns out any light from surrounding planets. SPHERE has been designed to optimally suppress the stars' light, allowing for images and spectra of surrounding planets. So far, direct imaging is the only way to detect planets whose distance from their host star is large – planets such as the unusual HIP 65426b.




Back Ground information


The research described here was published as G. Chauvin et al., "Discovery of a warm, dusty giant planet around HIP 65426" in the journal Astronomy and Astrophysics.

E-print of the article at arXiv

The MPIA researchers involved are Markus Feldt, Beth Biller (also University of Edinburgh), A.-L. Maire, J. Olofsson (also Universidad de Valparaíso), M. Samland, M. Janson (also Stockholm University), M. Keppler, G. D. Marleau (also University of Bern), Paul Mollière, Christoph Mordasini (also University of Bern), A. Müller, Thomas Henning, O. Möller-Nilsson, A. Pavlov, J. Ramos, Wolfgang Brandner, Taisyia Kopytova (also University of Arizona), J. Schlieder (also NASA Goddard Space Flight Center).

The SPHERE consortium is composed of 12 major European institutions which designed and built the SPHERE planet imager for the ESO's Very Large Telescope (eso1417): Institut de Planétologie et d'Astrophysique de Grenoble; Max-Planck-Institut für Astronomie in Heidelberg; Laboratoire d’Astrophysique de Marseille; Laboratoire d’Etudes Spatiales et d’Instrumentation en Astrophysique de l’Observatoire de Paris; Laboratoire Lagrange in Nice; ONERA; Observatoire de Genève; Italian National Institute for Astrophysics coordinated by the Osservatorio Astronomico di Padova; Institute for Astronomy, ETH Zurich; Astronomical Institute of the University of Amsterdam; Netherlands Research School for Astronomy (NOVA-ASTRON) and ESO.



Science Contact

Dr. Markus Feldt
(SPHERE CO-PI)
Phone:+49 6221 528-262
Email: feldt@mpia.de
Max-Planck-Institute for Astronomy, Heidelberg, Germany

Prof. Dr. Thomas Henning
Director - Max Planck Institute for Astronomy; Professor at the University of Heidelberg
Phone:+49 6221 528-200
Email: henning@mpia-hd.mpg.de
Max Planck Institute for Astronomy, Königstuhl 17, 69117 Heidelberg
Personal homepage
MPIA Heidelberg



Public Information Officer

Markus Pössel
Public Information Officer
Phone:(+49|0) 6221 528-261
Email: pr@mpia.de


Saturday, July 08, 2017

Hubble’s Hidden Galaxy

Credit:  ESA/Hubble & NASA


IC 342 is a challenging cosmic target. Although it is bright, the galaxy sits near the equator of the Milky Way’s galactic disc, where the sky is thick with glowing cosmic gas, bright stars, and dark, obscuring dust. In order for astronomers to see the intricate spiral structure of IC 342, they must gaze through a large amount of material contained within our own galaxy — no mean feat! As a result IC 342 is relatively difficult to spot and image, giving rise to its intriguing nickname: the “Hidden Galaxy”.

Located very close (in astronomical terms!) to the Milky Way, this sweeping spiral galaxy would be among the brightest in the sky were it not for its dust-obscured location. The galaxy is very active, as indicated by the range of colours visible in this NASA/ESA Hubble Space Telescope image, depicting the very central region of the galaxy. A beautiful mixture of hot, blue star-forming regions, redder, cooler regions of gas, and dark lanes of opaque dust can be seen, all swirling together around a bright core. In 2003, astronomers confirmed this core to be a specific type of central region known as an HII nucleus — a name that indicates the presence of ionised hydrogen — that is likely to be creating many hot new stars.