Large, Distant Comets More Common Than Previously Thought

This illustration shows how scientists used data from NASA's WISE spacecraft to determine the nucleus sizes of comets. They subtracted a model of how dust and gas behave in comets in order to obtain the core size. Credit: NASA/JPL-Caltech. › Larger view

Comets that take more than 200 years to make one revolution around the Sun are notoriously difficult to study. Because they spend most of their time far from our area of the solar system, many "long-period comets" will never approach the Sun in a person's lifetime. In fact, those that travel inward from the Oort Cloud -- a group of icy bodies beginning roughly 186 billion miles (300 billion kilometers) away from the Sun -- can have periods of thousands or even millions of years.

NASA's WISE spacecraft, scanning the entire sky at infrared wavelengths, has delivered new insights about these distant wanderers. Scientists found that there are about seven times more long-period comets measuring at least 0.6 miles (1 kilometer) across than had been predicted previously. They also found that long-period comets are on average up to twice as large as "Jupiter family comets," whose orbits are shaped by Jupiter's gravity and have periods of less than 20 years. 

Researchers also observed that in eight months, three to five times as many long-period comets passed by the Sun than had been predicted. The findings are published in the Astronomical Journal.

"The number of comets speaks to the amount of material left over from the solar system's formation," said James Bauer, lead author of the study and now a research professor at the University of Maryland, College Park. "We now know that there are more relatively large chunks of ancient material coming from the Oort Cloud than we thought."

The Oort Cloud is too distant to be seen by current telescopes, but is thought to be a spherical distribution of small icy bodies at the outermost edge of the solar system. The density of comets within it is low, so the odds of comets colliding within it are rare. Long-period comets that WISE observed probably got kicked out of the Oort Cloud millions of years ago. The observations were carried out during the spacecraft's primary mission before it was renamed NEOWISE and reactivated to target near-Earth objects (NEOs).

"Our study is a rare look at objects perturbed out of the Oort Cloud," said Amy Mainzer, study co-author based at NASA's Jet Propulsion Laboratory, Pasadena, California, and principal investigator of the NEOWISE mission. "They are the most pristine examples of what the solar system was like when it formed."

Astronomers already had broader estimates of how many long-period and Jupiter family comets are in our solar system, but had no good way of measuring the sizes of long-period comets. That is because a comet has a "coma," a cloud of gas and dust that appears hazy in images and obscures the cometary nucleus. But by using the WISE data showing the infrared glow of this coma, scientists were able to "subtract" the coma from the overall comet and estimate the nucleus sizes of these comets. The data came from 2010 WISE observations of 95 Jupiter family comets and 56 long-period comets.

The results reinforce the idea that comets that pass by the Sun more often tend to be smaller than those spending much more time away from the Sun. That is because Jupiter family comets get more heat exposure, which causes volatile substances like water to sublimate and drag away other material from the comet's surface as well. 

"Our results mean there's an evolutionary difference between Jupiter family and long-period comets," Bauer said.

The existence of so many more long-period comets than predicted suggests that more of them have likely impacted planets, delivering icy materials from the outer reaches of the solar system. 

Researchers also found clustering in the orbits of the long-period comets they studied, suggesting there could have been larger bodies that broke apart to form these groups. 

The results will be important for assessing the likelihood of comets impacting our solar system's planets, including Earth. 

"Comets travel much faster than asteroids, and some of them are very big," Mainzer said. "Studies like this will help us define what kind of hazard long-period comets may pose." 

NASA's Jet Propulsion Laboratory in Pasadena, California, managed and operated WISE for NASA's Science Mission Directorate in Washington. The NEOWISE project is funded by the Near Earth Object Observation Program, now part of NASA's Planetary Defense Coordination Office. The spacecraft was put into hibernation mode in 2011 after twice scanned the entire sky, thereby completing its main objectives. In September 2013, WISE was reactivated, renamed NEOWISE and assigned a new mission to assist NASA's efforts to identify potentially hazardous near-Earth objects.

For more information on WISE, visit:  https://www.nasa.gov/wise


News Media Contact

Elizabeth Landau
Jet Propulsion Laboratory, Pasadena, Calif.
818-354-6425
elizabeth.landau@jpl.nasa.gov

Source: JPL-Caltech/News

Comet Pan-STARRS Marches Across the Sky

NASA's NEOWISE mission captured a series of infrared images of comet C/2012 K1 -- also referred to as comet Pan-STARRS -- as it swept across our skies in May 2014.  Full image and caption

 

NEOWISE Spies Comet Pan-STARRS Against Galaxy Backdrop

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NASA's NEOWISE mission captured a series of pictures of comet C/2012 K1 -- also known as comet Pan-STARRS -- as it swept across our skies in May 2014.

The comet is named after the astronomical survey project called the Panoramic Survey Telescope and Rapid Response System in Hawaii, which discovered the icy visitor in May 2012. 

Comet Pan-STARRS hails from the outer fringes of our solar system, from a vast and distant reservoir of comets called the Oort cloud. 

The comet is relatively close to us -- it was only about 143 million miles (230 million kilometers) from Earth when this picture was taken. It is seen passing a much more distant spiral galaxy, called NGC 3726, which is about 55 million light-years from Earth, or 2 trillion times farther away than the comet.

Two tails can be seen lagging behind the head of the comet. The bigger tail is easy to see and is comprised of gas and smaller particles. A fainter, more southern tail, which is hard to spot in this image, may be comprised of larger, more dispersed grains of dust.

Comet Pan-STARRS is on its way around the sun, with its closest approach to the sun occurring in late August. It was visible to viewers in the northern hemisphere through most of June. In the fall, after the comet swings back around the sun, it may be visible to southern hemisphere viewers using small telescopes.

The image was made from data collected by the two infrared channels on board the NEOWISE spacecraft, with the longer-wavelength channel (centered at 4.5 microns) mapped to red and the shorter-wavelength channel (3.4 microns) mapped to cyan. The comet appears brighter in the longer wavelength band, suggesting that the comet may be producing significant quantities of carbon monoxide or carbon dioxide.

Originally called the Wide-field Infrared Survey Explorer (WISE), the NEOWISE spacecraft was put into hibernation in 2011 after its primary mission was completed. In September 2013, it was reactivated, renamed NEOWISE and assigned a new mission to assist NASA's efforts to identify the population of potentially hazardous near-Earth objects. NEOWISE is also characterizing previously known asteroids and comets to better understand their sizes and compositions.

NASA's Jet Propulsion Laboratory, Pasadena, California, manages the NEOWISE mission for NASA's Near-Earth Object Observation Program of its Planetary Science Division 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 the California Institute of Technology in Pasadena. Caltech manages JPL for NASA.

More information on NEOWISE is online at: http://www.nasa.gov/wise and http://www.jpl.nasa.gov/wise/

Whitney Clavin
Jet Propulsion Laboratory, Pasadena, Calif.
818-354-4673
whitney.clavin@jpl.nasa.gov

Source: JPL-Caltech

NASA's WISE Findings Poke Hole in Black Hole 'Doughnut' Theory

Active, supermassive black holes at the hearts of galaxies tend to fall into two categories: those that are hidden by dust, and those that are exposed. Image credit: NASA/JPL-Caltech.   Full image and caption

This infographic explains a popular theory of active supermassive black holes, referred to as the unified model -- and how new data from NASA's Wide-field Infrared Survey Explorer, or WISE, is at conflict with the model. Image credit: NASA/JPL-Caltech/NOAO/AURA/NSF/ESO. Full image and caption -  enlarge image

A survey of more than 170,000 supermassive black holes, using NASA's Wide-field Infrared Survey Explorer (WISE), has astronomers reexamining a decades-old theory about the varying appearances of these interstellar objects.

The unified theory of active, supermassive black holes, first developed in the late 1970s, was created to explain why black holes, though similar in nature, can look completely different. Some appear to be shrouded in dust, while others are exposed and easy to see.

The unified model answers this question by proposing that every black hole is surrounded by a dusty, doughnut-shaped structure called a torus. Depending on how these "doughnuts" are oriented in space, the black holes will take on various appearances. For example, if the doughnut is positioned so that we see it edge-on, the black hole is hidden from view. If the doughnut is observed from above or below, face-on, the black hole is clearly visible.

However, the new WISE results do not corroborate this theory. The researchers found evidence that something other than a doughnut structure may, in some circumstances, determine whether a black hole is visible or hidden. The team has not yet determined what this may be, but the results suggest the unified, or doughnut, model does not have all the answers.

"Our finding revealed a new feature about active black holes we never knew before, yet the details remain a mystery," said Lin Yan of NASA's Infrared Processing and Analysis Center (IPAC), based at the California Institute of Technology in Pasadena. "We hope our work will inspire future studies to better understand these fascinating objects."

Yan is the second author of the research accepted for publication in the Astrophysical Journal. The lead author is a post-doctoral researcher, Emilio Donoso, who worked with Yan at IPAC and has since moved to the Instituto de Ciencias Astronómicas, de la Tierra y del Espacio in Argentina. The research also was co-authored by Daniel Stern at NASA's Jet Propulsion Laboratory in Pasadena, California, and Roberto Assef of Universidad Diego Portales in Chile and formerly of JPL.

Every galaxy has a massive black hole at its heart. The new study focuses on the "feeding" ones, called active, supermassive black holes, or active galactic nuclei. These black holes gorge on surrounding gas material that fuels their growth. 

With the aid of computers, scientists were able to pick out more than 170,000 active supermassive black holes from the WISE data. They then measured the clustering of the galaxies containing both hidden and exposed black holes -- the degree to which the objects clump together across the sky.

If the unified model were true, and the hidden black holes are simply blocked from view by doughnuts in the edge-on configuration, then researchers would expect them to cluster in the same way as the exposed ones. According to theory, since the doughnut structures would take on random orientations, the black holes should also be distributed randomly. It is like tossing a bunch of glazed doughnuts in the air -- roughly the same percentage of doughnuts always will be positioned in the edge-on and face-on positions, regardless of whether they are tightly clumped or spread far apart.

But WISE found something totally unexpected. The results showed the galaxies with hidden black holes are more clumped together than those of the exposed black holes. If these findings are confirmed, scientists will have to adjust the unified model and come up with new ways to explain why some black holes appear hidden. 

"The main purpose of unification was to put a zoo of different kinds of active nuclei under a single umbrella," said Donoso. Now, that has become increasingly complex to do as we dig deeper into the WISE data."

Another way to understand the WISE results involves dark matter. Dark matter is an invisible substance that dominates matter in the universe, outweighing the regular matter that makes up people, planets and stars. Every galaxy sits in the center of a dark matter halo. Bigger halos have more gravity and, therefore, pull other galaxies toward them.

Because WISE found that the obscured black holes are more clustered than the others, the researchers know those hidden black holes reside in galaxies with larger dark matter halos. Though the halos themselves would not be responsible for hiding the black holes, they could be a clue about what is occurring.

"The unified theory was proposed to explain the complexity of what astronomers were seeing," said Stern. "It seems that simple model may have been too simple. As Einstein said, models should be made 'as simple as possible, but not simpler.'"

Scientists still are actively combing public data from WISE, which was put into hibernation in 2011 after scanning Earth's entire sky twice. WISE was reactivated in 2013, renamed NEOWISE, and given a new mission to identify potentially hazardous near-Earth objects.

For more information about NEOWISE, visit: http://neo.jpl.nasa.gov/programs/neowise.html

For more information about WISE, visit: http://www.nasa.gov/wise

J.D. Harrington
NASA Headquarters, Washington
202-358-5241
j.d.harrington@nasa.gov

Whitney Clavin
Jet Propulsion Laboratory, Pasadena, Calif.
818-354-4673
whitney.clavin@jpl.nasa.gov

The Search for Seeds of Black Holes

The galaxy NGC 4395 is shown here in infrared light, captured by NASA's Spitzer Space Telescope. Image credit: NASA/JPL-Caltech.  ›Full image and caption

How do you grow a supermassive black hole that is a million to a billion times the mass of our sun? Astronomers do not know the answer, but a new study using data from NASA's Wide-field Infrared Survey Explorer, or WISE, has turned up what might be the cosmic seeds from which a black hole will sprout. The results are helping scientists piece together the evolution of supermassive black holes -- powerful objects that dominate the hearts of all galaxies.

Growing a black hole is not as easy as planting a seed in soil and adding water. The massive objects are dense collections of matter that are literally bottomless pits; anything that falls in will never come out. They come in a range of sizes. The smallest, only a few times greater in mass than our sun, form from exploding stars. The biggest of these dark beasts, billions of times the mass of our sun, grow together with their host galaxies over time, deep in the interiors. But how this process works is an ongoing mystery.

Researchers using WISE addressed this question by looking for black holes in smaller, "dwarf" galaxies. These galaxies have not undergone much change, so they are more pristine than their heavier counterparts. In some ways, they resemble the types of galaxies that might have existed when the universe was young, and thus they offer a glimpse into the nurseries of supermassive black holes.

In this new study, using data of the entire sky taken by WISE in infrared light, up to hundreds of dwarf galaxies have been discovered in which buried black holes may be lurking. Infrared light, the kind that WISE collects, can see through dust, unlike visible light, so it's better able to find the dusty, hidden black holes. The researchers found that the dwarf galaxies' black holes may be about 1,000 to 10,000 times the mass of our sun -- larger than expected for these small galaxies.

"Our findings suggest the original seeds of supermassive black holes are quite massive themselves," said Shobita Satyapal of George Mason University, Fairfax, Va. Satyapal is lead author of a paper published in the March issue of Astrophysical Journal.

Daniel Stern, an astronomer specializing in black holes at NASA's Jet Propulsion Laboratory, Pasadena, Calif., who was not a part of the new study, says the research demonstrates the power of an all-sky survey like WISE to find the rarest black holes. "Though it will take more research to confirm whether the dwarf galaxies are indeed dominated by actively feeding black holes, this is exactly what WISE was designed to do: find interesting objects that stand out from the pack."

The new observations argue against one popular theory of black hole growth, which holds that the objects bulk up in size through galaxy collisions. When our universe was young, galaxies were more likely to crash into others and merge. It is possible the galaxies' black holes merged too, accumulating more mass. In this scenario, supermassive black holes grow in size through a series of galaxy mergers.

The discovery of dwarf galaxy black holes that are bigger than expected suggests that galaxy mergers are not necessary to create big black holes. Dwarf galaxies don't have a history of galactic smash-ups, and yet their black holes are already relatively big.

Instead, supermassive black holes might form very early in the history of the universe. Or, they might grow harmoniously with their host galaxies, feeding off surrounding gas. 

"We still don't know how the monstrous black holes that reside in galaxy centers formed," said Satyapal. "But finding big black holes in tiny galaxies shows us that big black holes must somehow have been created in the early universe, before galaxies collided with other galaxies." 

Other authors of the study include: N.J. Secrest, W. McAlpine and J.L. Rosenberg of George Mason University; S.L. Ellison of the University of Victoria, Canada; and J. Fischer of the Naval Research Laboratory, Washington.

WISE was put into hibernation upon completing its primary mission in 2011. In September 2013, it was reactivated, renamed NEOWISE and assigned a new mission to assist NASA's efforts to identify the population of potentially hazardous near-Earth objects. NEOWISE will also characterize previously known asteroids and comets to better understand their sizes and compositions.

NASA's Jet Propulsion Laboratory, Pasadena, Calif., manages and operates the NEOWISE mission for NASA's Science Mission Directorate. The WISE mission was selected competitively under NASA's Explorers Program managed by the agency's Goddard Space Flight Center in Greenbelt, Md. The science instrument was built by the Space Dynamics Laboratory in Logan, Utah. The spacecraft was built by Ball Aerospace & Technologies Corp. in Boulder, Colo. 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.

More information on WISE and NEOWISE can be found online at: http://www.nasa.gov/wise, http://wise.astro.ucla.edu and http://jpl.nasa.gov/wise

Whitney Clavin 818-354-4673
Jet Propulsion Laboratory, Pasadena, Calif.
whitney.clavin@jpl.nasa.gov

NASA's WISE Survey Finds Thousands of New Stars, But No 'Planet X'

A nearby star stands out in red in this image from the Second Generation Digitized Sky Survey. Image credit: DSS/NASA/JPL-Caltech. Full image and caption

Data from NASA's Wide-field Infrared Survey Explorer, or WISE, has found no evidence for a hypothesized body sometimes referred to as "Planet X." Image credit: Penn State University. Full image and caption - enlarge image

The third closest star system to the sun, called WISE J104915.57-531906, is at the center of the larger image, which was taken by NASA's Wide-field Infrared Survey Explorer (WISE). Image credit: NASA/JPL/Gemini Observatory/AURA/NSF. Full image and caption - enlarge image

After searching hundreds of millions of objects across our sky, NASA's Wide-Field Infrared Survey Explorer (WISE) has turned up no evidence of the hypothesized celestial body in our solar system commonly dubbed "Planet X."

Researchers previously had theorized about the existence of this large, but unseen celestial body, suspected to lie somewhere beyond the orbit of Pluto. In addition to "Planet X," the body had garnered other nicknames, including "Nemesis" and "Tyche."

This recent study, which involved an examination of WISE data covering the entire sky in infrared light, found no object the size of Saturn or larger exists out to a distance of 10,000 astronomical units (au), and no object larger than Jupiter exists out to 26,000 au. One astronomical unit equals 93 million miles. Earth is 1 au, and Pluto about 40 au, from the sun.

"The outer solar system probably does not contain a large gas giant planet, or a small, companion star," said Kevin Luhman of the Center for Exoplanets and Habitable Worlds at Penn State University, University Park, Pa., author of a paper in the Astrophysical Journal describing the results.

But searches of the WISE catalog are not coming up empty. A second study reveals several thousand new residents in our sun's "backyard," consisting of stars and cool bodies called brown dwarfs.

"Neighboring star systems that have been hiding in plain sight just jump out in the WISE data," said Ned Wright of the University of California, Los Angeles, the principal investigator of the mission.

The second WISE study, which concentrated on objects beyond our solar system, found 3,525 stars and brown dwarfs within 500 light-years of our sun.

"We're finding objects that were totally overlooked before," said Davy Kirkpatrick of NASA's Infrared and Processing Analysis Center at the California Institute of Technology, Pasadena, Calif. Kirkpatrick is lead author of the second paper, also in the Astrophysical Journal. Some of these 3,525 objects also were found in the Luhman study, which catalogued 762 objects.

The WISE mission operated from 2010 through early 2011, during which time it performed two full scans of the sky -- with essentially a six-month gap between scans. The survey captured images of nearly 750 million asteroids, stars and galaxies. In November 2013, NASA released data from the AllWISE program, which now enables astronomers to compare the two full-sky surveys to look for moving objects.

In general, the more an object in the WISE images appears to move over time, the closer it is. This visual clue is the same effect at work when one observes a plane flying low to the ground versus the same plane flying at higher altitude. Though traveling at the same speed, the plane at higher altitude will appear to be moving more slowly.

Searches of the WISE data catalog for these moving objects are uncovering some of the closest stars. The discoveries include a star located about 20 light-years away in the constellation Norma, and as reported last March, a pair of brown dwarfs only 6.5 light-years away -- making it the closest star system to be discovered in nearly a century.

Despite the large number of new solar neighbors found by WISE, "Planet X" did not show up. Previous speculations about this hypothesized body stemmed in part from geological studies that suggested a regular timing associated with mass extinctions on Earth. The idea was that a large planet or small star hidden in the farthest reaches of our solar system might periodically sweep through bands of outer comets, sending them flying toward our planet. The Planet X-based mass extinction theories were largely ruled out even prior to the new WISE study.

Other theories based on irregular comet orbits had also postulated a Planet X-type body. The new WISE study now argues against these theories as well.

Both of the WISE searches were able to find objects the other missed, suggesting many other celestial bodies likely await discovery in the WISE data.

"We think there are even more stars out there left to find with WISE. We don't know our own sun's backyard as well as you might think," said Wright.

WISE was put into hibernation upon completing its primary mission in 2011. In September 2013, it was reactivated, renamed NEOWISE and assigned a new mission to assist NASA's efforts to identify the population of potentially hazardous near-Earth objects. NEOWISE will also characterize previously known asteroids and comets to better understand their sizes and compositions.

JPL managed and operated WISE for NASA's Science Mission Directorate. The mission was selected competitively under NASA's Explorers Program managed by the agency's Goddard Space Flight Center in Greenbelt, Md. The science instrument was built by the Space Dynamics Laboratory in Logan, Utah. The spacecraft was built by Ball Aerospace & Technologies Corp. in Boulder, Colo. 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. More information is online at: http://www.nasa.gov/wise and http://wise.astro.ucla.edu and http://jpl.nasa.gov/wise.

 Contact:

Whitney Clavin
Jet Propulsion Laboratory, Pasadena, Calif.
818-354-4673 
Email: whitney.clavin@jpl.nasa.gov

J.D. Harrington
Headquarters, Washington
202-358-5241
Email: j.d.harrington@nasa.gov

Where the Wild Stars Are

Radiation and winds from massive stars have blown a cavity into the surrounding dust and gas, creating the Trifid nebula, as seen here in infrared light by NASA's Wide-field Infrared Survey Explorer, or WISE. Image credit: NASA/JPL-Caltech/UCLA.  Larger image

A storm of stars is brewing in the Trifid nebula, as seen in this view from NASA's Wide-field Infrared Survey Explorer, or WISE. The stellar nursery, where baby stars are bursting into being, is the yellow-and-orange object dominating the picture. Yellow bars in the nebula appear to cut a cavity into three sections, hence the name Trifid nebula.

Colors in this image represent different wavelengths of infrared light detected by WISE. The main green cloud is made up of hydrogen gas. Within this cloud is the Trifid nebula, where radiation and winds from massive stars have blown a cavity into the surrounding dust and gas, and presumably triggered the birth of new generations of stars. Dust glows in infrared light, so the three lines that make up the Trifid, while appearing dark in visible-light views, are bright when seen by WISE. 

The blue stars scattered around the picture are older, and they lie between Earth and the Trifid nebula. The baby stars in the Trifid will eventually look similar to those foreground stars. The red cloud at upper right is gas heated by a group of very young stars.

The Trifid nebula is located 5,400 light-years away in the constellation Sagittarius.

Blue represents light emitted at 3.4-micron wavelengths, and cyan (blue-green) represents 4.6 microns, both of which come mainly from hot stars. Relatively cooler objects, such as the dust of the nebula, appear green and red. Green represents 12-micron light and red, 22-micron light.

NASA's Jet Propulsion Laboratory, Pasadena, Calif., manages and operates the recently activated NEOWISE asteroid-hunting mission for NASA's Science Mission Directorate. The results presented here are from the WISE all-sky survey mission, which operated before NEOWISE, using the same spacecraft, in 2010 and 2011. WISE was selected competitively under NASA's Explorers Program managed by the agency's Goddard Space Flight Center in Greenbelt, Md. The science instrument was built by the Space Dynamics Laboratory in Logan, Utah. The spacecraft was built by Ball Aerospace & Technologies Corp. in Boulder, Colo. Science operations and data processing take place at the Infrared Processing and Analysis Center at the California Institute of Technology, Pasadena. Caltech manages JPL for NASA.

Whitney Clavin 818-354-4673
Jet Propulsion Laboratory, Pasadena, Calif.
whitney.clavin@jpl.nasa.gov

NASA-Sponsored 'Disk Detective' Lets Public Search for New Planetary Nurseries

Herbig-Haro 30 is the prototype of a gas-rich "young stellar object" disk around a star. The dark disk spans 40 billion miles (64 billion kilometers) in this image from NASA's Hubble Space Telescope, cutting the bright nebula in two and blocking the central star from direct view. Image credit NASA/Hubble/STScI.  Full image and caption

 

NASA is inviting the public to help astronomers discover embryonic planetary systems hidden among data from the agency's Wide-field Infrared Survey Explorer (WISE) mission through a new website, DiskDetective.org.

Disk Detective is NASA's largest crowdsourcing project whose primary goal is to produce publishable scientific results. It exemplifies a new commitment to crowdsourcing and open data by the United States government.

"Through Disk Detective, volunteers will help the astronomical community discover new planetary nurseries that will become future targets for NASA's Hubble Space Telescope and its successor, the James Webb Space Telescope," said James Garvin, the chief scientist for NASA Goddard's Sciences and Exploration Directorate.

WISE was designed to survey the entire sky at infrared wavelengths. From a perch in Earth orbit, the spacecraft completed two scans of the entire sky between 2010 and 2011. It took detailed measurements on more than 745 million objects, representing the most comprehensive survey of the sky at mid-infrared wavelengths currently available.

Astronomers have used computers to search this haystack of data for planet-forming environments and narrowed the field to about a half-million sources that shine brightly in infrared, indicating they may be "needles": dust-rich disks that are absorbing their star's light and reradiating it as heat.

"Planets form and grow within disks of gas, dust and icy grains that surround young stars, but many details about the process still elude us," said Marc Kuchner, an astrophysicist at NASA's Goddard Space Flight Center in Greenbelt, Md. "We need more examples of planet-forming habitats to better understand how planets grow and mature."

But galaxies, interstellar dust clouds and asteroids also glow in infrared, which stymies automated efforts to identify planetary habitats. There may be thousands of nascent solar systems in the WISE data, but the only way to know for sure is to inspect each source by eye, which poses a monumental challenge.

Public participation in scientific research is a type of crowdsourcing known as citizen science. It allows the public to make critical contributions to the fields of science, technology, engineering and mathematics by collecting, analyzing and sharing a wide range of data. NASA uses citizen science to engage the public in problem-solving.

Kuchner recognized that spotting planetary nurseries is a perfect opportunity for crowdsourcing. He arranged for NASA to team up with the Zooniverse, a collaboration of scientists, software developers and educators who collectively develop and manage citizen science projects on the Internet. The result of their combined effort is Disk Detective.

Disk Detective incorporates images from WISE and other sky surveys in brief animations the website calls flip books. Volunteers view a flip book and classify the object based on simple criteria, such as whether the image is round or includes multiple objects. By collecting this information, astronomers will be able to assess which sources should be explored in greater detail, for example, to search for planets outside our solar system.

"Disk Detective's simple and engaging interface allows volunteers from all over the world to participate in cutting-edge astronomy research that wouldn't even be possible without their efforts," said Laura Whyte, director of citizen science at Adler Planetarium in Chicago, Ill., a founding partner of the Zooniverse collaboration.

The project aims to find two types of developing planetary environments. The first, known as a young stellar object disk, typically is less than 5 million years old, contains large quantities of gas, and often is found in or near young star clusters. For comparison, our own solar system is 4.6 billion years old. The second planetary environment, known as a debris disk, tends to be older than 5 million years, possesses little or no gas, and contains belts of rocky or icy debris that resemble the asteroid and Kuiper belts found in our own solar system. Vega and Fomalhaut, two of the brightest stars in the sky, host debris disks.

WISE was shut down in 2011 after its primary mission was completed. But in September 2013, it was reactivated, renamed Near-Earth Object Wide-field Infrared Survey Explorer (NEOWISE), and given a new mission, which is 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.

NASA's Jet Propulsion Laboratory in Pasadena, Calif., manages and operates WISE for NASA's Science Mission Directorate. The WISE mission was selected competitively under NASA's Explorers Program managed by the agency's Goddard Space Flight Center. The science instrument was built by the Space Dynamics Laboratory in Logan, Utah. The spacecraft was built by Ball Aerospace & Technologies Corp. in Boulder, Colo. Science operations and data processing take place at the Infrared Processing and Analysis Center at the California Institute of Technology, which manages JPL for NASA.

For more information about Disk Detective, please visit: http://www.diskdetective.org

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


Whitney Clavin 818-354-4673
Jet Propulsion Laboratory, Pasadena, Calif.
whitney.clavin@jpl.nasa.gov

J.D. Harrington 202-358-5241
Headquarters, Washington
j.d.harrington@nasa.gov

Massive Black Hole Duo: Possible Sighting by NASA's WISE

Two black holes are entwined in a gravitational tango in this artist's conception. Supermassive black holes at the hearts of galaxies are thought to form through the merging of smaller, yet still massive black holes, such as the ones depicted here. Image credit: NASA.  Full image and caption

Astronomers have spotted what appear to be two supermassive black holes at the heart of a remote galaxy, circling each other like dance partners. The incredibly rare sighting was made with the help of NASA's Wide-field Infrared Survey Explorer, or WISE.

Follow-up observations with the Australian Telescope Compact Array near Narrabri, Australia, and the Gemini South telescope in Chile, revealed unusual features in the galaxy, including a lumpy jet thought to be the result of one black hole causing the jet of the other to sway.

"We think the jet of one black hole is being wiggled by the other, like a dance with ribbons," said Chao-Wei Tsai of NASA's Jet Propulsion Laboratory, Pasadena, Calif., who is lead author of a paper on the findings appearing in the Dec. 10 issue of Astrophysical Journal. "If so, it is likely the two black holes are fairly close and gravitationally entwined."

The findings could teach astronomers more about how supermassive black holes grow by merging with each other.

The WISE satellite scanned the entire sky twice in infrared wavelengths before being put into hibernation in 2011. NASA recently gave the spacecraft a second lease on life, waking it up to search for asteroids, in a project called NEOWISE.

The new study took advantage of previously released all-sky WISE data. Astronomers sifted through images of millions of actively feeding supermassive black holes spread throughout our sky before an oddball, also known as WISE J233237.05-505643.5, jumped out.

"At first we thought this galaxy's unusual properties seen by WISE might mean it was forming new stars at a furious rate," said Peter Eisenhardt, WISE project manager at NASA's Jet Propulsion Laboratory, Pasadena, Calif., and a co-author of the study. "But on closer inspection, it looks more like the death spiral of merging giant black holes."

Almost every large galaxy is thought to harbor a supermassive black hole filled with the equivalent in mass of up to billions of suns. How did the black holes grow so large? One way is by swallowing ambient materials. Another way is through galactic cannibalism. When galaxies collide, their massive black holes sink to the center of the new structure, becoming locked in a gravitational tango. Eventually, they merge into one even-more-massive black hole.

The dance of these black hole duos starts out slowly, with the objects circling each other at a distance of about a few thousand light-years. So far, only a few handfuls of supermassive black holes have been conclusively identified in this early phase of merging. As the black holes continue to spiral in toward each other, they get closer, separated by just a few light-years.

It is these close-knit black holes, also called black hole binaries, that have been the hardest to find. The objects are usually too small to be resolved even by powerful telescopes. Only a few strong candidates have been identified to date, all relatively nearby. The new WISE J233237.05-505643.5 is a new candidate, and located much farther away, at 3.8 billion light-years from Earth.

Radio images with the Australian Telescope Compact Array were key to identifying the dual nature of WISE J233237.05-505643.5. Supermassive black holes at the cores of galaxies typically shoot out pencil-straight jets, but, in this case, the jet showed a zigzag pattern. According to the scientists, a second massive black hole could, in essence, be pushing its weight around to change the shape of the other black hole's jet.

Visible-light spectral data from the Gemini South telescope in Chile showed similar signs of abnormalities, thought to be the result of one black hole causing disk material surrounding the other black hole to clump. Together, these and other signs point to what is probably a fairly close-knit set of circling black holes, though the scientists can't say for sure how much distance separates them.

"We note some caution in interpreting this mysterious system," said Daniel Stern of JPL, a co-author of the study. "There are several extremely unusual properties to this system, from the multiple radio jets to the Gemini data, which indicate a highly perturbed disk of accreting material around the black hole, or holes. Two merging black holes, which should be a common event in the universe, would appear to be simplest explanation to explain all the current observations."

The final stage of merging black holes is predicted to send gravitational waves rippling through space and time. Researchers are actively searching for these waves using arrays of dead stars called pulsars in hopes of learning more about the veiled black hole dancers (see http://www.nasa.gov/centers/jpl/news/pulsar20131106.html ).

The technical paper is online at http://arxiv.org/abs/1310.2257 .

NASA's Jet Propulsion Laboratory, Pasadena, Calif., manages and operates the WISE mission for NASA's Science Mission Directorate. The WISE mission was selected competitively under NASA's Explorers Program managed by the agency's Goddard Space Flight Center in Greenbelt, Md. The science instrument was built by the Space Dynamics Laboratory in Logan, Utah. The spacecraft was built by Ball Aerospace & Technologies Corp. in Boulder, Colo. 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. More information is online at http://www.nasa.gov/wise and http://wise.astro.ucla.edu and http://www.jpl.nasa.gov/wise .

Whitney Clavin 818-354-4673
Jet Propulsion Laboratory, Pasadena, Calif.
whitney.clavin@jpl.nasa.gov

The Galaxy's ancient brown dwarf population revealed

A brown dwarf from the thick-disk or halo is shown. Although astronomers observe these objects as they pass near to the solar system, they spend much of their time away from the busiest part of the Galaxy, and the Milky Way's disk can be seen in the background. Credit: John Pinfield.  An image is available from http://star-www.herts.ac.uk/~dpi/thickdisk_halo_BD.pnga and https://www.ras.org.uk/images/stories/press/thickdisk_halo_bd_jpg.jpg

A team of astronomers led by Dr David Pinfield at the University of Hertfordshire have discovered two of the oldest brown dwarfs in the Galaxy. These ancient objects are moving at speeds of 100-200 kilometres per second, much faster than normal stars and other brown dwarfs and are thought to have formed when the Galaxy was very young, more than 10 billion years ago. Intriguingly the scientists believe they could be part of a vast and previously unseen population of objects. The researchers publish their results in the Oxford University Press journal Monthly Notices of the Royal Astronomical Society.

Brown dwarfs are star-like objects but are much less massive (with less than 7% of the Sun’s mass), and do not generate internal heat through nuclear fusion like stars. Because of this brown dwarfs simply cool and fade with time and very old brown dwarfs become very cool indeed - the new discoveries have temperatures of 250-600 degrees Celsius, much cooler than stars (in comparison the Sun has a surface temperature of 5600 degrees Celsius).

Pinfield’s team identified the new objects in the survey made by the Wide-field Infrared Survey Explorer (WISE), a NASA observatory that scanned the mid-infrared sky from orbit in 2010 and 2011. The object names are WISE 0013+0634 and WISE 0833+0052, and they lie in the Pisces and Hydra constellations respectively. Additional measurements confirming the nature of the objects came from large ground-based telescopes (Magellan, Gemini, VISTA and UKIRT). The infrared sky is full of faint red sources, including reddened stars, faint background galaxies (large distances from our own Milky Way) and nebulous gas and dust. Identifying cool brown dwarfs in amongst this messy mixture is akin to finding needles in a haystack. But Pinfield's team developed a new method that takes advantage of the way in which WISE scans the sky multiple times. This allowed them to identify cool brown dwarfs that were fainter than other searches had revealed.

The team of scientists then studied the infrared light emitted from these objects, which are unusual compared to typical slower moving brown dwarfs. The spectral signatures of their light reflects their ancient atmospheres, which are almost entirely made up of hydrogen rather than having the more abundant heavier elements seen in younger stars. Pinfield comments on their venerable ages and high speeds, “Unlike in other walks of life, the Galaxy’s oldest members move much faster than its younger population”.

Stars near to the Sun (in the so-called local volume) are made up of 3 overlapping populations - the thin disk, the thick disk and the halo. The thick disk is much older than the thin disk, and its stars move up and down at a higher velocity. Both these disk components sit within the halo that contains the remnants of the first stars that formed in the Galaxy.

Thin disk objects dominate the local volume, with thick disk and halo objects being much rarer. About 97% of local stars are thin disk members, while just 3% are from the thick-disk or halo. Brown dwarfs population numbers probably follow those of stars, which explains why these fast-moving thick-disk/halo objects are only now being discovered.

There are thought to be as many as 70 billion brown dwarfs in the Galaxy’s thin disk, and the thick disk and halo occupy much larger Galactic volumes. So even a small (3%) local population signifies a huge number of ancient brown dwarfs in the Galaxy. "These two brown dwarfs may be the tip of an iceberg and are an intriguing piece of astronomical archaeology", said Pinfield. "We have only been able to find these objects by searching for the faintest and coolest things possible with WISE. And by finding more of them we will gain insight into the earliest epoch of the history of the Galaxy."

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Media contact

Dr Robert Massey
Royal Astronomical Society
Tel: +44 (0)20 7734 3307 x214
Mob: +44 (0)794 124 8035
rm@ras.org.uk

---

Science contacts

Prof David Pinfield
University of Hertfordshire
Tel: +44 (0)1707 284171
davidpinfield@googlemail.com

Dr Joana Gomes
University of Hertfordshire
j.gomes@herts.ac.uk

Dr Avril Day-Jones
University of Hertfordshire
avril_day_jones@hotmail.com

Dr Mariusz Gromadski
University of Val Paraiso
Val Paraiso, Chile
mariusz.gromadzki@uv.cl

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Further information

The results are published in the paper “A deep WISE search for very late type objects and the discovery of two halo/thick-disk T dwarfs: WISE 0013+0634 and WISE 0833+0052”, D. J. Pinfield et al, Monthly Notices of the Royal Astronomical Society, in press.

A pre-publication version of the paper is available on arXiv: http://arxiv.org/abs/1308.0495

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Useful links

University of Hertfordshire Centre for Astrophysics Research
http://www.herts.ac.uk/research/stri/research-areas/car

WISE homepage at NASA
http://www.nasa.gov/mission_pages/WISE/main/index.html

The Gemini Telescopes
http://www.gemini.edu/

The Magellan Telescope
http://obs.carnegiescience.edu/Magellan

VISTA homepage
http://www.vista.ac.uk/index.html

The UKIRT Infrared Deep Sky Survey homepage
http://www.ukidss.org/index.html

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Notes for editors

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.

Follow the RAS on Twitter via @royalastrosoc

 

WISE Catalog Just Got Wiser

The new AllWISE catalog will bring distant galaxies that were once invisible out of hiding, as illustrated in this image.  › Full image and caption

NASA's WISE mission has released a new and improved atlas and catalog brimming with data on three-quarters of a billion objects detected during two full scans of the sky.

WISE, which stands for Wide-field Infrared Survey Explorer, scanned the entire sky in infrared light in 2010, snapping a dozen pictures of every star and galaxy. By October of that year, the spacecraft ran out of the coolant needed to chill some of its heat-seeking detectors. NASA then decided to fund a second scan of the sky to look for asteroids and comets, in a project called NEOWISE.

But the images from that second sky scan were designed to catch moving asteroids, not stars and galaxies. Now NASA has funded a project called AllWISE to stack up all the WISE images, including those from the second sky scan, thereby doubling exposure times and making new stars and galaxies visible.

"By stacking up the data, we have created a monster database with dozens of individual measurements on every one of the infrared sources we detect," said Ned Wright of UCLA, the principal investigator of WISE.

One new feature of the enhanced WISE images is the ability to search for nearby stars, especially cooler ones that only show up in infrared light. Objects that are closer to us will appear to move across the sky over time in relation to background stars. This is the same reason why the planets march across our night skies while the stars seem to stay still. With the new atlas, astronomers can look at images of the sky taken six months apart; if something jumps across the images, then it must be located nearby and could be a never-before-seen neighbor.

The new catalog will also help with studies of distant galaxies, bringing those that were invisible to us before out of hiding.

"The extra depth of AllWISE lets us see galaxies so distant that their light was emitted in the first half of the history of the universe," said Peter Eisenhardt, the WISE project scientist at NASA's Jet Propulsion Laboratory, Pasadena, Calif.

In addition to AllWISE, NASA decided to wake up the WISE spacecraft again to search for more asteroids (see http://www.jpl.nasa.gov/news/news.php?release=2013-257 ).

The technical details for accessing the AllWISE data are online at: http://wise2.ipac.caltech.edu/docs/release/allwise/ .

NASA's Jet Propulsion Laboratory, Pasadena, Calif., manages and operates the newly activated NEOWISE mission for NASA's Science Mission Directorate. The WISE mission was selected competitively under NASA's Explorers Program managed by the agency's Goddard Space Flight Center in Greenbelt, Md. The science instrument was built by the Space Dynamics Laboratory in Logan, Utah. The spacecraft was built by Ball Aerospace & Technologies Corp. in Boulder, Colo. 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. More information is online at http://www.nasa.gov/wise and http://wise.astro.ucla.edu and http://www.jpl.nasa.gov/wise .

Whitney Clavin (818) 354-4673
Jet Propulsion Laboratory, Pasadena, Calif.
whitney.clavin@jpl.nasa.gov

Galaxy Growth Examined Like Rings of a Tree

New evidence from NASA's Wide-field Infrared Survey Explorer (WISE) and Galaxy Evolution Explorer (GALEX) missions provide support for the "inside-out" theory of galaxy evolution, which holds that star formation starts at the core of the galaxy and spreads outward. Image credit: NASA/JPL-Caltech.  › Full image and caption

Watching a tree grow might be more frustrating than waiting for a pot to boil, but luckily for biologists, there are tree rings. Beginning at a tree trunk's dense core and moving out to the soft bark, the passage of time is marked by concentric rings, revealing chapters of the tree's history.

Galaxies outlive trees by billions of years, making their growth impossible to see. But like biologists, astronomers can read the rings in a galaxy's disk to unravel its past. Using data from NASA's Wide-field Infrared Survey Explorer (WISE) and Galaxy Evolution Explorer (GALEX), scientists have acquired more evidence for the "inside-out" theory of galaxy growth, showing that bursts of star formation in central regions were followed one to two billion years later by star birth in the outer fringes.

"Initially, a rapid star-forming period formed the mass at the center of these galaxies, followed later by a star-forming phase in the outer regions. Eventually, the galaxies stop making stars and become quiescent," said Sara Petty of Virginia Tech, Blacksburg, Va., lead author of a paper appearing in the October 2013 issue of the Astronomical Journal. "This later star-forming phase could have been caused by minor mergers with gas-rich neighbors, which provide the fuel for new stars."

The discovery may also solve a mystery of elderly galaxies. The galaxies in the study, known as "red and dead" for their red color and lack of new star births, have a surprising amount of ultraviolet light emanating from the outer regions. Often, ultraviolet light is generated by hot, young stars, but these galaxies were considered too old to host such a young population.

The solution to the puzzle is likely hot, old stars. Petty and colleagues used a new multi-wavelength approach to show that the unexplained ultraviolet light appears to be coming from a late phase in the lives of older stars, when they blow off their outer layers and heat up.

GALEX and WISE turned out to be the ideal duo for the study. GALEX was sensitive to the ultraviolet light, whereas WISE sees the infrared light coming from older stars. GALEX is no longer operating, but WISE was recently reactivated to hunt asteroids, a project called NEOWISE (see http://www.jpl.nasa.gov/news/news.php?release=2013-257 ). Both telescopes have large fields of view, allowing them to easily capture images of entire galaxies.

"The synergy between GALEX and WISE produces a very sensitive measurement of where the hot, older stars reside in these red-and-dead galaxies," said Don Neill, co-author of the paper from the California Institute of Technology, Pasadena. "This allows us to map the progress of star formation within each galaxy."

Ned Wright of UCLA, a co-author of the study and the principal investigator of WISE before it was reactivated, compares the multi-wavelength range of the two telescopes to musical notes, "WISE itself covers the equivalent of a three-octave range, while WISE and GALEX together cover a seven-octave range."

The technical paper for this study is online at http://arxiv.org/abs/1307.6282 .

NASA's Jet Propulsion Laboratory, Pasadena, Calif., manages and operates the recently activated NEOWISE mission for NASA's Science Mission Directorate. The WISE mission was selected competitively under NASA's Explorers Program managed by the agency's Goddard Space Flight Center in Greenbelt, Md. The science instrument was built by the Space Dynamics Laboratory in Logan, Utah. The spacecraft was built by Ball Aerospace & Technologies Corp. in Boulder, Colo. Science operations and data processing take place at the Infrared Processing and Analysis Center at Caltech. Caltech manages JPL for NASA. More information is online at http://www.nasa.gov/wise and http://wise.astro.ucla.edu and http://www.jpl.nasa.gov/wise .

Caltech led the Galaxy Evolution Explorer mission and was responsible for science operations and data analysis. JPL managed the mission and built the science instrument. The mission was developed under NASA's Explorers Program managed by the Goddard Space Flight Center, Greenbelt, Md. Researchers sponsored by Yonsei University in South Korea and the Centre National d'Etudes Spatiales (CNES) in France collaborated on this mission. Graphics and additional information about the Galaxy Evolution Explorer are online at http://www.nasa.gov/galex and http://www.galex.caltech.edu .

Whitney Clavin 818-354-4673
Jet Propulsion Laboratory, Pasadena, Calif.
whitney.clavin@jpl.nasa.gov 

Coldest Brown Dwarfs Blur Star, Planet Lines

The locations of brown dwarfs discovered by NASA's Wide-field Infrared Survey Explorer, or WISE, and mapped by NASA's Spitzer Space Telescope, are shown in this diagram. The view is from a vantage point about 100 light-years away from the sun, looking back toward the constellation Orion. Image credit: NASA/JPL-Caltech.  Full image and caption

This artist's conception portrays a free-floating brown dwarf, or failed star. Image credit: NASA/JPL-Caltech. Full image and caption - enlarge image

In 2011, astronomers on the hunt for the coldest star-like celestial bodies discovered a new class of such objects using NASA's Wide-Field Infrared Survey Explorer (WISE) space telescope. But until now, no one knew exactly how cool the bodies' surfaces really are. In fact, some evidence suggested they could be at room temperature.

A new study using data from NASA's Spitzer Space Telescope shows that while these so-called brown dwarfs are indeed the coldest known free-floating celestial bodies, they are warmer than previously thought, with surface temperatures ranging from about 250 to 350 degrees Fahrenheit (125 to 175 degrees Celsius). By comparison, the sun has a surface temperature of about 10,340 degrees Fahrenheit (5,730 degrees Celsius).

To reach these surface temperatures after cooling for billions of years, these objects would have to have masses of only five to 20 times that of Jupiter. Unlike the sun, the only source of energy for these coldest of brown dwarfs is from their gravitational contraction, which depends directly on their mass. The sun is powered by the conversion of hydrogen to helium; these brown dwarfs are not hot enough for this type of "nuclear burning" to occur.

The findings help researchers understand how planets and stars form.

"If one of these objects were found orbiting a star, there is a good chance that it would be called a planet," said Trent Dupuy, a Hubble Fellow at the Harvard-Smithsonian Center for Astrophysics and a co-author of the study, appearing online Sept. 5 in the journal Science Express. But because they probably formed on their own and not in a planet-forming disk orbiting a more massive star, astronomers still call these objects brown dwarfs even if their mass is of planetary size.

Characterizing these cold brown dwarfs is challenging because they emit most of their light at infrared wavelengths and are very faint due to their small size and low temperature.

To get accurate temperatures, astronomers need to know the distances to these objects. "We wanted to find out if they were colder, fainter and nearby, or if they were warmer, brighter and more distant," explains Dupuy.

Using Spitzer, the team determined that the brown dwarfs in question are located at distances 20 to 50 light-years away.

To determine the distances to these objects, the team measured their parallax -- the apparent change in position against background stars over time. As Spitzer orbits the sun, its perspective changes and nearby objects appear to shift back and forth slightly. The same effect occurs if you hold up a finger in front of your face and close one eye and then the other. The position of your finger seems to shift when viewed against the distant background.

But even for these relatively nearby brown dwarfs, the parallax motion is small. "To be able to determine accurate distances, our measurements had to be the same precision as knowing the position of a firefly to within 1 inch (2.5 centimeters) from 200 miles (320 kilometers) away," explained Adam Kraus, professor at the University of Texas at Austin and the study's other co-author.

The new data also present new puzzles to astronomers who study cool, planet-like atmospheres. Unlike warmer brown dwarfs and stars, the observable properties of these objects don't seem to correlate as strongly with temperature. This suggests increased roles for other factors, such as convective mixing, in driving the chemistry at the surface.

This study examined the initial sample of the coldest brown dwarfs discovered in the WISE survey data. Additional objects discovered in the past two years remain to be studied, and scientists hope they will shed light on some of these outstanding issues.

NASA's Jet Propulsion Laboratory, Pasadena, Calif., 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. Data are archived at the Infrared Science Archive housed at the Infrared Processing and Analysis Center at Caltech. Caltech manages JPL for NASA.

For more information about Spitzer, visit http://spitzer.caltech.edu and http://www.nasa.gov/spitzer.

Whitney Clavin 818-354-4673
Jet Propulsion Laboratory, Pasadena, Calif.
whitney.clavin@jpl.nasa.gov

Monster Galaxies Lose Their Appetite With Age

This image shows two of the galaxy clusters observed by NASA's Wide-field Infrared Survey Explorer (WISE) and Spitzer Space Telescope missions. Galaxy clusters are among the most massive structures in the universe. The central and largest galaxy in each grouping, called the brightest cluster galaxy or BCG, is seen at the center of each image. Image credit: NASA/JPL-Caltech/SDSS/NOA .  › Full image and caption

Figure 1 (left) shows the cluster known as Abell 2199, which is relatively nearby at a distance of 400 million light-years from Earth (redshift of 0.0302). This image combines infrared data from WISE (in red) with shorter wavelengths of light extending into the visible spectrum from the Sloan Digital Sky Survey (in blue and green).

Figure 2 (right) is the cluster ISCS 1433.9+3330, which is significantly farther away at a distance of 4.4 billion light-years (redshift of 0.42). Infrared data from Spitzer (red) is combined with similar shorter wavelength data taken by the Mayall Telescope on Kitt Peak, Ariz.

Our universe is filled with gobs of galaxies, bound together by gravity into larger families called clusters. Lying at the heart of most clusters is a monster galaxy thought to grow in size by merging with neighboring galaxies, a process astronomers call galactic cannibalism.

New research from NASA's Spitzer Space Telescope and Wide-field Infrared Survey Explorer (WISE) is showing that, contrary to previous theories, these gargantuan galaxies appear to slow their growth over time, feeding less and less off neighboring galaxies.

"We've found that these massive galaxies may have started a diet in the last 5 billion years, and therefore have not gained much weight lately," said Yen-Ting Lin of the Academia Sinica in Taipei, Taiwan, lead author of a study published in the Astrophysical Journal.

Peter Eisenhardt, a co-author from NASA's Jet Propulsion Laboratory in Pasadena, Calif., said, "WISE and Spitzer are letting us see that there is a lot we do understand -- but also a lot we don't understand -- about the mass of the most massive galaxies." Eisenhardt identified the sample of galaxy clusters studied by Spitzer, and is the project scientist for WISE.

The new findings will help researchers understand how galaxy clusters -- among the most massive structures in our universe -- form and evolve.

Galaxy clusters are made up of thousands of galaxies, gathered around their biggest member, what astronomers call the brightest cluster galaxy, or BCG. BCGs can be up to dozens of times the mass of galaxies like our own Milky Way. They plump up in size by cannibalizing other galaxies, as well as assimilating stars that are funneled into the middle of a growing cluster.

To monitor how this process works, the astronomers surveyed nearly 300 galaxy clusters spanning 9 billion years of cosmic time. The farthest cluster dates back to a time when the universe was 4.3 billion years old, and the closest, when the universe was much older, 13 billion years old (our universe is presently 13.8 billion years old).

"You can't watch a galaxy grow, so we took a population census," said Lin. "Our new approach allows us to connect the average properties of clusters we observe in the relatively recent past with ones we observe further back in the history of the universe."

Spitzer and WISE are both infrared telescopes, but they have unique characteristics that complement each other in studies like these. For instance, Spitzer can see more detail than WISE, which enables it to capture the farthest clusters best. On the other hand, WISE, an infrared all-sky survey, is better at capturing images of nearby clusters, thanks to its larger field of view. Spitzer is still up and observing; WISE went into hibernation in 2011 after successfully scanning the sky twice.

The findings showed that BCG growth proceeded along rates predicted by theories until 5 billion years ago, or a time when the universe was about 8 billion years old. After that time, it appears the galaxies, for the most part, stopped munching on other galaxies around them.

The scientists are uncertain about the cause of BCGs' diminished appetites, but the results suggest current models need tinkering.

"BCGs are a bit like blue whales -- both are gigantic and very rare in number. Our census of the population of BCGs is in a way similar to measuring how the whales gain their weight as they age. In our case, the whales aren't gaining as much weight as we thought. Our theories aren't matching what we observed, leading us to new questions," said Lin.

Another possible explanation is that the surveys are missing large numbers of stars in the more mature clusters. Clusters can be violent environments, where stars are stripped from colliding galaxies and flung into space. If the recent observations are not detecting those stars, it's possible that the enormous galaxies are, in fact, continuing to bulk up.

Future studies from Lin and others should reveal more about the feeding habits of one of nature's largest galactic species.

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. Data are archived at the Infrared Science Archive housed at the Infrared Processing and Analysis Center at Caltech. Caltech manages JPL for NASA. For more information about Spitzer, visit http://spitzer.caltech.edu and http://www.nasa.gov/spitzer .

JPL managed and operated WISE for NASA's Science Mission Directorate. Edward Wright is the principal investigator and is at UCLA. The mission was selected competitively under NASA's Explorers Program managed by the agency's Goddard Space Flight Center in Greenbelt, Md. The science instrument was built by the Space Dynamics Laboratory in Logan, Utah. The spacecraft was built by Ball Aerospace & Technologies Corp. in Boulder, Colo. 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. More information is online at http://www.nasa.gov/wise and http://wise.astro.ucla.edu and http://jpl.nasa.gov/wise .

Whitney Clavin 818-354-4673
Jet Propulsion Laboratory, Pasadena, Calif.
whitney.clavin@jpl.nasa.gov  

NASA's WISE Finds Mysterious Centaurs May Be Comets

This artist's concept shows a centaur creature together with asteroids on the left and comets at right. Image Credit: NASA/JPL-Caltech. Full image and caption

PASADENA, Calf. -- The true identity of centaurs, the small celestial bodies orbiting the sun between Jupiter and Neptune, is one of the enduring mysteries of astrophysics. Are they asteroids or comets? A new study of observations from NASA's Wide-field Infrared Survey Explorer (WISE) finds most centaurs are comets.

Until now, astronomers were not certain whether centaurs are asteroids flung out from the inner solar system or comets traveling in toward the sun from afar. Because of their dual nature, they take their name from the creature in Greek mythology whose head and torso are human and legs are those of a horse.

"Just like the mythical creatures, the centaur objects seem to have a double life," said James Bauer of NASA's Jet Propulsion Laboratory in Pasadena, Calif. Bauer is lead author of a paper published online July 22 in the Astrophysical Journal. "Our data point to a cometary origin for most of the objects, suggesting they are coming from deeper out in the solar system."

"Cometary origin" means an object likely is made from the same material as a comet, may have been an active comet in the past, and may be active again in the future.

The findings come from the largest infrared survey to date of centaurs and their more distant cousins, called scattered disk objects. NEOWISE, the asteroid-hunting portion of the WISE mission, gathered infrared images of 52 centaurs and scattered disk objects. Fifteen of the 52 are new discoveries. Centaurs and scattered disk objects orbit in an unstable belt. Ultimately, gravity from the giant planets will fling them either closer to the sun or farther away from their current locations.

Although astronomers previously observed some centaurs with dusty halos, a common feature of outgassing comets, and NASA's Spitzer Space Telescope also found some evidence for comets in the group, they had not been able to estimate the numbers of comets and asteroids.

Infrared data from NEOWISE provided information on the objects' albedos, or reflectivity, to help astronomers sort the population. NEOWISE can tell whether a centaur has a matte and dark surface or a shiny one that reflects more light. The puzzle pieces fell into place when astronomers combined the albedo information with what was already known about the colors of the objects. Visible-light observations have shown centaurs generally to be either blue-gray or reddish in hue. A blue-gray object could be an asteroid or comet. NEOWISE showed that most of the blue-gray objects are dark, a telltale sign of comets. A reddish object is more likely to be an asteroid.

"Comets have a dark, soot-like coating on their icy surfaces, making them darker than most asteroids," said the study's co-author, Tommy Grav of the Planetary Science Institute in Tucson, Ariz. "Comet surfaces tend to be more like charcoal, while asteroids are usually shinier like the moon."

The results indicate that roughly two-thirds of the centaur population are comets, which come from the frigid outer reaches of our solar system. It is not clear whether the rest are asteroids. The centaur bodies have not lost their mystique entirely, but future research from NEOWISE may reveal their secrets further.

The paper is available online at: http://iopscience.iop.org/0004-637X/773/1/22/ .

JPL, managed by the California Institute of Technology in Pasadena, managed and operated WISE for NASA's Science Mission Directorate. The NEOWISE portion of the project was funded by NASA's Near Earth Object Observation Program. WISE completed its key mission objective, two scans of the entire sky, in 2011 and has been hibernating in space since then.

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


Whitney Clavin 818-354-4673
Jet Propulsion Laboratory, Pasadena, Calif.
whitney.clavin@jpl.nasa.gov

J.D. Harrington 202-358-5241
Headquarters, Washington                                                    
j.d.harrington@nasa.gov