Monday, January 26, 2015

A Recoiling, Supermassive Black Hole

The galaxy at the center of this image from the Hubble Space Telescope contains an X-ray source, CID-42, which is suspected of being the merged remnant of a pair of supermassive black holes and of being ejected from the host galaxy at a speed of several million miles per hour. Credit: X-ray: NASA/CXC/SAO/F.Civano et al; Optical: NASA/STScI; Optical (wide field): CFHT, NASA/STScI 


When galaxies collide, the central supermassive black holes that reside at their cores will end up orbiting one another in a binary pair, at least according to current simulations. Einstein's general theory of relativity predicts that masses in a binary system should radiate gravitational waves, analogous to the way that accelerating electrical charges radiate electromagnetic waves but very much weaker.

As they radiate away their energy in these waves, orbiting black holes will gradually come closer together until eventually they merge in a coalescence event that is expected to emit a strong burst of gravitational waves. Relativity predicts that the gravitational radiation from black hole coalescence will be preferentially emitted in one direction that depends on the spin- and mass-ratios of the two black holes. In order to conserve momentum, therefore, the newly formed single supermassive black hole will recoil. Indeed, recoiling supermassive black holes are predicted to be one of the key observable signatures of such binary mergers. As they speed away from the center of the galaxy, they are expected to carry along with them their local environments (the discs and hot gas regions).

Amazingly, a few of these bizarre, recoiling candidates have apparently been serendipitously spotted (they are so far only candidates because their character is not yet confirmed). One of them is an X-ray source known as CID-42, which the Hubble Space Telescope resolves into two bright components only a few thousand light-years apart (a relatively small distance in galactic terms). CfA astronomers Francesca Civano, Xiawei Wang, Avi Loeb, and Martin Elvis, together with their colleagues, used the Very Large Array radio facility to study the radio emission emitted by charged particles accelerated by the black holes in CID-42, and analyzed their data together with that from other facilities in an effort to confirm it as a recoil object. They find that all of the radio emission can be attributed to one of the two bright components, which also is the source of the X-ray emission. This source, their analysis concludes (although still not unequivocally), could indeed be a long-sought example of a recoiling black hole. The new research is a major step towards confirming the existence of these exotic objects, but further observations are still needed.

Reference(s): 

 "New Insights from Deep VLA Data on the Potentially Recoiling Black Hole CID-42 in the COSMOS Field," Mladen Novak, Vernesa Smolcic, Francesca Civano, Marco Bondi, Paolo Ciliegi, Xiawei Wang, Abraham Loeb, Julie Banfield, Stephen Bourke, Martin Elvis, Gregg Hallinan, Huib T. Intema, Hans-Rainer Klockner, Kunal Mooley and Felipe Navarrete, MNRAS, 447, 2282, 2015.




Friday, January 23, 2015

Dust filaments of NGC 4217

Credit: ESA/Hubble & NASA
Acknowledgement: R. Schoofs

 
In this image the NASA/ESA Hubble Space Telescope takes a close look at the spiral galaxy NGC 4217, 60 million light-years away. The galaxy is seen almost perfectly edge on and is a perfect candidate for studying the nature of extraplanar dust structures — the patterns of gas and dust above and below the plane on the galaxy, seen here as brown wisps coming off NGC 4217.

These tentacle-like filaments are visible in the Hubble image only because the contrast with their surroundings is so high. This implies that the structures are denser than their surroundings. The image shows dozens of dust structures some of which reach as far as 7000 light-years away from the central plane. Typically the structures have a length of about 1000 light-years and are about 400 light-years in width.

Some of the dust filaments are round or irregular clouds, others are vertical columns, looplike structures or vertical cones. These structures can help astronomers to identify the mechanisms responsible for the ejection of gas and dust from the galactic plane of spiral galaxies and reveal information on the transport of the interstellar medium to large distances away from galactic discs.

The properties of the observed dust structures in NGC 4217 suggest that the gas and dust was driven out of the midplane of the galaxy by powerful stellar winds resulting from supernovae — explosions that mark the deaths of massive stars.

This image was entered into the Hubble Hidden Treasures competition by contestant Ralf Schoofs.


Source: ESA/Hubble - Space Telescope


Thursday, January 22, 2015

IYL 2015: Chandra Celebrates The International Year of Light

M51, SNR E0519-69.0, MSH 11-62, Cygnus A, RCW 86



The year of 2015 has been declared the International Year of Light (IYL) by the United Nations. Organizations, institutions, and individuals involved in the science and applications of light will be joining together for this yearlong celebration to help spread the word about the wonders of light.

In many ways, astronomy uses the science of light. By building telescopes that can detect light in its many forms, from radio waves on one end of the "electromagnetic spectrum" to gamma rays on the other, scientists can get a better understanding of the processes at work in the Universe.

NASA's Chandra X-ray Observatory explores the Universe in X-rays, a high-energy form of light. By studying X-ray data and comparing them with observations in other types of light, scientists can develop a better understanding of objects likes stars and galaxies that generate temperatures of millions of degrees and produce X-rays.

To recognize the start of IYL, the Chandra X-ray Center is releasing a set of images that combine data from telescopes tuned to different wavelengths of light. From a distant galaxy to the relatively nearby debris field of an exploded star, these images demonstrate the myriad ways that information about the Universe is communicated to us through light.



The images, beginning at the upper left and moving clockwise, are:


M51
Messier 51 (M51):
This galaxy, nicknamed the "Whirlpool," is a spiral galaxy, like our Milky Way, located about 30 million light years from Earth. This composite image combines data collected at X-ray wavelengths by Chandra (purple), ultraviolet by the Galaxy Evolution Explorer (GALEX, blue); visible light by Hubble (green), and infrared by Spitzer (red).


SNR E0519-69.0
SNR E0519-69.0:
When a massive star exploded in the Large Magellanic Cloud, a satellite galaxy to the Milky Way, it left behind an expanding shell of debris called SNR 0519-69.0. Here, multimillion degree gas is seen in X-rays from Chandra (blue). The outer edge of the explosion (red) and stars in the field of view are seen in visible light from Hubble.


MSH 11-62
MSH 11-62:
When X-rays, shown in blue, from Chandra and XMM-Newton are joined in this image with radio data from the Australia Telescope Compact Array (pink) and visible light data from the Digitized Sky Survey (DSS, yellow), a new view of the region emerges. This object, known as MSH 11-62, contains an inner nebula of charged particles that could be an outflow from the dense spinning core left behind when a massive star exploded.


Cygnus A
Cygnus A:
This supernova remnant is the remains of an exploded star that may have been witnessed by Chinese astronomers almost 2,000 years ago. Modern telescopes have the advantage of observing this object in light that is completely invisible to the unaided human eye. This image combines X-rays from Chandra (pink and blue) along with visible emission from hydrogen atoms in the rim of the remnant, observed with the 0.9-m Curtis Schmidt telescope at the Cerro Tololo Inter-American Observatory (yellow).


RCW 86
RCW 86:
This galaxy, at a distance of some 700 million light years, contains a giant bubble filled with hot, X-ray emitting gas detected by Chandra (blue). Radio data from the NSF's Very Large Array (red) reveal "hot spots" about 300,000 light years out from the center of the galaxy where powerful jets emanating from the galaxy's supermassive black hole end. Visible light data (yellow) from both Hubble and the DSS complete this view.


In addition to these newly released images, the Chandra X-ray Center has created a new online repository of images called "Light: Beyond the Bulb" for IYL. This project places astronomical objects in context with light in other fields of science and research.

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.

For more information on "Light: Beyond the Bulb," visit the website at http://lightexhibit.org

For more information on the International Year of Light, go to http://www.light2015.org/Home.html


Fast Facts for Whirlpool Galaxy:

Credit: X-ray: NASA/CXC/SAO; UV: NASA/JPL-Caltech; Optical: NASA/STScI; IR: NASA/JPL-Caltech
Scale: Image: is 6 x 10 arcmin across. (About 52,000 x 87,000 light years)
Category: Normal Galaxies & Starburst Galaxies
Coordinates (J2000): RA 13h 29m 52.3s | Dec +47° 11' 54
Constellation: Canes Venatici
Observation Dates: 11 pointings between Mar 2000 and Oct 2012
Observation Time: 232 hours 10 min (9 days 16 hours 10 min)
Obs. IDs: 353, 354, 1622, 3932, 13812-13816, 15496, 15553
Instrument: ACIS
Also Known As: NGC 5194, NGC 5195
Color Code: X-ray (Purple); Ultraviolet (Blue); Optical (Green); Infrared (Red)
Distance Estimate: About 30 million light years


Fast Facts for SNR E0519-69.0:

Credit: X-ray: NASA/CXC/Rutgers/J.Hughes; Optical: NASA/STScI
Scale: Image is 1.5 arcmin across. (about 70 light years)
Category: Normal Galaxies & Starburst Galaxies
Coordinates (J2000): RA 05h 19m 34.90s | Dec -69° 02' 07.30"
Constellation: Dorado
Observation Dates: 4 pointings between Jun 2000 and Feb 2010
Observation Time: 25 hours 16 min (1 day 1 hour 16 min)
Obs. IDs: 118, 11241, 12062, 12063
Instrument: ACIS
Color Code: X-ray (Blue); Optical (Red, Green, Blue)
Distance Estimate: About 160,000 light years


Fast Facts for MSH 11-62:

Credit: X-ray: NASA/CXC/SAO/P.Slane et al; Optical: DSS; Radio: CSIRO/ATNF/ATCA
Scale: Image is 55 arcmin across. (256 light years)
Category: Normal Galaxies & Starburst Galaxies
Coordinates (J2000): RA 11h 11m 52.00s | Dec -60° 39' 12.00"
Constellation: Carina
Observation Dates: 1 pointing in Apr 2002 and 8 between Oct 2013 and Jan 2014
Observation Time: 131 hours 17 min (5 days 11 hours 17 min)
Obs. IDs: 2782, 14822-14824, 16496, 16497, 16512, 16541, 16566
Instrument: ACIS
Color Code: X-ray (Blue); Optical (Yellow); Radio (Pink)
Distance Estimate: About 16,000 light years


Fast Facts for Cygnus A:

Credit: X-ray: NASA/CXC/SAO; Optical: NASA/STScI; Radio: NSF/NRAO/AUI/VLA
Scale: Image is 2.7 arcmin across. (about 550,000 light years)
Category: Normal Galaxies & Starburst Galaxies
Coordinates (J2000): RA 19h 59m 28.30s | Dec +40° 44' 02.00"
Constellation: Cygnus
Observation Dates: 11 pointings between Mar 2000 and Sep 2005
Observation Time: 67 hours 35 min (2 days 19 hours 35min)
Obs. IDs: 359, 360, 1707, 5830, 5831, 6225, 6226, 6228, 6229, 6250, 6252
Instrument: ACIS
Color Code: X-ray: Blue; Optical: Yellow; Radio: Red
Distance Estimate: About 700 million light years


Fast Facts for RCW 86:

Credit: X-ray: NASA/CXC/MIT/D.Castro et al, Optical: NOAO/AURA/NSF/CTIOScale: Image is 19.5 arcmin across. (about 46.5 light years)
Category Normal Galaxies & Starburst Galaxies
Coordinates (J2000): RA 14h 45m 02.30s | Dec -62º 20' 32.00"
Constellation: Circinus
Observation Dates: 3 pointings in Feb, 2013
Observation Time: 28 hours 57 min (1 day 4 hours 57 min )
Obs. IDs: 14890, 15608, 15609
Instrument: ACIS
Also Known As: G315.4-2.1
Color Code: X-ray (Blue and Pink); Optical (Yellow)
Distance Estimate: About 8,200 light years 




Tuesday, January 20, 2015

Three Almost Earth-Size Planets Found Orbiting Nearby Star

This whimsical cartoon shows the three newly discovered extrasolar planets (right) casting shadows on their host star that can been seen as eclipses, or transits, at Earth (left). Earth can be detected by the same effect, but only in the plane of Earth's orbit (the ecliptic). During the K2 mission, many of the extrasolar planets discovered by the Kepler telescope will have this lucky double cosmic alignment that would allow for mutual discovery—if there is anyone on those planets to discover Earth. The three new planets orbiting EPIC 201367065 are just out of alignment; while they are visible from Earth, our solar system is tilted just out of their view.  Credit: K. Teramura, UH IfA. High-resolution version


MAUNA KEA, HI – A team of scientists recently discovered a system of three planets, each just larger than Earth, orbiting a nearby star called EPIC 201367065. The three planets are 1.5-2 times the size of Earth.

The outermost planet orbits on the edge of the so-called “habitable zone,” where the temperature may be just right for liquid water, believed necessary to support life, on the planet’s surface. The paper, “A Nearby M Star with Three Transiting Super-Earths Discovered by K2,” was submitted to the Astrophysical Journal today and is available here.

“The compositions of these newfound planets are unknown, but, there is a very real possibility the outer planet is rocky like Earth,” said Erik Petigura, a University of California, Berkeley graduate student who spent a year visiting the UH Institute for Astronomy. “If so, this planet could have the right temperature to support liquid water oceans.”

The planets were confirmed by the NASA Infrared Telescope Facility (IRTF) and the W. M. Keck Observatory in Hawaii as well as telescopes in California and Chile.

“Keck's contribution to this discovery was vital,” said Andrew Howard, a University of Hawaii astronomer on the team. “The adaptive optics image from NIRC2 showed the star hosting these three planets is a single star, not a binary. It showed that the planets are real and not an artifact of some masquerading multi-star system.”

Due to the competitive state of planet finding, and the fact that time on the twin Keck telescopes are scheduled months in advance, the team asked UC Berkeley Astronomer, Imke de Pater to gather some data during her scheduled run. 

“The collegiality of the Keck Observatory community is just wonderful,” Howard said. “Imke took time away from her own science observations to get us images of this system, all on a couple hours’ notice.”

The new discovery paves the way for studies of the atmosphere of a warm planet nearly the size of Earth. 

“We’ve learned in the past year that planets the size and temperature of Earth are common in our Milky Way galaxy,” Howard said. “We also discovered some Earth-size planets that appear to be made of the same materials as our Earth, mostly rock and iron.”

The astronomers next hope to determine what elements are in the planets’ atmospheres. If these warm, nearly Earth-size planets have thick, hydrogen-rich atmospheres, there is not much chance for life.

“A thin atmosphere made of nitrogen and oxygen has allowed life to thrive on Earth. But nature is full of surprises. Many extrasolar planets discovered by the Kepler Mission are enveloped by thick, hydrogen-rich atmospheres that are probably incompatible with life as we know it,” said Ian Crossfield, the University of Arizona astronomer who led the study.

The discovery is all the more remarkable because Kepler is now hobbled by the loss of two reaction wheels that kept it pointing at a fixed spot in space. Kepler, launched in 2009, was reborn in 2014 as “K2” with a clever strategy of pointing the telescope in the plane of the Earth’s orbit to stabilize the spacecraft. Kepler is back to mining the cosmos for planets by searching for eclipses, or transits, as planets orbit in front of their host stars and periodically block some of the starlight.

“I was devastated when Kepler was crippled by a hardware failure,” Petigura added. “It’s a testament to the ingenuity of NASA engineers and scientists that Kepler can still do great science.”

Kepler sees only a small fraction of the planetary systems in its gaze, those with orbital planes aligned edge-on to our view from Earth. Planets with large orbital tilts are simply missed by Kepler.

“It’s remarkable that the Kepler telescope is now pointed in the ecliptic, the plane that Earth sweeps out as it orbits the Sun,” Fulton explains. “This means that some of the planets discovered by K2 will have orbits lined up with Earth’s, a celestial coincidence that allows Kepler to see the alien planets, and Kepler-like telescopes in those very planetary systems (if there are any) to discover Earth.”

“Here’s looking at you, looking at me,” said Howard.

In addition to Howard and Petigura, UH graduate students Benjamin Fulton and Kimberly Aller, and UH astronomer Michael Liu were among the two dozen scientists who contributed to the study.

The W. M. Keck Observatory operates the largest, most scientifically productive telescopes on Earth. The two, 10-meter optical/infrared telescopes near the summit of Mauna Kea on the Island of Hawaii feature a suite of advanced instruments including imagers, multi-object spectrographs, high-resolution spectrographs, integral-field spectrographs and world-leading laser guide star adaptive optics systems. 

NIRC2 (the Near-Infrared Camera, second generation) works in combination with the Keck II adaptive optics system to obtain very sharp images at near-infrared wavelengths, achieving spatial resolutions comparable to or better than those achieved by the Hubble Space Telescope at optical wavelengths. NIRC2 is probably best known for helping to provide definitive proof of a central massive black hole at the center of our galaxy. Astronomers also use NIRC2 to map surface features of solar system bodies, detect planets orbiting other stars, and study detailed morphology of distant galaxies.

Keck Observatory is a private 501(c) 3 non-profit organization and a scientific partnership of the California Institute of Technology, the University of California and NASA.


Media Contact:

Steve Jefferson
Communications Officer
W. M. Keck Observatory
808.881.3827

sjefferson@keck.hawaii.edu



Monday, January 19, 2015

Venus Express snaps swirling vortex

Venus Express snaps swirling vortex 
Copyright ESA/VIRTIS/INAF-IASF/Obs. de Paris-LESIA/Univ. Oxford

Close-up view of south polar vortex (video)
Copyright: ESA/VIRTIS/INAF-IASF/Obs. de Paris-LESIA


This ghostly puff of smoke is actually a mass of swirling gas and cloud at Venus’ south pole, as seen by the Visible and Infrared Thermal Imaging Spectrometer (VIRTIS) aboard ESA’s Venus Express spacecraft.

Venus has a very choppy and fast-moving atmosphere – although wind speeds are sluggish at the surface, they reach dizzying speeds of around 400 km/h at the altitude of the cloud tops, some 70 km above the surface. At this altitude, Venus’ atmosphere spins round some 60 times faster than the planet itself. This is very rapid; even Earth’s fastest winds move at most about 30% of our planet’s rotation speed. Quick-moving Venusian winds can complete a full lap of the planet in just four Earth days.

Polar vortices form because heated air from equatorial latitudes rises and spirals towards the poles, carried by the fast winds. As the air converges on the pole and then sinks, it creates a vortex much like that found above the plughole of a bath. In 1979, the Pioneer Venus orbiter spotted a huge hourglass-shaped depression in the clouds, some 2000 km across, at the centre of the north polar vortex.

However, other than brief glimpses from the Pioneer Venus and Mariner 10 missions in the 1970s, Venus’ south pole had not been seen in detail until ESA’s Venus Express first entered orbit in April 2006.

One of Venus Express’ first discoveries, made during its very first orbit, was confirming the existence of a huge atmospheric vortex circulation at the south pole with a shape matching the one glimpsed at the north pole.

This south polar vortex is a turbulent mix of warming and cooling gases, all surrounded by a ‘collar’ of cool air. Follow-up Venus Express observations in 2007, including this image, showed that the core of the vortex changes shape on a daily basis. Just four hours after this image the vortex looked very different and a day later it had morphed into a squashed shape unrecognisable from the eye-like structure here.

A video of the vortex, made from 10 images taken over a period of five hours, can be seen here. The vortex rotates with a period of around 44 hours.

The swirling region shown in this VIRTIS image is about 60 km above the planet’s surface. Venus’ south pole is located just up and to the left of the image centre, slightly above the wispy ‘eye’ itself.

This image was obtained on 7 April 2007 at a wavelength of 5.02 micrometres. It shows thermal-infrared emission from the cloud tops; brighter regions like the ‘eye’ of the vortex are at lower altitude and therefore hotter.


Links



Source: ESA


The Cosmic Seeds of Black Holes

 
Simulation of the collapse of gas in the very early universe into a small black hole, the first step in producing a more massive black hole that will become the seed for the future development of a galaxy. (The scale of the image is 20 au; one au - astronomical unit - is the average distance of the Earth from the Sun. Credit: Becerra


Supermassive black holes with millions or billions of solar-masses of material are found at the nuclei of most galaxies. During the embryonic stages of these galaxies they are thought to play an important role, acting as seeds around which material collected. During the later lifetime of galaxies they can power dramatic outflowing jets of material (among other phenomena) as infalling dust and gas accretes onto the disks that typically surround them. These active, later phases of supermassive black holes can result in turning galaxies into an extremely bright objects like quasars, whose luminosities allow them to be seen at cosmic distances. In fact, quasars have recently been detected from eras less than a billion years after the big bang.

But where do all these black holes come from – especially the ones present in the early universe!? The explosive death of massive stars, one nominal route, can take many hundreds of millions of years while the star itself coalesces from ambient gas and then evolves, after which material must be added to the black hole seed to grow it into a supermassive monster. It is not clear that there is enough time in the early universe for this to happen. A second method has been proposed for these cosmic seeds, the direct collapse of primordial gas into seedlings that are much more massive – about ten thousand solar-masses - than are those present in stellar ashes.

Computer simulations have struggled for years to predict what happens in direct collapse, with mixed successes. CfA astronomers Fernando Becerra, Thomas Greif, and Lars Hernquist, and a colleague, have just published the most detailed 3-D simulation of the process in the early universe with an amazingly fine spatial scale precision -- as small as the solar-system -- and spanning a factor of over ten trillion in size and twenty orders of magnitude (a factor of one hundred million trillion) in gas density. They find that a small protostellar-like core of only 0.1 solar-masses can develop in only a few years from a suitable environment and then can grow into a supermassive black hole in only millions of years. In particular, they find that fragmentation, which had been predicted to disrupt the growth of these seedlings, is not a serious problem. Their result is a significant step towards explaining the cosmic origins of the seeds of galaxies.


Reference(s):

"Formation of Massive Protostars in Atomic Cooling Haloes," Fernando Becerra, Thomas H. Greif, Volker Springel, and Lars E. Hernquist, MNRAS 446, 2380, 2015.




Friday, January 16, 2015

The third way of galaxies

Credit: ESA/Hubble & NASA
Acknowledgement: J. Barrington


The subject of this image is NGC 6861, a galaxy discovered in 1826 by the Scottish astronomer James Dunlop. Almost two centuries later we now know that NGC 6861 is the second brightest member of a group of at least a dozen galaxies called the Telescopium Group — otherwise known as the NGC 6868 Group — in the small constellation of Telescopium (The Telescope).

This NASA/ESA Hubble Space Telescope view shows some important details of NGC 6861. One of the most prominent features is the disc of dark bands circling the centre of the galaxy. These dust lanes are a result of large clouds of dust particles obscuring the light emitted by the stars behind them.

Dust lanes are very useful for working out whether we are seeing the galaxy disc edge-on, face-on or, as is the case for NGC 6861, somewhat in the middle. Dust lanes like these are typical of a spiral galaxy. The dust lanes are embedded in a white oval shape, which is made up of huge numbers of stars orbiting the centre of the galaxy. This oval is, rather puzzlingly, typical of an elliptical galaxy.

So which is it — spiral or elliptical? The answer is neither! NGC 6861 does not belong to either the spiral or the elliptical family of galaxies. It is a lenticular galaxy, a family which has features of both spirals and ellipticals.

The relationships between these three kinds of galaxies are not yet well understood. A lenticular galaxy could be a faded spiral that has run out of gas and lost its arms, or the result of two galaxies merging. Being part of a group increases the chances for galactic mergers, so this could be the case for NGC 6861.

A version of this image was entered into the Hubble’s Hidden Treasures image processing competition by contestant Josh Barrington.


Source:  ESA/Hubble - Space Telescope


Thursday, January 15, 2015

A twist on planetary origins

An artist’s rendering of a protoplanetary impact. Early in the impact, molten jetted material is ejected at a high velocity and breaks up to form chondrules, the millimeter-scale, formerly molten droplets found in most meteorites. These droplets cool and solidify over hours to days. Image: NASA/California Institute of Technology

New study finds meteorites were byproducts of planetary formation, not building blocks

Meteors that have crashed to Earth have long been regarded as relics of the early solar system. These craggy chunks of metal and rock are studded with chondrules — tiny, glassy, spherical grains that were once molten droplets. Scientists have thought that chondrules represent early kernels of terrestrial planets: As the solar system started to coalesce, these molten droplets collided with bits of gas and dust to form larger planetary precursors.

However, researchers at MIT and Purdue University have now found that chondrules may have played less of a fundamental role. Based on computer simulations, the group concludes that chondrules were not building blocks, but rather byproducts of a violent and messy planetary process.

The team found that bodies as large as the moon likely existed well before chondrules came on the scene. In fact, the researchers found that chondrules were most likely created by the collision of such moon-sized planetary embryos: These bodies smashed together with such violent force that they melted a fraction of their material, and shot a molten plume out into the solar nebula. Residual droplets would eventually cool to form chondrules, which in turn attached to larger bodies — some of which would eventually impact Earth, to be preserved as meteorites.

Brandon Johnson, a postdoc in MIT’s Department of Earth, Atmospheric and Planetary Sciences, says the findings revise one of the earliest chapters of the solar system.

“This tells us that meteorites aren’t actually representative of the material that formed planets — they’re these smaller fractions of material that are the byproduct of planet formation,” Johnson says. “But it also tells us the early solar system was more violent than we expected: You had these massive sprays of molten material getting ejected out from these really big impacts. It’s an extreme process.”

Johnson and his colleagues, including Maria Zuber, the E.A. Griswold Professor of Geophysics and MIT’s vice president for research, have published their results this week in the journal Nature.


High-velocity molten rock

To get a better sense of the role of chondrules in a fledgling solar system, the researchers first simulated collisions between protoplanets — rocky bodies between the size of an asteroid and the moon. The team modeled all the different types of impacts that might occur in an early solar system, including their location, timing, size, and velocity. They found that bodies the size of the moon formed relatively quickly, within the first 10,000 years, before chondrules were thought to have appeared.

Johnson then used another model to determine the type of collision that could melt and eject molten material. From these simulations, he determined that a collision at a velocity of 2.5 kilometers per second would be forceful enough to produce a plume of melt that is ejected out into space — a phenomenon known as impact jetting.

“Once the two bodies collide, a very small amount of material is shocked up to high temperature, to the point where it can melt,” Johnson says. “Then this really hot material shoots out from the collision point.”

The team then estimated the number of impact-jetting collisions that likely occurred in a solar system’s first 5 million years — the period of time during which it’s believed that chondrules first appeared. From these results, Johnson and his team found that such collisions would have produced enough chondrules in the asteroid belt region to explain the number that have been detected in meteorites today.


Falling into place

To go a step further, the researchers ran a third simulation to calculate chondrules’ cooling rate. Previous experiments in the lab have shown that chondrules cool down at a rate of 10 to 1,000 kelvins per hour — a rate that would produce the texture of chondrules seen in meteorites. Johnson and his colleagues used a radiative transfer model to simulate the impact conditions required to produce such a cooling rate. They found that bodies colliding at 2.5 kilometers per second would indeed produce molten droplets that, ejected into space, would cool at 10 to 1,000 kelvins per hour.

“Then I had this ‘Eureka!’ moment where I realized that jetting during these really big impacts could possibly explain the formation of chondrules,” Johnson says. “It all fell into place.”

Going forward, Johnson plans to look into the effects of other types of impacts. The group has so far modeled vertical impacts — bodies colliding straight-on. Johnson predicts that oblique impacts, or collisions occurring at an angle, may be even more efficient at producing molten plumes of chondrules. He also hopes to explore what happens to chondrules once they are launched into the solar nebula.

“Chondrules were long viewed as planetary building blocks,” Zuber notes. “It’s ironic that they now appear to be the remnants of early protoplanetary collisions.”

Fred Ciesla, associate professor of planetary science at the University of Chicago, says the findings may reclassify chondrites, a class of meteorites that are thought to be examples of the original material from which planets formed.

“This would be a major shift in how people think about our solar system,” says Ciesla, who did not contribute to the research. “If this finding is correct, then it would suggest that chondrites are not good analogs for the building blocks of the Earth and other planets. Meteorites as a whole are still important clues about what processes occurred during the formation of the Solar System, but which ones are the best analogs for what the planets were made out of would change.”

This research was funded in part by NASA.


 
Source:  MIT News

Wednesday, January 14, 2015

Improved Saturn Positions Help Spacecraft Navigation, Planet Studies, Fundamental Physics

Artists's conception of Saturn and its moons, seen from above its pole
Credit: B. Kent, A. Angelich, NRAO/AUI/NSF 
Same image as above, without labels
 

Scientists have used the National Science Foundation's Very Long Baseline Array (VLBA) radio-telescope system and NASA's Cassini spacecraft to measure the position of Saturn and its family of moons to within about a mile -- at a range of nearly a billion miles. This feat improves astronomers' knowledge of the dynamics of our Solar System and also benefits interplanetary spacecraft navigation and research on fundamental physics.

The researchers, from the National Radio Astronomy Observatory (NRAO) and NASA's Jet Propulsion Laboratory (JPL), used the continent-wide VLBA to pinpoint the position of Cassini as it orbited Saturn over the past decade by receiving the signal from the spacecraft's radio transmitter. Combined with information about Cassini's orbit from NASA's Deep Space Network, the VLBA observations allowed the scientists to make the most accurate determinations yet of the position of the center of mass, called the barycenter, of Saturn and its numerous moons.

The scientists presented the results of their work at the American Astronomical Society's meeting in Seattle, Washington.

The measurement, some 50-100 times more precise than those provided by ground-based optical telescopes, was possible because of the VLBA's great resolving power, or ability to discern fine detail. With its 10 dish antennas spread from Hawaii to the Virgin Islands, the VLBA operates as a single radio telescope with a virtual size nearly equal to the Earth's diameter.

The result is a greatly improved ephemeris -- a table of predicted positions -- for the Saturnian system.

"An accurate ephemeris is one of the basic tools of astronomy, and this work is a great step toward tying together our understanding of the orbits of the outer planets and those of the inner planets," said Dayton Jones, of JPL, in Pasadena, California. "The orbits of the inner planets are well tied together, but those of the outer planets, including Saturn, have not been tied as well to each other or to those of the inner planets," Jones said.

The improved positional information will directly benefit scientists' ability to precisely navigate interplanetary spacecraft. In addition, it will help refine measurements of the masses of other Solar System objects. Also, the positional precision will improve predictions of when Saturn or its rings will pass in front of background stars, events that provide a variety of research opportunities.

Other benefits will come to studies of several aspects of fundamental physics. The new positional information will help researchers improve their precision when timing the radio pulses from pulsars -- spinning superdense neutron stars. Such timing will help answer unsolved questions about particle physics and the exact nature of the highly-compressed material inside a neutron star. Ongoing projects that time the pulses from multiple pulsars spread across our Milky Way Galaxy in an attempt to detect the effects of passing gravitational waves also will benefit from the improved Saturn ephemeris, which also improves the overall Solar System ephemeris.

VLBA measurements of the position of Cassini have even helped scientists who seek to make ever-more-stringent tests of Albert Einstein's theory of General Relativity by observing small changes in the apparent positions of strongly-emitting quasars as Saturn passes near them on the sky.

The position the scientists determined is that of the barycenter -- the center of mass -- of Saturn and its moons. When two bodies are in orbit, they both rotate about the barycenter. For example, the barycenter of the Sun and Jupiter is just outside the surface of the Sun, and the barycenter of the Earth and our Moon is about 1700 kilometers beneath the Earth's surface. The barycenter of Saturn and its largest moon, Titan, is about 30 kilometers from the center of Saturn. The barycenter of Saturn and all its moons (some 62 at current count) is what follows an elliptical orbit around the Sun.

In other studies, the VLBA has been used to measure the positions of Mars-orbiting satellites, and Voyager 1, the most distant man-made object, now some 12 billion miles (19 billion kilometers) from Earth on a journey that began with its launch in 1977.

In 2016, NASA's Juno spacecraft will begin orbiting Jupiter. "We plan to use similar techniques on this spacecraft, and improve the orbit for Jupiter as well," Jones said.

Jones worked with William Folkner, Robert Jacobson, and Christopher Jacobs, all of JPL, and Jon Romney, Vivek Dhawan, and Edward Fomalont, of the NRAO.

The National Radio Astronomy Observatory is a facility of the National Science Foundation, operated under cooperative agreement by Associated Universities, Inc. JPL, a division of the California Institute of Technology, Pasadena, manages the Cassini mission and Deep Space Network for NASA.


Media Contacts: 

Dave Finley, NRAO
(575) 835-7302

Preston Dyches, JPL
(818) 354-5011




NOAO: Smashing Results About Our Nearby Galactic Neighbors

The Blanco telescope from CTIO, and the sky as it would appear if your eye could see both optical and radio wavelengths. Blue and purple nebulosity shows hydrogen gas, which connects the Small Magellanic Cloud (at top right) and the Large Magellanic Cloud (middle right) and also stretches across the sky. Green circles show some of the DECam pointings of the SMASH survey, indicating the area over which Magellanic Cloud stars have been found. Image Credit: K. Olsen (NOAO/AURA/NSF), SMASH team, Roger Smith, and McClure-Griffiths.


SMASH DECam image in the Small Magellanic Cloud with moon for scale.


The Magellanic Clouds are the two brightest nearby satellite galaxies to our own Milky Way galaxy. From a new study it appears that not only are they much bigger than astronomers calculated, but also have non-uniform structure at their outer edge, hinting at a rich and complex field of debris left over from their formation and interaction. This is an early result from a survey called SMASH, for “Survey of the MAgellanic Stellar History”, carried out by an international team of astronomers using telescopes that include the Blanco 4-meter at Cerro Tololo Inter-American Observatory (CTIO) in Chile and presented today at the 225th meeting of the American Astronomical Society in Seattle, Washington.

The Large and Small Magellanic Clouds are dominant features in the Southern hemisphere sky. Although named after explorer Ferdinand Magellan who brought them to the attention of Europeans, they were already known to every early culture in the Southern hemisphere. The Large Cloud (LMC), covering about 5 degrees in angular size (10 lunar diameters), appears to the naked eye like a detached piece of the Milky Way. At a distance from us of about 160 thousand light years, even the brightest stars in these galaxies can’t be seen without a telescope.

As principal investigator Dr. David Nidever (University of Michigan) says, “We have a decent understanding of how large galaxies like the Milky Way form, but most galaxies in the universe are faint, distant, dwarf galaxies. The Magellanic Clouds are two of the few nearby dwarf galaxies, and SMASH is able to map out and study the structures in them like no other survey has been able to do before.”

“We knew from the earlier work of SMASH team members that the LMC was larger than we thought, but those observations probed only 1 percent of the area that we need to explore. SMASH is probing an area 20 times larger, and is confirming beyond doubt that the LMC is really large while also giving us a chance to map its structure in detail.” said Dr. Knut Olsen (National Optical Astronomy Observatory) one of the leaders of the SMASH team. The team has identified stars belonging to the LMC at angular distances up to 20 degrees away, corresponding to 55 thousand light years. This was done using a new camera, dubbed DECam, mounted on the CTIO Blanco 4-meter telescope, which allows the SMASH team to identify faint stars over a much larger area than ever before. 

With the Blanco telescope, SMASH can detect exceptionally diffuse stellar structures – up to 400,000 times fainter than the appearance of the faint band of the Milky Way in the night sky. This is possible because DECam can distinguish individual faint Magellanic stars over a huge area. (In astronomical parlance, the survey can reach a surface brightness limit of ~35 magnitudes per square arc second). That allows the team to detect stellar structures that were previously much too faint to see.

The team is also exploring the Magellanic Stream, a gaseous structure that connects the two Clouds and extends in front and behind them. The existence of the Magellanic Stream, first detected with radio telescopes over 30 years ago, clearly indicates that the two galaxies are interacting with each other and with our Milky Way. Astronomers have long expected to also find stars in the Stream but so far none have been detected. It’s likely this is because the stellar component of the Stream is too faint to have been detected until the availability of the new camera. As Dr. Nidever said, “SMASH’s ability to reveal super-faint stellar structures should not only allow us to finally detect the stellar component of the Magellanic Stream but also map out its structure which will give us a much better understanding of the Magellanic Clouds’ interaction history.”

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


Science Contacts

Dr. David Lee Nidever
University of Michigan, Ann Arbor
Department of Astronomy

dnidever@umich.edu
astro.lsa.umich.edu/~dnidever
434.249.6845 

Dr Knut Olsen
National Optical Astronomy Observatory
950 N Cherry Ave, Tucson AZ 85719 USA

kolsen@noao.edu




Tuesday, January 13, 2015

Comprehensive Andromeda Study Hints of Violent History

Dots show locations of stars in the Keck Observatory spectroscopic survey superimposed on an image of Andromeda. The stars are color coded according to their velocity relative to Earth, as measured from the spectra (negative velocity = moving towards Earth). The center of Andromeda is moving towards Earth at a speed of −300 km/s, whereas stars to the northeast (upper left) of the map have less negative velocities, indicating that they are moving away from Earth, relative to Andromeda's center. Credit: Claire Dorman and the European Space Agency. Hi-res image

This Hubble image of a crowded star field in the disk of the Andromeda galaxy shows that stars of different ages can be distinguished from one another on the basis of temperature (as indicated by color) and brightness. Credit: Ben Williams, Julianne Dalcanton, and the PHAT collaboration. Hi-res image

MAUNA KEA, HI – A detailed study of the motions of different stellar populations in Andromeda galaxy by UC Santa Cruz scientists using W. M. Keck Observatory data has found striking differences from our own Milky Way, suggesting a more violent history of mergers with smaller galaxies in Andromeda's recent past. The findings are being presented on Thursday, January 8, at the winter meeting of the American Astronomical Society in Seattle.

The structure and internal motions of the stellar disk of a spiral galaxy hold important keys to understanding the galaxy's formation history. The Andromeda galaxy, also called M31, is the closest spiral galaxy to the Milky Way and the largest in the local group of galaxies.

“In the Andromeda galaxy we have the unique combination of a global yet detailed view of a galaxy similar to our own. We have lots of detail in our own Milky Way, but not the global, external perspective,” said Puragra Guhathakurta, professor of astronomy and astrophysics at the University of California, Santa Cruz.
The new study, led by UC Santa Cruz graduate student Claire Dorman and Guhathakurta, combined data from two large surveys of stars in Andromeda conducted at the Keck Observatory in Hawaii as well as data from the Hubble Space Telescope.

The Spectroscopic and Photometric Landscape of Andromeda's Stellar Halo (SPLASH) survey used data from the 10-meter Keck II telescope, fitted with the DEIMOS multi-object spectrograph to measure radial velocities of more than 10,000 individual bright stars in Andromeda.

“The sheer light-gathering power of the Keck Observatory, the superb quality of DEIMOS spectra, free of instrumental/atmospheric artifacts, and its ability to obtain spectra of as many as 300 stars at once were crucial to the success of this experiment,” said Guhathakurta. “The Andromeda galaxy is about 2.5 million light years away so even its most luminous stars generally appear quite faint from our vantage point. To measure precise stellar velocities, the white light of each of these faint stars must be subdivided into thousands of wavelengths. The Keck/DEIMOS combination is the only one in the world capable of making these velocity measurements for large numbers of Andromeda stars.”

The recently completed Panchromatic Hubble Andromeda Treasury (PHAT) survey provided high-resolution imaging at six different wavelengths for more than half of these stars, Dorman said. The study presents the velocity dispersion of young, intermediate-age, and old stars in the disk of Andromeda, the first such measurement in another galaxy.

Dorman's analysis revealed a clear trend related to stellar age, with the youngest stars showing relatively ordered rotational motion around the center of the Andromeda galaxy, while older stars displayed much more disordered motion. Stars in a “well ordered” population are all moving coherently, with nearly the same velocity, whereas stars in a disordered population have a wider range of velocities, implying a greater spatial dispersion.

“If you could look at the disk edge-on, the stars in the well-ordered, coherent population would lie in a very thin plane, whereas the stars in the disordered population would form a much puffier layer,” Dorman explained.

The researchers considered different scenarios of galactic disk formation and evolution that could account for their observations. One scenario involves the gradual disturbance of a well-ordered disk of stars as a result of mergers with small satellite galaxies. Previous studies have found evidence of such mergers in tidal streams of stars in the extended halo of Andromeda, which appear to be remnants of cannibalized dwarf galaxies. Stars from those galaxies can also accrete onto the disk, but accretion alone cannot account for the observed increase in velocity dispersion with stellar age, Dorman said.

An alternate scenario involves the formation of the stellar disk from an initially thick, clumpy disk of gas that gradually settled. The oldest stars would then have formed while the gas disk was still in a puffed up and disordered configuration. Over time, the gas disk would have settled into a thinner configuration with more ordered motion, and the youngest stars would then have formed with the disk in that ordered configuration.
According to Dorman, a combination of these mechanisms could account for the team's observations. “Our findings should motivate theorists to carry out more detailed computer simulations of these scenarios,” she said.

The comparison to the Milky Way revealed substantial differences suggesting that Andromeda has had a more violent accretion history in the recent past. “Even the most well ordered Andromeda stars are not as well ordered as the stars in the Milky Way's disk,” Dorman said.

In the currently favored “Lambda Cold Dark Matter” paradigm of structure formation in the universe, large galaxies such as Andromeda and the Milky Way are thought to have grown by cannibalizing smaller satellite galaxies and accreting their stars and gas. Cosmologists predict that 70 percent of disks the size of Andromeda's and the Milky Way's should have interacted with at least one sizable satellite in the last 8 billion years. The Milky Way's disk is much too orderly for that to have happened, whereas Andromeda's disk fits the prediction much better.

“In this context, the motion of the stars in Andromeda's disk is more normal, and the Milky Way may simply be an outlier with an unusually quiescent accretion history,” Guhathakurta said.

Other researchers who collaborated with Dorman and Guhathakurta on this study include Anil Seth at the University of Utah; Daniel Weisz, Julianne Dalcanton, Alexia Lewis, and Benjamin Williams at the University of Washington; Karoline Gilbert at the Space Telescope Science Institute; Evan Skillman at the University of Minnesota; Eric Bell at the University of Michigan; and Katherine Hamren and Elisa Toloba at UC Santa Cruz. This research was funded by the National Science Foundation and NASA.

The W. M. Keck Observatory operates the largest, most scientifically productive telescopes on Earth. The two, 10-meter optical/infrared telescopes near the summit of Mauna Kea on the Island of Hawaii feature a suite of advanced instruments including imagers, multi-object spectrographs, high-resolution spectrographs, integral-field spectrographs and world-leading laser guide star adaptive optics systems.

DEIMOS (the DEep Imaging and Multi-Object Spectrograph) boasts the largest field of view (16.7 arcmin by 5 arcmin) of any of the Keck instruments, and the largest number of pixels (64 Mpix). It is used primarily in its multi-object mode, obtaining simultaneous spectra of up to 130 galaxies or stars. Astronomers study fields of distant galaxies with DEIMOS, efficiently probing the most distant corners of the universe with high sensitivity.

Keck Observatory is a private 501(c) 3 non-profit organization and a scientific partnership of the California Institute of Technology, the University of California and NASA.


Media Contact:

Steve Jefferson
Communications Officer
W. M. Keck Observatory
808.881.3827

sjefferson@keck.hawaii.edu


Science Contacts:

Claire Dorman
UC Santa Cruz

cdorman@ucolick.org

Puragra (Raja) Guhathakurta
(408) 455-3036
UC Santa Cruz

raja@ucolick.org




Monday, January 12, 2015

Tale of Two Black Holes

The real monster black hole is revealed in this new image from NASA's Nuclear Spectroscopic Telescope Array of colliding galaxies Arp 299
Image credit: NASA/JPL-Caltech/GSFC


A new high-energy X-ray image from NASA's Nuclear Spectroscopic Telescope Array, or NuSTAR, has pinpointed the true monster of a galactic mashup. The image shows two colliding galaxies, collectively called Arp 299, located 134 million light-years away. Each of the galaxies has a supermassive black hole at its heart.

NuSTAR has revealed that the black hole located at the right of the pair is actively gorging on gas, while its partner is either dormant or hidden under gas and dust. 

The findings are helping researchers understand how the merging of galaxies can trigger black holes to start feeding, an important step in the evolution of galaxies.

"When galaxies collide, gas is sloshed around and driven into their respective nuclei, fueling the growth of black holes and the formation of stars," said Andrew Ptak of NASA's Goddard Space Flight Center in Greenbelt, Maryland, lead author of a new study accepted for publication in the Astrophysical Journal. "We want to understand the mechanisms that trigger the black holes to turn on and start consuming the gas."

NuSTAR is the first telescope capable of pinpointing where high-energy X-rays are coming from in the tangled galaxies of Arp 299. Previous observations from other telescopes, including NASA's Chandra X-ray Observatory and the European Space Agency's XMM-Newton, which detect lower-energy X-rays, had indicated the presence of active supermassive black holes in Arp 299. However, it was not clear from those data alone if one or both of the black holes was feeding, or "accreting," a process in which a black hole bulks up in mass as its gravity drags gas onto it.

The new X-ray data from NuSTAR -- overlaid on a visible-light image from NASA's Hubble Space Telescope -- show that the black hole on the right is, in fact, the hungry one. As it feeds on gas, energetic processes close to the black hole heat electrons and protons to about hundreds of millions of degrees, creating a superhot plasma, or corona, that boosts the visible light up to high-energy X-rays. Meanwhile, the black hole on the left either is "snoozing away," in what is referred to as a quiescent, or dormant state, or is buried in so much gas and dust that the high-energy X-rays can't escape.

"Odds are low that both black holes are on at the same time in a merging pair of galaxies," said Ann Hornschemeier, a co-author of the study who presented the results Thursday at the annual American Astronomical Society meeting in Seattle. "When the cores of the galaxies get closer, however, tidal forces slosh the gas and stars around vigorously, and, at that point, both black holes may turn on."

NuSTAR is ideally suited to study heavily obscured black holes such as those in Arp 299. High-energy X-rays can penetrate the thick gas, whereas lower-energy X-rays and light get blocked.

Ptak said, "Before now, we couldn't pinpoint the real monster in the merger."

NuSTAR is a Small Explorer mission led by the California Institute of Technology in Pasadena and managed by NASA's Jet Propulsion Laboratory, also in Pasadena, for NASA's Science Mission Directorate in Washington. The spacecraft was built by Orbital Sciences Corporation, Dulles, Virginia. Its instrument was built by a consortium including Caltech; JPL; the University of California, Berkeley; Columbia University, New York; NASA's Goddard Space Flight Center, Greenbelt, Maryland; the Danish Technical University in Denmark; Lawrence Livermore National Laboratory, Livermore, California; ATK Aerospace Systems, Goleta, California, and with support from the Italian Space Agency (ASI) Science Data Center.

NuSTAR's mission operations center is at UC Berkeley, with the ASI providing its equatorial ground station located at Malindi, Kenya. The mission's outreach program is based at Sonoma State University, Rohnert Park, California. NASA's Explorer Program is managed by Goddard. JPL is managed by Caltech for NASA.

NASA is exploring our solar system and beyond to understand the universe and our place in it. The agency seeks to unravel the secrets of our universe, its origins and evolution, and search for life among the stars.

For more information, visit http://www.nasa.gov/nustar and http://www.nustar.caltech.edu/ .

Media Contact

Whitney Clavin
Jet Propulsion Laboratory, Pasadena, Calif.
818-354-4673

whitney.clavin@jpl.nasa.gov



Source: JPL-Caltech


Saturday, January 10, 2015

Volunteer 'Disk Detectives' Top 1 Million Classifications of Possible Planetary Habitats

A NASA-sponsored website designed to crowdsource analysis of data from the agency's Wide-field Infrared Survey Explorer (WISE) mission has reached an impressive milestone. In less than a year, citizen scientists using DiskDetective.org have logged 1 million classifications of potential debris disks and disks surrounding young stellar objects (YSO). This data will help provide a crucial set of targets for future planet-hunting missions.

"This is absolutely mind-boggling," said Marc Kuchner, an astrophysicist at NASA's Goddard Space Flight Center in Greenbelt, Maryland, and the project's principal investigator. "We've already broken new ground with the data, and we are hugely grateful to everyone who has contributed to Disk Detective so far."

Volunteers using DiskDetective.org, a NASA-sponsored citizen science website to find potential planetary nurseries, have made 1 million classifications in less than a year. Goddard astrophysicist Marc Kuchner, the project's principal investigator, explains how it works.Image Credit: NASA's Goddard Space Flight Center/S. Wiessinger. Download this video in HD formats from NASA Goddard's Scientific Visualization Studio

The marked asymmetry of the debris disk around the star HD 181327 (shown here in a Hubble image) suggests it may have formed as a result of the collision of two small bodies. Disk Detective aims to discover many other stellar disks using volunteer classifications of data from NASA's WISE mission.Image Credit:  NASA, ESA, G. Schneider (U. of Arizona), HST/GO 12228 Team


Combing through objects identified by WISE during its infrared survey of the entire sky, Disk Detective aims to find two types of developing planetary environments. The first, known as a YSO disk, typically is less than 5 million years old, contains large quantities of gas, and often is found in or near young star clusters. The second planetary habitat, known as a debris disk, tends to be older than 5 million years, holds little or no gas, and possesses 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.

Planets form and grow within disks of gas, dust and icy grains surrounding young stars. The particles absorb the star's light and reradiate it as heat, which makes the stars brighter at infrared wavelengths -- in this case, 22 microns -- than they would be without a disk.

Computer searches already have identified some objects seen by the WISE survey as potential dust-rich disks. But software can't distinguish them from other infrared-bright sources, such as galaxies, interstellar dust clouds and asteroids. There may be thousands of potential planetary systems in the WISE data, but the only way to know for sure is to inspect each source by eye.

Kuchner recognized that searching the WISE database for dusty disks was a perfect opportunity for crowdsourcing. He worked with 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.

At DiskDetective.org, volunteers watch a 10-second "flip book" of a disk candidate shown at several different wavelengths as observed from three different telescopes, including WISE. They then click one or more buttons that best describe the object's appearance. Each classification helps astronomers decide which images may be contaminated by background galaxies, interstellar matter or image artifacts, and which may be real disks that should be studied in more detail.

In March 2014, just two months after Disk Detective launched, Kuchner was amazed to find just how invested in the project some users had become. Volunteers complained about seeing the same object over and over. "We thought at first it was a bug in the system," Kuchner explained, "but it turned out they were seeing repeats because they had already classified every single object that was online at the time."

Some 28,000 visitors around the world have participated in the project to date. What's more, volunteers have translated the site into eight foreign languages, including Romanian, Mandarin and Bahasa, and have produced their own video tutorials on using it.

Many of the project's most active volunteers are now joining in science team discussions, and the researchers encourage all users who have performed more than 300 classifications to contact them and take part.
One of these volunteers is Tadeáš Černohous, a postgraduate student in geodesy and cartography at Brno University of Technology in the Czech Republic. "I barely understood what scientists were looking for when I started participating in Disk Detective, but over the past year I have developed a basic sense of which stars are worthy of further exploration," he said.

Alissa Bans, a postdoctoral fellow at Adler Planetarium in Chicago and a member of the Disk Detective science team, recalls mentioning that she was searching for candidate YSOs and presented examples of what they might look like on Disk Detective. "In less than 24 hours," she said, "Tadeáš had compiled a list of nearly 100 objects he thought could be YSOs, and he even included notes on each one."

Speaking at a press conference at the American Astronomical Society meeting in Seattle on Tuesday, Kuchner said the project has so far netted 478 objects of interest, which the team is investigating with a variety of ground-based telescopes in Arizona, California, New Mexico, Argentina and Chile. "We now have at least 37 solid new disk candidates, and we haven't even looked at all the new telescope data yet," he said.
Disk Detective currently includes about 278,000 WISE sources. The team expects to wrap up the current project sometime in 2018, with a total of about 3 million classifications and perhaps 1,000 disk candidates. The researchers then plan to add an additional 140,000 targets to the site.

“We’ve come a long way, but there’s still lots and lots more work to do -- so please drop by the site and do a little science with us!” added Kuchner.

WISE has made infrared measurements of more than 745 million objects, compiling the most comprehensive survey of the sky at mid-infrared wavelengths currently available. With its primary mission complete, the satellite was placed in hibernation in 2011. WISE was awoken in September 2013, renamed the Near-Earth Object Wide-field Infrared Survey Explorer (NEOWISE), and given a new mission to assist NASA's efforts in identifying the population of potentially hazardous near-Earth objects (NEOs).

Facilities involved in follow-up studies of objects found with Disk Detective include Apache Point Observatory in Sunspot, New Mexico; Palomar Observatory on Palomar Mountain, California; the Fred Lawrence Whipple Observatory on Mount Hopkins, Arizona; the Leoncito Astronomical Complex in El Leoncito National Park, Argentina; and Las Campanas Observatory, located in the Atacama Desert of Chile.

NASA is exploring our solar system and beyond to understand the universe and our place in it. We seek to unravel the secrets of our universe, its origins and evolution, and search for life among the stars. Today’s announcement shares the discovery of our ever-changing cosmos, and brings us closer to learning whether we are alone in the universe.


Related Links


Francis Reddy
NASA's Goddard Space Flight Center, Greenbelt, Maryland