Möbius strips of light made for the first time

• 19:00 29 January 2015 by Katherine Kornei

Twist a two-dimensional strip of paper then tape its ends together and it transforms into a one-sided loop. It's not magic; it's a Möbius strip. These mathematical structures show up everywhere from M.C. Escher drawings toelectrical circuits, but almost never in nature. Now, a team of physicists have shown for the first time that light can be coaxed into a Möbius shape.

"Light can kind of turn one-sided and single-edged under certain conditions," says Peter Banzer of the Max Planck Institute for the Science of Light in Erlangen, Germany.

Banzer and his colleagues were following up on predictions made by Isaac Freund at Bar-Ilan University in Israel, who first suggested in 2005 that light's polarisation, a property that describes how its electric field moves, could become twisted. If proved experimentally, the phenomenon could pave the way for fundamental studies of how light and matter interact, such as using light to trap tiny particles for biomedical purposes.

Let's twist again

In 2010, Freund proposed a way to test this: prepare two polarised beams of light and allow them to interfere with each other in a particular way. The interference will cause the polarisation to twist, forming a Möbius strip.

 

Banzer's team scattered two polarised green laser beams off a gold bead that was smaller than the wavelength of the light. The resulting inference introduced a polarisation pattern with either three or five twists, giving it a Möbius-like structure.

"These results are the first (experimental) proof that polarisation Möbius strips really exist, which has been a decade-long question in the community," Banzer says. "These findings emphasise the richness of light and its properties."

"The study is a brilliant tour de force at the cutting edge of optical technology," says Freund. "The real significance of this study goes far beyond verifying a particular prediction, because it demonstrates that it is possible to measure the full three-dimensional polarisation structure of light."

Journal reference: Science, DOI: 10.1126/science.1260635

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Asteroide 2004 BL86

WHERE IS PHILAE? WHEN WILL IT WAKE UP?

 

 

These are the two most popular questions currently being asked of the mission – especially on our social media channels – and ones that we will try to answer in this post, including inputs from the OSIRIS team, and from the Lander Control Centre at the German Aerospace Center (DLR).

Where is Philae?

Ever since Philae touched down on Comet 67P/Churyumov-Gerasimenko for the final time on 12 November – it is thought to have come into contact with the comet’s surface a total of four times including the final landing – the search has been on to identify it in images. While the CONSERT instrument has helped to narrow down a 350 x 30 m ‘landing strip’ on Comet 67P/C-G’s smaller lobe, a dedicated search in OSIRIS images has so far not been able to confirm the little lander’s final location.

Click for animation! The timestamp marked on the images are in UT (onboard spacecraft time).
Credits: ESA/Rosetta/MPS for OSIRIS Team MPS/UPD/LAM/IAA/SSO/INTA/UPM/DASP/IDA

Philae’s descent to the surface, the initial touchdown at Agilkia at 15:34 UT (onboard spacecraft time) and first rebound were well-documented with the OSIRIS narrow-angle camera. The team also identified what they believe to be the lander in a wide-angle shot taken at 17:18 UT above the rim of the large depression – named Hatmehit – on the comet’s small lobe. The image has been used to guide subsequent lander search efforts, and provides the basis for trajectory reconstructions. According to data recorded by Philae’s ROMAP instrument, the lander may have grazed the surface at 16:20 UT – so this image may have captured the result of that encounter.

Philae above the comet? Rosetta’s OSIRIS wide-angle camera captured this view of Comet 67P/Churyumov–Gerasimenko on 12 November 2014 at 17:18 GMT (onboard spacecraft time).
Credits: ESA/Rosetta/MPS for OSIRIS Team MPS/UPD/LAM/IAA/SSO/INTA/UPM/DASP/IDA

Philae’s onboard data subsequently recorded the next touchdown at 17:25 UT and its final touchdown at 17:32 UT, at a site that has now been named “Abydos” (the first touchdown site remains as Agilkia). Images sent back by the CIVA imager onboard the lander and subsequent reconstructions are providing clues as to the nature of the landing site, but a visual confirmation is still required to confirm its location.

Follow-up dedicated OSIRIS imaging campaigns that took place in late November and December from distances of 30 and 20 km from the centre of the comet (about 28 and 18 km from the surface, respectively) have not been successful in locating the lander. The campaigns specifically targeted the times that the lander would be illuminated – it is illuminated approximately 1.3 hours per comet revolution – and that Rosetta had the correct orbital position to be able to image it. However, the cameras were looking into long cast shadows from Rosetta’s terminator orbit, perpendicular to the Sun direction, which does not provide the optimum conditions for detecting the lander.

It is also important to note that Rosetta’s trajectory immediately following Philae’s touchdown allowed for good viewing conditions at the original landing site. Now that Rosetta has moved to a different orbit, and is further away from the comet, the chances of observing the lander are less (watch this video for a recap of the different trajectories following the landing).

The image below is an example of the images being used to search for the lander; it is a slightly cropped 2 x 2 mosaic taken by the OSIRIS narrow-angle camera on 13 December 2014 from a distance of about 20 km to the centre of the comet. For the 20 km imaging run 18 sets of two images were taken – one each with orange and blue filters to take advantage of the reflection of the lander solar panels, which differ compared to the cometary environment. The images were taken in the 2 x 2 rasters to ensure good surface coverage. The lander, about 1 metre across – the size of a household washing machine – would measure only about three pixels across in these images.

“We’re looking – by eye – for a set of three spots that correspond to the lander,” says OSIRIS principal investigator Holger Sierks from the Max Planck Institute for Solar System Research (MPS) in Germany. “The problem is that sets of three spots are very common all over the comet nucleus; Hatmehit and the area around its rim where we’re looking is full of boulders and we have identified several sets of three spots.”

Lander search area. The image is a 2 x 2 mosaic comprising OSIRIS narrow-angle camera images taken on 13 December 2014 from a distance of about 20 km to the centre of the comet. Credits: ESA/Rosetta/MPS for OSIRIS Team MPS/UPD/LAM/IAA/SSO/INTA/UPM/DASP/IDA

Although Rosetta is flying to within 6 km of the comet’s surface on 14 February, the planned trajectory foresees the closest approach on the lower part of the larger comet lobe (although the trajectory also takes Rosetta over the first touchdown point). This trajectory is planned such that the Sun will be directly behind the spacecraft, allowing the acquisition of shadow-free images. The close flyby will also allow the suite of science instruments on the orbiter to take spectra of the surface with unprecedented resolution and to directly sample the very innermost regions of the cometary coma in order to learn more about how the comet’s characteristic coma and tail develop.

“Rosetta’s busy science schedule is planned several months in advance, so a dedicated Philae search campaign was not built into the plan for the close flyby,” says ESA’s Rosetta project scientist Matt Taylor. “We’ll be focusing on “co-riding” observations from now on, that is, we won’t be changing the trajectory of Rosetta to specifically fly over the predicted landing zone in a dedicated search, but we can modify the spacecraft pointing and/or command images to be taken of the region if we’re flying close to the region and the science operations timeline allows.”

“After the flyby we’ll be much further away from the comet again, so are unlikely to have the opportunity for another dedicated lander search until later in the mission, maybe even next year,” adds ESA’s Rosetta mission manager Fred Jansen. “But the location of Philae is not required to be able to operate it, and neither does it need to be awake for us to find it.”

 

When will Philae wake up?

The likely orientation of Philae, shown in a visualisation of a topographic model of the comet's surface. Credits: ESA/Rosetta/Philae/CNES/FD

For those of you who followed the wake-up of Rosetta, you will know that it is not simply a case of switch on and get back to the science right away. The same goes for Philae.

At the original landing site, Philae was expected to receive around 6.5 hours of illumination per 12.4 hour comet day, with temperatures becoming too high by March 2015 to enable continued operations. Now, at its new location, the illumination is just 1.3 hours.

“Now we need the extra solar illumination provided by the comet’s closer proximity to the Sun by that time in order to bring the lander back to life,” says DLR’s Lander Project Manager Stephan Ulamec.

In fact, even by May, the Sun inclination will be such that it will be directly overhead of the predicted landing zone, although the lander’s orientation is such that it won’t be able to make full use of the maximum illumination on offer.

As for the process of wake up, and assuming Philae survived the low temperatures in its new residence, the earliest that the lander team expect it to be warm enough to boot up is in late March. But it will likely be May or June before there is enough solar illumination to use its transmitter, and to re-establish a communications link with Rosetta – the lander needs about 17 Watts to wake up and say “hello”.

Furthermore, the orbiter also has to be commanded to listen for Philae’s “I’m awake” signal, and be in a good position relative to the landing site to pick up the signal – although it can be up to 200 km away from the comet. It will be longer still before the battery is fully charged and Philae is ready to do science again, but that means there is a chance it will have a ringside seat for perihelion.

“We are already discussing and preparing which instruments should be operated for how long,” adds Stephan.

But even if Philae doesn’t wake up, it’s important to remember that it already completed its first science sequence on the comet, unexpectedly providing information from multiple locations on 67P/C-G.

Meanwhile Rosetta will continue to follow the comet on its orbit around the Sun and as it heads back towards the outer Solar System.

La gravedad como campo

La gravedad como campo

 

El hecho de que la fuerza de la gravedad también dependa de 1/r² como lo hace la fuerza de la electricidad, incita a pensar en el concepto de campo para describir la gravedad. Pero al contrario de lo que ocurre con la electricidad, la fuerza de gravedad es tan débil que sólo las grandes masas son capaces de ejercer unas fuerzas apreciables.

 

La gravedad puede eliminarse localmente mediante una aceleración. Por ejemplo, todos hemos visto los simuladores en los que trabajan los astronautas para recrear las condiciones de ingravidez. De aquí podemos deducir que las fuerzas de gravedad experimentadas se deben más al estado de movimiento del propio observador que a la gravedad en sí. Por ello, sólo las fuerzas diferenciales de la gravedad, denominadas fuerzas de marea, pueden considerarse reales. Es decir, cualquier concepto de campo gravitatorio debería basarse en los efectos de marea, no en la fuerza directa, siendo las ondas del campo gravitatorio ondas de marea. De esta forma, la gravedad objetiva, la que depende del observador, puede decirse que es un efecto secundario de marea.

 

Cuando un campo eléctrico actúa sobre una carga de prueba, la fuerza resultante puede representarse mediante un único vector, que puede descomponerse en tres dimensiones, en tres componentes perpendiculares. Sin embargo, el efecto de la gravedad de marea es más complicado, ya que en este caso tenemos 9 componentes vectoriales, a las que denominamos tensor, para describir un cizallamiento, una dilatación y una rotación. En resumen, el campo eléctrico es un campo vectorial y el gravitatorio es un campo tensorial.

 

El campo gravitatorio siempre estará dirigido hacia la masa que lo produce, luego podemos representarlo mediante líneas de fuerza. Una línea de fuerza se traza de tal forma que cada punto sea tangente a la dirección el campo siendo su densidad proporcional a la intensidad de éste.

 

Para llegar a una mejor comprensión de la fuerzas de marea, ya que este punto es fundamental para comprender este artículo, voy a introducir una explicación basándome en 3 ejemplos. De hecho, Einstein ya advirtió que la gravedad de marea es una manifestación de la curvatura del espacio-tiempo.

 

 

 

Ejemplo1.- Caída libre de dos partículas.

 

 

 

 

Imaginemos que soltamos dos partículas en caída libre y trayectorias paralelas. Mientras las vemos caer a la Tierra, a nuestros ojos parece que conservan estas trayectorias paralelas. Pero un análisis detallado y minucioso de la acción nos dice que esto no se cumple. Imaginemos que estas partículas tienen la capacidad de penetrar en la Tierra sin ser frenadas en absoluto. Las partículas se sienten atraídas por el centro de gravedad de la Tierra, es decir, por un único punto, lo que produce que se vayan acercando y colisionen en el centro de la Tierra. Para Einstein este corte de líneas inicialmente paralelas es una señal de la curvatura del espacio-tiempo.

Ejemplo 2.- Dos aviones que parten del Ecuador.

 

 

 

 

Otra forma de ver el ejemplo anterior consistiría en visualizar la trayectoria de dos aviones que parten desde el ecuador, en trayectorias paralelas hacia el polo Norte. Evidentemente, la geometría de la Tierra no es plana, por lo que las trayectorias rectas que son paralelas en el Ecuador convergen y se cortan en el polo norte. De aquí podemos deducir que una distorsión de la geometría plana puede desplazar la posición relativa de partículas vecinas, como si estuvieran actuando fuerzas de marea. Los dos aviones que en un principio parten en líneas paralelas, si no modifican su trayectoria chocarán en el polo norte.

Ejemplo 3.- Astronauta en caída libre hacia la Tierra.

 

 

 

 

Podemos intuir por los conocimientos que tenemos que la atracción gravitatoria en el astronauta es ligeramente diferente en las diversas partes de su cuerpo. Sus pies están más cerca de la Tierra que su cabeza, por lo que los atrae con mayor fuerza, estirando al astronauta de pies a cabeza. La gravedad también actúa hacia el centro del planeta con lo que podríamos decir que ejerce su acción ligeramente a la izquierda de su lado derecho y ligeramente a la derecha del lado izquierdo de su cuerpo, es decir, comprime los lados de su cuerpo hacia el centro. Desde el punto de vista del astronauta, la fuerza de gravedad hacia abajo ha desaparecido debido a los efectos de la caída libre. Pero lo que sí siente son las tensiones entre la cabeza y los pies y la compresión lateral. Éstas son producidas por las diferencia de gravedad entre las diferentes partes de su cuerpo. La tensión vertical y la compresión lateral son las fuerzas de marea o fuerzas gravitatorias de marea. Este mismo fenómeno es el que produce las mareas oceánicas terrestres.

Esta imagen ha sido obtenida mediante los datos aportados por el satélite GOCE encargado de estudiar el campo gravitatorio terrestre y muestra la caída libre de una manzana hacia la Tierra y la deformación que sufre en el proceso debido a las fuerzas de marea.

 

Talking to Pluto is hard! Why it takes so long to get data back from New Horizons

Posted by Emily Lakdawalla

2015/01/30 15:53 UTC

Topics: New Horizons, mission status, explaining technology

As I write this post, New Horizons is nearing the end of a weeklong optical navigation campaign. By taking photos of the Pluto system at regular intervals, New Horizons' navigators can precisely measure the observed positions of Pluto and its moons with respect to background stars, and determine the spacecraft's position. The last optical navigation images in the weeklong series will be taken tomorrow, but it will likely take two weeks or more for all the data to get to Earth. Two weeks! Why does it take so long? It's not like it's all that much data: 10 full-resolution LORRI images per day.

The short answer to that question is: Pluto is far away -- very far away, more than 30 times Earth's distance from the Sun -- so New Horizons' radio signal is weak. Weak signal means low data rates: at the moment, New Horizons can transmit at most 1 kilobit per second. (Note that spacecraft communications are typically measured in bits, not bytes; 1 kilobit is only 125 bytes.) Even at these low data rates, only the Deep Space Network's very largest, 70-meter dishes can detect New Horizons' faint signal.

Glen Nagle

DSS-43, the 70-meter dish at Canberra, Australia

Taken on November 10, 2011 while the Sun was surrounded by a "sunbow."

How much data is in a single LORRI image? (LORRI, which stands for Long Range Reconnaissance Imager, is New Horizons' highest-resolution camera.) LORRI's detector is 1024 pixels square. Like many modern space cameras, when the camera reads out its detector, it digitizes each pixel as a 12-bit number. Twelve million is an awful lot of bits, but fortunately LORRI's images are amenable to lossless compression, especially now when they contain mostly black space; they can be zipped up to about 2.5 Megabits without any loss of detail. They can be made even smaller with lossy JPEG compression, but for optical navigation, precision counts; the pictures have to be returned losslessly.

So, do the math. 2.5 Megabits, at 1 kilobit per second: it takes 42 minutes to return one LORRI photo to Earth. Most communications sessions last about eight hours. That's eleven images per communications session. And that assumes that New Horizons is transmitting only LORRI data, which it's not; there are other science instruments and spacecraft housekeeping data, too. The Deep Space Network has only three 70-meter dishes, and there is a lot of competition for time on them; New Horizons is lucky to get one communications session per day. And while New Horizons is pointing its dish at Earth, it can't point at anything else, including Pluto. It has to choose between communicating and taking data.

What all of this means is that whenever New Horizons is actively taking science data, it's building up a data backlog, which it fails to transmit completely in its next communications session. The New Horizons team wants to go into the close encounter phase with data recorders as empty as possible, clearing the decks for all that juicy data from the flyby. What to do?

They have a neat trick that can nearly double New Horizons' data transmission rate, but it comes at a cost of doing simultaneous science. New Horizons' radio system includes two Traveling Wave Tube Amplifiers or TWTAs (pronounced "twittas," like a Bostonian would say "twitters"). The TWTAs amplify the radio signals before they get broadcast from New Horizons' 2.1-meter dish. There are two TWTAs for redundancy: if one fails, the mission will still be able to return data to Earth. But the two TWTAs are not quite identical. One of them transmits radio signals with left-hand circular polarization, and one of them transmits with right-hand circular polarization.

Because they transmit with different polarization, both TWTAs can simultaneously transmit the same data through the dish antenna. On Earth, special hardware at the Deep Space Network can separately receive the two differently-polarized signals, and then combine them to make the signal stronger. Stronger signal means New Horizons can transmit at a higher data rate, about 1.9 times the rate with a single TWTA.

This two-TWTA mode wasn't developed until after launch; they deployed it early in the mission, and it worked well. But radio transmitters are power-hungry. New Horizons' nuclear power source has decayed since it launched nearly a decade ago, and there is no longer enough power to run both TWTAs at the same time as all the other spacecraft subsystems. If they want to nearly double their data rate and reduce their backlog, they need to shut something else down.

Amazingly, they can shut down their guidance and control system and use the saved power to run the second transmitter. But how can you point stably at Earth with your guidance system shut down? The answer is to turn New Horizons from a spacecraft whose orientation stays fixed in space to one that spins. Spinning spacecraft have incredibly stable pointing. It's costly in terms of precious hydrazine fuel to spin up and spin down the spacecraft, so they don't want to make the transition from three-axis to spin-stabilized very often. And you can't take photos from a spinning spacecraft (not with the cameras New Horizons has, anyway). But it's worth it to spend a little hydrazine and quit taking pictures a couple of times in order to get all the approach data down to Earth before the near-encounter phase starts.

So that's why New Horizons is going to spend two long periods of its Pluto approach taking no image data, with the spacecraft spinning and its high-gain antenna pointed at Earth. The two spin periods are scheduled right after trajectory correction maneuvers, rocket-firings that will fine-tune New Horizons' path past Pluto. The first spin period will last from March 10 to April 4; the second lasts from May 15 to May 27. For image fans like me, it'll be a little frustrating to know that Pluto will be getting bigger and bigger, yet New Horizons is not looking. But the consolation is that New Horizons will completely empty its memory on both occasions, sending everything it's got back to Earth, and making room for more and better data. And while the spacecraft is spinning, its particles instruments SWAP, PEPSSI, and SDC can all still take data.

 

New Horizons should be able to use this two-TWTA communication mode until well after the flyby, assuming, of course, that both transmitters remain healthy. It'll still take more than a year to get all the science data from the encounter back to Earth; it's a lot of data, and a skinny pipe. And it won't be able to use the two-TWTA communication mode forever. Eventually, the output of the nuclear power supply will decay to the point that even while spinning, New Horizons won't have enough power to run both transmitters simultaneously, and we'll be back to using just one at a time. The Kuiper belt object flyby will almost certainly require data return through only one transmitter. New Horizons is a lesson in patience!

 

Objetos transneptunianos sugieren que hay más planetas en el Sistema Solar

Posted on 17 enero, 2015 por Felipe Campos

 

 

Ilustración artística del planeta enano Makemake, un objeto transneptuniano. Crédito: IAU, M. Kornmesser (ESA/Hubble).

Los astrónomos llevan décadas debatiendo si queda algún oscuro planeta que descubrir dentro del Sistema Solar más allá de Plutón. Según los cálculos de científicos de la Universidad Complutense de Madrid (UCM) y la Universidad de Cambridge (Reino Unido), al menos dos planetas deben existir para explicar el comportamiento de los objetos transneptunianos extremos (ETNO).

La teoría establece que estos objetos que se mueven mucho más allá de Neptuno deberían distribuirse de forma aleatoria, y por un sesgo observacional, su órbita debe cumplir una serie de características: tener un semieje mayor con un valor de unas 150 UA (unidades astronómicas, o la distancia entre la Tierra y el Sol), una inclinación casi de 0° y un argumento o ángulo del perihelio (punto de la órbita más próximo a nuestra estrella) también cercano a 0° o a 180°.

Pero lo que se observa en una docena de estos cuerpos es bastante diferente: los valores del semieje mayor son muy dispersos (entre 150 UA y 525 UA), la inclinación media de la órbita ronda los 20° y su argumento del perihelio es de unos -31°, sin aparecer ni un solo caso cercano a 180°.

“Este exceso de objetos con parámetros orbitales distintos a los esperados nos hace pensar que algunas fuerzas invisibles están alterando la distribución de los elementos orbitales de los ETNO, y consideramos que la explicación más probable es que existen planetas desconocidos más allá de Neptuno y Plutón”, explica Carlos de la Fuente Marcos, científico de la UCM y coautor del trabajo.

“El número exacto es incierto, dado que los datos que tenemos son limitados, pero nuestros cálculos sugieren que por lo menos hay dos planetas, y probablemente más, en los confines de nuestro sistema solar”, añade el astrofísico.

Para realizar su estudio, los investigadores han analizado los efectos del denominado mecanismo Kozai, relacionado con la perturbación gravitacional que ejerce un cuerpo grande sobre la órbita de otro mucho más pequeño y lejano. Como referencia han considerado como funciona este mecanismo en el caso del cometa 96P/Machholz 1 por la influencia de Júpiter.

Dos problemas que resolver

A pesar de sus sorprendentes resultados, los autores reconocen que sus datos se enfrentan a dos problemas. Por un lado, su planteamiento está en contra de lo que predicen los modelos actuales de formación del Sistema Solar, que aseguran que no pueden existir planetas moviéndose en órbitas circulares más allá de Neptuno.

Sin embargo, el reciente descubrimiento del radiotelescopio ALMA de un disco de formación de planetas a más de 100 unidades astronómicas de la estrella HL Tauri, más joven y de menor masa que el Sol, sugiere que sí se pueden formar planetas a varios centenares de unidades astronómicas del centro del sistema.

Por otra parte, el equipo reconoce que su análisis está basado en una muestra con pocos objetos (13, concretamente), pero adelantan que en los próximos meses se van a hacer públicos más resultados con una muestra mayor. “Si se confirma, nuestro resultado puede ser realmente revolucionario en astronomía”, apunta De la Fuente Marcos.

El año pasado dos investigadores estadounidenses también descubrieron un planeta enano llamado 2012 VP113 en la nube de Oort, justo más allá de nuestro sistema solar. Los descubridores consideran que su órbita se ve influenciada por la posible presencia de una súper-Tierra oscura y gélida, de un tamaño hasta diez veces el de nuestro planeta.

El estudio “Flipping minor bodies: what comet 96P/Machholz 1 can tell us about the orbital evolution of extreme trans-Neptunian objects and the production of near-Earth objects on retrograde orbits” fue publicado en la edición del 11 de enero de 2015 deMonthly Notices of the Royal Astronomical Society.

El artículo “Extreme trans-Neptunian objects and the Kozai mechanism: signalling the presence of trans-Plutonian planets” fue publicado en la edición del 1 de septiembre de 2014 de Monthly Notices of the Royal Astronomical Society Letters.

Fuente: SINC

Will the Real Monster Black Hole Please Stand Up?

Will the Real Monster Black Hole Please Stand Up?

 

January 8, 2015

 

 

The real monster black hole is revealed in this new image from NASA's Nuclear Spectroscopic Telescope Array of colliding galaxies Arp 299. In the center panel, the NuSTAR high-energy X-ray data appear in various colors overlaid on a visible-light image from NASA's Hubble Space Telescope.

Image Credit: 

NASA/JPL-Caltech/GSFC

 

Full image and caption

 

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/ .

 

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

2015-007