Saturday, February 24, 2018

Magnetic Reconnection in the Sun

An ultraviolet picture of the sun's chromosphere, the thin layer of solar atmosphere sandwiched between the visible surface, the photosphere, and the corona. Astronomers have developed a simulation to address magnetic reconnection in the chromosphere. The image was taken by the Hinode spacecraft. JAXA/NASA


The Sun glows with a surface temperature of about 5500 degrees Celsius. On the other hand its hot outer layer, the corona, has a temperature of over a million degrees and ejects a wind of charged particles at a rate equivalent to about one-millionth of the moon's mass each year. Some of these particles bombard the Earth, producing auroral glows and occasionally disrupting global communications. In between these two regions of the Sun is the chromosphere. Within this complex interface zone, only a few thousand kilometers deep, the density of the gas drops with height by a factor of about one million and the temperature increases. Almost all of the mechanical energy that drives solar activity is converted into heat and radiation within this interface zone.

Charged particles are produced by the high temperatures of the gas, and their motions produce powerful, dynamic magnetic fields. Those field lines can sometimes break apart forcefully, but movement of the underlying charged particles often leads them to reconnect. There are two important, longstanding, and related questions about the hot solar wind: how is it heated, and how does the corona produce the wind? Astronomers suspect that magnetic reconnection in the chromosphere plays a key role.

CfA astronomer Nicholas Murphy and his three colleagues have completed complex new simulations of magnetic reconnection in hot ionized gas like that present in the solar chromosphere. (The lead author on the study, Lei Ni, was a visitor to the CfA.) The scientists include for the first time the effects of incompletely ionized gas in lower temperature regions, certain particle-particle effects, and other details of the neutral and ionized gas interactions. They find that the neutral and ionized gas is well-coupled throughout the reconnection region, and conclude that reconnection can often occur in the cooler portions of the zone. They also note that new, high-resolution solar telescopes are capable of studying smaller and smaller regions of low ionization for which their results are particularly applicable.

Reference(s):


"Magnetic Reconnection in Strongly Magnetized Regions of the Low Solar Chromosphere," Lei Ni, Vyacheslav S. Lukin, Nicholas A. Murphy, and Jun Lin, ApJ 852, 95, 2018.



Friday, February 23, 2018

Astronomers Discover S0-2 Star is Single and Ready for Big Einstein Test


The orbit of S0-2 (light blue) located near the Milky Way's supermassive black hole will be used to test Einstein's Theory of General Relativity and generate potentially new gravitational models. 

Lead author Devin Chu of Hilo, Hawaii is an astronomy graduate student at UCLA. The Hilo High School alumnus conducts his research with the UCLA Galactic Center Group, which uses the W. M. Keck Observatory on Hawaii Island to obtain scientific data. "Growing up on Hawaii Island, it feels surreal doing important research with telescopes on my home island. I find it so rewarding to be able to return home to conduct observations," Chu said. Credit: D. Chu

The UCLA Galactic Center Group takes a photo together during a visit to Keck Observatory, located atop Maunakea, Hawaii. Members of the group will return to the Observatory this spring to begin observations of S0-2 as the star travels towards its closest distance to the Galactic Center's supermassive black hole.



No companion found for famous young bright star orbiting Milky Ways supermassive black hole


Maunakea, Hawaii – Astronomers have the “all-clear” for an exciting test of Einstein’s Theory of General Relativity, thanks to a new discovery about S0-2’s star status. Credit: S. Sakai/A.GHEZ/W.M. Keck Observatory,/ UCLA Galactic Center Group

Up until now, it was thought that S0-2 may be a binary, a system where two stars circle around each other. Having such a partner would have complicated the upcoming gravity test.

But in a study published recently in The Astrophysical Journal, a team of astronomers led by a UCLA scientist from Hawaii has found that S0-2 does not have a significant other after all, or at least one that is massive enough to get in the way of critical measurements that astronomers need to test Einstein’s theory.

The researchers made their discovery by obtaining spectroscopic measurements of S0-2 using W. M. Keck Observatory’s OH-Suppressing Infrared Imaging Spectrograph (OSIRIS) and Laser Guide Star Adaptive Optics.

“This is the first study to investigate S0-2 as a spectroscopic binary,” said lead author Devin Chu of Hilo, an astronomy graduate student with UCLA’s Galactic Center Group. “It’s incredibly rewarding. This study gives us confidence that a S0-2 binary system will not significantly affect our ability to measure gravitational redshift.”

Einstein’s Theory of General Relativity predicts that light coming from a strong gravitational field gets stretched out, or “redshifted.” Researchers expect to directly measure this phenomenon beginning in the spring as S0-2 makes its closest approach to the supermassive black hole at the center of our Milky Way galaxy.

This will allow the Galactic Center Group to witness the star being pulled at maximum gravitational strength – a point where any deviation to Einstein’s theory is expected to be the greatest.

“It will be the first measurement of its kind,” said co-author Tuan Do, deputy director of the Galactic Center Group. “Gravity is the least well-tested of the forces of nature. Einstein’s theory has passed all other tests with flying colors so far, so if there are deviations measured, it would certainly raise lots of questions about the nature of gravity!”

“We have been waiting 16 years for this,” said Chu. “We are anxious to see how the star will behave under the black hole’s violent pull. Will S0-2 follow Einstein’s theory or will the star defy our current laws of physics? We will soon find out!”

The study also sheds more light on the strange birth of S0-2 and its stellar neighbors in the S-Star Cluster. The fact that these stars exist so close to the supermassive black hole is unusual because they are so young; how they could’ve formed in such a hostile environment is a mystery.

“Star formation at the Galactic Center is difficult because the brute strength of tidal forces from the black hole can tear gas clouds apart before they can collapse and form stars,” said Do.

“S0-2 is a very special and puzzling star,” said Chu. “We don’t typically see young, hot stars like S0-2 form so close to a supermassive black hole. This means that S0-2 must have formed a different way.”

There are several theories that provide a possible explanation, with S0-2 being a binary as one of them. “We were able to put an upper limit on the mass of a companion star for S0-2,” said Chu. This new constraint brings astronomers closer to understanding this unusual object.

“Stars as massive as S0-2 almost always have a binary companion. We are lucky that having no companion makes the measurements of general relativistic effects easier, but it also deepens the mystery of this star,” said Do.

The Galactic Center Group now plans to study other S-Stars orbiting the supermassive black hole, in hopes of differentiating between the varying theories that attempt to explain why S0-2 is single.



About OSIRIS


The OH-Suppressing Infrared Imaging Spectrograph (OSIRIS) is one of W. M. Keck Observatory’s "integral field spectrographs." The instrument works behind the adaptive optics system, and uses an array of lenslets to sample a small rectangular patch of the sky at resolutions approaching the diffraction limit of the 10-meter Keck Telescope. OSIRIS records an infrared spectrum at each point within the patch in a single exposure, greatly enhancing its efficiency and precision when observing small objects such as distant galaxies. It is used to characterize the dynamics and composition of early stages of galaxy formation. Support for this technology was generously provided by the Heising-Simons Foundation and the National Science Foundation. 



About Adaptive Optics


W. M. Keck Observatory is a distinguished leader in the field of adaptive optics (AO), a breakthrough technology that removes the distortions caused by the turbulence in the Earth’s atmosphere. Keck Observatory pioneered the astronomical use of both natural guide star (NGS) and laser guide star adaptive optics (LGS AO) and current systems now deliver images three to four times sharper than the Hubble Space Telescope. AO has imaged the four massive planets orbiting the star HR8799, measured the mass of the giant black hole at the center of our Milky Way Galaxy, discovered new supernovae in distant galaxies, and identified the specific stars that were their progenitors. Support for this technology was generously provided by the Gordon and Betty Moore Foundation, W. M. Keck Foundation, the National Science Foundation, and other Friends of Keck including The Bob and Renee Parsons Foundation, Change Happens Foundation, Mt. Cuba Astronomical Foundation, and Sanford and Jeanne Robertson.



About W. M. Keck Observatory


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

The data presented herein were obtained at Keck Observatory, which is a private 501(c) 3 non-profit organization operated as a scientific partnership among the California Institute of Technology, the University of California, and the National Aeronautics and Space Administration. The Observatory was made possible by the generous financial support of the W. M. Keck Foundation.

The authors wish to recognize and acknowledge the very significant cultural role and reverence that the summit of Maunakea has always had within the Native Hawaiian community. We are most fortunate to have the opportunity to conduct observations from this mountain.



Article Summary


A team of astronomers led by Devin Chu, a UCLA scientist from Hawaii, has found that S0-2 does not have a significant other after all, or at least one that is massive enough to get in the way of critical measurements that astronomers need to test Einstein’s Theory of General Relativity. Up until now, it was thought that S0-2 may be a binary, a system where two stars circle around each other. Having such a partner would have complicated the upcoming gravity test.





Contact

Mari-Ela Chock, 
Communications Officer
(808) 554-0567
mchock@keck.hawaii.edu



Thursday, February 22, 2018

Amateur Astronomer Captures Rare First Light of Massive Exploding Star

Observations of supernova "SN 2016gkg" taken with the Katzman Automatic Imaging Telescope (KAIT) at Lick Observatory. Credit: W.Zhenga/A. Filippenko (UC Berkeley)

Sequence of combined images (negatives, so black corresponds to bright) obtained by Víctor Buso as SN 2016gkg appears and brightens in the outskirts of the spiral galaxy NGC 613. Labels indicate the time each image was taken. The object steadily brightens for about 25 minutes, as shown quantitatively in the lower-right panel. Credit: V.Buso, M.Bersten, et al.

Supernova 2016gkg in spiral galaxy NGC 613; color image taken by a group of UC Santa Cruz astronomers on Feb. 18, 2017, with the 1-meter Swope telescope. Credit: C. Kilpatrick (UC Santa Cruz) and Carnigie Institution for Science, Las Campanas Observatory, Chile

Co-author Alex Filippenko, a UC Berkeley astronomer (right) with UC Santa Cruz Assistant Professor Ryan Foley (left), both of whom are longtime W. M. Keck Observatory users. Credit: © Laurie Hatch

Co-author Alex Filippenko's team included undergraduate students at UC Berkeley who helped research and monitor the changing brightness of Supernova 2016gkg. Credit: A. Filippenko



Maunakea, Hawaii – Thanks to lucky snapshots taken by an amateur astronomer in Argentina, scientists have obtained their first view of the initial burst of light from the explosion of a massive star.

During tests of a new camera, Víctor Buso captured images of a distant galaxy before and after the supernova's "shock breakout" – when a supersonic pressure wave from the exploding core of the star hits and heats gas at the star’s surface to a very high temperature, causing it to emit light and rapidly brighten.

To date, no one has been able to capture the "first optical light" from a normal supernova (one not associated with a gamma-ray or x-ray burst), since stars explode seemingly at random in the sky and the light from shock breakout is fleeting. The new data provide important clues to the physical structure of the star just before its catastrophic demise and to the nature of the explosion itself.

"Professional astronomers have long been searching for such an event," said UC Berkeley astronomer Alex Filippenko, who followed up the discovery with observations at the Lick and Keck observatories that proved critical to a detailed analysis of explosion, called SN 2016gkg. "Observations of stars in the first moments they begin exploding provide information that cannot be directly obtained in any other way."

"Buso’s data are exceptional," he added. "This is an outstanding example of a partnership between amateur and professional astronomers."

The discovery and results of follow-up observations from around the world will be published in the Feb. 22 issue of the journal Nature (and published online on Feb. 21).

On Sept. 20, 2016, Buso of Rosario, Argentina, was testing a new camera on his 16-inch telescope by taking a series of short-exposure photographs of the spiral galaxy NGC 613, which is about 80 million light years from Earth and located within the southern constellation Sculptor.

Luckily, he examined these images immediately and noticed a faint point of light quickly brightening near the end of a spiral arm that was not visible in his first set of images.

Astronomer Melina Bersten and her colleagues at the Instituto de Astrofísica de La Plata in Argentina soon learned of the serendipitous discovery and realized that Buso had caught a rare event, part of the first hour after light emerges from a massive exploding star.

She estimated Buso's chances of such a discovery, his first supernova, at one in 10 million or perhaps even as low as one in 100 million.

“It’s like winning the cosmic lottery,” said Filippenko.

Bersten immediately contacted an international group of astronomers to help conduct additional frequent observations of SN 2016gkg over the next two months, revealing more about the type of star that exploded and the nature of the explosion.

Filippenko and his colleagues obtained a series of seven spectra, where the light is broken up into its component colors, as in a rainbow, with the Shane 3-meter telescope at the University of California’s Lick Observatory near San Jose, California.

The researchers also performed spectroscopic observations using the Low Resolution Imaging Spectrometer (LRIS) and the DEep Imaging and Multi-Object Spectrograph (DEIMOS) at W. M. Keck Observatory on Maunakea, Hawaii.

The data allowed the international team to determine that the explosion was a Type IIb supernova: the explosion of a massive star that had previously lost most of its hydrogen envelope, a species of exploding star first observationally identified by Filippenko in 1987.

Combining the data with theoretical models, the team estimated that the initial mass of the star was about 20 times the mass of our sun, though it lost most of its mass, probably to a companion star, and slimmed down to about five solar masses prior to exploding.

Filippenko’s team continued to monitor the supernova’s changing brightness over two months with other Lick telescopes: the 0.76-meter Katzman Automatic Imaging Telescope and the 1- meter Nickel telescope.

“The Lick spectra, obtained with just a 3-meter telescope, are of outstanding quality in part because of a recent major upgrade to the Kast spectrograph, made possible by the Heising- Simons Foundation as well as William and Marina Kast,” Filippenko said.

Filippenko’s group, which included numerous undergraduate students, is supported by the Christopher R. Redlich Fund, Gary and Cynthia Bengier, the TABASGO Foundation, the Sylvia and Jim Katzman Foundation, many individual donors, the Miller Institute for Basic Research in Science and NASA through the Space Telescope Science Institute. Research at Lick Observatory is partially supported by a generous gift from Google.
ve obtained their first view of the initial burst of light from the explosion of a massive star.

During tests of a new camera, Víctor Buso captured images of a distant galaxy before and after the supernova's "shock breakout" – when a supersonic pressure wave from the exploding core of the star hits and heats gas at the star’s surface to a very high temperature, causing it to emit light and rapidly brighten.

To date, no one has been able to capture the "first optical light" from a normal supernova (one not associated with a gamma-ray or x-ray burst), since stars explode seemingly at random in the sky and the light from shock breakout is fleeting. The new data provide important clues to the physical structure of the star just before its catastrophic demise and to the nature of the explosion itself.

"Professional astronomers have long been searching for such an event," said UC Berkeley astronomer Alex Filippenko, who followed up the discovery with observations at the Lick and Keck observatories that proved critical to a detailed analysis of explosion, called SN 2016gkg. "Observations of stars in the first moments they begin exploding provide information that cannot be directly obtained in any other way."

"Buso’s data are exceptional," he added. "This is an outstanding example of a partnership between amateur and professional astronomers."

The discovery and results of follow-up observations from around the world will be published in the Feb. 22 issue of the journal Nature (and published online on Feb. 21).

On Sept. 20, 2016, Buso of Rosario, Argentina, was testing a new camera on his 16-inch telescope by taking a series of short-exposure photographs of the spiral galaxy NGC 613, which is about 80 million light years from Earth and located within the southern constellation Sculptor.

Luckily, he examined these images immediately and noticed a faint point of light quickly brightening near the end of a spiral arm that was not visible in his first set of images.

Astronomer Melina Bersten and her colleagues at the Instituto de Astrofísica de La Plata in Argentina soon learned of the serendipitous discovery and realized that Buso had caught a rare event, part of the first hour after light emerges from a massive exploding star.

She estimated Buso's chances of such a discovery, his first supernova, at one in 10 million or perhaps even as low as one in 100 million.

“It’s like winning the cosmic lottery,” said Filippenko.

Bersten immediately contacted an international group of astronomers to help conduct additional frequent observations of SN 2016gkg over the next two months, revealing more about the type of star that exploded and the nature of the explosion.

Filippenko and his colleagues obtained a series of seven spectra, where the light is broken up into its component colors, as in a rainbow, with the Shane 3-meter telescope at the University of California’s Lick Observatory near San Jose, California.

The researchers also performed spectroscopic observations using the Low Resolution Imaging Spectrometer (LRIS) and the DEep Imaging and Multi-Object Spectrograph (DEIMOS) at W. M. Keck Observatory on Maunakea, Hawaii.

The data allowed the international team to determine that the explosion was a Type IIb supernova: the explosion of a massive star that had previously lost most of its hydrogen envelope, a species of exploding star first observationally identified by Filippenko in 1987.

Combining the data with theoretical models, the team estimated that the initial mass of the star was about 20 times the mass of our sun, though it lost most of its mass, probably to a companion star, and slimmed down to about five solar masses prior to exploding.

Filippenko’s team continued to monitor the supernova’s changing brightness over two months with other Lick telescopes: the 0.76-meter Katzman Automatic Imaging Telescope and the 1- meter Nickel telescope.

“The Lick spectra, obtained with just a 3-meter telescope, are of outstanding quality in part because of a recent major upgrade to the Kast spectrograph, made possible by the Heising- Simons Foundation as well as William and Marina Kast,” Filippenko said.

Filippenko’s group, which included numerous undergraduate students, is supported by the Christopher R. Redlich Fund, Gary and Cynthia Bengier, the TABASGO Foundation, the Sylvia and Jim Katzman Foundation, many individual donors, the Miller Institute for Basic Research in Science and NASA through the Space Telescope Science Institute. Research at Lick Observatory is partially supported by a generous gift from Google.



About LRIS

The Low Resolution Imaging Spectrometer (LRIS) is a faint-light instrument capable of taking spectra and images of the most distant known objects in the universe. The instrument is equipped with a red arm and a blue arm to explore stellar populations of distant galaxies, active galactic nuclei, galactic clusters, and quasars. LRIS was used in observing distant supernovae by astronomers who received the Nobel Prize in Physics in 2011 for research determining that the universe was speeding up in its expansion. Support for LRIS was generously provided by Friends of Keck, including Change Happens Foundation and Mt. Cuba Astronomical Foundation.




About Deimos


The DEep Imaging and Multi-Object Spectrograph (DEIMOS) boasts the largest field of view (16.7arcmin by 5 arcmin) of any of the Keck Observatory 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. Support for DEIMOS was generously provided by the National Science Foundation.



About W.M. Keck Observatory

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

The data presented herein were obtained at Keck Observatory, which is a private 501(c) 3 non-profit organization operated as a scientific partnership among the California Institute of Technology, the University of California, and the National Aeronautics and Space Administration. The Observatory was made possible by the generous financial support of the W. M. Keck Foundation.


The authors wish to recognize and acknowledge the very significant cultural role and reverence that the summit of Maunakea has always had within the Native Hawaiian community. We are most fortunate to have the opportunity to conduct observations from this mountain.



Media Contact:

Mari-Ela Chock, 
Communications Officer
mchock@keck.hawaii.edu
(808) 554-0567



Shining Light on Dim Galactic Neighbors

On sky distribution of all known Milky Way satellite candidates with respect to the Magellanic Clouds and the neutral hydrogen gas of the Magellanic stream. For more details we refer to Nidever et al. (2010). The three candidates discussed in this study are highlighted in cyan.

False color RGB image of DES1 which is the small overdensity of stars in the centre of this field. The arrows in the lower right corner have a length of 15 arcseconds.


By measuring the brightness of about a dozen stars, lingering just outside of our galaxy, a team of astronomers believe they have solved a nearby intergalactic mystery. The researchers exposed the identities of three ultra-faint dwarf galaxy candidates using the Gemini South telescope. The team reports that the objects appear to be loose clusters of stars, not dwarf galaxies as some had previously believed. This finding has profound ramifications on the quantity of cold dark matter around our Milky Way and, by implication, other galaxies.

Using the Gemini Multi-Object Spectrograph (GMOS) at the Gemini South telescope in Chile, an international research team led by Dr. Blair C. Conn of the Australian National University studied three ultra-faint dwarf galaxy candidates, and found they were not as expected.

The three ultra-faint dwarf galaxy suspects, DES1, Eridanus III, and Tucana V, located in the vicinity of the Magellanic Clouds, were studied using a wide array of classification techniques. For each, fundamental properties including age, mass, luminosity, metallicity (ratio of heavier elements) and distance were determined. Based upon these parameters, the objects have instead been classified as star clusters.

While the brightness and metallicity are consistent with that of ultra-faint dwarf galaxies, their size and structure reveal their true nature. DES1 and Eri III are, according to the researchers, old, small, and highly elliptical stellar populations with very low metallicity.  Tuc V displays a low-level excess of stars at various locations across the GMOS field without a well-defined center. This suggests that Tuc V is either a star cluster in a late stage of dissolution, or a grouping of stars associated with the Small Magellanic Cloud (SMC) halo.

Classification of these faint objects as star clusters implies that they are not dominated by dark matter, as dwarf galaxies typically are, “and so we are still trying to define ultra-faint dwarf galaxies. Where are these smallest galaxies, what are their properties and how many are there? Answering these questions will help complete the census of Milky Way satellites and let us understand the history of our galaxy.”, says Conn.

Conn and his team are looking into the “Missing Satellites” problem which was originally identified almost two decades ago. Based on what is called the hierarchical formation scenario, many astronomers expected a large number of dwarf satellite galaxies, each containing a high fraction of dark matter, surrounding larger galaxies like our Milky Way. However, too few such satellites have been found to account for the expected amounts of dark matter.  Thus, classifying these ultra-faint objects is crucial to our understanding of dark matter in the Universe.

Watch for a feature article on this result in the April issue of GeminiFocus.



Abstract:

"We use deep Gemini/GMOS-S g,r photometry to study the three ultra-faint dwarf galaxy candidates DES1, Eridanus III (Eri III) and Tucana V (Tuc V). Their total luminosities, MV(DES1) =−1.42±0.50 and MV(Eri III) =−2.07±0.50, and mean metallicities, [Fe/H] =−2.38+0.21−0.19 and [Fe/H] =−2.40+0.19−0.12, are consistent with them being ultra-faint dwarf galaxies as they fall just outside the 1-sigma confidence band of the luminosity-metallicity relation for Milky Way satellite galaxies. However, their positions in the size-luminosity relation suggests that they are star clusters. 

Interestingly, DES1 and Eri III are at relatively large Galactocentric distances with DES1 located at DGC=74±4 kpc and Eri III at DGC=91±4 kpc. In projection both objects are in the tail of gaseous filaments trailing the Magellanic Clouds and have similar 3D-separations from the Small Magellanic Cloud (SMC): ΔDSMC,DES1 = 31.7 kpc and ΔDSMC,EriIII = 41.0 kpc, respectively. It is plausible that these stellar systems are metal-poor SMC satellites. Tuc V represents an interesting phenomenon in its own right. Our deep photometry at the nominal position of Tuc V reveals a low-level excess of stars at various locations across the GMOS field without a well-defined centre. A SMC Northern Overdensity-like isochrone would be an adequate match to the Tuc V colour-magnitude diagram, and the proximity to the SMC (12.1∘; ΔDSMC,TucV=13 kpc) suggests that Tuc V is either a chance grouping of stars related to the SMC halo or a star cluster in an advanced stage of dissolution."



Wednesday, February 21, 2018

Milky Way ties with neighbour in galactic arms race

The Milky Way and Andromeda prior to the merger. 
Credit: ICRAR

The Milky Way and Andromeda during the merger. 
Credit: ICRAR

The Milky Way and Andromeda during the merger—a close up.
Credit: ICRAR



Astronomers have discovered that our nearest big neighbour, the Andromeda galaxy, is roughly the same size as the Milky Way.

It had been thought that Andromeda was two to three times the size of the Milky Way, and that our own galaxy would ultimately be engulfed by our bigger neighbour.

But the latest research, published today, evens the score between the two galaxies.

It found the weight of the Andromeda is 800 billion times heavier than the Sun, on par with the Milky Way.

Astrophysicist Dr Prajwal Kafle, from The University of Western Australia node of the International Centre for Radio Astronomy Research, said the study used a new technique to measure the speed required to escape a galaxy.

“When a rocket is launched into space, it is thrown out with a speed of 11km/s to overcome the Earth’s gravitational pull,” he said.

“Our home galaxy, the Milky Way, is over a trillion times heavier than our tiny planet Earth so to escape its gravitational pull we have to launch with a speed of 550km/s.

“We used this technique to tie down the mass of Andromeda.”

Dr Kafle said the research suggests scientists previously overestimated the amount of dark matter in the Andromeda galaxy.

“By examining the orbits of high speed stars, we discovered that this galaxy has far less dark matter than previously thought, and only a third of that uncovered in previous observations,” he said.

The Milky Way and Andromeda are two giant spiral galaxies in our local Universe, and light takes a cosmologically tiny two million years to get between them.

With Andromeda no longer considered the Milky Way’s big brother, new simulations are needed to find out what will happen when the two galaxies eventually collide.

Dr Kafle used a similar technique to revise down the weight of the Milky Way in 2014, and said the latest finding had big implications for our understanding of our nearest galactic neighbours.

“It completely transforms our understanding of the local group,” he said.

“We had thought there was one biggest galaxy and our own Milky Way was slightly smaller but that scenario has now completely changed.

“It’s really exciting that we’ve been able to come up with a new method and suddenly 50 years of collective understanding of the local group has been turned on its head.”

University of Sydney astrophysicist Professor Geraint Lewis said it was exciting to be at a time when the data was getting so good.

“We can put this gravitational arms race to rest,” he said.





Publication Details
‘‘The Need for Speed: Escape velocity and dynamical mass measurements of the Andromeda galaxy’, published in the Monthly Notices of the Royal Astronomical Society on February 15th, 2018. Research paper available from here



Contact Information

Dr Prajwal Kafle
(ICRAR / The University of Western Australia)
Ph: +61 6488 7203       
E: Prajwal.Kafle@icrar.org

Pete Wheeler
(Media Contact, ICRAR)
Ph: +61 423 982 018
E: Pete.Wheeler@icrar.org



Friday, February 16, 2018

Hubble Sees Neptune's Mysterious Shrinking Storm

Three billion miles away on the farthest known major planet in our solar system, an ominous, dark storm – once big enough to stretch across the Atlantic Ocean from Boston to Portugal – is shrinking out of existence as seen in pictures of Neptune taken by NASA’s Hubble Space Telescope.

Immense dark storms on Neptune were first discovered in the late 1980s by NASA’s Voyager 2 spacecraft. Since then, only Hubble has had the sharpness in blue light to track these elusive features that have played a game of peek-a-boo over the years. Hubble found two dark storms that appeared in the mid-1990s and then vanished. This latest storm was first seen in 2015, but is now shrinking.



For the first time, NASA's Hubble Space Telescope has captured time-lapse images of a large, dark storm on Neptune shrinking out of existence. Credits: NASA Goddard's Scientific Visualization Studio.   This video is public domain and can be downloaded from NASA's Scientific Visualization Studio.


Like Jupiter’s Great Red Spot (GRS), the storm swirls in an anti-cyclonic direction and is dredging up material from deep inside the ice giant planet’s atmosphere. The elusive feature gives astronomers a unique opportunity to study Neptune’s deep winds, which can’t be directly measured.

The dark spot material may be hydrogen sulfide, with the pungent smell of rotten eggs. Joshua Tollefson from the University of California at Berkeley explained, “The particles themselves are still highly reflective; they are just slightly darker than the particles in the surrounding atmosphere.”

Unlike Jupiter’s GRS, which has been visible for at least 200 years, Neptune’s dark vortices only last a few years. This is the first one that actually has been photographed as it is dying.

“We have no evidence of how these vortices are formed or how fast they rotate,” said Agustín Sánchez-Lavega from the University of the Basque Country in Spain. “It is most likely that they arise from an instability in the sheared eastward and westward winds.”

This series of Hubble Space Telescope images taken over 2 years tracks the demise of a giant dark vortex on the planet Neptune. The oval-shaped spot has shrunk from 3,100 miles across its long axis to 2,300 miles across, over the Hubble observation period. Credits: NASA, ESA, and M.H. Wong and A.I. Hsu (UC Berkeley). Hi-res image


The dark vortex is behaving differently from what planet-watchers predicted. “It looks like we’re capturing the demise of this dark vortex, and it’s different from what well-known studies led us to expect,” said Michael H. Wong of the University of California at Berkeley, referring to work by Ray LeBeau (now at St. Louis University) and Tim Dowling’s team at the University of Louisville. “Their dynamical simulations said that anticyclones under Neptune’s wind shear would probably drift toward the equator. We thought that once the vortex got too close to the equator, it would break up and perhaps create a spectacular outburst of cloud activity.”

But the dark spot, which was first seen at mid-southern latitudes, has apparently faded away rather than going out with a bang. That may be related to the surprising direction of its measured drift: toward the south pole, instead of northward toward the equator. Unlike Jupiter’s GRS, the Neptune spot is not as tightly constrained by numerous alternating wind jets (seen as bands in Jupiter’s atmosphere). Neptune seems to only have three broad jets: a westward one at the equator, and eastward ones around the north and south poles. The vortex should be free to change traffic lanes and cruise anywhere in between the jets.

“No facilities other than Hubble and Voyager have observed these vortices. For now, only Hubble can provide the data we need to understand how common or rare these fascinating neptunian weather systems may be,” said Wong.

The first images of the dark vortex are from the Outer Planet Atmospheres Legacy (OPAL) program, a long-term Hubble project that annually captures global maps of our solar system’s four outer planets. Only Hubble has the unique capability to probe these worlds in ultraviolet light, which yields important information not available to other present-day telescopes. Additional data, from a Hubble program targeting the dark vortex, are from an international team including Wong, Tollefson, Sánchez-Lavega, Andrew Hsu, Imke de Pater, Amy Simon, Ricardo Hueso, Lawrence Sromovsky, Patrick Fry, Statia Luszcz-Cook, Heidi Hammel, Marc Delcroix, Katherine de Kleer, Glenn Orton, and Christoph Baranec.

Wong’s paper appears online in the Astronomical Journal on Feb. 15, 2018.

The Hubble Space Telescope is a project of international cooperation between NASA and ESA (European Space Agency). NASA’s Goddard Space Flight Center in Greenbelt, Maryland, manages the telescope. The Space Telescope Science Institute (STScI) in Baltimore conducts Hubble science operations. STScI is operated for NASA by the Association of Universities for Research in Astronomy, Inc., in Washington, D.C.

For additional imagery, visit: http://hubblesite.org/news_release/news/2018-08

For NASA’s Hubble web page, visit: www.nasa.gov/hubble


Ray Villard
Space Telescope Science Institute, Baltimore, Maryland
410-338-4514
villard@stsci.edu

Editor: Karl Hille

Source: NASA/Hubble

Thursday, February 15, 2018

Supermassive Black Holes Are Outgrowing Their Galaxies

Chandra Deep Field South 
Credit  X-ray: NASA/CXC/Penn. State/G. Yang et al & NASA/CXC/ICE/M. Mezcua et al.; 
Optical: NASA/STScI; Illustration: NASA/CXC/A. Jubett




The growth of the biggest black holes in the Universe is outrunning the rate of formation of stars in the galaxies they inhabit, according to two new studies using data from NASA's Chandra X-ray Observatory and other telescopes and described in our latest press release.

In this graphic an image from the Chandra Deep Field-South is shown. The Chandra image (blue) is the deepest ever obtained in X-rays. It has been combined with an optical and infrared image from the Hubble Space Telescope (HST), colored red, green, and blue. Each Chandra source is produced by hot gas falling towards a supermassive black hole in the center of the host galaxy, as depicted in the artist's illustration.

One team of researchers, led by Guang Yang at Penn State, calculated the ratio between a supermassive black hole's growth rate and the growth rate of stars in its host galaxy and found it is much higher for more massive galaxies. For galaxies containing about 100 billion solar masses worth of stars, the ratio is about ten times higher than it is for galaxies containing about 10 billion solar masses worth of stars.
Using large amounts of data from Chandra, HST and other observatories, Yang and his colleagues studied the growth rate of black holes in galaxies at distances of 4.3 to 12.2 billion light years from Earth. The X-ray data included the Chandra Deep Field-South and North surveys and the COSMOS-Legacy surveys.

Another group of scientists, led by Mar Mezcua of the Institute of Space Sciences in Spain, independently studied 72 galaxies located at the center of galaxy clusters at distances ranging up to about 3.5 billion light years from Earth and compared their properties in X-ray and radio waves. Their work indicates that the black hole masses were about ten times larger than masses estimated by another method using the assumption that the black holes and galaxies grew in tandem.

Hercules A
Credit: X-ray: NASA/CXC/SAO, Optical: NASA/STScI, Radio: NSF/NRAO/VLA


The Mezcua study used X-ray data from Chandra and radio data from the Australia Telescope Compact Array, the Karl G. Jansky Very Large Array (VLA) and Very Long Baseline Array. One object in their sample is the large galaxy in the center of the Hercules galaxy cluster. The image shown above includes Chandra data (purple), VLA data (blue) and HST optical data (appearing white).

Two papers describing these results have been accepted in the Monthly Notices of the Royal Astronomical Society (MNRAS). The work by Mezcua et al. was published in the February 2018 issue MNRAS (available online: https://arxiv.org/abs/1710.10268). The paper by Yang et al. will appear in its April 2018 issue (available online: https://arxiv.org/abs/1710.09399).

NASA's Marshall Space Flight Center in Huntsville, Alabama, manages the Chandra program for NASA's Science Mission Directorate in Washington. The Smithsonian Astrophysical Observatory in Cambridge, Massachusetts, controls Chandra's science and flight operations.




Fast Facts for Chandra Deep Field South:

Scale: Image is 9.25 arcsec (About 574,000 light years) across;
Category: Cosmology/Deep Fields/X-ray Background, Black Holes
Constellation: Fornax
Observation Date: 54 pointings between Oct 15, 1999 to Jul 22, 2010
Observation Time: 1111 hours 6 minutes (46 days 7 hours 6 min)
Obs. ID: 441, 581-582, 1431, 1672, 2239, 2312-2313, 2405-2406, 2409, 8591-8597, 9575, 9578, 9593, 9596, 9718, 12043-12055, 12123, 12128-12129, 12135, 12137-12138, 12213, 12218-12220, 12222-12223, 12227, 12230-12234
Instrument: ACIS
References: "Linking black hole growth with host galaxies: the accretion-stellar mass relation and its cosmic evolution",G. Yang et al., 2018, MNRAS, 475, 1887. arXiv:1710.09399 "The most massive black holes on the Fundamental Plane of Black Hole Accretion", M. Mazcua et al., 2018, MNRAS, 474, 1342. arXiv:1710.10268
Color Code: X-ray (Blue); IR (Red, Green); Optical (Green, Blue)
Distance Estimate: Range of about 12.7 - 12.9 billion light years


Monday, February 12, 2018

A red giant sheds its skin

Credit: ESO/M. Wittkowski (ESO)

This ghostly image features a distant and pulsating red giant star known as R Sculptoris. Situated 1200 light-years away in the constellation of Sculptor, R Sculptoris is something known as a carbon-rich asymptotic giant branch (AGB) star, meaning that it is nearing the end of its life. At this stage, low- and intermediate-mass stars cool off, create extended atmospheres, and lose a lot of their mass — they are on their way to becoming spectacular planetary nebulae.

While the basics of this mass-loss process are understood, astronomers are still investigating how it begins near the surface of the star. The amount of mass lost by a star actually has huge implications for its stellar evolution, altering its future, and leading to different types of planetary nebulae. As AGB stars end their lives as planetary nebulae, they produce a vast range of elements — including 50% of elements heavier than iron — which are then released into the Universe and used to make new stars, planets, moons, and eventually the building blocks of life.

One particularly intriguing feature of R Sculptoris is its dominant bright spot, which looks to be two or three times brighter than the other regions. The astronomers that captured this wonderful image, using ESO’s Very Large TelescopeInterferometer (VLTI), have concluded that R Sculptoris is surrounded by giant “clumps” of stellar dust that are peeling away from the shedding star. This bright spot is, in fact, a region around the star with little to no dust, allowing us to look deeper into the stellar surface.

This image captures an extremely small section of the sky: approximately 20x20 milliarcseconds. For comparison, Jupiter has an angular size of approximately 40 arcseconds.


Links


Source: ESO/Potw

Tuesday, February 06, 2018

TRAPPIST-1 Planets Probably Rich in Water

Artist’s impressions of the TRAPPIST-1 planetary system 

Artist’s impressions of the TRAPPIST-1 planetary system 

Artist’s impressions of the TRAPPIST-1 planetary system 

 
The ultracool dwarf star TRAPPIST-1 in the constellation of Aquarius 

 
The sizes, masses and temperatures of the seven TRAPPIST-1 planets and others

 
Properties of the seven TRAPPIST-1 planets compared to other known planets 

Properties of the seven TRAPPIST-1 planets 

Comparison of the properties of the seven TRAPPIST-1 planets 

Comparison of the TRAPPIST-1 system and the Solar System


Videos
 
ESOcast 150 Light: Planets around TRAPPIST-1 Probably Rich in Water
ESOcast 150 Light: Planets around TRAPPIST-1 Probably Rich in Water

Planet Parade: the seven planets of TRAPPIST-1
Planet Parade: the seven planets of TRAPPIST-1




First glimpse of what Earth-sized exoplanets are made of

A new study has found that the seven planets orbiting the nearby ultra-cool dwarf star TRAPPIST-1 are all made mostly of rock, and some could potentially hold more water than Earth. The planets' densities, now known much more precisely than before, suggest that some of them could have up to 5 percent of their mass in the form of water — about 250 times more than Earth's oceans. The hotter planets closest to their parent star are likely to have dense steamy atmospheres and the more distant ones probably have icy surfaces. In terms of size, density and the amount of radiation it receives from its star, the fourth planet out is the most similar to Earth. It seems to be the rockiest planet of the seven, and has the potential to host liquid water.

Planets around the faint red star TRAPPIST-1, just 40 light-years from Earth, were first detected by the TRAPPIST-South telescope at ESO’s La Silla Observatory in 2016. In the following year further observations from ground-based telescopes, including ESO’s Very Large Telescope and NASA’s Spitzer Space Telescope, revealed that there were no fewer than seven planets in the system, each roughly the same size as the Earth. They are named TRAPPIST-1b,c,d,e,f,g and h, with increasing distance from the central star [1].

Further observations have now been made, both from telescopes on the ground, including the nearly-complete SPECULOOS facility at ESO’s Paranal Observatory, and from NASA’s Spitzer Space Telescope and the Kepler Space Telescope.  A team of scientists led by Simon Grimm at the University of Bern in Switzerland have now applied very complex computer modelling methods to all the available data and have determined the planets’ densities with much better precision than was possible before [2].

Simon Grimm explains how the masses are found: "The TRAPPIST-1 planets are so close together that they interfere with each other gravitationally, so the times when they pass in front of the star shift slightly. These shifts depend on the planets' masses, their distances and other orbital parameters. With a computer model, we simulate the planets' orbits until the calculated transits agree with the observed values, and hence derive the planetary masses."

Team member Eric Agol comments on the significance: "A goal of exoplanet studies for some time has been to probe the composition of planets that are Earth-like in size and temperature. The discovery of TRAPPIST-1 and the capabilities of ESO’s facilities in Chile and the NASA Spitzer Space Telescope in orbit have made this possible — giving us our first glimpse of what Earth-sized exoplanets are made of!"

The measurements of the densities, when combined with models of the planets’ compositions, strongly suggest that the seven TRAPPIST-1 planets are not barren rocky worlds. They seem to contain significant amounts of volatile material, probably water [3], amounting to up to 5% the planet's mass in some cases — a huge amount; by comparison the Earth has only about 0.02% water by mass!

"Densities, while important clues to the planets' compositions, do not say anything about habitability. However, our study is an important step forward as we continue to explore whether these planets could support life," said Brice-Olivier Demory, co-author at the University of Bern.

TRAPPIST-1b and c, the innermost planets, are likely to have rocky cores and be surrounded by atmospheres much thicker than Earth's. TRAPPIST-1d, meanwhile, is the lightest of the planets at about 30 percent the mass of Earth. Scientists are uncertain whether it has a large atmosphere, an ocean or an ice layer.

Scientists were surprised that TRAPPIST-1e is the only planet in the system slightly denser than Earth, suggesting that it may have a denser iron core and that it does not necessarily have a thick atmosphere, ocean or ice layer. It is mysterious that TRAPPIST-1e appears to be so much rockier in its composition than the rest of the planets. In terms of size, density and the amount of radiation it receives from its star, this is the planet that is most similar to Earth.

TRAPPIST-1f, g and h are far enough from the host star that water could be frozen into ice across their surfaces. If they have thin atmospheres, they would be unlikely to contain the heavy molecules that we find on Earth, such as carbon dioxide.

"It is interesting that the densest planets are not the ones that are the closest to the star, and that the colder planets cannot harbour thick atmospheres," notes Caroline Dorn, study co-author based at the University of Zurich, Switzerland.

The TRAPPIST-1 system will continue to be a focus for intense scrutiny in the future with many facilities on the ground and in space, including ESO’s Extremely Large Telescope and the NASA/ESA/CSA James Webb Space Telescope.

Astronomers are also working hard to search for further planets around faint red stars like TRAPPIST-1. As team member Michaël Gillon explains [4]: "This result highlights the huge interest of exploring nearby ultracool dwarf stars — like TRAPPIST-1 — for transiting terrestrial planets. This is exactly the goal of SPECULOOS, our new exoplanet search that is about to start operations at ESO’s Paranal Observatory in Chile.”

 
Notes

 [1] The planets were discovered using the ground-based TRAPPIST-South at ESO’s La Silla Observatory in Chile; TRAPPIST-North in Morocco; the orbiting NASA Spitzer Space Telescope; ESO’s HAWK-I instrument on the Very Large Telescope at the Paranal Observatory in Chile; the 3.8-metre UKIRT in Hawaii; the 2-metre Liverpool and 4-metre William Herschel telescopes on La Palma in the Canary Islands; and the 1-metre SAAO telescope in South Africa.

[2] Measuring the densities of exoplanets is not easy. You need to find out both the size of the planet and its mass. The TRAPPIST-1 planets were found using the transit method — by searching for small dips in the brightness of the star as a planet passes across its disc and blocks some light. This gives a good estimate of the planet’s size. However, measuring a planet’s mass is harder — if no other effects are present planets with different masses have the same orbits and there is no direct way to tell them apart. But there is a way in a multi-planet system — more massive planets disturb the orbits of the other planets more than lighter ones. This in turn affects the timing of transits. The team led by Simon Grimm have used these complicated and very subtle effects to estimate the most likely masses for all seven planets, based on a large body of timing data and very sophisticated data analysis and modelling.

[3] The models used also consider alternative volatiles, such as carbon dioxide. However, they favour water, as vapour, liquid or ice, as the most likely largest component of the planets’ surface material as water is the most abundant source of volatiles for solar abundance protoplanetary discs.

[4] The SPECULOOS survey telescopes facility is nearly complete at ESO’s Paranal Observatory.



 
More Information


This research was presented in a paper entitled “The nature of the TRAPPIST-1 exoplanets”, by S. Grimm et al., to appear in the journal Astronomy & Astrophysics.

The team is composed of Simon L. Grimm (University of Bern, Center for Space and Habitability, Bern, Switzerland) , Brice-Olivier Demory (University of Bern, Center for Space and Habitability, Bern, Switzerland), Michaël Gillon (Space Sciences, Technologies and Astrophysics Research Institute, Université de Liège, Liège, Belgium), Caroline Dorn (University of Bern, Center for Space and Habitability, Bern, Switzerland; University of Zurich, Institute of Computational Sciences, Zurich, Switzerland), Eric Agol (University of Washington, Seattle, Washington, USA; NASA Astrobiology Institute’s Virtual Planetary Laboratory, Seattle, Washington, USA; Institut d’Astrophysique de Paris, Paris, France), Artem Burdanov (Space Sciences, Technologies and Astrophysics Research Institute, Université de Liège, Liège, Belgium), Laetitia Delrez (Cavendish Laboratory, Cambridge, UK; Space Sciences, Technologies and Astrophysics Research Institute, Université de Liège, Liège, Belgium), Marko Sestovic (University of Bern, Center for Space and Habitability, Bern, Switzerland), Amaury H.M.J. Triaud (Institute of Astronomy, Cambridge, UK; University of Birmingham, Birmingham, UK), Martin Turbet (Laboratoire de Météorologie Dynamique, IPSL, Sorbonne Universités, UPMC Univ Paris 06, CNRS, Paris, France), Émeline Bolmont (Université Paris Diderot, AIM, Sorbonne Paris Cité, CEA, CNRS, Gif-sur-Yvette, France), Anthony Caldas (Laboratoire d’astrophysique de Bordeaux, Univ. Bordeaux, CNRS, Pessac, France), Julien de Wit (Department of Earth, Atmospheric and Planetary Sciences, Massachusetts Institute of Technology, Cambridge, Massachusetts, USA), Emmanuël Jehin (Space Sciences, Technologies and Astrophysics Research Institute, Université de Liège, Liège, Belgium), Jérémy Leconte (Laboratoire d’astrophysique de Bordeaux, Univ. Bordeaux, CNRS, Pessac, France), Sean N. Raymond (Laboratoire d’astrophysique de Bordeaux, Univ. Bordeaux, CNRS, Pessac, France), Valérie Van Grootel (Space Sciences, Technologies and Astrophysics Research Institute, Université de Liège, Liège, Belgium), Adam J. Burgasser (Center for Astrophysics and Space Science, University of California San Diego, La Jolla, California, USA), Sean Carey (IPAC, Calif. Inst. of Technology, Pasadena, California, USA), Daniel Fabrycky (Department of Astronomy and Astrophysics, Univ. of Chicago, Chicago, Illinois, USA), Kevin Heng (University of Bern, Center for Space and Habitability, Bern, Switzerland), David M. Hernandez (Department of Physics and Kavli Institute for Astrophysics and Space Research, Massachusetts Institute of Technology, Cambridge, Massachusetts, USA), James G. Ingalls (IPAC, Calif. Inst. of Technology, Pasadena, California, USA), Susan Lederer (NASA Johnson Space Center, Houston, Texas, USA), Franck Selsis (Laboratoire d’astrophysique de Bordeaux, Univ. Bordeaux, CNRS, Pessac, France) and Didier Queloz (Cavendish Laboratory, Cambridge, UK).

ESO is the foremost intergovernmental astronomy organisation in Europe and the world’s most productive ground-based astronomical observatory by far. It is supported by 16 countries: Austria, Belgium, Brazil, the Czech Republic, Denmark, France, Finland, Germany, Italy, the Netherlands, Poland, Portugal, Spain, Sweden, Switzerland and the United Kingdom, along with the host state of Chile and by Australia as a strategic partner. ESO carries out an ambitious programme focused on the design, construction and operation of powerful ground-based observing facilities enabling astronomers to make important scientific discoveries. ESO also plays a leading role in promoting and organising cooperation in astronomical research. ESO operates three unique world-class observing sites in Chile: La Silla, Paranal and Chajnantor. At Paranal, ESO operates the Very Large Telescope and its world-leading Very Large Telescope Interferometer as well as two survey telescopes, VISTA working in the infrared and the visible-light VLT Survey Telescope. ESO is also a major partner in two facilities on Chajnantor, APEX and ALMA, the largest astronomical project in existence. And on Cerro Armazones, close to Paranal, ESO is building the 39-metre Extremely Large Telescope, the ELT, which will become “the world’s biggest eye on the sky”.


 
Links



Contacts

Simon Grimm
SAINT-EX Research Group, University of Bern, Center for Space and Habitability
Bern, Switzerland
Tel: +41 31 631 3995
Email:
simon.grimm@csh.unibe.ch

Brice-Olivier Demory
SAINT-EX Research Group, University of Bern, Center for Space and Habitability
Bern, Switzerland
Tel: +41 31 631 5157
Email:
brice.demory@csh.unibe.ch

Richard Hook
ESO Public Information Officer
Tel: +49 89 3200 6655
Cell: +49 151 1537 3591
Email:
rhook@eso.org

Source: ESO/News