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  • richardmitnick 3:54 pm on May 4, 2018 Permalink | Reply
    Tags: , Astronomy magazine, , , , , Wandering supermassive black holes   

    From Astronomy Magazine: “The Milky Way’s supermassive black hole may have a dozen nomadic siblings” 

    Astronomy magazine

    Astronomy Magazine

    April 27, 2018
    Jake Parks

    New research suggests that ‘wandering’ supermassive black holes are common within many types of galaxies — including the Milky Way.

    1
    Like most galaxies, the Andromeda galaxy (pictured above) is thought to house a supermassive black hole at its core. According to new research, galaxies roughly the mass of the Milky Way also likely contain about a dozen more ‘wandering’ supermassive black holes. NASA/JPL-Caltech

    At the center of the Milky Way sits a dark and dangerous beast: Sagittarius A*.

    SGR A* , the supermassive black hole at the center of the Milky Way. NASA’s Chandra X-Ray Observatory

    Located about 26,000 light-years from Earth, our galaxy’s only known supermassive black hole is roughly 4 million times as massive as the Sun, and its immense gravitational pull can nonchalantly annihilate any object that strays too close. Fortunately for us, Sagittarius A* is like a troll under a bridge — it does not leave its post.

    This tends to be the case for most supermassive black holes (SMBHs) found throughout the universe. However, sometimes a SMBH can be forced from the center of its host galaxy, particularly if it’s involved in a galactic merger with a bigger counterpart. For example, if a small galaxy merges with a larger one, the smaller galaxy’s SMBH will likely be thrown into a wide orbit around the newly formed galaxy, therefore becoming a ‘wandering’ supermassive black hole. Though astronomers have previously found evidence of these nomadic SMBHs on the outskirts of other galaxies, their overall prevalence is still largely unknown.

    But according to a new study published April 24 in The Astrophysical Journal Letters, wandering supermassive black holes may be quite common (and even observable) within many different types of galaxies — including the Milky Way.

    To carry out the study, the researchers took advantage of a new, state-of-the-art cosmological simulation called ROMULUS25. This N-body simulation uses an advanced supercomputer called Blue Waters to model how billions of individual particles interact and evolve over time.

    U Illinois Urbana-Champaign Blue Waters Cray Linux XE/XK hybrid machine supercomputer

    Though the ROMULUS25 simulation encompasses an astounding volume of over 15,000 cubic Megaparsecs (1 Megaparsec = 3 million light-years), it is still able to resolve the internal structure of galaxies and dwarf galaxies, as well as capture the orbital evolution of SMBHs following galactic mergers.

    3
    A sample of the ROMULUS25 simulation at redshift z = 0.4. The three slices of the simulation are focused on the same central group of galaxies (about 10 times as massive as the Milky Way), and shows the distribution of dark matter (left), the distribution of stars color-coded by composition (center; red are metal poor, blue are metal rich), and the distribution of stars color-coded by age (right; red are old, blue are young). White dots mark black holes. N-Body Shop (University of Washington).

    By extracting a sample of Milky-Way-mass galaxies from the simulation, the researchers were able to determine that any galaxy roughly the mass of the Milky Way, regardless of its recent merger history or morphology, likely contains about a dozen supermassive black holes, with roughly five being located within 30,000 light-years of the galaxy’s center. Although this slew of meandering SMBHs may seem intimidating (especially considering they roam for at least a few billion years), according to the study, they pose little threat to our tiny corner of the cosmos.

    “It is extremely unlikely that any wandering supermassive black hole will come close enough to our Sun to have any impact on our solar system,” said lead author Michael Tremmel, a postdoctoral fellow at the Yale Center for Astronomy and Astrophysics, in a press release. “We estimate that a close approach of one of these wanderers that is able to affect our solar system should occur every 100 billion years or so, or nearly 10 times the age of the universe.”

    So, even though the supermassive black hole at the center of the Milky Way may have a dozen disenfranchised siblings, by the time they could pose a threat to Earth, the Sun will have likely already burnt out. In the meantime, astronomers will continue working hard to definitely prove these wandering Goliaths actually exist. And once they do, the real fun can begin.

    See the full article here .

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  • richardmitnick 11:37 am on April 6, 2018 Permalink | Reply
    Tags: A telescope bigger than our planet reveals minute details in a nearby galaxy's center, Astronomers zoom in on a supermassive black hole's jets, , Astronomy magazine, , , , , Perseus Cluster of galaxies,   

    From Astronomy Magazine: “Astronomers zoom in on a supermassive black hole’s jets” 

    Astronomy magazine

    Astronomy Magazine

    April 03, 2018
    Alison Klesman

    A telescope bigger than our planet reveals minute details in a nearby galaxy’s center.

    1
    This image shows how radio telescopes on Earth and in space (left) combined to observe a very small region around another galaxy’s supermassive black hole (right). In this radio image, the black hole is located in the bright yellow-green spot at the top; a young jet about 3 light-years long shoots away from the black hole.
    Pier Raffaele Platania INAF/IRA (compilation); ASC Lebedev Institute (RadioAstron image).

    Supermassive black holes millions to billions of times the mass of our Sun lurk in the centers of most galaxies. In addition to feeding on nearby gas and dust, some of these black holes launch massive jets of plasma that not only dwarf the black hole itself, but the entire galaxy in which they reside. The mechanics of these jets, including exactly where they are launched, are still poorly understood, but observations such as those recently achieved using a combination of Earth- and space-based radio telescopes will help unlock the mysteries surrounding these dramatic structures.

    In a paper published April 2 in Nature Astronomy, an international collaboration of astronomers released observations of the jets around the black hole in the galaxy NGC 1275, located in the Perseus Cluster of galaxies about 230 million light-years away.

    Perseus galaxy cluster by NASA/Chandra

    Also known as Perseus A or 3C 84, this galaxy is classified as a Seyfert galaxy, meaning it has an “active” black hole currently feeding on surrounding material. That black hole is in the early stages of generating massive jets, which have now been mapped out via radio observations down to a mere 12 light-days from their origin around the black hole. That’s just a few hundred times the radius of the black hole itself (1 light-day is about 16 billion miles [26 billion kilometers]).

    What they found surprised them. “It turned out that the observed width of the jet was significantly wider than what was expected in the currently favored models where the jet is launched from the black hole’s ergosphere — an area of space right next to a spinning black hole where space itself is dragged to a circling motion around the hole,” said the paper’s lead author, Gabriele Giovannini from the Italian National Institute for Astrophysics, in a press release.

    Instead, “this may imply that at least the outer part of the jet is launched from the [much larger] accretion disk surrounding the black hole,” said said Tuomas Savolainen of Aalto University in Finland, and leader of the RadioAstron observing program that created the images.

    These images took advantage of a technique called very long baseline interferometry, or VLBI. This technique links several radio telescopes together to essentially observe with a “virtual” dish as large as the distance between the telescopes. In this case, the team linked Earth-based radio telescopes with a Russian 10-meter (33 feet) radio telescope orbiting Earth as part of the RadioAstron project, creating a virtual radio telescope with a diameter of over 200,000 miles (350,000 km), nearly the distance between Earth and the Moon.

    RadioAstron Spektr R satellite, the Astro Space Center of Lebedev Physical Institute in Moscow, Russia

    The larger the radio telescope, the finer the detail it can see, which allowed astronomers to zoom in on the region around NGC 1275’s black hole to look for clues about how and where the jet is generated. Their resulting images are 10 times better than anything previously achieved using ground-based radio telescopes alone. This same technique is the one utilized by the Event Horizon Telescope last year in an attempt to image the shadow of a supermassive black hole on its accretion disk; astronomers are eagerly awaiting the results, which should be announced later this year.

    Event Horizon Telescope Array

    Arizona Radio Observatory
    Arizona Radio Observatory/Submillimeter-wave Astronomy (ARO/SMT)

    ESO/APEX
    Atacama Pathfinder EXperiment

    CARMA Array no longer in service
    Combined Array for Research in Millimeter-wave Astronomy (CARMA)

    Atacama Submillimeter Telescope Experiment (ASTE)
    Atacama Submillimeter Telescope Experiment (ASTE)

    Caltech Submillimeter Observatory
    Caltech Submillimeter Observatory (CSO)

    IRAM NOEMA interferometer
    Institut de Radioastronomie Millimetrique (IRAM) 30m

    James Clerk Maxwell Telescope interior, Mauna Kea, Hawaii, USA
    James Clerk Maxwell Telescope interior, Mauna Kea, Hawaii, USA

    Large Millimeter Telescope Alfonso Serrano
    Large Millimeter Telescope Alfonso Serrano

    CfA Submillimeter Array Hawaii SAO
    Submillimeter Array Hawaii SAO

    ESO/NRAO/NAOJ ALMA Array
    ESO/NRAO/NAOJ ALMA Array, Chile

    South Pole Telescope SPTPOL
    South Pole Telescope SPTPOL

    Future Array/Telescopes

    Plateau de Bure interferometer
    Plateau de Bure interferometer

    NSF CfA Greenland telescope

    But while these observations don’t mesh exactly with expectations, “Our result does not yet falsify the current models where the jets are launched from the ergosphere, but it hopefully gives the theorists insight about the jet structure close to the launching site and clues how to develop the models,” said Savolainen.

    5
    The galaxy NGC 1275 contains the black hole around which jets were imaged in this study. This composite image shows detail from optical, radio, and X-ray observations. The purple X-ray lobes near the brightest part of the galaxy contain the young radio jets from the black hole.
    NASA, ESA, NRAO and L. Frattare (STScI). Science Credit: X-ray: NASA/CXC/IoA/A.Fabian et al.; Radio: NRAO/VLA/G. Taylor; Optical: NASA, ESA, the Hubble Heritage (STScI/AURA)-ESA/Hubble Collaboration, and A. Fabian (Institute of Astronomy, University of Cambridge, UK)

    ESO/NRAO/NAOJ ALMA Array in Chile in the Atacama at Chajnantor plateau, at 5,000 metres

    NASA/Chandra Telescope

    NRAO/Karl V Jansky VLA, on the Plains of San Agustin fifty miles west of Socorro, NM, USA, at an elevation of 6970 ft (2124 m)

    NASA/ESA Hubble Telescope

    This is only the second observation of jets at such close proximity to the black hole; the only other system that has been observed with this level of detail is M87. But the jets in M87 are much older, which, researchers say, may be why they look different from those in NGC 1275. “The jet in NGC 1275 was re-started just over a decade ago and is currently still forming, which provides a unique opportunity to follow the very early growth of a black hole jet,” said Masanori Nakamura from Academia Sinica in Taiwan, a co-author on the paper. “Continuing these observations will be very important.”

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  • richardmitnick 1:41 pm on March 2, 2018 Permalink | Reply
    Tags: , Astronomy magazine, , , , DOGs-dust-obscured galaxies, WISE1029   

    From Astronomy: “Can galaxies ignore their supermassive black holes?” 

    Astronomy magazine

    Astronomy Magazine

    February 22, 2018
    Alison Klesman

    Galaxies and their central supermassive black holes may not co-evolve as simply as we thought.

    1
    Supermassive black holes can generate massive outflows of gas as they grow. These outflows were believed to have a significant effect on the black hole’s host galaxy until an outlier was found. ESA/AOES Medialab.

    In recent decades, astronomers have discovered a supermassive black hole in the center of every large galaxy we see — including our own.

    2
    MASSIVE MONSTER. Hidden behind crowded thick dust is Sagittarius A*, the nearest supermassive black hole. While many other galaxies’ central supermassive black holes spew matter or energy, the monster at the center of our Milky Way remains strangely quiet.
    NASA/CXC/MIT/Frederick K. Baganoff, et al.

    SgrA* NASA/Chandra

    SGR A* , the supermassive black hole at the center of the Milky Way. NASA’s Chandra X-Ray Observatory

    They’ve even observed several apparent connections between the mass of the central black hole and the properties of the galaxy in which it resides. Such connections have led to theories that galaxies and their central supermassive black holes evolve together somehow, but recent findings have just thrown a wrench in that particular idea.

    Milky Way Galaxy Credits: NASA/JPL-Caltech/R. Hurt

    A team led by Yoshiki Toba of the Academia Sinica Institute of Astronomy and Astrophysics has used the Atacama Large Millimeter/submillimeter Array (ALMA) to observe a set of dust-obscured galaxies (DOGs) that give off bright infrared emission.

    ESO/NRAO/NAOJ ALMA Array in Chile in the Atacama at Chajnantor plateau, at 5,000 metres

    DOGs are believed to harbor black holes currently undergoing growth spurts, which typically spur outflows from the region around the feasting black hole. In one such galaxy, WISE1029, they observed that carbon monoxide (CO) gas in the galaxy’s disk, a crucial star-forming ingredient, was not affected by outflowing ionized gas (gas whose atoms have been stripped of electrons by strong radiation) from the central supermassive black hole. The total lack of a connection goes against current theory, which states that outflows should affect such star-forming gas, either by activating star formation or by stopping it. Their result was published December 18 in The Astrophysical Journal.

    “It has made the co-evolution of galaxies and supermassive black holes more puzzling,” said Yoshiki in a press release.

    2
    Emission from WISE1029’s carbon monoxide (left) and cold dust (right) shows no disruption associated with an outflow from the galaxy’s central supermassive black hole. ALMA (ESO/NAOJ/NRAO), Toba et al.

    WISE1029 is a particularly interesting target because the outflow of ionized gas from its black hole is considered extreme, which should have a significant effect on the molecular gas (such as CO) in the galaxy surrounding it. But ALMA’s detailed observations showed that the black hole’s outflow has not affected either the molecular gas or the ability of the galaxy to form stars.

    This is an odd result — outflows of ionized gas are frequently detected from supermassive black holes, but this is the first time the outflow has not been connected to a change in the galaxy’s molecular gas. Such an outlier suggests that astronomers cannot automatically assume such outflows will always change or quench star formation, and casts doubt on the idea that galaxies and their central supermassive black holes co-evolve in a simple way. One possibility is the outflow from the black hole may be shooting out perpendicular to the molecular gas in the disk, preventing the two from interacting — data from the Sloan Digital Sky Survey indicates that the black hole’s outflow of ionized gas is pointed directly toward Earth. So perhaps a specific orientation is needed to either cause or prevent interaction between the two.

    “Astronomers do not understand the real relation between the activity of supermassive black holes and star formation in galaxies,” said co-author Tohru Nagao of Ehime University. Indeed, it is one of the outstanding mysteries in the field of galaxy evolution, and one astronomers are focusing in on as the ability to observe details within single galaxies continues to improve.

    “Understanding such co-evolution is crucial for astronomy,” Yoshiki said. “By collecting statistical data of this kind of galaxies and continuing in more follow-up observations using ALMA, we hope to reveal the truth.”

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  • richardmitnick 8:33 am on February 17, 2018 Permalink | Reply
    Tags: , Astronomy magazine, , , ,   

    From Astronomy Magazine: “Celebrating Pluto’s discovery” 

    Astronomy magazine

    Astronomy Magazine

    February 15, 2018
    Alison Klesman

    1
    This is Pluto as it appeared to the New Horizons spacecraft during its approach of the dwarf planet in July 2015. NASA/Johns Hopkins University Applied Physics Laboratory/Southwest Research Institute.

    On February 18, 1930, Pluto was discovered by astronomer Clyde W. Tombaugh at the Lowell Observatory in Flagstaff, Arizona.

    Lowell Observatory, in Flagstaff, Arizona, USA

    Compared with the major planets in our solar system, Pluto has had a shorter but rockier history. Originally hailed as our solar system’s ninth planet, Pluto was reclassified as a dwarf planet by a 2006 vote of the International Astronomical Union — a move that remains controversial and challenged to this day.

    Pluto, regardless of the category into which it is sorted, has played a vital role in our understanding of the formation and evolution of our solar system. We now know it is part of a family of objects called the Kuiper Belt, comprised of icy, rocky remnants from the solar nebula’s earliest days. The Pluto system itself is larger than initially believed; its largest moon, Charon, wasn’t discovered until 1978, and only in the past two decades have astronomers uncovered four more tiny moons using the world’s most powerful telescopes.

    2
    An artist’s concept shows New Horizons flying through the Pluto system. Johns Hopkins University Applied Physics Laboratory/Southwest Research Institute.

    Until 2015, Pluto remained a dim dot through Earthbound telescopes, and a mere few pixels on images taken by the orbiting Hubble Space Telescope. On July 14, 2015, the New Horizons spacecraft flew past the Pluto system, forever changing our view of this distant world. Astronomy celebrated the accomplishment with our Year of Pluto, a wealth of fascinating articles looking back over our past expectations, guesses, and dreams about Pluto, and highlighting the unrivaled success of and the wealth of information unlocked by New Horizons over the course of just a few short hours.

    Circling the Sun on an elliptical orbit tilted relative to the plane of the planets, Pluto takes about 248 (Earth) years to make one trip; the tiny, icy world has not yet completed even a single orbit since its discovery. But despite its distance and its still-controversial status, Pluto remains one of the most beloved and fascinating objects in our solar system. Below, you can find links to some of our favorite articles on the history of Pluto, leading up to its discovery, its naming, and the 2015 flyby. Or we invite you to explore our full library of Pluto articles here: Year of Pluto.

    And if, like many, you believe Pluto should regain its place among the rightful planets of our solar system, stay tuned — Astronomy will be featuring an exclusive on the definition of the word planet, and how we might rethink it, in an upcoming magazine issue and online bonus feature.

    See the full article here .

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  • richardmitnick 8:19 am on February 17, 2018 Permalink | Reply
    Tags: , Astronomy magazine, , , , Lensed quasar RXJ1131−1231,   

    From Astronomy: “Astronomers report a possible slew of extragalactic exoplanets” 

    Astronomy magazine

    Astronomy Magazine

    February 09, 2018
    Mara Johnson-Groh

    Could a distant galaxy be home to a large population of unbound planets?

    1
    Astronomers have identified a population of rogue planets – planets not bound to or orbiting parent stars – in a lensing galaxy sitting between Earth and a distant quasar.
    NASA/JPL-Caltech

    Discoveries of exoplanets in our galaxy exceed 3,700 to date, but if that’s not enough for you, astronomers are now probing outside of the Milky Way to find exoplanets in other galaxies. A group of researchers at the University of Oklahoma has just announced the discovery of a large population of free-floating planets in a galaxy 3.8 billion light-years away. Their results were published February 2 in The Astrophysical Journal Letters.

    The researchers used a method known as quasar microlensing, which has traditionally been used to study the disk-like regions around supermassive black holes where material gathers as it spirals in toward the event horizon.

    2
    Credit: NASA/Jason Cowan (Astronomy Technology Center).

    When a distant quasar is eclipsed by a closer galaxy, the intervening galaxy will create several magnified replica images of the quasar. These replicas are further magnified by stars in the interloping galaxy to create a final super-magnified image that can be used to study the quasar in detail.

    Wild planets

    While studying the light emitted by the lensed quasar RXJ1131−1231 with the Chandra X-ray Observatory, the researchers noticed a particular wavelength of light emitted by iron was stronger than could be explained solely by the lensing effect of stars in the intervening galaxy.

    NASA/Chandra Telescope

    By modeling their results, the researchers concluded that the shifted energy signature was most likely caused by a huge population of planets with masses ranging from our Moon to Jupiter. The model that best matched the data found a ratio of 2,000 planets for every main sequence star in the galaxy —billions of stars. These planets are specifically “unbound” — not orbiting a star but wandering freely — as bound planets don’t have the same boosting effect seen in the data. Because the models only provided a wide range of potential planet masses, the researchers hope to identify the distribution of the sizes further with additional modeling.

    3
    RX J1131-1231 is about 6 billion light-years away. It is a lensed quasar; gravitational lensing caused by an intervening elliptical galaxy (center, yellow) has magnified and multiplied the image of RX J1131 into four images (pink) as seen with the Chandra X-ray Observatory.
    X-ray: NASA/CXC/Univ of Michigan/R.C.Reis et al; Optical: NASA/STScI

    NASA/ESA Hubble Telescope

    These preliminary results may just be the first out of the floodgates. “There are also other galaxies we’re working on,” says Xinyu Dai, lead author of the paper and researcher at the University of Oklahoma. “We think there are some signatures showing the presence of a small mass population, but we need to run detailed models to see if this is true or not.”

    Other Sightings

    This isn’t the first time astronomers have claimed a discovery of an exoplanet outside our galaxy. A signature consistent with a three-Earth-mass planet was detected in a galaxy 4 billion light-years away, but the one-time chance nature of the alignment causing the microlensing meant the discovery could not be confirmed with further observations. Similarly, a different version of microlensing using a star instead of a galaxy was previously used to probe the Andromeda Galaxy. A team found deviations in the light that they believed could be caused by an exoplanet six times as massive as Jupiter, but again the detection was never confirmed.

    The interloper star HIP 13044 was reported to itself host an exoplanet 25 percent larger than Jupiter, but subsequent follow-up found no evidence for the planet. Though this star is currently a part of the Milky Way, it originally came from a small galaxy that collided with the Milky Way six billion years ago.

    Vagabond stars like HIP 13044 may provide our best chance for examining exoplanets from other galaxies in detail. With current telescope technology, microlensing can point to a detection in other galaxies, but it cannot fully probe the properties of these candidates. Finding relatively nearby exoplanets around stars that originated abroad, however, may help us learn more about how exoplanets form and whether there are differences between planets born in different galaxies.

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  • richardmitnick 2:15 pm on December 1, 2017 Permalink | Reply
    Tags: , Astronomy magazine, , , , , The Sculptor dwarf galaxy   

    From Astronomy: “Astronomers measure the motions of stars in a nearby galaxy” 

    Astronomy magazine

    astronomy.com

    November 28, 2017
    Alison Klesman

    This first glimpse raises questions about the dark matter models we use.

    1
    The Sculptor dwarf galaxy is a satellite of the Milky Way, appearing here as a faint “cloud” of stars. ESO.

    When you look up at the night sky, the stars appear fixed — but things are not as they appear. In fact, every star in our galaxy is moving. While it’s easy for astronomers to measure whether a star is moving toward or away from us, it’s much harder to measure a star’s motion in the plane of the sky, or side to side. This is because the stars are so very distant, it takes years for even the most minute change to become visible. It’s why the constellations have appeared essentially the same over time; but given enough time, they will eventually warp and change as the motion of the stars that make them up becomes apparent.

    This “sideways” motion, called proper motion, has only ever been measured for stars in the Milky Way — until now. Recently, a group of astronomers combined data from the Hubble Space Telescope and the European Gaia mission to measure the proper motions of several stars in the Sculptor dwarf galaxy, a small, nearby satellite of the Milky Way. Their work, published yesterday in Nature Astronomy, now presents a possible challenge to the standard models of dark matter haloes believed to surround galaxies such as our own.

    The Gaia mission measures the positions of stars very precisely.

    ESA/GAIA satellite

    While most of these stars are in our Milky Way, its targets do include some stars in nearby galaxies, such as the Sculptor dwarf. The Hubble Space Telescope has also observed some of these same stars, measuring their positions 12 years ago.

    NASA/ESA Hubble Telescope

    Davide Massari of the University of Groningen and colleagues at the Kapteyn Astronomical Institute were able to combine the Gaia and Hubble data — no easy feat, as the two measure position differently — to find that 15 stars could be accurately tracked between the two epochs.

    “We determined how the stars move in this small galaxy,” Massari explained in a press release. “But our measured value was very surprising, as the standard models didn’t allow it.” Those standard models describe the expected distribution of dark matter in a huge halo around the Milky Way, inside which the Sculptor dwarf is embedded. That dark matter should dictate how the stars move; disagreement could mean the models are wrong and need updating.

    However, there is another explanation for the stars’ seemingly strange motions. “The models assume all stars to be in a single population of stars,” Massari said. But the Sculptor galaxy has at least two known populations of stars, one more compact and one more extended. The stars in each population experience different impacts from dark matter. If the stars measured in the study all belong to the compact population, it would explain why their motions disagree with the dark matter models, preserving those models with no need for alteration.

    In addition to measuring the motions of stars inside the Sculptor dwarf, the team also improved measurements of the galaxy’s orbit around the Milky Way. “This orbit is much wider than expected,” said Massari. “Previously, it was believed that the current spheroidal shape of Sculptor was in part the result of some close passages, but our measurements show that this is not the case.”

    As more Gaia measurements come in, they will continue to help astronomers chart the motions of stars in our galaxy and many others. This information will help us form a better picture of the galaxy we live in and the behavior of those around us, including the influence of the dark matter we can’t see.

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  • richardmitnick 1:13 pm on September 1, 2017 Permalink | Reply
    Tags: , Astronomy magazine, , , , Halo photometry, Scientists find that the stars in the Pleiades are variable   

    From Astronomy: “Scientists find that the stars in the Pleiades are variable” 

    Astronomy magazine

    Astronomy Magazine

    August 28, 2017
    Alison Klesman

    1
    The Pleiades is a young star cluster known for its seven brightest stars, called the Seven Sisters. NASA, ESA and AURA/Caltech

    The Pleiades is one of the most recognizable groups of stars in the northern sky. While to the naked eye this feature appears as seven bright stars, the Pleiades is actually a young open cluster about 100 million years old, containing 100 or more member stars. Though this cluster is less than 500 light-years from Earth, there is still much astronomers don’t know about it, in large part because its stars are too bright to observe with world-class telescopes. But now, a team of international astronomers has found a way around the problem, using the Kepler Space Telescope to discover and study variability in the Pleiades’ brightest stars.

    NASA/Kepler Telescope

    The work was led by Tim White of the Stellar Astrophysics Centre at Aarhus University in Denmark, and published August 11 in Monthly Notices of the Royal Astronomical Society. In their paper, they outline a new technique, called “halo photometry,” which is able to spot relative brightness changes in stars, even if they’re too bright to study directly. The algorithm looks at pixels on the camera detector next to, rather than those that fall directly on, the brightest part of stars. The algorithm measures changes in the values of those pixels to identify variability. As a result, the team discovered that the seven bright stars of the Pleiades are variable stars.

    Most of the stars are slowly pulsating B-type stars. These massive, bright stars change brightness every one to five days. Such stars are poorly understood, so adding the stars in the Pleiades to the current list of known variables and studying the Kepler data will help astronomers better understand the processes that affect these stars.

    But one star, Maia, was different. Maia exhibits regular changes every 10 days; curious, the team followed up by observing the star with the Hertzsprung SONG Telescope. By looking at spectra, which identify the chemical components of the star, they determined that the brightness changes Kepler saw co-occur with changes in the element manganese in the star’s atmosphere. Rather than pulsating like the other stars do, Maia’s changes appear to be “caused by a large chemical spot on the surface of the star, which comes in and out of view as the star rotates with a ten day period,” said co-author Victoria Antoci, an Assistant Professor at the Stellar Astrophysics Centre, in a press release.

    Funny enough, astronomers 60 years ago thought they had detected variability in Maia, but on the order of hours, not days. From those detections a new class of variables, Maia variables, was born — but now, says White, “Our new observations show that Maia is not itself a Maia variable!”

    2
    Kepler captured brightness variations in the Seven Sisters; astronomers noticed that one star, Maia, showed variability different from the others. Aarhus University/T. White

    Kepler’s forte is studying brightness changes in stars associated with the transit of orbiting planets. The satellite’s ability to accurately measure fluctuations in starlight also makes it an ideal tool to identify and study any cause of brightness changes from a star, such as pulsations or starspots. Kepler is now in its K2 mission, which has allowed the spacecraft to continue observing, even after the systems responsible for pointing the telescope failed.

    Kepler did not identify any transiting exoplanets during this study; however, the team says their new algorithm will allow Kepler and other planet-hunting telescopes to better search for planets around bright stars, which would have been otherwise skipped because they saturate the detector. They have also released the halo photometry algorithm as free open-source software for the community to use.

    See the full article here .

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  • richardmitnick 10:29 am on August 6, 2017 Permalink | Reply
    Tags: , Astronomy magazine, , , , MU69,   

    From Astronomy: “New Horizons may visit twice the object for the same price” 

    Astronomy magazine

    Astronomy Magazine

    August 04, 2017
    John Wenz

    MU69 could be hiding a strange secret: it’s one object, not two.

    1
    2014 MU69 is New Horizons’ next target. Now, data indicate it could be a contact binary – two objects orbiting each other so closely that they touch. NASA/JHUAPL/SwRI/Alex Parker.

    NASA/New Horizons spacecraft

    New Horizons is getting the ultimate two-for-one deal.

    The intrepid craft, which flew through the Pluto system in 2015, is en route to 2014 MU69, an icy remnant from our solar system’s formation that lives in the Kuiper Belt. While initially thought to be a chunk of ice less than a few dozen miles in size, a recent occultation event has revealed that MU69 might be even weirder.

    The object appears to have an odd shape, based on the occultation data (taken when an object passes in front of a background star). In a press release, NASA officials said that it’s either football shaped or, more intriguingly, a type of object called a contact binary.

    2
    If MU69 is not a contact binary, it might instead be football shaped. NASA/JHUAPL/SwRI/Alex Parker.

    A contact binary is composed of two objects close enough that they actually touch in an orbital dance around each other that leaves them relatively intact. The comet 67P explored by ESA’s Rosetta probe is believed to be a contact binary.

    We’ll find out for sure in 2019, when New Horizons flies by the object – or objects.

    See the full article here .

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  • richardmitnick 4:35 pm on April 20, 2017 Permalink | Reply
    Tags: , Astronomy magazine, , , The largest SETI initiative ever is reviewing 11 promising signals that probably aren’t aliens   

    From Astronomy: “The largest SETI initiative ever is reviewing 11 promising signals that probably aren’t aliens” 

    Astronomy magazine

    Astronomy Magazine

    April 20, 2017
    John Wenz

    1
    The Robert C. Byrd Radio Telescope at the Green Bank Observatory in West Virginia is one of the primary receivers looking for promising SETI signals.

    The Search for Extraterrestrial Intelligence (SETI) has been going for nearly 60 years now, and there have been plenty of false alarms in that time and nothing substantial. Now, a giant SETI initiative is looking into its initial round of data to follow up on 11 signals that they think could be aliens … but admit probably aren’t. Good to check, though, just in case.

    Two years ago, billionaire Yuri Milner put $100 million into a decade-long search for aliens known as the Breakthrough Listen initiative. It was the widest-scale SETI project announced since Project Phoenix in 1995, which itself was the successor of a cancelled 10 year, $100 million SETI effort by NASA.

    Breakthrough Listen is spearheaded by SETI Berkeley and taps into the wider SETI community to listen in worldwide for radio signals that might be artificial. They’ve also opened up the data to the public at large to look for narrowband signals — those in a specific wavelength that are more likely to be from a non-natural source. There are 692 targets in the initial rounds of data.

    The news is coming out of a two-day conference in California from the Breakthrough Initiatives organization, which is also sponsoring Breakthrough Starshot, a project based on using laser propulsion to power tiny spacecraft to the Alpha Centauri system (specifically Proxima Centauri) in a matter of decades.

    A live broadcast will take place today on Facebook at 6:10 p.m. EST (3:10 p.m. PST) with Andrew Siemion of SETI Berkeley discussing the initial results. You can watch it here.

    See the full article here .

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  • richardmitnick 10:47 am on April 19, 2017 Permalink | Reply
    Tags: , Astronomy magazine, Baryonic matter, Finding the Milky Way’s hydrogen halo   

    From Astronomy: “Finding the Milky Way’s hydrogen halo” 

    Astronomy magazine

    Astronomy Magazine

    April 19, 2017
    Alison Klesman

    2
    In 2012, Chandra spotted a hot hydrogen halo around the Milky Way. Now, astronomers are peering into the cooler hydrogen component of our galactic halo. NASA/CXC/M.Weiss; NASA/CXC/Ohio State/A.Gupta et al.

    Our galaxy is missing matter — baryonic matter, to be specific. Baryonic matter consists of baryons: particles such as protons and neutrons. It’s the everyday matter around you and makes up every element on the periodic table. Astronomers have been puzzled by the fact that the Milky Way and other galaxies are missing baryonic matter when the mass of their easily measured components, the disk and the bulge, are summed. Recent observations have indicated that galaxies may host a diffuse halo of gas out to great distances (hundreds of thousands of light-years), which is particularly hard to detect but could account for the missing matter. And now, as all-sky surveys amass ever more data, astronomers are finally starting to uncover more information about these halos.

    In a paper published in Nature Astronomy April 18, authors Huanian Zhang and Dennis Zaritsky describe their research exploring the Milky Way’s galactic halo of cool, diffuse hydrogen gas by observing the light of other galaxies as it passes through the halo on its way to Earth. When this light is broken up by a prism, it forms a spectrum that contains key details about the material the light has traveled through, which includes not only the matter in the distant galaxy from which it came, but also any intervening matter the light may have encountered on its journey — such as our galactic halo.

    This type of line-of-sight observation has been used before to study the galaxy’s halo, but has typically been limited to a few bright objects such as distant quasars (the extremely bright disks of gas and dust around supermassive black holes) or distant stars in our own galaxy’s halo. But with the ongoing releases of data from surveys such as the Sloan Digital Sky Survey (SDSS), millions of distant galaxy spectra are available for use. The vast amount of data allows astronomers to more easily separate out effects from the “nearby” gas in our galaxy’s halo as the light passes through it.

    Zhang and Zaritsky compiled a sample of 732,225 galaxy spectra from the 12th data release of the SDSS. By “stacking” or combining these spectra together, they were able to essentially boost the otherwise weak signal of the galaxy’s hydrogen halo, making it much easier to observe and characterize. The result was a clear detection of hydrogen-alpha, a specific “thumbprint” left on the light as it passed through the neutral hydrogen of the galactic halo.

    Based on the stacked signal, the pair determined that the gas could be moving at speeds up to 435 miles per second (700 kilometers per second). It has no net infall or loss, meaning it stays in the halo for the most part, rather than streaming away as outflows or falling inward to provide fuel for new stars. They also estimate the gas’ temperature could be about 21,000 degrees Fahrenheit (11,700 degrees Celsius).

    However, because Zhang and Zaritsky’s work combines hundreds of thousands of observations from all over the sky, it can’t provide fine details about the gas’ smaller-scale motions or temperature distribution. The work also focuses on only one component of many believed to belong to this galactic halo. In addition to cool hydrogen gas, the halo is thought to contain isolated hydrogen clouds and diffuse hot hydrogen gas that is visible in X-rays and was spotted by NASA’s Chandra X-ray Observatory.

    This work does help to lay the foundation for future exploration of this difficult-to-see but extremely massive component of our galaxy, which contains as much matter as all the stars in the bulge and disk of the galaxy put together. The authors conclude that more line-of-sight observations and analysis of additional spectral signatures left by this gas will help to flesh out the developing picture of our galaxy’s massive hydrogen halo.

    See the full article here .

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