SAO: Weekly Science Updates 2016

Find out the latest thinking about our universe.
User avatar
bystander
Apathetic Retiree
Posts: 18564
Joined: Mon Aug 28, 2006 2:06 pm
Location: Oklahoma

SAO: Colliding Galaxy Clusters

Post by bystander » Mon Dec 05, 2016 4:45 pm

Colliding Galaxy Clusters
Smithsonian Astrophysical Observatory
Weekly Science Update | 2016 Dec 02
[img3="The galaxy 3C438 and its cluster of galaxies as seen in the optical (left) and in X-rays by the Chandra X-ray Observatory (right). Astronomers have concluded that the hot gas is the result of a collision between two clusters of galaxies.
X-ray: NASA/CXC/CfA/R.P.Kraft; Optical: Pal.Obs. DSS
"]https://www.cfa.harvard.edu/sites/www.c ... 201647.jpg[/img3][hr][/hr]
Galaxy clusters contain a few to thousands of galaxies and are the largest bound structures in the Universe. Most galaxies are members of a cluster. Our Milky Way, for example, is a member of the "Local Group," a set of about fifty galaxies whose other large member is the Andromeda galaxy. The closest large cluster of galaxies to us, about fifty million light-years away, is the Virgo Cluster, with about 2000 members.

Clusters are believed to grow as the result of mergers between smaller galaxy groups and from the accretion of gas and dark matter. The energy released in these mergers is largely dissipated in the hot gas within the cluster, where X-ray observations can spot evidence for shocks and high temperatures. Mergers between two equally massive galaxy clusters provide particularly important diagnostics since these energetic collisions have the most dramatic and long-lasting effects. These major mergers are relatively rare events, however. The Bullet Cluster is one recently analyzed example, and because it also happens to act as a gravitational lens for background galaxies, it became famous for showing the distribution of its dark matter. ...

A Spectacular Bow Shock in the 11 keV Galaxy Cluster Around 3C 438 - Deanna L. Emery et al
Know the quiet place within your heart and touch the rainbow of possibility; be
alive to the gentle breeze of communication, and please stop being such a jerk.
— Garrison Keillor

User avatar
bystander
Apathetic Retiree
Posts: 18564
Joined: Mon Aug 28, 2006 2:06 pm
Location: Oklahoma

SAO: Solar-Like Oscillations in Other Stars

Post by bystander » Sat Dec 17, 2016 7:16 pm

Solar-Like Oscillations in Other Stars
Smithsonian Astrophysical Observatory
Weekly Science Update | 2016 Dec 09
[img3="The Hyades open star cluster in Taurus, one of the closest star clusters Astronomers using K2, the refurbished Kepler Space Telescope, studied solar-like oscillations in two stars in the cluster and used them to obtain stellar properties.
Credit: Jerry Lodriguss (Catching the Light), APOD 2012 Dec 24
"]https://www.cfa.harvard.edu/sites/www.c ... 201648.jpg[/img3][hr][/hr]
Our Sun vibrates due to pressure waves generated by turbulence in its upper layers (the layers dominated by convective gas motions). Helioseismology is the name given to the study of these oscillations, which can shed light on the inner workings of the Sun. Astronomers often detect brightness variations in other stars whose physical processes make them variable, like the Cepheid variable stars used to calibrate the cosmic distance scale, but it is much harder to detect solar-like oscillations in stars that are driven by convection near the star's surface ("astroseismology"). Open star clusters are well understood and provide benchmarks for studying stellar evolution, stellar rotation, stellar masses and ages, and many other properties, and so astroseismology would be a valuable addition by providing independent determinations of masses and ages for cluster members. But astronomers have not been able to perform such measurements on main sequence stars in an open cluster -- until now.

CfA astronomers Dave Latham, Allyson Bieryla, and Bob Stefanik were part of a team using K2, the refurbished Kepler Space Telescope to observe successfully these kinds of variations in main sequence stars. Kepler was designed to look for exoplanet transits through continuous and precise monitoring of a star's brightness. K2 stared at the stars in the Hyades cluster, about 155 light-years away, and took a brightness measurement roughly every minute for three months. The astronomers found small brightness variations across many timescales, but in two stars slightly larger than the Sun they found variations about every ten minutes that were particularly intense, signaling solar-like oscillations – the first ever such detections. Since the Hyades is an important standard cluster, the team had already been monitoring its stars for more than thirty-five years, and know that both of these two stars are single. The scientists conclude among other things that stars are very fast rotators (less than two days each; the Sun rotates in 26.2 days) which marks them as younger and quite different from the older, slower rotating population in the cluster. The new results illustrate the contribution that asteroseismology can make to the study of open star clusters, and the team plans to continue this work with future K2 observations. ...

Asteroseismology of the Hyades with K2: First Detection of
Main-sequence Solar-like Oscillations in an Open Cluster
- Mikkel N. Lund et al
Know the quiet place within your heart and touch the rainbow of possibility; be
alive to the gentle breeze of communication, and please stop being such a jerk.
— Garrison Keillor

User avatar
bystander
Apathetic Retiree
Posts: 18564
Joined: Mon Aug 28, 2006 2:06 pm
Location: Oklahoma

SAO: A Keplerian Disc Around a Massive Young Star

Post by bystander » Tue Jan 10, 2017 4:13 pm

A Keplerian Disc Around a Massive Young Star
Smithsonian Astrophysical Observatory
Weekly Science Update | 2016 Dec 16
[img3="A proposed sketch of the Keplerian disk (and the outflow) around a massive young star, as viewed from Earth. A new study using the SMA finds that this massive star, still in its early stages of life, is accreting material through a disk in a manner analogous to that used in lower mass stars. Credit: JD Ilee et al. 2016 MNRAS"]https://www.cfa.harvard.edu/sites/www.c ... 201651.jpg[/img3][hr][/hr]
A spinning solid disk, like a CD in its player, obviously moves faster at its outer edge than at its inner radii. A Keplerian disk, made up not of a single solid body but of many bodies orbiting under the rule of gravity, as deduced by Kepler, is the opposite: bodies at the outer edge move more slowly than those closer in. Thus the Earth orbits the Sun in 365 days, while Mercury does so in only 176 days. Keplerian motions are always predominant in disks around stars, including pre-planetary systems, unless winds or other physical processes interfere with the simple gravitational dominance of the central star.

Stars more massive than about eight solar-masses have a very short pre-main-sequence lifetimes, maybe only a few hundred thousand years. This means that they spend the entirety of their formation stages deeply embedded in their obscuring, parent molecular clouds. Such short formation time-scales also mean that there are far fewer nearby examples of young, massive stars when compared with their lower mass counterparts. All these factors contribute to the extreme difficulty of observing young massive stars and their disks directly. As a result, their formation mechanisms are poorly understood, and in particular the process by which young massive stars accrete their high masses is not known. ...

G11.92−0.61 MM1: A Keplerian Disc around a Massive Young Proto-O Star - J. D. Ilee et al
Know the quiet place within your heart and touch the rainbow of possibility; be
alive to the gentle breeze of communication, and please stop being such a jerk.
— Garrison Keillor

User avatar
bystander
Apathetic Retiree
Posts: 18564
Joined: Mon Aug 28, 2006 2:06 pm
Location: Oklahoma

SAO: Asymmetric Structure in the Supermassive Black Hole at the Galaxy’s Center

Post by bystander » Tue Jan 10, 2017 4:59 pm

Asymmetric Structure in the Supermassive Black Hole at the Galaxy’s Center
Smithsonian Astrophysical Observatory
Weekly Science Update | 2016 Dec 23
[img3="A multi-wavelength image of the field around Sagitarrius A*, the supermassive black hole at the center of the Milky Way galaxy (SgrA* is an imperceptible speck located at the center of this large field of sky). Astronomers have used an array of millimeter-wave telescope facilities to detect a small asymmetry that might be associated with the shadow of the black hole. Credit: NASA/CXC"]http://chandra.harvard.edu/photo/2014/sgra/sgra_525.jpg[/img3][hr][/hr]
The supermassive black hole candidate at the center of our Galaxy (associated with the radio source Sgr A*) is a prime candidate for studying the physical phenomena associated with accretion on to a supermassive black hole. Sgr A* is thought to accrete at an extremely low rate; analogous situations in X-ray binary stars suggest that a jet may be present, making it challenging to formulate a fully self-consistent model that simultaneously explains its spectrum, its variability, its size and its shape. Because Sgr A* is by far the closest supermassive black hole, its expected angular size (the shadow cast from its event horizon) is the largest of any known black hole candidate, making it a prime target for studies using very long baseline interferometry at mm wavelengths, which are capable of reaching spatial resolutions comparable to the expected shadow size.

CfA astronomer Shep Doeleman was a member of a team of twenty-two astronomers that used a combination of three widely separated millimeter telescope facilities, the Very Long Baseline Array, the Robert C. Byrd Green Bank Telescope, and the Large Millimeter Telescope Alfonso Serrano, to try to image the Sgr A* shadow. Their observations were taken in May of 2015 over the course of one evening, and the data from all the telescopes were analyzed to ascertain the geometry.

The scientists found some evidence for an asymmetric shape – a tiny extension that seems to protrude only a few AU from the central source (one astronomical unit is the average distance of the Earth from the Sun). This preliminary result could be due to scattering of the radiation by interstellar material, but it might also be associated with the black hole. Other observers have reported spotting some similar asymmetries, but the picture remains uncertain. The new result is a step forward, however, and future observations will try to refine and extend the current conclusions.

Asymmetric Structure in Sgr A* at 3mm from Closure Phase Measurements with VLBA, GBT and LMT - Christiaan D. Brinkerink et al
Know the quiet place within your heart and touch the rainbow of possibility; be
alive to the gentle breeze of communication, and please stop being such a jerk.
— Garrison Keillor

User avatar
bystander
Apathetic Retiree
Posts: 18564
Joined: Mon Aug 28, 2006 2:06 pm
Location: Oklahoma

SAO: Flares on Proxima Centauri

Post by bystander » Tue Jan 10, 2017 5:14 pm

Flares on Proxima Centauri
Smithsonian Astrophysical Observatory
Weekly Science Update | 2016 Dec 30
[img3="An image of the closest star to the Sun, star Promixa Centauri, and its surrounding field of stars. A new study of the flaring on Promixa Cen finds more magnetic activity that had been expected, with negative implications for its orbiting Earth-sized exoplanet, Proxima b. Credit: Marco Lorenzi"]https://www.cfa.harvard.edu/sites/www.c ... 201650.jpg[/img3][hr][/hr]
Stellar magnetic activity presents a challenge to the habitability of planets around M dwarf stars, the most abundant type of star. These stars have relatively low masses and small radii that make them easier targets around which to spot transiting exoplanet signatures than solar-type stars. Moreover, recent statistical studies have concluded that half of M dwarf stars host an exoplanet between about 0.5–1.4 Earth-radii in size orbiting in or near the "habitable zone" (with an orbital period shorter than 50 days). For such exoplanets, surface magnetic activity on the star, such as related to starspots, X-ray or UV flares, present significant hazards to any atmosphere present, at least until the stars reach a few billion years in age and mature to a more quiescent phase.

Proxima Centauri, the closest star to the Earth at a distance of 4.28 light-years, hosts Proxima b, a 1.27 Earth-mass exoplanet orbiting within the star’s habitable zone. Proxima Cen is therefore an important benchmark object for understanding low-mass stars, their planet formation, the evolution of their magnetic dynamos, and the impact of stellar activity on planetary atmospheres. CfA astronomer Dimitar Sasselov and four colleagues used the Canadian microsatellite MOST (Microvariability and Oscillations of Stars) to study Proxima Cen with 37.6 days of monitoring. They detected sixty-six flare events, the largest number of white-light flares observed to date on this star. Although less than the rate seen in other flare stars of a similar type, Proxima Cen does have more activity than was expected from its slow rotation rate (slow rotators generally have less vigorous magnetic activity); the reason for the odd behavior of Proxima Cen is a mystery. ...

MOST Observations of our Nearest Neighbor: Flares on Proxima Centauri - James R. A. Davenport et al
Know the quiet place within your heart and touch the rainbow of possibility; be
alive to the gentle breeze of communication, and please stop being such a jerk.
— Garrison Keillor