SAO: Weekly Science Updates 2019

Find out the latest thinking about our universe.
User avatar
bystander
Apathetic Retiree
Posts: 18009
Joined: Mon Aug 28, 2006 2:06 pm
Location: Oklahoma

SAO: Weekly Science Updates 2019

Post by bystander » Fri Jan 04, 2019 5:20 pm

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: 18009
Joined: Mon Aug 28, 2006 2:06 pm
Location: Oklahoma

Chandra Detection of a Circumnuclear Torus

Post by bystander » Fri Jan 04, 2019 5:30 pm

Chandra Detection of a Circumnuclear Torus
SAO Weekly Science Update | 2019 Jan 04
Most galaxies host supermassive black holes at their nuclei, each with millions or billions of solar-masses of material. There is thought to be a torus of dust and gas around the black holes, and an accreting disk that becomes very hot as material falls onto it, in turn heating the torus and circumnuclear gas and dust. Such an active galactic nucleus (AGN) radiates across the spectrum while the dust often blocks the innermost regions from view. Powerful bipolar jets of charged particles are often ejected as well. Radiation from the torus can be seen directly at infrared wavelengths and, when it scatters off the fast moving particles, at X-ray energies.

Active galactic nuclei (AGN) are among the most dramatic and interesting phenomena in extragalactic astronomy. All of the standard AGN models predict the presence of a torus and accretion disk but the details of the region have been difficult to study directly because the torus is thought to be relatively small, only hundreds of light-years in size. The ALMA millimeter array, however, has recently enabled detection of nearby AGN structures in both continuum and molecular line emission. NGC5643 is a face-on spiral galaxy that hosts an AGN and bipolar jets. Last year ALMA spotted an elongated structure in its nucleus about eighty light-years across (about 200 light-years across in emission from the cooler molecular gas component). Scientists had proposed that the structure was the expected AGN torus and the related molecular material responsible for the obscuration of the AGN and the collimation of the jets. ...

Chandra Detection of the Circumnuclear Molecular Torus of the
Compton-thick Active Galactic Nucleus in NGC 5643
~ G. Fabbiano 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: 18009
Joined: Mon Aug 28, 2006 2:06 pm
Location: Oklahoma

The Disintegrating Exoplanet K2-22b

Post by bystander » Fri Jan 18, 2019 8:35 pm

The Disintegrating Exoplanet K2-22b
SAO Weekly Science Update | 2019 Jan 11
Image
An artist's conception of K2-22b, an exoplanet slightly
smaller in size than Neptune. Observations suggest
that this exoplanet is in disintegrating, and has debris
in a trailing and leading dust tails. (Credit: NASA)

Exoplanet surveys have yielded many surprises over the years, and the discovery of "disintegrating" exoplanets was one of them. These are planets that produce asymmetric shapes in the dips of the light curves seen as they transit across the faces of their stars. The asymmetry is hypothesized to be due to tails of dusty material from the planets' disintegration. At present, only three such planets known around main sequence stars, one being K2-22b. There are currently over 3800 confirmed exoplanets, suggesting either that such objects are intrinsically rare or that they have very short lifetimes, in which case it is lucky to catch any in the act of disintegration. These systems have been under intense study to better understand their formation and evolution and to constrain the properties of the grains in the dust tails.

CfA astronomers George Zhou, Karen Collins, Allyson Bieryla, and Dave Latham were members of a team that obtained forty-five ground-based observations of the K2-22 system in their study of the evolution of its transit. K2-22b is a Neptune-sized exoplanet that orbits its star in only about nine hours; it is unusual in that it appears to have not only a trailing dust tail but a leading trail as well. The team’s observations of the dust tails included observing the transits at multiple wavelengths to try to use color to characterize the dust grain size or composition, but except in one transit event no differences were seen. The color information is, however, consistent with the previous model of dust grains as being small - comparable to or smaller than optical light wavelengths. The astronomers also confirmed the variability of the transits, thought to be evidence of the continuing rapid evolution of the dust tails. The scientists point out that this variability appears in all three disintegrating planets, and the shape variability occurs on all the timescales observed, from transit to transit and over several years. They conclude that a continuous observing campaign would be a valuable tool in unraveling the mystery of these dusty trails. ...

A Large Ground-based Observing Campaign of the Disintegrating Planet K2-22b ~ Knicole D. Colón 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: 18009
Joined: Mon Aug 28, 2006 2:06 pm
Location: Oklahoma

Making Stars When the Universe was Half Its Age

Post by bystander » Fri Jan 18, 2019 8:48 pm

Making Stars When the Universe was Half Its Age
SAO Weekly Science Update | 2019 Jan 18
The universe is about 13.8 billion years old, and its stars are arguably its most momentous handiwork. Astronomers studying the intricacies of star formation across cosmic time are trying to understand whether stars and the processes that produce them were the same when the universe was younger, about half its current age. They already know that from three to six billion years after the big bang stars were being made at a rate roughly ten times faster than they are today. How this happened, and why, are some of the key questions being posed for the next decade of research.

Star formation in a galaxy is thought to be triggered by the accretion of gas from the intergalactic medium (gas accretion via mergers between galaxies is thought to play a relatively minor role in the total numbers of stars produced). In galaxies that are actively making stars there is a tight relationship between their mass in stars and their rate of forming new stars, and this relationship approximately holds not only locally but even back when the universe was billions of years younger. In contrast, galaxies that are undergoing an active starburst - or the opposite, the quenching of star formation - fall above and below that relation respectively. The relationship supports the general picture of galaxy growth by gas accretion, except that for some reason smaller galaxies – those with fewer than about ten billion stars – seem to make slighter fewer stars than expected for their masses (the Milky Way is right at the turnover, with about ten billion stars and a rate of roughly one new star per year). A particularly significant consequence of this paucity, if real, is that simulations of galaxy growth do not show it, implying that the simulations are incorrect for smaller galaxies and that some physics is missing. ...

The MUSE Hubble Ultra Deep Field Survey XI. Constraining the low-mass end of
the stellar mass - star formation rate relation at z < 1
~ Leindert A. Boogaard et al
viewtopic.php?t=37800
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
Ann
4725 Å
Posts: 9318
Joined: Sat May 29, 2010 5:33 am

Re: Making Stars When the Universe was Half Its Age

Post by Ann » Sat Jan 19, 2019 6:07 am

Smithsonian Astrophysical Observatory wrote:

The relationship supports the general picture of galaxy growth by gas accretion, except that for some reason smaller galaxies – those with fewer than about ten billion stars – seem to make slighter fewer stars than expected for their masses (the Milky Way is right at the turnover, with about ten billion stars and a rate of roughly one new star per year).
What does it mean that the Milky Way is right at the turnover? Does it mean that if the Milky Way had made just slightly fewer stars than it does, then the Milky Way, too, would have made fewer stars than expected for its mass?

I find it interesting, by the way, that low-mass galaxies make fewer stars than expected for their masses. That would explain why small galaxies in the nearby universe still undergo bright starbursts. These galaxies have a lot of gas "to spare", and if they can get a starburst going, they have a lot of fuel available.

Ann
Color Commentator

BDanielMayfield
Don't bring me down
Posts: 1891
Joined: Thu Aug 02, 2012 11:24 am
AKA: Bruce
Location: East Idaho

Re: Making Stars When the Universe was Half Its Age

Post by BDanielMayfield » Sun Jan 20, 2019 6:22 am

Ann wrote:
Sat Jan 19, 2019 6:07 am
Smithsonian Astrophysical Observatory wrote:

The relationship supports the general picture of galaxy growth by gas accretion, except that for some reason smaller galaxies – those with fewer than about ten billion stars – seem to make slighter fewer stars than expected for their masses (the Milky Way is right at the turnover, with about ten billion stars and a rate of roughly one new star per year).
What does it mean that the Milky Way is right at the turnover? Does it mean that if the Milky Way had made just slightly fewer stars than it does, then the Milky Way, too, would have made fewer stars than expected for its mass?

I find it interesting, by the way, that low-mass galaxies make fewer stars than expected for their masses. That would explain why small galaxies in the nearby universe still undergo bright starbursts. These galaxies have a lot of gas "to spare", and if they can get a starburst going, they have a lot of fuel available.

Ann
That didn't make sense to me either Ann. The MW now has many times more than ten billion stars, and I'll expect that it even had many times more than that 6 BYA too.

Bruce
"Happy are the peaceable ... "

User avatar
bystander
Apathetic Retiree
Posts: 18009
Joined: Mon Aug 28, 2006 2:06 pm
Location: Oklahoma

A Primordial Star Forming Galaxy

Post by bystander » Mon Jan 28, 2019 6:04 pm

A Primordial Star Forming Galaxy
SAO Weekly Science Update | 2019 Jan 25
Galaxies with extremely high rates of star formation (from hundreds to thousands of solar-masses worth of stars per year) are rare. Our Milky Way, for example, makes only about one star a year. The process of star formation heats up dust to emit in the infrared, and extreme starburst galaxies that make this many per year shine so brightly they can be spotted at cosmological distances. When gravitational lensing by a fortuitously intervening galaxy or cluster of galaxies magnifies the signal, even farther away and cosmically earlier galaxies can be detected. To date only a handful of these extreme starburst galaxies have been confirmed from the universe’s first billion years of existence. Although still a small sample, they offer important insights into how stars were made at primordial times when most chemical elements were less abundant. They also help astronomers understand star formation in cases where the physical processes are so dramatic when compared to the process in our galaxy.

Far infrared and submillimeter sky surveys identified the first extreme galaxies from the emission of dust heated by their star formation activity. The rate of star formation is inferred from the luminosity of the galaxy, and this is calculated from the observed brightness and distance. As usual in astronomy, the distance parameter is key but difficult to measure. For these remote monsters it is generally obtained from the redshift of some strong lines emitted by the galaxy in the far infrared or submillimeter, typically from carbon monoxide (an abundant molecule) and/or from singly ionized atomic carbon. ...

A dusty star-forming galaxy at z = 6 revealed by strong gravitational lensing - Jorge A. Zavala et al
viewtopic.php?t=37735
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: 18009
Joined: Mon Aug 28, 2006 2:06 pm
Location: Oklahoma

Energetic Particles Can Bombard Exoplanets

Post by bystander » Mon Feb 18, 2019 6:42 pm

Energetic Particles Can Bombard Exoplanets
SAO Weekly Science Update | 2019 Feb 15
TRAPPIST-1 is a system of seven Earth-sized worlds orbiting an ultra-cool dwarf star about 120 light-years away. The star, and hence its system of planets, is thought to be between five-to-ten billion years old, up to twice as old as our own solar system. For scientists seeking evidence for life elsewhere, the advanced age provides more time for chemistry and evolution to operate than the Earth had. On the other hand, the planets are all close to the star (in fact they are probably tidally locked to the star with one side always facing it), and consequently would have soaked up billions more year's-worth of high energy radiation from the star’s winds, adversely affecting any atmospheres they host.

In a new paper in The Astrophysical Journal, CfA astronomers Federico Fraschetti, Jeremy Drake, Julian Alvardo-Gomez, Sofia Moschou, and Cecilia Garraffo and a colleague carry out theoretical simulations of the effects of high-energy protons from a stellar wind on nearby exoplanets. These particles are produced by stellar flares or by shock waves driven by magnetic events in the stellar corona. Measurements of solar eruptive events provide the scientists with a basis for their simulations.

The astronomers calculate the first realistic simulation of the propagation of energetic particles through the turbulent magnetic field environment of an M dwarf star and its wind, and they tailored the details to the TRAPPIST-1 system. They find that particles are trapped within the star's magnetic field and are directed into two polar streams focused onto the planets’ orbital plane - independent of many of the details. The scientists conclude that the innermost putative habitable planet in the system, TRAPPIST-1e, is bombarded by a proton flux up to a million times larger than that experienced by the present-day Earth. Nevertheless, there are many variables at play, for example the angle between the magnetic field and the rotation axis of the star, and consequently a large uncertainty remains in how these effects actually are manifest in individual situations.

Stellar energetic particles in the magnetically turbulent
habitable zones of TRAPPIST-1-like planetary systems
~ F. Fraschetti 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