AAS NOVA — Research Highlights 2017

Find out the latest thinking about our universe.
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Echoes from a Dying Star

Postby bystander » Thu Jun 01, 2017 4:10 pm

Echoes from a Dying Star
NOVA | American Astronomical Society | 2017 May 31

When a passing star is torn apart by a supermassive black hole, it emits a flare of X-ray, ultraviolet, and optical light. What can we learn from the infrared echo of a violent disruption like this one? ...

Discovery of a Mid-infrared Echo from the TDE Candidate in the Nucleus of ULIRG F01004-2237 - Liming Dou et al
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Probing Magnetic Fields of Early Galaxies

Postby bystander » Sun Jun 04, 2017 2:36 pm

Probing Magnetic Fields of Early Galaxies
NOVA | American Astronomical Society | 2017 Jun 02

How do magnetic fields form and evolve in early galaxies? A new study has provided some clever observations to help us answer this question. ...

Observed Faraday Effects in Damped Lyα Absorbers and Lyman Limit Systems:
The Magnetized Environment of Galactic Building Blocks at Redshift = 2
- J. S. Farnes et al
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A 3D View of a Supernova Remnant

Postby bystander » Fri Jun 16, 2017 7:01 pm

A 3D View of a Supernova Remnant
NOVA | American Astronomical Society | 2017 Jun 14

The Tycho supernova remnant was first observed in the year 1572. Nearly 450 years later, astronomers have now used X-ray observations of Tycho to build the first-ever 3D map of a Type Ia supernova remnant. ...

The Three-Dimensional Expansion of the Ejecta from Tycho's Supernova Remnant - Brian J. Williams et al
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Maxing Out the Mass of Early Stars

Postby bystander » Fri Jun 16, 2017 7:07 pm

Maxing Out the Mass of Early Stars
NOVA | American Astronomical Society | 2017 Jun 16

Primordial supermassive stars might be responsible for the earliest supermassive black holes in our universe. But just how big can a star grow before it inevitably collapses into a black hole? ...

On the Maximum Mass of Accreting Primordial Supermassive Stars - T. E. Woods et al
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Hidden Black Holes Revealed?

Postby bystander » Sat Jun 24, 2017 2:06 pm

Hidden Black Holes Revealed?
NOVA | American Astronomical Society | 2017 Jun 19

Supermassive black holes are thought to grow in heavily obscured environments. A new study now suggests that many of the brightest supermassive black holes around us may be escaping our detection as they hide in these environments. ...

Survival of the Obscuring Torus in the Most Powerful Active Galactic Nuclei - S. Mateos et al
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A Partly Cloudy Exoplanet

Postby bystander » Sat Jun 24, 2017 2:13 pm

A Partly Cloudy Exoplanet
NOVA | American Astronomical Society | 2017 Jun 21

Direct imaging of exoplanets was once only possible for the brightest of planets orbiting the dimmest of stars — but improving technology is turning this into an increasingly powerful technique. In a new study, direct-imaging observations of the Jupiter-like exoplanet 51 Eridani b provide tantalizing clues about its atmosphere. ...

Characterizing 51 Eri b from 1 to 5 μm: A Partly Cloudy Exoplanet - Abhijith Rajan et al
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Exploring the Minispiral at the Milky Way’s Center

Postby bystander » Sat Jun 24, 2017 2:21 pm

Exploring the Minispiral at the Milky Way’s Center
NOVA | American Astronomical Society | 2017 Jun 23

The region around Sgr A*, the 4-million-solar-mass black hole at the heart of our galaxy, is a complex and dynamic place. New Atacama Large Millimeter/submillimeter Array (ALMA) observations of the Milky Way’s center now reveal more about this harsh, inhospitable environment. ...

ALMA View of the Galactic Center Minispiral: Ionized Gas Flows around Sagittarius A* - Masato Tsuboi et al
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A New Clue in the Mystery of Fast Radio Bursts

Postby bystander » Fri Jun 30, 2017 2:36 pm

A New Clue in the Mystery of Fast Radio Bursts
NOVA | American Astronomical Society | 2017 Jun 28

The origin of the mysterious fast radio bursts has eluded us for more than a decade. With the help of a particularly cooperative burst, however, scientists may finally be homing in on the answer to this puzzle.

FRB 121102 Is Coincident with a Star-forming Region in Its Host Galaxy - C.G. Bassa et al

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How Tiny Collisions Shape Mercury

Postby bystander » Sat Jul 08, 2017 2:01 pm

How Tiny Collisions Shape Mercury
NOVA | American Astronomical Society | 2017 Jun 30

If space rocks are unpleasant to encounter, space dust isn’t much better. Mercury’s cratered surface tells of billions of years of meteoroid impacts — but its thin atmosphere is what reveals its collisional history with smaller impactors. Now new research is providing a better understanding of what we’re seeing. ...

Reconciling the Dawn–Dusk Asymmetry in Mercury's Exosphere
with the Micrometeoroid Impact Directionality
- Petr Pokorný, Menelaos Sarantos, Diego Janches
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Discovery of a Free-Floating Double Planet?

Postby bystander » Sat Jul 08, 2017 2:08 pm

Discovery of a Free-Floating Double Planet?
NOVA | American Astronomical Society | 2017 Jul 05

An object previously identified as a free-floating, large Jupiter analog turns out to be two objects — each with the mass of a few Jupiters. This system is the lowest-mass binary we’ve ever discovered. ...

The Young L Dwarf 2MASS J11193254-1137466 is a Planetary-Mass Binary - William M. J. Best et al
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Another Possibility for Boyajian’s Star

Postby bystander » Sat Jul 08, 2017 2:28 pm

Another Possibility for Boyajian’s Star
NOVA | American Astronomical Society | 2017 Jul 07

The unusual light curve of the star KIC 8462852, also known as “Tabby’s star” or “Boyajian’s star”, has puzzled us since its discovery last year. A new study now explores whether the star’s missing flux is due to internal blockage rather than something outside of the star. ...

An Explanation of the Missing Flux from Boyajian's Mysterious Star - Peter Foukal
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Exploring Disks Around Planets

Postby bystander » Tue Jul 11, 2017 2:18 pm

Exploring Disks Around Planets
NOVA | American Astronomical Society | 2017 Jul 10

Giant planets are thought to form in circumstellar disks surrounding young stars, but material may also accrete into a smaller disk around the planet. We’ve never detected one of these circumplanetary disks before — but thanks to new simulations, we now have a better idea of what to look for. ...

Effects of the Planetary Temperature on the Circumplanetary Disk and on the Gap - J. Szulágyi
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WASP-12b and Its Possible Fiery Demise

Postby bystander » Mon Jul 17, 2017 2:12 pm

WASP-12b and Its Possible Fiery Demise
NOVA | American Astronomical Society | 2017 Jul 12

Jupiter-like planets on orbits close to their hosts are predicted to spiral ever closer to their hosts until they meet their eventual demise — and yet we’ve never observed orbital decay. Could WASP-12b provide the first evidence? ...

The Apparently Decaying Orbit of WASP-12b - Kishore C. Patra et al
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Speeding Clouds May Reveal Invisible Black Holes

Postby bystander » Mon Jul 17, 2017 2:19 pm

Speeding Clouds May Reveal Invisible Black Holes
NOVA | American Astronomical Society | 2017 Jul 14

Several small, speeding clouds have been discovered at the center of our galaxy. A new study suggests that these unusual objects may reveal the lurking presence of inactive black holes. ...

Discovery of Two Small High-Velocity Compact Clouds in the Central 10 Parsecs of Our Galaxy - Shunya Takekawa et al
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Re: Maxing Out the Mass of Early Stars

Postby Ann » Thu Jul 20, 2017 8:35 am

bystander wrote:Maxing Out the Mass of Early Stars
NOVA | American Astronomical Society | 2017 Jun 16

Primordial supermassive stars might be responsible for the earliest supermassive black holes in our universe. But just how big can a star grow before it inevitably collapses into a black hole? ...

On the Maximum Mass of Accreting Primordial Supermassive Stars - T. E. Woods et al


I was away from home for much of June this year, so I missed one of the most incredibly fascinating new hypotheses this summer. Namely this one: How did the very young Universe build extremely massive black holes in a cosmic "blink of an eye"?

Artist's rendering of the accretion disk in ULAS J1120+0641, a very distant quasar
powered by a black hole with a mass two billion times that of the Sun.
Credit: ESO/M. Kornmesser
Evidence #1: Quasars. Quasars are supermassive black holes surrounded by an accretion disk (or torus) of gas and dust orbiting the black hole at dizzying speeds. Different parts of the torus orbit at different speeds. Various parts of the torus keep colliding and rubbing at one another at tremendous speeds, generating so much energy and light that quasars are definitely among the most luminous objects in the Universe, maybe the most luminous.

Evidence #2: Although quasars are found over a wide range of distances and epochs of the Universe, they were most common in the distant past.

Wikipedia wrote:
The peak epoch of quasar activity in the Universe corresponds to redshifts around 2, or approximately 10 billion years ago.


Evidence #3: Quasar SDSS J0100+2802.

University of Arizona wrote:

The discovery of this quasar, named SDSS J0100+2802, marks an important step in understanding how quasars, the most powerful objects in the universe, have evolved from the earliest epoch, only 900 million years after the Big Bang, which is thought to have happened 13.7 billion years ago. The quasar, with its central black hole mass of 12 billion solar masses and the luminosity of 420 trillion suns, is at a distance of 12.8 billion light-years from Earth.


So, question: How did the Universe build a 12 billion solar mass black hole, 3,000 times more massive than the supermassive black hole in the Milky Way, in only 900 million years???

You may think that's not so hard. There were some really massive stars in the very early Universe. In our own epoch, the most massive stars contain some 300 solar masses, but it has been suggested that the earliest generation of stars formed specimens that were far more massive, maybe... 1,000 solar masses? Suppose these first generation gargantuan stars collapsed directly into black holes, forming black holes of a thousand solar masses. So, in order to form a supermassive black hole of 12 billion solar masses, all you have to do is to form individual 1,000-solar mass black holes and have them merge... and you only need twelve million such individual black holes and find a way to make them all merge into a single black hole?

Reality check. A 1,000-solar mass black hole is an intermediate-mass black hole.

Wikipedia wrote:
An intermediate-mass black hole (IMBH) is a hypothetical class of black hole with mass in the range 100 to one million[citation needed] solar masses: significantly more than stellar black holes but less than supermassive black holes. There is as yet no unambiguous detection of an IMBH, but the indirect evidence from various directions is tantalizing.


So according to Wikipedia, intermediate-mass black holes in the nearby universe are so rare that they must be considered hypothetical, and we can't be sure that they exist in the first place. You may argue with Wikipedia about this, but the intermediate-mass black holes are clearly rare in the nearby universe.

But in the very young universe, they were so common that you could not only produce 12 million of them, but you could also make all these 12 million IMBH merge, to produce one single supermassive black hole? In 900 million years?

Maybe not.

Let's considered black hole mergers. With ever more sensitive detectors of gravitational waves, humanity has managed to spot no fewer than 6 stellar-mass black holes merging into 3 more massive, but still stellar-mass black holes. That's a far cry from 12,000,000 intermediate-mass black holes merging into 1 single supermassive black hole.

So how did the Universe make SDSS J0100+2802, the 12 billion black hole, in only 900 million years?

Maybe through stars whose mass was not just 1,000 solar masses. Not even through stars whose mass was 10,000 solar masses. No, there may have been stars whose mass was some 100,000 solar masses - ~300 times as massive as the most massive stars in the nearby universe! :shock:

For comparison, imagine the fattest man on Earth, and then imagine another man 300 times fatter... no... that's not possible.)

How can you grow a star of 100,000 solar masses?

AAS Nova wrote:

Quasars — supermassive black holes that are actively feeding — have been observed with enormous sizes (billions of solar masses) at very large distances (redshifts of z > 6). These monsters pose a problem: how could they have accreted so much mass in so little time since the beginning of the universe?

One theory is that these black holes formed from the direct collapse of stars. The larger the original star before collapse, the better the chances that the resulting black hole will be able to grow quickly. But even theorized Pop III stars (which have hundreds of solar masses) would have to accrete at rates higher than believed possible to achieve the black-hole masses we observe so quickly. For this reason, the commonly invoked explanation now is supermassive stars.
...
In ordinary star formation, halos of gas cool primarily due to emission by molecules. When these clouds cool, they fragment and then collapse into normal-sized stars.

In the supermassive star-formation scenario, hydrogen molecules in primordial halos are broken down — possibly by ultraviolet radiation from nearby star formation. This prevents the halos from cooling by molecular emission, instead allowing them to grow to an enormous 107–108 solar masses before they start cooling due to atomic emission. At this point they finally collapse to form a star.

Stars forming via this scenario quickly grow to be very massive, as the halo material falls onto the core at catastrophic rates of 0.01–10 solar masses per year. After a short period of this rapid accretion, the supermassive star then collapses into a black hole due to instability. But how massive could such a star grow before its collapse?
...
Imagine R1361a squared, and then some.
ESO/VLT/P. Crowther/C.J. Evans
Woods and collaborators found that for accretion rates above 0.1 solar masses per year, the supermassive stars generally collapsed into black holes at masses of 150,000–330,000 solar masses.
...
This also sets the maximum mass of the supermassive black holes formed by direct collapse of stars in the early universe. At hundreds of thousands of solar masses, these first quasars provide much more plausible seeds than Pop III stars for growing the billion-solar-mass monsters we observe at high redshifts. Supermassive stars may indeed be the key to the formation of the first and most luminous quasars in our universe.


So maybe that's how the very young Universe could build supermassive black holes in the blink of an eye.

By building supermassive stars in the blink of an eye, and collapsing them, in the blink of an eye, into "massive intermediate mass black holes" of up to some 300,000 solar masses.

Image
Hungry eater.
And then the newborn "massive intermediate mass black hole" could be left in peace to grow more massive by hungrily accreting gas from its vicinity in the extremely gas-rich and compact young Universe. Perhaps the enormous amounts of gas in the very young Universe would also have made it easier for binary black holes to merge, compared with the situation in the nearby Universe.

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Nearby Hot Stars May Change Our View of Distant Sources

Postby bystander » Fri Jul 21, 2017 2:48 pm

Nearby Hot Stars May Change Our View of Distant Sources
NOVA | American Astronomical Society | 2017 Jul 19

As if it weren’t enough that quasars — distant and bright nuclei of galaxies — twinkle of their own accord due to internal processes, nature also provides another complication: these distant radio sources can also appear to twinkle because of intervening material between them and us. A new study has identified a possible source for the material getting in the way. ...

Extreme Radio-Wave Scattering Associated with Hot Stars - Mark Walker et al

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Globular Clusters for Faint Galaxies

Postby bystander » Sun Jul 23, 2017 1:46 pm

Globular Clusters for Faint Galaxies
NOVA | American Astronomical Society | 2017 Jul 21

The origin of ultra-diffuse galaxies (UDGs) has posed a long-standing mystery for astronomers. New observations of several of these faint giants with the Hubble Space Telescope are now lending support to one theory. ...

Despite the many observations, UDGs still pose a number of unanswered questions. Chief among them: what are UDGs? Why are these objects the size of normal galaxies, yet so dim? There are two primary models that explain UDGs:

  1. UDGs were originally small galaxies, hence their low luminosity. Tidal interactions then puffed them up to the large size we observe today.
  2. UDGs are effectively “failed” galaxies. They formed the same way as normal galaxies of their large size, but something truncated their star formation early, preventing them from gaining the brightness that we would expect for galaxies of their size.
Now a team of scientists led by Pieter van Dokkum (Yale University) has made some intriguing observations with Hubble that lend weight to one of these models.

Extensive Globular Cluster Systems Associated with Ultra Diffuse Galaxies in the Coma Cluster - Pieter van Dokkum et al
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Re: Globular Clusters for Faint Galaxies

Postby Ann » Sun Jul 23, 2017 4:40 pm

bystander wrote:Globular Clusters for Faint Galaxies
NOVA | American Astronomical Society | 2017 Jul 21

The origin of ultra-diffuse galaxies (UDGs) has posed a long-standing mystery for astronomers. New observations of several of these faint giants with the Hubble Space Telescope are now lending support to one theory. ...

Despite the many observations, UDGs still pose a number of unanswered questions. Chief among them: what are UDGs? Why are these objects the size of normal galaxies, yet so dim? There are two primary models that explain UDGs:

  1. UDGs were originally small galaxies, hence their low luminosity. Tidal interactions then puffed them up to the large size we observe today.
  2. UDGs are effectively “failed” galaxies. They formed the same way as normal galaxies of their large size, but something truncated their star formation early, preventing them from gaining the brightness that we would expect for galaxies of their size.
Now a team of scientists led by Pieter van Dokkum (Yale University) has made some intriguing observations with Hubble that lend weight to one of these models.

Extensive Globular Cluster Systems Associated with Ultra Diffuse Galaxies in the Coma Cluster - Pieter van Dokkum et al


Wow! Chris, I think you were right! :shock: (Who'd have thought...?)

You have often said that globular clusters formed in the early Universe through special processes that only existed at the time when most galaxies were "laying down their own foundations". Therefore, there can be no such things as "young globular clusters", because globulars are the products of conditions and processes that are long gone. So a populous young cluster is just that: a young cluster, maybe as rich in stars as many true globulars, but still a different kind of beast.

AAS Nova wrote:

In general, UDGs [Ultra Diffuse Galaxies] appear to have more globular clusters than other galaxies of the same total luminosity, by a factor of nearly 7. These results are consistent with the scenario in which UDGs are failed galaxies: they likely have the halo mass to have formed a large number of globular clusters,In general, UDGs appear to have more globular clusters than other galaxies of the same total luminosity, by a factor of nearly 7. These results are consistent with the scenario in which UDGs are failed galaxies: they likely have the halo mass to have formed a large number of globular clusters, but they were quenched before they formed a disk and bulge. Because star formation never got going in UDGs, they are now much dimmer than other galaxies of the same size.but they were quenched before they formed a disk and bulge. Because star formation never got going in UDGs, they are now much dimmer than other galaxies of the same size.


This clearly suggest that globular clusters formed before the disks and bulges of galaxies formed. I have often put forward the hypothesis that globular clusters formed in the disks of early galaxies and then got scattered into the halos of the galaxies, but it would seem I was wrong about this.

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The Story of a Boring Encounter with a Black Hole

Postby bystander » Fri Jul 28, 2017 5:31 pm

The Story of a Boring Encounter with a Black Hole
NOVA | American Astronomical Society | 2017 Jul 24

Remember the excitement three years ago before the gas cloud G2’s encounter with the supermassive black hole at the center of our galaxy, Sgr A*? Did you notice that not much was said about it after the fact? That’s because not much happened — and a new study suggests that this isn’t surprising. ...

G2 and Sgr A*: A Cosmic Fizzle At The Galactic Center - Brian Morsony et al

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The Making of a Pre-Planetary Nebula

Postby bystander » Fri Jul 28, 2017 5:36 pm

The Making of a Pre-Planetary Nebula
NOVA | American Astronomical Society | 2017 Jul 26

The gas expelled by dying stars gets twisted into intricate shapes and patterns as nebulae form. Now a team of researchers might have some answers about how this happens. ...

Models of the Hydrodynamic Histories of post-AGB Stars. I. Multiflow Shaping of OH231.8+04.2 - Bruce Balick et al
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Throwing Icebergs at White Dwarfs

Postby bystander » Sat Jul 29, 2017 3:41 pm

Throwing Icebergs at White Dwarfs
NOVA | American Astronomical Society | 2017 Jul 28

Where do the metals come from that pollute the atmospheres of many white dwarfs? Close-in asteroids may not be the only culprits! A new study shows that distant planet-size and icy objects could share some of the blame. ...

Throwing Icebergs at White Dwarfs - Alexander P. Stephan, Smadar Naoz, B. Zuckerman
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Grounded Eyes on Distant Watery Skies

Postby bystander » Wed Aug 09, 2017 5:57 pm

Grounded Eyes on Distant Watery Skies
NOVA | American Astronomical Society | 2017 Aug 02

What can we learn about exoplanets from high-resolution, ground-based observations? A new view of the nearby upsilon Andromedae system has revealed a great deal about the system’s closest-in exoplanet — including the presence of water vapor in its atmosphere. ...

Detection of Water Vapor in the Thermal Spectrum of the Non-Transiting Hot Jupiter upsilon Andromedae b - Danielle Piskorz et al
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Collisions Around a Black Hole Mean Mealtime

Postby bystander » Wed Aug 09, 2017 6:03 pm

Collisions Around a Black Hole Mean Mealtime
NOVA | American Astronomical Society | 2017 Aug 04

When a normally dormant supermassive black hole burps out a brief flare, it’s assumed that a star was torn apart and fell into the black hole. But a new study suggests that some of these flares might have a slightly different cause. ...

Periodic Accretion-powered Flares from Colliding EMRIs as TDE Imposters - Brian D. Metzger, Nicholas C. Stone
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How Do Earth-Sized, Short-Period Planets Form?

Postby bystander » Wed Aug 09, 2017 6:09 pm

How Do Earth-Sized, Short-Period Planets Form?
NOVA | American Astronomical Society | 2017 Aug 07

Matching theory to observation often requires creative detective work. In a new study, scientists have used a clever test to reveal clues about the birth of speedy, Earth-sized planets. ...

Absence of a Metallicity Effect for Ultra-short-period Planets - Joshua N. Winn et al
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The Fate of Merging Neutron Stars

Postby bystander » Fri Aug 11, 2017 3:38 pm

The Fate of Merging Neutron Stars
NOVA | American Astronomical Society | 2017 Aug 09

When two neutron stars collide, the new object that they make can reveal information about the interior physics of neutron stars. New theoretical work explores what we should be seeing, and what it can teach us. ...

The Fate of Neutron Star Binary Mergers - Anthony L. Piro, Bruno Giacomazzo, Rosalba Perna
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