astrobites 2018

Find out the latest thinking about our universe.
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A Delicate Binary Dance

Post by bystander » Thu Nov 08, 2018 6:43 pm

A Delicate Binary Dance
Astrobites | 2018 Nov 06
Stephanie Hamilton wrote:
Sometimes the little things in life are the most important.

In the case of the Solar System’s life, those little things are asteroids, comets, and Kuiper Belt objects — the leftover debris that didn’t conglomerate into planets. The giant planets (Jupiter, Saturn, Uranus, and Neptune) have tugged these smaller objects around during the Solar System’s 4.5 billion year lifetime, often ejecting them completely. Astronomers can deduce the past behavior of the giant planets by studying the small bodies of the Solar System and how they are distributed. In other words, the Solar System’s smallest members are an important key to unlocking its dynamical past.

With several hundred thousand known asteroids and a few thousand known Kuiper Belt objects, astronomers are just starting to understand the Solar System’s complex history. However, the early days of our Solar System largely remain a mystery (and by early days, I actually mean the first several hundred million years). Various ideas have been proposed to explain how the planets formed and arrived at their current orbits. Each theory predicts variations in observable features of the Solar System, such as how small bodies are distributed. All generally agree that the giant planets underwent some degree of migration, yet none satisfactorily explain what we observe. Today’s bite throws another wrench into the story. The subject? A peculiar binary asteroid named (617) Patroclus-Menoetius. ...

Evidence for Very Early Migration of the Solar System Planets
from the Patroclus-Menoetius Binary Jupiter Trojan
~ David Nesvorný et al
viewtopic.php?t=38681
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Re: astrobites 2018

Post by bystander » Thu Nov 08, 2018 7:01 pm

No, astronomers did not just claim that ‘Oumuamua is an extraterrestrial probe
Astrobites | 2018 Nov 07
Samuel Factor wrote:
If you have been paying attention to space news recently you may have seen stories suggesting that the interstellar object ‘Oumuamua, which passed through our solar system just over a year ago, could have been an extraterrestrial probe. Some headlines are a bit sensational (e.g. Scientists say mysterious ‘Oumuamua’ object could be an alien spacecraft (NBC News), Mysterious interstellar object floating in space might be alien, say Harvard researchers (USA Today), or An Alien Spacecraft May Have Passed Through Our Solar System Last Year, Claim Scientists (IFL Science!)) while other articles are a little more doubtful (e.g. Interstellar object may have been alien probe, Harvard paper argues, but experts are skeptical (CNN)). Today’s paper is the source of these articles and, while the premise is a little less far-fetched than you might think, the conclusion lacks transparency. ...
Could Solar Radiation Pressure Explain 'Oumuamua's Peculiar Acceleration? ~ Shmuel Bialy, Abraham Loeb
viewtopic.php?t=37698
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Black Holes During the Cosmic Dawn

Post by bystander » Thu Nov 08, 2018 7:20 pm

Black Holes During the Cosmic Dawn
Astrobites | 2018 Nov 08
Joshua Kerrigan wrote:
Cosmologically important phenomena are typically discussed on the scales of gigaparsecs (Gpc); to give you some idea of the sizes involved, one Gpc could fit approximately 33 thousand Milky Way galaxies end-to-end. That’s a pretty crazy scale and with that in mind today we’ll gain an understanding for how astrophysical events beginning on the order of parsecs can have far-reaching affects cosmologically.

The cosmological period prior to the reionization of the Universe’s hydrogen is typically described as being the cosmic dawn. This stage in the history of the Universe is marked by the formation of the first stars and galaxies. But it doesn’t end there, connecting these large structures throughout the Universe is the Intergalactic Medium (IGM). The IGM during the cosmic dawn consists of mostly neutral hydrogen, and compared to galaxies, is much less dense (10-27 kg/m3 compared to the density of our Milky Way which is ~10-19 kg/m3). The UV radiation from these early stars and galaxies are what most astronomers and cosmologists believe led to reionization. Put simply, this ionizing radiation extended symmetrically from these sources and over time these regions of reionized IGM began to overlap leading to complete reionization. While this is our current `best guess’, cosmologists typically wonder: ‘What roles do other structures play during this period?’ One type of galaxy of interest are those containing Active Galactic Nuclei (AGN), which are galaxies with a very dense core with a supermassive black hole (SMBH) at its center that is accreting matter. These AGN are extremely luminous and can produce a lot of X-ray and UV emissions. What we’ll be exploring today is how these SMBH influence the surrounding regions. ...

Observing the Influence of Growing Black Holes on the Pre-reionization IGM ~ Evgenii O. Vasiliev, Shiv K. Sethi, Yuri A. Shchekinov
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Feeding black holes, up close and personal

Post by bystander » Tue Nov 13, 2018 4:31 pm

Feeding black holes, up close and personal
Astrobites | 2018 Nov 12
Joanna Ramasawmy wrote:
Supermassive black holes — the phenomenal engines that power the brightest objects in the universe, quasars — are observed only moments (ok, a few hundred million years) after the Big Bang. These observations present a major problem for astrophysics: how can these supermassive objects grow so large in such a short space of time?

There are a few competing scenarios for the formation of supermassive black holes, or SMBHs. ... A critical factor in working out which of these scenarios is most likely is our understanding of how black holes grow. And it’s complicated. The main ingredient is gas, but funnelling that gas into a black hole depends on processes spanning orders of magnitude in distance, from the megaparsecs-wide large scale structure of the cosmic web down to the relatively miniscule intricacies of gas falling into the event horizon of a black hole as small as our own solar system. Creating a simulation that can explore this detail as well as taking the largest structures in the universe into account is, as the authors of today’s astrobite put it, a “tremendous computational challenge”. ...

Zooming in on Supermassive Black Holes: How Resolving Their Gas Cloud Host
Renders Their Accretion Episodic
~ Ricarda S. Beckmann, Julien Devriendt, Adrianne Slyz
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A hidden reservoir of multi-planet systems?

Post by bystander » Tue Nov 13, 2018 4:44 pm

A hidden reservoir of multi-planet systems?
Astrobites | 2018 Nov 13
Eckhart Spalding wrote:
Kepler is dead, long live Kepler! It would be an understatement to say that the Kepler spacecraft transformed our understanding of exoplanets, and it’s sad to see it go. Kepler made an especially big impact on our understanding of exoplanet systems with Neptune- or Earth-sized planets, especially those close in to their stars, and with periods of fewer than ~100 days. In combination with ground-based transit and radial velocity (RV) surveys, the thousands of planets we now know of make it possible to actually do population syntheses and start to understand the demographics of exoplanet systems.

For example, we have learned that there is a pretty solid correlation between host star metallicity and the presence of hot Jupiter planets, which may be evidence for core-accretion models of planet formation. Strangely, systems of multiple, rocky planets appear around stars with a wide range of metallicities. Could it be that there just isn’t enough material in protoplanetary disks around metal-poor stars to feed Jovian-mass planets? Or are there severe observational biases in play? RV surveys have tended to avoid metal-poor stars, because they have fewer absorption lines to measure; maybe metal-poor stars haven’t been sampled enough? Even more curiously, systems with hot Jupiters appear to be very distinct from compact multi-planet systems: they tend not to overlap. To try to resolve some of these conundrums, the authors of today’s paper shed new light on the relation of exoplanet system type to host star metallicity. ...

Compact Multi-planet Systems are more Common around Metal-poor Hosts ~ John M. Brewer et al
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