However, according to a team of astronomers from Glasgow and Arizona, astronomers need not limit themselves to detecting waves caused by massive gravitational mergers. According to a study they recently produced, the Advanced LIGO, GEO 600, and Virgo gravitational-wave detector network could also detect the gravitational waves created by supernova. In so doing, astronomers will able to see inside the hearts of collapsing stars for the first time.The study, titled “Inferring the Core-Collapse Supernova Explosion Mechanism with Three-Dimensional Gravitational-Wave Simulations“, recently appeared online. Led by Jade Powell, who recently finished her PhD at the Institute for Gravitational Research at the University of Glasgow, the team argue that current gravitational wave experiments should be able to detect the waves created by Core Collapse Supernovae (CSNe).
How large does a scope need to be to directly image one of the nearer exoplanets?Let's assume we're targeting Epsilon Eridani's planet and the 'scope has a coronograph built in. Anyone able to crunch the numbers?
Quote from: redliox on 09/12/2017 12:06 amHow large does a scope need to be to directly image one of the nearer exoplanets?Let's assume we're targeting Epsilon Eridani's planet and the 'scope has a coronograph built in. Anyone able to crunch the numbers?You really don't need that large a telescope (assuming space based). The key things are the Inner Working Angle and contrast ratio between the star and planet.For example, MAPLE-150 (1.5m) would be able to resolve epsilon Eridani b:http://www.nuvucameras.com/wp-content/uploads/2014/09/91432R.pdf--- Tony
Quote from: jebbo on 09/12/2017 11:07 amQuote from: redliox on 09/12/2017 12:06 amHow large does a scope need to be to directly image one of the nearer exoplanets?Let's assume we're targeting Epsilon Eridani's planet and the 'scope has a coronograph built in. Anyone able to crunch the numbers?You really don't need that large a telescope (assuming space based). The key things are the Inner Working Angle and contrast ratio between the star and planet.For example, MAPLE-150 (1.5m) would be able to resolve epsilon Eridani b:http://www.nuvucameras.com/wp-content/uploads/2014/09/91432R.pdf--- TonyThat's hopeful. I believe I can understand what you mean by ratio (such as how a bright distant Jupiter might be easier to detect that a dark SuperEarth), but elaborate on IWA. What else would allow an exoplanet to be more than a pixel in an image as well?
The exoplanet WASP-19b has huge amounts of titanium oxide in its atmosphere, causing the atmosphere to 'reverse' so some of the upper layers are warmer than those lower down.
The cause of hot Jupiter radius inflation, where giant planets with Teq >1000 K are significantly larger than expected, is an open question and the subject of many proposed explanations. Rather than examine these models individually, this work seeks to characterize the anomalous heating as a function of incident flux, ϵ(F), needed to inflate the population of planets to their observed sizes. We then compare that result to theoretical predictions for various models. We examine the population of about 300 giant planets with well-determined masses and radii and apply thermal evolution and Bayesian statistical models to infer the anomalous power as a function of incident flux that best reproduces the observed radii. First, we observe that the inflation of planets below about M=0.5MJ appears very different than their higher mass counterparts, perhaps as the result of mass loss or an inefficient heating mechanism. As such, we exclude planets below this threshold. Next, we show with strong significance that ϵ(F) increases with Teq towards a maximum of ∼2.5% at Teq≈1500 K, and then decreases as temperatures increase further, falling to ∼0.2% at Teff=2500 K. This high-flux decrease in inflation efficiency was predicted by the Ohmic dissipation model of giant planet inflation but not other models. We also explicitly check the thermal tides model and find that it predicts far more variance in radii than is observed. Thus, our results provide evidence for the Ohmic dissipation model and a functional form for ϵ(F) that any future theories of hot Jupiter radii can be tested against.
Researchers subjected hydrocarbon samples in a laboratory to Neptune-like pressures. The samples, reminiscent of molecules found in the ice giant’s atmosphere, compressed into nanodiamonds.
Knowing how hydrocarbons might behave deep within an ice giant’s atmosphere will affect our understanding of how atmospheres transport heat and evolve over time, explained Kraus. What’s more, the implications of this research extend beyond our solar system to exoplanets, as a large fraction of the known exoplanets are similar in size or mass to our ice giants.The ability to model an ice giant atmosphere’s density from the top down to the core is a critical part of characterizing that planet. For example, an atmosphere made mostly of hydrogen is much puffier than one with diamonds, Kraus noted.A diamond-studded atmosphere also likely behaves very differently than one without diamonds. For example, atmospheric convection might have to overcome more hurdles, which may lead to sharp changes in chemical composition between different atmospheric layers, the researchers said. This could also inhibit heat flow.“These experiments can be used to improve our understanding of the behavior of common materials in the universe at high pressures and temperatures, which has a direct connection to modeling planetary interiors,” said Ravit Helled, a computational science and theoretical astrophysics professor at the University of Zurich in Switzerland, who was not involved in the study.
One of the most directly observable features of a transiting multi-planet system is their size-ordering when ranked in orbital separation. Kepler has revealed a rich diversity of outcomes, from perfectly ordered systems, like Kepler-80, to ostensibly disordered systems, like Kepler-20. Under the hypothesis that systems are born via preferred formation pathways, one might reasonably expect non-random size-orderings reflecting these processes. However, subsequent dynamical evolution, often chaotic and turbulent in nature, may erode this information and so here we ask - do systems remember how they formed? To address this, we devise a model to define the entropy of a planetary system's size-ordering, by first comparing differences between neighboring planets and then extending to accommodate differences across the chain. We derive closed-form solutions for many of the micro state occupancies and provide public code with look-up tables to compute entropy for up to ten-planet systems. All three proposed entropy definitions exhibit the expected property that their credible interval increases with respect to a proxy for time. We find that the observed Kepler multis display a highly significant deficit in entropy compared to a randomly generated population. Incorporating a filter for systems deemed likely to be dynamically packed, we show that this result is robust against the possibility of missing planets too. Put together, our work establishes that Kepler systems do indeed remember something of their younger years and highlights the value of information theory for exoplanetary science.
The accelerating expansion of the universe may not be real, but could just be an apparent effect, according to new research published in the journal Monthly Notices of the Royal Astronomical Society. The new study — by a group at the University of Canterbury in Christchurch, New Zealand — finds the fit of Type Ia supernovae to a model universe with no dark energy to be very slightly better than the fit to the standard dark energy model.
AbstractThe asteroid belt contains less than a thousandth of Earth’s mass and is radially segregated, with S-types dominating the inner belt and C-types the outer belt. It is generally assumed that the belt formed with far more mass and was later strongly depleted. We show that the present-day asteroid belt is consistent with having formed empty, without any planetesimals between Mars and Jupiter’s present-day orbits. This is consistent with models in which drifting dust is concentrated into an isolated annulus of terrestrial planetesimals. Gravitational scattering during terrestrial planet formation causes radial spreading, transporting planetesimals from inside 1 to 1.5 astronomical units out to the belt. Several times the total current mass in S-types is implanted, with a preference for the inner main belt. C-types are implanted from the outside, as the giant planets’ gas accretion destabilizes nearby planetesimals and injects a fraction into the asteroid belt, preferentially in the outer main belt. These implantation mechanisms are simple by-products of terrestrial and giant planet formation. The asteroid belt may thus represent a repository for planetary leftovers that accreted across the solar system but not in the belt itself.
The Hubble space telescope has seen a lot of weird things that defy easy definition. Here's one more for the list – a binary asteroid that's also a comet.Astronomers have found a pair of them, in fact, swirling around one another in the asteroid belt while leaving a stream of dust in their wake. Not only is it a beautiful example of how nature DNGAF about our categories, it raises some interesting questions on how many of these hybrids might be out there.The binary object itself was first spotted back in 2006 as part of the asteroid-searching Spacewatch program, resulting in it getting the not-so-glamorous name 2006 VW139.It wasn't until 2012 that astronomers realised something odd about it; this thing that was an asteroid with comet-like characteristics, namely a streaming tail.So-called main belt comets aren't new, but they're by no means common either. This asteroid is just one of about a dozen such objects ever discovered.What makes this particular one so unique is that it's in two pieces.2006 VW139 is made of a pair of equal-sized lumps orbiting one another at a distance of just under 100 kilometres (about 60 miles).
AbstractRecent multi-telescope observations of the repeating fast radio burst (FRB) FRB 121102 reveal a Gaussian-like spectral profile and associate the event with a dwarf metal-poor galaxy at a cosmological redshift of 0.19. Assuming that this event represents the entire FRB population, we make predictions for the expected number counts of FRBs observable by future radio telescopes between 50 MHz and 3.5 GHz. We vary our model assumptions to bracket the expected rate of FRBs and find that it exceeds one FRB per second per sky when accounting for faint sources. We show that future low-frequency radio telescopes, such as the Square Kilometre Array, could detect more than one FRB per minute over the entire sky originating from the epoch of reionization.
A sun-like star seems to have devoured some of its own planetary offspring, prompting researchers to nickname it after the titan Kronos from Greek mythology.The star HD 240430 is part of a binary system with HD 240429, and the two have now been nicknamed Kronos and Krios. The pair travel through the galaxy side by side some 320 light years from Earth.They both seem to be about 4 billion years old, suggesting they were born from the same interstellar cloud, and initially shared the same chemical make-up.But an analysis by Semyeong Oh at Princeton University and her team suggests the twins have led very different lives. Krios has noticeably smaller concentrations of elements like lithium, magnesium and iron floating in its atmosphere than its companion Kronos does.In fact, the stars are more chemically different than any pair yet discovered. “I initially thought these two stars must not be in a binary,” says Oh.
Star nicknamed Kronos after eating its own planetary childrenQuote A sun-like star seems to have devoured some of its own planetary offspring, prompting researchers to nickname it after the titan Kronos from Greek mythology.The star HD 240430 is part of a binary system with HD 240429, and the two have now been nicknamed Kronos and Krios. The pair travel through the galaxy side by side some 320 light years from Earth.They both seem to be about 4 billion years old, suggesting they were born from the same interstellar cloud, and initially shared the same chemical make-up.But an analysis by Semyeong Oh at Princeton University and her team suggests the twins have led very different lives. Krios has noticeably smaller concentrations of elements like lithium, magnesium and iron floating in its atmosphere than its companion Kronos does.In fact, the stars are more chemically different than any pair yet discovered. “I initially thought these two stars must not be in a binary,” says Oh.https://www.newscientist.com/article/2148182-star-nicknamed-kronos-after-eating-its-own-planetary-children/
Comparative exoplanetology? That’s the striking term that Angelos Tsiaras, lead author of a new paper on exoplanet atmospheres, uses to describe the field today. Kepler’s valuable statistical look at a crowded starfield has given us insights into the sheer range of outcomes around other stars, but we’re already moving into the next phase, studying planetary atmospheres. And as the Tsiaras paper shows, constructing the first atmospheric surveys.Tsiaras (University College, London) assembled a team of European researchers that examined 30 exoplanets, constructing their spectral profiles and analyzing them to uncover the characteristic signatures of the gases present. The study found atmospheres around 16 ‘hot Jupiters,’ learning that water vapor was present in each of them. Says Tsiaras:“More than 3,000 exoplanets have been discovered but, so far, we’ve studied their atmospheres largely on an individual, case-by-case basis. Here, we’ve developed tools to assess the significance of atmospheric detections in catalogues of exoplanets. This kind of consistent study is essential for understanding the global population and potential classifications of these foreign worlds.”
The tendency of planets to migrate early in a solar system’s history—like a planetary billiards game—would preclude the kind of stable environments that life needs to evolve. And a primitive, hydrogen-helium atmosphere would be very challenging for life. Exceptions to this general principle may still exist. For example, a planet’s original atmosphere can be lost due to radiation or impacts, as happened on Earth.Even so, it seems that Earth’s mass is close to the optimum for a life-hosting planet. Given the new modeling results and insights, it also appears that most Super-Earths are likely not to be habitable. In the end, however, only observations will answer this question for certain. Fortunately, we should able to determine the atmospheric compositions of some Super-Earth planets within a decade.
NASA's Hubble Space Telescope has photographed the farthest active inbound comet ever seen, at a whopping distance of 1.5 billion miles from the Sun (beyond Saturn's orbit). Slightly warmed by the remote Sun, it has already begun to develop an 80,000-mile-wide fuzzy cloud of dust, called a coma, enveloping a tiny, solid nucleus of frozen gas and dust. These observations represent the earliest signs of activity ever seen from a comet entering the solar system's planetary zone for the first time.The comet, called C/2017 K2 (PANSTARRS) or "K2", has been travelling for millions of years from its home in the frigid outer reaches of the solar system, where the temperature is about minus 440 degrees Fahrenheit. The comet's orbit indicates that it came from the Oort Cloud, a spherical region almost a light-year in diameter and thought to contain hundreds of billions of comets. Comets are the icy leftovers from the formation of the solar system 4.6 billion years ago and therefore pristine in icy composition."K2 is so far from the Sun and so cold, we know for sure that the activity — all the fuzzy stuff making it look like a comet — is not produced, as in other comets, by the evaporation of water ice," said lead researcher David Jewitt of the University of California, Los Angeles. "Instead, we think the activity is due to the sublimation [a solid changing directly into a gas] of super-volatiles as K2 makes its maiden entry into the solar system's planetary zone. That's why it's special. This comet is so far away and so incredibly cold that water ice there is frozen like a rock."Based on the Hubble observations of K2's coma, Jewitt suggests that sunlight is heating frozen volatile gases - such as oxygen, nitrogen, carbon dioxide, and carbon monoxide - that coat the comet's frigid surface. These icy volatiles lift off from the comet and release dust, forming the coma. Past studies of the composition of comets near the Sun have revealed the same mixture of volatile ices."I think these volatiles are spread all through K2, and in the beginning billions of years ago, they were probably all through every comet presently in the Oort Cloud," Jewitt said. "But the volatiles on the surface are the ones that absorb the heat from the Sun, so, in a sense, the comet is shedding its outer skin. Most comets are discovered much closer to the Sun, near Jupiter's orbit, so by the time we see them, these surface volatiles have already been baked off. That's why I think K2 is the most primitive comet we've seen."K2 was discovered in May 2017 by the Panoramic Survey Telescope and Rapid Response System (Pan-STARRS) in Hawaii, a survey project of NASA's Near-Earth Object Observations Program. Jewitt used Hubble's Wide Field Camera 3 at the end of June to take a closer look at the icy visitor.Hubble's sharp "eye" revealed the extent of the coma and also helped Jewitt estimate the size of the nucleus — less than 12 miles across — though the tenuous coma is 10 Earth diameters across.This vast coma must have formed when the comet was even farther away from the Sun. Digging through archival images, Jewitt's team uncovered views of K2 and its fuzzy coma taken in 2013 by the Canada-France-Hawaii Telescope (CFHT) in Hawaii. But the object was then so faint that no one noticed it."We think the comet has been continuously active for at least four years," Jewitt said. "In the CFHT data, K2 had a coma already at 2 billion miles from the Sun, when it was between the orbits of Uranus and Neptune. It was already active, and I think it has been continuously active coming in. As it approaches the Sun, it's getting warmer and warmer, and the activity is ramping up."But, curiously, the Hubble images do not show a tail flowing from K2, which is a signature of comets. The absence of such a feature indicates that particles lifting off the comet are too large for radiation pressure from the Sun to sweep them back into a tail.Astronomers will have plenty of time to conduct detailed studies of K2. For the next five years, the comet will continue its journey into the inner solar system before it reaches its closest approach to the Sun in 2022 just beyond Mars' orbit. "We will be able to monitor for the first time the developing activity of a comet falling in from the Oort Cloud over an extraordinary range of distances," Jewitt said. "It should become more and more active as it nears the Sun and presumably will form a tail."Jewitt said that NASA's James Webb Space Telescope, an infrared observatory scheduled to launch in 2018, could measure the heat from the nucleus, which would give astronomers a more accurate estimate of its size.The team's results will appear in the September 28 issue of The Astrophysical Journal Letters.