An Introduction to Black Holes.
Defined as “A dense, compact object whose gravitational pull is so strong that - within a certain distance of it - nothing can escape, not even light. Black holes are thought to result from the collapse of certain very massive stars at the ends of their evolution.”
Learn more about black holes here, and here. View images of black holes here.
The formation and evolution of pre-stellar discs
This series of radiation hydrodynamical calculations follows the collapse of one solar-mass molecular cloud cores all the way to the formation of the stellar core. This project was a follow-up to my 1998 barotropic calculations which discovered that rapidly-rotating first hydrostatic cores could develop rotational instabilities and evolve into large discs before the stellar core formed within them.
Calculation with beta=0.01:
In this calculation the initial molecular cloud core is rotating slowly quickly enough that the first hydrostatic core becomes dynamically rotationally unstable. However, in this case, the instability is stronger. The pre-stellar disc that is formed has a radius approaching 100 AU, and the end of one of the spiral arms manages to collect enough gas to form a self-gravitating fragment. All of this evolution occurs before the stellar core forms (which occurs at the end of the animation). This calculation was performed using 1 million SPH particles.
Credit: Simulation & visualisation by Matthew Bate, University of Exeter
New Cosmic ‘Scale’ Could Weigh Distant Black Holes.
“Swirling gas around black holes may be the key to estimating the masses of black holes otherwise too distant to weigh, according to a new study.
Supermassive black holes millions to billions of times the mass of the sun are thought to lurk at the heart of all large galaxies. Oddly, the properties of these black holes appear linked with a variety of properties of their parent galaxies, such as how bright the galaxies are and the speed of stars within them. This suggests a fundamental link between galaxy and black hole evolution.
The scientists tested their model on gas seen around the supermassive black hole in the galaxy NGC 4526, which is 53 million light-years away in the constellation of Virgo. They employed the Combined Array for Research in Millimetre-wave Astronomy (CARMA) telescope in California.
They estimate NGC 4526’s central black hole weighs about 450 million times the mass of the sun.”
Model IDs Habitable Zones Around Stars
Researchers searching the galaxy for planets that could pass the litmus test of sustaining water-based life must find whether those planets fall in what’s known as a habitable zone. New work, led by a team of Penn State Univ. researchers, will help scientists in that search.
Using the latest data, the Penn State Department of Geosciences team developed an updated model for determining whether discovered planets fall within a habitable zone – where they could be capable of having liquid water and thus sustaining life. The work, described in a paper accepted for publication in Astrophysical Journal, builds on a prior model by James Kasting, professor of geosciences at Penn State, to offer a more precise calculation of where habitable zones around a star can be found.
Read more: http://www.laboratoryequipment.com/news/2013/01/model-ids-habitable-zones-around-stars
A supernova remnant (SNR) is the structure resulting from the explosion of a star in a supernova. The supernova remnant is bounded by an expanding shock wave, and consists of ejected material expanding from the explosion, and the interstellar material it sweeps up and shocks along the way. Supernova remnants are considered the major source of galactic cosmic rays.
There are two common routes to a supernova: either a massive star may run out of fuel, ceasing to generate fusion energy in its core, and collapsing inward under the force of its own gravity to form a neutron star or a black hole; or a white dwarf star may accumulate (accrete) material from a companion star until it reaches a critical mass and undergoes a thermonuclear explosion.
An SNR passes through the following stages as it expands:
- Free expansion of the ejecta, until they sweep up their own weight in circumstellar or interstellar medium. This can last tens to a few hundred years depending on the density of the surrounding gas.
- Sweeping up of a shell of shocked circumstellar and interstellar gas. This begins the Sedov-Taylor phase, which can be well modeled by a self-similar analytic solution. Strong X-ray emission traces the strong shock waves and hot shocked gas.
- Cooling of the shell, to form a thin (< 1 pc), dense (1-100 million atoms per cubic metre) shell surrounding the hot (few million kelvin) interior. This is the pressure-driven snowplow phase. The shell can be clearly seen in optical emission from recombining ionized hydrogen and ionized oxygen atoms.
- Cooling of the interior. The dense shell continues to expand from its own momentum. This stage is best seen in the radio emission from neutral hydrogen atoms.
- Merging with the surrounding interstellar medium. When the supernova remnant slows to the speed of the random velocities in the surrounding medium, after roughly 30,000 years, it will merge into the general turbulent flow, contributing its remaining kinetic energy to the turbulence.
“Normal stars such as the Sun are hot balls of gas millions of kilometers in diameter. The visible surfaces of stars are called the photospheres, and have temperatures ranging from a few thousand to a few tens of thousand degrees Celsius. The outermost layer of a star’s atmosphere is called the “corona”, which means “crown”. The gas in the coronas of stars has been heated to temperatures of millions of degrees Celsius.
In medium-sized stars, such as the Sun, the outer layers consist of a rolling, boiling turmoil called convection. A familiar example of convection is a sea-breeze. The Sun warms the land more quickly than the water and the warm air rises and cools as it expands. It then sinks and pushes the cool air off the ocean inland to replace the air that has risen, producing a sea-breeze. In the same way, hot gas rises from the subsurface layers that extend to a depth of about 200,000 kilometers, cools at the surface and descends again.”
Isostasy, gravity, and the Moon! Last week the GRAIL lunar gravity mission published their first scientific results, and what they have found will send many geophysicists back to the drawing board to explain how the Moon formed and why it looks the way it does now.
Here’s an explainer of the first results from GRAIL.Source: The Planetary Society Facebook page.
News you might have missed:
Earlier this year the Cassini-Huygens mission sent back data revealing that Saturn’s moon Phoebe has more planet-like qualities than previously thought.
Scientists had their first close-up look at Phoebe when Cassini began exploring the Saturn system in 2004. Using data from multiple spacecraft instruments and a computer model of the moon’s chemistry, geophysics and geology, scientists found Phoebe was a so-called planetesimal, or remnant planetary building block. The findings appear in the April issue of the Journal Icarus.
Cassini images suggest Phoebe originated in the far-off Kuiper Belt, the region of ancient, icy, rocky bodies beyond Neptune’s orbit. Data show Phoebe was spherical and hot early in its history, and has denser rock-rich material concentrated near its center. Its average density is about the same as Pluto, another object in the Kuiper Belt. Phoebe likely was captured by Saturn’s gravity when it somehow got close to the giant planet.
“By combining Cassini data with modeling techniques previously applied to other solar system bodies, we’ve been able to go back in time and clarify why it is so different from the rest of the Saturn system,” said Jonathan Lunine, a co-author on the study and a Cassini team member at Cornell University, Ithaca, N.Y.Analyses suggest that Phoebe was born within the first 3 million years of the birth of the solar system, which occurred 4.5 billion years ago. The moon may originally have been porous but appears to have collapsed in on itself as it warmed up. Phoebe developed a density 40 percent higher than the average inner Saturnian moon.
“From the shape seen in Cassini images and modeling the likely cratering history, we were able to see that Phoebe started with a nearly spherical shape, rather than being an irregular shape later smoothed into a sphere by impacts,” said co-author Peter Thomas, a Cassini team member at Cornell.More than 60 moons are known to orbit Saturn, varying drastically in shape, size, surface age and origin. Scientists using both ground-based observatories and Cassini’s cameras continue to search for others.
Read more here
Jets of relativistic plasma created by the Supermassive Black Hole at the center of 3C 348; a galaxy in the Hercules Cluster 1000 times more massive than the Milky Way. The jets are focused beams of particles accelerated to more than half of light speed by the magnetic fields around the Black Hole. The jets extend more than a million light years into intergalactic space. This image is a combination of visible light observations by the Hubble Space Telescope and radio observations by the VLA Radio Telescope.
Annotated HR diagram
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Antares is a huge [700 times the diameter of the sun] star and is only about 600 light years away from us. Antares is also unusual because it is surrounded by a yellowish reflection nebula which astronomers believe is composed of material ejected from the star which then reflects the star’s yellow-red light.](http://25.media.tumblr.com/tumblr_me286eVmJs1qcbrp0o1_1280.jpg)
Antares is a huge [700 times the diameter of the sun] star and is only about 600 light years away from us. Antares is also unusual because it is surrounded by a yellowish reflection nebula which astronomers believe is composed of material ejected from the star which then reflects the star’s yellow-red light.
